Solubility Of Methane In Water Research Articles

Can the AMOEBA forcefield be used for high pressure simulations? The extreme case of methane and water.

We have performed classical molecular dynamics simulations using the fully polarizable Atomic Multipole Optimized Energetics for Biomolecular Applications (AMOEBA) forcefield implemented within the Tinker package to determine whether a more adequate treatment of electrostatics is sufficient to correctly describe the mixing of methane with water under high pressure conditions. We found a significant difference between the ability of AMOEBA and other classical, computationally cheaper forcefields, such as TIP3P, simple point charge-extended, TIP4P, and optimized potentials for liquid simulations-all atom. While the latter models fail to detect any effect of pressure on the miscibility of methane in water, AMOEBA qualitatively captures the experimental observation of the increased solubility of methane in water with pressure. At higher temperatures, the solubility of water in methane also increases; this seems to be associated with the breakdown of the fourfold hydrogen-bonded water network structure: bonding in water is weaker, so the energy cost of solution is lowered.

Gas solubility enhancement and hydrogen bond recombination regulated by terahertz electromagnetic field for rapid formation of gas hydrates

The low solubility of methane in water and the formation of hydrate film at methane-water interface restrict interfacial mass transfer between methane and water, thereby impeding the rapid formation of hydrate. Herein, THz electromagnetic field (TEMF) is introduced to destroy hydrogen bonds through resonance with water molecules for decreasing methane-water interfacial tension (IFT) and improving methane solubility in water. Thereafter, TEMF is removed to restore hydrogen bonding interaction for hydrate nucleation within bulk-phase water rather than at methane-water interface, thereby accelerating hydrate formation. The results show that a TEMF at 15.8 THz can increase methane solubility by 50-fold and provide more nucleation sites for hydrate formation by lowering the IFT by 15-fold. Furthermore, the hydrate nucleation follows “blob” nucleation at low solubility and Local Structuring Mechanism nucleation at high solubility. The higher solubility of methane shortens the induction period of hydrate nucleation form 58.5 ns to 29 ns. Particularly, small 512 cages form preferentially regardless of nucleation pathway. The underlying mechanism for TEMF-induced the acceleration of hydrate formation is attributed to the transition of water phase from a disordered to an ordered structure. This transition arises from the resonance of the TEMF with water molecules, disrupting the hydrogen bond between water molecules and providing sufficient driving force for their rearrangement after removing the TEMF. In rearrangement process, weakly hydrogen-bond interactions correspondingly are converted into strongly hydrogen-bond ones. These findings are expected to improve the understanding of hydrate formation mechanism and promote the applications of terahertz technology in gas hydrates.

Mechanistic Modeling of the Variability of Methane Emissions from an Artificial Reservoir

The mechanistic model LAKE2.3 was tested for its capability to predict of methane (CH4) emissions from reservoirs. Estimates of CH4 emissions from the Mozhaysk reservoir (Moscow region) provided by the model showed good agreement with instrumental in situ observations for several parameters of the water ecosystem. The average CH4 flux calculated by the model is 37.7 mgC-CH4 m−2 day−1, while according to observations, it is 34.4 mgC-CH4 m−2 day−1. Ebullition makes the largest contribution to the emissions from reservoirs (up to 95%) due to low methane solubility in water and the high oxidation rate of diffusive methane flux. During the heating period, an increase in methane emission is observed both in the model and empirical data, with a maximum before the onset of the autumn overturn. An effective parameter for calibrating the diffusive methane flux in the model is the potential rate of methane oxidation. For ebullition flux, it is the parameter q10 (an empirical parameter determining the relationship between methane generation and temperature) because methane production in bottom sediments is the most important. The results of this research can be used to develop mechanistic models and provide a necessary step toward regional and global simulations of lacustrine methane emission using LAKE2.3.

Assesment of the risk of degazation of the Black Sea: type of limnological disaster on lake Nyos reconsidered

The possibility of a repetition of the limnological catastrophe in the Black Sea is considered. It is shown that, in contrast to the volcanic lakes of Africa Nyos and Manun, where limnological catastrophes occurred in the 1980s, the concentration of dissolved gases in deep waters is significantly less than the saturation value. This eliminates the mechanism of so called “eruption” of carbon dioxide such as gas lift. However, on a smaller scale, significant methane releases are possible during strong eruptions of underwater mud volcanoes. The mechanism for the release of carbon dioxide from the lake into the atmosphere is so similar to a volcanic eruption that mathematical models developed for ordinary volcanoes are used to describe it. In both cases, the rise of erupted masses occurs due to an increase in the buoyancy of the gas-liquid mixture, which carries with it particles of the environment. The formation and growth of gas bubbles at intermediate depths occurs provided that the total partial pressure of all gases inside the bubble exceeds the hydrostatic pressure at a given depth. The article shows that the concentration of dissolved methane in the Black Sea is much less than the saturation level. Due to the relatively low solubility of methane in water, methane bubbles are able to overcome a significant depth range. And as additional components of the gas mixture, together with methane, carbon dioxide and hydrogen sulfide can thus enter the atmosphere. It was concluded that as the water temperature in the Black Sea increases due to climate change, the reserves of methane gas hydrate at the bottom of the sea will begin to decompose, which will also be accompanied by jet gas release. At the same time, methane can escape to the surface from depths of no more than 900 m.

Resonance-Induced Reduction of Interfacial Tension of Water-Methane and Improvement of Methane Solubility in Water.

Molecular dynamics simulations were performed to study the effect of the periodic oscillating electric field on the interface between water and methane. We propose a new strategy that utilizes oscillating electric fields to reduce the interfacial tension (IFT) between water and methane and increase the solubility of methane in water simultaneously. These are attributed to the hydrogen bond resonance induced by an electric field with a frequency close to the natural frequency of the hydrogen bond. The resonance breaks the hydrogen bond network among water molecules to the maximum, which destroys the hydration shell and reduces the cohesive action of water, thus resulting in the decrease of IFT and the increase of methane solubility. As the frequency of the electric field is close to the optimum resonant frequency of hydrogen bonds, IFT decreases from 56.43 to 5.66 mN/m; water and methane are miscible because the solubility parameter of water reduces from 47.63 to 2.85 MPa1/2, which is close to that of methane (3.43 MPa1/2). Our results provide a new idea for reducing the water-gas IFT and improving the solubility of insoluble gas in water and theoretical guidance in the fields of natural gas exploitation, hydrate generation, and nanobubble nucleation.

Solubility of Methane in Water: Some Useful Results for Hydrate Nucleation.

In this paper, the solubility of methane in water along the 400 bar isobar is determined by computer simulations using the TIP4P/Ice force field for water and a simple LJ model for methane. In particular, the solubility of methane in water when in contact with the gas phase and the solubility of methane in water when in contact with the hydrate has been determined. The solubility of methane in a gas-liquid system decreases as temperature increases. The solubility of methane in a hydrate-liquid system increases with temperature. The two curves intersect at a certain temperature that determines the triple point T3 at a certain pressure. We also determined T3 by the three-phase direct coexistence method. The results of both methods agree, and we suggest 295(2) K as the value of T3 for this system. We also analyzed the impact of curvature on the solubility of methane in water. We found that the presence of curvature increases the solubility in both the gas-liquid and hydrate-liquid systems. The change in chemical potential for the formation of hydrate is evaluated along the isobar using two different thermodynamic routes, obtaining good agreement between them. It is shown that the driving force for hydrate nucleation under experimental conditions is higher than that for the formation of pure ice when compared at the same supercooling. We also show that supersaturation (i.e., concentrations above those of the planar interface) increases the driving force for nucleation dramatically. The effect of bubbles can be equivalent to that of an additional supercooling of about 20 K. Having highly supersaturated homogeneous solutions makes possible the spontaneous formation of the hydrate at temperatures as high as 285 K (i.e., 10K below T3). The crucial role of the concentration of methane for hydrate formation is clearly revealed. Nucleation of the hydrate can be either impossible or easy and fast depending on the concentration of methane which seems to play the leading role in the understanding of the kinetics of hydrate formation.

Influence of Water Injection Pressure on Methane Gas Displacement by Coal Seam Water Injection

It is of great significance to study the pattern of displacing methane gas with water in the coal seam water injection process for the prevention and control of gas disasters. A two-phase displacement test device was used to conduct experiments on the water injection of coal samples to displace methane gas under different water injection pressures, and the influence of the water injection pressure on the displacement was analyzed. The test results show that with the same displacement time, the ratio of displaced methane increases with the increase in the water injection pressure. The displacement rate increases with the increase in the water injection pressure at the stage without water discharge, while the water displacement rate under different water injection pressures differed slightly; in the later displacement stage, a higher water injection pressure of the coal sample results in a faster attenuation of the displacement rate and water displacement rate due to the decrease in the methane content in the coal sample. There is a critical water injection pressure to displace methane gas. When the critical water injection pressure is exceeded, the displacement time does not change appreciably. Flowing water can displace a large amount of methane gas in coal, and the methane displacement rate increases with the increase in the water injection pressure. The high solubility of methane in water is the reason for the high methane displacement rate. The results of this study can provide theoretical guidance for coal seam water injection to control gas disasters.

Effect of Methane Solubility on Hydrate Formation and Dissociation: Review and Perspectives

Methane solubility in water is the foundation to make full sense of the mechanism of hydrate formation and dissociation. It is significant for realizing the safe and efficient exploitation of natural gas hydrate (NGH). This review discusses the calculation of methane solubility in gas–water and hydrate–water equilibrium systems, based on the hydrate phase equilibrium model theory, and the parameters used in the calculation process are described in detail. In addition, the influences of bubbles, capillary pressure, and salt on methane solubility are revealed. The difference in fugacity between the water phase and hydrate phase caused by the undersaturation of methane induces hydrate dissolution. Water injecting is a promising auxiliary method for hydrate exploitation, which will flush out the sand and gravel accumulated during the depressurization process. A novel hydrate exploitation method, which combines depressurization and a water injection method using double-split wells, is proposed. This novel method provides a new idea for efficient and sustainable exploitation of hydrate.

The performance of OPC water model in prediction of the phase equilibria of methane hydrate.

Molecular dynamics (MD) simulations were performed to determine the three-phase coexistence line of sI methane hydrates. The MD simulations were carried out at four different pressures (4, 10, 40, and 100 MPa) by using the direct phase coexistence method. In current simulations, water was described by either TIP4P/Ice or "optimal" point charge (OPC) models and methane was described as a simple Lennard-Jones interaction site. Lorentz-Berthelot (LB) combining rules were used to calculate the parameters of the cross interactions. For the OPC model, positive deviations from the energetic LB rule were also considered based on the solubility of methane in water. For the TIP4P/Ice water model, the obtained three phase coexistence temperatures showed good agreement with experiment data at higher pressures, which is consistent with previous predictions. For the OPC water model, simulations using the classic and the modified LB parameters both showed negative deviations to the experimental values. Our results also indicated that the deviation of the T3 prediction by the OPC model was not closely correlated with the predicted melting point of ice. At 4 MPa, the modified OPC model showed a better prediction of hydrate equilibrium temperature, even better than the prediction by TIP4P/Ice. Considering the relatively higher accuracy in biomolecular MD of the OPC model, it is suggested that this model may have a better performance in hydrate MD simulations of biomolecule-based additives.

Predicting methane solubility in water and seawater by machine learning algorithms: Application to methane transport modeling

The upward migration of methane from natural gas wells associated with fracking operations may lead to contamination of groundwater resources and surface leakage. Numerical simulations of methane transport in the subsurface environment require knowledge of methane solubility in the aqueous phase. This study employs machine learning (ML) algorithms to predict methane solubility in aquatic systems for temperatures ranging from 273.15 to 518.3 K and pressures ranging from 1 to 1570 bar. Four regression algorithms including regression tree (RT), boosted regression tree (BRT), least square support vector machine (LSSVM) and Gaussian process regression (GPR) were utilized for predicting methane solubility in pure water and mixed aquatic systems containing Na+, K+, Ca2+, Mg2+, Cl− and SO4-2. The experimental data collected from the literature were used to implement the models. We used Grid search (GS), Random search (RS) and Bayesian optimization (BO) for tuning hyper-parameters of the ML models. Moreover, the predicted values of methane solubility were compared against Spivey et al. (2004) and Duan and Mao (2006) equations of state. The results show that the BRT-BO model is the most rigorous model for the prediction task. The coefficient of determination (R2) between experimental and predicted values is 0.99 and the mean squared error (MSE) is 1.19 × 10−7. The performance of the BRT-BO model is satisfactory, showing an acceptable agreement with experimental data. The comparison results demonstrated the superior performance of the BRT-BO model for predicting methane solubility in aquatic systems over a span of temperature, pressure and ionic strength that occurs in deep marine environments.

Scaled charges at work: Salting out and interfacial tension of methane with electrolyte solutions from computer simulations

The solubility of methane in water decreases when a small amount of salt is present. This is usually denoted as the salting out effect (i.e., the methane is expelled from the solution when it contains small amounts of salt). The effect is important, for instance the solubility is reduced by a factor of three in a 4 m (mol/kg) NaCl solution. Some years ago we showed that the salting out effect of methane in water can be described qualitatively by molecular models using computer simulations. However the salting out effect was overestimated. In fact, it was found that the solubility of methane was reduced by a factor of eight. This points to limitations in the force field used. In this work we have carried out direct coexistence simulations to describe the salting out effect of methane in water using a recently proposed force field (denoted as Madrid-2019) based on the use of scaled charges for the ions and the TIP4P/2005 force field for water. For NaCl the results of the Madrid-2019 force field significantly improve the description of salting out of methane. For other salts the results are quite reasonable. Thus the reduction of the charge of the ions also seems to be able to improve the description of salting out effect of methane in water. Besides this we shall show that the brine-methane interface exhibits an increased interfacial tension as compared to that of the water-methane system. It is well known that electrolytes tend to increase the surface tension of liquid water, and this seems also to be the case for the interface between water and methane.

Methane dissolution inside bulk or porous-medium-confined water at near-hydrate equilibrium conditions

In this study, we perform a series of mass-balance-type calculations, in order to estimate the minimum volume of liquid water required to dissolve completely a single methane gas bubble, located inside different types of domains that are near or under hydrate equilibrium pressure/temperature conditions. We examine the case of methane bubble dissolution in the bulk, along with the cases of methane bubble dissolution within simple/regular networks of pores, where all pores have the same size. In our calculations, we consider experimental values for the equilibrium solubilities of methane in water, along the hydrate-forming line, as well as, values obtained from predictive tools that are based on different thermodynamic models. The effect of aqueous NaCl solutions on the results is also investigated. As a result of the relatively low solubility of methane in water, large volumes of water are required for complete dissolution of a methane bubble.

Pressure-Induced Miscibility Increase of CH4 in H2O: A Computational Study Using Classical Potentials.

Methane and water demix under normal (ambient) pressure and temperature conditions because of the polar nature of water and the apolar nature of methane. Recent experimental work has shown, though, that increasing the pressure to values between 1 and 2 GPa (10-20 kbar) leads to a marked increase of methane solubility in water, for temperatures which are well below the critical temperature for water. Here, we perform molecular dynamics simulations based on classical force fields-which are well-used and have been validated at ambient conditions-for different values of pressure and temperature. We find the expected increase in miscibility for mixtures of methane and supercritical water; however, our model fails to reproduce the experimentally observed increase in methane solubility at large pressures and below the critical temperature of water. This points to the need to develop more accurate force fields for methane and methane-water mixtures under pressure.

Methane biodegradation and enhanced methane solubilization by the filamentous fungi Fusarium solani.

Methane is one of the most important greenhouse gases emitted from natural and human activities. It is scarcely soluble in water; thus, it has a low bioavailability for microorganisms able to degrade it. In this work, the capacity of the fungus Fusarium solani to improve the solubility of methane in water and to biodegrade methane was assayed. Experiments were performed in microcosms with vermiculite as solid support and mineral media, at temperatures between 20 and 35 °C and water activities between 0.9 and 0.95, using pure cultures of F. solani and a methanotrophic consortium (Methylomicrobium album and Methylocystis sp) as a control. Methane was the only carbon and energy source. Results indicate that using thermally inactivated biomass of F. solani, decreases the partition coefficient of methane in water up to two orders of magnitude. Moreover, F. solani can degrade methane, in fact at 35 °C and the highest water activity, the methane degradation rate attained by F. solani was 300 mg m−3 h−1, identical to the biodegradation rate achieved by the consortium of methanotrophic bacteria.

Methane hydrate formation in the presence of ZnO nanoparticle and SDS: Application to transportation and storage

Due to natural gas benefits such as less carbon dioxide production compared to the other fossil fuels, its transmission technologies to the market are noticed these years and gas hydrate storage method could be considered as an option to storage and transportation. One way to overcome the low rate gas hydrate formation is using a mixture of surfactant and nanoparticles to enhance the hydrate formation rate. Hence, in this present contribution sodium dodecyl sulfate (SDS) (as a surfactant) and zinc oxide nanoparticles are used to promote hydrate formation process. The experiments were carried out at the temperature of 274.65 and 276.65 K, and the initial pressure of 50 and 60 bar in different additives concentrations. The results show that these additives can increase the amount of methane consumed, the rate of methane consumed and the mole number of water to hydrate conversion increases, however, these additives do not significantly affect the gas hydrate storage. Moreover, experimental results reveals that addition of SDS to the water not only improve the stabilization of zinc oxide nanoparticles in water but also increases the solubility of methane in water by lowering the surface tension. Also, as the novel outcome, these additives (SDS+ ZnO nanoparticles) decrease the induction time, however, the final storage capacity does not change significantly.

Geochemical characteristics of biodegraded natural gas and its associated low molecular weight hydrocarbons

After analyzing the molecular and isotopic compositions of 11 gas samples from Baka Gas Field, as well as the low molecular weight hydrocarbons (LMWHs) associated with them, the two types of natural gases are identified: biodegraded and non-biodegraded gases. No distinctions in molecular and isotopic compositions are observed between biodegraded and non-biodegraded methane, which may be partially due to the great solubility of methane in water. Anomalous molecular compositions and carbon and hydrogen isotopic ratios are observed among the biodegraded C2+ gas components, which become more significantly fractionated in propane than in ethane, most probably due to their selective depletion by different strains of bacteria. The biodegradation resistance for C6–C7 LMWHs associated with gases from Baka Gas Field follow the series Dimethylbutanes > Cyclohexane > Methylcyclopentane > 2-Methylpentane > 3-Methylpentane; Dimethylpentanes, 1,1-Dimethylcyclopentane and 1,2-Dimethylcyclopentanes > Methylcyclohexane >1,3-Dimethylcyclopentanes > 2-Methylhexane > 3-Methylhexane, respectively. Within the identical carbon numbers, two characteristics of biodegradation susceptibility for C6–C7 LMWHs are observed: total poly-branched alkanes are more resistant to biodegradation than cycloalkanes, and mono-branched ones tend to be depleted by bacteria more easily than cycloalkanes; and isomers with adjacent methyl groups tend to be more resistant to biodegradation. These two characteristics could be effective tools for the identification of biodegraded hydrocarbons and for the determination of the degree of bacterial decomposition. After comparison with previous studies, it is evident that the varieties in bacteria strains result in the discrepancy of biodegradation efficiency for certain light hydrocarbon isomers. This research improves the understanding of the geochemical characteristics of biodegraded gases and provides additional tools for the identification of biodegraded gases and their degree of biodegradation.

Application of equations of state to predict methane solubility under hydrate-liquid water two-phase equilibrium

Gas solubility in water under hydrate-liquid water (H-Lw) two-phase equilibrium is the foundation of gas hydrate kinetic study. It is significant for the simulation of multiphase pipeline flow, the stability and amount evaluation of natural gas hydrate resources in deep water as well as gas storage and separation. In the current work, thermodynamic models were established by combining van der Waals-Platteeuw theory with PR, VPT and TB equations of state separately, named as Model VPR, VVPT and VTB, to predict methane solubility in water under H-Lw equilibrium. The Henry’s law was also included for comparison. Available experimental data in literature were collected to test the applicability of these equations of state. In order to improve the predicting accuracy, binary interaction parameters in the asymmetric contribution term of non-density-dependent (NDD) mixing rules were modified. Good agreements between predicted and experimental data were obtained by Model VVPT with the modified NDD mixing rules.

Domestic wastewater treatment in parallel with methane production in a microbial electrolysis cell

Microbial electrolysis cells (MECs) have great potential as a technology for wastewater treatment in parallel to energy production. In this study we explore the feasibility of using a low-cost, membraneless MEC for domestic wastewater treatment and methane production in both batch and continuous modes. Low-strength wastewater can be successfully treated by means of an MEC, obtaining significant amounts of methane. The results also suggest that hydrogenotrophic methanogenesis reduce the incidence of homoacetogenic activity, thus improving the overall MEC performance. However, gas production rates are low and important aspects such as methane solubility in water still remain a challenge. Overall, MECs can offer competitive advantages not only for low-strength wastewater treatment but also as an aid to anaerobic methane production by improving the chemical oxygen demand (COD) removal and methane production rates.

Low energy emulsion-based fermentation enabling accelerated methane mass transfer and growth of poly(3-hydroxybutyrate)-accumulating methanotrophs

Methane is a low-cost feedstock for the production of polyhydroxyalkanoate biopolymers, but methanotroph fermentations are limited by the low solubility of methane in water. To enhance mass transfer of methane to water, vigorous mixing or agitation is typically used, which inevitably increases power demand and operational costs. This work presents a method for accelerating methane mass transfer without agitation by growing methanotrophs in water-in-oil emulsions, where the oil has a higher solubility for methane than water does. In systems without agitation, the growth rate of methanotrophs in emulsions is five to six times that of methanotrophs in the medium-alone incubations. Within seven days, cells within the emulsions accumulate up to 67 times more P3HB than cells in the medium-alone incubations. This is achieved due to the increased interfacial area of the aqueous phase, and accelerated methane diffusion through the oil phase.

Redlich–Kwong equation of state for modelling the solubility of methane in water over a wide range of pressures and temperatures

A thorough approach to the environmental and technological issues regarding natural gas extraction from underground and underwater reserves requires a very good understanding of the phase equilibrium between hydrocarbon gas and water. In this work we present an accessible way to predict methane-water phase equilibrium. For this purpose we selected from the literature experimental data for the solubility of methane in water, covering a large range of temperature (274.35 K–627.15 K) and pressure (0.57 MPa–197.26 MPa). Mathematical modelling was performed using the online available modelling tool Phase Equilibria, 2000 (PE2000) and applying the Redlich–Kwong equation of state. To best fit the calculated solubility to the experimental values, we estimated the binary interaction coefficient by data regression, and we used the results to verify the consistency of the experimental data. The binary interaction coefficient is dependent of temperature, and this connection can be quantified and further used to estimate the phase equilibrium at the needed conditions.