Modified UNIFAC

Solute/solvent GCS UNIFAC Modified UNIFAC Experiment PV2... 

Various thermodynamic methods based on -models (Wilson, NRTL, UNIQUAC) or group contribution methods (UNIFAC, modified UNIFAC, ASOG, PSRK) can be used for either calculating or predicting the required activity coefficients for the components under given conditions of temperature and composition (Reference 2). 

Figure 5.86 Experimental [3] and predicted excess enthalpies for different binary alkane - ketone systems ------original UNIFAC — modified UNIFAC...

P8.12 In the free DDBSP Explorer Version, search for solid-liquid equilibrium data for the mixture 2-propanol-benzene. Regress the two datasets simultaneously using the Wilson. NRTL, and UNIQUAC model. Check the performance of the three models. Compare the data to the results of the predictive methods UNIFAC, modified UNIFAC. and PSRK. Examine the different graphical representations. 

One problem limiting the consideration of salt extractive distillation is the fact that the performance and solubility of a salt in a particiilar system is difficult to predict without experimental data. Some recent advances have been made in modeling the X T.E behavior of organic-aqueous-salt solutions using modified UNIFAC, NRTL, UNIQUAC, and other approaches [Kumar, Sep. Sci. Tech., 28(1), 799 (1993)]. 

Larsen, B.L., Rasmussen, P., Fredenslund, A. A modified UNIFAC group-contribution of phase equilibria and heats of mixing. Ind. Eng. Chem. Res., 1987,26 2274-2286. 

Thomas, E.R., Eckert, C.A. Prediction of limiting activity coefficients by a modified separation of cohesive energy density model and UNIFAC. End. Eng. Chem. Process Des. Dev., 1984,23 194-209. 

Fitting of ki2 using different EOS (PR with volume correction (PRc r), SRK, PR with modified volume function (PR )) and pure prediction using UNIFAC model with scaling factor... 

Thomas, E.R, and Eckert, C.A. (1984). Prediction of Limiting Activity Coefficients by a Modified Separation of Cohesive Energy Density Model and UNIFAC. I EC.Process Des.Dev., 23, 194-209. 

Figure 8 faj Comparison of vapor-liquid equilibrium predictions from COSMO-SAC, UNI-FAC and modified UNIFAC models for water( 1) -h 1,4-dioxane(2) mixtures at temperatures 308.15 and 323.15 K, and (b) vapor-liquid equilibrium prediction from COSMO-SAC for benzene(l)/n-methylformamide(2) at temperatures of 318.15 and 328.15 K... 

For the analytical equations, there are two methods to compute the vapour-liquid equilibrium for systems. The equation of state method (also known as the direct or phi-phi method) uses an equation of state to describe both the liquid and vapour phase properties, whereas the activity coefficient method (also known as the gamma-phi approach) describes the liquid phase via an activity coefficient model and the vapour phase via an equation of state. Recently, there have also been modified equation of state methods that have an activity coefficient model built into the mixing mles. These methods can be both correlative and predictive. The predictive methods rely on the use of group contribution methods for the activity coefficient models such as UNIFAC and ASOG. Recently, there have also been attempts to develop group contribution methods for the equation of state method, e.g. PRSK. " For a detailed history on the development of equations of state and their applications, as well as activity coefficient models, refer to Wei and Sadus, Sandler and Walas. ... 

From the predictive category, we bring some examples of the application of the UNIFAC model. In one study, this model has been used to predict the solubility of naphtalene, anthracene, and phenanthrene in various solvents and their mixtures [8], They showed the applicability of the UNIFAC model in prediction of the phase behavior of solutes in solvents. There have been efforts to make the UNIFAC model more robust and powerful in the prediction of phase behaviors [14], In one study, the solubility of buspirone-hydrochloride in isopropyl alcohol was measured and evaluated by the modified UNIFAC model [15]. It was concluded that for highly soluble pharmaceutics, the modified form of the UNIFAC model was not suitable. In another study, the solubility of some chemical species in water and some organic solvents was predicted by the UNIFAC model [16]. For some unknown functional groups, they used other known groups which had chemical structures that were similar to unknown ones. 

Two modified versions of the UNIFAC model, based on temperature-dependent parameters, have come into use. Not only do they provide a wide temperature range of applicability, but also they allow correlation of various kinds of property data, including phase equilibria, infinite dilution activity coefficients, and excess properties. The most recent revision and extension of the modified UNIFAC (Dortmund) model is provided by Gmehling et al. [Ind. Eng. Chem. Res. 41 1678-1688 (2002)]. An extended UNIFAC model called KT-UNI-FAC is described in detail by Kang et al. [Ind. Eng. Chem. Res. 41 3260-3273 (2003)]. Both papers contain extensive literature citations. 

Gmehling, J. Li, J. Schiller, M. A modified UNIFAC model. 2. Present parameter matrix and results for different thermodynamic properties. Ind. Eng. Chem. Res. 1993, 32, 178-193. 

Lohmann J, Job R, and GmehlingJ. From UNIFAC to Modified UNIFAC (Dortmund). IndEng Chem Res 2001 40 957-964. 

Comparison of Predicted Infinite Dilution Activity Coefficients from the GCS, UNIFAC, AND Modified UNIFAC at 298.15 K... 

Table IV shows the prediction of the infinite dilution activity coefficient of ethanol in heptane at various temperatures using both methods discussed above, together with predictions from the UNIFAC and modified UNIFAC...

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