Catalytic degradation of polyethylene and polypropylene into liquid hydrocarbons with mesoporous silica

The catalytic degradation of polyolefinic polymers such as polyethylene (PE) and polypropylene (PP) was carried out at atmospheric pressure by batch operation at 430°C and 380°C using non-acidic mesoporous silica catalyst (FSM). A comparison with non-catalytic thermal degradation and catalytic degradation using solid acid catalysts (silica-alumina, zeolite ZSM-5), silicalite, and silica-gel was made. Compared with thermal degradation, non-acidic FSM catalyst accelerated the initial rate of degradation, increased the liquid product yield and promoted degradation into lower molecular weight products. Silicalite and silica-gel had very negligible effects on polymer degradation. When the batch reaction was repeated four times using the same FSM catalyst, the extent of the decline in the degradation rate was lower for PE than PP. Compared with the solid acid catalyst, which turned completely black in the cases of both PE and PP, the deposition of coke on the used FSM catalyst was extremely slight. It seems likely that the catalytic effect of FSM for polyolefinic polymer degradation is related more to the hexagonal pore structure system of FSM.