Catalytic pyrolysis of polyethylene

The influence of zeolite catalytic upgrading of the pyrolysis gases derived from the pyrolysis of polyethylene has been investigated. The yield and composition of the derived hydrocarbon gases and oils have been investigated in terms of the temperature of the catalyst. Polyethylene was pyrolysed in a fixed bed reactor and the pyrolysis gases passed to a secondary reactor containing Y-zeolite or zeolite ZSM-5 catalyst. The polyethylene was pyrolysed at 500°C and the temperature of the catalyst bed was 400, 450, 500, 550 or 600°C. The oils consisted of mainly aliphatic compounds represented by alkadiene, alkene and alkane hydrocarbons and their branched chain derivatives. The uncatalysed pyrolysis oil also contained low concentrations of aromatic hydrocarbons. After catalysis there was a marked increase in the concentration of aromatic compounds in the oil, which further increased in concentration as the temperature of catalysis was raised. The single ring compounds consisted of mainly toluene, ethylbenzene and xylenes and the two and three ring compounds were mainly, naphthalene and phenanthrene and their methyl derivatives. The Y-zeolite produced significantly greater concentration of aromatic hydrocarbons in the derived oils compared to when zeolite ZSM-5 catalyst was used.