Catalytic Pyrolysis of Low-Density Polyethylene over Alumina-Supported Noble Metal Catalysts

Abstract

The effects of Pt/Al2O3 and Rh/Al2O3 catalysts on the pyrolysis of low-density polyethylene (LDPE) at a temperature of 425 °C and residence time of 1 h was investigated in a batch stainless steel autoclave reactor. Preliminary observations showed that neither catalyst lowered the degradation temperature of LDPE. Generally, the presence of either catalyst influenced the secondary reactions and improved oil component distribution. Compared to the results from the noncatalytic pyrolysis of LDPE under similar conditions, the catalysts appeared to have caused a slight decrease in the proportion of oil product in favor of coke formation, which increased with increasing catalyst loading. The presence of both catalysts altered the composition of gas products, for instance, both catalysts increased the saturated aliphatic gases to up to 90 wt % of total gas product while alkene gases reduced. It appeared that the catalytic activity of the alumina support toward dehydrogenation and aromatization was predominant. The condensation of the aromatic compounds on the catalyst surface led to coke formation. Deactivation of the catalyst occurred after first use due to carbon deposition. Reactivation of the aged catalyst restored most of their physical properties with differences in their catalytic activities compared to fresh catalysts.