Causes of Deactivation of Oil Refining Chemical Catalysts

During the use process, the activity of the catalyst decreases with the increase of the use time, and the deactivation of the catalyst can even lead to the unsteady operation of the reaction system. Catalyst deactivation is related to many factors, and the qualitative and quantitative analysis of these factors is extremely complicated and difficult.

There are many reasons that affect catalyst deactivation. Generally divided into chemical inactivation, thermal inactivation and mechanical inactivation.

In fact, catalyst deactivation can be simply divided into three categories: poisoning, coking and clogging, sintering and thermal deactivation.

PART 1. Poisoned Inactivation

①Toxic analysis.

The decrease in the activity of the catalyst due to the influence of certain harmful impurities is called catalyst poisoning, and these substances are called poisons.

In most cases, poisons come from impurities in the feed, as well as catalyst poisoning due to strong adsorption of reaction products (eg, poison products from parallel or serial reactions) to active sites.

②Type of poisoning.

Since the poisoning is due to some interaction between the poison and the catalyst activity, the poison can be divided into three categories according to the nature and strength of this interaction:

(1) Temporary poisoning (reversible poisoning)

When the poison is adsorbed or formed on the active center, the bond strength generated is relatively weak. Appropriate methods can be taken to remove the poison and restore the activity of the catalyst without affecting the properties of the catalyst. This kind of poisoning is called reversible poisoning or temporary poisoning.

(2) Permanent poisoning (irreversible poisoning)

The poison interacts with the active component of the catalyst to form a strong chemical bond. It is difficult to remove the poison by ordinary methods to restore the activity of the catalyst, and this poisoning is called irreversible poisoning or permanent poisoning.

(3) Selective poisoning

After the catalyst is poisoned, it may lose its catalytic ability for a certain reaction, but it still has catalytic activity for other reactions. This phenomenon is called selective poisoning.

PART 2. Deactivation by Coking and Clogging

Carbonaceous deposits on the catalyst surface are called coking.

Coking may almost always occur in the heterogeneous catalytic reaction process using organic matter as raw material and solid catalyst as catalyst. Due to the deposition of carbonaceous substances and other substances in the catalyst pores, the pore size is reduced, so that the reactant molecules cannot diffuse into the pores, a phenomenon called clogging.

Therefore, clogging is often classified as coking, and the overall activity decline is called coking deactivation, which is the most common and common deactivation form of catalyst deactivation. Usually carbon-containing deposits can be removed by gasification with water vapor or hydrogen, so coking deactivation is a reversible process.

According to different reaction properties, coking can be divided into two categories: non-catalytic coking and catalytic coking. Non-catalytic coking refers to the process of generating tar and carbon in the gas phase or on a non-catalytic surface. The reaction temperature of non-catalytic coking is usually much higher than that of catalytic reaction, so under normal catalytic reaction conditions, catalytic coking is the main factor leading to catalyst deactivation.

PART 3. Sintering and Thermal Deactivation

Sintering and thermal deactivation of catalysts refers to the changes in catalyst structure and properties caused by high temperature.

High temperature in addition to cause sintering of the catalyst. It will also cause other changes, mainly including: changes in chemical composition and phase composition, semi-melting, grain growth, active components are embedded in the carrier, and active components are lost due to the formation of volatile substances or sublimable substances.