Group contribution methods solvents

Tyn-Calus This correlation requires data in the form of molar volumes and parachors = ViCp (a property which, over moderate temperature ranges, is nearly constant), measured at the same temperature (not necessarily the temperature of interest). The parachors for the components may also be evaluated at different temperatures from each other. Quale has compiled values of fj for many chemicals. Group contribution methods are available for estimation purposes (Reid et al.). The following suggestions were made by Reid et al. The correlation is constrained to cases in which fig < 30 cP. If the solute is water or if the solute is an organic acid and the solvent is not water or a short-chain alcohol, dimerization of the solute A should be assumed for purposes of estimating its volume and parachor. For example, the appropriate values for water as solute at 25°C are = 37.4 cmVmol and yn = 105.2 cm g Vs mol. Finally, if the solute is nonpolar, the solvent volume and parachor should be multiplied by 8 Ig. 

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... 

Flash point is one of the most important fire safety characteristics and hence it is a very important consideration in solvent design. The flammability limit of a solvent is characterized by its flash point, which is the temperature at which the mixture of air and vapor above the liquid can be ignited (Mullin, 1961). It is the lowest point at which the vapor pressure of a liquid will produce a flammable mixture. The flash point of the solvent can be estimated using the following group contribution method (ICAS, 2003)... 

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... 

One of the obstacles in this aim is the lack of experimental thermodynamic data for activity coefficients in ionic liquids, which could be a basis for such solvent selection. In the past years several groups have started to measure such data however, there is a lack of data because the number of suitable anions and cations, and even more the number of ionic liquids, are rapidly increasing compared to the rate (or speed) of measurements. Reliable inter- and extrapolation schemes and group contribution methods are still missing. Thus the search for an appropriate ionic liquid for a certain task can, at present, only be made randomly or by systematic measurements. 

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... 

This equation is quite accurate in comparison with group contributing methods [40] or other predictive LSER methods [41]. For compounds where the solvatochromic parameters are known, the mean absolute error in log Dy is about 0.16. It is usually less than 0.3 if solvatochromic parameters of the solute and solvent must be estimated according to empirical rules [42], In contrast to the prediction of gas-liquid distribution coefficients, which is usually easier, the LSER method allows a robust estimation of liquid-liquid distribution coefficients. However, these equations always involve empirical terms, despite their being physico-chemically founded thermodynamic models. However, this is considered due to the fundamental character of the solvatochromic scales. 

Oishi. T.. Prausnitz, J.M. Estimation of solvent activities in polymer solutions using a group-contribution method. Ind. Eng. Chem. Process Res. Dev., 1978, 17(3) 333-339. 

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... 

Oishi, T. Prausnitz, J. M., "Estimation of Solvent Activities in Polymer Solutions Using a Group-Contribution Method," Ind. Eng. Chem. Process Des. Dev., 17, 333 (1978). 

The calculation of the activity coefficient of a solid in a saturated solution of a n-component mixture constitutes the main difficulty in predicting the solid solubility. Generally speaking, the activity coefficient of a solid in a saturated solution of a n-component mixture can be predicted using either group-contribution methods, such as UNIFAC and ASOG, or the experimental solubilities of the solid in subsystems of the multi-component mixed solvent combined with the Wilson, NRTL, etc. equation (Acree, 1984 Prausnitz et al., 1986). 

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). 

Elbro, H.S., Fredeslund, A. and Rasmussen, P. (1991). Group Contribution Method for the Prediction of Liquid Densities as Function of Temperature for Solvents, Oligomers, and Polymers. lnd.Eng.Chem.Res., 30,2576-2582. 

The required activity coefficients can either be calculated (predicted) with the help of thermodynamic models (group contribution methods) or obtained from factual data banks. The procedure for the selection of selective solvents for extractive distillation processes is given in refs. 4 and 5. The capacity C, of extractants can be estimated using activity coefficients at infinite dilution. 

This is a model for log P calculation based on a group-contribution method proposed by Wang Remdao et al. [Wang, Fu et al, 1997 Wang, Gao et al, 2000]. The model is defined in terms of the solvent accessible surface area and the atomic charges of 76 atom-types, together with five additional correction factors, as... 

This is the log calculated by a group-contribution method proposed by Hou and Xu [Hou and Xu, 2002 Hou and Xu, 2003a Hou and Xu, 2003b] based on the calculation of —> solvent accessible surface area for 100 atom/group types, together with two additional correction factors, and defined as... 

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