Consider a distillation column for separating ethanol from water at 1 atm. The feed is a 10 mol% ethanol bubble-point liquid, the bottoms contains 1 mol% ethanol, and the distillate is 80 mol% ethanol. R/R_min = 1.5. Phase-equilibrium data are given in Exercise 7.29, and constant molar overflow applies. 

(a) How many theoretical plates are required above and below the feed if a plate column is used? 

(b) How many transfer units are required above and below the feed if a packed column is used? 

(c) Assuming the plate efficiency is 80% and the plate spacing is 18 inches, how high is the plate column? 

(d) Using an H_OG value of 1.2 ft, how high is the packed column? 

(e) Assuming that HTU data are available only on the benzene– toluene system, how would one go about applying the data to obtain the HTU for the ethanol–water system?

Data From Exercise 7.29

A continuous distillation unit, consisting of a perforated-tray column  with a partial reboiler and a total condenser, is to be designed  to separate ethanol and water at 1 atm. The bubble-point feed contains 20 mol% alcohol. The distillate is to contain 85 mol% alcohol, and the recovery is to be 97%.