Plastics: Squaring the Circular Economy
Emerging analytical methods for more precise quantification of hydrocarbon composition and impurity detection may prove essential to realizing a circular plastic economy
Melissa N. Dunkle | | 12 min read | Discussion
Plastics are an integral part of our daily lives, found in everything from synthetic fabrics used for clothing to food packaging, building materials, and more. As the global population has grown, so has the production of plastics, which reached 475 million tons in 2022 (1,2). However, only about 12 percent of this plastic is collected for recycling (3,4). So where does the rest go? Approximately 80 percent of the remaining plastic is never recovered; it is either mismanaged, ending up in landfills, or incinerated, following the traditional linear economy model for plastics (5,6). A global shift is needed to transition from this linear economy to a circular economy for plastics, requiring action not just from governments and industries but also from consumers.
Governments are beginning to create legislation that mandates minimum recycled content in plastics. For example, the EU's Single-Use Plastics Directive requires that plastic bottles contain at least 25 percent recycled plastic by 2025, increasing to 30 percent by 2030 (7). As we move towards a circular economy for plastics, similar legislation around minimum recycled content for other plastic materials is expected to be implemented by various countries worldwide.
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Achieving a circular economy for plastics will require different recycling technologies to close the loop. While mechanical recycling for rigid plastic bottles is well-established, not all types of plastics can be easily recycled this way. For this reason, advanced recycling (also known as chemical recycling) is gaining attention as a viable alternative. In mechanical recycling, the polymer structure is maintained, but in advanced recycling, plastics are broken down into their original monomers. Several technology routes can be used for advanced recycling, including solvolysis, pyrolysis, and gasification. For more detailed information on advanced recycling technologies, readers can refer to various review articles on the topic (8, 9, 10).
While industry plays a crucial role in innovating and developing new technologies to support a circular economy, consumers must also recognize how their choices impact the environment. This includes being mindful of the products they purchase and ensuring proper sorting and disposal of waste. However, staying well-informed can be challenging given the sheer volume of information in the media, where public opinion can sometimes outweigh scientific facts. For example, at the supermarket, I’ve noticed that many items previously offered in single-use plastic containers are now available in PLA-coated paper (PLA: polylactic acid), and single-use plastic bags have been replaced by paper bags for loose food items. But which option is truly better for the environment?
If we only consider specific aspects of a life cycle assessment (LCA), we might draw skewed or biased conclusions. Therefore, a standardized approach to LCAs is crucial (11). For guidance, ISO 14040:2006/Amd 1:2020 and ISO 14044:2006/Amd 2:2020 standards are available (12,13). When considering a cradle-to-grave LCA of plastics versus other alternatives, and factoring in recycling at the end of life, plastics can sometimes achieve a lower LCA score. For instance, a study on single-use food containers found that plastic packaging offered several environmental benefits over PLA-coated paper, resulting in a better cradle-to-grave LCA score for plastic (14). Similarly, studies comparing single-use plastic bags to paper bags (and other materials) have indicated that plastic, particularly high-density polyethylene (HDPE), can be the more environmentally friendly option (15,16).
This doesn’t mean that plastic will always have a better LCA score, but it underscores the importance of creating awareness based on scientific facts using standardized approaches.
Dow’s Sustainability Goals
Protecting the Climate and Advancing a Circular Economy are two key focus areas for Dow (17,18). A major initiative from Dow in protecting the climate is climate mitigation through decarbonization. Dow has developed a Path2Zero plan aimed at reducing scope 1 and 2 emissions within its assets, as well as working with suppliers to reduce scope 3 emissions. While the plan includes a stepwise approach to emission reductions, the long-term goal is to achieve carbon neutrality (covering scope 1, 2, and 3 emissions) by 2050. Dow has initiated this effort with the Fort Saskatchewan Path2Zero expansion project in Alberta, Canada, investing in the world’s first net-zero emission, integrated ethylene cracker (addressing scope 1 and 2 emissions) (19,20).
To advance a circular economy, Dow has announced its Transform the Waste goal, committing to transforming plastic waste and other forms of alternative feedstocks into 3 million metric tons of circular and renewable solutions annually by 2030 (17,18). This goal will be achieved through a combination of mechanical recycling, advanced recycling of plastics, and the incorporation of bio-based options.
The need for analytical data
Analytical evaluation and data processing are key components in achieving plastics circularity. While this example focuses on advanced recycling through pyrolysis, it’s important to note that such evaluations and data are equally crucial when considering mechanical recycling or other advanced recycling technologies.
In advanced recycling via pyrolysis, the importance of analytical data becomes clear. Pyrolysis involves heating waste plastic to temperatures that thermally decompose it into three fractions: gas, oil, and char. For advanced recycling purposes, the oil fraction is considered a potential feedstock for steam cracking. However, depending on the composition of the waste plastic feed, the oil fraction may contain not only hydrocarbons but also undesired impurities. These impurities can include nitrogen species (e.g., from the degradation of polyamide in the plastic feed), oxygenates (e.g., from polyvinyl alcohol, polyethylene terephthalate, or additives), aluminum (e.g., from poly-Al packaging), chlorine (e.g., from polyvinylchloride or additives), and more.
Additionally, the hydrocarbon composition of plastic pyrolysis oils does not align with current steam cracker specifications, where the Platts open naphtha specification is typically used as a guideline (21). Plastic pyrolysis oils often contain high levels of olefins (e.g., from polyethylene, polypropylene, and other polymers) and aromatics (e.g., from polyethylene terephthalate, polystyrene). Therefore, crude plastic pyrolysis oils cannot be used as a steam cracker feedstock without significant upgrading.
To select an appropriate upgrading strategy, it’s essential to conduct a thorough analytical evaluation of the plastic pyrolysis oils to understand both the hydrocarbon composition and the impurity profile. This information is crucial for making informed decisions about which upgrading technologies will effectively remove or eliminate the impurities and improve the hydrocarbon composition, bringing the plastic pyrolysis oil into specification.
While the chemical industry has decades of experience analyzing fossil-based feedstocks, it would be a mistake to assume that these established methods can be directly applied to the analysis of crude plastic pyrolysis oils. Crude plastic pyrolysis oils differ significantly from fossil-based feedstocks in terms of hydrocarbon composition, final boiling point, impurities, and more. As a result, research groups in both industry and academia are actively developing new analytical methods. Significant effort has been dedicated to method development for the accurate quantification of the hydrocarbon composition in crude plastic pyrolysis oils (22, 23, 24), as well as for the identification and quantification of impurity profiles (25, 26, 27, 28).
For the analytical evaluation of crude plastic pyrolysis oils, much focus has been placed on gas chromatography (GC). In the works mentioned above, both one-dimensional GC and comprehensive GC (GC×GC) were utilized, and various detector technologies were exploited. One of the newer detectors being evaluated is the vacuum ultraviolet detector (VUV), which is still relatively new to the market. GC-VUV was introduced in 2014 (29), and since then, the technique has shown promise for the characterization of the hydrocarbon composition of various materials, including crude plastic pyrolysis oils. While GC×GC can also provide insight into the hydrocarbon composition of materials, the co-elution of olefins and naphthenes in the same elution band of the 2D plot can complicate data processing when both compound classes are present. However, GC×GC is compatible with various GC detectors, including (but not limited to) mass spectrometry and element specific detectors, making this technique well suited for the characterization of the impurity profile of crude plastic pyrolysis oils.
The evaluation of crude plastic pyrolysis oils is a burgeoning area of research, with each analysis yielding new and insightful information, making it an exciting time to be an analytical chemist.
Moving forward
There are many challenges to overcome to make plastics circularity a reality. Change isn’t easy, and achieving it on a global scale will require concerted efforts from governments, industry, and consumers.
One perspective not yet discussed in this article is the cost associated with transitioning from a linear plastics economy to a circular one. According to a recent McKinsey report, the plastics industry may need to invest as much as $100 billion to achieve 20–30 percent recycled content in materials (5). Cost is just one factor that will influence the speed at which plastics circularity is implemented. Other critical considerations include technology readiness and economic feasibility, among many others.
However, before moving forward, it may be necessary to take a step back. As mentioned earlier, only around 12 percent of produced plastic is currently being collected for recycling. Optimizing existing collection and sorting infrastructures and processes is essential to increase this percentage. This challenge presents an interesting opportunity for analytical scientists, as current automated optical sorters have limitations in detecting different types of plastics. Enhancing automated sorting capabilities and possibly integrating artificial intelligence are areas worth watching.
Transitioning from a linear to a circular plastics economy will take time, but the journey has already begun. McKinsey reports that chemical industry players have committed to achieving 7 million metric tons per year of advanced recycling capacity by 2030 (30). It is challenging to predict what the landscape will look like beyond 2030, as this will depend heavily on legislation and the technological advancements that still need to occur.
In conclusion, change is happening, and progress is being made to transition from a linear economy to a circular plastics economy. For those working in this field, this represents a new and exciting area of research, where success means making a positive impact on the environment. Even if you’re not directly involved in this field, you can still contribute; we are all consumers, and our choices have an impact.
Image Credit: Collage created using Adobe Stock images
- OECD, “Global plastics use has quadrupled in 30 years, mainly driven by emerging economies: In million tonnes (Mt), 1950-202,” in: Global Plastics Outlook: Economic Drivers, Environmental Impacts and Policy Options, OECD Publishing (2022). DOI: 10.1787/a882998d-en.
- OCED, “Plastics use by polymer - projections,” (2023). DOI: 10.1787/b9bae4d1-en
- McKinsey & Company, “Addressing the challenges of plastic waste: Circularity and leakage” (2022).
- OECD, “Plastic waste collected for recycling,” OECD Environment Statistics (Database) (2023). DOI: 10.1787/09084a0e-en.
- McKinsey & Company, “McKinsey, What is circularity?” (2024).
- OECD, “Global Plastics Outlook” (2022). DOI: 10.1787/de747aef-en.
- EU, “Directive (EU) 2019/904 of the European Parliament and of the Council of 5 June 2029 on the reduction of the impact of certain plastic products on the environment,” Official Journal of the European Union (OJEU) (2019). Available at: http://data.europa.eu/eli/dir/2019/904/oj.
- J. Jiang et al., “From plastic waste to wealth using chemical recycling: A review,” J Environ Chem Eng (2022). DOI: 10.1016/j.jece.2021.106867.
- K. Ragaert, L. Delva, and K.V. Geem, “Mechanical and chemical recycling of solid plastic waste,” Waste Manag, 69, 24–58 (2017). DOI: 10.1016/j.wasman.2017.07.044.
- M. Solis and S. Silveira, “Technologies for chemical recycling of household plastics – A technical review and TRL assessment,” Waste Manag 105, 128–138 (2020). https://DOI: 10.1016/j.wasman.2020.01.038.
- R. Banerjee and S.S. Ray, “Sustainability and Life Cycle Assessment of Thermoplastic Polymers for Packaging: A Review on Fundamental Principles and Applications,” Macromol Mater Eng, 307 (2022). DOI: 10.1002/mame.202100794.
- ISO, “ISO 14040:2006/Amd 1:2020 - Environmental management - Life cycle assessment - Principles and framework” (2020). Available at: https://www.iso.org/.
- ISO, “ISO 14044:2006/Amd 2:2020 - Environmental management - Life cycle assessment - Requirements and guidelines” (2020). Available at: https://www.iso.org/.
- K. Peantham and V. Varabuntoonvit, “Sustainable solutions in single-use food containers: A comprehensive life cycle assessment comparing plastic (PP) and its green alternative (PLA coated kraft paper, PLA),” Environ Eng Res 29, 230729–0 (2024). DOI: 10.4491/eer.2023.729.
- I.D.L. Gómez and A.S. Escobar, “The dilemma of plastic bags and their substitutes: A review on LCA studies,” Sustain Prod Consum, 30, 107–116 (2022). DOI: 10.1016/j.spc.2021.11.021.
- A. Ahamed at al., ELife cycle assessment of plastic grocery bags and their alternatives in cities with confined waste management structure: A Singapore case study,” J Clean Prod, 278, 123956 (2021). DOI: 10.1016/j.jclepro.2020.123956.
- Dow, Intersections 2023 Progress Report - Advancing our ambition (2024). Available at: corporate.dow.com.
- Dow, “Ambition & Governance Overview” (2023). Available at: https://investors.dow.com.
- The Canadian Press, “‘First of its kind’: Dow invests $9 billion on Alberta net-zero petrochemical project” (2023). Available at: www.thecanadianpressnews.ca/.
- Reuters, “Dow approves investment for $6.5 bln Path2Zero project in Canada” (2023).
- S&P Global Platts, “Specifications Guide: Europe and Africa Refined Oil Products” (2020). Available at: www.spglobal.com/platts.
- M.N. Dunkle et al., “Method development and evaluation of pyrolysis oils from mixed waste plastic by GC-VUV,” J Chromatogr, A 1637, 461837 (2021). DOI: 10.1016/j.chroma.2020.461837.
- M.N. Dunkle et al., “Comparing different methods for olefin quantification in pygas and plastic pyrolysis oils: Gas chromatography-vacuum ultraviolet detection versus comprehensive gas chromatography versus bromine number titration,” J Chromatogr, A 1713, 464569 (2024). DOI: 10.1016/j.chroma.2023.464569.
- ASTM-D8519, “Standard Test Method for Determination of Hydrocarbon Types in Waste Plastic Process Oil Using Gas Chromatography with Vacuum Ultraviolet Absorption Spectroscopy Detection (GC-VUV)” (2023). Available at: astm.org.
- H.E. Toraman at al., “Detailed compositional characterization of plastic waste pyrolysis oil by comprehensive two-dimensional gas-chromatography coupled to multiple detectors,” J. Chromatogr. A, 1359, 237–246 (2014). DOI: 10.1016/j.chroma.2014.07.017.
- M. Kusenberg et al., “A comprehensive experimental investigation of plastic waste pyrolysis oil quality and its dependence on the plastic waste composition,” Fuel Process, Technol, 227, 107090 (2022). DOI: 10.1016/j.fuproc.2021.107090.
- M. Kusenberg et al., “A. Eschenbacher et al., “Opportunities and challenges for the application of post-consumer plastic waste pyrolysis oils as steam cracker feedstocks: To decontaminate or not to decontaminate?” Waste Manag, 138, 83–115 (2022). DOI: 10.1016/j.wasman.2021.11.009.
- M. Roosen et al., “Detailed Analysis of the Composition of Selected Plastic Packaging Waste Products and Its Implications for Mechanical and Thermochemical Recycling,” Environ Sci Technol, 54, 13282–13293 (2020). DOI: 10.1021/acs.est.0c03371.
- K.A. Schug et al., “Vacuum Ultraviolet Detector for Gas Chromatography,” Anal Chem 86, 8329-8335 (2014). DOI: 10.1021/ac5018343.
- McKinsey, “A unique moment in time: Scaling plastics circularity, McKinsey” (2023). Available at: https://www.mckinsey.com/.
Senior Research Scientist, Dow Benelux, The Netherlands
