Catalytic in Organic Syntheses

359 Pages·1976·7.308 MB·English

by  Paul Rylander (Eds.)

Catalysis in
Organic Syntheses
1976
EDITED BY
Paul N. Rylander
Engelhard Industries Division
Engelhard Minerals and Chemicals Corp.
Menlo Park, New Jersey
Harold Greenfield
Uniroyal Chemical
Division of Uniroyal Inc.
Naugatuck, Connecticut
ACADEMIC PRESS, INC. New York San Francisco London 1976
A Subsidiary of Harcourt Brace Jovanovich, Publishers
COPYRIGHT © 1976, BY ACADEMIC PRESS, INC.
ALL RIGHTS RESERVED.
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ACADEMIC PRESS, INC.
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United Kingdom Edition published by
ACADEMIC PRESS, INC. (LONDON) LTD.
24/28 Oval Road, London NW1
Library of Congress Cataloging in Publication Data
Conference on Catalysis in Organic Syntheses, 5th,
Boston, 1975.
Catalysis in organic syntheses.
Includes bibliographical references and index.
1. Chemistry, Organic-Synthesis-Congresses.
2. Catalysis-Congresses. I. Rylander, Paul Nels,
Date II. Greenfield, Harold, Date III. Title.
QD262.C56 1975 547'.2 76-4507
ISBN 0-12-605340-5
PRINTED IN THE UNITED STATES OF AMERICA
List of Contributors
Robert L. Augustine, Seton Hall University, South Orange, N.J.
07079
Madan M. Bhasin, Union Carbide Corp., Chemicals and Plastics,
South Charleston, W. Va. 25303
Dale W. Blackburn, Smith Kline & French Laboratories, Philadelphia,
Pa. 19101
Willie Clements, University of Alabama, University, Ala. 35486
Darryl R. Fahey, Phillips Petroleum Co., Bartlesville, Okla. 74004
John Carl Falk, Borg-Warner Corp., Des Plaines, III. 60018
Patrick K. Gallagher, Bell Laboratories, Murray Hill, N.J. 17974
Harold Greenfield, Uniroyal Chemical, Naugatuck, Conn. 06770
Robert H. Grubbs, Michigan State University, East Lansing, Mich.
48823
Susan Hathaway, University of New Hampshire, Durham, N.H.03824
Harlin Hiramoto, University of Alabama, University, Ala. 35486
Stephan Jacobson, University of Alabama, University, Ala. 35486
David W. Johnson, Jr., Bell Laboratories, Murray Hill, N.J. 07974
John F. Knifton, Texaco Inc., Beacon, N.Y. 12508
John R. Kosak, E.I. duPont de Nemours and Co., Deepwater, N.J.
08023
Sidney H. Levinson, Smith Kline & French Laboratories, Philadelphia,
Pa. 19101
James E. Lyons, Sun Oil Co., Marcus Hook, Pa. 19061
Irving L. Mador, Allied Chemical Co., Morristown, N.J. 07960
Russell E. Malz, Jr., Uniroyal Chemical, Naugatuck, Conn. 06770
William F. Masler, University of New Hampshire, Durham, N.H.
03824
Sheldon W. May, Georgia Institute of Technology, Atlanta, Ga.
30332
John L. Miesel, Lilly Research Laboratories, Greenfield, Ind. 46140
vii
LIST OF CONTRIBUTORS
James D. Morrison, University of New Hampshire, Durham, N.H.
03824
George O. P. O'Doherty, Lilly Research Laboratories, Greenfield,
Ind. 46140
John M. Owen, Lilly Research Laboratories, Greenfield, Ind. 46140
Babubhai A. Patel, Seton Hall University, South Orange, N.J. 07079
Sawit Phisanbut, Michigan State University, East Lansing, Mich.
48823
Charles U. Pittman, Jr., University of Alabama, University, Ala.
35486
George W. Roberts, Engelhard Industries, Edison, N.J. 08817
John A. Scheben, U.S. Industrial Chemicals Co., Cincinnati, Ohio
45237
Larry R. Smith, University of Alabama, University, Ala. 35486
E.M. Sweet, Michigan State University, East Lansing, Mich. 48823
Eva M. Vogel, Bell Laboratories, Murray Hill, N.J. 07974
viii
Preface
The contents of this book reflect an idea born in the early 1960's.
At that time, a group of men, whose daily work involved application
of catalysis to organic syntheses, felt the need for a forum where
those with similar interests could meet and exchange views. The New
York Academy of Sciences was approached and asked to sponsor a
conference dealing entirely with practical applications of catalysis.
The Academy proved enthusiastic about the suggestion, and in 1966
the first meeting was held in New York under the joint chairmenship
of Joseph M. O'Connor, Morris Freifelder, and Melvin A. Rebenstorf.
The conference was given the awkward but embracing title of
"Conference on Catalytic Hydrogénation and Analogous Pressure
Reactions." It was realized at the time the group would grow to have
other major interests in addition to hydrogénation, but just what
they would be was not then clear. The uncertainty about future
events was anticipated in the flexible phrase, "Analogous Pressure
Reactions." This first conference was a success, and was followed by
the second, third, and fourth conferences held under the chairman­
ships of Joseph M. O'Connor, Melvin A. Rebenstorf, and Paul N.
Rylander, respectively. The value of these conferences is attested to
by the fact that each was sponsored by the New York Academy of
Sciences despite the Academy's firm rule not to sponsor more than
one conference in the same area. The proceedings of the four con­
ferences have been published in the Annals of the New York Acad­
emy of Sciences, Volumes 148, 158, 172, and 214, respectively.
Gradually, it became clear that the original name of the conference
did not accurately describe the groups' changing interests, and, when
the fifth conference was held in Boston in April, 1975, it was given
the name "Fifth Conference on Catalysis in Organic Syntheses." This
conference was produced independently by a small group, whose
members choose to call themselves The Organic Reactions Catalysis
ix
PREFACE
Society. A salutary development arising from these collective con­
ferences has been a meshing of the interests of organic chemists with
those of catalytic chemists, and in recognition of this development
The Organic Reactions Catalysis Society became affiliated in 1975
with the North American Catalysis Society.
Catalysis in Organic Syntheses is a collection of papers given at the
Fifth Conference. Their diversity reflects the scope of the subject.
Most of the papers are about both organic chemistry and catalysis
simultaneously, and it is difficult to determine where one discipline
begins and the other ends. A few of the papers attempt to look at the
shadowy world of heterogeneous catalysts' surfaces and to relate
catalyst properties with catalytic performance. In another paper a
visitor from the field of chemical engineering examines the often
overlooked effects of mass and heat transfer on catalyst per­
formance. The breadth of interest evidenced in this collection of
papers makes it clear that it will often be difficult to ascertain from
what field the key will come that will open the lock to the solution
of a perplexing problem in organic syntheses by catalysis.
It is a pleasure to express our thanks to Engelhard Industries,
Uniroyal, Merck, Sharpe and Dohme, Strem Chemical, and the Catal­
ysis Society of New England for their moral and material support of
the Fifth Conference. We are indebted and grateful to Mrs. Rebeca
Trautner, Ms. Mariya Bower, and Mrs. Irene Tafaro for their skill and
care in preparing this often difficult material for camera-ready copy.
The formulas reflect Mrs. Trautner's artistic talents.
χ
THE INFLUENCE OF MASS AND HEAT TRANSFER
ON THE PERFORMANCE OF HETEROGENEOUS CATALYSTS
IN GAS/LIQUID/SOLID SYSTEMS
GEORGE W. ROBERTS
Engelhard Minerals and Chemicals Corporation
Engelhard Industries Division
Research and Development Department
Menlo Park
Edison, New Jersey 08817
ABSTRACT
The influence of mass and heat transport on the perfor­
mance of heterogeneous catalysts is reviewed, with particular
emphasis on systems where the catalyst is suspended as discrete
particles in a liquid, and where at least one reactant is gase­
ous and the other occurs primarily in the liquid phase. The
transport processes which necessarily accompany the catalytic
reaction are defined, and the existence of concentration and
temperature profiles throughout the three-phase system is es­
tablished. These concentration and temperature differences can
change the apparent catalyst performance; catalyst activity,
selectivity and life are briefly reviewed in this light.
Rate expressions are defined for the various transport and
reaction steps occurring in the catalytic system, and these are
combined to give an overall rate expression. From this, the
various possible rate-limiting steps are analyzed. Finally,
methods for determining the rate-limiting step from laboratory
experiments are developed. These methods fall into two cate­
gories: 1) diagnostic experiments, and; 2) calculative ap­
proaches. Certain rate-limiting steps, such as gas/liquid mass
transport, are best approached experimentally, whereas others,
such as pore diffusion, are most amenable to a calculative di­
agnosis.
INTRODUCTION
The ultimate objective of virtually all research in het­
erogeneous catalysis is to understand how the formulation of
1
GEORGE W. ROBERTS
the catalyst and the selection of operating conditions influ­
ence the chemistry of the reactions which take place. Unfortu­
nately, the physical processes of heat and mass transport,
which necessarily accompany all heterogeneous catalytic reac­
tions, can distort, or even totally obscure the instrinsic
chemical relationships between the reaction and the catalyst.
Under improper experimental conditions, the apparent reaction
kinetics, the product distribution and the catalyst life will
be determined much more by the nature of these transport pro­
cesses than by the chemistry of the system.
Many of the classical works on the interaction between
heat transport, mass transport and chemical reaction were
published over three decades ago [Damkohler (1938), Frank-
Kamenetskii (1939), Thiele (1939), Zeldovitch (1939)]. The
literature in this area is now voluminous as well as being
highly mathematical. With two notable exceptions, [Satterfield
and Sherwood (1963), Satterfield (1970)], no real attempt has
been made to reduce this literature to a form that is useful to
the catalytic chemist.
The present paper is an attempt to fill the need for a very
basic treatment of the interactions between transport processes
and chemical reaction. The specific objectives are: 1) to
provide a sound qualitative basis for understanding why the pro­
cesses of heat and mass transport alter the behavior of hetero­
geneous catalytic reactions, and how these alterations are
exhibited; 2) to present some easily-applied, quantitative tools
for determining the importance of reaction-transport interac­
tions in the laboratory.
The following five sections proceed gradually from a quali­
tative to a quantitative description of reaction-transport
interactions. The fundamentals of transport processes are re­
viewed in Section I I, and the existence of concentration and
temperature gradients in all heterogeneous catalytic systems is
established. Section III is devoted to explaining how these
concentration and temperature gradients effect the apparent
activity, selectivity and life of the catalyst. The concept of
rate-limiting steps is reviewed in Section IV, leading into
Section V, which deals with the quantitative analysis of various
rate-limiting steps. Finally, in Section VI, some simple proce­
dures for determining the rate-limiting step from experimental
data are presented, , , U , i
This paper will be concerned primarily with three-phase
(gas/liquid/solid) systems, where the catalyst particles are
suspended in a liquid, and where a gas phase is in intimate
contact with the liquid. The liquid may contain one or more
of the reactants in solution, but at least one of the reactants
occurs mainly in the gas phase. Many important industrial re­
actions fall into this category, including a wide variety of
2
HETEROGENEOUS CATALYSIS IN GAS/LI QUI D/SOLID SYSTEMS
hydrogénation reactions. Despite the practical importance of
this type of system, comprehensive discussions of the special
transport problems that occur in these systems are rather rare.
Any one of several different types of reactors may be used
with the type of gas/liquid/solid system described above, in­
cluding batch reactors, continuous slurry reactors and the so-
called "ebullating bed", Fixed-bed reactors will not be treated
in this paper. However, an excellent review of methods for
analyzing transport limitations in fixed beds has been presented
by Mears (1971).
A MECHANISTIC PICTURE OF REACTION/TRANSPORT INTERACTIONS
System Definition
Figure 1 is a physical picture of the catalytic system
which will be treated. Porous catalyst particles are assumed
to be suspended in a liquid phase. These catalyst particles
almost always have a higher density than the liquid, so that
some form of agitation is required to prevent the catalyst from
settling to the bottom of the reactor. Agitation also pre­
vents the discrete catalyst particles from forming larger aggre­
gates, which would settle more rapidly and which would general­
ly be less efficient catalysts than the original particles. The
required agitation is frequently provided by a mechanical stir­
rer, although it can also be provided by bubbling gas rapidly
through the liquid, or by circulating the liquid continuously
through the reactor at a high velocity.
The liquid is assumed to be in contact with a gas phase,
which may be present either as bubbles embedded in the liquid,
as a continuous phase on top of the liquid, or in some combi­
nation of these two forms.
The important behavioral features of the system shown in
Figure 1 can be illustrated by considering a simple, catalytic
reaction, say A + B-> C. In order to make the following dis­
cussion as general as possible, it is assumed that reactant A
is supplied to the reactor as a gas, and remains primarily in
the gas phase. This assumption does not preclude the possibil­
ity that some A will dissolve in the liquid, which, in fact,
always occurs to some extent. Reactant A is analogous to H2 in
most hydrogénation reactions.
Reactant Β is supplied to the reactor in the liquid phase,
and remains primarily in the liquid. Thus, Β is analogous to
the organic molecule that is hydrogenated in any of a large
variety of organic hydrogénation reactions, e.g., the hydrogé­
nation of benzene to cyclohexane.
In general, heat is either liberated or absorbed due to the
occurrence of a chemical reaction. To sustain the analogy with
hydrogénation, it is assumed that the reaction is exothermic.
3
GEORGE W. ROBERTS
FIGURE I
SCHEMATIC DIAGRAM OF GAS/LIQUID/SOLID CATALYTIC SYSTEM
[GAS]
A
SOLID
CATALYST
PARTICLE
\
* HEAT
GENERALIZED REACTION:
A (GAS) + Β (LIQUID) -C (LIQUID)
[EXOTHERMIC]
To simplify the analysis which follows, the reaction is
considered to be essentially irreversible at reaction conditions.
Therefore, there is no need to specify whether the product C is
a liquid or a gas at reaction conditions. However, in most
hydrogénations, the product will accumulate primarily in the
liquid phase.
The next step in the analysis is to identify the transport
processes, i.e., the mass and heat transfer steps, which must
occur in order for the chemical reaction to proceed. Consider­
ing Reactant A first, it is evident from Figure 1 that A must
4