Alky Unit

[Milutin]

Dear all

In our refinery as I suppose in many other refineries we are short for i-C4 as feed to alkilation unit. As I know for C4 alkylation unit, ratio of C4 olefins an i-C4 is about 1:1.2 respectively. And we run our alky unit in that manner, it is sulphuric acid alky unit.

During discussion with some of my colleagues they mentioned that is possible to run alky unit with ratio C4= to i-C4, 1 : 0.9 respectively. In my opinion it is not possible, because if we have ratio 1 : 0.9 we will consume i-C4 cooling media, and i-C4 recycle from disobutaniser column.

Is it possible to run alky unit with ratio 1:0.9?

Regards,

Milutin

 

[UmeshMathur]

The normal practice is to consume almost all of the olefin in the alkylation reaction. Therefore, the iC4 is always comfortably in excess of the stoichiometric ratio. The excess iC4 is recycled.

Recall that the iC4 in the feed is usually not 100% pure - it comes with some nC4 which goes straight through the reactor. Generally, the nC4 is separated, but not completely, from the iC4 recycle in the deisobutanizer column.

I have never seen a C4-/iC4 ratio less than about 1 : 1.10