Regarding the Aspen Data Regression in Aspen Plus for LLE and VLE, we have two main binary interaction parameters aij and bij (referred to as elements number 1 and 2).
We would like to know the different between those two parameters, since from the published literature we found that several researchers only regress to get bij, and others regress the experimental data to get both aij and bij parameters.
Thank you.
Both of aij, bij are the parameters of NRTL. For more accurate regression in Aspen Plus you can even regress c and d parameters.
tau parameters is defined as a polynomial expression with several parameters. Considering more parameters can improve your data regression and better predicted data in LLE and VLE calculation
If you are using NRTL, regression of NRTL by Aspen will results in acceptable data which are corresponding to experimental data
Thank you for your answer Mr. Sajad.
I understand it well.
Furthermore, I just curious why some researcher only regress bij and the aij was set to zero, and others regress the both aij-bij parameters. Is there any special reason for this?
As well as, I found in Aspen Plus. Aspen Plus also regress and provide the binary parameters for LLE and VLE in term of only bij or both aij-bij parameters.
Greetings Gregorius,
The bij parameters from the NRTL equation are temperature dependent and if you can regress these parameters from a robust data set you will usually be in a much better position with respect to modeling a particular system. If you have enough data sets (at various temps) for regression, then you could try to regress both parameters. Some people regress the aij first then regress the bij with the aij parameter present. T If data is only available at a single temp then regression of the aij parameter may be a better choice.
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