Copyrolysis of naphtha with polyalkene cracking products; the influence of polyalkene mixtures composition on product distribution

The steam cracking (copyrolysis) of naphtha with oils/waxes from thermal decomposition of polyalkenes has been investigated as a process for chemical recycling of plastic wastes. High-density polyethylene (HDPE), two-component mixture (LDPE/PP) and three-component mixture (HDPE/LDPE/PP) were thermally decomposed in a batch reactor at 450 °C, thus forming oil/wax products. Subsequently, these products were dissolved in heavy naphtha in the amount of 10 mass% to obtain steam cracking feedstock. The composition of gaseous and liquid products during copyrolysis was studied at 780 °C and 820 °C in dependence on residence time from 0.08 s to 0.51 s. The obtained results were compared with the product composition from steam cracking of naphtha at identical experimental conditions. The decomposition of polyalkene oils/waxes during copyrolysis was confirmed on the basis of analysis of liquid products. It was shown that more ethene and propene was formed during copyrolysis of oil/wax from HDPE in comparison with naphtha and both mixtures and so oil/wax from HDPE seems to be favourable component of steam cracking feedstock. There were slight differences between product compositions from copyrolysis of two- and three-component mixtures. The presence of HDPE in three-component mixture supported formation of gas and ethene. The presence of oil/wax form PP enhanced formation of propene and branched alkenes. For both type of polyalkenic mixtures the yields of desired low molecular alkenes and alkanes were higher or approximately the same as from naphtha. The results confirm suitability of oils/waxes from polyalkenes as a co-feed for steam cracking units.