Biomedical Engineering Reference
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(a) What fraction of the by-product from the process enters the river?
(b) At this flow rate what size tank would be required to react 99% of the by-product
before entering the river?
5.28. A 10,000-gal-holding tank receives an aqueous by-product effluent stream from a batch
chemical process. The constant-volume tank is well mixed and drains into a river. A
batch process is recycled every 8 h, and in the cleanup of the reactor 1000 gal are rapidly
drained into the tank at the end of each batch run. The by-product decomposes in the
tank with a rate coefficient of 0.2 h 1 .
(a) What fraction of the by-product from the process enters the river?
(b) At this discharge rate what size tank would be required to react 99% of the by-
product before entering the river?
5.29. We wish to treat a stream 1 m 3 /h containing 2 mol/L A to produce 90% conversion in
the reaction
A
/
B
;
r ¼ kC A C B
with k
¼
1/4 (units of minutes, moles, and liters).
(a) Find
s
in the best single reactor.
(b) Find
in two equal-volume CSTRs.
(c) Find the reactor volumes for minimum
s
in two reactors in series.
5.30. We wish to treat 10 L/min of liquid feed containing 1 mol-A/L to 99% conversion. The
reaction is given by
s
k 1 C A
1 þ k 2 C A
2 A
/
R
þ
U
;
r ¼
2.5 min 1 and k 2 ¼
5 L/mol. Suggest a good arrangement for doing this
using two CSTR's. Find the sizes of the two units needed.
5.31. We wish to explore various reactor setups for the transformation of A into R. The feed
contains 99% A, 1% R; the desired product is to consist of 10% A, 90% R. The
transformation takes place by means of the elementary reaction
where k 1 ¼
þ
/
þ
A
R
R
R
That
is,
the rate of reaction is given by r
¼
kC A C R . Here the rate constant
1L $ mol 1
$ min 1 . The concentration of active materials is
C A 0 þ C R 0 ¼ C A þ C R ¼ C 0 ¼ 1 mol
k
¼
L
throughout. What reactor holding time (i.e. mean residence time) will yield a product in
which C R ¼
=
0.9 mol/L?
(a) In a plug flow reactor without recycle?
(b) In a plug flow reactor with optimum recycle?
(c) In a CSTR?
(d) In a minimum size setup without recycle by a combination of one PFR and one
CSTR?
5.32. A three-stage CSTR is used for the reactionA
products. The reaction occurs in aqueous
solution and is secondorderwith respect toA,with k A ¼
/
$ min 1 . The inlet
concentration of A and the inlet volumetric flow rate are 1.5 mol $ L 1 and 2.5 L $ min 1 ,
0.040 L $ mol 1
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