Rethinking choline chloride in deep eutectic solvents for biomass fractionation: A critical reassessment of...

The widespread adoption of choline chloride (ChCl) based deep eutectic solvents (DESs) has significantly advanced lignocellulosic biomass fractionation. While traditionally viewed as a benign component, ChCl is actually a reactive participant that accelerates delignification, suppresses lignin condensation, and enhances hemicellulose dissolution. However, the presence of ChCl also imposes considerable operational bottlenecks, including accelerated pseudo-lignin formation, mass transfer limitation, solvent loss via parasitic esterification, and the substantial energy requirements of evaporative recycling, compromising the overall process economics. A comparative reassessment reveals that effective matrix deconstruction is achievable using alternative ChCl-free platforms. To successfully mitigate these operational bottlenecks, strategies including solvent engineering, process intensification, and advanced solvent recycling techniques are proposed. Furthermore, we introduce a four-point decision-making framework that evaluates solvent viability based on systems-level performance comparisons, downstream lignin valorization targets, synergy with advanced process intensification, and the feasibility of non-evaporative solvent recovery. Ultimately, we encourage the biorefining community to rethink ChCl's intrinsic necessity, shifting from empirical combinatorial solvent proliferation toward demanding rigorous, comparative justification in solvent design.