A distillation column is separating phenol from p-cresol at 1 atm pressure. The distillate composition desired is 0.96 mole fraction phenol. An external reflux ratio of L/D =4 is used, and the reflux is returned to the column as a saturated liquid. The equilibrium data can be represented by a constant relative volatility, Alpha (phenol -cresol) = 1.76 (Perry et aI., 1963, pp. 13-3). CMO can be assumed.
a. What is the vapor composition leaving the third equilibrium stage below the total condenser? Solve this by an analytical stage-by-stage calculation alternating between the operating equation and the equilibrium equation.
b. What is the liquid composition leaving the sixth equilibrium stage below the total condenser? Solve this problem graphically using a McCabe-Thiele diagram plotted for Alpha(p-c) =1.76.