Biomedical Engineering Reference
In-Depth Information
-
r
A
=
kC
A
(
C
A0
-
C
A
)
1
-
r
A
PFR
0
C
Ae
C
Ai
C
A0
0
C
A
FIGURE E5-6.2
A sketch of one single recycle plug flow reactor on the reciprocal of reaction rate vs concen-
tration plane.
r
A
)
1
vs
C
A
plot. The recycle
of the effluent stream into the reactor caused the concentration of A entering the reactor to be
lower than
C
A0
and thus ensures a finite value of (
Figure E5-6.2
illustrate the recycle plug flow reactor on the (
r
A
)
1
. Since the volume of the PFR is
proportional to the area under the rate curve, the finite value of (
r
A
)
1
ensures a finite
reactor volume requirement. For the fixed volume reactor, this ensures the concentration
of the effluent to be lower than the feed concentration.
5.7. DISTRIBUTED FEED AND WITHDRAW
Chemical and biological reactions normally involve multiple components and multiple
reactions occurring simultaneously. In some cases, the desired products are formed from
an equilibrium limiting step whereby the efficiency is restricted due to the maximum amount
of desired products can be formed at a given feed composition. In some cases, the desired
product is an intermediate product along the overall reaction pathway. Still, in other cases,
the reaction that forms the desired product has a different concentration dependence on
rate. All these cases would benefit if one could either feed some of the reactants gradually
or remove the some of products from reaction mixture.
5.7.1. Distributed Feed
For parallel reactions, multiple products form the same set of reactants at the same reaction
conditions. There are several ways to optimize the bioprocess system for desired product
production (and thus efficiency) or selectivity
s
P/A
or
S
P/A
: 1) selection of pressure (if gas
phase reaction), temperature, and different solvents; 2) catalyst selection or development; 3)
changing type of reactor; and 3) changing the way the reactants are being added to the reactor.
In this section, we are interested in how the selectivity can be altered by changing the way the
reactants are fed to the reactor.
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