Influence of anti-solvents on lignin fractionation of eucalyptus globulus via green solvent system pretreatment

• Selective dissolution of lignin via ionic liquid–ethanol–water mixture.
• Low-boiling point anti-solvents employed for lignin precipitation.
• High-purity and low-molecular weight lignins get fractionated.

This study focused on the anti-solvents precipitation process of lignin fractionation. Eucalyptus globulus wood was pretreated by ionic liquid–ethanol–water mixture before anti-solvents precipitation experiments. The influence of potential anti-solvents on lignin fractionation was extensively studied. Water, methanol, dichloromethane and iso-propanol were proven effective for lignin fractionation by the formation of precipitation. Lignin fractionation performance (yield and purity) was significantly affected by temperature and anti-solvents dosage. The purity of fractionated lignins increased with growing anti-solvents dosage and temperature. While the yield of fractionated lignins decreased as temperature rose. An increase in anti-solvents dosage could dramatically improve lignin yield. Lignin yield increased to a maximum value, but decreased when the anti-solvents dosage increased further. For different anti-solvents, the sequence on lignin yield was: iso-propanol > water > dichloromethane > methanol. While the sequence of anti-solvents on lignin purity displayed in reverse with lignin yield. Lignins fractionated by different anti-solvents were characterized by FT-IR and GPC. Results showed that the fractionated lignins were G–S type, of low molecular weight, with narrow distribution range (450–2250 g/mol) and extremely low polydispersity (Mw/Mn) value (1.12–1.13). These fractionated lignins could be promising materials for the production of high value chemical and fuels.