UNIFAC group contribution 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. 

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... 

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). 

Finally, if none of these routes is available, the UNIFAC group contribution method can be used to calculate the activity coefficients of the components of a binary mixture and hence a VLE curve can be drawn. For the solvents Irequently used in industrial amounts this method should be needed only very seldom. 

The key to the use of equation 3.25 for the prediction of solubilities in non-ideal systems is a reliable estimation of the activity coefficient 7. For organic solutes in organic solvents, this may be achieved (Gmehling, Anderson and Prausnitz, 1978) by the UNIFAC group contribution method which is discussed, together with other techniques for the prediction of solubility data, in section 3.10. 

To estimate the solubility of an organic solid solute in a solvent it is only necessary to know its melting point, enthalpy of fusion and relevant activity coefficient. Gmehling, Anderson and Prausnitz (1978) have shown that this activity coefficient can be estimated by the UNIFAC group contribution method, and they report a number of cases where the solubilities of a variety of organic solids in single and mixed solvents are accurately predicted. Even eutectic temperatures and compositions may be estimated for some binary systems. 

When considering solvent S for extraction of solute A from species B, Pretel and coworkers (1994) use the UNIFAC group-contribution method to obtain estimates of four solvent properties ... 

The Antoine equation coeffieients A, B, C for various organic solvents can be found elsewhere. The UNIFAC group contribution method was used to calculate the activity coefficient of each solvent ... 

Shell Research [2,3] has developed a relatively easy applicable empirical method for obtaining the activity coefficients, calculated with help of graphs, an example of which is given in Figure 2.13. A more sophisticated computer-assisted technique has been described by Walsham [4] and later developments make use of the work by Gmelin and Rasmussen [5,6] and utilise the UNIFAC group contribution method developed by Fredenslund [6,7] for the calculation of the activity coefiicients. 

For the calculation of evaporation rates the model of Walsham and Edwards [12] who use activity coefficients to calculate corrected relative evaporation rates is a good starting point. Nowadays these activity coefficients are, however, calculated with the UNIFAC group contribution method [6,7] and the evaporation rates take into account evaporative cooling of the blend [13]. 

The flashpoints can also be calculated using the UNIFAC group contribution method as described earlier in this chapter. Adequate computer programs for performing such calculations are already available and are rapidly gaining acceptance in the industry. 

Chapter 5 gives a comprehensive overview on the most important models and routes for phase equilibrium calculation, including sophisticated phenomena like the pressure dependence of liquid-liquid equilibria. The abilities and weaknesses of both models and equations of state are thoroughly discussed. A special focus is dedicated to the predictive methods for the calculation of phase equilibria, applying the UNIFAC group contribution method and its derivatives, that is, the Mod. UNIFAC method and the PSRK and VTPR group contribution equations of state. Furthermore, in Chapter 6 the calculation of caloric properties and the way they are treated in process simulation programs are explained. 

In 1975, the UNIFAC group contribution method was published by Fredenslund etal. [27, 52, 53]. Like the ASOG method, the UNIFAC method is based on the... 

The method of Cao et ai, by its construction, is also suitable only for well-defined mixtures [27,32]. However, for such mixtures it offers the advantage of being completely predictive. In the spirit of the UNIFAC group contribution method for activity coefficents, Cao et al. used the following expression for the dynamic viscosity ... 

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