Towards High-Quality Petrochemical Feedstocks from Plastic Waste Pyrolysisoils: Contaminant Removal Via Filtration and Its Impact on Steam Cracking

Chemical recycling of plastic waste has the potential to overcome current hurdles of post-consumer
plastic waste recycling as it is believed to be more robust towards contaminants and mixed feedstocks
compared to mechanical recycling. Converting waste polymers into its chemical building blocks via
(thermo)chemical processes such as pyrolysis followed by steam cracking enables the production of
virgin-grade polymer products to close the material loop towards a circular economy1-4. However,
chemical recycling via pyrolysis and steam cracking still faces several hurdles which are related to the
high variety of different polymers present in plastic waste and the extensive use of plastic additives that
lead to contamination of the corresponding pyrolysis oils5, 6. In fact, it has been shown that contaminants
are the main factor that decides if plastic waste pyrolysis oils are acceptable for industrial steam crackers
or if the operational risks will hamper the use of these alternative feedstocks. Particularly, metal
contaminants that originate from additives are highly problematic in terms of crucial aspects such as
fouling, coke formation or downstream catalyst poisoning7. This has been shown in our recent study
where steam cracking of crude plastic waste pyrolysis oils led to a substantial increased coke formation
compared to pure fossil naphtha cracking. The observed coke formation could be directly related to high
concentrations of contaminants, in particular, of metal contaminants in the pyrolysis oils8.
In this study, we are following-up on the observed metal-related coke formation by investigating the
potential of filtration as an effective upgrading step to remove metal contaminants from crude plastic
waste pyrolysis oil using different filtration media. The pyrolysis oils have been produced from
contaminated post-consumer plastic waste which was processed at Ghent University in Belgium8. In
order to assess the effect of the filtration step on the steam cracking performance, continuous
experiments have been performed in a bench-scale steam cracking unit including the detailed on-line
analysis of the entire product range and the assessment of the radiant coil coke formation. Based on
the detailed analysis of the filtrates using inductively coupled plasma – optical emission spectrometry
(ICP-OES), it was found that a substantial reduction of metals was reached with the tested media,
however, with different removal efficiencies based on the media filtration grades. By means of the total
metal concentration in the filtered pyrolysis oils, between 25.0% and 81.5% of the metals were removed.
Steam cracking tests show that a substantial reduction in coke formation could be achieved by filtering
out metal contaminants from the crude plastic waste pyrolysis oils. Furthermore, the removal of certain
metals allows to shed further light on the individual impacts of strong coke formation inducers such as
sodium, iron and nickel. With this study it is shown that high efficiency filtration is an effective treatment
step to overcome one of the most critical obstacles for the application of plastic waste derived feedstocks
used in steam cracking.

References
1. M. Solis, et al., Waste Manage., 2020, 105, 128-138.
2. O. Dogu, et al., Prog. Energy Combust. Sci., 2021, 84, 100901.
3. K. Ragaert, et al., Waste Manage., 2017, 69, 24-58.
4. R. Palos, et al., Energy Fuels, 2021, 35, 3529-3557.
5. M. Kusenberg, et al., Fuel Process. Technol., 2022, 227, 107090.
6. M. Roosen, et al., Environ. Sci. Technol., 2020, 54, 13282-13293.
7. M. Kusenberg, et al., Waste Manage., 2022, 138, 83-115.
8. M. Kusenberg, et al., Waste Manage., 2022, 141, 104-114.