Effect of pyrolysis operating conditions on the catalytic co-pyrolysis of low-density polyethylene and polyethylene terephthalate with zeolite catalysts

In this study, the catalytic (co-)pyrolysis of low-density polyethylene (LDPE) and polyethylene terephthalate (PET) with HZSM-5 and HY zeolite catalysts was conducted in a micro-pyrolysis reactor coupled to a two-dimensional gas chromatography system. Pyrolysis operating conditions, such as the pyrolysis temperature, the catalyst to feedstock (CF) ratio, and the LDPE:PET ratio, were varied. It was found that for the co-pyrolysis of LDPE and PET, HZSM-5 led to higher yields of C2-C4 olefins and monoaromatic products. Lower CF ratios increased the yield of C2-C4 olefins for LDPE pyrolysis, but decreased benzene yield for PET pyrolysis, concomitant with an increased yield in benzoic acid. A lower temperature of 400°C which was sufficient for the pyrolysis of LDPE, led to incomplete conversion of PET. Surface response diagrams were used to visualize the impact of the various pyrolysis operating conditions on the yield of C2-C4 olefins and BTEX, which serve as target products for the circular economy.