Table Of ContentA CS S Y M P O S I UM SERIES 638
Heterogeneous Hydrocarbon
Oxidation
org 001
s.w
s.ac38.f
ub06 Barbara K. Warren, EDITOR
p://p996- Union Carbide Corporation
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ou Developed from a symposium sponsored by
DP
the Division of Colloid and Surface Chemistry,
and the Division of Petroleum Chemistry, Inc.
American Chemical Society, Washington, DC
In Heterogeneous Hydrocarbon Oxidation; Warren, B., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
QD 305 .H5H47 1996 Copy 1
Heterogeneous hydrocarbon
oxidation
Library of Congress Cataloging-in-Publication Data
Heterogeneous hydrocarbon oxidation / Barbara K. Warren, editor,
S. Ted Oyama, editor
p. cm.—(ACS symposium series, ISSN 0097-6156; 638)
"Developed from a symposium sponsored by the Division of Colloid
and Surface Chemistry, and the Division of Petroleum Chemistry, Inc."
Symposium held in conjunction with the 211th National Meeting of the
American Chemical Society, New Orleans, La., Mar. 24-29, 1996.
org 001 Includes bibliographical references and indexes.
s.w
s.ac38.f ISBN 0-8412-3422-1
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p://p996- 3. 1C. oHmybdursoticoanr—boCnso—ngOrexsisdeast.i on—Congresses. 2. Catalysis—Congresses.
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on Oct996 | d 5Q4D7'3.00150.H4559H3—47d c21909 6 96-24782
2.32 13, 1 CIP
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y 217.66.ate: Augu This book is printed on acid-free, recycled paper.
bD
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wnlblic American Chemical Society
ou
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In Heterogeneous Hydrocarbon Oxidation; Warren, B., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
Advisory Board
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ober 8, oi: 10.1 Mary E. Castellion GNoerothrg Cea rWoli.n Ra oSbtaetret Us niversity
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In Heterogeneous Hydrocarbon Oxidation; Warren, B., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
Foreword
iHE ACS SYMPOSIUM SERIES was first published in 1974 to
provide a mechanism for publishing symposia quickly in book
form. The purpose of this series is to publish comprehensive
books developed from symposia, which are usually "snapshots
in time" of the current research being done on a topic, plus
org 001 some review material on the topic. For this reason, it is neces
s.w
s.ac38.f sary that the papers be published as quickly as possible.
b6 Before a symposium-based book is put under contract, the
u0
p://p996- proposed table of contents is reviewed for appropriateness to
12 | htt1/bk-1 tphaep etrosp iacr ea nedx cfolurd ecdom aptr ethheisn sipvoeinnets,s aonfd thoteh ecrosl leacrteio na.d dSedom teo
02
20 round out the scope of the volume. In addition, a draft of each
ober 8, oi: 10.1 Tpahpise ra niso npyemero-uresv ireewvieedw pprrioorc etsos fiisn aslu paecrcveipsetadn cbey othr er eojregcatinoinz.
n Oct96 | d er^) of the symposium, who become the editor(s) of the book.
2.32 o13, 19 Tmheen daauttiohnosr s otfh ebno rthev itshee threeivri epwaepresr sa ancdc otrhdei negd tioto rtsh,e prreecpoamre
7.66.15August wcahmoe crha-erceka dthya ct oaplyl ,n eacnedss saurbym rietv itshioe nfsi nhaal vpe abpeeerns mtoa dthe.e editors,
y 21ate: As a rule, only original research papers and original re
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In Heterogeneous Hydrocarbon Oxidation; Warren, B., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
Preface
CATALYTIC HYDROCARBON OXIDATION PROCESSES include reactions
for functionalization of organic molecules to make intermediates as well
as reactions involved in total combustion of hydrocarbons to carbon
oxides. The processes of selective oxidation and combustion share a
number of characteristics, but they also represent opposing extremes of
g 1 product selection. For both types of processes, a great deal of informa
or00
acs.8.pr tion about the underlying chemical and chemical engineering principles
bs.63 exists, and it can be used to improve current technologies and invent new
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October 6 | doi: 1 ikeisn. etiTcso paincsd cmovecehreadn isimncsl,u dcea taclayttaiclyasltly saycnttihvees issi,t ecsa, taalnydst acdhvaarnaccetde ripzraotcioenss,
32 on 3, 199 applications.
6.152.gust 1
6u Acknowledgments
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bD We are grateful to the authors who cooperated in the preparation of this
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Do Pu Heterogeneous Hydrocarbon Oxidation," cosponsored by the Divisions of
Colloid and Surface Chemistry and Petroleum Chemistry, Inc., at the
211th National Meeting of the American Chemical Society in New Orle
ans, Louisiana, March 24-29, 1996. These participants made the sympo
sium a success and this book possible.
We are also very grateful to have had financial support from Union
Carbide Corporation, BP Chemicals, ARCO Chemical Company, Exxon
Chemical Company, and the ACS Divisions of Petroleum Chemistry, Inc.,
and Colloid and Surface Chemistry to cover partial costs of this sympo
sium. Finally, we acknowledge and thank the donors of the Petroleum
ix
In Heterogeneous Hydrocarbon Oxidation; Warren, B., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
Research Fund, administered by the American Chemical Society, for par
tial support of this scientific meeting.
BARBARA KNIGHT WARREN
Union Carbide Corporation
3200 Kanawha Turnpike
P.O. Box 8361
South Charleston, WV 25303
S. TED OYAMA
Department of Chemical Engineering
Virginia Polytechnic Institute and State University
org 001 133 Randolph Hall
acs.8.pr Blacksburg, VA 24061
bs.63
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p://p996- May 7, 1996
8, 2012 | htt0.1021/bk-1
October 6 | doi: 1
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6.152.gust 1
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In Heterogeneous Hydrocarbon Oxidation; Warren, B., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
Chapter 1
Factors Affecting Selectivity in Catalytic
Partial Oxidation and Combustion Reactions
S. Ted Oyama
Departments of Chemical Engineering and Chemistry, Virginia
Polytechnic Institute and State University, 133 Randolph Hall,
Blacksburg, VA 24061-0211
org 001
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6.15gust Control of selectivity is one of the central problems in catalytic hydrocarbon oxidation
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DoPu combustion.
The reactions of methane are diverse and provide a good illustration of the role
of selectivity in oxidation.
Table 1
Products of Methane Oxidation
Reactant Products
Species CH4 C2H6 C2H4 CH3OH HCHO HCOOH CO C0
2
Oxidation
-4 -3 -2 -2 0 +2 +2 +4
state
69 74 91 295 503 579 801
kJ/mol CH4
0097-6156/96/0638-0002$15.00/0
© 1996 American Chemical Society
In Heterogeneous Hydrocarbon Oxidation; Warren, B., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
1. OYAMA Selectivity in Catalytic Oxidation & Combustion Reactions 3
In the course of the various transformations the formal oxidation state of
carbon increases to values that depend on the chemical species formed. The degree of
oxidation required depends on the process. For oxidative coupling the desired
products are Clh and C2H4, for chemicals production the end products are CHOH,
2 3
HCHO and HCOOH, in syngas formation the target is CO, while in catalytic
combustion the objective is full oxidation to C0.
2
There has been limited success in the direct production of partial oxidation
products from methane. Methane coupling to C2 products has been studied over a
number of catalysts and maximum yields are less than 40% (2,3,4). Oxygenates have
been obtained over oxides of vanadium (5,6), molybdenum (7,8), and iron (9) as well
as biological (P-450, and methane monooxygenase) (10,11) catalysts and yields have
been even lower, less than 10%. Syngas (CO + H) has been produced in high
2
selectivity (> 90%) at low contact times with noble metals supported on monoliths
org 001 (12,13,14) and at high contact times on perovskite (75) and pyrochlore (16) oxides.
s.acs.38.ch differentI.n tIhne p caarst eth oef coabtjaelcyttiivce ciosm tob uacsthiioenv e(1 f7ul,l1 o8x,1id9a,2ti0o)n tohfe m perothbalneme t oo fC sOe2le catnivdi tHy 0is
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2.32 13, 1 Kinetics or Thermodynamics?
6.15gust The network of reactions involving methane is complex, with many parallel and
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y 21ate: reactions, while the dashed lines show other possible pathways.
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Figure 1
Reaction Network of Methane Oxidation
In Heterogeneous Hydrocarbon Oxidation; Warren, B., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
4 HETEROGENEOUS HYDROCARBON OXIDATION
Any part of the network dealing with an intermediate can be simplified and
described by a simple series of reactions:
ki
A + O > B
k
2
B + O >C
In this sequence A is methane, O is oxygen, B is a partly oxidized species, C is the end
member of the oxidation chain, C0, and ki and k are effective rate constants.
2 2
Depending on whether the objective is partial or total oxidation, the desired product is
either B or C. As seen from the Table 1 the standard free energy of formation is
highly negative for C0. Thermodynamically C0 formation is highly favored, and it
2 2
org 001 is often stated that stopping at B requires kinetic control (7).
s.acs.38.ch reductioInn athned soixmipdlaetsiot nc assteep ths em raayt eb oe fg fiovremna btiyo n of B on a surface undergoing
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02
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n Oct96 | d r = k2KB(B)K0(Q)
o9 2 K(A) + K(B) + K(C) + K(0)
2.32 13, 1 A B c 0
6.15gust In these equations the small case k's represent rate constants while the upper
7.6Au case K's refer to equilibrium adsorption constants. The selectivity to B of the process
21e: is given by the relation giving the maximum value of (B).
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This results in
(ff)max hKA
(4)
(A) kK
2 B
Equation (3) shows that selectivity is intimately connected with the rates of the
reactions involved in the sequence. Equation (4) demonstrates that both kinetic and
thermodynamic factors are involved in determining the selectivity to B. Since in
general the intermediate product is more functionalized than the reactant, it is more
reactive and is also more strongly adsorbed, so k > kj and K > K . This is
2 B A
particularly true for alkane oxidations, and thus, obtaining a large selectivity to B is a
challenge. For non-alkanes there are cases in which K » K, and high selectivity
A B
can be obtained, for example, in the oxidation of methanol to formaldehyde (24).
One way to improve selectivity to the intermediate product is by reducing the
rate of the second step, but this is usually accompanied by a decrease in the rate of the
In Heterogeneous Hydrocarbon Oxidation; Warren, B., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
