Methane Hydrate Dissociation Conditions Research Articles

Aqueous Solid Formation Kinetics in High-Pressure Methane at Trace Water Concentrations.

Natural gas containing trace amounts of water is frequently liquefied at conditions where aqueous solids are thermodynamically stable. However, no data are available to describe the kinetics of aqueous solid formation at these conditions. Here, we present experimental measurements of both solid formation kinetics and solid-fluid equilibrium for trace concentrations of (12 ± 0.7) ppm water in methane using a stirred, high-pressure apparatus and visual microscopy. Along isochoric pathways with cooling rates around 1 K·min-1, micron-scale aqueous solids were observed to form at subcoolings of (0.3-8.6) K, relative to an average equilibrium melting temperature of (253 ± 1.9) K at (8.9 ± 0.08) MPa; these data are consistent with predicted methane hydrate dissociation conditions within the uncertainty of both the experiment and model. The 36 measured formation events were used to construct a cumulative formation probability distribution, which was then fitted with a model from Classical Nucleation Theory, enabling the extraction of kinetic and thermodynamic nucleation parameters. While the resulting nucleation parameter values were comparable to those published for methane hydrate formation in bulk-water systems, the observed growth kinetics were distinctly different with only a small percentage of the water in the system converting into micron-scale solids over the experimental time scale. These results may help explain how cryogenic heat exchangers in liquefied natural gas facilities can operate for long periods without blockages forming despite being at very high subcoolings for aqueous solids.

Experimental investigation and modeling on the dissociation conditions of methane hydrate in clayey silt cores

AbstractAs the majority of global natural gas hydrate reserve, the dissociation conditions of hydrate in clayey silts are of great significance for its efficient production. In this work, the dissociation conditions of methane hydrate in clayey silt cores were experimentally measured by step‐heating method at the temperature range of 280.76–289.55 K and pressure range of 8.11–15.03 MPa, respectively. Various cores including quartz powder, montmorillonite, and South China Sea sediments at the water content range of 20%–33% were used for investigation. The results showed that the dissociation temperatures of methane hydrate in clayey silt cores depressed compared to bulk hydrate. The grain size, salinity, and lithology of clayey silt cores significantly affect the dissociation conditions of hydrate. In comparison to grain size, salinity, and lithology had a more significant influence on the equilibrium temperature depression. The dissociation temperature depression of methane hydrate was considered as a consequence of the water activity depression which is caused by the effect of capillary, salt, or clay. A water activity meter was used to measure the water activity in clayey silt cores. The influence of salt component and mineral characteristics on the water activity was investigated. By combining the measured water activity data with the Chen‐Guo model, a novel water activity measurement (WAM) method for the hydrate dissociation conditions prediction was proposed. With the maximum deviation less than 12%, the predicted results are in good agreement with the experimental data. It demonstrated that the WAM method could effectively predict the dissociation conditions of methane hydrate in clayey silts with convenience and accuracy.

Study on the dissociation characteristics of methane hydrate in clayey silts

Most natural gas hydrate (NGH) resources worldwide are in clayey silt sediments. For the efficient production of NGH, a thorough understanding of the dissociation characteristics of NGH in clayey silt is essential. In this work, an experimental method for clayey silt NGH sample preparation and determination of the dissociation conditions has been established. The dissociation conditions of methane hydrate in clayey silt formed at different initial pressures and water contents have been measured, and the dissociation characteristics have been discussed. Methane hydrate is found to form in pores of different sizes in clayey silts. The filling status of the methane hydrate in the clayey silt pores might affect its dissociation characteristics. As the temperature increases, the hydrate in the smaller pores dissociates first, the hydrate in the larger pores dissociates later, and the final equilibrium conditions are consistent with the dissociation conditions of bulk hydrate. As the initial pressure increases or the water content decreases, the proportion of hydrate in the pores increases. When the clayey silt is saturated (water content 37%), hydrate rapidly forms on the surface, forming a mass transfer barrier and preventing further hydrate formation. The hydrate reforms when the hydrate in the small pores of surface sediments dissociates as the temperature increases. The methane hydrate in clayey silt exhibits multistage dissociation and complex reformation characteristics.

Methane Hydrate Dissociation Conditions in High-Concentration NaCl/KCl/CaCl2 Aqueous Solution: Experiment and Correlation

The dissociation conditions of methane hydrate in high concentration aqueous solutions of NaCl, KCl, and CaCl2 are reported in this work. A total of 80 sets of H–L–V equilibrium data of methane hyd...

Effect of EMIM-BF4 Ionic Liquid on Dissociation Temperature of Methane Hydrate in the Presence of PVCap: Experimental and Modeling Studies

Most of the studies done on kinetic hydrate inhibitors (KHIs) are related to the effect of KHIs on hydrate formation, and there are a limited number of research works on hydrate dissociation conditions in the presence of KHIs. In the subject of hydrate remediation, knowing the effects of KHIs on hydrate dissociation conditions is necessary. In this work, first, the effect of the presence of poly vinyl caprolactam (PVCap) as a KHI on methane hydrate dissociation conditions has been studied and the results show that dissociation temperature of methane hydrate in the presence of PVCap is higher than the noninhibited system and increases hydrate stability conditions. Then, at the second stage, the effects of EMIM-BF4 as a synergist for PVCap on methane hydrate dissociation conditions have been investigated. Different concentrations of EMIM-BF4 and PVCap have been studied, and a thermodynamic model has been developed to predict hydrate dissociation temperature. The experiments reveal that adding EMIM-BF4 to an...

Can 2-methyl-2-butene and isoprene form clathrate hydrates?

In order to establish whether 2-methyl-2-butene and isoprene can form hydrates, experimental hydrate dissociation data were measured for the following systems: methane + water, 2-methyl-2-butene + methane + water and isoprene + methane + water. An isochoric pressure search method was used to perform the measurements in the ranges of (274.6 to 288.3) K and (3.25 to 13.35) MPa. The reported results are discussed in terms of the ability of isoprene (2-methyl-1, 3-butadiene) and 2-methyl-2-butene to interfere with methane hydrate dissociation conditions. It is found that the two C5 hydrocarbons are likely not hydrate formers. However, a further confirmation via appropriate analytical tools is recommended.

Understanding the characteristic of methane hydrate equilibrium in materials and its potential application

Understanding the phase characteristic of methane hydrate in materials is of recent interest in several fields. In this study, methane hydrate dissociation conditions in nine water wetted porous materials (ZIF-8, MIL-53(Al), HKUST-1, nanoporous activated carbon, zeolite 13X, and four silica gels) with pore diameters ranging from 0.35 to 100 nm as well as in two nonporous quartz sands were systematically investigated. The adsorption properties of methane in some selected adsorbents were also studied. For microporous materials, our results confirmed that methane hydrate cannot form due to the size limitation for the nucleation of a methane hydrate crystal. In contrast, for mesoporous materials with a pore diameter of 6.2 nm or bigger, hydrate formed in their pores and significantly shifted dissociation temperatures and pressures compared to the bulk hydrate were observed. The largest temperature shift was found to be ∼6 K in materials possessing 6.2-nm-diameter pores, and this shift decreased to less than 1 K in structures having 45-nm-diameter pores. For macroporous materials with a pore diameter of 100 nm or for nonporous quartz systems, the influence of pore sizes on the methane hydrate phase equilibrium was found to be marginal. Furthermore, from studying the adsorption characteristic of methane in 25 wt% wetted MIL-53(Al), 30 wt% wetted HKUST-1, and 10 wt% wetted nanoporous activated carbon, we demonstrated that the penetration of water molecules into the pores of microporous materials was not only unable to form methane hydrate but also substantially deteriorated the gas adsorption ability. To exploit simultaneously adsorption and hydrate formation in wetted microporous materials for gas storage, both the hydrophobicity and aperture pore size of materials are critical toward the selection of promising adsorbents.

Experimental Study and Thermodynamic Modeling of Methane Hydrate Dissociation Conditions in the Simultaneous Presence of BMIM-BF4 and Ethanol in Aqueous Solution

Experimental and thermodynamic results for methane hydrate dissociation conditions in the simultaneous presence of ethanol and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) ionic liquid (IL) in aqueous solution are presented. Three different aqueous solutions including solution 1 (0.0142 mole fraction of ethanol, 0.0060 mole fraction of BMIM-BF4), solution 2 (0.0348 mole fraction of ethanol, 0.0059 mole fraction of BMIM-BF4) and solution 3 (0.0549 mole fraction of ethanol, 0.0058 mole fraction of BMIM-BF4) were used. An isochoric pressure-search method was used to perform the measurements. The experimental pressure and temperature ranges are (3.18 to 8.32) MPa and (273.6 to 283.3) K, respectively. The thermodynamic inhibition effects of these solutions on methane hydrate dissociation were observed and solution 3 leads to the strongest inhibition effect. The average hydrate dissociation temperature reduction for methane hydrate in the presence of solutions 1, 2, and 3 are approximately 1.0, 2.2,...

Insight into increased stability of methane hydrates at high pressure from phase equilibrium data and molecular structure

The methane hydrate dissociation conditions are measured at high pressures (up to 200 MPa) to fundamentally understand the hydrate properties. The results show an increased enthalpy of dissociation, from about 53 to 58 kJ/mol, as the hydrate equilibrium pressures transition from low (<80 MPa) to higher pressures (up to 200 MPa), indicating greater stability for the hydrates. Molecular simulations are used to understand and explain the increased stability with increasing pressure, by calculating the enthalpy and molecular structure of the phases.

Inhibition effect of 1-ethyl-3-methylimidazolium chloride on methane hydrate equilibrium

The dissociation conditions of methane hydrate in the presence of 0.1, 0.2, 0.3 and 0.4 mass fraction of 1-ethyl-3-methylimidazolium chloride (abbreviated by EMIM-Cl hereafter) were experimentally determined. A high pressure micro-differential scanning calorimeter equipped with a motorized pump was applied to measure the dissociation temperature of the (hydrate+liquid water+vapor) three-phase equilibrium under a constant pressure process with a pressure ranging from (5.0 to 35.0)MPa. The addition of EMIM-Cl would inhibit the methane hydrate formation. The most significant inhibition effect was observed at 0.4 mass fraction of EMIM-Cl in aqueous solution to lower the dissociation temperature by 12.82K at 20.00MPa in comparison to that of the (methane+water) system. The Peng–Robinson–Stryjek–Vera equation of state incorporated with COSMO-SAC activity coefficient model and the first order modified Huron–Vidal mixing rule were applied to evaluate the fugacity of vapor and liquid phase. A modified van der Waals and Platteeuw model with an explicit pressure dependence of the Langmuir adsorption constant was applied to determine the fugacity of hydrate phase. The predictive thermodynamic model successfully describes the tendency of phase behavior of methane hydrate in the presence of EMIM-Cl in the range from 0.1 to 0.4 mass fraction with absolute average relative deviation in predicted temperature of 0.70%.

Experimental investigation on the dissociation conditions of methane hydrate in the presence of imidazolium-based ionic liquids

In this work, the performance of nine ionic liquids (ILs) as thermodynamic hydrate inhibitors is investigated. The dissociation temperature is determined for methane gas hydrates using a high pressure micro deferential scanning calorimeter between (3.6 and 11.2)MPa. All the aqueous IL solutions are studied at a mass fraction of 0.10. The performance of the two best ILs is further investigated at various concentrations. Electrical conductivity and pH of these aqueous IL solutions (0.10 mass fraction) are also measured. The enthalpy of gas hydrate dissociation is calculated by the Clausius–Clapeyron equation. It is found that the ILs shift the methane hydrate (liquid+vapour) equilibrium curve (HLVE) to lower temperature and higher pressure. Our results indicate 1-(2-hydroxyethyl) 3-methylimidazolium chloride is the best among the ILs studied as a thermodynamic hydrate inhibitor. A statistical analysis reveals there is a moderate correlation between electrical conductivity and the efficiency of the IL as a gas hydrate inhibitor. The average enthalpies of methane hydrate dissociation in the presence of these ILs are found to be in the range of (57.0 to 59.1)kJ⋅mol−1. There is no significant difference between the dissociation enthalpy of methane hydrate either in the presence or in absence of ILs.

Thermodynamic modeling of aqueous ionic liquid solutions and prediction of methane hydrate dissociation conditions in the presence of ionic liquid

Heterosegmented statistical associating fluid theory (SAFT) is developed to model the thermodynamic properties of aqueous imidazolium ionic liquid solutions. A set of transferable parameters is obtained, and in general, the model well represents the density, the activity coefficients, and the osmotic coefficients of aqueous ionic liquid solutions. This heterosegmented SAFT, coupled with the Van der Waals and Platteeuw theory for hydrate phase, is also found to well predict the methane hydrate dissociation conditions in the presence of imidazolium ionic liquids and well captures the roles of pressure, anion type, alkyl length of the cation, and ionic liquid concentration on the hydrate inhibition performance of the ionic liquids.

Experimental measurement and thermodynamic modeling of methane hydrate dissociation conditions in the presence of aqueous solution of ionic liquid

In this communication, dissociation conditions of methane hydrate in the presence of pure water and aqueous solutions of three ionic liquids including 1-butyl-3-methylimidazolium tetrafluoroborate (0.10, 0.15 and 0.20 mass fraction), 1-butyl-3-methylimidazolium dicyanamide (0.10 mass fraction), and tetraethyl-ammonium chloride (0.10 mass fraction) were experimentally measured and are reported. The data were obtained in the 2.48–6.58MPa pressure range and 272.1–282.0K temperature range. A high-pressure equilibrium cell was used for performing the measurements pursuing the isochoric pressure search method. The hydrate dissociation conditions are modeled using the solid solution theory of van der Waals and Platteeuw for the hydrate phase along with the Peng–Robinson equation of state for the gas phase. For modeling of the aqueous phase, the NRTL model is applied. Acceptable agreement between the experimental data and the model results is observed.

Experiment and thermodynamic modeling of methane hydrate equilibria in the presence of aqueous imidazolium-based ionic liquid solutions using electrolyte cubic square well equation of state

Methane hydrate dissociation conditions in the presence of imidazolium based aqueous ionic liquid solutions including 1-buthyl-3-methylimidazolium methyl sulfate ([BMIM][MeSO4]), 1-ethyl-3-methylimidazolium hydrogen sulfate ([EMIM][HSO4]), 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIM][EtSO4]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) and 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate ([OH-EMIM][BF4]) are investigated. Isochoric method is used to measure experimental data in temperature range of 281.9–287.4K and in pressure range of 7.08–12.16MPa. The studied ionic liquids present a thermodynamic inhibition behavior on methane hydrate and cause to shift the hydrate equilibrium dissociation conditions to the higher pressures/lower temperatures. It is found that the most effective thermodynamic inhibitor is [OH-EMIM][BF4] and among alkylsulfate-containing ionic liquids, the thermodynamic inhibition effects of two ionic liquids such as [EMIM][HSO4] and [BMIM][MeSO4] are better than that of [EMIM][EtSO4]. Furthermore, the electrolyte cubic square-well equation of state (eCSW EoS) is coupled with the van der Waals–Platteuw model and applied to predict the hydrate dissociation pressures of the methane+ionic liquid+water systems. A good agreement between the results of the model with the experimental data indicates the reliability of this model to predict the hydrate equilibrium conditions.

Measurements for the dissociation conditions of methane hydrate in the presence of 2,5-dihydrofuran and 3,4-dihydro-2H-pyran

This study reports the equilibrium conditions for the dissociation of methane hydrate in the presence of cyclic ethers of 2,5-dihydrofuran (C4H6O) and 3,4-dihydro-2H-pyran (C5H8O) as additives. For the water-soluble additive of 2,5-dihydrofuran, the hydrate–liquid water–vapor (H–Lw–V) three-phase equilibrium conditions were measured using the isochoric method in the pressures ranging from 6 to 12MPa and temperatures ranging from 291 to 300K. For the water-insoluble additive of 3,4-dihydro-2H-pyran, the hydrate–liquid water–liquid additive–vapor (H–Lw–La–V) four-phase equilibrium conditions were measured in the same pressure range with temperature range from 296 to 300K. The experimental results show that both additives have significant promotion effects on the formation of methane hydrates. At a specific pressure, the maximum increase in methane hydrate equilibrium temperature is approximately 13K for both additives. In order to simulate the seawater environment, this study also measured the methane hydrate dissociation conditions by adding these two additives to a brine system with 0.035 mass fraction NaCl. The equilibrium temperature at an isobar of the brine system shows a decrease of 1–2K for both additives in comparison to that of the pure aqueous system.

The performance of ionic liquids and their mixtures in inhibiting methane hydrate formation

The performance of 1-ethyl-3-methylimidazolium chloride (EMIM-Cl), one of novel ionic liquid inhibitors for gas hydrate, in inhibiting methane hydrate at low and high ionic liquid concentrations is investigated in a pressure range of 10–20MPa. Experiments on methane hydrate dissociation conditions in the presence of mixed ionic liquid and conventional inhibitors, such as sodium chloride (NaCl) and monoethylene glycol (MEG), as well as a mixture containing two ionic liquids, EMIM-Cl and 1-ethyl-3-methylimidazolium bromide (EMIM-Br), are also performed to investigate any possible synergistic effects. It is observed that single component solutions of EMIM-Cl demonstrate a progressive increase in inhibition effect with increasing concentration, which may surpass the effectiveness of MEG at high concentrations. Although the thermodynamic inhibition performance of the mixtures of EMIM-Cl and MEG does not show any synergistic effects at low pressures, it does at higher pressures. The mixture of EMIM-Cl and EMIM-Br also shows a synergistic effect at higher pressures. Unlike MEG or NaCl, inhibitors containing EMIM-Cl or EMIM-Br demonstrate an increase in inhibition effectiveness as pressure increases.

Measurements for the Dissociation Conditions of Methane Hydrate in the Presence of 1,3,5-Trioxane and Oxolan-2-ylmethanol

The dissociation conditions for methane hydrates in the presence of (0.0104 to 0.0350) mole fraction ((0.05 to 0.15) mass fraction) 1,3,5-trioxane aqueous or brine solutions and (0.0192 to 0.0702) mole fraction ((0.10 to 0.30) mass fraction) oxolan-2-ylmethanol (tetrahydrofurfuryl alcohol, THFA) aqueous solutions were experimentally measured in this study. The hydrate phase dissociation conditions were measured with an apparatus which was operated at high pressure and low temperature conditions. The liquid water–hydrate–vapor (Lw-H-V) three-phase equilibrium dissociation temperatures and pressures for methane hydrate in the presence of these additives were determined by employing the isochoric method. New experimental data are reported within the pressure range from (4 to 10) MPa for the methane + water + 1,3,5-trioxane hydrate system and from (9 to 15) MPa for the methane + water + oxolan-2-ylmethanol hydrate system, respectively. It is demonstrated that the addition of 1,3,5-trioxane has a promotion effect on the formation of methane hydrate. In addition, the liquid–hydrate–vapor (L-H-V) three-phase equilibrium dissociation conditions for brine solution with water and 0.011 mole fraction (0.035 mass fraction) NaCl were also measured in this study with the addition of 1,3,5-trioxane. The promotion effect for methane hydrate formation in brine environments is also observed. On the other hand, the results of adding oxolan-2-ylmethanol show the inhibition effect on the formation of methane hydrate.

Measurements for the Dissociation Conditions of Methane Hydrate in the Presence of 2-Methyl-2-propanol

The dissociation conditions for methane hydrates in the presence of (0.1 to 0.5) mass fraction 2-methyl-2-propanol aqueous solutions were experimentally measured in this study. The liquid water−hydrate−vapor (Lw−H−V) three-phase dissociation temperatures and pressures were determined using the isochoric method. New experimental data were reported within the pressure range from (4 to 10) MPa. It is demonstrated that the addition of 2-methyl-2-propanol had a promotion effect on the formation of methane hydrate. The liquid−hydrate−vapor (L−H−V) three-phase dissociation conditions for brine systems with methane + 0.035 mass fraction NaCl aqueous solution were also measured in this study with the addition of 2-methyl-2-propanol. The promotion effect for methane hydrate formation in brine environments was also observed with a 2-methyl-2-propanol additive.

Dissociation Conditions of Methane Hydrate in Mesoporous Silica Gels in Wide Ranges of Pressure and Water Content

The temperature of methane hydrate dissociation in silica mesopores has been monitored within a wide range of pressures from 10 MPa to 1 GPa. Because the determination of pore size appears to be crucial for the studied phenomenon, several methods of calculation have been applied. According to our findings, the size that corresponds to the mean size of the most representative pores is to be considered as the most reliable. It was concluded that the shape of hydrate particles replicates a host space of pores and may have a complex (e.g., fractal) shape. An attempt to simulate the curvature of hydrate particles by globular (quasi-spherical), elongated (quasi-cylindrical), or any intermediate models has been done. The quasi-spherical model seems to be more adequate for hydrate particles in small pores (<8 nm), while the quasi-cylindrical model fits better the experimental data for hydrate particles in larger pores. According to our experimental results, the hydrate can be formed in pores only by capillary condensate, without involving the water layers tightly bound by the surface, and pressure has an insignificant effect on the decrease of the dissociation temperature of the confined hydrate. A new effect of the formation of hydrates at a temperature higher than the bulk hydrate dissociation temperature has been observed for silica gels with the narrowest pores studied.

Circuit behaviour of oscillating CdS platelets: Gopinath, A., Davies, H., Electronics Letters, Vol 5, No 3 (6 February 1969) p 42 (1407)

In this communication, dissociation conditions of methane hydrate in the presence of pure water and aqueous solutions of three ionic liquids including 1-butyl-3-methylimidazolium tetrafluoroborate (0.10, 0.15 and 0.20 mass fraction), 1-butyl-3-methylimidazolium dicyanamide (0.10 mass fraction), and tetraethyl-ammonium chloride (0.10 mass fraction) were experimentally measured and are reported. The data were obtained in the 2.48–6.58 MPa pressure range and 272.1–282.0 K temperature range. A high-pressure equilibrium cell was used for performing the measurements pursuing the isochoric pressure search method. The hydrate dissociation conditions are modeled using the solid solution theory of van der Waals and Platteeuw for the hydrate phase along with the Peng–Robinson equation of state for the gas phase. For modeling of the aqueous phase, the NRTL model is applied. Acceptable agreement between the experimental data and the model results is observed.