Marine chitin valorization by ionic liquids and deep eutectic solvents: Dissolution, green extraction and conversion

Worldwide, marine shell waste generated from the seafood industry has emerged as a significant environmental challenge. Indeed, this shell waste represents an abundant source of various valuable products, particularly chitin. However, the extraction and subsequent processing of chitin are hindered by the inherently resistant structure of these chitin-rich feedstocks, coupled with strong hydrogen bonding between chitin chains. Recently, the application of ionic liquids (ILs) and deep eutectic solvents (DESs) for the extraction and processing of chitin has garnered significant attention, owing to their sustainable nature, low toxicity, and the potential for reusability. This review systematically illustrates the recent progress in the use of ILs and DESs for the dissolution and green extraction of chitin. The fabrication strategies of chitin-based derivative materials in ILs are also illustrated. Emphases are placed on conversion of chitin into high-value chemicals with the assistance of ILs/DESs, including N-containing compounds (3-acetamido-5-acetylfuran, 3A5AF) and nitrogen-free chemicals [5-hydroxymethylfurfural (5-HMF) and levulinic acid (LA)]. The fundamental principles, current challenges, and prospects in this field are demonstrated. This review should benefit the community for a systematic understanding of the chitin chemistry and conversion.