Thermochemical liquefaction of biomass with ionic liquids: Exploring a sustainable pathway for a cleaner bio-oils production

Abstract

This work targets a process of biomass liquefaction to produce bio-oil using several ionic liquids. Since these liquids have high thermal stability and good conductivity, as well as being easy to recover and reuse, they may be considered a good alternative for biomass upcycling. The biomass liquefaction was carried out with reaction time and temperature of 90 min and 160 °C, respectively, with an ionic liquid concentration of 3% (m/m) against solvent mass, using microwave irradiation (MW). From the tests carried out, the liquefaction process with acidic ionic liquids, such as trihexyl (tetradecyl)phosphonium hydrogen sulfate ([P666,14][HSO4]), 1-methylimidazolium hydrogen sulfate ([C2Mim][HSO4]) and 1-butylimidazolium hydrogen sulfate ([C4Mim][HSO4]), promoted the highest conversions, about 20.7%, 16.3% and 14.2%, respectively. The less acidic ionic liquids, the 1-butyl-3-methylimidazoliumformate ([C4Mim][HCOO]) and 1-butyl-3-methylimidazolium acetate ([C4Mim][CH3COO]), enabled conversions of 8.3% and 9.2%, respectively. Based on the results, it is remarkable that the combination of cation-anion influences the good performance of ionic liquid in biomass processing. To characterize the obtained products, the Fourier Transform Infrared Spectroscopy (FTIR) technique, elemental analysis, scanning electron microscopy analysis and thermogravimetric analysis were used. The elemental analysis allowed calculating the higher heating value of bio-oils, indicating an energy recovery of the overall process.