Butane/Propane (LPG) Equilibrium Diagram

[Mauer]

Hi everyone, i´m trying to design a distillation column to separate a mixture of butane/propane (LPG) using the McCabe-Thiele method. Does anyone know where can i find this XY Equilibrium Diagram?



Thank You



Mauer

 

[mbeychok]

Maeur:

The McCabe-Thiele diagram method is only good for a binary mixture. I want to point out that LPG could be a multi-component mixture of n-propane, iso-propane, n-butane, iso-butane and perhaps even some of the various butylenes. The exact composition of the LPG depends upon which refinery produced it and when they produced it.

I would also point out that the McCabe-Thiele method is rarely used any longer in industry. One of the various available simulation models is far more commonly used. Is this question of yours perhaps just a homework problem?

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[Mauer]

Dear Milton Beychok:

Certainly i'm still a student, but i posted this message because right now i´m working at a company that produces ecological refrigerants.

I'm involved in a proyect to separate butane and propane from GLP, and the first thing i thought of was to use the McCabe-Thiele method to get a raw idea of the dimension of the tower, treating GLP as a binary mixture.


I also checked your link and your book seems really intesting, i´m going to recomend it at my university. By the way if you're interested in ecological refrigerants you can visit

http://www.ecofreezeinternational.com

, the site is spanish but there's available an english version.



Gracias


Mauer

 

[Zoobie]

Milton is right. You need to consider what else is in the LPG. I have never tried to assume that LPG was a binary mixture because I have always had access to a process simulator (HYSYS, etc.). I don't know what sort of error you will have using McCabe-Thiele as I have never done it that way. This method will tell you the number of ideal stages you need but I would be concerned that with the presence of various butane species and other heavy and light ends, that you will not get a very good picture.

I also wanted to point out what might be an error (see my reference/definition below).

Isopropane (from

http://zenstoves.net/Canister.htm)

The term isopropane suggests that this is structural isomer of propane, but since propane is a three carbon hydrocarbon, a structural isomer doesn't exist. Isopropane is instead a commercial term used to describe isobutane/propane mixes (and sometimes butane/propane mixes).

 

[mbeychok]

zoobie:

You are perfectly correct ... my fingers were moving faster than my brain. Thanks for picking up on my error.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[25362]

Depropanizers are quite common. For tutorials look for books on petroleum processing, in particular sections on light ends fractionation, for example: Watkins' Petroleum Refinery Distillation (Gulf).

 

[Mauer]

Thank you all a lot, i found your advices really helpful. Just one last question how do you think about using ASPEN for this design?



Mauer

 

[joerd]

Should do the job, as long as you have the right composition and the right thermodynamic package (PR or SRK).

Cheers,
Joerd

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[wfn217]

Why not construct the curve using Raoult's Law?

 

[UmeshMathur]

It's a bit late to respond to wfn217's post, but this system is definitely not ideal. In this day and age, rigorous process simulation is de rigeur for all commercially significant work. Why would anyone use ANY approximate graphical method (except students doing work for pedagogical reasons)?

 

[wfn217]

Above,

He doesn't have any software. Raoult's law should be OK for butane/propane system.

 

[joerd]

What makes you think he doesn't have any software? Also, the system is LPG, not butane/propane.

Cheers,
Joerd

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.