By Krista Sutton.

New Energy Risk helps accelerate the commercialization of industrial technologies that are solving global challenges. One of the technology platforms that we see increasingly is pyrolysis technology being deployed in the development of a more circular plastic economy. A key challenge for those developing these projects is securing a bankable feedstock agreement for waste plastic. This challenge is magnified by the fact that the industry has not developed a standardized feedstock specification for pyrolysis of waste plastic.

The Big Picture

Increasing awareness of the extent of plastic pollution and the focus on sustainability are creating demand for recycled material in consumer products. The market incentives are growing and come from many different sources including consumer preferences and a  willingness to pay a premium for recycled products, plastic taxes, corporate pledges, recycling mandates, single use plastic bans or taxes, extended producer responsibility programs, upsets in the global supply chain following China’s national sword policy [8], subsidized local recycling programs, and increased landfill fees to name a few.

Today the recycling value chain largely consists of mechanically recycling (sorting, shredding, washing, drying, grinding, melting, granulating, and compounding) diverse plastic streams to produce recycled granules that can replace virgin plastic granules in the manufacturing of some plastic products, notably not always the same plastic products that the recycled products came from as there are stringent restrictions on products like food grade packaging.

Advanced recycling involves technologies that break down plastics at a chemical level to monomers that can be fed into petrochemical plants to make new polymers. Such advanced recycling technologies are currently being commercialized. However, today’s supply chain for waste plastics has evolved to meet the needs of mechanical recyclers and not advanced recyclers. With advanced recycling scaling up there is a need to understand the overlap and the differences in feedstocks for these processes and how the supply chain might look different in the future.

Figure 1 – Generic plastic value chain [10], [11], [12], [13], [14]

How Does Pyrolysis Fit In?

Pyrolysis, while not a new process in other industries nor the only process used for advanced recycling, is new to the waste plastic space and is the leading technology in this developing sector. For a quick refresh on the pyrolysis process read Brad Price’s blog post A Primer on Pyrolysis. Currently, there is no standardized feedstock specification for plastic pyrolysis, which can create challenges for startups and other businesses in the plastic supply chain.

As pyrolysis technology scales there are a couple key factors driving supply chain and value chain development.

1. What pyrolysis product quality can the customer (downstream petrochemical plants) accept?
2. What streams of plastic are available in large quantities on a consistent basis that can be processed to meet those customers’ demands?

The main product of pyrolysis of plastic is a liquid stream (pyoil) that is either sold with or without being separated into different boiling ranges and fed to existing processes in the petrochemical industry that make monomers for new plastic products. Perhaps not surprisingly, the downstream processes in the petrochemical industry along with pyrolysis plant operability considerations will dictate the quality of the pyoil and limit the acceptable levels of containments allowed in the pyrolysis feed streams.

To complicate matters, the current infrastructure setup for collection of waste plastic via mechanical recycling at Material Recovery Facilities (MRFs) will dictate the availability of the different types of feed.

A Proposed Waste Plastic Feedstock Specification

The Alliance to End Plastic Waste, a global non-profit whose mission is to end plastic waste in the environment and invests in innovative waste management solutions, conducted a study surveying current pyrolysis operators about their feedstock streams and contaminants. Aggregating all the responses provides a good starting point for an industry specification to show what is being processed today and to start the conversation on what plastic waste streams could be targeted going forward, and how waste managers might change their operations to meet growing pyrolysis feed demand. This specification shows that pyrolysis can handle more contaminants than mechanical recycling but there are still restrictions. One of the key specifications is the PVC/PDVC content, which needs to be kept to a minimum for corrosion mitigation while also acknowledging that, with current sorting technology for waste streams, it cannot be eliminated entirely. Another key specification concerns organic contaminants, providing guidance on how much post-consumer plastic can be accepted by pyrolysis operators and a target to help drive down organic contaminants in post-consumer plastic waste streams in the future so that more post-consumer material can be recycled.

Figure 2 – From Feedstock Quality Guidelines for Pyrolysis of Waste Plastic published by Alliance to End Plastic Waste August 2022 [1]

For more details on each plastic type see the Appendix below.

Individual pyrolysis operators will vary specs based on economically available feed material in their location, different restrictions of their pyrolysis technology and equipment at the plant, and differing customer expectations and restrictions so this represents a generalized target that conveys trends in the industry.

Why Is a Feedstock Specification Important?

There are overlapping feedstock streams between mechanical recycling and pyrolysis plants, and both benefit from consistent, well sorted and cleaned feed streams, although the purity and contaminant restrictions for mechanical recycling are more stringent. As a result, pyrolysis brings some advantages and opportunities:

1. Ability to process mixed and colored PP and PE streams
2. Ability to process multi-material plastics (PP/PE mixed films with small amounts of aluminum, PET, PVC, EVOH, or nylon contaminants)
3. Ability to process feed streams with more organic contaminants, which is a major barrier to increasing the amount of post-consumer plastic that is mechanically recycled.
4. Ability to process feeds that have historically been uneconomic to mechanically recycle (PS and LDPE/HDPE films)
5. Ability for the product to be integrated into existing petrochemical supply chains and comingled with virgin plastic feedstock materials.
6. Ability to supply food grade and medical grade applications, avoiding downcycling common in mechanical recycling applications due to decreased mechanical integrity of the material from contaminants and added thermal and mechanical stress during melting and reextrusion.

There are also some drawbacks; mainly the energy intensity, the highly-trained workforce needed to operate pyrolysis plants, and the yield (it is not possible to recover 100 percent of the recycled plastic feedstock as new plastic products). These drawbacks mean that pyrolysis is best placed as a complementary solution to mechanical recycling; able to accept streams that are rejected from MRFs but still fit within specified contaminant limits for pyrolysis. Pyrolysis can also be used for end-of-life plastics that can no longer be mechanically recycled and plastic streams that have historically not been collected because there has been no economically viable way to mechanically recycle them (e.g. films, multi-material products, polystyrene etc).

A waste plastic pyrolysis plant feed specification is a starting point in communicating to all the participants in the plastic value chain which plastic resins can be targeted by pyrolysis operators. Such a specification will change with new advancements and growth in the circular plastic sector.

A feed specification for pyrolysis will impact, and will in turn be informed by:

• Expansion and advancement in collection of waste plastic as additional recycling infrastructure is built
• Sorting at MRFs that are transforming to accommodate and optimize both advanced recycling and mechanical recycling feed quality requirements as well as implementing advanced sorting technologies (ex. Infrared spectroscopy, hyperspectral imaging, florescence imaging, or use of markers and tracers)
• Optimization of pyrolysis plant yields, product quality, and operability
• Technical innovation in pre- and post-pyrolysis treatment technology to treat contaminants
• Product recipes, as manufacturers start targeting higher and higher percentages of recycled material and responding to new requirements from customers and regulatory bodies to incorporate end of life in product design
• Market development and transparency; sellers and buyers would have a standard to compare different material and price, which provides the larger financial markets with more understanding of waste plastic as a resource. Transactions will become more efficient and transparent with increasing understanding of value chain drivers and opportunities for further investment
• Collaboration of government, private business, research, and other parties, leading to more informed policy, technological advancement, quicker scaling, increased efficiency, increased transparency, and increased sustainability throughout the value chain

Going forward, the chemically recycled plastic value chain is likely to evolve iteratively with market dynamics and technological advances but progress starts with a shared understanding of what can be recycled and how it can be recycled most economically.

Further Reading – How Are Plastics Classified?

To understand how this specification came about, let’s dive in and look at the different plastic resins in the context of pyrolysis and mechanical recycling. Plastic goods are classified by Resin Identification Codes (RICs), which are used somewhat consistently internationally and printed or embossed on plastic products. It is a common misconception that these symbols mean the plastic product is recyclable when, in reality, it’s a mark to identify what specific type of plastic a product is made from.

Figure 3 – Resin Identification Numbers [3]

Polyethylene Terephthalate (PET): PET (the ubiquitous plastic water bottle) is recyclable but must be segregated as its own stream to be mechanically recycled by grinding, cleaning, and remelting back to pellets. Pyrolysis processes can take a limited amount of PET because it introduces oxygen into the process, which can be problematic as it produces high yields of gases and char which are not circular products and are uneconomic to make use of. There is ongoing development on some other chemical recycling processes for PET involving different process reactants, catalysts, and operating conditions, but in all cases, PET needs to be segregated from other plastics and is therefore not a candidate for mixed plastic pyrolysis feed.

High Density Polyethylene (HDPE): Rigid HDPE (food and cleaning product containers) is recyclable and does get collected, sorted, and mechanically recycled today. However, a lot of this material gets rejected at the MRFs due to organic contamination, color, or other additives, and ends up in the landfill. HDPE is an acceptable feed for pyrolysis and the pyrolysis process is more forgiving of contaminants, making the HDPE rejected from mechanical recycling an ideal feedstock for pyrolysis.

Polyvinyl Chloride (PVC): PVC (pipes, lawn furniture, hoses, window frames) is not collected from household curbside service but there are specialty businesses that will recycle it at certain drop-off locations. The main issue with PVC and the reason it is considered a contaminant in most mechanical and chemical recycling processes is the high chlorine (Cl) content and the additives that are used in PVC manufacturing. PVC in pyrolysis feed should be minimized as Cl forms hydrochloric acid (HCl) and in the presence of water will cause corrosion in the plant and transport infrastructure. Cl is also a catalyst poison in downstream petrochemical processes. PVC can be mechanically recycled although it is difficult due to the special formulations and additives in each PVC product, which means each PVC product would have to be separated from other PVC products to maintain quality and usefulness of the recycled material (ex. only the same formula PVC pipes could be recycled into new pipes, only the same types of PVC hoses could be mechanically recycled into new hoses etc)

Low Density Polyethylene (LDPE): LDPE (squeeze bottles, film packaging for food) is generally not recyclable through curbside service although some locations will accept it. LDPE plastic bags (shopping bags) are not recycled through curbside pickup. There are receptacles for LDPE bags at grocery stores but usage of this collection system remains low, meaning that most plastic bags are not recycled and end up in landfills. Plastic bags need to be segregated from the mechanical recycling supply chain because they will jam machinery in sorting facilities. However, there is no issue with LDPE as a feedstock for either mechanical recycling or pyrolysis. LDPE is an opportunity for both mechanical and chemical recycling but must overcome the economic barriers of segregated collection and preparation.

Polypropylene (PP): PP (pallets, bottle caps, jars, bumpers, plastic bins, straws etc.) is recyclable through regular curbside service and is a main feedstock for mechanical recycling. This is also a main feedstock for pyrolysis and is accepted in pure or mixed streams if containments are low enough.

Polystyrene (PS): PS (packing peanuts, coffee cups, takeout containers, etc.) is not readily recycled in current mechanical recycling plants and not collected and aggregated through curbside recycling programs. Pyrolysis of polystyrene is still early in commercialization but is being processed by pyrolysis operators today despite the underdeveloped supply chain.

Others: Polycarbonate (PC), Acrylic plastics (ex. ABS), Polyamide (Nylon): Largely considered as contaminants in both mechanical and chemical recycling and not collected for recycling through curbside programs with very few exceptions.

 

Works Cited

[1] Gendell, Adam, and Vera Lahme. Feedstock Quality Guidelines for Pyrolysis of Plastic Waste. Eunomia, Aug. 2022, p. 43, https://endplasticwaste.org/-/media/Project/AEPW/Alliance/Our-Stories/Feedstock-Quality-Guidelines-for-Pyrolysis-of-Plastic-Waste.pdf?rev=44dca58903154225b453b358c80c4dc3&hash=3D9ADC9211C4DE44ED8E0F2B87A3ACBE

[2] Resin Identification Code (RIC) | Environmental Claims on Packaging: A Guide for Alameda County Businesses. http://guides.stopwaste.org/packaging/avoiding-pitfalls/resin-identification-code.

[3]  StackPath. https://www.recyclingtoday.com/article/the-outlook-for-advanced-recycling/.http://guides.stopwaste.org/packaging/avoiding-pitfalls/resin-identification-code

[4] Chemical and Mechanical Recycling Can Coexist. Will They? 16 Sept. 2022, https://www.ptonline.com/blog/post/chemical-and-mechanical-recycling-can-coexist-will-they-

[5]  StackPath. https://www.recyclingtoday.com/news/greenback-chemical-mechanical-recycling-coexist-europe-uk/. Accessed 28 Mar. 2023.

[6] Circular Plastics | Economist Impact. https://impact.economist.com/sustainability/circular-economies/inside-the-circle-circular-plastics. Accessed 28 Mar. 2023.

[7] What Can Go in Your Curbside Recycling Bin? | LoadUp. https://goloadup.com/what-can-go-curbside-recycling-bin/. Accessed 28 Mar. 2023.

[8] Brooks, Amy L., et al. “The Chinese Import Ban and Its Impact on Global Plastic Waste Trade.” Science Advances, vol. 4, no. 6, June 2018, p. eaat0131. DOI.org (Crossref), https://doi.org/10.1126/sciadv.aat0131.[9] Mangold, H. and von Vacano, B. (2022), The Frontier of Plastics Recycling: Rethinking Waste as a Resource for High-Value Applications. Macromol. Chem. Phys., 223: 2100488. https://doi.org/10.1002/macp.202100488

[9] Mangold, H. and von Vacano, B. (2022), The Frontier of Plastics Recycling: Rethinking Waste as a Resource for High-Value Applications. Macromol. Chem. Phys., 223: 2100488. https://doi.org/10.1002/macp.202100488

[10] Petrochemical icons created by Eucalyp – Flaticon

[11] Waste icons created by noomtah – Flaticon

[12] Oil refinery icons created by maswan – Flaticon

[13] Plastic icons created by photo3idea_studio – Flaticon

[14] Landfill icons created by Umeicon – Flaticon