Example P05.03a Experimental VLE Data and Modified UNIFAC and VTPR

Predictions for the Mixture Ethanol - Water

Part A: modified UNIFAC


Compare the experimental data for the system ethanol–water measured at 70 °C (see Figure 5.30 resp. Table 5.2) with the results of the group contribution method modified UNIFAC and the group contribution equation of state VTPR.





input data

reference: Mertl I., Collect.Czech.Chem.Commun., 37(2), 366-374, 1972


This area contains the mod. UNIFAC parameters, group fragmentation, ...

mod. UNIFAC - Parameters:

There are 4 different subgroups and 3 main groups involved in the calculation. These are shown together with their ID (group number) and (in case of subgrous) the R and Q values in the following vectors. In order to identify the main group that a subgroup belongs to, the index vector s2m is defined. s2mi yields the main group address in the main group vectors, that subgroup i belongs to. The matrix contains the frequency of subgroup i in component j. The matrices , and contain the coefficients for the temperature dependent interaction parameters.

This area contains the activity coefficient function for mod. UNIFAC

In addition, vapor pressure equations for the two components are required for the calculation of the VLE. For this purpose the Wagner equation with parameters from Appendix A will be used:

Vapor pressure constants for the Wagner equation (Appendix A):


The pure component vapor pressures of the components are:

Calculation of partial pressures, total pressure and vapor mole fractions:

Calculation of experimental activity coefficients:

Experimental and calculated vapor phase compositions and total pressure are shown in the following table:

x ycalc y1,exp Pcalc Pexp


Graphical Comparison: