Van Der Waals Platteeuw Model Research Articles

Effect of particle size, water saturation, inorganic salt and methane on the phase equilibrium of CO2 hydrates in sediments

Understanding the thermal stability of gas hydrate in complex marine geological environment is of importance to hydrate-based carbon sequestration. In this work, the factors affecting the equilibrium of CO2 hydrate in ocean sediments, including quartz sands, inorganic salts and gas impurities were quantitatively measured in a temperature range from 273 to 283 K and a phase equilibrium model of hydrate was established. To reveal the distribution in pore structure, the micro-morphologies of hydrate-bearing sediments were measured by cryo-SEM. Results showed that reduction of initial water saturation, addition of NaCl and CH4 were found to have inhibitory effect on CO2 hydrate equilibrium. Initial water saturation reduced the equilibrium temperature by the capillary pressure, but only 0.3–0.7 K temperature depression was observed as the water saturation reduced to 5 %. About 5.7 K in the average temperature depression was found by the addition of 10 wt% NaCl and 24 mol% CH4. NaCl and CH4 influenced the hydrate equilibrium by changing the water activity and chemical potential of hydrate water lattice. SEM images showed that the hydrate formed in pores of quartz sand had porous surface and coated the sand particles like a layer of cells which are 5–20 μm in diameter, suggesting the hydrate layer exists between the liquid and gas phase. Based on the van der Waals-Platteeuw model, a hydrate equilibrium model was developed. The model provided a good prediction of the hydrate equilibrium in the presence of quartz sand, NaCl and CH4 with an averaged deviation of ±4.2 %, which had the potential to be applicated in more complexed ocean sedimentary environment.

Benedict–Webb–Rubin–Starling Equation of State + Hydrate Thermodynamic Theories: An Enhanced Prediction Method for CO2 Solubility and CO2 Hydrate Phase Equilibrium in Pure Water/NaCl Aqueous Solution System

Accurately predicting the phase behavior and physical properties of carbon dioxide (CO2) in pure water/NaCl mixtures is crucial for the design and implementation of carbon capture, utilization, and storage (CCUS) technology. However, the prediction task is complicated by CO2 liquefaction, CO2 hydrate formation, multicomponent and multiphase coexistence, etc. In this study, an improved method that combines Benedict–Webb–Rubin–Starling equation of state (BWRS EOS) + hydrate thermodynamic theories was proposed to predict CO2 solubility and phase equilibrium conditions for a mixed system across various temperature and pressure conditions. By modifying the interaction coefficients in BWRS EOS and the Van der Waals–Platteeuw model, this new method is applicable to complex systems containing two liquid phases and a CO2 hydrate phase, and its high prediction accuracy was verified through a comparative evaluation with a large number of reported experimental data. Furthermore, based on the calculation results, the characteristics of CO2 solubility and the variation of phase equilibrium conditions of the mixture system were discussed. These findings highlight the influence of hydrates and NaCl on CO2 solubility characteristics and clearly demonstrate the hindrance of NaCl to the formation of CO2 hydrates. This study provides valuable insights and fundamental data for designing and implementing CCUS technology that contribute to addressing global climate change and environmental challenges.

Molecular dynamics simulation of methane hydrates: Prediction of the phase equilibria using extracted microscopic parameters from SAFT-VR Mie EOS

This paper explores the three-phase equilibrium of structure-I methane hydrate by utilizing the extracted Mie potential parameters for non-bonded molecular interactions in the LAMMPS molecular dynamics simulator. An in-house code was developed to numerically solve the SAFT-VR Mie equation of state (EOS). To reduce numerical errors, unlike common practices, we incorporated all partial derivatives analytically in the code. The microscopic simulation parameters for methane and water molecules were selected so that saturation pressure and liquid density data from EOS were fitted on experimental data. Using this approach, the three-phase (V−Lw−H) equilibrium temperatures for pressure values of 30, 70, 100, and 300 bar were calculated. The solubility of methane in the aqueous phase at three-phase equilibrium was also determined. The results were validated against available laboratory data. To evaluate the performance of Mie potential parameters, the MD simulations were repeated using three well-known force fields for methane molecules, namely, Optimized Potentials for Liquid Simulations-United Atom (OPLS-UA), Universal force field (UFF), and General Amber force field (GAFF). The TIP4P/Ice force field was used for water molecules in all cases. The comparison with experimental data reveals that while the accuracy of the UFF force field is the highest, our simulation approach outperforms OPLS-UA and GAFF force fields in predicting methane solubility in the aqueous phase. Besides molecular dynamics simulation, the van der Waals-Platteeuw model was combined with the SAFT VR Mie EOS to account for the hydrate phase. In our case study, the SAFT-VR Mie + vdW-P model proved to be more accurate in predicting the three-phase equilibrium data compared to the MD approach.

A model to predict the thermodynamic stability of abiotic methane-hydrogen binary hydrates in a marine serpentinization environment

Abiotic methane (CH4) and hydrogen (H2), which are produced during marine serpentinization, provide abundant gas source for hydrate formation on ocean floor. However, previous models of CH4–H2 hydrate formation have generally focused on pure water environments and have not considered the effects of salinity. In this study, the van der Waals–Platteeuw model, which considered the effects of salinity on the chemical potentials of CH4, H2, and H2O, was applied in a marine serpentinization environment. The model uses an empirical formula and the Peng–Robinson equation of state to calculate the Langmuir constants and fugacity values, respectively, of CH4 and H2, and it uses the Pitzer model to calculate the activity coefficients of H2O in the CH4–H2–seawater system. The three-phase equilibrium temperature and pressure predicted by the model for CH4–H2 hydrates in pure water demonstrated good agreement with experimental data. The model was then used to predict the three-phase equilibrium temperature and pressure for CH4–H2 hydrates in a NaCl solutions, for which relevant experimental data are lacking. Thus, this study provides a theoretical basis for gas hydrate research and investigation in areas with marine serpentinization.

A novel four-phase equilibrium calculation algorithm for water/hydrocarbon systems containing gas hydrates

In this study, we developed an algorithm for vapor–liquid–aqueous–hydrate four-phase equilibrium calculations. The algorithm was formulated in a stage-wise manner: a stability test was first conducted, followed by flash calculations if instability was determined. In addition to using the van der Waals–Platteeuw model for predicting the presence of a hydrate phase, we proposed a novel criterion for determining the onset of hydrate dissociation. Sample calculations were conducted for several fluids. We successfully plotted the pressure–temperature and pressure–composition phase diagrams of these fluids by conducting point-to-point equilibrium calculations with the newly developed four-phase equilibrium calculation algorithm.

In situ experimental study on the effect of mixed inhibitors on the phase equilibrium of carbon dioxide hydrate

Electrolytes and alcohols are two thermodynamic inhibitors commonly used to prevent hydrate growth in gas and oil pipelines in the gas industry. Although the phase behavior of CO2 hydrate in the presence of electrolyte and/or alcohol has been extensively studied, the knowledge of the combined effect of these two as mixed inhibitors on CO2 hydrate is still very limited. In this study, the influence of mixed inhibitors comprising an electrolyte (selected from sodium chloride and calcium chloride) mixed with an alcohol (selected from methanol, ethanol, ethylene glycol, n-propanol, and isopropanol) on the thermodynamic properties of carbon dioxide hydrate was investigated. Observations on CO2-H2O-NaCl-alcohol system were performed using high-pressure optical cell (HPOC) technology. The experiments were carried out at low temperatures of 263–283 K and high pressures up to 4 MPa, focusing on the phase equilibrium of liquid, hydrate, and carbon dioxide gas in HPOC. Experimental results reveal that the inhibition strength of the mixed inhibitor is clearly enhanced; in some cases, the inhibition intensity of the mixed inhibitor is greater than the sum of its components because of the synergistic effect. For example, under a pressure of ∼ 2 MPa, the temperature depressions of 10 wt% methanol and 10 wt% sodium chloride for CO2 hydrate are 4.53 K and 4.87 K, respectively; the mixture of these two can produce a temperature depression as high as 12.53 K. Our results also show that the inhibition strength of the inhibitor, single or mixed, increases with the pressure. Based on our results, an improved van der Waals Platteeuw (vdWP) model is proposed to predict the hydrate stability conditions in the CO2-H2O-inhibitor solution. Results from this study provide a ground for a better understanding of the thermodynamic properties of carbon dioxide hydrate under extreme conditions.

Raman Spectroscopic Study on a CO2-CH4-N2 Mixed-Gas Hydrate System

Accurate determination of the characteristics of coal mine gas separation products is the key for gas separation applications based on hydrate technology. Gas hydrates are synthesized from gases with two types of compositions (CO2-CH4-N2). The separation products were analyzed by in situ Raman spectroscopy. The crystal structure of the mixed-gas hydrate was determined, and the cage occupancy and hydration index were calculated based on the various vibrational modes of the molecules according to the “loose cage-tight cage” model and the Raman band area ratio combined with the van der Waals-Platteeuw model. The results show that the two mixed-gas hydrate samples both have a type I structure. Large cages of mixed-gas hydrate are mostly occupied by guest molecules, with large cage occupancies of 98.57 and 98.52%; however, small cages are not easy to occupy, with small cage occupancies of 29.93 and 33.87%. The average cage occupancies of these two hydrates are 81.41 and 82.36%, and the stability of the crystal structure of the mixed-gas hydrate in the presence of 75% CO2 is better than that of the mixed-gas hydrate in the presence of 70% CO2. The hydration indices of the two hydrate gas samples are 7.14 and 6.98, which are greater than the theoretical value of structure l.

An Accurate Model to Calculate CO2 Solubility in Pure Water and in Seawater at Hydrate–Liquid Water Two-Phase Equilibrium

Understanding of CO2 hydrate–liquid water two-phase equilibrium is very important for CO2 storage in deep sea and in submarine sediments. This study proposed an accurate thermodynamic model to calculate CO2 solubility in pure water and in seawater at hydrate–liquid water equilibrium (HLWE). The van der Waals–Platteeuw model coupling with angle-dependent ab initio intermolecular potentials was used to calculate the chemical potential of hydrate phase. Two methods were used to describe the aqueous phase. One is using the Pitzer model to calculate the activity of water and using the Poynting correction to calculate the fugacity of CO2 dissolved in water. Another is using the Lennard–Jones-referenced Statistical Associating Fluid Theory (SAFT-LJ) equation of state (EOS) to calculate the activity of water and the fugacity of dissolved CO2. There are no parameters evaluated from experimental data of HLWE in this model. Comparison with experimental data indicates that this model can calculate CO2 solubility in pure water and in seawater at HLWE with high accuracy. This model predicts that CO2 solubility at HLWE increases with the increasing temperature, which agrees well with available experimental data. In regards to the pressure and salinity dependences of CO2 solubility at HLWE, there are some discrepancies among experimental data. This model predicts that CO2 solubility at HLWE decreases with the increasing pressure and salinity, which is consistent with most of experimental data sets. Compared to previous models, this model covers a wider range of pressure (up to 1000 bar) and is generally more accurate in CO2 solubility in aqueous solutions and in composition of hydrate phase. A computer program for the calculation of CO2 solubility in pure water and in seawater at hydrate–liquid water equilibrium can be obtained from the corresponding author via email.

Kinetic and thermodynamic study of CO2 storage in reversible gellan gum supported dry water clathrates

The effects of "Dry Gel" on the carbon dioxide hydrate formation and storage capacity were studied. Gel-supported dry water (Dry Gel) was prepared by mixing gelling agents, hydrophobic silica nanoparticles, water, and air in a high-speed blender. The kinetic parameters of carbon dioxide hydrate formation such as mole of consumed gas, induction time, gas uptake rate, storage capacity, final conversion of water to hydrate, and apparent rate constant were investigated in the presence of dry gel with different gel strength (0 to 15 wt.%) at two silica ratios (5 and 10 wt.%). The experiments of hydrate formation were performed using a 200 cc stainless-steel vessel with and without stirring under the initial condition of 21 bars and 15 °C. Meanwhile, the thermodynamic recyclability of both dry water and dry gels over multiple hydrate cycles were studied. Besides, we utilized the diffusion-reaction kinetics model of Englezos and Bishnoi for calculating the apparent rate constant of hydrate growth. The van der Waals-platteeuw model, through a reversed micelle approach, was used to obtain hydrate phase equilibrium conditions. Results revealed that the amount of gas uptake increased significantly in both dry water and dry gel systems compared to pure water. It was found that dry gel with 15 wt.% gellan gum could substantially improve the storage and recyclability of CO2 hydrate by decreasing the decay percent from 68.8 to 5.1 over repeating seven hydrate cycles.Moreover, the more Nano-silica content, the better the storage repeatability was observed. It was also shown that the equilibrium hydrate formation conditions were approximately stable in the presence of dry gels. Mixing seemed to be critical for multiple freezing-thawing hydrate cycles since it could reduce the reaction and induction time significantly. Finally, the dry water and dry gel can be used as a promising platform for carbon dioxide capturing using clathrate through the recyclability of hydrate formation.

Phase behavior of high-pressure CH4-CO2 hydrates in NaCl solutions

Understanding the phase behavior of CH4-CO2 hydrates formed in NaCl solutions is important for gas recovery from hydrate reservoirs, CO2 sequestration, and flow assurance. The observations of CH4-CO2 hydrates formed in NaCl solutions are limited at high-pressure and high-temperature conditions. In this work, a high-pressure experimental apparatus is built to investigate the phase behavior of CH4-CO2 hydrates. The interfacial phenomenon is observed during hydrate formation and dissociation. The phase boundary of CH4-CO2 hydrates is determined by using the isochoric pressure-search method with pressure above 10 MPa. A novel theoretical model is developed to calculate the phase boundary pressure of hydrates by implementing a modified PR EoS for the fluid phases, the van der Waals-Platteeuw model for the hydrate phase, and the Pitzer model for the effect of ions. It is revealed that the roughness of water–gas interface is greatly increased at the initial hydrate formation stage due to the occurrence of fine pillars at the interface, which is explained by two hypotheses, i.e., the non-equilibrium state of gas and water phases and the non-uniform lateral growth of hydrates at the interface. The roughness decreases as time goes by during hydrate formation owing to the thickness growth of the hydrate film. The deviation of the calculated phase boundary pressure from the 86 collected experimental data points of CH4-CO2 hydrates formed in pure water is 3.7%, and is 5.3% for the 24 collected phase boundary data points of CH4-CO2 hydrates formed in the NaCl solutions, which proves the reliability of the newly developed model. The measured phase boundary data points of CH4-CO2 hydrates formed in NaCl solutions in this work extend the phase boundary pressure up to 61.99 MPa and the temperature to 295.09 K, which have filled the blank of the database in the high-pressure and high-temperature region. The deviations of the calculated phase boundary pressure from these two groups of measured ones are 8.9% and 6.2% respectively.

Separation processes for carbon dioxide capture with semi-clathrate hydrate slurry based on phase equilibria of CO2 + N2 + tetra-n-butylammonium bromide + water systems

The objective of this work was to assess multi-stage separation processes for CO2 capture based on semi-clathrate hydrate (SCH) adsorption media. Phase equilibria were determined for CO2+tetra-n-butyl ammonium bromide (TBAB), N2+TBAB and CO2+N2+TBAB SCH and correlated with a modified van der Waals–Platteeuw model. Experimental CO2 separation factors ranged from 5 to 10, whereas calculated values were all around 18 implying inhomogeneous absorption in the slurries. For simulation conditions, hydrate mass fractions less than 0.09 were estimated to prevent aggregation of the hydrate solids. A two-stage batch separation process allowed enrichment of CO2 to more than 90mol% from a 20mol% CO2 feed. A three-stage continuous countercurrent separation process allowed a CO2 recovery of about 90%. Separation performance of semi-clathrate hydrates ranked favorably among the CO2 separation methods, showing that SCH adsorption media have excellent potential for carbon capture applications.

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.

SIMULATION AND EXPERIMENTAL STUDY OF METHANE-PROPANE HYDRATE DISSOCIATION BY HIGH PRESSURE DIFFERENTIAL SCANNING CALORIMETRY

Abstract Binary and ternary systems composed of methane-water and methane-propane-water, respectively, were studied using high pressure differential scanning calorimetry. The methodology was validated by comparing results for the binary system to experimental data obtained in the literature. The hydrate dissociation temperatures for the ternary system (methane-propane-water) at 21 MPa were experimentally determined for different compositions of the gas mixture and mole fractions of propane higher than 0.1 in the ternary system. Our results are in good agreement with the values predicted by applying the Cubic Plus Association (CPA) equation of state coupled with van der Waals-Platteeuw model for the hydrate phase. Although experimental results are considered satisfactory for both binary and ternary systems, higher deviations between our values and the simulated ones for the ternary system, considering peak temperature instead of the extrapolated onset as the hydrate dissociation temperature, are believed to be a consequence of dynamic effects that promote the formation of a heterogeneous hydrate and are negligible for the binary system.

An experimental and modeling study on incipient hydrate-forming conditions for ternary guests of carbon dioxide, nitrogen and sulfur dioxide

In carbon dioxide capture and sequestration (CCS) processes, captured CO2 may encounter conditions of hydrate formation due to the presence of water. For stable, long-term operation of CCS processes, hydrate-phase equilibrium data are essential. Captured CO2 from combustion of fossil fuel may include other impurities such as N2 and SO2. Phase equilibria including a single impurity (N2 or SO2) have been reported by other researchers, but no experimental observations have been obtained for ternary guest systems. In this work, the incipient hydrate-forming temperatures for a binary guest of CO2 and N2 and a ternary guest of CO2, N2 and SO2 were experimentally measured at 2.0–3.5 MPa. An effect of the ratio between guest components and water was observed. The experimental results were compared with calculations using an equation of state based on a hydrogen-bonding nonrandom lattice fluid (NLF-HB) combined with the van der Waals-Platteeuw model. The model predictions were in good agreement with experimental data with an overall average deviation of 2.6%.

Thermodynamic modeling of hydrate formation conditions using different activity coefficient models in the presence of tetrahydrofuran (THF)

The clathrate hydrate is a major problem in gas transportation lines and on the other hand, can be used as a tool for natural gas storage. Moreover, it could be used for gas separation such as monoxide and dioxide carbon from combustion chambers. In this work, a thermodynamic model is developed to calculate gas hydrate formation conditions of single and binary gases in the absence and presence of the thermodynamic promoter such as tetrahydrofuran (THF). A three-phase solid–liquid–gas equilibrium calculation is carried out so that the van der Waals–Platteeuw model is applied for the hydrate phase, SRK EoS for the gas phase and the different activity coefficient models such as local composition and group contribution models for the aqueous solution. The binary interaction parameters for the present activity coefficient models are adjusted through the optimization of the hydrate formation data for the single gases in the presence and absence of THF. Using the local composition and group contribution models, allows one to compare the calculated results with experiment through the percent of Absolute Average Deviation (AAD %)-in pressures and temperatures of the gas hydrate formation conditions so that it is observed the present results are in a good agreement with the experiment.

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.

Numerical Study on the Effect of Thermodynamic Phase Changes on CO2 Leakage

Due to the concerns about the effect of greenhouse gases on the climate, Geologic CO2 storage is a very active area of research. One of the biggest risks associated with such projects is the possibility of leakage. Detrimental environmental consequences present a need to study potential leakage scenarios. Stored CO2 may leak if possible leakage pathways are available and favorable. Pressure and temperature decrease from the leakage source to the surface. Below the CO2 saturation pressure, liquid condensation of the CO2 occurs. At even lower temperatures and pressures, in the presence of water, hydrate formation occurs. CO2-hydrate forms when free water is available and the temperature is below 283 K and pressure is below 647 psi. During leakage, decreases in the temperature and pressure results in a CO2 phase change that affects the leakage flux. The purpose of this study is to estimate the leakage flux for different scenarios taking thermodynamic phase changes into account.A numerical model with coupled mass and energy balances was developed and used to estimate the flux as a function of time. Due to wide temperature and pressure changes over the course of the simulation, an accurate fluid properties model is required to reduce fluid properties related errors. Multi-parameter Span-Wagner equation of state for CO2 is used to achieve this. The numerical model allows for CO2 to exist in gas, liquid and hydrate phases. Hydrate formation was modelled using the van der Waals-Platteeuw model. Heat flux from the surroundings play an important role in effecting a phase change. Example calculations indicate a cyclical nature of the leakage flux under certain conditions. These calculations indicate the importance pressure of the leakage source (aquifer), the amount of water in the pathway (fracture/faults), the geothermal gradient and the surface temperature besides the thickness and the permeability of the fracture.

Mutual effects of paraffin waxes and clathrate hydrates: A multiphase integrated thermodynamic model and experimental measurements

This paper presents an extensive analysis of complex wax and hydrate forming systems employing an integrated wax-hydrate thermodynamic model. The developed model uses integration of the UNIQUAC activity coefficient model, CPA equation of state and van der Waals-Platteeuw model, for the description of waxes, fluids and hydrates, respectively. Our recently published multiphase “Gibbs energy minimization” flash algorithm [1] is extended here to identify waxy solid phase(s) and is shown to be robust in characterizing complex systems where several phases, i.e., solid wax, vapour, liquid hydrocarbon, liquid aqueous, ice and hydrate phases (structure sI and sII) may coexist.The accuracy of model predictions is first validated by calculating the wax amount and composition in water-free systems for which experimental data are available. It is then used to explore the mutual effects of hydrates and waxes starting from a simple binary system of methane + n-heptadecane in the presence of water. The model is then used to analyse four multicomponent mixtures and a recombined light oil.The analysis includes investigations into the impact of hydrate formation on wax phase boundary, amount and composition and vice versa, as well as a variety of secondary important effects including the influence of the amount of light end in the feed and impact of the free aqueous phase on the wax amount and phase boundary.

Phase equilibria, solubility and modeling study of CO2/CH4 + tetra-n-butylammonium bromide aqueous semi-clathrate systems

Interest has grown in tetra-n-butylammonium bromide (TBAB) semi-clathrates due to their formation at lower pressures and higher temperatures than conventional gas hydrates. This study focuses on TBAB semi-clathrates formed with carbon dioxide and methane and is to our knowledge the first study to report and model semi-clathrate former solubility under hydrate–liquid–vapor equilibrium conditions. A thermodynamic model was developed using the Trebble–Bishnoi equation of state to calculate vapor and liquid phase fugacity. Liquid activity was determined using the electrolyte non-random two liquid model (eNRTL). The solid semi-clathrate phase was modeled using a modified van der Waals–Platteeuw model (vdW–P), with parameters re-optimized based on the data obtained in this study. Equilibrium conditions were successfully modeled over the temperature range of 281–294K, pressure range of 377–11,000kPa and TBAB composition range of 5–40wt%. The model functioned well for carbon dioxide with an average absolute relative error (AARE) of 4.7% for pressure prediction and an AARE of 17.5% for solubility. Methane was more difficult to model and yielded AAREs of 21.6% for pressure and 32.5% for solubility. Further understanding of semi-clathrate crystal structure and interactions between methane and TBAB would aid in improving the model.

Thermodynamic model for predicting equilibrium conditions of clathrate hydrates of noble gases + light hydrocarbons: Combination of Van der Waals–Platteeuw model and sPC-SAFT EoS

In this communication, equilibrium conditions of clathrate hydrates containing mixtures of noble gases (Argon, Krypton and Xenon) and light hydrocarbons (C1–C3), which form structure I and II, are modeled. The thermodynamic model is based on the solid solution theory of Van der Waals–Platteeuw combined with the simplified Perturbed-Chain Statistical Association Fluid Theory equation of state (sPC-SAFT EoS). In dispersion term of sPC-SAFT EoS, the temperature dependent binary interaction parameters (kij) are adjusted; taking advantage of the well described (vapor+liquid) phase equilibria. Furthermore, the Kihara potential parameters are optimized based on the P–T data of pure hydrate former. Subsequently, these obtained parameters are used to predict the binary gas hydrate dissociation conditions. The equilibrium conditions of the binary gas hydrates predicted by this model agree well with experimental data (overall AAD P∼2.17).