The formation of methane hydrates is a promising route for safe and efficient natural gas storage, but slow nucleation kinetics and foaming from surfactant promoters hinder their practical use. To address these challenges, this study evaluates a new class of highly effective kinetic biopromoters synthesized from d-glucono-1,5-lactone and 11 amino acids (GDL+AA). Methane hydrate formation was investigated in high-pressure autoclaves under static and dynamic conditions, complemented by differential scanning calorimetry (DSC), visual observation, pelletization, stability testing, molecular dynamics, and quantum chemical simulations. GDL+AA compounds exhibited a pronounced promoting effect at low concentration (0.05 wt %), initiating hydrate formation in 19-25 min compared with 54 min for sodium dodecyl sulfate (SDS) and 45 min for the unmodified amino acids. Methane uptake reached 0.160 mol/mol, and water-to-hydrate conversion was 88-96% in high-pressure autoclave tests. DSC experiments confirmed higher hydrate formation onset temperature (-9 degrees C for GDL+Met vs SDS: -16 degrees C; Met: -16 degrees C) and higher water to hydrate conversion (99.3% for GDL+Met vs SDS: 70.0%; Met: 28.7%). Visual observations under static conditions corroborated accelerated hydrate growth. Molecular dynamics and quantum-chemical calculations elucidated the mechanism of action of the GDL+AA derivatives. No foaming occurred in the GDL+AA systems during formation or dissociation. Hydrate pellets from GDL+AA showed high density and mechanical strength and high methane retention stability for engineering applications. Chemical modification with gluconic acid significantly enhanced the kinetic performance compared with unmodified amino acids. The synthesis is water-based and mild and uses biocompatible, biodegradable materials, aligning with green chemistry principles. GDL+AA compounds are scalable, efficient, and environmentally sustainable promoters of solidified natural gas.

Morphology and growth rate of carbon dioxide hydrate on the interface between liquid carbon dioxide and humic acid solutions were studied in this work. It was found that after the growth of the hydrate film at the interface, further growth of hydrate due to the suction of water in the capillary system formed between the wall of the cuvette and the end boundary of the hydrate layer occurs. Most probably, substantial effects on the formation of this capillary system may be caused by variations in reactor wall properties, for example, hydrophobic-hydrophilic balance, roughness, etc. We found, that the rate of CO2 hydrate film growth on the surface of the humic acid aqueous solution is 4-fold to lower in comparison with the growth rate on the surface of pure water. We suppose that this is caused by the adsorption of humic acid associates on the surface of hydrate particles and, as a consequence, by the deceleration of the diffusion of dissolved carbon dioxide to the growing hydrate particle.

The paper presents an experimental study of the process of methane hydrate formation from stabilized water foam. In all cases, the hydrate formation front started from the region inside the foam. Upon reaching the foam-solution boundary, it initiated the formation of polycrystalline conical conglomerates at this boundary - hydrate needles oriented deep into the solution. A mechanism for their formation and subsequent spontaneous shortening of some of them is proposed.

В работе исследована нуклеация гидрата метана из чистой воды и 2 мас. % раствора малоновой кислоты. Эксперименты проводились в стеклянных ампулах с обычной либо увеличенной гидрофильностью поверхности. Для увеличения гидрофильности поверхности использовались обработка хромовой смесью с последующим кипячением в воде. Показано, что более быстрая нуклеация (меньшие индукционные периоды) имеют место на более гидрофобных стенках. Если вместо чистой воды берется 2 мас. % раствор малоновой кислоты, индукционные периоды для большей части образцов существенно увеличиваются, причем этот эффект более выражен для гидрофилизированных стенок ампул. В работе обсуждаются возможные причины этих изменений. Визуальные наблюдения показали, что как минимум в большинстве случаев нуклеация гидрата в стеклянных ячейках в растворах малоновой кислоты происходит на поверхности контакта раствор — стекло, а не на трехфазной линии контакта раствор — стекло — газ.

The work investigated the nucleation of methane hydrate from pure water and a 2 wt

The processes of formation (and decomposition) of methane hydrate from water adsorbed in the pores of spherical granules of mesoporous alumina (Al 2 O 3 ) have been investigated using the low-field NMR spin - spin relaxation time (T 2 ) and DSC methods. Analysis of the obtained data showed that changes observed in the relaxation time spectra represent a strong case in favor of the model envisaging hydrate growth in pore spaces without conspicuous water transfer through the volume content of the sample with mesoporous structure. As the supercooling strength of the liquid phase enhances, the size of the pores in which hydrate formation takes place decreases. At this, the size of the hydrate particles previously formed in larger pores tends to increase. Hydrate nucleation was shown to be followed by intensive and rapid hydrate formation in some parts of the alumina granules in the sample. The " skipping " mechanism of hydrate formation between granules remains unclear.

The effect of secondary spontaneous boiling of submerged jets formed during the collapse of vapor bubbles during the bulk boiling of water subcooled to the saturation temperature at the end of a laser optical fiber is experimentally discovered. Keywords: submerged jet, subcooled liquid boiling, laser.

Polymeric models of the core prepared with a Raise3D Pro2 3D printer were employed for methane hydrate formation. Polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), carbon fiber reinforced polyamide-6 (UltraX), thermoplastic polyurethane (PolyFlex), and polycarbonate (ePC) were used for printing. Each plastic core was rescanned using X-ray tomography to identify the effective porosity volumes. It was revealed that the polymer type matters in enhancing methane hydrate formation. All polymer cores except PolyFlex promoted the hydrate growth (up to complete water-to-hydrate conversion with PLA core). At the same time, changing the filling degree of the porous volume with water from partial to complete decreased the efficiency of hydrate growth by two times. Nevertheless, the polymer type variation allowed three main features: (1) managing the hydrate growth direction via water or gas preferential transfer through the effective porosity; (2) the blowing of hydrate crystals into the volume of water; and (3) the growth of hydrate arrays from the steel walls of the cell towards the polymer core due to defects in the hydrate crust, providing an additional contact between water and gas. These features are probably controlled by the hydrophobicity of the pore surface. The proper filament selection allows the hydrate formation mode to be set for specific process requirements.

It is known that injection of carbon dioxide into the petroleum reservoir(CO 2 flooding) is one of the effective methods for enhanced oil recovery. CO 2 flooding may be complicated by formation of CO 2 hydrate plugs. It makes topical investigation of CO 2 hydrate formation in the system gaseous CO 2 –oil–water. In this work, the growth rates of carbon dioxide hydrate films at the water–oil as well as the water–gas interface are studied in the pressure range of 2.30–3.04 MPa and at temperatures between –5.4 and 5.0°C. It is found that the growth rate for the water–oil interface is 3.5 times lower than that for the water–gas interface with carbon dioxide. It is hypothesised that the observed decrease in the growth rate is related to the mechanical resistance of the oil components adsorbed on the interface to the growth of the hydrate film. The growth rate of the film has been shown to depend on the experimental procedure,most likely due to the different initial concentrations of carbon dioxide in the aqueous solutions.

The object of an experimental study is a vapor bubble formed in a subcooled liquid due to absorption of laser radiation transmitted into the working volume through a thin optical fiber. Evolution of a bubble is characterized by its rapid growth and collapse with the generation of a hot submerged jet. Some features of the process under study are considered in relation to the field of medicine. Normal saline is used as the working fluid. It is shown that under the same conditions (radiation power, optical fiber diameter, and initial temperature of liquid), the dimensions reached by a vapor bubble in saline are much smaller than those in pure water. A significant influence of the shape of a fiber tip on the nature of the process under study was revealed.

The results of visual studies of the growth of methane and carbon dioxide hydrates from highly dilute aqueous solutions of acids and alkalis, as well as from the same solutions with the addition of 0.1 wt % sodium dodecyl sulfate, are presented. It was found that in addition to the growth of hydrate films at the water-gas interface (for solutions without sodium dodecyl sulfate) and the growth of a loose mass of hydrate on the walls of the reactor in the case of solutions with sodium dodecyl sulfate, there is also growth of the hydrate film on the free walls of the reactor. We speculate what these hydrate films form from the wetting water films located on the walls. In addition, growth of relatively large hydrate agglomerates on the reactor walls was observed. They look like "growing directly from the wall". Presumably, this is due to the possibility of film transfer of water between the formed hydrate films and the walls of the reactor. Possible features of the hydrate formation process caused by the formation of hydrates on wetting films are also discussed.

The effect of secondary spontaneous boiling of submerged jets formed during the collapse of vapor bubbles during the bulk boiling of water subcooled to the saturation temperature at the end of a laser optical fiber is experimentally discovered.

This paper presents the results of an experimental study of the effect of laser radiation power on the growth and collapse dynamics of vapor bubbles formed near the end-face of an optical fiber through which the radiation is transmitted into the liquid. It is shown that this influence is insignificant in the power range from 3 to 10 W. We propose a hypothesis that this effect is due to the fact that experiments with different radiation power have bubbles occurring and growing under similar temperature conditions. Our proposition has been confirmed by numerical simulations. (c) 2021 Elsevier Ltd. All rights reserved.

There is an urgent need for new drugs to overcome the challenge of the ever-growing drug resistance towards tuberculosis. A new, highly efficient anti-tuberculosis drug, Perchlozone (thioureidoiminomethylpyridinium perchlorate, Pz), is only available in an oral dosage form, though injectable forms and inhalation solutions could be better alternatives, offering higher bioavailability. To produce such forms, nano- and micro-particles of APIs would need to be prepared as dispersions with carriers. We use this case study to illustrate the principles of selecting solvents and excipients when preparing such formulations. We justify the choice of water–THF (19.1 wt % THF) as solvent and mannitol as carrier to prepare formulations of Pz—a poorly soluble compound—that are suitable for injection or inhalation. The formulations could be prepared by conventional freeze-drying in vials, making the proposed method suitable for industrial scaling. A similar strategy for selecting the organic solvent and the excipient can be applied to other compounds with low water solubility.

A single act of boiling a liquid underheated to the saturation temperature is experimentally investigated when the liquid is exposed to continu ous-wave laser radiation introduced into the working volume by means of a thin optical fiber. It is shown that a vapor bubble formed near the end of the optical fiber during collapse forms a hot cumulative jet, the phenomenon of secondary boiling around which is observed. The secondary vapor inclusion formed around the jet has an extended shape, moves, and evolves together with it. The significant effect of this inclusion on jet-propagation dynamics is demonstrated.

It was shown that hydrated crystals of sodium dodecyl sulfate (SDS), which precipitate from dilute SDS solutions sharply accelerate nucleation of methane gas hydrate. This finding adds significant details to the available information on the mechanisms of hydrate formation from SDS solutions and can form the basis for the development of a new class of kinetic promoters of hydrate formation.

A comparative investigation of methane hydrate formation from 0.1 wt % solutions of an alkaline extract of humic acids (HA) and sodium dodecyl sulfate (SDS) has been carried out. It was demonstrated that the hydrate grows as a voluminous loose mass squeezed onto the reactor walls in both cases. It turns that about 75% of water transforms into hydrate within 15-20 min. Thus, natural HA can act as kinetic hydrate promoters. At the same time, SDS increases the hydrate nucleation rate compared to pure water under the studied conditions (12.5-13.0 MPa and -5 degrees C), while HA retards the hydrate nucleation. Visual observation of the hydrate growth in the solutions of HA and SDS allowed us to propose a new mechanism of hydrate growth in the form of a porous loose mass squeezed upward over the reactor walls. The mechanism relates to overgrowing of the hydrate film formed at the gas-solution interface into the solution volume. This results in squeezing some part of the solution onto the reactor walls. Simultaneous contact of the gas, solution, and hydrate facilitates the rapid transformation of the squeezing solution into a loose hydrate mass. Then this mass soaks up the solution due to the capillary forces.

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.