The cracking catalyst is continuously regenerated and regenerated between the reactor and the regenerator. Usually, the carbon content of the catalyst (to be activated) is about 1% when it leaves the reactor. The carbon deposits need to be burned in the regenerator to restore the activity of the catalyst. For amorphous aluminum silicate catalyst, the carbon content of regenerated catalyst (regenerant) is required to be reduced to less than 0.5%, for molecular sieve catalyst is generally required to be reduced to less than 0.2%, and for ultra-stable Y molecular sieve catalyst is even required to be reduced to less than 0.05%. Regeneration can recover the activity lost due to coking, but cannot recover the inactivation due to structural changes and metal contamination. The regeneration process of cracking catalyst determines the thermal balance and production capacity of the whole unit, so the regeneration of catalyst must be attached great importance in the study of catalytic cracking.
The coke deposited on the catalyst is mainly the reaction condensation product, the main components are carbon and hydrogen, when the cracking raw material contains sulfur and nitrogen, the coke also contains sulfur and nitrogen. Because coke itself is a mixture of many compounds, and there is no definite composition, so it is impossible to write the molecular formula, so its chemical reaction equation can only be generally expressed in the following table:
Regeneration reaction is an exothermic reaction, the thermal effect is quite large, enough to provide heat for the thermal balance of the device, and even a considerable amount of residual heat. The main influencing factors in the process of catalytic cracking catalyst regeneration are regeneration temperature, oxygen partial pressure, carbon content of regenerator, structure form of regenerator and regeneration time.