Energy recovery from cross-linked polyethylene wastes using pyrolysis and CO2 assisted gasification

High-temperature gasification is an attractive alternative technology for clean energy production from plastic wastes and provides a sustainable pathway for their disposal. Waste cross-linked polyethylene (XLPE) offers good potential energy recovery source because of its high energy density of around 47 MJ/kg that can be converted to syngas using pyrolysis or gasification. CO2 assisted gasification can provide clean and efficient syngas that can be converted further to valuable products. This can effectively decrease the carbon foot-print from the utilization of polyethylene wastes. This paper examines pyrolysis and CO2 assisted gasification of XLPE waste with focus on the kinetics, product yield and syngas yield properties (yield of carbon monoxide, hydrogen, and hydrocarbon) at different temperatures. Pyrolysis experiments were carried out to estimate the impact of the gasifying agent over pyrolysis. Pyrolysis and CO2 assisted gasification were conducted at several temperatures in the range 973 K to 1173 K in steps of 50 K. The results were compared with high-, medium-, low-density polyethylene as well as ultra-high molecular weight polyethylene. Higher temperatures provided increased syngas yields from pyrolysis. The activation energy of pyrolysis from single-step kinetic analysis of TGA data revealed increases with an increase in branching and cross-linking. The reaction profiles of the single step of all the samples (except medium density polyethylene) were found to be closely represented by the Avrami-Erofeev models. Results also revealed that gasification generated more syngas, hydrogen, and energy than pyrolysis. Gasification consumed the CO2 to generate syngas with a mass-specific heating value similar to natural gas suggesting efficient utilization of both CO2 and XLPEs for clean and efficient energy production.