Universal functional activity coefficient

When it is necessary to estimate activity coefficients where no data or very limited data are available, estimates may be made by using a group contribution method. In this case, a molecule is divided into fimctional groups, or subgroups of the molecule. These subgroups are assumed to act independently of the molecule in which they appear. Molecular interactions are accounted for by properly weighted sums of group interactions. Fredenslund, Jones, and Prausnitz developed the method for UNIQUAC and named it as universal functional activity coefficient (UNIFAC). Smith, van Ness, and Abbott report the equations for the activity coefficients of multicomponent solutions and their parameters. These equations are very... 

The UNIFAC (universal functional activity coefficient) method [16] is similar to the ASOG method and is based on the four postulates of Wilson and Deal [13] regarding solution of groups. In UNIFAC, the activity coefficient is made of two parts. 

The choice of a plasticizer is mainly ruled hy its compatibility with the polymer material involved. Indeed, as explained by the plasticization theories, plasticizer molecules have to deeply penetrate into the macromolecules network and remain stable inside. Thereby, the initial emulsion during the mixing process using an extruder or roll mixers requires a thermodynamically favourable plasticizer/polymer pair. In order to quantify the compatibility, several approaches have been developed. The most complex ones are the QSAR (Quantitative Structure-Activity Relationship) or UNIFAP (Universal Functional Activity coefficient for Polymers),which are highly effective, but need extensive amounts of data and consequently might be uncomfortable to employ in a first approach. 

Modeling of a semibatch reactor (Figure 16.1) enables to determine the reaction rate pseudoconstants. For lack of physical data, a number of assumptions have to be made. The volume of the liquid phase is the function of composition, temperature, pressure, and mass of EO reacted with raw material. At a constant temperature (185 5°C), the volume of the liquid phase increases due to an increased solubility of EO. However, the rate of change is relatively low compared to the reaction rate. The universal functional activity coefficient (UNIFAC) method [43] was used to calculate the activity coefficients. The method was adopted for the heterogeneous liquid-liquid-vapor system as the limited solubility of liquid components was observed. The... 

One possible approach is UNIFAC (universal functional activity coefficient) and its many variants, particularly UNI-FAP (UNIFAC for polymers) [1]. This is a classic group contribution methodology that relies on fitting of large data sets of various properties. In areas where these large data sets exist, the methods are most fruitful. But despite the enthusiasm of the proponents of these methods, there is not a reliable body of results applicable to the sorts of questions of interest to this chapter. 

The Wong-Sandler mixing rules extend the use of cubic equations of state to mixtures that were previously only correlated with activity-coefficient models. For many mixtures, the Gibbs-function model parameters in the equation of state could be taken to be independent of temperature, thereby allowing extrapolation of phase behaviour over wide ranges of temperature and pressure. For example, for (ethanol-h water) the activity-coefficient model reported in DECHEMA is at a pressure of 0.4 MPa and this model provides reasonable predictions of the phase boundaries at pressures up to 20 MPa. This means the method can be used with UNIversal Functional Activity Coefficient (known by the acronym UNIFAQ and other group-contribution methods to predict properties at elevated pressure. 

More reliable phase behaviour predictions for binary ionic liquid systems with carbon dioxide or organics come from group-contribution equations of state, such as the universal functional activity coefficient (UNIFAC) method, the group-contribution nonrandom lattice ffuid equation of... 

These models are semiempirical and are based on the concept that intermolecular forces will cause nonrandom arrangement of molecules in the mixture. The models account for the arrangement of molecules of different sizes and the preferred orientation of molecules. In each case, the models are fitted to experimental binary vapor-liquid equilibrium data. This gives binary interaction parameters that can be used to predict multicomponent vapor-liquid equilibrium. In the case of the UNIQUAC equation, if experimentally determined vapor-liquid equilibrium data are not available, the Universal Quasi-chemical Functional Group Activity Coefficients (UNIFAC) method can be used to estimate UNIQUAC parameters from the molecular structures of the components in the mixture3. 

Here C is the concentration of component i in grams per liter, and t/ is the activity coefficient of component i on this concentration scale. The quantity m° is the standard state chemical potential of component i and is a function of temperature only. The standard state of solute component i is chosen so that In t/ — 1 as c, — 0. In Equation 4, R is the universal gas constant, 8.314 X 107 ergs/(deg mole), and T is the absolute temperature. The quantity In t/ is a function of the concentration of all q solutes thus... 

UNIQUAC functional group activity coefficient universal quasi-chemical [15]... 

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. 

Uniquac Functional-group Activity Coefficient (where UNIQUAC = Universal Quasi-Chemical)... 

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. 

The UNIFAC computer program (UNIversals quasichemical Functional group Activity Coefficients) has received broad acceptance throughout the profession... 

A group contribution method called UNIFAC, an acronym which stands for the UNIQUAC Functional Group Activity Coefficient (UNIQUAC stands for the Universal Quasi-chemical Activity Coefficient), has been developed for estimating liquid-phase activity coefficients in non-electrolyte mixtures. The UNIFAC method is fully described by Fredenslund, Jones and Prausnitz (1975) and Skold-Jorgensen, Rasmussen and Fredenslund (1982). 

A wide-spread and widely applicable procedure for the calculation of the activity or the activity coefficient of non-electrolytic liquid mixtures is the so-called UNIFAC (Universal Functional Group Activity Coefficient) method (Reid et al. 1977). T. Oihsi and J. M. Prausnitz reported about an extension of the procedure which can be used to determine the activity of substances dissolved in amorphous polymers (Oishi and Prausnitz... 

The UNIFAC (the universal qrrasi-cherrrical function group activity coefficient) is one of the best methods in estimating activity coefficient that has been established to date (Fredenslrmd et al., 1975 Fredenslrmd et al., 1977 Magnussen et al., 1981) has been successfully applied for the prediction of several LLE systems. This model depends on interaction parameters between each pair of components in the systerrr, which can be obtained by between each of the main groups. 

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