Page 127 - Introduction to chemical reaction engineering and kinetics

5.7 Problems for Chapter 5 109

(i) A + B + C
or (ii) A -+ B,
v
A-+C
“OF
B + C
or (iii) A +
0 5-2 Suppose the reaction in Example 5-4 was studied in a CSTR operated at steady-state, and the

results given below were obtained. Calculate the values of kf and k,, and hence write the rate
law. Assume T to be the same, constant density, and no D in the feed.

flh 1 2 3 4
100 CAIC~~ 76.5 65.9 57.9 53.3
0 5-3 The liquid-phase hydrolysis of methyl acetate (A) to acetic acid and methyl alcohol is a re-
V
“O-T
versible reaction (with rate constants kf and k,, as in equation 5.3-3). Results of an experiment
carried out at a particular (constant) temperature in a BR in terms of the fraction hydrolyzed
(f~) measured at various times (t), with CA0 = 0.05 mol L-t (no products present initially),
are as follows (Coulson et al., 1982, p. 616):

tls 0 1350 3060 5340 7740 00
f* 0 0.21 0.43 0.60 0.73 0.90

(a) Write the chemical equation representing the reaction.
(b) Obtain a rate law for this reaction, including values of the rate constants. State any as-
sumption(s) made.
5-4 In an experiment (Williams, 1996) to evaluate a catalyst for the selective oxidation of propene
(CsH6) to various products, 1 g of catalyst was placed in a plug-flow reactor operated at 450°C
and 1 bar. The feed consisted of propene and air (21 mole % 02,79% NZ (inert)). GC analysis
of the inlet and outlet gas gave the following results, the outlet being on a water-free basis
(Hz0 is formed in the oxidation):

Substance Inlet mole % Outlet mole %
10.0 ?
propene (C3H6)
18.9 ?
oxygen (02)
nitrogen (N2, inert) 71.1 78.3
acrolein (C3H40) 0 3.17
propene oxide (CsHsO) 0 0.40
acetaldehyde (CzH40) 0 0.59
carbon dioxide 0 7.91

(a) If the feed rate of C3H6 is FQQ~ = 1 mm01 min-‘, at what rate do (i) CsH6. (ii) 02, and
(iii) Hz0 leave the reactor?
(b) What is j&, the fractional conversion of CsHh?
(c) What is the selectivity or fractional yield of each of acrolein, propene oxide, and acetalde-
hyde with respect to propene?
(d) What is the rate of reaction expressed as (i) (-TQQ); (ii) rc,n,o (in mm01 min-’ (g
cat)-‘)? Assume that the reactor acts as a differential reactor (Section 3.4.1.3.1).
5-5 Repeat Example 5-6 for a CSTR with V = 15 L and 4 = 1.5 L min-‘.