CO2-facilitated upcycling of polyolefin plastics to aromatics at low temperature

Yi Ding; Shuchi Zhang; Cheng Liu; Yu Shao; Xiulian Pan; Xinhe Bao

doi:10.1093/nsr/nwae097

CO₂-facilitated upcycling of polyolefin plastics to aromatics at low temperature

Natl Sci Rev. 2024 Mar 15;11(5):nwae097. doi: 10.1093/nsr/nwae097. eCollection 2024 May.

Authors

Yi Ding¹, Shuchi Zhang^{1

2}, Cheng Liu^{1

2}, Yu Shao^{1

3}, Xiulian Pan¹, Xinhe Bao^{1

3}

Affiliations

¹ State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
² University of Chinese Academy of Sciences, Beijing 100049, China.
³ Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China.

Abstract

Plastics are one of the most produced synthetic materials and largest commodities, used in numerous sectors of human life. To upcycle waste plastics into value-added chemicals is a global challenge. Despite significant progress in pyrolysis and hydrocracking, which mainly leads to the formation of pyrolysis oil, catalytic upcycling to value-added aromatics, including benzene, toluene and xylene (BTX), in one step, is still limited by high reaction temperatures (>500°C) and a low yield. We report herein CO₂-facilitated upcycling of polyolefins and their plastic products to aromatics below 300°C, enabled by a bifunctional Pt/MnO_x-ZSM-5 catalyst. ZSM-5 catalyzes cracking of polyolefins and aromatization, generating hydrogen at the same time, while Pt/MnO_x catalyzes the reaction of hydrogen with CO₂, consequently driving the reaction towards aromatization. Isotope experiments reveal that 0.2 kg CO₂ is consumed per 1.0 kg polyethylene and 90% of the consumed CO₂ is incorporated into the aromatic products. Furthermore, this new process yields 0.63 kg aromatics (BTX accounting for 60%), comparing favorably with the conventional pyrolysis or hydrocracking processes, which produce only 0.33 kg aromatics. In this way, both plastic waste and the greenhouse gas CO₂ are turned into carbon resources, providing a new strategy for combined waste plastics upcycling and carbon dioxide utilization.

Keywords: aromatics; bifunctional catalysis; carbon dioxide; polyolefins; upcycling.