4- A continuous rectifying column handles a mixture consisting of 40 per cent of benzene by mass and60 per cent of toluene at the rate of 4 kg/s, and separates

it into a product containing 97 per cent of benzene and a liquid containing 98 per cent toluene. The feed is liquid at its boiling-point. (a) Calculate the mass flows of distillate and waste liquor. (b) If a reflux ratio of 3.5 is employed, how many plates are required in the rectifying part of the column? (c) What is the actual number of plates if the plate-efficiency is 60 per cent? Mole fractionof benzenein liquid0.10.20.30.40.50.60.70.80.9 Mole fractionof benzenein vapour0.220.380.510.630.70.780.850.910.96