Hydrogen clusters in clathrate hydrate.
27 Sep 2002-Science (American Association for the Advancement of Science)-Vol. 297, Iss: 5590, pp 2247-2249
TL;DR: High-pressure Raman, infrared, x-ray, and neutron studies show that H2 and H2O mixtures crystallize into the sII clathrate structure with an approximate H2/H2Omolar ratio of 1:2.
Abstract: High-pressure Raman, infrared, x-ray, and neutron studies show that H2 and H2O mixtures crystallize into the sII clathrate structure with an approximate H2/H2O molar ratio of 1:2. The clathrate cages are multiply occupied, with a cluster of two H2 molecules in the small cage and four in the large cage. Substantial softening and splitting of hydrogen vibrons indicate increased intermolecular interactions. The quenched clathrate is stable up to 145 kelvin at ambient pressure. Retention of hydrogen at such high temperatures could help its condensation in planetary nebulae and may play a key role in the evolution of icy bodies.
Citations
More filters
TL;DR: This critical review of the current status of hydrogen storage within microporous metal-organic frameworks provides an overview of the relationships between structural features and the enthalpy of hydrogen adsorption, spectroscopic methods for probing framework-H(2) interactions, and strategies for improving storage capacity.
Abstract: New materials capable of storing hydrogen at high gravimetric and volumetric densities are required if hydrogen is to be widely employed as a clean alternative to hydrocarbon fuels in cars and other mobile applications. With exceptionally high surface areas and chemically-tunable structures, microporous metal–organic frameworks have recently emerged as some of the most promising candidate materials. In this critical review we provide an overview of the current status of hydrogen storage within such compounds. Particular emphasis is given to the relationships between structural features and the enthalpy of hydrogen adsorption, spectroscopic methods for probing framework–H2 interactions, and strategies for improving storage capacity (188 references).
4,511 citations
TL;DR: Natural gas hydrates have an important bearing on flow assurance and safety issues in oil and gas pipelines, they offer a largely unexploited means of energy recovery and transportation, and could play a significant role in past and future climate change.
Abstract: Natural gas hydrates are solid, non-stoichiometric compounds of small gas molecules and water. They form when the constituents come into contact at low temperature and high pressure. The physical properties of these compounds, most notably that they are non-flowing crystalline solids that are denser than typical fluid hydrocarbons and that the gas molecules they contain are effectively compressed, give rise to numerous applications in the broad areas of energy and climate effects. In particular, they have an important bearing on flow assurance and safety issues in oil and gas pipelines, they offer a largely unexploited means of energy recovery and transportation, and they could play a significant role in past and future climate change.
2,419 citations
TL;DR: Different methods for hydrogen storage are discussed, including high-pressure and cryogenic-liquid storage, adsorptive storage on high-surface-area adsorbents, chemical storage in metal hydride and complex hydrides, and storage in boranes.
Abstract: Hydrogen is a promising energy carrier in future energy systems. However, storage of hydrogen is a substantial challenge, especially for applications in vehicles with fuel cells that use proton-exchange membranes (PEMs). Different methods for hydrogen storage are discussed, including high-pressure and cryogenic-liquid storage, adsorptive storage on high-surface-area adsorbents, chemical storage in metal hydrides and complex hydrides, and storage in boranes. For the latter chemical solutions, reversible options and hydrolytic release of hydrogen with off-board regeneration are both possible. Reforming of liquid hydrogen-containing compounds is also a possible means of hydrogen generation. The advantages and disadvantages of the different systems are compared.
1,222 citations
TL;DR: Hydrogen storage capacities in THF-containing binary-clathrate hydrates can be increased to ∼4 wt% at modest pressures by tuning their composition to allow the hydrogen guests to enter both the larger and the smaller cages, while retaining low-pressure stability.
Abstract: The storage of large quantities of hydrogen at safe pressures is a key factor in establishing a hydrogen-based economy. Previous strategies--where hydrogen has been bound chemically, adsorbed in materials with permanent void space or stored in hybrid materials that combine these elements--have problems arising from either technical considerations or materials cost. A recently reported clathrate hydrate of hydrogen exhibiting two different-sized cages does seem to meet the necessary storage requirements; however, the extreme pressures (approximately 2 kbar) required to produce the material make it impractical. The synthesis pressure can be decreased by filling the larger cavity with tetrahydrofuran (THF) to stabilize the material, but the potential storage capacity of the material is compromised with this approach. Here we report that hydrogen storage capacities in THF-containing binary-clathrate hydrates can be increased to approximately 4 wt% at modest pressures by tuning their composition to allow the hydrogen guests to enter both the larger and the smaller cages, while retaining low-pressure stability. The tuning mechanism is quite general and convenient, using water-soluble hydrate promoters and various small gaseous guests.
732 citations
TL;DR: Thermodynamic, x-ray diffraction, and Raman and nuclear magnetic resonance spectroscopy measurements show that clusters of H2 can be stabilized and stored at low pressures in a sII binary clathrate hydrate.
Abstract: Thermodynamic, x-ray diffraction, and Raman and nuclear magnetic resonance spectroscopy measurements show that clusters of H2 can be stabilized and stored at low pressures in a sII binary clathrate hydrate. Clusters of H2 molecules occupy small water cages, whereas large water cages are singly occupied by tetrahydrofuran. The presence of this second guest component stabilizes the clathrate at pressures of 5 megapascals at 279.6 kelvin, versus 300 megapascals at 280 kelvin for pure H2 hydrate.
691 citations
References
More filters
Book•
01 Jan 1990TL;DR: In this paper, the authors compared the properties of hydrates and ice with those of natural gas and showed the effect of thermodynamic inhibitors on the formation of hydrate formation and dissolution process.
Abstract: PREFACE Overview and Historical Perspective Hydrates as a Laboratory Curiosity Hydrates in the Natural Gas Industry Hydrates as an Energy Resource Environmental Aspects of Hydrates Safety Aspects of Hydrates Relationship of This Chapter to Those That Follow Molecular Structures and Similarities to Ice Crystal Structures of Ice Ih and Natural Gas Hydrates Comparison of Properties of Hydrates and Ice The What and the How of Hydrate Structures Hydrate Formation and Dissociation Processes Hydrate Nucleation Hydrate Growth Hydrate Dissociation Estimation Techniques for Phase Equilibria of Natural Gas Hydrates Hydrate Phase Diagrams for Water + Hydrocarbon Systems Three-Phase (LW-H-V) Equilibrium Calculations Quadruple Points and Equilibrium of Three Condensed Phases (LW-H-LHC) Effect of Thermodynamic Inhibitors on Hydrate Formation Two-Phase Equilibrium: Hydrates with One Other Phase Hydrate Enthalpy and Hydration Number from Phase Equilibrium Summary and Relationship to Chapters Which Follow A Statistical Thermodynamic Approach to Hydrate Phase Equilibria Statistical Thermodynamics of Hydrate Equilibria Application of the Method to Analyze Systems of Methane + Ethane + Propane Computer Simulation: Another Microscopic-Macroscopic Bridge Summary Experimental Methods and Measurements of Hydrate Properties Experimental Apparatuses and Methods for Macroscopic Measurements Measurements of the Hydrate Phase Data for Natural Gas Hydrate Phase Equilibria and Thermal Properties Summary and Relationship to Chapters that Follow References Hydrates in the Earth The Paradigm Is Changing from Assessment of Amount to Production of Gas Sediments with Hydrates Typically Have Low Contents of Biogenic Methane Sediment Lithology and Fluid Flow Are Major Controls on Hydrate Deposition Remote Methods Enable an Estimation of the Extent of a Hydrated Reservoir Drilling Logs and/or Coring Provide Improved Assessments of Hydrated Gas Amounts Hydrate Reservoir Models Indicate Key Variables for Methane Production Future Hydrated Gas Production Trends Are from the Permafrost to the Ocean Hydrates Play a Part in Climate Change and Geohazards Summary Hydrates in Production, Processing, and Transportation How Do Hydrate Plugs Form in Industrial Equipment? How Are Hydrate Plug Formations Prevented? How Is a Hydrate Plug Dissociated? Safety and Hydrate Plug Removal Applications to Gas Transport and Storage Summary of Hydrates in Flow Assurance and Transportation APPENDICES INDEX
6,037 citations
Book•
[...]
18 Nov 1999
TL;DR: In this paper, the physics of ice and its structure are discussed, including elasticity, thermal, and lattice dynamical properties, as well as the deformation of polycrystalline ice.
Abstract: 1. Introduction 1.1 The importance of ice 1.2 The physics of ice and structure of the book 1.3 The water molecule 1.4 The hydrogen bond 2. Ice Ih 2.1 Introduction 2.2 Crystal structure 2.3 Zero-point entropy 2.4 Lattice energy and hydrogen bonding 2.5 The actual structure 2.6 Summary 3. Elastic, thermal, and lattice dynamical properties 3.1 Introduction 3.2 Elasticity 3.3 Thermal properties 3.4 Spectroscopy of lattice vibrations 3.5 Modelling 4. Electrical properties-theory 4.1 Basics 4.2 Frequency dependence of the Debye relaxation 4.3 The static susceptibility ?s 4.4 Protonic point defects 4.5 Jaccard theory 4.6 Ice with blocking electrodes 4.7 Time constraints 4.8 Summary 5. Electrical properties-experimental 5.1 Introduction 5.2 Techniques 5.3 Pure ice 5.4 Doped ice 5.5 Charge exchange at ice-metal electrodes 5.6 Space-change effects 5.7 Injection and extraction of charge carriers 5.8 Thermally-stimulated depolarization 6. Point defects 6.1 Introduction 6.2 Thermal equilibrium concentrations 6.3 Diffusion and mobility 6.4 Molecular defects 6.5 Protonic point defects 6.6 Nuclear magnetic resonance 6.7 Muon spin rotation, relaxation, and resonance 6.8 Chemical impurities 6.9 Electronic defects 6.10 Photoconductivity 6.11 Review 7. Dislocations and planar defects 7.1 Introduction to dislocations 7.2 Dislocations in the ice structure 7.3 Direct observation of dislocations 7.4 Dislocation mobility 7.5 Electrical effects 7.6 Stacking faults 7.7 Grain boundaries 8. Mechanical properties 8.1 Introduction 8.2 Plastic deformation of single crystals 8.3 Plastic deformation of polycrystalline ice 8.4 Brittle fracture of polycrystalline ice 8.5 Summary 9. Optical and electronic properties 9.1 Introduction 9.2 Propagation of electromagnetic waves in ice 9.3 Infrared range 9.4 Visible optical range-birefringence 9.5 Ultraviolet range 9.6 Electronic structure 10. The surface of ice 10.1 Introduction 10.2 Surface structure 10.3 Optical ellipsometry and microscopy 10.4 Electrical properties of the surface 10.5 Nuclear magnetic resonance 10.6 Scanning force microscopy 10.7 Surface energy 10.8 Review of experimental evidence 10.9 Theoretical models 10.10 Conclusions 11. The other phases of ice 11.1 Introduction 11.2 Ice XI-the ordered form of ice Ih 11.3 Ices VII and VIII 11.4 Ice VI 11.5 Ice II 11.6 Ices III, IV, V, IX, and XII 11.7 Ice X and beyond 11.8 Cubic ice (Ice Ic) 11.9 Amorphous ices 11.10 Clathrate hydrates 11.11 Lattice vibrations and the hydrogen bond 12. Ice in nature 12.1 Lake and river ice 12.2 Sea ice 12.3 Ice in the atmosphere 12.4 Snow 12.5 Glacier and polar ice 12.6 Frozen ground 12.7 Ice in the Solar System 13. Adhesion and friction 13.1 Experiments on adhesion 13.2 Physical mechanisms of adhesion 13.3 Friction
1,288 citations
TL;DR: In this paper, the authors explore the study of dense hydrogen as an archetypal problem in condensed-matter physics and present a detailed study of the dynamic, structural, and electronic properties of the system.
Abstract: During the past five years, major progress has been made in the experimental study of solid hydrogen at ultrahigh pressures as a result of developments in diamond-cell technology. Pressures at which metallization has been predicted to occur have been reached (250-300 Gigapascals). Detailed studies of the dynamic, structural, and electronic properties of dense hydrogen reveal a system unexpectedly rich in physical phenomena, exhibiting a variety of transitions at ultrahigh pressures. This colloquium explores the study of dense hydrogen as an archetypal problem in condensed-matter physics.
503 citations
TL;DR: The structure of the tetrahydrofuran/hydrogen sulfide double hydrate has been determined from three-dimensional single-crystal data as discussed by the authors, and the analysis confirmed the clathrate host lattice characteristic of 17 cubic (Type II) gas hydrates.
Abstract: The structure of the tetrahydrofuran/hydrogen sulfide double hydrate has been determined from three‐dimensional single‐crystal data. The analysis confirmed the clathrate host lattice characteristic of 17‐A cubic (Type II) gas hydrates. The hexakaidecahedral voids enclose tetrahydrofuran molecules which appear to undergo free rotation. Statistically, 46% of the pentagonal dodecahedra are occupied by hydrogen sulfide molecules.
406 citations
TL;DR: In this article, the authors report neutron and synchrotron X-ray diffraction studies that determine the thermodynamic behavior of methane hydrate at pressures up to 10 GPa.
Abstract: Methane hydrate is thought to have been the dominant methane-containing phase in the nebula from which Saturn, Uranus, Neptune and their major moons formed. It accordingly plays an important role in formation models of Titan, Saturn's largest moon. Current understanding assumes that methane hydrate dissociates into ice and free methane in the pressure range 1-2 GPa (10-20 kbar), consistent with some theoretical and experimental studies. But such pressure-induced dissociation would have led to the early loss of methane from Titan's interior to its atmosphere, where it would rapidly have been destroyed by photochemical processes. This is difficult to reconcile with the observed presence of significant amounts of methane in Titan's present atmosphere. Here we report neutron and synchrotron X-ray diffraction studies that determine the thermodynamic behaviour of methane hydrate at pressures up to 10 GPa. We find structural transitions at about 1 and 2 GPa to new hydrate phases which remain stable to at least 10 GPa. This implies that the methane in the primordial core of Titan remained in stable hydrate phases throughout differentiation, eventually forming a layer of methane clathrate approximately 100 km thick within the ice mantle. This layer is a plausible source for the continuing replenishment of Titan's atmospheric methane.
309 citations