Page 15 - The engineering of chemical reactions

Overall Organization xv
We regard the “essential” aspects of chemical reaction engineering to include multiple
reactions, energy management, and catalytic processes; so we regard the first seven chapters
as the core material in a course. Then the final five chapters consider topics such as
environmental, polymer, solids, biological, and combustion reactions and reactors, subjects
that may be considered “optional” in an introductory course. We recommend that an
instructor attempt to complete the first seven chapters within perhaps 3/4 of a term to allow
time to select from these topics and chapters. The final chapter on multiphase reactors is of
course very important, but our intent is only to introduce some of the ideas that are important
in its design.
We have tried to disperse problems on many subjects and with varying degrees
of difficulty throughout the book, and we encourage assignment of problems from later
chapters even if they were not covered in lectures.
The nonlinearities encountered in chemical reactors are a major theme here because
they are essential factors, both in process design and in safety. These generate polynomial
equations for isothermal systems and transcendental equations for nonisothermal systems.
We consider these with graphical solutions and with numerical computer problems. We try
to keep these simple so students can see the qualitative features and be asked significant
questions on exams. We insert a few computer problems in most chapters, starting with
A+ B+C-+ D+ . . . . and continuing through the wall-cooled reactor with diffusion
and mass and heat transfer effects. We keep these problems very simple, however, so that
students can write their own programs or use a sample Basic or Fortran program in the
appendix. Graphics is essential for these problems, because the evolution of a solution
versus time can be used as a “lab” to visualize what is happening.
The use of computers in undergraduate courses is continuously evolving, and different
schools and instructors have very different capabilities and opinions about the level and
methods that should be used. The choices are between (1) Fortran, Basic, and spread-
sheet programming by students, (2) equation-solving programs such as Mathematics and
MathCad, (3) specially written computer packages for reactor problems, and (4) chemical
engineering flowsheet packages such as Aspen. We assume that each instructor will decide
and implement specific computer methods or allow students to choose their own methods
to solve numerical problems. At Minnesota we allow students to choose, but we introduce
Aspen flowsheets of processes in this course because this introduces the idea of reactor-
separation and staged processes in chemical processes before they see them in Process
Design. Students and instructors always seem most uncomfortable with computer problems,
and we have no simple solutions to this dilemma.
One characteristic of this book is that we repeat much material several times in
different chapters to reinforce and illustrate what we believe to be important points. For
example, petroleum refining processes, NO, reactions, and safety are mentioned in most
chapters as we introduce particular topics. We do this to tie the subject together and show how
complex processes must be considered from many angles. The downside is that repetition
may be regarded as simply tedious.
This text is focused primarily on chemical reactors, not on chemical kinetics. It is
common that undergraduate students have been exposed to kinetics first in a course in
physical chemistry, and then they take a chemical engineering kinetics course, followed
by a reaction engineering course, with the latter two sometimes combined. At Minnesota
we now have three separate courses. However, we find that the physical chemistry course