【Weekly Topic】What impact does conversion rate have on product distribution and quality?

1. An increased oil-to-catalyst ratio results in more catalyst particles coming into contact with each hydrocarbon molecule, which not only promotes the cracking of the feedstock but also accelerates the cracking of olefins in gasoline, leading to a decrease in the olefin content in gasoline. 2. The increased catalyst activity leads to an intensified hydrogen transfer reaction, resulting in a reduced olefin content in gasoline. 3. The initial boiling point of gasoline increases, resulting in a shorter boiling range; this leads to a decrease in the proportion of low-boiling-point fractions in gasoline, and consequently to a reduction in its olefin content. 4. When the reaction temperature rises, the decomposition reactions (that produce olefins) and aromatization reactions increase more rapidly than the hydrogen transfer reactions, which in turn leads to an increase in the olefin and aromatic content in gasoline. 5. The higher the activity of the catalyst, the faster the rate of catalytic cracking reaction; an increased rate of catalytic cracking slows down the thermal cracking reaction, thereby reducing the content of dienes in gasoline. 6. The effect of hydrogen transfer reduces the amount of olefins in gasoline, while an increase in reaction temperature inhibits this hydrogen transfer reaction, resulting in an increase in the olefin content in gasoline. 7. Under the combined action of secondary cracking and hydrogen transfer reactions, the heavy olefins in gasoline are converted into propylene and isoparaffins, resulting in a significant reduction in the olefin content in gasoline. 8. It promotes the hydrogen transfer reaction of olefins in gasoline, thereby reducing the olefin content in it. 9. The low reaction temperature prevents further cracking of small hydrocarbon molecules, which facilitates the occurrence of the hydrogen transfer reaction; as a result, the dry gas yield decreases. 10. To reduce the olefin content in gasoline, measures are taken to ensure that the already formed gasoline fractions continue to react; through deep reaction of the gasoline, the olefin components in it can be effectively converted. 11. An increase in reaction temperature will enhance the role of thermal cracking reactions in the cracking process, further reducing the selectivity for high-value products, and at the same time decreasing the capacity for hydrogen transfer reactions, which is not conducive to reducing the olefin content in gasoline. 12. Thermal cracking reactions are an important source of olefins, especially dienes and similar compounds. The reaction temperature increased by more than 10°C. This intensifies the cracking reaction and increases the opportunities for secondary cracking downstream of the riser, which inevitably leads to an increase in the olefin content. 13. An increase in reaction temperature exacerbates thermal cracking and secondary cracking, resulting in a rise in the amount of olefins, especially dienes, and this directly shortens the induction period of gasoline. The catalytic dry gas contains a large amount of hydrogen, and this hydrogen has a passivating effect on metals such as nickel adsorbed on the catalyst. The hydrocarbons in the dry gas react on the highly active molecular sieves of the catalyst, which helps to reduce the dry gas yield and increase the liquid yield.

This post was last edited by wyt1234 on 2010-12-9 09:11. 1. The reaction temperature has a significant impact on both the reaction rate and the properties of the product; the cracking reaction is the main reaction in catalytic cracking, and a large amount of olefins are produced during this process. Since the cracking reaction is an endothermic process, while the isomerization, aromatization, and hydrogen transfer reactions are exothermic processes, for MIP process technology, increasing the reaction temperature in zone 1 facilitates the cracking reaction, whereas reducing the reaction temperature in zone 2 promotes isomerization, aromatization, and hydrogen transfer of the hydrocarbons produced in zone 1, thereby achieving the goal of reducing the olefin content in gasoline. 2. An increase in reaction pressure raises the concentration of reactants and the reaction time, which is beneficial for reaction rate and conversion rate. In residue cracking, a large amount of steam is used in the reaction (accounting for 10% of the feedstock volume). Although the reaction pressure is increased, the vapor pressure of hydrocarbons remains low; this helps to reduce coking rates and increase gasoline yield. It also facilitates an increase in the amount of olefins in the gasoline vapor, thereby raising the octane rating of the gasoline. At the same time, it has no significant effect on the dry gas and liquefied gas yields. 3. At the same reaction temperature and feed rate, an increase in the preheating temperature of the feedstock leads to a decrease in the catalyst circulation rate, an increase in the regeneration temperature, a decrease in the catalyst-to-oil ratio, a reduction in conversion rate, a decrease in coke formation rate, and a decline in gasoline yield. 4. At a certain total conversion rate, the recycle ratio reflects the one-pass conversion rate, and it decreases as the one-pass conversion rate increases. If the cracking conditions are relaxed, the one-pass conversion rate decreases and the recycle ratio increases, which can increase diesel yield and decrease gasoline yield; however, the overall light oil yield still increases. On the other hand, the quality of light diesel has also improved, with its cetane number increasing and its freezing point decreasing. The greatest negative effect of increasing the reprocessing ratio is the increased heat required for reaction and distillation, leading to higher energy consumption. It also limits the production capacity of the device, requiring a reduction in output as a trade-off. Of course, for heavy oil catalysis, excess heat is the main problem, as the heavy ring hydrocarbons present in reprocessed oil and slurry are difficult to crack. If the oil slurry is not removed, the coking rate will **increase**, and it will also be difficult to control the solid content of the oil slurry; therefore, an operation with a high recycle ratio is not advisable. Moreover, the light oil yield will not decrease significantly, and the amount of gasoline will actually increase. 5. An increase in the oil-to-fuel ratio leads to a higher conversion rate and an increased coke yield; meanwhile, the yields of liquefied gas and gasoline as well as the octane rating of gasoline increase, while the density, aniline point, bromine value, and olefin content of gasoline decrease. 6. The activity and selectivity of catalytic cracking catalysts play a particularly important role in determining the product distribution in catalytic cracking. Timely removing some of the catalyst and adding fresh catalyst to maintain an appropriate activity of the balance agent is one of the effective methods to improve the economic efficiency of catalytic cracking units. Increasing the activity of the catalyst is beneficial for hydrogen transfer reactions, thereby helping to reduce olefins in gasoline. 7. An increase in the carbon content of the regenerator corresponds to a decrease in the amount of zeolite molecular sieves in the catalyst, which leads to a decline in conversion rate and gasoline yield, an increase in the yields of dry gas and coke, as well as an increase in the olefin content and bromine value of gasoline.

1. Simply put, the higher the conversion rate, the better the product quality and distribution (in industry). 2. However, product quality and distribution are still affected by selectivity.

Due to the complex reaction system, the conversion rate of a particular substance is constrained by the conditions of the system, such as catalyst, temperature, concentration distribution, etc. For complex reaction systems, selectivity is very important. It can’t be generalized. It is necessary to determine an appropriate conversion rate based on the characteristics of the system in order to achieve overall system optimization. There should be an optimal conversion rate, which can be analyzed and simulated using software.