Page 331 - Elements of Chemical Reaction Engineering Ebook

302 Multiple Reactions Chap. 6

For constant-pressure batch systems we would simply substitute N, for 4 in the
equations above. For constant-volume batch systems we woulduse concentrations:
Cj = Nj/V, (6-27)

We see that we have j coupled ordinary differential equations that must
be solved simultaneously with either a numerical package or by writing an
ODE solver. In fact, this procedure has been developed to take advantage of
the vast number of computation techniques now available on mainframe (e.g.,
Simusolv) and personal computers (POLYMATH, Mathematica, MATLAB).

Example 6-5 Combining Mole Balances, Rate Laws, and Stoichiometry
for Multiple Reachns

Consider again the reaction in Example 6-4. Write the mole balances on a PFR in
terms Qf molar flow rates for each species.
NO+~NH, + ~N,+H,o
2
Reaction 1:
6
Reaction 2: 2N0 N,+O2

1
Reaction 3: O2+-N2 NO2
2
Solution
For gas-phase reactions, the concentration of species j is

For no pressure drop and isothermal operation,

F.
cj=c,2 036-5.1)
FT
In combining the mole balance, rate laws, and stoichiometry, we will use our results
from Example 6-4, The total molar flow rate of all the gases is

(E6-5.2)

We now rewrite mole balances on each species in the total molar flow rate.
Using the results of (1) Mole balance on NO:
Example 64

(E6-5.3)