FEEDSTOCK
Model pyrolysis feedstock spec
Items made of PE and PP such as containers, trays, cups, films, and bags.
Minimum 85% PE or PP Maximum moisture content: 7% Maximum total contamination: 15%
The following individual contaminants must not be present in amounts exceeding their speci- fied thresholds, and the combined presence of all contaminants should not exceed 15%:
PVC/PVDC: 1% PET/EVOH/Nylon: 5% PS: 7%
Rigid metal/glass/dirt/fines: 7% Paper/organics: 10%
Source: Alliance to End Plastics Waste
into the pyrolysis process which can cause corro- sion to equipment and persist into the pyrolysis oil as heteroatoms (atoms of any element other than hydrogen or carbon). The potential for chlorine damage led several operators to express a near- zero tolerance for PVC/PVDC, although others indicated a threshold higher than 1%. The model contamination limit for PS is 7%. The
report says: “Polystyrene is generally not viewed as a prohibitive contaminant, and one operator even expressed a preference for using measured amounts of polystyrene as a process aid. Nonethe- less, it is common for pyrolysis operators to set limits on the amount of polystyrene in their feedstock.” The materials used in multilayer films are
particularly problematic. The model specification places a 5% limit on contamination from PET, PA and EVOH. Oxygen atoms in the feedstock results in oxygenated products, which reduce yield and negatively impact the quality of pyrolysis oil. Also, some more complex hydrogen-carbon structures, such as PA and PET, do not break down as easily as those of PE and PP, and some by-products of their decomposition act as impurities in the finished product. “Offtakers can accommodate these impurities by diluting the product with larger volumes of virgin hydrocarbons, using the product for lower-grade
Chemical Recycling – Global Insight 2023
applications such as fuel, or conducting hydrotreat- ment, in which hydrogen atoms are reacted with the product to chemically combine with impurities, facilitating their removal. Hydrotreatment can also be done by the pyrolysis operator prior to the offtaker, but this is rare and generally viewed by pyrolysis operators as being cost-prohibitive,” the report says. A 7% contamination limit applies to metal, glass,
dirt and fines. The main problem with these contaminants is their abrasive effect on process equipment. As they are relatively heavy, they can also increase costs as input feedstock is typically purchased on a per-unit-weight basis. Pyrolysis operators did not express any specific concern about the aluminium used in laminated packaging. Responding companies gave a fairly broad
range of thresholds for contamination by paper and organics, and the report suggests a 10% limit. Post-pyrolysis refinement can remove impurities, such as by-products of hydrogen, present in the oil. Hydrotreatment, for example, is a process in which hydrogen atoms are reacted with the product to chemically combine with impurities, facilitating their removal. But, as the report points out, hydro- treatment plants are high-cost and are therefore ruled out by pyrolysis operators. The report concludes that both mechanical and
pyrolysis recycling operators require well-sorted, clean and largely homogenous feedstock, but a difference is that pyrolysis operators can take a mix of polyolefins and colours and have a different set of considerations surrounding contaminant threshold limits. One development that would benefit both mechanical and pyrolysis recycling, it says, is changing packaging design to reduce the number of materials. This has started to happen with the launch of mono-material films designed to substitute widely-used multilayer polyolefin films. The report says the model feedstock specifica- tion describes a recycling stream that does not exist at scale today. It says it is important to under- stand what barriers exist to creating that stream, and to find solutions that take into account existing feedstock streams for mechanical recycling. It is expected that some operators will have
different tolerances to the thresholds in the model feedstock specification. This is similar to feedstock specifications for mechanical recyclers where each recycler has its own process and value considera- tions. The report also notes that many pyrolysis operators are in early stages of refining and optimising their processes, and their feedstock requirements are likely to evolve over time. �
https://endplasticwaste.org
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