Solid Acid-Catalyzed Dehydration of Sugars to 5-Hydroxymethylfurfural, subsequent Aldol ...

185 Pages·2014·9.15 MB·English

Solid Acid-Catalyzed Dehydration of Sugars to
5-Hydroxymethylfurfural, subsequent Aldol Condensation
and Hydrogenation over Bifunctional Spinel Oxides

Von der Fakultät für Mathematik, Informatik und Naturwissenschaften der RWTH Aachen
University zur Erlangung des akademischen Grades einer Doktorin der
Naturwissenschaften genehmigte Dissertation

vorgelegt von
Diplom-Chemikerin
Kristina Pupovac
aus Zadar

Referent: Prof. Dr. Regina Palkovits
Korreferent: Prof. Dr. Ferdi Schüth
Tag der mündlicher Prüfung: 13. Dezember 2013

Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbar.
Die Vorliegende Arbeit wurde am Max-Planck-Institut fur Kohlenforschung in Mülheim
an der Ruhr unter der Leitung von Frau Prof. Dr. Regina Palkovits und Herrn Prof. Dr.
Ferdi Schüth angefertigt.
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“Auch eine Reise von tausend Meilen
beginnt mit einem einzigen Schritt.“
Lao-Tse

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Acknowledgements

First and foremost, I would like to thank my advisor, Prof. Dr. Regina Palkovits, for her
support, guidance and confidence in my work. I would like to express my sincere gratitude
and appreciation for her inspiring discussions, valuable suggestions and encouragement
throughout my research. Moreover, I would like to thank her for her mentorship that
broadened my vision and helped me to develop my own perspective.
I am also heartily thankful to Prof. Dr. Ferdi Schüth for giving me the opportunity to work
in his group. The diversity of research in the Schüth’s Lab attracts many exceptional
graduate students and postdocs, and it has been an honor to work alongside such incredible
individuals.
I wish to express my appreciation to Dr. Claudia Weidenthaler for her precious help and
discussions as well as for the excellent skills in being a rabbit.
I would like to thank Dr. Wolfgang Schmidt for greatly enlarging my knowledge in
nitrogen adsorption.
I am deeply thankful to HPLC, TEM, GC, MS and NMR departments for the numerous
measurements. Without Heike Hinrichs, Alfred Deege, Bernd Spliethoff, Dr.Bodo
Zibrowius, Manfred Scheppat, Marion Blumenthal, Werner Joppek, Frank Kohler, Sylvia
Ruthe and Jutta Rosentreter, this work would not have been possible.
I would like to thank Karl-Josef Vaeßen from the RWTH Aachen University for his
valuable contribution to this work with the TPD measurements.
I thank Dr. Marcus Rose for proofreading this thesis.
I would also like to thank the IT department, and especially Marcus Hermes, for great
support.
My sincere appreciation goes to Angelika Rathofer, Annette Krappweis and Kirsten
Kalischer for their support and engagement.
Special thanks go to Kameh and Murhat for their sincere friendship for all these years,
enthusiastic help, inspiring discussions and advices. The same thank also go to Valeria,
Felix and Caro N. for the nice time and wonderful theater evenings.
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I would like to thank Hebert, Heitor, Nadine, Sarah, Niklas, Daniel, Paola, Jakob, Mats,
Mano, JP, Jan, Tobi G., Tobi Z., Stefano, Wojciech, Julia, Xingyu, Ivy, and all the other
colleagues from the AK Schüth and AK Rinaldi for the unforgettable time and the nice
activities inside and outside the institute.
I gratefully acknowledge the founding by the Cluster of Excellence “Tailor-Made Fuels
from Biomass” and the basic founding of the MPG.
Finally, and most importantly, I would deeply like to thank my beloved parents and sister
as well as Nada Janjic and Ljubica Sinkovic for their lovely support and patience in all
these years and for encouraging me to face the difficulty. You are the source of my
inspiration and happiness. Without you all this would never have been possible. Volim vas
puno!

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Abstract
The growing demand of fossil fuel resources comes at a time of diminishing reserves of these
non-renewable resources. To sustain modern civilization an alternative resource must be found
to continue the supply of energy and chemicals. In addition, implementation of an alternative
feedstock implies the development of new catalyst systems and processes.
Being renewable, biomass is the only sustainable source of energy and organic carbon.
Utilizing straightforward chemical methods, biomass can be transformed into
5-hydroxymethylfurfural (HMF), a platform chemical that can serve as an important
intermediate to biofuels and commodity chemicals. This thesis describes the reaction systems
for the selective conversion of carbohydrates to HMF and its further upgrading to potential
biofuels via aldol condensation and subsequent hydrogenation reactions.
Dehydration of sugars to HMF was conducted in a two-phase solvent system based on
environmentally benign solvents. Thereby, the employment of novel acidic resin catalysts was
demonstrated. Varying the physico-chemical properties of the catalysts makes it possible to
identify factors governing the dehydration reaction. Accordingly, a high density of accessible
acid sites and low cross-linker content facilitated the highest selectivity towards the desired
HMF product. Recycling experiments were performed to prove the stability of polymeric
materials as solid acid catalyst. With the aim to produce a variety of potential biofuels,
upgrading of HMF via a C-C bond forming reaction was chosen. Here, liquid-phase aldol
condensation of HMF and acetone catalyzed over solid bases was investigated. Thereby, Mg-
Al hydrotalcites with different Mg/Al molar ratios and spinel oxides such as MgAl O ,
2 4
ZnAl O and CoAl O were synthesized and characterized. Temperature-programmed CO
2 4 2 4 2
desorption measurements verified the Brønsted OH- groups as the active basic sites.
Moreover, in the case of Mg-Al hydrotalcites calcination and subsequent rehydration were
required to generate suitable active sites. The larger surface area of mesoporous spinels
provided more accessible active sites leading to higher catalytic activity. To investigate the
reusability of the materials as solid base catalyst recycling tests were performed.
Furthermore, with the aim to design a multifunctional catalyst and with respect to process
integration, metal was introduced into a mesoporous spinel. Noble as well as non-noble
metal loaded spinel oxides showed high activity in both aldol condensation and subsequent
hydrogenation into potential biofuels. Thereby, Cu/MgAl O enabled selective formation
2 4
of previously unreleased product. Noteworthy, transfer hydrogenation was successfully
employed utilizing Cu/MgAl O and isopropanol as a hydrogen donor.
2 4
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To My Family

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Content
1. Introduction & Motivation.................................................................................1
2. Solid acid-catalyzed dehydration of carbohydrates into HMF.....................11
2.1. State of the art......................................................................................................11
2.1.1. Carbohydrates as renewable chemical raw materials..................................11
2.1.2. HMF- a versatile building block..................................................................16
2.1.3. Synthesis of HMF........................................................................................17
2.1.4. Catalysts for the synthesis of HMF.............................................................19
2.1.5. Types of solvents for conversion of carbohydrates to HMF.......................21
2.2. Scope of this chapter............................................................................................25
2.3. Dehydration of fructose and fructose-containing materials into HMF................25
2.3.1. Two-phase solvent system for the dehydration of fructose to HMF...........25
2.3.2. Choice of the extracting solvent..................................................................26
2.3.3. Effect of the reaction temperature on the dehydration reaction..................28
2.3.4. Reaction mechanism and kinetic analysis...................................................30
2.3.5. Effect of the initial fructose concentration..................................................35
2.3.6. Screening of the catalysts............................................................................36
2.3.7. Dehydration of fructose to HMF catalyzed over sP-STY-DVB catalysts...39
2.3.8. Influence of the acid site density on the dehydration of fructose................40
2.3.9. Acid site density vs. BET s.a.......................................................................43
2.3.10. Influence of the DVB content......................................................................45
2.3.11. Dehydration of alternative feedstocks.........................................................47
2.3.12. Recycling of sP-STY-DVB catalysts..........................................................51
2.4. Conclusions.........................................................................................................52
3. Aldol condensation rection between HMF and acetone................................54
3.1. State of the art......................................................................................................54
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3.1.1. Aldol condensation reaction........................................................................54
3.1.2. Mechanism of aldol condensation reaction.................................................57
3.1.3. Solid base catalysts......................................................................................59
3.1.4. Catalysis over solid base catalysts...............................................................62
3.2. Main reaction investigated in this chapter: Aldol condensation between HMF and
acetone................................................................................................................66
3.3. Scope of this chapter............................................................................................68
3.4. Aldol condensation between HMF and acetone over Mg-Al hydrotalcites........68
3.4.1. Hydrotalcites (HTs).....................................................................................68
3.4.2. Characterization of the Mg-Al hydrotalcites...............................................71
3.4.3. Catalytic performance of Mg-Al hydrotalcites............................................77
3.4.4. Generating the Brønsted OH- groups on the surface of calcined hydrotalcite
.....................................................................................................................86
3.4.5. Influence of the water content of calcined/rehydrated hydrotalcite on its
activity.........................................................................................................92
3.4.6. Influence of the temperature on the aldol condensation reaction between
HMF and acetone........................................................................................95
3.4.7. Recycling of rehydrated HT catalysts.........................................................96
3.5. Aldol condensation between HMF and acetone over spinel oxide catalysts.......97
3.5.1. Spinel oxides...............................................................................................97
3.5.2. Characterisation of spinel catalysts...........................................................100
3.5.3. Catalytic performance of spinel catalysts..................................................102
3.5.4. Correlation between catalytic activity and basic properties of the spinel
catalysts.....................................................................................................104
3.5.5. Effect of the amount of spinel catalyst on the reaction.............................106
3.5.6. Effect of the reaction temperature.............................................................107
3.5.7. Effect of the specific surface area..............................................................108
3.5.8. Recycling of spinel catalyst.......................................................................110
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3.5.9. Determination of the reaction order and proposed reaction mechanism for
the aldol condensation reaction between HMF and acetone.....................112
3.6. Conclusions.......................................................................................................116
4. Hydrogenation of HMF aldol product..........................................................117
4.1. State of the art....................................................................................................117
4.1.1. Catalysts for the hydrogenation reaction...................................................117
4.1.2. Supported metal catalysts via impregnation..............................................118
4.1.3. Mechanism of hydrogenation....................................................................120
4.1.4. Importance of hydrogenation....................................................................121
4.1.5. Hydrogenation of biomass-derived platform chemicals............................123
4.2. Scope of this chapter..........................................................................................125
4.2.1. Hydrogenation of HMF aldol product over commercial catalysts............126
4.2.2. Hydrogenation of (1) over Pd, Pt and Ru supported on spinels................128
4.2.3. Investigation of the course of the hydrogenation reaction........................132
4.2.4. Recycling of Ru/CoAl O ..........................................................................133
2 4
4.2.5. Hydrogenation of (1) over noble metal free catalysts...............................134
4.2.6. Transfer hydrogenation of (1) over Cu/MgAl O ......................................139
2 4
4.2.7. Recycling of Cu/MgAl O .........................................................................141
2 4
4.3. Conclusions.......................................................................................................142
5. Final remarks..................................................................................................144
6. Experimental...................................................................................................146
6.1. Materials preparation.........................................................................................146
6.1.1. Preparation of mesostructured materials...................................................146
6.1.1.1. Preparation of SBA-15 mesoporous silica........................................146
6.1.1.2. Preparation of supported SiWA and PWA on SBA-15.....................146
6.1.1.3. Preparation of propylsulfonic acid-functionalized SBA-15 (SBA-15-
(CH ) SO H)..........................................................................................................146
2 3 3
6.1.1.4. Preparation of 2-ethylphenylsulfonic acid-functionalized SBA-15
(SBA-15-(CH ) PhSO H)......................................................................................147
2 2 3
x