Determination of Optimum Conditions for the Production of Activated Carbon Derived from Separate Varieties of Coconut Shells

Activated carbons were produced from coconut shells of tall and dwarf tree varieties. The activated carbon from the tall tree variety was initially synthesized using 1 M concentration of each of ZnCl2, H3PO4, and KOH solutions. From the adsorptive tests conducted using methylene blue solution, the activated carbon produced with H3PO4 gave the best absorbance and adsorptive performance. Coconut shells of dwarf tree variety were then obtained and treated with same mass of coconut shells of the tall tree variety using varied concentrations of the acid in order to determine whether the optimum concentration and temperature for producing carbon black from the coconut shells are distinct or similar for both varieties. The process was also modelled using the Differential Response Method (DRM) in order to determine the yields and adsorptive performances of the activated carbons by varying the carbonization temperature and concentration. The results from experiment and the developed mathematical model were both found to be in agreement giving the optimum concentration of phosphoric acid and pH for producing activated carbon to be 0.67 M and 2.07 for the tall tree variety and 1 M and 1.98 for the dwarf variety at optimum temperatures in the range of 450–575°C and 575°C, respectively.https://www.yrdcarbon.com/

Activated carbon, a carbonaceous material with characteristic surface area and highly developed porous structure, consists of 87 to 97% carbon with other trace elements [1]. It can be produced from coal, wood, agricultural, and paper wastes for the adsorption of methylene blue [2]. Applications of activated carbon include air and water purification, water filtration, ground water remediation, adsorption of poisons, and drug overdoses. These and several other reasons are behind its increased market demand. According to [3], its preparation involves carbonization of the precursor below 800°C in an inert atmosphere before carbonization. In this research, coconut shells were used because they are cheap and readily available in Nigeria. The shells contain volatile matter and moisture that are removed by the application of heat [4]. Gratuito et al. [5] carried out process optimization of activated carbon yield produced from coconut shells using RSM. Different methods are available for producing activated carbon but for specific industrial application, a solid adsorbent with wide pore size distribution can be preferably obtained via chemical activation [6]. Activated carbons obtained from snail shells and apple peels were discussed [6, 7]. Hung [8] used a fluidized bed reactor to convert crushed coconut shells to activated carbon, syngas, bio-oils, and water while, in [9], bamboo was used to prepare activated carbon of high surface area. The various methods for preparing activated carbon from carbon precursors are contained in [10]. Karacan et al. [11] optimized the manufacturing conditions for producing activated carbon from lignite. Ketcha et al. [12] prepared activated carbon from maize cobs using zinc chloride as activating agent. The reduction of hexamine III cobalt was carried out using activated carbon produced from coconut shells as catalyst [13], while the work of Mourao et al. [14] considered the influence of oxidation on the adsorptive capacity of activated carbon synthesized from lignocellulosic precursors. The preparation and characterization of activated carbons from cellulosic waste materials for waste water treatment were carried out [15–17]. Before carbonization, the raw materials are impregnated with chemicals such as acid, strong base, or salt [18]. Production and characterization of activated carbons from coconut shells were discussed [19]; their adsorption capacities were determined by contacting them separately with methyl red and potassium permanganate. Shalna and Yogamoortthi [20] produced activated carbon with high chromium removal efficiency from tea dust using H3PO4 as the activating agent. Sodeinde [21] used activated carbon produced from coconut shells impregnated with ZnCl2 to obtain cobalt II from cobalt III, and the results were similar to those of Long et al. [13]. Bagasse, apricot stones, hazelnut, almond, pistachio, and walnut hard shells when used as precursors for producing activated carbon show that activation temperature/time and chemical-to-carbon impregnation ratio are important parameters for determining the quality of activated carbon [22]. Coconut fibre was used for synthesizing activated carbon using H3PO4 as activating agent [23]. Several works on synthesis of activated carbon via chemical activation involve the use of popular chemicals such as H3PO4, ZnCl2 and KOH as activating agents; however, H3PO4 is preferred to ZnCl2 because of the adverse effect ZnCl2 has on the environment, hence the reason for its limitation in use in the food and pharmaceutical industries [24]. activated carbon pellets canadaThe use of other raw materials such as rubber, wood dust [24], and sugar cane bagasse pith [25] has also been exploited as raw materials for producing activating carbon. Tan et al. [26] also conducted an optimization study on activated carbon produced from coconut husk which was found suitable for the removal of 2,4,6-trichlorophenol using KOH treatment and CO2 gasification. This paper focuses on determining the optimum temperature and concentration for the synthesis of activated carbon with excellent adsorptive performance using DRM since previous works had their intents on obtaining the best activating agent, carbon yield, carbon-to-chemical impregnation ratio, and so forth. The mathematical approach widely used is RSM. Till date, no research work states the optimum temperature and concentration(s) of H3PO4 required for producing one or more varieties of coconut shell activated carbon; again, this brings to mind the need to find out if the optimum conditions for producing activated carbon with excellent adsorptive performance is the same for separate varieties of coconut shells.