Achieving efficient pretreatment of corn straw at elevated temperatures via constraining cellulose degradation

Abstract

Greatly reducing the cellulose crystallinity and lignin content of lignocellulose can substantially improve the enzymatic hydrolysis efficiency, dramatically reducing the enzyme dosage; however, it is difficult to be simultaneously achieved. A solution was put forward - biomass pretreatment was carried out with the binary system consisted of 1-n-butyl-3-methylimidazole chloride (BMIMCl) and arginine (Arg) at temperatures higher than the glass transition temperature of lignin (Tg-lignin). The cellulose crystallinity decreased because of hydrogen bonding with BMIMCl. Delignification was promoted via raising the temperature higher than the Tg-lignin, while cellulose degradation was constrained by Arg. The delignification rate reached 90.36 %. The yield of cellulose remained at a level of 88.89 %, while the Crystallinity Index (CI) of cellulose decreased from 36.13 % (raw corn straw) to 13.50 % (regenerated material, RM). It was found that the average molecular weight (Mw) of lignin decreased from 1632 g/mol to 584 g/mol after pretreatment, indicating the lignin was depolymerized; the 2D-HSQC result showed the β-O-4′ bond of lignin was broken. Because the cellulose crystallinity and the lignin content of the regenerated material were reduced greatly at the same time, the RM was easily hydrolyzed by cellulase. The enzymatic hydrolysis glucose yield of the RM was 3.75 times that of raw corn straw when the enzyme dosage was only 0.41 FPU/g sample, reaching 99.5 %. The IL was successfully recycled four times, and the recovery rate was higher than 93 % each time. RM obtained in four cycles maintained high lignin removal rate and enzymatic hydrolysis glucose yield. The degradation products of hemicellulose and lignin were the main impurities in the recovered IL. This work may provide a new solution for green and efficient biomass pretreatment.