9474

Selectivity in a Semibatch Reactor

The parallel reactions and are carried out in an isothermal semibatch reactor. Both reactions are first-order in , but the desired reaction to form the product is second-order in , whereas the unwanted side reaction is first-order in . This Demonstration compares two scenarios: ( pure is fed to a reactor that initially contains only , and (2) pure is fed to a reactor that initially contains only . The overall selectivity (the number of moles of in the reactor divided by the number of moles of in the reactor, ) is much higher when all the is initially in the reactor and is fed to the reactor over a 10-minute time period. This scenario keeps the concentration of high and a high concentration of favors the desired reaction, which is second-order in . For either scenario, the addition of the second reactant stops after 10 minutes, when the amount of second reactant added equals the initial amount of the first reactant in the reactor. This allows the two scenarios to be compared for the same amounts of each reactant available for reaction.
You can vary the activation energies of the desired and unwanted reactions and the isothermal reactor temperature to determine how selectivity and moles of products and reactants change.

SNAPSHOTS

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DETAILS

Rate laws:
= rate of desired reaction
= rate of undesired reaction
= rate constant for desired reaction
= rate constant for undesired reaction
= concentration of
= concentration of
= pre-exponential factor for desired reaction
= pre-exponential factor for undesired reaction
= activation energy for desired reaction
= activation energy for undesired reaction
= ideal gas constant
= temperature 

Concentration of reactants and products:
=
=
=
=
=
= volume, changes with time
= moles of in reactor
= moles of in reactor
= moles of desired product, , in reactor
= moles of undesired product, , in reactor
= concentration of
= concentration of
= selectivity of
Material balances for system where is fed into pure :
= inlet molar flow rate of
= inlet volumetric flow rate
= time

Mole balance for system where is fed into pure :
Only and differ from above balance,
= inlet molar flow rate of
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