Predictive group contribution methods

For molecules which differ in size or shape interactions between the surface of the molecules, different Gibbs excess models, such as NRTL [34] or UNIQUAC [35], are recommended, respectively. The predictive group contribution method UNIFAC [36] will fail if several polar groups compose a solvent or solute molecule. As a... 

It seems promising to use for such predictions group-contribution methods, such asUNIFAC (i3). The application of UNIFAC to the solubility of naphthalene in nonaqueous mixed solvents provided satisfactory results (14). Unfortunately, the accuracy of the UNIFAC regarding the solubility of solids in aqueous solutions is controversial (15—17). Large deviations from the experimental activity coefficients at infinite dilution and octanol/water partition coefficients have been reported (16, 17) when the classical old version of UNIFAC interaction parameters (13) was used. To improve the prediction of the activity coefficients at infinite dilution and of the octanol/water partition coefficients of environmentally important substances, special ad hoc sets of parameters for environmental applications were introduced (16-18). 

The third edition of "Properties of Gases and Liquids" by Reid et al. (1977) lists useful group contribution methods for predicting critical properties. Contributions to the second... 

An extensive series of studies for the prediction of aqueous solubility has been reported in the literature, as summarized by Lipinski et al. [15] and jorgensen and Duffy [16]. These methods can be categorized into three types 1 correlation of solubility with experimentally determined physicochemical properties such as melting point and molecular volume 2) estimation of solubility by group contribution methods and 3) correlation of solubility with descriptors derived from the molecular structure by computational methods. The third approach has been proven to be particularly successful for the prediction of solubility because it does not need experimental descriptors and can therefore be applied to collections of virtual compounds also. 

A newer approach uses group-contribution methods to predict solubihty. It has been remarkably successful when apphed to nonpolymer solutions and there are indications that it will be equally successful for treating polymer solutions (17). 

QSAJi Methods for Fluid Solubility Prediction. Several group contribution methods for predicting Hquid solubiHties have been developed. These methods as weU as other similar methods are often called quantitative stmcture-activity relationships (QSARs). This field is experiencing rapid development. 

Second Virial Coefficient. A group contribution method including polar and nonpolar contributions has been proposed for second virial coefficients (241). This method has been appHed to both pure components and mixtures, the latter through prediction of cross-second virial coefficients. 

In many cases, it is possible to replace environmentally hazardous chemicals with more benign species without compromising the technical and economic performance of the process. Examples include alternative solvents, polymers, and refrigerants. Group contribution methods have been conunonly used in predicting physical and chemical properties of synthesized materials. Two main frameworks have... 

For organic liquids, the group contribution method proposed by Chueh and Swanson (1973a,b) will give accurate predictions. The contributions to be assigned to each molecular group are given in Table 8.3 and the method illustrated in Examples 8.7 and 8.8. 

The UNIQUAC equation developed by Abrams and Prausnitz is usually preferred to the NRTL equation in the computer aided design of separation processes. It is suitable for miscible and immiscible systems, and so can be used for vapour-liquid and liquid-liquid systems. As with the Wilson and NRTL equations, the equilibrium compositions for a multicomponent mixture can be predicted from experimental data for the binary pairs that comprise the mixture. Also, in the absence of experimental data for the binary pairs, the coefficients for use in the UNIQUAC equation can be predicted by a group contribution method UNIFAC, described below. 

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. 

Seaton, W. H., "Group Contribution Method for Predicting the Potential of a Chemical Composition to Cause an Explosion," Safety in the Chemical Laboratory, 66, No. 5, A137 (1989). 

Minakata D, Li K, Westerhoff P, Crittenden J (2009) Development of a group contribution method to predict aqueous phase hydroxyl radical (HO ) reaction rate constants. Environ Sci Technol 43 6220-6227... 

Stefanis, E., L. Constantinou, and C. Panayiotou, "Accurate Group-Contribution Method for Predicting Pure Component Properties of Biochemical and Safety Interest", Industrial and Engineering Chemistry Research, 43, 6253-6262, (2004)... 

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... 

Two very simple types of QSPR have been developed early on in the evolution of polymer property prediction, namely van Krevelen s group contribution methods [122] and Bicerano s system [123], which mainly relies on the use of topological descriptors. Group contributions regard the overall properties of the polymer as the scalar sum of the properties of the chemical groups contained in the molecules making up the polymer. 

Van Krevelen s group contributions are widely used for the prediction of Tg and perform reasonably well. When experimentally determined Tg values for 600 polymers are compared to predictions from group contributions, it could be shown that approximately 80% of the calculated Tg values were within 20 K of the experimental result [122]. A serious limitation of any group contribution method, however, is that only polymers with structural groups for which contributions have been developed can be predicted. 

An ultimate goal o-f theory in this -field is not only to model a given mixed sur-factant system, but to be able to predict the properties o-f any arbitrary system. A group contribution method based on measurements -from many systems may be the ultimate means to this goal, whatever speci-fic mathematical model is -found most use-ful. Such systematic studies o-f sur-factant structure as those o-f Rosen (see Chapter 11) will provide a data base -for such correlations. A number o-f important systems have yet to receive su-f-ficient attention. Examples o-f such sur-factant pairs are ethoxylated anionic/nonionic, ethoxylated anionic/nonethoxylated anionic, and nonethoxylated nonionic/ionic. 

Gas-liquid chromatography Group contribution method of predicting GLC... 

The interaction between solvents is important. For example, the development of a successful crystallization process for purification and isolation of an organic compound requires the selection of a suitable solvent or solvent mixture to date, no logical method has been estabhshed for determining the best solvent combination. The process chemist or engineer often employs a trial-and-error procedure to identify an appropriate solvent system, the success of which is dependent on experience and intuition. One approach utilizes a group-contribution method (UNIFAC) to predict a... 

Group contribution method for predicting probability and rate of aerobic biodegradation. Environ. Sci. Technol.,... 

The chapter is divided into the following sections. First, a brief introduction to group contribution methods is given with a major emphasis on the concept and limitations of this technique. An introduction to the use of chemical graph theory and how it applies to polymers and in particular to the dielectric constant is given next. Application of the method to a number of polyimides is then demonstrated and predictions are compared to experimental results. 

Boethling, R. S., P. H. Howard, W. Meyland, W. Stiteler, J. Beauman, and N. Tirado, Group contribution method for predicting probability and rate of aerobic biodegradation , Environ. Sci. Technol., 28,459-465 (1994). 

Tabak, H. H. Govind, R. (1993). Development of nonlinear group contribution method for prediction of biodegradation kinetics from respirometrically derived kinetic data. In Emerging Technologies in Hazardous Waste Management III, ed. D. W. Tedder F. G. Pohland, ACS Symposium Series 518, pp. 159-90. Washington, DC American Chemical Society. 

---