2 replies to this topic

[process.eng88]

I have read that the most appropriate thermodynamic model for fatty acids is UNIQ-NTH since it takes into account the effect of dimerisation, solvation and association of fatty acids in vapour phase at low pressure.These phenomena should be taken into account because the association will drastically affect the volatility of the acids.

I hope someone can provide me a custom fpk file for UNIQ-NTH fluid package so that I can import it into HYSYS 2006.5 ?

(Unlike HYSYS 7.0, HYSYS 2006.5 is unable to use the thermodynamic fluid packages of ASPEN PLUS 2006.5)


Alternatively, are there any similar fluid packages in HYSYS 2006.5 which take into account the aforementioned phenomena ?

The following research uses Lee-Kesler-Plocker model to fatty acids distillation in HYSYS.
However, I don't know how accurate is Lee-Kesler-Plocker relative to UNIQ-NTH in terms of modelling fatty acids distillation. Does Lee-Kesler-Plocker take into account the aforementioned phenomena (underlined) ?

[process.eng88]

I've been informed that Lee-Kessler-Plocker doesn’t account for dimerization/association.

HYSYS Doesn’t have the Nothnagel option for UNIQUAC but it does have the Virial option which is the Hayden – O’Connel method for dealing with dimerization (found in Aspen Plus as UNIQUAC-HOC).

Both, HYSYS and Aspen Plus don't have the activity coefficients of fatty acids for UNIQUAC-Virial/ UNIQUAC-HOC.

Experimental vapour liquid equilibrium data could be used in Aspen Properties to regress the necessary interaction coefficients.

[Chellani]

Few inputs
1. I doubt on "HYSYS and Aspen Plus don't have the activity coefficients of fatty acids for UNIQUAC-Virial/ UNIQUAC-HOC"; do you mean Binary Interaction Parameters (BIPs)? I am not sure about Aspen Plus but HYSYS should have BIPs for common systems to calculate activity coefficients (liquid phase non-ideality).
2. Can you search for dimerization / acids in online guide of HYSYS, I remember there was specific vapor phase model (may be virial/LK) for these systems. If online guide claims that it is specifically for acids, it should handle vapor phase dimerization.
3. Hyprotech had developed a product i.e. Thermo Workbench, I don't know that Aspen has this or not. This is really good product for thermo analysis using which you can calculate your BIPs (by regressing experimental data) and export it to simulator. If you can't find that, write basic calculation in excel for regression. I've posted an excel sheet for NRTL, try modifying that for UNIQUAC (unfortunately that assumes vapor phase to be ideal, you got to work on that).
4. I had developed very simple scilab program to calculate activity coefficient for acids (it was for acetic acid + water + few salts) using experimental data. Finding experiemental data for common acids + water shouldn't be a problem. If you can't regress / can't find data, do let me know; I'll try to search those programs and data.

Hope this helps.

Edited by Chellani, 28 November 2011 - 11:12 AM.