A gas mixture containing 55 mol% propane and 45 mol% propylene is to be separated into products containing 10 and 90 mol% propane by adsorption in a continuous, countercurrent adsorption system operating at 25°C and 1 atm. The adsorbent is silica gel, for which equilibrium data are given in Exercise 15.9. Determine by the McCabe-Thiele method:

(a) The adsorbent flow rate per 1,000 m3 of feed gas at 25°C and 1 atm if 1.2 times the minimum rate is used, and

(b) The number of theoretical stages required.