GENERAL RESEARCH Solubility of Gases in Binary Liquid Mixtures: An Experimental and Theoretical Study of the System Noble Gas + Trifluoroethanol + Water Ana M. Mainar, † Juan I. Pardo, ‡ Jesu ´ s Santafe ´ , † and Jose ´ S. Urieta* ,† Departamento de Quı ´mica Orga ´ nica-Quı ´mica Fı ´sica, Facultad de Ciencias, Universidad de Zaragoza, Ciudad Universitaria, Plaza san Francisco, 50009 Zaragoza, Spain, and Centro Polite ´ cnico Superior, Universidad de Zaragoza, Marı ´a de Luna 3, 50018 Zaragoza, Spain Solubilities of noble gases (He, Ne, Ar, Kr, and Xe) in mixtures of water + 2,2,2-trifluoroethanol (TFE) at 298.15 K and 101.33 kPa partial pressure of gas are reported. Our procedure for the estimation of these solubilities from the experimental data is described in detail. From these data, the Henry’s constants at the vapor pressure of water (the least volatile component), the standard changes in the Gibbs energy for both the solution process and the solvation process, and the so-called excess Henry’s constant are calculated. Finally, three prediction methods are applied, and their results are compared and discussed. Introduction The importance of solutions and mixtures of nonelec- trolytes is difficult to overestimate. Hence, the growth in both the experimental and theoretical thermody- namic study of these systems has been extraordinary. Whereas liquid mixtures have been very extensively studied, this is not the case for solutions of gases in liquids. However, such solutions are not less relevant. For example, the solubilities of gases in liquids provide information about the solvophobicity 1 of the liquid solvent, information that can be used for practical purposes such as the choice of adequate media for some chemical processes. At a more fundamental level, these solubilities also allow for the estimation of solvent molecular parameters, as in the case of those corre- sponding to the Lennard-Jones potential. 2 It can be said that gases act as probes for certain characteristics of the solvent into which they dissolve. If data for solutions of gases in pure liquids are not as common as those for binary liquid mixtures, the lack of data is even more pronounced in the case of solutions of gases in binary liquid mixtures. Thus, this kind of solution is well worth considering. In fact, this paper is part of a study on the solubilities of a wide set of gases (He, Ne, Ar, Kr, Xe, H 2 ,N 2 ,O 2 , CH 4 ,C 2 H 6 ,C 2 H 4 , CF 4 , SF 6 , and CO 2 ) in mixtures of water and a fluoro alcohol, namely, 2,2,2-trifluoroethanol (TFE) or 1,1,1,3,3,3- hexafluoropropanol. These liquid mixtures have been used to modulate some of the properties influencing the kinetics of Diels-Alder-type reactions. 3 The aim of this investigation is to measure the solubilities, then to calculate related thermodynamic properties, and finally to interpret all of these data. As a preliminary step, the solubilities of the gases in the pure fluoro alcohols were determined. 4,5 Now, we report the solubilities of the noble gases helium, neon, argon, krypton, and xenon in the mixture water + 2,2,2- trifluoroethanol (TFE) at a temperature of 298.15 K and a partial pressure of gas of 101.33 kPa. Confirmation of the above-mentioned lack of data is given by the fact that, as far as we know, only one other systematic study of the solubilities of noble gases in a binary liquid mixture has been conducted. 6 In our studies, the quan- tity of alcohol in the mixtures covers a range between 10 and 90% by volume. The solubilities are expressed in terms of the mole fraction of gas dissolved and also the Henry’s constant as a function of the liquid-phase composition as given by the mole fraction of TFE. Estimation of the solubilities required the development of a calculation method, which is explained in detail. The solubility values allow for the calculation of the changes in the standard Gibbs energy for both the solution and solvation processes. A simple method for obtaining the Gibbs energies for the solution process and the solubilities in the systems considered is derived from the relationship between the Gibbs energies and the depth of the potential well of the gases. In turn, the Gibbs energies for the solvation process provide useful information about the behavior of the liquid solvent mixture in the water-rich zone. Finally, three prediction methods, namely, the equa- tion of Krichevsky 7 (related to the so-called excess Henry’s constant), the equation of Shulgin and Ruck- enstein, 8 and the scaled particle theory (SPT) 2,9-11 are considered to verify their validity in these ternary solutions. Experimental Section Materials. The gases used were helium (99.995%), argon (99.9990%), krypton (99.95%), and xenon * To whom correspondence should be addressed. Phone number: 34 976 761298. Fax number: 34 976 761202. E-mail: urieta@posta.unizar.es. † Facultad de Ciencias. ‡ Centro Polite ´cnico Superior. 1439 Ind. Eng. Chem. Res. 2003, 42, 1439-1450 10.1021/ie020329o CCC: $25.00 © 2003 American Chemical Society Published on Web 03/04/2003