Page 356 - Elements of Chemical Reaction Engineering Ebook

Chap. 6 Questions and Problems 327
Addirinnul information:
k,, = 0.25 dm6/mo12. min uo = 10dm3/min

k,, = 0.1 dm3/mol. min C,, = 1.5 mol/dm3

k,, = 5.0 dm6/mo12.min C,, = 2.0 mol/dm3
Plot the species concentrations and the conversion of A as a function of
the distance (i.e., volume) down a 50-dm3 PFR. Note any maxima.
Determine the effluent concentrations and conversion from a 50-dm3
CSTR. (Ans.: C, = 0.61, C, = 0.79, C, = 0.25, and C, = 0.45 motldm3)
Plot the species concentrations and the conversion of A as a function of
time when the reaction is carried out in a semibatch reactor initially con-
taining 40 dm' of liquid. Consider two cases: (1) A is fed to B, and (2) B
is fed to A. What differences do you observe for these two cases?
Va~y the ratio of B to A (1 < OB < 10) in the feed to the PFR and describe
what you find. What generalizations can you make from this problem?
P6-1481 The production of maleic anhydride by the air oxidation of benzene was
recently studied using a vanadium pentoxide catalyst [Chem. Eng. Sci , 43,
1051 (1988)J. The reactions that occur are:

9
Reaction 1: C,j H, + - 02 4 C, H,O, + 2C02 f 2H2O
2
Reaction 2: C,H,O, + 30, ---+ 4C0, + H,O

15
Reaction 3: C,H, + -02 ---+ 6C02 + 3H,O
2
Because these reactions were carried out in excess air, volume change with
reaction can be neglected, and the reactions can be written symbolically as a
pseudo-first-order reaction sequence

L k,
A--J-+.B~~C

where A = benzene, B = maleic anhydride, C = products (H20, CO?), D =
products (COz, H,O). The corresponding pseudo specific reaction rates, ki,
are (in all m3/kg cat.. s ):

k, = 4280 exp[- 12,66O/T(Kl] k, = 70,100 exp[-15,000/T(K:i]
k, = 26 exp [ - 10,80O/T(K)]
At 848 IC, k, = 1.4 X kz = 1.46 X k, = 7.65 X loT5. These reac-
tions are carried out isothermally in both a CSTR and a PBR. Benzene enters
the reactor at a concentration of 6.01 rnol/dm3. The total volumetric flow rate
is 0.0025 m3/s.
(a) Which reactions will dominate at low temperatures and which will dom-
inate at high temperatures? For the sake of comparison, assume that
848 K is a moderate temperature,