Catalysis 2026 Issue

Pathways to chemical recycling of waste plastic pyrolysis oil

Chemical recycling is essential for managing problematic plastic waste, highlighting the pathways and challenges in converting waste plastics into high-quality feedstocks

Trine Dabros and Milica Folić Topsoe

C hemical recycling, particularly via pyrolysis and advanced hydroprocessing, offers a viable pathway to take advantage of mixed and contaminated plas- tic waste streams. Overcoming feedstock variability, scaling up technologies, and maturing value chain collaboration are critical for achieving a circular plastics economy. Continued investment, innovation and regulatory support will be essential for realising the full potential of chemical recycling and addressing the global plastic waste challenge. Need to address plastic waste The linear plastic economy, characterised by the widespread use of single-use plastics, has resulted in rapidly increas- ing plastic waste streams worldwide. According to the Organisation for Economic Co-operation and Development (OECD),1 only 9% of plastic waste is recycled globally (15% is collected for recycling, but 40% of that is disposed of as residues). Additionally, 19% is incinerated, 50% ends up in landfill, and 22% evades waste management systems altogether. This scenario not only threatens ecosystems but also represents a substantial missed economic opportunity. Addressing plastic waste requires a multifaceted approach, commonly summarised as the three Rs: reduce, reuse, and recycle. While reduction and reuse are essential strategies, recycling remains critical for closing the loop and reducing reliance on virgin plastics. Mechanical and chemical plastic recycling Plastic recycling follows two complementary paths: mechanical and chemical. Mechanical recycling is well established and most effective for clean, sorted, single- polymer waste streams, such as polyethylene terephthalate (PET) bottles. This process typically involves shredding, washing, and recompounding plastics to produce new products. While mechanical recycling is energy-efficient and can yield high-quality materials, repeated cycles often degrade polymer properties, resulting in downcycling to lower-value products such as textiles or garden furniture. Chemical recycling Chemical recycling encompasses a suite of technologies designed to process mixed and contaminated plastic waste that cannot be mechanically recycled. These technologies

break down polymers into monomers or other feedstocks, enabling the production of virgin-quality plastics suitable for food and pharmaceutical applications. Key chemical recycling methods include: • Dissolution recycling: Dissolves polymers for purification and reprocessing. • Solvolysis: Uses solvents (for example, water, alcohols, glycols) to depolymerise plastics into monomers. • Thermochemical liquefaction: Converts plastics into virgin plastic feedstock equivalents (such as naphtha) via pyrolysis or into syngas via gasification. Pyrolysis and hydrothermal liquefaction Thermochemical liquefaction technologies, such as pyrol- ysis (catalytic or non-catalytic) and hydrothermal liquefac- tion (HTL), convert solid plastic waste into liquid products known as plastic pyrolysis oil (PPO) or waste plastic pyrol- ysis oil (WPO). Broadly speaking, pyrolysis involves heating plastics in the absence of oxygen, producing oils, gases, and char. The resulting liquid phase resembles naphtha steam cracker feedstock but contains significant contaminants, including metals (for example, silicon, iron, phosphorus), halogens (for example, fluorine, chlorine, bromine), and heteroatoms (for example, nitrogen, oxygen, sulphur). The process has certain preferences in terms of plastic feed- stock, but most can handle mechanical recycling rejects effectively, stressing the benefits of complementarity. Several generations of reactor designs are on the mar- ket, with mechanical engineering design being in focus. Some of the more recent processes also aim to incorpo- rate catalysts, solvents, or additives, introducing a chemical engineering component. Two-step pyrolysis processes, While reduction and reuse are essential strategies, recycling remains critical for closing the loop and reducing reliance on virgin plastics

Catalysis 2026