Maximizing Selectivity in the Trambouze Reactions

time

5800

k

1

0.0005

k

3

0.01

This Demonstration shows the start-up of a CSTR (continuous stirred-tank reactor) under conditions that maximize the selectivity of a desired product in a parallel reactions scheme.

Consider the following reactions taking place in a CSTR: species

A

decomposes by three simultaneous reactions to form three products—one desired,

B

, and two undesired,

X

, and

Y

,

A

r

X

=

k

1

→

X

,

A

r

B

=

k

2

c

A

→

B

,

A

r

Y

=

k

3

2

c

A

→

Y

.

These are called the Trambouze reactions [1]. Here

r

i

and

k

j

with

i=X,B,Y

and

j=1,2,3

are the reaction rates and rate constants, respectively, and

c

A

is the concentration of species

A

.

The selectivity of species

B

is given by the ratio

effluentflowrateofB

flowrateofundesieredproducts

=

s

B

=

k

2

c

A

k

1

+

k

3

2

c

A

,

the reactor residence time is

τ=

c

A

in

-

c

A

k

1

+

k

2

c

A

+

k

3

2

c

A

, the CSTR is operated at an effluent concentration of species

A

,

c

A

, that maximizes the selectivity

s

B

of the desired product

B

, the feed stream contains only species

A

at a concentration equal to 1, and the initial concentrations of species

A,

X

,

B

, and

Y

are taken equal to zero, with

k

2

=0.0015

. The optimum effluent concentration of reactant

A

,

c

A

, and the time plot of the reactor start-up are shown for values of time

k

1

and

k

3

that are set by the user.