Aromatic fuel oils produced from the pyrolysis-catalysis of polyethylene plastic with metal-impregnated zeolite catalysts

Pyrolysis-catalysis of high density polyethylene (HPDE) was carried out in a fixed bed, two stage reactor for the production of upgraded aromatic pyrolysis oils. The catalysts investigated were Y-zeolite impregnated with transition metal promoters with 1 wt.% and 5 wt.% metal loading of Ni, Fe, Mo, Ga, Ru and Co to determine the influence on aromatic fuel composition. Pyrolysis of the HDPE took place at 600 °C in the first stage of the reactor system and the evolved pyrolysis gases were passed to the second stage catalytic reactor, which had been pre-heated to 600 °C. Loading of metals on the Y-zeolite catalyst led to a higher production of aromatic hydrocarbons in the product oil with greater concentration of single ring aromatic hydrocarbons produced. The single ring aromatic compounds consisted of mainly toluene, ethylbenzene and xylenes, while the 2-ring hydrocarbons were mainly naphthalene and their alkylated derivatives. There was a reduction in the production of multiple ring aromatic compounds such as, phenanthrene and pyrene. The addition of the promoter metals appeared to have only a small influence on aromatic oil content, but increased the hydrogen yield from the HDPE. However, there was significant carbon deposition on the catalysts in the range 14-22 wt.% for the 1% metal-Y-zeolite catalysts and increased to 18-26 wt.% for the 5 wt.% metal-Y-zeolite catalysts.