A straw oil used to absorb benzene from coke-oven gas is to be steam-stripped in a sieve-plate column at atmospheric pressure to recover the dissolved benzene. Equilibrium conditions at the operating temperature are approximated by Henry's law such that, when the oil phase contains 10 mol% C6H6, the C6H6 partial pressure above the oil is 5.07 kPa. The oil may be considered nonvolatile. The oil enters containing 8 mol% benzene, 75% of which is to be recovered. The steam leaving contains 3 mol% C6H6.

(a) How many theoretical stages are required?

(b) How many moles of steam are required per 100 mol of oil-benzene mixture?

(c) If 85% of the benzene is to be recovered with the same oil and steam rates, how many theoretical stages are required?