Waste Water Treatment by Photo.fenton Process 2006

WASTEWATER

TREATMENT BY HIGH EFFICIENCY

HETEROGENEOUS PHOTO-FENTON

PROCESS

Massimo Ricciardi

Unione Europea UNIVERSITÀ DEGLI STUDI DI SALERNO

Fondo sociale europeo Programma Operativo Nazionale 2000/2006

“Ricerca Scientifica, Sviluppo Tecnologico, Alta Formazione” Regioni dell’Obiettivo 1 – Misura III.4

“Formazione superiore ed universitaria”

Department of Chemical and Food Engineering

Ph.D. Course in Chemical Engineering (III Cycle-New Series)

WASTEWATER TREATMENT BY HIGH EFFICIENCY HETEROGENEOUS PHOTO-

FENTON PROCESS

Supervisor Ph.D. student Prof. Paolo Ciambelli Ing. Massimo Ricciardi Scientific Referees Prof. Diana Sannino Prof. Lyubov A. Isupova Ph.D. Course Coordinator Prof. Paolo Ciambelli

To my family

Acknowledgments In onore alla verità, lo spazio per le gratitudini potrebbe occupare un

capitolo di questa tesi, e più che un'esagerazione è una maniera di esprimere l’avere avuto la fortuna di lavorare con tanta gente e dalla quale ho ricevuto sempre aiuto, stima, amicizia e solidarietà, ragioni per le quali sono molto grato.

In primo luogo voglio ringraziare il Prof. Paolo Ciambelli da cui ho

ricevuto fiducia, conoscenze e tutto il suo aiuto per portare a termine questa tesi di dottorato.

Un ringraziamento particolare va alla Prof.ssa Diana Sannino, per il suo

appoggio durante tutte le fasi di questo lavoro e per l'aiuto che mi ha offerto quando ho avuto bisogno di lei; a lei, devo, infatti, il raggiungimento di questo importante traguardo.

Voglio inoltre ringraziare il Prof. Vincenzo Palma per la sua disponibilità

e per la sua costante presenza durante i tre anni di dottorato. Un ringraziamento va alla Prof.ssa Lyubov Isupova per la sua proficua

collaborazione e per i suoi preziosi suggerimenti. Vorrei ringraziare il Sig. Antonio Mormile per la sua puntuale

collaborazione. Ringrazio la Prof.ssa Paola Russo, il Dr Vincenzo Vaiano, la Dr.ssa

Maria Sarno, la Dott.ssa Ivana Orlando e gli Ingegneri Arianna Ruggiero, Emma Palo, Giuseppa Matarazzo, Antonietta Maria Manna, Elvirosa Brancaccio e Caterina Leone che mi hanno fatto capire quanto sia importante collaborare in un ambiente piacevole e stimolante.

Ma ringrazio soprattutto mia madre, mio padre, mio fratello e Rossella

per avermi sostenuto in ogni occasione.

Publications list

1. P. Ciambelli, D. Sannino, M. Ricciardi, L.A. Isupova; Monolith perovskites catalyst for photo-Fenton reaction. The Third European Conference on Oxidation and Reduction Technologies for ex-Situ Treatment of Water, Air and Soil and in-Situ Treatment of Soil and Groundwater (ECOR-3) September 11 - 13, 2006, Göttingen, Germany, p.90-91.

2. P. Ciambelli, D. Sannino, M. Ricciardi, L.A. Isupova; Monolith supported perovskite catalyst for photo-Fenton pollutant oxidation. SCI 2006 - XXII congresso nazionale della Società Chimica Italiana. September 10-15, 2006, Firenze, Italy, p.276.

I

Contents I Introduction..................................................................................... 1

I.1 Removal of organic compounds............................................... 3 I.1.1 Incineration.......................................................................... 4 I.1.2 Air stripping ......................................................................... 4 I.1.3 Adsorption onto activated carbon........................................ 5 I.1.4 Wet oxidation ....................................................................... 5 I.1.5 Electrochemical oxidation ................................................... 6 I.1.6 Photochemical processes ..................................................... 7 I.1.7 Biological oxidation ............................................................. 8 I.1.8 Chemical oxidation .............................................................. 8 I.1.8.1 Classical Chemical Treatments...................................... 11 I.1.8.2 Advanced Oxidation Processes (AOPs)......................... 13

I.2 Fenton and photo-Fenton reaction.......................................... 15 I.2.1 Basic Principles ................................................................. 15 I.2.1.1 The Fenton Process........................................................ 15 I.2.1.2 The photo-Fenton process.............................................. 19

I.3 Aim of the work...................................................................... 20 II State of the art ............................................................................... 21

II.1 The homogeneous Fenton reaction......................................... 21 II.2 The heterogeneous Fenton reaction........................................ 22

II.2.1 The heterogeneous Fenton reaction with zeolite ........... 22 II.2.2 The heterogeneous Fenton reaction with perovskite ..... 23

II.3 UV/oxidation processes.......................................................... 23 II.3.1 Photolysis of hydrogen peroxide.................................... 23 II.3.2 The homogeneous photo-Fenton reaction ..................... 25 II.3.3 The heterogeneous photo-Fenton reaction .................... 25

III Experimental methods.............................................................. 29 III.1 Catalyst characterization ........................................................ 29

III.1.1 ICP-MS .......................................................................... 29 III.1.2 Thermal analysis (TG-MS) ............................................ 30 III.1.3 N2 adsorption measurements ......................................... 33 III.1.4 The micro Raman spectroscopy..................................... 33 III.1.5 SEM analysis ................................................................. 34

II

III.1.6 NIR-UV-VIS DRS ........................................................... 35 III.1.7 XRD spectroscopy.......................................................... 35

III.2 Laboratory apparatus for catalytic Fenton oxidation.............. 35 III.3 Laboratory apparatus for catalytic photo-Fenton oxidation.... 37 III.4 Laboratory apparatus for total organic carbon analysis.......... 39 III.5 Analytical method for H2O2 determination............................. 40

IV Experimental results: Fenton oxidation of acetic acid on FeY zeolite .................................................................................................... 43

IV.1 Samples preparation ............................................................... 43 IV.1.1 The HY based catalyst.................................................... 43

IV.2 Catalysts characterisation ....................................................... 45 IV.2.1 Specific surface area and chemical analysis ................. 45 IV.2.2 X-ray diffraction spectroscopy (XRDS) ......................... 45

IV.3 Catalytic activity tests............................................................. 46 IV.3.1 Homogeneous catalytic Fenton oxidation...................... 46 IV.3.1.1 Acetic acid solution ................................................... 47 IV.3.1.2 Real wastewater......................................................... 47 IV.3.2 Heterogeneous catalytic Fenton oxidation .................... 48 IV.3.2.1 Effect of reaction temperature ................................... 48 IV.3.3 Thermal analysis ............................................................ 50 IV.3.4 Leaching test .................................................................. 53

V Experimental results: characterization of the perovskite based monolith....................................................................................................... 55

V.1 Sample preparation ................................................................. 55 V.2 Thermal analysis..................................................................... 56 V.3 X-ray analysis ......................................................................... 58 V.4 SEM analysis .......................................................................... 59 V.5 Micro Raman spectroscopy .................................................... 60 V.6 Specific surface area ............................................................... 61 V.7 NIR-UV-VIS DRS.................................................................. 61

VI Experimental results: Fenton oxidation of acetic acid on LaMeO3 perovskite..................................................................................... 65

VI.1 Catalytic activity tests............................................................. 65 VI.1.1 Catalytic decomposition of H2O2 on LaMnO3 and LnFeO3

....................................................................................... 65 VI.1.2 Fenton oxidation of acetic acid on LaMnO3 (3.67%) .... 67 VI.1.3 Fenton oxidation of acetic acid on Pt/LaMnO3 ............. 69 VI.1.4 Fenton oxidation of acetic acid on LaFeO3 (2.24%) ..... 70 VI.1.5 Fenton oxidation of acetic acid on LaCuO3................... 72 VI.1.6 Fenton oxidation of acetic acid on LaNiO3.................... 75 VI.1.7 Fenton oxidation of acetic acid on LaCoO3................... 77

VI.2 Leaching test........................................................................... 78 VII Experimental results: photooxidation of acetic acid.............. 81

VII.1 Photooxidation test conditions and typical trends .............. 81

III

VII.2 Photolysis reactions............................................................ 84 VII.2.1 Photolysis of hydrogen peroxide in absence of acetic acid

....................................................................................... 84 VII.2.2 Photolysis of hydrogen peroxide in the presence of acetic

acid ....................................................................................... 85 VII.3 Photocatalytic decomposition of H2O2............................... 87

VII.3.1 Homogeneous photocatalytic decomposition of H2O2 ... 87 VII.3.2 Heterogeneous photocatalytic decomposition of H2O2.. 88

VII.4 Photocatalytic decomposition of acetic acid ...................... 91 VII.5 Catalyst samples for photo-Fenton tests............................. 93 VII.6 Catalytic photo-Fenton oxidation....................................... 93

VII.6.1 Homogeneous photo-Fenton oxidation.......................... 93 VII.6.2 Heterogeneous photo-Fenton oxidation ........................ 95 VII.6.2.1 Heterogeneous photo-Fenton oxidation on LaMnO3 (3.67%) ................................................................................... 95 VII.6.2.2 Heterogeneous photo-Fenton oxidation on Pt/LaMnO3 ................................................................................... 97 VII.6.2.3 Heterogeneous photo-Fenton oxidation on LaFeO3 (2.24%) ................................................................................... 98 VII.6.2.4 Heterogeneous photo-Fenton oxidation on LaCuO3.. 99 VII.6.2.5 Heterogeneous photo-Fenton oxidation on LaCoO3 100 VII.6.2.6 Heterogeneous photo-Fenton oxidation on LaNiO3 101 VII.6.2.7 Heterogeneous photo-Fenton oxidation on LnFeO3 (48%) ................................................................................. 103 VII.6.2.8 Heterogeneous photo-Fenton oxidation on LnFeO3 (88%) ................................................................................. 103 VII.6.2.9 Heterogeneous photo-Fenton oxidation on Pt/Ln2O3 .... ................................................................................. 104 VII.6.2.10 Heterogeneous photo-Fenton oxidation on Pd/Ln2O3 ... ................................................................................. 105

VII.7 Thermal analysis .............................................................. 106 VII.8 Catalytic activity comparison........................................... 107

VII.8.1 Heterogeneous vs homogeneous Photo-Fenton........... 107 VIII Experimental results: photo-Fenton oxidation of acetic acid

on LaMnO3, LaFeO3 and LnFeO3 .......................................................... 109 VIII.1.1 Comparison of catalytic activity of the monolith with

respect to powder catalysts ............................................................... 109 VIII.1.2 Effect of mass catalyst ............................................. 112 VIII.1.3 Effect of pH.............................................................. 113 VIII.1.4 Effect of H2O2 concentration ................................... 116 VIII.1.5 Effect of dosage of H2O2.......................................... 117

VIII.2 Leaching test .................................................................... 121 IX Heterogeneous photo-Fenton: reaction mechanism hypothesis

.................................................................................................. 123

IV

X Experimental results: photo-Fenton oxidation of alcohols on LaMeO3 ..................................................................................................... 129

X.1 Photolysis.............................................................................. 129 X.1.1 Photolysis of ethanol.................................................... 129 X.1.2 Photolysis of methanol ................................................. 130

X.2 Catalytic photo-Fenton oxidation of ethanol on LaMnO3 (3.67%) .............................................................................................. 131

X.3 Catalytic photo-Fenton oxidation of methanol on LaMnO3 (3.67%) .............................................................................................. 131 XI Experimental results: photo-Fenton oxidation of synthetic

winery wastewater on LaMeO3 ............................................................... 133 XI.1 Photolysis of synthetic winery wastewaters (red wine)........ 135 XI.2 Photolysis of synthetic winery wastewaters (red wine not

containing sulphites) .............................................................................. 137 XI.3 Catalytic photo-Fenton oxidation of synthetic winery

wastewaters (red wine) on LaMnO3 (3.67%)......................................... 139 XI.4 Catalytic photo-Fenton oxidation of synthetic winery

wastewaters (local red wine not containing sulphites) on LaMnO3 (3.67%) .............................................................................................. 141

XI.5 Catalytic photo-Fenton oxidation of the synthetic winery wastewaters (red wine local not containing sulphites) on LnFeO3 (48%) ... .............................................................................................. 142

XI.6 Effect of dosage of H2O2 (red wine local not containing sulphites) .............................................................................................. 144

XI.7 Leaching test......................................................................... 146 XII Conclusions.............................................................................. 149 XIII References ................................................................................ 151

V

Index of figures

Figure 1. Line graph of the evolution of contamination levels (on an arbitrary scale) of natural waters in countries with sustainable development. From left to right the lines represent municipal faecal waste drainage, industrial effluents, nutrients and micro-pollutants. Contamination levels due to environmental problems increase until a solution is found and subsequently decrease......................................... 2

Figure 2. Line graph of contamination levels (on an arbitrary scale) of natural waters in non-sustainable developed countries. From left to right the lines represent municipal faecal waste drainage, industrial effluents, nutrients and micro-pollutants. Environmental problems have increased with no solution yet having been found................................. 3

Figure 3. Mechanism of electrochemical processes. ...................................... 6 Figure 4. The water photolysis reaction......................................................... 7 Figure 5. Oxidation power of selected oxidizing species. .............................. 9 Figure 6. Suitability of water treatment technologies according to COD

contents (Andreozzi et al., 1999). ........................................................ 11 Figure 7. Oxidizable compounds by hydroxyl radicals (Bigda, 1995). ........ 14 Figure 8. Mechanism of Fenton reaction. .................................................... 15 Figure 9. Mechanism of photo-Fenton reaction. .......................................... 15 Figure 10. Proportion of Fe2+ and the species in equilibrium with it at 25°C.

............................................................................................................. 16 Figure 11. Concentration of Fe3+ in solution in relation to the pH at 25°C. 17 Figure 12. Proportion of Fe3+ and the existing species in equilibrium with it

at 25°C................................................................................................. 17 Figure 13. The Fenton Reaction: scheme of mechanism.............................. 18 Figure 14. Reaction of ferrous ion combined with hydrogen peroxide. ....... 19 Figure 15. The photo-Fenton Reaction: scheme of mechanism. .................. 19 Figure 16. Photo-induced reactions. ............................................................ 20 Figure 17. TGAQ500 Thermogravimetric Analyzer..................................... 30 Figure 18. SDTQ600 Simultaneous DSC/TGA............................................. 30 Figure 19. Pfieffer Vacuum Benchtop Thermostar mass spectrometer. ....... 31 Figure 20. TG and DTG curves. ................................................................... 32 Figure 21. Costech Sorptometer 1040. ......................................................... 33

VI

Figure 22. Dispersive MicroRaman (Invia, Renishaw). ............................... 34 Figure 23. Laboratory apparatus for catalytic Fenton oxidation................. 36 Figure 24. Laboratory apparatus for the catalytic photo-Fenton oxidation.37 Figure 25. Sealed stainless-steel batch photoreactor. .................................. 37 Figure 26. Components of the sealed stainless-steel batch photoreactor. ... 38 Figure 27. The ultraviolet spectrum of the UV lamp used............................ 39 Figure 28. Set-up of experiment for total organic carbon analysis. ............. 40 Figure 29. Y structure. .................................................................................. 44 Figure 30. X-Ray diffraction spectra of FeY and HY catalysts..................... 46 Figure 31. Conversion as a function of time of homogeneous catalytic

reaction with acetic acid at T=25°C. Experimental conditions: pHt=0=2.67, mcatalyst= 1.426 g............................................................... 47

Figure 32. Conversion as a function of time of a heterogeneous catalytic reaction with liming solution at T=25°C. Experimental conditions: pHt=0=2.0, mcatalyst= 0.379 g................................................................. 48

Figure 33. Conversion as a function of time of reaction in the case of the FeY catalyst at T=25°C. Experimental conditions: pHt=0=2.67, mcatalyst= 0.170 g. ................................................................................................ 49

Figure 34. Conversion as a function of time of reaction in the case of the FeY catalyst at T=70°C. Experimental conditions: pHt=0=2.67, mcatalyst= 0.170 g. ................................................................................................ 50

Figure 35. Thermal analysis performed on FeY sample before catalytic activity test. .......................................................................................... 51

Figure 36. Thermal analysis performed on FeY sample after catalytic activity test at T=25°C in air flow.................................................................... 52

Figure 37. Thermal analysis performed on FeY sample after catalytic activity test at T=70°C in air flow.................................................................... 52

Figure 38. Leaching test on FeY after catalytic test at T=70°C................... 53 Figure 39. Perovskite structure. ................................................................... 55 Figure 40. Thermal analysis of perovskite precursors. ................................ 57 Figure 41. X-ray diffraction patterns of cordierite carrier and supported

perovskite catalysts. P perovskite peaks; C, lanthanum oxy-carbonate peaks. ................................................................................................... 58

Figure 42. SEM data on a carrier and on supported catalysts: (a) carrier, (b) carrier+Ln2O3, (c) carrier+LaMnO3, (d) carrier+Ln2O3+LaMnO3. .. 59

Figure 43. Raman spectra of LaMnO3 (3.67 %) and LaMnO3 with Pt samples. ............................................................................................... 60

Figure 44. Raman spectra of LaFeO3 monolith and LaFeO3 powder........... 61 Figure 45. Band-gap calculus from the DR–UV–vis spectra of LaMnO3..... 62 Figure 46. Band-gap calculus from the DR–UV–vis spectra of Pt/LaMnO3..

............................................................................................................. 62 Figure 47. Band-gap calculus from the DR–UV–vis spectra of LaFeO3...... 63 Figure 48. Band-gap calculus from the DR–UV–vis spectra of LnFeO3

(48%). .................................................................................................. 63

VII

Figure 49. Band-gap calculus from the DR–UV–vis spectra of LnFeO3 (88%). .................................................................................................. 64

Figure 50. Catalytic decomposition of H2O2 with LaMnO3 (2.57%). Experimental conditions: pHt=o=5.3, mcatalyst= 19 g, [H2O2]t=0= 0.083 mol/l..................................................................................................... 66

Figure 51. Catalytic decomposition of H2O2 with LnFeO3 (88%). Experimental conditions: pHt=o=5.4, mcatalyst= 15 g, [H2O2]t=0= 0.083 mol/l..................................................................................................... 66

Figure 52. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaMnO3 (3.67%) catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 4.9 g, [H2O2]t=0= 0.083 mol/l..................................................................................................... 67

Figure 53. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaMnO3 (3.67%) catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 4.9 g, [H2O2]t=0= 0.167 mol/l..................................................................................................... 68

Figure 54. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of Pt/LaMnO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 6.0 g, [H2O2]t=0= 0.083 mol/l..................................................................................................... 69

Figure 55. Total organic carbon removal as function of time of reaction in the case of Pt/LaMnO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 6.0 g, [H2O2]t=0= 0.167 mol/l. ............................ 70

Figure 56. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaFeO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 5.4 g, [H2O2]t=0= 0.083 mol/l..................................................................................................... 71

Figure 57. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaFeO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 5.4 g, [H2O2]t=0= 0.167 mol/l..................................................................................................... 72

Figure 58. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaCuO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 6.4 g, [H2O2]t=0= 0.083 mol/l..................................................................................................... 73

Figure 59. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaCuO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 5.4 g, [H2O2]t=0= 0.167 mol/l..................................................................................................... 74

Figure 60. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaNiO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 6.0 g, [H2O2]t=0= 0.083 mol/l..................................................................................................... 75

VIII

Figure 61. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaNiO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 6.0 g, [H2O2]t=0= 0.167 mol/l. .................................................................................................... 76

Figure 62. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaCoO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 5.4 g, [H2O2]t=0= 0.087 mol/l. .................................................................................................... 77

Figure 63. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of the LaCoO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 5.4 g, [H2O2]t=0= 0.167 mol/l. .................................................................................................... 78

Figure 64. Catalytic photo-Fenton oxidation in nitrogen stream on LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; mcatalyst= 4.9 g; C0

CH3COOH= 0.021 mol/l; C0H2O2= 0.083 mol/l; P= 1 atm; T=25°C;

pH=3.9, QN2= 250 Ncc/min. ................................................................ 82 Figure 65. Carbon dioxide concentration formed during catalytic photo-

Fenton oxidation in nitrogen stream on LaMnO3 (3.67%). ................. 83 Figure 66. Photolysis of H2O2 in absence of acetic acid. Experimental

conditions: V tot.: 100 ml; C0H2O2= 0.167 mol/l; P= 1 atm; T=25°C;

pH=3.9................................................................................................. 84 Figure 67. Photolysis of H2O2 in the presence of acetic acid. Experimental

conditions: V tot.: 100 ml; H2O2/CH3COOH= 4; C0H2O2= 0.083 mol/l;

P= 1 atm; T=25°C; pH=3.9................................................................ 85 Figure 68. Photolysis of H2O2 in the presence of acetic acid. Experimental

conditions: V tot.: 100 ml; H2O2/CH3COOH= 8; C0H2O2= 0.167 mol/l;

P= 1 atm; T=25°C; pH=3.9................................................................ 86 Figure 69. Photocatalytic decomposition of H2O2 with Fe2(C2O4)3.

Experimental conditions: V tot.: 100 ml; mcatalyst= 0.7 g; C0H2O2= 0.083

mol/l; P= 1 atm; T=25°C; pH=3.9. .................................................... 87 Figure 70. Photocatalytic decomposition of H2O2 with Fe2(C2O4)3.


mol/l; P= 1 atm; T=25°C; pH=3.9. .................................................... 88 Figure 71. Photocatalytic decomposition of H2O2 with LaMnO3 (3.67%).


mol/l; P= 1 atm; T=25°C; pH=3.9. .................................................... 89 Figure 72. Photocatalytic decomposition of H2O2 with LaMnO3 (3.67%).


mol/l; P= 1 atm; T=25°C; pH=3.9. .................................................... 89 Figure 73. Photocatalytic decomposition of H2O2 with Pt/LaMnO3.


mol/l; P= 1 atm; T=25°C; pH=3.9. .................................................... 90

IX

Figure 74. Photocatalytic decomposition of H2O2 with Pt/LaMnO3. Experimental conditions: V tot.: 100 ml; mcatalyst= 6.0 g; C0

H2O2= 0.167 mol/l; P= 1 atm; T=25°C; pH=3.9. .................................................... 91

Figure 75. Photocatalytic decomposition of acetic acid with LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; mcatalyst= 4.9 g; TOCt=0= 250 ppm; P= 1 atm; T=25°C; pH=3.9. ............................... 92

Figure 76. Photocatalytic decomposition of acetic acid with LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; mcatalyst= 4.9 g; TOCt=0= 500 ppm; P= 1 atm; T=25°C; pH=3.9. ............................... 92

Figure 77. Homogeneous photo-Fenton with Fe2(C2O4)3. Experimental conditions: V tot.: 100 ml; mcatalyst= 0.7 g; C0

CH3COOH= 0.021 mol/l; C0

H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9. ............................ 94 Figure 78. Heterogeneous photo-Fenton with LaMnO3 (3.67%).

Experimental conditions: V tot.: 100 ml; mcatalyst= 4.9 g; C0CH3COOH=

0.021 mol/l; C0H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9. ........ 95

Figure 79. Heterogeneous photo-Fenton with LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; mcatalyst= 4.9 g; C0


H2O2= 0.167 mol/l; P= 1 atm; T=25°C; pH=3.9. ........ 96 Figure 80. Heterogeneous photo-Fenton with LaMnO3 with Pt. Experimental

conditions: V tot.: 100 ml; mcatalyst= 6.0 g; C0CH3COOH= 0.021 mol/l;

C0H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9. ............................ 97

Figure 81. Heterogeneous photo-Fenton with LaMnO3 with Pt. Experimental conditions: V tot.: 100 ml; mcatalyst= 6.0 g; C0


H2O2= 0.167 mol/l; P= 1 atm; T=25°C; pH=3.9. ............................ 98 Figure 82. Heterogeneous photo-Fenton with LaFeO3 (2.24%). Experimental


C0H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9. ............................ 99

Figure 83. Heterogeneous photo-Fenton with LaCuO3. Experimental conditions: V tot.: 100 ml; mcatalyst= 6.4 g; C0


H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9. .......................... 100 Figure 84. Heterogeneous photo-Fenton with LaCoO3. Experimental


C0H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9. .......................... 101

Figure 85. Heterogeneous photo-Fenton with LaNiO3. Experimental conditions: V tot.: 100 ml; mcatalyst= 6.0 g; C0


H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9. .......................... 102 Figure 86. Heterogeneous photo-Fenton with LnFeO3 (48%). Experimental



Figure 87. Heterogeneous photo-Fenton with LnFeO3 (88%). Experimental conditions: V tot.: 100 ml; mcatalyst= 15.3 g; C0


H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9. .......................... 104

X

Figure 88. Heterogeneous photo-Fenton with Pt/Ln2O3. Experimental conditions: V tot.: 100 ml; mcatalyst= 4.4 g; C0


H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9. .......................... 105 Figure 89. Heterogeneous photo-Fenton with Pd/Ln2O3. Experimental



Figure 90. Thermal analysis performed on the LaMnO3 (2.69%) sample before and after the catalytic activity test.......................................... 107

Figure 91. Heterogeneous vs homogeneous photo-Fenton. ....................... 108 Figure 92. Comparison of catalytic activity of the monolith LaMnO3 (2.69%)

with respect to powdered catalyst. Experimental conditions: V tot.: 100 ml; mcatalyst= 6.0 g; C0

CH3COOH= 0.021 mol/l; C0H2O2= 0.083 mol/l; P= 1

atm; T=25°C; pH=3.9. ...................................................................... 110 Figure 93. Comparison of catalytic activity of the monolith LaMnO3 (2.69%)

with respect to powder not supported. Experimental conditions: V tot.: 100 ml; mcatalyst (monolith)= 5.0 g; mcatalyst (powder)= 0.184 g; C0


H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9. ...... 111 Figure 94. Comparison of catalytic activity of the monolith LaFeO3 with

respect to powder. Experimental conditions: V tot.: 100 ml; mcatalyst

(monolith)= 6.0 g; mcatalyst (powder)= 0.122 g; C0CH3COOH= 0.021 mol/l;


Figure 95. Comparison of catalytic activity of the monolith LaMnO3 (2.57%) with different mass. Experimental conditions: V tot.: 100 ml; mcatalyst= 14.0 g – 4.9 g; C0


atm; T=25°C; pH=3.9. ...................................................................... 113 Figure 96. Effect of pH reaction on catalytic activity of monolith LaMnO3

(3.67%). Experimental conditions: V tot.: 100 ml; mcatalyst= 4.9 g; C0

CH3COOH= 0.021 mol/l; C0H2O2= 0.083 mol/l; P= 1 atm; T=25°C. . 114

Figure 97. Effect of pH reaction on catalytic activity of monolith LaMnO3 (2.69%). Experimental conditions: V tot.: 100 ml; mcatalyst= 5.6 g; C0

CH3COOH= 0.021 mol/l; C0H2O2= 0.083 mol/l; P= 1 atm; T=25°C. . 115

Figure 98. Comparison of catalitic activity on LaMnO3 (3.67%) on changing H2O2. concentration........................................................................... 116

Figure 99. Effect of dosage of H2O2 on the catalytic activity of LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; mcatalyst= 4.9 g; C0

CH3COOH= 0.021 mol/l; C0H2O2= 0.014 mol/l; CH2O2/t= 0.009 M/h; P=

1 atm; T=25°C................................................................................... 117 Figure 100. Effect of dosage of H2O2 on the catalytic activity of LnFeO3

(48%). Experimental conditions: V tot.: 100 ml; mcatalyst= 14 g; C0

CH3COOH= 0.021 mol/l; C0H2O2= 0.012 mol/l; CH2O2/t= 0.006 M/h; P=

1 atm; T=25°C................................................................................... 118 Figure 101. Effect of dosage of H2O2 on the catalytic activity of LnFeO3

(88%). Experimental conditions: V tot.: 100 ml; mcatalyst= 15.3 g;

XI

C0CH3COOH= 0.021 mol/l; C0

H2O2= 0.022 mol/l; CH2O2/t= 0.021 M/h; P= 1 atm; T=25°C................................................................................... 118

Figure 102. Photolysis of hydrogen peroxide............................................. 124 Figure 103. Catalytic decomposition of H2O2. ........................................... 125 Figure 104. Illustration of the photo-Fenton process................................. 127 Figure 105. Photolysis of ethanol. Experimental conditions: V tot.: 100 ml;

H2O2/C2H5OH= 2; C0H2O2= 0.042 mol/l; C0

C2H5OH= 0.021; P= 1 atm; T=25°C; pH=6.5. .............................................................................. 130

Figure 106. Photolysis of methanol. Experimental conditions: V tot.: 100 ml; H2O2/CH3OH= 1; C0

H2O2= 0.042 mol/l; C0CH3OH= 0.021 mol/l; P= 1

atm; T=25°C; pH=5.5....................................................................... 130 Figure 107. Catalytic photo-Fenton oxidation of ethanol on LaMnO3

(3.67%). Experimental conditions: V tot.: 100 ml; H2O2/C2H5OH= 2; C0

H2O2= 0.042 mol/l; C0C2H5OH= 0.021; P= 1 atm; T=25°C; pH=6.5.

........................................................................................................... 131 Figure 108. Catalytic photo-Fenton oxidation of methanol on LaMnO3

(3.67%). Experimental conditions: V tot.: 100 ml; H2O2/CH3OH= 1; C0

H2O2= 0.042 mol/l; C0CH3OH= 0.021 mol/l ; P= 1 atm; T=25°C;

pH=5.5. ............................................................................................. 132 Figure 109. Photolysis of synthetic winery wastewaters obtained by diluting

commercial red wine. Experimental conditions: V tot.: 100 ml; H2O2/TOCwine= 1; C0

H2O2= 0.042 mol/l; P= 1 atm; T=25°C; pH=4.2............................................................................................................ 135

Figure 110. Photolysis of synthetic winery wastewaters obtained by diluting commercial red wine. Experimental conditions: V tot.: 100 ml; H2O2/TOCwine= 2; C0

H2O2= 0.042 mol/l; P= 1 atm; T=25°C; pH=4.2............................................................................................................ 136

Figure 111. Photolysis of synthetic winery wastewaters obtained by diluting commercial red wine not containing sulphites. Experimental conditions: V tot.: 100 ml; H2O2/TOCwine= 1; C0

H2O2= 0.042 mol/l; P= 1 atm; T=25°C; pH=4.2.................................................................... 137


H2O2= 0.084 mol/l; P= 1 atm; T=25°C; pH=4.2.................................................................... 138

Figure 113. Catalytic photo-Fenton oxidation of synthetic winery wastewaters obtained by diluting commercial red wine on LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; H2O2/TOCwine= 1; C0

H2O2= 0.042 mol/l; P= 1 atm; T=25°C; pH=4.2. .......................... 139 Figure 114. Catalytic photo-Fenton oxidation of synthetic winery

wastewaters obtained by diluting commercial red wine on LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; H2O2/TOCwine= 2; C0

H2O2= 0.042 mol/l; P= 1 atm; T=25°C; pH=4.2. .......................... 140

XII

Figure 115. Catalytic photo-Fenton oxidation of synthetic winery wastewaters obtained by diluting local red wine on LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; H2O2/TOCwine= 1; C0

H2O2= 0.042 mol/l; P= 1 atm; T=25°C; pH=4.2. ........................................ 141


H2O2= 0.084 mol/l; P= 1 atm; T=25°C; pH=4.2. ........................................ 142

Figure 117. Catalytic photo-Fenton oxidation of synthetic winery wastewaters obtained by diluting local red wine on LnFeO3 (48%). Experimental conditions: V tot.: 100 ml; H2O2/TOCwine= 1; C0

H2O2= 0.042 mol/l; P= 1 atm; T=25°C; pH=4.2. ........................................ 143

Figure 118. Effect of dosage of H2O2 on the catalytic activity of LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; mcatalyst= 4.9 g; TOC0

wine= 500 mg/l; C0H2O2= 0.006 mol/l; CH2O2/t= 0.009 M/h; P= 1

atm; T=25°C; pH=4.2. ...................................................................... 144 Figure 119. Effect of dosage of H2O2 on the catalytic activity of LnFeO3

(48%). Experimental conditions: V tot.: 100 ml; mcatalyst= 14 g; TOC0

wine= 500 mg/l; C0H2O2= 0.006 mol/l; CH2O2/t= 0.012 M/h; P= 1

atm; T=25°C; pH=4.2. ...................................................................... 145

XIII

Index of tables

Table 1. Characteristic of the UV lamp utilised........................................... 38 Table 2. Procedure of ion exchange for samples. ........................................ 44 Table 3. Microporous volume of HY and FeY.............................................. 45 Table 4. List of perovskite-based catalysts characterised............................ 56 Table 5. pH and oxygen dissolved values for the catalytic decomposition of

hydrogen peroxide. .............................................................................. 67 Table 6. Metal ion analysis of the some catalyst used for the catalytic Fenton

reaction................................................................................................ 79 Table 7. List of catalysts tested. ................................................................... 93 Table 8. Comparison of hydrogen peroxide consumption of the photo-Fenton

of LaMnO3 (3.67%) with dosage of H2O2 with respect to the photo/LaMnO3 system with H2O2/CH3COOH=4. ............................. 119

Table 9. Comparison of hydrogen peroxide consumption of the photo-Fenton of LnFeO3 (48%) with dosage of H2O2 with respect to the photo/LnFeO3 system with H2O2/CH3COOH=4................................ 120

Table 10. Comparison of hydrogen peroxide consumption of the photo-Fenton of LnFeO3 (88%) with dosage of H2O2 with respect to the photo/LnFeO3 system with H2O2/CH3COOH=4................................ 120

Table 11. Metal ion analysis of the some catalysts used for the catalytic photo-Fenton reaction. ...................................................................... 121

Table 12. Comparison of hydrogen peroxide consumption of photo-Fenton of LaMnO3 (3.67%) with dosage of H2O2 with respect to the photo/LaMnO3 system with H2O2/ TOCwine =2.................................. 145

Table 13. Comparison of hydrogen peroxide consumption of the photo-Fenton of LnFeO3 (48%) with dosage of H2O2 with respect to the photo/LnFeO3 system with H2O2/ TOCwine =1................................... 146

Table 14. Metal ion analysis of the some catalysts used for the catalytic photo-Fenton reaction of synthetic winery wastewater..................... 147

Abstract Advanced oxidation processes (AOPs) are an attractive alternative for

treating wastewater containing organic substances. Currently, AOPs widely studied are the Fenton process (Fe2+/H2O2) and photolysis (H2O2/UV). In the development of heterogeneous catalysts for Fenton wastewater treatment, various powder formulations have been investigated. Recent studies have also been devoted to UV-enhanced Fenton process. Limitations due to the use of homogeneous catalysts, such as limited pH range, production of Fe containing sludge, and deactivation could be overcome by heterogeneous catalysts.

In this work, an innovative application of monolith structured perovskite catalysts in heterogeneous photo-Fenton reaction of acetic acid, methanol and ethanol, chosen as model pollutants, and of winery wastewater has been reported.

A recirculating stainless-steel photocatalytic sealed batch reactor, useful to test several catalysts both in powder and in a structured form has been specifically developed

It has been found that, from values of TOC removal and carbon dioxide evolved in gas phase, the total carbon mass balance was closed to 100%, indicating the complete mineralization of the acetic acid, without formation of noxious by-products.

The results showed that use of a heterogeneous structured catalyst in the photo-Fenton reaction greatly improves TOC removal with respect to homogeneous ones and leads to better use of H2O2.

Among Fe-zeolites, Fe-, Mn-, Co-, Ni-, Cu-based perovskites, lanthanides oxides, in the presence or in the absence of low amounts of Pd and Pt, best performances were shown by LaMnO3 and LnFeO3 structured catalysts.

The study then focused on Mn and Fe perovskites, by optimising operative process conditions with resulting low H2O2 initial concentrations, pH=6, catalyst/wastewater mass ratio of 5 wt%.

The use of perovskite structured catalysts also leads to a widened pH range of operation.

It has been shown that in photo-Fenton processes, efficiency depends on optimal dosage of H2O2. Lower H2O2 consumption with total TOC removal within 7 hours can be reached by H2O2 step addition.

A reaction mechanism, involving H2O2 and CH3COOH competitive adsorption on catalyst surface and the oxidation of adsorbed acetic acid by UV-generated hydroxyls radicals, has been hypothesized.

Finally, it has been evidenced that photocatalytic advanced oxidation based on H2O2 is an appropriate purification treatment for winery wastewaters.

I Introduction One of the characteristics that best defines today’s society in what are

known as developed countries is the production of waste products. There is practically no human activity that does not produce waste products and in addition there is a direct relationship between the standard of living in a society or country and the amount of waste products produced. Approximately 23% of the world’s population live in developed countries, consume 78% of the resources and produce 82% of the waste products (Blanco et al., 1996). In addition, it has to be pointed out that the volume of residual waste increases in an exceptional way with regards to a country’s level of industrialisation. At present, there are some five million known substances registered, of which approximately 70,000 are widely used worldwide, and it is estimated that 1,000 new chemical substances are added to the list each year.

The need for sustainable growth is countered by the reality of demographic growth.

Many countries are experiencing a period of non-sustainable growth, with very variable macroeconomic achievements in various countries. Even in the case where some countries have achieved beneficial macroeconomic progress, these achievements are not reflected in the standard of living and quality of life of large sections of the population.

These large contrasts are reflected in the problems related to the rational management of water, which cannot be dealt with unilaterally, but by many different procedures.

A recent publication (Schertenleib et al., 2000) contains a general description of the problems that societies have had to face regarding water use as society evolved. Countries with sustainable development have, one by one, confronted the problems related to biological contamination, icuding levels of heavy metals, intensive use of nutrients, and organic contaminants at very low levels. Water disinfection, the treatment of effluents before being discharged into water systems, the limitation and substitution of nitrates and phosphates in products that are used on a massive scale and developments in analytical chemistry and in ecotoxicology are examples of some of the “tools” used to combat these problems. The evolution of contamination

Chapter I

2

levels (on an arbitrary scale) of natural waters in countries with sustainable development is shown in Figure 1. It should be noted that the time needed to resolve each problem as it arises, has become shorter over the decades.

Figure 1. Line graph of the evolution of contamination levels (on an arbitrary scale) of natural waters in countries with sustainable development. From left to right the lines represent municipal faecal waste drainage, industrial effluents, nutrients and micro-pollutants. Contamination levels due to environmental problems increase until a solution is found and subsequently decrease.

In contrast, countries with non-sustainable development are represented in Figure 2. There is no doubt that many developing countries can be included in this category, or even in more complicated situations with more primitive stages of development. The problems deriving from the toxicological effects of organic compounds, active at very low levels, must be resolved at the same time as water disinfection for rural communities. It is clear that innovative procedures are needed to deal with a wide range of problems which vary notably in the scale of application and the complexity of the problems themselves (Blesa, 2001).

Up until relatively recently, the discharging of waste into the environment was the only way of eliminating it, until the self-cleaning capacity of the environment was no longer sufficient. Permitted levels of pollution have been vastly exceeded, causing such environmental contamination that our natural resources cannot be employed for certain uses because their characteristics have been altered. The main problem stems from waste coming from industry and agriculture, along with environmental contamination caused by the population.

Introduction

3

Figure 2. Line graph of contamination levels (on an arbitrary scale) of natural waters in non-sustainable developed countries. From left to right the lines represent municipal faecal waste drainage, industrial effluents, nutrients and micro-pollutants. Environmental problems have increased with no solution yet having been found.

Phenols, pesticides, fertilizers, detergents and other chemical products are disposed of untreated directly into the environment, by controlled or uncontrolled discharging, and with no treatment strategy.

In this general context, it is very clear that the strategy to continue in the search of solutions to this problem which is in sensitive growth, mainly in developing countries, will concentrate on two fundamental aspects:

1. The development of appropriate methods for decontamination of drinking, ground and surfaces waters.

2. The development of appropriate methods for wastewater containing toxic or non-biodegradable compounds.

I.1 Removal of organic compounds

The treatment processes of different types of effluents to be used must guarantee the elimination or recuperation of the pollutant in order to reach the strict authorized levels for the discharge of these effluents. The levels of pollutants allowed in discharge waters, are directly related to the type of pollutant present in the effluent.

In general, the elimination of organic pollutants in an aqueous solution need to undergo one or more basic treatment techniques (Weber et al., 1986), (Chuang et al., 1992): chemical oxidation, air desorption, liquid-

Chapter I

4

liquid extraction, adsorption, inverse osmosis, ultra-filtration and biological treatment. Depending on the compound present in the solution destructive methods can be used such as, for example, chemical oxidation, incineration or degradation, which allow efficient elimination of the pollutant from an aqueous form. Non-destructive methods can also be used such as, liquid-liquid extraction and absorption, that allow recuperation of the pollutant. Application of one or other of the methods depends on concentration in the effluent. It is necessary to choose the most adequate method according to the characteristics of the concentration. For high concentrations of pollutants, techniques such as incineration or certain chemical oxidation methods are advisable. On the other hand for low concentrations of pollutants, adsorption, membrane techniques, and other chemical oxidation methods are suitable. The choice of one or other of the methods basically depends on the cost of the process and other factors like the concentration and volume flow of the effluent to be treated.

The most widely used treatment methods of organic compounds are described below.

I.1.1 Incineration

Incineration is a useful method for small quantities of wastewater with high pollutant concentration. However, it presents the disadvantage of requiring large investments and also has high energy costs. The incinerators normally used for this process are similar to those used for sludge or industrial residues, and they can be horizontal, vertical or fluidized beds. One fundamental economic aspect in the incineration of organic solutions is the auxiliary fuel needed to maintain combustion. In the case of textile industries, incineration has been used in the treatment of sludge from textile wastewater and the ash is landfilled (Masselli et al., 1970).

Incineration can also be used to minimize the quantity of textile wastewater.

I.1.2 Air stripping

Air stripping involves the transfer of volatile organics from a liquid phase to the air phase by greatly increasing the air/water contact area. Typical aeration methods include packed towers, diffusers, trays, and spray aeration. This method has the advantage that it’s more established and more widely understood than chemical oxidation. It can be accurately designed from theory and experience without the need for design tests. If air emissions are not regulated, air stripping is by far the simplest and cheapest solution for the removal of volatile compounds from water. In the case of textile

Introduction

5

wastewater, air stripping used as pretreatment resulted in high solvent removal (Kabdasli et al., 2000).

I.1.3 Adsorption onto activated carbon

Carbon adsorption is an advanced wastewater treatment method used for the removal of recalcitrant organic compounds as well as residual amounts of inorganic compounds such as nitrogen, sulfides, and heavy metals. This is a separation method in which the contaminant is transferred from a water phase, where it is dissolved, to the surface of active carbon where it is accumulated for its subsequent extraction or destruction.

Adsorption onto activated carbon is widely used for wastewater treatment. Thus, it is used in the control of colour and odours, in the removal of organic compounds or trihalomethane precursors, to remove chlorine and in general to remove toxic compounds.

This method has also been combined with others and significant improvement has been obtained (Cañizares et al., 1999). Many studies have been found in the literature regarding the treatment of textile wastewater by means of activated carbon (Lin and Lai, 2000), (Yeh et al., 2002).

Most of them showed the high effectiveness of the carbon activated adsorption process in the reduction of COD (Chemical Oxidation Demand) and colour removal from textile wastewater.

I.1.4 Wet oxidation

In wet oxidation processes, organic and inorganic compounds are oxidized in the aqueous phase with oxygen or air, at high pressure and high temperature conditions. The temperature depends on the nature of the compounds to be degraded, however it oscillates between 150 and 350ºC. Pressure goes from 20 to 200 bar. COD removal ranges from 75 to 90% (Li et al., 1991). The mechanism of wet oxidation has been deeply studied and seems to take place by means of a free radical process. Among the compounds that have been catalogued as readily oxidizable by means of wet oxidation are aliphatic, aliphatic chlorides and aromatic compunds, which do not contain halogenated functional groups such as phenols or anilines. Compounds containing halogen and nitro functional groups have been found to be difficult to be degraded by this method (Scott, 1997). Experimental results indicate that over 90% removal of phenol or phenolic compounds can be achieved in wet oxidation wastewater treatment. The activated sludge process combined with wet oxidation, if appropriately operated, is capable of

Chapter I

6

drastically reducing COD concentration in high concentrated chemical wastewater to meet safe discharge requirement (Lin and Chuang, 1994).

I.1.5 Electrochemical oxidation

The use of electrochemical oxidation for the destruction of organic compounds in water solutions has been tried on bench and pilot plant scale (Boudenne et al., 1996), (Brillas et al., 1998), but is not used commercially because of high operating costs. One of the main advantages of electrochemical processes is that electrons are released by or spent by the electrodes, supplying a clean reactant, which does not increase the number of chemical molecules involved in the process. Nevertheless, electrochemila processes present some disadvantages, such as:

Electrochemical treatment is expensive in comparison with other processes and the mechanism in water is complex.

The effluent must be conductor. If the stream to be treated does not present good conductivity salt should be added.

Electrochemical oxidation of organic compounds is thermodynamically favoured against the competitive reaction of oxygen production by oxidation of water. However, the kinetics of oxidation of water is much faster than the kinetics of oxidation of organic compounds, among other reasons because of its higher concentration (Palau, 1998).

The mechanism of electrochemical processes involves three stages: electrocoagulation, electroflotation and electrooxidation. (Figure 3):

Figure 3. Mechanism of electrochemical processes.

Anodic oxidation is generally considered to be a direct technique, involving the direct transfer of an electron from the organic molecule to the electrode, thus generating a cationic radical. The fate of the cationic radical, the pH and the nature of the electrodes influence (in a decisive manner) the products formed. Radical combinations have frequently been observed.

Many articles have also been published on the application of electrochemical processes in textile industry wastewater treatment. In a large number of these articles, the efficiency of this method for colour removal has been proven (Lin and Peng 1994), (Vlyssides et al., 2000), (Zappi et al.,

Introduction

7

2000), (Gutierrez et al., 2001). It has also been used in combination with coagulation to remove colour, turbidity and COD.

I.1.6 Photochemical processes

For the oxidation of organic pollutants, a series of researchers have proposed direct photo-oxidation with ultraviolet light (Petersen et al. (1988). However, there are a number of limitations to its use. The first being that the organic compound to be eliminated must absorb light in competition with other compounds in the effluent to be treated. The second is that organic compounds generate a wide variety of photochemical reactions that can produce products that are more complex for degradation. In addition, not all the radiation emitted by the source of radiation is fully exploited, only the radiation absorbed and only a part of this produces chemical changes. This means that some reactions of photodegradation have very slow kinetics.

The addition of energy as radiation to a chemical compound is the principle of photochemical processes. Molecules absorb this energy and reach excited states with decay times long enough to take part in chemical reactions.

A large number of studies (Legrini et al., 1993) deal with the degradation of chemicals in water using Hg emission at 253.7 nm produced by low-pressure mercury lamps. However, results showed that 253.7 nm irradiation alone could not be used as an effective procedure for the removal of organic substances from water. This method may be useful for the degradation of substituted aromatic compunds, however it is totally inefficient for effective removal of chlorinated aliphatics. It should be noted, however, that low-pressure Hg lamps are quite efficient for water disinfection purposes. Medium and high-pressure lamps, with a broader emission spectrum, have been used more frequently for the degradation of contaminants. Medium-pressure Hg lamps emit particularly strongly in the spectral region between 254 and 400 nm and are not only effective in generating hydroxyl radicals from hydrogen peroxide or ozone, for example, but also by causing electronic transitions in a large number of organic molecules.

In photochemical reactions, hydroxyl radicals may be generated by water photolysis (Cervera et al., 1983) (Figure 4):

Figure 4. The water photolysis reaction.

Photolysis involves the interaction of light with molecules to bring about their dissociation into fragments. This reaction is a poor source of radicals, and in the reaction medium large quantity of reaction intermediates that absorb part of the radiation are generated, which causes the photo-oxidation

Chapter I

8

kinetics of the contaminants to decrease considerably. This make the process valid only for effluents with a low concentration of pollutants. Photochemical treatment, although partially solving the problem of the refractory compounds, has some negative aspects in its practical application, such as the high cost of UV radiation production. Furthermore, not all the emitted radiation is used, only the radiation absorbed, and only a fraction of this radiation produces chemical changes. This means that some photodegradation reactions have very low yields and slow kinetics.

To accelerate the process, other oxidants such as hydrogen peroxide and/or ozone, metallic salts or semiconductors like TiO2 can be added, giving rise to so-called Advanced Oxidation Processes. Instead of UV lamps, solar light could be used as radiation energy to degrade some compounds.

No effect was observed during direct photolysis of NB with a 150-W mercury-xenon lamp in the study carried out by (Lipczynska-Kochany 1992).

I.1.7 Biological oxidation

Biological treatment, generally by means of activated sludge (Wiesmann and Putnaerglis 1986), (Givens et al., 1991) in adequate conditions (Wu et al., 1994) has unquestionable advantages for the destruction of organic compounds. However, many organic pollutants cannot be effectively eliminated by biological oxidation in the treatment of municipal or residual waters or natural waters. Its application in the treatment of effluents with phenols, nitro aromatic, ether aliphatic compounds and textile waters is quite restricted because of the high toxicity inherent in these wastes, the need to adjust the pH to an adequate value and add food and oxygen in adequate quantities for the transforming microorganisms, as the viability of the process depends fundamentally on the health and activity of the latter. There are two kinds of processes in the biological treatment of biological compounds: aerobic and anaerobic (Eckenfelder et al. 1989). Aerobic processes are used more because of their efficiency and operational simplicity (Ruiz et al., 1992), (Urano et al., 1986), (Kameya et al., 1995). The results showed that it could be a good solution in the treatment of industrial wastewater (Pala and Tokat, 2001).

I.1.8 Chemical oxidation

Oxidation, by definition, is a process by which electrons are transferred from one substance to another. This leads to a potential expressed in volts referred to a normalized hydrogen electrode. From this, oxidation potentials

Introduction

9

of the different compounds are obtained. Figure 5 shows the potentials of the most commonly used oxidizers (Munter et al., 2001).

Figure 5. Oxidation power of selected oxidizing species.

Chemical oxidation appears to be one of the solutions able to comply with the legislation with respect to discharge in a determined receptor medium. It can also be considered as an economically viable preliminary stage to secondary treatment of biological oxidation for the destruction of non-biodegradable compounds which inhibit the process.

The optimization of the process (Akata and Gurol, 1992) arises in those conditions in which non-biodegradable material is eliminated, but with a minimum amount of oxidizer. That is to say, carrying out the oxidation to cause the formation of biodegradable compounds and not those of CO2 and H2O. It can be said to be an appropriate technique for small loads of pollutants; load meaning the concentration of the pollutant multiplied by the volume of flow of the effluent to be treated. This would otherwise become an expensive technique, because of its large oxidizer consumption, and it would have fewer possibilities in relation to other more appropriate techniques for greater loads, as could be the selective absorption of

Chapter I

10

pollutants when the concentration of the pollutant is high, or biological oxidation for low concentrations.

In addition to the polluting load, for chemical oxidation to be economically profitable, the concentration of the polluting load in the effluent has to be taken into account. This operation is easier to apply in the destruction of compounds like phenol, nitrobenzene, some colorants and their derivatives for concentrations between 100 and 500 mg/l. In the case of higher concentrations, other operations come into play such as selective absorption or incineration, in those cases where recuperation is not desired. For lower concentrations, techniques such as absorption and biological oxidation are advisable.

In general it can be said that chemical oxidation shows good prospects for use in the elimination of non-biodegradable compounds in the following cases:

1. For the treatment of high concentrations of the compound to be eliminated, without the interference of other possible compounds. For example, when incineration is not a viable alternative because the volume of flow of the effluent is great. Optimization is obtained because the reactant is consumed in attacking the desired compound. The existence of other compounds, which can oxidize, leads to a high level of consumption of the reactant.

2. As a pretreatment of currents, to reduce toxicity by avoiding causing problems of inhibition in the biomass when being introduced in a biological treatment (activated sludge). Intermediate levels of oxidation are aimed at, with a reduced consumption of oxidizer, so that the effluent is ready to be biologically treated.

3. As a final treatment for the adjustment of the effluent for the desired discharging conditions.

A reference parameter when using chemical oxidation as a treatment process is the COD (Figure 6).

Introduction

11

Figure 6. Suitability of water treatment technologies according to COD contents (Andreozzi et al., 1999).

Only waters with relatively small COD contents (≤ 5 g/l) can be suitably treated by means of these processes since higher COD contents would require the consumption of excessively large amounts of expensive reactants. In those cases, it would be more convenient to use wet oxidation or incineration: waste water with COD higher than 20 g/l should undergo autothermic wet oxidation (Mishra et al., 1995).

Chemical oxidation processes can be divided into two classes: Classical Chemical Treatments. Advanced Oxidation Processes (AOPs).

I.1.8.1 Classical Chemical Treatments

Classical chemical treatments generally consist of the addition of an oxidizing agent to the water containing the contaminant to be oxidized. Among the most widely used are (Chamarro et al. 1996):

Chlorine: This is a good chemical oxidizer for water purification because it destroys microorganisms. It is a strong, cheap oxidant, it is very simple to feed into the system and it is well known. Its main disadvantages are its low selectivity, the high amounts of chlorine required and that it usually produces carcinogenic organochloride by-products.

Potassium permanganate: This has been extensively used in the treatment of water for decades. It can be introduced into the system as a solid or as a solution prepared on site. This oxidant is strong but expensive and it works properly in a wide pH range. One of the disadvantages of the use of potassium permanganate as an

Chapter I

12

oxidizer is the formation of magnesium dioxide throughout oxidation, which precipitates and has to be eliminated afterwards by clarifying or filtration, both of which mean extra costs.

Oxygen: The reaction of organic compounds with oxygen does not take place in normal temperature and pressure conditions. The values of temperature and pressure needed are high to increase the oxidizing character of the oxygen in the reaction medium and to assure the liquid state of the effluent. It is a mild oxidant that requires large investments in installations. However, its low operating costs make the process attractive.

Hydrogen peroxide: This is a multipurpose oxidant for many systems. It can be applied directly or with a catalyst. The catalyst normally used is ferrous sulphate (the so-called Fenton process, which will be presented below). Other iron salts can be used as well. Other metals can also be used as catalyst, for example, Al3+, Cu2+. Its basic advantages are:

1. It is one of the cheapest oxidizers that is normally used in residual waters.

2. It has high oxidizing power. 3. It is easy to handle. 4. It is water-soluble. 5. It does not produce toxins or colour in by-products.

It can also be used in the presence of ultraviolet radiation and oxidation is based on the generation of hydroxyl radicals which will be considered an advanced oxidation process.

An option to the addition of hydrogen peroxide to the reaction medium is its production on site. One production possibility is by electroreduction of the oxygen dissolved in the reaction medium. This option is not used very often, because it is expensive and increases the complexity of the system.

Ozone: This is a strong oxidant (like hydrogen peroxide and oxygen) that presents the advantage of not introducing “strange ions” into the medium. Ozone is effective in many applications, like the elimination of color, disinfection, elimination of smell and taste, and the elimination of magnesium and organic compounds. In standard conditions of temperature and pressure it has a low solubility in water and is unstable (Whitby, 1989). It has an average life of a few minutes. Therefore, to have the necessary quantity of ozone in the reaction medium a greater quantity has to be used. Among the most common oxidizing agents, it is only surpassed in oxidant power by fluorine and hydroxyl radicals. Although included among classical chemical treatments, the ozonation of dissolved compounds in water can also constitute an AOP by itself as hydroxyl radicals are generated from the decomposition of ozone, which is catalyzed by the hydroxyl ion or initiated by the presence of traces

Introduction

13

of other substances, such as transition metal cations. As the pH increases, so does the rate of decomposition of the ozone in water. The major disadvantage of this oxidizer is that it has to be produced on site and needs installation in an ozone production system in the place of use. Therefore, the cost of this oxidizer is extremely high, and this must be kept in mind when deciding on the most appropriate oxidizer for a given system. In addition, as it is a gas, a recuperation system has to be foreseen and that will make the obtaining system even more expensive (Benitez et al., 1997). Ozonation is used in many drinking water plants as a tertiary treatment and also for the oxidation of organic pollutants of industrial (paper mill industry) or agriculture (water polluted by pesticides) effluents. Extensive research has been carried out to investigate the kinetics of the ozonation reaction of various organic and inorganic compounds such as carboxylic acids, phenols, amino acids, organometallic compounds, etc. In the case of phenol, some studies have been done in order to establish a kinetic model to predict the magnitude of the gas-liquid reaction between ozone and phenol. Contreras and co-workers (Contreras et al., 2001) studied the elimination of nitrobenzene from aqueous solutions by means of ozonation and enhanced ozonation. With regard to textile wastewaters ozonation has been found to be very efficient for the decolorization of textile wastewaters (Balcioglu et al., 1999), (Ciardelli et al., 2001), (Sevimli et al., 2002). Ozone treatment may be enhanced by the addition of hydrogen peroxide.

I.1.8.2 Advanced Oxidation Processes (AOPs)

AOPs were defined by (Glaze et al., 1987) as near ambient temperature and pressure water treatment processes which involve the generation of highly reactive radicals (especially hydroxyl radicals) in sufficient quantity to effect water purification. These treatment processes are considered as very promising methods for the remediation of contaminated ground waters, surface waters, and wastewaters containing non-biodegradable organic pollutants. Hydroxyl radicals are extraordinarily reactive species that attack most organic molecules. The kinetics of reaction are generally first order with respect to the concentration of hydroxyl radicals and to the concentration of the species to be oxidized.

Hydroxyl radicals are also characterized by a low selectivity of attack, an attractive feature for an oxidant to be used in wastewater treatment. Several different organic compounds are susceptible to removal or degradation by means of hydroxyl radicals, as shown in Figure 7. Nevertheless, some of the simplest organic compounds, such as acetic, maleic and oxalic acids, acetone

Chapter I

14

or simple chloride derivatives such as chloroform or tetrachloroethane, cannot be attacked by OH• radicals (Bigda, 1995). Depending upon the nature of the organic species, two types of initial attacks are possible: the hydroxyl radical can abstract a hydrogen atom to form water, as with alkanes or alcohols, or it can be added to the contaminant, as is the case for olefins or aromatic compounds.

Figure 7. Oxidizable compounds by hydroxyl radicals (Bigda, 1995).

The attack by hydroxyl radical, in the presence of oxygen, initiates a complex cascade of oxidative reactions leading to mineralization. As a rule of thumb, the rate of destruction of a contaminant is approximately proportional to the rate constants for the contaminant with the hydroxyl radical.

The versatility of AOPs is also enhanced by the fact that they offer different ways of HO• radicals production, thus allowing a better compliance with the specific treatment requirements. It has to be taken into account, though, that a suitable application of AOPs to wastewater treatment makes use of expensive reactants such as hydrogen peroxide and/or ozone.

The most important advanced oxidation treatments based on the use of H2O2 are Fenton and photo-Fenton process.

Introduction

15

I.2 Fenton and photo-Fenton reaction

The Fenton reaction was discovered by (Fenton, 1894). Forty years later the (Haber-Weiss, 1934) mechanism was postulated, which revealed that the effective oxidative agent in the Fenton reaction was the hydroxyl radical. The Fenton reaction can be outlined as follows (Figure 8):

Figure 8. Mechanism of Fenton reaction.

where M is a transition metal such as Fe or Cu. In the absence of light and complexing ligands other than water, the most

accepted mechanism of H2O2 decomposition in acid homogeneous aqueous solution, which involves the formation of hydroxyperoxyl (HO2

•/O2-) and

hydroxyl radicals HO• (De Laat and Gallard, 1999), (Gallard and De Laat, 2000).

The HO• radical mentioned above, once in solution attacks almost every organic compound.

Fenton reaction rates are strongly increased by irradiation with UV/visible light (Ruppert et al., 1993), (Pignatello and Sun, 1993). During the reaction, Fe3+ ions are accumulated in the system and after Fe2+ ions are consumed, the reaction practically stops. Photochemical regeneration of ferrous ions (Fe2+) by photoreduction of ferric ions (Fe3+) is the proposed mechanism. The newly generated ferrous ions react with H2O2 generating a second HO• radical and ferric ion, and the cycle continues (Figure 9):

Figure 9. Mechanism of photo-Fenton reaction.

Fenton and photo-Fenton reaction depend not only on H2O2 concentration and iron added, but also on the operating pH value.

I.2.1 Basic Principles

I.2.1.1 The Fenton Process

The oxidative decomposition and transformation of organic substrates by H2O2/Fe2+ (known as Fenton’s reagent) has been known of nearly a century (1894). This method has the advantage that hydrogen peroxide, used as oxidant, is cheaper than other oxidants and it also has the advantage of using

Chapter I

16

iron as catalyst. Iron is the second most abundant metal and the fourth most abundant element on earth. In water it is present as ferric or ferrous ions, which form complexes with water and hydroxyl ions depending on pH and the temperature. Figure 10, shows the percentage of Fe2+ and the species that appear together with it, in relation to the pH at 25 °C and where it is possible to see that up to a pH level around 8, Fe2+ exists in solution.

Figure 10. Proportion of Fe2+ and the species in equilibrium with it at 25°C.

From this, it can be concluded that Fe2+ in the Fenton system will be in this form and in solution. Figure 11 shows the concentration of Fe3+ in solution in relation to the pH at 25°C. This representation has been carried out for a pH of between 2 and 3.2 because this is the solubility limit. As can be observed, the solubility of Fe3+ is very high for a pH lower than 2 and too small for a pH higher than 3.2. Therefore, in Fenton conditions Fe3+ will be in solution if pH is maintained < 3.2.

Introduction

17

Figure 11. Concentration of Fe3+ in solution in relation to the pH at 25°C.

Figure 12 shows the proportion of Fe3+ species that are in equilibrium in

relation to the pH (Safarzadeh-Amiri, 1996).

Figure 12. Proportion of Fe3+ and the existing species in equilibrium with it at 25°C

From this figure, the low solubility of Fe3+ and all its species can be seen

at pH 3. At pH 3 the solubility of Fe3+ is around 4 mg/l. According to (Eisenhauer,

1964), in spite of the low solubility of Fe3+ in presence of phenol in the reaction medium, ferric hydroxide does not precipitate throughout oxidation because it is transformed into Fe2+ due to the reaction of Fe3+ with some products of phenol oxidation. The commonly mentioned disadvantage of the

Chapter I

18

Fenton method is the necessity to work at low pH (normally below 4), because at higher pH ferric ions would begin to precipitate as hydroxide. In addition, by this process the maximum mineralization reached is around 40-60 %.

Although the Fenton reagent has been known of more than a century and shown to be a powerful oxidant, the mechanism of the Fenton reaction is still under intense and controversial discussion. Generation of HO• radicals by the dark reaction of H2O2 with ferrous salt has been the subject of numerous studies during the last decade (Chen and Pignatello, 1997), (Hislop and Bolton, 1999). The oxidizing species generated in the Fenton reaction have been discussed by many researchers but are still controversial (Macfaul, 1998), (Goldstein, 1999), (Kremer, 1999). The recognition of the HO• radical as the active intermediate is not yet universal and even doubts as to its very existence in the system have been raised, (Bossmann et al., 1998) outlined clearly that recent thermodynamic calculations have demonstrated that the outher-sphere electron-transfer reaction between Fe2+ and H2O2, as it is rationalized by the classic mechanism proposed by Haber and Weiss, cannot take place, because the formation of H2O2 by intermediates is not favored.

In contrast, the formation of a hydrated Fe2+-H2O2 complex is thermodynamically favored. However, in the main studies of the Fenton reagent, it is generally considered that the reaction between H2O2 and Fe2+ in an acidic aqueous medium (pH ≤ 3) produces HO• radicals and can involve the steps presented below (Figure 13).

Figure 13. The Fenton Reaction: scheme of mechanism.

The hypothesis of (Haber and Weiss, 1934), that the Fenton reaction involves the formation of ΗΟ• radicals has been proved by many techniques, including EPR spectroscopy. Although a considerable number of researchers, by using the EPR spintrapping technique, have found evidence

Introduction

19

for the formation of ΗΟ• radicals from the Fenton reagent (Rosen et al., 2000), it has also been reported by others that this species is not the only oxidizing intermediate, but also some type of high-valent iron-oxo intermediates are present (Kremer, 1999), (Bossmann et al., 1998). Using EPR spin-trapping, three types of oxidizing species (free HO•, bound HO•, and high-valence iron species, which is probably a ferryl ion, (FeIV) were detected by (Yamazaki and Piette, 1991). In the present work, the principal oxidant is assumed to be ΗΟ• radical, but others such as iron-oxo species cannot be ruled out.

I.2.1.2 The photo-Fenton process

Basic chemistry, as well as applications of Fe2+/H2O2 and Fe3+/H2O2 system for hazardous waste treatment are used. Ferrous ion combined with hydrogen peroxide (Fenton’s reagent) reacts stoichiometrically to give HO• according to Figure 14:

Figure 14. Reaction of ferrous ion combined with hydrogen peroxide.

In the dark, the reaction is retarded after complete conversion of Fe2+ to Fe3+. Nowadays, it is known that the oxidizing power of the Fenton system can be greatly enhanced by irradiation with UV or UV-visible light.This effectiveness has been proven with the total mineralization of many organic compounds in aqueous solution. The reason for the positive effect of irradiation on the degradation rate include the photo-reduction of Fe3+ to Fe2+ ions, which produce new HO• radicals with H2O2 (Figure 15) according to the following mechanism:

Figure 15. The photo-Fenton Reaction: scheme of mechanism.

There are more equations (as shown in chapter 1 and 3) involved in the mechanism of hydroxyl radical generation, but those cited are the most significant. The main compounds absorbing light in the Fenton system are ferric ion complexes, e.g. [Fe3+ (OH)-]2+ and [Fe3+ (RCO2)-]2+ , which produce additional Fe+2 by following (Figure 16) photo-induced, ligand-to-metal charge-transfer reactions (Sagawe, 2001).

Chapter I

20

Figure 16. Photo-induced reactions.

Additionally, the first equation yields HO• radicals, while the second equation results in a reduction of the total organic carbon (TOC) content of the system due to the decarboxylation of organic acid intermediates. It is very important to note that both reactions form the ferrous ions required for the Fenton reaction. The overall degradation rate of organic compounds is considerably increased in the photo-Fenton process, even at lower concentration of iron salts present in the system.

I.3 Aim of the work

Homogeneous photo-Fenton has been widely investigated as an innovative for environmental applications such as detoxification processes in water. In contrast, very few studies have been conducted concerning heterogeneous photo-Fenton. Concerning this last aspect, the study has been devoted to the selection of solid catalyst, able to substitute the Fenton homogeneous catalyst. The kind and shape of solid catalysts and photo-Fenton operative conditions process have been investigated on model wastewaters.

II State of the art

II.1 The homogeneous Fenton reaction

The homogeneous Fenton reaction is already in use in industrial wastewater purification processes (Centi et al., 2000).

For example, a study was made of catalytic wet hydrogen peroxide oxidation of propionic acid with a homogeneous iron catalyst (Fe(NO3)3) at room temperature and 70 °C as a function of the time of reaction. The H2O2/substrate ratio was 1.5 times the stoichiometric value necessary to completely oxidize all the propionic acid present in solution to CO2.

Propionic acid was used as a model reactant, because it gives rise to acetic and formic acids as primary intermediates. These two carboxylic acids are the common products of the oxidation of several organic molecules (Delanghe et al., 1991) and acetic acid is one of the most ‘recalcitrant’ molecules (Gallezot et al., 1996), (De Leitenburg et al., 2004). As a probe molecule, propionic acid can thus give direct information on reactivity in the attack on the carbon chain as well as information on the reactivity of its primary products of oxidation (formic and acetic acids).

Maximum activity around a pH of 4 was observed in propionic acid conversion. Upon decreasing or increasing the initial pH of the solution below or above 4, the rate of hydrogen peroxide decomposition increased due to partial transformation of iron to other species catalysing this reaction.

A number of studies on the degradation of Nitrobenzene in aerated aqueous solutions by the Fenton reagent have been reported (Lipczynska-Kochany, 1991). Nitrobenzene is one of the most representative nitroaromatic compounds, which is present in several wastewaters. Phenol is also the most typical and common model compounds used in the application of different advanced oxidation processes as treatment methods (Benitez et al., 2000), (Vicente et al., 2002). Some organic catalyst supports have been studied, such as styrene divinyl benzene (SDB) co-polymer as support for Pt catalyst in catalytic oxidative nitrate removal from wastewater (Huang et al., 2001).

Chapter II

22

II.2 The heterogeneous Fenton reaction

Several studies have been published concerning supporting a Fenton catalyst to various carriers, such as brick grain (Chou et al., 2001), MgO (Pak et al., 1999), SiO2 (Huling et al., 2000), and zeolite (Centi et al., 2000), (Fajerwerg and Debellefontaine, 1996), (Fajerwerg, et al., 1997), (Larachi et al., 1998), (Centi et al., 2001), (Neamtu et al., 2004). Also copper or iron containing pillared clays were used as Fenton catalysts (Abdellaoui et al., 1999).

II.2.1 The heterogeneous Fenton reaction with zeolite

Zeolite shows a possible role in enhancing the rate of reaction by the local change of the concentration of the reactants inside zeolite microcavities. A zeolite named as FeZSM-5 is the most active heterogeneous Fenton-type catalyst. The studies of (Centi et al., 2000) on FeZSM-5 in wet hydrogen peroxide oxidation of diluted propionic acid solutions at atmospheric pressure in a batch reactor, shows that the solid catalyst has a higher rate of conversion (the rate of reaction is higher for the homogeneous catalyst by a factor of about 3–5) of the substrate as well as a lower sensitivity with respect to pH than Fe3+ ions in solution at the same reaction conditions (temperature, amount of H2O2, amount of iron). However, the solid catalyst has a major drawback in its higher rate of hydrogen peroxide decomposition to water and oxygen.

Although it was demonstrated that the activity of the solid catalyst is not related to leached iron ions, slight leaching of iron was found to be present, especially at the higher reaction temperatures. This could cause deactivation with prolonged use.

Calcination is probably necessary to burn the organic species which remain trapped in the zeolite which delay the start of the activity of the zeolite during consecutive catalytic experiments.

The use of FeZSM5 as a heterogeneous catalyst under mild conditions (T=90°C, H2O2 stoichiometric ratio, 1.5, atmospheric pressure in a batch reactor) allows significant TOC removal and total elimination of phenol at pH=5 (Fajerwerg et al., 1997).

FeZSM-5 is also active in oxidation of diethylnitrophenil phosphate, which is hardly detoxified by other methods (Kuznetsova et al., 2004).

Catalytic wet peroxide oxidation on Fe-exchanged Y zeolite of Procion Marine H-EXL and of dye-bath effluents containing this dye can be a suitable pre-treatment method for complete decolorization of effluents from textile dyeing and finishing processes, once the optimum operating conditions are established. Catalytic oxidation by hydrogen peroxide of an

State of the art

23

aqueous solution of Procion Marine H-EXL on FeY leads to TOC and COD removals when the system operates at pH = 5, T = 50 °C, 1 g/l catalyst and 20 mmol/l H2O2. The catalytic oxidation of synthetic textile wastewater assures better color and COD removals (>90%) after an operational time of 60 min (Neamtu et al., 2004).

II.2.2 The heterogeneous Fenton reaction with perovskite

Additionally, perovskite-type oxides have attracted great interest for the development of environment-friendly catalytic materials. They have been used in processes such as catalytic combustion of automobile control emissions (Seiyama et al., 1992) and the catalytic destruction of chlorinated compounds (Sinquin et al., 2001).

Catalytic wet peroxide oxidation of phenolic aqueous solution over LaTi1−xCuxO3 perovskites has shown complete removal of aromatic compounds and high TOC reduction (ca. 90%) under mild reaction conditions (temperature of 80 ◦C and initial peroxide concentration lower than stoichiometric) (Sotelo et al., 2004).

II.3 UV/oxidation processes

The UV/oxidizer system involves direct excitation of the substrate due to radiation with the subsequent oxidation reaction. Even so, there may be synergism between the oxidizer and the ultraviolet radiation, which causes the global effect to be different from the additive effect. UV/oxidation processes generally involve generation of OH. radicals through UV photolysis of H2O2 or photo-Fenton.

II.3.1 Photolysis of hydrogen peroxide

The most direct method for the generation of hydroxyl radicals is through the cleavage of H2O2. Photolysis of H2O2 yields hydroxyl radicals by a direct process with a yield of two radicals formed per photon absorbed by 254 nm (Baxendale and Willson, 1957). The scheme of the radical reactions is (eqs.1-14):

Initiation (eq. 1): H2O2 +hv→2OH. (1)

Chapter II

24

Hydroxyl-radical propagation and termination steps (eqs. 2-7): OH.+H2O2→O2

-+H2O+H+ (2) OH.

.+HO2-→O2

-+OH-+H+ (3) OH.+HCO3

-→CO3-.+H2O (4)

OH.+CO3

2-→CO3-.+OH- (5)

OH.+O2

-→ OH-+O2 (6) OH.+organic compound→ products (7) Superoxide and carbonate-radical propagation and termination steps (eqs.

8-14): O2

-+H2O2→OH.+OH-+O2 (8) O2

-+HCO3-→HO2

-+CO3-. (9)

O2

-+CO3-.→O2+CO3

-2. (10) 2 O2

-+2H2O→H2O2+2OH-+O2 (11) CO3

-.+H2O2→HCO3-+O2

-+H+ (12) CO3

-.+HO2-→HCO3

-+O2- (13)

CO3

-. + organic compound→ ? (14) Low-pressure mercury vapor lamps with a 254 nm peak emission are the

most common UV source used in the UV/H2O2 system. The maximum absorbance of H2O2 occurs at about 220 nm. If low-pressure lamps are used, a high concentration of H2O2 is needed to generate sufficient hydroxyl radicals. However, high concentration of H2O2 scavenges the radicals, making the process less effective (eqs.15-17):

OH.+H2O2→HO2.+H2O (15)

HO2

.+H2O2→OH.+H2O2+O2 (16) HO2

.+ HO2.→ H2O2+O2 (17)

State of the art

25

II.3.2 The homogeneous photo-Fenton reaction

A number of studies on the degradation of 4-chlorophenol (Ghaly et al., 2001), nitrophenols (Kiwi et al., 1994), (Trapido and Kallas, 2000) and phenols by photo-Fenton have been reported (Kavitha et al., 2004).

Phenol is also the most typical and common model compound used in the application of different advanced oxidation processes as a treatment method (Benitez et al., 2000), (Vicente et al., 2002).

For example, in photo-Fenton processes (solar/UV light), complete degradation of phenol was observed at 50% of ferrous ion catalyst as compared with the Fenton process suggesting the importance of solar/UV light in the process of mineralisation. In the Fenton process, carboxylic acids such as acetic acid and oxalic acid were formed as end products during the degradation of phenol while in photo-Fenton processes, both these ions were identified during the early stages of phenol degradation and were oxidized almost completely at 120min of the reaction time (Kavitha et al., 2004).

An improvement of photoassisted Fenton processes is the UV-vis/ferrioxalate/H2O2 system, which has recently been demonstrated to be more efficient than photo-Fenton for the abatement of organic pollutants.

The use of ferrioxlate in the photo-Fenton reaction for the degradation of organic pollutants was reported to be very effective in the degradation of 2-propanol.

The ferrioxalate complex [Fe(C2O4)3]3- is higly photoreactive and the reduction of Fe(III) to Fe (II) can occur at a wavelength further into the visible spectrum (about 550 nm) (Hislop and Bolton, 1999).

II.3.3 The heterogeneous photo-Fenton reaction

Many efforts have been made to develop heterogeneous photo-Fenton catalysts for wastewater treatment (Fernandez et al., 1998); (Li Puma and Yue, 2000); (Bossmann et al., 2001), (Feng et al., 2003). In general, two types of heterogeneous photo-Fenton catalysts are used in the degradation of organic compounds. One is the suspended catalyst and the other is the fixed bed catalyst. Compared with the suspended catalyst, the biggest advantage of a fixed bed catalyst lies in the fact that after wastewater treatment, separation of catalyst from reaction solution is not needed, and the catalyst can be used for a batch photo-reactor as well as a continuous photo-reactor even though the fixed bed catalyst normally exhibits a decreased photo-catalytic activity due to the decrease in specific surface area.

For example, (Bossmann et al., 2001) prepared Fe(III)-doped zeolite Y catalyst through a simple ion exchange reaction (Fe3+ vs. Na+) and used it as a suspended photo-Fenton catalyst for the degradation of polyvinyl alcohol.

Chapter II

26

However, this catalyst exhibited very poor catalytic activity because after 120 min reaction, dissolved organic carbon remains at a high level.

Recently, laponite and bentonite clay-based Fe nanocomposite (Fe-Lap-RD and Fe-B) have been developed as suspended photo-Fenton catalysts for the degradation of organic dyes including azo dye Orange II and reactive dye HE-3B in the presence of UVC light and H2O2. Under optimal conditions (pH=3.0, H2O2 (C=10mM), and lamp of 8W-UVC), 100% discoloration and 50–60% TOC removal of 0.2mM Orange II can be achieved in 90 and 120 min, respectively (Feng et al., 2005).

While (Maletzky et al., 1999), (Sabhi and Kiwi, 2001) prepared iron ions immobilised on nafion perfluorinated to degrade chlorophenols. 42 % TOC removal of 1.4 mM of 4-chlorophenol can be achieved in 300 min.

This process can take place in neutral pH solutions with close to equal efficiency as in acidic solutions, which removes the need for costly pH adjustments when subsequent biological degradation is to be used. The membrane could be reused through many cycles, without leaching out of a significant amount of Fe(III) ions from the membrane, which would cause loss of efficiency (Sabhi and Kiwi, 2001).

In a recent review, attention has been called to the fact that carbon nanotubes (CNT) are attractive and competitive catalyst supports when compared to activated carbon due to the combination of their electronic, adsorption, mechanical and thermal properties (Serp et al., 2003). Some recent works have concentrated on the preparation of new hybrid materials CNT-TiO2. A sol-gel method has been used to prepare a composite material made of CNT within a TiO2 matrix (Vincent et al., 2002). Multi-walled carbon nanotube-based titania composite material has also been prepared by an impregnation method (Hernadi et al., 2003), which provided a homogeneous inorganic cover layer on the surface of purified MWCNT. Rutile TiO2 has been immobilized on the sidewall of MWCNT by a simple one-step scheme, which produces three distinct morphologies of hybrid MWCNT at different reaction temperatures (Huang et al., 2003). Coating MWCNT surface with TiO2 has been performed by a sol-gel method using different alkoxides and by hydrothermal hydrolysis of TiOSO4, which can lead to different morphologies (Jitianu et al., 2004). Recently, composite nano-fibers made of polyacrilonitrile (PAN) matrix, into which both MWCNT and titanium dioxide particles were incorporated by electrospinning, were introduced by (Kedem et al., 2005). It was found that the coupling between the photocatalyst and the CNT affected the self photodegradation of the fibers as well as the photodegradation of various contaminants such as CCl4 (Kedem, 2005). Hence, composites containing carbon nanotubes are believed to provide many applications and exhibit cooperative or synergetic effects between the metal oxides and carbon phases.

State of the art

27

Early findings regard the application of photocatalytic advanced oxidation with hydrogen peroxide to the purification treatment for winery wastewaters (Navarro et al., 2005). Wine and grape wastewaters are more difficult to treat than other wastewaters from food processing plants. Wineries generate effluents that are characterized by high organic matter concentration, acidity, unpleasant odours and noticeable seasonal variability, being discharged only during grape harvest and racking periods (3–4 months per year) (Brucculeri et al. 2005).

III Experimental methods

III.1 Catalyst characterization

To characterize the samples studied in this work the following techniques were used:

• Inductively coupled plasma-mass spectrometry (ICP-MS); • Thermal analysis (TG-MS); • N2 adsorption at -196 °C to obtain specific surface area and

porosity characteristics: • Micro Raman spectroscopy; • SEM analysis; • Near infrared, ultraviolet and visible diffuse reflectance

spectroscopy (NIR-UV-VIS DRS).

III.1.1 ICP-MS

Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is extensively used to detect and quantify the presence of the majority of the elements in the periodic table and is a very powerful tool for trace (ppb-ppm) and ultra-trace (ppq-ppb) elemental analysis. In ICP-MS, the plasma is formed from Argon gas and reaches very high temperatures of up to approximately 7000 K. The plasma is used to atomize and ionize the elements in a sample. The sample to be analysed is introduced into the plasma as a fine aerosol. As the sample aerosol passes through the plasma, it collides with free electrons, argon cations and neutral Argon atoms. The result is that any molecules initially present in the aerosol are quickly and completely broken down into charged atoms. The resulting ions are then passed through a series of apertures (cones) into the high vacuum analyzer. The isotopes of the elements are identified by their mass-to-charge ratio (m/z) and the intensity of a specific peak in the mass spectrum is proportional to the amount of that isotope (element) in the original sample. An ICP-MS Agilent 7500 E

Chapter III

30

instrument was used for the analysis of Fe. Alternatively, it was used for the analysis of Mn, Co, Cu, Fe and Ni an ICP-AES Varian “Liberty II” by courtesy of SSIP (Napoli).

III.1.2 Thermal analysis (TG-MS)

The performances of samples as a function of temperature were determined by air flow thermal analysis (TG-MS). The apparatus used were a TGAQ500 (Figure 17) thermogravimetric analyzer (TA Instruments) and a SDTQ600 (Figure 18) simultaneous DSC/TGA (TA Instruments). Both analyzers can be coupled to a Pfieffer Vacuum Benchtop Thermostar mass spectrometer (MS) (Figure 19).

Figure 17. TGAQ500 Thermogravimetric Analyzer.

Figure 18. SDTQ600 Simultaneous DSC/TGA.

Experimental methods

31

Figure 19. Pfieffer Vacuum Benchtop Thermostar mass spectrometer.

TGAQ500 measures weight changes in a material as a function of

temperature. The system works in a temperature range of 20-1000 °C, and weight variation resolution is 0.1mg . The sample, loaded in a crucible made of platinum and connected to the balance arm by a small hook, is progressively heated in the oven. A thermocouple controls the oven temperature and a second thermocouple reads the sample temperature. Sample pan loading and furnace movement are totally automated and there is a touch screen data display to change operating parameters. Typically, measurements are carried out with 20 mg of the sample in chromatographic air flow (60 Ncc/min) with a heating rate of 10 °C/min in the temperature range of 20- 800 °C.

The results are displayed as TG curves showing the mass variations as functions of temperature or time, and DTG curves showing the conversion rate (mass loss percentage per unit time) as functions of temperature or time.

Figure 20 contains the typical trends of the TG and DTG curves.

Chapter III

32

-1

0

1

2

3

DTG

(%/m

in)

86

88

90

92

94

96

98

100

TG (%

)

0 100 200 300 400 500 600Temperature (°C)

Figure 20. TG and DTG curves.

SDTQ600 provides simultaneous measurement of weight change (TGA) and heat flow (DSC) on the same sample from ambient to 1500 °C. It features a proven horizontal dual beam design with automatic beam growth compensation, and the ability to analyze two TGA samples simultaneously. DSC heat flow data is dynamically normalized using the instantaneous sample weight at any given temperature. The sample is loaded into a crucible made of alumina and heated in the horizontal oven. There are two thermocouples to control the oven temperature and the sample temperature. Measurements are carried out with about 30 mg of sample in chromatographic air flow (100 Ncc/min) with a heating rate of 10 °C/min in the temperature range of 20- 800 °C.

The Pfieffer Vacuum Benchtop Thermostar mass spectrometer can measure the gas evolved from thermal analyzers up to 300 AMU. The evolved gases are introduced into a heated quartz capillary, which is extremely fine, in order to produce the necessary high vacuum when the evolved gases enter the mass spectrometer. The heated capillary is necessary in order to prevent condensation of the hot gases on cold surfaces. The analysis of gases is performed by a very highly sensitive quadrupole mass detector. The necessary high vacuum is obtained through 2 stages of vacuum pumps that are integrated into a compact housing. The first stage is a rotary pump; second stage is a turbo molecular pump.

Both systems, the Mass Spectrometer and Thermal Balance, are connected to a common PC for data acquisition.


33

III.1.3 N2 adsorption measurements

In order to study the porosity of catalyst powders, N2 adsorption measurement were carried out at -196 °C with a Costech Sorptometer 1040 (Figure 21).

The measurement was performed by continuous-flow method after sample pre-treatment at 150 °C for 2 h in He flow, in order to measure total specific surface area (via single and multi-point methods) and micropore volume (via micropore method).

Figure 21. Costech Sorptometer 1040.

III.1.4 The micro Raman spectroscopy

Raman spectroscopy is a technique for the identification and quantification of the chemical components of specimens.

When light is scattered by any form of matter, the energies of the majority of the photons are unchanged by the process, which can be elastic or Rayleigh scattering. However, about one in one million photons or less, lose or gain energy that corresponds to the vibrational frequencies of the scattering molecules. This can be observed as additional peaks in the scattered light spectrum. The process is known as Raman scattering and the spectral peaks with lower and higher energy than the incident light are known as Stokes and anti-Stokes peaks respectively.

Chapter III

34

Laser Raman spectra of powder samples were obtained with a Dispersive MicroRaman (Invia, Renishaw) (Figure 22), equipped with a 514.5 nm diode-laser, in the 200-900 cm-1 Raman shift range.

Figure 22. Dispersive MicroRaman (Invia, Renishaw).

III.1.5 SEM analysis

The scanning electron microscope (SEM) is a type of electron microscope capable of producing high resolution images of a sample surface. Due to the manner in which the image is created, SEM images have a characteristic three-dimensional appearance and are useful for judging the surface structure of the sample.

In a typical SEM, electrons are thermionically emitted from a tungsten or lanthanum hexaboride cathode and are accelerated towards an anode; alternatively electrons can be emitted via field emission (FE). Tungsten is used because it has the highest melting point and lowest vapour pressure of all metals, thereby allowing it to be heated for electron emission. The electron beam, which typically has energy ranging from a few hundred eV to 50 keV, is focused by one or two condenser lenses into a beam with a very fine focal spot sized 1 nm to 5 nm. The beam passes through pairs of scanning coils in the objective lens, which deflect the beam in a raster fashion over a rectangular area of the sample surface. As the primary electrons strike the surface they are inelastically scattered by atoms in the sample. Through these scattering events, the primary electron beam effectively spreads and fills a teardrop-shaped volume, known as the interaction volume, extending from less than 100 nm to around 5 µm into the surface. Interactions in this region lead to the subsequent emission of electrons which are then detected to produce an image. The textural features of supported perovskites were studied by SEM with a BS-350 machine of the Boreskov Institute of Catalysis (Russia) (resolution limit is about 5–10 nm).


35

III.1.6 NIR-UV-VIS DRS

Near infrared, ultraviolet and visible diffuse reflectance spectroscopy (NIR-UV-VIS DRS) was carried out in the 200-1100 nm range with a PerkinElmer lambda 35 spectrophotometer equipped with a reflection sphere in the 200-1100 nm range.

III.1.7 XRD spectroscopy

X-Ray diffraction was performed to verify whether the ionic exchange induced changes in the zeolite structure. Spectra of powder are analysed with the step-scan method of 2θ =0.02, with a D8000 Bruker diffractometer.

III.2 Laboratory apparatus for catalytic Fenton oxidation

The Figure 23 is an illustration of laboratory apparatus for the experiment set up.

Chapter III

36

Figure 23. Laboratory apparatus for catalytic Fenton oxidation.

Catalytic tests for oxidation with hydrogen peroxide were carried out in a glass batch reactor at ambient temperature. Continuous stirring of 250 ml or 100 ml of freshly prepared aqueous solution containing an organic compound concentration corresponding to TOC of 1000 mg/l or 500 mg/l in contact with ambient air was performed by a helical mixer. A concentrated solution of H2O2 was added to achieve a fixed H2O2/substrate stoichiometric ratio. The catalysts were added both in powder form and from precursor aqueous solutions. Temperature was monitored by a PT100 probe. Temperature control was obtained by placing a glass batch reactor in a thermostatic bath.

Alternatively, for tests on structured catalysts at ambient temperature, a closed vessel batch reactor placed on an oscillating plate was employed.

The TOC of the solution was measured as function time with devoted instrumental laboratory plant, designed, realised and optimised to the purpose, as described in paragraph III.4 . The H2O2 concentration was determined by H2O2/TiOSO4 complex (λ = 405 nm) UV-Vis analyses.

Agita

Termo

Siringa

pH-

Bagno

PH electrodeSampling needle

PT 100 probe Helical mixer


37

III.3 Laboratory apparatus for catalytic photo-Fenton oxidation

The Figure 24 an illustration of laboratory apparatus for the experiment set up.

Gas out

Thermocouple Condenser

CO

CO2

Analyzers

N2

CO2/N2

CO/N2

1 2

3 4

H2O Out

H2O INCooler (T=O°C)

Pump

8 W mercury vapor lamp emitting at 254 nm

Structured catalyst

Gas outThermocouple Condenser

CO

CO2

Analyzers

N2

CO2/N2

CO/N2

1 2

3 4

H2O Out

H2O INCooler (T=O°C)

Pump

8 W mercury vapor lamp emitting at 254 nm

Structured catalyst

Gas outThermocouple CondenserCondenser

CO

CO2

Analyzers

N2

CO2/N2

CO/N2

1 2

3 4

1 2

3 4

H2O OutH2O Out

H2O INH2O INCooler (T=O°C)Cooler (T=O°C)

PumpPump

8 W mercury vapor lamp emitting at 254 nm8 W mercury vapor lamp emitting at 254 nm

Structured catalystStructured catalyst

Figure 24. Laboratory apparatus for the catalytic photo-Fenton oxidation.

Catalytic tests were carried out in a properly designed sealed stainless-steel batch photoreactor.

Figure 25. Sealed stainless-steel batch photoreactor.

Air

Chapter III

38

Organic compound aqueous solutions containing total organic carbon concentration (TOC) in the range 250-500 mg/l (pH 3.9) and H2O2 0.083-0.167 mol/l were used. H2O2 concentration of 0.083 mol/l was chosen according to the reaction (eq. 18):

CH3COOH + 4 H2O2→2 CO2+6 H2O (18) A 8 W mercury vapor lamp double envelope in special soft glass and

quartz glass as inner material, was chosen for the emission at 254 nm (Table 1).

Table 1. Characteristic of the UV lamp utilised.

Lamp Wattage (W)

Length (L,mm)

Diam. (D, mm)

Lamp current (A)

UV Output µW/cm2

(at 1m)

Average Life (h)

8 214 20.6 0.230 16.3 3000 The monolith catalysts were placed in the bottom of reactor in an holder,

represented in fig. Figure 26.

Figure 26. Components of the sealed stainless-steel batch photoreactor.

The Figure 27 shows the ultraviolet spectrum of the UV lamp used.


39

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

5

240 260 280 300 320 340 360 380 400

Wave lenght, nm

Spec

tral

irra

dian

ce, a

.u.

Figure 27. The ultraviolet spectrum of the UV lamp used.

TOC has been evaluated as function of time by COX obtained by catalytic combustion at T=850°C. The H2O2 concentration was determined by H2O2/TiOSO4 complex (λ = 405 nm) UV-Vis analyses. Continuous mixing of model wastewaters was realised by gas fine bubbling under monolith holder (Q=250 Ncc/min). and external recirculation. Before reimmission into the reactor, the solution was cooled by a cold trap. The volume (100 ml) of freshly prepared aqueous solution of the carboxylic acid with TOC of 500 mg/l was added to the reactor together with the catalyst, Then a concentrated solution of H2O2 was added to achieve a fixed H2O2/substrate stoichiometric ratio. The TOC of the solution was measured as function time. At the reactor outlet the gases pass through a cold trap (0°C) in order to assure water condensation, prior to the gas analysers for measurements of CO and CO2 concentrations.

The catalytic properties of micromonolithic samples with volume 5.5- 6.5 cm3 and weight 5-6 g were tested in the photo-Fenton reaction under atmospheric pressure at 25 °C.

III.4 Laboratory apparatus for total organic carbon analysis.

In order to determine the quantity of organically bound carbon, the organic molecules must be broken down to single carbon units and converted to a single molecular form that can be measured quantitatively. TOC methods utilize heat and oxygen, ultraviolet irradiation, chemical oxidants, or combinations of these oxidants to convert organic carbon to carbon dioxide (CO2).

Chapter III

40

TOC has been determined by the high temperature combustion method by means of a catalyst (Pt/Al2O3) at T=850°C, with a stream of hydrocarbon free air to oxidize the organic carbon.

Laboratory apparatus (Figure 28) consists of mass flow controllers (Brooks) operating on each gas; an injection system; a NDIR continuous analyser (Hartmann & Braun Uras 10E) for measurements of CO and CO2 concentrations at the reactor outlet and a paramagnetic analyser (Hartmann & Braun Magnos 6G) for continuous monitoring of O2 concentration.

In particular, the injection of a fixed volume of the solution (250 ml) was realized by means of a microliter syringe (Hamilton), with a pneumatic system at pressure P= 2 bar, in the heated line (T=170°C) before the reactor. At the reactor outlet the gases pass through a cold trap (0°C) in order to assure water condensation, prior to going through the gas analysers.

Finally, the signals from the analysers are acquired and processed by personal computer.

The CO and CO2 concentration data were jointly integrated to calculate total organic carbon. The gas flow with a rate of 250 Ncc/min and composition of 21 % vol of O2 in N2 was feed.

Figure 28. Set-up of experiment for total organic carbon analysis.

III.5 Analytical method for H2O2 determination

This method involves reacting a sample which contains residual H2O2 with titanium sulphate to produce a yellow peroxo-complex. The sample is then analyzed by spectrophotometer at 405 nm, and the absorption compared to a standardized curve.

This procedure is appropriate for determining residual H2O2 present in waters and wastewaters in concentrations ranging from 1 - 10 mg/l in undiluted samples, or higher concentrations provided appropriate dilution.

The procedure is reported below:

Air

Gas out

CondenserCO

CO2

O2

Analyzers

MFC Control Unit

Reactor

Thermocouple

Furnace

N2

CO2/N2

CO/N2

1 2

3 4

Heater

Heated line

Air

Gas out

CondenserCO

CO2

O2

Analyzers

MFC Control Unit

Reactor

Thermocouple

Furnace

N2

CO2/N2

CO/N2

1 2

3 4

Heater

Heated line

Gas out

CondenserCO

CO2

O2

Analyzers

MFC Control Unit

ReactorReactor

ThermocoupleThermocouple

Furnace

N2

CO2/N2

CO/N2

1 2

3 4

Heater

Heated line Heated line


41

1. Sample pre-treatment: filter the sample if it is cloudy and prepare appropriate dilutions.

2. Transfer 1.0 mL sample to a 25-50 ml beaker. 3. Pipet 9.0 ml ultrapure water into the beaker and stir to mix. 4. Add 1.0 mL TiSO4 solution to the beaker and stir to mix. 5. Allow the solution to develop color for 2 minutes. 6. Spectrophotometric measurement: turn on the instrument and

allow it to warm up for 5 - 10 minutes, set the instrument wavelength to 405 nm, insert ultrapure water blank and adjust instrument needle to full scale (0% Absorbance), insert sample and read Absorbance, determine H2O2 concentration by referencing from known H2O2 concentrations.

IV Experimental results: Fenton oxidation of acetic acid on FeY

zeolite

IV.1 Samples preparation

IV.1.1 The HY based catalyst

Synthetic HY with an Si/Al ratio of 11.5 (Engelhard) was used as the parent zeolite (Figure 29).

Chapter IV

44

Figure 29. Y structure.

The FeY sample was prepared by ion exchange starting from the ammonium form of HY zeolite (Si/Al = 2.6). Ion exchange was carried out at 80 °C using a 0.01 M aqueous solution of (CH3COO2)2(Fe). The time of ion exchange was 8 h and the amount of iron introduced into the zeolite was 6 wt.%. After drying at 120°C overnight, the samples were calcined typically at 550 °C for 2 hours.

Table 2 contains the sample prepared, with indications of the number of exchanges, the total time of exchanges, the form of the starting zeolites and the concentration of the metal solutions.

Table 2. Procedure of ion exchange for samples.

Sample Number of exchanges

Total time, h

Starting cation

(CH3COO2)2Fe mol/l

Fe, % weight

FeY 1 8 H+ 0.01 6

Experimental results: Fenton oxidation of the acetic acid on FeY zeolite

45

IV.2 Catalysts characterisation

IV.2.1 Specific surface area and chemical analysis

Surface area and porosity were obtained by N2 adsorption at 77 K. The microporous volume obtained by the t-plot method is 0.206 cm3/g for

HY, as shown in Table 3, and decreases for FeY.

Table 3. Microporous volume of HY and FeY.

Catalysts Nominal Fe content, wt%

Fe by ICP analysis wt,%

Microporous volume cm3/g

HY 0 - 0.206

FeY 6.0 6.1 0.154

Iron exchange leads to a small reduction in volume.

IV.2.2 X-ray diffraction spectroscopy (XRDS)

X-Ray diffraction spectra of FeY and HY catalysts are reported in Figure 30.

Chapter IV

46

5 10 15 20 25 30 35 40

FeY HY

Inte

nsity

, a.u

.

2 teta

Figure 30. X-Ray diffraction spectra of FeY and HY catalysts.

For an HY sample the diffraction peaks are in good agreement with literature data (Treacyand, Higgins, 2001). Moreover it can be observed that no substantial difference appears by comparing the peaks of the calcined FeY sample. However the presence of other phases related to iron in a lower amount than 6 wt% cannot be excluded.

IV.3 Catalytic activity tests

In order to verify that acetic acid was converted in a heterogeneous catalytic process, blank experiments were performed. A control test was carried out with the reactor loaded with 250 ml of freshly prepared aqueous solution of acetic acid with TOC of 1000 mg/l. No conversion of acetic acid was detected during this test, indicating the necessity of the catalyst for the observed reaction.

IV.3.1 Homogeneous catalytic Fenton oxidation

Catalytic homogeneous tests of wet oxidation with hydrogen peroxide were carried out in a glass batch reactor under continuous stirrring in contact with air atmosphere at T=25 °C.


47

IV.3.1.1 Acetic acid solution

A freshly prepared aqueous solution reaction (V=250 ml) of acetic acid with TOC of 1000 mg/l was added to the reactor together with 1.426 g of the catalyst (Fe(NO3)3, corresponding to a total amount of iron ions of 3.53*10-3 moles. Then a concentred solution of H2O2 was added to achieve a H2O2/substrate stoichiometric ratio, defined as the amount of hydrogen peroxide required to completely oxidize the substrate to CO2.

Reported in Figure 31 are the results for catalytic wet hydrogen peroxide oxidation (CWHPO) of acetic acid with a homogeneous iron catalyst at room temperature as a function of the time of reaction.

The total organic removal of acetic acid increases up to 30% after 4 hours.

0

200

400

600

800

1000

1200

0 1 2 3 4

t, h

TOC

, ppm

0

5

10

15

20

25

30

35

TOC

Rem

oval

, %

TOC TOC removal

Figure 31. Conversion as a function of time of homogeneous catalytic reaction with acetic acid at T=25°C. Experimental conditions: pHt=0=2.67, mcatalyst= 1.426 g.

IV.3.1.2 Real wastewater

Wastewaters derived from liming of bovine leather make up 31% of the total amount of wastewaters. This is characterized by a high COD and high salt content (chromium salts, sulfides, chloride ions, etc.).

The freshly prepared aqueous solution reaction (V=250 ml) of the wastewater derived from liming with TOC of 276 mg/l was added to the reactor together with 0.379 g of the catalyst (Fe(NO3)3, corresponding to a

Chapter IV

48

total amount of iron ions of 9.4*10-4 moles. Then a concentred solution of H2O2 (1360 mg/l) was added.

Reported in Figure 32 are the results for catalytic wet hydrogen peroxide oxidation (CWHPO) of the liming solution with a homogeneous iron catalyst at room temperature as a function of the time of reaction. The conversion of the liming solution after 4h is about 35%.

0

50

100

150

200

250

300

0 1 2 3 4t, h

TOC

, ppm

0

5

10

15

20

25

30

35

40

TOC

rem

oval

, %

TOC TOC removal

Figure 32. Conversion as a function of time of a heterogeneous catalytic reaction with liming solution at T=25°C. Experimental conditions: pHt=0=2.0, mcatalyst= 0.379 g.

IV.3.2 Heterogeneous catalytic Fenton oxidation

Catalytic heterogeneous tests of wet oxidation on FeY with hydrogen peroxide were carried out in a glass batch reactor under continuous stirrring at T=25 °C or at T=70°C in contact with air atmosphere.

IV.3.2.1 Effect of reaction temperature

In order to elucidate the effect of temperature on FeY activity, preliminarily catalytic tests were carried out at two temperatures, T=25 °C and T=70 °C.


49

Summarized in Figure 33 are the results obtained using the FeY catalyst in the following initial reaction conditions: pH=2.67, mcat = 0.170 g FeY, T=25°C, and initial amount of H2O2 in the stoichiometric ratio with hydrogen peroxide amount necessary to completely oxidize acetic acid to CO2. For acetic acid this ratio is 4. The results are reported as residual TOC as a function of the reaction time.

By monitoring Total Organic Carbon (TOC) during catalytic experiment revealed that there is a small change in total carbon content of the solution as shown in Figure 33. In particular, TOC removal after 4h is about 20%.

0

200

400

600

800

1000

0 1 2 3 4t, h

TOC

, ppm

0

5

10

15

20

25

TOC

rem

oval

, %

TOC TOC removal

Figure 33. Conversion as a function of time of reaction in the case of the FeY catalyst at T=25°C. Experimental conditions: pHt=0=2.67, mcatalyst= 0.170 g.

Summarized in Figure 34 are the results obtained using FeY for reaction conditions: pH=2.67, mcat = 0.170 g FeY, T=70°C. and initial H2O2/substrate values with respect to the stoichiometric amount of hydrogen peroxide necessary to completely oxidize acetic acid to CO2. For acetic acid this ratio is 4. The results are reported as residual TOC as function of reaction time at different temperatures.

TOC removal after 4h is about 13%, which is smaller than for catalytic tests performed at T= 25°C. This effect is probably due to a higher decomposition rate of H2O2 (Centi et al., 2000).

Chapter IV

50

0

200

400

600

800

1000

0 1 2 3 4

t, h

TOC

, ppm

0

5

10

15

20

25

TOC

rem

oval

, %

TOC TOC removal

Figure 34. Conversion as a function of time of reaction in the case of the FeY catalyst at T=70°C. Experimental conditions: pHt=0=2.67, mcatalyst= 0.170 g.

IV.3.3 Thermal analysis

Thermal analysis was carried out on the FeY sample after calcination and after catalytic tests at 25°C and 70°C.

Results of thermal analysis performed on calcined FeY are reported in Figure 35.


51

1

2

3

Hea

t Flo

w (W

/g)

-0.5

0.0

0.5

1.0

1.5

2.0

Der

iv. W

eigh

t (%

/min

)

75

80

85

90

95

100

Wei

ght (

%)

0 200 400 600 800 1000

Temperature (°C)

Q

Exo Up Universal V3.9A TA Instruments

Figure 35. Thermal analysis performed on FeY sample before catalytic activity test.

A high weight loss (about 20%) is observed between 20 and 300°C, corresponding to physisorbed and held water. Over 300°C a very low loss rate can be observed. No mass signals related to CO2 were reported.

Results of thermal analysis carried out on the FeY sample after the catalytic activity test at 25°C are reported in Figure 36. Besides the weight loss at temperatures lower than 200°C due to the removal of water, three other case of weight loss with derivative weight maximum temperature respectively of 210°C, 325°C and, lower, 475°C are observed, accompanied by three peaks due to M/Z=44 MS signals. This phenomenon could be due to the oxidation of organic fragment or acetic acid that remain trapped in the zeolite after catalytic tests or a desorption of COx species, as reported in literature (Neamtu et al., 2004).

Chapter IV

52

0

1

2

3

Hea

t Flo

w (W

/g)

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

Der

iv. W

eigh

t (%

/min

)

75

80

85

90

95

100

105

Wei

ght (

%)

0 200 400 600 800 1000

Temperature (°C)Exo Up Universal V3.9A TA Instruments

Figure 36. Thermal analysis performed on FeY sample after catalytic activity test at T=25°C in air flow.

Results of thermal analysis carried out on the FeY sample after the catalytic activity test performed at 70°C are reported in Figure 37.

Figure 37. Thermal analysis performed on FeY sample after catalytic activity test at T=70°C in air flow.

0

2

4

Hea

t Flo

w (W

/g)

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

Der

iv. W

eigh

t (%

/min

)

70

75

80

85

90

95

100

Wei

ght (

%)

0 200 400 600 800 1000

Temperature (°C)Exo Up Universal V3.9A TA Instruments

44


53

The sample shows similar weight losses, but more intense evidencing that the phenomenon depends on applied temperature during catalytic tests and deeper investigation are necessaries to attribute every weight loss. By monitoring MS signals in the range m/z = 29-210 three peaks related to CO2 release are showed.

IV.3.4 Leaching test

Leaching tests were carried out to check the potential of leaching of iron from zeolite during catalytic tests, analysing the solution by ICP-MS. Both iron removal from zeolite and the iron solution concentration have to be monitored to be compared. In this case also, the solid was separated after oxidation (T=70°C). This method allowed direct determination of the presence of iron ions in solution.

100

120

140

160

180

200

220

240

260

280

300

0 1 2 3 4 5

t, h

Iron

conc

entr

atio

n, p

pb

Figure 38. Leaching test on FeY after catalytic test at T=70°C.

The data (Figure 38) shows low dissolution (0.05 % with respect to initial

value) of iron on the zeolite at various times during acetic acid oxidation (T=70°C).

V Experimental results: characterization of the

perovskite based monolith

V.1 Sample preparation

The monolithic honeycomb perovskite-based catalyst was developed at the Boreskov Institute of catalysis SB RAS. The perovskite structure is showed in Figure 39.

Figure 39. Perovskite structure.

Preparation consists in supporting the active components on the refractory carrier. Supported 3d oxides (MeOx) and perovskites (LaMeO3) with Me = Mn, Co, Fe, Ni, Cu (Table 4) were prepared by impregnation of thin wall (wall thickness 0.4 mm) monolithic honeycomb cordierite supports (triangular channels of 2.5 mm size, specific area = 2 m2/g, mean pore radius of 0.12 microns) with solutions of nitrate salts in ethylene glycol with added citric acid. The procedure is as follows. Solutions (20 ml) of nitrate salts (room temperature saturated nitrate solutions were mixed in required proportions) with added citric acid (8 g in 4 ml) and ethylene glycol (2.5 ml) were prepared and heated up to 50 °C. Monolith substrates cut as cylinders with diameter 21–22 mm and 50 mm in height were dipped into the solution for 5–10 min. Then, the samples were taken out of the solution, blown out by

Chapter V

56

air, dried in the air and calcined at 900 °C for 4 h. During the drying stage, at 100–200 °C, a film of polymerized metal–ether complexes strongly adhering to the monolithic support walls is formed on internal and external surfaces. After annealing at temperatures exceeding 500 °C, the organic residue is burned, and a grainy porous perovskite-supported layer emerges.

Table 4. List of perovskite-based catalysts characterised.

Perovskite catalyst Chemical composition (active phase, %)

LaMnO3 3.67 LaMnO3 2.69 LaMnO3 2.57 LaFeO3 2.24 LaNiO3 2.52 LaCoO3 2.94 LaCuO3 2.66 H2PtCl6/LaMnO3 2.69 LnFeO3/Al2O3/Zr0.9Co0.1O2 88 LnFeO3/Al2O3/Zr0.9Co0.1O2 48 H2PtCl6/Ln2O3 7.04 H2PdCl4/Ln2O3 8.17

Samples were calcined in air at 900 °C for 4h. Noble (Pt or Pd) metals (=

0.1 %) were supported by wet impregnation from different salts on the cordierite substrate which were either pure or precovered by the oxide sublayer. After Pt or Pd loading, samples were either directly dried under air or, before drying, treated with hydrazine hydrate.

Perovskite oxides LnFeO3 (Ln= La2O3, CeO2,…) with triangular channels (side 4 mm) and wall thickness (1.2 mm) were obtained by the mechanoceramic route (Ciambelli et al., 1999). Monolith catalysts were prepared by kneading a powdered active component with alumina based binder (aluminium hydroxide) and zirconia doped with cobalt in acid media followed by extrusion of the plastic pastes, drying and calcination at 900 °C for 4 h.

V.2 Thermal analysis

Thermal analysis was carried out by the Boreskov Institute of Catalysis (Russia) on a DQ-1500 device, (Isupova et al., 2002). Samples (200 mg) were heated with a ramp of 10 °C/min up to 900 °C under air atmosphere.

Experimental Results: characterization of perovskite based monolith.

57

Figure 40 shows the TG, DTG and DTA curves of LaMnO3, LaCuO3, LaCoO3, LaFeO3 and LaNiO3 perovskite precursors.

As evidenced by the DTG minima, the two samples showed initial weight loss at temperatures lower than 120 °C due to the adsorbed water loss. The processes of gas evolution from the precursor at air annealing are completed only at temperatures exceeding 700 °C. Hence, this temperature was chosen as a minimum catalyst calcination temperature.

Figure 40. Thermal analysis of perovskite precursors.

Chapter V

58

V.3 X-ray analysis

X-ray analysis was performed by the Boreskov Institute of Catalysis (Russia) with a URD-6 diffractometer using Cu Kα radiation. The 2θ scan region was 10–70°. Typical particle sizes were estimated from the broadening of 400 diffraction peak (cubic index) not splitted due to hexagonal distortion of the perovskite structure. Calcination of unsupported LaMeO3 (Me = Fe, Mn) precursors at 900 °C leads to formation of well-crystallized perovskite particles with typical sizes 80–100 nm. The perovskite structure as well as cobalt, nickel and copper simple oxides admixtures (Co3O4, NiO, CuO), respectively, were revealed in the calcined precursors. In the case of cordierite-supported samples, the mixture of cordierite and perovskite phases was observed after catalyst annealing at 900 °C(Figure 41), (Isupova et al., 2005).

Figure 41. X-ray diffraction patterns of cordierite carrier and supported perovskite catalysts. P perovskite peaks; C, lanthanum oxy-carbonate peaks.

For supported lanthanum manganites and ferrites, the type of structure (hexagonal and orthorhombic, respectively) corresponds to stable modifications. In the case of cuprates, nickelates and cobaltites, instead of a stable hexagonal phase, a cubic modification was revealed. Hence, for the latter systems, pronounced interaction between the active component and the support certainly takes places. Most probably, a part of support is dissolved in the acidic polymerized solution at the impregnation stage (e.g. Al cations were detected in the acidic solution after the impregnation stage), which can be facilitated by a strong complexation ability of mixed citric acid–ethylene glycol ethers. After precursor decomposition and calcination, a part of aluminum cations enters into metastable perovskite-like solid solution, thus affecting their structural properties. According to X-ray analysis particle size of supported perovskites is in the range 30–40 nm.

X-ray microanalysis revealed that in the case of cordierite supported catalysts prepared using the Pechini method, the cations of an active component have a nearly uniform distribution across the wall thickness as


59

well as forming a separate layer with 2–3 mm thickness covering the walls of the monolithic support.

V.4 SEM analysis

The textural features of supported perovskites were studied by SEM with a BS-350 machine by the Boreskov Institute of Catalysis (Russia) (resolution limit is about 5–10 nm). SEM analysis (Figure 42) revealed that the active oxide component was distributed nearly uniformly within the wall forming a surface layer of 2-3 mm thickness which repeated the carrier surface relief. The morphology of this porous layer composed of separate grains is nearly independent of the calcination temperature. The supported active component or sublayer form a grainy layer which repeats the carrier surface relief. Separate grains compose this grainy layer, and its morphology is nearly independent of the calcination temperature. On the wall’s cross-section a well developed internal pore structure of cordierite and the surface layer of supported oxides, 2–3 mm in thickness (Isupova et al., 2005).

Figure 42. SEM data on a carrier and on supported catalysts: (a) carrier, (b) carrier+Ln2O3, (c) carrier+LaMnO3, (d) carrier+Ln2O3+LaMnO3.

Chapter V

60

V.5 Micro Raman spectroscopy

In Figure 43 Raman spectra of LaMnO3 and LaMnO3 with Pt are reported.

2 0 0 0

70 0 0

12 0 0 0

170 0 0

2 2 0 0 0

2 70 0 0

3 2 0 0 0

2 0 0 3 0 0 4 0 0 50 0 6 0 0 70 0 8 0 0 9 0 0

Raman shift, cm-1

Cou

nts

LaMnO3 LaMnO3 with Pt

Figure 43. Raman spectra of LaMnO3 (3.67 %) and LaMnO3 with Pt samples.

The Raman spectrum of LaMnO3 with Pt shows Pt species bands (411 cm-1, 391 cm-1) superimposed upon typical absorptions from the support.

In Figure 44 Raman spectra of LaFeO3 monolith and LaFeO3 powder are reported.


61

8000

9000

10000

11000

12000

13000

14000

15000

16000

17000

18000

200 300 400 500 600 700 800 900

Raman shift, cm-1

Cou

nts

LaFeO3 monolith

LaFeO3 powder

Figure 44. Raman spectra of LaFeO3 monolith and LaFeO3 powder.

The monolith and powder show bands at 310, 440, 630 cm-1.

V.6 Specific surface area

Specific surface area (SSA) was determined by a routine BET procedure using the Ar thermal desorption data in the Boreskov Institute of Catalysis (Russia).

The specific surface area for the prepared bulk perovskites calcined at 900 °C is 13 m2/g (for Me = Fe, Mn, Co, Ni) and 3 m2/g (for Me = Cu), respectively.

For all supported oxides calcined at 900 °C the specific surface area is about 2 m2/g. For all supported catalysts, the specific surface area is about 4–6m2/g.

For the LnFeO3 monoliths, the specific surface area is about 15-20 m2/g.

V.7 NIR-UV-VIS DRS

Figure 45 depicts the diffuse reflectance UV–vis spectra of the LaMnO3 (3.67%). The Kubelka–Munk function, F(R), can be considered proportional to the absorption of radiation (Anderson et al., 1997). A plot of the square of the absorbed light (proportional to the square of the Kubelka-Munk function F(R)) vs the energy of irradiation was used to obtain the band gap Eg. The Kubelka-Munk function is given by (eq.19):

F(R) = (1 - R)2/2R) (19) where R is the measured reflectance.

Chapter V

62

On this basis, the value of Eg, the band gap of the LaMnO3 catalyst (3.67%) is at 2.75 eV (Figure 45).

5

10

15

20

25

30

35

40

2 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 2,9 3 3,1 3,2 3,3 3,4 3,5 3,6 3,7 3,8

hv, eV

(F(R

)*hv

)2

Figure 45. Band-gap calculus from the DR–UV–vis spectra of LaMnO3.

On this basis, the value of Eg, the band gap of the Pt/LaMnO3 catalyst is at 2.25 eV (Figure 46).

0

10

20

30

40

50

60

2 2,2 2,4 2,6 2,8 3 3,2 3,4 3,6 3,8 4hv, ev

(F(R

)*hv

)2

Figure 46. Band-gap calculus from the DR–UV–vis spectra of Pt/LaMnO3..


63

On this basis, the value of Eg, the band gap of the LaFeO3 catalyst is at 1.90 eV (Figure 47).

0

2

4

6

8

10

12

14

16

18

20

1 1,2 1,4 1,6 1,8 2 2,2 2,4 2,6 2,8 3 3,2 3,4 3,6 3,8 4hv, ev

(F(R

)*hv

)2

Figure 47. Band-gap calculus from the DR–UV–vis spectra of LaFeO3.

On this basis, the value of Eg, the band gap of the LnFeO3 (48%) catalyst is at 2.10 eV (Figure 48).

0

50

100

150

200

250

300

350

400

1 1,2 1,4 1,6 1,8 2 2,2 2,4 2,6 2,8 3hv, ev

(F(R

)*hv

)2

Figure 48. Band-gap calculus from the DR–UV–vis spectra of LnFeO3 (48%).

On this basis, the value of Eg, the band gap of the LnFeO3(88%) catalyst is at 2.10 eV (Figure 49).

Chapter V

64

0

200

400

600

800

1000

1200

1 1,2 1,4 1,6 1,8 2 2,2 2,4 2,6 2,8 3hv, ev

(F(R

)*hv

)2

Figure 49. Band-gap calculus from the DR–UV–vis spectra of LnFeO3 (88%).

VI Experimental results: Fenton oxidation of acetic acid on

LaMeO3 perovskite

VI.1 Catalytic activity tests

Acetic acid oxidation was carried out in a batch glass reactor of 250 ml placed on an oscillating plate, a pH glass electrode and oxygen dissolved (O.D.) glass electrode were used to monitor the pH and O.D.. Pieces of structured catalysts of about 5g were tested for acetic acid oxidation in aqueous solution (500 ppm as TOC) in the presence of H2O2 ranging between 0.083-0.167 mol/l.

VI.1.1 Catalytic decomposition of H2O2 on LaMnO3 and LnFeO3

In the catalytic test on LaMnO3 (2.57%), with initial concentration of hydrogen peroxide equal to 0.083 mol/l, an H2O2 consumption of 82 % is achieved after 3 hours (Figure 50).

Chapter VI

66

0

500

1000

1500

2000

2500

3000

0 1 2 3 4t, h

H2O

2, pp

m

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

H2O2, ppm H2O2 conversion, %

Figure 50. Catalytic decomposition of H2O2 with LaMnO3 (2.57%). Experimental conditions: pHt=o=5.3, mcatalyst= 19 g, [H2O2]t=0= 0.083 mol/l.

In Figure 51 a similar H2O2 conversion for the catalytic decomposition of hydrogen peroxide in the presence of LnFeO3 (88%) is observed.

0

500

1000

1500

2000

2500

3000

0 1 2 3 4 5 6t, h

H2O

2, pp

m

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%


Figure 51. Catalytic decomposition of H2O2 with LnFeO3 (88%). Experimental conditions: pHt=o=5.4, mcatalyst= 15 g, [H2O2]t=0= 0.083 mol/l.

pH increases during the reaction (Table 5). The catalysts promote the formation of the hydroxyl radicals. The results show that the perovskite catalysts are able to decompose H2O2 to O2 as shown by the increase of dissolved oxygen after the test.

Experimental results: Fenton oxidation of acetic acid on LaMeO3 perovskite.

67

Table 5. pH and oxygen dissolved values for the catalytic decomposition of hydrogen peroxide.

Catalyst pHinitial value pHfinal

value O.D.initial

value (ppm) O.D.final value (ppm)

LaMnO3 (2.57%)

5.3 6.4 - -

LnFeO3 (88%)

5.4 6.2 0 15

VI.1.2 Fenton oxidation of acetic acid on LaMnO3 (3.67%)

After 5 hours (Figure 52), a poor level of CH3COOH oxidation is reached on LaMnO3 (3.67%) shown by low TOC removal.

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6

t,h

TOC

rem

oval

, %

0

1

2

3

4

5

6

7

8

9

10

H2O

2 con

vers

ion,

%

TOC removal, %H2O2 conversion, %

Figure 52. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaMnO3 (3.67%) catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 4.9 g, [H2O2]t=0= 0.083 mol/l.

For the same system with higher initial H2O2 concentration, equal to 0.167 mol/l (Figure 53), only slightly higher final TOC removal is observed. Specifically about 3% of the initial TOC disappears after t=5 hours.

Chapter VI

68

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5t, h

TOC

rem

oval

, %

Figure 53. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaMnO3 (3.67%) catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 4.9 g, [H2O2]t=0= 0.167 mol/l.

As a consequence, it must be pointed out that the perovskites do not catalyse the Fenton reaction. In addition, their H2O2 decomposition ability appears inhibited by the presence of acetic acid.


69

VI.1.3 Fenton oxidation of acetic acid on Pt/LaMnO3

By using LaMnO3 with Pt (Figure 54) about 10% of TOC removal is obtained when an H2O2 consumption of 8% is achieved.

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5 4t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal, %

H2O2 conversion, %

Figure 54. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of Pt/LaMnO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 6.0 g, [H2O2]t=0= 0.083 mol/l.

For the same catalyst with H2O2 concentration equal to 0.167 mol/l (Figure 55) similar TOC removal can be obtained. Specifically, about 8% of the initial TOC disappears after t=4 hours.

Chapter VI

70

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4t, h

TOC

rem

oval

, %

Figure 55. Total organic carbon removal as function of time of reaction in the case of Pt/LaMnO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 6.0 g, [H2O2]t=0= 0.167 mol/l.

Pt appears to promote the Fenton oxidation activity of perovskites.

VI.1.4 Fenton oxidation of acetic acid on LaFeO3 (2.24%)

In the system with LaFeO3 (2.24%) (Figure 56) about 4% of TOC removal is quickly obtained with an H2O2 consumption of 3% after one hour.


71

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4t, h

TOC

rem

oval

, %

0

1

2

3

4

5

6

7

8

9

10

H2O

2 con

vers

ion,

%

TOC removal, %

H2O2 conversion, %

Figure 56. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaFeO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 5.4 g, [H2O2]t=0= 0.083 mol/l.

The increase in H2O2 initial concentration equal to 0.167 mol/l (Figure 57),does not result in higher TOC removal; in addition, after one hour the TOC removal is halved with respect to that obtained at lower initial H2O2 concentration.

Chapter VI

72

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4t, h

TOC

rem

oval

, %

0

1

2

3

4

5

6

7

8

9

10

H2O

2 con

vers

ion,

%

TOC removal, %

H2O2 conversion, %

Figure 57. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaFeO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 5.4 g, [H2O2]t=0= 0.167 mol/l.

VI.1.5 Fenton oxidation of acetic acid on LaCuO3

On LaCuO3 (Figure 58) about 4% of TOC removal with a H2O2 consumption of 6% is achieved.


73

0

1

2

3

4

5

6

7

8

9

10

0 0,5 1 1,5 2 2,5 3 3,5 4

t, h

TOC

rem

oval

, %

0

1

2

3

4

5

6

7

8

9

10

H2O

2 con

vers

ion,

%


Figure 58. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaCuO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 6.4 g, [H2O2]t=0= 0.083 mol/l.

For the same system with H2O2 concentration equal to 0.167 mol/l (Figure 59) we have similar TOC removal, specifically about 4% of the initial TOC disappears after t=4 hours.

Chapter VI

74

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4t, h

TO

C r

emov

al, %

Figure 59. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaCuO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 5.4 g, [H2O2]t=0= 0.167 mol/l.


75

VI.1.6 Fenton oxidation of acetic acid on LaNiO3

On LaNiO3 (Figure 60) about 4% of TOC removal is obtained when an H2O2 consumption of 2% is achieved.

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4t, h

TOC

rem

oval

, %

0

1

2

3

4

5

6

7

8

9

10

H2O

2 con

vers

ion,

%


Figure 60. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaNiO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 6.0 g, [H2O2]t=0= 0.083 mol/l.

With higher H2O2 initial concentration (Figure 61) TOC removal rises to about 10% after t=4 hours.

Chapter VI

76

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4

t, h

TO

C r

emov

al, %

Figure 61. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaNiO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 6.0 g, [H2O2]t=0= 0.167 mol/l.


77

VI.1.7 Fenton oxidation of acetic acid on LaCoO3

In the system with LaCoO3 (Figure 62) about 4% of TOC removal is obtained when an H2O2 consumption of 1% is achieved.

0

1

2

3

4

5

6

7

8

9

10

0 0,5 1 1,5 2 2,5 3 3,5 4t, h

TOC

rem

oval

, %

0

1

2

3

4

5

6

7

8

9

10

H2O

2 con

vers

ion,

%


Figure 62. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of LaCoO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 5.4 g, [H2O2]t=0= 0.087 mol/l.

For the same system with H2O2 concentration equal to 0.167 mol/l (Figure 63) we have similar TOC removal, up to 5% after t=5 hours.

Chapter VI

78

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5t, h

TOC

rem

oval

, %

Figure 63. Total organic carbon removal and H2O2 conversion as a function of time of reaction in the case of the LaCoO3 catalyst at T=25°C. Experimental conditions: pHt=o=3.9, mcatalyst= 5.4 g, [H2O2]t=0= 0.167 mol/l.

VI.2 Leaching test.

Leaching tests were carried out to check the potential of leaching of metals from the perovskite during catalytic tests, analysing the solution by ICP-AES. The solid catalyst was separated after oxidation. This method allowed direct determination of the presence of metal ions in solution.


79

Table 6. Metal ion analysis of the some catalyst used for the catalytic Fenton reaction.

Catalyst [H202]= mol/l Metal iont=0 (ppm)

Metal ionfinal

time (ppm) LaMnO3 (2.69%)

0.083 Mn= 0 Mn= 20

Pt/LaMnO3 0.083 Mn= 0 Mn= 5.7 LaFeO3 0.083 Fe= 0 Fe= 0.02 LaCuO3 0.083 Cu= 0 Cu= 4.1 LaCoO3 0.083 Co= 0 Co= 0.75 LaNiO3 0.083 Ni= 0 Ni= 0.23

The data (Table 6) show a small dissolution of the metal on the

perovskite after acetic acid oxidation. However, Mn leaching both from LaMnO3 and Pt/LaMnO3 are significant

with respect to emission limits in EU regulations (2 ppm). Also Cu content is higher than permitted for the discharge into surface water.

VII Experimental results: photooxidation of acetic acid

VII.1 Photooxidation test conditions and typical trends

Catalytic tests were carried out feeding 250 Ncc/min air or nitrogen at the bottom of the stainless steel sealed photoreactor.

In order to distinguish the contribution of the different reactions participating in the photo-Fenton reaction, the following tests were performed.

Photolysis tests of H2O2 were effected on 100 ml of solution and H2O2 in the range 0.083-0.167 mol/l were used.

Photolysis tests of acetic acid were performed on 100 ml of solution and acetic acid aqueous solutions containing total organic carbon concentration (TOC) of 500 mg/l at pH 3.9.

Photolysis tests of H2O2 and CH3COOH were performed on 100 ml of solution, H2O2 in the range 0.083-0.167 mol/l and acetic acid aqueous solutions containing total organic carbon concentration (TOC) of 500 mg/l at pH 3.9.

Finally, photo-Fenton tests on acetic acid aqueous solutions containing total organic carbon concentration (TOC) of 500 mg/l at pH 3.9 and H2O2 in the range 0.083-0.167 mol/l were carried out.

An 8 W mercury vapor lamp emitting at 254 nm was placed in the reactor. Then the lamp was switched on and the reaction started. Very small samples of treated solution (500 µl) were taken for analyses every hour, to avoid changing in the contact time during the test. Gas which evolved from the sealed photoreactor during the reaction were analysed by CO/CO2 IR analyser (ABB) in order to verify the carbon balance.

TOC was evaluated by COX emission obtained by catalytic combustion at T=850°C. H2O2 concentration was determined by H2O2/TiOSO4 complex (λ = 405 nm) UV-Vis analyses (see Chapter V).

A typical trend of photocatalytic tests is reported in Figure 64 with reference to LaMnO3 (3.67%). At the run starting time, the air or nitrogen

Chapter VII

82

stream was passed through the reactor in the absence of irradiation at ambient temperature for t=10 min.

After 5 hours of irradiation, we observed TOC removal of 30% (Figure 64).

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5

t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal, % H2O2 conversion, %

Figure 64. Catalytic photo-Fenton oxidation in nitrogen stream on LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; mcatalyst= 4.9 g; C0

CH3COOH= 0.021 mol/l; C0H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9,

QN2= 250 Ncc/min.

In Figure 65 the concentration of CO2 detected in the gas phase during the photo-Fenton reaction on LaMnO3 is showed.

Experimental results: photooxidation of acetic acid

83

0

100

200

300

400

500

600

700

800

900

1000

0 50 100 150 200 250 300 350 400 450 500

t, min

CO

2, pp

m

Figure 65. Carbon dioxide concentration formed during catalytic photo-Fenton oxidation in nitrogen stream on LaMnO3 (3.67%).

No formation of CO was observed. CO2 concentration reached a maximum value of about 850 ppm, after an irradiation time of 150 min and then decreased to 0 ppm after 500 min evidencing the stripping completion of CO2 produced.

Moreover, from the values of TOC removal and carbon dioxide concentration formed, the total carbon mass balance was closed to about 98%; particularly, the weight in mg of carbon evaluated from CO2 analysed and the weight in mg of carbon evaluated from TOC removal were respectively 28.16 and 28.69. This indicates that complete mineralization of acetic acid is obtained in photo-Fenton oxidation.

Chapter VII

84

VII.2 Photolysis reactions

VII.2.1 Photolysis of hydrogen peroxide in absence of acetic acid

In Figure 66 it is shown that, after 5 hours, about 70% of the initial concentration of hydrogen peroxide is converted.

0

1000

2000

3000

4000

5000

6000

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5t, h

H2O

2, pp

m

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vesr

ion,

%

H2O2 ppm H2O2 conversion

Figure 66. Photolysis of H2O2 in absence of acetic acid. Experimental

conditions: V tot.: 100 ml; C0H2O2= 0.167 mol/l; P= 1 atm; T=25°C;

pH=3.9.


85

VII.2.2 Photolysis of hydrogen peroxide in the presence of acetic

acid

In Figure 67 it is shown that after 5 hours, in the photolysis of acetic acid with hydrogen peroxide with a molar ratio H2O2/CH3COOH=4 about 76% of H2O2 is converted, when TOC removal was about 35%.

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6

t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal photolysis H2O2 conversion, photolysis

Figure 67. Photolysis of H2O2 in the presence of acetic acid. Experimental conditions: V tot.: 100 ml; H2O2/CH3COOH= 4; C0

H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.

In the presence of higher quantities of H2O2 (Figure 68) at H2O2/CH3COOH=8, about 70% of H2O2 is converted after 5 hours. Further H2O2 increase does not result in greater TOC conversion (35%).

Chapter VII

86

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6

t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal photolysis, % H2O2 conversion photolysis, %

Figure 68. Photolysis of H2O2 in the presence of acetic acid.

Experimental conditions: V tot.: 100 ml; H2O2/CH3COOH= 8; C0H2O2=

0.167 mol/l; P= 1 atm; T=25°C; pH=3.9.


87

VII.3 Photocatalytic decomposition of H2O2

VII.3.1 Homogeneous photocatalytic decomposition of H2O2

In Figure 69 it is shown, that after 4 hours, in homogeneous photocatalytic decomposition of hydrogen peroxide (C0

H2O2= 0.083 mol/l) about 97% of H2O2 is consumed.

0

500

1000

1500

2000

2500

3000

0 1 2 3 4 5 6 7t, h

H2O

2, pp

m

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%


Figure 69. Photocatalytic decomposition of H2O2 with Fe2(C2O4)3. Experimental conditions: V tot.: 100 ml; mcatalyst= 0.7 g; C0

H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.

In Figure 70 it is shown, that after 4 hours, in homogeneous photocatalytic decomposition of hydrogen peroxide (C0

H2O2= 0.167 mol/l) about 95% of H2O2 is consumed with a similar reaction rate.

Chapter VII

88

0

1000

2000

3000

4000

5000

6000

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5t, h

H2O

2, pp

m

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%


Figure 70. Photocatalytic decomposition of H2O2 with Fe2(C2O4)3. Experimental conditions: V tot.: 100 ml; mcatalyst= 0.7 g; C0

H2O2= 0.167 mol/l; P= 1 atm; T=25°C; pH=3.9.

VII.3.2 Heterogeneous photocatalytic decomposition of H2O2

The heterogeneous photocatalytic decomposition of H2O2, in the presence of LaMnO3 (3.67%), with initial concentration of hydrogen peroxide equal to 0.083 mol/l, proceeds as in the absence of catalyst (Figure 71).


89

0

500

1000

1500

2000

2500

3000

0 1 2 3 4 5 6t, h

H2O

2, pp

m

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

H2O2 LaMnO3 with H2O2 only, ppm

H2O2 conversion LaMnO3 with H2O2 only, %

Figure 71. Photocatalytic decomposition of H2O2 with LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; mcatalyst= 4.9 g; C0

H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.

In the same system with initial concentration of hydrogen peroxide equal to 0.167 mol/l, (Figure 72) a higher hydrogen peroxide conversion is noted.

0

10 0 0

2 0 0 0

3 0 0 0

4 0 0 0

50 0 0

6 0 0 0

0 1 2 3 4 5t, h

H 2O2,

ppm

0

10

2 0

3 0

4 0

50

6 0

70

8 0

9 0

10 0

H 2O2 c

onve

rsio

n, %


Figure 72. Photocatalytic decomposition of H2O2 with LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; mcatalyst= 4.9 g; C0

H2O2= 0.167 mol/l; P= 1 atm; T=25°C; pH=3.9.

Chapter VII

90

In the photo-system Pt/LaMnO3, with initial concentration of hydrogen peroxide equal to 0.083 mol/l, an H2O2 consumption of 52 % is achieved after 3 hours (Figure 73).

0

500

1000

1500

2000

2500

3000

0 1 2 3 4t, h

H2O

2, pp

m

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%



H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.

In the same system with initial concentration of hydrogen peroxide equal to 0.167 mol/l, (Figure 74) a higher hydrogen peroxide conversion is noted.


91

0

1000

2000

3000

4000

5000

6000

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5t, h

H2O

2, pp

m

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%



H2O2= 0.167 mol/l; P= 1 atm; T=25°C; pH=3.9.

VII.4 Photocatalytic decomposition of acetic acid

In the photo/LaMnO3, in the presence of acetic acid only with the initial concentration of the acetic acid equal to 0.010 mol/l, a TOC removal of 7 % is achieved after 1 hour (Figure 75), and then remains constant.

Chapter VII

92

0

5

10

15

20

25

30

35

40

45

50

0 1 2 3t, h

TOC

rem

oval

, %

TOC removal LaMnO3 with acetic acid only , %

Figure 75. Photocatalytic decomposition of acetic acid with LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; mcatalyst= 4.9 g; TOCt=0= 250 ppm; P= 1 atm; T=25°C; pH=3.9.

In the same system, in the presence of acetic acid only with initial concentration of the acetic acid equal to 0.021 mol/l, a slightly lower conversion of about 6% is achieved (Figure 76), after 2 hours.

0

1

2

3

4

5

6

0 1 2 3 4 5 6

t, h

TOC

rem

oval

, %

TOC removal of acetic acid w ith acetic acid only, %

Figure 76. Photocatalytic decomposition of acetic acid with LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; mcatalyst= 4.9 g; TOCt=0= 500 ppm; P= 1 atm; T=25°C; pH=3.9.


93

VII.5 Catalyst samples for photo-Fenton tests

A list of catalysts tested in CH3COOH photo-Fenton oxidation is reported in Table 7.

The monolithic honeycomb perovskite-based catalysts were prepared by the Boreskov Institute of catalysis SB RAS and were previously described (see Chapter V). Powder perovskites were also tested for comparison. Fe2(C2O4)3 was chosen as the reference homogeneous catalyst.

Table 7. List of catalysts tested.

Perovskite catalyst Chemical composition (active phase, %)

Catalyst kind-form

LaMnO3 3.67 Supported-Structured LaMnO3 2.69 Supported-Structured LaMnO3 2.57 Supported-Structured LaMnO3 100 Bulk-Powder LaFeO3 2.24 Supported-Structured LaFeO3 100 Bulk-Powder LaNiO3 2.52 Supported-Structured LaCoO3 2.94 Supported-Structured LaCuO3 2.66 Supported-Structured H2PtCl6/LaMnO3 2.69 Supported-Structured LnFeO3/Al2O3/Zr0.9Co0.1O2 88 Bulk-Supported-Structured LnFeO3/Al2O3/Zr0.9Co0.1O2 48 Bulk-Supported-Structured H2PtCl6/Ln2O3 7.04 Bulk-Supported-Structured H2PdCl4/Ln2O3 8.17 Bulk-Supported-Structured

VII.6 Catalytic photo-Fenton oxidation

VII.6.1 Homogeneous photo-Fenton oxidation

For the photo-ferrioxalate system with H2O2/CH3COOH=4, about 24% of the initial TOC disappears when an H2O2 consumption of up to 90 % was achieved (Figure 77).

Chapter VII

94

0102030405060708090

100

0 1 2 3 4 5t, h

TOC

rem

oval

, %

0102030405060708090100

H2O

2 con

vers

ion,

%

TOC removal homogeneous photoFentonH2O2 conversion homogeneous photoFenton

Figure 77. Homogeneous photo-Fenton with Fe2(C2O4)3. Experimental conditions: V tot.: 100 ml; mcatalyst= 0.7 g; C0

CH3COOH= 0.021 mol/l; C0H2O2=

0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.


95

VII.6.2 Heterogeneous photo-Fenton oxidation

VII.6.2.1 Heterogeneous photo-Fenton oxidation on

LaMnO3 (3.67%)

With the heterogeneous structured catalyst LaMnO3 (3.67%), about 54 % of TOC removal is obtained within 5 hours and higher H2O2 consumption (96 %) also with respect to H2O2 photolysis (Figure 78). TOC removal ends when all H2O2 is consumed.

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6t, h

TO

C r

emov

al, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal, LaMnO3 H2O2 conversion, LaMnO3



H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.

When a molar ratio of H2O2/CH3COOH=8 is used, about 59 % of TOC removal is obtained with almost total H2O2 consumption (Figure 79).

Chapter VII

96

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6

t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal, LaMnO3

H2O2 conversion, LaMnO3



H2O2= 0.167 mol/l; P= 1 atm; T=25°C; pH=3.9.


97


Pt/LaMnO3

In the photo/Pt/LaMnO3 system with H2O2/CH3COOH=4, about 54 % of TOC removal is obtained when an H2O2 consumption of 98 % is achieved (Figure 80).

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal,Pt/ LaMnO3

H2O2 conversion, LaMnO3



H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.

In the photo-Pt/LaMnO3 system, no significant increase was obtained by employing H2O2/CH3COOH=8, 55 % of TOC removal and an H2O2 consumption of 99 %, was also achieved (Figure 81).

Chapter VII

98

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal, Pt/LaMnO3

H2O2 conversion,Pt/LaMnO3



H2O2= 0.167 mol/l; P= 1 atm; T=25°C; pH=3.9.


LaFeO3 (2.24%)

In the photo/LaFeO3 (2.24%) system with H2O2/CH3COOH=4, about 60 % of TOC removal is obtained when an H2O2 consumption of 90 % is achieved (Figure 82).


99

0

10

2 0

3 0

4 0

50

6 0

70

8 0

9 0

10 0

0 1 2 3 4 5 6t, h

TOC

rem

oval

, %

0

10

2 0

3 0

4 0

50

6 0

70

8 0

9 0

10 0

H 2O2 c

onve

rsio

n, %

TOC removal LaFeO3, % H2O2 conversion, LaFeO3, %

Figure 82. Heterogeneous photo-Fenton with LaFeO3 (2.24%). Experimental conditions: V tot.: 100 ml; mcatalyst= 5.4 g; C0


H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.


LaCuO3

In the photo/LaCuO3 system with H2O2/CH3COOH=4, about 65 % of TOC removal is obtained when an H2O2 consumption of 100 % is achieved (Figure 83).

Chapter VII

100

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal, LaCuO3 H2O2 conversion, LaCuO3

Figure 83. Heterogeneous photo-Fenton with LaCuO3. Experimental conditions: V tot.: 100 ml; mcatalyst= 6.4 g; C0


0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.


LaCoO3

In the photo/LaCoO3 system with H2O2/CH3COOH=4, about 52 % of TOC removal is obtained when an H2O2 consumption of 87 % is achieved (Figure 84).


101

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7

t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal, LaCoO3 H2O2 conversion, LaCoO3

Figure 84. Heterogeneous photo-Fenton with LaCoO3. Experimental conditions: V tot.: 100 ml; mcatalyst= 5.4 g; C0


0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.


LaNiO3

In the photo/LaNiO3 system with H2O2/CH3COOH=4, about 49 % of TOC removal is obtained when an H2O2 consumption of 89 % is achieved (Figure 85).

Chapter VII

102

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal, LaNiO3 H2O2, conversion, LaNiO3

Figure 85. Heterogeneous photo-Fenton with LaNiO3. Experimental conditions: V tot.: 100 ml; mcatalyst= 6.0 g; C0


0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.


103


LnFeO3 (48%)

In the photo/LnFeO3 system with H2O2/CH3COOH=4, about 40 % of TOC removal is obtained when an H2O2 consumption of 100 % is achieved (Figure 86).

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 co

nver

sion

, %




0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.


LnFeO3 (88%)

In the presence of the catalyst with a high load of perovskite a lower conversion is noted, particularly about 29 % of TOC removal is obtained when an H2O2 consumption of 100 % is achieved (Figure 87).

Chapter VII

104

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5 4t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%




0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.

For bulk structured ferrites, faster H2O2 and TOC conversion were observed, since their concentration levelled off after 2 hours. Maximum TOC removal appears limited by H2O2 consumption.


Pt/Ln2O3

In the photo-Pt/Ln2O3 system with H2O2/CH3COOH=4, about 46 % of TOC removal is obtained when an H2O2 consumption of 94 % is achieved (Figure 88).


105

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%


Figure 88. Heterogeneous photo-Fenton with Pt/Ln2O3. Experimental conditions: V tot.: 100 ml; mcatalyst= 4.4 g; C0


0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.


Pd/Ln2O3

In the photo-Pd/Ln2O3 system, with H2O2/CH3COOH=4, about 47 % of TOC removal is obtained when an H2O2 consumption of 94 % is achieved (Figure 89).

Chapter VII

106

0

5

10

15

20

25

30

35

40

45

50

0 1 2 3 4 5 6

t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%


Figure 89. Heterogeneous photo-Fenton with Pd/Ln2O3. Experimental conditions: V tot.: 100 ml; mcatalyst= 4.4 g; C0


0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.

VII.7 Thermal analysis

Results of thermal analysis carried out on the LaMnO3 (2.69%) sample before and after a catalytic activity test at 25°C is reported in Figure 90. A high weight loss of the catalyst used is observed between 20 and 300°C, corresponding to physisorbed and held water.

Other weight loss with derivative weight maximum temperature, 345°C is observed.

This phenomenon could be due to the oxidation of the organic fragments or the acetic acid that remained adsorbed on the perovskite after catalytic tests.


107

-0.4

-0.2

0.0

0.2

Hea

t Flo

w (W

/g)

-1

0

1

2

3

4

Der

iv. W

eigh

t (%

/min

)

80

85

90

95

100

105

Wei

ght (

%)

0 200 400 600 800Temperature (°C)

La MnO3 before test––––––– La MnO3 after test– – – –

Figure 90. Thermal analysis performed on the LaMnO3 (2.69%) sample before and after the catalytic activity test.

VII.8 Catalytic activity comparison

VII.8.1 Heterogeneous vs homogeneous Photo-Fenton

Figure 91 shows higher total organic removal for heterogeneous photo-Fenton with respect to homogeneous photo-Fenton.

Chapter VII

108

0

10

20

30

40

50

60

0 1 2 3 4 5 6

t, h

TOC

rem

oval

, %

Fe2(C2O4)3

LaCoO3

LaMnO3

LaFeO3

Ln2O3 - Pt

Ln2O3 -PdLaNiO3

LaCuO3

LaMnO3-Pt

Figure 91. Heterogeneous vs homogeneous photo-Fenton.

Heterogeneous catalysts show higher TOC removal efficiency, despite the fact that the homogeneous catalyst is faster in a shorter reaction time. However, Fe2+ activity appears to decrease after one hour reaching a lower final degree of TOC reduction with respect to the catalysts, both heterogeneous perovskites and rare earth oxides.

The most interesting catalysts are LaFeO3 and LaMnO3 and LaNiO3. The addition of Pd and Pt does not significantly enhance catalytic performance, and so it is more economically convenient not to use noble metals.

Because of the higher environmental compatibility of Fe and Mn, for which regulated emissions are 2 ppm, the following studies have focused on LaFeO3 and LaMnO3.

VIII Experimental results: photo-Fenton oxidation of acetic

acid on LaMnO3, LaFeO3 and LnFeO3

VIII.1.1 Comparison of catalytic activity of the monolith with

respect to powder catalysts

Photo-Fenton CH3COOH oxidation has also been performed on powder catalysts in order to observe the presence of diffusive phenomena. A test was performed on supported LaMnO3 monolith powdered on an agate grinder.

Figure 93 shows higher total organic removal (about 55%) on the monolith with respect to the powder catalyst supported (about 43%) with H2O2 consumption of 100 %, although after 1 h TOC removal is higher for the powder catalyst.

Chapter VIII

110

0

10

2 0

3 0

4 0

50

6 0

70

8 0

9 0

10 0

0 1 2 3 4t, h

TOC

rem

oval

%

0

10

2 0

3 0

4 0

50

6 0

70

8 0

9 0

10 0

H 2O2 c

onve

rsio

n, %

TOC removal monolith, % TOC removal powder, %H2O2 conversion monolith, % H2O2 conversion powder, %

Figure 92. Comparison of catalytic activity of the monolith LaMnO3 (2.69%) with respect to powdered catalyst. Experimental conditions: V tot.: 100 ml; mcatalyst= 6.0 g; C0


atm; T=25°C; pH=3.9.

A second experiment was performed by using a perovskite powder in a

similar amount to that present on the monolith piece; by considering 2.69% of the supported perovskites on a monolith fragment of 6.0 g, it can be evaluated that 184 mg of LaMnO3 have to be employed.

Figure 93 shows higher total organic removal (about 55%) for the monolith with respect to the powder perovskite (about 52%) when H2O2 consumption of 100 % is achieved.

Experimental results: photo-Fenton oxidation of acetic acid on LaMnO3, LaFeO3 and LnFeO3

111

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5 4t, h

TOC

rem

oval

%

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal monolith, % TOC removal powder, %H2O2 conversion monolith, % H2O2 conversion powder, %

Figure 93. Comparison of catalytic activity of the monolith LaMnO3 (2.69%) with respect to powder not supported. Experimental conditions: V tot.: 100 ml; mcatalyst (monolith)= 5.0 g; mcatalyst (powder)= 0.184 g; C0


H2O2= 0.083 mol/l; P= 1 atm; T=25°C; pH=3.9.

In the same way LaFeO3 powder was tested and the comparison reported in Figure 94. Same total organic removal (about 54%) for the monolith and the powder LaFeO3 catalyst. A higher H2O2 consumption for the powder was observed.

Photo-Fenton heterogeneous activity resulted unaffected by diffusional limitations, the effected tests proceeded in chemical regime and photoactivity is to be ascribed to the perovskite phase in wich the active phase for the reaction took place.

Chapter VIII

112

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal LaFeO3 monolith, %TOC removal LaFeO3 powder, %H2O2 conversion LaFeO3 monolith, %H2O2 conversion LaFeO3 powder, %

Figure 94. Comparison of catalytic activity of the monolith LaFeO3 with respect to powder. Experimental conditions: V tot.: 100 ml; mcatalyst (monolith)= 6.0 g; mcatalyst (powder)= 0.122 g; C0

CH3COOH= 0.021 mol/l; C0H2O2= 0.083 mol/l;

P= 1 atm; T=25°C; pH=3.9.

VIII.1.2 Effect of mass catalyst

Figure 95 shows lower total organic removal (about 35%) for the test with a higher mass monolith, when an H2O2 consumption of 100 % is achieved.


113

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5 4t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal, m=14 g %H2O2 conversion, m=4.9 g % H2O2 conversion, m=14 g %TOC removal m=4.9 g, %

Figure 95. Comparison of catalytic activity of the monolith LaMnO3 (2.57%) with different mass. Experimental conditions: V tot.: 100 ml; mcatalyst= 14.0 g – 4.9 g; C0


atm; T=25°C; pH=3.9.

Higher catalyst mass leads to faster H2O2 consumption, since the perovskite is able to catalyse its decomposition (see Chapter VII, par. VII.3).

VIII.1.3 Effect of pH

Figure 96 shows the effect of pH reactions on the catalytic activity of monolith LaMnO3 (3.67%); particularly, by increasing the pH to pH=6, the total organic removal goes up to about 57%. Raising the pH further (equal to 8) brings total organic removal down 22%. At pH=6, H2O2 conversion is slower than at pH=3.9, while in more basic conditions, decomposition is faster but incomplete (70%).

Chapter VIII

114

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7

t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal pH=3.9, % TOC removal pH=6.0, %TOC removal pH=8, % H2O2 conversion pH=3.9, %H2O2 conversion pH=6, % H2O2 conversion pH=8, %


CH3COOH= 0.021 mol/l; C0H2O2= 0.083 mol/l; P= 1 atm; T=25°C.

At lower perovskite contents, on monolith LaMnO3 (2.59%), the pH increase (pH=7), causes a decrease in total organic removal at 35% (Figure 97), due to faster H2O2 consumption.


115

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal pH=3.9, % TOC removal pH=7.0, %H2O2 conversion pH=3.9, % H2O2 conversion pH=7.0, %


CH3COOH= 0.021 mol/l; C0H2O2= 0.083 mol/l; P= 1 atm; T=25°C.

Chapter VIII

116

VIII.1.4 Effect of H2O2 concentration

By increasing molar ratio R=H2O2/CH3COOH, the initial TOC removal rate decreases while final TOC abatement increases (Figure 98).

Higher H2O2 conversion for R=2.

0

10

20

30

40

50

60

70

0 1 2 3 4 5 6t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%

TOC removal, R=4, % TOC removal, R=8, %TOC removal, R=2, % H2O2 conversion, R=4, %H2O2 conversion, R=8, % H2O2 conversion, R=2, %

Figure 98. Comparison of catalitic activity on LaMnO3 (3.67%) on changing H2O2. concentration.

A lower H2O2/CH3COOH ratio results in faster H2O2 conversion. When H2O2 is totally consumed, the reaction stops, giving a stabilization in the TOC value.


117

VIII.1.5 Effect of dosage of H2O2

To render the photo-Fenton processes competitive with other processes, it is essential that their applications represent a low cost operation, which basically implies a low consumption of H2O2 dosage. Controlled concentration of H2O2 permits higher TOC reductions in shorter times, owing to the H2O2 auto-scavenger effect that traps OH. generated by photolysis according to reactions 15-17 of Chapter II. OH. radicals react with H2O2 to form HO2

. which couples with itself to give O2 and H2O2. As a consequence, high initial levels of H2O2 do not lead to that can be employed OH. useful for the photo-Fenton reaction, but low levels do not produce sufficient OH. for the reaction. So it seems necessary to perform the reaction with an adjusted concentration of H2O2 during all of the reaction time. To this purpose, the objective of this evaluation is to select the best operational dosage of H2O2 in photo-Fenton processes.

To realise these operative conditions, step addition of H2O2 was performed, by adding small volumes of concentrated solution of H2O2 each hour. Figure 99 reports the typical trend thus obtained of H2O2 concentrations, resulting in a saw tooth profile. Levels of H2O2 concentrations lay in a value range that in this case is comprised between 210 and 850 ppm. For the photo-Fenton process on LaMnO3 (3.67%), the global mean addition of H2O2 is equal to 0.009 M/h. Total organic removal of up to 70% was achieved.

0102030405060708090

100

0 1 2 3 4 5 6t, h

TOC

rem

oval

, %

0

200

400

600

800

1000

1200

H2O

2, pp

m

TOC removal LaMnO3 with H2O2 added, % H2O2, ppm

Figure 99. Effect of dosage of H2O2 on the catalytic activity of LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; mcatalyst= 4.9 g; C0

CH3COOH= 0.021 mol/l; C0H2O2= 0.014 mol/l; CH2O2/t= 0.009 M/h; P= 1

atm; T=25°C.

Chapter VIII

118

In the photo-Fenton process with LnFeO3 (48%) (Figure 100), the addition of H2O2 equal to 0.006 M/h increases total organic removal from 40% (H2O2/CH3COOH =4) to 76%.

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6t, h

TOC

rem

oval

, %

0

50

100

150

200

250

300

350

400

450

500

H2O

2, pp

m

TOC removal LnFeO3 (48%) with H2O2 added, % H2O2, ppm

Figure 100. Effect of dosage of H2O2 on the catalytic activity of LnFeO3 (48%). Experimental conditions: V tot.: 100 ml; mcatalyst= 14 g; C0


H2O2= 0.012 mol/l; CH2O2/t= 0.006 M/h; P= 1 atm; T=25°C.

In the photo-Fenton process with LnFeO3 (88%) (Figure 101), the global mean addition of H2O2 equal to 0.022 M/h increases total organic removal from 29% obtained at initial molar ratio H2O2/CH3COOH =4 up to 100%.

0

10

2 0

3 0

4 0

50

6 0

70

8 0

9 0

10 0

0 1 2 3 4 5 6t, h

TOC

rem

oval

, %

- 10 0

10 0

3 0 0

50 0

70 0

9 0 0

110 0

13 0 0

150 0H 2O

2, pp

mTOC removal LnFeO3 (88%) w ith H2O2 added, % H2O2, ppm

Figure 101. Effect of dosage of H2O2 on the catalytic activity of LnFeO3 (88%). Experimental conditions: V tot.: 100 ml; mcatalyst= 15.3 g; C0


H2O2= 0.022 mol/l; CH2O2/t= 0.021 M/h; P= 1 atm; T=25°C.


119

Table 8 shows a comparison of hydrogen peroxide consumption of the photo-Fenton of LaMnO3 (3.67%) with step dosage of H2O2 with respect to the photo/LaMnO3 system that starts with H2O2/CH3COOH=4. There is a smaller hydrogen peroxide consumption in presence of dosage of hydrogen peroxide with respect to the photo/LaMnO3 system without dosage. Particularly it is noted that a higher final total organic carbon removal (70%) in the presence of dosage of hydrogen peroxide with respect to the photo/LaMnO3 system with initial molar ratio H2O2/CH3COOH=4 (54 %). Moreover, a smaller specific consumption defined by molar ratio H2O2/CH3COOH is noted; specifically, it is ranged 1.7 mol/mol (2.2 gH2O2/gC) 3.3 mol/mol (4.8 gH2O2/gC) in the test with dosage, while it is ranged between 2.0 mol/mol (2.8 gH2O2/gC) and 7.5 mol/mol (10.8 gH2O2/gC) in the test without dosage.

Table 8. Comparison of hydrogen peroxide consumption of the photo-Fenton of LaMnO3 (3.67%) with dosage of H2O2 with respect to the photo/LaMnO3 system with H2O2/CH3COOH=4.

TOC removal, %

Dosage H2O2 consumption, ppm

Dosage H2O2 cons., gH2O2/gc

No dosage H2O2 cons., ppm

No Dosage H2O2 cons., gH2O2/gc

20 222 2.2 283 2.8

50 1204 4.8 2689 10.8

70 1683 4.8 - -

Table 9 shows a comparison of hydrogen peroxide consumption of the

photo-Fenton of LnFeO3 (48%) with dosage of H2O2 with respect to the photo/LnFeO3 system with H2O2/CH3COOH=4. There is lower hydrogen peroxide consumption in the presence of dosage of hydrogen peroxide with respect to the photo/LnFeO3 system with H2O2/CH3COOH=4. To be specific a higher final total organic carbon removal (76%) is noted in the presence of dosage of hydrogen peroxide with respect to the photo/LnFeO3 system with H2O2/CH3COOH=4 (40 %). Moreover, a smaller specific consumption is noted defined by molar ratio H2O2/CH3COOH; specifically, it is varied in the 1.0 mol/mol (1.5 gH2O2/gC) 3.1 mol/mol (4.4 gH2O2/gC) range in the test with dosage, while it reaches a value equal to 12.6 mol/mol (17.9 gH2O2/gC) in the test without dosage.

Chapter VIII

120

Table 9. Comparison of hydrogen peroxide consumption of the photo-Fenton of LnFeO3 (48%) with dosage of H2O2 with respect to the photo/LnFeO3 system with H2O2/CH3COOH=4.

TOC removal, %





30 222 1.5 2689 17.9

50 1204 4.8 - -

76 1683 4.4 - -

The Table 10 shows a comparison of hydrogen peroxide consumption of

the photo-Fenton of LnFeO3 (88%) with dosage of H2O2 with respect to the photo/LnFeO3 system with H2O2/CH3COOH=4. There is lower hydrogen peroxide consumption in the presence of dosage of hydrogen peroxide with respect to the photo/LnFeO3 system with H2O2/CH3COOH=4. Particularly higher final total organic carbon removal (100%) is noted in the presence of dosage of hydrogen peroxide with respect to the photo/LnFeO3 system with H2O2/CH3COOH=4 (30 %). Moreover, smaller specific consumption is noted defined by molar ratio H2O2/CH3COOH; particularly, it is varied in the 3.1 mol/mol (4.5 gH2O2/gC) 5.3 mol/mol (7.6 gH2O2/gC) range in the test with dosage, while it results equal to 18.0 mol/mol (26.4 gH2O2/gC) in the test without dosage.

Table 10. Comparison of hydrogen peroxide consumption of the photo-Fenton of LnFeO3 (88%) with dosage of H2O2 with respect to the photo/LnFeO3 system with H2O2/CH3COOH=4.

TOC removal, %





20 446 4.5 2604 26.4

60 2453 8.2 - -

100 3814 7.6 - -


121

VIII.2 Leaching test

Leaching tests were carried out to check the potential of leaching of the metals from the perovskite during the catalytic tests, analysing the solution by ICP-AES. This method allowed direct determination of the presence of metal ions in solution.

Table 11. Metal ion analysis of the some catalysts used for the catalytic photo-Fenton reaction.

Catalyst [H202]= mol/l

pH Metal iont=0 (ppm)

Metal ionfinal time (ppm)

LaMnO3 (3.67%)

0.083 3.9 Mn= 0 Mn= 14

LaMnO3 (3.67%)

0.083 7.0 Mn= 0 Mn= 0.03

LaMnO3 (3.67%)

0.083 8.0 Mn= 0 Mn= 0.19

LaMnO3 (3.67%)

0.021 M/h 3.9 Mn= 0 Mn= 0.6

LaMnO3 (2.57%) High mass catalyst

0.083 3.9 Mn= 0 Mn= 88

LnFeO3 (88%)

0.083 3.9 Fe=0 Fe= 0.03

LnFeO3 (48%)

0.083 3.9 Fe=0 Fe= 0.03

LnFeO3 (88%)

0.006 M/h 3.9 Fe=0 Fe= 0.03

The data (Table 11) shows a small dissolution of the metal on the

perovskite after acetic acid oxidation for all the catalysts, except for the test performed on LaMnO3 (2.57%) with high mass catalyst (Mn=88 ppm). However, the use of Fe-based perovskites could be desiderable.

IX Heterogeneous photo-Fenton: reaction mechanism hypothesis

In the absence of the catalyst and acetic acid, UV light induces homogeneous H2O2 decomposition by the following reactions (eqs. 20-23) (Figure 102):

•→+ OHhOH 222 ν (20) OHHOOHOH 2222 +•→+• (21) 2222 OOHHOOHHOO ++•→+• (22) 22222 OOHHOHO +→•+• (23)

Chapter IX

124

HOOH 222 → HOOH 222 → HOOH 222 →

O2(g)

Figure 102. Photolysis of hydrogen peroxide.

In the absence of the UV light and acetic acid, for the system H2O2/catalyst, H2O2 decomposition occurred according the following simplified scheme (Figure 103) (eqs. 24-25):

)()( 2222 adsOHlOH → (24)

)(21)()( 2222 gOlOHadsOH +→ (25)

Heterogeneous photo-Fenton: reaction mechanism hypothesis

125

Figure 103. Catalytic decomposition of H2O2.

With the simultaneous presence of the catalyst and acetic acid (but in absence of UV light), homogeneous H2O2 decomposition was inhibited, because of competitive adsorption of CH3COOH that became prevalent on catalyst surface (eq. 26). The catalyst is able to initiate the reaction, but both reactants and products seem to be anchored on the surface.

)()( 33 adsCOOHCHlCOOHCH → (26) Photo-Fenton oxidation can occur by reaction between OH. UV-

generated and surface adsorbed CH3COOH/oxidation products, regenerating the active sites. On the basis of these observations, there is a synergic effect between UV light and the catalyst. In fact, hydroxyl radicals generated by H2O2 decomposition (activated by UV light) can react with acetic acid in the liquid phase and on the catalyst surface leading to complete mineralization of the hydrocarbon (Figure 104) through the probable formation of

O2(g

H2O2(l)

H2O2ads

O2(g)

)

Chapter IX

126

intermediate radicals ( •R ) generated by the reaction between acetic acid and hydroxyl radicals (eqs. 27-32).

•→+ OHhOH 222 ν (27)

OHHOOHOH 2222 +•→+• (28)

2222 OOHHOOHHOO ++•→+• (29)

22222 OOHHOHO +→•+• (30)

)()( 33 adsCOOHCHlCOOHCH → (31)

23 )( COROHadsCOOHCH →•→•+ (32) The effect of step dosage of H2O2 is carried out in order to limit the UV

induced decomposition of H2O2, which subtracts and scavenges OH..

Heterogeneous photo-Fenton: reaction mechanism hypothesis

127

Figure 104. Illustration of the photo-Fenton process.

HOOH 222 →

CO2(g)

CxHyOz(l

CxHyOz(ad

)(21)()( 2222 gOlOHlOH +→

CO2(g)

H2O2(l

H2O2a

O2(g)

O2(g)

)

s)

X Experimental results: photo-Fenton oxidation of alcohols on

LaMeO3

X.1 Photolysis

X.1.1 Photolysis of ethanol

In Figure 105 it is shown, that after 4 hours, in the photolysis of ethanol with hydrogen peroxide (H2O2/C2H5OH= 2) about 69% of H2O2 is converted, when TOC removal was about 47%.

Chapter X

130

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5 4

t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%


Figure 105. Photolysis of ethanol. Experimental conditions: V tot.: 100 ml; H2O2/C2H5OH= 2; C0

H2O2= 0.042 mol/l; C0C2H5OH= 0.021; P= 1 atm;

T=25°C; pH=6.5.

X.1.2 Photolysis of methanol

In Figure 106 it is shown, that after 3.5 hours, in the photolysis of methanol with hydrogen peroxide (H2O2/CH3OH= 1) about 50% of H2O2 is converted, when TOC removal is about 40%.

0102030405060708090

100

0 0,5 1 1,5 2 2,5 3 3,5 4t, h

TOC

rem

oval

, %

0

1020

3040

50

6070

8090

100

H2O

2 con

vers

ion,

%


Figure 106. Photolysis of methanol. Experimental conditions: V tot.: 100 ml; H2O2/CH3OH= 1; C0

H2O2= 0.042 mol/l; C0CH3OH= 0.021 mol/l; P= 1

atm; T=25°C; pH=5.5.

Experimental results: photo-Fenton oxidation of alcohols on LaMeO3

131

X.2 Catalytic photo-Fenton oxidation of ethanol on LaMnO3

(3.67%)

In Figure 107 it is shown, that after 5 hours, in catalytic photo-Fenton oxidation of ethanol on LaMnO3 (3.67%) with the hydrogen peroxide (H2O2/C2H5OH= 1) there is similar TOC removal with respect to the photolysis; particularly, about 100% of H2O2 is converted, when TOC removal is about 50%.

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%


Figure 107. Catalytic photo-Fenton oxidation of ethanol on LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; H2O2/C2H5OH= 2; C0

H2O2= 0.042 mol/l; C0C2H5OH= 0.021; P= 1 atm; T=25°C; pH=6.5.

X.3 Catalytic photo-Fenton oxidation of methanol on LaMnO3

(3.67%)

In Figure 108 it is shown, that after 4 hours, in the catalytic photo-Fenton oxidation of the methanol on LaMnO3 (3.67%) with the hydrogen peroxide (H2O2/CH3OH= 1) there is higher TOC removal with respect to the photolysis; particularly, about 74% of H2O2 is converted, when TOC removal is about 47%.

Chapter X

132

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5 4t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%


Figure 108. Catalytic photo-Fenton oxidation of methanol on LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; H2O2/CH3OH= 1; C0

H2O2= 0.042 mol/l; C0CH3OH= 0.021 mol/l ; P= 1 atm; T=25°C; pH=5.5.

XI Experimental results: photo-Fenton oxidation of synthetic

winery wastewater on LaMeO3

Wine distilleries produce large volumes of wastewaters, called “vinasses”, the composition of which varies widely according to the raw material distilled: wine, pressed grapes, etc. In general, all of them have an acidic pH and a high organic substrate content with chemical oxygen demand in the range 10±40 g/l. Usually these effluents are eliminated through public sewerages, and therefore this represents a large-scale environmental problem, due to the pollution that they introduce in surface and underground waters.

Although little attention has been paid in the past to this problem, at the present moment and as a consequence of the potential hazards caused by this waste, many countries have limited its discharge and tried to develop alternative technologies to reduce its toxic effect by degrading the main organic substances present. Among these technologies, biological processes have been recognized as effective methods for the degradation of wastewaters with a high organic pollutant load, such as those coming from wine distilleries. As a result, aerobic treatment systems, such as aerated lagoons or activated sludge plants, are used to remove the contamination generated by these residues.

However, several problems have been encountered during aerobic treatments which are linked to the high toxicity of effluents. They lead to the partial inhibition of biodegradation, because some microorganisms are particularly sensitive to the organic compounds present, especially phenolic compounds. Therefore, other treatments, such as chemical oxidation have recently been investigated successfully for the purification of wastewaters with these type of phenolic substances. Among these procedures, photo-Fenton processes have increasingly been used because hydrogen peroxide has many of the oxidizing properties desirable for water treatments: it is a powerful oxidant that degrades a large number of organic compounds in general and specifically phenolic compounds.

Chapter XI

134

The conditions applied in each experiment were modified using different H2O2/TOCinitial ratio (M/M) and the following conditions:

• Organic matter concentration: 500 mg C/l (measured as TOC). • H2O2 concentration: 0.042 and 0.084 M, corresponding to

H2O2/TOCinitial ratio (M/M) = 1 and 2 respectively. Different oxidation systems have been investigated using synthetic

samples, which were representative of real winery wastewaters. Similar properties were achieved by diluting commercial red wine (“Chianti” or local wine not containing sulphites) with ultra-pure water, obtaining approximately the amount of the organic matter equal to 500 mg C/l (measured as TOC).

Experimental results: photo-Fenton oxidation of synthetic winery wastewater on LaMeO3

135

XI.1 Photolysis of synthetic winery wastewaters (red wine)

Figure 109 shows photolysis of synthetic winery wastewaters with H2O2/TOCwine= 1 obtained by diluting commercial red wine. Total organic removal is about 12% when H2O2 conversion is 48%.

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5 4t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%



H2O2= 0.042 mol/l; P= 1 atm; T=25°C; pH=4.2.

The higher concentration of H2O2 (H2O2/TOCwine= 2) slightly increased total organic removal; particularly, total organic removal is about 23%, when H2O2 conversion is 22% (Figure 110).

Chapter XI

136

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5 4t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%



H2O2= 0.042 mol/l; P= 1 atm; T=25°C; pH=4.2.


137

XI.2 Photolysis of synthetic winery wastewaters (red wine not

containing sulphites)

Figure 111 shows photolysis of synthetic winery wastewaters with H2O2/TOCwine= 1 obtained by diluting commercial red wine not containing sulphites. Total organic removal is about 25% when H2O2 conversion is 47%.

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%



H2O2= 0.042 mol/l; P= 1 atm; T=25°C; pH=4.2.

Chapter XI

138

Figure 112 shows the photolysis of synthetic winery wastewaters with H2O2/TOCwine= 2 obtained by diluting commercial red wine not containing sulphites. Total organic removal is about 48% when H2O2 conversion is 63%.

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5 4t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 co

nver

sion

, %



H2O2= 0.084 mol/l; P= 1 atm; T=25°C; pH=4.2.


139

XI.3 Catalytic photo-Fenton oxidation of synthetic winery

wastewaters (red wine) on LaMnO3 (3.67%)

In Figure 113 it is showed that after 4 hours, in catalytic photo-Fenton oxidation of synthetic winery wastewaters obtained by diluting commercial red wine on LaMnO3 (3.67%) with hydrogen peroxide (H2O2/TOCwine = 1) there is higher TOC removal with respect to photolysis; particularly, about 26% of H2O2 is converted, when TOC removal is about 17%.

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5 4t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%



H2O2= 0.042 mol/l; P= 1 atm; T=25°C; pH=4.2.

The higher concentration of H2O2 (H2O2/TOCwine= 2) slightly increased total organic removal; particularly, total organic removal is about 20%, when H2O2 conversion is 33% (Figure 114).

Chapter XI

140

0102030405060708090

100

0 0,5 1 1,5 2 2,5 3 3,5 4t, h

TOC

rem

oval

, %

0102030405060708090100

H2O

2 con

vers

ion,

%



H2O2= 0.042 mol/l; P= 1 atm; T=25°C; pH=4.2.


141

XI.4 Catalytic photo-Fenton oxidation of synthetic winery

wastewaters (local red wine not containing sulphites) on

LaMnO3 (3.67%)

In Figure 115 it is showed that after 3 hours, in catalytic photo-Fenton oxidation of synthetic winery wastewaters obtained by diluting local red wine, not containing sulphites, on LaMnO3 (3.67%) with hydrogen peroxide (H2O2/TOCwine= 1) about 35% of H2O2 is converted, when TOC removal is about 29%.

0

10

2 0

3 0

4 0

50

6 0

70

8 0

9 0

10 0

0 0 ,5 1 1,5 2 2 ,5 3 3 ,5 4t, h

TOC

rem

oval

, %

0

10

2 0

3 0

4 0

50

6 0

70

8 0

9 0

10 0

H 2O2 c

onve

rsio

n, %



H2O2= 0.042 mol/l; P= 1 atm; T=25°C; pH=4.2.

In Figure 116 it is showed that after 3 hours, in catalytic photo-Fenton

oxidation of synthetic winery wastewaters obtained by diluting the local red wine, not containing sulphites, on LaMnO3 (3.67%) with the hydrogen peroxide (H2O2/TOCwine= 2) about 79% of H2O2 is converted, when TOC removal is about 51%.

Chapter XI

142

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%



H2O2= 0.084 mol/l; P= 1 atm; T=25°C; pH=4.2.

XI.5 Catalytic photo-Fenton oxidation of the synthetic winery

wastewaters (red wine local not containing sulphites) on

LnFeO3 (48%)

In Figure 117 it is showed, that after 3 hours, in catalytic photo-Fenton oxidation of synthetic winery wastewaters obtained by diluting the local red wine, not containing sulphites, on LnFeO3 (48%) with hydrogen peroxide (H2O2/TOCwine= 1) about 50% of H2O2 is converted, when TOC removal is about 30%.


143

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3

t, h

TOC

rem

oval

, %

0

10

20

30

40

50

60

70

80

90

100

H2O

2 con

vers

ion,

%


Figure 117. Catalytic photo-Fenton oxidation of synthetic winery wastewaters obtained by diluting local red wine on LnFeO3 (48%). Experimental conditions: V tot.: 100 ml; H2O2/TOCwine= 1; C0

H2O2= 0.042 mol/l; P= 1 atm; T=25°C; pH=4.2.

Chapter XI

144

XI.6 Effect of dosage of H2O2 (red wine local not containing

sulphites)

In the photo-Fenton process with LaMnO3 (3.67%) (Figure 118), the addition of H2O2 equal to 0.009 M/h increases total organic removal from 43% (H2O2/TOCwine =2) to 50%.

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7

t, h

TOC

rem

oval

, %

0

200

400

600

800

1000

1200

1400

H2O

2, pp

m

TOC removal LaMnO3 (3.67%) with H2O2 added, % H2O2, ppm

Figure 118. Effect of dosage of H2O2 on the catalytic activity of LaMnO3 (3.67%). Experimental conditions: V tot.: 100 ml; mcatalyst= 4.9 g; TOC0

wine= 500 mg/l; C0

H2O2= 0.006 mol/l; CH2O2/t= 0.009 M/h; P= 1 atm; T=25°C; pH=4.2.

Table 12 shows a comparison of hydrogen peroxide consumption of the photo-Fenton of LaMnO3 (3.67%) with step dosage of H2O2 with respect to the photo/LaMnO3 system that starts with H2O2/TOCwine=2. There is lower hydrogen peroxide consumption in the presence of dosage of hydrogen peroxide with respect to the photo/LaMnO3 system without dosage. Particularly, a higher final total organic carbon removal (49%) is noted in the presence of dosage of hydrogen peroxide with respect to the photo/LaMnO3 system with initial molar ratio H2O2/ TOCwine=2 (43 %). Moreover, a smaller specific consumption defined by molar ratio H2O2/TOCwine is noted. Particularly, it varies in the 0.5 mol/mol (0.6 gH2O2/gC) 3.9 mol/mol (5.6 gH2O2/gC) range in the test with dosage, and in the 5.6 mol/mol (8.0 gH2O2/gC) 5.8 mol/mol (8.2 gH2O2/gC) range in the test without dosage.


145

Table 12. Comparison of hydrogen peroxide consumption of photo-Fenton of LaMnO3 (3.67%) with dosage of H2O2 with respect to the photo/LaMnO3 system with H2O2/ TOCwine =2.

TOC removal, %





15 48 0.6 600 8.0

30 453 3.0 1144 7.6

43 1201 5.6 1773 8.2

In the photo-Fenton process with LnFeO3 (48%) (Figure 119), the

addition of H2O2 equal to 0.012 M/h increases total organic removal from 30% (H2O2/TOCwine =1) to 70%.

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7 8t, h

TOC

rem

oval

, %

0

200

400

600

800

1000

1200

1400

H2O

2, pp

mTOC removal LnFeO3 (48%) with H2O2 added, % H2O2, ppm

Figure 119. Effect of dosage of H2O2 on the catalytic activity of LnFeO3 (48%). Experimental conditions: V tot.: 100 ml; mcatalyst= 14 g; TOC0

wine= 500 mg/l; C0

H2O2= 0.006 mol/l; CH2O2/t= 0.012 M/h; P= 1 atm; T=25°C; pH=4.2.

Table 13 shows a comparison of hydrogen peroxide consumption of the photo-Fenton of LnFeO3 (48%) with step dosage of H2O2 with respect to the photo/LnFeO3 system that starts with H2O2/TOCwine=1. There is higher hydrogen peroxide consumption in the presence of dosage of hydrogen peroxide with respect to the photo/LnFeO3 system without dosage.

Chapter XI

146

Nevertheless, a higher final total organic carbon removal (68%) is noted in presence of the dosage of hydrogen peroxide with respect to the photo/LaMnO3 system with initial molar ratio H2O2/ TOCwine=1 (30 %). Moreover, a smaller specific consumption defined by molar ratio H2O2/TOCwine is noted; more specifically it varied in the 1.3 mol/mol (1.8 gH2O2/gC) 5.6 mol/mol (7.9 gH2O2/gC) range in the test with dosage, while it varied in the 2.0 mol/mol (2.9 gH2O2/gC) 3.3 mol/mol (4.8 gH2O2/gC) range in the test without dosage.

Table 13. Comparison of hydrogen peroxide consumption of the photo-Fenton of LnFeO3 (48%) with dosage of H2O2 with respect to the photo/LnFeO3 system with H2O2/ TOCwine =1.

TOC removal, %





10 91 1.8 143 2.9

30 655 4.4 715 4.8

68 2701 7.9 - -

XI.7 Leaching test

The data of the dissolution (Table 14) show a small dissolution of the metal on the perovskite after synthetic winery wastewater oxidation for all the catalysts.


147

Table 14. Metal ion analysis of the some catalysts used for the catalytic photo-Fenton reaction of synthetic winery wastewater.

Catalyst [H202]= mol/l

pH Metal iont=0 (ppm)

Metal ionfinal time (ppm)

LaMnO3 (3.67%)

0.084 4.2 Mn= 0 Mn= 0.22

LaMnO3 (3.67%)

0.009 M/h 4.2 Mn= 0 Mn= 0.12

LnFeO3 (48%)

0.084 4.2 Fe=0 Fe= 0.03

LnFeO3 (48%)

0.006 M/h 4.2 Fe=0 Fe= 0.03

Mn and Fe final concentration resulted lower than legal emissions limits

(2 ppm).

XII Conclusions

Heterogeneous Fenton catalytic oxidation resulted a promising technology for treating aqueous solutions containing not biodegradable organic substances.

The difference in TOC removal in homogeneous and heterogeneous Fenton-type oxidation greatly encourages the use and the study of the heterogeneous catalytic system.

Heterogeneous Fenton catalytic oxidation is effective in the treatment of real tannery wastewaters.

Higher performances were obtained by adding UV irradiation to Fenton system.

The use of a heterogeneous structured catalyst in the photo-Fenton reaction greatly improves TOC removal and leads to better use of H2O2, leading to enlarge pH range of operation, without formation of sludge or enhancement in metal leaching from the solid catalyst. Particularly, LaMnO3 and LaFeO3 resulted the best catalysts for this process.

It has been found that, from the values of TOC removal and carbon dioxide concentration formed, the total carbon mass balance was closed to 100%, indicating that the mineralization of the acetic acid is complete after oxidation treatment.

In photo-Fenton processes, the efficiency depends from optimisation of H2O2 concentration level, that can be achieved by continuous dosage of H2O2 during reaction time, since TOC removal is dependent by H2O2 utilisation for oxidation with respect to its decomposition to oxygen.

It has also been found that the photocatalytic advanced process based on H2O2 is an appropriate purification treatment of synthetic winery wastewaters, by combining LnFeO3 and LaMnO3 monoliths with step dosage of H2O2. In this conditions, TOC removal higher than 65 % could be reached in 7 hours, without significant metal leaching.

XIII References

• Abdellaoui, M., Barrault, J., Bouchoule, C., Srasra, N.F., Bergaya, F. (1999). J.Chim. Phys. Phys.-Chim. Biol., 96 (3), 419–429.

• Akata, A. and Gurol, M. (1992). Ozone Sci. & Eng., 14, 367-380.

• Anderson, C. Bard, A.J. (1997). J. Phys. Chem. B 101, 2611.

• Andreozzi, R., Caprio, V., Insola, A. and Marotta, R. (1999). Catal Tod, 53, 51-59.

• Balcioglu, I. and Arslan, I. (1999). Journal of Advanced Oxidation Technologies, 4, 189-195.

• Barrault, J., Abdellaoui, M., Bouchoule, C., Majeste, A., Tatibouet, J.M., Louloudi, A., Papayannakos, N., Gangas, N.H. (2000). Appl. Catal. B 27 (4), L225–L230.

• Baxendale, J.H., and Willson, J.A. (1957). Trans. Faraday Soc. 53, 344-356.

• Benitez, F., Beltran, F., Acero, J. and Pinilla, M. (1997), Ind. Eng. Chem. Res., 36, 638-644.

• Benitez, F., Beltran-Heredia, J., Acero, J. and Rubio, F. (2000), Chemosphere, 41, 1271-1277.

• Bigda, R. (1995), Chem. Eng. Progr., 91, 62-66. • Blanco, J. and Malato, S. (1996). Cuadernos

Monográficos 31. Instituto de Estudios Almerienses de la Diputación de Almería. Almería ,España.

• Blesa, M. (2001). Blesa. M.A. eds., Digital Grafic, xi-xiv, La Plata, Argentina.

• Bossmann, S., Oliveros, E., Gob, S., Siegwart, S., Dahlen, E., Payawan, L., Straub, M., Worner, M. and Braun, A. (1998). J. Phys.Chem. 102, 5542-5550.

• Bossmann, S.H., Oliveros, E., Gob, S., Kantor, M., Goppert, A., Lei, L., Yue, P.L., Braun, A.M. (2001). Water Sci. Technol. 44 (5), 257–262.

Chapter XIII

152

• Boudenne, J., Cercleir, O., Galéa, J. and Van Der Vlist, E. (1996). Appl. Catal. B:Environ., 143(2), 185-202.

• Brillas, E., Sauleda, R. and Casado, J. (1998). J. Electrochem. Soc., 145, 2253-2262.

• Brucculeri, M., D. Bolzonella, P. Battistoni, F. Cecchi, (2005). Water Sci. Technol. 51(1), 89-98.

• Cañizares, P., Dominguez, J., Rodrigo, M., Villaseñor, J. and Rodriguez, J. (1999). Ind. Eng. Chem. Res., 38, 3779-3785.

• Centi, G., Perathoner, S., Torre, T., Verduna, M.G. (2000). Catal. Today 55 (1/2), 61–69.

• Centi, G., S. Perathoner, G. Romeo. (2001). Stud. Surf. Sci. Catal. 135, 5156-5163.

• Cervera, S. and Esplugas, S. (1983). Energía , 9, 103-107.

• Chamarro, E., Marco, A., Prado, J. and Esplugas, S. (1996). Química & Industria, 1, 28-32.

• Chen, R. and Pignatello, J. (1997). Environ. Sci. Technol., 31, 2399-2406.

• Chou, S., Huang, C., Huang, Y.-H.. (2001). Environ. Sci. Technol. 35 (6), 1247–1251.

• Chuang, T., Cheng, S. and Tong, S. (1992). Ind. Eng. Chem. Res., 31, 2466-2472.

• Ciambelli, P,. V. Palma, S. F. Tikhov, V. A. Sadykov , L. A. Isupova, L. Lisi, (1999). Catal. Today 47, 199-207.

• Ciardelli, G., Capannelli, G. and Bottino, A. (2001). Water Sci. & Technol., 44, 61-67.

• Contreras, S., Rodríguez, M., Chamarro, E., Esplugas, S. and Casado, J. (2001). Water Sci. Technol., 44, 39-46.

• De Laat, J. and Gallard, H. (1999). Environ. Sci. & Technol., 3, 2726-2732.

• Goi D; De Leitenburg C; Trovarelli A; Dolcetti G. (2004). Environmental technology, 25(12), 1397-1403.

• Delanghe, B. C.I. Mekras, N.J.D. Graham. (1991). Ozone Sci. Eng. 13(6), 639-73.

• Eckenfelder, W., Argaman, Y. and Miller, E. (1989). Environmental Progress, 8, 40-45.

• Eisenhauer, H. (1964). J. Water Pollut. Control Fed., 36, 1116-1128.

• Fajerwerg, K. Foussard, J.N., Perrard, A., Debellefontaine. H., (1997). Water Sci. Technol. 35 (4), 103-110.

References

153

• Fajerwerg, K., Debellefontaine. H. (1996). Appl. Catal. B: Environ. 10(4), L229-L235.

• Feng, J.; Hu, X.; Yue, P.L., (2005). Water Research 39, 89–96.

• Feng, J., Hu, X., Yue, P.L., Zhu, H.Y., Lu, G.Q., (2003). Ind. Eng. Chem.Res. 42, 2058–2066.

• Fenton, H. (1894) “Oxidation of tartaric acid in presence of iron”, J. Chem. Soc. Trans., 65, 899-910.

• Fernandez J. , Bandara J. , Lopez A. , Albers P., and Kiwi J. (1998). Chem. Commun. 14, 1493-1494

• Gallard, H. and De Laat, J. (2000). Wat. Res., 34, 3107-3116.

• Gallezot, P., N. Laurain, P. Isnard. (1996). Appl. Catal. B: Environ. 9(1-4), L11-L17.

• Ghaly, M.Y., Hartel, G., Mayer, R., Haseneder, R., (2001). Waste Management. 21, 41–47.

• Givens, S., Brown, E., Gelman, S., Grady, C. and Skedsvold, D. (1991). Environmental Progress ENVPDI. 10(2), 133-146.

• Glaze, W. and Chapin, D. (1987). Ozone Sci. & Eng., 9, 335-342.

• Goldstein, S. (1999). Am. Chem. Soc., 32, 547-550. • Gutierrez, M., Pepio, M., Crespi, M. and Mayor, N.

(2001). Coloration Technology, 117, 356-361. • Haber, F. and Weiss, J. (1934). J. Proc. Roy. Soc.

London A, 147, 332-351. • Hernadi, K. E. Ljubovic, J.W. Seo, L. Forro, (2003).

Acta Mater. 51(5), 1447-1452. • Hislop, K. and Bolton, J. (1999). Environ. Sci. Technol.,

33, 3119-3126. • Huang, Q., Gao, L. (2003). J. Mater. Chem. 13, 1517-

1520. • Huang, T.L., MacInnes, J.M., Cliffe, K.R.. (2001). Water

Res. 35, 2113–2120. • Huling, S.G., Arnold, R.G., Jones, P.K., Sierka, R.A..

(2000), J. Environ. Eng. 126 (4), 348–353. • Isupova, L.A.; Sutormina, E.F.; Kulikovskaya, N.A.;

Plyasova, L.M.; Rudina, N.A.; Ovsyannikova, I.A.; Zolotarskii, I.A.; Sadykov, V.A., (2005). Catalysis Today 105, 429–435

• Isupova, L.A.; Alikina, Galina M.; Tsybulya, Sergei V.; Salanov, Aleksei N.; Boldyreva, Nataliya N.; Rusina, Elena S.; Ovsyannikova, Izabella A.; Rogov, Vladimir

Chapter XIII

154

A.; Bunina, Rimma V.; Sadykov, Vladislav A. (2002). Catalysis Today 75, 305–315.

• Jitianu, A., T. Cacciaguerra, R. Benoit, S. Delpeux, F. Beguin, S.Bonnamy, (2004). Carbon 42, 1147-1151.

• Kabdasli, I. and Gurel, M. (2000). Environmental Technology, 21, 1147-1155.

• Kameya, T., Murayama, T., Kitano, M. and Urano, K. (1995). The Science of The Total Environment, 170, 31-41.

• Kavitha, V., Palanivelu, K. (2004). Chemosphere 55, 1235–1243.

• Kedem, S., (2005). M.Sc. Thesis, Technion. • Kedem, S., Schmidt, Y., Paz, Y., Cohen, Y. (2005).

Langmuir, 21, 5600-5604. • Kiwi, J., Pulgarin, C., Peringer, P. (1994). Appl. Catal.

B: Environ. 3, 335–350. • Kremer, M. (1999). Phys. Chem., 1, 3595-3607. • Kuznetsova, E. V.; Savinov, E. N.; Vostrikova, L. A.;

Echevskii, G. V. (2004). Water Science and Technology, 49 (4), 109-115.

• Larachi, F., S. Levesque, A. Sayari. (1998). J. Chem. Biotechnol.: 73(2), 127-130.

• Legrini, O., Oliveros, E. and Braun, A. M. (1993), Chem. Rev., 93, 671-698.

• Li Puma, G., Yue, P.L., (2000). Conference on Advanced Oxidation Technologies for Water and Air Remediation. London, Ontario, Canada. June 26–30. p. 105.

• Li, L., Peishi, C. and Earnest, F. (1991). AIChE J. 37, 1687-1697.

• Lin, S. and Chuang, T. (1994). Toxical. Environ. Chem. 44, 243-258.

• Lin, S. and Lai, C. (2000). Wat. Res., 34, 763-772. • Lin, S. and Peng, C. (1994). Wat. Res., 28, 277-282. • Lipczynska-Kochany, E. (1991). Chemosphere, 22, 529-

536. • Lipczynska-Kochany, E. (1992). Chemosphere, 24,

1369-1380. • Macfaul (1998). Acc. Chem. Res., 31, 159-162. • Maletzky, P.; Bauer, R.; Lahnsteiner, J.; Pouresmael, B.

(1999) Chemosphere, 38(10), 2315-2325. • Masselli, J., Masselli, N. and Burford, M. (1970), Proc.

S. Water Resour. Pollut. Contr. Conf., 19, 37-48.

References

155

• Mishra, V., Mahajani, V. and Joshi, J. (1995), Ind. Eng. Chem. Res., 34, 2-48.

• Munter, R., Preis, S., Kallas, J., Trapido, M. and Veressinina, Y. (2001), Kemia-Kemi, 28, 354-362.

• Navarro, P., J. Sarasa, D. Sierra, S. Esteban, J.L. Ovelleiro, (2005) Water Sci. Technol. 51(1), 113-120.

• Neamtu, M.; Zaharia, C.; Catrinescu, C.; Yediler, A.; Macoveanu, M.; Kettrup, A. (2004). Applied Catalysis B: Environmental 48, 287–294.

• Pak, D.W., Chang, W.S.. (1999). Water Sci. Technol. 40 (4/5) 115–121.

• Pala, A. and Tokat, E. (2001). Wat. Res., 36, 2920-2925 • Palau, R. (1998). Master Experimental en Química,

Dpto. Ingeniería Química y Metalurgia, Universitat de Barcelona.

• Petersen, D., Watson, D. and Winterlin, W. (1988). J.Environ.Sci.Health,Part B, 23, 587-603.

• Pignatello, J. and Sun, Y. (1993). ACS Symp. Ser. 518, 77-105.

• Rosen, G., Tsai, P., Barth, E., Dorey, G., Casara, P., Spedding, M. and Halpern, H. (2000). J. Org. Chem., 65, 4460-4463.

• Ruiz, B., Prats, R. and Zoffmann, C. (1992). Ingenieria Química, 279, 53-56.

• Ruppert, G., Bauer, R. and Heisler, G. (1993). J. Photochem. Photobiol. A, 73, 75- 78.

• Sabhi and Kiwi, (2001). Water Research 35 (8), 1994-2001.

• Safarzadeh-Amiri, A., Bolton, J. and Cater, S. (1996). Solar Energy, 56, 439-443.

• Sagawe, G., Lehnard, A., Lubber, M. and Bahnemann, D. (2001). Helvetica Chimica Acta, 84, 3742-3759.

• Schertenleib, R. and Gujer,W. (2000). EAWAG News, 48: 3-5.

• Scott, G. (1997). “Design, characterization and performance of a bench-scale continuous wet oxidation system”, Chem. Oxidation. Technol., 6, 156-186.

• Seiyama, T. Catal. Rev.-Sci. Eng. (1992). 34(4), 281-300.

• Serp, P., Corrias, M., Kalck, P. (2003). Appl. Catal. A, 253(2),337-358.

• Sevimli, M. and Kinaci, C. (2002). Water Sci.Technol., 45, 279-286.

Chapter XIII

156

• Sinquin, G., Petit, C., Libs, S., Hindermann, J.P., Kiennemann, A. (2001). Appl.Catal. B: Environ. 32(1-2), 37-47.

• Sotelo, J. L.; Ovejero, G.; Martinez, F.; Melero, J. A.; Milieni, A.. (2004). Applied Catalysis B: Environmental 47, 281–294.

• Trapido, M., Kallas, J., (2000). Environ. Technol. 21, 799–808.

• Treacyand, Higgins, (2001). “Collection of simulated XRD powder patterns for zeolites”, Elsevier.

• Urano, K. and Kato, Z. (1986). Journal of Hazardous Materials, 13, 147-149.

• Vicente, J., Rosal, R. and Diaz, M. (2002). Ind. Eng. Chem. Res., 41, 46-51.

• Vincent, P., Brioude, A., Journet, C., Rabaste, S., Purcell, S.T., Brusq, J.L., Plenet, J.C. (2002). J. Non-Cryst. Solids 311(2), 130-137

• Vlyssides, A., Papaioannou, D., Loizidou, M., Karlis, P. and Zorpas, A. (2000). Waste Management, 20, 569-574.

• Weber, R. and Smith, E. (1986). Environ.Sci.&Technol., 20, 970-979.

• Whitby, G. (1989). Ozone Sci. & Eng. 11, 313-324. • Wiesmann, U. and Putnaerglis, A. (1986).

Ger.Chem.Eng., 9, 284-291. • Wu, J., Bewtra, J., Biswas, N. and Taylor, K. (1994).

Can. J. Chem. Eng., 72, 881-886. • Yamazaki, I. and Piette, L. (1991). J. Am. Chem. Soc.,

113, 7588-7593. • Yeh, R., Hung, Y., Liu, R., Chiu, H. and Thomas, A.

(2002). International Journal of Environmental Studies, 59, 607-622.

• Zappi, G., Arbesman, S. and Weinberg, N. (2000). Annual conference and exposition on water quality and wastewater treatment, 73rd, Anaheim, CA, United State, Oct.14-18, 2966-2969.

Waste Water Treatment by Photo.fenton Process 2006

Documents

Transcript of Waste Water Treatment by Photo.fenton Process 2006