Importance of lignin removal in enhancing biomass hydrolysis in hot-compressed water

Beech wood was pretreated by ethanol/water mixture or sodium chlorite/acetic acid mixture to prepare two representative samples rich in cellulose/lignin and cellulose/hemicellulose, respectively. These samples were then hydrolysed in hot-compressed water (HCW) using a semi-continuous reactor under optimal conditions where the secondary reactions in the liquid products were minimised. The glucose recovery in the primary liquid products from hydrolysis in HCW is enhanced to ∼80% for the cellulose/hemicellulose rich sample from ∼56% for the raw sample, while that for the cellulose/lignin rich sample only increases slightly to ∼64%. Despite its highest crystallinity index, the cellulose/hemicellulose rich sample achieves the highest glucose recovery at the shortest reaction time during hydrolysis in comparison with the raw and cellulose/lignin rich samples, clearly demonstrating the importance of lignin removal in enhancing hydrolysis reaction rate and sugar recovery during biomass hydrolysis in HCW.