Section 4: Plastics recycling
Chemical recycling technologies
As shown elsewhere in this report, the field of bioplastics is showing encouraging progress. However, bioplastics’ performance – in the eyes of the consumer – doesn’t yet match traditional, petrochemically-derived plastics such as polyethylene (PE), polypropylene (PP), polyesters, acrylics, polystyrene, and poly vinyl chloride (PVC).
Until bioplastics can replicate the performance of traditional plastics, the latter are likely to be required. And though recycling is one way to partially mitigate this issue, of the 380m tonnes of plastic produced annually worldwide, only sixteen percent is recycled, twenty-five percent is incinerated, and forty-four percent goes to landfill or the natural environment.
A notional square metre of landfill filled only with waste plastics 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. MR involves the recovery of waste plastics through mechanical processes such as grinding, washing, separating, drying, re-granulating, and compounding. The product from these mechanical processes can then be converted back into plastic products.
MR processes have a number of drawbacks:
They are not suited to process waste plastic on a large scale
They are only suited for particular types of plastics such as PE or PP. PVC (commonly found in lightweight building pipes) cannot be recycled by MR processes and complex plastic products – e.g., in packaging – are challenging
The processes can cause damage to the plastic materials, affecting the quality of the recycled material and limiting its lifespan before going to landfill
All plastics recycled by this method will ultimately end up in landfill
Chemical plastic recycling (CR) technologies, such as depolymerisation, offer much potential. These technologies provide a pathway to restart the polymerisation process necessary for plastic production and thus recycle the plastic for further use without the need to resort to landfill. In some cases, CR can recycle plastics that MR cannot. The resulting products represent a supply of virgin-quality feedstocks for the plastics supply chain. 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 – pyrolysis: processes that use heat to break down polymeric materials into monomers or oligomers; the resulting products are again purified so that they can be used as a feedstock for polymer production
Global patent activity
Initial data analysis for global patent activity included all priority filings. However, in some countries the total priority filings far outweighs the number of such filings which eventually progress to applications in further countries. This is particularly true of priority filings originating from China where only five percent were progressed internationally. As such, the majority of the innovations to which Chinese priority filings relate are likely not of sufficient commercial importance outside China. Accordingly, to pick up the necessary trends in the analysis, results provided below are limited to exclude such priority filings. Filings that progress outside China are included. The patent filing analysis in this section is focused on picking up trends for innovations in the field of chemical recycling processes. The data relating to priority filings over the past forty years shows a strong upward trend starting in the early 1990s, indicating that innovation in this technology is gathering speed and will continue this upward trend for the next few years. For the purposes of this research, we have considered priority filings up to 2019, as the complete dataset for priority filings in 2020 will not be available until mid-2022.
Figure 4.1 Priority filing trend - chemical recycling of plastics Click graph to enlarge
Note: Due to an 18-month lag between patent application and full publication of patent data, data from 2021 has not been reported, and data from 2020 includes data through May 2020.
Companies filing in the area of waste plastic chemical recycling When reviewing the top ten assignees for this technology, the number of patent families allocated to an assignee historically is not necessarily an indication of recent activity in recycling. For example, Figure 4.2 shows the top ten filers in chemical polymer recycling without limit of time. The dataset for this is not delimited by an earliest priority date and shows that the top filers in this area are Nippon Steel Corp. and Toshiba Corp., each with 107 patent families, followed by Eastman Chemical Co. (ECC), with 62 patent families. Figure 4.3 also shows the top ten filers in the technical field of chemical polymer recycling, but with a dataset delimited to patent families with an earliest priority date within the last twenty-five years. Interestingly, the results in Figure 4.3 show that Nippon Steel Corp. and Toshiba Corp. have not been as active in this field over the past twenty-five years as the historical results from Figure 4.2 show. Figure 4.2 Top ten assignees by families Click graph to enlarge
Figure 4.3 Top ten assignees by patent family - filed (earliest priority date) within last 25 years Click graph to enlarge
Note: Due to an 18-month lag between patent application and full publication of patent data, data from 2021 has not been reported, and data from 2020 includes data through May 2020.
Whether the dataset is delimited by an earliest priority date or not, Eastman Chem Co. (ECC) remains one of the top filers and with one exception, the earliest priority for ECC’s 61 patent families is 2019, as shown in Figure 4.4.
Figure 4.4 Eastman Chem Co. priority filing trend - chemical recycling technologies Click graph to enlarge
Note: Due to an 18-month lag between patent application and full publication of patent data, data from 2021 has not been reported, and data from 2020 includes data through May 2020.
ECC is a top patent filer in this area of innovation whilst also being a relatively new entrant which is perhaps an indicator of the growing importance of this field. Of the other notable filers, we see Bridgestone (with interest in rubber recycling), Chevron (polyethylene), and Solvay (PVDC). The backward citations (citations in a patent to an earlier published patent) made by the ECC patent families show that the majority referenced twelve of the twenty SABIC (Saudi Aramco subsidiary) patent families in the dataset. Four of SABIC’s patent families, with an earliest priority date of between March 2015 and February 2016, are cited by over half of the EEC patent families. The relevant SABIC patent families relate to an improved process for pyrolyzing mixed plastic waste. The process of those families allows for integration, hydrogenation, dichlorination and hydrocracking of the waste plastic feedstock. Interestingly, several types of polymers can be processed together and converted into a hydrocarbon product that meets steam cracker feed requirements. The pattern in Eastman’s filing over the past three years suggests that SABIC’s filings in 2015 and 2016 appear to have inspired an explosion of activity by Eastman, and indeed other companies, in this technical field over the past five years. This is potentially related to Eastman’s interest in the carbon renewal technology which may be competitive to its polyester renewal technology. Eastman’s polyester recycling technology has also played a big part in its investing USD 250m and building “...one of the world's largest plastic-to-plastic molecular recycling facilities at its site in Kingsport, Tenn.”
Implications for innovation and future patent filings Pyrolysis techniques for mixed polymer waste and dedicated PET depolymerisation through methanolysis are only two areas of polymer recycling innovation. Developing technologies that breakdown existing petrochemically derived plastics in other ways remain a priority. In the coming years we may see more filings relating to enzymatic breakdown of existing polymers, a number of such are being filed by Tianjin and Sichuan Universities in China relating to PET breakdown using engineered microorganisms. Carbios, a French company, are also key filers in this emergent area. Another area that offers promising potential is the use of ring opening polymerisation (ROP) and ring closing depolymerisation (RCD) to provide a chemical recycling to monomer route. Much interest in this area focuses on polymers with existing ROP monomers such as lactones and epoxides and therefore has application for suitable polyesters such as polycaprolactone which is derived from lactone polymerisation by ring opening and polycarbonates which are the product of carbon dioxide and a ring opened epoxide copolymerisation. From our review of the dataset, this area is still in its nascence however, there is notable activity from Colorado State University with three patent families filed within the last ten years, relating to the polymers of (a) ring-fused gamma butyrolactones, (b) polyesters and (c) polythioesters; all of which can be polymerised and depolymerised in a ROP-RCD cycle. Princeton university has also entered this space within the last five years, with a patent family explicitly covering a ring-opening depolymerisation catalyst for polymers or oligomers having a backbone that includes cyclobutane units.
There are many companies commercially interested in this area of polymer chemical recycling, not least current polymer and monomer producers. It remains to be seen to what extent they will be able to adapt to the changing demands for recyclable plastics and continue to innovate in this area.
David Walsh Partner, BSc PhD CChem CSci MRSC CPA EPA MITMA
Sarah Abou-Shehada Trainee Patent Attorney, MChem, MRes, PhD