11.07 - Activity Models at Special Compositions

Special Compositions

Fitting the M2 model parameters using Excel. (uakron.edu, 6min)  Computing the A12 and A21 values from a azeotropic data is just like fitting at a single data point. The procedure is illustrated in this presentation for the benzene+ethanol system at 68.24C where the azeotropic composition is xE=0.448, like Example 11.6 in the textbook. Also following that example, the application of accurate Antoine constants and bubble temperature computation is illustrated. As another problem, you might be given infinite dilution activity coefficients. For example, Lazzaroni et al. list the ginfM=2.03 and ginfB=2.10 at 313K for the 1-butanol+methylethylketone system. Taking the limits of Eqn. 11.37 shows that A12=ln(ginf1) and A21=ln(ginf2). Predict whether this system is expected to exhibit an azeotrope at 760 mmHg.

Comprehension Questions: You may assume the SCVP model for purposes of the calculations below (but you should use more accurate vapor pressure estimates for more professional purposes).

1. At 760 mm Hg the system acetone(1)+hexane(2) exhibits an azeotrope at 68 mole percent acetone with a boiling point of 49.8°C.
a. Estimate the A12 and A21 parameters.
b. Estimate the bubble point pressure and vapor composition of 10 mole percent acetone at this temperature.
2. Acetonitrile+water forms an atmospheric pressure azeotrope at 70 mole% acetonitrile, 76°C.
a. Estimate the A12 and A21 parameters.
b. Estimate the bubble point pressure and vapor composition of 80 mole percent acetonitrile at this temperature.