If a 100 kg mol mixture of n-hexane and n-octane containing 50 mole% n-hexane is to be separated by flash distillation @ 1 atm to obtain 40 kg mol in distillated (ie. v=40 kg mol) a) whatare the compositions of the liquid and vapor phases when v = 40 kg mol? b) what is the flash drum temperature?

(a)

(b)

Explanation:

Hello,

The Rachford-Rice equation should be used in this case:

The distribution coefficients could be approximated via Raoult's law and the Antoine equation for the vapor pressure:

For n-hexane: A=6,9895, B=1216,92 and C=227,451

For n-octane: A=7,14462, B=1498,96 and C=225,874

*Those values and the Antoine law are used in °C and mmHg.

Replacing each value in the Rachford-Rice equation and solving for T, one gets the flash drum temperature as 95.24°C (attached picture), thus, the compositions in both the liquid and the vapor phases are:

Best regards.