WOLFRAM|DEMONSTRATIONS PROJECT

Separation of a Reactive Ternary Mixture: Olefin Metathesis

​
composition profile
1
2
reflux ratio
7
Consider a ternary mixture of components
A
,
B
, and
C
with relative volatilities
α
13
=4
and
α
23
=0.25
. The mixture is subject to an equilibrium-limited chemical reaction
2C⇌A+B
with reaction rate
r=k
2
x
C
-
x
A
x
B
K
eq
, where the equilibrium constant,
K
eq
=0.25
. The mixture is fed to a reactive distillation column with 13 plates; the feed stage location is stage 5, the reactive stages run from 2 to 7, and the feed composition contains 100% mole
C
. The feed flow rate is chosen as 100 kmol/hr. For simplicity, we assume constant molal overflow (CMO) and neglect heat effects.
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 with the composition of
A
versus the composition of
B
in mole %. In the second profile, the feed composition is shown by a purple dot and reactive stages 2 to 7 are displayed in blue.
The Damköhler number,
Da
, is set to 200. The reboil ratio is chosen so that distillate and bottom flow rates are equal (i.e.,
s=R+1
, where
s
is the reboil ratio and
R
is the reflux ratio). For this very large Damköhler number, the simulation represents a situation close to reaction equilibrium (i.e.,
r=0
).
This reaction mechanism corresponds to the case of a metathesis or disproportionation of olefins (for example cis2-pentene ⇌ cis2-butene + cis2-hexene).