Recycling of low-density polyethylene and polypropylene via copyrolysis of polyalkene oil/waxes with naphtha: product distribution and coke formation

摘要

The thermal decomposition of polyalkenes was investigated as a recycling route for the production of petrochemical feedstock. Low-density polyethylene (LDPE) and polypropylene (PP) were thermally decomposed individually in a batch reactor at 450℃, thus forming oil/ wax products. Then these products were dissolved in primary heavy naphtha to obtain steam cracking feedstock. The selectivity and kinetics of copyrolysis for 10 mass% solutions of oil/waxes from LDPE or PP with naphtha in the temperature range from 740 to 820℃ at residence times from 0.09 to 0.54 s were studied. The decomposition of polyalkene oil/waxes during copyrolysis was confirmed. It was shown that the yields of the desired alkenes (ethene, propene), according to polymer type, increased or only slightly decreased compared to the yields from naphtha. In addition to the primary reactions, the secondary reactions leading to coke formation have also been studied. The formation of coke during copyrolysis of LDPE wax with naphtha was comparable to the coking of pure naphtha. Slightly higher formation of coke was obtained at PP wax solution at the beginning of the measurements, on the clean surface of the reactor. After a thin layer of coke covered the walls, the production was the same as that from naphtha. The results confirm the possibility of polyalkenes recycling via the copyrolysis of polyalkene oils and waxes with conventional liquid steam cracking feedstocks on already existing industrial ethylene units.