Inside Green Innovation: Progress Report - Third Edition highlights:
- In 2021 plastic recycling patent filings have reached an all time high.
- Drop in filings from previous highest filer Eastman, but the rest of the sector show growth.
- Pyrolysis is still by far the main source of chemical recycling innovation, and continues to grow rapidly, but there is also growth in other emerging technologies such as biodegradation and electrolysis.
- Strong growth is also found in innovation for the downstream processing of the treated polymer waste.
The evolution of innovation and patents in chemical recycling
The variety of plastics and compositions containing plastic have produced a reliance on them in a considerable range of applications. Traditional petrochemical-derived plastics, such as polyethylene (PE), polypropylene (PP), polyesters, polyacrylics, polystyrene and polyvinyl chloride (PVC) have evolved over decades, offering highly-specialised properties for such applications. They remain highly valuable materials, essential in many areas, and this seems set to continue until greener alternatives can sufficiently replicate their performance.
However, continued use will also likely require that such plastics become easier to recycle because the majority of plastic waste takes decades to biodegrade.
Recycling non-biodegradable plastic is one way to partially mitigate its environmental impact.
In 2019, of the approximately 350 million tonnes of plastic waste worldwide, nine percent was recycled, 19 percent incinerated, 49 percent went to landfill, and 22 percent was uncollected litter, with 6.1 million tonnes (Mt) of plastic waste leaking into aquatic environments, such as rivers, and 1.7 Mt flowing into the oceans.
It is feasible that with new technologies combined with appropriate international regulations, much more plastic could be recycled per year, leading to a significant reduction in environmental impact. The challenge is to overcome various political, societal and economic (including technical) obstacles to achieve the goal of a sustainable, circular plastic economy.
The myriad of plastic compositions and uses is a weakness when it comes to recycling. A square metre of landfill waste plastics will include a huge variety of polymers with different chemical compositions, structures, and properties. This makes recycling difficult, as different polymers will often require bespoke recycling processes.
At present, mechanical recycling (MR) is an established method for recycling plastic waste, by recovering waste thermoplastics through mechanical processes such as grinding, washing, separating, drying, re-granulating, and compounding. The resulting material can then be converted back into plastic products.
However, there are drawbacks to the MR processes:
- Plastics recycled by this method can only be recycled a limited number of times and will, even if repeatedly recycled, ultimately end up in landfill or the natural environment.
- Not all plastics can be recycled through MR. For example, PVC (commonly found in lightweight building pipes) cannot be recycled in this way and composite plastic products (for example packaging) also are challenging.
This article endeavours to measure global progress in the development of technologies used to recycle plastic, to gauge where and which recycling methods are taking hold, and the new plastics recycling technologies – or iterations of foundational technology – that are emerging.
Chemical plastic recycling
Chemical plastic recycling (CR) technologies, such as depolymerisation (converting a polymer back into monomers), offer much potential. These technologies can provide a pathway to re-use the base monomer necessary for plastic production and so recycle plastic more effectively without it going to landfill. By using processes that turn plastic waste back into base chemicals and chemical feedstocks, chemical recycling could dramatically increase plastics recycling and divert plastic waste from landfill or incineration. However, due to the varied nature of different plastics, there is unlikely to be a single solution, with a wide range of CR technology developing depending on the polymer in question.
CR technologies can be broadly separated into three main categories:
- Thermal recycling: processes that use heat to break down polymeric materials into its monomers or other smaller molecular fragments; 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 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 molecules e.g., oligomers, dimers and monomer.
When looking at patent data – assuming that innovators want to protect proprietary plastics recycling technology for commercial benefit, making patents a barometer of progress – we do not see innovation developing at equal rates across all types of technologies. Some areas are emerging as more technically, and commercially, viable than others. For example, some monomers have a higher production cost than others making recycling more commercially viable for more expensive monomers than for low-cost monomers such as ethylene.
Global patent filing trend
At the highest level, interest in CR technologies is currently very high, with the number of global patent filings increasing dramatically over the last three years (Figure 1). This trend will likely continue, given growing pressure on manufacturers to move toward a sustainable, circular plastic economy.
Figure 1: Thirty-year trend – global priority filings – chemical recycling
(Priority filing = the first time a patent application for a unique invention has been filed (the first filing))
Top filing territories
The recent surge has come primarily from entities operating in the US and Europe. In 2019, 56 percent of new CR patent applications came from these two territories. It is notable, however, that there was a slight dip in US activity during the most recent year complete data is available (2021). Filings from South Korea on the other hand, have doubled from 2020 to 2021. On this trajectory, South Korea may overtake Europe with the highest number of filings, so far, in CR technologies in the next reporting year (2022).
Figure 2: Ten-year trend - global priority filings by terrirtory - chemical recycling
Top filing entities
In our last report (based on data through 2020), Eastman Chemical was the top filer, with 71 percent of filings among the top ten applicants combined (and 14 percent of total global filings). However, that dominance has eased (Figure 3).
Figure 3: Filing activity (2011-2021) - top ten filers - chemical recycling
Eastman is now responsible for a 26 percent share of filings among the top ten filers (and a 4.5 percent share of total global filings). While the number of Eastman’s patent filings has dropped by about 50 percent since 2019, the fall in its percentage share among the top ten filers is greater because other companies’ have begun to file, or have increased their filings at a higher rate. Notable growth has come from Sabic, LG Chemical and IFP Energies Nouvelles in particular.
Plastic manufacture and recycling are, in principle, a capital-intensive industry. In addition, the development and implementation of a single new plant will often result in a large number of related but distinct patent applications. As such, it may be expected that the most heavily invested commercial entities would be filing the bulk of the patent applications. And this is at least in part the case. Indeed, Eastman have over recent years invested heavily in the world’s largest material-to-material molecular recycling plant in Port Jerome sur Seine, France.
The ratio of unique patent applicants to new patent filings per year has dropped in recent years (Figure 4), showing that more entities are filing multiple applications per year. The number of new entities has more than doubled since 2018, showing a strong pull for new entrants into the sector. 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.
Figure 4: Thirty-year trend – global priority filings and unique assignees by year - chemical recycling
(Patent assignee = the owner of a patent/application, also known as the ‘applicant’ (for a patent application), patentee (for a granted patent), or proprietor.)
A wide range of CR technologies
Several different areas of CR technology have grown in recent years.
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 5).
Figure 5: Ten-year trend - global priority filings - thermal recycling
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 6).
Figure 6: Ten-year trend - global priority filings - pyrolysis
Microwave recycling is an emerging variant of pyrolysis thermal recycling technology that currently has a relatively low number of filings (compared to other thermal recycling techniques) but has shown steady, increasing growth for the past seven years (Figure 7).
Figure 7: Ten-year trend - global priority filings - microwave depolymerisation for recycling of plastics
Hydrothermal treatment (HTT) is a type of thermal recycling that uses high heat and pressure to generate a form a solvolysis depolymerisation with the reaction system solvent. The system is heated to high temperatures under high-pressure to melt and then dissolve the mixed plastics feedstocks under supercritical conditions. The number of patent filings relating to hydrothermal treatment is also currently at a low level, but again this emerging technology is following the overall filing growth trend for plastic recycling.
A recent patent filing relating to hydrothermal treatment includes a partial oxidation process. In this process, the plastic material is granulated and partially liquified by heating in a closed autoclave at a temperature in the range of about 200 DEG C. to 250 DEG C. and a pressure in the range of about 150 psig to 750 psig, while the plastic material is in contact with a pumpable hydrocarbonaceous liquid solvent.
Chemical depolymerisation refers to chemical processes that break down the polymers to their chemical building blocks (monomers and oligomers). Such processes include chemical treatment by solvolysis, hydrolysis, methanolysis, glycolysis and/or ammonolysis.
The number of patent filings relating to chemical depolymerisation is significantly lower than those filed in relation to thermal recycling processes (Figure 8). Further, while there had been strong growth up to 2020, it is notable that the number of new filings fell significantly in 2021, bucking the otherwise strong growth trend in the sector. Whereas in other areas of CR technology the drop-off in new Eastman filings in 2021 was made up for by significant growth from other entities, we have not seen that effect to the same extent for depolymerisation technologies. While there has been growth from other entities, it has not been enough to off-set the significant drop in new filings from Eastman in 2021.
Figure 8: Ten-year trend - global priority filings - Chemical depolymerisation
Recycling of plastic waste by electrolysis is another emerging technology that may provide a route to breakdown polymers into industrially useful chemicals. Electrolysis involves the application of electricity to assist with chemical reactions that lead to the breakdown of polymers. An innovative process for recycling PET plastic has been developed by the University of Colorado Boulder called “electrochemical plastic dissolution”, which involves grinding up PET into a powder-like substance and mixing it with a chemical solution for electrolysis. An extra molecule [N-DMBI]+ salt is added, forming a ‘reactive mediator’ that breaks down the PET molecules when the electrical current is applied. The global filing trend for electrolysis recycling technology follows the general growth trend of other emerging technologies such as microwave and HTT, from a similar very low starting point (Figure 8).
Another emerging technology following the same general growth trend is recycling through microbial biodegradation. Patent filings in this area have grown steadily since 2015 (Figure 9).
Patent filings relating to biodegradation of plastics typical fall into one of two main categories:
- Novel microorganisms having an ability to degrade plastics
- Methods of degrading polymers, such as polystyrene, polyethylene and polyurethane, using known microorganisms in combination with novel auxiliary components and/or processing conditions.
The National Renewable Energy Laboratory in Colorado has developed a technology that uses chemical catalysts and engineered bacteria to convert a mix of common plastic waste into a useful product. The innovation relates to a process that uses readily-available catalysts and a modified soil bacterium, Pseudomonas putida, to transform polystyrene, polyethylene terephthalate (PET) and high-density polyethylene (HDPE) into a group of biodegradable compounds called polyhydroxyalkanoates, which may be used in biomedical applications such as sutures.
Figure 9: Ten-year trend - global priority filings - biodegradation
Innovations related to different stages of chemical recycling
The plastic chemical recycling process involves more than just breaking down waste polymer. Once broken down, the resulting mixture must be processed to extract, and potentially further modify, the desired product(s). There are growing levels of innovation in these downstream parts of the overall process. For example, there has been recent growth in the number of patent applications about modifying the feedstock produced from the initial treatments (Figure 10).
Figure 10: Ten-year trend - global priority filings - recovery of products
The University of Wisconsin-Madison has developed a new technique that applies pyrolysis in a first stage to form a pyrolysis oil. The pyrolysis oil contains large amounts of olefins — a class of hydrocarbons which are the building blocks for many polymers and chemicals, including various types of polyesters, surfactants, alcohols and carboxylic acids. This innovative method then applies a further stage in which the olefins are recovered from pyrolysis oil and used in homogeneous hydroformylation catalysis. Olefins are converted into aldehydes, which can then be further reduced into important industrial alcohols. This method produces higher-value materials, such as ingredients used to make soaps, cleaners and other more useful polymers, and other more useful polymers.
If the number of patent filings relating to the core recycling processes continues to grow as expected, we should see expansion in related downstream technologies. This should also lead to innovation around linking different types of processing technologies to glean the best of each, while mitigating any disadvantages.
Implications for innovation and future patent filings
A slow decline from 2010 to 2018 in patent activity in the chemical recycling sector ended in 2019, where data shows a sharp increase in related patent filings. This trend shows no real signs of slowing down, with pyrolysis still the main area of innovation.
Chemical recycling businesses are gaining more investment from companies such as Nestlé, Coca-Cola, and Danone. For example, Nestlé Waters, PepsiCo and Suntory Beverage & Food Europe have joined a consortium (founded by Carbios and L’Oréal) to support the world’s first enzymatic technology for recycling plastics. Carbios has created a novel method that breaks down PET plastic waste into monomers, which can then be used to produce high-quality PET plastic.
The number of companies innovating in this area, and their resulting inventions is growing. Combined with the wider political and societal pressure, this reinforces the expectation that CR growth and innovation is set to continue.