The experimental data on hydrogen solubility in methane gas hydrate and new data on phase equilibria in the hydrogen - methane - water system are presented in this work. The solubility data were ...obtained for hydrogen partial pressures from 0.8 to 5.4 MPa. It was found that hydrogen solubility in methane and carbon dioxide hydrates is almost the same and the dependence of hydrogen content on hydrogen partial pressure can be fitted with the equation ln(CH2) = −4.332(54) + 0.919(62)-ln(PH2), where CH2 is the hydrogen content in the hydrate (wt%) and PH2 is the hydrogen partial pressure (MPa). The data obtained in this work were compared with available data on hydrogen solubility in sI and sII hydrates. Analysis of data on the solubility of hydrogen in sII double hydrates with different thermodynamic promoters (tetrahydrofuran, cyclopentane, propane, tetrathiophene, furan) taken from various literature sources also shows a relatively small scatter with respect to the straight line approximating them. In general, the fraction of free small 512 cages filled with hydrogen decreases in the following order: sI methane hydrate > sI CO2 hydrate > sII hydrates.
•Analysis of the literature data on filing of the 512 cages with hydrogen is shown.•The data on hydrogen content in sII hydrates can be considered as one data set.•Hydrogen filling of 512 cages in: sI CH4 hydrate < sI CO2 hydrate < sII hydrates.•The linear regressions for the hydrogen contents in hydrates are presented.
Experimental studies on the synthesis of HFC 134a hydrate in the liquid HFC 134a – water system were performed. Despite today's lack of research on the use of HFC 134a hydrate for desalination of ...seawater and separation of harmful impurities by HFC 134a hydrate synthesis, this method has prospects for development: HFC 134a hydrate is synthesized at relatively high temperature and low pressure; it is poorly soluble in water, which simplifies gas hydrate separation from water–salt solution; it has high volumetric storage density and relatively high thermal conductivity. In spite of its low solubility in water, HFC hydrate exhibits relatively high growth rates. The growth of various crystalline forms and the peculiarities of their occurrence in pure water, aqueous salt solution, as well as with the addition of surfactant are considered. The use of SDS increases the HFC hydrate growth rate. For the first time, it was shown that the intensive growth of HFC 134a hydrate in the form of needles throughout the entire volume of the liquid allows increasing the efficiency of desalination. It is important to consider the desalination process comprehensively, taking into account the crystal forms, crystal growth rate, crystal defects, as well as taking into account the degree of salt removal. Simultaneously with the bubble growth, a thin gas hydrate film is shown to grow on the bubble surface. A detailed consideration of the stages of such hydrate growth is provided to explain the high-speed synthesis of porous HFC hydrate due to boiling of liquid HFC and vaporization.
•The use of SDS increases the HFC-134a hydrate growth rate.•Hydrate growth rate in a metal cuvette is almost twice as high as in a glass one.•In aqueous salt solution, the hydrate growth rate is lower than in pure water.•“Needle” crystal hydrate allows removing 92–94 % of salt.
The growth features of a hydrate film at the interface between liquid carbon dioxide and pure water and sodium dodecyl sulfate solution were studied. It was found in all cases that in a Teflon cell a ...hydrate film is formed on the contact surface of the liquid phases, after which no visible changes are observed for an indefinitely long time. In experiments with pure water in a steel cell after the water-CO
2
surface is covered with hydrate the hydrate film is slowly deformed as a result of growth along the line of contact between the hydrate and the cell wall. In experiments with a solution of sodium dodecyl sulfate the deformation of the hydrate film is much more pronounced, and the degree of conversion of the water into hydrate is increased significantly.
Isothermal nucleation of methane hydrate in the emulsions of water in oil has been studied experimentally at a pressure of 12.5 MPa within the temperature range of −3.0 to −4.9 °C (supercooling ...17.8–19.7 °C). It was demonstrated that the experimental survival curves are composed of two regions with different slopes to the time axis. Nucleation rates calculated for initial and final (in parentheses) regions of survival curves turned out to be equal to 0.00065 (0.00055), 0.00036 (0.00017), and 0.00018 (0.00010) s–1 m–2 for temperatures −4.9, −4.0, and −3.0 °C, respectively. The experimental data were extrapolated to the regions of higher and lower supercooling values using a known expression describing the dependence of the nucleation rate on temperature. It may be expected that the information concerning the temperature dependence of hydrate nucleation rates in water–oil systems will be useful to optimize the consumption of kinetic hydrate inhibitors during the development of oil and gas deposits.
•A model describing CH4-CO2 exchange in hydrate at T below 273.15 K was proposed.•The model considers decrease of CO2 diffusion coefficient with time.•50 % of CH4 substitution with CO2 in hydrate may ...take up to 30 years.
Currently, gas hydrates are considered to be a potential resource of natural gas in the future. Vast quantities of gas hydrates deposits are located in the deep sea or in the permafrost zone. Among the other potential methods for extracting natural gas from these deposits is the injection of CO2 into a hydrate-bearing reservoir. This method assumes that carbon dioxide will replace methane molecules in the clathrate framework, so this method may be able to provide long-term burial for greenhouse gas CO2 along with the getting of burning gas. Understanding the kinetics of this process might be crucial for assessing the feasibility of implementation of this technology, but there is currently no clear understanding about the applicability of standard equations for heterogeneous reactions to describe the kinetics of this process. In this paper, we present some recent kinetic data on CH4/CO2 exchange at temperature below the ice melting point, focusing on the composition of hydrates. We also propose theoretical explanations for the obtained data.
Transverse relaxation times T2 spectra for models of thawing hydrate-bearing sediment have been studied in this work. The samples were prepared from aqueous THF solution and powders of quartz ...microspheres or their mixtures with kaolin. It was shown that individual bands in the spectra of T2 times are traced, they correspond to proton relaxation in solid hydrate, aqueous solution of THF and to a thin layer of liquid located at the boundary between hydrate and solid particles. It was experimentally established that the low-field NMR may be applied to study the formation/melting kinetics of THF hydrates in porous media and as a tool to investigate phase transformations in porous media.
•Low-field NMR relaxation was used to study the model hydrate-bearing sediments.•The model hydrate-bearing sediments contained tetrahydrofuran hydrate.•Intensity of liquid band may be used to study formation/melting kinetics such models.•Intensity of solid hydrate band is temperature-dependent.•The method may be used to detailed study of hydrate melting in the samples.
The work investigated the nucleation of methane hydrate from pure water and a 2 wt % aqueous solution of malonic acid. The experiments were conducted in glass vials with typical or increased surface ...hydrophilicity. To increase the surface hydrophilicity, treatment with a sulfochromic mixture followed by boiling in water was used. It has been shown that faster nucleation (shorter induction period) occurs on more hydrophobic walls. The induction period for 2 wt % solutions of malonic acid increases significantly, with this effect pronouncing more for the hydrophilized vials’ walls. The paper discusses possible reasons for such evolution. For malonic acid solutions in glass cells, visual observations have shown that hydrate nucleation preferably occurs not at the three-phase solution–glass–gas contact line but at the solution–glass interface.
Temperature dependence of methane hydrate nucleation rate in 50 wt% water in oil emulsion was studied within the temperature range from +2 to −6 °C (supercooling values: 13–21 °C). It turned out that ...the temperature dependence of nucleation rate in this temperature interval cannot be described by the equations of the classical nucleation theory. This point is discussed with use of available literature data. An approach to the analysis of isothermal survival curves is suggested. Using the approach allows us to establish the amount of nucleation centers in the system and their relative activity. A probable number of nucleation centers and the effect of temperature on the manifestation activity of these centers were determined for the obtained experimental data.
•The temperature dependence of the rate of methane hydrate nucleation in the w/o emulsion is investigated.•The temperature dependence of nucleation rate could not be described with the equations of the classical theory.•The activation of a nucleation center is a time-dependent process.•It is very probable that the mechanism of gas hydrate nucleation does not correspond to the classical one.•New approach to the analysis of survival curves is proposed.
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Outcrops of the coal-bearing Tankhoi Formation (Oligocene–Pliocene), traced along the southern shore of Lake Baikal, submerge under its Southern Basin, where several hydrate-bearing zones of the ...focused hydrocarbon fluid discharge have been found. To test the hypothesis that coals of the Tankhoi Formation can be the sources of hydrocarbon gases in these zones, we collected coal samples from the Shakhterskaya Gorka outcrop. Experiment on gas generation from the selected samples was carried out in a special autoclave at a temperature of 90°C for eight months. This paper presents the obtained results, which confirm an important role of the process of gas generation from coals in the formation of fluids in the Kedr mud volcano. The further migration of gases was accompanied by the biodegradation and formation of secondary microbial methane due to CO
2
reduction. This was one of the reasons for the carbon isotopic pattern observed in methane (heavier than –50‰ VPDB) and carbon dioxide (positive values) taken from the near-surface sediments and hydrates of the Kedr mud volcano, as well as for the significant enrichment of authigenic siderites in the heavy
13
C isotope.
The products of mechanosynthesis in the systems “superstoichiometric fluorocarbon nanomaterial CF
1.2
–thermally expanded graphite” are studied using X-ray photoelectron spectroscopy and ...low-temperature nitrogen adsorption to identify texture characteristics. A correlation is revealed between the conductivity of the composites and functional composition of their surface layers. The obtained results are explained by the fact that mechanosynthesis products contain mesoporous carbon-fluorocarbon nanocomposites consisting of micro- and nanoparticles CF
1+
x
coated by an outer nanolayer
sp
2
-C–
sp
3
-C–F.
