Pretreatment of corncob with green deep eutectic solvent to enhance cellulose accessibility for energy and fuel applications

Abstract

Fossil fuels are the primary source of energy for a long period in spite of excessive environmental hazards, such as greenhouse gas emissions. Production of energy and fuel from lignocellulosic biomass has been the goal of the study in pursuit of renewable alternatives to fossil materials. Corncob is common agricultural biomass waste found in many countries. It can be utilized to produce bioenergy, but the conversion efficiency is limited. Pretreatment may be applied to improve the efficiency of corncob conversion; for example, by the fractionation of lignocellulosic biomass. Choline chloride (ChCl) and glycerol are considered as synthetic deep eutectic solvents (DESs), also known as green solvents. DESs are expected to fractionate hemicellulose and lignin from raw biomass, and the accessibility of cellulose may be enhanced. In this work, pretreatment of corncob with DES prepared from ChCl and glycerol was investigated at varying reaction temperatures (60–150 °C), residence times (6–15 h), and ChCl-to-glycerol molar ratios (1:0.5-4). The results showed that hemicellulose and lignin were effectively extracted from the raw corncob, and therefore, cellulose content in the remaining solid residue, known as cellulose-rich material (CRM), can be improved by least 140%. The reaction temperature, residence time, and presence of ChCl in the DES influenced the pretreatment of corncob significantly. Increases in reaction temperature and residence time led to a higher cellulose content in CRMs and an increased extraction of hemicellulose and lignin from the raw corncob. Without the ChCl in DES, the cellulose content in CRMs and the extraction of hemicellulose and lignin from the sample were decreased markedly. The optimal condition at 150 °C, 12-h residence time, and 1:4 ChCl-to-glycerol molar ratio could be used to improve the cellulose content of CRMs from the raw corncob by more than 150%. The CRM with improved lignocellulosic properties can be used as a feedstock in further bioenergy/fuel application.