Catalyst characteristics and applications in petrochemical products
Petrochemical Catalyst
An important type of product in the catalyst industry, used in chemical processing processes in the production of petrochemical products. There are many types of catalysts. According to their catalytic functions, they mainly include oxidation catalysts, hydrogenation catalysts, dehydrogenation catalysts, hydroformylation catalysts, polymerization catalysts, hydration catalysts, dehydration catalysts, alkylation catalysts, and isomerization catalysts. , disproportionation catalyst, etc., the first five are used in larger amounts. Today Xiaoqi will take you to learn about the characteristics and applications of these catalysts for your reference!
Oxidation Catalyst
Most of the processes used in the petrochemical industry to manufacture oxygen-containing products are selective oxidation processes. Selective oxidation products account for 80% of the total organic chemical products; the catalyst used must first have high catalytic selectivity. Selective oxidation catalysts can be divided into gas-solid phase oxidation catalysts and liquid phase oxidation catalysts.
Take the production of ethylene glycol as an example. Among the production costs of ethylene glycol, the unit consumption costs of oxygen and ethylene account for 85-90% of the cost, and the unit consumption of both oxygen and ethylene mainly depends on the selectivity of the catalyst. Therefore, the core competition in the ethylene glycol unit is the competition of catalysts. Highly selective catalysts not only directly determine the unit cost of raw materials such as ethylene and oxygen, but also produce less by-products and impurities, resulting in higher quality ethylene glycol and ethylene oxide products.
Gas-solid phase oxidation catalyst
The gas-solid phase oxidation catalyst consists of a carrier silicon carbide or α-alumina and an active component vanadium-titanium series oxide, which is mainly divided into the following five categories:
(1) Silver catalyst for ethylene oxidation to ethylene oxide, using silicon carbide or α-alumina as a carrier (adding a small amount of barium oxide as a cocatalyst). After continuous improvement of catalysts and process conditions, the weight yield based on ethylene has exceeded 100%.
(2) A catalyst made of vanadium-titanium oxide as an active component and sprayed on silicon carbide or corundum, used to oxidize o-xylene to produce phthalic anhydride. A catalyst made by spraying active components of vanadium-molybdenum oxides on corundum, and is used for the oxidation of benzene or butane to produce maleic anhydride.
Oxidation of o-xylene to phthalic anhydride
The improvement of this type of catalyst is towards multi-component development, and eight-component catalysts have appeared. The shape of the carrier has also been changed from spherical to annular, semicircular, etc. to facilitate heat transfer. The general trend is to pursue high load, high yield and high purity of products.
(3) Alcohol is oxidized to aldehydes or ketones, such as methanol to formaldehyde using silver-pumice (or alumina), iron oxide-molybdenum oxide and electrolytic silver catalysts.
(4) Ammonia oxidation catalyst. In the 1960s, a catalyst was developed with a bismuth-molybdenum-phosphorus composite oxide catalytic component supported on silicon oxide. Propylene, ammonia, and air were passed through the catalyst. Acrylonitrile can be synthesized in one step.
Synthetic reaction of acrylonitrile
In order to improve selectivity and yield and reduce environmental pollution, the catalyst is constantly being improved, and some new catalysts contain up to 15 elements.
(5) Oxychlorination catalyst. A copper chloride-alumina catalyst was developed in the 1960s. Dichloroethane can be obtained by passing ethylene, hydrogen chloride and air or oxygen in an ebullating bed reactor. Dichloroethane is thermally cracked to obtain vinyl chloride monomer. This method is very beneficial to the development of polyvinyl chloride in areas where electricity is expensive and petrochemical industry is developed.
Liquid phase oxidation catalyst
Catalyst used for oxidizing aromatic hydrocarbon side chains to aryl acids, such as p-xylene in acetic acid solution, adding cobalt acetate and a small amount of ammonium bromide, heating, and air oxidation to produce terephthalic acid.
Ethylene and propylene are oxidized to acetaldehyde and acetone (Wack method), using a copper chloride solution catalyst containing a small amount of palladium chloride, passing in olefins, air or oxygen, and obtaining the required content after one or two steps of reaction. oxygen compounds.
Reaction to produce propylene oxide by chlorohydrin method
The liquid phase oxidation catalyst method severely corrodes the reaction equipment and has been gradually replaced by the organic peroxide method. This method is only used to prepare propylene oxide.
Hydrogenation Catalyst
This type of catalyst is used in the product production process and is also widely used in the refining process of raw materials and products. It is divided into three categories according to different hydrogenation conditions:
1
Selective hydrogenation catalyst
When ethylene and propylene obtained by cracking petroleum hydrocarbons are used as polymerization raw materials, they must first be selectively hydrogenated to remove trace impurities such as alkynes, dienes, carbon monoxide, carbon dioxide, and oxygen, without causing any loss of olefins. The catalyst used is generally palladium, platinum or nickel, cobalt, molybdenum, etc. supported on alumina. By controlling the amount of active material, the carrier and the manufacturing method of the catalyst, selective hydrogenation catalysts with different properties can be obtained. Others, such as the refining of pyrolysis gasoline and the hydrogenation and reduction of nitrobenzene to aniline, also use selective hydrogenation catalysts.
2
Non-selective hydrogenation catalyst
Catalyst for deep hydrogenation to saturated compounds. Such as the nickel-alumina catalyst used for hydrogenating benzene to produce cyclohexane, the hydrogenation of phenol to produce cyclohexanol, and the skeleton nickel catalyst used for hydrogenating adiponitrile to produce hexamethylenediamine.
3
Hydrogenolysis Catalyst
The process of hydrogenating and hydrogenolyzing oil to produce higher alcohols using copper chromite as a catalyst.
Dehydrogenation Catalyst
High temperature dehydrogenation catalytic technology
Iron-chromium oxide-potassium oxide can dehydrogenate ethylbenzene (or n-butene) into styrene (or butadiene) at high temperature and in the presence of a large amount of water vapor.
Low-temperature dehydrogenation catalytic technology
Since dehydrogenation generally requires high temperature, reduced pressure or a large amount of diluent.670213959370.jpg” width=”276″ height=”220″ srcset=”https://www.bdma.com.cn/wp-content/uploads/2023/02/1670213959370.jpg 276w, https://www. bdma.com.cn/wp-content/uploads/2023/02/1670213959370-220×175.jpg 220w” sizes=”(max-width: 276px) 100vw, 276px” title=”Characteristics and Application Illustrations of Catalysts in Petrochemical Products 1 ” alt=”Characteristics and Application Illustrations of Catalysts in Petrochemical Products 1″ />
Anhydrous aluminum trichloride-hydrogen chloride catalyst for the reaction of benzene and ethylene to produce ethylbenzene
③Alkylation of phenols, such as alkylation of p-cresol with isobutylene:
Since both sulfuric acid and hydrofluoric acid are highly acidic, they can cause serious corrosion to equipment. Therefore, from the perspective of production safety and environmental protection, these two catalysts are not ideal catalysts. At present, there are many studies on the use of solid super acid as an alkylation catalyst, but so far it has not reached the stage of industrial application.
Isomerization catalyst
The action or process of mutual conversion of one isomer into another isomer. A process that changes the structure of a compound without changing its composition and molecular weight. Generally refers to changes in the position of atoms or groups in organic compound molecules. Often carried out in the presence of a catalyst.
Catalysts mainly fall into the following categories:
① Friedel-Crafts type catalyst, commonly used are aluminum trichloride-hydrogen chloride, boron fluoride-hydrogen fluoride, etc. This type of catalyst has high activity and low reaction temperature, and is used for liquid phase isomerization, such as the isomerization of n-butane into isobutane, the isomerization of xylene, etc.
② Precious metal catalysts with solid acid as carrier, such as platinum-alumina, platinum-molecular sieve, palladium
-Alumina, etc. This type of catalyst is a dual-functional catalyst, in which the metal component plays a role in hydrogenation
And dehydrogenation, solid acid plays the role of isomerization.
When using this type of catalyst, the reaction needs to be carried out in the presence of hydrogen, so it is also called a hydroisomerization catalyst and is used for gas phase isomerization. Isomerization of alkanes, alkenes, aromatics, and cycloalkanes can also be used. In particular, only this type of catalyst is effective for the isomerization of ethylbenzene into xylenes and naphthenes. Its advantages are less coking and long service life.
③ Non-noble metal catalysts using solid acids as carriers, such as nickel-molecular sieves, etc., generally require the presence of hydrogen for gas phase isomerization, but cannot isomerize ethylbenzene into xylene.
④ZSM-5 molecular sieve catalyst is mainly used for the gas phase or liquid phase isomerization of xylene.
Disproportionation Catalyst
Applying the disproportionation process, one hydrocarbon can be converted into two different hydrocarbons. Therefore, disproportionation is one of the important methods to regulate the supply and demand of hydrocarbons in industry. The most important applications are the disproportionation of toluene to increase the production of xylene and simultaneously produce high-purity benzene, and the triolefin process of propylene disproportionation to produce polymer-grade ethylene and high-purity butenes (mainly cis and trans-2-butene).
Toluene disproportionation reaction
Toluene is converted into benzene and xylene using silica-alumina catalysts. Currently, molecular sieve catalysts are popular in research, such as mordenite type silk molecular sieves.
