Hydrate Equilibrium Research Articles

The effect of regenerated MEG on hydrate inhibition performance over multiple regeneration cycles

Mono-ethylene glycol (MEG) is a favorable gas hydrate inhibitor mainly due to its recoverability through MEG regeneration facilities, and thus reducing costs. However, it is not clear how the hydrate inhibition performance of MEG is affected by multiple regeneration cycles. In this study, MEG samples that were regenerated and reclaimed over multiple cycles using an innovative bench-scale MEG pilot plant which can simulate field-like MEG operations, were assessed on their hydrate inhibition performance. The cycled MEG samples were carefully analyzed in the laboratory for their composition, and each sample was tested in a high-pressure sapphire cell for methane hydrate inhibition performance. The study found a directly proportional relationship between the number of cycles and the shift in hydrate equilibrium phase boundary. A maximum equilibrium shift of 2.21 °C was recorded for a 20 wt% MEG/deionized water sample that had experienced 9 regeneration cycles compared to pure MEG. The analysis suggests that the shift in hydrate equilibrium phase boundary was due to thermal degradation of MEG within the regeneration and reclamation units due to the presence of acetic acid. The study found that even though the operation was below MEG degradation temperature range, repeated heating of MEG may have caused its degradation. Additionally, the phase equilibria are empirically modeled as a function of the number of cycles to aid MEG end-users. Application of the model to experimental results provided accurate outcomes, and had an average relative difference of 1.24% when determining equilibrium temperatures.

Effect of Substituents on the Reactivity of Ninhydrin with Urea

AbstractNinhydrin, i. e. the stable hydrate of the reactive species indanetrione, is a well‐known compound used for the quantification of ammonia and amino acids. However, substituent effects on the reactivity of ninhydrin with nucleophiles are not described. In this work, the kinetics of the reaction of C4‐ and C5‐ substituted ninhydrins with urea was studied and monitored by 13C‐NMR. Surprisingly, the obtained results show that electron donating groups (EDGs) as well as electron withdrawing groups (EWGs) decrease the rate of the reaction. EDGs decrease the electrophilicity of indanetrione, resulting in slower overall kinetics than unsubstituted ninhydrin. The calculated Gibbs free energy differences for the dehydration of unsubstituted and substituted ninhydrins and the subsequent reaction with urea showed that the dehydration of the compounds is more sensitive to electronic effects than the subsequent reaction with urea. Therefore, although EWGs increase the electrophilicity of indanetrione, this is more than counterbalanced by an adverse shift of the hydration equilibrium towards the unreactive hydrate (i. e. ninhydrin), resulting in slower kinetics as well.

A new approach of studying mixed gas hydrates involving propane at non-equilibrium conditions and final state: An experimental study and modeling

Metastable clathrate hydrates are a promising energy source in the shallow geosphere and present challenges in flow assurance, energy storage, and carbon capture sequestration. While they have been widely studied, little pertinent data is available for common propane hydrates concerning hydrate phase composition, nor its volume or the amount of converted water. This was the initial motivation for our work. Therefore, with a novel technique, propane hydrate composition and volume were measured dynamically at non-equilibrium conditions over time and at the final states for slow and quick rates of crystallization. Surprisingly, equilibrium pressure, hydrate volume and composition are different according to crystallization rate. The hydrate volume and water conversion in the quick crystallization process were larger. Moreover, at a slow crystallization rate, in a hydrocarbon mixture, enclathration of propane is more considerable and the hydrate crystals appear to be more homogeneous. Furthermore, the hydrate crystallization of a gas mixture is closer to the thermodynamic equilibrium at slow crystallization rates where the impact of kinetics is slight. A new compilation of propane Kihara parameters was presented. Unlike methane, ethane and carbon dioxide, for propane we strongly recommend two Kihara parameters, one for pure and the other for mixtures of propane. A thermodynamic model based on classical van der Waals and Platteuw model was also used to investigate the effects of kinetics. The simulation results have a satisfactory accordance with the experimental data from literature to predict the hydrate equilibrium pressure. The consequence of this research could have a substantial impact on design calculations in which the assumption of thermodynamic equilibrium are done. For instance, at present there would be excess hydrates volume estimations for pipe-lines, equilibrium conditions in energy storage and transportation or carbon capture sequestration and thus increase expenses or loss of productivity where propane is concerned.

Characterization of cyclopentane clathrates with gaseous guests for gas storage and separation

In this study, stability conditions and characterization of guest gas (CH4 and N2) + CP hydrates were investigated with a primary focus on phase equilibria and microscopic analyses. Four-phase (H-LW-LCP-V) equilibria of the CH4 + CP and N2 + CP hydrates measured at the pressure range of 0–11 MPa demonstrated that CP could significantly reduce hydrate equilibrium pressure at any given temperature and, thus, could be used as a powerful thermodynamic promoter for gas hydrates containing CH4 and N2. Powder X-ray diffraction revealed that guest gas (CH4 and N2) + CP hydrates are indexed using a cubic sII unit cell (space group Fd3m) and that the inclusion of guest gases does not affect the original structure of CP hydrates. It was confirmed from 13C NMR spectra that CH4 molecules are enclathrated only in the small 512 cages of sII CH4 + CP hydrates and that the cage occupancy of CH4 molecules in the small 512 cages of sII CH4 + CP hydrates is relatively lower than that of sI CH4 hydrate. Time-dependent in situ Raman spectra also indicated the occupation of guest gases in the CP hydrate and an absence of structural transformation caused by the inclusion of guest gases. The findings of this study can broaden our understanding of cage-specific occupation of guest molecules in gas hydrates and, thus, provide important information on the application of CP hydrates to gas storage and separation.

A new predictive thermodynamic framework for phase behavior of gas hydrate

This study presents a thermodynamic framework for predicting hydrate equilibrium pressure of gas species including methane, ethane, propane, nitrogen, carbon dioxide and hydrogen sulfide and their mixtures. For this purpose, Peng–Robinson–Stryjek–Vera equation of state (PRSV-EOS) along with modified Huron-Vidal (MHV1) mixing rule and UNIQUAC model were employed to calculate fugacity and activity coefficient of water in equilibrated fluid phases. To represent phase behavior of solid hydrate, a modified version of van der Waals and Platteeuw (vWd-P) model was utilized which accounts for guest interaction with water molecules beyond first shell of cavity and also asymmetry of encapsulated molecules and cage structure. In addition, dissolution of gas compounds in aqueous phase and subsequent non-ideality of water was taken into account. It was realized that both physical phenomena are of marked influence on the prediction accuracy.In contrast to conventional modelling approaches which scarify some part of equilibrium data to regress some adjustable parameters, advantageously, our model does not require any pre-matching. It was observed that present framework gives accurate prediction for equilibrium pressure of hydrates of CH4, C2H6, C3H8, CO2, N2 and H2S with overall average absolute percent deviation (AAPD) 3.2, 3.4, 3.7, 1.5, 2.8 and 1.3, respectively. Also, incipient pressure of hydrate formed by binary gas mixtures comprised of aforementioned single components could accurately be predicted by proposed approach, which is detailed in the manuscript. Overall, formation pressures predicted by proposed modelling approach are more accurate (or at least comparable) to outstanding models presented in the hydrate literature.

Prediction of the conditions for sour gas hydrate formation in the presence of methanol inhibitor

ABSTRACTIn this work a new thermodynamic model for accurate prediction of H2S and CO2 containing sour gas hydrate equilibrium dissociation temperatures in the presence of a gas hydrate thermodynamic inhibitor (methanol) is presented. The average absolute deviation between the predicted and measured sour gas hydrates dissociation temperatures (AADT%) considering pure and mixed acid gases in the presence of methanol inhibitor is about 0.274% which is much lower than those obtained by the other available thermodynamic models. The proposed approach is quite reliable over wide ranges of methanol and acid gases concentrations and can be used for performance evaluation of other gas hydrate inhibitors regarding the design of sour natural gas flow assurance systems in oil and gas industries.

Experimental measurement and thermodynamic modeling of equilibrium condition for natural gas hydrate in MEG aqueous solution

Comprehensive information about the hydrate formation and dissociation conditions is necessary for design and operation of different processes in the petroleum industry. This study investigated the natural gas hydrate equilibrium conditions in the presence of mono ethylene glycol aqueous solution as a widely used thermodynamic hydrate inhibitor in the oil and gas industries. Stepwise heating method was used for the hydrate formation and dissociation tests in a 250 cm3 stainless steel equilibrium cell. To validate and verify the performance of the apparatus and the method used, methane hydrate equilibrium data were measured and compared to a number of selected experimental data in the literature. This verification showed that the experimental procedure was accurate. The equilibrium temperatures of synthetic natural gas (SNG) hydrates in the absence of MEG aqueous solutions at various pressures of 3.95, 4.49, 5.36, 6.50, 6.85, and 8.20 MPa were 289.9, 290.9, 291.7, 293.1, 293.5 and 294.5 K, respectively. The equilibrium data for natural gas hydrate in the presence of 0.10 and 0.20 mass fractions of MEG in the water for pressure range of 3.90–8.20 MPa were also comparatively measured. The results showed that the natural gas hydrate equilibrium temperature decreased about 2.5 and 5 K in the presence of 0.10 and 0.20 mass fractions of MEG, respectively. The modified statistical thermodynamic model based on van der Waals and Platteeuw solid solution theory and the PVTsim software were applied to predict and evaluate hydrate equilibrium conditions. Thermodynamic model predictions matched reasonably well with the experimental results.

Formation Behaviors of CO2 Hydrate in Kaoline and Bentonite Clays with Partially Water Saturated

CO2 hydrates can be used for long term storage of CO2 in the deep ocean. Clay minerals are the most important components of the marine sediments. In this study, the formation behaviors of carbon dioxide hydrate in kaoline clay and bentonite clay with partially water saturated were studied in a closed system. The mass ratio of water to Kaoline and Bentonite clays is 20%. The experiments were carried out at the temperature of 279.15 K and the initial formation pressure range of 4.8-3.4 MPa. The liquefaction of the carbon dioxide was observed in the cooling process by setting the temperature of the water bath to the valued experimental temperature. The temperature in the crystallizer begins to rise quickly when the hydrate starts to form and then decreases gradually after reaching the highest value. For the experiments in kaoline clay, the temperature decreases gradually along with the equilibrium hydrate formation temperature, and the hydrate formation rate is controlled by the heat transfer process. The final conversion of the water to hydrate increases with the increase of the initial formation pressure and restrained by the equilibrium hydrate formation pressure. For the experiments in bentonite clay, the temperature during the hydrate formation is much higher than the equilibrium temperature for CO2 hydrate formation. The final pressure is much higher than the equilibrium pressure of CO2 hydrate, and increases with the increase of the initial formation pressure, indicating that the equilibrium pressure CO2 hydrate in bentonite clay is higher than the bulk CO2 hydrate.

Hydrate-based Synchronously Capture of CO2 and H2S for Clean H2 with New Synergic Additives

The integrated gasification combined cycle (IGCC) process, possessing high efficiency and environmental advantages, produces H2-rich syngas at high pressures. Acid gases carbon dioxide (CO2) and hydrogen sulfide (H2S) are important and highly undesirable contaminants for syngas, and hydrate-based removal of these contaminants is environmentally attractive. This work experimental investigated the hydrate-based acidic gases (CO2 and H2S) capture for clean hydrogen (H2) fuel from syngas with new synergic additives, which comprise physical gas solvent (TMS) and traditional hydrate promoter (TBAB). The results show that, with the synergic additives, the equilibrium hydrate formation pressure can be moderated by about 90%, the gas selectivity can be improved by 50%, and the formation rate and gas storage capacity can also be improved. Furthermore, the promotion effect can be enhanced when with the help of H2S. It has been testified that CO2 and H2S could be synchronously captured through the hydrate formation process.

PH Dependence of the Imidazole-2-carboxaldehyde Hydration Equilibrium: Implications for Atmospheric Light Absorbance

Imidazole-2-carboxaldehyde (IC) has been identified as an aqueous “brown carbon” absorber and a possible atmospheric photosensitizer. IC exists in a pH-dependent equilibrium between its aldehyde and geminal diol form; the diol form is the dominant species in solution at pH <5. Calculated molar absorptivity coefficients are 13700 ± 200 cm–1 M–1 at 287 nm for the aldehyde and 7800 ± 100 cm–1 M–1 at 212 nm for the diol. This shift from aldehyde to diol changes the peak light absorption of the aqueous solution from 287 to 212 nm, which is beyond the actinic range and may have implications for radiative forcing. The observed pH-dependent shift in the hydration equilibrium of IC is driven by the interaction between its hydration and protonation equilibria. Calculated pKa values are 2.5 ± 0.4 and 5.94 ± 0.05 for the aldehyde and diol, respectively, and are consistent with the trend toward increasing diol as the pH decreases. The acid–base equilibrium affects both the solubility and the major species in solution ...

Spatially Heterogeneous Surface Water Diffusivity around Structured Protein Surfaces at Equilibrium.

Hydration water on the surface of a protein is thought to mediate the thermodynamics of protein-ligand interactions. For hydration water to play a role beyond modulating global protein solubility or stability, the thermodynamic properties of hydration water must reflect on the properties of the heterogeneous protein surface and thus spatially vary over the protein surface. A potent read-out of local variations in thermodynamic properties of hydration water is its equilibrium dynamics spanning picosecond to nanosecond time scales. In this study, we employ Overhauser dynamic nuclear polarization (ODNP) to probe the equilibrium hydration water dynamics at select sites on the surface of Chemotaxis Y (CheY) in dilute solution. ODNP reports on site-specific hydration water dynamics within 5-10 Å of a label tethered to the biomolecular surface on two separate time scales of motion, corresponding to diffusive water (DW) and protein-water coupled motions, referred to as bound water (BW). We find DW dynamics to be highly heterogeneous across the surface of CheY. We identify a significant correlation between DW dynamics and the local hydropathy of the CheY protein surface, empirically determined by molecular dynamics (MD) simulations, and find the more hydrophobic sites to be hydrated with slower diffusing water. Furthermore, we compare the hydration water dynamics on different polypeptides and liposome surfaces and find the DW dynamics on globular proteins to be significantly more heterogeneous than on intrinsically disordered proteins (IDPs), peptides, and liposomes. The heterogeneity in the hydration water dynamics suggests that structured proteins have the capacity to encode information into the surrounding hydration shell.

New insight into prediction of phase behavior of natural gas hydrate by different cubic equations of state coupled with various mixing rules

Progress in hydrate thermodynamic study necessitates robust and fast models to be incorporated in reservoir simulation softwares. However, numerous models presented in the literature makes selection of the best, proper predictive model a cumbersome task. It is of industrial interest to make use of cubic equations of state (EOS) for modeling hydrate equilibria. In this regard, this study focuses on evaluation of three common EOSs including Peng–Robinson, Soave–Redlich–Kwong and Valderrama–Patel–Teja coupled with van der Waals and Platteeuw theory to predict hydrate P–T equilibrium of a real natural gas sample. Each EOS was accompanied with three mixing rules, including van der Waals (vdW), Avlonitis non-density dependent (ANDD) and general non-quadratic (GNQ). The prediction of cubic EOSs was in sufficient agreement with experimental data and with overall AARD% of less than unity. In addition, PR plus ANDD proved to be the most accurate model in this study for prediction of hydrate equilibria with AARD% of 0.166. It was observed that the accuracy of cubic EOSs studied in this paper depends on mixing rule coupled with them, especially at high-pressure conditions. Lastly, the present study does not include any adjustable parameter to be correlated with hydrate phase equilibrium data.

Hydrate Equilibrium Modelling with the Cubic two-state Equation of State

A combination of the cubic two-state equation of state and the van der Waals–Platteeuw model was employed for the description of the hydrate formation thermodynamics, with and without inhibitors. The model parameters were determined from the properties of pure compounds and from phase equilibrium data of binary gas–water and water–inhibitor mixtures. With these parameters, predictions were performed for multicomponent gas–water–inhibitor systems. For single-gas hydrates, the average absolute deviations found for equilibrium pressure did not exceed 8%, whereas for multi-gas hydrates, these deviations were 23% maximum. The proposed model produced good predictions in the presence of inhibitors (methanol, ethanol, ethylene glycol and triethylene glycol), with increasing deviations at higher concentrations of inhibitors.

Enhanced depressurisation for methane recovery from gas hydrate reservoirs by injection of compressed air and nitrogen

Abstract Enhanced depressurisation for methane recovery from gas hydrate-bearing sediments was experimentally studied by injection of compressed air and nitrogen. Experiments were conducted in simulated sediments (silica sand) from 273.4 K to 283.0 K and initial system pressures ranging from 3.8 MPa to 7.2 MPa before air or nitrogen injection. The results show that injection of air and nitrogen made it possible to implement conventional depressurisation in multiple stages. In each pressure stage, methane hydrate was quickly dissociated by the injected air or nitrogen due to direct shift of the methane hydrate equilibrium phase boundary. Methane hydrate dissociation at high pressures enables methane recovery inside the methane hydrate stability zone. Depressurisation well above the methane hydrate dissociation pressure generated a methane-rich gas phase of up to 90 mol% methane depending on the injected gas. Injection of compressed air or nitrogen provides a potential approach to improve the technical feasibility and economic viability of conventional depressurisation method for methane recovery from most gas hydrate reservoirs with severe conditions such as low permeability or dispersed hydrates.

Thermophysical properties of aqueous lysine and its inhibition influence on methane and carbon dioxide hydrate phase boundary condition

In this study, the thermophysical properties of lysine amino acid, alongside its methane and carbon dioxide hydrate inhibition effect is reported. The physical properties (density, viscosity, and refractive index) of aqueous lysine solution are measured at 5 wt% and 10 wt% in the temperature range of 298.15–313.15 K at 5 K intervals. The hydrate inhibition potential of lysine is tested in the temperature and pressure range of 1.87–10.45 MPa and 276.45–285.15 K, respectively, at 5 wt% and 10 wt% using the T-cycle method in a sapphire cell hydrate reactor. The density, viscosity and refractive index of the aqueous lysine solution are found to increase with increasing concentration, but decreases with increasing temperature. Furthermore, the presence of lysine significantly inhibited both methane and carbon dioxide hydrate by shifting the methane and carbon dioxide hydrate equilibrium phase boundary condition to higher pressures and/or lower temperatures region. The lysine hydrate inhibition impact is increased with increasing concentration. An average depression temperature of 1.44 K and 1.49 K is observed at 10 wt% for methane and carbon dioxide hydrate, respectively. In addition, the hydrate dissociation enthalpies in the presence and absence of lysine are calculated using the Clausius-Clapeyron equation. The findings are useful as it presents data which can be used to understand the effect of amino acids physical properties on their thermodynamic hydrate inhibition influence.

Effect of aromatic/aliphatic based ionic liquids on the phase behavior of methane hydrates: Experiments and modeling

Abstract In this study, eight ionic liquids (ILs) from the two varieties of ILs, namely, aromatic and aliphatic ILs, have been considered to carry out experimental studies for their effect on the phase behavior of methane hydrate. We have employed five aromatic based ILs with several cations, such as 1-butyl-3-methyl imidazolium, 1-hexyl-3-methyl imidazolium, 1-octyl-3-methyl imidazolium and various anions, such as [Cl]−, [Br]−, [HSO4]−, and three aliphatic based ILs with various cations, such as di-ethyl-ammonium, tri-propyl-ammonium, tri-butyl-ammonium and [HSO4]− anion. All the experiments were performed in the hydrate equilibrium pressure and temperature ranges of 3.86–7.66 MPa and 276.68–283.18 K, respectively. It has been observed that all the investigated ILs have shown inhibition effect on methane hydrate system. Aromatic ionic liquids have shown their dominance over aliphatic ionic liquids in terms of methane hydrate inhibition. ILs with similar class of cation with varying carbon chain length have not shown significant improvement in hydrate inhibition. However, the replacement of anion by [HSO4]− in imidazolium-based ILs improves methane hydrate inhibition. 1-butyl-3-methyl imidazolium sulphate ([BMIM]+[HSO4]−) found to be the best methane hydrate inhibitor among all investigated ILs. In addition, a phase behavior model incorporating a single tuning parameter has been proposed to predict the phase behavior of methane hydrate in the presence of various ionic liquids and salt solutions. The absolute average deviation in pressure (AARD-P, %) for proposed model with an experimental data generated in this work and for various data sets from the literature has been found to be within ±2.90% of the experimental values. Both cation and anion of the ionic liquids have shown to exhibit inhibition effect on the methane hydrate phase stability. The study indicates that the selection of ionic liquids with tunable cation and anion may provide an opportunity to design the best inhibitor for methane hydrate.

Gas hydrates inhibition via combined biomolecules and synergistic materials at wide process conditions

The motive of this research to present a systematic study in context of implementation of gas hydrate inhibitors that are obtained via naturally occurring amino acids (L-Alanine, Glycine, L-Histidine, L-Phenylalanine and L-Asparagine). These materials are tested for methane (CH4) hydrate inhibition purposes from both thermodynamically and kinetically perspectives at wide process conditions. In this presented work, all studied amino acids have been tested at both 1 wt % as low dosage inhibitors as well as at higher concentrations up to 5 wt %. Furthermore, Polyethylene-oxide (PEO) and Vinyl Caprolactum (VCap) were used at 1 wt % in studied aqueous solutions as synergetic compounds to enhance the inhibition performance for CH4 hydrate inhibition. Gas hydrate experiments were carried out by using rocking cell apparatus, from which pressure, temperature equilibrium data were obtained at recorded time and these data were translated into inhibitor performance evaluation from both thermodynamics and kinetic inhibition perspectives. This study includes the discussions of the effect of solubility limitation of studied amino acids, the effect of inhibitor concentration effect on the thermodynamic shift of the hydrate equilibrium curve, the role of side chain in amino acids in kinetic hydrate inhibition, the hydrophobic interactions of alkyl chain in water for synergistic point of view. The results showed that the suitability of amino acids combined with synergistic materials for high kinetic inhibition performance, which provided an additional time shift up to 35 h in hydrate formation at moderate process conditions up to 55 bars, specifically when L-Alanine was used.

Modeling phase equilibrium with a modified Wong-Sandler mixing rule for natural gas hydrates: Experimental validation

As natural gas hydrate forms at low temperature and high pressure (i.e., near critical region), vapor phase fugacity calculation becomes crucial in this region due to the intermolecular interactions. This work introduces the modified form of the Wong-Sandler mixing rule in the Peng-Robinson (PR) and Patel-Teja (PT) equation of state (EoS) models to revamp the fugacity calculation of vapor phase. This mixing rule which is based on the excess Gibbs free energy leads to precisely capture the polar and asymmetric properties of mixture components. The modified Wong-Sandler mixing rule is formulated by representing its correction factors for energy and co-volume parameters in terms of temperature and gas-phase composition. Here, the hydrate phase fugacity is determined by the Chen-Guo model that is coupled with an EoS model for hydrate equilibrium analysis. On the other hand, the liquid phase nonideality is estimated by using the Wilson activity-coefficient model. The proposed modified Wong-Sandler based phase equilibrium models are shown to be better than the existing phase rule based models with the three example natural gas hydrate systems (CH4+N2, CH4+C2H6, CH4+C2H4) using tetrahydrofuran asa thermodynamic promoter. Validating these models with real time data sets, it is further investigated that the PT based model shows a better performance compared to the PR equation of state. This apart, these two models show their superiority over the existing PT-van der Waals (PT-vdW) model, for which, a new parameter set is proposed for the said three systems for their improved performance.

Propane, n-butane and i-butane stabilization effects on methane gas hydrates

The goal of this work is to analyse the hydrate equilibria of methane+propane, i-butane and n-butane gas mixtures. Experimental hydrate equilibrium data was acquired for various compositions of these components in methane, ranging from 0.5 to 6.8mol%. Applying this information with the Clausius-Clapeyron equation, the extent of hydrate promotion was demonstrated quantitatively by calculating the slope of the equation and the dissociation enthalpy (ΔHd). Methane equilibria was found to be most sensitive towards propane and i-butane, where very small concentrations were sufficient to increase the thermodynamic conditions for hydrate equilibrium drastically. The degree of hydrate stabilisation, i.e. transition from sI to sII hydrate, was immediate – there was no detectable composition slightly above 0.0mol% where propane or i-butane did not have a sII hydrate-promoting impact, although one was implied with the aid of Calsep PVTsim calculations. Addition of n-butane to methane was far less sensitive and was deemed inert from 0.0 to 0.5mol%. It was concluded that the sII hydrate was favoured when the n-butane composition exceeded 0.5–0.75mol%. The influence of composition on stability was quantified by determining the gradient of ΔHd versus mol% plots for the initial steep region that represents the increasing occupancy of the sII guests. Average gradients of 11.66, 26.64 and 43.50kJ/mol.mol% were determined for n-butane, propane and i-butane addition to methane respectively. A hydrate-inert range for propane/i-butane (in methane) was suspected according to the perceived inflection point when less 0.5mol%, implying the gradient was very low at some minute concentration range starting at 0.0mol%. Awareness of these sI to sII transition regions is beneficial to natural gas recovery and processing as a small percentage of these components may remain without being detrimental in terms of promoting the hydrate equilibria.

Two- and three-phase equilibrium experimental measurements for the ternary CH4 + CO2 + H2O mixture

Experimental measurements are reported for the ternary methane + carbon dioxide + water mixture under three-phase hydrate equilibrium conditions utilizing a recently-introduced experimental apparatus. In addition to measuring the three-phase equilibrium pressure and temperature conditions, vapor and liquid phase analysis measurements are also reported. In particular, we performed gas chromatographic analysis of the vapor phase and the solubility of each gas in the aqueous phase was measured under three-phase equilibrium conditions. Additionally, two-phase equilibrium solubility measurements are also reported at pressure and temperature conditions that are in the close neighborhood of hydrate-formation conditions.