Which assumption that you made in solving this problem would you characterize as least valid and why?

Question

A liquid mixture of diethyl ketone (1) and n-hexane (2) is fed into a flash distiller operating at 328 K and 0.45 bar. The feed rate is 2.15 mol/s and the feed is 40% (by mol) of the n-hexane. What is the composition and amount of the resulting phase(s)? Note that the vapor pressure of diethyl ketone at this temperature is 0.29 bar and that of the n-hexane is 0.9015 bar. Answer the question using ONLY the given information.

Answer 1

Overall Balance:



Component Balance on (1):



Raoult’s Law on (1):



Raoult’s Law on (2):



Plug set of 4 equations into solution software to solve for the 4 unknowns:

L ?=1.018 mol/s

V ?=1.132 mol/s

x_1=0.738

y_1=0.476



The least valid assumption made was assuming that the liquid solution was ideal. A mixture of diethyl ketone which is polar and n-hexane which is non-polar is usually not treated as an ideal solution due to the non-polar to polar interactions that exist. But a better answer that uses a real solution model is not possible to implement from just the given information.



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