Activity coefficients in organic

Since the substrates for which organic solvents are attractive media normally have lower activity coefficients in organic solvents than in water, the KM-values determined from plots of rate vs. substrate concentration will generally be higher in organic media. The validity of this approach has been ascertained for several systems [81, 86]. 

The use of UNIFAC for estimating activity coefficients in binary and multicomponent organic and organic—water systems is recommended for those systems composed of nonelectrolyte, nonpolymer substances for which only stmctural information is known. UNIFAC is not recommended for systems for which some reUable experimental data are available. The method, including revisions through 1987 (39), is available in commercial software packages such as AspenPlus (174). 

Some organic compounds can be in solution with water and the mixture may still be a flammable mixture. The vapors above these mixtures such as ethanol, methanol, or acetone can form flammable mixtures with air. Bodurtha [39] and Albaugh and Pratt [47] discuss the use of Raoult s law (activity coefficients) in evaluating the effects. Figures 7-52A and B illustrate the vapor-liquid data for ethyl alcohol and the flash point of various concentrations, the shaded area of flammability limits, and the UEL. Note that some of the plots are calculated and bear experimental data verification. 

Diedenhofen, M., Eckert, F., Mamt, A. Prediction of infinite dilution activity coefficients of organic compounds in ionic liquids using COSMO-RS. J. Chem. Eng. Data 2003, 48, 475 79. 

The formal Galvani potential, described by Eq. (22), practically does not depend on the concentration of ions of the electrolyte MX. Since the term containing the activity coefficients of ions in both solutions is, as experimentally shown, equal to zero it may be neglected. This results predominantly from the cross-symmetry of this term and is even more evident when the ion activity coefficients are replaced by their mean values. A decrease of the difference in the activity coefficients in both phase is, in addition, favored by partial hydration of the ions in the organic phase [31 33]. Thus, a liquid interface is practically characterized by the standard Galvani potential, usually known as the distribution potential. 

The quotient VQ/V poc has been substituted by C, since this quantity should be constant for a given sorbent. Equation 14 illustrates that KQC is proportional to Kow but is modified by two terms, (y0/yoc/w) and w/oc w "h h account for the differences in activity coefficients in the aqueous and organic phases, respectively. In the following discussion, we examine the factors that influence the activity coefficients in the organic phases (y0/y0C/w) and the activity coefficients in the aqueous phase (yw/0c w)-... 

Bhatia, S.R. and Sandler, S.l. Temperature dependence of infinite dilution activity coefficients in octanol and octanol/water partition coefficients of some volatile halogenated organic compounds. J. Chem. Eng. Data, 40(6) 1196-1198,1995. 

When nonnegligible concentrations of the electrolyte are present in the organic solvent, ion-ion interactions superimpose on the ion-solvent ones, or the secondary medium ejfect. Although an equation similar to Eq. (2.43) may be used for determining the activity coefficient in the new medium, it is necessary to employ the appropriate value of A in this equation that depends on the relative permittivity of the medium A(org) = A(aq)(eaq/e ,g) Unless very water-rich mixed solvents are used, different numerical values of the parameters in the denominator and the second term on the right-hand side of Eq. (2.43) have to be employed. 

A common sitnation is that the electrolyte is completely dissociated in the aqueons phase and incompletely, or hardly at all, in the organic phase of a ternary solvent extraction system (cf. Chapter 3), since solvents that are practically immiscible with water tend to have low valnes for their relative permittivities e. At low solnte concentrations, at which nearly ideal mixing is to be expected for the completely dissociated ions in the aqneons phase and the undissociated electrolyte in the organic phase (i.e., the activity coefficients in each phase are approximately nnity), the distribntion constant is given by... 

Bike, D.M., Brennecke, J.F., and Maginn, E.J., Rredicting infinite-dilution activity coefficients of organic solutes in ionic liquids, Ind. Eng. Chem. Res., 43, 1039, 2004. 

Solubilities and Aqueous Activity Coefficients of Organic Liquids Solubilities and Aqueous Activity Coefficients of Organic Solids Solubilities and Aqueous Activity Coefficients of Organic Gases Illustrative Example 5.1 Deriving Liquid Aqueous Solubilities, Aqueous Activity Coefficients, and Excess Free Energies in Aqueous Solution from Experimental Solubility Data... 

So far, we have focused on how differences in molecular structure affect the solubilities and activity coefficients of organic compounds in pure water at 25°C. The next step is to evaluate the influence of some important environmental factors on these properties. In the following we consider three such factors temperature, ionic strength (i.e., dissolved salts), and organic cosolutes. The influence of pH of the aqueous solution, which is most important for acids and bases, will be discussed in Chapter 8. 

Figure 5.6 Illustration of the effect of a completely water-miscible solvent (CMOS, i.e., methanol) on the activity coefficient of organic compounds in water-organic solvent mixtures decadic logarithm of the activity coefficient as a function of the volume fraction of methanol. Note that the data for naphthalene (Dickhut et al., 1989 Fan and Jafvert, 1997) and for the two PCBs (Li and Andren, 1994) have been derived from solubility measurements whereas for the anilins (Jayasinghe etal., 1992), air-water partition constants determined under dilute conditions have been used to calculate y,f.

Estimating the Solubilities and the Activity Coefficients of Organic Pollutants in Organic Solvent -Water Mixtures... 

Explain in words how environmentally relevant inorganic salts affect the aqueous solubility of a (a) liquid, (b) solid, and (c) gaseous compound. Is it true that the effect is linearly related to the concentration of a given salt What is the magnitude of the effect of salt on the aqueous activity coefficient of organic compounds in typical seawater ... 

Explain in words how organic cosolvents affect the activity coefficients in water-solvent mixtures Which organic solvents are most effective Is it true that the effect of an organic cosolvent is linearly related to its volume fraction in the solvent-water mixture Below which volume fraction can the effect of an organic cosolvent be neglected ... 

Note that many of the activity coefficients of organic compounds in dilute aqueous solution, y , that we used in Chapter 5 were derived from experimental air-water partition constants (Ki lv/) using Eq. 6-7. Finally, we should point out that in the literature, similar to air-solid surface partitioning (Section 11.1), partition constants are quite often reported as the reciprocal quantity of the air-solvent partition constants as defined above, that is, as solvent-air partition constants. However, it does not really matter in what form such constants are given, as long as we pay... 

In order to calculate the aqueous concentration of compound / at equilibrium, one needs to know its mole fraction, jcimix, in the mixture (or its molar concentration, Cimix, and the molar volume, Vmix, of the mixture), as well as its activity coefficients in the organic (ymix) and the aqueous (yiw) phases. Very often, when dealing with complex mixtures, V is not known and has to be estimated. At a first approximation, this can be done from the density, pmix, of the liquid mixture, and by assuming an average molar mass, M, of the mixture components ... 

P 7.1 Estimating Activity Coefficients of Organic Compounds in Organic Solvents... 

Grain, C. F., Activity Coefficient . In Handbook of Chemical Property Estimation Methods Environmental Behavior of Organic Compounds, W. J. Lyman, W. F. Reehl and D. H. Rosenblatt, Eds., McGraw-Hill, New York, NY, 1982b, pp. 11-1 - 11-53. 

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