Preparation and Characterization of Granular Activated Carbon from Acacia Nilotica Stalk by KOH Activation C.B.Shivayogimath 1, M.N.Hiremath 2, Lokeshappa.B 3 1 Professor and Head, Dept of Civil Engineering, B.E.C. Bagalkot, Karnataka, India, 2 Associate Professor, Department of Civil Engineering, AITM, Bhatkal-581320, Karnataka, India. 3 Professor, Department of Civil Engineering, UBDTCE, Davanagere Abstract: This work was focused on the production and characterization of low cost granular activated carbon from Acacia Nilotica stalk by KOH activation. Activated carbon and precursor material were analyzed for physical, elemental and proximate analyses, and the effect of carbonization temperatures for 600, 700, 800 and 900 C was examined. It was observed that BET surface area and pore volume of the prepared activated carbon were found to be 1065 m 2 /g 83% respectively for 800 C. The results show that Acacia nilotica trees/plants are regarded as one of the worst weeds because of its invasiveness, potential for spread, and economic and environmental impacts, can be used as a promising low cost precursor for the production of activated carbon. Index Terms: Activated Carbon, BET Surface Area, Carbonization, Acacia Nilotica, KOH Activation. I. INTRODUCTION Activated carbon (AC) is a highly porous material carbonized at high temperature and given chemical treatment to obtain large internal pore area and surface area providing cost effective and efficient adsorbents[1-2].peculiar property of activated carbon is its high surface area up to 3500 m 2 /g. Activated carbons can be prepared in various forms such as, powdered activated carbon (PAC), granular activated carbon (GAC), extruded activated carbon (EAC), bead activated carbon (BAC) and polymer activated carbons. Practically powdered activated carbon (PAC) and granular activated carbon (GAC) are much extensively used adsorbent in the treatment of water and waste water for the removal of organic and inorganic matter [3-4]. History of activated carbon goes back to the year 1500 BC, where there is a evidence of use of charcoal nothing but present days activated carbon by Egyptians [5]. There is a evidence for the use activated carbon by the Hindu s in 1794 for sugar refinement [6]. Activated carbon can be prepared from various carbonaceous materials such as wood, peat, coal, bone and corals as natural materials, and shell, hulls, nuts, stones from fruits and nuts, saw dust, corncob, sunflower stalks, straw as agricultural byproducts and residues.and activated carbons can also be prepared from fly ash, baggase, baggase pith, palm oil ash, etc, as industrial wastes and by products [10-30]. Activated carbon can be prepared either by physical (or dry) activation or chemical activation, which involves two steps; in the first step, the precursor material will undergo carbonization process (600-900 0 C) in the absence of air, and second step involves activation/oxidation by carbon dioxide, oxygen, steam, etc. [31-35]. Application of Activated Carbon Application carbons produced from various materials can be used in the following two phases of application. Liquid Phase Application Liquid phase application is the most extensively used phase of application, as it accounts for nearly 80% of the total usage of activated carbon [9]. Liquid phase applications generally has large fraction of macropore, this helps the liquid phase materials to diffuse more quickly into the rest of the pore structure. Gas Phase Application Gas phase application accounts only 20% of the total usage of activated carbon [9]. Activated carbon used in gas phase usage requires smaller pore size while activated carbon for liquid phase application tends to have larger pore size. Activated carbon for gas phase application is hard and dense granular material produced from highdensity raw material such as coconut shell, palm kernel shell, coal, or coke [5]. 201
From the literature it has been observed that, study on utilization of acacia nilotica stalk as a precursor material for the preparation of activated carbon was not reported. Even from other precursor materials, the characterization of activated carbon by varying the carbonization temperature is still lacking. Therefore the present work is to study the feasibility of production of granular activated carbon from acacia nilotica stalk by chemical activation with KOH, under temperatures of 600 0 C, 700 0 C, 800 and 900 0 C. II. MATERIALS AND METHODS The precursor material used was acacia nilotica stalk, Acacia nilotica trees/plants shown in fig 2, are regarded as one of the worst weeds because of its invasiveness, potential for spread, and economic and environmental impacts. It is widely distributed throughout arid and semi-arid zones of the world. It is distributed throughout the greater part of India in forest areas, roadsides, farmlands, tank foreshores, agricultural fields, village grazing lands, wastelands, bunds, along the national highways and railway lines. Mostly it occurs as an isolated tree and rarely found in patches to a limited extent in forests, presently about 20% of the total geographical area of India is wasteland. Pprecursor material used was acacia nilotica stalk, Acacia Nilotica trees are growing abundantly in entire north Karnataka region as weed and which is generally being used as a fuel wood by the local poor people. The precursor material i.e. acacia nilotica stalk of 4-6 mm in diameter was cut into length of 10-20 mm in size, was collected from the field of Mundaragi area of Gadag district. Chemicals Used The chemical activation agent used was Potassium Hydroxide (KOH Pellets) and the reagent was Hydrochloric acid of 3 N (HCL), both were procured from Merc Specialties Private Limited, Mumbai. Characterization of precursor material The precursor material was subjected to elemental and chemical properties and the results are presented in Table 1. Cost analysis was carried out to determine the actual cost incurred on production of 1 kg of Granular Activated Carbon and is presented in Table.4. (a) (B) Fig -1: A twig of Acacia nilotica showing (a) flowers and (b) Pods of Acacia nilotica. Table- 1: Elemental analysis (%) of precursor material ELEMENT VALUE IN % Corbon 48.00 Hydrogen 6.00 Oxygen 44.00 Nitrogen 0.40 202
Fig -2: Images of (a) Acacia Nilotica Tree (b) Precursor material (c) Oven dried precursor material (d) Prepared Granular activated carbon Activation 25g of KOH pellets were dissolved in 1 liter of distilled water, and oven dried; 100 g of cooled precursor material was thoroughly mixed in the KOH solution in a beaker, and agitated by a magnetic stirrer at 80 0 C for 1 h. The beaker was taken out of the magnetic stirrer and the material was strained out, cooled and washed 4 to5 times with distilled water till the ph of washed water was reached near to 7. Then the washed precursor material was kept in the oven for 24 h at 110± 5 0 C; then the oven dried material was cooled to room temperature, and kept in the muffle furnace for carbonization process at 600 0 C for 2 h. Subsequently, the material was cooled and kept in a beaker which contained 3N HCl, for 30 min at 80 0 C and stirred by a magnetic stirrer; it was washed again with distilled water for 4 to 5 times or till the ph of washed water reached to nearly 7. Then the material was dried in an oven for 12 hours under 110± 5 0 C, before being used for further analysis. The procedure was repeated for temperatures of 700 0 C, 800 and 9 00 o C, to assess the effect of carbonization temperature. Characterization of Granular Activated Carbon The porous properties of the prepared activated carbon samples were analyzed by observing the SEM images. SEM, surface area and particle size analysis tests were carried out at National Institute of Technology, Karnataka, India. The surface area and porosity determination were performed by gas sorption analyzer NOVA 22OO, Quatachroma. Other tests were done as per the requirement of IS 2752: 1995, which are tabulated in Table 4. 203
Table- 2: Requirements for Granular Activated Carbons as per IS 2752: 1995 Characteristics Requirement For Type 1 (For use as a base for respirator carbons and solvent recovery) Adsorption capacity for carbon tetrachloride, percent by mass, Min 55 ------- Moisture, percent by mass, Max 5 5 Ash, percent by mass, Max 5 6 Hardness number, Min 90 90 Retentivity index, percent by mass, Min 45 -------- Adsorption capacity in terms of iodine 900 450 number, Min Half dechlorination value, cm, 4 7 Surface area, m2/g, Min 900 550 Requirement for Type 2 (For use in water treatment) III. RESULTS AND DISCUSSION The results of various tests on the activated carbon sample under various temperatures are tabulated in Table 3. It is observed that the highest surface area of 1065m 2/ /g is obtained at the carbonization temperature of 800 o C, followed by 565 m 2/ /g at 600 o C and 880 m 2/ /g at 700 o C. The surface morphology examined by SEM (Fig-.5 to Fig-6), clearly reveals that activated carbon carbonized at 800 0 C is fragmented and has porous surface texture; this indicates that the prepared activated carbon is highly porous with high adsorption capacity. Table-3: Surface area, ash content and moisture content of activated carbon CHARACTERISTIC AT 600 0 C AT 700 0 C AT 800 0 C AT 900 0 Ash content % 5.8 4.9 3.7 4.4 C Moisture content % 4.1 3.8 2.4 3.5 Surface area m 2 /g 590 880 1065 910 Iodine number 480 720 980 840 Pore Volume 44% 61% 83% 68% Fig -4: Effect of Temperature on Surface Area of Activated Carbon 204
Fig-:5 SEM Image of granular activated carbon prepared from acacia nilotica stalk carbonized at 800 0 C Table -4: Cost analysis of prepared activated carbon and commercial activated carbon Cost Towards Acacia Nilotica Procurement of precursor 02.00 material Chemicals 75.00 Electrification 33.00 Labour 150.00 Miscellaneous 05.00 Total Cost/Kg Rs.265/Kg IV. CONCLUSION It was revealed from the studies, that inferior wood stalks of Acacia Nilotica which is abundant in entire India including north Karnataka as a weed,, can profitably be exploited and used as potential raw materials (precursor materials) for the preparation of highly porous Activated Carbon. From the above study it can be concluded that highly porous Granular Activated carbon with surface area of 1065 m2/g can be produced from acacia nilotica stalk. To produce carbon with high surface area and larger pore volume KOH treatment is a preferred route of activation. For KOH activation the temperature between 750-790 C is optimum for getting highly porous carbon with pore size, after which the widening of pores begins and product starts becoming more and more mesoporous. It was also revealed from the cost analysis, that cost of the prepared low cost adsorbent Rs.275/Kg, have proved to be cost effective compared to the costly commercial activated carbon. ACKNOWLEDGEMENT The authors acknowledge the Head of the department of Material Science, NITK, Surathkal, for providing help in undertaking surface area analysis, particle size analysis and SEM report. REFERENCES [1] Hassler John.W, Purification with Activated Carbon: Industrial, Commercial and Environmental, Chemical Publishing Company Inc., New York, N.Y. 1974. [2] Matson.Jameset.al, Carbon: Surface Chemistry and Adsorption from Solution; Marcel Dekker Inc., New York 1971. [3] Derbyshire. F et.al, Activated Carbons-Production and Applications, in: J. W. Patrick, (Edit.), Porosity in Carbon, Halsted Press, New York (1995). [4] Stenzel. Mark. H., Remove Organics by Activated Carbon Adsorption, Chemical Engineering Progress, 89: 4 (1993). 205
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