Chemical and Biochemical Processes
Reaction Engineering Tutorial 4
Reactors in Series
1.
First draw a diagram:
First we calculate concentration and molar flowrate after the PFR
C
A1
= C
A0
(1X
A1
) = 5(10.55) = 2.25 mol m
3
F
A1
= F
A0
(1X
A1
) = 2(10.55) = 0.9 mol s
1
Next we must apply the CSTR design equation to the stirred tank.
But we must note
that the feed to the stirred tank is the outlet stream from the plug flow reactor, and
therefore the design equation is:
)
(
2
1
2
A
A
A
R
r
X
F
V

′
=
Where in these notes,
2
A
X
′
denotes local conversion change across the CSTR.
X
A2
is
reserved to represent overall conversion in the PFRCSTR combination.
As with all applications of the design equation, we have to substitute in a rate
equation, in this case first order, giving:
(
29
2
1
2
2
2
2
1
2
1
)
(
A
A
A
A
A
A
A
A
R
X
kC
X
kC
X
r
X
F
V
′

′
=
′
=

′
=
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Then we rearrange algebraically to get
2
A
X
′
:
111
.
0
9
.
0
)
25
.
2
)(
05
.
0
)(
1
(
1
9
.
0
)
25
.
2
)(
05
.
0
)(
1
(
1
0
0
0
0
2
=
+
=
+
=
′
A
A
r
A
A
r
A
F
kC
V
F
kC
V
X
And hence C
A2
= C
A1
(1
2
A
X
′
) = 2.25(10.111) = 2 mol m
3
Overall conversion X
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 Spring '10
 reddy
 Equations, Reaction, Quadratic equation, Elementary algebra, CSTR

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