Deep eutectic solvents for catalytic biodiesel production from liquid biomass and upgrading of solid biomass into 5-hydroxymethylfurfural

Abstract

Serious environmental issues triggered by abundant carbon dioxide emissions and the gradual depletion of traditional fossil fuels are calling for the development of renewable energy. Efficient catalytic valorization of renewable liquid/solid biomass into various biofuels and high-value-added platform chemicals is of great value and significance, and has become a focus for researchers. In this regard, biodiesel, as a typical green biofuel, together with 5-hydroxymethylfurfural (HMF) as a key biorefining precursor for various biofuels and high-value chemicals have received increasing emphasis in the field of sustainable liquid/solid biomass valorization. Importantly, deep eutectic solvents (DESs) with various merits of low cost, high tunability, long-term sustainability and low environmental impact are widely recognized as promising alternatives to traditional solvents for the industrial production of biodiesel and HMF. The significant progress that has been made in the synthesis of biodiesel and HMF using DESs as green solvents makes it of great interest to timely summarize the recent advances in this research field. Therefore, this review systematically analyzes the recent developments in the application of DESs as co-solvents, catalysts, and extractants for the transformation of liquid biomass (fatty acids, oils) to biodiesel, as well as the upgrading of solid biomass (monosaccharide, disaccharide and polysaccharide, etc.) to HMF. In addition, the corresponding composition, classification, and important physical–chemical properties of DESs are discussed. More importantly, the relevant reaction mechanisms and potential design principles of DESs working in biodiesel and HMF synthesis are outlined accordingly. Finally, considering the economic cost issue, the possibility of DES recycling and reuse is also emphasized, showing bright future prospects for the application of DESs in biomass conversion. This review aims to set the trajectory for future advances in efficient and sustainable utilization of renewable biomass with DESs, advancing the process of carbon neutrality.