Water effect on the characterization of 1-butyl-3-methylimidazolium hydrogen sulfate and lignin dissolution

Abstract

ABSTRACT Lignin dissolution plays an important role in the conversion process of lignin. This work focused on the lignin dissolution in a binary mixture of 1-butyl-3-methylimidazolium hydrogen sulfate([BMIM]HSO4) and water. To understand the lignin dissolution behavior in the binary mixture of [BMIM]HSO4/H2O, the molecular interactions of [BMIM]HSO4 and H2O were first investigated by simple methods based on the viscosity and UV spectra. Then three different lignin samples, enzymatic hydrolysis lignin, alkali lignin, and organosolv Lignin, were employed to investigate the dissolution ability of [BMIM]HSO4/water with different mass fraction of [BMIM]HSO4([BMIM]HSO4%). The molecular interactions and lignin solubility of [BMIM]HSO4/H2O strongly depended on the mass fraction of [BMIM]HSO4([BMIM]HSO4%). A turning point for the formation of bi-continuous system at [BMIM]HSO4% of 63% was observed by the changing trend of viscosity and UV absorption. [BMIM]HSO4/H2O with 60-90% of [BMIM]HSO4% had excellent ability to dissolve EHL, and achieved the maximum value at 70% of [BMIM]HSO4%. It was indicated that the bi-continuous [BMIM]HSO4/H2O was the most effective in lignin dissolution. Lignin was regenerated with a recovery rate of 94.29%. Compared the regenerated lignin and the raw lignin, [BMIM]HSO4 altered the arrangement structure of lignin without no changes in the chemical structures. This study provided ideas for the process design of lignin dissolution and conversion in the [BMIM]HSO4/H2O system.