Microwave-assisted deep eutectic solvents pretreatment for lignocellulose: Kinetics, intensified mechanism and process optimization

The lignocellulosic pretreatment via deep eutectic solvents (DES) can be intensified by microwave heating (MH), but the intensification mechanism is still ambiguous. Hence, this study compared the pretreatment performance between MH and conventional heating (CH), and microwave intensification mechanism was disclosed by reaction kinetic study. The experimental results showed significant increase of pretreatment performance under MH compared to CH for different temperatures. Based on the shrinking core model, DES diffusion was the rate-controlling step for the initial stage of biomass dissolution, but surface chemical reaction dominated the subsequent stage. Benefitting from effective biomass deconstruction under microwave field (verified by SEM), the energy barrier for DES diffusion was reduced and the collision frequency between biomass components and DES was increased, so greater rate constants of DES diffusion and chemical reaction stages in MH-assisted pretreatment were obtained. Finally, the operating conditions of MH- and CH-assisted pretreatment were optimized by response surface methodology.