Hydrate

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

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.

Abstract: The reaction of M(II) acetate hydrate (M = Co, Ni, and Zn) with 1,3,5-benzenetricarboxylic (BTC) acid yields a material formulated as M3(BTC)2·12H2O. These compounds are isostructural as revealed by their XRPD patterns and a single crystal structure analysis performed on the cobalt containing solid [monoclinic, space group C2, a = 17.482 (6) A, b = 12.963 (5) A, c = 6.559 (2) A, β = 112.04°, V = 1377.8 (8) A, Z = 4]. This solid is composed of zigzag chains of tetra-aqua cobalt(II) benzenetricarboxylate that are hydrogen-bonded to yield a tightly held 3-D network. Upon liberating 11 water ligands per formula unit a porous solid results, M3(BTC)2·H2O, which was found to reversibly and repeatedly bind water without destruction of the framework. The proposed 1-D channels of the monohydrate have a pore diameter of 4 × 5 A, which is typical of those observed in zeolites and molecular sieves. The successful inclusion of ammonia into the porous solid was demonstrated. Larger molecules and others without a reactiv...

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.

Abstract: Clathrate hydrates, ice-like host–guest systems containing guest molecules in cages of hydrogen-bonded water molecules exist in three well-characterized cubic forms, and a less well-characterized tetragonal form1,2 On the basis of 2H and l29Xe NMR measurements and X-ray and neutron powder diffraction results, we now report a new hexagonal hydrate structure requiring both large and small guest molecules to stabilize the structure This hydrate is expected to be isostructural with the hexagonal clathrasil dodecasil-lH (see ref 14 for clathrasil nomenclature) As for the cubic clathrate hydrates, the new hydrate structure may occur naturally