Enhancing lignocellulosic biorefinery sustainability: mechanisms and optimization of microwave-responsive deep eutectic solvents for rapid delignification

Attaining sustainability and carbon neutrality necessitates a transition towards cleaner biorefinery, while the exploitation of sustainable and eco-friendly pretreatment techniques, as a pivotal stage in lignocellulose biorefinery, represents a challenge. Here, an ultrafast biomass pretreatment strategy enabled by microwave (MW) responsive deep eutectic solvent (DES) is proposed. The solvent properties (Kamlet-Taft parameters) of DES under MW participation are closely correlated with wheat straw fractionation efficiency. The lignin removal exhibits a positive correlation with polarity/polarizability (π*) and hydrogen-bond-donating ability (α), establishing a strong relationship between the tunable DES properties and MW responsiveness. MW reinforces the delignification efficiency of DES with relatively high π* and α, as corroborated by comparative analysis with conventional heating (CH) pretreatment. The reinforcement by MW moderates the pretreatment process and enables ultrafast lignocellulose deconstruction (130 ℃, 150 s, and 96.1% lignin removal), subsequently with 92.4% enzymatic hydrolysis and 8.8 g microbial lipid/100 g wheat straw at a remarkably low severity factor (R0). Life cycle assessment manifests the environmental benefits of MW-assisted DES in mitigating impacts by 63.1%, including global warming potential, resource depletion-fossil fuels, and ecotoxicity, in comparison to CH pretreatment. MW-DES exhibits an economic superiority based on life cycle cost analysis, with pretreatment cost 44.1% lower than CH-DES. The mechanistic insights into MW intensification of DES with specific properties provide a viable protocol for tailoring green solvents with enhanced MW responsiveness for efficient and sustainable biorefineries.