Explain the basic principles of catalytic cracking reactors

Basic Principles of Catalytic Cracking Reactors I. Characteristics of the Catalytic Cracking Process The catalytic cracking process involves subjecting feedstock to a series of chemical reactions in the presence of a catalyst, at temperatures of 470–530 degrees and pressures of 0.1–0.3 megapascals, thereby converting it into gases, light products such as gasoline and diesel, as well as coke. The feedstocks for catalytic cracking are generally heavy distillates, such as vacuum distillates and coker distillates. With the continuous advancement of catalytic cracking technology and catalyst processes, the range of feedstocks available for catalytic cracking has been further expanded; partial or all of the residue oil can also be used as catalytic feedstocks. The catalytic cracking process has the following characteristics: (1) It yields a high yield of light oils, ranging from 70% to 80%, whereas the yield of light oils from the initial distillation of crude oil is only 10% to 40%. The light oils referred to here mean the combination of gasoline, kerosene, and diesel. (2) Catalytic gasoline has a high octane number, with a research octane number of over 85. Gasoline also has good stability. (3) Catalyzed diesel has a low cetane number; it is often used together with straight-run diesel or undergoes hydrorefining to increase its cetane number in order to meet specification requirements. (4) Catalytic cracking gas products account for about 10–20%, of which around 90% is C8 and C4. (known as liquefied petroleum gas). C8, C4 ； The component contains a large amount of olefins. Therefore, this type of product is an excellent raw material for the petrochemical industry and for producing components used in high-octane gasoline. Depending on the raw materials used, the catalyst, and the operating conditions, the yield and composition of the various products obtained from catalytic cracking vary slightly. Generally, the yield of gaseous products is 10–20%, the yield of gasoline is 30–50%, the yield of diesel does not exceed 40%, and the yield of coke is around 5–7%. Based on the yields and product quality of the aforementioned products, it can be seen that the main purpose of the catalytic cracking process is to produce gasoline. Given China’s national conditions and the development of transportation and agriculture, there is a high demand for diesel. By adjusting the operating conditions, it is possible to increase diesel production while still manufacturing gasoline; this is a characteristic of China’s catalytic cracking technology. II. Chemical Principles of Catalytic Cracking (I) Chemical reactions that may occur under catalytic cracking conditions 1. Cracking of alkanes into smaller molecules of alkenes and alkanes. 2. Cracking of alkenes into even smaller molecules of alkenes. 3. Dealkylation of alkylaromatics. 4. Breakage of side chains in alkylaromatics. 5. Cracking of naphthenes into alkenes; if a naphthane has only a single ring, then the ring does not open. 6. Hydrogen transfer reactions, such as: naphthane + alkene → aromatic hydrocarbon + alkane. 7. Isomerization reactions: alkanes → isomeric alkanes; alkenes → isomeric alkenes. 8. Aromatization reactions: alkenes undergo cyclodehydrogenation to form aromatic hydrocarbons. 9. Condensation reactions: monocyclic aromatic hydrocarbons can condense to form polycyclic aromatic hydrocarbons; eventually, these can further condense to form coke, with hydrogen being released in the process, thereby saturating the alkenes. For example, in the aforementioned chemical reactions, cracking reactions, hydrogen transfer reactions, and condensation reactions are the characteristic reactions of catalytic cracking.

Basic Principles of Catalytic Cracking Reactors I. Characteristics of the Catalytic Cracking Process The catalytic cracking process involves subjecting feedstock to a series of chemical reactions in the presence of a catalyst, at temperatures of 470–530 degrees and pressures of 0.1–0.3 megapascals, thereby converting it into gases, light products such as gasoline and diesel, as well as coke. The feedstocks for catalytic cracking are generally heavy distillates, such as vacuum distillates and coker distillates. With the continuous advancement of catalytic cracking technology and catalyst processes, the range of feedstocks available for catalytic cracking has been further expanded; partial or all of the residue oil can also be used as catalytic feedstocks. The catalytic cracking process has the following characteristics: (1) It yields a high yield of light oils, ranging from 70% to 80%, whereas the yield of light oils from the initial distillation of crude oil is only 10% to 40%. The light oils referred to here mean the combination of gasoline, kerosene, and diesel. (2) Catalytic gasoline has a high octane number, with a research octane number of over 85. Gasoline also has good stability. (3) Catalyzed diesel has a low cetane number; it is often used together with straight-run diesel or undergoes hydrorefining to increase its cetane number in order to meet specification requirements. (4) Catalytic cracking gas products account for about 10–20%, of which around 90% is C8 and C4. (known as liquefied petroleum gas). C8, C4 ； The component contains a large amount of olefins. Therefore, this type of product is an excellent raw material for the petrochemical industry and for producing components used in high-octane gasoline. Depending on the raw materials used, the catalyst, and the operating conditions, the yield and composition of the various products obtained from catalytic cracking vary slightly. Generally, the yield of gaseous products is 10–20%, the yield of gasoline is 30–50%, the yield of diesel does not exceed 40%, and the yield of coke is around 5–7%. Based on the yields and product quality of the aforementioned products, it can be seen that the main purpose of the catalytic cracking process is to produce gasoline. Given China’s national conditions and the development of transportation and agriculture, there is a high demand for diesel. By adjusting the operating conditions, it is possible to increase diesel production while still manufacturing gasoline; this is a characteristic of China’s catalytic cracking technology. II. Chemical Principles of Catalytic Cracking (I) Chemical reactions that may occur under catalytic cracking conditions 1. Cracking of alkanes into smaller molecules of alkenes and alkanes. 2. Cracking of alkenes into even smaller molecules of alkenes. 3. Dealkylation of alkylaromatics. 4. Breakage of side chains in alkylaromatics. 5. Cracking of naphthenes into alkenes; if a naphthane has only a single ring, then the ring does not open. 6. Hydrogen transfer reactions, such as: naphthane + alkene → aromatic hydrocarbon + alkane. 7. Isomerization reactions: alkanes → isomeric alkanes; alkenes → isomeric alkenes. 8. Aromatization reactions: alkenes undergo cyclodehydrogenation to form aromatic hydrocarbons. 9. Condensation reactions: monocyclic aromatic hydrocarbons can condense to form polycyclic aromatic hydrocarbons; eventually, these can further condense to form coke, with hydrogen being released in the process, thereby saturating the alkenes. For example, in the aforementioned chemical reactions, cracking reactions, hydrogen transfer reactions, and condensation reactions are the characteristic reactions of catalytic cracking.

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