Page 238 - Elements of Chemical Reaction Engineering 3rd Edition

210 Isothermal Reactor Design Chap. 4

corresponding 2160 mol/day of lost product made the process uneconomical.
Scoundiels, Inc. say that they can guarantee 66% conversion if Clueless will
purchase 500 more kg of catalyst at one and a half times the original cost. As
a result, Clueless contacted Sgt. Ambercromby from Scotland Yard (on loan to
the L.A.P.D.) about possible industrial fraud. What are the first three questions
Sargent Ambercromby asks? What are potential causes for this lost conversion
(support with calculations)? What do you think Sgt. Ambercromby suggests to
rectify the situation (with Dan Dixon, Reaction Engineering Alumni W'97).
P4-10, The formation of diphenyl discussed in Section 3.1.4 is to be carried out at
760°C. The feed is to be pure benzene in the gas phase at a total pressure of
5 atm and 760°C. The specific reaction rate is 1800 ft3/lb mol. s and the con-
centration equilibrium constant is 0.3 as estimated by the Davenport trispeed
oximeter. The batch reactor volume [part (d)] is 1500 dm3. Also, the inside
of the batch reactor is corroding badly, as evidenced by the particulate mate-
rial that is falling off the sides onto the bottom of the reactor, and you may
not need to address this effect.
(a) What is the equiiibrium conversion? (X, = 0.52)
Calculate the reactor volume necessary to achieve 98% of the equilibrium
conversion of benzene in a
(b) PFR (with a benzene feed of 10 lb mohin)
(c) CSTR (with a benzene feed of 10 lb mol/min)
(d) Calculate the volume of a constant-volume batch reactor that processes
the same amount of benzene each, day as the CSTR. What is the corre-
sponding reactor cost? (Hint: Recall Table 4-1.)
(e) If the activation energy is 30,202 Btu/lb mol, what is the ratio of the ini-
tial rate of reaction (Le., X = 0) at 1400°F to that at 800"F?
P4-11B The gaseous reaction A --+ B has a unimoiecular reaction rate constant
of 0.0015 min-l at 80°F. This reaction is to be carried out in parallel tubes
10 ft long and 1 in. inside diameter under a pressure of 132 psig at 260°F. A
production rate of 1000 Ib/h of B is required. Assuming an activation energy
of 25,000 caVg mol, how many tubes are needed if the conversion of A is to
be 90%? Assume perfect gas laws. A and B ekh have molecular weights of
6
58. (From California Professional Engineers Exam.)
P4-12, The irreversible elementary reaction 2A ---+ B takes place in the gas
phase in an isothermal tubular (plug-Jlow) reactor. Reactant A and a diluent
C are fed in equimolar ratio, and conversion of A is 80%. If the molar feed
rate of A is cut in half, what is the conversion of A assuming that the feed rate
of C is left unchanged? Assume ideal behavior and that the reactor tempera-
ture remains unchanged. What was the point of this problem? (From Califor-
nia Professional Engineers Exam.)
P4-13B Compound A undergoes a reversible isomeiization reaction, A e
,
B
over a supported metal catalyst. Under pertinent conditions, A and B are liq-
uid, miscible, and of nearly identical density; the equilibrium constant for the
reaction (in concentration units) is 5.8. In afied-bed isotheml flow reactor
in which backmixing is negligible (i.e., plug flow), a feed of pure A under-
goes a net conversion to B of 55%. The reaction is elementary. If a second,
identical flow reactor at the same temperature is placed downstream from the
first, what overall conversion of A would you expect if:
(a) The reactors are directly connected in series? (Am: X = 0.74.)
(b) The products from the first reactor are separated by appropriate process-
ing and only the unconverted A is fed to the second reactor?
(From California Professional Engineers Exam.)