WOLFRAM|DEMONSTRATIONS PROJECT

Separation of a Reactive Ternary Mixture with a Distillation Column

​
composition profile
1
2
Damköhler number
5
reflux ratio
5
reboil ratio
10.
10.5
11.
11.5
12.
reactive stages
0
2
4
6
8
10
12
14
0.0
0.2
0.4
0.6
0.8
1.0
stage number
composition

Consider a ternary mixture of components
A
,
B
, and
C
with relative volatilities
α
13
=5
and
α
23
=3
. This mixture is subject to an equilibrium-limited chemical reaction
A+B⇌C
with reaction rate
r=kx
A
x
B
-
x
C
K
eq

, where the equilibrium constant
K
eq
=1.5
. This mixture is fed to a reactive distillation column such that the total number of plates is equal to 14, the feed stage location is stage number 5, the reactive stages are from stage 2 to stage 7, and the feed composition is equimolar in
A
and
B
(i.e., the feed is composed of 40% mole
A
, 40% mole
B
, and 20% mole
C
). The feed flow rate is chosen equal to 100 kmol/hr. For simplicity, the constant molal overflow (CMO) assumption is made and heat effects are neglected.

This Demonstration shows two profiles: (1) the composition versus plate number for components
A
,
B
, and
C
(in red, blue, and green, respectively) with the reactive zone shown in light blue and (2) a ternary diagram where the composition of
A
versus the composition of
B
is in % mole. In the second profile, the feed composition is shown by a magenta dot and the reactive stages (stages 2 to 7) are displayed in blue.

You can set the values of the Damköhler number,
Da
, the reflux ratio, and the reboil ratio. When
Da=0
, one recovers the case where no reaction is taking place. If
Da
is very large, the simulation represents a situation close to reaction equilibrium (i.e.,
r=0
).

One snapshot shows a case where the reflux ratio is very high, a situation close to the total reflux operation. For such a situation, the bottom is almost pure
C
and the distillate contain very little
C
. The distillation flow is very small and the distillate stream can be recycled if desired. Thus, for this specific operation, one can produce
C
, if
C
is the desired reaction product, and convert both reactants
A
and
B
with a single piece of equipment.