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1
Nour, Sherif. "17-O NMR on Crystalline Hydrades Hydrates: Impact of Hydrogen Bonding." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/32849.
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The water molecules in inorganic hydrate salts adopt different geometries and are involved in different hydrogen bond interactions. In this work, magic-angle spinning (MAS) and static 17O solid-state NMR experiments are performed to characterize the 17O electric field gradient (EFG) and chemical shift (CS) tensors of the water molecules in a series of inorganic salt hydrates which include: oxalic acid hydrate, barium chlorate hydrate, sodium perchlorate hydrate, lithium sulphate hydrate, and potassium oxalate hydrate, which were all enriched with 17O water. Data were acquired at magnetic field strengths of 9.4, 11.75, and 21.1 T. Gauge-including projector-augmented-wave density functional theory (GIPAW DFT) calculations are performed on barium chlorate hydrate and oxalic acid hydrate where structural changes including the Ow-H•••O distance, H-O-H angle, and O-H distance are employed to understand their impact on the NMR parameters. Furthermore, simplified molecular models consisting of a metal cation and a water molecule were built to establish the effect the M-Ow distance has on the parameters. The computational studies are then used to understand the experimental results. The 17O quadrupolar coupling constant ranged from 6.75 MHz in K2C2O4•H2O to 7.39 MHz in NaClO4•H2O while the asymmetry parameter ranged from 0.75 in NaClO4•H2O to 1.0 in K2C2O4•H2O and the isotropic chemical shift ranged from -15.0 ppm in NaClO4•H2O to 19.6 ppm in BaClO3•H2O. The computational results revealed the trends for each parameter, where there is an increasing trend for quadrupolar coupling constant and span as a function of increasing hydrogen bond distance, decreasing trend for the three chemical shift tensors as a function of increasing M-Ow distance and unclear trends for asymmetry parameter and skew due to competing electronic factors. Overall, this study provides benchmark 17O NMR data for water molecules in crystalline hydrates, including the first measurement of 17O chemical shift anisotropy for such materials.
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Alfvén, Linda, and Sorin Ignea. "Characterization of Gas hydrates." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-203043.
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Gas hydrates are naturally occurring crystalline formations consisting of crystal structural “cages” which make up cavities where gas molecules can be trapped. Hydrates are formed under specific pressure and temperature conditions in the ground, which limits their presence to permafrost and deep sea continental margins. The interest for gas hydrates has grown bigger in the past time, mainly because of the potential as a new energy source but also because of the possibility of carbon dioxide (CO2) storage and its potential linkage to different geological hazards. Gas hydrates are still relatively poorly understood with many questions to be answered. Therefore research in this area is important. In our study we have been focusing on characterization of gas hydrate structures and their gas composition. By using the two different analytical methods X-ray powder diffraction (XRD) and gas chromatography. For this study to be successfully carried out we needed access to equipment and expertise which is only to be found in few places on Earth. Our lab work was therefore done at Pontifica Universidade Catolica do Rio Grande do Sul in Porto Alegre Brazil where a research project in gas hydrates is on going. Because of the research projects secrecy we do not know where our gas hydrate samples come from which mean we cannot link our results to any geographic area. The structural analysis shows structure I hydrate which is characterized by the presence of small gas molecules such as hydrocarbons. The results from the gas content validated that it is structure I since large concentrations of methane gas (CH4) and sulphur gas (H2S) were detected. The presence of these gases implies that the formation conditions are in a marine environment at the sulphate-methane transition zone (SMTZ).
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Hughes, Thomas John. "Plug Formation and Dissociation of Mixed Gas Hydrates and Methane Semi-Clathrate Hydrate Stability." Thesis, University of Canterbury. Chemical and Process Engineering, 2008. http://hdl.handle.net/10092/1579.
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Gas hydrates are known to form plugs in pipelines. Hydrate plug dissociation times can be predicted using the CSMPlug program. At high methane mole fractions of a methane + ethane mixture the predictions agree with experiments for the relative dissociation times of structure I (sI) and structure II (sII) plugs. At intermediate methane mole fractions the predictions disagree with experiment. Enthalpies of dissociation were measured and predicted with the Clapeyron equation. The enthalpies of dissociation for the methane + ethane hydrates were found to vary significantly with pressure, the composition, and the structure of hydrate. The prediction and experimental would likely agree if this variation in the enthalpy of dissociation was taken in to account.
In doing the plug dissociation studies at high methane mole fraction a discontinuity was observed in the gas evolution rate and X-ray diffraction indicated the possibility of the presence of both sI and sII hydrate structures. A detailed analysis by step-wise modelling utilising the hydrate prediction package CSMGem showed that preferential enclathration could occur. This conclusion was supported by experiment.
Salts such as tetraisopentylammonium fluoride form semi-clathrate hydrates with melting points higher than 30 ℃ and vacant cavities that can store cages such as methane and hydrogen. The stability of this semi-clathrate hydrate with methane was studied and the dissociation phase boundary was found to be at temperatures of about (25 to 30) K higher than that of methane hydrate at the same pressure.
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Sadeq, Dhifaf Jaafar. "Gas Hydrates Investigation: Flow Assurance for Gas Production and Effects on Hydrate-bearing Sediments." Thesis, Curtin University, 2018. http://hdl.handle.net/20.500.11937/75809.
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This thesis was aimed to study gas hydrates in terms of their equilibrium conditions in bulk and their effects on sedimentary rocks. The hydrate equilibrium measurements for different gas mixtures containing CH4, CO2 and N2 were determined experimentally using the PVT sapphire cell equipment. We imaged CO2 hydrate distribution in sandstone, and investigated the hydrate morphology and cluster characteristics via μCT. Moreover, the effect of hydrate formation on the P-wave velocities of sandstone was investigated experimentally.
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Rojas, González Yenny V. "Tetrahydrofuran and natural gas hydrates formation in the presence of various inhibitors." Thesis, Curtin University, 2011. http://hdl.handle.net/20.500.11937/2332.
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The aim of this thesis is to investigate the formation process of tetrahydrofuran (THF) hydrates and natural gas hydrates, and the effect of kinetic hydrate inhibitors (KHIs) on the formation and growth of these hydrates. Kinetic experiments were conducted in pressure cells in the presence of, or without, KHIs. Interfacial and electrokinetic techniques, including surface tension, Langmuir monolayers and zeta potential, were used to study the adsorption preferences of the inhibitors in two different interfaces, air–liquid and hydrate–liquid. For comparison purposes, selected thermodynamic hydrate inhibitors (THIs) and antiagglomerators (AAs) were investigated in some of the experiments. Sodium chloride was used in experiments where suitable.Four well known KHI polymers, including a terpolymer of N-vinylpyrrolidone, Nvinylcaprolactam and dimethylamino-ethylmethacrylate (Gaffix VC713), poly(Nvinylcaprolactam) (Luvicap EG), and poly(N-vinylpyrrolidone) (PVP40, Mn=40k and PVP360, Mn=360k), were selected for the investigation. A copolymer containing both poly(ethylene oxide) and vinylcaprolactam segments (PEO-VCap) that was developed in the Polymer Research lab in Curtin University, was also investigated. Other chemicals, including methanol (MeOH) and monoethylene glycol (MEG) were used as THIs. Sodium dodecyl sulphate (SDS) was used as an AA.During the THF hydrates kinetic studies, several experimental parameters that are associated with the nucleation and crystal growth process were investigated. The onset of THF hydrates formation, the maximum temperature spike, the magnitude of the temperature rise associated with the hydrate formation, the rate of hydrate formation, and the temperature at the end-point of the hydrate formation, were reported to compare inhibition efficiency. Subcooling was used as the driving force for hydrates formation. The experimental results show that the kinetics of the THF hydrate is affected by the physical chemical environment, which includes the concentration and types of additives used for the inhibition of the hydrates. In comparison to the system containing no inhibitor, there was an increase in subcooling and a reduced onset temperature of hydrates formation when various inhibitors were used.Surface tension studies have demonstrated that the adsorption of KHIs molecules at the air–liquid interface is directly related to its effectiveness inhibiting hydrates. The differences in the fundamental properties of the polymer molecules, such as molecular weight and flexibility of the polymer chain, have an impact on the different adsorption behaviours at the air–liquid interface for all of them. The inhibition efficiency of KHIs was enhanced in the presence of NaCl 3.5 wt% for all the inhibitors, and seemed to be associated to maximum packing of polymer molecules in the monolayer and low surface tension values. The zeta potential results, measured at the THF hydrate–liquid interface, have shown some correspondence with the surface tension results at the air liquid–interface. The compound, with a higher adsorption at the air liquid–interface also showed a higher adsorption at the surface of the THF hydrate. It was observed, that the inhibitor showing the higher adsorption on zeta potential measurements was more effective for reducing the onset temperature of hydrates formation.The kinetic studies have been extended to structure II natural gas hydrates systems, to examine whether the hypothesis proposed for THF hydrates systems were applicable to the gas hydrate systems. Gaffix VC713, Luvicap EG, PVP40 and PEO-VCap were used in this investigation. The gas hydrate formation rate was always slower when KHIs were present in the liquid phase. In all cases, the presence of KHI decreases the temperature of the onset hydrate formation. Polymers, such as PVP40 and PEO-VCap, that showed the worse and the best inhibition performances respectively in THF crystals, exhibited the opposite inhibition performance in gas hydrate crystals. This suggests that a different mechanism of KHIs surface adsorption could be operating on different hydrates surfaces.Overall, the investigation of the kinetics of formation and inhibition on THF hydrates and natural gas hydrates in the presence of KHIs, indicate that the gas hydrate formation rate during gas hydrate formation, is always slower when KHIs are present in the liquid phase. The inhibition mechanism of KHIs in the THF hydrates systems may differ significantly from that of the gas hydrate systems. Adsorption studies, demonstrate that the adsorption of KHIs are directly related to their effectiveness inhibiting hydrates. Surface tension and zeta potential approaches provide valuable information for understanding hydrates formation and inhibition mechanisms.
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Le, Thi Xiu. "Experimental study on the mechanical properties and the microstructure of methane hydrate-bearing sandy sediments." Thesis, Paris Est, 2019. http://www.theses.fr/2019PESC1039.
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Les hydrates de méthane (MHs), composés de gaz de méthane et d’eau, se forment naturellement à haute pression et faible température dans les sédiments marins ou pergélisols. Ils sont actuellement considérés comme une ressource énergétique (principalement MHs dans les sédiments sableux) mais aussi une source de géo-hasards et du changement climatique (MHs dans les sédiments grossiers et fins). La connaissance de leurs propriétés mécaniques/physiques, qui changent considérablement avec la morphologie et distribution des hydrates dans les pores, est très importante pour minimiser les impacts environnementaux liés aux futures exploitations du gaz de méthane à partir des sédiments sableux contenant des MHs (MHBS). La plupart des études expérimentales concernent MHBS synthétiques à cause des difficultés pour récupérer des échantillons intacts. Différentes méthodes ont été proposées pour former MHs dans les sédiments au laboratoire pour reconstituer des sédiments naturels, mais sans grand succès. Cette thèse a pour objectif d’évaluer la morphologie, la distribution des MHs dans les MHBS synthétiques à différentes échelles et d’étudier les effets des MHs (leur morphologie et teneur en hydrate) sur les propriétés mécaniques des MHBS. Deux méthodes de formation d’hydrates dans les sédiments sableux ont été proposées. Au niveau macroscopique, la distribution des hydrates au niveau des pores est évaluée en se basant sur la vitesse de propagation d’onde de compression (mesurée et calculée à partir des modèles existants). Des essais triaxiaux ont été utilisés pour étudier l’influence des MHs à différentes teneurs en hydrate sur les propriétés mécaniques des MHBS. Par ailleurs, l’Imagerie par Résonance Magnétique a été utilisée pour étudier la cinétique de formation/dissociation d’hydrates et aussi la distribution des hydrates sur l’ensemble de l’échantillon. Les résultats montrent qu’un cycle de température en conditions non drainées complète la redistribution des hydrates dans les pores après la saturation en eau de l’échantillon à haute teneur en hydrate. La distribution des hydrates sur l’ensemble de l’échantillon devient plus homogène avec la saturation en eau suivie par un cycle de température. En outre, les propriétés mécaniques des sédiments augmentent avec l’augmentation de la teneur en hydrate.A l’échelle du grain, la tomographie aux rayons X (XRCT) et celle au Synchrotron XRCT (SXRCT, Synchrotron SOLEIL) ont été utilisées pour observer la morphologie et la distribution des MHs au niveau des pores des sédiments sableux. Ce travail n’a pas été facile car il nécessitait des dispositifs expérimentaux compliqués (pour maintenir la haute pression et faible température) mais aussi en raison du faible contraste entre MHs et l’eau sur les images de XRCT, SXRCT. Des dispositifs spécifiques ont été développés pour étudier la formation d’hydrates, la morphologie et la distribution à l’échelle du grain des MHs en utilisant XRCT, SXRCT. De plus, une nouvelle méthode a été développée pour déterminer plus précisément les fractions volumiques d’un milieu triphasé à partir des images XRCT. Des observations au Microscope Optique (en coopération avec l’Université de Pau) ont également été faites pour confirmer diverses morphologies de MHs dans les sédiments sableux. Les morphologies et distributions d’hydrates observées sont comparées avec les modèles existants. Les observations montrent que la formation des MHs dans les sédiments sableux est un processus instable et compliqué. Différentes morphologies et distributions au niveau des pores des MHs peuvent coexister. Il parait indispensable de tenir compte des vraies morphologies et distributions au niveau des pores des MHs pour les études numériques utilisant des modèles simplifiés.Mots-clés: hydrate de méthane, sédiments sableux, formation, dissociation, morphologies, distribution, propriétés mécaniques, XRCT, SXRCT, microscope optique, essais triaxiaux, modèle de mécanique des roches<br>Methane hydrates (MHs), being solid ice-like compounds of methane gas and water, form naturally at high pressure and low temperature in marine or permafrost settings. They are being considered as an alternative energy resource (mainly methane hydrate-bearing sand, MHBS) but also a source of geo-hazards and climate change (MHs in both coarse and fine sediments). Knowledge of physical/mechanical properties of sediments containing MHs, depending considerably on hydrate morphologies and pore-habits, is of the importance to minimize the environmental impacts of future exploitations of methane gas from MHBS. Existing experimental works mainly focus on synthetic samples due to challenges to get cored intact methane hydrate-bearing sediment samples. Various methods have been proposed for MH formation in sandy sediments to mimic natural MHBS, but without much success. The main interests of this thesis are to investigate morphologies and pore-habits of MHs formed in synthetic MHBS at various scales and to study the effects of MHs (MH morphology and MH saturation) on the mechanical properties of MHBS.Two MH formation methods (modified from two methods existing in the literature) have been first proposed to create MHs in sandy sediments at different pore-habits. At the macroscopic scale, MH pore-habits have been predicted via comparisons between sonic wave velocities, measured and that calculated based on rock physic models. The effects of MHs formed following the two proposed methods (at different hydrate saturations) on the mechanical properties of MHBS were investigated by triaxial tests. Furthermore, Magnetic Resonance Imaging (MRI) has been used to investigate the kinetics of MH formation, MH distribution along with sample height and also MH dissociation following the depressurization method which has been considered as the most economical method for MH production from MHBS. A temperature cycle in undrained conditions was supposed to not only complete MH redistribution in pore space after the water saturation of the sample at high hydrate saturation but also make MHs distributed more homogeneously in the sample even at low hydrate saturation. Furthermore, the mechanical properties of sediments (e.g. stiffness, strength) were found higher at higher MH saturation.At the grain scale, the MH morphologies and pore habits in sandy sediments were observed by X-Ray Computed Tomography (XRCT, at Navier laboratory, Ecole des Ponts ParisTech) and Synchrotron XRCT (SXRCT, at Psiche beamline of Synchrotron SOLEIL). It has been really challenging due to not only the need of special experimental setups (needing both high pressure and low temperature controls) but also poor XRCT, SXRCT image contrast between methane hydrate and water. Specific experimental setups and scan conditions were then developed for pore-scale investigations of MH growth and MH morphologies in sandy sediments by using XRCT, SXRCT. Besides, a new method has been developed for accurate determination of volumetric fractions of a three-phase media from XRCT images. Observations (at better spatial and temporal resolution) via Optical Microscopy (in cooperation with the University of Pau) were finally used to confirm diverse MH morphologies in sandy sediments. Comparisons between observed MH morphologies, pore habits, and existing idealized models have been discussed. Methane hydrate formation in sandy sediments was supposed to be an unstable and complex process. Different types of MH morphologies and pore habits could exist in the sample. It seems vital that numerical studies on the mechanical behavior of gas hydrates in sediments, based on four idealized hydrate pore-habits, should take into account realistic hydrate morphologies and pore habits.Keywords:Methane hydrates, sandy sediments, formation, dissociation, morphologies, pore-habits, mechanical properties, XRCT, SXRCT, optical microscopy, triaxial tests, rock physic model
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Jang, Jaewon. "Gas production from hydrate-bearing sediments." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41145.
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Gas hydrates are crystalline compounds made of gas and water molecules. Methane hydrates are found in marine sediments and permafrost regions; extensive amounts of methane are trapped in the form of hydrates. The unique behavior of hydrate-bearing sediments requires the development of special research tools, including new numerical algorithms (tube- and pore-network models) and experimental devices (high pressure chambers and micromodels). Hydraulic conductivity decreases with increasing variance in pore size distribution; while spatial correlation in pore size reduces this trend, both variability and spatial correlation promote flow focusing. Invading gas forms a percolating path while nucleating gas forms isolated gas bubbles; as a result, relative gas conductivity is lower for gas nucleation than for gas invasion processes, and constitutive models must be properly adapted for reservoir simulations. Physical properties such as gas solubility, salinity, pore size, and mixed gas conditions affect hydrate formation and dissociation; implications include oscillatory transient hydrate formation, dissolution within the hydrate stability field, initial hydrate lens formation, and phase boundary changes in real field situations. High initial hydrate saturation and high depressurization favor gas recovery efficiency during gas production from hydrate-bearing sediments. Even a small fraction of fines in otherwise clean sand sediments can cause fines migration and concentration, vuggy structure formation, and gas-driven fracture formation during gas production by depressurization.
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Zugic, Minjas. "Raman spectra of clathrate hydrates." Thesis, King's College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271176.
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Barboux, Philippe. "Conductivite protonique dans les hydrates." Paris 6, 1987. http://www.theses.fr/1987PA066034.
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Barboux, Philippe. "Conductivité protonique dans les hydrates." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37602594d.
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Barros, Parigi Rafael. "Methane hydrates: Investigating the influence of sediment type on modeled methane escape in the high latitude Northern Hemisphere." Thesis, Stockholms universitet, Institutionen för geologiska vetenskaper, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-192841.
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Methane hydrates have drawn the attention of climate scientists in the past decades due to the potency of methane as a greenhouse gas and the widespread occurrence of hydrates both in terrestrial and marine environments, which, if destabilised, could enhance global warming. This study aims to investigate how much impact sediment type has on modeled methane escape at the feather edge of stability for methane hydrates in the high latitude Northern Hemisphere (45° to 75° N). This area is characterised by cool bottom-water temperatures leading to a shallow gas hydrate stability zone (GHSZ), and has been disproportionally influenced by contemporary seawater warming. Calculations were performed to establish the depths of the upper and lower boundaries of the feather edge of the GHSZ. These limits were used to estimate seafloor areas covered by three select sediment types that have different petrophysical properties - hemipelagic clay, calcareous ooze and siliceous ooze. Modeling of methane flux for 300 years following a 3°C warming during the first 100 years was performed using TOUGH + HYDRATE for each of the three sediment types. The sediments behaved significantly differently, with siliceous ooze releasing the most methane gas, and calcareous ooze releasing the least. Estimates of total methane gas release were also performed on the areas covered by the three sediments between latitudes 45° to 75° N, and showed that, over the course of 300 years, up to 5 times the current methane concentration in the atmosphere could become susceptible to leaving methane hydrate reservoirs.
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Townson, Iwan Meredydd. "Microbial inhibition of methane clathrate hydrates." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/41022.
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Two microbial species were tested for inhibition of methane hydrates in a stirred crystallizer (subcooling of 2.34 K). The ice associating Chryseobacterium sp. Strain C14, grown in 0.5 wt% Tryptic Soy Broth (TSB) delayed hydrate nucleation, on average, by 30.3 hours compared to 37.9 hours for the PVP solutions. Escherichia coli TG2 in 0.5 wt% TSB was used as a non ice associating bacteria control and surprisingly had the longest induction period of 118.1 hours, suggesting that it was 3 times more effective as a hydrate inhibitor than PVP. The 0.5 wt% aq. TSB solution without bacteria delayed hydrate nucleation an average of 6.7 hours, whilst bacteria without TSB also showed significant inhibition. However, for the bacteria and bacteria + TSB systems, nucleation times were far more sporadic and time dependant than the simple systems of pure water and PVP. PVP decreased hydrate growth rate but increased gas consumption by nearly 4 fold. TSB without bacteria promoted gas consumption by over 2 fold but exhibited a slightly higher growth rate than the pure water solution. Reasons for the differences in growth profiles may be a result of the observed morphological differences in the hydrate phase. Chryseobacterium in 0.5 wt% aq. TSB had a distinct time dependency in growth characteristics and promoted growth rate almost 3 fold. E. coli in 0.5 wt% TSB showed a unique S-curve growth profile where the initial growth rate was very low. The differences in growth profiles of the two bacteria suggest different inhibition mechanisms. Ice-associating proteins likely play a significant role in hydrate formation, especially for Chryseobacterium which has shown inhibition of ice recrystallization. However, the interaction of other non-ice associating macromolecules may play a primary role in the observed inhibition and that biofilm formation may act as a barrier between the gas-liquid and/or heterogeneous nucleating solid-liquid interfaces which may help explain the significant inhibition observed by E. coli. Considering that both species of bacteria yielded significant hydrate inhibition, albeit somewhat unpredictable, but since the procedure is simple, the potential of employing bacteria as ‘Microbial Hydrate Inhibitors’ looks promising. However, consistent inhibition
will be a challenge to overcome so that these organisms could be used as other KHI solutions.
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Wang, Qian. "Structure and Thermodynamic of Halogen Hydrates." Thesis, University of California, Irvine, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1535376.
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<p> So far to our knowledge, the bromine-xenon double clathrate hydrate has not yet been completely studied. In recent research in Janda lab at UC Irvine, we obtained the thermodynamic properties and structure of bromine-xenon double clathrate by applying UV-Vis spectroscopy and determining the total vapor pressure of the clathrate. In both of the TS-I and CS-II structures, bromine could only stay in the bigger size cages, while introducing xenon as a helper gas to occupy the smaller cages. Based on this concept, we hypothesize that the bromine-xenon double clathrate has the TS-I structure type below 273K, and the CS-II structure type above this temperature. Also we calculated the enthalpy of dissociation of the TS-I bromine-xenon double clathrate as 12.305±0.170kJ/mol/K, and the CS-II clathrate as 16.574±0.143 kJ/mol/K.</p>
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Hardwick, Jack. "Simulating hydrates in shallow marine sediments." Thesis, Durham University, 2018. http://etheses.dur.ac.uk/12775/.
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With global energy needs growing alongside a drive to reduce carbon emissions, there is a demand for cleaner, alternative energy. Methane hydrates are one such resource that is being investigated with the goal of future potential exploitation. 99 % of this resource is found within marine environments where, particularly in shallow marine sediments, there is a concern that rising ocean temperatures may lead to widespread methane release as hydrate dissociates. Multi-component, multi-phase (MCMP) modelling can be used to forecast the behaviour of methane hydrate dissociation in these contexts. However, there is a lack of agreement across literature on how best to numerically solve and mathematically describe the hydrate dissociation problem. The objective of this PhD is to develop new numerical models from first principles using the Method of Lines (MOL) approach. The MOL is attractive because it takes advantage of widely available high quality, ordinary differential equation solvers. However, a significant challenge is that the MOL requires formulating the problem in terms of persistent primary dependent variables. A kinetic model was developed and used to simulate experimental data from a well studied hydrate dissociation experiment. This study improved on previous work by reconciling more of the dataset. A three-phase permeability model was developed for this purpose, which invokes a critical threshold whereby permeability is dramatically reduced in the presence of very small hydrate saturations. Due to numerical instability associated with upscaling the hydrate kinetics, the MOL is challenging to solve for regional scale problems using the kinetic model. An alternative model which maintains phases in equilibrium by removing the hydrate kinetics was therefore developed. Preliminary work applied this equilibrium model to a regional scale ocean warming driven hydrate dissociation problem. Permeability in the presence of hydrate is a strong function of pore morphology as hydrate grows within porous media. Constraining this relationship can lead to better estimations of methane emissions driven by ocean warming and methane recovery in economically attractive hydrate deposits.
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Wilson, Craig W. "High-pressure studies of ammonia hydrates." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/8921.
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Ammonia and water are major components of many planetary bodies, from comets and icy moons such as Saturn's Titan to the interiors of the planets Neptune and Uranus. Under a range of high pressures and/or low temperatures known to occur in these planetary bodies, ammonia and water form a series of compounds known as ammonia hydrates. Ammonia and water form three stoichiometric compounds, ammonia hemihydrate, ammonia monohydrate and ammonia dihydrate, which have ammonia-to-water ratios of 2:1, 1:1 and 1:2 respectively. Therefore a good understanding of the three stable ammonia hydrates is required for modelling the interiors of these bodies. Additionally, the ammonia hydrates are the simplest systems to incorporate mixed (N-H O and O-H N) hydrogen bonds. Such bonds are important biochemically, and along with O-H O H-bonds, mixed H-bonds are responsible for the second-order structure of DNA, and they are also responsible for the proton transfer reactions in enzymic processes. The understanding of these bonds and processes rests on the knowledge of the relationship between bond strength and geometry, and the ammonia hydrates provide a rich range of geometries against which models of such mixed H-bonds can be tested. X-ray and neutron diffraction techniques have been used to investigate the behaviour of the ammonia-water complex and further the understanding of this system. This includes solving the structure of a phase which was previously thought to be an ammonia monohydrate phase, but has been shown here to be a mixture of an ammonia hemihydrate phase and Ice VII. In addition to this, x-ray and neutron diffraction experiments have been performed to explore how this phase behaves under changing pressure and temperature conditions, and what other implications that this has on the ammonia-water system. It has been found that ammonia hemihydrate can also form a structural phase observed to form in both ammonia monohydrate and ammonia dihydrate within the same pressure and temperature regime, which opens the possibility of a solid solution existing between all three stoichiometric ammonia hydrates.
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Longo, Jean Paulo Nakatu. "Electrical impedance measurements of clathrate hydrates." Universidade Tecnológica Federal do Paraná, 2015. http://repositorio.utfpr.edu.br/jspui/handle/1/1406.
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PETROBRAS<br>Dentre os desafios no processo de produção de hidrocarbonetos na indústria de óleo e gás, uma área em destaque nos últimos anos é conhecida como garantia de escoamento, a qual envolve assegurar de forma contínua que os fluidos (óleo ou gás) escoem pelas tubulações que conectam o poço aos sistemas de separação na superfície. Um dos principais problemas enfrentados está ligado à deposição de hidratos de gás em tubulações, podendo estes diminuir o diâmetro útil ou até obstruir as tubulações, gerando perdas financeiras consideráveis devido a, principalmente, parada de produção. Hidratos de gás ou clatratos são estruturas cristalinas sólidas semelhantes ao gelo, normalmente formados por moléculas de água e gás em determinadas condições de pressão e temperatura. Atualmente não existe uma técnica de medição estabelecida para monitoração da formação de hidratos em tubulações. Uma técnica candidata é a medição da impedância (ou o espectro de impedância) dos fluidos, pois se trata de uma técnica simples, robusta e de baixo custo. Com o objetivo de investigar o processo de formação de hidratos de forma controlada, foram realizados e analisados diversos experimentos com três sistemas de medição diferentes operando três células de medição distintas. Um sistema totalmente comercial, um sistema misto e um sistema dedicado foram utilizados para realizar medidas de impedância do processo de formação de hidratos. Os testes foram realizados com uma substância modelo (tetrahidrofurano – THF) em mistura com água, com a qual é possível a formação de hidratos sem a necessidade do uso de uma célula pressurizada. Os dois primeiros sistemas (comercial e misto) são capazes de medir o espectro de impedância na faixa 101 Hz até 107 Hz. Já o sistema dedicado opera em frequência fixa (tipicamente 5 MHz). Os resultados mostraram-se promissores no que diz respeito à monitoração da formação de hidratos, já que diferenças consideráveis nos valores de impedância são observadas para a mistura de THF-água em estado líquido e com a presença de hidratos. Dessa maneira, o sistema desenvolvido aliado ao processamento dos dados experimentais pode ser empregado em trabalhos futuros como ferramenta simples para monitorar a formação de hidratos em tubulações.<br>Among the challenges in the oil and gas industry for hydrocarbon production, a featured area in recent years is known as flow assurance, which involves to guarantee the continuously stream of fluids (oil or gas) through pipelines connecting wellhead to separation systems at topside. One of the main problems is related to the deposition of gas hydrates in pipelines, since these deposits may reduce the effective pipe diameter or even clog pipelines, causing considerable financial losses mainly due to production stop. Gas hydrates or clathrates are crystalline solid ice-like structures, typically formed by water and gas molecules under certain conditions of pressure and temperature. Currently there is no established measurement technique for monitoring the hydrate formation in pipelines. One candidate technique is impedance (or impedance spectrum) measurement of fluids, since it is simple, robust and low cost. With the objective of investigating hydrate formation in a controlled environment, several experiments with three different measuring systems operating three different measuring cells have been performed and evaluated. A fully commercial, a mixed, and a dedicated measuring system were applied for obtaining impedance data of hydrates formation. The experimental tests were performed with a model substance (tetrahydrofuran - THF) in mixture with water which allows the monitoring of hydrates formation at ambient pressures (i.e. no need to use a pressurized cell). The first two systems (commercial and mixed) are able to measure the impedance spectrum in the range 10 Hz to 10 MHz. The dedicated system operates at a fixed frequency (typically 5 MHz). The results show that considerable differences in impedance values are observed for the THF-water mixture in liquid conditions and with the presence of hydrates, hence being promising in hydrates formation monitoring. In this way, the developed measurement system allied to appropriated data processing routines has the potential to be applied as simple tool to monitor hydrate formation in pipes.
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Lavanant, Yves. "Etude du comportement mécanochimique des hydrates." Dijon, 1993. http://www.theses.fr/1993DIJOS062.
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A partir d'une recherche réalisée dans trois domaines: 1) la mise au point d'un dispositif original automatisé permettant de suivre en continu la déshydratation (ou la réhydratation) mécanique tout en maintenant constante la pression de vapeur d'eau dans l'enceinte de broyage; 2) la détermination des courbes p(t) caractéristiques de l'équilibre de déshydratation de plusieurs hydrates; 3) l'analyse comparée du comportement mécanochimique des hydrates d'une famille iso structurale et des fréquences de libration des molécules d'eau et leur structure, les résultats significatifs suivants ont été trouvés: i) les seules déshydratations mécaniques possibles correspondent à l'évolution vers leur forme stable des hydrates qui, dans les conditions de pression de vapeur d'eau (p#b#r) et de température (t#b#r) imposées pour le broyage, sont métastables; ii) il n' y a d'activation mécanique d'une déshydratation thermique que si l'hydrate concerne est métastable dans les conditions de pression de vapeur d'eau et de température fixées pour le traitement mécanique et à l'origine du traitement thermique; iii) un hydrate présente des propriétés mécaniques différentes selon qu'il est sous sa forme stable (il est alors élastique) ou sous sa forme métastable (il a un comportement plastique); iv) la métastabilité d'un hydrate a été définie par un indice pour une pression donnée p. Des corrélations paraissent exister entre la métastabilité relative des hydrates et, d'une part leur stabilité mesurée par g#2#9#8# et, d'autre part la fréquence de libration de leurs molécules d'eau de structure
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BARRON, CECILE. "Destructuration d'amidons peu hydrates sous cisaillement." Nantes, 1999. http://www.theses.fr/1999NANT2091.
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La destructuration de l'amidon sous cisaillement, en milieu faiblement hydrate (25 - 30% b. H. ), a ete etudiee dans des conditions experimentales semblables a celles rencontrees en extrusion. Ce procede a ete simule a l'echelle du laboratoire par l'utilisation d'un rheometre a pre-cisaillement, le rheoplast. Pour des conditions de traitements thermomecaniques controlees (25<t<190\c, 0<<75s - 1, 15<t<30s), des etats intermediaires de transformations ont ete obtenus a partir d'amidons de diverses origines botaniques (pois lisse, mais cireux, ble et pois ride), et analyses a chaque echelle structurale (granulaire, cristalline et moleculaire). Les resultats acquis a partir de traitements isolant le role de chaque variable (temperature, cisaillement, temps) ont montre que la perte des structures granulaire et cristalline est prealable a toute degradation macromoleculaire significative. Alors que l'apport de chaleur induit la fusion des cristallites, l'apport d'energie mecanique affecte en priorite la structure granulaire par fragmentation. La destructuration complete n'est pas necessaire pour obtenir une phase continue deformable dont la viscosite a ete mesuree pour des taux de transformation superieurs a 50%. Un bilan energetique simplifie de la zone de traitement a ete etabli dans le but de modeliser la transition de la poudre en une suspension amylacee, en cours de transformation. L'evolution de la matiere est decrite pour des temps de traitement realistes, mais les energies mecaniques calculees sont surestimees. Ce modele confirme l'initiation du processus pres des pieces en mouvement et le role predominant de l'energie dissipee par frottements interparticulaires. Ce terme initialement preponderant decroit au profit de la dissipation d'energie mecanique au sein de la suspension amylacee. Cette approche peut etre extrapolee a l'extrusion et etendue a des substrats plus complexes, et permettrait de simuler la production de matiere partiellement destructuree.
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Kogon, Remi Albert Boris <1984>. "1H NMR Relaxation Characterization Of Hydrates." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amsdottorato.unibo.it/9773/1/1H%20NMR%20Relaxation%20Characterization%20of%20Hydrates.pdf.
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To distinguish the components of NMR signals from hydrated materials and to monitor their evolution after the addition of water to the powders, during the first two days of hydration.
To implement the 3 Tau Model in a MATLAB script, called 3TM, provided with a Graphical User Interface (GUI), to easily use the 3 Tau Model with NMRD profiles.
The 3 Tau Model, developed a few years ago is used for interpreting the dispersion (NMRD profiles, dependence on the Larmor frequency) of the longitudinal relaxation times, for liquids confined in porous media. This model describes the molecular dynamics of confined molecules by introducing three characteristic correlation times and additional outputs.
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De, Prunelé Alexis. "Dynamics of gas hydrate-bearing pockmarks : learnings from two cases studies from the Gulf of Guinea." Thesis, Brest, 2015. http://www.theses.fr/2015BRES0017/document.
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Cette étude doctorale a consisté à décrire la dynamique géochimique de deux pockmarks à hydrates de gaz de la marge africaine en considérant deux approches différentes. La première zone d’étude, appelée Preowei, est située au large du Nigéria. Elle est caractérisée par un grand nombre de pockmarks de tailles différentes, plus ou moins proche les uns des autres. Les analyses géochimiques des échantillons de fluides interstitiels, combinées aux données géophysiques (séismiques) ont permis de mieux comprendre le schéma de migration des hydrocarbures pour un ensemble composé de quatre pockmarks très rapprochés. L’utilisation de ces données géochimiques dans un modèle de transport- réaction a conduit à une datation de plusieurs séquences de libération de gaz au sein de ces structures. Un schéma conceptuel décrivant les processus de formation et d’évolution temporelle des pockmarks a été proposé pour synthétiser les conclusions obtenues. Finalement, cette étude a montré que l’ensemble des pockmarks étudiés sont actifs depuis 2700 ans, qu’ils sont en phase de formation d’hydrates pour certains, et de carbonates pour d’autres. La deuxième structure étudiée est le pockmark Regab. Il est situé au large du Gabon, au nord du canyon sous-marin alimenté par le fleuve Congo. Il est caractérisé par la présence d’hydrates affleurant et une faune abondante et très variée sur toute sa surface. L’originalité de ce travail a été d’étudier la distribution de la mégafaune présente sur ce pockmark en fonction de la nature des fluides qui migrent dans le sédiment superficiel, et qui est libérés dans la colonne d’eau. Une attention particulière a été portée au méthane car c’est un élément central dans le cycle énergétique des microorganismes qui vivent en symbiose avec cette mégafaune. Trois nouveaux habitats ont été étudiés. Les données obtenues, associées à celle de la littérature ouverte, renforcent les conclusions des travaux antérieurs. Les Mytilidés ont besoin de très fortes concentrations de méthane pour se développer. Elles colonisent les zones de sortie de bulles et celle caractérisées par des hydrates affleurants. Les tapis bactériens sont associés à des zones où l’oxydation anaérobique du méthane se déroule dans le sédiment superficiel, avec une méthanogenèse dans la couche sous-jacente. Les Vésicomydé polychètes vivent dans des zones pauvres en méthane et sont très sensibles à sa variation de concentration<br>The present work describes the dynamics of two pockmark areas, off West Africa. The intention is to propose two different approaches to study the relationships between fluid migration and pockmarks. The first investigated area corresponds to a pockmark cluster called Preowei, located off Nigeria. Geochemical analyses and modeling were combined with seismic data to detail the hydrocarbon migration pattern at this area, with implication on both the pockmark formation and the evolution of their morphology. The proposed interpretation seeks to identify the conceptual bases of pockmark evolution over time at this area. It is argued that the cluster has been active for at least 2700 years, and it is still at the stage of hydrate formation for some pockmarks and carbonate formation for other. The second investigated pockmark, called Regab, is located off Gabon. It is a giant pockmark of 800-m diameter, characterized by an ecosystem rich in fauna, with a large variety of living species. The main core of the work done on this pockmark was focused on finding a link between the fluid chemistry and the spatial distribution of the living communities which populate it. This was achieved by combining new geochemical and bathymetric results with a well-compiled dataset from the literature
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Ding, Tao. "Gas hydrates to capture and sequester CO₂." Master's thesis, Mississippi State : Mississippi State University, 2004. http://library.msstate.edu/etd/show.asp?etd=etd-11102004-141404.
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Beltrán, Roldán Juan Guillermo. "Equilibrium and morphology studies of clathrate hydrates." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66763.
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Phase equilibria and morphology of clathrates or gas hydrates were investigated. Four-phase equilibrium conditions (hydrate-liquidaq-liquid-vapor) and three-phase equilibrium conditions (hydrate-liquidaq-vapor) were determined for the systems methane + carbon dioxide + neohexane + water and methane + carbon dioxide + water, respectively. It was found that the equilibrium mole fraction of carbon dioxide in the vapor phase follows opposite trends in both systems, with respect to equilibrium pressure, at rather constant temperature. Structure H equilibrium occurred at lower pressures and temperatures than structure I when the equilibrium vapor phase was methane rich. This phenomenon appeared to be reversed as the equilibrium vapor phase became richer in carbon dioxide. A novel reactor was designed in order to acquire high-resolution images of clathrate phenomena occurring at high pressures. Methane clathrate formation on water films without previous hydrate formation history was studied and it was found that hydrates formed in three layers, each with a clearly distinct morphology. This difference in morphology disappeared as the clathrate aged. Higher driving forces produced smaller hydrate grains and smoother surfaces than lower driving forces within the water film. The converse was true for the periphery. Dissociation started on the perimeter of the hydrate layer and proceeded until numerous gas bubbles were observed within the film. As hydrate dissociation spread throughout the film, water receded until it regained its original shape. Moreover, images revealed that an extremely thin hydrate film grew outside of the water boundary. It was found that this growing, thin film could induce nucleation in neighboring water droplets. Finally, the formation and decomposition of methane clathrate in water films containing silica gel particles were examined. It was observed that the hydrate front engulfed the parti<br>L'équilibre de phases et la morphologie des hydrates de gaz ont été étudiés. Les conditions d'équilibre à quatre phases (hydrates-liquideaq-liquide-vapeur) et à trois phases (hydrates-liquideaq-vapeur) ont été déterminées pour les systèmes méthane + dioxyde de carbone + neohexane + eau et méthane + dioxyde de carbone + eau, respectivement. On a constate que la fraction molaire du dioxyde de carbone dans la phase vapeur suivait des tendances contraires dans les deux systèmes, quand a la pression d'équilibre, pour une température relativement constante. Il fut aussi observe que l'équilibre des hydrates de structure H se produit a plus basses pressions et températures que celui des hydrates de structure I quand la phase vapeur est riche en méthane ; ce phénomène étant contraire quand la phase vapeur devient riche en dioxyde de carbone a l'équilibre.Un réacteur a été conçu pour acquérir des images à haute résolution de phénomènes relatifs à la formation des hydrates à haute pression. La formation des clathrates de méthane sur des pellicules vierges a été étudiée et il a été établi que les hydrates se formaient en trois couches, chacune d'elles avec une morphologie unique. Cette différence de morphologie s'estompait à mesure que le clathrate vieillissait. Des petits grains et des surfaces lisses ont été observes dans la pellicule pour de plus grandes forces d'entraînement, alors qu'^a plus basses forces d'entraînement les grains étaient grands et les surfaces rugueuses ; le contraire s'est produit en périphérie de la pellicule. La dissociation a commence dans le périmètre de la pellicule d'hydrates et a progresse jusqu'a l'apparition de nombreuses bulles gazeuses ; a mesure que la dissociation devenait omniprésente, la pellicule d'eau reculait pour retrouver sa forme originale. Il a aussi été possible de déceler qu'une pellicule extrêmement fin
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Shafiei, Rami. "Thermal imaging of tetrahydrofuran hydrates heat spread." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=95244.
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The research of gas hydrates has always been of industrial and scientific interests as their formation pose problems to the oil/gas industry while they also present a future energy resource as methane hydrates naturally occur in the earth crust. In the present study, Infrared imaging technology is utilized to observe and study heat spread of the formation and decomposition of tetrahydrofuran (THF) hydrates. Also, using infrared imaging technology, hydrates crystals are observed in the presence of poly(N-vinylpyrrolidone) (PVP) to study the crystals growth in presence of a kinetic inhibitor. THF was utilized due to its easy attainability conditions which make them suitable for lab experiments.<br>La recherche des hydrates de gaz a toujours été des intérêts industriels et scientifiques que leur formation poser des problèmes à l'industrie pétrolière / gaz alors ils présentent également une ressource énergétique future que les hydrates de méthane se produisent naturellement dans la croûte terrestre. Dans la présente étude, la technologie d'imagerie infrarouge est utilisée pour observer et étudier la propagation de la chaleur de la formation et la décomposition de tétrahydrofurane (THF) hydrates. En outre, en utilisant la technologie d'imagerie infrarouge, les hydrates de cristaux sont observés dans la présence du poly (N-vinylpyrrolidone) (PVP) pour étudier la croissance des cristaux en présence d'un inhibiteur de cinétique. THF a été utilisé en raison de ses conditions attainability facile qui les rendent aptes à des expériences de laboratoire.
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Igboanusi, Udennaka Paul. "Properties and Production of Natural Gas Hydrates." Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.519605.
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Nash, Karen. "Spectroscopic studies of atmospherically relevant acid hydrates." Thesis, University of York, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326422.
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Russo, Manuela. "Titanium oxide hydrates : optical properties and applications." Thesis, Queen Mary, University of London, 2010. http://qmro.qmul.ac.uk/xmlui/handle/123456789/597.
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TiO2 has been extensively studied in the last decades due to its interesting optical and electronic properties, which, combined with low fabrication costs, renders this material very attractive for applications in photovoltaic and photocatalysis. However, the performances of titania in specific device applications were found to be strongly dependent on the synthetic methods selected for its production. The majority of such synthetic procedures rely on the hydrolysis of suitable precursors and often produce an amorphous solid, generally referred as the “amorphous” titanium oxide beside the crystalline titania. In this thesis, we thus set out to investigate amorphous materials produced by the hydrolysis of titanium tetrachlorides and tetraisopropoxide. We show that these amorphous products consists of titanium oxide hydrates, which are relatively stable at room temperature and fully convert into crystalline titania only after extended temperature treatments. We also find that titanium oxide hydrates may display highly desirable characteristic such as a strong photochromic response – especially when placed in a suitable chemical environment. In the following chapter, we then show 3 that hybrid systems can be readily prepared of titanium oxide hydrates with, for instance, macromolecular materials such as poly(vinylalcohol). The amorphous nature of the titanium oxide hydrates allows to introduce more than 90 vol.% of the inorganic species into such systems – compared to 15 vol.% or less when producing hybrids comprising, e.g., crystalline nanoparticles of TiO2. Therefore, materials can be realized that display a refractive index n of at least 2.1, without compromising transparency of the resulting structures. Remarkably, n can not only be adjusted by varying the content of the inorganic species, but also through suitable heat treatments and/or irradiation with UV-light. Potential applications for such new, versatile and tunable optical systems are also discussed in this thesis.
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Cao, Zhitao 1974. "Modeling of gas hydrates from first principles." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8496.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2002.<br>Includes bibliographical references.<br>Ab initio calculations were used to determine the H20-CH4 potential energy surface (PES) accurately for use in modeling gas hydrates. Electron correlation was found to be treated accurately by the second-order Moller-Plesset method (MP2). However, a large basis set, cc-pVQZ, was found to be necessary in order to compute the binding energies to within 0.1 kcal/mol of the basis set limit. In order to sample accurately the PES, the H2O-CH4 energy of interaction was computed at 18,000 points. For these computations to be feasible, a new method was developed in which all 18,000 points were computed using MP2/6-3 1++G(2d,2p) and then corrected to near the accuracy of MP2/cc-pVQZ. The PES calculated from the six-dimensional numerical potential agrees very well with far infrared vibration-rotation-tunneling spectroscopic data and experimental second virial coefficient data at the potential minimum and larger separations. In order to study the application of different potential forms to describe phase equilibrium for Structure I gas hydrates, molecular computations were performed and results were compared. Although simple potential forms can be fit satisfactorily to experimental P-T data for ethane and cyclopropane hydrates using the van der Waals and Platteeuw model, they fail to predict accurately cage occupancies of methane hydrates. Predicted phase equilibria and cage occupancies for methane hydrates using the ab initio potential are in close agreement with experimental P-T data and measured cage occupancies. The comparison showed that only the first-principles ab initio potential is able to physically characterize both the microscopic and macroscopic behaviors of methane hydrates.<br>(cont.) Various sets of thermodynamic reference properties currently available in the literature were examined by applying the van der Waals and Platteeuw model to predict monovariant 3-phase equilibria for hydrate forming binary mixtures from 260 to 320 K. Experimental uncertainties were found to be large enough to cause significant changes in the prediction of dissociation pressures. The ab initio methane-water intermolecular potential was used to obtain the reference properties with significantly small deviations, and the resulting parameters are able to give the best prediction of phase equilibria over the entire temperature range.<br>by Zhitao Cao.<br>Ph.D.
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Roberts, Harrison R. "Re+: Changing the Way the World Hydrates." Thesis, The University of Arizona, 2010. http://hdl.handle.net/10150/146197.
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Public concerns regarding drinking water sources are amassing as unhealthy contaminants become more prevalent. In 2008, Congress dedicated a hearing to the dangers of bottled water. Dangers such as plastic bottles leaking antimony, causing pulmonary injuries and skin cancer. Additionally, 2.5 million plastic bottles are thrown away every hour. As a result, bottled water profits dropped 6% in the first quarter of 2009, and 24 colleges have banned plastic bottles on their campus. Re+ delivers purified water to consumers on-the-go through single serve water bottle refill kiosks; helping them save money, and save the environment. Our target market will be exposed to a new type of vending experience that will seek to satisfy them beyond a physiological level. Through customizable bottles, customizable beverage options, and retail space that offers recognition and familiarity, consumers can fulfill their needs while simultaneously assisting a sustainable effort. Re+ employs on-site filtration, allowing for lower packaging and distribution costs, resulting in a business that is more efficient than bottled water, and has a minimum environmental impact. Re+ maintains the goal of diminishing plastic bottle waste by encouraging consumers to re-fresh, re-fill and re-use their water bottles.
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Dashti, Hossein. "Carbon dioxide capture using gas hydrates technology." Thesis, Curtin University, 2019. http://hdl.handle.net/20.500.11937/75679.
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Carbon dioxide (CO2) capture has been a significant topic of research and development activities over the past two decades. As a highly potential novel method, hydrate-based CO2 capture (HBCC) has received increasing attention within related industries, due to such advantages as the mild operating pressure and temperature that is required, the ease of regeneration and its unique separation mechanism. This thesis studied the kinetics modeling of gas hydrate formation for CO2 hydrates.
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Oignet, Jérémy. "Approche exergétique d'un procédé de réfrigération secondaire par coulis d'hydrates." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066590/document.
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L’utilisation des coulis d’hydrates comme Fluides Frigoporteurs Diphasiques (FFD) permet de réduire l’impact environnemental des systèmes frigorifiques car ces fluides possèdent une densité énergétique élevée. Leur application pour le stockage d’énergie thermique serait une réponse à une problématique industrielle de distribution de froid (climatisation, procédés de refroidissement). Un montage expérimental constitué d’une boucle de circulation et d’un réacteur de formation a été utilisé afin d’évaluer les caractéristiques thermo-hydrauliques des coulis d’hydrates de CO2 et a permis de déterminer les viscosités et les coefficients d’échange convectif des coulis. A l’aide de ces paramètres, une étude énergétique et exergétique a été réalisée sur le système. Cette étude a permis de développer un modèle numérique capable d’évaluer la distribution de l’énergie dans différents éléments du montage expérimental (réacteur de formation des hydrates et échangeur de chaleur pour la dissociation des hydrates), ainsi que de déterminer les pertes exergétiques engendrées par ces éléments. Un bon accord entre les données expérimentales et le modèle numérique pour le suivi en température du coulis lors de sa formation et dissociation a été montré. L’étude a confirmé que les fluides diphasiques présentent une plus grande efficacité énergétique et moins de pertes exergétiques que les fluides monophasiques<br>Hydrates slurries as two-phase secondary refrigerants (FFD) reduces the environmental impact of refrigeration systems because these fluids have a high energy density. Their use for cold storage could be a solution to an industrial cold distribution at various temperature levels (air-conditioning, cooling process or preservation temperature). An experimental device composed of a circulation loop and a formation tank enables to characterize the thermal-hydraulic properties of CO2 hydrates slurries in order to determine the viscosities and the convective heat transfer coefficients of hydrates slurries. With these hydraulic and thermal parameters, an energy study was carried out on the system. Within this study a numerical model was developed to evaluate the energy distribution in different experimental elements (hydrate formation tank and hydrates dissociation heat exchanger) and to determine the exergetic losses created by these components. A good agreement between the experimental data and the numerical model for the temperature evolution of the slurry has been shown. The study has confirmed that multi-phases fluids provide higher energy efficiency and less exergetic losses than one-phase fluids
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Borchardt, Lars, Winfried Nickel, Mirian Casco, et al. "Illuminating solid gas storage in confined spaces – methane hydrate formation in porous model carbons." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-221847.
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Methane hydrate nucleation and growth in porous model carbon materials illuminates the way towards the design of an optimized solid-based methane storage technology. High-pressure methane adsorption studies on pre-humidified carbons with well-defined and uniform porosity show that methane hydrate formation in confined nanospace can take place at relatively low pressures, even below 3 MPa CH4, depending on the pore size and the adsorption temperature. The methane hydrate nucleation and growth is highly promoted at temperatures below the water freezing point, due to the lower activation energy in ice vs. liquid water. The methane storage capacity via hydrate formation increases with an increase in the pore size up to an optimum value for the 25 nm pore size model-carbon, with a 173% improvement in the adsorption capacity as compared to the dry sample. Synchrotron X-ray powder diffraction measurements (SXRPD) confirm the formation of methane hydrates with a sI structure, in close agreement with natural hydrates. Furthermore, SXRPD data anticipate a certain contraction of the unit cell parameter for methane hydrates grown in small pores.
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Myre, Denis. "Synthesis of Carbon Dioxide Hydrates in a Slurry Bubble Column." Thesis, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/19789.
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Carbon dioxide hydrates were synthesized in a 0.10m I.D. and 1.22m tall bubble column equipped with a cooling jacket for heat removal. Visual observations at different driving forces (pressures between 2.75 and 3.60 MPa and temperatures between 0 and 8ºC) were recorded with a digital camera through a sight glass of 118.8 by 15.6 mm. The superficial gas velocity was varied from 20 to 50 mm/s to attain different levels of turbulence in the liquid. The growth rate was found to be dependent on the sequence/method used to reach the operating temperature and pressure. A greater supersaturation was obtained when the system temperature and pressure were reached with very low or no bubble-induced mixing. As a result, hydrates nucleated and grew immediately when starting the gas flow with the reactor volume being quickly filled with hydrates. Moreover, the hydrate growth rate and solution final density were higher when operating conditions partially condensed CO2 resulting in greater interphase mass transfer rates. In parallel, since hydrate formation is an exothermic process and the reaction is often limited by the rate of heat removal, heat transfer measurements were achieved in a simulated hydrate environment. The instantaneous heat transfer coefficient and related statistics gave insight on the role of bubbles on heat transfer and hydrodynamics.
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Martin, Ana Isabel. "Hydrate Bearing Sediments-Thermal Conductivity." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6844.
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The thermal properties of hydrate bearing sediments remain poorly studied, in part due to measurement difficulties inside the hydrate stability envelope. In particular, there is a dearth of experimental data on hydrate-bearing sediments, and most available measurements and models correspond to bulk gas hydrates. However, hydrates in nature largely occur in porous media, e.g. sand, silt and clay.
The purpose of this research is to determine the thermal properties of hydrate-bearing sediments under laboratory conditions, for a wide range of soils from coarse-grained sand to fine-grained silica flour and kaolinite. The thermal conductivity is measured before and after hydrate formation, at effective confining stress in the range from 0.03 MPa to 1 MPa. Results show the complex interplay between soil grain size, effective confinement and the amount of the pore space filled with hydrate on the thermal conductivity of hydrate-bearing sediments.
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Abbasi, Ghazanfer R. "Investigating the wettability effect on gas hydrate bearing sediments." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2023. https://ro.ecu.edu.au/theses/2650.
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Natural gas trapped in hydrate deposits is a potentially enormous source of energy which can in principle be extracted from the underground reservoir structures. These reserves can potentially also catastrophically release very large quantities of greenhouse gases to the atmosphere. Natural Gas Hydrate (NGH) occurs in sediments under certain pressure and temperature conditions and has the potential to meet the increasing global energy demand. However, an efficient exploitation of NGH requires a precise characterization and understanding of the hydrate formation, accumulation and dissociation mechanisms. In this work, a comprehensive study has been conducted to augment the understanding of NGH and their wettability behaviour in hydrate bearing sediments. Systematic experiments were conducted to address this by developing various approaches presented in this work. The approaches adopted to achieve the study objectives were: i) review of previous research on NGH, ii) the effect of wettability on gas hydrate in sediment, iii) the influence of rock wettability on the electrical resistivity of hydrate bearing sediments (HBS), (iv) wettability effect on measured velocity properties of HBS.
In this context, the micro-structural characterization of gas hydrate is essential and requires the use of specialized methods and equipment. While traditional imaging and characterization tools offer fundamental microstructure analysis, X-ray micro-computed tomography (μCT) has gained recent attention to produce high resolution three dimensional (3D) images of pore structure and pore habits of hydrate-bearing sediments and provide spatial distribution and morphology of gas hydrate. Micro-CT (μCT) offers direct visualization of hydrate structure and growth habits at high resolution ranging from macro-metric to micro-metric scale, therefore, it is extensively used in natural gas hydrate characterization. This review, therefore, summarizes the theoretical basis of μCT imaging spanning the setup of the experimental apparatus and visualization techniques. The applications of μCT in natural gas hydrate reservoirs characterization – hydrate types and constituent, physical and chemical properties of gas hydrates as well as their occurrence and accumulation are presented. Hydrate characterization using μCT imaging including the general understanding of hydrate pore habit prediction, hydrate saturation and percolation behaviour, hydrate seepage and permeability and the influence of hydrate saturation on the mechanical properties of hydrate-bearing sediments (HBSs) are explicitly discussed. Lastly, conclusions and recommendations for future research are provided. Thus, this review offers a reference for understanding in the application of micro-CT to evaluate gas hydrates – which in turn contributes towards the exploitation of these energy resources.
One key parameter which is well known to strongly influence fluid distribution, saturation and production is rock wettability. However, the effect of wettability on gas hydrate in sediment has not been investigated yet. We thus used nuclear magnetic resonance (NMR) spectrometry to measure relaxation times (T₂ and T₁) and the corresponding surface relaxivity of tetrahydrofuran (THF) hydrate during formation and dissociation in water- and oil-wet Bentheimer sandstone. We also measured the NMR porosities and hydrate saturations at different temperatures during hydrate formation/dissociation for both water-wet and oil-wet sandstone. Significantly higher hydrate saturation was observed in water-wet sandstone (when compared to oil-wet sandstone) at all stages of hydrate formation and dissociation. Furthermore, the T₂ spectra moved from the lower relaxation domain (before hydrate formation) to the fast relaxation domain (after hydrate formation) in both, water-wet and oil-wet sandstone. However, water-wet sandstone generally had a T₂ relaxation range due to the higher water affinity to water-wet rock and the associated faster demagnetization of the water molecules. These results demonstrate that low-field NMR can be used to quantify the rock wettability and observe hydrate behaviour in geologic sediments. This fundamental information thus aids in the development of gas extraction from hydrate reservoirs, and the assessment of potential greenhouse gas emissions from such reservoirs into the atmosphere.
Classically, rock wettability is one of the key factors in predicting fluid flow behavior, fluid distribution, reserves and productivities. However, the effect of wettability on electric resistivity of hydrate formations is only poorly understood. Thus, to evaluate the influence of rock wettability on the electrical resistivity (note that resistivity logging is a key well logging tool) of hydrate-bearing sandstone, Nuclear Magnetic Resonance experiments were conducted. Clearly, the effective porosity and liquid saturation increased with increasing temperature, due to hydrate dissociation. Furthermore, resistivity index, rock resistivity (Rt), and formation factor all decreased with increasing liquid saturation, and the formation factor demonstrated a positive correlation with hydrate saturation, though formation factor for oil-wet (OW) sandstone was higher than that of the water-wet (WW) sandstone. This work will thus significantly improve the fundamental understanding of the petrophysical properties of gas hydrate reservoirs, so that energy production can be optimized, geo-hazards can be avoided, and the hydrate gun hypothesis can be better assessed.
Furthermore, the effect of wettability on velocity properties of hydrate formations is poorly understood. Thus, to evaluate the key information about wettability effect on measured velocity properties of hydrate bearing sandstone, we conducted several experiments followed by NMR measurements. The P-wave velocities of water wet, and oil wet sandstones were obtained before and after hydrate formation. Our results demonstrate that the percentage of velocity in water wet sample is higher than oil wet sample which indicates high hydrate saturation in water wet sandstone. This is also confirmed by the NMR results which also showed that the hydrate saturation in water wet sandstone is higher than that in oil wet sandstone. This study can be used to quantify the hydrate occurrence in different wetting conditions. This study provides insights on acoustic velocity measurements for hydrate formation in the gas production pipelines.
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Rodriguez, Machine Carla Thais. "Raman spectroscopic study of CO2 capture and separation by semi-clathrate hydrates crystallization and investigation of exchange processes in hydrates." Electronic Thesis or Diss., Université de Lille (2018-2021), 2021. http://www.theses.fr/2021LILUR003.
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Aujourd’hui, les combustibles fossiles sont largement brûlés pour répondre aux besoins énergétiques croissants des populations humaines et aux enjeux industriels. De grandes quantités de gaz à effet de serre sont ainsi rejetées dans l’atmosphère et contribuent au réchauffement de la planète. Pour cette raison, des techniques d’atténuation du dioxyde de carbone (CO2) efficaces et respectueuses de l’environnement sont nécessaires, comme le captage et de stockage du carbone (CCS) en post-combustion, notamment à l’aide du processus de séparation à base d’hydrates (HBSP). Le HBSP consiste en l’encapsulation de petites molécules de gaz (e.g. CO2, azote (N2), méthane (CH4)) dans des composés cristallins semblables à de la glace, formant des hydrates de clathrate ou hydrates. Des travaux antérieurs ont montré que l’ajout de promoteurs tels que le bromure de tetrabutylammonium (TBAB) améliore considérablement le mécanisme de piégeage du gaz dans l’hydrate de semi-clathrate (sc). C’est pourquoi le HBSP peut s’avérer être une technique appropriée pour le captage sélectif du CO2 et la récupération d’énergie, bien qu’il soit encore nécessaire d’approfondir les connaissances fondamentales que nous avons des processus impliqués avant de pouvoir considérer un déploiement routinier à grande échelle. Ce travail vise à mieux comprendre les processus de séparation et de capture du CO2 à l’aide de l’hydrate sc, ainsi qu’à explorer les processus d’échange dans les hydrates de clathrate pour ouvrir une perspective vers les applications industrielles.Tout d’abord, une revisite des propriétés vibrationnelles de clathrates de CO2 est effectuée par spectroscopie Raman ex-situ à haute résolution pour révéler la distribution de cette molécule dans les hydrates en fonction des paramètres composition, pression et température. Seule une étude a rapporté la répartition des molécules de CO2 dans les petites et grandes cages des hydrates, mais avec une interprétation contestable, probablement due à l’effet de la résonance de Fermi qui en complique l’interprétation. Une des nouveautés de ce travail est l’identification des changements de fréquence en fonction de l’environnement structurel du CO2, améliorant ainsi notre connaissance des mécanismes d’encapsulation. De plus, des analyses Raman à haute résolution corroborées par mesures de diffraction de neutrons sont effectuées sur des sc de TBAB à base de CO2 à des fins de caractérisation.Par la suite, l’étude se concentre sur l’influence du protocole de formation (cristallisation rapide ou lente) sur les mécanismes d’encapsulation, la structure et la sélectivité de CO2+N2-TBAB par mesures Raman in-situ. Un nouveau point de dissociation est obtenu et nos résultats Raman mettent en évidence une performance variable du système sur la sélectivité en CO2 loin de ce point, alors qu’un meilleur résultat est obtenu proche de la dissociation. De même, les facteurs de séparation atteignent leurs plus grandes valeurs proches de la dissociation, en fonction toutefois de la structure du cristal de sc. La variation morphologique de la surface est suivie par microscopie optique et présente une transformation continue avec la température (cristaux polygonaux ou empilés évoluant en cristaux de TBAB-sc cylindriques). De plus, l’influence de la cinétique de formation sur la séparation et la sélectivité du CO2 est explorée.Enfin, une application potentielle de la séparation et du captage du CO2 par HBSP est abordée en étudiant le mécanisme d’échange lors de l’exposition d’un hydrate de clathrate de CO2 à l’azote gazeux. Même si les hydrates de CO2 et de N2 cristallisent respectivement dans les structures sI et sII, après injection de N2, ils forment une structure sI avec une occupation préférentielle des petites cages par les molécules de N2. Ensuite, la cinétique d’échange est analysée avec une perspective supplémentaire de récupération de méthane par injection de CO2 et de CO2+N2<br>Nowadays, fossil fuels are constantly burnt to fulfill the increasing human and industrial demand in energy, and as a consequence, large quantities of greenhouse gases such as carbon dioxide (CO2) are released in the atmosphere and contribute to global warming. It is therefore pressing to develop efficient post-combustion CO2 mitigation techniques that are also efficient and environment-friendly, and as such, Carbon Capture and Storage (CCS) technologies involving the Hydrate-Based Separation Process (HBSP) have attracted a lot of attention. HBSP consists in encapsulating small gas molecules (e.g. CO2, nitrogen (N2), methane (CH4)) within crystalline ice-like compounds known as clathrate hydrates or hydrates. Previous works have shown that promoters like tetra-n-butyl ammonium bromide (TBAB) considerably improves the guest-gas trapping mechanism in semi-clathrate hydrate (sc). Hence, while HBSP proves to be a suitable technique for selective CO2 capture and energy recovery, advancing the fundamental understanding of processes at play is still needed before large-scale practical applications can be routinely considered. This work aims to better comprehend CO2 separation and capture processes using sc-hydrate technology, while also exploring exchange processes in hydrates to open a perspective towards industrial applications.First, the guest distribution in the hydrate phases of CO2¬-based clathrate hydrates as a function of parameters (initial composition, p, T) is revisited and elucidated by ex-situ high-resolution Raman spectroscopy. Up to now, there is a gap in the literature regarding the discrimination of the contribution of the small and large cages in CO2-based hydrates, mainly due to the Fermi resonance effect. So far, only a single study has attempted to distinguish these contributions in CO2-clathrates, however with a questionable interpretation. One of the novelties of the present work is to revisit the vibrational properties of CO2-clathrates to identify distinct frequency shifts depending on the structural environment of CO2 molecules, thereby improving our knowledge of CO2 encapsulation mechanisms in hydrates. High-resolution Raman analysis and neutron diffraction analyses are additionally performed in CO2-based TBAB-semi-clathrates for characterization purposes.Second, the influence of two different formation protocols (quick and slow crystallization protocols, commonly used in hydrate formation) on the encapsulation mechanisms, the structure, and the selectivity of CO2+N2-TBAB compounds is investigated by in-situ Raman spectroscopy. A new dissociation point (pressure and temperature) is obtained and our results highlight that slow hydrates formation rates exert a variable performance on CO2 selectivity at temperatures far from the dissociation point, while a better performance is observed when approaching dissociation. Similarly, separation factors reach their greatest values close to the dissociation, depending however on the sc crystal structure formed. Surface morphology variation is monitored by optical microscopy and exhibits a continuous transformation with temperature, starting from a rough surface coated with polygonal or stacked shaped crystals to the formation of columnar TBAB-sc crystals near dissociation. Moreover, the influence of the formation kinetics on CO2 separation and selectivity is explored.Finally, a potential application of CO2 separation and capture by HBSP is addressed through the investigation of the exchange mechanism when exposing CO2 clathrate hydrates to N2 gas. Even though CO2 and N2 hydrates crystallize in structure sI and sII, respectively, it is a CO2-N2 mixed hydrate with a preferential occupation of the small cages by N2 molecules that forms upon N2 injection. The exchange kinetics is analyzed from the perspective of methane recovery from CO2 and CO2+N2 injections
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Tabatabaei-Nejad, Seyyed Ali Reza. "Phase behaviour modelling of petroleum wax and hydrates." Thesis, Heriot-Watt University, 1999. http://hdl.handle.net/10399/593.
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Westacott, Robin E. "Direct free energy calculations applied to clathrate hydrates." Thesis, University of Reading, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283787.
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Martinez, de Baños Maria Lourdes. "Mechanisms of formation and dissociation of cyclopentane hydrates." Thesis, Pau, 2015. http://www.theses.fr/2015PAUU3037/document.
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Les mécanismes de formation et dissociation d’hydrates de cyclopentane (CP), qui forment á pression ambiante et á des températures entre 0ºC et 7ºC, ont été observés dans/sur/proche des gouttes d’eau immergées dans du CP á des échelles qui vont du micron jusqu’au millimètre. Plusieurs techniques d’observation ont été utilisées, telles que la macrophotographie et la microscopie optique en champ clair, par contraste interférentiel différentiel (CID), par fluorescence et par réflectance confocale. Des substrats hydrophiles et hydrophobes ont été utilisés. Dans une première série d’expériences, un procédé millifluidique simple a été mis au point. Il permet de générer, stocker et surveiller simultanément une centaine de gouttelettes de même volume (de l’ordre de μl), régulièrement espacées. Elles sont séparées par la phase ‘invité’ (CP) dans un tuyau en polymère fluoré (PFA) transparent. Chacune d’elles se comporte comme un réacteur indépendant. Une vision sur l’effet mémoire est obtenue en menant des mesures statistiques sur la nucléation des hydrates quand les gouttes d’eau sont refroidies au-dessous de 7°C. Cette méthode permet aussi de visualiser des événements dans des gouttes individuelles, tels que la naissance et la croissance de l’hydrate (surtout lorsqu’un additive tel qu’un inhibiteur est rajouté dans l’eau), ainsi que la formation d’une émulsion de CP dans l’eau pendant la dissociation de l’hydrate. Dans une deuxième série d’expériences, une seule goutte d’eau est posée ou pendue d’un substrat en verre et immergée dans du CP. Elle est observée par microscopie sous des séquences différentes de refroidissement – échauffement. Il a été observé que la cristallisation d’hydrates dépend fortement du sous-refroidissement. Deux nouveaux phénomènes ont été observés:(i) la propagation d’un « halo » d’hydrate le long de l’interface verre/CP depuis la ligne de contact de la goutte d’eau.(ii) cristallisation de l’hydrate dans une émulsion 2D de CP dans l’eau.Les deux types d’outils développés dans cette thèse ouvrent des nouvelles perspectives pour élucider les mécanismes de formation et dissociation d’hydrates en présence d’additives (promoteurs et inhibiteurs) et en présence d’un substrat minéral. Les applications comprennent les hydrates dans des environnements sédimentaires, séparation de gaz, etc<br>The mechanisms of formation and dissociation of cyclopentane (CP) hydrates, which form at ambient pressure and temperatures between 0°C and 7°C, have been observed in/on/near water drops immersed in CP at scales ranging from a few nanometers to the millimeter by a variety of techniques including macrophotography and optical microscopy under various modes: bright field, differential interference contrast (DIC), fluorescence and confocal reflectance. The substrates used are either hydrophobic or hydrophilic. In a first series of experiments, a simple millifluidic method is implemented. It allows to generate, store and monitor at the same time almost a hundred of regularly-spaced water droplets of equal volume (in the µl range) separated by the guest (CP) phase in a transparent fluorinated polymeric (PFA) (hydrophobic) tubing, each droplet behaving as an independent reactor for hydrate crystallization. Insights into the ‘memory effect’ are gained by measuring the statistics of hydrate nucleation events in these reactors when chilling below 7°C the water drops. The method also allows the visualization of single-drop events such as hydrate birth and growth, and the formation of a CP-in-water emulsion upon hydrate melting, especially when an additive such as an inhibitor is added to the water. In a second series of experiments, a single water droplet in CP, either sitting or hanging from a glass substrate, is observed by microscopy under various cooling and heating sequences. Hydrate crystallization (nucleation and growth) is observed to strongly depend on subcooling at the water drop/CP interface. Two novel phenomena are visualized in detail:(i) the propagation, from the contact line of the water drop, of a hydrate halo along the glass/CP interface. (ii) hydrate crystallization in a two-dimensional CP-in-water emulsion.The two types of tools developed in this thesis open new perspectives for elucidating the mechanisms of hydrate formation and dissociation in presence of additives (promoters and inhibitors) and in the presence of a mineral substrate. Applications include hydrates in sedimentary environments, flow assurance, gas separation, etc
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Hamzaoui, Jamal El. "Recherche de l'origine du comportement mécanochimique des hydrates." Dijon, 1986. http://www.theses.fr/1986DIJOS040.
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On étudie la déshydratation mécanique de 27 sels hydrates au cours du broyage à différentes températures sous pression de vapeur d'eau contrôlée. La stabilité mécanique des sels est proportionnelle à l'énergie d'activation de leur décomposition thermique. Elle dépend, par ailleurs, de la nature chimique des hydrates.
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Choukroun, Mathieu. "Étude expérimentale et thermodynamique des hydrates sous pression." Nantes, 2007. http://www.theses.fr/2007NANT2086.
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D’intenses processus photochimiques empêchent la persistance du méthane atmosphérique de Titan sur des durées qui dépassent 100 millions d’années. La dissociation d’un réservoir interne de clathrates de méthane est un mécanisme de renouvellement probable. La présence d’ammoniac étant invoquée sur Titan, des expériences haute pression – basse température ont été réalisées dans les systèmes H2O-NH3, H2O-CH4, et H2O-NH3-CH4 pour apporter des contraintes sur ce processus. L’étude de la fusion des glaces dans les systèmes H2O-NH3 et H2O-NH3-CH4 a apporté de nouvelles données expérimentales, qui ont permis d’établir un modèle thermodynamique des glaces et de l’eau liquide, puis un modèle de l’effet de l’ammoniac sur l’activité de l’eau. Les expériences sur la dissociation des clathrates de méthane dans H2O-CH4 ont mis en avant deux effets : l’éventuelle présence d’azote et la faiblesse des concentrations en méthane des échantillons (inférieures à 0. 2-0. 3 %) entraînent une diminution de la température de dissociation pouvant atteindre 15 K et 40 K, respectivement. Les données de dissociation obtenues dans le système ternaire H2O-NH3-CH4 suggèrent un rôle significatif de l’ammoniac. Un modèle de cryovolcanisme sur Titan a été proposé, selon lequel la dissociation d’une couche superficielle de clathrates de méthane par des cryomagmas provenant de la fusion d’hydrates d’ammoniac peut permettre le maintien des quantités atmosphériques actuelles de méthane sur des durées pouvant atteindre 2 milliards d’années. Un cryovolcanisme épisodique durant l’histoire de Titan permettrait d’expliquer les quantités actuelles de méthane atmosphérique<br>Intense photochemical processes preclude the persistence of Titan’s current atmospheric methane abundance over 100 million years. Dissociation of an internal methane clathrate hydrates reservoir is a likely replenishment mechanism. As the presence of ammonia has long been suggested on Titan, high pressure – low temperature experiments have been conducted in the H2O-NH3, H2O-CH4, and H2O-NH3-CH4 systems to bring new constraints on this process. New experimental data on the melting of ices in the H2O-NH3 and H2O-NH3-CH4 systems have been acquired, which allowed developing first a thermodynamic model of ices and liquid water, and then a model of the effect of ammonia on liquid water’s activity. Experiments on the dissociation of methane clathrate hydrates in H2O-CH4 have shown its dependence on two effects : presence of nitrogen and low methane contents of the samples (below 0. 2-0. 3%) induce a decrease in the dissociation temperature of up to 15 K and 40 K, respectively. Dissociation data obtained in the ternary system H2O-NH3-CH4 suggest a significant impact of ammonia. A model of cryovolcanism applicable to Titan is proposed. It suggests that the dissociation of a superficial clathrate layer, due to interactions with cryomagmas originating from the melting of ammonia hydrates, could sustain the atmospheric methane current abundances over periods as long as 2 billion years. Episodic cryovolcanism during Titan’s history could explain the current methane amounts in its atmosphere
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Picard, Vincent. "Etude du comportement thermique des oxalates hydrates d'yttrium." Dijon, 1993. http://www.theses.fr/1993DIJOS028.
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Les oxalates neutres Y#2(C#2O#4)#3, nH#2O (n=6 et 10) et l'oxalate acide YH(C#2O#4) 3H#2O sont les pr2curseurs de la synth7se de l'oxyde Y#2O#3. La d2shydratation sous pression de vapeur conduit à d'autres phases, dont la stœchiométrie en eau est égale a 3,5-3-2,5 et 2H#2O par mole de sel anhydre. Le dihydrate est egalement produit lors de la transformation du sel acide. Le trihydrate est la seule forme réellement stable dans les conditions ambiantes. La structure cristalline a été établie et comparée à celles du deca- et de l'hexahydrate. Cette comparaison révèle (I) la grande régularité de l'évolution de la compacité de ces structures lorsque la stœchiométrie en eau varie. (II) le rôle prédominant joué par l'eau dans la stabilité de ces structures. (III) l'origine des stœchiométries a 3,5-2,5 et 2H#2O. (IV) enfin, l'impossibilit2 pour l'oxalate anhydre d'être isolé autrement qu'à l'état amorphe. Les filiations structurales qui existent entre les oxalates et les produits de leur décomposition (l'oxycarbonate Y#2O#2CO#3 et l'oxyde Y#2O#3) permettent de comprendre le caractère limité des modifications morphologiques qui accompagnent la décomposition. C'est la fragmentation des cristaux précurseurs lors de l'étape de déshydratation qui détermine donc les formes et dimensions des grains d'oxyde produits
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Araújo, Ana Catarina Fernandes. "Molecular modeling of intermolecular interactions in acid hydrates." Master's thesis, Universidade de Aveiro, 2012. http://hdl.handle.net/10773/10947.
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Mestrado em Química<br>Esta dissertação explora o mundo nanoscópico de pequenos agregados onde as pontes de hidrogénio têm um papel preponderantes usando métodos quânticos ab-initio. No capítulo introdutório, a área da química computacional é apresentada e algumas noções teóricas referentes aos métodos ab-initio, discutidas. No Capítulo 2, o desempenho de vários níveis de teoria é avaliado através do estudo de pequenos agregados de água. O capítulo 3 discute a influência dos critérios de optimização no resultado deste processo, alertando para erros comuns. No Capítulo 4, hidratos gasosos de ácido trifluoroacético (TFA), nas formas dissociada e não-dissociada, são apresentados. Um número mínimo de 4 moléculas de água é necessário para induzir a transferência do protão do TFA para a rede de moléculas de água adjacente . No entanto, 5 moléculas de água são necessárias para que o agregado dissociado se torne mais estável que o seu análogo não dissociado. O Capítulo 5 propõe um novo esquema para o cálculo ab-initio de valores de pKa. Este esquema serve-se de hidratos de ácido microsolvatado, nas formas dissociada e não dissociada, em modelo de solvatação contínuo, para calcular a energia livre de dissociação em solução. Para o conjunto de espécies testadas, incluindo 10 ácidos carboxílicos, 1 amina e 2 aminoácidos, o erro médio absoluto é 1.11, o declive experimental 1.2 e o coeficiente de correlacção 0.92, o que indica um nível de exactidão aceitável.<br>This dissertation concerns the study of small hydrogen bonded systems through the use of quantum mechanical ab-initio methods. In the introductory chapter, the field of computational chemistry is presented and some basic theoretical notions concerning ab-initio methods are discussed. In Chapter 2, the performance of various levels of theory is assessed through the study of small water clusters. Chapter 3 discusses the influence of optimization criteria in the outcome of the optimization procedure, warning against common pitfalls. In Chapter 4, gas-phase hydrates of trifluoroacetic acid (TFA), in both dissociated and undissociated forms, are presented. A minimum of 4 water molecules is necessary to induce proton transfer from TFA to the neighboring water molecule network. However, 5 water molecules are needed to render the dissociated hydrate more stable than its undissociated counterpart. Chapter 5 proposes a new scheme for the ab-initio calculation of pKa values. It uses microsolvated acid hydrates, in both dissociated and undissociated forms, within a continuum solvation model, to calculate the dissociation free energy in solution. For the data set used, including 10 carboxylic acids, 1 amine and 2 aminoacids, the mean usigned error (MUE) of calculated pKa values is 1.11, the experimental slope 1.2 and the correlation 0.92, which denotes a reasonable level of accuracy.
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Ding, Luyi Carleton University Dissertation Chemistry. "Studies on structure and dynamics in clathrate hydrates." Ottawa, 1995.
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Hamzaoui, Jamal El. "Recherche de l'origine du comportement mécanochimique des hydrates." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb37598189v.
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Franzyshen, Stephen Keith. "Acidic and Chemical Properties of Molten Salt Hydrates." W&M ScholarWorks, 1985. https://scholarworks.wm.edu/etd/1539625305.
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Friedman, Ross Aaron. "The dehydration of pharmaceutical hydrates under mechanical load." Diss., University of Iowa, 2014. https://ir.uiowa.edu/etd/3224.
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Nearly one-third of all pharmaceutical substances on the market are able to sorb water into their crystal lattices to form hydrates, which can often compromise stability during processing and/or storage[1]. The tendency of a hydrate to lose its water of crystallization during the manufacturing process of tablet compression is of particular concern to formulation scientists. The amount of water freed as a function of increasing compaction pressure can be explained by the mobility of water within the compact. The mobility of water is determined by the size and shape of the crystal lattice, the numbers and strengths of the hydrogen bonds, and the presence of high-energy sites of disorder[2]. Due to their differing crystal structures, theophylline monohydrate (THM), citric acid monohydrate (CAM), theophylline-water-citric acid cocrystal hydrate (CATHP hydrate), and dicalcium phosphate dihydrate (DCPD) make for interesting model systems to examine the dehydration under mechanical load.
The thermal dehydration of both powders and tablets was carried out via thermal gravimetric analysis (TGA). By comparing the temperatures required to start removal of water loss from the powder to that of the tablet, the average amount of water of crystallization that is freed by the compaction process may be quantified. The average amount of water freed by the compaction process results from a competition between the mechanically-induced disorder of the crystal structure that increases the molecular mobility of water within the tablets, and the trapping of water within the interparticulate void spaces at high compaction pressures.
The compressibilities, compactabilities, and tabletabilities of the materials were calculated as a function of increasing compaction pressure. The consolidation of the powder bed under pressure was modeled by out-of-die Heckel Analysis which demonstrated the ease of deformation of the model compounds. XRD was utilized to show the decrease in overall order of the crystal lattice as a result of compression as well as anisotropy within the tablets. Crystallographic approaches were utilized to demonstrate the compactness of the crystal structure, and how it affects water mobility.
Relaxation pulse experiments (T1, T2) utilizing solid-state NMR were used to directly probe the mobilities of the water molecules within the crystal lattice of THM. The results from T1 and T2 relaxation experiments directly measure the change in molecular mobility of water within the tablets as a function of compaction pressure. This provided independent verification of the trends in molecular mobility and average water freed as a function of compaction pressure observed during TGA dehydration. Raman spectroscopy was used to indirectly measure the polarizability and vibrational motions of THM, and these results corroborate those obtained from ssNMR and TGA dehydration experiments. Overall, this work highlights the potential impact that tablet compression can have on API hydrate stability.
1. Hilfiker R (editor). 2006. Polymorphism in the Pharmaceutical Industry. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co, KGaA.
2. Byrn SR, Pfeiffer RR, Stowell JG. 1999. Solid-state chemistry of drugs. SSCI, Inc.
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English, Phillip Martin. "Structural studies of titanyl and zirconyl sulphate hydrates." Thesis, Curtin University, 2011. http://hdl.handle.net/20.500.11937/983.
Full textAbstract:
The aim of this thesis was to use a combination of computer simulations and experimental methods to gain insight into the unknown structure of the material titanyl sulphate dihydrate, TiOSO4*2H2O.Samples of TiOSO4*2H2O, along with TiOSO4*H2O, were produced and analysed using X-ray and neutron diffraction at both laboratory and synchrotron facilities. Both ex-situ and in-situ experiments were performed in order to analyse both the structure and growth of the crystals. The diffraction data resulting from these experiments was then used in various structure determination programs. A unit cell was able to be determined from the synchrotron X-ray diffraction patterns, and the first neutron diffraction pattern of a TiOSO4*2D2O sample was produced. In-situ synchrotron X-ray diffraction studies showed that the formation of the crystals followed a single step process, and indicated the possibility of meta-stable phases being present in the sample.In parallel with the experimental studies, computer modelling was used to develop and create candidate TiOSO4*2H2O structures. Initially both forcefield and first principles techniques were validated against a series of test cases. These included the first such calculations for the TiOSO4 and TiOSO4*H2O structures. The candidate structures of TiOSO4*2H2O thus produced were then used as input into the structural determination step.Structure determination was attempted with multiple approaches, using the determined unit cell and a variety of space group settings. Despite a thorough treatment and validation of the method using the diffraction data and known structure of TiOSO4*H2O, the structure was unable to be solved. However, structural motifs consistent with a layered, needle-like morphology, as observed in experimental studies, were commonly found to be present in solutions offered by these approaches. Future use of techniques such as the substitution of isotopic titanium in neutron diffraction may provide enough information to more accurately determine atomic positions.
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Wang, Shuo. "Investigation of inhibition performance of kinetic hydrates inhibitors." Thesis, Curtin University, 2012. http://hdl.handle.net/20.500.11937/2241.
Full textAbstract:
The aim of this thesis is to investigate the inhibition process of tetrahydrofuran (THF) hydrates in presence of two kinetic hydrate inhibitors (KHIs), poly(N-vinylcaprolactam) and poly(vinylcaprolactam /vinylpyrrolidone/ dimethylaminoethyl methacrylate), and the effect of these KHIs on the formation and growth of THF hydrates at various experimental conditions, using a ball-stop rig and a rheometer. Other chemicals, including ethanol, ethylene glycol, and sodium chloride salt were used to investigate their synergic effect to the KHIs.
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Smith, Callum Conway. "Analysis of Natural Gas Hydrates using Inert Gases." Thesis, Curtin University, 2017. http://hdl.handle.net/20.500.11937/57085.
Full textAbstract:
This research focuses on the analysis of natural gas hydrates with the use of inert gases. Phase equilibria for several natural gas and methane-containing gas mixtures are analysed and used in the understanding of the influence each non-methane component instils towards the thermodynamic conditions for hydrate equilibria. Correlations and new thermodynamic data, namely dissociation enthalpies, are presented. These values are also used to compare the stability of structure I to structure II hydrates and establish a composition range where a transition occurs.
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Jung, Jongwon. "Gas production from hydrate-bearing sediments:geo-mechanical implications." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/42841.
Full textAbstract:
Gas hydrate consists of guest gas molecules encaged in water molecules. Methane is the most common guest molecule in natural hydrates. Methane hydrate forms under high fluid pressure and low temperature and is found in marine sediments or in permafrost region. Methane hydrate can be an energy resource (world reserves are estimated in 20,000 trillion m3 of CH4), contribute to global warming, or cause seafloor instability. Research documented in this thesis starts with an investigation of hydrate formation and growth in the pores, and the assessment of formation rate, tensile/adhesive strength and their impact on sediment-scale properties, including volume change during hydrate formation and dissociation. Then, emphasis is placed on identifying the advantages and limitations of different gas production strategies with emphasis on a detailed study of CH4-CO2 exchange as a unique alternative to recover CH4 gas while sequestering CO2. The research methodology combines experimental studies, particle-scale numerical simulations, and macro-scale analyses of coupled processes.