In this work, the difference in neon solubility in ice Ih and liquid water along the ice melting curve has been studied at pressures up to 2000 bar. At pressures up to 700 bar, this difference appeared to be close to zero. At higher pressures, the difference increases up to 13.6 °C at 2000 bar. The data obtained may be fitted by the polynomial Sice−SliqH2O = − 1.0200·10–3·P − 8.0038·10–7·P2 + 2.3916·10–9·P3, where Sice−SliqH2O is the difference in neon solubility in solid ice and liquid water in cm3 of neon (at standard temperature and pressure) per 1 g of ice Ih, and P – pressure in bars. Unfortunately, there is no data on the solubility of neon in liquid water at high pressures, so it is currently impossible to obtain reliable information on the absolute values of neon solubility in ice Ih. Estimated values for the solubility of neon in liquid water and ice Ih along the ice melting line are proposed.

The research involved synthesizing b-cyclodextrin hydrates of the b-CD·nH2O (n = 11.9–0.9) composition. The obtained compounds were studied by powder X-ray diffraction (XRD), which revealed the transition from a monoclinic unit cell to an orthorhombic one with a decrease in the water content in the samples. The pressure of saturated vapor of the water in the b-CD·nH2O (n = 10.6–7.0) hydrates was measured by static tensimetry with membrane null-manometer over a wide temperature range (293–384 K) under conditions of a quasi-constant hydrate composition. The measured vapor pressure increases in proportion to the increase in the water content of the hydrate samples. The experimental data reduced to a single composition of b-CD·1H2O were approximated by the lnp(1/T) equation, from which the thermodynamic parameters (∆prH°T and ∆prS°T) of the process of b-cyclodextrin hydrate dehydration were calculated. This information was used to estimate the binding energies of the water molecules to the b-CD framework

Protons of coal-sorbed water were found to produce a continuous H-1 NMR Hahn-echo spectrum over a chemical shift range of approximately 0 to 5 ppm. All experimentally obtained spectra were deconvoluted into three-peak resolution: a peak of free water at 4.8 ppm and two peaks displaced to the region of lower chemical shifts. Analysis of the obtained spectra and the intensities of deconvolution peaks on the moisture content of the samples showed that the behavior of various bands in the spectra of lignites and medium and highly metamorphosed coals is qualitatively different from each other. In the case of lignites and bituminous coals, an increase in humidity leads to a shift of bands in the spectra from -1 ... +2 ppm (the most strongly bound water) to a position characteristic of free water (4.8 ppm). For coking coal, lean coal and anthracite, the direction of the shift is opposite: from similar to 4.8 ppm for the samples with low water content to similar to 3 ppm for the samples saturated with water. We attribute this behavior to the low binding energy of water molecules on hydrophobic graphite-like surfaces of highly metamorphosed coals and the strong shielding of water protons by pi-electron clouds of aromatic surfaces.

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Ionic clathrate hydrates (ICHs) belong to one of the groups of a wide class of clathrate hydrates. In the crystal structures of ICHs, cation-anion pairs of guest molecules, typically tetraalkylammonium/phosphonium salts, are included into the host framework of hydrogen-bonded water molecules. Because of their suitable phase change temperature and latent heat, ICHs are considered as promising phase change materials for application in cold energy storage and transportation. The presence of vacant cavities in ICHs structures, which can incorporate small gas molecules such as, for example, H-2, CH4, CO2, N-2, H2S, determines the possibility of their use for the separation and storage of gases. The formation of these double ICHs occurs under much milder pressure and temperature conditions compared to the pure gas hydrates of the same gases. Studying of the structural characteristics and thermophysical properties of ICHs and double ICHs with gases is the necessary basis for their effective applications in different practical ends. This work reviews information related to the new details and features of the structures of ICHs and double ICHs with gases revealed over the last decade or a little more as well as some thermophysical data such as hydrate numbers, temperatures and enthalpies of dissociation. This review focuses only on ICHs of tetrabutyl-, tetraisoamylammonium (TBA, TiAA), and tetrabutylphosphonium (TBP) salts, which are the most common representatives of this class of compounds. One of the sections is devoted to ICHs of TBA and TiAA with polymeric anions such as cross-linked polyacrylates. The purpose of the present paper is to review the studies that have been relatively little addressed in previous works.

Ionic clathrate hydrates formed from aqueous solutions of tetra-n-butylammonium bromide in the course of rapid cooling (30 K min−1) to −35 °C have been examined. An earlier unknown metastable hydrate of cubic structure I was obtained from the solutions with concentrations from 3.2 to 4.8 mol%.

Structure, morphology, and composition of the gas for natural gas hydrates sampled in the Kedr-1 mud volcano (Lake Baikal) are studied. It is shown that all these hydrates have cubic structure II, and the hydrate‐bound gas contains about 14% of ethane (the rest is methane). One of the samples is a porous monolithic hydrate layer sandwiched between the layers of hydrate granules. The hydrate has similar structures and compositions in the layer and in the granules. As far as we know, no such morphology features of natural hydrates have been reported so far. Possible mechanisms underlying the formation of such objects are discussed.

Изучена структура, морфология и состав газа для природных газовых гидратов, отобранных на грязевом вулкане Кедр-1 (оз. Байкал). Показано, что все эти гидраты имеют кубическую структуру II, а связанный газ содержит около 14 % этана (остальное метан). Один из образцов представлял собой пористый монолитный слой гидрата с прилегающими к нему сверху и снизу слоями гранул гидрата. И в слое, и в гранулах гидрат имел одну и ту же структуру и состав. Насколько нам известно, ранее такие особенности морфологии природных гидратов не описаны. Обсуждаются возможные пути формирования подобных объектов.

The formation and decomposition of methane hydrate in the mesopores of two polymorphous modifications of Al2O3 and the state of water adsorbed in the mesopores were studied in the work. It is demonstrated that adsorbed water may have several energy states differing from each other in the degree of interaction with pore walls. Methane hydrate may be formed from different types of water present in the sample, and the amount of water transformed into hydrate depends on the conditions of hydrate formation. A conceptual model explaining the observations is proposed.

Mixed type phase change material (PCM) based on the tetra-n-butylammonium bromide (TBAB) hydrate loaded in a composite matrix included poly(vinyl alcohol) (PVA) and natural halloysite clay nanotubes can be used for the cold storage. Poly(vinyl alcohol) provides the formation of a cryogel, while the clay nanotubes promote the hydrate nucleation reducing the supercooling of the formed hydrate. At the same time, the cryogel formation ensures the sedimentation stability of halloysite inside the dispersion. The relationship between the concentration of the target compound in the initial solution, the presence/absence of halloysite, and specific enthalpy of the phase transition made it possible to optimize the properties of this material for cold storage. The formation of two hydrates in the systems under study with different water content as well as the possibility of recrystallization of the low content water hydrate into the high content water one and during the melting of ice was experimentally revealed. The obtained PCM melted at a temperature of 9-13 degrees C and had a melting enthalpy up to 196 J/g. It was shown that the halloysite is a nucleator for TBAB hydrates. Adding 1 mass% of halloysite to the composite increases the temperature of hydrate onset by 2 degrees C. The best thermal stability in an open system was shown for the 1:50 M ratio. The energy capacity of such material does not decrease during 50 cycles of the reversible melting-crystallization phase transition, which indicates the stability of the TBAB-PVA-halloysite system. As both halloysite clay nanotubes and poly(vinyl alcohol) cryogel are biocompatible, encapsulation of tetra-n-butylammonium bromide hydrate in such material will protect the environment from harmful effects of a quaternary ammonium salt and expand the scope of this cold accumulator. The halloysite as an additive for phase change composites is also low-cost, readily available from natural mineral deposits, and non-toxic.

Представлены результаты структурных исследований образцов придонных газовых гидратов оз. Байкал, добытых в ходе экспедиций 2005—2018 гг. Показано, что в состав исследованных гидратов входят преимущественно метан и этан. В состав более 85 % образцов входит гидрат кубической структуры I с содержанием этана до 4.2 мол.%. В образцах, содержащих гидрат кубической структуры II, концентрация этана составляла 12—14 мол.%. Уточненные параметры элементарных ячеек природных гидратов хорошо соответствуют данным, полученным при исследованиях искусственно синтезированных гидратов. Обсуждаются возможные механизмы образования гидратов кубической структуры II. Кратко рассмотрены аргументы в пользу вероятного наличия рассеянных газовых гидратов в придонных слоях Байкальских осадков и возможности небольших вариаций в составе гидратного газа в различных фрагментах гидратов, отобранных из одного и того же гидратного слоя.

The structures of an ionic clathrate hydrate of tetra-n-butylammonium nitrate TBANO3·26.7H2O and mixed TBA(NO3)1−x(OH)x·(31.5 − x)H2O hydrate obtained from a mixture of tetra-n-butylammonium nitrate and tetra-n-butylammonium hydroxide are determined by single crystal X-ray diffraction. These structures are new types of superstructures based on classical tetragonal structure I with four- and twofold unit cells volumes for TBANO3·26.7H2O and TBA(NO3)1−x(OH)x·(31.5 − x)H2O respectively. The superstructures form as a result of ordering in the arrangement of multicompartment cavities of the water-anionic framework. A TBA cation is displaced from the center of combined cavities due to the anisotropic environment of the anions, which leads to an additional symmetry reduction. The modes of the nitrate anion incorporation into the water framework of ionic clathrate hydrates are determined for the first time.

The development of special autoclaves with automatic temperature control (Nikolaev Institute of Inorganic Chemistry) had enabled reproduction of Lake Baikal tectonically active zone typical conditions (80°C, 5 MPa). This article describes in details the equipment developed and demonstrates some results obtained using the equipment. In series of thermobaric experiments on the cultivation of bottom sediment microbial communities, we have determined the microbial community potential to transform organic matter via the formation of dibenzothiophenes, tri- and monoaromatic steroids as well as petroleum biomarkers (retene and gammacerene). The particular bottom sediment geochemical environment associated with hydrocarbon discharge imply the composition of microbial communities and, hence, the organic matter transformation degree as well as a compound spectrum resulting from the destruction of organic matter under thermobaric conditions. The presence of microorganisms with an unusual metabolism suggests the promising potential for such studies both in application to Lake Baikal and worldwide.

Методом рентгеноструктурного анализа определены структуры ионного клатратного гидрата нитрата тетра-н-бутиламмония TBANO3⋅26.7H2O и смешанного гидрата TBA(NO3)1–x(OH)x⋅ ⋅(31.5 – x)Н2O, полученного из смеси нитрата тетра-н-бутиламмония и гидроокиси тетра-н-бутиламмония. Это два новых типа сверхструктур, полученные на базе «классической» тетрагональной структуры I, с элементарными ячейками четырехкратного для TBANO3⋅26.7H2O и двукратного для TBA(NO3)1–x(OH)x⋅(31.5 – x)Н2O объема. Образование сверхструктур происходит в результате упорядочения в расположении многосекционных полостей водно-анионного каркаса. Смещение катиона из центра комбинированной полости вследствие анизотропного окружения анионами приводит к дополнительному понижению симметрии. Впервые определены способы включения нитрат-анионов в водный каркас ионных клатратных гидратов.

The structure of near-bottom gas hydrate samples obtained in Lake Baikal during the expeditions in 2005–2018 are reported. The hydrates contain mainly methane and ethane. More than 85% of the samples contain hydrate of cubic structure I (sI) with up to 4.2 mol.% ethane. The concentration of ethane in the samples containing hydrate of cubic structure II (sII) is 12–14 mol.%. Refined unit cell parameters of natural hydrates are in good agreement with the data obtained in the studies of artificially synthesized hydrates. Possible mechanisms for the formation of sII hydrates are discussed. Some arguments are provided in favor of a probable presence of dispersed gas hydrates in the near-bottom layers of Baikal sediments and the possibility of small variations in the composition of hydrate gas in different hydrate fragments taken from the same hydrate layer.

Experiments on the formation and dissociation of carbon dioxide gas hydrate formed from water that was adsorbed in two sub-bituminous coals and anthracite were carried out. Preliminarily, the coal samples were studied using various physicochemical methods. It was demonstrated that the conditions of the hydrate decomposition in coal do not differ substantially from the equilibrium conditions of carbon dioxide hydrate. In all the cases, the conversion of water to hydrate increases with increasing the pressure of the hydrate former and the initial humidity of coal samples. At the same time, it turned out that the amount of unreacted water in the sample also increases with an increase in the initial humidity of coal sample. A phenomenological model explaining the observed features of the hydrate formation in coal was proposed on the basis of the data obtained. In this model, the hydrate formation in coal is considered as a two-stage process: (1) a partial displacement of coal-sorbed water from the pore space into macropores and on the coal surface due to competitive sorption of carbon dioxide, and (2) the formation of hydrate from water droplets formed in the first stage.

Achievable supercooling for the formation of methane hydrate from water emulsionswas studied in seven different crude oils and in decane. The experiments were performed under constant rate cooling from +20 to -15 degrees C and a pressure of methane of 12 MPa. It was demonstrated that the shapes and positions of the resulting survival curves depend on the density, viscosity and dispersive power of oil samples used in the experiments, as well as on the degree of oil oxidation. In addition, results of the experiments on ice freezing under the same emulsions are presented. The results obtained in the work allowed us to discuss the possibility and features of primary and secondary nucleation of the hydrate and ice in the systems under consideration. (C) 2018 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. Co., Ltd. All rights reserved.

The crystal structure of the ionic clathrate hydrates of peralkylonium salts consists of hydrogen-bonded water molecules and anions forming host cage-like water-anion lattice, while peralkylonium cations are included into the cages of the lattice as guests. The ionic clathrate hydrates of some peralkylonium salts are considered as potentially applicable in various fields including gas separation, gas storage and transportation, cold storage and transportation. In this work, we report a synthesis and experimental measurements of compositions, melting points, enthalpies of fusion, as well as the results of the PXRD studies of eight ionic clathrate hydrates of tetrabutylammonium carboxylates formed in (C4H9)4NCnH2n+1CO2–H2O (n = 0–3) binary systems. The enthalpies of fusion values of these hydrates are measured for the first time. Three structural types were observed in the studied systems: on the base of tetragonal structure-I, cubic structure-I, and hexagonal structure-I. The data on thermal properties of studied ionic clathrate hydrates indicate that they are promising as phase change materials for cold storage and air-conditioning systems.

The review covers a wide range of issues related to the nucleation, growth and dissociation of gas hydrates. The attention is focused on publications of the last 1015 years. Along with the mathematical models used to describe these processes, the results of relevant experimental studies are surveyed. Particular sections are devoted to the gas hydrate self-preservation effect, the water memory effect in the hydrate formation, development of catalysts for hydrate formation and the effect of substances dissolved in the aqueous phase on the formation of hydrates. The main experimental techniques used to study gas hydrates are briefly considered.