Advances in Pyrolysis Recycling of Polyethylene Terephthalate (PET)

Polyethylene terephthalate (PET) is a widely used thermoplastic polymer, predominantly found in packaging and textiles. The disposal of PET waste has become a global challenge due to its resistance to natural degradation. Mechanical recycling, although commonly employed, faces issues such as low efficiency and material degradation, making it difficult to achieve efficient reuse. In contrast, chemical recycling, particularly pyrolysis, shows greater potential for application. PET pyrolysis can produce valuable chemicals, such as terephthalic acid and ethylene glycol, which are the primary raw materials for PET synthesis, thus enabling resource recycling. Although the pyrolysis process features a short reaction time and broad operating conditions, the product selectivity of direct PET pyrolysis remains low, limiting its practical application. Catalytic pyrolysis of PET, with the addition of catalysts like zeolites or metal-loaded zeolites, enhances reaction efficiency and selectivity, yielding higher-value aromatic compounds (e.g., benzene, toluene, xylene, benzoic acid, etc.), thereby significantly improving the profitability of recycling. Furthermore, co-pyrolysis of PET with biomass or other plastics can enhance product quality and reduce the complexity of waste separation due to the synergistic effects between different waste materials, thus improving solid waste management efficiency. This review provides an overview of the latest research progress in PET pyrolysis, the catalytic pyrolysis of PET, and its co-pyrolysis with other organic solid wastes. It delves into the distribution of pyrolysis products and reaction mechanisms of the three types of pyrolysis under various reaction conditions. Several limitations and challenges in current research are also highlighted. First, while catalytic pyrolysis has made significant progress in improving product selectivity, the stability and reusability of catalysts still require further optimization. Additionally, although the co-pyrolysis of PET with other organic wastes demonstrates synergistic effects, the significant differences in pyrolysis characteristics among various wastes call for further exploration and improvements in process design and operational conditions. This review also suggests several focal points for future research: (1) optimizing catalyst performance, particularly enhancing durability and selectivity, to reduce costs and improve pyrolysis efficiency; (2) conducting in-depth studies on the co-pyrolysis mechanisms of PET with other wastes, identifying optimal waste ratios and reaction conditions; (3) developing efficient post-treatment technologies to improve the physicochemical properties of pyrolysis oils for broader applications in fuel or chemical production; and (4) exploring novel waste pyrolysis technologies and equipment to enhance scalability and industrial applicability in waste management. This review offers valuable insights for facilitating the resource recovery of PET waste and sustainable management of organic solid wastes.