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Volume 111
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Pyrolysis of polyolefin plastics under CO2 atmosphere: Reaction behavior and product distribution over a wide temperature range
Qidian Sun, Maoxian Wang, Zhe Fu, Yi Cheng *
Department of Chemical Engineering, Tsinghua University, Beijing, 100084, China
10.1016/j.partic.2026.02.013
Volume 111, April 2026, Pages 253-263
Received 30 December 2025, Revised 6 February 2026, Accepted 18 February 2026, Available online 6 March 2026, Version of Record 13 March 2026.
E-mail: yicheng@tsinghua.edu.cn
Highlights

• Temperature governs gaseous product distribution during polyolefin pyrolysis.

• At moderate temperatures the introduction of CO2 reduces light olefin yields by promoting secondary reactions.

• Near-complete conversion into CO is realized when the second-stage temperature exceeds 1500 °C.


Abstract

Chemical recycling of polyolefin plastics is a key approach to mitigating plastic pollution and enabling carbon resource circularity. In this work, the pyrolysis behaviors and product distributions of polyethylene (PE) and polypropylene (PP) are systematically investigated under N2 and CO2 atmospheres over a wide temperature range of 500–1600 °C using thermogravimetric analysis (TGA) and a two-stage tubular reactor. TGA results indicate that below 500 °C, CO2 behaves similarly to N2 as a physically inert carrier gas and does not affect the primary thermal decomposition of polyolefins. Two-stage pyrolysis experiments reveal the temperature thresholds for the chemical activation of CO2, at which CO2 starts to participate in reactions with pyrolysis intermediates, occurring at approximately 900 °C for PP and 1100 °C for PE, as evidenced by the formation of CO. Within the temperature range of 800–1000 °C, light olefins such as ethylene and propylene dominate the gaseous products; however, the introduction of CO2 leads to a slight decrease in light olefin yields compared with those obtained under N2. At higher temperatures of 1100–1400 °C, light olefins undergo extensive secondary cracking and reforming reactions, resulting in a pronounced shift of products toward syngas, accompanied by significant solid carbon deposition. When the temperature is further increased above 1500 °C, carbon deposition is effectively eliminated, and near-complete conversion of PE and PP into syngas, predominantly CO, is achieved. These results demonstrate the feasibility of switching product selectivity from light olefin recovery to syngas production within a single reaction system through temperature regulation, providing important insights for the design of high-value chemical recycling processes for waste polyolefin plastics.

Graphical abstract
Keywords
Polyolefin plastics; Pyrolysis; CO2 atmosphere; Light olefins; Syngas
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