Roles of water and aluminum sulfate for selective dissolution and utilization of hemicellulose to develop sustainable corn stover-based biorefinery

The roles of water and aluminum sulfate (Al2(SO4)3) in one-step selective catalytic transformation of hemicellulose in corn stover were investigated. At 130 °C, 90.2 wt% hemicellulose contained was selectively dissolved and further converted to 85.1 wt% xylose in the presence of Al2(SO4)3, while keeping cellulose (92.1 wt%) and lignin (88.4 wt%) insignificantly converted. The hemicellulose hydrolysate could be further transformed to lactic acid with the yield of 82.2 wt% using Lactobacillus plantarum via fermentation. H2O formed hydrogen bonds with the intermolecular linkages connecting hemicellulose with cellulose and lignin in corn stover, which was helpful to dissolve hemicellulose. The hydrolysis of Al2(SO4)3 formed H+ (Brønsted acid), which enhanced selectively the conversion of hemicellulose to xylose. While the active Lewis acid [Al(OH)2(H2O)x]+, formed from the hydrolysis of Al2(SO4)3, could promote the selective dissolution of hemicellulose. The aluminum species could also form complex compounds with –OH1 and C1–O6 of xylan unit by hydrogen bonds, promoting the production of xylose, as well as inhibiting its further degradation. These findings provided new strategies to develop a low-cost and sustainable corn stover-based biorefinery by understanding and controlling complex reaction networks in biomass conversion.