Page 12 - The engineering of chemical reactions

xii Preface

We next used the texts of Hill and then Fogler in our chemical reactors course.
These books are adapted from Levenspiel, as they used the same notation and organization,
although they reduced or omitted reactions of solids and complex reactors, and their notation
required fairly qualitative consideration of nonisothermal reactors. It was our opinion that
these texts actually made diffusion in porous pellets and heat effects seem more complicated
than they need be because they were not sufficiently logically or mathematically based.
These texts also had an unnecessary affinity for the variable density reactor such as A + 3 B
with ideal gases where the solutions require dealing with high-order polynomials and partial
fractions. In contrast, the assumption-of constant density (any liquid-phase reactor or gases
with diluent) generates easily solved problems.
At the same time, as a chemist I was disappointed at the lack of serious chemistry
and kinetics in reaction engineering texts. All beat A + B to death without much mention
that irreversible isomerization reactions are very uncommon and never very interesting.
Levenspiel and its progeny do not handle the series reactions A + B + C or parallel
reactions A --f B, A + C sufficiently to show students that these are really the prototypes
of all multiple reaction systems. It is typical to introduce rates and kinetics in a reaction
engineering course with a section on analysis of data in which log-log and Arrhenius plots
are emphasized with the only purpose being the determination of rate expressions for single
reactions from batch reactor data. It is typically assumed that any chemistry and most
kinetics come from previous physical chemistry courses.
Up until the 1950s there were many courses and texts in chemical engineering on
“Industrial Chemistry” that were basically descriptions of the industrial processes of those
times. These texts were nearly devoid of mathematics, but they summarized the reactions,
process conditions, separation methods, and operating characteristics of chemical synthesis
processes. These courses in the chemical engineering curriculum were all replaced in the
1950s by more analytical courses that organized chemical engineering through “principles”
rather than descriptions because it was felt that students needed to be able to understand the
principles of operation of chemical equipment rather than just memorize pictures of them.
Only in the Process Design course does there remain much discussion of the processes by
which chemicals are made.
While the introduction of principles of chemical engineering into the curriculum
undoubtedly prepared students to understand the underlying equations behind processes,
succeeding generations of students rapidly became illiterate regarding these processes and
even the names and uses of the chemicals that were being produced. We became so involved
in understanding the principles of chemical engineering that we lost interest in and the
capability of dealing with processes.
In order to develop the processes of tomorrow, there seems to be a need to combine
principles and mathematical analysis along with applications and synthesis of these princi-
ples to describe processes. This is especially true in today’s changing market for chemical
engineers, where employers no longer are searching for specialists to analyze larger and
larger equipment but rather are searching for engineers to devise new processes to refurbish
and replace or retrofit old, dirty, and unsafe ones. We suggest that an understanding of how
and why things were done in the past present is essential in devising new processes.
Students need to be aware of the following facts about chemical reactors.

1. The definition of a chemical engineer is one who handles the engineering of chemical
reactions. Separations, fluid flow, and transport are details (admittedly sometimes very