Methane Hydrate Nucleation Research Articles

Non-equilibrium characteristics and regulation methods of methane hydrate nucleation on the substrate surface

Non-equilibrium characteristics and regulation methods of methane hydrate nucleation on the substrate surface

Metal plate-based promotion on methane hydrate nucleation: Insights into the influence of metal type and surface properties

Hydrate-based technologies hold significant promise in the fields of gas storage, water desalination and gas separation, but their application is restricted by the long induction time and high degree of randomness associated with hydrate nucleation. In this study, we conducted experimental investigations to access the influence of metal plates (Mg, Al and Zn) on methane hydrate nucleation under both pure water and acidic conditions. The results demonstrated that Mg plate exhibited the strongest promotion effect on methane hydrate nucleation. The presence of acid significantly accelerated hydrate nucleation in the Zn plate system, but conversely reduced the promotion effect of Al plate. In conjunction with the in-situ morphology evolution of hydrate nucleation, methane-liquid–metal interface was found to play a crucial role in the metal-induced promotion effect. Two nucleation modes were proposed accordingly: (i) in pure water, hydrate nucleation initiated exclusively at the methane-liquid–metal interface without extra nucleation site (Mode 1), and (ii) in acidic condition, hydrate nucleation occurred with evident multiple nucleation sites (Mode 2). Furthermore, SEM imaging, AFM and contact angle characterization revealed that the surface properties of metal plate (e.g., hydrophilicity and roughness) were the key factors in determining the effectiveness of the promotion effect. Liquid climbing upward along the metal plate surface was vital for metal plates to promote gas hydrate formation. Overall, this study provides new insights into hydrate nucleation promotion and suggests a straightforward way to enhance hydrate nucleation by modifying surface properties

Nucleation of Methane Hydrate in Surfactant Solutions in Cells Made of Teflon, Stainless Steel, and Glass

Nucleation of Methane Hydrate in Surfactant Solutions in Cells Made of Teflon, Stainless Steel, and Glass

Dual nature of methanol as a thermodynamic inhibitor and kinetic promoter of methane hydrate formation in a wide concentration range

Methanol (MeOH) is a common thermodynamic inhibitor of gas hydrates. However, its impact on the kinetics of methane hydrate formation has not been systematically investigated. We have thoroughly examined the effect of MeOH in a wide concentration range on the nucleation and growth kinetics of methane hydrate. The onset temperature To and subcooling ΔTo of methane hydrate were determined under ramp cooling of 1 K/h. The mean To is not affected by methanol in the 0–2.5mass% range but decreases within 2.5–50mass%. At the same time, it was revealed that ΔTo for 1–40mass%MeOH is significantly smaller than that of water, making methanol a hydrate nucleation promoter within the concentration range. The relationship between ΔTo and the methanol concentration shows a minimum of 0.53 ± 0.36 K (at 20mass%). Adding 1–30mass% of methanol reduces the stochasticity of the methane hydrate nucleation events. The hydrate nucleation rate increases by an order of magnitude at 1.5 K subcooling when 5 % of MeOH is added to water. Besides, methanol enhances the methane hydrate growth at 1–40mass%, with the maximum rate occurring at 10mass% MeOH. Despite the excellent promoting properties of methanol, extrapolation suggests that MeOH may inhibit both nucleation and growth of methane hydrate in more concentrated solutions (≥50mass%).Methanol has a dual nature as a thermodynamic inhibitor and a kinetic promoter of methane hydrate formation. The kinetic promotion function of methanol is observed within a specific range (1–40mass%), but in more concentrated systems, it seems to be reversed.

Hydrate Formation with the Memory Effect Using Classical Nucleation Theory

Methane hydrate formation is analytically studied in the presence of the water memory effect using the classical nucleation theory. The memory effect is introduced as a change in nucleation site from a three-dimensional heterogenous nucleation on a solid surface with cap-shaped hydrate clusters (3D-HEN) to a two-dimensional nucleation on the solid hydrate residue surface with monolayer disk-shaped hydrate clusters (2D-NOH). The analysis on the stationary nucleation of methane hydrate under isobaric conditions shows that the memory effect caused an average decrease of 4.4 K in metastable zone width, or subcooling. This decrease can be erased at higher dissociation temperatures (ΔT > 17.2 K) due to a decrease in the concentration of 2D-NOH nucleation sites. Moreover, the probability of hydrate formation is estimated for the purpose of quantifying risk associated with methane hydrate formation in the presence of the memory effect.

Nucleation of Methane Hydrate from Water and Aqueous Solutions of Malonic Acid in Glass Cells with Varying Surface Hydrophilicity

Nucleation of Methane Hydrate from Water and Aqueous Solutions of Malonic Acid in Glass Cells with Varying Surface Hydrophilicity

Methane hydrate formation enhanced by thermally expanded graphite with multi-sized pores

Methane hydrate has been endowed with great potential in energy storage and transportation, but the sluggish formation kinetics restrict its industrial application. Herein the thermally expanded graphite (EG), with multi-sized pore structure that can be effectively controlled by expanding and grinding processes, is used to promote the nucleation and growth of methane hydrates. The results demonstrate that the EG exhibits a remarkable promotion in the formation of methane hydrate from water, with high gas storage capacity of 143 V/V, short induction time of 10 min, and rapid gas storage rate of 1 V·V·min−1, which are attributed to its well-designed multi-sized pore structure. Thereinto, the nano-sized pores can effectively adsorb guest molecules, increasing the guest–host contact area; meanwhile, the micron-sized pores with moderate scale not only provide abundant channels for mass transfer of reactants but also enable good thermal conductivity for heat transfer to soundings. This work provides an insight into the promotion effect of multi-sized porous medium in hydrate formation, and offers an effective strategy for fabricating high-performance promotors through pore designing.

Synergistic effect of ultrasound combined with bubble enhanced rapid nucleation and growth of methane hydrate

The synergistic effect between ultrasound and bubbles serves to amplify the nucleation-enhancing effect of bubbles, effectively addressing the crucial challenges of limited gas–liquid interface and intricate nucleation. Based on this, this study proposed a new method of ultrasound combined with microbubbles and bubbling to enhance hydrate nucleation and growth. A visualization experimental system for the growth of methane hydrates enhanced by ultrasound combined with bubbles was developed. The optimal conditions for ultrasound-enhanced methane hydrate nucleation were quantitatively determined. Subsequently, the enhancement effects of ultrasound combined with microbubbles and bubbling systems were systematically analyzed. Under the influence of ultrasound, the nucleation induction period was reduced from 860 min to 7.5 min, and the complete reaction time was shortened to less than 100 min, resulting in a 3.2-fold increase in methane gas conversion. The combination of ultrasound and microbubble method reduced the nucleation induction time to 6.7 min and increased the growth rate by 10.6%. Furthermore, the combination of ultrasound and bubbling method, by fragmenting large nuclei into smaller ones and inducing secondary nucleation, enhanced mass transfer and increased the growth rate of hydrates by 4.4–5.2 times, with a gas conversion increase of 77.5 %–80 %. A novel finding was made in this study, where under the combined effect of ultrasound and bubbling, the stable formation of slurry hydrates was discovered, providing a new idea for the promotion of high-efficiency energy storage technology for hydrates.

Methane hydrate formation in slit-shaped pores: Impacts of surface hydrophilicity

Gas hydrate accumulation and hydrate-based gas storage and transportation technology are intimately linked to the formation process of hydrates in the pore space. However, the molecular mechanism underlying this process remains unclear. Here, we employ molecular simulations to investigate methane hydrate formation in surface-modified silica pores, with specific emphasis on the impact of pore surface characteristics. Our results show that under the same thermodynamic conditions, methane hydrate shows no preference towards either the hydrophobic or hydrophilic pore surface, and tends to nucleate in the central part of the hydrophilic slit. It means that whilst the surface properties can impact the dynamics and structure of the molecules on it, thus affecting methane concentration and, as a result, the probability of cage formation, the confinement effect ultimately controls the nucleation process. Furthermore, the pre-filling of the pores with methane can significantly accelerate hydrate formation. This is because methane bubbles adsorbed in the pores can noticeably elevate methane concentration in solution. Moreover, the hydrophobic surface can help with methane dissolution in water, which can both promote the transportation of molecules between methane bubbles and enhance methane hydrate nucleation. This study enhances understanding of the hydrate formation process in pores, which can aid in the design of gas hydrate promoters or inhibitors that meet the demands of hydrate technologies.

Effects of wax on the formation of methane hydrate in oil-dominate systems: Experiments and molecular dynamics simulations

Hydrate formation and wax deposition in underwater multiphase pipelines have become two vital problems affecting the flow assurance safety. Experiments and molecular dynamics (MD) simulations were performed to investigate the effect of wax crystals on hydrate nucleation and growth. Our experimental results showed that wax crystals had an inhibitory effect on hydrate growth, but played a dual role in methane hydrate nucleation (promotion and inhibition). The addition of wax could decrease mass transfer coefficient of methane by increasing viscosity of oil phase, which lower methane supply from the oil bulk phase to the oil–water interface. The simulation results revealed that the wax crystals at the interface influenced the mass transfer of methane molecules instead of providing heterogeneous nucleation sites. Small wax crystal adjacent to the oil–water interface accelerated methane supersaturation dissolution and restricted gas diffusion in the aqueous phase because of adsorption to methane, which promoted hydrate nucleation and shifted the nucleation position toward the oil–water interface. While the large wax crystal could effectively block the methane mass transfer from oil phase to aqueous phase by covering the oil–water surface, which reduced the concentration of methane in the aqueous phase and prolonged the induction time of hydrate formation. These results of this work would provide a better understanding of the interaction mechanism between hydrate and wax.

Turning gas hydrate nucleation with oxygen-containing groups on size-selected graphene oxide flakes

Gas hydrate is a promising alternative for gas capture and storage due to its high gas storage capacity achieved with only structured water molecules. Nucleation is the critical controlling step in gas hydrate formation. Adding an alien solid surface is an effective approach to regulate gas hydrate nucleation. However, how the solid surface compositions control the gas hydrate nucleation remains unclear. Benefiting from the fact that the surface compositions of graphene oxide (GO) can be finely tuned, we report the effect of functional groups of size-selected GO flakes on methane hydrate nucleation. The carbonyl and carboxyl of GO flakes showed a more prominent promotion for methane hydrate nucleation than the hydroxyl of GO flakes. Surface energy, zeta potential, Raman spectra, and molecular dynamics simulation analysis were used to reveal the regulation mechanism of the functional groups of size-selected GO flakes on methane hydrate nucleation. The GO flakes with abundant carbonyl and carboxyl exhibited higher charge density than those enriched in hydroxyl. The negatively charged GO flakes can induce water molecules to form an ordered hydrogen-bonded arrangement via charge-dipole interactions. Therefore, the water molecules surrounding the carboxyl and carbonyl showed a more ordered hydrogen-bonded structure than those around the hydroxyl of GO flakes. The ordered water arrangement, similar to methane hydrate cages, significantly accelerated methane hydrate nucleation. Our study shows how the surface chemistry of solids control gas hydrate nucleation and sheds light on the design of effective heterogeneous nucleators for gas hydrate.

Effect of Methanol on the Kinetics of Nucleation and Growth of Methane Hydrate

Effect of Methanol on the Kinetics of Nucleation and Growth of Methane Hydrate

Methane hydrate nucleation path and structure evolution revealed by Markov modelling

A deep understanding of hydrate formation path is currently one of the most important thresholds for the energy, environmental and safety applications of hydrate. Methane hydrate, a kind of clean energy and the most widespread hydrate clathrates, is selected as the research focus in this study. The trajectories of the hydrate growth are generated by Molecular Dynamics (MD) simulations. Then, these trajectories are analyzed by applying the Markov State Model for the first time, from which the evolution path and structure conversion are extracted. The results show that nine independent meta-stable states can be identified. The findings reveal the existence of nine distinct metastable states during the hydrate formation process. Transitions between these states occur at nanosecond timescales, considerably slower than conventional MD simulations. Moreover, based on the state transitions, a single-track path traversing the metastable states leads to the final state, while two bidirectional paths arise due to the infiltration or escape of methane molecules. These results facilitate the sampling and observation of the hydrate formation process in laboratory conditions and inspire strategies for controlling hydrate evolution.

Nucleation of Methane Hydrate in the Presence of Nanofibrillar Cellulose

Nucleation of Methane Hydrate in the Presence of Nanofibrillar Cellulose

Homogeneous nucleation of crystalline methane hydrate in molecular dynamics transition paths sampled under realistic conditions.

Methane hydrates are important from a scientific and industrial perspective, and form by nucleation and growth from a supersaturated aqueous solution of methane. Molecular simulation is able to shed light on the process of homogeneous nucleation of hydrates, using straightforward molecular dynamics or rare event enhanced sampling techniques with atomistic and coarse grained force fields. In our previous work [Arjun, T. A. Berendsen, and P. G. Bolhuis, Proc. Natl. Acad. Sci. U. S. A. 116, 19305 (2019)], we performed transition path sampling (TPS) simulations using all atom force fields under moderate driving forces at high pressure, which enabled unbiased atomistic insight into the formation of methane hydrates. The supersaturation in these simulations was influenced by the Laplace pressure induced by the spherical gas reservoir. Here, we investigate the effect of removing this influence. Focusing on the supercooled, supersaturated regime to keep the system size tractable, our TPS simulations indicate that nuclei form amorphous structures below roughly 260K and crystalline sI structures above 260K. For these temperatures, the average transition path lengths are significantly longer than in our previous study, pushing the boundaries of what can be achieved with TPS. The temperature to observe a critical nucleus of certain size was roughly 20K lower compared to a spherical reservoir due to the lower concentration of methane in the solution, yielding a reduced driving force. We analyze the TPS results using a model based on classical nucleation theory. The corresponding free energy barriers are estimated and found to be consistent with previous predictions, thus adding to the overall picture of the hydrate formation process.

Molecular Dynamics Studies of the Process of Crystallization and Growth of Gas Hydrates in a Strongly Supercooled Two-Phase "Methane-Water System"

The processes of nucleation and growth of methane hydrate in a highly supercooled two-phase "methane-water" system obtained using various cooling protocols are considered. It has been shown that, at sufficiently high cooling rates, crystalline forms of methane hydrate can still form in the system. It was found that, at a cooling rate of γ=1.0 K/ps, the process of nucleation and growth of gas hydrate was observed in all independent molecular dynamics iterations, while at a cooling rate of γ=10.0 K/ps, no nucleation event was observed in ~26.7% of numerical experiments. It was found that with an increase in the cooling rate of the system, an increase in the average time scale of nucleation tauc and a decrease in the critical size of the nucleus nc are observed. It is shown that at a sufficiently deep level of supercooling of the system, the scenario of homogeneous crystalline nucleation is realized at the initial stage of the phase transition. Keywords: molecular dynamics, crystallization, methane hydrate.

Молекулярно-динамические исследования процесса кристаллизации и роста газовых гидратов в сильно переохлажденной двухфазной системе "метан-вода"

The processes of nucleation and growth of methane hydrate in a highly supercooled two-phase methane–water system obtained using various cooling protocols are considered. It has been shown that, at sufficiently high cooling rates, crystalline forms of methane hydrate can still form in the system. It was found that, at a cooling rate of γ = 1.0 K/ps, the process of nucleation and growth of gas hydrate was observed in all independent molecular dynamics iterations, while at a cooling rate of γ = 10.0 K/ps, no nucleation event was observed in ~26.7% of numerical experiments. It was found that with an increase in the cooling rate of the system, an increase in the average time scale of nucleation τc and a decrease in the critical size of the nucleus nc are observed. It is shown that at a sufficiently deep level of supercooling of the system, the scenario of homogeneous crystalline nucleation is realized at the initial stage of the phase transition.

Влияние метанола на кинетику нуклеации и роста гидрата метана

In the present work, we experimentally investigated the nucleation and growth kinetics of methane hydrate in the presence of aqueous methanol solutions at alcohol concentrations of 0, 1, 2.5, 5, 10, and 20 mass %. It was found that the addition of methanol statistically significantly reduces the supercooling of the methane hydrate onset ΔTo even at low concentrations. The value of ΔTo decreases bya factor of 5 when transitioning from water to 20 mass% methanol. We have observed that as the alcohol content increases, there isa correlation with an increase in the amount of hydrate at the end of the cooling stage. Adding methanol to water also increases the rate of methane hydrate growth. Thus, our experimental data indicate the role of methanol as a kinetic promoter of methane hydrate nucleation and growth, and the dual nature of methanol which is also a thermodynamic hydrate inhibitor.

Получение и исследование свойств сульфосукцинатов циклических спиртов для применения в технологии хранения и транспортировки газа в гидратной форме

The article presents the synthesis of several cyclic alcohol sulfosuccinates and the study results of their influence on the kineticsof methane hydrate formation in high-pressure autoclaves. The effect of the structure of the tested compounds on foaming, induction time, and water-to-hydrate conversion is considered in comparison with sodium dodecyl sulfate. The process of obtaining the substances used is presented in detail. It was found that an increase in the size of the cycloalkyl fragment from C5 to C7 leads to some acceleration of the nucleation and growth of methane hydrate. In contrast, the transition to a cycle containing eight carbon atoms decreasesthe promoting effect. It is shown that the impact of the synthesized compounds on accelerating the formation of gas hydratesis comparable to that for sodium dodecyl sulfate. At the same time, the proposed reagents possess better performance characteristics (do not contribute to foaming).

Kinetic Inhibition Effect of Valine on Methane Hydrate Nucleation Time in Oil System

Amino acids are known as novel kinetic hydrate inhibitor (KHI) for hydrate mitigation, however, the performance in oil system is not well justified up to date. In this study, the kinetics of methane hydrates in oil dominated systems using valine amino acid has been studied in a high-pressure gas hydrate reactor at 80 bar and 1 °C using the constant cooling method. Drilling oil was used in this work to mimic the oil phase in flow assurance. The results shows that valine delays hydrate formation nucleation time 4 times compared with pure water systems. This finding is contrary to most claims in literature that shows that valine promotes hydrate in gas dominated system. However, the inhibition impact of valine exhibited in this work might be due to the presence of oil with is absence in the most literature studies. The findings in the work are useful for hydrate mitigation using amino acids in flow assurance.