[aseem]

Hey i am not getting this one. Its a question from Robert E. Treybal ch 9 problems 9.8.


A jacketed kettle is originally charged with 30mol of a mixture containing 40mol% benzene, 60mol% toluene. The vapors from the kettle pass directly to a condenser and the condensate os withdrawn. Liquid of the same composition as the charged is continuously added to the kettle at the rate of 15mol/h. Heat to the kettle remains const. The mixture is ideal, and the average relative volatility is 2.51. The distillation is essentially differential.
  a) How long will the still have to be operated before vapor containing 50mol% benzene is produced, and what is the composition of the composite distillate?
  b) If the rate at which heat is supplied to the kettle is incorrectly regulated so that 18 mol/h of vapor is generated, how long will it take until vapor containing 50mol %  benzene is produced?


hoping for help ASAP!!
thanx in advance