Page 11 - The engineering of chemical reactions

PREFACE

learned about chemical reactors at the knees of Rutherford Aris and Neal Amundson,
when, as a surface chemist, I taught recitation sections and then lectures in the Reac-
I tion Engineering undergraduate course at Minnesota. The text was Aris’ Elementary
Chemical Reaction Analysis, a book that was obviously elegant but at first did not seem
at all elementary. It described porous pellet diffusion effects in chemical reactors and the
intricacies of nonisothermal reactors in a very logical way, but to many students it seemed to
be an exercise in applied mathematics with dimensionless variables rather than a description
of chemical reactors.
We later used Octave Levenspiel’s book Chemical Reaction Engineering, which was
written with a delightful style and had many interesting figures and problems that made
teaching from it easy. Levenspiel had chapters on reactions of solids and on complex
reactors such as fluidized beds, topics to which all chemical engineering students should
be introduced. However, the book had a notation in which all problems were worked in
terms of the molar feed rate of one reactant F~~ and the fractional conversion of this
reactant X. The “fundamental equations” for the PFTR and CSTR given by Levenspiel
were V = FAN 1 dX/rA (X) and V = FA,Xf r-A(X), respectively. Since the energy balance
is conventionally written in terms of spatial variations of properties (as is the general
species balance), there was no logical way to solve mass and energy balance equations
simultaneously, as we must do to consider nonisothermal and nonideal reactors. This
notation also prohibits the correct handling of multiple reaction systems because there is
no obvious X or r,J with multiple reactions, and Levenspiel could only describe selectivity
and yield qualitatively. In that notation, reactors other than the perfect plug flow and the
perfectly stirred reactor could not be handled because it did not allow consideration of
properties versus position in the reactor. However, Levenspiel’s books describe complex
multiphase reactors much more thoroughly and readably than any of its successors, certainly
more than will be attempted here.
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