Extractive Distillation Column to Separate Isopropyl Alcohol from Water

reflux ratio R

2.

reboil ratio s

0.52

The binary mixture of water and isopropyl alcohol (isopropanol or propan-2-ol) presents a positive azeotrope at 1 atm. This azeotrope contains

69.8

mole % isopropanol. It is possible to break this azeotrope using extractive distillation. Possible entrainers include: (1) 1,2-ethanediol or ethylene glycol, (2) DSMO (or dimethyl sulfoxide), (3)

N

-methyl-2-pyrrolidone or NMP, (4)

N

-methyl-2-piperidone, and (5)

N

-methyl-6-caprolactam.

In this Demonstration, DSMO is used as an entrainer in an extractive distillation column. The column has 41 plates, a partial reboiler, and a total condenser. This column has an upper feed entering the column at plate 5 and containing pure DSMO with a flow rate of 1708 mol/min. The column has also a lower feed entering the column at plate 25 and containing

30%

mole isopropanol and

70%

mole water. This lower feed has a flow rate of 1666 mol/min. You can set the reflux and reboil ratios,

R

and

s

. For

R=2

and

s=0.52

, the distillate obtained is almost pure isopropanol (

99.6

mole %) and the bottom is a mixture of water

(40.48

mole %) and DSMO

(59.39

mole %), which can be easily separated in a second distillation column—the entrainer regeneration column.