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Reaction Mechanism and Deactivation Pathways in Zeolite ... 2.3.2.5 Metal cations on ion-exchange...

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  • 1

    Institut für Technische Chemie

    der Technischen Universität München

    Lehrstuhl II

    Reaction Mechanism and Deactivation Pathways in Zeolite

    catalyzed Isobutane/2-Butene Alkylation

    Andreas Feller

    Vollständiger Abdruck der von der Fakultät für Chemie der Technischen Universität

    München zur Erlangung des akademischen Grades eines

    Doktors der Naturwissenschaften

    genehmigten Dissertation.

    Vorsitzender: Univ.-Prof. (Komm.) Dr. Walter Nitsch, em.

    Prüfer der Dissertation:

    1. Univ.-Prof. Dr. Johannes A. Lercher

    2. Univ.-Prof. Dr. Thomas Bein, Ludwig-Maximilians-

    Universität München

    3. Univ.-Prof. Dr. Klaus Köhler

    Die Dissertation wurde am 27.11.2002 bei der Technischen Universität München eingereicht

    und durch die Fakultät für Chemie am 17.01.2003 angenommen.

  • i

    Thank you!

    The experimental work of this dissertation was carried out in the time span from January 99

    until July 2002 at the Institut für Technische Chemie, Lehrstuhl II under the supervision of

    Prof. Johannes A. Lercher.

    I am very much indebted to Johannes for trusting me with this important project, for making

    things possible that otherwise would have been impossible, for giving us the chance to meet a

    lot of scientists from all over the world, and for fruitful discussions (scientific and political).

    I learned a lot in this time; to not blame circumstances being not the least of it.

    I am grateful for the funding by Süd-Chemie AG via the EUROFUEL project, and also for

    preparing and supplying of catalyst samples by Marcus Breuninger.

    I’d like to say thank you to the Twente-crew, who gave me a warm welcome, especially

    Gautam, who introduced me into the secrets (and “Voodoo”) of alkylation.

    Thank you to Cristina and Hilton, my friends of the early München days; it was great fun to

    share the office with you!

    Thanks to Stefan for performing the diploma thesis in a tough period of the project.

    Thank you Alex and Iker, you helped me a lot and you introduced Spanish/Colombian

    rhythm into the alkylation group.

    Thank you to all my colleagues, Bavarian, German and from the “rest of the world”. It has

    been a great experience to meet people from all over the world. I enjoyed being with you.

    Thank you to the technical crew, Martin, Andreas and Xaver; without you, no setup in this

    group would work!

    Danke an Annette, Denise und Agnes für das Aushalten meiner Launen während der Höhen

    und Tiefen dieser Zeit.

    Danke Marzena für Dein Da sein.

  • ii

    1 General introduction 1 1.1 Scope of this thesis 3

    1.2 References 5

    2 Chapter 2 6

    2.1 Introduction 7

    2.2 Alkylation mechanism 8

    2.2.1 Overall product distribution 9

    2.2.2 Initiation steps 11

    2.2.3 Alkene addition and isomerization 13

    2.2.4 Hydride transfer 16

    2.2.5 Oligomerization and cracking 21

    2.2.6 Self-alkylation 24

    2.2.7 Product and acid degradation 25

    2.2.8 Pathways to allylic and cyclic compounds 26

    2.2.9 Summary 27

    2.3 Physico-chemical phenomena influencing the reaction 28

    2.3.1 Properties of liquid acid alkylation catalysts 28

    2.3.2 Properties of zeolitic alkylation catalysts 30

    2.3.2.1 Adsorption and diffusion of hydrocarbons 30

    2.3.2.2 Brønsted acid sites 32

    2.3.2.3 Lewis acid sites / extra-framework aluminum 34

    2.3.2.4 Silicon/aluminum ratio 36

    2.3.2.5 Metal cations on ion-exchange positions 38

    2.3.2.6 Structure types of zeolites 39

    2.3.3 Other solid acids 42

    2.3.3.1 Sulfated zirconia and related materials 42

    2.3.3.2 Heteropolyacids 43

    2.3.3.3 Acidic organic polymers 44

    2.3.3.4 Supported metal halides 45

    2.3.4 The influence of process conditions 46

  • iii

    2.3.4.1 Reaction temperature 47

    2.3.4.2 Paraffin/olefin ratio and olefin space velocity 50

    2.3.4.3 Olefin feed composition 51

    2.4 Industrial processes and process developments 53

    2.4.1 Liquid acid catalyzed processes 53

    2.4.1.1 Sulfuric acid catalyzed processes 54

    2.4.1.2 Hydrofluoric catalyzed processes 56

    2.4.2 Solid acid catalyzed processes 58

    2.4.2.1 UOP Alkylene™ Process 60

    2.4.2.2 Akzo Nobel/ABB Lummus AlkyClean™ process 61

    2.4.2.3 LURGI EUROFUEL® process 62

    2.4.2.4 Haldor Topsøe FBA™ process 63

    2.5 Conclusions 64

    2.6 References 64

    3 Chapter 3 75

    3.1 Introduction 76

    3.2 Experimental 77

    3.2.1 Material synthesis 77

    3.2.2 Catalyst characterization 78

    3.2.3 Catalytic experiments 79

    3.3 Results 80

    3.3.1 Physicochemical characterization 80

    3.3.2 Activity and selectivity in alkylation of iso-butane with n-butene 84

    3.3.3 Influence of the acidity 88

    3.3.4 Influence of the reaction temperature 91

    3.3.5 Influence of olefin space velocity and paraffin/olefin ratio 92

    3.3.6 Reactions with partly deactivated catalyst 94

    3.4 Discussion 96

    3.4.1 Reactions influencing the product distribution 96

    3.4.2 Influence of Na+ exchange level 98

    3.4.3 Reactions leading to heavy-end products 98

  • iv

    3.4.4 “Self-alkylation” and its importance for alkylation 99

    3.4.5 Influence of the reaction temperature 102

    3.4.6 Influence of the olefin space velocity 104

    3.5 Conclusions 105

    3.6 Acknowledgments 106

    3.7 References 106

    4 Chapter 4 109

    4.1 Introduction 110

    4.2 Experimental 111

    4.2.1 Catalyst preparation 111

    4.2.2 Catalyst characterization 112

    4.2.3 Coke characterization 112

    4.2.4 Catalytic experiments 114

    4.3 Results and interpretation 115

    4.3.1 Physicochemical characterization 115

    4.3.2 Alkylation experiments 115

    4.3.3 Characterization of the deactivated catalysts 116

    4.3.4 Characterization of the recovered deposits 122

    4.3.5 MALDI-TOF mass spectrometry 129

    4.4 Discussion 135

    4.4.1 Chemical nature of the deposits 135

    4.4.2 Routes of formation of coke compounds 136

    4.4.3 Interaction of the coke molecules with the acid sites 138

    4.5 Conclusions 140

    4.6 Acknowledgments 141

    4.7 References 141

    5 General conclusions 144

    6 Summary 146

    7 Zusammenfassung 146

  • 1

    1 General introduction

    Alkylation of iso-butane with C3-C5 alkenes in the presence of strong acids leads to the

    formation of a complex mixture of branched alkanes, called alkylate, which is an excellent

    blending component for gasoline. Alkylate has a high octane number, low Reid vapor

    pressure (RVP) and it is free of aromatics, alkenes and contains nearly no sulfur. The clean

    air regulations in the E.U. and the U.S.A., concerning the contents of alkenes, sulfur and

    aromatics, particularly benzene, in the gasoline will become increasingly strict. Table 1-1

    gives a summary about important reformulated gasoline (RFG) specifications. Regarding

    these specifications, it is obvious that alkylate is an ideal component of RFG.

    Table 1-1: Development of RFG specifications in the European Union.

    1999 2000 2005

    Sulfur, max. ppm wt. 500 150 50 (10)*

    Aromatics, max. vol.% No spec. 42 35

    Benzene, max. vol.% 5 1 1

    Alkenes, max. vol.% No spec. 18 18

    Octane, RON min 95/98 95/98 95/98

    RVP, max. kPa 80 60 60 * Potentially to be available in 2005, possibly mandatory in 2007/2008

    Refiners have the choice of blending different product streams to meet the specifications.

    This is shown exemplary for sulfur in Table 1-2. Concerning the sulfur contents, reformate

    would be an ideal blendstock, however, it contains mainly aromatic compounds; therefore its

    usage cannot be considerably increased. Methyl-tertiary-butyl ether (MTBE), which is a high

    octane oxygenate, has been found to cause drinking water to be malodorous already in ppb

    concentrations (leaking out from underground storage tanks into the ground water). As a

    consequence, it will be phased out in several countries (1). Alcohols such as ethanol that

    could conceivably replace the ethers as oxygenate source suffer from a very high blending

    vapor pressure when mixed into gasoline, thus, limiting their usefulness. The only way to

  • 2

    clean-burning, high-octane gasoline with no limitations imposed by the specifications is to

    utilize branched alkanes.

    Table 1-2: Sulfur sources in gasoline.

    Blending component Sulfur, ppm Typical % of Gasoline % Contribution to sulfur FCC Gasoline 800 30-50 90

    LSR Gasoline 150 3 5

    Alkylate 16 10 2

    MTBE 20 5 1

    Butanes 10 5

  • 3

    regeneration unit is displayed in Figure 1-1.

    Figure 1-1: Process units in a modern refinery.

    While the products from alkylation are perfect gasoline components, the catalysts are far

    from being ideal. The only catalysts industrially employed are sulfuric and anhydrous

    hydrofluoric a

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