A mixture of 45 mol% of isobutane in n-pentane, under conditions such that there is 40 mol% steam, will be rectified to obtain a 2 mol% n-pentane distillate. The pressure at saturation occurs at 308 kPa. The feed comes out as a saturated liquid. Using the following information based on enthalpy data at 527.67 R, determine the minimum number of stages for separation.
Equilibrium constants for isobutane and n-pentane:
P = 308 kPa (3.04 atm abs)
T (°F) Kacs Kics
100 0.36 1.7
140 0.70 2.6
160 0.90 3.1
150 0.80 2.9
120 0.50 2.1
80 0.25 1.3
70 0.10 1.1