Group contribution models coefficient

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. 

It is very satisfying and useful that the COSMO-RS model—in contrast to empirical group contribution models—is able to access the gas phase in addition to the liquid state. This allows for the prediction of vapor pressures and solvation free energies. Also, the large amount of accurate, temperature-dependent vapor pressure data can be used for the parameterization of COSMO-RS. On the other hand, the fundamental difference between the liquid state and gas phase limits the accuracy of vapor pressure prediction, while accurate, pure compound vapor pressure data are available for most chemical compounds. Therefore, it is preferable to use experimental vapor pressures in combination with calculated activity coefficients for vapor-liquid equilibria predictions in most practical applications. 

As an example of how this may be used, we return to the group contribution model for the octanol-water partition coefficient discussed above. As already shown, this model was quite good for monofunctional (i.e., only one nonalkyl group) solutes when applied to multiple functional solutes, the large deviations shown in Fig. 4a were found. The failure of the GCSKOW model is the result of strong proximity effects in multifunctional compounds. 

The goal of predictive phase equilibrium models is to provide reliable and accurate predictions of the phase behavior of mixtures in the absence of experimental data. For low and moderate pressures, this has been accomplished to a considerable extent by using the group contribution activity coefficient methods, such as the UNIFAC or ASOG models, for the activity coefficient term in eqn. (2.3.8). The combination of such group contribution methods with equations of state is very attractive because it makes the EOS approach completely predictive and the group contribution method... 

Tochigi, K., Kojima, K., and Sako, T., Prediction of VLE in polymer solutions using EoS-group contribution model consistent with the second virial coefficient condition. Fluid Phase Equilibria, 117, 55-60, 1996. 

A recent alternative to group-contribution activity-coefficient estimation methods is based on interactions between surface charge distributions (determined by quantum-mechanical calculations) of molecules in solution. The solvation model used for the charge-distribution calculation is known as COSMO the most widely used method based on this technique is called COSMO-RS [47]. 

Repeat Illustration 12.1-1 using the UNLF.AC group contribution model to estimate the naphthalene activity coefficient. 

When there is no built-in binary parameter in Aspen, and also when we cannot find any experimental data in the open literature, another option is to use the group contribution model in Aspen to predict liquid activity coefficient for this binary pair or the entire component system. UNIFAC is an activity coefficient model, like NRTL or UNIQUAC, but it... 

Prediction of Infinite Dilution Activity Coefficients for Polyisoprene (PIP) Systems with Two Predictive Group Contribution Models... 

As an alternative to experimental measurements, CMC can be predicted using thermodynamic models like the group contribution activity coefficient model UNIFAC (Flores et al, 2(X)1 Chen, 1996 Cheng,... 

The Achard model combines the UNIFAC group contribution model modified by Larsen et al. [LAR 87], the Pitzer-Debye-Hiickel equation [PIT 73a, PIT 73b] and solvation equations (Figure 2.1). The latter are based on the definition of the number of hydration for each ion, which corresponds to the assumed number of water molecules chemically related to the charged species. It divides the activity coefficient into two terms ... 

BEN 10] Ben Gaida L., Dussap C.G., Gros J.B., Activity coefficients of concentrated strong and weak electrolytes by a hydration equilibrium and group contribution model . Fluid Phase Equilibria, vol. 289, no. 1, pp. 40-48, 2010. 

It took a little over half a century for the next major development to occur. G. Wilson in 1964 introduced the idea of local compositions which led to an expression for y,- bearing his name and later to the NRTL and UNIQUAC expressions by J. Prausnitz and his co-workers (1967 and 1975). The expressions have two main advantages over the van Laar model first, their parameters have a built-in temperature dependency making them very useful in distillation applications (why ) second, they provide successful prediction of multicomponent activity coefficients from binary ones. Finally, based on the UNIQUAC model, Fredenslund and his co-workers (1977) have developed a group-contribution model, UNIFAC, that can be used for the estimation of activity coefficients for a large variety of systems. 

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