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Transcript of Orsina VERDES a, Livia AVRAM a, A. POPA a A. ERDÕHELYI b and V. Z. SASCA a a Institute of Chemistry...
Orsina VERDESa, Livia AVRAMa, A. POPAa A. ERDÕHELYIb and V. Z. SASCAa
a Institute of Chemistry Timisoara-Romanian Academyb Institute of Physical Chemistry and Material Science-University of Szeged
Study of the Ethanol Conversion Kinetics on
CsxH3-xPW12O40 Catalysts
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
INTRODUCTION
In the last time much attention has been paid to biomass as alternative
resource to petroleum, since biomass is a renewable resource and its
combustion does not lead to increased of CO2 in the atmosphere.
The search for renewable resources has stimulated the production of
hydrocarbons and others organic intermediary compounds from ethanol over
different acidic solid catalysts as the ethanol is the one of the main biomass-
derived products.
The H3-xPW12O40 and its salts, especially with Cs, are effective
catalysts in ethanol conversion to ethylene and the reaction kinetics is
interesting to the catalysis theory and industrial application also.
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
EXPERIMENTAL
The FTIR absorption spectra (diffuse reflectance mode) were
recorded “in situ” with a Bio-Rad FTIR spectrometer
equipped with diffuse reflectance attachment (Thermo-electron
corporation) and BaF windows with a wave number accuracy
of ± 4 cm-1. Typically 32 scans were registered. The whole
optical path was purged by CO2 and H2O free air generated by a
Balston purge gas generator. The catalysts were pre-treated at 573 K for 30 min, and then the
ethanol was introduced by bubbling of Ar gas through the ethanol at 273 K for 120 min. After, the
cell was flushed with He stream for 30 min, respectively with O2 for 20 min and finally the catalyst
was heated linearly with a heating of 10 K/min from 573K to 723 K. The IR spectra were recorded
for each of the experiment steps on H3PW and CsxH3-xPW, x= 2.5 and 3.
FTIR measurements of ethanol adsorption-desorption
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
EXPERIMENTAL
The conversion of ethanol was studied on the H3PW and CsxH3-xPW, x= 2.5 catalysts by continuous flow of reactant technique-CFRT. A micro reactor with fixed catalyst bed of about 100 mg was connected to the heated six-port valve with a loop for sampling as it can be seen in Fig. 1. The temperatures inside the catalyst bed were between from 473 K to 623 K and the reactant mixtures (11vol % and 22 vol% of ethanol in nitrogen) were obtained in the evaporator (2) by introducing the liquid ethanol in the nitrogen flow of the 30 ccm/min with a Hamilton syringe and a device which pushes its piston.
The reaction products analysis was carried out with the GC-FID equipped with a stainless steel column of 3 m length 2 mm inner diameter, packed with Porapak QS 80-100 mesh. The N2 carrier gas with the flow of the 30 cm3/min was used. The splitting was of 1:6 volume ratios. For a better separation of reaction products, a programme of temperature for the column was set up: 5 min at 323 K, then heating from 323 K to 473 K with the heating rate of 10 K/min and the last, an isothermal heating at 473 K for 5 min. The total time for a complete analysis was 25 min.
Catalytic activity tests
Figure 1. The installation scheme for the catalytic activity measurement by CFRT:
1. Four port valve; 3. Evaporator of liquid sample; 3. Micro reactor heated by electric furnace; 4. Four port
valve, 5-6 Six-port valve with gas sample loop; 7. Gas-chromatograph; 8. Integrator.
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
Catalysts primary structure
.
RESULTS AND DISCUSSION
The 3200-3400 cm-1 band is assigned to crystallization water-hydrogen bonded and to hydrogen-bond vibrations (hydrogen-bonds formed between neighbouring KUs). The 1715 cm-1 band is ascribed to hydroxonium ions, H3O+ or H5O2+, δ vibrations and the 1615 cm-1 band is assigned to δ vibrations of nonprotonated water molecules.
The specific absorbtion bands of the Keggin Unit - [PW12O40]
4-
are: νasP-Oi-W; 1060-1080; νasW-Ot, 960-1000; νasW-Oc-W, 840-910; νasW-Oe-W, 780-820 cm-1.
Figure 2. The FTIR spectra: (1) H3PW•6-7H2O and (2) Cs2.5H0.5PW•6H2O.
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
Catalysts primary structure
.
RESULTS AND DISCUSSION
Figure 3. The FTIR spectra: (1)H3PW•x1H2O (2) Cs2.5H0.5PW•x4H2O after heating at: (a) 573 K, 1 hour and (b) 873 K, 1 hour.
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
4000 3500 3000 2500 2000 1500 1000 500
T (%
)
Wavenumber (cm-1)
1
2
a) b)
Catalysts
.
RESULTS AND DISCUSSION
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
1) EtOH/573 K/0,5 min, 2) EtOH/573 KC/1 min,3) EtOH/573 K/15 min, 4) EtOH/573 K /60 min,5) EtOH/573 K /120 min, 6) He/573 K /30 min.7) O2/573 K/0.5 min, 8) O2/573 K /20 min,9) O2/623 K, 10) O2/673 K, 11) O2/723 K.
1) EtOH /573 K /1 min, 2) EtOH /573 K /15 min,3) EtOH /573 K /60 min, 4) Et /573 K /120 min.5) He/573 K/30 min, 6) O2/573 K /1 min, 7) O2/ 573 K /20 min, 8) O2/673 K/677-683 K,9) O2/ 623 K/600-626 K, 10) O2/723 K/700-726 K.
Figure 4 a,b. The FTIR spectra registered in diffuse reflectance mode for the ethanol absorption/desorption on the H3PW12O40 (a) and Cs2.5H0.5PW12O40 (b).
a) b)
Ethanol Conversion Kinetics
The adsorption-desorption studies of ethanol by the FTIR in diffuse reflectance mode were carried out in purpose to observe the ethanol chemisorbed species and thus to clarify the reaction mechanism. In the FTIR spectra registered during the adsorption of ethanol at 573 K and desorption under He, respectively under O2, the main absorption bands could be assigned to: - CH3 stretch and C-H deformation vibrations which belong to chemisorbed ethanol (1490, 1385, 1365 and 1330 cm-1); - O=C=O asymmetric stretch vibration of the adsorbed CO2 at 2350 cm-1, -C=O from carbonyl between 1650 and 1780 cm-1,- OCO stretch vibration from carboxylates and carbonates at 1650 cm-1 (asymmetric), 1480 cm-1 (symmetric) and 1220 cm-1 (bending); -ethoxy group deformation vibrations in the range 3000-2800 cm-1; -intermolecular H-bonded alcohol species at about 3600 cm-1 and -OH stretch vibration from molecular ethanol bonded on surface of the hydrogen–bridge bonds which gives a large broad band centered at about 3400 cm-1.
The dehydration of ethanol in the presence of strong Brönsted acid sites could involve a complex series of reactions, including oligomerization, aromatization, cracking and hydrogenation. The reaction products detected on CsxH3-xPW catalysts were: methane, C2 fraction (ethylene, ethane), C3 (propene, propane), C4 (butane, butene), C5 (pentane, pentene), C6 (hexane, hexene) and diethyl ether. The aromatic compounds, as benzene, toluene and xylene, could be also present but in undetectable quantities. In plus, very small quantities of H2 and CO were detected with GC-TCD.
RESULTS AND DISCUSSION
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
Reaction mechanism for ethanol conversion on Bronsted acid sites:
C2H5OH + H+ ... OUK2- C2H5OH2
+ ... OUK2- ... (1)
OUK2- ... C2H5OH2
+ [-OC2H5]UK ... H2O ... (2)
[-OC2H5]UK C2H4 + H+ ... OUK2- (3)
and/or
[-OC2H5]UK + C2H5OH (C2H5 )2O + H+ ... OUK2- (4)
[-OC2H5]UK could react also with C2H4 according to the next equation:
C2H4 + [-OC2H5]UK CH3- (CH2)3 – OUK2- ... (5)
CH3 – (CH2)3 – OUK2- (CH3)2 – CH=CH2 + OUK
2- ... (6)
RESULTS AND DISCUSSION
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
Ethanol Conversion Kinetics
Figure 5 a, b. The ethanol conversion on the H3PW12O40 for 11 vol% (a) and 22 vol% (b) ethanol in N2 at different temperatures.
RESULTS AND DISCUSSION
a) b)
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
0
20
40
60
80
100
0 100 200 300 400 500 600 700
Time, min
Eth
ano
l co
nve
rsio
n, %
623 K
573 K
548 K
523 K
498 K
473 K
20
30
40
50
60
70
80
90
100
0 100 200 300 400 500 600 700
Time, minE
than
ol C
onv
ersi
on, %
623 K
573 K
598 K
523 K
498 K
473 K
Ethanol Conversion Kinetics
RESULTS AND DISCUSSION
Figure 6 a, b. The ethylene and diethyl ether selectivity on the H3PW12O40 for 11 vol% (a) and 22 vol% (b) ethanol in N2 at different temperatures.
b)a)
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
0
10
20
30
40
50
60
70
80
0 100 200 300 400 500 600 700
Time, min
Sel
ectiv
ity, %
Ethylene 623 K Diethyl ether 623 K
Ethylene 573 K Dietyl ether 573 K
Ethylene 548 K Diethyl ether 548 K
Ethylene 523 K Diethyl ether 523 K
Ethylene 498 K Diethyl ether 498 K
Ethylene 473 K Diethyl ethe 473 Kr
0
10
20
30
40
50
60
70
80
90
0 100 200 300 400 500 600 700
Time, min.
Sel
ectiv
ity, % Ethylene 623 K Diethyl ether 623 K
Ethylene 573 K Diethyl ether 573 KEthylene 548 K Diethyl ether 548 KEthylene 523 K Diethyl ether 523 KEthylene 498 K Diethyl ether 498 KEthylene 473 K Diethyl ether 473 K
Ethanol Conversion Kinetics
RESULTS AND DISCUSSION
Figure 7 a, b. The C4 hydrocarbons selectivity on the H3PW12O40 for 11 vol% (a) and 22 vol% (b) ethanol in N2 at different temperatures.
b)a)
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,45
0,5
0 100 200 300 400 500 600 700
Time, min
C4
Hyd
roca
bon
Sel
ectiv
ity, %
623 K
573 K
548 K
523 K
498 K
473 K
35;4,26770;1,7
0
0,2
0,4
0,6
0,8
1
0 100 200 300 400 500 600 700
Time, min.C
4 H
yd
rocarb
on
Sele
cti
vit
y, %
623 K
573 K
548 K
523 K
498 K
473 K
35;3,9435:3,53
Ethanol Conversion Kinetics
RESULTS AND DISCUSSION
Figure 8 a, b. The ethanol conversion on the Cs2.5H0.5PW12O40 for 11 vol% (a) and 22 vol% (b) ethanol in N2 at different temperatures.
b)a)
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
40
50
60
70
80
90
100
0 100 200 300 400 500 600 700
Time, min
Eth
an
ol
co
nv
ers
ion
, %
623 K
573 KC
548 K
523 K
498 K
473 K
30
40
50
60
70
80
90
100
0 100 200 300 400 500 600 700
Time, minE
than
ol C
on
vers
ion
, %
623 K
573 K
548 K
523 K
498 K
483 K
473 K
Ethanol Conversion Kinetics
RESULTS AND DISCUSSION
Figure 9 a, b. The ethylene and diethyl ether selectivity on the Cs2.5H0.5PW12O40 for 11 vol% (a) and 22 vol% (b) ethanol in N2 at different temperatures.
b)a)
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
0
10
20
30
40
50
60
70
80
0 100 200 300 400 500 600 700
Time, min
Sel
ectiv
ity, %
Ethylene 623 K Diethyl Ether 623 KEthylene 573 K Diethyl Ether 573 KEthylene 548 K Diethyl Ether 548 KEthylene 523 K Diethyl Ether 523 KEthylene 498 K Diethyl Ether 498 KEthylene 473 K Diethyl Ether 473 K
0
10
20
30
40
50
60
70
80
90
0 100 200 300 400 500 600 700
Time, minS
elec
tivity
, %
Ethylene 623 K Ethylene 573 K Ethylene 523 KEthylene 498 K Ethylene 483 K Ethylene 473 KDiethyl ether 623 K Diethyl ether 573 K Diethyl ether 523 KDiethyl ether 498 K K Diethyl ether 483 K Diethyl ether 473 K
Ethanol Conversion Kinetics
RESULTS AND DISCUSSION
Figure 10 a, b. The C4 hydrocarbons selectivity on the Cs2.5H0.5PW12O40 for 11 vol% (a) and 22 vol% (b) ethanol in N2 at different temperatures.
b)a)
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
0,00
0,10
0,20
0,30
0,40
0,50
0 100 200 300 400 500 600 700
Time, min
C4
Sel
ecti
vity
, %
623 K 573 K
548 K 573 K
498 K 473 K
35;3%
0,00
0,10
0,20
0,30
0,40
0,50
0 100 200 300 400 500 600 700
Time, min
C4
Sel
ecti
vity
,%
623 KC 573 K
548 K 523 K
498 K 483 K
473 K
35;6.8235;6.23
Ethanol Conversion Kinetics
RESULTS AND DISCUSSION
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
Ethanol Conversion KineticsThe measurements of catalytic activity at the temperatures of the 473
K,
498 K and 523 K for 11 mol% and 22 mol% ethanol in reaction mixture were
used for kinetic parameters calculation based on the reaction rate equations:
r=k[pi]n (7), k=A*e-Ea/RT (8)
where k=reaction constant rate and pi = ethanol partial pressure (kPa).
The kinetic parameters of the ethanol transformation to reaction
products
on the Cs2.5H0.5PW12O40 were calculated from the logarithmic form of the reaction
rate equation (7) and reaction constant rate (8), for three temperatures at each of
the two ethanol partial pressures:
lnr= lnA-Ea/RT+nlnpi or lnr=-(Ea/R)*1/T+lnA+nlnpi (9)
That is equivalent with: y=ax+b, y=lnr, x=1/T and b=lnA+nlnpi
RESULTS AND DISCUSSION
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
y = -1,352x + 8,686
R2 = 0,9997
y = -1,435x + 8,827
R2 = 0,9999y = -1,476x + 8,90
R2 = 0,9999
y = -1,415x + 8,763
R2 = 0,9979
5,75
5,80
5,85
5,90
5,95
6,00
6,05
6,10
6,15
1,90 1,95 2,00 2,05 2,10
1000/T, 1/K
ln r
2nd Sample
3rd Sample
4th Sample
5th sample
y = -0,475x + 7,668
R2 = 0,9899
y = -0,472x + 7,649
R2 = 0,9597
y = -0,4405x + 7,573
R2 = 0,9917
y = -0,3949x + 7,467
R2 = 0,99936,62
6,66
6,70
6,74
6,78
1,90 1,95 2,00 2,05 2,10
1000/T, 1/Kln
r
2nd Sample
3rd Sample
4th Sample
5th Sample
Figure 11 a, b. The plotting of the logarithmic form of the ethanol conversion rate vs the inverse absolute temperature on the H3PW12O40 for 11 vol% (a) and 22 vol% (b) ethanol in N2.
Ethanol Conversion Kinetics
a) b)
Figure 12 a, b. The plotting of the logarithmic form of the ethylene formation rate vs the inverse absolute temperature on the H3PW12O40 for 11 vol% (a) and 22 vol% (b) ethanol in N2.
RESULTS AND DISCUSSION
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
y = -2,849x + 11,389
R2 = 0,9689
y = -3,072x + 11,786
R2 = 0,9707y = -3,114x + 11,848
R2 = 0,9685
y = -3,0649x + 11,7186
R2 = 0,9829
5,20
5,30
5,40
5,50
5,60
5,70
5,80
5,90
6,00
1,90 1,95 2,00 2,05 2,10 2,15
1000/T, 1/K
ln r
2nd Sample
3rd Sample
4th Sample
5th sample
y = -10,924x + 27,947
R2 = 0,9797
y = -10,154x + 26,08
R2 = 0,986
y = -11,353x + 28,621
R2 = 0,9545
y = -8,9189x + 23,386
R2 = 0,9922
4,40
4,90
5,40
5,90
6,40
6,90
1,90 1,95 2,00 2,05 2,101000/T
ln r
2nd Sample
3rd sample
4th Sample
5th sample
Ethanol Conversion Kinetics
b)a)
Figure 13. The plotting of the logarithmic form of the ethanol conversion rate vs the inverse temperature on the Cs2.5H0.5PW12O40 for 11 vol% (a) and 22 vol% (b) ethanol in N2.
RESULTS AND DISCUSSION
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
y = -0,8905x + 7,8132
R2 = 0,9988
y = -0,9207x + 8,5204
R2 = 0,9909
5,80
6,00
6,20
6,40
6,60
6,80
7,00
1,90 1,95 2,00 2,05 2,10
1000/T
ln r
11 vol.% EtOH
22 vol.% EtOH
y = -4,2169x + 14,007
R2 = 0,9929
y = -4,8521x + 15,856
R2 = 0,9899
5,00
5,30
5,60
5,90
6,20
6,50
6,80
1,90 1,95 2,00 2,05 2,10
1000/Tln
r
11 vol.% EtOH
22 vol,% EtOH
Figure 14. The plotting of the logarithmic form of the ethylene formation rate vs the inverse absolute temperature on the Cs2.5H0.5PW12O40 for 11 vol% (a) and 22 vol% (b) ethanol in N2 .
Ethanol Conversion Kinetics
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
Catalysts: Cs2.5H0.5PW12O40
Process: Ethanol conversionEa-apparent activation energy=7.55±0.15 kJ/molA-preexponential factor= 22584±113 andn-reaction order=1.
Process: Ethylene formation:Ea-apparent activation energy=37.7±2.6 kJ/molA-preexponential factor= 3649132 n-reaction order=0.5.
RESULTS AND DISCUSSION
CONCLUSIONS
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
The best catalyst is the Cs2.5H0.5PW12O40 with high catalytic
activity and selectivity to ethylene.
The values of thekinetical parameter: Ea-apparent activation
energy,
A-preexponential factor and n-reaction order were calculated for
the ethanol conversion and ethylene formation.
The elucidation of the reaction mechanism needs supplementary FTIR “in situ” investigation.
Acknowledgment: Financial support of this work by Cross Border Cooperation Programme 2007-2013, HURO 0901, is gratefully acknowledged.
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA
Two countries, one goal, joint success!
The financial support of the Romanian Academy for the research
programme from Institute of ChemistryTimisoara which was the
basis of this cooperation project is also gratefully acknowledged.
Thank you for attention!
NEW TRENDS AND STRATEGIES IN THE CHEMISTRY ... 3-4 NOV 2011 TIMISOARA