Model UNIFAC

UNIFAC andASOG Development. Pertinent equations of the UNIQUAC functional-group activity coefficient (UNIFAC) model for prediction of activity coefficients including example calculations are available (162). Much of the background of UNIFAC involves another QSAR technique, the analytical solution of groups (ASOG) method (163). 

Chen, F., Holten-Andersen, J., Tyle, P. (1993) New developments of the UNIFAC model for environmental application. Chemosphere 26, 1225-1354. 

In contrast to the NRTL-SAC model, the UNIFAC model developed by Fredenslund et. al. [29] divides each molecule into a set of functional groups that interact with each other on a binaiy basis and whose interactions are combined together to describe the global liquid phase interaction between molecules. Because the segments in UNIFAC are based on functional groups it is possible to model a system provided that all of the molecular structures are known. The problem with pharmaceutical sized molecules is that existing UNIFAC parameter tables do not contain many of the group interaction parameters that are necessary, and even when they do, the interactions are fitted to a database of chemicals that are much smaller and simpler than pharmaceuticals, and typically fail to represent them adequately. 

Kuramochi, H., Noritomi, H., Hoshino, D., and Nagahama, K. Measurements of solubilities of two amino acids in water and prediction by the UNIFAC model, Biotechnol Prog., 12(3) 371-379, 1996. 

Peters, C. A., S. Mukherji, and W. J. Weber Jr., UNIFAC modeling of multicomponent nonaqueous phase liquids containing polycyclic aromatic hydrocarbons , Environ. Toxicol. Chem., 18, 426-429 (1999b). 

Chen, F., J. Holten-Andersen, and H. Tyle, New Developments of the UNIFAC Model for Environmental Application. Chemosphere, 1993 26, 1325-1354. 

Using a Flory-Huggins and a UNIFAC model for the calculation of the solid- and liquid-phase activities, respectively, it was possible to determine the adsorptive properties as a function of the ion-exchange capacity of the resin [20],... 

The method can be applied for saturated fatty acids, unsaturated fatty acids, fatty esters, fatty alcohols and acyl-glycerols. The regression is based on 1200 data points. The absolute deviation in predicting vapor pressure is 6.82%. Another advantage of Eq. (14.1) is the capability of predicting the VLE of mixtures of fatty acids and esters by using the UNIFAC model for liquid activity. The comparison with experimental data shows good accuracy not achieved by other methods [40]. 

Jefferson Tester I would like to shift gears and direct a question to John Prausnitz regarding his comments. You didn t talk very much about some of your own contributions and those of your students, for instance, the NRTL equation and UNIQUAC-UNIFAC models for nonideal solutions now in widespread use throughout the chemical industry and certainly employed by many people making practical calculations. There have been extensions of that local composition approach, in particular to electrolyte systems, by C. C. Chen and others. I wonder how you personally feel about that and... 

The original UNIFAC model(Fredenslund et al., 1975) was used in this work, as it is a widely applicable model with the most available parameters which are updated and extended regularly. For gas/n-alkane systems, temperature dependent interaction parameters were used, and the UNIFAC expression ... 

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... 

As it was pointed out by Chen et al. [22] the calculation of solubility data requires a proper estimation of sublimation pressures. The data were correlated using the PR EOS with classical mixing rules and the UNIFAC model with previously determined anu, parameters. 

Influence of sublimation pressure (P"ub) on the calculation of the solubility (for PR and UNIFAC models, ki2 and L12 were fitted respectively together with the parameters of the sublimation pressure). 

Finally, we must select appropriate methods of estimating thermodynamic properties. lime (op. cit.) used the SRK equation of state to model this column, whereas Klemola and lime (op. cit.) had earlier used the UNIFAC model for liquid-phase activity coefficients, the Antoine equation for vapor pressures, and the SRK equation for vapor-phase fugacities only. For this exercise we used the Peng-Robinson equation of state. Computed product compositions and flow rates are shown in the table below. 

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... 

Figure 2 UNIFAC model and Hansen model results versus experimental data for aspirin solubility in various solvents at room temperature...

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. 

In conclusion, it was stated that the UNIFAC model is not a proper model for use in crystallization and related processes. The UNIFAC model also has been utilized to predict the solubility of some aromatic components as well as long-chain hydrocarbons [17]. The results showed that the predictions for the linear hydrocarbons are not as good as the ones for the aromatics. 

In which yi is the activity coefficient of component i in the solution, yf is the combinatorial part and ytR is the residual part. Up to this point, all of the group contribution and activity coefficient methods (i.e. NRTL-SAC) have been the same, but the methods in which the activities have been calculated are different. In the UNIFAC model, the combinatorial part for component i is found from the following equation [8] ... 

Figure 3. The algorithm of converging to the solubility of a ternary system using the UNIFAC model.

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