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Recovery of Hydrogen and Helium from Their Mixtures Using Metal Hydrides

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Recovery of Hydrogen and Helium from Their Mixtures Using Metal Hydrides RECOVERY OF HYDROGEN AND HELIUM FROM THEIR MIXTURES USING METAL HYDRIDES by MUZAFFER TONGUC OZTEK B.S. Middle East Technical University, 1999 A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in the Department of Chemistry in the College of Arts and Sciences at the University of Central Florida Orlando, Florida Summer Term 2005 © 2005 Muzaffer Tonguc Oztek ii ABSTRACT Waste streams of hydrogen and helium mixtures are produced at the Kennedy Space Center during purging of the hydrogen systems and supply lines. This process is done prior to and after hydrogen servicing. The purged waste gases are lost to the atmosphere, resulting in an annual loss of 2 million and 0.1 million standard cubic meters of helium and hydrogen, respectively. Recovery of these gases will have an economic benefit. Metals, alloys, and intermetallics are known to react with hydrogen in favorable conditions; therefore, they have the possibility of serving as separating and recovery agents. In this study, Mg2Ni, VTiNi and LaNi5 were studied for the separation of H2 from He, using differential scanning calorimetry and thermal volumetric analysis. The ability of LaNi5 to react with hydrogen reversibly at room temperature was verified, and further analysis focused on this compound. Size reduction and activation of LaNi5 by mechanical milling was investigated using different milling parameters for the purpose of activating the material for hydrogen absorption. Because it has been shown that addition of aluminum to LaNi5 resulted in improved hydriding and dehydriding properties, that system was studied further here. In this study, aluminum was added to LaNi5 by mechanical milling. Hydriding properties and elemental compositions of the samples were determined afterwards. The hydrogen absorption rate and capacity were compared to that of LaNi5. iii Both LaNi5 and its Al doped derivatives exhibited a reduced rate of hydrogen uptake and a reduced hydrogen capacity in the presence of helium. The effects of coating the samples with either gold-palladium or platinum were investigated. It was observed that coating the samples with Pt reduced the negative effect of He, whereas AuPd coating did not have any effect. Larger scale studies were done using a continuous U-tube hydride reactor, built and tested for separation of H2 from a 20:80 H2:He mixture. The amount of hydrogen retained in the bed was determined and found to be less than that for the batch systems. iv I dedicate this work to my family members Baris, Nevin, Taylan and Bilgesu for making me what I am. v ACKNOWLEDGMENTS I first would like to thank Dr. Michael D. Hampton for providing his endless support, patience and especially encouragement throughout the course of my studies. He was a model research advisor and a friend as well to turn Hydrogen Heaven into a very pleasant work environment. I am also very grateful to Dr. Darlene K. Slattery at the Florida Solar Energy Center, my co-advisor, for her input. The current and past members of the Hydrogen Heaven group are also remembered with appreciation; Mirna, Dr. Lomness, Dorian, Edgar, Irene, Gail, Juliana, Oscar and other fellow students who helped me to find the answers in times of trouble and shared the fun in times of success, thank you very much. The assistance from the all faculty and staff of the UCF Chemistry Department has played a great role, therefore they deserve a big thank you also. I must especially thank Dr. Brooks C. Madsen and Dr. Christian A. Clausen who contributed their unique academic expertise during the course of my education and valuable comments and critiques for my thesis. Despite the thousands of miles between us, the remarkable morale support I received from my mother Nevin and wise guidance from my father Baris kept me on alert and aware of what could be achieved with ambition and hard working. Thank you a million times. vi I also would like to cheer for my friends who supported me indirectly, by giving their understanding and motivating me. Melih, Kemal, Erkan, Atilla, and all the others, thanks a lot. The members of Tavuk; Aydin, Emre, Emre, Ercan and Ozgur also deserve a big thank you. You are all one of a kind. My friends Havva, Aysun and Banu have been a role model to me with their successes in the academia and they deserve special thanks also. Umut, Erbil, Alper, with you guys we’ve learned how to learn and, this is irreplaceable. And last but not least, Kimberly, thank you so much for being there when I needed you. With your loving and caring friendship and a lot more, it has been and is still a joyful journey. vii TABLE OF CONTENTS ABSTRACT.......................................................................................................................iii ACKNOWLEDGMENTS ................................................................................................. vi TABLE OF CONTENTS.................................................................................................viii LIST OF FIGURES ........................................................................................................... xi LIST OF TABLES........................................................................................................... xiv 1. INTRODUCTION .......................................................................................................... 1 1.1. Hydrogen Separation And Recovery .................................................................. 2 1.2. Metal Hydrides....................................................................................................4 1.2.1. Formation of Hydrides................................................................................ 4 1.2.2. Characterization of Metal Hydrides............................................................ 6 1.2.3. Examples of Hydrides............................................................................... 10 1.3. LaNi5 ................................................................................................................. 11 1.4. Mechanical Alloying......................................................................................... 14 1.5. Crystallography Of Hydrides............................................................................ 17 2. EXPERIMENTAL........................................................................................................ 23 2.1. Chemicals and Reagents ................................................................................... 23 2.2. Equipment and Instrumentation........................................................................ 23 2.2.1. Differential Scanning Calorimetry (DSC) ................................................ 25 2.2.1.1. Hydriding and Dehydriding Procedures ........................................... 27 2.2.1.2. Thermal Activation Procedure.......................................................... 28 2.2.2. U-Tube Reactor......................................................................................... 29 viii 2.2.2.1. Hydriding and Dehydriding Procedures ........................................... 30 2.2.2.2. Activation procedure......................................................................... 31 2.3. Sample Preparation........................................................................................... 32 2.4. Sample characterization and Analysis .............................................................. 33 3. RESULTS AND DISCUSSIONS................................................................................. 35 3.1. Hydride Formers ............................................................................................... 35 3.1.1. Mg2Ni........................................................................................................ 36 3.1.2. VTiNi ........................................................................................................ 40 3.1.3. LaNi5 ......................................................................................................... 44 3.1.3.1. Effect of Ball Milling........................................................................ 45 3.1.3.2. Effect of Thermal Activation............................................................ 46 3.1.3.3. Effects of Type of Mill, Milling Speed and Milling Atmosphere .... 48 3.1.3.4. Effect of Milling Time and Ball to Powder Ratio............................. 52 3.1.3.5. Dehydriding of LaNi5 ....................................................................... 53 3.2. Aluminum in LaNi5........................................................................................... 55 3.2.1. Interaction With Pure Hydrogen............................................................... 55 3.2.2. Hydrogen Uptake From Hydrogen – Helium Mixtures............................ 59 3.2.2.1. VTiNi ................................................................................................ 60 3.2.2.2. LaNi5 ................................................................................................. 62 3.2.2.3. LaNi5 with Al.................................................................................... 64 3.2.2.4. AuPd and Pt Coating on LaNi5 ......................................................... 67 3.3. Parr Reactor...................................................................................................... 70 3.4. U-Tube Hydriding Reactor ............................................................................... 74 ix 3.5. X-Ray Diffraction ............................................................................................
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