Enhancement of catalytic combustion and thermolysis for treating polyethylene plastic waste

Polyethylene (PE) occupies a large proportion in waste plastics, while its natural degradation rate is slow, if without timely recycling treatment, which would directly lead to serious ecological and environmental problems. Incineration and thermolysis methods based on thermochemical conversion are commonly used effective ways for the treatment of plastic waste, which presented the advantages of high efficiency and low pollution. In this paper, cone calorimeter and tubular thermolysis furnace-mass spectrometer (MS) combination platform were applied for the catalytical combustion and thermolysis characteristics of PE with three kinds of catalysts, which were H-Zeolite Standard Oil Corporation Of New York (Socony) Mobil-Five (HZSM-5), H-ultra stable Y zeolite (HUSY), and Mobil Composition of Matters-41 (MCM-41), respectively. Under the effect of MCM-41, the heat release rate (HRR) of samples under different heat flux (25, 35, 45 kW/m(2)) was decreased by 59.7%, 48.8%, and 46.6%, and the time to peak HRR was advanced in 60 s, 27 s, and 10 s, respectively. Therefore, the burning efficiency could be controlled and the fire risk would be declined with the addition of catalysts. With the increase of the catalyst pore diameter, the combustion efficiency was enhanced, while rising incineration temperature would not necessarily mean an increase in combustion efficiency. During thermolysis, HZSM-5 was most effective catalyst for the conversion of PE to alkenes and aromatic hydrocarbons (AHs) such as benzene, toluene, and xylene (BTX). Among the three catalysts, the microporous HZSM-5 showed higher catalytic performance due to its strong acidity and suitable pore structure. This work enriches the combustion and thermolysis mechanism of PE, and provides reference and basis for the design of waste plastic recycling processing.

Automated summary

Polyethylene (PE) is a major component of waste plastics with slow natural degradation. Incineration and thermolysis are effective methods for plastic waste treatment. The addition of catalysts like MCM-41 can control burning efficiency and reduce fire risks. HZSM-5 is the most effective catalyst for the conversion of PE to aromatic hydrocarbons.