Traditional petrochemically-derived plastics, such as polyethylene (PE), polypropylene (PP), polyesters, polyacrylics, polystyrene, and polyvinyl chloride (PVC), have evolved over decades, offering highly specialised properties for multiple applications. They remain highly valuable materials and this will likely continue until greener alternatives can replicate, or nearly replicate, their performance.
However, continued use will also likely rely on plastics becoming easier to recycle as petrochemically-derived plastic waste is a pollutant, taking potentially decades to biodegrade. Recycling plastic is one way to partially mitigate this issue. In 2018, of the approximately 360m tonnes of plastic produced worldwide, 21% was recycled, 21% was incinerated, and 54% went to landfill or the natural environment.
A notional square metre of landfill filled with waste plastics only, will include a huge variety of polymers with different chemical compositions, structures, and properties. Each of these polymers would benefit from a bespoke recycling process, but this presents practical difficulties.
At present, so-called mechanical recycling (MR) is an established method for recycling plastic waste, involving the recovery of 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.
There are drawbacks, however, to the MR processes:
- All plastics recycled by this method will ultimately end up in landfill or the natural environment
- MR processes are suited only for some plastics, such as PE or PP; PVC (commonly found in lightweight building pipes) cannot be recycled by MR processes, and complex plastic products – for example, from packaging – are challenging
Chemical plastic recycling (CR) technologies, such as depolymerisation, offer much potential. These technologies offer a pathway to provide the virgin monomer necessary for plastic production and so recycle plastic more effectively for further use without it eventually 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.
In some cases, CR can recycle plastics that MR cannot. The resulting products may provide feedstocks for further polymer production.
CR technologies can be separated into three categories:
- Solvent purification: plastic is dissolved in a suitable solvent before a series of purification steps separate the polymer material from additives and contaminants
- Chemical depolymerisation: processes that break down the polymers to their chemical building blocks (monomers) via a chemical reaction; monomers are recovered from the process and purified for use as a feedstock for polymer production
- Thermal depolymerisation/feedstock recycling – processes that use heat to break down polymeric materials into monomers or oligomers; the resulting products are again purified for use as a feedstock for polymer production
Global patent activity
The data relating to priority patent filings in chemical recycling processes over the past forty years shows a strong upward trend starting in the early 1990s, peaking around 2000, followed by a gradual downward trajectory. This slow decline in filings continued until 2019-2020, until a significant increase in priority filings. The data indicates that this technology is gathering speed with an upward trend likely to continue due to continuing consumer and regulatory pressure on the plastics industry.
Figure 1 : Forty-year trend: priority filings – chemical recycling of plastics
The forty top patent filers are shown below in Figure 2. This data shows that each of these companies have their own filing profile and the global filing trend (in Figure 1) is not dependent on a single company’s patent portfolio.
Figure 2: Thirty-five year landscape: annual priority filings, top 40 filers only – chemical recycling of plastics
Notable companies
Figure 3 shows the top twenty-five filers by aggregate priority filings in chemical polymer recycling over the last five years. Some of the dominant players of the past shown in Figure 2, such as Nippon Steel Corp. and Toshiba Corp., have not been as active during this most recent period.
Figure 3: Filing activity 2015-2020: annual priority filings, top 25 filers only – chemical recycling of plastics
Over the last ten years, Eastman Chem Co. (ECC) is the top filer, despite having begun filing in this area only in 2019, as shown in Figure 3 and Figure 4.
Many other companies filed a significant number of patent applications during this 2019-2020 filings surge:
- Sabic Global Technologies BV (SABIC) made 30 priority filings within the past 10 years, 13 of which were filed in 2020
- Shell INT Research (Shell) made 12 priority filings from 2018 – 2020
- NAN YA Plastics Corp. made 11 priority filings from 2019 – 2020
- IFP Energies Nouvelles made 16 priority filings from 2019 – 2020
Borealis AG and Carbios have also invested in this area, filing 17 and 20 priority applications respectively, over the last ten years.
The increase in filing activity across companies observed in 2019-2020 may have been triggered by the earlier increase in filings seen in 2015-2018, by companies such as SABIC and Carbios.
Figure 4: Notable companies – recent priority filings by year
Recent patent filings cover a wide range of technologies, such as SABIC’s applications for processes to prepare hydrocarbons or aromatics from waste plastic feedstocks. This involves processing waste plastics by hydrotreatment (treatment with H2), performing thermal cracking (pyrolysis) and a separation operation to obtain different C4 streams.
Shell appears to be focusing on recovering aliphatic hydrocarbons from liquid hydrocarbon feedstock streams which originate from (mixed) waste plastics. This method comprises a liquid-liquid extraction step, with no need for hydrotreatment. The aliphatic hydrocarbons can be further cracked in a steam cracker to produce high-value chemicals, including ethylene and propylene monomers, to produce virgin plastics.
Some of Borealis AG’s patent applications relate to processes for reducing malodour in hydrocarbon streams. Aldehydes often result in malodour of recycled hydrocarbon compositions, therefore affecting how suitable recycled hydrocarbon compositions are for further applications. The shredded hydrocarbons (typically polyethylene and polypropylene) from recycling sources, are subjected to a gas flow, without stirring, for an extended period to achieve a composition with reduced aldehyde content. The treated hydrocarbon composition is then recovered and extruded to yield pellets with a reduced malodour.
IFP Energies Nouvelles (French Institute of Petroleum) filed several priority applications in 2020, one of which related to an optimized method for processing plastic pyrolysis oils. This involves treating the pyrolysis oil in the presence of a hydrotreating catalyst to obtain a hydrocarbon composition with reduced impurities. The treated hydrocarbon composition can then be steam cracked to produce the necessary monomers.
Most popular chemical recycling methods
The data reveals growth in several areas of research and development in recent years. A particular process of interest is pyrolysis. This process breaks down plastic feedstock (typically, polyolefins (polyethylene (PE), polypropylene (PP), polybutylene (PB), polystyrene (PS) and/or PMMA (poly-methymethacrylate) into a range of basic hydrocarbons (oligomers and monomers) by heating in the absence of oxygen (aka thermal cracking). Normally, basic hydrocarbons form an oil that can be used directly as fuel, or as synthetic building blocks for polymers. Figure 5 shows that most filings in the chemical recycling field relate, in some way, to the pyrolysis process. Several process improvements are discussed above.
Solvolysis recycling is the dissolution of a product and is used to break down certain plastics, such as expanded polystyrene, into monomers. Solvolysis appears to be a less-explored area that offers promising potential, with filings relating to solvolysis significantly increasing in 2020 – with Eastman again a dominant filer.
A further notable process is gasification: mixed waste materials are heated to very high temperatures (~1000 - 1500°C), with low levels of oxygen, which breaks the molecules down to their simplest components, to produce syngas. Filings for this process have been steady over the past 20 years, with increases in 2019 and 2020.
Figure 5: Twenty-year trend: global priority filings – by specific chemical recycling technology area
Implications for innovation and future patent filings
The data shows a slow decline in patent activity in the chemical recycling field between 2010 and 2018, but a sharp increase since 2019, with a high number of filings specifically relating to pyrolysis. This is clearly the main area of innovation, with many companies filing patent applications.
The sudden rise in filings in 2019 shows an increasing investment by the polymer industry in this area and, from the further increase in filings in 2020, we would potentially anticipate this to continue. The University of Nottingham has discussed how solvolysis processes are “the next generation of carbon fibre recycling technology, as they offer the recovery of chemical products from the polymer as well as the recovery of high-grade carbon fibre with minimal degradation”.
At present, the most common recycling process used to recover carbon fibre from composite waste is pyrolysis (as expected from the data), in which heating it to a high temperature burns off the resin. Therefore, we may see an increase in the number of patent applications filed for solvolysis overall and specifically in this area.
David Walsh Partner
Amelia Barton European Patent Attorney