3 replies to this topic

[brian00]

Hello,

I'm a recent ChE grad working on a consulting project and I need to develop a pressure vs. temperature curve for a system of dimethyl ether / ethanol. My thoughts are to model this using a modified Raoult's Law (although open for suggestions here).

Unfortunately I don't have access to the software I used as an undergrad (Aspen, etc.) to obtain the activity coefficients. Just wondering if anyone knows of an inexpensive / free-ware alternative that will calc. these parameters using UNIFAC, etc.


Thanks,

- Brian

[MrShorty]

Hello,

I'm a recent ChE grad working on a consulting project and I need to develop a pressure vs. temperature curve for a system of dimethyl ether / ethanol. My thoughts are to model this using a modified Raoult's Law (although open for suggestions here).

Unfortunately I don't have access to the software I used as an undergrad (Aspen, etc.) to obtain the activity coefficients. Just wondering if anyone knows of an inexpensive / free-ware alternative that will calc. these parameters using UNIFAC, etc.


Thanks,

- Brian

Modified Raoult's law seems fine, as long as you are staying at low pressures where you can safely assume the vapor is an ideal gas.

There are several UNIFAC calculators out there. Put "UNIFAC calculator" into your favorite search engine and you should find several.

If you are allowed to, it wouldn't be that difficult to write your own code/spreadsheet for UNIFAC (or other activity coefficient equation such as the Wilson, NRTL, or UNIQUAC). I would actually recommend this course of action because, not only will you get an activity coefficient calculator, but you'll become more familiar with the equation(s), and you will have a code block/spreadsheet that you can adapt to whatever situation you find yourself needing.

Because it is an estimation method, I don't usually like to rely solely on UNIFAC. I would generally prefer to use real VLE data to correlate NRTL or Wilson parameters. Again, this shouldn't be too difficult to program on your own (especially when you can assume ideal gas in the vapor).

Hope that helps.

[Madhan Kumar]

 Unifac group contribution method.pdf   90.66KB   64 downloadsHi dear,

I have attached file for calculating VLE for ethanol & water mixture using UNIFAC group contribution method. This i created for my own study purpose.
I recommend you to go through the book properties of gases & liquid by Bruce poling.

Hope the template & model may be useful to solve / create activity coefficient data for any compounds you want.

Cheers
MK_CHEM

[siretb]

I completely agree with Mr Shorty.
Do not rely only on UNIFAC. It is easy to code UNIQUAC or NRTL and find , or regress, the proper coefficients.