Recently, a team led by Dr. Xiulian Pan, a researcher at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, has made new advancements in the field of plastic catalytic conversion and recycling. They have achieved the coupling and upgrading of carbon dioxide with polyolefin waste plastics under relatively mild conditions to recycle high-value chemicals such as aromatics with high selectivity. The related findings have been published in the National Science Review.
Plastic is an essential synthetic polymer material crucial for modern societal living and industrial production. Addressing the environmental and health impacts of the rapidly increasing plastic waste has become a significant global challenge. Among various plastic products, polyolefins, represented by polyethylene and polypropylene, account for about 55% and are the most produced and consumed plastics. Due to the chemical inertness of polyolefin molecules, they are challenging to degrade under natural conditions. Achieving selective cleavage and recombination of carbon-carbon bonds in polyolefins under relatively mild conditions poses a major challenge in this field.
The schematic diagram of the reaction. Provided by Dalian Institute of Chemical Physics.
The OXZEO catalytic system is an innovative catalyst design concept proposed by Academician Bao Xin and Researcher Pan Xiulian's team in 2016, combining the functional characteristics of metal oxides and zeolite molecular sieves to provide two independent reaction active sites in space. In this work, the team expanded the OXZEO catalytic design concept to the coupling upgrade recycling of carbon dioxide and polyolefin waste plastics, using carbon dioxide as a hydrogen acceptor and converting it into hydrocarbons, promoting the conversion of polyolefins into aromatics. By creating a Pt-modified MnOx-ZSM-5 bifunctional catalyst, the team separated the activation of carbon dioxide and the deconstruction-aromatization of polyolefins active sites on metal/metal oxides and molecular sieves. Under relatively mild conditions of 300°C and 1 MPa, a one-step transformation was achieved to produce high-value chemicals such as aromatics, with an aromatic yield of 64%, including benzene, toluene, and xylene accounting for 60%. The research showed that for every kilogram of polyolefin, 0.2 kilograms of carbon dioxide could be consumed, with 90% of the carbon dioxide converted into aromatic products, while generating 0.64 kilograms of aromatics, 0.28 kilograms of liquefied gas, and naphtha.
The catalytic system designed in this work is applicable to the upgrading recycling of polyethylene, polypropylene, and their plastic products. Moreover, the developed technological route not only selectively produces high-value aromatics from polyolefin waste plastics under relatively mild conditions but also provides a new pathway for the conversion and utilization of carbon dioxide, simultaneously enabling the resource utilization of both polyolefins and carbon dioxide waste.
Related paper information: https://doi.org/10.1093/nsr/nwae097
