Catalytic cracking of heavy fractions from the pyrolysis of waste HDPE and PP

•Pyrolysis of automotive waste HDPE and PP plastics.•Preparation of distillation ends from HDPE and PP pyro-oils.•Catalytic cracking of HDPE-wax and PP-wax in MAT.•Comparison of cracking products of linear and branched polymer-waxes.•HDPE-wax increases gas-yield while PP-wax increases gasoline-yield.

In the present paper, automotive waste plastics were considered as a potential source of fuels and chemicals. The feedstock in the experimental tests was represented by the heaviest fractions from the distillation of pyro-oil from the pyrolysis of high-density polyethylene (HDPE-wax) and polypropylene (PP-wax). Due to their very high viscosity both polymer-waxes were, prior to processing, diluted in atmospheric gas oil (GO). Mixtures with hydrotreated vacuum gas oil (HVGO) were also prepared and processed under simulated fluid catalytic cracking conditions via a MAT-test. The product distribution was similar to the one shown by the commercial FCC process: light gases (C1, C2), LPG, gasoline fraction, light and heavy cycle oil. To maintain optimal performance a commercial FCC equilibrium catalyst (FCC-ECAT) was used. When processing HDPE and PP waxes, high yields of profiling products - propylene and gasoline were obtained. In the case of the PP-wax feed without HVGO, the yield of gasoline was even higher than in case of pure HVGO. When cracking HDPE-wax feed mixtures the product distribution was oriented more towards the production of propylene. The composition of liquid products considering all types of feedstock consisted mainly of iso-alkanes and aromatics. The calculated values of microactivity for the HDPE-wax and PP-wax feedstock, with or without HVGO, were significantly higher than in the case of pure HVGO.