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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

, and

with relative volatilities

, and

. The mixture is subject to an equilibrium-limited chemical reaction

A+B⇌C+D

with reaction rate

r=k

, with equilibrium constant

. 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

and

(i.e., the feed is composed of 50 mole%

and 50 mole%

). 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

, and

(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

and

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,

, and the reflow ratio,

, 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

and

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