Table Of ContentDeactivation and
Regeneration of
Zeolite Catalysts
CATALYTIC SCIENCE SERIES
Series Editor: Graham J. Hutchings (Cardiff University)
Published
Vol. 1 Environmental Catalysis
edited by F. J. J. G. Janssen and R. A. van Santen
Vol. 2 Catalysis by Ceria and Related Materials
edited by A. Trovarelli
Vol. 3 Zeolites for Cleaner Technologies
edited by M. Guisnet and J.-P. Gilson
Vol. 4 Isotopes in Heterogeneous Catalysis
edited by Justin S. J. Hargreaves, S. D. Jackson and G. Webb
Vol. 5 Supported Metals in Catalysis
edited by J. A. Anderson and M. F. García
Vol. 6 Catalysis by Gold
edited by G. C. Bond, C. Louis and D. T. Thompson
Vol. 7 Combinatorial Development of Solid Catalytic Materials:
Design of High-Throughput Experiments, Data Analysis,
Data Mining
edited by M. Baerns and M. HoleÁa
Vol. 8 Petrochemical Economics: Technology Selection in a Carbon Constrained World
by D. Seddon
Vol. 9 Deactivation and Regeneration of Zeolite Catalysts
edited by M. Guisnet and F. R. Ribeiro
CATALYTIC SCIENCE SERIES — VOL. 9
Series Editor: Graham J. Hutchings
Deactivation and
Regeneration of
Zeolite Catalysts
Michel Guisnet
Fernando Ramôa Ribeiro
Technical University of Lisbon, Portugal
Imperial College Press
ICP
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DEACTIVATION AND REGENERATION OF ZEOLITE CATALYSTS
Catalytic Science Series — Vol. 9
Copyright © 2011 by Imperial College Press
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PREFACE
In industrial practice, the progressive deactivation of solid catalysts is
a major economic concern and mastering their stability has become as
essentialascontrollingtheiractivityandselectivity.Forthesereasons,there
isa strongmotivationtounderstandthe mechanismsleadingto anylossin
activity and/orselectivity andto find outthe efficientpreventivemeasures
and regenerative solutions that open the way towards cheaper and cleaner
processes.
This book covers both the fundamental and applied aspects of solid
catalystdeactivationandencompassesthelateststateoftheartinthefield
of reactions catalysed by zeolites. This particular choice is justified by the
widespread use of molecular sieves in refining, petrochemicals and organic
chemicals synthesis processes, by the large variety in the nature of their
active sites (acid, base, acid-base, redox, bifunctional) and, especially, by
their peculiarfeatures,interms ofcrystallinity,structuralorder,molecular
size of their pores, etc. which make them ideal models for understanding
deactivation phenomena.
The covered topics range from methods and techniques of
characterizing aged catalysts and deactivating species, to the mechanisms
of poisoning, coking and thermal alterations, to kinetic modelling, then to
the means developed to prevent deactivation and optimize regeneration.
In the last part of the book, a series of selected refining, petrochemical
andfinechemicalprocessesprovidethereaderwiththeoreticalinsightsand
practical hints on the deactivation mechanisms and draw attention to the
key role played by the loss and regeneration of activity in process design
and industrial practice.
Review papers are regularly published on this topic of great
economic importance, in particular in the Proceedings of the International
Symposiums on Catalyst Deactivation that have been periodically
organized since 1980. However, only a few books have been published on
this subject so far, the last one dated 1988. This means that most of the
graduates, post-graduate students and researchers active in heterogeneous
v
vi Preface
catalysis cannot rely on recent bibliographic data when dealing with this
key topic. When preparing this book, our primary aim was to fill this gap,
providing reference text not only for scholars carrying out their studies
in the field of industrial chemistry and chemical engineering, but also for
professionals involved in academic and industrial research, coping with
everyday issues of deactivation and regenerationof solid catalysts.
We would like to thank all the authors who, by their fundamental
and/or industrial expertise, have significantly served this ambitious
objective.We hope thatthis bookwillcontributebothto theimprovement
of industrial processes and to original and fruitful research on the
multifaceted aspects not yet fully understood of catalyst deactivation.
Special thanks are due to ProfessorAvelino Corma,a worldwide renowned
expert in catalysis and in zeolites who has agreed to introduce this work.
Thanks are also due to all those who have kindly collaborated with us
onthisbook,especiallytoNunoFonsecawhohasdevotedasignificantpart
of his time to the hard task of preparing many figures and formatting all
the chapters of this book.
Michel GUISNET
Fernando RAMOˆA RIBEIRO
May 2010
FOREWORD
It is possible to say that catalysis in general, and solid catalysts in
particular, are key elements for developing efficient and environmentally
benign chemical processes. In this sense, industry is asking for selective
catalysts able to perform a high number of turnovers. Essentially, this
is another way of saying that the optimal catalysts should minimize the
formation of sub-products, while producing sufficient kilograms of the
desiredproductperkilogramofcatalysttorendertheprocesseconomically
feasible. However, it is most common that solid catalysts also catalyse
someundesiredreactions,leadingtoproducts thatremainadsorbedonthe
surface,poisoningtheactivesitesorblockingaccesstothem,andgradually
causing catalyst activity decay.
Sometimes one may accept a loss of activity if catalyst poisoning also
resultsinanimprovementofselectivity.However,whenapointisreachedat
whichtheremainingactivityistoolow,theprocessbecomesimpracticable.
While it is obvious that the main objective of scientists and
industrialists is to design and synthesize solid catalysts with well defined
homogeneoussinglesites,activeonlyforthedesiredreaction,itisalsoclear
that this objective is difficult to fulfill and 100% selectivity with ‘clean’
catalytic events is rarely achieved. In other words, most solid catalysts
becomedeactivatedsoonerratherthanlaterandtheyshouldberegenerated
to keep the process economical.
Catalystregenerationcanbe performedcontinuously with movingbed
processes when the lifetime of the catalyst is short, or it can be done
in situ for fixed bed processes when the lifetime of the catalyst is long
enough.Thereareothercases,however,whereinthe catalystisirreversibly
deactivated and has to be discharged and replaced.
Regardless of the regeneration system used, the fact that the catalyst
deactivates and needs to be regenerated implies an economic cost either
through further investment in the unit (moving bed systems) or because
of the decrease in production during the programmed shutdown of the
unit for regeneration. It is therefore obvious that improving catalyst life
vii
viii Foreword
and regeneration is a key issue and that a better understanding of the
catalytic processes resulting in catalyst deactivation and regenerationis of
paramount importance.
Zeolites are probably the most successful solid catalysts in oil refining,
petrochemicalsandchemicalsindustries,andmorerecentlyinthetreatment
and purification of exhaust from mobile sources. Zeolites, which consist of
crystallinemicroporousmolecularsieveswithporediametersintherangeof
many reactant molecules, have introduced unique shape selectivity effects
in a variety of catalytic processes.
Thepresenceofregularporesofmoleculardimensionscanbeablessing
oracursefromthecatalystdecaypointofview.Indeed,insomecasesshape
selectivity effects avoid the formation of poisons or molecules that may
block the pores, and catalyst life improves with respect to the amorphous
counterpart catalyst over which the above molecules can be performed
withoutspaceconstraints.Ontheotherhand,anddependingonpore-cavity
shapeanddimensionality,bulkymoleculescouldbuildupinsidethecrystals
and impede the diffusion of reactants to the active sites by blocking the
pores, leading to rapid deactivation of the catalyst. It appears, then, that
zeolites with their crystalline structure andwelldefined poresare excellent
catalysts to study the structure–activity–selectivity–decayrelationship.
In this book, a number of authors well-known in the field of solid
catalyst deactivation and regeneration have treated the deactivation and
regenerationofzeolitecatalystsinaglobalway.Theyhavedescribedatthe
molecularandmacroscopiclevelthechemicalandphysicalprocessesleading
to catalyst deactivation. To do this they have characterized the chemical
species responsible for catalyst deactivation and to follow they elaborate
onthe reactionsandmechanismsofformationinvolved.Kinetic models for
deactivationarethenestablished,withspecialemphasisondeactivationby
coke formation.
Theunderstandingofthemechanismsofdeactivationisthebasisupon
whichtheauthorshaveproposedmethodsforpreventingordiminishingthe
rate of deactivation and, when necessary, they show how to better achieve
regeneration.
Though the fundamentals and the methodology on catalyst
deactivation and regeneration presented in this book can be used for any
catalytic process, a series of industrially relevant case studies are also
presented. The specific processes have been very well selected since they
illustrate different situations ranging from catalyst deactivation occurring
in a few seconds up to several years, from reversible to irreversible
Foreword ix
deactivation, and from mono- to bifunctional catalysis. Finally, they have
introduced a chapter of much interest today that involves the deactivation
of molecular sieves in the synthesis of organic chemicals.
This book is very rationally planned and constructed by the editors,
whohavegreatexperienceandknowledgeonthe subject.Additionally,the
differentauthorshavedoneasuperjobindevelopingtheirchapters,making
aspecialefforttocoversuchabroaddisciplineinarelativelylimitedspace.
The result is a well written and informative book that is an excellent
introduction to zeolite catalyst deactivation and remediation for those
wishing to learn or do research on the subject, as well as a reference book
forthosealreadyworkinginthefield,regardlessofwhethertheycomefrom
industry or academia.
Avelino CORMA
Polytechnical University of Valencia (Spain)
August 2010
