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Understanding the Impact of Mass Balance Approaches on Pyrolysis Yield

Anthony Schiavo, Research Director
May 19, 2021

Mass balance approaches are one of the emerging regulatory schemes designed to tackle the issue of accounting for thermal recycling approaches – see our companion blog here. In mass balance approaches, the post-consumer waste and/or biomass inputs are physically mixed with conventional fossil oil or gas. However, the recycled or bio-based content can be attributed only to chosen portions of the overall output from the process.

We discuss the pros and cons of this approach in the companion piece, but the following is the important element: The free attribution of recycled content to chosen outputs has a substantial impact on the apparent yield of recycled plastics.

In our model of pyrolysis in Lux's Sustainable Plastics Roadmap, we modeled three major points that impact the polymer yield of the pyrolysis process.

  1. First, the yield of pyrolysis oil: How much raw oil output is there from a ton of plastic waste vs. byproducts like process gas and char?

  2. Second is the yield of the hydrotreating process: How much oil is lost in upgrading pyrolysis oil to a ready-to-crack product?

  3. Last is the polymer yield: When fed into a refinery, how much of that upgraded pyrolysis oil ends up as monomers or polymer inputs vs. fuels or heavy products?

Making Sense of Sustainability

Mass balance approaches have a major impact on this last category of polymer yield. In reality, the yield of polymer products is limited by the refining approach and the composition of the oil; it's typically less than 20% but can be as high as the mid-60% range for some crude-to-chemicals approaches.

However, the free assignment of mass input to product output under mass balance approaches would allow chemical companies to allocate the entire volume of pyrolysis oil input to polymer outputs. Thus, raising the attributed polymer yield of pyrolysis oil to 100%.

It's important to recognize that this change is only on paper – the actual yield of a barrel of pyrolysis oil is not changing. This has the biggest impact at low levels of pyrolysis oil blending, as the total volume of polymers produced from all sources (pyrolysis oil and fossil oil) is much larger than the total volume of actual pyrolysis oil-derived polymers.

The polymer yield is one of the biggest point pain points of pyrolysis-based recycling. As we called out in the Sustainable Plastics Roadmap, pyrolysis is a good way to manage unrecyclable waste but a poor way to make plastics due to the low polymer yield. The impact of mass balancing approaches is hard to understate.

Lux Research - Materials - Newsletter

In our likely case scenario, pyrolysis has an overall polymer yield of 9% (it's so low because we expect a substantial portion of pyrolysis developers to not crack the pyrolysis into polymers). Under a mass balance scheme, the apparent polymer yield could rise to 100%, adding an additional 14 million tons of polymer yield to pyrolysis – increasing output by an order of magnitude over our likely case scenario. 

Lux Research Recycled Plastics Output

This would drive the global share of sustainable plastics from 15% in our likely case scenario to around 19.5%, a 30% increase. There could be substantial financial benefits to the chemicals industry if recycled polymers command a price premium or if there are regulatory incentives that reward polymer output. If chemical companies can sell "recycled" plastic for $100 more per ton (well within the existing premiums for PET, for example), the adoption of mass balance approaches would bring in an additional $1.4 billion.

It's important to recognize that these changes do not reflect any actual difference in real recycling. They are simply a difference in how recycled content is accounted for. Organizations – especially those in policymaking roles – need to recognize that the adoption of mass balance approaches is likely to amount to a multibillion-dollar subsidy for the chemicals and oil and gas players building out pyrolysis capacity.

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