Page 234 - Elements of Chemical Reaction Engineering 3rd Edition

206 Isothermal Reactor Design Chap. 4

(b) After Ptting the exit conversion as a function of the pressure drop
parameter a in Example 4-7, what generalization can you make? How
would your answers change for an $qual molar feed? What if the catalyst
particles in Example 4-7 were p:acqd in 100 tubes placed in series rather
than in 100 tubes placed in parallel?
(c) Reconsider Example 4-8. Plot the conversion profile for the case when the
entering pressure is increased by a factor of 5 and the particle diameter is
decreased by a factor of 5. (Recall that alpha is a function of the particle
diameter and Po.) What did you learn from your plot? What should be
your next settings of a and Po to learn more? Assume turbulent flow.
(a) Consider adding an inert to the reaction in Example 4-9, keeping the total
molar flow rate at a constant. Plot the exit conversion and the equilibrium
conversion as a function of the mole fraction of an inert. What are the
advantages and disadvantages of adding an inert?
(e) Rework Example 4-10. Plot the molar flow rates of A, B, and C as a
function of reactor length (i.e., volume) for different values of k, between
k, = 0.0 (a conventional PFR) and k, = 7.0 min-’. What parameters
would you expect to affect your results the most? Vary the parameters
k, k,, K,, F,, to study how the reaction might be optimized. Ask such
questions as: What is the effect of the ratio of k to k,, or of k, z C,, to
K,, or ... to ... ? What generalizations can you make? How would your
answer change if the reactor temperature were raised significantly?
(f) In Example 4- 1 1, plot the time at which maximum rate of reaction occurs
(e.g., in the example the maximum rate is 0.00017 molSrdm3.s at
t = 25 s) as a function of the entering molar feed rate of B. What if you
were asked to obtain the maximum concentration of C and D in Example
4-1 l? What would you do?
(9) Vary some of the operating costs, conversions, and separations in Figure
4-1 1 to learn how the profit changes. Ethylene oxide, used to make eth-
ylene glycol, sells for $0.56/lb. while ethylene glycol sells for $0.38/lb.
Is this a money-losing proposition? Explain.
(h) What if you assumed that the reaction in Example 4-1 1 was first-order in
methyl amine (B) and zero-order in bromine cyanide. Since it is in
excess at the start of the reaction, show that the concentration of methyl
amine at any time t is

Up to what time and under what conditions is the assumption valid? [See
W. Emst, AZChE J., 43, p. 1114 (1997).1
(i) What should you do if some of the ethylene glycol splashed out of the
reactor onto your face and clothing? (Hint: Recall http://www.siri.org/.)
G) What safety precautions should you take with the ethylene oxide forma-
tion discussed in Example 4-6? With the bromine cyanide discussed in
Example 4-1 l?
(k) write a polymath program to replace the analytical solution given in Example
4-4. Vary a numb of par;lmeters (eg., k, y,q), CACJ and describe what YOU find.
P4-3~ If it takes 11 minutes to cook spaghetti in Ann Arbor, Michigan, and 14 min-
utes in Boulder, Colorado, how long would it take in Cuzco, Peru? Discuss
ways to make the spaghetti more tasty. If you prefer to make a creative spa-
ghetti dinner for family or friends rather than answering this question, that’s
OK, too; you’ll get full credit. (Ans. t = 21 min)