Production of C₅-C₁₂ olefins by catalytic pyrolysis of low-density polyethylene with MCM-41 in CO₂/N₂

The current high volume of plastic waste, but low recycling rate, has led to environmental pollution and wasted energy. Greenhouse gas CO₂ can facilitate thermal cracking to dehydrogenate waste plastics, and has potential value for producing olefins. In this work, the pyrolysis properties of low-density polyethylene (LDPE) were studied by thermogravimetric analysis and Py-GC/MS. The effect of the pyrolysis atmosphere, using N₂ or CO₂, with various MCM-41 catalyst ratios on pyrolysis product distribution, were investigated. The experimental results show that the olefin selectivity under a N₂ atmosphere was from 30.32 % to 44.66 % which increased as the MCM-41 catalyst was increased. Under a CO₂ atmosphere, the olefin selectivity reached a maximum of 60.39 %. The Boudouard reaction was also enhanced by the introduction of CO₂. The carbon content of the subdivided olefins showed that in CO₂, the promotion of C₅-C₁₂ olefins was relatively weak when non-catalyzed or at low catalytic ratios, but increased significantly at higher MCM-41 catalyst ratios. With a ratio of LDPE: MCM-41 = 5:4, the CO₂ atmosphere showed the greatest promotion of C₅-C₁₂ olefins over N₂, with an increase of 14.66 % compared to N₂, representing a 48.54 % yield of the liquid product. Producing C₅-C₁₂ olefins under these conditions maximized energy efficiency. These results show that catalytic pyrolysis of LDPE under a CO₂ atmosphere has great potential to produce C₅-C₁₂ olefins, which can be used to produce high-value chemicals such as naphtha and gasoline. This opens new opportunities for the chemical recycling of plastic waste.