UNIFAC Fredenslund

Traditional activity coefficient based thermodynamic models have been successfully used to describe several LLE systems. The nonrandom two-liquid (NRTL) model of Renon and Prausnitz (1968) and the universal quasi-chemical (UNIQUAC) method of Abrams and Prausnitz (1975) models have been used to correlate LLE data for the many multi-component mixtures (Ghanadzadeh et al., 2009 Se and Aznar, 2002), while a group contribution method (UNIFAC) (Fredenslund et. al., 1977) has been widely used to predict the LLE systems. 

Fredenslund, A., J. Gmehling, and P. Rasmussen "Vapor-Liquid Equilibria using UNIFAC," Elsevier, New York, 1977. 

When no experimental data at all are available, activity coefficients can sometimes be estimated using the UNIFAC method (Fredenslund et al., 1977a, b). However, for many real engineering problems it is often necessary to obtain new experimental data. 

A. Fredenslund, J. Gmehting, and P. Rasmussen, Uapor—Eiquid Using UNIFAC, a Group Contribution Method, Elsevier Scientific Publishing,... 

Fredenslund, A., Gmehling, J., and Rasmussen, P., Vapor-Liquid Equilibria using UNIFAC, Elsevier Scientific Publishing Co., 1977. 

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. 

The linearisation method of Naphtali and Sandholm has been used by Fredenslund et al. (1977) for the multicomponent distillation program given in their book. Included in then-book, and coupled to the distillation program, are methods for estimation of the liquid-vapour relationships (activity coefficients) using the UNIFAC method (see Chapter 8, Section 16.3). This makes the program particularly useful for the design of columns for... 

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. 

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. 

Fredenslund, A. Gmehling, J. Rasmussen P. "Vapor-Liquid Equilibria Using UNIFAC. A Graph Contribution Method" ... 

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

The UNIFAC (UNIQUAC functional group activity coefficient) method is an extension of the UNIQUAC (Universal quasi chemical) method, which has been used widely in chemical process engineering to describe partitioning in organic systems as occur in petroleum and chemical processing (Fredenslund et al., 1975,1977). It has been applied less frequently to aqueous systems. It expresses the activity coefficient as the sum of a "combinational" component, which quantifies the nature of the area "seen" by the solute molecule, and a "residual" component, which is deduced from group contributions. Arbuckle (1983,1986), Banerjee (1985), Banerjee and Howard (1988), and Campbell and Luthy (1985) have tested the applicability of the method to water solubility. 

Gmehling, J., P. Rasmussen, and A. Fredenslund. 1982. Vapor-Liquid Equilibria by UNIFAC Group Contribution. Revision and Extension. 2. lnd. Eng. Chem. Process. Des. Dev. 21 118-127. 

When gas solubility data are lacking or are unavailable at the desired temperature, they can be estimated using available models. The method of Prausnitz and Shair (1961), which is based on regular solution theory and thus has the limitations of that theory. The applicability of regular solution theory is covered in detail by Hildebrand et al. (1970). A more recent model, now widely used, is UNIFAC, which is based on structural contributions of the solute and solvent molecular species. This model is described by Fredenslund et al. (1977) and extensive tabulations of equilibrium data, based on UNIFAC, have been published by Hwang et al. (1992) for aqueous systems where the solute concentrations are low and the solutions depart markedly from thermodynamic equilibrium. 

Another group contribution method that has been applied to the prediction of soil sorption is the UNIquac Functional-group Activity Coefficient (UNIFAC, where UNIQUAC = Universal Quasichemical) approach (Fredenslund et al., 1977). Ames and Grulke (1995) applied the method to a small diverse set of chemicals, with rather poor results. They did not report any correlations, but from their results it can be shown that the correlation of observed and predicted log values using the Bondi method was n = 17, R2 = 0.571, 5 = 0.524, and F = 20.0 eight chemicals were predicted with an error of < 0.5 log units, 7 chemicals were predicted with an error between 0.5 and 1.0 log units, and 2 chemicals were predicted with an error of > 1.0 log units. 

Aage Fredenslund, Jurgen Gmehling, and Peter Rasmussen, Vapor-Liquid Equilibriums using UNIFAC. A Group-Contribution Method, Elsevier, Amsterdam, The Netherlands, 1977. 

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