Page 245 - Elements of Chemical Reaction Engineering 3rd Edition

Chap. 4 Questions and Problems 21 7

(a) Plot the equilibrium conversion of ethyl acetate as a function of time.
(b) Plot the conversion of ethyl acetate, the rate of reaction, and the concen-
tration of butanol as a function of time.
(c) Repeat parts (a) and (b) for different values of the butanol feed rate and
of the amount of ethyl acetate in the vat.
(d) Rework part (b) assuming that ethanol evaporates (reactive distillation) as
soon as it forms.
(e) Use POLYMATH or some other ODE solver to learn the sensitivity of
conversion to various combinations of parameters.
(f) Discuss what you learned from this problem and what you believe to be
the point of this problem.
(g) Write a question that requires critical thinking and then explain why :your
question requires critical thinking. [Hint: See Preface p.xx]
P4-27, A catalyst is a material that affects the rate of a chemical reaction, yet
emerges unchanged from the reaction. For example, consider the elemenmy
reaction
A+B + C'rR
where B is a catalyst. The reaction is taking place in a semibatch reactor, in
which 100 ft3 of a solution containing 2 Ib mol/ft3 of A is initially present. No
B is present initially. Starting at time t = 0, 5 ft3/min of a solution containing
0.5 Ib mol/ft3 of B is fed into the reactor. The reactor is isothermal, and
k = 0.2 ft3/lb mol - min .
(a) How many moles of C are present in the reactor after half an hour?
(b) Plot the conversion as a function of time.
(c) Repeat parts (a) and (b) for the case when the reactor initially contiins
100 ft3 of B and A is fed to the reactor at a concentration of 0.02 Ib
m0Vft3 and at a rate of 5 ft3/rnin. The feed concentration of B is 0.5 Ib
moVft3.
(d) Discuss what you Yearned from this problem and what you believe to be
the point of this problem.
P4-28c An isothermal reversible reaction A B is carried out in an aqueous
solution. The reaction is first-order in both directions. The forward rate con-
stant is 0.4 h-' and the equilibrium constant is 4.0. The feed to the plant con-
tains 100 !kg/m3 of A and enters at the rate of 12 m3/h. Reactor effluents pass
to a separator, where B is completely recovered. The reactor is a stirred tank
of volume 60 m3. A fraction of the unreacted effluent is recycled as a solution
containing 100 kg/m3 of A and the remainder is discarded. Product B is wcrrth
$2 per kilogram and operating costs are $50 per cubic meter of solution eniter-
ing the separator. What value of j' maximizes the operational profit of the
A+B -
plant? What fraction A fed to the plant is converted at the optimum? (H. S.
Shankar; ZIT Bombay)
P4-29, (CSTR train) The elementary liquid-phase reaction

C
is to be carried out in a CSTR with three impellers (Figure P4-29). The mix-
ing patterns in the CSTR are such that it is modeled as three equal-sized
lCSTRs in series. Species A and B are fed in separate lines to the CSTR,
which is initially filled with inert material. Each CSTR is 200 dm3 and the
3volumetric flow to the first reactor is 10 dm3/min of A and 10 dm3/min of B.