Catalytic cracking
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Why is the catalytic cracking of petroleum fractions considered a parallel-sequence reaction?
Since the feedstock produces various products such as coke, gasoline, diesel, and gases during the reaction process, and these intermediate products also undergo further reactions to evolve into the final products of coke and gases, it is referred to as a parallel-sequential reaction
When the feedstock undergoes cracking, reactions occur in several directions at the same time; such reactions are called parallel reactions. At the same time, as the reaction depth increases, the intermediate products continue to react, and this type of reaction is called a sequential reaction. An important characteristic of parallel sequential reactions is that the degree of reaction has a significant impact on the distribution of product yields. That is, as the reaction time increases and the degree of conversion rises, the yields of the final product gases and coke continue to increase, while the yields of intermediate products such as light oil and light fuel oil initially increase, reach a maximum, and then decrease. This is because once a certain reaction depth is reached, further deepening the reaction causes the intermediate products to decompose into substances with lower boiling points (for example, light oil decomposes into gases, and light fuel oil decomposes into lighter oils), and their decomposition rate exceeds their formation rate. *It is customary to refer to a reaction that occurs after the initial reaction products are formed as a secondary reaction.
It can be understood simply as follows: at high temperatures, the recombined substance breaks down into lighter components such as gasoline and diesel, which are then further broken down into lighter hydrocarbons such as dry gas, liquefied gas, and coke; this is a sequential reaction； Under highly active catalysts, the reformed components may directly form coke, light hydrocarbons, etc., which is a parallel reaction.
It can be understood simply as follows: at high temperatures, the recombined substance breaks down into lighter components such as gasoline and diesel, which are then further broken down into lighter hydrocarbons such as dry gas, liquefied gas, and coke; this is a sequential reaction； Under highly active catalysts, the reformed components may directly form coke, light hydrocarbons, etc., which is a parallel reaction.