Among the three common gas hydrate structures, structure-H (sH) hydrate has been regarded as forming only in the laboratory since it was first reported in 1987. However, natural gas hydrate samples obtained from the Cascadia margin showed that sH hydrate can form naturally. Not only was the sH hydrate found in natural samples, but it was also discovered that n-alkanes such as n-pentane and n-hexane, considered to have too large molecular size to be sH hydrate formers, can act as co-guests of sH hydrates in mixtures with other sH hydrate formers. In this study, thermodynamic measurements and spectroscopic analysis of powder X-ray diffraction and 13C solid-state NMR methods, were performed for synthetic hydrate samples in order to identify the accommodation of n-alkanes with five or more carbon atoms. In addition, some new hydrate guests were found to form sH hydrates. From the present results, it is clear that, so far, our understanding of gas hydrates and guest enclathration needs to be revised and expanded in order to explain new findings.

No description available.

A gas hydrate refers to the state in which hydrogen-bonded water molecules form a rigid lattice structure of so-called "cages", wherein "guest" molecules of natural gas are entrapped. Not unlike ice, gas hydrates are prone to form at low temperatures and high pressures; however, their crystalline structure allows them to remain stable at temperatures and pressures under which the phase limits of ice would otherwise be exceeded. To date, a number of instances of gas hydrates forming in the subsurface of Arctic climates below layers of permafrost have been identified, however the challenge of identifying past occurrences of methane hydrates during episodes of global cooling and glacial advance remains relatively unmet. During these periods of glacial/permafrost cover, the presence of hydrates could have a significant impact on the groundwater flow system due to the significant reduction of the porosity and permeability of hydrate saturated sediments. The purpose of this study is to investigate whether there is evidence to suggest that methane hydrates could have formed in the sedimentary units of the Michigan Basin at the Bruce nuclear site near Kincardine, Ontario, particularly when subjected to the impacts of glacial ice sheet loading. This study aims to provide insight into whether the potential impact of gas hydrates should be considered in the design of the proposed deep-geologic repository (DGR) for low- and intermediate-level nuclear waste. This study presents a framework employing regional-scale numerical modelling to estimate the evolution of temperature, pressure and salinity profiles across the study area, combined with thermodynamic predictive modelling to identify potential paleo-methane hydrate stability zones in the subsurface at the Bruce nuclear site. This study represents the first step to ultimately assess the extent of paleo-methane hydrates and their impact on subsurface conditions at the site. Transient subsurface conditions at the Bruce nuclear site were modelled over a period of 120,000 years (120 ka), encompassing episodes of glacial advance and retreat during the Pleistocene epoch. The spatial and transient outputs from numerical modelling of the study area were then used as inputs to thermodynamic predictive modelling of methane hydrate stability. The results of this study show that, based upon the subsurface temperature, pressure and salinity histories determined using a three-dimensional regional-scale numerical modelling approach, paleo-conditions at the Bruce nuclear site become conducive with methane hydrate stability during the study period. Two separate episodes of methane hydrate stability were identified - lasting from 62.5 to 56 thousand years before present (kaBP) and from 23 to 13.5 kaBP, respectively - which were found to correspond to periods of glacial advance across the study area. The vertical extent of the estimated hydrate stability zones varied across the site, however it generally followed the limits of the Upper Silurian units, penetrating to deeper elevations towards the south west end of the study area.

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1990. / Includes bibliographical references. / Microfiche. / xiii, 161 leaves, bound ill. 29 cm

The interaction between sunlight and our atmosphere is one of the most fundamental processes affecting weather and climate. The majority of the Sun�s radiation is produced in the ultraviolet, visible and near-infrared regions of the electromagnetic spectrum. These spectral regions correspond to the energies of vibrational overtone and electronic transitions. The composition of our atmosphere is complex, and many trace species have a large influence on its chemistry and dynamics. Hydrogen bound hydrated complexes are trace species that could play an important role in the Earth�s atmosphere. However, before this role can be quantified, spectral identification and characterisation of these complexes is essential. We have developed vibrational local mode Hamiltonians to simulate the absorption spectra of hydrated complexes. To test the approximations made in the vibrational model, we have peformed calculations on the diatomics OH, HF and CO, which can be considered to act as pure local modes. When highly correlated ab initio methods and large basis sets are used to calculate the potential energy and dipole moment curve, the simulated vibrational transitions of the diatomics are in excellent agreement with experiment. We have derived approximate vibrational Hamiltonians which describe the OH-stretching and HOH-bending modes of vibration in the complexes H₂O�H₂O, H₂O�HO₂ and H₂O�HO. The calculated spectrum of H₂O�H₂O has been used to assess its atmospheric importance, and to succesfully guide experimental efforts to detect H₂O�H₂O in the laboratory and the Earth�s atmosphere. The calculated transition energies and intensities of H₂O�H₂O and H₂O�HO are in good agreement with experimental matrix isolation and gas-phase studies. To investigate the effect of low frequency modes on OH-stretching overtone spectra we have simulated the spectrum of HOONO. We have derived a Hamiltonian that couples the NOOH-torsional mode to the high frequency OH-stretching and OOH-bending modes. The simulated spectrum is in good agreement with the experimentally observed spectrum. We find that the OH-stretching spectra are perturbed strongly only if the barrier to torsion is low. We have also investigated changes in the electronic spectrum of hydrated complexes and the corresponding parent monomers. Upon complex formation, the lowest-lying electronic transition in the hydroxyl radical is strongly redshifted outside the region of monomeric absorption.

Thesis (M. Phil.)--University of Hong Kong, 1999. / Disk of copy 1 shelved at the back of the text. Includes bibliographical references (leaves 154-159).

No description available.

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains viii, 93 p. : ill. (some col.), col. map. Includes abstract. Includes bibliographical references.

An isobaric flow loop added to the Gas Hydrate And Sediment Test Laboratory Instrument (GHASTLI) is being investigated as a means of rapidly forming methane hydrate in watersaturated sand from methane dissolved in water. Water circulates through a relatively warm source chamber, dissolving granular methane hydrate that was pre-made from seed ice, then enters a colder hydrate growth chamber where hydrate can precipitate in a water-saturated sand pack. Hydrate dissolution in the source chamber imparts a known methane concentration to the circulating water, and hydrate particles from the source chamber entrained in the circulating water can become nucleation sites to hasten the onset of hydrate formation in the growth chamber. Initial results suggest hydrate grows rapidly near the growth chamber inlet. Techniques for establishing homogeneous hydrate formation throughout the sand pack are being developed.

No description available.