Hydrothermal Liquefaction of Mixed Plastic Waste for Heavy Oil Production and Chemical Feedstock Recovery

Abstract

The rapid accumulation of mixed plastic waste has created significant environmental challenges, necessitating the development of sustainable waste-to-resource conversion technologies. This study investigates the hydrothermal liquefaction (HTL) of mixed plastic waste for the production of heavy oil and recovery of valuable chemical feedstocks under high-temperature and high-pressure conditions. The process utilizes subcritical and near-critical water environments to promote thermal decomposition and depolymerization of plastic materials into energy-rich liquid products. Experimental analyses were conducted to evaluate the influence of reaction temperature, residence time, pressure, catalyst presence, and feedstock composition on product yield, oil quality, and chemical composition. Results demonstrated that hydrothermal liquefaction effectively converts mixed plastic waste into heavy oil with high calorific value and significant hydrocarbon content suitable for further refining and industrial utilization. The process also enabled the recovery of useful chemical feedstocks, including aromatic compounds, light hydrocarbons, and oxygenated intermediates, contributing to resource valorization and circular economy objectives. Product characterization revealed that optimized operating conditions improved oil stability, reduced solid residue formation, and enhanced conversion efficiency. Kinetic and thermochemical analyses indicated that polymer degradation mechanisms are strongly influenced by process temperature and water-mediated reaction pathways. Compared with conventional thermal pyrolysis, hydrothermal liquefaction exhibited improved heat transfer characteristics and lower environmental impact due to reduced emission generation and efficient handling of mixed plastic streams. The findings highlight the potential of HTL as an economically viable and environmentally sustainable approach for plastic waste management, renewable fuel production, and recovery of value-added chemical feedstocks for industrial applications.