
Global plastic production has steadily increased, reaching 400 million tons in 2022, raising significant concerns about plastic waste management and its environmental impact. This rise has led to the accumulation of plastic waste, often referred to as "white pollution," in oceans and ecosystems worldwide. To address these challenges, efforts have been made to recycle plastic waste. By 2022, about 10% of plastics were produced from recycled materials or captured carbon, but this remains insufficient to achieve carbon neutrality and ensure long-term sustainability.
Currently, over 90% of recycled plastics are processed through mechanical recycling, which involves melting and reshaping plastics without changing their chemical structures. While this method is economical and convenient for uniform materials like polyethylene terephthalate (PET) bottles and polyvinyl chloride (PVC) pipes, it requires precise separation by the categories of composition and it is less feasible for mixed plastic waste. Complex waste streams pose significant separation challenges, with low accuracy and high costs. Additionally, plastics containing PVC, which accounts for 12.7 % of global plastic production, present further risks. When incinerated or landfilled, they can release hazardous chemicals, such as dioxins and HCl, causing serious environmental damage.
Chemical recycling presents a promising solution for upcycling mixed plastics into value-added products without releasing toxic substances into the environment. However, PVC remains a challenging material for chemical recycling due to the production of HCl and other chlorine-containing byproducts, which can cause equipment corrosion and catalyst deactivation. Currently, pyrolysis is the primary method for recycling PVC-containing mixed plastics, as it is a relatively straightforward approach. However, this process operates at high temperatures, and despite pre-dechlorination steps, HCl-induced corrosion is inevitable. Plastic waste recycling is not only essential for addressing environmental concerns such as "white pollution" and the CO2 crisis, but also needs to be economically viable. High energy input, expensive catalysts, and complex reaction systems can hinder the broader application of recycling technologies. Therefore, the development of highly tolerant, stable and economic systems for the upcycling of mixed plastic waste, especially halide-containing materials, is crucial to ensuring both environmental and economic sustainability.
In our work, we developed a highly Cl-tolerant, noble-metal-free catalytic system for co-upcycling PVC and polypropylene (PP) mixed plastics, achieving complete depolymerization of both materials at room temperature. Chemical upcycling of inert polyolefins like PP or polyethylene (PE) is particularly challenging due to their stable C(sp3)–C(sp3) bonds, which typically require high temperatures (>180°C) for depolymerization via pyrolysis or catalytic hydrocracking. The Cl-tolerant [C4Py]Cl-AlCl3 ionic liquid demonstrated excellent dechlorination efficiency for PVC, generating HCl and dechlorinated PVC without breaking its carbon chain. When co-upcycling PVC and PP, the system depolymerized both plastics into Cl-free liquid hydrocarbons, recovering up to 97.4 wt.% of C and H, with chlorine converted to HCl. Additives both organic (dimethyl phthalate and diisobutyl phthalate)and inorganic materials (CaCO3) are wildly existed in the post-consumer plastic wastes to increase their properties. The system also exhibited high tolerance to common plastic additives (e.g. dimethyl phthalate, diisobutyl phthalate, CaCO3), maintaining depolymerization activity with up to 12% additives. The catalyst remained stable across multiple cycles—three for PVC-PP conversion and five for PVC-heptane conversion—and could be regenerated via H2 treatment.
This chloroaluminate-based ionic liquid, already used industrially, is a promising candidate for large-scale PVC-PP mixed plastic co-upcycling. For large scale application, careful design is needed to ensure efficient recycling, regeneration, and separation of the ionic liquid. This catalytic process offers notable advantages: it operates at room temperature without the need for noble metals or external hydrogen sources, such as H2 or organic hydrogen donors, significantly reducing energy input and costs. Therefore, this approach provides a sustainable, cost-effective solution for chemically recycling mixed plastic wastes containing PVC, offering a promising way to address global plastic waste challenges.
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