Inorganic, Polymeric and Composite Membranes: Structure-Function and Other Correlations covers the latest technical advances in topics such as structure-function relationships for polymeric, inorganic, and composite membranes. Leading scientists provide in depth reviews and disseminate cutting-edge research results on correlations but also discuss new materials, characterization, modelling, computational simulation, process concepts, and spectroscopy. Unified by fundamental general correlations theme Many graphical examples Covers all major membrane types
Front Cover 1
Inorganic, Polymeric and Composite Membranes: Structure, Function and Other Correlations 4
Copyright 5
Dedication 6
Contents 8
Contributors 16
Preface 20
Chapter 1: Correlations 22
Introduction 22
Scientific laws and correlations 24
Principles 24
Theories 24
Laws 25
Properties 27
Effects 27
Equations 28
Dimensionless Numbers 31
Criteria 32
Approximations, Factor, Curves 32
Correlations 34
Important properties in membrane science 35
Examples of correlations in the membrane separation field 37
Summary 43
Acknowledgments 43
References 43
Chapter 2: Review of Silica Membranes for Hydrogen Separation Prepared by Chemical Vapor Deposition 46
Introduction 46
Silica Membranes for Hydrogen Separation 46
Chemical Vapor Deposition: Principles 48
Synthesis of Silica Membranes via Chemical Vapor Deposition 50
Silica Membranes Supported on Vycor Glass 58
Silica Membranes Supported on Alumina 69
Conclusions 77
Acknowledgments 77
References 77
Chapter 3: Amorphous Silica Membranes for H2 Separation Prepared by Chemical Vapor Deposition on Hollow Fiber Supports 82
Introduction 82
Experimental 86
Results and discussion 87
Pure Hollow Fiber Support Properties 88
Mesoporous Silica Layer 90
Amorphous .-Alumina Layer 93
Silica Precursor and Carrier Gas Flow Rate Effects on the Membrane Separation Performance 94
Gas Separation Mechanism 95
Conclusions 96
Acknowledgments 97
References 97
Chapter 4: Ab Initio Studies of Silica-Based Membranes: Activation Energy of Permeation 100
Introduction 100
Previous theoretical studies on dense silica-based membranes 101
Method of calculation 102
Results and discussion 103
Conclusions 110
Acknowledgments 110
References 110
Chapter 5: Review of CO2/CH4 Separation Membranes 112
Introduction 112
Discussion 114
Zeolite Membranes and Carbon Molecular Sieves 114
Silica Membranes 118
Polymeric Membranes 119
Mixed-matrix Membranes 123
Supported ionic Liquid and Polyionic Membranes 124
Overall results 128
Conclusions 130
Acknowledgments 131
References 131
Chapter 6: Gas Permeation Properties of Helium, Hydrogen, and Polar Molecules Through Microporous Silica... 138
Introduction 138
Experimental 140
Fabrication of Silica and Co-Doped Silica Membranes by Sol-Gel Method 140
Gas Permeation/Separation Measurements for Silica Membranes 141
Results and discussion 141
Improved Hydrothermal Stability of Amorphous Silica Membranes 141
Helium and Hydrogen Permeation Properties Through Amorphous Silica Membranes 146
Permeation Properties of Polar Molecules (NH3, H2O) Through Amorphous Silica Membranes 148
Conclusions 154
References 155
Chapter 7: Correlation Between Pyrolysis Atmosphere and Carbon Molecular Sieve Membrane Performance Properties 158
Introduction 158
Theory and background 159
Transport in CMS Membranes 159
Structure of CMS Membranes 160
Effect of Pyrolysis Atmosphere on Separation Performance of CMS Membranes 161
Experimental 163
Materials 163
Characterization Methods 166
Results and discussion 167
Correlation Between Oxygen Exposure and CMS Separation Performance 167
Correlation Between Oxygen Concentration and CMS Separation Performance 182
Possible Mechanism of Oxygen "Doping" Process During Pyrolysis 190
Conclusion 191
Acknowledgements 192
References 192
Chapter 8: Review on Prospects for Energy Saving in Distillation Process with Microporous Membranes 196
Introduction 196
Potential of membrane separation technology for large-scale reduction in energy consumption 197
Why zeolite membranes are promising 200
Synthesis technique of zeolite membranes 202
Seeding Technique (Secondary Growth Method) 202
Masking Technique 203
Use of SDA for Microstructural Optimization 204
De-watering technology using zeolite membranes 205
De-watering of Alcohol 205
De-watering of Organic Acids 207
De-watering for C1 Chemistry 208
Concluding remarks 209
References 210
Chapter 9: Xylene Separation Performance of Composition-Gradient MFI Zeolite Membranes 216
Introduction 216
Experimental 219
Bilayer Membrane Synthesis and Characterization 219
Pervaporation Experiments 221
Results and discussion 222
Membrane Characteristics 222
Binary Pervaporation Through Single and Bilayer Membranes 223
Reversal of Bilayer Structure 228
Stability at Higher PX Feed Concentrations 230
Conclusions 231
Acknowledgments 232
References 232
Chapter 10: Membrane Extraction for Biofuel Production 234
Introduction 234
Removal of Acetic Acid from Biomass Hydrolysates 236
Extraction of 5-Hydroxymethylfurfural 238
Glycerol Extraction 239
Material and methods 239
Removal of Acetic Acid from Biomass Hydrolysates 240
HMF Extraction 242
Glycerol Extraction 242
Results 242
Conclusions 251
Acknowledgments 252
References 252
Chapter 11: A Review of Mixed Ionic and Electronic Conducting Ceramic Membranes as Oxygen Sources for High-Temperature Reactors 256
Introduction 256
General attributes of oxygen-conducting MIEC ceramic materials 257
Oxygen Nonstoichiometry 257
Self-Adjusting Phase Equilibria 258
Chemical Expansivity 259
Microstructure of Oxygen-MIEC Ceramics 260
Common oxygen-MIEC membrane materials 261
Fluorites 261
Perovskites 262
SCF-Based Materials 264
Dual-Phase Composite Materials 269
Membrane Modifications to Improve Oxygen Flux 270
Surface Modifications 273
Membrane Thickness Reduction 274
MIEC membranes for synthesis gas production 276
Synthesis Gas Production Overview 276
Benefits of MIEC Membranes for Synthesis Gas Production 278
Overview of Work to Date 279
Effect of Reaction Temperature on Membrane Performance 281
Effect of Reaction Environment on Membrane Oxygen Flux 282
Conclusions 284
Acknowledgments 285
References 285
Chapter 12: Critical Factors Affecting Oxygen Permeation Through Dual-phase Membranes 296
Introduction 296
Design of dual-phase membranes with high stability and permeability 299
Experimental investigation of dual-phase membranes 301
Pure Electronic Conductor or Mixed Conductor? 301
Surface Exchange 302
Preparation Methods for Powders 303
Sintering Temperature 307
Ratio Between the Two Phases 309
Other Factors 310
Conclusions 311
Acknowledgments 311
References 312
Chapter 13: High Temperature Gas Separations Using High Performance Polymers 316
Introduction 316
Experimental 318
Instrumentation 318
Permeability Gas Testing 318
Positron Annihilation Lifetime Spectroscopy 319
Results and discussion 319
Conclusions 327
Acknowledgments 327
References 327
Chapter 14: Using First-principles Models to Advance Development of Metal Membranes for High Temperature Hydrogen Purificatication 330
Introduction 330
DFT-based modeling of crystalline metal membranes 332
Cluster Expansion Methods 334
Applications of DFT Calculations to Crystalline Membrane Materials 335
Amorphous metal membranes 337
Computational Approaches for Amorphous Metals 338
Amorphous Structures 338
Binding Energy of Interstitial H in Amorphous Alloys 339
H-H Interactions 340
H Solubility in Amorphous Alloys 341
Hydrogen Diffusion in Amorphous Alloys 343
Corrected Diffusivities 344
The Thermodynamic Correction Factor 345
Hydrogen Permeability Through Amorphous Alloys 347
Conclusion 348
Acknowledgments 349
References 349
Chapter 15: High Performance Ultrafiltration Membranes: Pore Geometry and Charge Effects 354
Introduction 354
Pore geometry effects 356
Fluid Flow 356
Solute Transport 357
Pore Size Distribution Effects 360
Electrostatic interactions 362
Fluid Flow 362
Solute Transport 365
Concentration polarization effects 368
Conclusions 371
Acknowledgment 372
References 372
Index 374
Membrane Science and Technology, Vol. 14, Suppl. (C), 2011
ISSN: 0927-5193
doi: 10.1016/B978-0-444-53728-7.00002-1
Chapter 2 Review of Silica Membranes for Hydrogen Separation Prepared by Chemical Vapor Deposition
Sheima Jatib Khatib1, S. Ted Oyama1,2,*, Kátia R. de Souza1,3 and Fábio B. Noronha3
1 Department of Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
2 Department of Chemical Systems Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan
3 Instituto Nacional de Tecnologia—INT, Av. Venezuela 82, CEP 20081-312, Rio de Janeiro, Brazil
*Corresponding author:
E-mail address: oyama@vt.edu, ted_oyama@chemsys.t.u-tokyo.ac.jp
Abstract
The application of inorganic silica membranes for sulfur hexafluoride selectivity separation at elevated temperatures has attracted much attention due to their good permselectivity and mechanical strength. These membranes are usually in the form of a thin layer of silica (selective layer) deposited on a thick porous support. One of the methods which is successfully used for deposition of the silica layers is the chemical vapor deposition (CVD), due to its versatility and reproducibility as well as high selectivities obtained with the membranes formed by this method. This chapter starts with a brief description of the basic principles of CVD and its application in the preparation of silica membranes, followed by a complete literature review which surveys the studies that have been carried out on supported silica membranes prepared through CVD and applied in hydrogen separation with two of the most commonly used supports, Vycor glass and alumina.
Keywords
silica membrane, CVD, hydrogen separation, inorganic membrane, Vycor, alumina, hydrogen permeability, permselectivity
Introduction
Silica Membranes for Hydrogen Separation
Hydrogen is an important industrial feedstock for the production of fuels and many chemicals [1,2] and in fuel cell applications [3], and the purification of hydrogen is an important unit operation. Hydrogen separation using membranes has emerged as an important technology, and although polymeric membranes have seen some application [4], they have limited permeance and selectivity, and inorganic materials have attracted attention. The most well-known material is palladium, but it suffers from high costs, and susceptibility to metallic failure by hardening, and poisoning by sulfur and other extraneous elements. This review focuses on silica-based membranes prepared by chemical vapor deposition (CVD), which are potentially low cost, are thermally stable, and are immune to poisons.
Practical application of these membranes requires high permeation rates as well as good selectivities, which can be obtained with membranes of low thickness and an absence of cracks and pinholes. In addition, the membranes must be mechanically strong for use in practical equipment and have long life and resistance to poisons. To meet these requirements (mechanical strength and high permeability), ceramic membranes can be produced by applying a thin film of the selective material on a thick porous support, usually in tubular form. For this purpose, film deposition technology has been exploited in membrane science.
For potential industrial applications like high-temperature hydrogen separation and simultaneous reaction and separation, inorganic silica membranes offer unique advantages, such as high selectivities, and high stability at elevated temperatures and in chemically aggressive atmospheres. And, for this reason, considerable attention has been paid to them by researchers [5-18]. Moreover, the application of these inorganic membranes in membrane reactors, using catalytically active or passive membranes has proved to be promising, since yields above equilibrium have been obtained by the continuous separation of the hydrogen product from the reaction system [19-25]. Figure 2.1 shows a typical membrane reactor applied to the steam reforming of ethanol.
Figure 2.1 Schematic diagram of a membrane reactor applied to the steam reforming of ethanol reaction.
The supported silica membranes are made by depositing the separation layer from suitable precursors suspended in a liquid or a gaseous medium. Deposition from the liquid phase involves techniques such as dip coating in polymeric or particulate suspensions (sol–gel technique), while deposition from the gas phase is usually carried out by CVD due to its versatility. Thus, silica membranes are usually in the form of silica layers placed on ceramic supports such as porous Vycor glass [5,10] and alumina [11,12,15-18], and are deposited usually by sol–gel [13-16] techniques or CVD [5-12] of silica precursors. Sol–gel modification provides relatively high gas permeation rates, mainly due to the very thin top layers, in the order of 50–100 nm and a good selectivity as opposed to CVD methods where there is an attendant loss of permeability, though the selectivity is enhanced. The sol–gel method, however, suffers from a lack of reproducibility.
This review will pay attention to the work that different groups have carried out with supported silica membranes for hydrogen separation prepared by CVD. But before, some basic principles and notions of CVD will be described.
Chemical Vapor Deposition: Principles
CVD is a technique that modifies the properties of membrane surfaces by depositing a layer of a solid product of the same or different compound through chemical reactions in a gaseous medium surrounding the component at an elevated temperature. Depending on the type of application, the product can be grown on flat substrates, fibers, or particles.
Generally, CVD systems include a system for delivering a mixture of reactive and carrier gases, and a heated reaction chamber where film formation occurs. The gas mixture (which typically consists of hydrogen, nitrogen, or argon, and volatile reactive compounds such as metal halides, carbonyls, or alkoxides) is flowed over the substrate that is heated to the desired temperature. Over the past years, different types of CVD methods have been developed, including thermal CVD, plasma-assisted CVD, and laser CVD [26].
The deposition of coatings by CVD can be achieved in a number of ways such as decomposition, oxidation, hydrolysis, or compound formation. These reactions between various constituents may occur in the vapor phase over the heated substrate, with the products depositing over the surface and forming a film. Most commonly, they proceed by adsorption of the gaseous reactants on the solid substrate followed by surface reactions. Thus, the mechanisms of CVD reactions involve reactions taking place on the solid surface and sometimes in the gas phase. Figure 2.2 illustrates the seven mechanistic steps that have been hypothesized to occur during a vapor deposition process [27].
Figure 2.2 Schematic diagram of the mechanistic steps that occur during the CVD process: (1) transport of reactant gases into the reaction chamber, (2) intermediate reactants formed from reactant gases, (3) diffusion of reactant gases through the gaseous boundary layer to the substrate, (4) absorption of gases onto the substrate surface, (5) single or multistep reactions at the substrate surface, (6) desorption of product gases from the substrate surface, (7) forced exit of product gases from the system.
(Figure adapted from Ref. [27]).
Although CVD procedures of membrane films have not been studied in such detail, empirical conditions for growing good-quality membranes have been identified and developed. All the same, some qualitative principles have been developed to help understand the CVD process for film formation [28]. A possible simplified reaction sequence for deposition is the following:
(2.1)
(2.2)
(2.3)
(2.4)
(2.5)
etc.
In the scheme, B is an active gas phase intermediate that can react on the solid or can form oligomers in the gas phase. The oligomerization reactions (2.3)-(2.5) can be purely physical, reversible events related to condensation, or can involve bond breaking and formation. The growth of particles in the gas phase follows a nucleation path where a small nucleus is formed and then grows. The surface film formation can follow any number of mechanisms such as island formation, or layer-by-layer growth. In both cases, lowering the reactant concentration will reduce the first-order steps ( 2.1) and (2.2) and more strongly, the oligomer and particle-forming steps (2.3)-(2.5).
Another possible scheme involves two gaseous reactants, C and D, reacting as...
| Erscheint lt. Verlag | 4.5.2011 |
|---|---|
| Sprache | englisch |
| Themenwelt | Naturwissenschaften ► Chemie ► Anorganische Chemie |
| Naturwissenschaften ► Chemie ► Technische Chemie | |
| Technik ► Umwelttechnik / Biotechnologie | |
| ISBN-10 | 0-444-53729-5 / 0444537295 |
| ISBN-13 | 978-0-444-53729-4 / 9780444537294 |
| Haben Sie eine Frage zum Produkt? |
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