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[harsh]

Dear Friends and Respected Sir,

I want to Know how the distillation of C3 cut from the crude oils takes place?

I want to separate the propylene from it.

C3 cut contains propane, propylene and other light components. (I don't know the percentage)

Propylene boils at 225ºK i.e. (approximately -50ºC)

I saw a distillation column in which light component leave the column from the top, propane from the bottom, and propylene from the upper side, I have drawn a rough diagram of distillation column.
The Pressure inside the column is 2.24 Psi g.
My Question is: At what pressure and temperature I will get Propylene out from the distillation column?

Attached Files

•  rough_diagram.doc   57KB   38 downloads

[abhi_agrawa]

Harsh,

Few things that you should first decide:

What is the composition of the Feed to Propylene Tower?
What propylene purity are you looking for?

If you feed to the tower is primarily Propane and Propylene, then you may use the McCabe Thiele method for deciding the number of trays. This will also set whether the propylene draw will be from the side of the tower or from the reflux drum.

The feed composition is extremely critical, as propane and propylene have as very small relative volatility and to separate them you need exceptionally tall towers, commonly referred to as super-fractionators. Often the propylene fractionator is split in two towers, with a total of more than 200 actual trays.


As you have said, boiling point of pure propylene at 1 atm pressure is about -50 deg C. Now if your propylene tower top pressure is 2.24 psig, you would need refrigeration to condense the overhead. Often the tower pressure is increased to allow cooling water to condense the overhead. So to answer your question "At what pressure and temperature I will get Propylene out from the distillation column?", it depends on the column pressure. I have seen propylene columns, where the product temperatures are about 40 deg C, of course these operate at higher pressures.

Hope this helps,
abhishek