Recyclable Hydrophobic Deep Eutectic Solvent for Ambient Recovery of Native-Structured Chitin from Crustacean Shells

Crustacean shells, the primary source of chitin, impose significant environmental burdens and necessitates sustainable recovery approaches. Here, we report a hydrophobic deep eutectic solvent (HDES) composed of procaine, l-menthol, and acetic acid that achieves efficient chitin extraction under ambient conditions while exhibiting exceptional recyclability enabled by intrinsic hydrophobic phase separation. The HDES achieves 98.35% demineralization and 88.77% deproteinization at room temperature. Structural analysis confirms that the HDES preserves α-chitin crystallinity and acetylation, preventing depolymerization and deacetylation typically caused by strong acids and alkalis. Crucially, its hydrophobic character drives efficient phase separation. During chitin extraction, acetic acid is largely consumed in the demineralization step. Upon water addition, proteins and soluble salts partition into the aqueous phase, while the HDES remains as a distinct hydrophobic layer that can be readily recovered. Molecular density profiles reveal that l-menthol and procaine are confined within the hydrophobic region, thereby preventing water-induced disruption of the hydrophobic phase. As a result, the HDES retains stable extraction performance over 5 consecutive cycles, requiring only replenishment of the consumed acetic acid. This work presents an HDES platform that couples high extraction efficacy with repeatable solvent recovery, offering a scalable and sustainable strategy for biomass valorization.