Page 67 - Elements of Chemical Reaction Engineering 3rd Edition

Sec. 2.2 Design Equations 39

I FAc, = C,,u, = (0.14442 mol/dm3)(6.0 dm3/s) = 0.867 mol/s

We will use this value of FAo together with either Table 2-2 or Figure 2-1 to size a
number of reactor schemes in Examples 2-2 through 2-5.

Now that we have a relationship [Equation (2-lo)] between the molar
flow rate and conversion, it is possible to express the design equations (i.e.,
mole balances) in terms of conversion for the $ow reactors examined in
Chapiter 1.

CSTR or Backmix Reactor. The equation resulting from a mole balance on
species A for the reaction

b c d
A+ - B __I$ -C+-D
n a a
occuring in a CSTR was given by Equation (1-6), which can be arranged to
FAo- FA = -rAV (2-11)

We now substitute for the exiting molar flow rate of A, FA, in tenns of
the conversion X and the entering molar flow rate, FAo, by using Equation
(2-10) in the form
Design
FA,
f3r and combining it with Equation (2-1 1) to give

LJ-- FAOX = -rAV (2- 12)
equation F A
We can rearrange Equation (2-12) to determine the CSTR volume neces-
sary ito achieve a specified conversion X.

(2- 13)

Since the exit composition from the reactor is identical to the cornpolsition
inside the reactor, the rate of reaction is evaluated at the exit conditions.

Tubular Flow Reactor (PFR). After multiplying both sides of the tubular
reactor design equation (1-10) by - 1, we express the mole balance equation
for species A in the reaction given by Equation (2-2) as

-dFA -
-- (2- 14)
dV - rA
For a flow system, FA has previously been given in terms of the entering molar
flow rate FA0 and the conversion X: