Simultaneous pretreatment and catalytic conversion of polyolefins into hydrocarbon fuels over acidic zeolite catalysts

Abstract

The effect of pre-degradation treatment in catalytic pyrolysis of polymer was assessed using thermogravimetric analysis (TGA) and pyrolysis reactor experiments of different polymers on various catalysts. Intimate contact between the polymer and catalyst was achieved using physical, mechanical and thermal treatments. The results from the TGA analysis show that pre-degradation treatment has greatly improved the performance of the catalyst attaining maximum degradation at lower temperature. Pre-degradation treatment had increased the liquid yield and lowered the coke yield at various extents depending on the catalyst structure and acidity. The ZSM-5 catalyst with high Si/Al ratio showed maximum amount of (C5–C9) and ZSM-5 with lower Si/Al ratio has maximum percentage of (C14–C20). Based on the performance of the pre-degradation treatment methods, normal mixing produced the maximum amount of lighter fractions and therefore pre-degradation treatment can serve to enhance the gasoline fraction while the diesel fraction can be optimised using the co-pressing method, where polymer and catalyst particles were thoroughly mixed and co-pressed together into mixed particles. Coke characterisation showed coke formed by linear low density polyethylene contained more volatile coke components while polypropylene coke had higher percentage of hard coke. ZSM-5 had lower retention of coke components with volatile coke precursors. The volatility of the coke increases while coke concentration and decreases as the catalyst amount decreases. Pre-degradation treatment facilitated the formation of soft coke components that are easy to remove in inert atmosphere.