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Tutorial 12 Continuous Distillation - Unknown mole fractions

An ethanol-water mixture (MW of ethanol = 46, MW of water = 18) is separated using continuous distillation operating at 101.32 kPa pressure. The feed rate is 453.6 kg/hr and enters the column at its boiling point. Its density at 30oC is 905.80 kg/m3. A reflux ratio of 1.5 is to be used. The distillate has a density of 822.20 kg/m3 at 30 oC and the bottoms has a density of 990.14 kg/m3 at 30 oC. (You may assume the density of water at 30 oC to be 1000.0 kg/m3 )

Determine the following:

(a) The amounts of distillate and bottoms in kg-moles/hr and their concentrations in mole fraction ethanol, and
(b) The number of theoretical trays required.
(c) For the same number of theoretical trays determined in part (b), find the reflux ratio required to produce a distillate of 0.74 mole fraction ethanol.

How does your answer for part (c) compare with the original reflux ratio of 1.5 ?

Equilibrium data for ethanol-water system at 1 atm pressure are given below:

Ethanol-Water System VLE


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