Multicomponent Simple Batch Distillation

relative volatility

α

21

between B and A

0.2

relative volatility

α

23

between B and C

4

Consider three components

A

,

B

, and

C

having the following relative volatilities

α

21

and

α

23

computed relative to

B

.

The heaviest component is component

C

, the lightest component is

A

, and

B

is the intermediate boiling component. Thus we have

α

21

<1

and

α

23

>1

.

A batch still is charged with a 120 kmol mixture containing 20%

A

, 30%

B

and 50%

C

. The distillation removal rate is assumed constant and equal to 1 kmol/hr. The Demonstration computes the composition of the liquid remaining in the still as well as the composition of the distillate and plots the mole fractions of component

A

,

B

, and

C

in the distillate (yellow, magenta and blue curves, respectively). The four snapshots correspond to various selections of

α

21

and

α

23

. We observe perfect separation between the three components when

α

21

<<1

and

α

23

>>1

. Indeed, components

A

,

B

, and

C

exit the column separately and successively (i.e., following the order of volatility), while when

α

21

and

α

23

are both close to unity, there is almost no separation and the three components exit the still together.