Energy-efficient eco-friendly marine waste treatment: Recovery of caprolactam from fishing net waste using seashell-derived catalyst

Fishing net waste (FNW) is marine waste having significantly negative effects on the marine environment and ultimately human health. Herein, we endeavored to use a catalyst made from seashells for the recovery of caprolactam (CPL) from FNW (made of polyamide 6; free of any other materials like floats, lead lines, and sand) via a catalytic pyrolysis under CO2 atmosphere. The catalytic pyrolysis of FNW in CO2 over the seashell-derived catalyst yielded 77.7 wt% CPL at 500 °C. It was simulated on a large-scale based on data from laboratory-scale experiments, and energy analysis and life-cycle assessment (LCA) were carried out. The proposed integrated process consists of three steps: FNW-to-CPL conversion via catalytic pyrolysis, CPL recovery, and heat and power production. An effective separation process consisting of in series of flash and distillation columns was designed by considering the characteristics of resulting mixture, and the overall process allows the production of CPL from FNW with a high yield (74.3 %). This value is only 3.4 % point lower than the experimental yield of CPL (77.7 %), and the energy requirements (0.21 MW heating energy) are met internally. The results of the LCA suggest that the proposed strategy can help solve the problem of marine pollution from debris such as FNW.