Page 132 - Introduction to chemical reaction engineering and kinetics

114 Chapter 5: Complex Systems

a catalyst of VzOs - Moos on silica gel. In a series of experiments, they varied the space time
r = W/F, where W is the weight of catalyst and F is the total molar flow rate of gas (T in (g
cat) h mol-‘), and analyzed for M and CO2 (C) in the outlet stream. (W/F is analogous to the
space time V/q, in equation 2.3-2.) For one series at 350°C and an inlet ratio (FJFB), = 140,
they reported the following results, with partial pressure p in atm:

r = WIF l@PB 103PM 102Pc 102PH,0
0 1.83 0 0 0
61 1.60 1.36 0.87 0.57
99 1.49 1.87 1.30 0.84
131 1.42 2.20 1.58 1.01
173 1.34 2.71 1.82 1.18
199 1.32 2.86 1.93 1.25
230 1.30 3.10 1.97 1.30
313 1.23 3.48 2.24 1.47

In the following, state any assumptions made and comment on their validity.
(a) Since there are six species involved, determine, from a stoichiometric analysis, how many
of the partial pressures (pi) are independent for given (T, P), that is, the smallest number
from which all the others may be calculated. Confirm by:alculation for W/F = 313.
(b) For W/F = 313, calculate (i) fa; (ii) Ym and Ycm; (iii) Sm and Sc,n.
(c) From the data in the table, determine whether CdHz03(M) and CO2 are primary or sec-
ondary products.
(d) From the data given and results above, construct a reaction network, together with corre-
sponding rate laws, and determine values of the rate constants.
(e) The authors used a three-step reaction network to represent all their experimental data
(only partial results are given above):

c&j(B) + 402 -+ QH20s(M) + 2Coz + 2H20; rl = klpB

CJH203 + 302 + 4CO2 + H20; I.2 = k2p~

C.5H6 + go2 + 6CO2 + 3H@;rs = k3pB

Values of the rate constants at 350°C reported are: ki = 1.141 X 10m3; k2 = 2.468 X 10m3;
ks = 0.396 X 10m3 mol h-’ (g cat)-‘.
(i) Obtain expressions for pa and PM as functions of T.
(ii) Calculate the five quantities in (b) and compare the two sets of results.
(iii) Does this kinetics model predict a maximum in M? If so, calculate values of T,,,~~
and pM,max .
(iv) Are there features of this kinetics model that are not reflected in the (partial) data
given in the table above? (Compare with results from (c) and (d).)