Page 38 - The engineering of chemical reactions

22 Reaction Rates, the Batch Reactor, and the Real World

cycle-C3Hs + C3H6
or in symbols
A -+ =\

Propylene will not significantly transform back to cyclopropane, and we call this reaction
irreversible. The irreversible first-order reaction
A+B

is the most used example in chemical kinetics, and we will use it throughout this book as
the prototype of a “simple” reaction. However, the ring opening of cyclopropane to form
propylene (which has absolutely no industrial significance) is one of only a handful of
irreversible isomerization reactions of the type A -+ B.
Next consider the motion of the double bond in butylenes
tram-2-C:= + cis-2-C:=
cis-2-C2= + tram-2-C2’
4
4
l-C:= + tram-2-C:=
iso-Ci= * tram-2-C:=
[Throughout this book we will refer to chemicals and processes by their common
names and by chemical symbols. We believe that it is essential for chemical engineers to
be literate in all the designations used by organic chemists and by customers. One of the
important skills of a successful engineer is the ability to deal with colleagues in their own
language, rather than being confined to one set of units and notation. Examples of names
and symbols are butylenes versus butenes, and styrene versus phenylethene. (What is the
common name of polymerized chloroethene? Answer: PVC.) Students unfamiliar with
particular notations may want to review them from organic chemistry texts. The material
in those courses really is important, in spite of what you probably thought when you were
taking them.]
The above reactions all have one reactant and one product, and we write them as

A-+B
However, the reactions of butylenes will all proceed among each other and are described
as reversible; so there are 12 reactions among the four butylenes.
We write each of these as
AfB
signifying that the process involves both A -+ B and B -+ A. We can write the complete set
of butylene isomerization reactions as shown in Figure 2-1. Since each of these molecules
can isomerize to all the others, this is a set of 12 chemical reactions.
Next consider the formation of nitric oxide from air

;N2 + ;02 + NO