Afeed stream containing 25 mole% methanol and 75 mole% water is separated in a continuous distillation column with a total reboiler and a partial condenser. the distillate has a methanol composition of 95 mole%. the methanol composition in the bottoms is 1 mole%. the column is operated at 1 atm.

a. what are the number of equilibrium stages required to do the separation if the feed is flashed to produce 50 mole% saturated liquid and 50% saturated vapor in the flash stage? assume the reflux ratio is 3.75 and you may assume the feed flowrate is 1000 kmol/hr.

b. what is l/d if the operating lines becomes simply yj+1 =xj