Methane Hydrate Formation Process Research Articles

Freshwater Recovery and Removal of Cesium and Strontium from Radioactive Wastewater by Methane Hydrate Formation.

As human society has advanced, nuclear energy has provided energy security while also offering low carbon emissions and reduced dependence on fossil fuels, whereas nuclear power plants have produced large amounts of radioactive wastewater, which threatens human health and the sustainability of water resources. Here, we demonstrate a hydrate-based desalination (HBD) technology that uses methane as a hydrate former for freshwater recovery and for the removal of radioactive chemicals from wastewater, specifically from Cs- and Sr-containing wastewater. The complete exclusion of radioactive ions from solid methane hydrates was confirmed by a close examination using phase equilibria, spectroscopic investigations, thermal analyses, and theoretical calculations, enabling simultaneous freshwater recovery and the removal of radioactive chemicals from wastewater by the methane hydrate formation process described in this study. More importantly, the proposed HBD technology is applicable to radioactive wastewater containing Cs+ and Sr2+ across a broad concentration range of low percentages to hundreds of parts per million (ppm) and even subppm levels, with high removal efficiency of radioactive chemicals. This study highlights the potential of environmentally sustainable technologies to address the challenges posed by radioactive wastewater generated by nuclear technology, providing new insights for future research and development efforts.

Insights into behaviors of guest and host molecules in methane hydrate formation process in the presence of kinetic inhibitors via in-situ micro-Raman spectroscopy

In-situ microscopic observation on methane hydrate formation in the presence of kinetic hydrate inhibitor, poly (vinyl caprolactam) (PVCap) or poly (N-isopropyl acrylamide) (PNIPAM), is conducted with a confocal Raman imaging microscope, and the behaviors of CH4 molecules and water molecules in hydrate formation process are studied to understand the inhibition mechanism. It is found that both PVCap and PNIPAM have influences on hydrate formation, but their interactions with host and guest molecules are different. PVCap with cyclic pendant groups works better on preventing hydrate formation from the gas–liquid interface into the bulk solution, while PNIPAM with acyclic pendant groups is more effectively on inhibiting hydrate growth to well-ordered clathrate structures. Those are caused by the difference in the prominent inhibition mechanism of the two types of kinetic hydrate inhibitors, lactam-based PVCap mainly limiting the diffusion of CH4 molecules from the gaseous phase to the liquid phase, while non-lactam PNIPAM undermining hydrate growth by retarding the rearrangement of water molecules to form clathrate structures.

Simulation of methane hydrate formation in coarse‐ to fine‐grained sediments in the Nankai Trough, Japan

AbstractThe properties of host sediments and pore water considerably affect both the occurrence and formation processes of methane hydrate. In coarse‐grained layers, hydrates are generally concentrated preferentially in the pore space, and their formation is influenced by pore water salinity. To understand how geophysical and geochemical factors control the distribution of methane hydrates, we conducted numerical simulations using a one‐dimensional flow model under different reservoir and fluid conditions in the Kumano Forearc Basin, Nankai Trough, Japan. Assuming an estimated range of methane flux between 0.002 and 1.9 kg m−2 year−1, three flow scenarios were considered. When the methane flux was relatively small, the results coincided with the observed hydrate distribution. In general, a low‐methane flux decreases the hydrate saturation upward from the bottom of the methane hydrate stability, whereas a high‐methane flux increases the saturation downward. These results also suggest that the sediment structure, such as the fracture distribution, influences the sediment stress conditions and constrains the flow regime. We further examined the effects of permeability changes in the heterogeneous lithological units on the simulation results using typical permeabilities of 10−13 m2 for sand and 10−15 m2 for mud. The results showed that hydrate saturation sharply increased and decreased in adjacent high‐ and low‐permeability units, respectively. The consideration of complex stratigraphic conditions and variable fluid configurations provides an understanding of the environmental factors controlling hydrate generation and distribution, which is important for hydrate resource extraction and geohazard prevention.

Synthesis of mixed methane-ethylene hydrate with ice powder

The study of gas hydrate researched by the ice powder method is helpful for us to understand the storage, separation, transportation and transformation of gas on the solid surface. In this work, the change regulation has been studied that temperature, pressure, hydrate saturation, and conversion rate in the formation process of methane-ethylene mixed hydrate, which exploring the internal action mode of the methane-ethylene mixed hydrate. The experimental results show that under the condition of −4.0 °C and 4 MPa, the conversion rates of methane, methane-ethylene (with mole ratios 2, 1, and 0.5), and ethylene hydrate are 5.30%, 11.95%, 16.57%, 19.93%, and 26.84%, respectively. And more, the conversion efficiencies of hydrate are 0.36, 0.81, 0.96, 1.58, and 6.58, respectively. The above data show that with the increase of ethylene content, the formation of hydrate is easier, which proves that ethylene can promote the formation efficiency of methane hydrate. The above results have reference value for understanding the formation of natural gas hydrates, so as to promote the development and application of gas hydrate. • There is no induction period in the process of ice powder generating methane, ethylene, and methane-ethylene mixed hydrate. • The ethylene molecules in the methane hydrate formation process can increase the reaction rate of the system. • It provides theoretical support for the development and utilization of natural gas hydrates.

Molecular Insights into the Impacts of Calcite Nanoparticles on Methane Hydrate Formation

Despite the potential broad utility of nanoparticles in hydrate-related fields, there remains a paucity of studies on the impacts of nanoparticles on gas hydrate formation. In this study, massive microsecond molecular dynamics simulations were performed to investigate the roles of calcite nanoparticles on the formation processes of methane hydrate. Our results indicate that calcite nanoparticles prefer to be in the water phase close to the water/gas interface. They inhibit methane hydrate nucleation because a layer of bound water with a thickness of 0.75 nm forms around each nanoparticle which results in an extremely low methane concentration region. Thus, methane hydrate nucleates away from the nanoparticle, and no clear connection between the nucleated hydrate and the nanoparticle is observed. The nanoparticles associate easily, and a water layer with a thickness of 1.15 nm forms between the associated nanoparticles. Moreover, methane hydrate growth is not influenced by calcite nanoparticles until the growth front approaches the bound water around the nanoparticle. These molecular insights of the impacts of calcite nanoparticles on methane hydrate formation are beneficial for the application of nanoparticles in hydrate mining and hydrate-related technologies.

Study on the kinetics of methane hydrate formation in the carbon microtube system

The current studies focused mostly on the promotion effects of nano-sized carbon nanotubes on hydrates, while the effect of carbon microtubes on the kinetics of methane hydrate formation is rarely mentioned. Therefore, this paper added 3–15 μm multi-walled carbon microtubes (MWCMTS) to a 4L autoclave (under the conditions of 3–6 MPa, and 0–5 ℃) to investigate the influence of the micron-medium concentration on the kinetics of hydrate formation. The results demonstrated that the addition of micro-carbon nanotubes could reduce the nucleation time of methane hydrate; a higher degree of subcooling could shorten the reaction time. Furthermore, the increase in carbon nanotube concentration could lead to higher gas storage capacity. Gas storage capacity was the highest at 32.4 V/V under the condition of 13:3 gas–liquid ratio; this rate was over 3 times larger than that of the pure water system. Micro-carbon nanotube-pure water system methane hydrate formation process was prone to the “platform period” phenomenon. However, this phenomenon would have on impact the final water conversion rate under the conditions of a sufficient driving force. Therefore, this study proved that carbon microtubes had an obvious effect on the promotion of methane hydrate formation and could be used as a cost-effective promoter.

Methane Hydrate Formation in Hollow ZIF-8 Nanoparticles for Improved Methane Storage Capacity

Methane hydrate has been extensively studied as a potential medium for natural gas storage and transportation. Due to their high specific surface area, tunable porous structure, and surface chemistry, metal–organic frameworks are ideal materials to exhibit the catalytic effect for the formation process of gas hydrate. In this paper, hollow ZIF-8 nanoparticles are synthesized using the hard template method. The synthesized hollow ZIF-8 nanoparticles are used in the adsorption and methane hydrate formation process. The effect of pre-adsorbed water mass in hollow ZIF-8 nanoparticles on methane storage capacity and the hydrate formation rate is investigated. The storage capacity of methane on wet, hollow ZIF-8 is augmented with an increase in the mass ratio of pre-adsorbed water and dry, hollow ZIF-8 (RW), and the maximum adsorption capacity of methane on hollow ZIF-8 with a RW of 1.2 can reach 20.72 mmol/g at 275 K and 8.57 MPa. With the decrease in RW, the wet, hollow ZIF-8 exhibits a shortened induction time and an accelerated growth rate. The formation of methane hydrate on hollow ZIF-8 is further demonstrated with the enthalpy of the generation reaction. This work provides a promising alternative material for methane storage.

Plasma-assisted nanotechnology for enhancement of the rate of production and storage of natural gas hydrates: Experimental study and kinetic modeling

In the present work, the novel technique of dielectric barrier discharge (DBD) humid air plasma has been presented for processing and functionalization of nanoparticles and enhancing the rate of methane hydrate production. It is shown that the rate of gas to hydrate (GTH) production is significantly promoted by applying the proposed DBD plasma on the surface structure of graphene nanosheets (GN). The plasma processing leads to considerable enhancement of dispersion, stability and specific surface area of graphene nanoparticles such that the gas–liquid interfacial area and fluid microconvection rate and thus the GTH conversion rate are significantly increased. It is found that at the optimum operating conditions of 60 ppm of plasma treated graphene nanoparticles at a frequency of 6 kHz, a voltage of 8 kV, and a processing time of 6 min, it is possible to achieve a 5 fold increase in GTH conversion as compared to the case of pure water in a one-hour hydrate production process. A new kinetic model for prediction of the gas to hydrate energy conversion process is also presented and the predicted results are validated by using the experimental data at different operating conditions. The average absolute deviation percent (AAD%) and the coefficient of determination (R2-value) of the predicted gas consumptions regarding methane hydrate formation process are about 1.97% and 0.98 respectively suggesting the excellent accuracy of the proposed kinetic model. The proposed plasma functionalization technique is robust and eco-friendly without operational difficulty of conventional surfactants and can have potential application for considerable enhancement of the rate of production and storage of natural gas hydrates.

Dynamics investigation on methane hydrate formation process with combined promotion methods

Abstract Rapid generation of natural gas hydrates is the basis for the application of hydrate storage and transportation. In this work, the kinetic parameters of methane hydrate formation (gas consumption, gas consumption rate constant and reaction space velocity) both in the liquid continuous impinging stream (LIS) system and sodium dodecyl sulfate (SDS) + water and LIS combination system were investigated in a liquid-continuous impinging stream reactor. The gas consumption rate constant was 3.40 × 10−8 mol2 s−1 J−1 without the impinging stream, while it increased with the increase of impinging strength and reached the maximum value of 3.68 × 10−8 mol2 s−1 J−1 when the impinging strength was 0.21. In the SDS + water and LIS combination system, when the SDS concentration was 600 mg/L, the maximum gas consumption rate constant was 3.99 × 10−8 mol2 s−1 J−1 without the impinging stream, while it reached the maximum value of 4.61 × 10−8 mol2 s−1 J−1 when the impinging strength was 0.38. The results showed that the impinging stream can effectively promote the formation rate of methane hydrate, and single mechanical promotion was better than non-promoting mode but combination promotion methods was better than single mechanical promotion.

Hydrate Formation in Reactor with Cooling Spiral

This paper deals with methane hydrate formation from SDS solution of 0.1 wt% in reactor with cooling spiral. Intensity of methane hydrate formation process in a vertical and horizontal cylindrical reactor with a cooled spiral at three fixed volumes of a surfactant solution was compared. The dependence of the gas content of the obtained samples depending on volume of the liquid phase and on the position of the reactor was revealed. The hypotheses about influence of diffusion at the interface and capillary effect on the cooled element on the gas content were examined. Also the efficiency of gas supply mode was tested. The best result for gas consumption in single gas injection mode is 60,21 L•L–1 achieved with a liquid volume of 300 ml in a vertical reactor. The best result for gas consumption in constant gas supply mode is 161,3 L•L–1 achieved with a liquid volume of 500 ml in a horizontal reactor.

Well-defined meso/macroporous materials as a host structure for methane hydrate formation: Organic versus carbon xerogels

A series of xerogels with a properly designed porous structure and surface chemistry have been synthesized and evaluated as a host structure to promote the nucleation and growth of methane hydrates. Organic xerogels (OGs) have been synthesized from resorcinol-formaldehyde mixtures using a sol-gel approach and microwave heating. These xerogels are hydrophilic in nature and possess designed meso/macrocavities in the pore size range 5–55 nm. Carbon xerogels (CGs) have been synthesized from their organic counterparts after a carbonization treatment at high temperature. Interestingly, the carbonization process does not alter/modify substantially the porous network of the parent xerogels, while developing new micropores. Under water-supplying conditions, the two types of xerogels exhibit a large improvement in the methane adsorption capacity compared to the pure physisorption process taking place in dry conditions (up to 200% improvement), and associated with a significant hysteresis loop. These excellent values must be associated with the promoting effect of these xerogels in the water-to-hydrate conversion process. The comparison of OGs and CGs as a host structure anticipates that surface chemistry, total pore volume and pore size are critical parameters defining the extent and yield of the methane hydrate formation process.

Heterogeneity properties of methane hydrate formation in a pilot-scale hydrate simulator

The accumulation and distribution features of gas hydrates are the significant issues affecting the hydrate resource assessment, the hydrate dissociation behaviors, and the risk evaluation of hydrate exploitation. This work aims to investigate the methane hydrate formation process by numerical simulation based on the experimental data in a pilot-scale hydrate simulator. Methane hydrate is formed by multi-step water injection method. Simulation results of the evolutions of the temperature, the system pressure, the mass of formed hydrate, and the remaining mass of methane gas are in good agreement with those of the experiment. The spatial distributions of the gas, water, and hydrate are all found to be very heterogeneous in the vessel during the whole simulation period. The free methane gas tends to accumulate in the pores near the upper boundary because of buoyancy and diffusion effects, while the liquid water shows an opposite trend under the gravity and capillary effects. Finally, the formed hydrates are found to be mainly accumulated in the upper area of the reactor due to the more favorable gas-water contact conditions, and the hydrate saturation decreases from the roof to the bottom layer by layer. In addition, the inhomogeneity of methane hydrate is more pronounced along the vertical direction than the horizontal one during the formation process. Generally, the heterogeneous formation of gas hydrate is dominated by the migration processes of gas and water in porous media. Moreover, the selected kinetic model is also important for the description of the heterogeneous hydrate formation behavior.

Experimental and modelling studies on the effects of nanofluids (SiO2, Al2O3, and CuO) and surfactants (SDS and CTAB) on CH4 and CO2 clathrate hydrates formation

Sodium dodecyl sulfate (SDS) with concentrations of 300 ppm and 500 ppm; cetyl trimethylammonium bromide (CTAB) with concentrations of 220 ppm and 700 ppm; and water-based nanofluids of SiO2, Al2O3, and CuO with concentrations of 0.1, 0.3, and 0.5 wt% were used as kinetic promoters in methane hydrate formation process at initial conditions of 274.15 K and 5.5 MPa and carbon dioxide hydrate formation process at initial conditions of 274.15 K and 3 MPa. Englezos and Bishnoi model was utilized for calculating the apparent rate constant of hydrate growth and van der Waals-platteeuw model coupled with CPA equation of state was used to model hydrate phase equilibrium conditions. SDS with a concentration of 500 ppm and CTAB with a concentration of 700 ppm are the most effective promoters in increasing the average apparent rate constant and water to hydrate conversion. SiO2 nanofluid with a concentration of 0.3 wt% shows the most promising promotion effects by reducing the induction times of CO2 and CH4 hydrates formation by 70 and 74%, respectively. Aqueous solution of SDS with a concentration of 500 ppm is the most effective promoter that can enhance the average apparent rate constant of CO2 and CH4 by 350 and 200%, respectively.

Oleic acid potassium soap: A new potential kinetic promoter for methane hydrate formation

Low gas hydrate formation rate is one important reason that limits the application of hydrate-based technologies, while development of new kinetic promoter is an alternative method to solve this problem. In this work, oleic acid potassium soap (OPS) was proposed to use as a new potential kinetic promoter to improve methane hydrate formation process. t80 was greater than 360 min when methane hydrate formed in redistilled water, while t80 can decrease to within 100 min with the addition of OPS. Compared OPS with published kinetic promoter of sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS), the promoting effect of OPS was better than SDBS, and had similar promoted effect with SDS. In addition, both thermodynamic and kinetic results showed that addition of OPS had little effect of methane hydrates equilibrium conditions. Promoting effect mechanism of OPS was that the doublebond and hydrophobic groups enhanced the solubility of methane, which finally improved methane hydrate formation.

Insights into induction time and agglomeration of methane hydrate formation in diesel oil dominated dispersed systems

Induction time and agglomeration of methane hydrate formation in dispersed systems play an important role in exploitation of natural gas hydrate, prevention of gas hydrate plug, and application of hydrate-based technologies. In this work, an autoclave with particle video microscope (PVM) probe was used to detect induction time of methane hydrate formation as a function of the water cut, dosage of sorbitan monolaurate (Span 20), and subcooling. Forty-one experiments and thirty-six experiments of induction time have been conducted for methane hydrate formation at constant pressure and at nonconstant pressure, respectively. The results showed subcooling was the major factor that affects induction time during methane hydrate formation process. Subcooling of 4 K can be seen as an inflection point because the average methane hydrate formation time was less than 200 min when the subcooling was greater than 4 K, while methane hydrate formation time exhibited more stochastic when the subcooling was less than 4 K. The results also suggested that there exists a transformation range of subcooling (TRS) during methane hydrate formation process. The agglomerated mechanism of methane gas hydrate may be changed when the subcooling is greater than TRS, and subcooling of 4 K is included in the TRS.

Experimental investigation into formation/dissociation characteristics of methane hydrate in consolidated sediments with resistance measurement

Natural gas hydrates (NGHs) are considered as a powerful potential energy resource. In this work, an experimental system containing a digital electrical bridge for resistance measurement was developed to gain an improved understanding of the formation/dissociation characteristics of NGHs in consolidated sediments. Using the apparatus, a dynamic methane hydrate formation method for sandstone cores was developed that can maintain a constant gas flow in the core during the methane hydrate formation process. As opposed to the traditional method that maintains a constant pressure in the core, higher resistance, permeability, and hydrate saturation for the core were obtained following methane hydrate formation equilibrium by using the proposed method. In order to investigate the methane hydrate formation characteristics in sandstone cores, the influences of core permeability, temperature, initial water saturation, and salinity on the resistance and hydrate saturation of two cores were analyzed in detail. The experimental results demonstrate that a relative lower temperature and higher initial water saturation in the core correspond to a higher hydrate saturation and water-to-hydrate conversation ratio. In the process of methane production from continent hydrate, the water output from the core with methane extraction was experimentally measured for the first time. It was found that, owing to the existence of free gas in the core holder, both the core resistance and methane production rate were not changed linearly with time. The methane production amount increased with an increase in initial water saturation, decrease in production pressure, or increase in pore volume in the core. It was demonstrated that water output is not a serious problem in the development of continental natural gas hydrate.

Controllable methane hydrate formation through trace carbon dioxide charging

An initial method to efficiently control methane hydrate formation process was investigated in this work. This method included an in-situ injection of a small amount of CO2 into the reactor during the nucleation stage to explore hydrate formation in 0.5mmol/L sodium dodecyl sulfate (SDS) solutions. Results showed that charging CO2 higher than 2% in the mixed gases could induce immediate methane hydrate growth stage. Furthermore, when 3% CO2 was injected into the reaction system at different time points, the times required for hydrate formation were all shortened significantly. Especially at the injection points of more than 30min, the subsequent crystals growth began immediately after CO2 injection. Besides, the formed hydrates tended to aggregate in the vicinity of CO2 injection zones. Such promotion effect was possibly caused by the triggering effect of preferentially formed CO2 hydrates in the reaction system. This work provides a novel and simple method to control hydrate formation process, which is of great significance to the transportation and storage of natural gas.

Preparation of –SO3−-coated nanopromoters for methane hydrate formation: effects of the existence pattern of –SO3− groups on the promotion efficiency

The –SO3−-coated nano-promoters resulted in methane hydrate formation process completing within 1–2 h, and displayed storage capacity over 140 v/v.

Effect of three representative surfactants on methane hydrate formation rate and induction time

The effects of three types of surfactants on methane hydrate formation process were investigated. Three different classes of surfactants involving anionic (sodium dodecyl sulfonate), cationic (hexadecyl trimethyl ammonium bromide) and non-ionic (poly oxy ethylene (40) octyl phenyl ether) have been used. Thermodynamics of hydrate formation, formation rate, kinetic constants and induction time in the presence of surfactants with various concentrations were analyzed. Critical micelle concentrations (CMCs) of these surfactants in water were determined by induction time measurements in various concentrations under methane hydrate formation conditions. The critical micelle concentration (CMC) at the methane hydrate formation conditions for SDS, HTABr and TritonX-405 solutions were obtained at 450, 380 and 950ppm, respectively. The experimental results indicated that hydrate formation rate increased with the use of surfactants for all concentrations and induction time decreased. It was found that for surfactants, CMC at hydrate formation conditions was less than CMC at ambient conditions.

Effects of particle and pore sizes on the formation behaviors of methane hydrate in porous silica gels

The formation behaviors of methane hydrate in porous media with different particle and pore sizes were studied in a closed system in the temperature range of 267.15–278.15 K. The silica gels were applied as the porous media for the experiments, in which the diameter ranges of the silica gel particles are 0.105–0.150 mm, 0.150–0.200 mm and 0.300–0.450 mm, respectively, and the mean pore diameters are 9.03 nm, 12.95 nm, 17.96 nm and 33.20 nm, respectively. The formation processes of methane hydrate show different behaviors in porous silica gels with different particle sizes. For the particle diameter range of 0.300–0.450 mm, three formation periods were observed for the experiments with the high driving force. For the particle diameter ranges of 0.105–0.150 mm and 0.150–0.200 mm, there is no remarkable discrete formation period, the hydrate durations of different experiments are basically same at the bath temperature above the freezing point and decrease with the increase of the temperature at the bath temperature below the freezing point. The formation rate of methane hydrate increases with the decrease of the particle size and the increase of the pore size. The final gas consumption increases with the increase of the mean pore diameter but is slightly affected by the particle size.