A review on catalytic pyrolysis of plastic wastes to high-value products

With the continuous increase of plastic wastes and the decrease of fossil energy, pyrolysis has emerged as a promising technology for the valorization of plastic wastes to produce fuels and chemicals. Properties of common plastics, mainly polyethylene terephthalate (PET), polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), polystyrene (PS) and their mixtures are discussed with a focus on the pyrolysis mechanism and product distribution. The application of the most common catalysts (microporous/mesoporous zeolites, base catalysts, and clays) shows overwhelming advantages over thermal cracking, and an in-depth understanding of catalysts in several catalytic processes (ex-situ catalysts, tandem catalysts, bi-functional catalysts, multi-modal pore catalysts, and regenerated catalysts) is critical for efficient fuel production. Despite high-quality liquid fuels obtained, further upgrading (filtration, hydrogenation, distillation, liquid–liquid extraction or blending with conventional fuels) is required before their commercial application. Non-condensable gas is another co-product that can be upgraded for heat generation or as the precursor of high-value products (ethylene, propylene, carbon nanotubes (CNTs), etc.). Finally, a more integrated techno-economic assessment process is conducted based on feedstock logistics, utilization of liquid fuels, full use of co-products, capital and operating costs. This review aims to inspire both fundamental and applied research efforts for the production of high-value products from the catalytic pyrolysis of plastic wastes and their full utilization to create the necessary technological and economic push for a circular economy.