Page 240 - Elements of Chemical Reaction Engineering 3rd Edition

212 Isothermal Reactor Design Chap. 4

waste
water

0 -2
Figure P4-17 [See R. H. Kadlec and R. L. Knight, Treatment of Wetlands, CRC
Press, Lewis Publishers, Boca Raton, Fla., 1996.1

(3) condensation at a rate of 0.5 kmol/m2. h
Compare your results for each of the three cases.
(d) Use POLYMATH to carry out a sensitivity analysis of the various param-
eter values and their ratios (e.g., what is the effect of this ratio QlkCAo
on the conversion)?
(e) A heated political battle is currently raging between those who want to
preserve wetlands (which are currently protected by law) in their natural
state and those who want to make them available for commercial devel-
opment. List arguments on both sides of this issue, including one or more
arising from a consideration of this problem. Then take a position one
way or the other and justify it briefly. (Your grade doesn't depend on
what position you take, only on how well you defend it.) [Part (e) sug-
gested by Prof. Richard Felder, North Carolina State University.]
(f) Without solving any equations, suggest a better model for describing the
wetlands. (Hint: An extended version of this problem can be found on
the CD-ROM.)
Additional information:
W = width = 100 m, u, = entering volumetric flow rate = 2 m3/h
L = length = 1000 m, C,, = entering concentration of toxic = mol/dm3
D = average depth = 0.25 m, pm = molar density of water = 55.5 kmol
~,0/m3
Q = evaporation rate = 1.1 1 X kmolh. m2,
k, = specific reaction rate = 16 X h-I
P4-18,, Ethyl acetate is an extensively used solvent and can be formed by the vapor-phase
esterification of acetic acid and ethanol. The reaction was studied using a
microporous resin as a catalyst in a packed-bed reactor [Id. Eng. Chem. Res.,
26(2), 198( 1987)]. The reaction is first-order in ethanol and pseudo-zero-order
in acetic acid. For an equal molar feed rate of acetic acid and ethanol the specific
reaction rate is 1.2 dm3*/g cat min. The total molar feed rate is 10 mol/min,
the initial pressure is 10 atm, the temperature is 118°C and the pressure drop
parameter, a, equals 0.01 g-'.
(a) Calculate the maximum weight of catalyst that one could use and main-
tain an exit pressure above 1 atm. (Ans.: W = 99g)
(Is) Determine the catalyst weight necessary to achieve 90% conversion.
What is the ratio of catalyst needed to achieve the last 5% (85 to 90%)