Hydrothermal processing of polyethylene in superheated steam and supercritical water into fuels and chemicals

作者：Daniel Lachos‐Perez, Kalsoom Jan, Evan Yu, Akash Patil, Wan‐Ting Chen · 发表于：Energy Conversion and Management · 年份：2024 · DOI：10.1016/j.enconman.2024.119355 · 被引用次数：17 · 研究领域：Subcritical and Supercritical Water Processes、Thermochemical Biomass Conversion Processes、Catalysts for Methane Reforming

This study aims to elucidate the mass transfer behavior and reaction mechanisms governing the depolymerization of polyethylene (PE) during hydrothermal processing (HTP). It specifically focuses on the comparative effects of superheated steam (SHS, defined as water heated beyond its boiling point at a given pressure without undergoing condensation) and supercritical water (SCW, formed above the critical point of water) conditions on PE depolymerization, providing an unprecedented analysis of these two environments. The effects of pressure ranging from 5.5 to 23 MPa, polymer concentrations between 30–83 wt%, and temperatures of 425 and 450 °C. The oil, gas, and solid products obtained were analyzed by quantifying their total yields, and the chemical compositions of the oil, aqueous phase products and gas were analyzed using gas chromatography mass spectrometry (GC–MS) and gas chromatography coupled to a thermal conductivity detector (GC-TCD) respectively. The results show comparable oil yields (∼83 %) between reactions conducted at lower pressures with SHS and those operated at 23 MPa with SCW. Notably, the chemical composition of the oils − primarily olefins and paraffins − remained identical regardless of changes in pressure; the same was observed when increasing polymer concentration under conditions with SHS. At higher temperatures (450 °C), complete conversion of PE into valuable chemicals, including benzene, toluene, ethylbenzene, and xylene (BTEX) in the oil was observed...