Biomedical Engineering Reference
In-Depth Information
in a CSTR with A and B ideal gases starting with A at 1 atm for
(a) no diluent in the feed,
(b) 1 atm of inert diluent,
(c) 9 atm of diluent,
(d) 99 atm of diluent.
(e) Compare the volumes required for 90% conversion in these situations with those
predicted using the constant-density approximation.
5.24. The aqueous reversible reaction
r ¼ kC A k 0 C B
A
!
B
;
is to be carried out in a series of reactors with separation of unreacted B between
stages. At each stage, the reaction goes to 50% of the equilibrium composition. How
many stages are required for 90% conversion of the initial A for k
0.2 min 1 ,
¼
1if
(a) all B is extracted between stages,
(b) 50% of B is extracted between stages.
(c) Find
K eq ¼
with complete extraction if the reactors are CSTRs.
s
if the reactors are PFRs.
5.25. A reaction A
(d) Find
s
kC n . Using two
50-L CSTRs in series, it is found that with a feed of 2.0 mol/L, after the first reactor
C A ¼
/
products is known to obey the rate expression r
¼
1.0 mol/L and after the second C A ¼
0.3 mol/L.
(a) Find n .
(b) What volume PFR will be required to obtain 90% conversion for this reaction at the
same feed rate?
5.26. A certain equipment catalog lists CSTRs as costing
¼ 1000 þ 100V 1=2
CSTR
and PFRs as
$PFR
¼ 500 þ 100V
where $ is in dollars and V is in liters.
(a) Why might the cost of a chemical reactor be roughly proportional to its surface area?
For what reactor geometries might the costs of chemical reactors have these
dependences on their volumes? How should the cost of a spherical CSTR depend on
its volume?
(b) At what volume will the costs of a CSTR and PFR be equal in this catalog?
(c) We find that a 1000-L PFR will process 500 mol/h of a reactant in a first-order
reaction to 90% conversion. How does the cost of this reactor compare with a CSTR
for the same conversion?
(d) Repeat this calculation for processing 1000 mol/h to 90% conversion.
5.27. A 10,000-galion holding tank receives an aqueous by-product effluent stream from
a continuous chemical process. The tank is well mixed and drains into a river. The tank
receives 2400 gal/day of a certain by-product that decomposes in the tank with a rate
coefficient of 0.2 h 1 .
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