Semiclathrate Hydrate Formation Research Articles

Study of the Effect of Tetrabutylammonium Halide Aqueous Solutions on the Gas Storage of Methane and Carbon Dioxide

In this study, the effect of tetrabutylammonium halide aqueous solutions on the gas storage of CH4 and CO2 gases were studied with molecular dynamics (MD) simulations. The results show that the surface tension and the gas molecules adsorbed at the interface decreases and increases, respectively, in the presence of TBAX (X: Br, Cl, F) in the aqueous phase compared to pure water at similar gas pressures. Both of these factors may facilitate gas uptake into cages during semi-clathrate hydrate formation. CO2 showed a stronger intermolecular interaction with the water molecules since it was preferentially adsorbed at the interface, leading to a higher surface density as compared to CH4. Moreover, the relative increase in CH4 adsorption on the surface was because of the hydrophobic interactions between the CH4 molecules and the n-alkyl chains of the cation. The counter-ions of TBAXs can affect their surface activity. TBAX salts enhance the tetrahedral ordering of water molecules at the interface compared to the bulk, leading to a potential mechanism for forming semi-clathrate hydrates.

Thermodynamic effects of the interaction of multiple solutes and dodecahedral-cage deformation on the semi-clathrate hydrate formation with CH4-CO2

The accurate prediction of thermodynamic equilibrium hydrate formation pressure (Peq) is crucial to the industrial application of hydrate-based gas separation. This study evaluated Peq of CH4-CO2 gas mixtures with different TBAB solutions at different temperatures. Unlike previously reported models, the proposed model accounted for the effects of interaction of multiple solutes and the deformation of dodecahedral (D)-cages on Peq, thereby minimizing deviations in predictions. The effects of the interaction of multiple solutes on Peq can be attributed to gas dissolution and the presence of electrolytes. For accurate prediction, the proposed model incorporated the aforementioned effects based on the electrolyte-cubic plus association equation of state and the parameters for interaction among guest molecules in cages Furthermore, the proposed model can quantitatively describe the effects of gas dissolution, the presence of electrolytes and deformation of D-cages on the Peq values for corresponding systems.

Molecular dynamics simulations of interfacial structure, dynamics, and interfacial tension of tetrabutylammonium bromide aqueous solution in the presence of methane and carbon dioxide.

The interfacial behavior of tetrabutylammonium bromide (TBAB) aqueous solutions in the absence of gas and the presence of methane and carbon dioxide gases is studied by molecular dynamics simulations. The aqueous TBAB phase, at concentrations similar to the solid semiclathrate hydrate (1:38 molratio), has a smaller interfacial tension and an increase in the gas molecules adsorbed at the interface compared to that in pure water. Both these factors may contribute to facilitating the uptake of the gases into the solid phase during the process of semiclathrate hydrate formation. At similar gas pressures, CO2 is adsorbed preferentially compared to CH4, giving it a higher surface density, due to the stronger intermolecular interactions of CO2 molecules of the solution at the interface. The increase in relative adsorption of CH4 at the solution surface compared to that in pure water surface is due to the hydrophobic interactions between the n-alkyl chains of the TBA+ cation and methane gas.

Effects of Tween 80 on clathrate and semiclathrate CO2 hydrate formation kinetics for carbon capture from CO2-rich gas mixtures

In this study, Tween 80 was chosen as a kinetic promoter to study the effect of non-ionic surfactant on CO2 hydrate formation kinetics. The experiments were carried out in a thermostatic reactor using CO2-rich gas mixtures with Tween 80 (0–3000 ppm) in both clathrate hydrates and tetra-n-butyl ammonium bromide (TBAB) semiclathrate hydrates. Analysis of variance (ANOVA) was used to analyze the difference among experimental results, and a decision box was proposed to evaluate the performance of systems studied. The apparent improvement in the induction time, gas uptake yield, and gas separation performance were observed in 1000-ppm or 2000-ppm Tween 80 in semiclathrate hydrates. Increased pressure further improved the kinetic promotion effect of Tween 80. However, a higher concentration of 3000-ppm Tween 80 was found to result in an inhibition effect on CO2 uptake yield in semiclathrate hydrates, although the induction time remained short. Compared with common anionic and cationic surfactants, 2000-ppm Tween 80 showed the best CO2 separation performance from gas mixtures in semiclathrate hydrates. No inhibition effect was observed in clathrate hydrates with studied concentrations of Tween 80.

An electrical resistivity-based method for measuring semi-clathrate hydrate formation kinetics: Application for cold storage and transport

Tetra-n-butylammonium bromide (TBAB) semi-clathrate hydrate has a large latent heat and suitable phase transition temperatures to be used as a phase change material for cold energy storage and transport. The mass fraction of hydrates in the semi-clathrate hydrate slurry is a key parameter determining the cold carrying capacity and flow properties. We developed a new experimental methodology based on electrical resistivity to quantify the hydrate fraction in semi-clathrate hydrate slurry during hydrate formation. Relationship between electrical resistivity and hydrate fraction of semi-clathrate hydrate slurry was established based on Bruggeman’s effective-medium approximation. After validation, this method was employed to quantitatively investigate the effect of temperature on TBAB hydrate formation from 20 wt% TBAB/water system. As the temperature was lowered from 278.2 K to 274.2 K, the induction time was reduced by 97.8% and the hydrate growth rate was enhanced by over 2.5 times. At 274.2 K and 276.2 K, type A hydrates were preferentially formed followed by a structural transition to type B. At 278.2 K, only type A hydrates were observed. Furthermore, given an appropriate concentration, amino acid L-tryptophan was identified to be a good kinetic promoter for TBAB hydrate formation. The presence of 500 ppm L-tryptophan reduced the induction time by 60% and boost the hydrate growth rate by more than 32%. The electrical resistivity-based method developed in this work has shown simplicity, low cost, high accuracy, and repeatability. It would enable precise investigation of semi-clathrate hydrate kinetics in the future for cold energy applications and beyond.

The role of Tween 80 and SDS in the kinetics of semi-clathrate hydrates formation for carbon dioxide capture from flue gas

ABSTRACT The present study focuses on integrated experimental evaluation of a concentration effect in nonionic and anionic surfactants on semi-clathrate hydrates formation during the capture low-pressure carbon dioxide from the flue gas (N2 (83.13 mol.%)/CO2 (16.87 mol.%)). Semi-clathrate hydrates of tetra n-butylammonium bromide (TBAB) are favorable materials with phase changes due to their moderate hydrate formation conditions. The kinetics of CO2-N2-TBAB semi-clathrate hydrate formation was studied in the presence and absence of Tween-80 as a nonionic surfactant and sodium dodecyl sulfate (SDS) as an anionic one. The experiments were performed in a stirred batch reactor at a constant temperature of 273.55 K and an initial pressure of 2.1 MPa. 5.0 wt.% TBAB’s aqueous solutions were tested both in the absence of surfactants and in presence of Tween-80 and SDS at different concentrations (500, 1500, 3000 ppm). The separation factor and recovery for CO2 at low pressure were in situ controlled depending on the surfactant concentration. Adding 1500 ppm of Tween-80 provided optimal conditions for the СО2/N2 separation process; the separation factor was 9.5, the СО2 recovery was 53.1%.

Response to Comments on Effect of Salts on TBAB Semi Clathrate Hydrate Formation: Application to Produced Water Desalination

The focus of our original paper was mainly on the thermodynamic equilibrium of semiclathrate hydrate formation in the presence of salts that are common in produced water. We concluded that “TBAB hydrate formation is highly favorable in comparison with ice, suggesting the thermodynamic effectiveness of using TBAB as a hydrate former for hydrate based desalination”. Lee and Kang claim that the paper has “some incorrect and missing points, which led to the wrong analysis”. We disagree with the comments, because they are based on a misinterpretation of our objectives and analysis. However, we do agree that we should have provided more information on our analysis in the original paper. In our response, we focused on addressing these comments in detail.

Kinetic study of semiclathrate hydrates formed with CO2 in the presence of tetra-n-butyl ammonium bromide and tetra-n-butyl phosphonium bromide

The kinetics of semiclathrate hydrates formation with CO2 in the presence of tetra-n-butyl ammonium bromide (TBAB), tetra-n-butyl phosphonium bromide (TBPB), and TBAB + TBPB were investigated. The experiments were conducted at the stoichiometric concentration of TBAB hydrate (2.57 mol%) and three subcoolings (ΔT = 6 K, 9 K, and 12 K) with the initial pressure fixed at 2.8 MPa. It was found that adding TBPB into the TBAB solution can promote hydrate nucleation, and this promotion effect at a lower subcooling (ΔT = 6 K) was stronger compared to that at higher subcoolings (ΔT = 9 K and 12 K). The gas consumption obtained in TBAB, TBPB, and TBAB + TBPB solutions decreased with the increase of subcooling, despite the increase of the rate of hydrate growth. At a given subcooling, gas consumption (CO2 uptake) in TBAB + TBPB solutions was greater than that in TBAB and TBPB solutions, indicating that hydrate formation kinetics and the CO2 storage capacity were improved in the TBAB + TBPB solution. The largest gas consumption was obtained at ΔT = 6 K in the TBAB + TBPB solution, which was 28.7% and 17.2% larger than those obtained in TBAB and TBPB solutions, respectively. Therefore, a mixture of TBAB + TBPB is a promising option to improve the kinetics of semiclathrate hydrate formation with CO2.

The roles TBAF and SDS on the kinetics of methane hydrate formation as a cold storage material

Semiclathrate hydrate formation from low mass fractions of TBAF and methane is introduced as a potential for storing the cold energy, in this research. The influence of SDS on methane + TBAF semiclathrate hydrate is studied. Amount of gas encaged in hydrate cavities, storage capacity and initial apparent rate constant (kapp) of TBAF-methane semiclathrate hydrate formation is evaluated in presence of TBAF with mass fractions of 2 and 4 wt%, SDS with a concentration of 400 ppm at feed pressures of 4 and 8 MPa. The experiments were carried out in isothermal condition of 278.15 K in a 169 cm3 stirred batch reactor. Results showed, compared with pure water, the addition of low weight fractions of TBAF enhances the amount of gas encaged in hydrate cavities and storage capacity and reduces the kapp of gas hydrate formation. Simultaneous utilization of SDS and TBAF presented a negative effect on the kinetics of hydrate formation, compared with TBAF solution and SDS solution. The influence of feed pressure of the reactor on the kinetics of methane + TBAF semiclathrate hydrate with and without SDS is studied. Increasing the feed pressure of the reactor from 6 to 8 MPa, noticeably, promoted the kinetics of hydrate formation.

Thermodynamic modeling and experimental measurement of semi-clathrate hydrate phase equilibria for CH4 in the presence of cyclohexane (CH) and tetra-n-butyl ammonium bromide (TBAB) mixture

In the current study, the effect of tetra-n-butyl ammonium bromide (TBAB) and cyclohexane mixture on CH4 semi-clathrate hydrate formation was studied. Semi-clathrate dissociation conditions for CH4 + TBAB + cyclohexane + water were investigated at different concentrations of TBAB (0.05, 0.10, and 0.15) mass fraction in the presence of cyclohexane at the pressure and temperature ranges of 1–8 MPa and 275.1–295 K, respectively. In addition, a thermodynamic model was suggested to predict the phase equilibria of our system, which is divided into four phases, where the van der Waals–Platteeuw Solid Solution Theory has been used to predict the hydrate phase. For gas phase, The SRK equation of state was applied. For oil phase, the cyclohexane activity coefficient in the organic phase was calculated by the non-random two-liquid model (NRTL). Finally, to determine the activity coefficient of the electrolyte species in the aqueous phase, the semi-empirical electrolyte NRTL (eNRTL) activity model was used. The results showed that the proposed model has an acceptable agreement with the experimental semi-clathrate hydrate dissociation data with an approximately average absolute relative deviation of 5.4%.

Phase equilibrium data for semiclathrate hydrates formed with tetra-n-butylammonium (bromide or chloride) and tetra-n-butylphosphonium (bromide or chloride) under hydrogen + carbon dioxide pressure

Semiclathrate hydrates are host–guest materials that can be used for CO2 capture due to their unique gas selectivity. CO2 capture from H2 + CO2 mixed gas is possible by semiclathrate hydrates formed by tetra-n-butylammonium (TBA) and tetra-n-butylphosphonium (TBP) salts. TBA bromide (TBAB), TBA chloride (TBAC), TBP bromide (TBPB) and TBP chloride (TBPC) are widely available ionic substances for semiclathrate hydrate formation. In order to understand their gas capture properties, phase equilibrium data of these materials are necessary. Here we report experimental three phase (gas–hydrate–aqueous phase) equilibrium data measured in (TBAB, TBAC, TBPB or TBPC) + H2 + CO2 + H2O systems. The comparison with the literature data suggested that H2 can be incorporated in the TBAB and TBAC hydrates together with CO2, but TBPB and TBPC hydrates reject H2. The hydrate phases were identified by single crystal X-ray diffraction analyses. The TBAB, TBPB and TBPC form the same or similar hydrate phases, i.e., orthorhombic and hexagonal phases. The TBAC formed the tetragonal hydrate phase. The present results suggest that different CO2 capture properties are obtained by these semiclathrate hydrates.

Investigation of the kinetics of TBAB + carbon dioxide semiclathrate hydrate in presence of tween 80 as a cold storage material

Because of large cold storage capacity and suitable freezing temperature of hydrate slurries, these materials could be used as a medium to store the cold energy in air conditioning systems. Semiclathrate hydrates of tetra n-butylammonium bromide (TBAB) are favorable phase change materials (PCMs), due to their moderate hydrate formation conditions. The kinetics of carbon dioxide - TBAB semiclathrate hydrate formation in presence and absence of tween 80 as a non-anionic surfactant is investigated in this research. The experiments were performed in a 169 cm3 stirred batch reactor at initial pressure of 3.2 MPa and isothermal condition of 276.15 K. Aqueous solutions of TBAB with concentrations of 0–15 wt% in presence and absence of tween 80 with concentrations of 500 and 1500 ppm are tested. The results revealed that utilization of TBAB with concentrations of 5–15 wt%, inhibits the kinetics of formed hydrates. By increasing the concentration of TBAB the amount and rate of gas uptake and storage capacity (SC) of formed hydrates decreases. Tween 80 with a concentration of 500 ppm presented a slight positive effect on the kinetics of hydrate formation in presence and absence of TBAB. While 1500 ppm of this additive inhibited the kinetics of formed hydrates.

Modeling Phase Behavior of Semi-Clathrate Hydrates of CO2, CH4, and N2 in Aqueous Solution of Tetra-n-butyl Ammonium Fluoride

Abstract Semi-clathrate hydrates are members of the class of clathrate compounds. In comparison with clathrate hydrates, where the networks are formed only by H2O molecules, the networks of semi-clathrate hydrates are formed by mixtures of H2O and quaternary ammonium salts (QASs). The addition of QASs to the solution enables to improve the formation of semi-clathrate hydrates at much milder conditions comparing to clathrate hydrates. In this work, we study the phase equilibria of semi-clathrate hydrates of CH4, CO2, and N2 gas in an aqueous solution of tetra-n-butyl ammonium fluoride (TBAF). An extension of the Chen–Guo model is proposed as a thermodynamic model. The Peng–Robinson equation of state (PREOS) was applied to calculate the fugacity of the gas phase and in order to determine the water activity in the presence of TBAF, a correlation between the system temperature, the TBAF mass fraction, and the nature of the guest molecules has been used. These equations were solved simultaneously and through optimizing tuning parameters via the Nelder–Mead simplex algorithm. The results are compared to experimental data and good agreement is observed.

Kinetics of (TBAF\u2009+\u2009CO2) semi-clathrate hydrate formation in the presence and absence of SDS

In this communication, the impacts of adding SDS (sodium dodecyl sulfate), TBAF (tetra-n-butylammonium fluoride) and the mixture of SDS + TBAF on the main kinetic parameters of CO2 hydrate formation (induction time, the quantity and rate of gas uptake, and storage capacity) were investigated. The tests were performed under stirring conditions at T = 5 °C and P = 3.8 MPa in a 169 cm3 batch reactor. The results show that adding SDS with a concentration of 400 ppm, TBAF with a concentration of 1–5 wt%, and the mixture of SDS + TBAF, would increase the storage capacity of CO2 hydrate and the quantity of gas uptake, and decrease the induction time of hydrate formation process. The addition of 5 wt% of TBAF and 400 ppm of SDS would increase the CO2 hydrate storage capacity by 86.1% and 81.6%, respectively, compared to pure water. Investigation of the impact of SDS, TBAF and their mixture on the rate of gas uptake indicates that the mixture of SDS + TBAF does not have a significant effect on the rate of gas uptake during hydrate formation process.

Solubility of Nitrogen Gas in Aqueous Solution of Tetra-n-Butylammonium Bromide

Semiclathrate hydrates are water-based host-guest compounds formed from aqueous solutions of ionic guest substances. These materials can greatly moderate formation pressures and temperatures from canonical gas hydrates. This is a significant advantage for industrial applications such as gas separation and storage. $$\hbox {N}_{2}$$ gas is a major component contained in various flue gases and is usually mixed with $$\hbox {CO}_{2}$$ . Semiclathrate hydrates can separate these gases under moderate thermodynamic conditions. Tetra-n-butylammonium bromide (TBAB) is a widely used ionic guest substance. To develop the application technologies and their theoretical models, solubility data of $$\hbox {N}_{2}$$ gas in TBAB aqueous solutions are required. In this study, we report $$\hbox {N}_{2}$$ gas solubility measured by an absolute gravimetric method for the semiclathrate hydrate formation system of $$\hbox {TBAB} + \hbox {H}_{2}\hbox {O} + \hbox {N}_{2}$$ . The measurement pressures, temperatures and TBAB mass fractions were 3 MPa, 5 MPa and 7 MPa, 292.15 K, 302.15 K and 307.15 K, and 0 (pure water), 0.10, 0.20, 0.32 and 0.40, respectively. The uncertainties were 0.056 MPa, 0.44 K and 0.00012 in mole fraction. Although the technical difficulty lays on measurements of small $$\hbox {N}_{2}$$ gas solubility by the absolute gravimetric method, our data implied the unique gas dissolution property of aqueous TBAB solution depending on the TBAB concentration. The aqueous TBAB solutions with mass fractions of 0.10 and 0.20 had similar $$\hbox {N}_{2}$$ gas solubility as that in pure water. With higher mass fractions, 0.32 and 0.40, the $$\hbox {N}_{2}$$ gas solubility slightly increased from that in pure water, which implies the salting-in effect of TBAB.

Kinetic study of hydrate formation for argon + TBAB + SDS aqueous solution system

In this communication, the effects of initial temperature and pressure, aqueous TBAB (tetra-n-butylammonium bromide) solution concentration, and sodium dodecyl benzene sulfonate (SDS) concentration on the kinetic behaviour of semi-clathrate hydrates of Ar+aqueous TBAB solutions were investigated. Kinetic experiments were performed in a high pressure equilibrium cell with an inner volume of approximately 40cm3 at initial temperatures of (281, 285 and 287.5)K and initial pressures of (6.1, 8.1 and 10.1)MPa. The results indicate that induction time decreases significantly with an increase in the initial pressure. However, the kinetic constant, and consumption of Ar during the semi-clathrate hydrate formation, increases. The same trends were detected with a decrease in the initial temperature, at a constant pressure. In addition, with an increase in the TBAB concentration, from 0.1 to 0.3mass fraction TBAB, the rate of semi-clathrate hydrate nucleation and consumption of Ar, increases during the hydrate formation, while the induction time decreases, significantly. The results therefore show a positive kinetic effect of TBAB on Ar hydrates which indicates that TBAB is a reliable promoter to increase the rate of argon hydrate formation. The results for the addition of SDS (at concentrations of 100, 200ppm) at initial temperatures of 285K and initial pressures of (6.1 and 8.1)MPa indicate that SDS increases the induction time of the semi-clathrate hydrate formation for the system of Ar+0.1mass fraction TBAB+0.9mass fraction water, but there is no systematic trend between induction times and the SDS concentrations for this system.

Investigation on methane recovery from low-concentration coal mine gas by tetra-n-butyl ammonium chloride semiclathrate hydrate formation

This work presents an investigation of using tetra-n-butyl ammonium chloride (TBAC) semiclathrate hydrate to separate CH4 from a low-concentration coal mine gas containing 30mol% CH4, 60mol% N2, and 10mol% O2. Phase equilibrium data of TBAC semiclathrate hydrate formed in the presence of low-concentration coal mine gas with TBAC concentration ranging from 0.49mol% to 3.3mol% were measured and reported. A high pressure micro-differential scanning calorimeter (HP µ-DSC) was employed to characterize the phase behaviors of TBAC semiclathrate hydrate formed in the presence of coal mine gas with TBAC concentration fixed at 3.3mol% (the stoichiometric concentration of TBAC semiclathrate). It was found that pure TBAC semiclathrate hydrate coexists with the TBAC-coal mine gas mixed hydrate in the pressure range of (1.4–6.2MPa). In addition, kinetic experiments were performed to elucidate the effects of TBAC concentration, subcooling, and sodium dodecyl sulfate (SDS) concentration on CH4 separation efficiency and an optimum experimental condition for semiclathrate-based CH4 recovery was screened. The highest CH4 recovery and separation factor were obtained at the conditions of 0.49mol% TBAC, △T=8K, and 900ppm SDS. It was found that CH4 recovery obtained at 0.49mol% TBAC is comparable with that obtained at 0.29mol% TBAB, whereas CH4 concentration of the gas mixture released from the TBAC hydrate (49.6mol%) is increased substantially comparing to that obtained at 0.29mol% TBAB (42.5mol%).

Gas-containing semiclathrate hydrate formation by tetra-n-butylammonium carboxylates: Acrylate and butyrate

Semiclathrate hydrates are water-based host-guest materials that consist of water and ionic guest substances such as quaternary ammonium salts. Widely-used tetra-n-butylammonium (TBA) salts are designed for gas selectivity and capacity with respect to the industrial application of these materials. This study reported on the formation of semiclathrate hydrates of TBA carboxylates with guest gas characterized by phase equilibrium measurements and single crystal X-ray diffraction. Specifically, TBA acrylate and TBA butyrate are used for ionic guest substances, and this may induce a tetragonal P42/mmm semiclathrate hydrate structure. In the four systems of (TBA acrylate or TBA butyrate) + (CH4 or CO2) + H2O, the measured three (gas–hydrate–aqueous) phase equilibrium data exhibited better promotion effects due to the TBA acrylate and TBA butyrate when compared with that of the widely-used TBA bromide. The slopes on pressure–temperature plane suggest differences in the incorporation of CH4 and CO2 in these hydrates. Characterization of the hydrate phases by X-ray diffraction analyses supports this mechanism. However, it is necessary to further understand the complicated gas incorporation in semiclathrate hydrate structures that are handled by ionic guest substances and the guest gas itself.

Semiclathrate hydrate process for pre-combustion capture of CO2 at near ambient temperatures

CO2 capture has become an important part in building a sustainable energy system featuring the clean use of fossil fuels with low carbon footprint. Hydrate-based gas separation (HBGS) is one of the potential technologies to capture carbon dioxide from pre-combustion (fuel gas) stream. Promoters are often employed to moderate the formation conditions of hydrates. Tetra-n-butylammonium fluoride (TBAF) exhibits great thermodynamic promotion on hydrate formation. In this study the kinetic performance of the formation process of CO2-H2-TBAF semiclathrate hydrate was evaluated under different experimental pressures (6MPa, 4MPa and 2MPa) and temperatures (298K, 292K and 286K), with the stoichiometric TBAF concentration (3.38mol%). Gas uptake measurement and visual observations showed that at a given pressure, the total gas uptake decreased with the decrease of experimental temperature due to high mass transfer resistance caused by rapid growth of TBAF hydrate. The highest gas uptake was achieved by experiments conducted at 6.0MPa and 298.0K. It was the highest among semiclathrate promoters with stoichiometric concentration, but lower compared with THF. The major advantage of the use of TBAF is that the HBGS process can be operated at near ambient temperatures compared to other promoters. The CO2 composition in the hydrate phase was between 65.2 and 93.1mol%, highly dependent on the experimental conditions. Variance analysis was employed to evaluate the impact of pressure and temperature on gas uptake. Gas solubility measurements were conducted to provide further insights into the kinetic performance of CO2-H2-TBAF semiclathrate hydrate formation.

Separation of methane-ethylene via forming semi-clathrate hydrates with TBAB

The formation conditions of CH4-C2H4 hydrate in water and 10 wt% tetra-n-butyl ammonium bromide (TBAB) solution were measured in this work. On this basis, the equilibrium separation of CH4-C2H4 via TBAB semi-clathrate hydrate formation was conducted at constant temperature and pressure. The results show that the influence of TBAB on the formation of CH4-C2H4 hydrate changes with temperature. At low temperature, TBAB forms semi-clathrate hydrate and acts as a promoter for CH4-C2H4 hydrate. At high temperature, TBAB exists as a salt compound and behaves as an inhibitor for CH4-C2H4 hydrate. CH4-C2H4 can be efficiently separated via TBAB semi-clathrate hydrate formation under proper temperature and pressure. The results indicate that C2H4 can not be encased in the dodecahedral cages of TBAB hydrate. Therefore, the concentration of C2H4 in hydrate could be as low as 0.55 mol% and the recovery of C2H4 could reach 99.85% in equilibrium gas.