Effects of enzymatic hydrolysis and physicochemical properties of lignocellulose waste through different choline based deep eutectic solvents (DESs) pretreatment

DESs are promising green solvents in lignocellulose pretreatment. In this work, four choline chloride based DESs were synthesized and their physicochemical properties were evaluated. Herbaceous lignocellulose (wheat straw, sorghum straw) and woody lignocellulose biomass (poplar wood, pine wood) were selected as pretreated substrates. In order to reveal the mechanism that pretreatment can improve the efficiency of enzymatic hydrolysis, the pretreated lignocellulose and lignin were analyzed. SEM, FT-IR and XRD characterization revealed the microstructural changes of pretreated lignocellulose, including the increase of surface roughness and pore erosion, changes of polysaccharide/lignin chemical groups, the increase of CrI. The efficient delignification increased the accessibility of enzyme to cellulose, the lignin content negatively affected enzymatic hydrolysis conversion. Furthermore, GPC analysis showed that the polydispersity of sulfonated lignin was reduced after pretreatment, lignin had more homogeneous molecular structures. The degree of unsaturation was calculated according to the elemental composition of sorghum straw and lignin. The unsaturation of pretreated sorghum straw decreased, that may be due to the removal of partial lignin. The elemental composition of acid insoluble lignin (separated from sorghum straw) reflects the increase of unsaturation of lignin after pretreatment.