Separation of a Partially Miscible Mixture Shown by Graphical Method

reboil ratio of first column

1.2

reboil ratio of second column

0.2

McCabe & Thiele Diagram

operational setup

Consider a binary mixture of water and nitromethane

(

CH

3

NO

2

)

at 1 atm. This mixture exhibits the vapor-liquid equilibrium behavior of partially miscible mixtures (equilibrium data is available in [1]). Thus, in order to separate water from nitromethane, one has to use a two-column system with an intermediate decanter. This Demonstration shows the required operational setup, which will produce two product streams: a pure water stream and a water-free stream.

Assume that the feed to the first column is a saturated vapor containing

24mole%

water flowing at

1000kg-mole/day

and that the feed to the second column is a saturated liquid containing

96mole%

water flowing at

500kg-mole/day

. The bottom compositions are set to

2mole%

water and

99mole%

water for columns 1 and 2, respectively.

External mass balances give the flow rates of the bottom products of both columns,

B

1

=788.66

and

B

2

=711.33

kg-mole/day

.

The Demonstration uses the McCabe and Thiele graphical method to compute the number of stages for both columns. You can set the two reboil ratios.