9 replies to this topic

[mubarak56]

how to calculate margulas equation constants A12 and A21 for ethanol,water mixture??????/

[latexman]

What do you want the model to do?

 

If you want to hit the azeotrope dead on, just use the azeotrope point for a one point fit.  This can be calculated by hand.

 

If you want to use it over a wide range of concentrations, you need to fit (g^E) data.  This is best done using a statistical program/package, like JMP from SAS.

Edited by latexman, 16 May 2013 - 03:23 PM.

[mubarak56]

actually i want to find values of activity coefficient for construction of VLE diagram.

but i dont know how can i find A12 and A21 in margulus model????

[Art Montemayor]

The correct name is the Margules Equation.  If you can't spell correctly, you can't look it up.

 

Go to:

 

for an explanation.

[latexman]

http://lmgtfy.com/?q... water margules

[Art Montemayor]

Latex:

 

That has got to be the "coolest" & most innovative post to date in these Forums! 

 

Thank you for the lesson in retrieving data from the Web.   (I would sure like to know how to program a series of responses just like that).

 

Thanks.

[thorium90]

If Latex's reply is something similar, im gonna LOLOLOL!!!

 

 

 

I got it!!! I only changed the stuff after q=    , and remembering to add a + between each word and adding http://   before it

 

http://lmgtfy.com/?q...le that for you

Edited by thorium90, 16 May 2013 - 12:06 PM.

[mubarak56]

hahahahahha.........

nice one......  

actually i know all about Margules Equation but real question is in Margules Equation how can i find values of A12 and A21 constants because they are temperature dependent. is there any relation between these constants and temperature????
 

[latexman]

It would be easiest (for us) if you could attach what you have done so we can see your issue.

 

If that is not possible, and I do not see why it would not, please be much more specific.  Are you using the two-suffix Margules or the three-suffix Margules or the four-suffix Margules?  Frankly, with your nomenclature of "A12 and A21" it looks to me like you are using the Wilson equation.  Is that possible?  By the way, the Margules constants are not temperature dependent.  The activity coefficients are related to the Margules constants, temperature, and compostion by the governing equation.  For example, for the two-suffix Margules:

 

g^E = Ax₁x₂

 

RT ln (activity coefficient ₁) = Ax₂²

 

RT ln (activity coefficient ₂) = Ax₁²

 

Also, please show us your data to be fit.

Edited by latexman, 16 May 2013 - 03:46 PM.

[MrShorty]

There are basic 2 ways to obtain parameters for the Margules (or any activity coefficient) equation.

 

1) You can look the parameters up in a database somewhere. I don't know what resources you have available to you, or even if this is appropriate for the problem at hand.

 

2) You can use VLE information to regress the parameters. If you have infinite dilution activity coefficients, it is fairly simple to solve for A12 and A21 in the Margules equation. If you have other VLE information, you can use that to fit parameters.

 

Is your problem one where you are expected to look up the parameters, or one where you are expected to derive the parameters from VLE data?