Catalytic cracking catalyst poisoning

Why is there no reply? Let me start by saying that the likelihood of catalyst poisoning due to calcium is lower compared to nickel, vanadium, and sodium. However, if the calcium content in the feedstock is high and electrodesalination is not thorough, poisoning can occur. This leads to a decrease in catalyst activity, reduced reaction depth, a higher yield of oil slurry with lower density, a drop in the temperature of the regeneration bed, a significant reduction in gas production, fluctuations in density and pressure drop at the inlet of the centrifuge, caking of the catalyst, and in severe cases, blockage of the material channels

There are many similar articles on the forum; it’s worth searching for them, as they provide more detailed analysis than information available elsewhere!

Thank you for your advice! Kaichuan, my mentor and good friend

The effect of iron poisoning on FCC catalysts is similar to that of nickel, but at lower levels of poisoning, the impact on the catalysts is mild; it is only at higher levels of poisoning (> 5000 ug/g) that the damage to the catalysts becomes severe. The toxic effects of iron manifest in two ways: firstly, iron poisoning also leads to a decrease in the acidity of the catalysts and a reduction in their activity； Secondly, Fe itself also has a dehydrogenation effect, which reduces the yield of light oil and increases the yields of coke and hydrogen. The design principle of iron passivators is similar to that of nickel passivators; a substance that can react with Fe is added to form large-grained solid solutions with iron, thereby reducing the activity of iron. The phenomena associated with high iron content generally include: an increase in the regenerated dilute-phase density, low slurry density, a decrease in light yield; in severe cases, the catalyst turns yellowish. The most obvious sign of iron poisoning is the yellowing, or even reddening, of the catalyst; if the catalyst is reflective and shiny, it indicates calcium poisoning. A soil-yellow color indicates iron poisoning. Poisoning caused by other metals cannot be detected by color. After heavy metal poisoning, the selectivity of the catalyst is reduced, resulting in increased yields of coke and gases, a decrease in liquid yield, and an increase in the unsaturation of the product. Additionally, the yields of C3 and C4 in the gas decrease. Heavy metals in the raw materials can cause varying degrees of poisoning to the system catalysts, thereby reducing their selectivity. Generally speaking, in cases of severe calcium poisoning, the catalyst appears shiny to the naked eye; upon shutdown, glassy aggregates of catalyst can be found at the bottom of the regenerator. In more severe cases, these aggregates can even block the sulfidation lines! If iron poisoning is severe, the catalyst takes an earthy yellow color; the effects of iron and nickel poisoning on the catalyst are essentially the same, leading to dehydration and a significant increase in the hydrogen-to-methane ratio in the dry gas ； If vanadium and sodium poisoning is severe, the resulting sodium vanadate directly destroys the catalyst framework, causing the catalyst to be damaged! Therefore, high levels of any type of heavy metal should be taken very seriously! ! System catalyst poisoning directly affects the product distribution and yield, leading to increased yields of coke and dry gas! Therefore, to carry out catalytic cracking, it is necessary to first prepare the feedstock properly and ensure quality at the source; only then can yield be considered! ! ! ! ! ! ! Primarily affected by iron poisoning. Current measures mainly involve enhancing water separation from crude oil tanks and adding desalting agents in electrodesalination processes, to keep the total iron level below 15 ppm. Even so, the catalyst is occasionally poisoned, even though the iron ion concentration is not very high. I would like to ask the experts: what is the reason? Sulfur exists on the catalyst in two forms: reversibly adsorbed sulfur and irreversibly adsorbed sulfur. The irreversibly adsorbed sulfur is mainly adsorbed on the metal surface and certain strong acid sites. Its adsorption amount has no relation to the partial pressure of H2S in the gas stream during sulfidation; it depends solely on the active metal components. Reversible adsorption mainly occurs on the carrier, and its amount is related to the number of aluminum ions (Al3+) on the surface area of the carrier. The presence of chloride ions inhibits the adsorption of this portion of sulfur. Irreversibly adsorbed sulfur can suppress the hydrogen activity of the catalyst, thereby improving its selectivity. Under certain conditions, sulfur will be the most persistent poison for modern binary (poly)metal reformation catalysts. However, under certain conditions, sulfur can also be beneficial to reforming catalysts. For instance, when a reforming unit is started up, the catalyst must be presulfurized to suppress the excessively high number of active sites on the catalyst during the initial stage of operation, thereby preventing excessive coke formation and prolonging the unit’s operating cycle! I. Hazards caused by the process: When a reforming catalyst is sulfur-poisoned, its platinum activity decreases, which leads to a reduction in the dehydration and dehydrocyclization reactions (metal-catalyzed reactions), while the hydrocracking reactions (acid-catalyzed reactions) increase. In such cases, the following phenomena typically occur: (1) A decrease in hydrogen production ； (2) Decrease in the purity of recycled hydrogen ； (3) Increased C3 and C4 yields, enhanced cracking performance ； (4) The total temperature drop of the reaction (∑△T) decreases ； (5) Decrease in the yield of C5+ liquid products ； (6) Increasing the operation intensity does not improve catalyst activity ； (7) The catalyst coking rate increases (stability decreases). The trace elements that may be present in distillate oil hydrogenation units include heavy metals such as Fe, Ni, V, Hg, Pb, as well as soluble organometallic compounds like Ca and As. In addition, there are additives used during the processing in upstream units, such as defoamers like Si, preservatives like P, desalting agents like Na, and metal contaminants from oil storage and transportation such as Fe. All of these can deposit on the surface and within the pores of the catalysts, ultimately leading to blockages of the catalyst pores and poisoning of the active centers, thereby rendering the catalysts inactive ； Furthermore, the chlorine content in the feed oil and fresh hydrogen also has a significant impact on the operation and safe functioning of the hydrogenation unit. 1. Na is primarily introduced into the system through the addition of alkali (NaOH) in the atmospheric and vacuum distillation units. Na can cause rapid deactivation of the catalyst; when the feed oil contains 1% to 3% Na, the catalyst’s activity is reduced by 50%. Na can penetrate into the microporous structure of the catalyst, and in catalysts with cracking capabilities, it can neutralize the acidic sites, thereby reducing their cracking efficiency as well as the mechanical strength of the catalyst. The most severe consequence of Na poisoning is that, during catalyst regeneration, Na can promote sintering at high temperatures and penetrate into the catalyst to cause sintering, thereby reducing the catalyst’s surface area and leading to the aggregation of active metals. Generally, if the Na content on the catalyst exceeds 0.25%, it cannot be regenerated ； Furthermore. Na contamination can also cause an increase in system pressure drop. 2. As is present in certain crude oils; for example, the Daqing crude oil in China has a high arsenic content, reaching 2800 ppb, and chemicals used in oil field drilling can also introduce it. As exists in the form of organic compounds and is primarily found in the light fractions such as steam, coal tar, and diesel from atmospheric and vacuum distillation units. Its toxic mechanism lies in the combination of As with the metals present in metal sulfides. The catalyst contains 0.1% As, with a 50% loss in activity. The maximum allowable As content in the catalyst is 500–1000 μg/g. Arsenic poisoning of hydrogenation catalysts is a permanent form of poisoning. Before replacing the catalyst contaminated with arsenic, the hydrogenation reactor, heating furnace tubes, high-pressure heat exchangers, etc., must be treated to remove arsenic, in order to prevent the newly installed catalyst from becoming contaminated again. 3. Si comes from defoamers or anti-coking agents, and is commonly found in light fractions such as gasoline and diesel produced in delayed coking and vacuum distillation processes. Si poisoning occurs mainly because it deposits evenly within the catalyst’s pores during the hydrogenation process, blocking these pores and reducing the catalyst’s specific surface area and pore volume, thereby causing poisoning of the catalyst ； During regeneration, SiO2 and MoO3 combine to form an inactive phase. Therefore, catalyst Si poisoning is a permanent form of poisoning, and the silicon content in the hydrogenation feed should be reduced as much as possible. Given the destructive effect of silicon on catalysts, non-silicon antifoamers or anti-coking agents are now widely used in delayed coking units and vacuum distillation units, reducing the impact of silicon on catalysts to an negligible level. 4. Ni and V are present in the heavier fractions of crude oil, existing in the form of macromolecules (resins and asphalts) in fractions with temperatures above 500°C. During the processing of heavy oil, such as in catalytic cracking and coking, most of the macromolecular compounds containing Ni and V turn into coke; however, a small portion of them breaks down into smaller molecules containing heavy metals, such as vanadium porphyrins and nickel porphyrins, which end up in the diesel fuel after further processing and are then introduced into hydrogenation units. The mechanism of Ni and V poisoning is the blockage of the pores in the catalyst. When the catalyst contains 3–4% (Ni+V), its activity is reduced by 50%. 5. Trace elements such as P, Ca, K, and Mg may also be present in the hydroprocessing feed distillate oil. These elements are present in lower amounts in atmospheric residue and vacuum residue, and even less so in straight-run diesel and diesel produced through secondary processing. They can have a negative impact on the activity of catalysts, and they can increase the system pressure drop, thereby raising the operating costs of the facility. However, due to the extremely low content, the impact can be ignored. 6. The iron content in the crude oil is the main cause of bed clogging and increased pressure drop. Table 2 shows the relationship between the iron content of the raw materials and the operation cycle of the plant. As can be seen from Table 2, the iron content in the crude oil directly affects the start-up cycle. Table 2 Relationship between iron content in the feedstock and the operation cycle. Units: A, B, C. Iron content in the feedstock in μg/g; average number of operating days: 0.36 for unit A, 1595 for unit B; 2–3.5 for unit C, 258 for unit D; 3.2–9 for unit E, 102 for unit F. There are two main sources of iron in the hydrogenation feedstock: iron originally present in the crude oil, and iron generated during the processing process. Iron in crude oil or distillates may exist in the form of suspended inorganic substances, or as oil-soluble salts and complexes. Most of the existing iron can be removed by deep electrodeionization. Most of the iron in the hydrogenation feedstock is process iron. Especially when the material choice for equipment such as atmospheric and vacuum distillation units is inappropriate, the iron content can increase by several dozen times. The relevant literature provides a detailed examination of the sources of iron in hydroprocessing feed oils, and it is concluded that the iron content is directly related to the acid value of the crude oil, particularly to the content of naphthenic acids. As the amount of naphthenic acid increases, the iron content in the hydrogenation feed doubles. Naphthenic acids are present in most crude oils, with typical concentrations ranging from 0.02% to 2.0%. Their molecular weight is around 200–350, and they are mainly found in kerosene, diesel, and heavier fractions. In environments above 230°C, naphthenic acid exhibits strong corrosivity, with the highest level of corrosivity at 270–280°C; this corrosivity increases again when the temperature reaches 350°C. Naphthenic acid causes iron corrosion to produce oil-soluble iron naphthenate. Especially when highly active hydrogen sulfide, elemental sulfur, and thiols are present in the crude oil, it can accelerate the corrosion of iron by naphthenic acids. Ferrocyclohexanecarboxylic acid readily undergoes hydrogenolysis in the reactor and reacts with hydrogen sulfide to form iron sulfide. This iron sulfide is a non-stoichiometric, polymeric “cluster” that contains Fe–S, Fe–Fe, and S–S bonds. Typically, the number of iron atoms is less than that of sulfur atoms, denoted as Fesx. The attraction between iron sulfide clusters is strong, allowing them to easily aggregate and cover the upper layer of the catalyst. At high temperatures, this iron sulfide can promote the coking reaction of the coking precursor, which in turn accelerates bed blockage and an increase in pressure drop. Experts recommend that hydrogenation feedstocks should meet the following specifications: particles larger than 0.8 μm < 0.2 μg/g; organic and inorganic chloride content < 1.0 μg/g; iron content < 1.0 μg/g; nickel and vanadium content < 1.0 μg/g. The phenomenon whereby trace impurities present in the reaction feedstock significantly reduce or even eliminate the activity and selectivity of the catalyst. The essence of poisoning is a certain chemical reaction between trace impurities and the active centers of the catalyst, resulting in the formation of inactive species. Adsorption complexes are formed in gas-solid multiphase catalytic reactions. One type is when the interaction between the poison and the active component is weak; in such cases, the activity can be restored by simple methods. This is known as reversible poisoning or temporary poisoning. The other category is irreversible poisoning, for which it is impossible to restore activity using simple methods. To reduce the activity of side reactions, it is sometimes necessary to selectively poison the catalyst. 　　Catalysts can lose their activity during use due to various factors, one of the important ones being poisoning. There are several possible causes of catalyst poisoning: small amounts of impurities present in the catalyst, strong adsorption (usually chemical adsorption) on the active centers, or chemical reactions with the active centers that result in the formation of other substances – all of these can poison the active centers. Additionally, such toxic substances may also be present in the reaction products ； During the preparation of the catalyst, impurities present in the support interact with the active components, and may also poison the active sites. 　　Toxins come in various forms; for a given catalyst, it is only by considering the reaction it catalyzes that it can be determined what substances are toxic. In other words, toxins affect not only the catalyst itself but also the reaction that this catalyst facilitates. During the period of stable activity, catalysts often experience a significant decline in their activity due to contact with small amounts of impurities; this phenomenon is known as catalyst poisoning. Substances that cause a catalyst to lose its catalytic activity are known as catalyst poisons. If activity can be restored after the toxic factor is removed, it is called temporary poisoning; otherwise, it is called permanent poisoning. 　　Some catalysts are toxic in certain reactions; some of these toxins have a temporary effect, while others are permanent. For example, in the synthesis of ammonia, iron-based catalysts are affected by water and oxygen as toxins. When such poisoning occurs, the catalyst can be reactivated through reduction or heating methods. This type of poisoning is temporary, or reversible ； Compounds of sulfur or phosphorus are also toxic to this catalyst and this reaction; when poisoning occurs as a result of them, it is very difficult to reactivate the catalyst, and this represents permanent poisoning, or irreversible poisoning. The latter type of poisoning can be prevented. 　　Poisoning not only affects the activity of catalysts, leading to a decrease in their activity, but also influences their selectivity. Poisoning is a practical problem frequently encountered when using catalysts in chemical production; however, our understanding of it remains incomplete. As for how to prevent poisoning and detoxify catalysts, these issues must be addressed through practical experience

Our company specializes in solving catalyst poisoning problems. It mainly depends on whether you want to remove the contaminant through electrodesalination in crude oil pretreatment or by passivating it on the surface of the catalyst

Are you a catalyst company or a specialized firm? Do you have any successful cases that you could share here? It would be useful to know to what extent the contamination was severe, and what positive changes occurred after you resolved the issue