Abstract: Production of Activated Carbon from Residue of Liquorices Chemical Activation T.Kaghazchi *, M.Soleimani, M.Madadi Yeganeh, Department of Chemical Engineering, AmirKabir University of Technology, No.424, Hafez Ave., Tehran, Iran, Tel. & Fax: +98(21) 66405847, E-mail: kaghazch@aut.ac.ir Activated carbons are materials widely used in several processes, mainly as effective adsorbents Important applications are related to their use in water and industrial wastewater treatment for removal of flavor, color, odor and other undesirable organic impurities. Apart from such interesting properties as very high surface area, different pore-size distributions and different functional groups, which can be modified by changing activation conditions, the availability and abundance and consequently low price of the raw materials, have made activated carbon to appear as an economical product in the industries. Activated carbon can be produced from a large variety of raw materials. Common examples of commercial feed stocks are coal, wood and agricultural wastes such as coconut shell, fruit stones (apricot and cherry stones), hard shell (almond and pecan shell), bagasse, olive waste, etc. In this work, the production of activated carbon from residue of liquorices by chemical activation has been studied. The activation was performed using phosphoric acid under different operating conditions. The effects of parameters such as particle size, impregnation ratio of chemical agent, final activation temperature and heating rate on the physico-chemical properties of activated carbon were investigated. Production tests for the effects of these factors were designed with Taguchi method. Experimental results showed that the selection of impregnation ratio of chemical agent plays a very important role in the properties of activated carbon. The properties of prepared activated carbon at optimum operating conditions such as surface area (1130m 2 /g) and iodine number (923 mg I 2 /gr C), were compared to those of commercial activated carbons. Keyword: activated carbon, production, residue of liquorices, characterization 1-Introduction Activated carbons are materials widely used in several processes, mainly as effective adsorbents. Activated carbon is a generic term for a family of highly porous carbonaceous materials none of which can be characterized by a structural formula or by chemical analysis. Activated carbon in the form of granules, powders or shaped can be produced from virtually any carbonaceous solid precursor by physical or chemical activation methods [1-5].
Activated carbon can be produced from a large variety of raw materials, basically by two methods: physical and chemical activation or combination of both methods. The physical or thermal activation method involves carbonization of raw material at elevated temperature (500-900 C) in an inert atmosphere and the subsequent activation at high temperature (800-1000 C) in a CO 2 or steam atmosphere. In chemical activation method, a simultaneous carbonization and activation can be obtained by impregnation with dehydrating agent such as phosphoric acid or zinc chloride at lower temperature. In this method, a carbonized product with a well-developed porosity (after appropriate washing) could be obtained in a single operation. The common feature of all substances used in the chemical activation process is that they are dehydrating agents that influence pyrolytic decomposition and inhibit formation of tar, thus enhancing the yield of production of activated carbon [2-8]. Activated carbons have been widely used for the separation of gases, the recovery of solvents, the removal of organic pollutants from drinking water, wastewater treatment and as a catalyst support [1-3, 5, 9]. The physical and chemical properties of activated carbon (such as surface area, bulk density, ash content) vary with the feed materials used and the way of activation. These properties may not relate directly to their effectiveness in the applications of activated carbon, but they are important for commercial utilization [9-12]. Process economics normally dictated the selection of readily available inexpensive feed stocks. Common examples of commercial raw materials are coal, lignite, peat and agricultural by-products such as woods, fruit stones (apricot & cherry stones), hard shell (almond and pecan shell), coconut shell, bagasse, olive waste, [2, 3, 6, 9-11]. Agricultural and forestry residues or generally biomass residues wastes could be used as suitable raw materials for the production of activated carbon. Agricultural wastes widely available in Iran are of little or no economic value and in fact cause disposal problems. The vast quantity of waste is generally dumped in landfills [13, 14]. In this work, the production of activated carbon from residue of liquorices has been studied. Liquorice has been in medicinal industry and as a sweetener. Residue of liquorices widely available in the central part of Iran and have little economic value. The activation process was performed by phosphoric acid solution under different operating conditions. In this study, the effect of preparation conditions such as heating rate, impregnation ratio, particle size and activation time on the properties of activated carbons was investigated. 2-Experimental 2.1. Chemical analysis of raw materials In order to assess the composition of the raw material, the content of lignin, cellulose, extractable materials and ash content were determined according to TAPPI standards. In lignin and cellulose test, the particle size of initial raw materials must be between 60-80 mesh [15-17].
2.2. Production of activated carbon: Activated carbon was produced from domestic agricultural by-product, residue of liquorices by chemical activation process as follows [14, 18]. The raw material was ground in a laboratory mill and sieved to various particle size fractions using a conventional sieve-shaker. The selected fraction of particle size was dried and impregnated with H 3 PO 4. This mixture was left in an air oven at 100 C for 24 hours; subsequently, the mixture was subjected to carbonization and an activation process in a programmable electrical furnace (Nabertherm, Labothem MODEL C19) to a final carbonization temperature of 400 C. After cooling to room temperature, the samples were washed with hot distilled water (80 C) until water ph reached a value of approximately 5. The samples were dried over night at100 C in an air oven. Production tests were designed with Taguchi method and effects of parameters such as particle size, impregnation ratio of chemical agent, final activation time and heating rate on the physico-chemical properties of activated carbon were investigated. According to Taguchi method, L9 orthogonal array with four columns and nine rows is suitable for these experiments. The experimental layout for these parameters using the L9 orthogonal array is listed in Table 1. In these experiments, the iodine number of activated carbons was selected as response of the system and optimum operating conditions was determined based on this parameters. According to Taguchi method, L 9 array was suitable for these experiments. Arrangement of these parameters and selected levels of them in L 9 array was shown in Table 1. Table 1. Arrangement of factors in L 9 orthogonal array Parameters Size of raw material (mesh) Impregnation ratio (%) Heating rate( C/min) Activation time(hr) Number of experiment 1 12-16 50 2.5 0.5 2 12-16 100 5.0 1.0 3 12-16 150 10.0 2.0 4 16-35 50 5.0 2.0 5 16-35 100 10.0 0.5 6 16-35 150 2.5 1.0 7 35-60 50 10.0 1.0 8 35-60 100 2.5 2.0 9 35-60 150 5.0 0.5 Impregnation ratio (wt %) defined as (gram of H 3 PO 4 per gram residue of liquorice) 100. Production efficiency of this process was determined from the following equation:
activated carbon weight production efficiency = *100 (1) raw material weight The agent (H 3 PO 4 ) is also an important factor, and it is reused after concentration. The percent of H 3 PO 4 recovery was calculated with equation (2): product weight before washing- product weight after washing recovery = * 100 (2) H PO weight for impregnation 3 4 2.3. Characterization of activated carbon Activated carbon was characterized by selected physical and chemical properties. 2.3.1. Iodine number The Iodine number of prepared activated carbon was measured by titration at 30 C based on the standard method (ASTM Designation D4607-860).This parameter was used to evaluate the activated carbon adsorption capacity [19]. 2.3.2. Surface area measurement The surface area (S BET ) of activated carbons was measured by N 2 adsorption at 77 K using a Quantachrom AUTO ZORB-1. Before measuring the isotherm, the samples were heated at 200 C for 2 h in vacuum to degassing [20]. 2.3.3. Bulk density Apparent or bulk density is a measure of the weight of material that can be obtained in a given volume under specified conditions. The volume used in this determination includes, in addition to the volume of the skeletal solid, the volume of the voids among the particles and the volume of the pores within the particles. A10 ml cylinder was filled to a specified volume with activated carbon that had been dried in an oven at 80 C for 24hr. The cylinder was weighted. The bulk density was then calculated as [21]: Bulk density= [weight of dry material (g)/vol. of packed dry material (ml)]. (3) The volume of this vessel was calibrated by measuring the volume of water at ambient temperature that the vessel can contain. 2.3.4. Ash content The Ash content (Ash %) of an activated carbon is the residue that remains when the carbonaceous portion is burned off. Ash content of activated carbon was determined by standard methods (ASTM Designation D2866-94, 1999) [22]. Approximately 1-2 gr of powdered activated carbon was placed into weighted ceramic
crucibles. Activated carbon and crucibles were dried 24 h at 80 and reweighed to obtain the dry carbon weight. The sample were heated in an electrical furnace at 650 ± 25 C for 3 hr. The crucibles were cooled in desiccator, and remaining solids (ash) were weighted. Percent of ash was calculated by: %Ash = [remaining solids wt (g)/ original carbon wt (g)]*100 (4) 3. Results and Discussion 3.1 Chemical analysis of raw materials The content of lignin and cellulose may be one of the criteria parameter for the selection of appropriate raw material in the production of the activated carbon. The chemical composition of the residue of liquorice is as follows: Cellulose (wt. %): 56.5 Lignin (wt. %): 22.5 Extractable materials (wt. %): 7.95 Ash (wt. %): 6.81 3.2 Properties of the activated carbons The properties of the activated carbon depend on the treatment conditions and the choice of raw materials. In this work, the effect of operating conditions on the production efficiency, physico- chemical properties of the activated carbons obtained under different conditions are shown in Table 2. In these experiments, the iodine number of activated carbons was selected as response of the system in Taguchi method and optimum operating conditions was determined based on this parameters. In figures 1-4, system response versus the level of factors was shown. Test no. Table 2.properties of activated carbon in different operating condition Iodine number Bulk density Surface Area Ash (%) Production Chemical (mg I 2 /gr) (kg/m 3 ) (m 2 /g) efficiency (%) recovery (%) 1 419 253 989.4 20.23 46.4 94.6 2 528 251 1017.6 9.20 44.5 82.6 3 633 180 1044.9 8.60 41.2 82.3 4 269 234 950.4 17.36 48.9 80.8 5 539 270 1020.5 9.68 42.7 94.1 6 749 238 1075.0 11.50 42.5 89.7 7 342 270 969.3 11.38 46.0 83.7 8 873 167 1107.2 5.27 39.2 86.9 9 708 175 1064.3 5.06 40.0 86.2
700 641 Iodine number(mgi2/g C) 600 500 400 300 200 100 526.666 518.666 0 12-16 16-35 35-60 particle size(mesh) Figure.1 Average response at different levels of particle size of raw material Iodine number(mgi2/gc) 800 696.466 700 646.533 600 500 400 343.333 300 200 100 0 50 100 150 Impregnation ratio(%) Figure2. Average response at different levels of impregnation ratio 800 700 680 600 501.733 504.6 500 400 300 200 100 0 2.5 5 10 Heating rate(0c/min) Figure3. Average response at different levels of heating rate Iodine number(mgi2/gc)
600 590 591.399 Iodine number(mgi2/gc) 580 570 560 550 540 530 520 555.533 539.399 510 0.5 1 2 Activation time(hr) Figure4. Average response at different levels of activation time The optimum operating condition was achieved using residue of liquorice with 35-60 mesh and impregnation ratio 150% with heating rate 2.5 C/min to a final carbonization temperature of 400 C for 2hr. Properties of the produced activated carbon under optimal condition are: Surface area: 1130 m 2 /g, Iodine number: 923 mg I 2 /gr, Ash: 6.55%. Another step of Taguchi method is the analysis results or ANOVA table. The ANOVA table shows which parameters significantly affect the performance characteristic and the contribution of each treatment process parameters on the adsorption characteristic (Iodine number) of the activated carbons. The percentage contribution of each parameter in the total sum of the squared deviations can be used to evaluate the importance of the parameter change on the performance characteristic [23]. Table 3- Results of the analysis of the variance (ANOVA table) Factor Sum of squares Variance Percentage of contribution Particle size 28001 14000 8.91 Impregnation ratio 219268 109634 69.75 Heating rate 62837 31418 19.99 Activation time 4267 2133 1.36 Total 314373 100.00 Results of ANOVA, which are shown in table 3, indicate that the impregnation ratio is the significant production treatment parameter due to its highest percentage contribution (69.75%) among the operating treatment parameters; however activation time in the range studied has not considerable effect on the iodine number of activated carbon. 4. Conclusions World consumption of activated carbons is steadily increasing and new applications are ever emerging, particularly those concerning environmental pollution remediation that will tend to sustain the demand. Therefore it is necessary to the exploitation of new sources for
production of activated carbon. Agricultural wastes could be considered as suitable raw materials for the production of these adsorbents. The physical and chemical properties of activated carbon (such as surface area, bulk density, ash content) vary with the feed material used and the way of activation. These properties do not relate directly to the effectiveness of their applications, but they are important for commercial utilization. In this work, the production of activated carbon from residue of liquorices by chemical activation has been studied. The activation was performed using phosphoric acid under different operating conditions. The effects of parameters such as particle size, impregnation ratio of chemical agent, final activation temperature and heating rate on the physico-chemical properties of activated carbon were investigated. Production tests for the effects of these factors were designed with Taguchi method. The results showed that the selection of impregnation ratio of chemical agent plays a very important role in the adsorption properties of activated carbon. The surface area (1130 m 2 /g) and iodine number (923 mg I 2 /gr C) of the produced activated carbon were compared to those of imported commercial ones. 5. References 1- A.Dorbrowksi, Adsorption: from Theory to Practice, Adv. Colloid & interface Sci., 2001, 93, 135-224. 2- Bansal R.C. et al, Active carbon, 1988 3- Patric, J.W., Porosity in Carbons, Chapter 9, London, 1995. 4- Zanzi, R. and et al, Pyrolysis of biomass in Presence of Steam for Preparation of Activated Carbon, Liquid and Gaseous Product, Proceeding of the 6 th World Congress of Chemical Engineering, Australia, 23-27 sect. 2001 5- Streat, M. and Naden, D., Ion Exchange and Sorption Process in Hydrometallurgy, John Wiley, 1987. 6- Moreno Castilla, C. et al, Chemical and Physical Activation of Olive-mill Waste water to Produce Activated Carbon, Carbon, p1415-1420, 2001. 7- Teng HJ, Lin HC., Activated carbon production from low ash sub bituminous coal with CO 2 activation. Am. Inst Chem. Eng., 44 (5):1170 7, 1998. 8- Evans M.J.B., et al., "The production of chemically-activated carbon", Carbon, vol. 37, 269-274, 1999. 9- Heschel, W. and Klose, E., On the Suitability of Agricultural By-products for the Manufacture of Granular Activated Carbon, Fuel, 74(12), 1786-1791, 1995. 10- Gergva, K. et al, A Comparison of Adsorption Characteristics of Various Activated Carbon, Journal of Chemical Technology and Biotechnology, 56, 77-82, 1993. 11- Hayashi J., et al., "Preparing activated carbon from various nutshells by chemical activation with K 2 CO 3 ", Carbon, vol. 40, 2381-2386, 2002. 12- Ahmenda M., et al., "Production of granular activated carbons from selected agricultural by-products and evaluation of their physical, chemical and adsorption
properties", Bioresource Technology, vol. 71, 113-123, 2000. 13- Soleimani M., Kaghazchi T., "Adsorption of gold from liquid wastes on activated carbon prepared from apricot stones", CHISA 2002, 15 th International Congress of chemical & Process Engineering, 25-29 Aug. 2002, Praha, Czech. 14- Kaghazchi T., Soleimani M., "Chemical activation of agricultural wastes to produce activated carbon", 7 th Asia-Pacific International Symposium on combustion and energy utilization, 15-17 December 2004, Hong Kong 15- Preparation of wood for chemical analysis", TAPPI standards, T 264 om-88,1988. 16- "Acid-insoluble lignin in wood and pulp ", TAPPI standards, T 222 om-88,1988. 17- "Ash in wood, pulp, paper and paperboard: combustion at 525 C", TAPPI standards, T211 om-93,1993. 18- M. Soleimani, T. Kaghazchi, Chemical activation of agricultural wastes to produce Activated carbon,5scce &3SCPE, Iran, 2005 19- "Standard test method for determination of Iodine Number of activated carbon", ASTM standard, Designation D4607-94, 2000 20- Brunauer, S, B, P.H. Emmett, F. Teller, J. Am. Chem. Soc., 73, 309, 1951. 21- Snell- Ettre, Encyclopedia of industrial chemical analysis, vol.8, 1968 22- "Standard test method for total ash content of activated carbon", ASTM standard, Designation D2866-94, 2000. 23- Roy Ranjit K, 1990, A primer on the Taguchi method, Van Nostrand Reinhold, New York.