Parametric Life Cycle Assessment of Chemical Recycling of Nylon-6 to Caprolactam

Chemical recycling is gaining attention to advance the circular economy. This study presents the first life cycle assessment (LCA) of real-world waste polyamide 6 (PA6) remonomerization to caprolactam, evaluating four depolymerization routes: acidic, hydrothermal, alcoholysis, and alkaline. We established an automated Python-Aspen Plus-LCA workflow, systematically mapping variations in PA6 waste composition and key process parameters onto probability distributions of environmental impacts. Results show that the hydrothermal process has the highest impacts in six of nine categories, while the solvent-free, alkaline NaOH route consistently shows the lowest. Despite lower energy demands, the acidic H₃PO₄ process is not environmentally superior to the alcoholysis route. For the hydrothermal route, results are strongly driven by the water-to-feed ratio. However, its global warming potential (GWP) remains above that of fossil-based caprolactam. In contrast, the alcoholysis and acidic processes lower GWP by ∼35%, whereas the NaOH route achieves an ∼80% reduction to 1.46 kg CO₂-eq/kg caprolactam. Although chemical recycling can mitigate impacts, no process consistently meets the net-zero emission carbon budget needed to limit global warming to 1.5 °C. As the NaOH process comes closest to this target and demonstrates the strongest environmental and economic performance, future research should focus on scaling-up solvent-free chemical recycling.