Enhancing\nRecycling of Polyamide 6 and Polyethylene\nMultilayer Plastics through Sequential Hydrothermal Liquefaction

This study investigates the optimization of hydrothermal\nliquefaction\n(HTL) for the chemical recycling of polyamide 6 (PA6) and polyethylene\n(PE) multilayer plastic films. A two-step HTL process was employed\nusing subcritical water to selectively depolymerize PA6 into caprolactam,\nfollowed by supercritical water to convert PE into hydrocarbons. Experiments\non raw PA6 yielded up to 88 wt % caprolactam under optimized conditions\n(325 °C, 30 min). In the two-step process, caprolactam recovery\nfrom multilayer films approached 100%. Supercritical HTL produced\noil yields of 44–61 wt % from PE. The carbon and nitrogen balances demonstrated\nefficient recovery of hydrocarbons and nitrogen removal. These results\nsuggest the feasibility of integrating this process into existing\nplastic waste recycling frameworks.