KGaA, Weinheim 1.2 History of Molecular Sieve Materials 5 1.2.1 Aluminosilicate Zeolites and Silica Molecular Sieves 6 1.2.2 The Materials Explosion Since the 1980s 7... 2.3 Zeolite Fram
Trang 1Santi Kulprathipanja
Zeolites in Industrial Separation and Catalysis
Trang 3Santi Kulprathipanja
Zeolites in Industrial Separation and Catalysis
Trang 4R Xu, W Pang, J Yu, Q Huo, J Chen
Chemistry of Zeolites and
Related Porous Materials
Synthesis and Structure
Volume 4 Microporous and
Mesoporous Solid Catalysts
2006
ISBN: 978-0-471-49054-8
R.A van Santen, M Neurock
Molecular Heterogeneous Catalysis
A Conceptual and Computational Approach
2006 ISBN: 978-3-527-29662-0
J Hagen
Industrial Catalysis
A Practical Approach
2006 ISBN: 978-3-527-31144-6
F Schüth, K.S.W Sing, J Weitkamp (Eds.)
Handbook of Porous Solids
5 Volumes
2002 Hardcover ISBN: 978-3-527-30246-8
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Zeolites in Industrial Separation and Catalysis
Trang 6be free of errors Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.
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© 2010 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim
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Trang 7Zeolites in Industrial Separation and Catalysis Edited by Santi Kulprathipanja
Copyright © 2010 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim
1.2 History of Molecular Sieve Materials 5
1.2.1 Aluminosilicate Zeolites and Silica Molecular Sieves 6
1.2.2 The Materials Explosion Since the 1980s 7
Trang 82.3 Zeolite Framework Types 31
2.4 Pores, Channels, Cages and Cavities 32
2.5 Materials Versus Framework Types 34
2.6 Structures of Commercially Signifi cant Zeolites 35
2.6.1 Linde Type A (LTA) 36
3.2 Synthesis of Zeolites and Aluminophosphate Molecular Sieves 62
3.2.1 Hydrothermal Synthesis – The Key to Metastable Phases 62
3.2.2 Typical Zeolite Syntheses 63
3.2.3 Important Synthesis Parameters – Zeolites 65
3.2.4 Typical Aluminophosphate Syntheses 66
3.2.5 Important Synthesis Parameters – Aluminophosphates 67
3.2.6 Dewatering, Filtration and Washing of Molecular Sieve Products 67
3.3 Forming Zeolite Powders into Usable Shapes 68
3.3.1 Chemical Engineering Considerations in Zeolite Forming 68
3.3.2 Ceramic Engineering Considerations in Zeolite Forming 69
3.3.3 Bound Zeolite Forms 70
3.3.4 Other Zeolite Forms – Colloids, Sheets, Films and Fibers 70
3.4 Finishing: Post-Forming Manufacturing of Zeolite Catalysts and
Adsorbents 71
3.4.1 Post-Forming Crystallization 71
3.4.2 Stabilization and Chemical Modifi cation of Zeolites 72
3.4.3 Ion Exchange and Impregnation 74
3.4.4 Drying and Firing 75
3.5 Selected New Developments in Catalyst and Adsorbent Manufacture 75
Trang 94.2 Multi-Technique Methodology 86
4.2.1 Identifi cation of the Structure of a Newly Invented Zeolite 86
4.3 X-Ray Powder Diffraction Characterization of Zeolitic Systems 91
4.3.1 Interpretation of Powder Diffraction Data for Zeolites 91
4.3.2 Phase Identifi cation and Quantifi cation 92
4.3.3 Unit Cell Size Determination 94
4.3.4 Crystallite Size 95
4.3.5 Rietveld Refi nement 96
4.4 Electron Microscopy Characterization of Zeolitic Systems 97
4.4.1 Importance of Electron Microscopy for Characterizing
4.4.3.5 STEM Application to Metals in Zeolites and Coke Analysis 109
4.5 Infrared Spectroscopy Characterization of Zeolitic Systems 111
4.5.1 Introduction to Infrared Spectroscopy 111
4.5.7 In Situ/In Operando Studies 136
4.5.8 Characterization of Metal-Loaded Zeolites 136
4.5.8.1 Cation Exchange for Adsorption/Separation 137
4.5.8.2 Metal-Loading for Catalysis 138
4.5.8.3 Noble Metal-Loading for Catalysis 138
4.5.8.4 Non-Noble Metal-Loading for Catalysis 139
Trang 104.6 NMR Characterization of Zeolitic Systems 140
O and Other Nuclei 151
4.6.2.6 Diffusion of Hydrocarbons in Zeolites 151
Santi Kulprathipanja and Robert B James
5.2.2.4 Trace Component Removal 175
5.3 R&D Adsorptive Separation 176
5.3.1 Aromatic Hydrocarbon Separation 176
5.3.2 Non-Aromatic Hydrocarbon Separation 176
Trang 115.4 Summary Review of Zeolites in Adsorptive Separation 191
6.3 Liquid Phase Adsorption 206
6.3.1 Sanderson’s Model of Intermediate Electronegativity 207
6.5.1.1 Zeolite Framework Structure 212
6.5.1.2 Metal Cation Exchanged in Zeolite 212
6.5.1.3 Zeolite SiO2/Al2O3 Molar Ratio 216
6.5.1.4 Moisture Content in Zeolite 218
6.5.1.5 Characteristics of the Desorbent 219
6.5.4.1 Ion Exchange Capacity 224
6.5.4.2 Ion Exchange Selectivity 224
Trang 127.2.2.1 Industrial Uses and Demand 241
7.2.2.2 Method of Production 241
7.2.2.3 Characteristics of Zeolitic Adsorptive Process 242
7.3 Other Signifi cant Processes 243
7.3.3.1 Industrial Uses and Demand 245
7.3.3.2 Method of Production: Adsorbent–Desorbent 245
8.2 Normal Paraffi n Separations 249
8.2.1 Characteristics of Adsorbent for Normal Paraffi n
8.2.3 Simulated Moving Bed Operation: Sorbex Process 256
8.2.3.1 Adsorbent Allocation within the Molex Process 256
8.2.3.2 Critical Sorbex Zone Parameters 257
8.2.4 Light Normal Paraffi n Separation (Gasoline Range nC5–6) 258
8.2.4.1 Industrial Use and Demand 258
8.2.4.2 Unique Operating Parameters 258
8.2.5 Intermediate Normal Paraffi n Separation (C6–10) 260
8.2.5.1 Industrial Use and Demand 260
8.2.5.2 Unique Operating Parameters 260
8.2.6 Heavy Normal Paraffi n Separation (C10–18) 261
8.2.6.1 Industrial Use and Demand 262
8.2.6.2 Unique Operating Parameters 262
Trang 138.3 Mono-Methyl Paraffi ns Separation (C10–16) 263
8.3.1 Industrial Use and Demand 263
8.3.2 Unique Operating Parameters 264
8.4 Olefi n Separations 265
8.4.1 C4 Separations 266
8.4.1.1 Industrial Use and Demand 266
8.4.1.2 Unique Operating Parameters 266
8.4.2 Detergent Range Olex C10–16 267
8.4.2.1 Industrial Use and Demand 267
8.4.2.2 Unique Operating Parameters 268
8.5 Carbohydrate Separation 269
8.5.1 Industrial Use and Demand 269
8.5.2 Unique Operating Parameters 269
8.6 Liquid Adsorption Acid Separations 269
8.6.1 Citric Acid Separation 270
8.6.1.1 Industrial Use and Demand 270
8.6.1.2 Unique Operating Parameters 270
8.6.2 Free Fatty Acid Separation 270
8.6.2.1 Industrial Use and Demand 270
8.6.2.2 Unique Operating Parameters 270
9.3.7 Kelvin Equation and Capillary Condensation 279
9.4 Mass Transfer in Formed Zeolite Particles 280
9.4.1 Adsorption Wave Speed 282
9.4.2 Adsorption Wave Shape and Length 283
9.4.3 Linear Driving Force Approximation and Resistance Modeling 284
9.4.4 Diffusion Mechanisms in Formed Zeolites 286
9.4.4.1 Fluid Film Diffusion 286
9.4.4.2 Macro-Pore Diffusion 286
9.4.4.3 Intra-Crystalline Diffusion 287
9.5 Industrial TSA Separations (Purifi cation) 288
9.5.1 Dehydration 289
Trang 149.6.1 PSA Air Separation 297
9.6.2 PSA H2 Purifi cation 299
Jessica O’Brien-Abraham and Jerry Y.S Lin
10.1 Introduction 307
10.2 Synthesis and Properties of Zeolite Membranes 309
10.2.1 In Situ Crystallization 309
10.2.2 Secondary (Seeded) Growth 311
10.2.3 Characterization of Zeolite Membranes 313
10.3 Transport Theory and Separation Capability of Zeolite
Membranes 314
10.3.1 Permeation Through Zeolite Membranes 314
10.3.2 Zeolite Membrane Separation Mechanisms 316 10.3.3 Infl uence of Zeolite Framework Flexibility 319
10.4 Zeolite Membranes in Separation and Reactive
Trang 1511.2 Compositions of Mixed-Matrix Membranes 332
11.2.1 Non-zeolite/Polymer Mixed-Matrix Membranes 333
11.2.2 Zeolite/Polymer Mixed-Matrix Membranes 333
11.3 Concept of Zeolite/Polymer Mixed-Matrix Membranes 334
11.4 Material Selection for Zeolite/Polymer Mixed-Matrix
Membranes 336
11.4.1 Selection of Polymer and Zeolite Materials 336
11.4.1.1 Selection of Polymer Materials 336
11.4.1.2 Selection of Zeolite Materials 337
11.4.1.3 Compatibility between Polymer and Zeolite Materials 339
11.4.2 Modifi cation of Zeolite and Polymer Materials 339
11.5 Geometries of Zeolite/Polymer Mixed-Matrix Membranes 341
11.5.1 Mixed-Matrix Dense Films 341
11.5.2 Asymmetric Mixed-Matrix Membranes 342
11.5.2.1 Flat Sheet Asymmetric Mixed-Matrix Membranes 343
11.5.2.2 Hollow Fiber Asymmetric Mixed-Matrix Membranes 345
11.5.2.3 Thin-Film Composite Mixed-Matrix Membranes 346
11.6 Applications of Zeolite/Polymer Mixed-Matrix Membranes 346
11.6.1 Gas Separation Applications 347
11.6.2 Liquid Separation Applications 347
12.1 History of Catalytic Uses of Zeolites 355
12.1.1 R&D Uses Versus Industrial Application of Zeolite Catalysis 355
12.2 Literature Review of Recent Developments in Catalytic Uses of
12.2.2.1 Light Olefi n Oligomerization 358
12.2.2.2 Heavier Olefi n Oligomerization 364
12.2.3 Alkylation Reactions 364
12.2.3.1 Alkylation of Isobutane 364
12.2.3.2 Benzene Alkylation 364
12.2.4 Aromatics Reactions 369
12.2.4.1 Transalkylation of Toluene to Xylene and Benzene 369
12.2.4.2 Xylene and Ethylbenzene Isomerization 369
Trang 1612.2.8 Hydrotreating and Hydrocracking 383
12.2.9 Reactions Using Heteroatom Substituted Zeolites 387
12.2.9.1 Epoxidation 387
12.2.9.2 Other Oxidations 387
12.3 Future Trends in Catalysis by Zeolites 393
Zeolite Catalysis in Refi ning and Petrochemicals 403
13.4.2 Signifi cance of Acid Strength 421
13.4.3 Signifi cance of Acid Site Density 423
Trang 1713.7.2 Reactant Shape Selectivity 435
13.7.3 Transition State Shape Selectivity 435
13.7.4.7 Other Examples of Product Shape Selectivity 446
13.7.5 Crystal Size Effects 446
13.8.3.1 Isobutane Alkylation by 2-Butylene 450
13.8.3.2 Aromatic–Alkene and Aromatic–Alcohol 453
13.8.4 Alkane Cracking 455
13.8.4.1 Classic Cracking Mechanism, Bimolecular 455
13.8.4.2 Monomolecular Cracking Mechanism 456
13.8.4.3 Kinetics of Cracking 458
13.8.4.4 Effect of Pore Size and Acid Site Density on
Cracking 461
13.8.5 Aromatic Transformation 462
13.8.5.1 Transalkylation and Disproportionation 462
13.8.5.2 Ethylbenzene Conversion to Xylenes 463
14.2.2 Bifunctional Paraffi n Isomerization Mechanism 480
14.2.3 Zeolitic Paraffi n Isomerization Catalysis 482
14.2.4 Industrial Zeolitic Isomerization Catalysts and Processes 483
14.2.5 Summary 484
Trang 1814.3 Olefi n Isomerization 484
14.3.1 General Considerations 484
14.3.2 Cis–Trans and Double Bond Isomerization 485
14.3.3 Skeletal Isomerization (Butenes, Pentenes, Hexenes) 486
14.3.4 Skeletal Isomerization (Longer-Chain Olefi ns) 488 14.3.5 Olefi n Isomerization Summary 488
14.4 C8 Aromatics Isomerization 488
14.4.1 The Chemistry of C8 Aromatics Isomerization 489
14.4.1.1 Feed Composition and Characteristics 489
14.4.1.2 Reaction Product Composition and Characteristics 49014.4.1.3 Isomerization Reactions 491
14.4.2 C8 Aromatics Isomerization Catalysts 494
14.4.3.3 Modeling/Optimization of Commercial Units 497
14.4.3.4 Process Flow Schemes 498
14.4.4 Future Developments 499
14.4.5 C8 Aromatics Isomerization Summary 500
Deng-Yang Y Jan and Paul T Barger
15.2.1.3 Physicochemical Characterization of Active Sites 507
15.3 Paraffi n/Olefi n Alkylation 507
15.3.1 Motor Fuel Alkylation 507
15.3.1.1 Process Chemistry: Feeds, Products and Reactions 50815.3.1.2 Catalysts 509
15.3.1.3 Physicochemical Characterization of Active Sites 51115.4 Benzene Alkylation 512
15.4.1 Ethylbenzene (Ethylene Alkylation), Cumene and Detergent
Trang 1915.4.3 Styrene and Ethylbenzene from Methylation of
Toluene 515
15.4.3.1 Process Chemistry: Feeds, Products and Reactions 515
15.4.3.2 Catalysts 516
15.4.3.3 Physicochemical Characterization of Active Sites 516
15.5 Alkylbenzene Disproportionation and Trans-Alkylation 517
15.5.1 Process Chemistry: Feeds, Products and Reactions 517
15.5.2 Catalysts 517
15.5.3 Physicochemical Characterization of Active Sites 518
15.6 Paraffi n/Olefi n to Aromatics 518
15.6.1 C3/C4 Paraffi n to Aromatics and C3/C4 Paraffi n/Olefi n to
Aromatics 518
15.6.1.1 Process Chemistry: Feeds, Products and Reactions 518
15.6.1.2 Catalysts 519
15.6.1.3 Physicochemical Characterization of Active Sites 519
15.6.2 C6/C7 Paraffi n to Aromatics (Zeolitic Reforming) 520
15.6.2.1 Process Chemistry: Feeds, Products and Reactions 520
15.6.2.2 Catalysts 520
15.6.2.3 Physicochemical Characterization of Active Sites 520
15.7 Methanol to Olefi ns and Aromatics 521
15.7.1 Methanol to C2–C4 Olefi ns 521
15.7.2 Methanol to Aromatics 522
15.7.3 Catalysts 523
15.7.3.1 Physicochemical Characterization of Active Sites 524
15.7.4 Reaction Mechanism of Methanol to Hydrocarbons 527
16.2 Critical Zeolite Properties 536
16.2.1 Framework Types and Compositions 536
16.2.2 Stabilization Methods 539
16.2.3 Property–Function Relationship 542
16.2.3.1 Acid Strength Requirements for Product Control and Infl uence of
Spatial Distribution on Selectivity 544
16.2.3.2 Pore Geometry and Framework Composition 545
16.3 Chemistry of Bond Scission Processes 546
16.3.1 Heteroatom Removal: Desulfurization Denitrogenation and
Deoxygenation 546
16.3.2 Boiling Point Reduction 551
16.3.2.1 Paraffi n Cracking 551
16.3.2.2 Aromatic and Naphthene Ring Opening 554
16.4 Fluidized Catalytic Cracking 556
16.4.1 Process Confi guration and Catalysts 557
Trang 2016.4.2 The Changing Role of the FCC: Transportation Fuel Production or
Petrochemical Feed Production 560
16.5 Hydrocracking and Hydroisomerization 560
16.5.1 Process Confi gurations and Catalysts 561
16.5.2 Catalyst Requirements for the Hydrocracker 561
16.5.3 The Changing Role of the Hydrocracker in a Reformulated Fuels
Environment 565
16.6 Conclusions 566
Trang 21Preface
Zeolites in Industrial Separation and Catalysis Edited by Santi Kulprathipanja
Copyright © 2010 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim
Zeolites have an enormous impact on our daily lives, both directly and indirectly For example, upstream hydrocarbons such as aromatics and olefi ns are produced using zeolite catalysts The aromatics or olefi ns are then separated from the reac-tion mixtures using zeolite adsorbents The purifi ed components produced by these zeolite - based methods are then used in downstream processes to produce products that we use daily, such as clothes, furniture, foods, construction materials and materials to build roads, automobile parts, fuels, gasoline, etc In addition to the indirect impacts mentioned above, zeolites also have a direct impact on our daily lives For example, zeolites are used as builders in detergent formulations With the important features mentioned above, I am pleased to accept Wiley -
VCH ’ s invitation to edit this book entitled “ Zeolites in Industrial Separation and Catalysis ” , which explores the broader scope of zeolite technology and further
examines zeolite applications My hope is that the knowledge gained from this book will generate more innovation in the fi eld of zeolites
This is the fi rst book to offer a practical overview of zeolites and their cial applications Each chapter is written by a globally recognized and acclaimed leader in the fi eld The book is organized into three parts The fi rst part discusses the history and chemistry of zeolites, the second part focuses on separation proc-esses and the third part explores zeolites in the fi eld of catalysis All three parts are tied together by their focus on the unique properties of zeolites that allow them
commer-to function in different capabilities as an adsorbent, a membrane and a catalyst Each of the chapters also discusses the impact of zeolites within the industry The fi rst part of the book documents the history, structure, chemistry, formula-tion and characterizations of zeolites in Chapters 1 – 4 The past 60 years have seen
a progression in molecular sieve materials from aluminosilicate zeolites to porous silica polymorphs, microporous aluminophosphate - based polymorphs, metallosilicate and metallophosphate compositions, octahedral – tetrahedral frame-works, mesoporous molecular sieves and, most recently, hybrid metal organic frameworks (MOFs)
Introductory Chapter 1 provides a historical overview of molecular sieve als Chapter 2 covers the defi nition of a zeolite and describes their basic and composite building units and how they are linked in zeolite frameworks It defi nes pores, channels, cages and cavities; and it gives references for fi nding detailed
Trang 22materi-information about all framework types Chapter 2 also describes the framework structures and cation locations for some of the commercially signifi cant zeolites
in more detail
Chapter 3 outlines zeolite synthesis, modifi cation and the manufacturing of zeolite - based catalysts and adsorbents Extensive patent references are given to provide the reader with a historical perspective Some of the pitfalls associated with the operation of synthesis and manufacturing units are also described Characterization is the foundation for the development and commercialization
of new zeolites and zeolite - containing catalysts and adsorbents Chapter 4 provides
an overview of the most commonly employed characterization techniques and emphasizes the utility and limitations of each of these methods An example is provided as to how a multi - technique characterization approach is necessary in order to determine the structure of a newly invented zeolite Techniques covered
in this chapter include X - ray powder diffraction, electron microscopy, infrared (IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and physical/chemical methods
The second part of the book covers zeolite adsorptive separation, adsorption mechanisms, zeolite membranes and mixed matrix membranes in Chapters 5 – 11 Chapter 5 summarizes the literature and reports adsorptive separation work on specifi c separation applications organized around the types of molecular species being separated A series of tables provide groupings for: (i) aromatics and deriva-tives, (ii) non - aromatic hydrocarbons, (iii) carbohydrates and organic acids, (iv)
fi ne chemical and pharmaceuticals, (v) trace impurities removed from bulk als Zeolite adsorptive separation mechanisms are theorized in Chapter 6 Chapter 7 gives a review of the technology and applications of zeolites in liquid adsorptive separation of petrochemical aromatic hydrocarbons The application of zeolites to petrochemical aromatic production may be the area where zeolites have had their largest positive economic impact, accounting for the production of tens
materiof millions materiof tonnes materiof high value aromatic petrochemicals annually The non aromatic hydrocarbon liquid phase adsorption review in Chapter 8 contains both general process concepts as well as suffi cient individual process details for one to understand both commercially practiced and academic non - aromatic separations
In Chapter 9 , the major industrial gas separations enabled by zeolite - based products are examined and classifi ed by the method of regeneration employed Thermal swing regeneration and pressure swing regeneration are the two most prevalent processes for gas separations After delineating a number of useful equilibrium models that are used in the fi eld, mass transfer in formed zeolite products is covered in some detail, providing the reader with some estimation methods that enable the determination of mass transfer from fi rst principles and allowing for prediction of the performance of packed - bed contactors With that background, the basics of thermal swing dehydration are used to teach the basic methodology behind gas phase adsorption process design After dealing with dehydration, other purifi cation processes are discussed, including CO 2 removal, sulfur removal, VOC abatement and removal of heavy metals, including mercury Pressure swing adsorption (PSA) separations are then dealt with on a high level,
Trang 23highlighting differences that result in PSA from thermal swing behavior Finally some novel rotating contactors that are making inroads into the commercial adsorption fi eld are discussed This book introduces novel separators such as zeolite membranes and mixed - matrix membranes Zeolite membranes and mixed - matrix membranes are described in Chapters 10 and 11 , respectively Zeolite membranes are composed of inorganic zeolites Chapter 10 describes how one can fabricate submicron particle - size zeolites into a membrane confi guration In contrast, mixed - matrix membranes are composed of inorganic zeolites and poly-mers Chapter 11 provides a brief introduction to combining polymers and inor-ganic zeolites into mixed - matrix membranes Both chapters have a comprehensive review of zeolite and zeolite/polymer mixed - matrix membranes They cover the materials, separation mechanisms, methods, structures, properties and antici-pated potential applications of the zeolite and zeolite/polymer mixed - matrix membranes
The third and last part of the book (Chapters 12 – 16 ) deals with zeolite catalysis Chapter 12 gives an overview of the various reactions which have been catalyzed
by zeolites, serving to set the reader up for in - depth discussions on individual topics in Chapters 13 – 16 The main focus is on reactions of hydrocarbons cata-lyzed by zeolites, with some sections on oxidation catalysis The literature review
is drawn from both the patent and open literature and is presented primarily in table format Brief notes about commonly used zeolites are provided prior to each table for each reaction type Zeolite catalysis mechanisms are postulated in Chapter
13 The discussion includes the governing principles of performance parameters like adsorption, diffusion, acidity and how these parameters fundamentally infl u-ence zeolite catalysis Brief descriptions of the elementary steps of hydrocarbon conversion over zeolites are also given The intent is not to have an extensive review of the fi eld of zeolite catalysis, but to select a suffi ciently large subset of published literature through which key points can be made about reaction mecha-nisms and zeolitic requirements
The chemistry of isomerization technology is discussed in Chapter 14 zation technology provides the means to convert less valuable hydrocarbon isomers into more valuable ones Zeolites, with their precise morphologies, can be made into exceptional catalysts with high selectivity The ability to adjust zeolite chem-istry through innovative synthesis or post - synthesis treatments further enhances their versatility in isomerization applications Chapter 15 describes some of the key technologies involving carbon – carbon bond formation In this class of reac-tions, zeolite catalysts are well established in industrial olefi n oligomerization and aromatic alkylation and transalkylation processes More recently, zeolites or other molecular sieves have found commercial application for paraffi n cyclization to aromatics and the conversion of methanol to hydrocarbons ranging from light olefi ns to aromatics In addition, research into the use of zeolites as a replacement for liquid acid catalysts for the alkylation of paraffi ns with olefi ns, which has yet
Isomeri-to be applied on a full commercial scale, is discussed
Chapter 16 discusses carbon – carbon bond breaking and rearrangement The chapter attempts to identify the key properties of zeolites which must be tailored
Trang 24for optimum performance in the various application fi elds Specifi cally, this chapter emphasizes the need to control a multiplicity of properties simultaneously
in order to achieve the desired performance Thus, channel geometry, acid site strength and spatial distribution as well as particle morphology all must be adjusted
as an ensemble to deliver the desired catalysis Beyond the fundamentals, this chapter provides an overview of key technologies employing the breaking and rearranging of hydrocarbon bonds
Enjoyment and love of technical contributions to the scientifi c community are
my motivations in organizing my thoughts, inviting experts to write the chapters and editing this book The book ’ s success also comes from the authors of the book chapters: Edith M Flanigen, Robert W Broach, Stephen T Wilson, Robert L.Bedard, Steve A.Bradley, Wharton Sinkler, Thomas M Mezza, Sesh Prabhakar, Robert B James, Stanley J Frey, Stephen W Sohn, Steve Dunne, Jerry Lin, Jessica
O ’ Brien, Chunqing Liu, Christopher P Nicholas, Hayim Abrevaya, John E Bauer, Paula L Bogdan, Feng Xu, Gregory J Gajda, Deng - Yang Y Jan, Paul T Barger and Suheil F Abdo I am very thankful for their excellent technical contributions Thanks are also due to the UOP ’ s publication committee for reviewing the chap-ters and allowing the book to be published
I would also like to thank my associates at UOP and my graduate students from the Petroleum and Petrochemical College at Chulalongkorn University, with whom I have had the pleasure of teaching and learning from Finally, I would like
to thank my family, especially my wife Apinya for supporting my love and ment of the work
UOP, A Honeywell Company Des Plaines, Illinois, USA
Trang 25
UOP, A Honeywell Company
50 East Alonquin RoadDes Plaines, IL 60017USA
Jessica O’Brien-Abraham
Jerry Y.S Lin
Arizona State UniversityDepartment of Chemical EngineeringECG202, PO Box 876006
Tempe, AZ 85287-6006USA
Zeolites in Industrial Separation and Catalysis Edited by Kulprathipanja
Copyright © 2010 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim
Trang 27is evident from the fact that publications and patents are steadily increasing each year
1.1.1
Molecular Sieves and Zeolites
Molecular sieves are porous solids with pores of the size of molecular sions, 0.3 – 2.0 nm in diameter Examples include zeolites, carbons, glasses and oxides Some are crystalline with a uniform pore size delineated by their crystal structure, for example, zeolites Most molecular sieves in practice today are zeolites
Zeolites are crystalline aluminosilicates of group IA and group IIA elements, such as sodium, potassium, magnesium and calcium [2] Chemically, they are represented by the empirical formula:
M O Al O2n ⋅ 2 3⋅ySiO2⋅wH O2
where y is 2 – 200, n is the cation valence and w represents the water contained in
the voids of the zeolite Structurally, zeolites are complex, crystalline inorganic polymers based on an infi nitely extending three - dimensional, four - connected framework of AlO 4 and SiO 4 tetrahedra linked to each other by the sharing of oxygen ions Each AlO 4 tetrahedron in the framework bears a net negative charge which is balanced by an extra - framework cation The framework structure contains
Zeolites in Industrial Separation and Catalysis Edited by Santi Kulprathipanja
Copyright © 2010 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim
1
Trang 28intracrystalline channels or interconnected voids that are occupied by the cations and water molecules The cations are mobile and ordinarily undergo ion exchange The water may be removed reversibly, generally by the application of heat, which leaves intact a crystalline host structure permeated by the micropores and voids which may amount to 50% of the crystals by volume The intracrystalline channels
or voids can be one - , two - or three - dimensional The preferred type has two or three dimensions to facilitate intracrystalline diffusion in adsorption and catalytic applications
In most zeolite structures the primary structural units, the AlO 4 or SiO 4 hedra, are assembled into secondary building units which may be simple polyhe-dra, such as cubes, hexagonal prisms or cubo - octahedra The fi nal framework structure consists of assemblages of the secondary units (see Chapter 2 ) More than 70 novel, distinct framework structures of zeolites are known They exhibit pore sizes from 0.3 to 1.0 nm and pore volumes from about 0.10 to 0.35 cm 3
/g Typical zeolite pore sizes include: (i) small pore zeolites with eight - ring pores, free diameters of 0.30 – 0.45 nm (e.g., zeolite A), (ii) medium pore zeolites with 10 - ring pores, 0.45 – 0.60 nm in free diameter (ZSM - 5), (iii) large pore zeolites with 12 - ring pores of 0.6 – 0.8 nm (e.g., zeolites X, Y) and (iv) extra - large pore zeolites with 14 - ring pores (e.g., UTD - 1)
The zeolite framework should be viewed as somewhat fl exible, with the size and shape of the framework and pore responding to changes in temperature and guest species For example, ZSM - 5 with sorbed neopentane has a near - circular pore of 0.62 nm, but with substituted aromatics as the guest species the pore assumes an elliptical shape, 0.45 to 0.70 nm in diameter
Some of the more important zeolite types, most of which have been used in commercial applications, include the zeolite minerals mordenite, chabazite, eri-onite and clinoptilolite, the synthetic zeolite types A, X, Y, L, “ Zeolon ” mordenite, ZSM - 5, beta and MCM - 22 and the zeolites F and W
1.1.2
Nomenclature
There is no systematic nomenclature developed for molecular sieve materials The discoverer of a synthetic species based on a characteristic X - ray powder diffraction pattern and chemical composition typically assigns trivial symbols The early syn-thetic materials discovered by Milton, Breck and coworkers at Union Carbide used the modern Latin alphabet, for example, zeolites A, B, X, Y, L The use of the Greek alphabet was initiated by Mobil and Union Carbide with the zeolites alpha, beta, omega Many of the synthetic zeolites which have the structural topology of mineral zeolite species were assigned the name of the mineral, for example, syn-thetic mordenite, chabazite, erionite and offretite.The molecular sieve literature is replete with acronyms: ZSM - 5, - 11, ZK - 4 (Mobil), EU - 1, FU - 1, NU - 1 (ICI), LZ - 210, AlPO, SAPO, MeAPO, etc (Union Carbide, UOP) and ECR - 1 (Exxon) The one publication on nomenclature by IUPAC in 1979 is limited to the then - known zeolite - type materials [3]
Trang 29The Atlas of Zeolite Structure Types [4] , published and frequently updated by the
IZA Structure Commission, assigns a three - letter code to be used for a known framework topology irrespective of composition Illustrative codes are LTA for Linde zeolite A, FAU for molecular sieves with a faujasite topology (e.g., zeolites
X, Y), MOR for the mordenite topology, MFI for the ZSM - 5 and silicalite gies and AFI for the aluminophosphate AlPO 4 - 5 topology The acceptance of a newly determined structure of a zeolite or molecular sieve for inclusion in the
topolo-offi cial Atlas is reviewed and must be approved by the IZA Structure Commission
The IZA Structure Commission was given authority at the Seventh International Zeolite Conference (Tokyo, 1986) to approve and/or assign the three - letter struc-ture code for new framework topologies
The defi nition and usage of the term “ zeolite ” has evolved and changed, cially over the past decade, to include non - aluminosilicate compositions and struc-
espe-tures Beginning with the second revised edition of the Atlas [5] , the term “ zeolite
and zeolite - like materials ” is introduced to try and capture the range of materials
of interest The inclusion of a structure in the Atlas is limited to three - dimensional,
tetrahedral oxide networks with a framework density less than about 21 T - atoms per 1000 Å 3
irrespective of framework composition Similarly the term zeolite has been broadened in the mineralogy literature to include tetrahedral framework compositions with T - elements other than Al and Si but where classic zeolite prop-erties are exhibited (e.g., structures containing open cavities in the form of chan-nels and cages, reversible hydration – dehydration characteristics [6] ) Very recently
as a sign of the times the term “ nanoporous ” materials has been applied to zeolites and related molecular sieves [7]
1.1.3
Early History
The history of zeolites began in 1756 when the Swedish mineralogist Cronstedt discovered the fi rst zeolite mineral, stilbite [8] He recognized zeolites as a new class of minerals consisting of hydrated aluminosilicates of the alkali and alkaline earths Because the crystals exhibited intumescence when heated in a blowpipe
fl ame, Cronstedt called the mineral a “ zeolite ” (derived from two Greek words, zeo and lithos , meaning “ to boil ” and “ a stone ” ) From 1777 through about the 1800s
various authors described the properties of zeolite minerals, including adsorption properties and reversible cation exchange and dehydration St Claire Deville reported the fi rst hydrothermal synthesis of a zeolite, levynite, in 1862 [9] In 1896 Friedel developed the idea that the structure of dehydrated zeolites consists of open spongy frameworks after observing that various liquids such as alcohol, benzene and chloroform were occluded by dehydrated zeolites [10] Grandjean in 1909 observed that dehydrated chabazite adsorbs ammonia, air, hydrogen and other molecules [11] , and in 1925 Weigel and Steinhoff reported the fi rst molecular sieve effect [12] They noted that dehydrated chabazite crystals rapidly adsorbed water, methyl alcohol, ethyl alcohol and formic acid but essentially excluded acetone, ether or benzene In 1927 Leonard described the fi rst use of X - ray diffraction for
Trang 30identifi cation in mineral synthesis [13] Taylor and Pauling described the fi rst single crystal structures of zeolite minerals in 1930 [14, 15] In 1932 McBain established the term “ molecular sieve ” to defi ne porous solid materials that act as sieves on a molecular scale [16]
Thus, by the mid - 1930s the literature described the ion exchange, adsorption, molecular sieving and structural properties of zeolite minerals as well as a number
of reported syntheses of zeolites The early synthetic work remains ated because of incomplete characterization and the diffi culty of experimental reproducibility
unsubstanti-Richard M Barrer began his pioneering work in zeolite adsorption and synthesis in the mid - 1930s to 1940s He presented the fi rst classifi cation of the then - known zeolites based on molecular size considerations in 1945 [17] and
in 1948 reported the fi rst defi nitive synthesis of zeolites, including the synthetic analog of the zeolite mineral mordenite [18] and a novel synthetic zeolite [19] much later identifi ed as the KFI framework Barrer ’ s work in the mid - to late 1940s inspired Robert M Milton of the Linde Division of Union Carbide Corpora-tion to initiate studies in zeolite synthesis in search of new approaches for separa-tion and purifi cation of air Between 1949 and 1954 Milton and coworker Donald
W Breck discovered a number of commercially signifi cant zeolites, types A, X and
Y In 1954 Union Carbide commercialized synthetic zeolites as a new class of industrial materials for separation and purifi cation The earliest applications were the drying of refrigerant gas and natural gas In 1955 T.B Reed and D.W Breck reported the structure of the synthetic zeolite A [20] In 1959 Union Carbide mar-keted the “ ISOSIV ” process for normal – isoparaffi n separation, representing the
fi rst major bulk separation process using true molecular sieving selectivity Also
in 1959 a zeolite Y - based catalyst was marketed by Carbide as an isomerization catalyst [21]
In 1962 Mobil Oil introduced the use of synthetic zeolite X as a hydrocarbon cracking catalyst In 1969 Grace described the fi rst modifi cation chemistry based
on steaming zeolite Y to form an “ ultrastable ” Y In 1967 – 1969 Mobil Oil reported the synthesis of the high silica zeolites beta and ZSM - 5 In 1974 Henkel introduced zeolite A in detergents as a replacement for the environmentally suspect phos-phates By 2008 industry - wide approximately 367 000 t of zeolite Y were in use in catalytic cracking [22] In 1977 Union Carbide introduced zeolites for ion - exchange separations
1.1.4
Natural Zeolites
For 200 years following their discovery by Cronstedt, zeolite minerals (or natural zeolites) were known to occur typically as minor constituents in vugs or cavities
in basaltic and volcanic rock Such occurrences precluded their being obtained
in mineable quantities for commercial use From the late 1950s to 1962 major geologic discoveries revealed the widespread occurrence of a number of natural
Trang 31zeolites in sedimentary deposits throughout the western United States The coveries resulted from the use of X - ray diffraction to examine very fi ne - grained (1 – 5 μ m) sedimentary rock Some zeolites occur in large, nearly mono - mineralic deposits suitable for mining Those that have been commercialized for adsorbent applications include chabazite, erionite, mordenite and clinoptilolite [23]
Mordenite and clinoptilolite are used in small volume in adsorbent applications including air separation and in drying and purifi cation [24] Natural zeolites have also found use in bulk applications as fi llers in paper, in pozzolanic cements and concrete, in fertilizer and soil conditioners and as dietary supplements in animal husbandry
1.2
History of Molecular Sieve Materials
The theme of research on molecular sieve materials over the past nearly 60years has been a quest for new structures and compositions The major discoveries and advances in molecular sieve materials during that period are summarized in Table 1.1
The history of commercially signifi cant molecular sieve materials from 1954 to
2001 was reviewed in detail by one of us (E.M.F., ref [1] ) Highlights from that review and the subsequent history are presented here The reader is referred to Chapter 2 for the structures of the materials and to Chapter 3 and ref [25] for a detailed discussion on zeolite synthesis
Table 1.1 Evolution of molecular sieve materials
Mesoporous molecular sieves Octahedral – tetrahedral frameworks
Germanosilicate zeolites
Trang 321.2.1
Aluminosilicate Zeolites and Silica Molecular Sieves
The early evolution of aluminosilicate zeolites, in the 1950s to 1970s, is rized in Table 1.2 , based on increasing framework Si/Al composition The four somewhat arbitrary categories are: (i) “ low ” , (ii) “ intermediate ” , (iii) “ high ” silica zeolites and (iv) “ silica ” molecular sieves
The transition in properties accompanying the increase in the framework Si/Al are generalized here but should only be viewed as trends The thermal stability increases from about 700 ° C in the low silica zeolites to 1300 ° C in the silica molecular sieves The surface selectivity, which is highly hydrophilic in the low silica zeolites, is hydrophobic in the high silica zeolites and the silica molecular sieves The acidity tends to increase in strength with increasing Si/Al ratio As the Si/Al ratio increases, the cation concentration and ion exchange capacity (propor-tional to the aluminum content) decreases The structures of the low silica zeolites are predominantly formed with four, six and eight rings of tetrahedra In the intermediate silica zeolites we see the onset of fi ve rings in mordenite and omega zeolite In the high silica zeolite structures and the silica molecular sieves we fi nd
a predominance of fi ve rings of tetrahedra, for example, silicalite
The low silica zeolites represented by zeolites A and X are aluminum - saturated, have the highest cation concentration and give optimum adsorption properties in terms of capacity, pore size and three - dimensional channel systems They repre-sent highly heterogeneous surfaces with a strongly hydrophilic surface selectivity The intermediate Si/Al zeolites (Si/Al of 2 – 5) consist of the natural zeolites eri-onite, chabazite, clinoptilolite and mordenite, and the synthetic zeolites Y, mor-denite, omega and L These materials are still hydrophilic in this Si/Al range The high silica zeolites with Si/Al of 10 – 100 can be generated by either thermo-chemical framework modifi cation of hydrophilic zeolites or by direct synthesis In
Table 1.2 The early evolution of aluminosilicate molecular
sieve materials
Composition and examples
“ Low ” Si/Al zeolites (1 to 1.5): A, X
Highly siliceous variants of Y, mordenite, erionite
Trang 33the modifi cation route stabilized, siliceous variants of Y, mordenite, erionite and over a half - dozen other zeolites have been prepared by steaming and acid extrac-tion These materials are reported to be hydrophobic and organophilic and repre-sent a range of pore sizes from 0.4 to 0.8 nm A very large number of high - silica zeolites prepared by direct synthesis have now been reported, including beta, ZSM - 5, - 11, - 12, - 21, - 34, NU - 1, FU - 1 and ferrisilicate and borosilicate analogs of the aluminosilicate structures Typical of the reported silica molecular sieves are silicalite, fl uoride silicalite, silicalite - 2 and TEA - silicate ZSM - 5 and silicalite have achieved commercial signifi cance
In summary, when we compare the properties of the low and intermediate zeolites with those of the high silica zeolites and silica molecular sieves, we fi nd that their resulting properties allow the low and intermediate zeolites to remove water from organics and to carry out separations and catalysis on dry streams In contrast, the hydrophobic high silica zeolites and silica molecular sieves can remove and recover organics from water streams and carry out separations and catalysis in the presence of water
1.2.2
The Materials Explosion Since the 1980s
Overall the period since the 1980s can be described as a period of explosion in the discovery of new compositions and structures of molecular sieves This can perhaps be seen most vividly by comparing the numbers of structure types con-
tained in the various editions of the Atlas of Zeolite Structure Types [4] The fi rst
edition (1978) contained 38 structure types, the second edition (1987) 64, the third edition (1992) 85 and the most recent edition (2007) 176 Thus 112 new structure types have been discovered since 1978 However, the reader should be cautioned
that a signifi cant number of the structure types included in the Atlas are not truly
microporous or molecular sieve materials (i.e., they are not stable for the removal
of as - synthesized guest species, typically water or organic templates) and therefore cannot reversibly adsorb molecules or carry out catalytic reactions Unfortunately,
the Atlas gives only limited information on the stability of the structures described
1.2.2.1 The 1980s
In the 1980s there was extensive work carried out on the synthesis and applications
of ZSM - 5 and a proliferating number of other members of the high silica zeolite family In 1982 microporous crystalline aluminophosphate molecular sieves were
described by Wilson et al [26] at Union Carbide, and additional members of the
aluminophosphate - based molecular sieve family, for example, SAPO, MeAPO, MeAPSO, ElAPO and ElAPSO, were subsequently disclosed by 1986 [27] Consid-erable effort in synthesizing metallosilicate molecular sieves was reported when the metals iron, gallium, titanium, germanium and others were incorporated during synthesis into silica or aluminosilicate frameworks, typically with the ZSM - 5 (MFI) topology [28] Additional crystalline microporous silica molecular sieves and related clathrasil structures were reported
Trang 34The 1980s saw major developments in secondary synthesis and modifi cation chemistry of zeolites Silicon - enriched frameworks of over a dozen zeolites were described using methods of: (i) thermochemical modifi cation (prolonged steam-ing) with or without subsequent acid extraction, (ii) mild aqueous ammonium
fl uorosilicate chemistry, (iii) high - temperature treatment with silicon tetrachloride and (iv) low - temperature treatment with fl uorine gas Similarly, framework metal substitution using mild aqueous ammonium fl uorometallate chemistry was reported to incorporate iron, titanium, chromium and tin into zeolite frameworks
by secondary synthesis techniques
Aluminophosphate - Based Molecular Sieves In 1982 a major discovery of a new
class of aluminophosphate molecular sieves was reported by Wilson et al [26] By
1986 some 13 elements were reported to be incorporated into the phate frameworks: Li, Be, B, Mg, Si, Ti, Mn, Fe, Co, Zn, Ga, Ge and As [27] These new generations of molecular sieve materials, designated AlPO 4 - based molecular sieves, comprise more than 24 structures and 200 compositions
The > 24 structures of AlPO 4 - based molecular sieves reported to date include zeolite topological analogs and a large number of novel structures The major structures are shown in Table 1.3 They include 15 novel structures as well as seven structures with framework topologies related to those found in the zeolites
Saturation
H 2 O pore volume,
cm 3 /g
Species Structure
type
Pore size, nm
Saturation
H 2 O pore volume,
cm 3 /g
Trang 35CHA ( - 34, - 44, - 47), ERI ( - 17), GIS ( - 43), LEV ( - 35), LTA ( - 42), FAU ( - 37) and SOD ( - 20) Also shown is the pore size and saturation water pore volume for each structure type The structures include the fi rst very large pore molecular sieve, VPI - 5, with an 18 - ring one - dimensional channel with a free pore opening of 1.25 nm [29] , large pore (0.7 – 0.8 nm), intermediate pore (0.6 nm), small pore (0.4 nm) and very small pore (0.3 nm) materials Saturation water pore volumes vary from 0.16 to 0.35 cm 3
/g, comparable to the pore volume range observed in zeolites (see Chapter 2 for detailed structures)
The addition of another element to the aluminophosphate reactants, for example,
Si, metal ions Mg, Co, Mn, Fe, as well as other elements, led to the nophosphate family “ SAPO ” , the metalloaluminophosphate family “ MeAPO ” and other elements, the “ ElAPO ” family, where the added element is incorporated into the hypothetical AlPO 4 framework
silicoalumi-The aluminophospahate molecular sieve product composition expressed in terms of oxide ratios is:
xR Al O⋅ 2 3⋅1 0 ±0 2 P O2 5⋅yH O2
where R is an amine or quaternary ammonium ion The AlPO 4 molecular sieve
as synthesized must be calcined at 400 – 600 ° C to remove the R and water, yielding
a microporous aluminophosphate molecular sieve
The characteristics of aluminophosphate molecular sieves include a univariant framework composition with Al/P = 1, a high degree of structural diversity and
a wide range of pore sizes and volumes, exceeding the pore sizes known previously
in zeolite molecular sieves with the VPI - 5 18 - membered ring material They are neutral frameworks and therefore have nil ion - exchange capacity or acidic catalytic properties Their surface selectivity is mildly hydrophilic They exhibit excellent thermal and hydrothermal stability, up to 1000 ° C (thermal) and 600 ° C (steam)
The silicoaluminophosphate ( SAPO ) family [30] includes over 16 microporous structures, eight of which were never before observed in zeolites The SAPO family includes a silicon analog of the 18 - ring VPI - 5, Si - VPI - 5 [31] , a number of large - pore
12 - ring structures including the important SAPO - 37 (FAU), medium - pore tures with pore sizes of 0.6 – 0.65 nm and small - pore structures with pore sizes of 0.4 – 0.43 nm, including SAPO - 34 (CHA) The SAPOs exhibit both structural and compositional diversity
struc-The SAPO anhydrous composition can be expressed as 0 – 0.3R(Si x Al y P z )O 2 ,
where x , y and z are the mole fraction of the respective framework elements The mole fraction of silicon, x , typically varies from 0.02 to 0.20 depending on synthesis conditions and structure type Martens et al have reported compositions with the SAPO - 5 structure with x up to 0.8 [32] Van Nordstrand et al have reported the
synthesis of a pure silica analog of the SAPO - 5 structure, SSZ - 24 [33]
The introduction of silicon into hypothetical phosphorus sites produces tively charged frameworks with cation - exchange properties and weak to mild acidic catalytic properties Again, as in the case of the aluminophosphate molecular sieves, they exhibit excellent thermal and hydrothermal stability
Trang 36In the metal aluminophosphate ( MeAPO ) family the framework composition contains metal, aluminum and phosphorus [27] The metal ( Me ) species include the divalent forms of Co, Fe, Mg, Mn and Zn and trivalent Fe As in the case of SAPO, the MeAPOs exhibit both structural diversity and even more extensive compositional variation Seventeen microporous structures have been reported, 11
of these never before observed in zeolites Structure types crystallized in the MeAPO family include framework topologies related to the zeolites, for example,
- 34 (CHA) and - 35 (LEV), and to the AlPO 4 s, e.g., - 5 and - 11, as well as novel structures, e.g., - 36 (0.8 nm pore) and - 39 (0.4 nm pore) The MeAPOs represent the fi rst demonstrated incorporation of divalent elements into microporous frameworks
The spectrum of adsorption pore sizes and pore volumes and the hydrophilic surface selectivity of the MeAPOs are similar to those described for the SAPOs The observed catalytic properties vary from weakly to strongly acidic and are both metal - and structure - dependent The thermal and hydrothermal stability of the MeAPO materials is somewhat less than that of the AlPO 4 and SAPO molecular sieves
The MeAPO molecular sieves exhibit a wide range of compositions within the
general formula 0 – 0.3R(Me x Al y P z )O 2 The value of x , the mole fraction of Me,
typically varies from 0.01 to 0.25 Using the same mechanistic concepts described for SAPO, the MeAPOs can be considered as hypothetical AlPO 4 frameworks that have undergone substitution In the MeAPOs the metal appears to substitute exclusively for aluminum resulting in a negative (Me 2+
) or neutral (Me 3+
) work charge Like SAPO, the negatively charged MeAPO frameworks possess ion - exchange properties and Bronsted acid sites
The MeAPSO family further extends the structural diversity and compositional variation found in the SAPO and MeAPO molecular sieves These quaternary frameworks have Me, Al, P and Si as framework species [27] The MeAPSO struc-ture types include framework topologies observed in the binary AlPO 4 and ternary (SAPO, MeAPO) compositional systems and the novel structure - 46 with a 0.7 nm pore The structure of - 46 has been determined [34]
Quinary and senary framework compositions have been synthesized containing aluminum, phosphorus and silicon, with additional combinations of divalent (Me) metals In the ElAPO and ElAPSO compositions the additional elements Li, Be,
B, Ga, Ge, As and Ti have been incorporated into the AlPO 4 framework [27] Most of the catalytic interest in the AlPO 4 - based molecular sieves have centered
on the SAPOs which have weak to moderate Bronsted acidity, and two have been commercialized: SAPO - 11 in lube oil dewaxing by Chevron and SAPO - 34 in methanol - to - olefi ns conversion by UOP/Norsk Hydro Spurred on by the success
of TS - 1 in oxidation catalysis, there is renewed interest in Ti, Co, V, Mn and Cr substituted AlPO 4 - based materials For a review of recent developments in the AlPO 4 - based molecular sieves see [35]
Metallosilicate Molecular Sieves A large number of metallosilicate molecular sieves have been reported, particularly in the patent literature Those claimed
Trang 37include silicates containing incorporated tetrahedral iron, boron, chromium, arsenic, gallium, germanium and titanium Most of the earlier work has been reported with structures of the MFI type Others include metallosilicate analogs
of ZSM - 11, - 12, THETA - 1, ZSM - 34 and beta The early metallosilicate molecular sieves are reviewed in detail by Szostak [28] More recently crystalline microporous frameworks have been reported with compositions of beryllosilicate, such as nabe-site [36] , lovdarite [37] and OSB - 1 [38] Zinc silicates with signifi cant framework
Zn include VPI - 7 [39] , VPI - 8 [40] , VPI - 9 [41] and CIT - 6 [42] There has also been
a dramatic increase in new frameworks prepared by incorporating Ge into silicate and aluminosilicate frameworks (see below) Fe and Ga incorporation has so far produced the same structure types as Al incorporation In contrast, framework incorporation of B, Be, Ge and Zn in metallosilicate compositions can yield novel structures diffi cult or impossible to obtain with Al To date only B, Be, Ga, Ge, Fe,
Ti and Zn have been suffi ciently characterized to confi rm structural incorporation The titanium - silicalite composition, TS - 1, has achieved commercialization in selective oxidation processes and iron - silicalite in ethylbenzene synthesis
Other Framework Compositions Crystalline microporous frameworks have been reported with compositions of: beryllophosphate [43] , aluminoborate [44] , alumi-noarsenate [45] , galloarsenate [46] , gallophosphate [47] , antimonosilicate [48] and germanosilicate [49]
Harvey et al [43] reported the synthesis of alkali beryllophosphate molecular
sieves with the RHO, GIS, EDI and ANA structure topologies and a novel ture, BPH Simultaneously, the fi rst beryllophosphate mineral species were
struc-reported: tiptopite [with the cancrinite ( CAN ) topology] by Peacor et al [50] and pahasapaite (with the RHO topology) by Rouse et al [51]
In the late 1980s Bedard et al reported the discovery of microporous metal sulfi des, based on germanium (IV) and Sn (IV) sulfi de frameworks [52] The microporous sulfi des are synthesized hydrothermally in the presence of alkylammonium templating agents The GeS 4 - based compositions include one or more framework - incorporated metals: Mn, Fe, Co, Ni, Cu, Zn, Cd and Ga Over
a dozen novel structures were reported which have no analogs in the microporous
oxides Ozin et al have extended this work to a large number of microporous
sulfi des and selenides [53] It should be noted that the microporous sulfi des and selenides are prone to structure collapse upon calcination to remove the template species
1.2.2.2 The 1990s
The explosion in the discovery of new compositions and structures observed in the 1980s continued through the 1990s Some three dozen or more novel tetrahe-dral structures were synthesized in the 1990s, based on aluminosilicate, silica, metallosilicate and metallophosphate frameworks Three are especially notewor-thy The gallophosphate cloverite ( - CLO) has the fi rst 20 - ring pore (0.4 × 1.32 nm
in diameter) and the lowest observed framework density (number of T - atoms per
1000 Å 3
): 11.1 [54] The cloverite structure contains the D4R and alpha cages
Trang 38remi-niscent of the aluminum - rich zeolite Type A (LTA), combined with the rpa cage found in the aluminophosphate structures It is an interrupted framework struc-ture and thus has somewhat limited thermal stability The siliceous zeolite UTD -1(DON) contains a 14 - ring pore (0.75 × 1.0 nm in diameter) and is the fi rst aluminosilicate with a pore size larger than a 12 - ring [55] CIT - 5 (CFI), a second
14 - R structure with a pure silica composition and a 0.8 nm pore, was reported by
Wagner et al [56]
Stucky et al discovered a generalized method for preparing a large number of
metallo - aluminophosphate and metallo - gallophosphate frameworks containing transition metals The method utilizes amine SDAs and high concentrations of transition metal and phosphate in mixed solvents, typically alcohol and water Two
of the novel structures (UCSB - 6, UCSB - 10) have multi - dimensional 12 - ring nels connecting large cages In addition numerous zeolite structure analogs were also observed [57] Unfortunately, the high framework charge reduces structural stability when template removal is attempted
Gier et al reported zinc and beryllium phosphates and arsenates with the X
(FAU), ABW and SOD structures reminiscent of the early aluminum - rich thetic zeolite chemistry The synthesis of ZnPO 4 - X (FAU) is especially spectacular Crystallization occurs almost instantaneously at 0 ° C [58] Concurrent with ease of synthesis, the structure is thermally unstable
Table 1.4 lists some of the major new structures reported in the 1990s ingly, as organic SDAs tended to dominate discovery of new frameworks, there were no new aluminum - rich synthetic zeolites reported in either the 1980s or the 1990s The new aluminosilicate structures were all high silica or pure silica in composition It awaited the 2000s for new aluminosilicate zeolite materials with low to medium Si/Al to be reported (see below)
Not to be outdone by humankind there were a number of new zeolite minerals discovered in nature during the 1990s The zeolite mineral boggsite ( BOG ) has a novel framework topology with three - dimensional pores combining 10Rs and 12Rs, and it has not yet been reproduced synthetically [61] Tschernichite is an aluminum - rich mineral analog of the synthetic zeolite beta [62] Gottardiite is a new mineral analog of synthetic zeolite Nu - 87 [63] The zeolite mineral terrano-vaite ( TER ) has a novel structure with pentasil chains and a two - dimensional 10R channel [64] Mutinaite is a high - silica zeolite mineral analog of ZSM - 5 with the
Table 1.4 Major new synthetic structures of the 190s
Species Structure type Pore size, nm Ring size Reference
Trang 39highest silica content of all known zeolite minerals (Si/Al = 7.7) [65] The structure
of the zeolite mineral perlialite was reported [66] to have the same topology as that
of the synthetic zeolite L (LTL), some 35 years after the synthesis of zeolite L Tschortnerite ( TSC ) surely is the most remarkable novel zeolite mineral discov-ered [67] Its unique framework topology contains fi ve different cages: D - 6Rs,
D - 8Rs, sodalite cages, truncated cubo - octahedra and a unique 96 - membered cage
Cu - containing clusters are encapsulated within the truncated cubo - octahedra The pore structure is three - dimensional with 8R channels, and the framework density
of 12.2 is among the lowest known for zeolites The framework is alumina - rich with Si/Al = 1, unusual for zeolite minerals
Two major new classes of molecular sieve type materials were reported in the 1990s: (i) microporous frameworks based on mixed octahedral - tetrahedral frameworks in contrast to the previously described tetrahedral frameworks and (ii) mesoporous molecular sieves with pore sizes ranging from about 2 nm to greater than 10 nm
Octahedral – Tetrahedral Frameworks The microporous materials described tofore were all based on tetrahedral frameworks Microporous titanosilicate mate-rials with mixed octahedral – tetrahedral frameworks were reported in the 1990s The framework linkage is through TiO 6 octahedra and SiO 4 tetrahedra Chapman and Roe described the titanosilicate GTS - 1, a structural analog of the mineral pharmacosiderite, with a three - dimensional channel system and 8 - R pores [68] Kuznicki and coworkers reported the synthesis of the titanosilicates ETS - 4 and ETS - 10 [69] Their respective pore sizes are 0.4 and 0.8 nm ETS - 4 is the synthetic analog of the rare titanosilicate mineral zorite The novel structure ETS - 10 con-tains a three - dimensional 12 - R pore system and shows a high degree of disorder (ref [61] ) ETS - 10 has achieved commercial status in adsorption applications
Mesoporous Molecular Sieves A major advance in molecular sieve materials was
reported in 1992 by researchers at Mobil Kresge et al and Beck et al described a
new family of mesoporous silicate and aluminosilicate materials, designated M41S [70] The members of the family include: MCM - 41 (with a one - dimensional hex-agonal arrangement of uniform open channels 0.2 – 10 nm in diameter), a cubic structure MCM - 48 (with a three - dimensional channel system with pore sizes
∼ 0.3 – 10 nm) and a number of lamellar structures The order in the structure is derived from the channel arrangement The silica or aluminosilicate wall outlining the channel is disordered and exhibits properties much like amorphous silica or silica – alumina
Within the same time - frame and independently, Inagaki and coworkers reported
a mesoporous material designated FSM - 16, prepared by hydrothermal treatment
of the layered sodium silicate kanemite, NaHSi 2 O 5 3H 2 O [71] Chen et al
substanti-ated that FSM - 16 and MCM - 41 bear a strong resemblance to each other, both with narrow mesopore distributions and similar physicochemical properties, but with FSM - 16 having higher thermal and hydrothermal stability due to the higher degree
of condensation in the silicate walls [72]
Trang 40Both mesoporous materials are synthesized hydrothermally with a surfactant liquid crystal as the template (see synthesis section below) They exhibit very high surface areas and pore volumes, of the order of 1000 m 2
/g and 1.5 cm 3
/g, respectively
Since this initial work there has been a plethora of literature on mesoporous molecular sieves In addition to the silica and aluminosilicate frameworks similar mesoporous structures of metal oxides now include the oxides of Fe, Ti, V, Sb, Zr,
Mn, W and others Templates have been expanded to include nonionic, neutral surfactants and block copolymers Pore sizes have broadened to the macroscopic size, in excess of 40 nm in diameter A recent detailed review of the mesoporous molecular sieves is given in ref [73] Vartuli and Degnan have reported a Mobil M41S mesoporous - based catalyst in commercial use, but to date the application has not been publicly identifi ed [74]
In a tour de force of detective work, Di Renzo et al uncovered an obscure United States patent fi led in 1969 and issued in 1971 to Chiola et al , describing a low -
density silica Reproduction of that patent resulted in a product having all of the properties of MCM - 41 [75]
1.2.2.3 The New Millennium
Recent developments in zeolite synthesis and new materials include: (i) the use
of combinatorial methodologies, microwave heating, multiple templates or SDAs and concentrated fl uoride media in synthesis, (ii) synthesis using the charge density mismatch ( CDM ) concept, (iii) synthesis in ionothermal media, (iv) syn-thesis with complex “ designer ” templates or SDAs, (v) synthesis of nanozeolites, (vi) zeolite membranes and thin fi lms (vii) and germanosilicate zeolites [76] Several of these developments are discussed here
A major return to the early lower Si/Al aluminosilicate zeolites of Milton and Breck was undertaken in the early part of this century A novel synthetic strategy denominated the charge density mismatch ( CDM ) technique was pioneered by Lewis and coworkers at UOP The method features the initial formation of a CDM aluminosilicate reaction mixture characterized by the mismatch between the charge density on the organoammonium structure - directing agent ( SDA ) and the charge density on the aluminosilicate network that is expected to form For example, with a large SDA (low charge density) in an aluminosilicate reaction mixture with a low Si/Al ratio (high charge density), the crystallization of a zeolite
is diffi cult or impossible, even with variation of hydroxide levels and crystallization temperature Crystallization can be induced by the controlled addition of supple-mental SDAs that have charge densities that are more suitably matched to that of the desired low ratio aluminosilicate network (e.g., alkali metal SDAs) Advantages
of this approach are greater control over the crystallization process and reliable cooperation of multiple templates The approach is demonstrated in the TEA - TMA template system, in which the new zeolites UZM - 4, UZM - 5 and UZM - 9 are syn-thesized with Si/Al of 2 – 5 [77] The UZM family contains structures related to previously known topologies, such as UZM - 4 (BPH) [78] , UZM - 9 (LTA) [78] and UZM - 12 (ERI) [79] , as well as new framework types such as UZM - 5 (UFI) [80]