From batch to flow: integrating in-line (deep) eutectic solvents with sequential downstream processing for sustainable biomass valorization

Abstract

(Deep) eutectic solvents (DES) have emerged as versatile and tunable alternatives to conventional solvents for biomass valorization. Nevertheless, most DES-based processes are still performed in static (batch) configurations, which limit scalability, reduce processing efficiency, and increase both cycle downtime and the number of operational steps. These limitations can be significantly mitigated in semi-continuous or continuous-flow systems, where intensified mass and energy transfer, together with improved control over kinetic and thermodynamic parameters, enable more efficient operations. This review critically advocates a transition in DES-based extraction systems toward process intensification, aligned with the principles of green chemistry and green engineering. Particular emphasis is placed on the transition from batch to (semi)continuous modes integrated with sequential downstream steps and real-time analysis, for which several potential process configurations are proposed. Hybrid systems combining pressurized-DES extraction with solid-phase extraction (SPE), membrane separation, or liquid–liquid extraction (LLE) are discussed for their potential to enhance concentration, fractionation, and purification of valuable compounds derived from biomass. Finally, this review outlines future directions, including the integration of sustainability metrics and the adoption of artificial intelligence (AI)-assisted solvent selection and process optimization, paving the way for next-generation DES-based (semi)continuous biorefineries.