Solvent selection via molecular design-driven evaluation for microwave-assisted biomass pretreatment: TEA and LCA of deep eutectic solvents

Microwave-assisted organosolv pretreatment can effectively separate the major components in lignocellulosic biomass, while selected solvent significantly influences the feasibility and sustainability of biorefinery process. This study performed a molecular design-driven evaluation to illustrate the matching strategy of solvent and process by developing integrated biorefinery processes with feedstock input of 0.4 million tons/year using different organosolv pretreatment. The selected organic solvents included deep eutectic solvents (DES), glycerol (GO), ethyl lactate (EL), γ-valerolactone (GVL), and water as a control. The environmental impact of each solvent was evaluated by life cycle assessment (LCA), and result indicated the production of DES had moderate environmental impacts compared to others. Referring to entire biorefinery process coupled with microwave technology, the energy consumption and environmental impacts associated with microwave-assisted DES pretreatment were consistently lower than others (GO, GVL and EL), when 1 kg ethanol was used as a functional unit. First, the high dielectric loss endowed DES with strong interaction with microwave field, facilitating the separation of three major components in biomass and promoting product yields. Second, low volatility and heat capacity enabled DES to be easily heated and recovered. These characteristics placed DES in a competitive position in terms of environmental impacts. Techno-economic analysis (TEA) further confirmed the feasibility of the DES-based biorefinery process, demonstrating a minimum ethanol selling price (MESP) of 2476.54 $/ton, which was the lowest among all tested solvents. In this way, the practical implementation of biorefinery processes must consider the pretreatment solvent recovery and cost.