Thermo-catalytic co-pyrolysis of waste plastic and hydrocarbon by-products using β-zeolite

In this study, thermo-catalytic co-pyrolysis of different high-molecular weight hydrocarbon mixtures (Fischer–Tropsch paraffin mixture, heavy residue of waste polyethylene thermal cracking and waste polyethylene from agricultural sector) was studied in a two-zone semi-batch reactor system at 450 °C, using Beta zeolite catalyst. The yields and compositions of co-pyrolysis products were studied depending on feedstock, catalyst and its placement (one or two-step pyrolysis). Some results were compared to our previous work, when catalyst free or thermal pyrolysis was compared with ZSM-5 promoted thermo-catalytic pyrolysis with the same feedstocks and layout as in the present case. It was found that the two-step pyrolysis (placing the Beta-zeolite in the 2nd reactor) resulted more gaseous product with higher hydrogen and methane content. In terms of liquid products, the composition shifted towards the heavy ends, which means that the C₂₁₊ and diesel fuel boiling ranged hydrocarbon content became higher, comparing to the one-step pyrolysis. In terms of feedstock composition, it was concluded that the higher Fischer–Tropsch wax and waste polyethylene contents enhance the gas and gasoline formation, while heavy residue obtained from waste polyethylene pyrolysis contributed to the formation of JET fuel-like hydrocarbons in higher amount if the catalyst were placed in the 1st reactor.