Insights into catalytic valorization of different lignin feedstocks into liquid fuels with microwave heating in hydrogen-donor solvents

Abstract

Microwave-assisted valorization of alkaline lignin, dealkaline lignin, and lignosulfonate over CuNiAl-based catalysts was investigated in hydrogen-donor solvents. The effect of lignin structures, solvents, and catalysts was investigated concerning the bio-oil yields and properties. A common phenomenon was observed that the highest bio-oil yields were all obtained in methanol over CuNiAl-based oxides under mild conditions. The synergistic and promotional effect of catalyst and solvent was discussed in detail, considering the elemental composition, HHV, and molecular weights of bio-oil. The bio-oil yields improved, and the molecular weights decreased with the increased Cu content in the catalysts, indicating the promotional effect of Cu during the lignin depolymerization. CuNiAl-based catalysts exhibited to be effective to convert lignin to bio-oil with higher HHV and decreased molecular weights, confirming the hydrogenation/hydrodeoxygenation during microwave-assisted hydrogenolysis.