Page 131 - Introduction to chemical reaction engineering and kinetics

5.7 Problems for Chapter 5 113

Construct a suitable reaction network for this system, and estimate the values of the rate con-
stants involved (assume a first-order rate law for each reaction).

5-17 In pulp and paper processing, anthraquinone (AQ) accelerates the delignification of wood and
improves liquor selectivity. The kinetics of the liquid-phase oxidation of anthracene (AN) to
AQ with NO2 in acetic acid as solvent has been studied by Rodriguez and Tijero (1989) in
a semibatch reactor (batch with respect to the liquid phase), under conditions such that the
kinetics of the overall gas-liquid process is controlled by the rate of the liquid-phase reaction.
This reaction proceeds through the formation of the intermediate compound anthrone (ANT):

C14H10 (AN) F C14Hg0 (ANT)TCt4Hs02 (AQ)

The following results (as read from a graph) were obtained for an experiment at 95°C in
which cAN,o = 0.0337 mol L-l.

tlmin CAN CANT CAQ
mol L-l
0 0.0337 0 0
10 0.0229 0.0104 0.0008
20 0.0144 0.0157 0.0039
30 0.0092 0.0181 0.0066
40 0.0058 0.0169 0.0114
50 0.0040 0.0155 0.0144
60 0.0030 0.0130 0.0178
70 0.0015 0.0114 0.0209
80 0.0008 0.0088 0.0240
90 0.0006 0.0060 0.0270

If each step in the series network is first-order, determine values of the rate constants ki and
kz in s-l.
5-18 Duo et al. (1992) studied the kinetics of reaction of NO, NH3 and (excess) 02 in connection
with a process to reduce NO, emissions. They used an isothermal PFR, and reported measured
ratios CNO/CNO,~ and CNH~/CNH,,~ for each of several residence times, t. For T = 1142 K, ad
inlet concentrations cN0, o = 5.15X 10m3, CNH~,~ = 8.45~ 10m3, and CO~,~ = 0.405 mol rnm3, they
obtained results as follows (as read from graphs):

tls: 0.039 0.051 0.060 0.076 0.102 0.151 0.227
cNOIcN0.o : 0.756 0.699 0.658 0.590 0.521 0.435 0.315
CNH&NH3.0: 0.710 0.721 0.679 0.607 0.579 0.476 0.381

(a) If the other species involved are N2 and H20, determine a permissible set of chemical
equations to represent the system stoichiometry.
(b) Construct a reaction network consistent with the results in (a), explaining the basis and
interpretation.
(c) Calculate the value of the rate constant for each step in (b), assuming (i) constant density;
(ii) constant co,; (iii) each step is irreversible and of order indicated by the form of the
step. Comment on the validity of assumptions (i) and (ii).

5-19 Vaidyanathan and Doraiswamy (1968) studied the kinetics of the gas-phase partial oxidation
of benzene (C6H6, B) to maleic anhydride (C4Hz.03, M) with air in an integral PFR containing