Low-temperature treatment of waste crosslinked polyethylene with ruthenium catalyst

Abstract

A method of processing of waste cross-linked polyethylene (PEX) by low-temperature pyrolysis with a Ru/Al2O3 catalyst was developed. The catalyst used, even in a small amount, significantly supported the splitting of the PEX structure, so that the yield of the key product, oil, reached 90%. Further, an energy gas with a HHV of 48.5 MJ/kg was obtained, suitable for further use. The minority products were paraffin and a solid carbonaceous residue. A mass and energy balances of the process and their comparison with those without a catalyst were carried out. In the case of catalyzed pyrolysis, it was found that 96.5% of the energy content of the starting raw material was preserved in the products with a high utility value. More in details, the ruthenium catalyst favorably affected the low-temperature pyrolysis of waste PEX, as the amount of main product, oil, obtained with the catalyst was clearly higher (90%) compared to the amount of oil obtained without one (85%). The composition of the pyrolysis gas was also favorably influenced by the ruthenium catalyst as the gaseous hydrocarbon contents were significantly higher compared to those of uncatalyzed pyrolysis. A small amount of Ru was needed for such effects, since the Ru/PEX ratio was 0.75/100 (g/g). This fact compensates, or at least partially, the relatively high price of this catalyst compared to, for example, nickel-based or FCC catalysts. Minority products, paraffin and solid carbon residue are well usable in practice. Paraffin is a necessary substance in a number of industries (medicine, cosmetics, wood impregnation, construction, candle production, skiing wax production); the solid carbonaceous residue can be used as clean sulfur-free and low-ash fuel.