Question
A distillation column is fed continuously with a binary mixture containing 30 mol % ethanol and 70 mol % water; the feed flow rate is
A distillation column is fed continuously with a binary mixture containing 30 mol % ethanol and 70 mol % water; the feed flow rate is 100 kmol h-1 of a two-phase mixture containing 60 % vapour. The column is to produce two products: a distillate containing 75 mol % ethanol and a bottoms product containing 98 mol % water. The column is equipped with a partial reboiler and a total condenser and may be assumed to operate at a pressure of 1 bara and with a reflux ratio of 1.3. (a) Calculate the distillate and bottoms flow rates and hence find the recovery of ethanol in the distillate product. [5 marks] (b) Find the minimum reflux ratio and hence comment on the choice of the reflux ratio given above. [5 marks] (c) Find the minimum number of equilibrium stages required to perform this separation at total reflux. [3 marks] (d) Find the actual number of stages required to perform this separation at a reflux ratio of 1.3 and for a Murphree vapour phase efficiency of 80%; the partial reboiler may be assumed to be an equilibrium stage. [6 marks] (e) Estimate the mole fractions of ethanol in the vapour and liquid phases of the feed stream. Find also the temperature of the feed and compare it with the temperatures in the condenser and reboiler.
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