UNIFAC group method

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) ... 

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... 

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. 

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. 

The procedure is based on the UNIFAC-Free Volume method developed by T. Oishi and J. M. Prausnitz, "Estimation of Solvent Activities in Polymer Solutions Using a Group-Contribution Method," Ind. Eng. Chem. Process Des. Dev., 17, 333 (1978). The UNIFAC-FV method is presented by Aa. Fredenslund, J. Gmehling, and P. Rasmussen, Vapor-Liquid Equilibria Using UNIFAC, Elsevier Scientific Publishing, New York (1977). The group... 

The group interaction parameter anm is found from the large sets of VLE and LLE data in the literature, which are tabulated for many subgroups. It is worth noting that a m a. There are some modifications to the original UNIFAC equation in order to make the model robust for some complex systems. In the UNIFAC-DM method, the modification is made on the combinatorial part ... 

Estimation of liquid mixture viscosity without any mixture data is difficult because the viscosity is strongly affected by large molecular size differences and strong cross interactions between the different types of molecules. Viscosity-composition plots for aqueous mixtures can have maxima or minima, and viscosities for these mixtures are particularly difficult to estimate. The UNIFAC-VISCO method described below can be used to predict liquid viscosity of organic mixtures without any mixture data. It is relatively successful even for large differences in molecular size, but it is currently limited in scope by the small number of group contributions available. 

A number of methods based on regular solution theory also are available. Only pure-component parameters are needed to make estimates, so they may be applied when UNIFAC group-interaction parameters are not available. The Hansen solubility parameter model divides the Hildebrand solubility parameter into three parts to obtain parameters 8d, 5p, and 5 accounting for nonpolar (dispersion), polar, and hydrogenbonding effects [Hansen,/. Paint Technot, 39, pp. 104-117 (1967)]) An activity coefficient may be estimated by using an equation of the form... 

Viscosity is a difficult property to predict and flexible predictive models will require further experimental data in order to obtain a better understanding of this property. Many prediction methods are available in literature for the viscosity of pure component and their mixtures [88] most of these are generally based on group contributions (e.g., the Orrick-Erbar method [89], the Sastry-Rao method [90], and the UNIFAC-VISCO method [91]), the corresponding states concept (e.g., Przezdziecki and Sridhar [92], Chatter] ee and Vasant [93], Teja and Rice [94, 95],... 

It should, however, be pointed out that in the above case, if one simply ascribes a single solubility parameter to each monomer, it is Impossible to predict an overall negative enthalpy of mixing. It has also been noted that a window of miscibility can be explained by a favorable specific interaction without recourse to a cross term. If one separates the normal dispersive forces from the specific interaction, then as a first approximation, when the solubility parameters of the two polymers are similar the unfavorable dispersive interactions are small and specific interactions yield miscibility. For a copolymer/polymer mixture the solubility parameters might be expected to match at some specific copolymer composition (32). A method of combining the features of both the specific interaction and the cross term is to use something similar to the UNIFAC group contribution system and model all the interactions, both favorable and unfavorable within the system. 

When using the UNIFAC model one needs to identify the functional subgroups present in each molecule by means of the UNIFAC group table. Next, similar to the UNIQUAC model, the activity coefficient for each species is written as eqn. (2.4.14), except for the the residual term, which is evaluated by a group contribution method in UNIFAC, The residual contribution of the logarithm of the activity coefficient of group k in the mixture. In F., is obtained from... 

When the UNIFAC group contribution method is used for the prediction of phase equilibrium properties of a mixture, two types of input parameters are used in the prediction. One set is made up of the volume (R,) and shape or surface area (Qi)... 

The program WSUNF is used to predict VLE by means of the PRSV EOS coupled with the Wong-Sandler mixing rule and the UNIFAC group contribution method... 

Option 5 - the UNIFAC group-contribution method constructs the activity coefficient out of parameters that have been correlated to specific molecular fragments. It works in the same cases as the NRTL equation, but UNIFAC can predict activity coefficients in the absence of specific data provided all the molecular fragments have been correlated from other data. 

Gottlieb, M. and Herskowitz, M., Estimation of the Flory-Huggins parameter for poly(dimethylsilox-ane) solutions by the UNIFAC group contribution method. Macromolecules, 14, 1468, 1981. 

Banneijee (h) determined the solubilities of mixtures of several chlorobenzenes with one another and with toluene and benzyl alcohol. The results agreed satisfactorily with predictions from equation (8). The water phase activity coefficients were obtained from the pure component solubilities via equation (6). The organic phase activity coefficients for mixtures of chlorobenzenes with hydrocarbons were predicted by the UNIFAC group contribution method. Mixtures containing only chlorobenzenes were essentially ideal, Yi = When benzyl alcohol was used as a cosolute, the agreement with equation (8) was improved by using UNIFAC to predict the activity coefficient in the aqueous phase. 

Fredenslund. A., J.G. Gmehling, M.L. Michelsen, P. Rasmussen and J.M. Praus-nitz, Computerized Design of Multicomponent Distillation Columns Using the UNIFAC Group Contribution Method for Calculating Activity Coefficients. Ind Eng. Chem. Process Des. Dev., 16, 450-62 (1977). 

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