Microwave-assisted hydrothermal liquefaction for biomass valorization: Insights into the fuel properties of biocrude and its liquefaction mechanism

Abstract

In contrast to the conventional liquefaction, microwave-assisted hydrothermal liquefaction (MW-HTL) is a recently developed technology for the production of biocrude for energy recovery; however, the exploration on liquefaction process under microwave radiation still presents a gap in understanding. In this study, two samples with typical components were adopted for MW-HTL, and a series of multiple techniques were used to analyze the fuel properties of biocrude as well as the corresponding changes of organic substances. Results found that microwave radiation facilitates the liquefaction process by inhibiting the secondary reactions during heating period and the excessive polymerization during liquefaction processes, resulting in an increase of approximately 39.8–43.9 % of yield, 3.9–4.0 % of higher heating values, and 46.6–59.0 % of energy recovery efficiency than that of biocrude obtained from the conventional liquefaction under similar conditions. The interaction depends on a process termed dipolar polarization was found as the main reason for this improvement, which involves the adsorption of microwave radiation by polar groups in sample within the MW field. Overall, these findings not only provide an efficient process to produce biocrude with superior quality, but also offer a fundamental support on biomass valorization in terms of energy utilization.