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 traditional disposal methods have become insufficient. The autoclave hydrothermal processing method, employing supercritical liquid as a solvent, offers notable advantages for plastic thermal decomposition, including high conversion efficiency and superior product yield. The main objective of this study is to explore the characteristics of wax products derived from the hydrothermal conversion of LDPE plastic, thereby facilitating research into heavy hydrocarbons outside the range of petrol fuel. Thus, the impact of temperature and polar solvent on the product distribution has been profoundly examined. The findings show that at temperatures below 420 °C, the hydrothermal wax displays a hardness comparable to paraffin and is insoluble in conventional solvents. The solid wax product yield reaches 98.8 % at 425 °C, representing the optimal result among all tested conditions. The addition of polar solvents enhance the efficiency of LDPE chain scission, whereas the presence of oxygen broadens the distribution of oxygenated products. Adding 100 % ethanol solvent results in 78 % liquid phase and 22 % gas phase, while adding 100 % acetic acid results in a reduction of carbon chains from 22.2 to 15.3. Ethanol-induced chemical cyclization in the hydrothermal wax resulted in the formation of liquid aromatic compounds (25.96 %). In contrast, acetic acid led to further cracking of the wax, leading to the production of a higher proportion of light hydrocarbons (83.2 %).