Understanding lignin treatment in dialkylimidazolium-based ionic liquid-water mixtures

The treatment of enzymatically hydrolyzed lignin (EHL) in dialkylimidazolium-based ionic liquid (IL)-water mixtures (50-100wt% IL content) was investigated at 150°C for 3h. pH, IL type, and IL content were found to greatly influence the degradation of lignin and the structure of regenerated lignin. 1-Butyl-3-methylimidazolium methylsulfonate-water mixtures with low pH facilitated lignin depolymerization but destroyed the regenerated lignin substructure. Regenerated lignin with low molecular weight and narrow polydispersity index (2.2-7.7) was obtained using a 1-butyl-3-methylimidazolium acetate-based system. Water addition inhibited lignin depolymerization at 50-100wt% IL content, except for 70wt% 1-butyl-3-methylimidazolium chloride-water mixture. Compared with pure IL treatment, obvious differences were observed in the breakdown of inter-unit linkages and ratio of syringyl to guaiacyl units in regenerated lignin with IL-water treatment.