WOLFRAM|DEMONSTRATIONS PROJECT

Dynamic Behavior of a Reactive Distillation Column: Mixture of Four Components

​
reflux ratio
5.55
reboil ratio
6.55
distillate composition
bottom composition
Consider a mixture of four components
A
,
B
,
C
, and
D
with relative volatilities
α
CD
=7
,
α
AD
=4
, and
α
BD
=3
. The mixture is subject to an equilibrium-limited chemical reaction
A+B⇌C+D
with reaction rate
r=k
x
A
x
B
-
x
C
x
D
K
eq
, with equilibrium constant
K
eq
=5
. The mixture is fed to a reactive distillation column with 17 plates. The feed stage location is stage number 10, the reactive stages are stages 6 to 14, and the feed composition is equimolar in
A
and
B
(i.e., the feed is composed of 50 mole%
A
and 50 mole%
B
). The feed, a saturated liquid, has a flow rate of 10 kmol/min. For simplicity, constant molal overflow (CMO) is assumed and heat effects are neglected.
The molar hold-up of the condenser and reboiler are set equal to 2000 and 5000 kmol, respectively. The hold-up in the reactive and nonreactive trays is chosen to be 200 kmol. The reaction rate constant is equal to 5 and the Damköhler number defined by
Da=
H/F
1/k
is 100.
This Demonstration shows the distillate and bottom compositions versus time for components
A
,
B
,
C
, and
D
(in blue, magenta, brown, and green, respectively) for user-set values of the reboil and reflux ratios.
Two snapshots show good conditions where almost pure
C
and
D
exit the column. This can only be achieved if the distillate and bottom flow rates are equal, which is always the case if the reboil ratio,
s
, and the reflow ratio,
R
, are chosen so that
s=R+1
. Hence, this reactive distillation setup can achieve conversions near 100% in addition to the simplification of the operation scheme: no reactor is followed by separation units and there is no recycling of unreacted components
A
and
B
.