Acid in ionic liquid: An efficient system for hydrolysis of lignocellulose

Acid in ionic liquid was demonstrated as an efficient system for hydrolysis of lignocellulosic materials with improved total reducing sugars (TRS) yield under mild conditions. TRS yields were up to 66%, 74%, 81% and 68% for hydrolysis of corn stalk, rice straw, pine wood and bagasse, respectively, in C(4)mimCl in the presence of 7 wt% hydrogen chloride at 100 degrees C under atmospheric pressure within 60 min. Different combinations between ionic liquids, such as C(6)mimCl, C(4)mimBr, AmimCl, C(4)mimHSO(4), and SbmimHSO(4), and acids, including sulfuric acid, nitric acid, phosphoric acid, as well as maleic acid, afforded similar results albeit longer reaction time was generally required comparing with the combination of C(4)mimCl and hydrochloric acid. FTIR spectra and elemental analysis of the recovered residues indicated that modification of lignin occurred during sulfuric acid catalyzed hydrolysis. In addition, kinetic modeling based on experimental data suggested that the hydrolysis likely followed a consecutive first-order reaction sequence, where k(1) and k(2), the rate constants for TRS formation and TRS degradation, were determined as 0.068 min(-1) and 0.007 min(-1), respectively. This novel system may be valuable to facilitate cost-efficient conversion of biomass into biofuels and biobased products.