Activity coefficients acetone/water

The effect of solvent concentration on the activity coefficients of the key components is shown in Fig. 13-72 for the system methanol-acetone with either water or methylisopropylketone (MIPK) as solvent. For an initial-feed mixture of 50 mol % methanol and 50 mol % acetone (no solvent present), the ratio of activity coefficients of methanol and acetone is close to unity. With water as the solvent, the activity coefficient of the similar key (methanol) rises slightly as the solvent concentration increases, while the coefficient of acetone approaches the relatively large infinite-dilution value. With methylisopropylketone as the solvent, acetone is the similar key and its activity coefficient drops toward unity as the solvent concentration increases, while the activity coefficient of the methanol increases. 

FIG. 13-72 Effect of solvent concentration on activity coefficients for acetone-methanol system, (a) water solvent, (h) MIPK solvent. 

Gmehhng and Onken (op. cit.) give the activity coefficient of acetone in water at infinite dilution as 6.74 at 25 C, depending on which set of vapor-liquid equilibrium data is correlated. From Eqs. (15-1) and (15-7) the partition ratio at infinite dilution of solute can he calculated as follows ... 

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. 

The liquid phase activity coefficients y and y2 depend upon temperature, pressure and concentration. Typical values taken from Perry s Chemical Engineers Handbook114) are shown in Figure 11.8 for the systems m-propanol-water and acetone-chloroform. In the former, the activity coefficients are considered positive, that is greater than unity, whilst in the latter, they are fractional so that the logarithms of the values are negative. In both cases, y approaches unity as the liquid concentration approaches unity and the highest values of y occur as the concentration approaches zero. 

The treatment has been extended to dioxan/water and dioxan/alcohol mixtures, where the concentration of self-associated alcohol has to be calculated from activity coefficient data. It was found that alcoholysis of 4-nitro-benzoyl chloride in ether and dioxan can be accounted for solely on the grounds of specific solvation, but in the case of acetone some of the reaction proceeds by a mechanism without specific solvation, possibly due to dielectric solvation of the transition state. Table 24 shows the relative reactivities of associated alcohol in several solvents. Hudson et al.l72b propose that in carbon tetrachloride the smallest associate is probably the trimer whereas in the ethers the corresponding associate has an open structure, viz. 

Figure 13.23. Examples of vapor-liquid equilibria in presence of solvents, (a) Mixture of-octane and toluene in the presence of phenol, (b) Mixtures of chloroform and acetone in the presence of methylisobutylketone. The mole fraction of solvent is indicated, (c) Mixture of ethanol and water (a) without additive (b) with 10gCaCl2 in 100 mL of mix. (d) Mixture of acetone and methanol (a) in 2.3Af CaCl2 ip) salt-free, (e) Effect of solvent concentration on the activity coefficients and relative volatility of an equimolal mixture of acetone and water (Carlson and Stewart, in Weissbergers Technique of Organic Chemistry IV, Distillation, 1965). (f) Relative volatilities in the presence of acetonitrile. Compositions of hydrocarbons in liquid phase on solvent-free basis (1) 0.76 isopentane + 0.24 isoprene (2) 0.24 iC5 + 0.76 IP (3) 0.5 iC5 + 0.5 2-methylbutene-2 (4) 0.25-0.76 2MB2 + 0.75-0.24 IP [Ogorodnikov et al., Zh. Prikl. Kh. 34, 1096-1102 (1961)].

Flgurs 1J Effect of composition an liquid activity coefficients, fa) For the positive-deviation system n-propanol water at 1 atm (6) for toe negative-deviation system acetone-chloroform at 1 atm. (From R. H. Ferry, Chemical Engineer Handbook, 5th ed.. 1973, Copyright by McGraw-Hill. Inc. Reprinted by permission.)... 

The magnitude of the deviations from Raoult s law increases with the difference in nature between the components. For instance, the normal propanol-water system (Fig. 1.3a) and the acetone-chloroform system (Fig. 1.36) show large activity coefficients, the highest being 13. On the other hand, the highest-activity coefficient in a mixture of isobutane-normal butane, which are similar to each other, is smaller than 1.1 (at about 100 psia). 

Figure 1.4 Activity coefficient ratios (a in the positive-deviation system, n-propanol-water (6) in the negative-deviation system, acetone-chloroform.

Next, we specify the x, between 0 and 1, and estimate the total pressure P and yx from Eq. (1.193) to prepare the total pressure and equilibrium compositions shown in Table 1.10. In Figure 1.9, we can compare both the Tyx and Pyx diagrams obtained from Raoult s law and the NRTL model using the Aspen Plus simulator. As we see, ideal behavior does not represent the actual behavior of the acetone-water mixture, and hence we should take into account the nonideal behavior of the liquid phase by using an activity coefficient model. 

Figure 12.9 Logarithms of the activity coefficients at 323.15 K (50°C) for six binary liquid systems (a) chloroform(1)/n-heptane(2) ( b acetone(1)/methanol(2) (c)ace-tone(1)/chloroform(2) (d) ethanol(1)/n-heptane(2) (e) ethanol(1)/chloroform(2) (f j ethanol(1 )/water(2)...

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