Plastics recycling

Chemical plastic recycling (CR) technologies, such as depolymerisation (converting a polymer back into monomers), has great potential. CR technologies provide a way of converting polymeric waste, by changing its chemical structure, back into substances that can be used as raw materials for the manufacturing of further plastics or other products. However, due to the nature of plastics there is unlikely to be a one-size-fits all solution and a wide range of CR technologies are developing.

CR technologies can be roughly separated into three main categories:

• Thermal recycling: processes that use heat to break down polymeric materials into smaller components; the resulting products are purified for use as feedstock for polymer production or for use in other suitable areas, for example, as a fuel. Processes include pyrolysis, gasification, and hydrothermal treatment (HTT).
• Chemical depolymerisation: catalytic or chemical processes that break down the polymers to their chemical building blocks (monomers and oligomers) via a chemical reaction; monomers are recovered from the process and purified for use as a feedstock for polymer production. Processes include solvolysis, hydrolysis, methanolysis, glycolysis, and ammonolysis.
• Biodegradation: the breakdown of organic matter by microorganisms, such as bacteria and fungi; for example, polymer-degrading microorganisms may excrete extracellular enzymes which degrade the polymer into smaller molecule e.g., oligomers, dimers, and to monomers.

Interest in CR technologies is currently very high, with the number of global patent filings increasing dramatically over the last four years (Figure 2), albeit with a slowing of the growth rate seen in 2023. Nevertheless, an overall growth trend will likely continue, given growing pressure on manufacturers to embrace a sustainable, circular plastic economy and the need to close the gap between the amount of plastic waste produced and recycled.

In our previous report (based on data through 2022), it was discussed how Eastman Chemical has been the top filer for the last three years. However, their filing numbers have significantly decreased in 2023, allowing BASF’s increasing filing numbers to propel them to top filer. BASF have filed over three times more patent filings in 2023 than in 2022 (shown in Figure 4).

Some of the top filers are filing patents in 2023 relating to:

• Processes for manufacturing aldehydes and alcohols from plastic waste using a hydroprocessing method
• Processes for recycling polyethylene terephthalate (PET) by glycolysis
• Methods for producing pyrolysis oil from waste plastics, which includes melting waste plastic feedstock and process oil stream, pyrolyzing the molten material to obtain a pyrolysis product, and purifying
• Methods for producing a regenerated polyolefin resin using extrusion
• Systems and methods for microwave hydrolytic dechlorination of mixed plastic waste.

The drop in the number of filings from the current top ten filers, when the overall global filings are still increasing, suggests potential for a continued shift in the top filers list as other companies seek to bring new facilities on line and the large level of innovation that typically goes hand-in-hand with that capital investment.

The ratio of unique patent applicants to new patent filings per year has dropped in recent years (Figure 5), showing that more entities are filing multiple applications per year. However, the number of new entities has more than tripled since 2018, showing a strong pull for new entrants into the sector. Both of these indicators are promising signs for the technology as a whole.

We are also seeing research institutions in the top filing charts, reflective of the early-stage of development in which many aspects of CR technology currently find themselves, despite the large-scale commercialisation that is taking place in parallel – exemplifying the wide range of innovation that is needed to broadly solve the plastic waste problem.

Several different areas of CR technology have grown in recent years.

Thermal recycling

Thermal recycling involves the application of heat to treat and decompose waste materials through different approaches. The number of global filings relating to thermal recycling has rapidly increased over the last few years, following the overall trend (Figure 6).

Pyrolysis and gasification are two similar thermal recycling processes. Both methods decompose waste materials by exposing waste to low amounts of oxygen and very high temperatures. Pyrolysis uses no oxygen, while gasification allows a low amount of oxygen in the process. These processes break down plastic waste (typically, polyolefins such as polyethylene (PE), polypropylene (PP), polybutylene (PB), polystyrene (PS) or PMMA (polymethymethacrylate)) into a range of basic hydrocarbons. Normally, basic hydrocarbons form an oil that can be used directly as fuel, or as synthetic building blocks in polymer production.

Pyrolysis continues to remain the most applied method contributing to most of the filings relating to thermal recycling (and indeed CR as a whole), far outstripping filings in related technologies such as gasification and hydrothermal treatment (as shown by Figure 7).

Despite the wide array of different plastics, consumers interact daily with only a handful of them.

The most common types of plastics are:

• Polyethylene Terephthalate (PET or PETE) – lightweight, strong, typically transparent and is often used in food packaging and fabrics
• High-Density Polyethylene (HDPE) – strong and resistant to moisture and chemicals, which makes it ideal for cartons, containers, pipes, and other building materials
• Low-Density Polyethylene (LDPE) – softer, clearer, and more flexible version of HDPE. It is often used as a liner inside beverage cartons, in corrosion-resistant work surfaces, and other products
• Polyvinyl Chloride (PVC or Vinyl) – hard and rigid plastic is resistant to chemicals and weathering, making it ideal for building and construction, high-tech, and medical applications
• Polypropylene (PP) – one of the most durable and heat-resistant types of plastic, making it ideal for applications including food packaging and food storage.
• Polystyrene (PS) - a thermoplastic polymer that is hard and brittle, and softens when heated and is mainly used in protective packaging, containers, lids, bottles, and trays.
• These plastics require different recycling technologies. Some methods of chemical recycling can break down more than one type of plastic. However, due to different types of plastics having a wide range of varying properties, many cannot be recycled together. Therefore, the plastic type must be considered when innovating in chemical recycling.

Figure 7 shows the number of new patent applications over the last ten years by plastic type. While innovation continued to grow across all of the main types of plastic until 2022, Figure 7 suggests that there has been a slight drop in momentum for the most common plastic types. Polypropylene (PP) has remained the plastic most targeted for chemical recycling innovation in the last 5 years, closely followed by polyvinyl chloride (PVC) and polyethylene terephthalate (PET). The number of patent filings relating the chemical recycling of HDPE and LDPE have been consistently lower than the other plastic types, but have been increasing year upon year.