Biomedical Engineering Reference
In-Depth Information
(a) Which type of ideal isothermal flow reactors (CSTR or PFR) is preferred? Briefly
state why?
(b) What is the yield of R and reactor holding time if the fractional conversion of A is
90% for the reactor chosen in part a.?
5.48. Propylene (P) and chlorine (C) react in gas phase to produce allyl chloride (A)
C 3 H 6 þ
Cl 2 /
H 2 C
¼
CHCH 2 Cl
þ
HCl
r 1 ¼ k 1 p P p C
and 1,2-dichloropropane (D),
H 2 CClCHClCH 3 r 2 ¼ k 2 p P p C
The kinetic experiments show that k 1 ¼ 206000 exp
C 3 H 6 þ
Cl 2 /
mol/(m 3
7610 K
T
$ s $ bar 2 ) and
k 2 ¼ 11:7 exp
mol/(m 3
1920 K
T
$ s $ bar 2 ). Allyl chloride is the desired product.
Either CSTR or PFR can be used to carry out the reaction. Neglect the pressure drop
in the reactor and the reactors can be operated at isothermal conditions between 25
and 450 C. The feed to the reactor will be 1 bar propylene and 1 bar chlorine.
(a) What is the optimum operating temperature in a CSTR? In a PFR?
(b) Find the local selectivity s A/P .
(c) What is the overall selectivity to allyl chloride in a CSTR for a 90% conversion?
(d) What is the overall selectivity to allyl chloride in a PFR for a 90% conversion?
5.49. The liquid phase reaction
A
%
B
r ¼ k 1 C A k b C B
is
to
be
carried
out
in
a
flow reactor.
The
rate
constants
are:
k f ¼ exp 13:18
min 1 and k b ¼ exp 24:78
min 1 . The heat capac-
39800
RT
82600
RT
124 J/(mol K). The reactor can be operated between 290 and
500 K. The feed will be pure A.
(a) What is the optimum operating temperature or temperature progression if a PFR is
used?
(b) What is the maximum possible fractional conversion?
(c) For a CSTR capable of delivering a holding time of 1 min, what is the heat exchanger
capability ( UA H ) required for a conversion of 0.62 if the feed and heat exchanging
fluid are both at 290 K?
5.50. Enzyme E catalyzes the aqueous decomposition of reactant A to products R and B as
follows:
ities are: C PA ¼ C PB ¼
200C A C E 0
2 þ C A
where r is in mol/L/min, C A and C E0 are in mol/L. The reaction is to carry out in a plug
flow reactor. In the feed stream, the concentrations of the enzyme and reactant A are
0.001 mol/L and 10 mol/L, respectively. How does density change in the reactor? Find
the space time and mean residence time required to drop the reactant concentration to
0.025 mol/L.
enzyme
A
!
R
þ
B
;
r ¼
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