Production of low molecular oil from typical polyolefin plastics through molten salts thermal treatment

Abstract

The resource recovery based on pyrolysis has become the mainstream disposal method for polyolefin plastics in recent years. However, the poor heat transfer characteristics and uneven temperature distribution of plastics lead to inferior product quality. To address these problems, molten salts thermal treatment was performed to conduct targeted regulation of the process. It revealed that the excellent heat storage and thermal conductivity of molten salts provide a strengthened heat source for plastics, promoting product homogenization and high-value conversion. It reduced the energy barrier of the reaction and prompted the conversion of macromolecular components to light oil. Meanwhile, the catalysis of alkali metal salts effectively inhibited the transition cracking of major oil components. The yield of pyrolysis oil increased while the valuable products gradually accumulated, such as α-olefins (ranging from 26.48 % to 31.06 %) and styrene (ranging from 48.89 % to 64.03 %). Additionally, the kinetics of hydrogen could be used to analyze the dynamic processes of plastic pyrolysis well and the activation energy was significantly reduced with molten salts. The contracting volume model was considered to be the most suitable reaction model, providing critical insight for the thermal treatment of plastics at larger scales.