4 replies to this topic

[saeed.s]

Dear frinds,
I could not manage to calculate DEAH ( (C2H5)2 AL H) properties with aspen plus estimation(molecular structure definition). software error is :

WARNING IN PHYSICAL PROPERTY SYSTEM
FUNCTIONAL GROUP GENERATION FOR THE UNIFAC METHOD CANNOT BE COMPLETED
FOR COMPONENT DEAH. THE FOLLOWING ATOMS WERE NOT MATCHED:
AL 3

and i dont know why, is there any idea? thank you

[Chellani]

Really not sure but the probability of one thing going wrong here is too high i.e. structure not being closed / you have free bonds e.g. if you would like to define ethanol using UNIFAC, you should add OH and CH3. If you add CH2 instead of CH3, bonds aren’t satisfied.
Honeywell’s UniSim® Design and HYSYS would prompt you an error message before adding a component if bonds aren’t satisfied. Not sure how aspen Plus handles this.

[saeed.s]

Really not sure but the probability of one thing going wrong here is too high i.e. structure not being closed / you have free bonds e.g. if you would like to define ethanol using UNIFAC, you should add OH and CH3. If you add CH2 instead of CH3, bonds aren’t satisfied.
Honeywell’s UniSim® Design and HYSYS would prompt you an error message before adding a component if bonds aren’t satisfied. Not sure how aspen Plus handles this.

Thanks for your reply, Aspen plus dont show error about free bonds because it complete free bonds with hydrogen.

[MrShorty]

Which properties are you trying to calculate? UNIFAC is a group contribution method for determining thermodynamic properties; in particular, phase equilibria in mixtures. As with any predictive method, the calculations depend on having appropriate input parameters for each group. To my knowledge, there are no published UNIFAC parameters for Al. In short, UNIFAC doesn't know how to handle Al.

I would suggest studying the UNIFAC method so you know what Aspen is trying to do that generates the error. I believe there are suitable descriptiions of UNIFAC and the solution of groups concept on the internet or you might try an appropriate text (Poling, Prausnitz, and O'Connell's book The Properties of Gases and Liquids has a good discussion of UNIFAC).

[saeed.s]

Which properties are you trying to calculate? UNIFAC is a group contribution method for determining thermodynamic properties; in particular, phase equilibria in mixtures. As with any predictive method, the calculations depend on having appropriate input parameters for each group. To my knowledge, there are no published UNIFAC parameters for Al. In short, UNIFAC doesn't know how to handle Al.

I would suggest studying the UNIFAC method so you know what Aspen is trying to do that generates the error. I believe there are suitable descriptiions of UNIFAC and the solution of groups concept on the internet or you might try an appropriate text (Poling, Prausnitz, and O'Connell's book The Properties of Gases and Liquids has a good discussion of UNIFAC).

Thanks for your reply,Aspen plus estimation use many property packages to estimate component properties that one of them is UNIFAC working based on functional group. The major problem is Aspen can not recognize AL atom , this problem also exist for other component like boron ,..
I think it s because of some problem in my software. I was wondering if one of you check it with your aspen software to make us sure about this issue