Membranes Minimum reflux ratio

Distillation to 90-volZ ethanol requires multistage operation. The process calculations were performed according to the Ponchon-Savarit method.(12) Assuming the concentration of the ethanol bottoms stream to be 1 volZ, and a reflux ratio of 1.5 times the minimum, the heat input to the reboiler corresponds to an energy requirement of 3.2 kWh/gal of 90-volZ product as distillate, or about 2.7 times that of a CCRO process employing the hypothetical, improved membrane. 

In a given application, 100 mol/s of a saturated liquid containing 37 mol% ethanol and 63 mol% water must be separated to yield a product which is 99 mol% ethanol, and a residue containing 99 mol% water. The solution will be fed to a distillation column operating at atmospheric pressure, with a partial reboiler and a total condenser. The reflux ratio will be 1.5 times the minimum. The distillate will enter a membrane with parameters am = 70 and 0 = 0.6. The membrane boosts the concentration so that the permeate stream is the ethanol-rich product (xp = 0.99). The retentate stream is returned as a saturated liquid to the column to the tray at the nearest liquid concentration. 

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