4 replies to this topic

[Celopsin.Khan]

How do I go about calculating the Critical Temperature Of a Gas Mixture?

 

I know the % mole composition of gaseous mixture.  Any recommended co-relations or graphs?

 

Thanking in anticipation.

Edited by Art Montemayor, 13 January 2015 - 04:08 PM.

[srfish]

The most popular method seems to be that of Lee-Kesler. It is presented in Perry's Chemical Engineering Handbook in Chapter 4 (Thermodynamics).. A computer program is presented in Daubert.

[PingPong]

If you need the real critical temperature of the gas mixture, you need to run a simulator to calculate the phase envelope.

 

If you need the pseudo critical temperature of the gas mixture, there are several methods, each with slightly different mixing rules, such as Lee-Kesler.

[serra]

since you do not specifically require the true crical temperature (which as suggested by Ping Pong can be calculated with complex procedures) possibly you can accept an estimate,
as suggested by srfish several methods are available,
you may start from The Properties Of Gases and Liquids, 4th Edition,
for not too different molecules you can calculate (easily) pseudocritical temperature with Kay's rule

Tcm = y1*Tc1+y2*Tc2+y3*Tc3...
where y1,y2,y3 are molar fractions of components in mixture

for hydrocarbons the authors suggest the method of Li,
similar to Kay's rule but with different fractions calculated from critical volumes
Tcm = x1*Tc1+x2*Tc2+x3*Tc3...

where
x1 = y1*Vc1/(y1*Vc1+y2*Vc2+y3*Vc3+...)
x2 = y2*Vc2/(y1*Vc1+y2*Vc2+y3*Vc3+...)

another method is that of Chueh and Prausnitz, based on a similar procedure but more complex.

 

You can easily write these procedures in Excel and compare results.

Edited by serra, 13 January 2015 - 04:50 PM.

[Bobby Strain]

Only the first is pseudo-critical temperature. Others are an approximation of true critical. You must need the value for something. Lots of correlations are based on the pseudo value. So, it's best to know what is required for your purpose, which you have not shared with us.

 

Bobby