UNIFAC group

Fig. 4. UNIFAC group interaction parameter matrix, the ISi represents parameters fit and parameters not available (168). A represents an aromatic...

Data Reduction Correlations for G and the activity coefficients are based on X T.E data taken at low to moderate pressures. The ASOG and UNIFAC group-contribution methods depend for validity on parameters evaluated from a large base of such data. The process... 

Fredenslund, A., Gmehling, J., Michelsen, M. L., Rasmussen, P. and Prausnitz, J. M. (1977a) Ind. Eng. Chem. Proc. Des. and Dev. 16, 450. Computerized design of multicomponent distillation columns using the UNIFAC group contribution method for calculation of activity coefficients. 

UNIFAC group contribution method (Jensen et al. 1981, Yair and Fredenslund 1983, Burkhard et al. 1985a, Banerjee et al.1990) ... 

Gmehling, J., Rasmussen, R, Fredenslund, A. (1982) Vapor-liquid equilibria by UNIFAC group contribution. Revision and extension. 2 Ind. Eng. Chem. Process Des. Dev. 21, 118-127. 

Yair, O. B., Fredenslund, A. (1983) Extension of the UNIFAC group-contribution method for the prediction of pure-component vapor pressure. Ind. Eng. Chem. Fundam. Des. Dev. 22, 433 -36. 

Solubility modelling with activity coefficient methods is an under-utilized tool in the pharmaceutical sector. Within the last few years there have been several new developments that have increased the capabilities of these techniques. The NRTL-SAC model is a flexible new addition to the predictive armory and new software that facilitates local fitting of UNIFAC groups for Pharmaceutical molecules offers an interesting alternative. Quantum chemistry approaches like COSMO-RS [25] and COSMO-SAC [26] may allow realistic ab-initio calculations to be performed, although computational requirements are still restrictive in many corporate environments. Solubility modelling has an important role to play in the efficient development and fundamental understanding of pharmaceutical crystallization processes. The application of these methods to industrially relevant problems, and the development of new... 

The liquid phase activity coefficient, which is a function of the subgroups, composition and temperature, can be evaluated using the UNIFAC group contribution method (Freedunslund et al., 1975). 

The vapour pressure of BHET is approximately three orders of magnitude lower than that of EG. Nevertheless, evaporation of BHET still occurs in significant amounts under vacuum. In Figure 2.26, the experimentally determined vapour pressure of BHET is compared to the vapour pressure predicted by the Unifac group contribution method [95], The agreement between the measured and calculated values is quite good. In the open literature, no data are available for the vapour pressure of dimer or trimer and so a prediction by the Unifac method is shown in Figure 2.26. The correspondence between measured and predicted data for BHET indicates that the calculated data for dimer and trimer... 

Campbell, J.R. and Luthy, R.G. Prediction of aromatic solute partition coefficients using the UNIFAC group contribution model. Environ. Sci. Technol, 19(10) 980-985, 1985. 

UNIFAC Approach Jensen et al. [16] have employed the UNIFAC group contribution approach to develop an estimation method for pure-component vapor pressures. The model developed applies to hydrocarbons, alcohols, ketones, acids, and chloroalkanes of less than 500 molecular mass and in the vapor pressure region between 10 and 2000 mmHg. Burkhard et al. [8] extended this model to chlorinated aromatic compounds such as chlorobenzenes and PCBs. 

Jensen, T., A. Fredenslund, and P. Rasmussen, Pure-Component Vapor Pressures Using UNIFAC Group Contribution. Ind. Eng. Chem. Fundam., 1981 20, 239-246. 

There are several theoretical models to estimate the solubility of a solute in a solvent. However, use of dielectric constant is one of the oldest and simplest approach and is very popular with the formulators. Fractional method to estimate the dielectric constant is the simplest approach and is not the most accurate. However, it offers a good starting point for the estimation. In addition, the solubility of a solute is dependent on the dielectric constant of a solvent mixture and not to the particular composition. Other approaches, such as solubility parameter method and UNIFAC group theory contributions are less frequently used by industry formulators. 

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