Question
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To what extent is pretreatment needed to protect hydrotreaters/hydrocrackers from impurities when upgrading WPO to petrochemical feedstocks?
Mar-2025
Answers
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Trine Dabros, Topsoe, trar@topsoe.com
Raw waste plastic pyrolysis oils (WPOs) are highly contaminated with elemental traces of metals and impurities like silicon, iron, phosphorous, halogens (F, Cl, Br) and heteroatoms like nitrogen, oxygen, and sulfur. Due to the high content of contaminants, WPOs can be fed directly to fluid catalytic crackers (FCCs) or steam crackers only at very high dilution rates.
To increase the recycled content in a steam cracker feed stream, hydrotreating and optionally also hydrocracking is required to bring the WPO onto a specification suitable for large scale downstream processing. These hydrotreating and hydrocracking steps must be tailored for contaminant removal and adjustment of oil properties (such as the boiling point curve) to enable smooth and issue free operation of existing assets with this new type of feedstock. Several of these contaminants are known from traditional fossil refinery feedstocks, but with plastic derived oils, they are now locked in different molecular structures and present in different concentrations. This means that known hydroprocessing steps need to be combined and adapted in an optimal way to meet the demands of this new feedstock. Further performance improvements can be achieved with customized catalysts which maximize the uptake of certain contaminants.
At Topsoe, we have been gaining experience analyzing and testing a vast number of new and challenging non-fossil feedstocks for close to three decades - from renewable bio-based feeds used in the HydroFlex™ process yielding renewable diesel and sustainable aviation fuel, to plastic derived feeds used in the PureStep™ process for circular plastic via naphtha. To get a broad understanding of a new feedstock such as WPO, it is crucial to cover various plastic sources and capture liquefaction technology differences by obtaining it from different providers, to analyze it in-depth, not just for bulk properties like total contaminant content, but also for the identity of the individual contaminant species. This can be done in parallel with catalyst development and pilot plant testing, two vital steps in technology development. This way of working has led to the successful start-up of two industrial references on hydroprocessing of WPOs in Europe in 2024 and 2025 with the Topsoe PureStep™ technology.
Until now, the focus on pretreatment and contaminant removal in WPOs has mainly been on meeting the steam cracker feedstock requirements for given contaminants. But another important aspect is to assess the impact of hydroprocessed WPOs also in the steam cracker and refine the specification requirements further. Therefore, Topsoe is currently looking at bridging the knowledge gap between hydroprocessing and steam cracking by investigating the impact of different hydroprocessed WPOs on the steam cracker yields and incorporating this feedback in further development.
Hydroprocessing of WPOs can be understood as a pretreatment necessary to integrate WPO in the existing production facilities. However, some caution is needed when using the term pretreatment, as several of the steps in plastic recycling require some kind of pretreatment. This can for example be the sorting and cleaning steps required for plastic waste before pyrolysis or it can be post-pyrolysis single contaminant clean-up steps as is the case for use of sorbents. A combination of hydroprocessing and other pretreatment steps could have economic benefits, but that would depend on the continued development and optimization of the non-hydroprocessing technologies. Overall, the value chain is still new and through collaboration across and learnings from the operating assets slowly coming on stream, further process efficiency and cost benefits can be expected.
Mar-2025
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