Mechanistic insights into temperature-responsive deep eutectic solvent for alginate recovery and solvent recycling

Conventional alginate extraction from brown seaweed typically relies on harsh, non-recyclable chemicals, limiting process sustainability. This study presents temperature-responsive deep eutectic solvents (TRDES) as circular, recyclable extractants for alginate recovery. Using computational screening with COSMO-RS and experimental validation of TRDES affinity and alginate partitioning, TRDES1 (o-cresol: ethanolamine) was identified as the most promising combination, and was optimised and reused over eight cycles, yielding up to 55.6 ± 14.4 mg/g DW. COSMO-RS modelling validated the observed increase in extraction efficiency over successive cycles, showing enhanced partition coefficients and reduced Gibbs free energy of transfer with reuse. The process enabled mild extraction of functional alginate with increasing efficiency over the cycles. The main solvent parameters for TRDES design found to govern extraction and recyclability were capacity (C), partition coefficient (K), and Gibbs free energy (ΔG). Optimal performance was achieved with moderate TRDES–water capacity (1.27 × 10 1 to 3.15 × 10 1 ), low TRDES capacity (<1.2), and K > 1. This work establishes a theoretical framework with design rules for future TRDES development based on computational and experimental analysis and highlights the need for novel, biocompatible TRDES systems. As demonstrated, combining computational screening with these design principles enables the use of recyclable solvents. Incorporating natural compounds into TRDES design enhances both process efficiency and sustainability, facilitating the integration of DES technologies into circular biorefineries and supporting environmentally responsible biomass valorisation. • TRDES enabled combined recyclable and circular alginate extraction and recovery. • Alginate with characteristics and yield similar to current methods was obtained. • TRDES was reused for eight cycles with consecutive increased alginate recoveries. • Solvent parameters and design rules for future TRDES development were established.