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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