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Signature Redacted Department of Materials Science and Engineering 12 July 31, 2015 Acid-Base Catalysts for Polycondensation of Acetaldehyde in Flow by ARCHVES Marcella R. Lusardi OF TECHNOLOGY B.S. Chemical Engineering OCT 28 2015 Columbia University, 2012 M.S. Earth Resources Engineering LIBRARIES Columbia University, 2013 SUBMITTED TO THE DEPARTMENT OF MATERIALS SCIENCE AND ENGINEERING IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN MATERIALS SCIENCE AND ENGINEERING AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY SEPTEMBER 2015 C 2015 Massachusetts Institute of Technology. All rights reserved. Signature of Autho r: Signature redacted Department of Materials Science and Engineering 12 July 31, 2015 Certified by: Signature redacted____ Klavs F. Jensen Warren K. Lewis Professor of Chemical Engineering and Professor of Materials Science and Engineering Thesis Supervisor I I / ~ Accepted by: Signature redacted Donald Sadoway Chair, epartmental Committee on Graduate Students Acid-Base Catalysts for Polycondensation of Acetaldehyde in Flow by Marcella R. Lusardi Submitted to the Department of Materials Science and Engineering on July 31, 2015 in Partial Fulfillment of the Requirements for the Degree of Master of Science in Materials Science and Engineering ABSTRACT Acetaldehyde is used as a bio-oil model compound in a polycondensation reaction over two acid- base catalysts, pelletized Evonik P25 TiO 2 and an activated hydrotalcite-like compound (HTlc), to produce high molecular weight molecules in the transportation fuel range. The catalytic performance of these materials is evaluated in a gas phase, atmospheric flow system with a packed bed microreactor designed to mimic process conditions in one step of the overall bio-oil upgrading scheme. The HTlc is activated through calcination at 500 'C followed by rehydration in decarbonated H 20, generating the active acid-base hydroxyl pairs. Materials are characterized through XRD, low temperature N2 adsorption-desorption isotherm experiments, TGA, and XPS. In initial experiments, high conversions are achieved but all converted acetaldehyde forms carbonaceous deposits on the catalyst surfaces over a range of temperatures and residence times. When the catalyst bed is reduced by 80%, decreasing both residence time and vapor-solid contact area, high conversions are maintained and the production of liquid phase condensation products is observed on the order of seconds. While yields are low, it is promising that tuning the packed bed results in decreased deposits and generation of liquid phase products. Further adjustments of reaction parameters and catalyst activity are of interest as future work, including shorter residence times and bed lengths, co-feeding a reaction inhibitor, and specific catalyst syntheses for control over active sites. Thesis Supervisor: Klavs F. Jensen Title: Warren K. Lewis Professor of Chemical Engineering and Professor of Materials Science and Engineering 3 4 Acknowledgements I first thank my thesis advisor Klavs Jensen, for providing me with a project I truly enjoy, being a terrific bouncing board for ideas, and helping me to grow immensely as a researcher. I really appreciate his thoughtful guidance and support, as well as his ability to connect smaller project components with the larger picture. I am grateful for all of my labmates in the Jensen group, who are always available for helpful discussions in the lab and make the work environment a happy and warm place to be. I would like to thank my parents, my sisters Arielle and Bella, and my grandparents for being a constant source of encouragement, support, and love. Lastly I would like to thank Ravi Netravali, my best friend and biggest inspiration. 5 6 Contents 1 Introduction...............................................................................................................................13 1.1 M otivation............................................................................................................................13 1.2 Overview of biofuels............................................................................................................14 1.3 Upgrading bio-oil into biofuels........................................................................................ 16 1.3.1 Bio-oil deoxygenation........................................................................................... 16 1.3.2 Carbon-carbon bond synthesis............................................................................... 17 2 The A ldol condensation reaction........................................................................................ 21 2.1 Reaction m echanism s and catalysts............................................................................... 21 2.1.1 Base-catalyzed mechanism .................................................................................... 21 2.1.2 A cid-catalyzed mechanism .................................................................................... 23 2.1.3 Cooperative acid-base catalyzed m echanism ...................................................... 24 2.2 Related w ork......................................................................................................................25 2.2.1 Base-only and acid-only catalysts........................................................................ 25 2.2.2 Bifunctional catalysts........................................................................................... 26 2.2.3 Lim itations of existing work................................................................................. 29 7 3 Bifunctional acid-base materials for polycondensation of acetaldehyde.........................31 3.1 M aterials in literature...................................................................................................... 31 3.2 Active sites and m echanism s........................................................................................ 33 3.2.1 P25 TiO 2 ................................................................................................................... 33 3.2.2 Hydrotalcite-like com pounds................................................................................ 36 3.3 Polycondensation chem istry........................................................................................... 39 4 Experim ental m ethods and m aterials characterization ................................................... 41 4.1 Developm ent of the flow system .................................................................................... 41 4.1.1 System goals ............................................................................................................. 41 4.1.2 System design ........................................................................................................ 43 4.2 M aterials preparation and characterization.................................................................... 46 4.2.1 Pelletized P25 TiO 2 ................................................... .................................... .. .... 46 4.2.2 Activated hydrotalcite-like com pound.................................................................. 48 4.3 Therm al Stability ............................................................................................................... 54 5 Performance of acid-base catalysts in acetaldehyde polycondensation in flow .............. 57 5.1 Tem perature experim ents ............................................................................................... 57 5.2 Residence tim e experim ents .......................................................................................... 60 5.3 Shortened bed experim ents........................................................................................... 63 6 Conclusion ................................................................................................................................. 69 Bibliography .............................................................................................................................. 71 8 List of Figures 1-1 Percent (by weight) of different families of bio-oil compounds ................................... 15 1-2 Elemental composition of crude oil compared to a bio-oil produced from fast-pyrolysis of sw itch g rass.........................................................................................................................16 1-3 Schem atic of the aldol condensation reaction............................................................... 18 1-4 Scope of aldol condensation in the upgrading of low molecular weight ketones and ald eh y d es ........................................................................................................................... 19 2-1 Base-catalyzed mechanism for aldol condensation of a generic carbonyl compound ...... 22 2-2 Acid-catalyzed mechanism for aldol condensation of a generic carbonyl compound ...... 23 2-3 Proposed acid-base-catalyzed mechanism for aldol condensation of a generic carbonyl comp ou n d ........................................................................................................................... 24 2-4 Mechanism for rehydrated LDH with bifunctional hydroxyl group pairs.....................27 3-1 Proposed mechanism of acetaldehyde condensation on the surface of P25 TiO 2 ... ... 35 3-2 Anions in interlayer galleries maintain charge neutrality of the M"'-substituted M"- hydroxide in a H Tlc ...................................................................................................... 37 3-3 Proposed acid-base
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