Synthesis of Amine-Modified Aerogel Sorbents and Metal- Organic Framework-5 (MOF-5) Membranes for Carbon Dioxide Separation by Teresa M. Rosa A Thesis Presented in Partial Fulfillment of the Requirements for the Degree Master of Science Approved October 2010 by the Graduate Supervisory Committee: Jerry Y.S. Lin, Co-Chair Robert Pfeffer, Co-Chair David Nielsen Lenore Dai ARIZONA STATE UNIVERSITY December 2010 ABSTRACT Amine-modified solid sorbents and membrane separation are promising technologies for separation and capture of carbon dioxide (CO ) from combustion 2 flue gas. Amine absorption processes are mature, but still have room for improvement. This work focused on the synthesis of amine-modified aerogels and metal-organic framework-5 (MOF-5) membranes for CO separation. 2 A series of solid sorbents were synthesized by functionalizing amines on the surface of silica aerogels. This was done by three coating methods: physical adsorption, magnetically assisted impact coating (MAIC) and atomic layer deposition (ALD). CO adsorption capacity of the sorbents was measured at room 2 temperature in a Cahn microbalance. The sorbents synthesized by physical adsorption show the largest CO adsorption capacity (1.43-1.63 mmol CO /g). An 2 2 additional sorbent synthesized by ALD on hydrophilic aerogels at atmospheric pressures shows an adsorption capacity of 1.23 mmol CO /g. Studies on one 2 amine-modified sorbent show that the powder is of agglomerate bubbling fluidization (ABF) type. The powder is difficult to fluidize and has limited bed expansion. The ultimate goal is to configure the amine modified sorbents in a micro-jet assisted gas fluidized bed to conduct adsorption studies. MOF-5 membranes were synthesized on α-alumina supports by two methods: in situ synthesis and secondary growth synthesis. Characterization by scanning electron microscope (SEM) imaging and X-ray diffraction (XRD) show that the membranes prepared by both methods have a thickness of 14-16 µm, and a MOF-5 crystal size of 15-25 µm with no apparent orientation. Single gas i permeation results indicate that the gas transport through both membranes is determined by a combination of Knudsen diffusion and viscous flow. The contribution of viscous flow indicates that the membranes have defects. ii ACKNOWLEDGEMENTS I would like to thank my advisors, Dr. Jerry Lin and Dr. Robert Pfeffer for their understanding, guidance and thoughtful advice during my journey through the project. I would also want to thank Dr. David Nielsen and Dr. Lenore Dai for serving on my committee. I would also like to thank my current and former labmates with whom I had the pleasure to work: Carrie, Jay, Matt, Tyler, Nick, Shriya, Haibing, Zhenxia, Chao, Xiaoli, Bo, Peter, Ding, Taylor and Stephanie. Thanks for your help, support and friendship all these years and thanks for providing a stimulating and fun environment in which to learn and grow. Carrie, I truly appreciate all your help and suggestions during the writing process of this document. Special thanks go to Fred Peña for his invaluable help and assistance that made possible the completion of this project. Thanks for all your numerous suggestions, and for helping with all the project issues. Thanks to Marty and David, from the machine shop, for making such a beautiful job with the columns. Thanks to the CSSS staff for their tremendous help with their equipment. I cannot finish without saying how grateful I am to my family. They have always supported and encouraged me to do the best in all areas of my life. They never let me down, and were a real support throughout all these years in school. Finally, I want to thank my soon-to-be husband, on whose constant encouragement and love I have relied throughout my time in graduate school. Teresa iii TABLE OF CONTENTS Page LIST OF TABLES ................................................................................................ vii LIST OF FIGURES ............................................................................................. viii CHAPTER 1 BACKGROUND .............................................................................................1 1.1 Introduction ...............................................................................................1 1.2 Amine Immobilized Solid Sorbents for CO Sorption .............................2 2 1.2.1 Recent work. ....................................................................................3 1.2.2 Silica aerogels. .................................................................................4 1.3 Reactions between amines and CO . ........................................................6 2 1.4 Gas Fluidization. .......................................................................................8 1.4.1 General characteristics of fluidized beds. ........................................8 1.4.2 Assisted fluidization by a micro-jet. ..............................................10 1.4.3 Hydrodynamic characteristics. .......................................................10 1.5 Membrane separation ..............................................................................12 1.5.1 Metal-organic framework (MOF-5). ..............................................12 1.5.2 Synthesis of MOF-5 membranes. ..................................................14 1.5.2.1 In situ hydrothermal synthesis method. .............................14 1.5.2.2 Secondary growth hydrothermal synthesis method. ..........15 1.6 Research Objectives and Structure of Thesis..........................................16 iv CHAPTER Page 2 AMINE-FUNCTIONALIZED AEROGELS.................................................19 2.1 Introduction .............................................................................................19 2.1.1 Magnetically assisted impact coating (MAIC). .............................19 2.1.2 Atomic layer deposition (ALD). ....................................................21 2.2 Experimental ...........................................................................................22 2.2.1 Synthesis of amine-functionalized aerogels...................................22 2.2.1.1 Physical adsorption of amines on aerogels. .......................23 2.2.1.2 Amine coated aerogels by MAIC batch process. ...............24 2.2.1.3 Amine coated aerogels by ALD. ........................................25 2.2.2 TGA-DSC measurements. .............................................................25 2.2.3 Carbon dioxide adsorption using Cahn microbalance. ..................26 2.2.4 Fluidization experiments with aerogels. ........................................27 2.3 Results and Discussion ...........................................................................29 2.3.1 TGA-DSC measurements. .............................................................29 2.3.2 CO adsorption measurements in microbalance. ...........................31 2 2.3.2.1 Physical adsorption samples. .............................................31 2.3.2.2 MAIC samples. ..................................................................34 2.3.2.3 ALD samples. ....................................................................40 2.3.3 Fluidization of aerogels..................................................................48 2.4 Conclusions .............................................................................................52 v CHAPTER Page 3 METAL-ORGANIC FRAMEWORK-5 MEMBRANES..............................54 3.1 Introduction .............................................................................................54 3.2 Experimental ...........................................................................................54 3.2.1 Synthesis of MOF-5 membranes. ..................................................54 3.2.2 Membrane characterization. ...........................................................57 3.3 Results and Discussion ...........................................................................60 3.3.1 MOF-5 microstructure. ..................................................................60 3.3.2 XRD and SEM of MOF-5 membranes. .........................................63 3.3.3 Gas permeation of MOF-5 membranes..........................................66 3.4 Conclusions .............................................................................................70 4 SUMMARY AND RECOMMENDATIONS................................................71 4.1 Summary .................................................................................................71 4.2 Recommendation ....................................................................................72 REFERENCES ......................................................................................................74 APPENDIX A EXPERIMENTAL PROCEDURES FOR MOF-5 MEMBRANES .............79 B EXPERIMENTAL PROCEDURES TO MODIFY AEROGELS ................84 vi LIST OF TABLES TABLE Page 1.1 Physical Characteristics of Cabot Nanogel Fine Particles .................................6 1.2 MOF-5 Properties ............................................................................................13 2.1 Physical/Chemical Characteristics of Amine Compounds Selected for Modification of Aerogel Surface .....................................................................23 2.2 CO2 uptake and experimental conditions of sorbents prepared by physical adsorption ..........................................................................................32 2.3 CO2 upta and experimental conditions of sorbents prepared by MAIC process ..................................................................................................35 2.4 CO2 upta and experimental conditions of sorbents prepared by ALD process ...............................................................................................41 2.5 Uptake of hydrophilic aerogels prepared by ALD at atmospheric pressure ....45 3.1 Summary of intercept α, slope β and β/α through secondary growth membrane ............................................................................................67 3.2 Summary of intercept α, slope β and β/α through in situ membrane ...............69 A.1 Temperature Program for Sintering Supports .................................................80 vii LIST OF FIGURES FIGURE Page 1.1. Schematic diagram of hydrophilic aerogels and hydrophobic aerogels after surface modification. R represents –CH groups.. ......................5 3 1.2. Three classes of amines: primary amines have one hydrogen atom replaced by an alkyl group R; secondary amines have two atoms replaced, and tertiary have all three atoms replaced. .........................................7 1.3. Geldart classification of powders according to fluidization properties at air ambient conditions. ..................................................................9 1.4. Diagram of pressure drop as function of gas velocity. ...................................11 1.5. Illustration of the MOF-5 framework. ............................................................13 2.1. Schematic diagram of the batch MAIC device. ..............................................20 2.2. Illustration of ALD process based on alternate surface reactions ...................22 2.3. Schematic of amines used in each synthesis method.. ..................................263 2.4. Diagram of Cahn microbalance system for CO adsorption studies...............26 2 2.5. Schematic diagram of the fluidized bed setup.. ..............................................28 2.6. TGA/DSC of Triameen-modified aerogel under nitrogen atmosphere. .........30 2.7. TGA/DSC of Duomeen-modified aerogel under nitrogen atmosphere. .........30 2.8. TGA/DSC of unmodified aerogel under nitrogen atmosphere. ......................31 2.9.Weight of CO adsorbed in a sample of hydrophobic aerogel 2 modified by physical adsorption of Triameen T. .............................................33 2.10.Weight of CO adsorbed in a sample of hydrophobic aerogel modified 2 by physical adsorption of Duomeen T. ............................................................33 viii FIGURE Page 2.11.Weight of CO adsorbed in a sample of hydrophilic aerogel 2 modified by physical adsorption of Duomeen T..............................................34 2.12.Weight of CO adsorbed in a sample of hydrophobic aerogel 2 modified by physical adsorption of PEI...........................................................34 2.13.Weight of CO adsorbed in a sample of aerogel modified by MAIC 2 of Triameen T. .................................................................................................35 2.14.Weight of CO adsorbed in a sample of aerogel modified by MAIC 2 of γ-APS. ..........................................................................................................36 2.15.Weight of CO adsorbed in a sample of aerosil 200 modified by 2 MAIC of Triameen T. ......................................................................................36 2.16.Weight of CO adsorbed in a sample of aerosil 200 modified by 2 MAIC of γ-APS. ..............................................................................................37 2.17. Weight of aerogel sample modified by MAIC of Triameen T. ....................38 2.18. Sample weight of unmodified hydrophobic aerogels. ..................................39 2.19. Weight of CO adsorbed in a sample of unmodified aerogels. .....................39 2 2.20.Weight of CO adsorbed in a sample of aerogel modified by 2 ALD (sample 1). ..............................................................................................42 2.21.Weight of CO adsorbed in a sample of aerogel modified by 2 ALD (sample 2). ..............................................................................................42 2.22.Weight of CO adsorbed in a sample of aerogel modified by 2 ALD (sample 3). ..............................................................................................43 ix