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

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Solid Acid-Catalyzed Dehydration of Sugars to 5-Hydroxymethylfurfural, Subsequent Aldol Condensation and Hydrogenation Over Bifunctional Spinel Oxides 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. ii “Auch eine Reise von tausend Meilen beginnt mit einem einzigen Schritt.“ Lao-Tse iii 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. iv 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! v 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 MgAl2O4, ZnAl2O4 and CoAl2O4 were synthesized and characterized. Temperature-programmed CO2 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/MgAl2O4 enabled selective formation of previously unreleased product. Noteworthy, transfer hydrogenation was successfully employed utilizing Cu/MgAl2O4 and isopropanol as a hydrogen donor. vi To My Family vii 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 viii 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
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