With the substantial increase in global plastic consumption over the past 50 y, society faces the challenges of managing and recovering resources from considerable amounts of plastic waste. A promising strategy for use in addressing this problem is to upcycle plastic waste into valuable materials via thermochemical conversion, and hydrothermal liquefaction, which uses low-cost and green H2O, has attracted attention as a sustainable technology. In this study, we introduced an aquathermolysis system using oil-soluble Fe-2-ethylhexanoate (Fe-2EH) as a catalyst precursor under superheated steam conditions to convert highly contaminated polyolefin plastic waste to liquid fuel. The excellent dispersibility and decomposition behavior of Fe-2EH facilitated the formation of highly dispersed in situ Fe-based catalysts, enabling their involvement in the early stages of aquathermolysis. The presence of H2O and the in situ catalyst significantly promoted the decomposition of C–X bonds (X = Cl, S, N, or O) rather than C–C bonds, and C–C cleavage was driven by thermal energy. Moreover, the presence of H2O with the catalysts reduced the proportion of non-paraffinic products, including olefins and aromatics that cause char/coke formation. During the reaction, the in situ catalyst particles comprised nanosized Fe oxide cores with Fe hydroxide-rich surfaces, preventing the accumulation of metal contaminants. Based on deuterium tracing studies, the H transfer index of the catalyst was closely related to the catalytic performance. These results indicated that catalytic aquathermolysis using Fe-2EH is an efficient system for use in improving product quality by effectively removing contaminants and suppressing char/coke formation.
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