Exploring the potential of hydrothermal waxes derived from polyethylene: Product characterization and insights from solvent effects

Abstract

The accumulation of plastic waste poses a serious environmental challenge, and their traditional disposal methods became insufficient. The autoclave hydrothermal processing method, employing supercritical water as a solvent, offers notable advantages for plastic pyrolysis, including high conversion efficiency and superior product yield.The main objective of this study is to enhance the characterisation of wax product from hydrothermal conversion of PE plastic, thereby facilitating research into heavy hydrocarbons outside the gasoline and diesel range. Thus, the impact of temperature and polar solvent on the product distribution have been profoundly examined. The findings demonstrate that at temperatures below 420°C, the hydrothermal wax displays a hardness comparable to paraffin and is insoluble in conventional solvents. The addition of polar solvents enhanced the efficiency of PE chain scission, whereas the presence of oxygen broadened the product distribution. Ethanol induced chemical cyclisation in the hydrothermal wax, resulting in the formation of liquid aromatic compounds (25.96%). In contrast, acetic acid resulted in the softening of the wax, leading to the production of a higher proportion of light hydrocarbons (83.2%). The characteristics of hydrothermal wax were analysed using thermogravimetric analysis (TG), gas chromatography-mass spectrometry (GC-MS), Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H NMR) and carbon nuclear magnetic resonance (13C NMR). Finally, the molecular formulas were validated through the use of heteronuclear multiple bond correlation (HMBC) spectroscopy.