Deep eutectic solvent-mediated hydrothermal treatment for biomass conversion: a review

Hydrothermal treatment is an emerging technology for the processing of biomass into various value-added products. Deep eutectic solvents (DESs) emerge as green solvents for biomass processing. Recently, DES-mediated hydrothermal treatment (DES-HTT) has emerged as a cutting-edge technique for promoting biomass conversion, merging the principles of HTT with the unique properties of DESs. To keep up the pace of rapid development of DESs and HTT, it is necessary to summarize the progress of this green technology. Herein this review summarizes the progress of the use of DES-HTT in biomass conversion, including DES-mediated hydrothermal pretreatment for dewatering, bioconversion and/or fractionation of biomass, DES-mediated hydrothermal extraction of lipid from biomass, and DES-mediated hydrothermal carbonization for functional hydrochar and carbon dot synthesis. This review also analyzes the future challenges and research directions in biomass conversion via DES-HTT. Finally, this review facilitates the valorization of biomass via the combination of advantages from DESs and HTT.