Page 311 - Elements of Chemical Reaction Engineering 3rd Edition

Chap. 6 Multiple Reactions 283

Ak’B-C k2
Series reactions
An example of a series reaction involving ethylene oxide (E.O.) is its
reaction with arnmonia to form mono-, di-, and triethanolamine:

C/H,>H~+ NH3 __j HOCHzCH2NHz

EO_) (HOCH2CH2)2NH (HOCH2CH2),,N
In recent years the shift has:been toward the production of diethanolamine as
the desired product rather than triethanolamine.
Multiple reactions involve a combination of bo& series and parallel reac-
tions, such as
A+B + C+D
A+C E
An example of a combination of parallel and series reactions is the formation
of butadiene froim ethanol:
+
C2H,
H20
Simultaneous series C,H,OH j
and parallel
reactions C:,HSOH __j CH3CHO + H2
C2 H4 + CH3CHO + H, -t HZO
C4
Independent reactions are of the type
Independent A-B
reactions
C ___) D+E
and occur in feed stocks containing many reactants. The cracking of crude oil
to form gasoline is an example where independent reactions take place.
The first p;zrt of this chapter will be concerned primarily with parallel
reactions. Of particular interest are reactants that are consumed in the fonma-
tion of a desired product, D, and the formation of an undesired product, U, in
a competing or side reaction. In the reaction sequence
A-LD

A k’+U

we want to minimize the formation of U and maximize the formation of D,
because the greater the amount of undesired product formed, the greater the cost
of separating the undesired product U from the desired product D (Figure 6-1).
In a highly efficient and costly reactor scheme in which very little of
undesired product U is formed in the reactor, the cost of the separation process

The economic could be quite low. On the other hand, even if a reactor scheme is inexpensive
incentive and inefficient, resulting in the formation of substantial amounts of U, the cost