Discussion on catalyst deactivation experienced in actual production

There are generally three types of catalyst deactivation: 1. Coking deactivation, which is the most severe and fastest form of deactivation; it can cause a significant loss of the catalyst’s activity within just 1 second. However, this type of deactivation is temporary and the catalyst can regain its functionality after regeneration. 2. Hydrothermal deactivation: During use, the catalyst is repeatedly exposed to high temperatures and water vapor, which causes changes in its surface structure, a reduction in specific surface area and pore volume, and damage to the crystal structure of the molecular sieve. This leads to a decline in the catalyst’s activity and selectivity, and once this deactivation occurs, it is irreversible. 3. Poisoning and deactivation: Crude oils, especially heavy crude oils, often contain certain heavy metals such as iron, nickel, copper, vanadium, calcium, etc. These metals can poison or contaminate the catalyst, resulting in a decrease in its activity.

The reasons for catalyst deactivation are generally classified into three categories: poisoning, sintering and thermal deactivation, and coking and blockage. 1. Inactivation caused by poisoning (1) Temporary poisoning (reversible poisoning): When a toxin adsorbs onto or reacts with the active center, the bonds formed are relatively weak; it is possible to use appropriate methods to remove the toxin, thereby restoring the catalyst’s activity without affecting its properties. This type of poisoning is known as reversible poisoning or temporary poisoning. (2) Permanent poisoning (irreversible poisoning): When a toxin interacts with the active components of a catalyst, strong chemical bonds are formed, making it difficult to remove the toxin using conventional methods in order to restore the catalyst’s activity. This type of poisoning is known as irreversible or permanent poisoning. (3) Selective poisoning: After catalyst poisoning, it may lose its catalytic ability for a certain reaction, but remain catalytically active for other reactions; this phenomenon is known as selective poisoning. In a cascade reaction, if the poison only poisons the active sites that trigger subsequent reactions, it can halt the reaction at an intermediate stage, yielding intermediates in high yield. 2. Deactivation caused by coking and blockage: Carbonaceous deposits on the surface of the catalyst are known as coking. Coking almost always occurs in multiphase catalytic reaction processes that use organic substances as raw materials and solids as catalysts. The phenomenon in which the pore size decreases (or the pore openings shrink) due to the deposition of carbonaceous substances and/or other materials within the catalyst pores, preventing reactant molecules from diffusing into those pores, is known as clogging. Therefore, clogging is often classified under coking, and the overall decline in activity is referred to as coking deactivation; it is the most widespread and common form of catalyst deactivation. Typically, carbonaceous deposits can be removed through gasification in reaction with water vapor or hydrogen, so coking and deactivation are reversible processes. Compared to catalyst poisoning, there are many more substances that cause catalyst coking and blockage than catalyst poisons. In actual coking studies, it has been found that catalyst coking involves a rapid initial deactivation, followed by a quasi-steady state in terms of activity. It has been reported that coking deposition occurs mainly during the initial stage (within 0.15 seconds), and it has also been observed that approximately 50% of the carbon formed gets deposited within the first 20 seconds. Coking deactivation is also reversible; by controlling coking during the early stages of the reaction, the activity of the catalyst can be significantly improved. This is precisely why research on coking deactivation is becoming increasingly active. 3. Sintering and thermal deactivation (solid-state transformation): The sintering and thermal deactivation of catalysts refer to the changes in the structure and properties of the catalysts caused by high temperatures. In addition to causing sintering of the catalyst, high temperatures can also lead to other changes, including alterations in chemical and phase composition, semi-melting, grain growth, the encapsulation of active components by the carrier, and the loss of active components due to the formation of volatile or sublimable substances. In fact, at high temperatures, all catalysts will gradually undergo irreversible structural changes; the rate of these changes varies depending on the catalyst. Sintering and thermal deactivation are related to various factors, such as the pretreatment, reduction, and regeneration processes of the catalyst, as well as the promoters and carriers added. Of course, the reasons for catalyst deactivation are complex; the deactivation of each catalyst does not occur solely due to one of the categories mentioned above, but is often caused by two or more factors.

1. A few years ago, I encountered a case of catalyst deactivation due to poisoning. The operating conditions at that time were terrible; when the catalyst was taken out, it was dark brown in color, which indicated that the catalyst had been poisoned by iron. Subsequent analysis of the raw materials revealed that the iron content in them was significantly above the acceptable level. After further investigation, it was determined that the high sulfur content in the crude oil caused severe corrosion of the equipment such as the trays, which led to an excessive amount of iron entering the catalyst feed and causing poisoning of the catalyst. The situation improved after a large number of catalyst replacements were carried out. 2. The most common issue is excessive charring, which leads to a decrease in the catalyst’s catalytic efficiency and an increase in its carbon content, thereby reducing its activity. This problem can generally be resolved by adjusting the blending ratio, reprocessing the oil slurry, modifying the charring ratio, and increasing the main air flow. 3. We have really never encountered hydrothermal deactivation, as the catalyst replacement is quite frequent in our case.

1 means that the carbon content on the surface area of the catalyst is no more than 0.1%; 2 refers to the situation where a high-temperature catalyst comes into contact with water vapor; 3 means that the catalyst has its chemical properties altered by heavy metals. To prevent the catalyst from becoming inactive, it is possible to enhance the coking effect. It is best not to inject steam into the regenerator, and instead metal passivators should be used

We also experienced a situation once where the yield was extremely low, and salt buildup occurred in the distillation column; this was attributed to catalyst sodium poisoning. Sampling analysis showed a sodium content of 16,000 on the catalyst, with an activity of only 47.

The topic raised by the original poster is quite broad; what the people above have said makes sense – there are different types of catalysts as well as various ways in which they can become poisoned. Examples of catalyst deactivation include: 1. Sulfur poisoning, which can be reversed ； ⒉Heavy metal poisoning is irreversible ； ⒊Sodium poisoning, which destroys the catalyst structure, is also irreversible.

Coking, thermal failure, heavy metal poisoning, mechanical wear

There was once an instance of deactivation of the hydrocracking catalyst, primarily due to a low control temperature during hydrorefining, poor nitrogen removal from the feedstock, and the adsorption of nitrogen-containing compounds on the acidic sites of the hydrocracking catalyst, which led to its deactivation. Solution: Increase the reaction temperature; activity will be restored after one week. Other reasons for the deactivation of hydrogenation catalysts: carbon deposition on the catalyst surface, and high-temperature reduction of the catalyst to its metallic state at low hydrogen sulfide concentrations. Water in the feedstock for catalytic cracking can cause thermal collapse of the catalyst.

In fact, the most common cause of inactivation in normal production is still heavy metal poisoning. The properties of the raw materials used in our factory are very unstable and keep changing; laboratory analyses cannot keep up with these changes. As a result, the catalysts become severely deactivated due to sodium, nickel, and alumina, which has led to several instances of a decrease in performance. At this point, it is usually necessary to purchase a resurrection balance agent for a complete replacement

The scope is too broad. I’ve seen cases where desulfurization agents become inactive due to saturation; etherification agents become inactive when their useful life is exhausted; precious metal catalysts become inactive as a result of poisoning; hydrogenation catalysts also become inactive due to poisoning or when their useful life is over. Catalytic cracking catalysts are constantly in a cycle of deactivation and regeneration. Last edited by longsky on 2009-3-19 at 13:26.]

In production, pay close attention to the properties of the feed oil and take more samples for observation. The use of passivators and lift pipes to enhance the utilization of dry gas also yields good results. Depending on the type of installation, efforts should be made to minimize hydrothermal deactivation; generally, two-stage coking leads to a more gradual deactivation process. The choice of catalyst type and the control strategies employed are also very important

In normal catalytic cracking operations, heavy metals are commonly found. For example, the raw materials may have a high content of heavy metals or poor desalination efficiency. We used to experience frequent tripping due to electrodialysis at atmospheric pressure, and the desalination efficiency was poor, which led to sodium poisoning of the catalyst; as a result, we had to replace the catalyst to maintain its activity, incurring significant losses. Furthermore, the residual carbon content in the raw materials is extremely high, exceeding 8%, and the catalyst also contains a high amount of carbon, which leads to temporary poisoning of the catalyst. This reduces the processing capacity, but recovery occurs quite quickly.