Effect of Temperature on LLE

For practically insoluble mixmres we can estimate the effect of temperature change on LLE with some confidence. As shown in Eq. 11.4, the solubility is inversely proportional to the activity coefficient. If we take the In of both sides of Eq. 11.4, differentiate with respect to temperature, and then substitute from Eq. 7.32, we find. 

If we assume that (h° — hi) (minus the differential heat of mixing, see Eq. 6.11) is a constant, independent of temperature, then we can integrate Eq. 11.6, finding 

Comparing this term-by-term with Eq. 11.7, we conclude that 

FIGURE 11.9 Benzene water solubility data, in the form suggested by Eq. 11.7. The points are the values from Table 11.1. The lines are least-squares fits of the data. In this formulation temperature increases from right to left  

Example 11.8 Gasoline is put into the tank of an auto, saturated with water at 50°F. A sudden cold wave cools the auto and its fuel system to 20°F. How much water would we expect to come out of solution in the gasoline What would its effect likely be  

---

Figure 9.27 Effect of temperature on LLE in mixtures of phenol, water, and triethylamine. At 10°C a consolute point occurs in mixtures lean in phenol, while at 75°C a consolute point occurs in mixtures lean in triethylamine. At 10°C pure phenol solidifies. Compositions plotted here as weight fractions. Adapted from Walas [5],...

---