Enhanced production and separation of short-chain glucan oligomers from corn stover in an unacidified LiBr molten salt hydrate via pre-extraction of hemicellulose

Abstract

Selective production of glucose from cellulose in a molten salt hydrate (MSH) shows high efficiency but the separation of glucose is still challenging. To address this issue, we proposed a stepwise method, where cellulose was first hydrolyzed into glucan oligomers and separated via anti-solvent precipitation, followed by being hydrolyzed into glucose under mild conditions. For potential industrial applications, using raw biomass as a substrate is more attractive due to its commercial advantages. However, directly hydrolyzing raw corn stover in an MSH resulted in a low glucan oligomer yield and sugar concentration, together with insufficient separation efficiency. This work demonstrated that the generation of acetic acid during hemicellulose hydrolysis is the critical factor affecting glucan oligomer selectivity. To address this issue, a pre-extraction method using auto-hydrolysis was proposed to remove hemicellulose before MSH hydrolysis. After pre-extraction, the obtained glucan oligomer yield could be enhanced from 59.9% to 79.5%, with the separation efficiency increased from 53.7% to 80.6% by methanol precipitation. Besides, increasing the raw corn stover concentration led to an increase in acetic acid and resulted in glucan oligomer degradation. However, after removing hemicellulose, the concentration of glucan oligomers could be significantly enhanced from less than 72.1 to 121.5 mg mL⁻¹. Thus, pre-extraction of hemicellulose followed by MSH hydrolysis provides a potential application for directly producing glucan oligomers from raw biomass with improved yield and separation efficiency.