Activated carbon production from pretreated and fermented agricultural residues

Abstract

All forms of lignocellulosic biomass consist of three major chemical components: cellulose, hemicellulose and lignin. The remaining lignin from bioethanol production can be utilized as a feedstock for green chemicals. The purpose of this study was to produce activated carbon from pretreated and fermented agricultural residues and to investigate the influence of different process conditions such as feedstock type, impregnation ratio, and carbonization temperature on the pore structure of the products. This is the first study that investigated the production of activated carbon as a high value-added product from lignin-rich residues generated from bioethanol processes. The first step in the experimental path of the study was the recovery of lignin-rich biomass samples. Four samples were prepared from ethanol production wastes; the first one was from the pretreatment of corn stover, the second one was from pretreatment of wheat straw, the third one was from fermentation of corn stover, and the fourth one was from fermentation of wheat straw. The second step was the chemical characterization of feedstocks. In the third step, feedstocks were impregnated with 30%, 40% and 50% (w/w) H3PO4 and then carbonized with a rate of 20ºC/min to carbonization temperatures of 400ºC, 500ºC, 600ºC and 700ºC. The N2 adsorption/desorption capacities of products were compared according to their specific surface area and pore volume by applying the Brunauer-Emmett-Teller (BET) equation. The results demonstrated that the best way to produce activated carbon from lignin-rich residue was using pretreated wheat-based lignin, which was impregnated with 40% H3PO4 concentration and carbonized at 700ºC. In addition, both pretreated corn and fermented wheat-based products, which were impregnated with 50% H3PO4 and carbonized at 500ºC, had quite well developed specific surface area. Interestingly, mesoporous structures dominate in H3PO4-impregnated lignocellulosic material-based activated carbon. Therefore, these carbons are ideal for the adsorption of large molecules and decolorization.