Dissolving and Efficient Fractionation of Chitin and Synchronous Preparation of Calcium Lactate from Crayfish Shell Waste Using Amino Acid-Based Deep Eutectic Solvents

Chitin is a natural biomass material with wide sources and high application potential, but the solvents for dissolving chitin are very limited. In this work, ternary alkaline deep eutectic solvents (DESs) containing amino acids, urea, and 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) were prepared, which can successfully achieve the dissolution of chitin and can be recycled. By adjusting the type of amino acids and the amount of DBU, the maximum solubility of chitin can reach 6.0 wt %. In addition, unlike the reported acidic DES system, this new ternary alkaline DES not only efficiently extracted chitin from crayfish shell waste but also efficiently prepared calcium lactate (CL), which successfully realized the effective recycling of calcium resources. Through 11 sets of extraction conditions, proteins in the crayfish shell were effectively removed, and the yields of chitin and CL remained above 85 and 90%, respectively. Finally, chitin nanofibers were successfully prepared by ultrasonic treatment with extracted regenerated chitin. Further processing of the chitin nanofibers can yield chitin films with high transparency and high tensile strength (63.2 MPa). It provides a novel DES system to dissolve chitin and an environmentally friendly utilization strategy to efficiently extract chitin and prepare CL from crayfish shell waste, thereby producing high-performance functional materials.