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To what extent is pretreatment needed to protect hydrotreaters/hydrocrackers from impurities when upgrading WPO to petrochemical feedstocks?

Mar-2025

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Daniel Hogg, KBR, daniel.hogg@kbr.com

The extent of pretreatment required is dependent upon the waste plastic oil contaminant load, the potential for coprocessing, and the requirements and limitations of the downstream conversion units. These parameters need to be studied and well defined in to understand the implications. The broad range of contaminants found in waste plastic oils and the concentrations can be highly variable depending on the types of bulk waste plastic processed, method of pyrolysis oil generation, or even the sourced region. It is often difficult for an owner-operator to predict what their continuous waste plastic supply stream will look like for future operations. Often the few sample analyses they have performed have not been completely characterized to fully understand the concerns and potential risks to the hydroprocessing units. The contaminant levels with waste plastics pyrolysis oils are orders of magnitude higher than conventional fossil feedstocks. Typical hydroprocessing units and downstream conversion units are generally not capable of processing these feedstocks without some measure of pretreatment. Highly reactive diolefins are characteristic of most waste plastic pyrolysis oils and must be properly managed before the recycled materials can be further processed. If not properly reduced, diolefins will polymerize to form gums in the downstream hydroprocessing reactors resulting in a unit shutdown due to unacceptably high differential pressures. Silicon particles are highly problematic and often found in elevated quantities in waste plastic oils. Silicon forms a barrier on hydroprocessing catalyst surfaces and reduces the overall reaction rates, expected catalyst life, and considerably increases pressure drop in the reactor. High levels of chlorides are also endemic of pyrolysis oils. Halides are well known hazards in hydroprocessing units and sublimation of associated ammonium salts must be carefully studied and addressed in the unit design and heat integration. Metal species common to waste plastic oils can permanently poison or inhibit hydroprocessing catalysts and therefore should be removed prior to further processing. The pick-up of metals such as arsenic, mercury, tin, and lead are quite different from the uptake of metals common to conventional hydrodemetallization reactors, such as phosphorus, iron, and vanadium. A guard bed should be designed specifically to eliminate these contaminants in an efficient manner. KBR has the benefit of collaborating globally with multiple operators and has insight into commonly found waste plastics pyrolysis oil compositions, as well as a good understanding of outlier concerns. We have aligned a set of intelligent assumptions based on our experience to ensure that the Upgrading Unit design can adequately manage all waste plastic pyrolysis oil contaminants.

Mar-2025
Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

The processing of WPPO (Waste Plastics Pyrolysis Oil) in hydroprocessing units represents a great challenge due to the high variety and amount of impurities in this kind of feed like halogens, metals, silicon, oxygen, sulfur, nitrogen, chlorides, and the high concentration of unsaturated molecules. This characteristic makes essential an adequate pretreatment step in the hydroprocessing units aiming to protect the active catalyst beds and ensure adequate lifecycle to the processing unit. Some studies indicates that the best catalyst formulation to processing WPPO feeds is a mixing of MCM-41 with adequate pore distribution and zeolite applied in the pretreating reactor aiming to ensure adequate cracking of large molecules and impurities removal, protecting the main reactor which contain the hydrotreating/hydrocracking catalysts. The main objective of the pretreatment section is to stabilize the feed removing contaminants and unsaturations from the molecules, making the hydroprocessing reactions easier and reducing the poisoning rate of the hydroprocessing catalysts. Considering the characteristics of the WPPO feeds, this section is essential to ensure economic and sustainable operations. A good reference regarding the hydrotreating process dedicated to processing WPPO is the MAXFLUX (TM) technology licensed by Sulzer Company.

Mar-2025
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
Rainer Rakoczy, Clariant, rainer.rakoczy@clariant.com

Utilisation and conversion of waste plastic pyrolysis oil is of increasing industrial interest. There are multiple options from a technical standpoint utilising these materials with the highest desire to get the materials back to steam crackers to follow a circular economy concept. Nevertheless, a low-hanging fruit may be the utilisation of older or smaller process equipment in a refinery or a refinery complex with certain access to petrochemical equipment utilising small quantities of an available WPO source to treat or pretreat it for application through coprocessing in the hydrocracker or catalytic cracker. Clariant has expanded the proprietary Clarity, HDMax, and even Hydex portfolio to handle this demanding feedstock and convert it towards feedstock for the aforementioned processes.

Mar-2025
Chris Ploetz, Burns & McDonnell, cploetz@burnsmcd.com

When used as a petrochemical feedstock, the composition and physical properties of raw WPO, also called waste plastic pyrolysis oil (WPPO) or plastic pyrolysis oil (PPO), can cause various challenges in downstream processes. The nature of these challenges varies depending on the disposition of the oil as steam cracker feed, FCC feed, or hydroprocessing unit feed. Usage of these oils in a steam cracker or FCC supports circularity in the polyolefins market (for example, high-density polyethylene [HDPE], low-density polyethylene [LDPE], and polypropylene [PP]), whereas usage in a hydroprocessing unit (with subsequent processing through a reformer and aromatics complex) supports circularity in the aromatic derivatives market (for example, polyethylene terephthalate [PET], polystyrene, and nylon).

From the perspective of downstream processing as a petrochemical feedstock, notable characteristics of WPO include the following: high vapour pressure, low flash point, wide boiling range with heavy tail, high pour point, high levels of unsaturation (including diolefins), chemically bound oxygen and nitrogen, chemically bound halogens (primarily chlorine due to PVC in waste plastic), metals and other heteroatoms (for example, silicon and phosphorus), and particulates (reactor solids consisting of carbonaceous char and calcium halides).

All of these properties can be problematic in downstream processing, but the issues are magnified if the feed is to be 100% pyrolysis oil. In lieu of this, many refinery and petrochemical operators are considering pyrolysis oil blending at relatively small fractions with traditional feedstocks in order to reduce the adverse impacts of raw pyrolysis oil while still gaining credit for recycled content via certification from International Sustainability and Carbon Certification (ISCC) Plus or other third parties.

Specific pretreatment needs upstream of a hydroprocessing unit should focus on addressing diolefins, metals, silicon, phosphorus, and particulates. Diolefins should be saturated in a selective hydrogenation unit (SHU) to avoid oligomerisation at high temperatures in the reactor feed preheat train. Metals, silicon, and phosphorus should be removed using guard beds to avoid poisoning and pluggage/fouling of the main reactor catalyst bed.

Primary particulate removal should be accomplished at the pyrolysis facility, but users of WPO should also install filtration systems to prevent plugging of exchangers, catalyst beds, and control valves. Within the hydroprocessing unit, metallurgy should be evaluated for the presence of chemically bound chlorine and other halogens, which will react to form hydrochloric acid (HCl) and hydrofluoric acid (HF) within the reactor. These acidic compounds will ultimately be removed with the acidic sour water decant streams at the cold separator vessels downstream from the reactor.

Additionally, any user of WPO needs to consider the high vapour pressure (if unstabilised), low flash point, and high pour point. The vapour pressure of unstabilised pyrolysis oil can preclude storage in atmospheric tanks. The low flash point (typically <<100˚F) requires pyrolysis oils to be treated as a flammable liquid despite being relatively heavy. The high pour point (substantially above summer ambient temperatures) requires heat tracing or other methods of maintaining adequate storage and process temperatures to avoid pluggage due to wax build-up.

Although these pretreatment steps add cost to a project, new technology is not required; all these strategies are within the general experience of the refining and petrochemical industry. Catalyst and adsorbent providers are actively working to optimise their products and services to meet the needs of the pyrolysis oil market. Each WPO user should craft these considerations into a tailored pretreatment scheme that meets the needs of their specific application, considering the actual properties of the candidate pyrolysis oil and the needs of the downstream process.

Mar-2025
Woody Shiflett, Blue Ridge Consulting, blueridgeconsulting2020@outlook.com

WPOs contain a myriad of contaminants that are highly variable depending on what waste plastics constitute the pyrolysis process feedstock and what type of pyrolysis process is employed (thermal and catalytic). Some of these contaminants are in the form of particulates. Many of these contaminants can be removed simply by depth filtration in pretreatment reactors or beds, as has been reported in a joint Ghent University/Pall Corporation study. Mixed polyolefin pyrolysis oils tested have shown some 80% of metals removed in this manner and exhibit 40-60% less coke formation downstream.

Fossil fuel feed contaminants tend to be limited to Ni and V in the heaviest stocks (vacuum gasoil [VGO], deasphalted oil [DAO], and residue), Fe in many feeds from upstream corrosion products, or Si in lighter coker-derived feeds (naphtha and kero). WPO can introduce high levels of Na (as 10s-100s ppm), higher levels of Si and Fe (10s of ppm), some Pb (~ <10 ppm), and significantly high levels of chlorine (Cl) (100s of ppm). Clearly, in any case, some significant pretreatment is and will be required.

Most technology providers and catalyst suppliers actively engage in guard catalyst and ‘hydrodemetallisation’ catalyst development to meet the needs of emerging feedstocks, with the renewables co-processing and hydroprocessing area being a somewhat recent example over the prior decade or two.

WPO processing guard catalyst development is and will be following. Speciality guard material innovators and suppliers, such as Crystaphase (Houston, TX), are and will be tailoring specialised trapping guard systems to address these needs. As WPO processes enter full commercial-scale applications, more detailed physical and chemical characterisation of contaminants will be needed in order to design and optimise appropriate pretreatment and guard material processes and products.

Mar-2025
Scott Sayles, Becht, ssayles@becht.com

Waste plastic oil (WPO) has potential impurities that cause catalyst deactivation. The types of impurities depend on the plastic type being fed to the liquefaction device. Typical feed contaminants are nitrogen, oxygen, olefins, phosphorus, silicon, and chlorides. For example, polyvinyl chloride (PVC) has the most difficult composition, mainly due to the chloride concentration and some metal stabilisers, while polypropylene has the least. The waste plastic received is a mixture of all plastic types. Some sorting is used to remove the hardest-to-process plastics, but the resulting feed is typically a mix of plastic types.

The level of contamination that reaches the hydroprocessing reactors determines the rate of catalyst deactivation. The higher the contamination, the shorter the run length that is observed; this is similar to fossil fuel deactivation. The individual contaminants have individual deactivation rates, and they are also cumulative. The contaminants are at higher concentrations and lower boiling ranges than the equivalent fossil fuels, resulting in higher overall catalyst deactivation. The plastic liquefaction step does not seem to impact the contaminant concentration. However, a pretreatment unit such as that used for renewable feeds is not required.

The method of producing the plastic oil also determines the level of contamination, with hydroliquefaction (HTL) removing more contaminants and pyrolysis retaining more contaminants in the liquid phase.

Mar-2025