A distillation column with a total condenser and a partial reboiler is separating an ethanolwater mixture. The feed is 20 mol% ethanol, feed rate is 1000 kmol/h, and q for the feed is 1.13. A distillate composition of 80 mol% ethanol and a bottoms composition of 2 mol% ethanol are desired. The external reflux ratio is 5/3. The reflux is returned as a saturated liquid. CMO is assumed. For VLE, use the constants for ethanol-water VLE for y = f(x) (6th-order polynomial)

a) Is the CMO approximation valid?

b) Calculate the number of stages needed at total reflux. Calculate the minimum reflux ratio.

c) How does the reflux ratio changes as the thermal state (q) of the feed is varied?

d) Find the optimum feed stage location and the number of stages required for the desired separation, D and B. How is the separation affected as the feed stage location is changed?