Impurity tolerance and effects in catalytic cracking of household mixed plastic waste

Abstract

Chemical recycling is considered as a promising approach for recovering chemical substances from plastic waste for original or other purposes, and catalytic cracking is one of the most efficient processes compared to the other chemical recycling technologies. However, its feasibility for household mixed plastic waste has not been verified given the heterogeneous properties and mixed impurities, and how the impurities affect the process and products is also unclear. In this study, systematic field sampling was conducted and identified the composition and properties of 31 subfractions of household mixed plastic waste. Catalytic cracking experiments and carbon flow analysis were then performed to investigate the effects of various impurities on the yields and compositions of major products. Plastic impurities reduced the yield and carbon content of oil products to a moderate extent, but these effects were not magnified with the increase of the plastic impurity contents. Food waste impurities significantly reduced the oil products by 11 %–18 % and increased the oxygenated compounds and decreased the carbon contents, owing to the water and organic contents in the impurities. Metal impurity had marginal effects to the major products; while paper impurity contents showed a negative correlation with the oil product yields, as well as carbon and alkanes. This study demonstrates the feasibility of catalytic cracking for recycling household mixed plastic waste and its tolerance for most impurities. The results also imply that the removal of food waste impurities is important for ensuring high-quality targeted oil products for further utilization as a substitute of naphtha.