J. Environ. Eng. Manage., 19(3), 173-178 (2009) 173

DEVELOPMENT AND CHARACTERSTICS OF ACTIVATED CARBONS FROM JATROPHA HUSK, AN AGRO INDUSTRIAL SOLID WASTE, BY CHEMICAL

ACTIVATION METHODS

Kumar Ramakrishnan and Chinnaiya Namasivayam* Environmental Chemistry Division, Department of Environmental Sciences

Bharathiar University Coimbatore 641 046, India

Key Words: Jatropha husk, chemical activation, activated carbons, characteristics

ABSTRACT

Jatropha curcus is a drought-resistant perennial species that grows well in marginal/poor soil. The bio-diesel obtained from its seeds is used as fuel for automobiles. Huge volumes of Jatropha husk is generated in the bio-diesel industries. The present study deals with the preparation of a variety of activated carbons from Jatropha husk, an agro industrial solid waste by chemical activation methods. The physico-chemical characteristics of activated Jatropha husk carbon (AJHC) and surface morphology are reported. Preliminary study shows that the low-cost AJHC is capable of removing organics and inorganics from water.

*Corresponding author Email: cnamasi@yahoo.com

INTRODUCTION The presence of inorganic and organic pollutants

in wastewater is on the increase and several of them are not efficiently removed by conventional wastewa-ter treatment processes and pose problems such as odor, toxicity and foaming. Activated carbons are ex-cellent adsorbents and thus are used to purify, decolor-ize, detoxicate, filter or remove dissolved substances. They are also used as catalyst in industrial processes [1]. Activated carbon has long been serving the indus-trial need of decolorization and removal of unwanted dissolved impurities from aqueous and non aqueous media [2]. Activated carbons made from conventional raw materials such as coconut shell, bitminus coal, peat and lignite, however, are expensive [3]. Activated carbons are prepared by physical and chemical activa-tion methods. There are two important advantages of chemical activation over physical activation. One is lower temperature in which the process is accom-plished. The other is that the global yield of the chemical activation tends to be greater since burn-off char can be avoided [4]. Acid activation followed by the thermal treatment increases the adsorption capac-ity to a large extent due to the increased surface area and pore volume [5,6].

A number of reports are found in literature for the preparation of activated carbons by acid activation methods from cheaper and readily available materials

like bamboo [7], peach stones [8], grass and wood [9], tamarind wood [10], from the agricultural wastes like coir pith [3], pea nut hull [11], rice husk [12], fruit peel [13], sugar beet pulp [14], grain sorghum [15], wheat husk [16,17] and from the industrial waste product like black slurry [18-20]. The acid treatment can change the surface functional groups and pore structure. The acid activation increases the acidity of activated carbon but the change in textural structure varies depending on the acid used [21]. Chemical ac-tivating reagents such as ZnCl2, alkali metal hydrox-ide or CsCl were also used to prepare activated car-bons from coir pith [3], fallen leaves [22], coconut husk [23], fir wood [24], waste news paper [25], kraft lignin [26], sugar cane [27] and nut shell [28], etc.

Jatropha curcus is a multipurpose non-edible oil yielding perennial shrub and is a drought tolerant plant. Its seeds are used to produce bio-diesel. Indian railways uses 2 million kL diesel per year. Indian Government has decided to use bio-diesel at 5% level in the regular diesel. So it has started planting Jatro-pha along both sides of the railway tracts, which will cover an area of 2500 km2. Also the state governments give subsidy to the farmers to cultivate the plant in waste lands. Several international funding agencies such as World Bank, Rockfeller Foundation, Appropri-ate Technology International, Intermediate Technology Development Group - USA, UK and Biomass Users Network are supporting the promotion of Jatropha

174 J. Environ. Eng. Manage., 19(3), 173-178 (2009)

for bio-diesel purpose [29]. Jatropha husk (JH) will be generated in large quantities as an agro-industrial solid waste in the bio diesel production industries. JH constitutes nearly 80% of the dried vegetable.

This paper presents preparation of a number of activated JH carbon (AJHC) using different acids, steam, ZnCl2, NaOH and their characteristics. All the chemicals used are of analytical reagent grade from Loba Chem Ltd. and Merck Ltd. (Mumbai, India). The characteristics of activated carbons were analyzed using standard methods according to literature [30].

MATERIALS AND METHODS

JH was collected from Tamilnadu Agricultural

University, Coimbatore, India. The dry raw JH was washed with tap water five times then washed with double distilled water to remove earthy impurities. Then it was dried in an air oven at 105 ± 5 °C for 8 h. A number of activated carbons were developed using water, acids, ZnCl2, and NaOH and characterized us-ing standard methods.

1. Steam Activation

The washed, dried and crushed JH (450 g) was

mixed with 100 mL of water and filled in a steel con-tainer with a tight lid. This container was placed in another concentric steel container with another lid. The linear space was filled with sand which was con-solidated layer by layer up to the brim of the container. This arrangement achieved a near total absence of ex-posure of the carbonizing material to air, allowing only a limited presence of oxygen trapped in the voids of the material being activated. This setup was placed in a muffle furnace for 1 h at 800 °C. After cooling, the carbon was taken out and sieved to 250-500 µm size (60-35 mesh ASTM) and designated as steam ac-tivated JH carbon (Steam-AJHC) and stored in air tight plastic containers.

2. Chemical Activation with Acids

Concentrated acids such as H2SO4, HCl, HNO3,

and H3PO4 were used for acid activation. One part of the dried JH (100 g) was treated with 2.8 parts by weight of concentrated acid and kept in an air oven at 185 ± 5 °C for 24 h. The carbonized material was washed with distilled water (500 mL) four times and then washed with 1% NaHCO3 solution. Finally the carbonized material was soaked in 1% NaHCO3 solu-tion overnight for the removal of residual acid. The material was washed with water several times until the pH of the supernatant was < 7.0. Then it was dried at 105 ± 5 °C for 8 h. The dried material was sieved to 250-500 µm size (60-35 mesh ASTM) and designated as acid AJHC.

Activated carbons were also prepared using the

activating agents such as hydrogen peroxide and am-monium persulphate. That is, in the sulphuric acid ac-tivation procedure 0.62 part of H2O2 or 0.16 part of ammonium persulphate by weight was added. Use of H2O2/ammonium persulfate will remove all adhering organic particles [17,31-33].

3. Chemical Activation with Zinc Chloride

The washed, dried and crushed JH (450 g) was

mixed with 2.0 L hot water containing 450 g of ZnCl2 for 1 h, then the remaining solution was drained off and oven dried at 60 °C for 12 h. The material was carbonized using the carbonization setup mentioned in the steam activation method at 800 °C for 1 h. After cooling, the excess zinc chloride was leached out by immersing it in hot 1.0 M HCl solution for 24 h kept in an air oven at 80 °C. It was then repeatedly washed with hot water until the chloride had disappeared from the wash water (tested by the silver nitrate method). This material was subsequently oven-dried at 105 ± 5 °C for 8 h and sieved to 250-500 µm size (60-35 mesh ASTM) and designated as ZnCl2 activated JH carbon (ZnCl2-AJHC).

4. Chemical Activation with Sodium Hydroxide

Powdered raw JH (450 g) was mixed with 2.25 L

of 1 M NaOH. The mixture was allowed to stand for 24 h at room temperature and then dried at 105 ± 5 °C. The material was carbonized using the carbonization setup mentioned in the steam activation method at 800 °C for 1 h. After cooling, the excess NaOH on the ac-tivated carbon particles was leached out by immersing it in 1.0 M HCl solution and washed with distilled wa-ter until the pH of the supernatant was above 4.0. Then it was dried at 105 ± 5 °C for 8 h. The dried ma-terial was sieved to 250-500 µm size (35-60 mesh ASTM) and designated as sodium hydroxide activated JH carbon (NaOH-AJHC).

The AJHCs were dried in vacuum desiccators at room temperature which were then used for taking scanning electron microscope (SEM) pictures for sur-face morphology examination (JMS-840A, Japan Elec-tric Optics Ltd., Tokyo, Japan) [34].

RESULTS AND DISCUSSION

1. Yield Percentage

The yield of AJHC is calculated by using the fol-

lowing expression and reported in Table 1.

Yield of AJHC%Yield 100%

Weight of JH taken=

The thermal degradation of biomass results in solid, liquid and gas products and the yield depends

Ramakrishnan and Namasivayam: Characteristics of AC from Jatropha Husk 175

Table 1. Percent yield of AJHCs

upon process parameters such as sample size, reaction temperature, residence time and reacting medium [35]. In this present study for preparation of AJHCs, the JH

was used in crushed form. That means the particle size was not uniform and also the chemicals used in this study such as concentrated acids and other activating reagents have different reactive efficiency depending upon their concentrations, physical and chemical properties.

2. SEM Observations

The surface morphology of the AJHCs obtained

before and after the treatment of physical and chemi-cal activation methods using steam, acids and activat-ing agents are shown in Fig. The micrographs clearly show honeycomb voids structure similar to the char based carbon. They are highly porous in nature with different pore structures. The SEM pictures show

No Type of carbon % Yield 1 2 3 4 5 6 7 8 9

H2SO4-AJHC HCl-AJHC HNO3-AJHC H3PO4-AJHC H2SO4 + H2O2-AJHC H2SO4 + (NH4)2S2O8 -AJHC Steam-AJHC ZnCl2 -AJHC NaOH-AJHC

50 46 33 44 43 45 29 31 21

Fig. 1. SEM graphs from different AJHC. (a) Thermal, (b) H2SO4, (c)HCl, (d) H3PO4, (e) HNO3, (f) H2SO4 + H2O2, (g) H2SO4 +(NH4)2S2O8, (h) NaOH, (i) ZnCl2 and (j) steam.

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)

(j)

176 J. Environ. Eng. Manage., 19(3), 173-178 (2009)

Table 2. Physico-chemical characteristics of AJHC prepared by acid activation method using different acids with or without H2O2/(NH4)2S2O8, steam, ZnCl2 and NaOH activation methods

No Parameter H2SO4 HCl HNO3 H3PO4 H2SO4 + H2O2 H2SO4 + (NH4)2S2O8 Steam ZnCl2 NaOH

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

pH

Conductivity (μS cm-1)

Specific gravity

Bulk density (g mL-1)

Porosity (%)

Moisture (%)

Ash (%)

Volatile matter (%)

Fixed carbon (%)

Surface area (m2 g-1)

Ion exchange capacity (meq g-1)

Solubility in water (%)

Solubility in 0.25 M HCl

Sodium (%)

Potassium (%)

Calcium (%)

Phosphorous (%)

Iodine number

pHzpc

Iron (%)

6.98

0.12

0.77

0.47

55

15

12.5

36

64

244

0.13

18

0.03

0.14

0.007

0.07

0.17

301

5.0

0.01

6.33

0.23

0.86

0.33

62

10

7.2

61

39

242

0.18

13

0.03

0.29

0.01

0.01

0.13

157

5.45

0.06

5.53

0.46

0.79

0.45

43

10

8.9

51

48

191

0.17

15

0.04

0.46

0.05

0.17

0.75

477

6.0

0.05

6.74

0.26

0.95

0.47

50

15

10.2

48

51

291

0.13

8

0.02

0.15

0.01

0.01

0.35

81

5.35

0.04

7.35

0.13

1.37

0.43

69

11

13.2

30

70

100

0.13

5

0.09

0.11

0.01

0.01

0.35

383

5.4

0.04

6.93

0.07

0.77

0.52

32

8

12.9

29

71

107

0.17

12

0.09

0.16

0.01

0.01

0.65

320

5.0

0.02

8.11

0.75

1.07

0.25

77

4

31.8

65

34

402

-Nil-

8

0.09

0.04

0.02

0.007

0.08

122

8.9

0.04

6.01

0.02

1.03

0.20

81

4

0.5

96

3

449

-Nil-

2

0.1

0.55

0.04

0.11

0.27

91

6.8

0.04

7.8

0.34

1.06

0.23

79

2

7.4

75

38

371

-Nil-

6

0.1

0.17

0.009

0.003

0.04

138

8.2

0.02

that when the JH is treated with activants, the opening of the pores in the surface of the char occurs, due to extraction of some materials from the surface by the chemical activation [36]. This may not be true for all activants, because not all activants have the same re-active properties.

The SEM picture of the thermally activated JH carbon (Thermal-AJHC) is shown in Fig. 1a for com-parison with SEM pictures of the AJHCs prepared us-ing chemical activants. There is no uniform and well developed pore structure on the surface of the Ther-mal-AJHC. Physically and chemically AJHCs show tremendous, perfect and constructed pore structures on the surface (Figs. 1b-1j). High surface area and pore structure are the basic parameters for an effective ad-sorbent. When the porosity increases the surface area also increases.

The number of pores present in HNO3-AJHC micrograph is lower than those present in ZnCl2-AJHC. This can be confirmed from pore percentage values given in Tables 2. The micrograph of ZnCl2-AJHC shows a compressed and lanky structure due to the formation of more interspaces between the monolayers by ZnCl2-AJHC (Fig. 1i). Thus it gives a higher volume of closed and narrow monolayer pore structure. Higher volume of pores developed from the chemical activation acts as a route for the contami-nants to enter into the micropores [37]. The surface of the Steam-AJHC (Fig. 1j) is fractured and fragmented compared with those of other AJHCs. This means the walls of the smaller pores get thinner and fractured due to the activation by steam [38].

3. Characteristics of AJHC

Table 2 shows the significant physico-chemical properties of AJHCs obtained from chemical activa-tion with various activating agents and steam. The moisture content percent of AJHCs obtained from the raw material JH by acid activation using different concentrated acids such as H2SO4, HCl, HNO3, H3PO4, H2SO4, + (NH4)2S2O8 and H2SO4 + H2O2 are 15, 10, 10, 15, 8 and 11, respectively. This suggests that ex-tensive porosity has been introduced during the acid treatment in the structure of all carbons. In the case of H2SO4 + (NH4)2S2O8, activation AJHC shows lower moisture per cent as well as lower porosity, 32%. The ash content generally gives an idea about the inor-ganic constituents associated with carbons. It is con-cluded that the inorganic constituents such as sodium, calcium, potassium etc. are very poor in all the AJHCs. In Table 2 the ZnCl2-AJHC shows that the water solu-bility is 2%. This shows the ZnCl2-AJHC has poor leaching property compared to all the other AJHCs. But in the case of solubility in acid, all AJHCs are very poor in leaching property. The specific gravity and porosity of the oven made AJHC is lower than furnace made AJHCs. The porosity of the AJHCs in-creases in the order: H2SO4 + (NH4)2S2O8 < HNO3 < H3PO4 < H2SO4 < HCl < H2SO4 + H2O2 < Steam < NaOH < ZnCl2. The ammonium persulfate with con-centrated sulfuric acid activation gives least porosity. The surface area increases in the order: H2SO4 + H2O2

< H2SO4 + (NH4)2S2O8 < HNO3 < HCl < H2SO4 < H3PO4 < NaOH < Steam < ZnCl2. The surface area of H2SO4 + H2O2–AJHC does not fit into the order com-pared to the porosity order of AJHCs. The surface ar-eas of AJHCs using steam, ZnCl2 and NaOH are higher compared to the acid activated carbons. The

Ramakrishnan and Namasivayam: Characteristics of AC from Jatropha Husk 177

ZnCl2-AJHC has the highest surface area of 449 m2 g-1 due to the highest porosity (81%).

Preliminary studies showed that the AJHCs can be used as effective adsorbents for the removal of toxic metal ions, anions, organics and dyes from water. As the raw material of the carbon is disposed as waste, the water treatment methods using them are expected to be economical.

CONCLUSIONS

JH is disposed as waste in the bio-diesel produc-

tion industries. A number of activated carbons were developed using water, acids, ZnCl2, and NaOH and characterized using standard methods. All AJHCs have excellent physio-chemical properties and the SEM pictures showed that they had constructed sur-face morphology structures. Preliminary studies showed that they can be used as effective adsorbents for the removal of contaminants from water. As the raw material of the carbons is disposed as waste, ap-plications of the JH activated carbons to the water treatments are expected to be economical.

ACKNOWLEDGEMENTS

The authors are thankful to Prof. P. Venkatacha-

lam, Department of Bio Energy, Tamilnadu Agricul-tural University, Coimbatore, India for providing JH. One of the authors (KR) gratefully acknowledges Bharathiar University for awarding the University Re-search Fellowship.

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Discussions of this paper may appear in the discus-sion section of a future issue. All discussions should be submitted to the Editor-in-Chief within six months of publication.

Manuscript Received: January 2, 2009 Revision Received: March 27, 2009

and Accepted: March 31, 2009