Impurity sulfate produced in upstream process of nylon 54 salt (cadaverine succinate) are significantly impacting the product quality. In the present study, we elucidated the mechanism underlying the crystallization of the nylon 54 salt; using sulfate ions as the only inorganic impurity before crystallized nylon 54 salt, we revealed the principles underlying their impact. Specifically, sulfate ions profoundly affect the thermodynamics and kinetics of nylon 54 salt crystallization. The solubility of the monomer salt decreased. At 288.15 K, the solid-liquid interfacial energy, critical nucleation radius, and Gibbs free energy increased 0.104 mJ . m −2 , 2.890 × 10 −10 m, and 9.668 × 10 −22 J respectively. The increased nucleation barrier further hinders the crystallization of nylon 54 salt. Molecular dynamics simulations reveal that sulfate impurities reduce molecular diffusion, enhance hydrogen bond formation, increase intermolecular and overall interaction energy. Thus, our study provides valuable insights into the one-step separation of bio-based cadaverine and succinic acid in a coproduction system.
Nylon 54 is a novel, biodegradable polyamide with excellent thermal resistance and water absorption properties. It can be polymerized using bio-based cadaverine and succinic acid as monomers. Traditional separation methods isolate individual monomers from the fermentation broth through acidification or alkalization, resulting in significant amounts of waste salts; however, synchronous separation of dibasic acids and diamines has not been reported. This study investigated an integrated process for the separation and extraction of nylon 54 salts from a co-fermentation broth without acidification or alkalization. We meticulously optimized the operational parameters of the integrated process to achieve maximum separation efficiency. Following microfiltration, ultrafiltration, and decolorization, the bacterial eliminating rate was ≥99.83%, and the protein concentration was ≤40 mg/L. The absorbance of the decolorized solution was ≤0.021 at 430 nm, and the recovery rate of nylon 54 salt reached 97%. Then, the pretreated solution was passed through sequential chromatographic columns, which effectively removed organic acid by-products (such as acetic acid and lactic acid), SO42−, and NH4+ from the fermentation broth, resulting in a cadaverine yield of 98.01% and a succinic acid yield of 89.35%. Finally, by concentrating and crystallizing the eluent, the simulated fermentation broth yielded nylon 54 salt with a purity of 99.16% and a recovery rate of 58%, and the real fermentation broth yielded nylon 54 salt with a purity of 98.10% and a recovery rate of 56.21%. This integrated process offers a sustainable and environmentally friendly pathway for the complete biosynthesis of nylon 54 salt and has the potential to be extended to the preparation of other nylon salts.
危险品化学品经营许可证（带存储）