[curiouscat]

Say you had to separate X & Y via a batch fractionating still with a fixed number of stages. Further assume your Reflux ratio & top product fraction drawoff rates are fixed.

Would you get better separation (i.e. purer top) with or without a vacuum? What's a sound scientific way to analyse this problem. (My impression is vacuum would almost always improve relative volatalities & hence separation. Is this right?)

Let's assume both X & Y are infinitely heat stable & X is lower BP. Let's assume no azeotropes or other pathologies. If it matters, lets assume atm. BP of X & Y are 80 & 150 C.