Biomedical Engineering Reference
In-Depth Information
8.17. The production of L -malic acid (used in medicines and food additives) was produced
over immobilized cells of Bacillus flavum MA-3.
fumarase HOOCCH 2 CH
¼
þ
ð
Þ
HOOCCH
CHCOOH
H 2 O
!
OH
COOH
The following rate law was obtained for the rate of formation of product:
S
K m þ
r max
P
P
r P ¼
1
S
N
where r max ¼
76 Mol/(L $ day), K m ¼
0.048 mol/L, and P
N ¼
1.69 mol/L. Design
a reactor to process 10 m 3 /day of 1.2 mol/L of fumaric acid (S).
(a) A batch reactor is chosen. The required conversion of fumaric acid is 99%. The total
preparation time (loading, unloading and cleaning) is 3 h for each batch.
(b) A CSTR is chosen. The required fumaric acid conversion is 99%.
8.18. One-hundred fifty moles of S per hour are available in concentration of 0.5 mol/L by
a previous process. This stream is to be reacted with B to produce P and D. The reaction
proceeds by the aqueous-phase reaction and catalyzed by an enzyme E,
þ
þD
S
B
%
P
S is the limiting substrate, and B is in excess. Michaelis e Menten rate parameters are
r max ¼
2.0 mol $ L 1
$ min 1 and K m ¼
0.02 mol/L when the enzyme loading 0.001 g/L.
CSTR has been selected to carry out the process. S costs $0.1/mol, P sells for $0.8/mol,
and the enzyme E costs $50/g. The cost of operating the reactor is $0.1 L 1
$ h 1 .
Assume no value or cost of disposal of unreacted S and entrained enzyme E (i.e.
separation or recovery cost to S is identical to the fresh S cost).
(a) What is the relationship between rate of formation of P and enzyme loading?
(b) Perform a mole balance on the reactor to relate the concentration of exiting S with
reactor size.
(c) What is the optimum concentration of S at the outlet of the reactor? What is the
optimum enzyme loading? What is the optimum reactor size?
(d) What is the cash flow per mole of product from the process?
(e) What is the cost of enzyme per unit cost of substrate?
8.19. We have an opportunity to supply 500 mol of P per hour to enter the market. P is to be
produced by
S
P
/
0.1 mol $ L 1
Catalyzed by an enzyme E. Michaelis e Menten rate parameters are r max ¼
$
min 1
0.01 mol/L when the enzyme loading 0.001 g/L. CSTR has been
selected to carry out the process. There is a stream containing S at 2 mol/L is available
for use. S costs $0.2/mol, P sells for $1.5/mol, and the enzyme E costs $80/g. The cost of
operating the reactor is $0.1 L 1
and K m ¼
$ h 1 . Assume no value or cost of disposal of unreacted S
and entrained enzyme E (i.e. separation or recovery cost to S is identical to the fresh
S cost).
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