Microwave-assisted Catalytic Pyrolysis of Commercial Residual Lignin with In-Situ Catalysts to Produce Homogenous Bio-Oil and High-Yield Biochar with Enriched Pores

High-value utilization of residual lignin from the commercial bioconversion process is crucial for the more industrially relevant and feasible bioethanol production. Residual lignin generated from pulp and paper industry faces the similar situation. Bio-crude and biochar production via microwave-assisted pyrolysis is an emerging technology among current residual lignin conversion strategies. In this study, microwave-assisted pyrolysis performances based on the commercial bioconversion residual lignin and black liquor lignin (kraft pulping process) were systematically explored with the in-situ catalysis process. The results showed high amount of residual chemicals existing in both lignin samples successfully served as in-situ microwave absorbers and catalysts, which indicated a more economically feasible process. Pyrolysis parameters were further systematically studied with the goal of achieving optimized products distribution and quality. The results showed that with insitu microwave absorbers and catalysts, the bioconversion residual lignin favored bio-oil production (36% yield) with phenols, hydrocarbons and easters as the predominant components. While the black liquor lignin favored the production of biochar with high yield (57%), larger BET surface area (183 m2/g) and pore volume (0.123 cm3/g). Because of their unique chemical components and in-situ catalysts, both commercial residual lignin samples produced higher yield and better-quality biochar compared to raw softwood sawdust. In addition, the homogenous bio-oil production was also achieved from the microwave-assisted pyrolysis of bioconversion residual lignin by process optimization.