Quantitative structures and thermal properties of Miscanthus x giganteus lignin after alcoholamine-based ionic liquid pretreatment

Alcoholamine-based ionic liquid (IL) pretreatment has been potential due to low cost ( similar to $1.0/4) and efficient delignification. However, valuable exploration of lignin during this pretreatment has not been systematically studied and this hinders its further commercialized application. In this study, the effects of mild and efficient ethanolamine acetate [EOA}[OAc] pretreatment on the structural and thermal feature of Miscanthus x giganteus (M x g) lignin were evaluated in detail. The ionic liquid lignin (ILL), and residual-enzymatic hydrolysis-mild acidolysis lignin (R-EMAL) were compared with the original-enzymatic hydrolysis-mild acidolysis lignin (O-EMAL). Results determined that Guaiacyl (G) was the predominant unit in all the lignins. As compared to O-EMAL, ILL had higher yield, high purity, less beta-O-4 ether linkages, and more COOH contents as well as a higher thermal stability owing to formation of slightly condensed structures. Additionally, depolymerization of the lignin occurred as the reduction of the molecular weight, and cleavage of beta-O.4 ether linkages. Furthermore, REMAL was similar to O-EMAL as approximative beta-O-4 ether linkages, molecular weight and thermal stability. The structural elucidation of M x g lignin could provide a good theoretical basis for economic improvement of the alcoholamine-based biorefinery and efficient conversion of lignocellulose to high value-added lignin-based products.