No / Cocrystallization of modafinil, (1), and 1,4-diiodotetrafluorobenzene, (2), in toluene leads to the formation of a metastable modafinil channel hydrate containing an unusual hydrogen bonded dimer motif involving the modafinil molecules that is not seen in anhydrous forms of modafinil. Computational methodologies utilizing bias drift-free differential evolution optimization have been developed and applied to a series of molecular clusters and multicomponent crystals in the modafinil/water and modafinil/water/additive systems for the additive molecules (2) or toluene. These calculations show the channel hydrate is less energetically stable than the anhydrous modafinil but more stable than a cocrystal involving (1) and (2). This provides theoretical evidence for the observed instability of the channel hydrate. The mechanism for formation of the channel hydrate is found to proceed via templating of the modafinil molecules with the planar additive molecules, allowing the formation of the unusual hydrogen-bonded modafinil dimer. It is envisaged that the additive is then replaced by water molecules to form the channel hydrate. The formation of the channel hydrate is more likely in the presence of (2) compared to toluene due to the destabilizing effect of the larger iodine molecules protruding into neighboring modafinil clusters. / Science Foundation Ireland, IRCSET, UCC 2012 Strategic Research Fund

The objective of this study is to determine hydrate formation conditions of a multicomponent polymer based drilling fluid. During the study, experimental work is carried out by using a system that contains a high-pressure hydrate formation cell and pressure-temperature data is recorded in each experiment. Different concentrations of four components of drilling fluid, namely potassium chloride (KCl), partially hydrolyzed polyacrylicamide (PHPA), xanthan gum (XCD) and polyalkylene glycol (poly.glycol) were used in the experiments, to study their effect on hydrate formation conditions.

The flow assurance industry is progressively moving away from avoidance of hydrate formation towards risk management. Risk management allows hydrates to form but prevents hydrates from agglomerating and forming a plug, or delays hydrate formation within the timescale of the residence time of the water in the hydrate-prone section of the flow line. A key factor in risk management for an oil-dominated system is the stability of the emulsified water with gas hydrate formation. It is shown using Differential Scanning Calorimetry (DSC) that gas hydrate formation and dissociation has a destabilizing effect on W/O emulsions, and can even lead to a free water phase through agglomeration and coalescence of dissociated hydrate particles. Gas hydrate formation/dissociation has been shown to cause rapid hydrate agglomeration and emulsion destabilization. High asphaltene content crude oils are shown to resist hydrate destabilization of the emulsion.

Potential applications of gas hydrates, including carbon dioxide sequestration in the deep ocean, coal bed methane–produced water treatment, storage and transportation of natural gas, and gas separations, are based on continuous, large-scale production of gas hydrates. A novel three-phase injector/reactor was developed at Oak Ridge National Laboratory for the continuous synthesis of gas hydrates. The reactor receives water and a hydrate-forming species and rapidly forms hydrate with a residence time of a few seconds. The reactor was designed to maximize interfacial area between reactants, thus minimizing mass transfer barriers and thermal effects that negatively affect conversion of reactants into hydrate. The cohesiveness and the density of the hydrate product desired for specific applications can be controlled by slight variations in the geometry of an exchangeable internal piece of the reactor, the choice of the guest gas, and by the regulation of operating parameters such as pressure, temperature, reactant ratios, and degree of emulsification. In general, spraying one reactant into the other, within the jet-break up regime, results in the highest conversions. The reactor has been field tested for ocean carbon sequestration and in the laboratory for coal-bed methane produced-water treatment using liquid carbon dioxide. In this paper, the application of the reactor for ocean carbon sequestration will be discussed.

It is well known that water molecules at room temperature tend to form ‘iceberg’ structures around the hydrocarbon chains of surfactant molecules dissolved in water. The entropy reduction (times the absolute temperature T) associated with the iceberg structure can be considered as the net driving force for self-assembly. More recently, many investigators measured long-range attractive forces between hydrophobic surfaces, which are likely to result from structuring of the water molecules in the vicinity of the hydrophobic surfaces. Similarly, the hydrophobic nature of most gas hydrate formers may induce ordering of water molecules in the vicinity of dissolved solutes. In the present work, the surface forces between thiolated gold surfaces have been measured using an atomic force microscope (AFM) to obtain information on the structure of the thin films of water between hydrophobic surfaces. The results have been used to develop a new concept for the formation of gas hydrates.

The objective of this study is to determine hydrate formation conditions of methane- hydrogen sulfide mixtures. During the study, an experimental work is carried out by using a system that contains a high-pressure hydrate formation cell and pressure-temperature data is recorded in each experiment. Different H2S concentrations and both brine and distilled water are used in the experiments and the Black Sea conditions, which are suitable for methane-hydrogen sulfide hydrate formation are examined. Considering the pressure-temperature data obtained, hydrate equilibrium conditions are determined as well as the number of moles of free gas in the hydrate formation cell. The change in the number of moles of free gas in the hydrate formation cell with respect to time is considered as a way of determining rate of hydrate formation. Effects of H2S concentration and salinity on hydrate formation conditions of methane-hydrogen sulfide mixtures are also studied. It is observed that an increase in the salinity shifts the methane-hydrogen sulfide hydrate equilibrium condition to lower equilibrium temperatures at a given pressure. On the other hand, with an increase in H2S concentration the methane hydrogen sulfide hydrate formation conditions reach higher equilibrium temperature values at a given pressure. After the study, it can be also concluded that the Black Sea has suitable conditions for hydrate formation of methane hydrogen sulfide mixtures, considering the results of the experiments.

The paper presents results of the experimental research on the process of CO2 gas hydrates formation in the porous media of sediments under positive and negative temperatures. The subject of research were sediment samples of various compositions including those selected in the permafrost area. The research was conducted in a special pressure chamber, which allowed to monitor pressure and temperature. Using the monitoring results it was possible to make quantitative estimation of the kinetics of CO2 hydrates accumulation in the model sediments. In the course of the research it was demonstrated, that active hydrates accumulation occurred in frozen sediments under negative temperatures (about -4 оС). At the same time a comparative analysis of СО2 and СН4 hydrates accumulation was made in the porous media of the sediment under negative temperatures. The performed experiments enabled to estimate an influence of temperature, sediment composition and water content on kinetics of CO2 hydrates accumulation in porous media. Besides, we made an estimation of the amount of hydrates, which could be formed in hydrates containing sediments at freezing of the remaining pore water.

Studying clathrate hydrates is, ideally, a simple task: one just have to keep water under a gas pressure. However, when trying to collect measurements in an accurate and repeatable way, things mess up. When, in particular, kinetic characterizations are required, not only pressure and temperature have to be measured: also particular parameters such as gas evolved/trapped during time, heat released/adsorbed during time, critical phenomena related to additive addition, etc, should be collected in a finer way. In the last years a growing interest has been devoted to investigations on the effects of a wide range of compounds capable to affect the thermodynamics and, in particular, kinetics of clathrate hydrate formation. The study of the effects of these compounds, called conditioners, requires an improvement of the performances of usual lab facilities by introducing a new strategy for the measurement of further characterizing parameters. Presently no standardization of the apparatus designed for clathrate hydrate studies exists, nor any commercial instrumentations are available. Generally, apparatus used are custom-made by the same research team according with the peculiar research requirements To do this we have designed, built, calibrated and tested a novel apparatus that, in addition to the ability of measuring usually unexplored parameters, is based on the idea of obtaining as many parameters as possible in a single formation batch. This in order to solve the problem of collecting a dataset that can be processed homogeneously, thus minimizing errors due stochastic behaviours. Using such an apparatus, several kinds of measurement are presented here, which are related directly to the clathrate hydrate investigation fields, but also more generally related to the study of equilibrium phases involving gaseous components.

We present an experimental study on the formation and dissociation characteristics of carbon dioxide (CO2) gas hydrates using Raman spectroscopy. The CO2 hydrates were formed from sodium chloride/water solutions with salinities of 0–10 wt %, which were pressurized with liquid CO2 in a stirred vessel at 6 MPa and a subcooling of 9.5 K. The formation of the CO2 hydrate resulted in a hydrate gel where the solid hydrate can be considered as the continuous phase that includes small amounts of a dispersed liquid water-rich phase that has not been converted to hydrate. During the hydrate formation process we quantified the fraction of solid hydrate, xH, and the fraction of the dispersed liquid water-rich phase, xL, from the signature of the hydroxyl (OH)-stretching vibration of the hydrate gel. We found that the fraction of hydrate xH contained in the hydrate gel linearly depends on the salinity of the initial liquid water-rich phase. In addition, the ratio of CO2 and water was analyzed in the liquid water-rich phase before hydrate formation, in the hydrate gel during growth and dissociation, and after its complete dissociation again in the liquid water-rich phase. We observed a supersaturation of CO2 in the water-rich phase after complete dissociation of the hydrate gel and were able to show that the excess CO2 exists as dispersed micro- or nanoscale liquid droplets in the liquid water-rich phase. These residual nano- and microdroplets could be a possible explanation for the so-called memory effect.

No description available.