Research progress and challenges in the upcycling of polyolefin plastics through chemical oxidation

Polyolefin plastics are widely used in daily life and industrial production due to their excellent performance and low cost. However, the massive disposal of used plastics poses a significant challenge to the environment and resources. Traditional methods such as landfilling, incineration, and mechanical recycling are difficult to meet the demands of “carbon peaking and carbon neutrality goals” and “resource recycling”. Converting waste polyolefin plastics into high-value chemicals through chemical recycling is an important way to address plastic environmental pollution and promote carbon resource recycling. Significant progress has been made in recent years. This article reviews the important progress made in the research on the chemical oxidation upgrading recycling of polyolefin plastics in recent years, summarizing the relevant research results including thermal catalytic oxidation, photocatalytic oxidation, photo-thermal catalysis, and electrocatalytic oxidation, and discusses the reaction mechanisms. Thermal catalytic oxidation technology can convert polyolefins into oxygen-containing high-value compounds under milder conditions. The oxidants evolved from early nitric oxide and nitric acid to green oxidants such as air and hydrogen peroxide, with corresponding reaction conditions becoming increasingly mild. The obtained chemicals have evolved from short-chain products to high-value long-chain dicarboxylic acids, and with the development of efficient catalysts, product selectivity has gradually increased, but there is still a gap in achieving the goal of obtaining a single high-value product. Photocatalytic oxidation technology uses electrons and holes generated under light exposure to convert plastics into small molecular substances, with products evolving from carbon dioxide to small organic acids and hydrocarbons, and the selectivity and added value of the products are continuously improving. This method has the obvious advantages of being environmentally friendly and having mild conditions, but the reaction efficiency and product selectivity need to be improved. Photo-thermal catalytic technology combines the advantages of photocatalysis and thermal catalysis, promoting the oxidation reaction of polyolefins through photo-thermal effects, with many applications in the dechlorination of polyvinyl chloride and the upgrading recycling of polystyrene. Electrocatalytic oxidation technology produces strong oxidizing substances through electrochemical methods, oxidizing polyolefins into organic acids; this method is carried out at lower temperatures and pressures. The current state of research in both photo-thermal catalysis and electrocatalysis is rather constrained, necessitating further advancements in the development of efficient catalysts and a deeper comprehension of the underlying mechanisms. Despite the encouraging progress made in the chemical oxidation upgrading recycling technology of polyolefin plastics, challenges still exist in the development of high-performance catalysts, in-depth understanding of reaction mechanisms, and the feasibility of reaction scale-up. Future research needs to focus on solving these problems to promote the practical application of plastic oxidation upcycling, achieve high-value recycling of waste plastics, and sustainable development of the environment.