Coconut shell activated carbon as an alternative adsorbent of inhibitors from lignocellulosic biomass pretreatment

Abstract

The phenolic compounds and furaldehydes released during the pretreatment of lignocellulosic biomass can negatively affect the enzymatic hydrolysis and alcoholic fermentation steps in biorefineries. This work proposes the use of coconut shell activated carbon (CSAC) as an agroindustrial residue-based adsorbent for the removal of the main inhibitors released in the hydrothermal pretreatment of sugarcane bagasse. The prepared CSAC showed a pore distribution favorable for the adsorption of molecules of different sizes, together with a negative surface charge profile in the pH range from 2 to 10. Adsorption isotherms showed that the CSAC presented high affinity for the phenolic compounds vanillin (monomeric) and tannic acid (oligomeric), as well as for the total phenolics present in an inhibitor cocktail. The CSAC also showed efficient adsorption of the phenolic compounds from the pretreatment liquor, without any removal of the sugars, hence displaying a useful high degree of selectivity. The enzymatic hydrolysis of pretreated sugarcane bagasse in the presence of the liquor treated with 2% (m/v) CSAC resulted in a 30% increase in the amount of glucose released, while the alcoholic fermentation efficiency was enhanced up to 14-fold, with complete removal of furaldehydes. These findings indicated that CSAC is an efficient and selective adsorbent of phenolic and furaldehyde inhibitors. It represents an alternative renewable material that could be used to improve the efficiencies of both the enzymatic hydrolysis and the alcoholic fermentation processes in future biorefineries.