Page 317 - Elements of Chemical Reaction Engineering 3rd Edition

Desired
the
Sec. €1.1 ~ ~ ~ ~ i ~ i n gProduct in Parallel Reactions 289
E~~~~~~ 6-2! ~ ~ n i ~ i ~ n ~Products for TWO Reactants
Unwanted
A+B -
A+B -
For the parallel reactions
D
U

consider all possible combinations of reaction orders and select the reaction scheme
that will maximize S,, .

Cave 6: a,>a2, Let a =ai-a2 and b = where a and b are
positive constants. Using these definitions we can write Equation (6-1 1) in the form

(E6-2.1)

To maximize the ratio rD/ru, maintain the concentrations of both A and E as high
as possible. To do this, use:

* A tubular reactor.
* A batch reactor.
e High pressures (if gas phase).

Casen: a,>ac2, $l<P2.Leta=a,-a2andb=~,-P1,whereaandbarepos-
itive constants. Using these definitions we can write Equation (E6-2.1) in the f;orm

(E6-2.2)

To make S,, as large as possible we want to make the concentration of A high and
the concentration of B low. To achieve this result, use:

A semibatch reactor in which B is fed slowly into a large amount of A (Figure
6-3d).
0 A tubular reactor with side streams of E continually fed to the reactor (Figure
6-30.
8 A series of small CSTRs with A fed only to the first reactor and small
amounts of B fed to each reactor. In this way I3 is mostly consumed beFore
the CSTR exit stream flows into the next reactor (Reverse of Figure 6-3i).

CasIIk 0iI6a2, B1<Pz.;Let a=or,-al and b=p2-P1, whereaandbare
positive constants. Using these definitions we can write Equation (E-2.1) in the form