[naren.iitr]

why air does not pass through from regenerator to the riser along with regenerated catalyst?

[eugenedakin]

Hello naren.iitr,

Could you help me understand a little more about your question?  Which catalyst are we looking at?  What type of regeneration is being performed (temperatures, size, vessel type, etc.)?  Which portion of the reaction is not using air?

Thanks for your help.

Sincerely,

Eugene

[naren.iitr]

Hello Mr. Eugene
Actually this question was asked in my campus interview. Since air is being used to regenerate spent catalyst (Zeolites/ ZSM-5) in the regenerator and catalyst is being recirculated between the regenerator and reactor where cracking of gas oil occurs in a fluidised bed.the question was asked is why air also doesnot pass through to the reactor section along with the catalyst? 

[eugenedakin]

Hi naren.iitr,

I am taking a guess at the answer.

When catalytic cracking of hydrocarbon occurs, an excess of hydrogen is required.  These hydrogen molecules attach to the 'broken' hydrocarbon chains where clevage occured. 

My guess is that the presence of oxygen (along with other elements) would cause side reactions such as H2O, and other derivatives.  Also, most catalysts operate an an elevated temperature, and the presence of oxygen increases the possibility of a fire.

Its just a guess, and I hope this helps.

Sincerely,

Eugene