Semiclathrate Hydrates Research Articles

Thermodynamic model of phase equilibria of tetrabutyl ammonium halide (fluoride, chloride, or bromide) plus methane or carbon dioxide semiclathrate hydrates

In this work, based on the van der Waals–Platteeuw (vdW–P) theory, a thermodynamic approach is proposed to determine the phase equilibria of semiclathrate hydrates formed with tetrabutyl ammonium halide (fluoride, chloride, or bromide) and guest gas (CH4 or CO2). The Peng–Robinson equation of state (PR-EoS) and electrolyte-Non-Random Two-Liquid (e-NRTL) activity model are employed to obtain the fugacity of gaseous hydrate formers and activity coefficients of species in the aqueous phase, respectively. In addition, two modifications for evaluations of vapor pressure of water in the empty hydrate lattice and Langmuir constants relating to the salt concentrations in aqueous solution and temperature are applied. It is shown that the model results are in acceptable agreement with the experimental data on phase equilibria for studied systems over wide temperature, pressure, and salt concentration ranging from 280.1 to 304.8K, from 0.172 to 9.932MPa, and from 0.02 to 0.35, respectively.

Impact of experimental pressure and temperature on semiclathrate hydrate formation for pre-combustion capture of CO2 using tetra-n-butyl ammonium nitrate

TBANO3 (tetra-n-butyl ammonium nitrate) is a promising liquid phase promoter for capturing CO2 via HBGS (hydrate based gas separation) technology. In this study, the impact of experimental pressure and temperature on formation of mixed CO2–H2-TBANO3 semiclathrate hydrate for the optimum 1.0 mol% TBANO3 reported by Babu et al. [1] was investigated. Experimental pressures of 3.0, 4.5 and 6.0 MPa and temperatures of 274.2, 276.2 and 278.2 K were employed. Irrespective of the experimental pressure, shorter induction time was observed for experiments conducted at 274.2 K when compared to the experiments at other temperatures. At a given pressure, the total gas uptake increased with increase in experimental temperature. Similarly at a given temperature, the total gas uptake increases with an increase in pressure. Higher rate of hydrate formation was observed at experimental pressure of 6.0 MPa than at 3.0 and 4.5 MPa irrespective of the experimental temperature. The CO2 composition in hydrate was between 87.5 and 93.2 mol%. Finally, the gas consumption for 1.0 mol% TBANO3 as promoter was much higher than other promoters of quaternary salts like tetra-n-butyl ammonium bromide and tetra-n-butyl ammonium fluoride at comparable concentration and driving force.

Experimental Measurement and Thermodynamic Modeling of Hydrate Dissociation Conditions for the Argon + TBAB + Water System

Gas hydrate (clathrate hydrate) dissociation data at low to moderate pressures are necessary for practical applications, e.g., for gas separation. However, it is often known or recognized that the separation conditions encountered exist at high pressures and low temperatures. One solution to this problem is the application of the quaternary ammonium salts (QAS) semiclathrate hydrates such as tetra-n-butyl ammonium bromide (TBAB) which can moderate the hydrate dissociation conditions. The addition of TBAB to the solution enables a shift in the pressure-temperature diagrams to lower pressures and higher temperatures. In this study, the isochoric pressure search method1,4,13,28,34−37 was used to measure hydrate dissociation conditions for the argon + TBAB + water system. The measurement of hydrate dissociation conditions were performed at various TBAB concentrations, namely, (0, 0.05, 0.10, 0.20, and 0.30) mass fraction. The experiments were performed in the temperature range of (274 to 293.6) K and pressures ranging from (0.34 to 12.32) MPa. Results indicate that TBAB has a significant promotion effect on argon hydrate formation. In addition, increasing the TBAB concentration increases its promotion effect. A thermodynamic model was developed to predict the hydrate dissociation conditions for the system of argon + TBAB + water. The results show good agreement between the experimental measurements and model results.

Experimental Measurements and Modeling of the Dissociation Conditions of Tetrabutylammonium Chloride Semiclathrate Hydrates in the Presence of Hydrogen

Dissociation conditions of hydrogen semiclathrate hydrates with tetrabutylammonium chloride (TBAC) are measured using a differential scanning calorimeter at the TBAC weight fraction of 0.10, 0.20, 0.35, and 0.50 in the pressure range up to 15.5 MPa. The hydrogen storage capacity of TBAC semiclathrate hydrate is estimated with measured equilibrium data, dissociation enthalpies, and the Clapeyron equation. The amount of hydrogen stored in the semiclathrate hydrate is found to be 0.11 wt % at 15.5 MPa. The model proposed by Paricaud [J. Phys. Chem. B 2011, 115, 288–299] is applied to predict the dissociation condition of the H2 semiclathrate hydrate with TBAC. The parameters in the model have been determined by describing the liquid–vapor–hydrate three phase lines measured in this work and from the literature. The hydrogen storage capacity predicted by the model is in excellent agreement with the experimental value.

Phase Equilibrium Conditions for the Double Semiclathrate Hydrate Formed with Tetraamylammonium Chloride Plus CH4, CO2, or N2

Phase equilibrium conditions of the CH4, CO2, or N2 semiclathrate hydrates formed with tetraamylammonium chloride (TAAC: C20H44NCl) aqueous solution at 0.328 mass fraction, corresponding to the stoichiometric composition of TAAC·38H2O, were experimentally measured. The experimental data were obtained in the temperature range of (279.9 to 292.8) K and pressure range of (2.11 to 16.40) MPa by employing an isochoric pressure-search method. The results showed that double semiclathrate hydrates of TAAC + CH4, TAAC + CO2, and TAAC + N2 all had an obvious advantage in thermal stability compared to the corresponding pure CH4, CO2, and N2 hydrates. In addition, some comparisons were made between our data and experimental equilibrium data from the open literature for semiclathrate hydrates formed with various semiclathrate hydrate formers.

Phase equilibria of semiclathrate hydrates for methane + tetra n-butylammonium chloride (TBAC), carbon dioxide + TBAC, and nitrogen + TBAC aqueous solution systems

The equilibria of semiclathrate hydrates for the systems of tetra-n-butylammonium chloride (TBAC)+water+gas (methane, carbon dioxide, or nitrogen) and TBAC + water were measured. The experiments were performed in the temperature range of 277.1–293.2K and the pressure range of 1.02–9.83MPa at 0.05, 0.15, and 0.22mass fraction of TBAC. An isochoric pressure-search method was employed to generate the phase equilibrium data. The experimental results show that the presence of TBAC moderates the hydrate formation (dissociation) conditions remarkably (in the concentration ranges studied in this work). Moreover, pressure reduction is dependent on TBAC concentration. By increasing the concentration of TBAC from 0.05mass fraction to 0.22mass fraction, its promotion effect increases and the pressure–temperature curves of the double gas+TBAC semiclathrate shift to the stabilized regions. The isobaric dissociation temperature of TBAC+methane semiclathrates is close to that of TBAC+carbon dioxide semiclathrates.

Modeling the Dissociation Conditions of Carbon Dioxide + TBAB, TBAC, TBAF, and TBPB Semiclathrate Hydrates

The thermodynamic approach developed by Paricaud [J. Phys. Chem. B 2011, 115, 288–299] is applied to predict the dissociation conditions of semiclathrate hydrates made with tetra-n-butyl ammonium bromide (TBAB), tetra-n-butyl ammonium chloride (TBAC), tetra-n-butyl ammonium fluoride (TBAF), and tetra-n-butyl phosphonium bromide (TBPB). The SAFT-VRE equation of state is used to describe the properties of fluid phases, and a good description of osmotic and mean activity coefficients of electrolyte solution is obtained. The temperature–composition diagrams of water + tetra-n-alkylammonium/alkylphosphonium salt binary systems are well described by the model. Group contribution methods are proposed to predict the fusion enthalpies and the congruent melting points of semiclathrate hydrates. The van der Waals and Platteeuw theory is combined with the model to calculate the dissociation conditions of carbon dioxide semiclathrate hydrates. The liquid–vapor–hydrate three phase lines can be accurately described over...

2-2-4 ガス分離プロセス構築に向けたセミクラスレートハイドレートのガス吸着および拡散特性(Session 2-2 ハイドレート 1)

2-2-4 ガス分離プロセス構築に向けたセミクラスレートハイドレートのガス吸着および拡散特性(Session 2-2 ハイドレート 1)

2-2-2 セミクラスレートハイドレートの相平衡に与える添加物の影響(Session 2-2 ハイドレート 1)

2-2-2 セミクラスレートハイドレートの相平衡に与える添加物の影響(Session 2-2 ハイドレート 1)

Phase Equilibrium Data of the Double Tetrabutylammonium Chloride Plus Carbon Dioxide or Nitrogen Semiclathrate Hydrate

In this paper, phase equilibrium data of the double tetrabutylammonium chloride (TBACl: C16H36ClN) semiclathrate hydrate with a guest gas (CO2 or N2) at four different TBACl concentrations (0.06, 0.15, 0.34, and 0.44 mass fraction) were experimentally measured by employing an isochoric pressure-search method in the temperature range of (282.9 to 293.2) K and at pressures up to 13.57 MPa, respectively. The results demonstrated that double TBACl + CO2 (or N2) semiclathrate hydrates had an obvious advantage in thermal stability compared to pure CO2 (or N2) hydrates. And the strongest stabilization effect was observed with the application of TBACl at 0.34 mass fraction, corresponding to TBACl·30H2O. In addition, the results were compared with the corresponding data reported in open literature. The comparisons showed that some literature data seemed to be not reliable.

Thermodynamic properties of semiclathrate hydrates formed from the TBAB + TBPB + water and CO2 + TBAB + TBPB + water systems

Semiclathrate hydrates formed from binary systems of tetra-n-butylammonium bromide (TBAB)+water and tetra-n-butylphosphonium bromide (TBPB)+water have been investigated for their promising application in the refrigeration system. In the present work, semiclathrate hydrates in the ternary system of TBAB+TBPB+water were studied for the first time, in the presence and absence of CO2 pressure. Using DSC technique, the dissociation temperatures of semiclathrate hydrates were determined at the mass fraction of salt mixture ranges from 0.05 to 0.60 with variable composition from pure TBAB to pure TBPB. At any salt concentration tested, the dissociation temperature of semiclathrate hydrates increased regularly with TBAB composition increase. Applying CO2 pressure in the TBAB+TBPB+water system resulted in further increase of dissociation temperature due to the gas enclathration in the mixed hydrate structure. The phase transition enthalpy of semiclathrate hydrates were investigated at wsalts=0.40 and variable TBPB compositions, without CO2 and with pCO2=1.0MPa. It was found that the dissociation enthalpies of CO2-free and CO2-containing semiclathrate hydrates are almost independent of the TBPB salt composition. From our current results, TBAB+TBPB+CO2 hydrates appear as valuable phase change materials to be used as hydrate slurries for cold storage and transportation in applications requiring variable working temperatures.

Phase equilibrium conditions of semi-calthrate hydrates of (tetra-n-butyl ammonium chloride + carbon dioxide)

In the present work, hydrate equilibrium conditions for (tetra-n-butyl ammonium chloride (TBAC)+carbon dioxide+water) mixtures were investigated. Tetra-n-butyl ammonium chloride was reported to form a semi-clathrate hydrate. The experiments were carried out within the TBAC mass fraction range of (0.05 to 0.3). The experimental results showed that the presence of TBAC decreased the formation pressure of carbon dioxide double hydrate within the experimental temperature range. Moreover, pressure reduction was dependent on the TBAC concentration.

Phase equilibrium of semiclathrate hydrates of methane in aqueous solutions of tetra-n-butyl ammonium bromide (TBAB) and TBAB–NaCl

Phase equilibria of semiclathrate hydrates are important for their successful engineering applications due to more favorable process conditions compared to classical gas hydrate systems. Though sufficient information on the phase equilibria of semiclathrate hydrates of methane (CH4) in tetra-n-butyl ammonium bromide (TBAB) seems to be available, there are pronounced disagreements on the phase equilibrium data, particularly for 0.05 and 0.20 mass fraction (w) of TBAB. In this work, experimental studies are carried out to generate the equilibrium pressure (P) and temperature (T) for hydrates and semiclathrate hydrates of CH4 in an aqueous solution containing wTBAB=0.05 and 0.20 at P and T range of 1.02–13.73MPa and 281.63–294.54K, respectively. This study tries to clarify the discrepancy of published data in the literature and their reliability. Additionally, we present interesting insights into the phase behavior of semiclathrate hydrate of methane in TBAB based on the formation and dissociation curves observed in the experiments. It is observed that there existed two equilibrium points during the dissociation of semiclathrate hydrates of methane in TBAB; one closely corresponds to the pure methane hydrate phase stability curve and the second one to the semiclathrate hydrate system of methane. In addition phase equilibrium data is generated for the quaternary system of CH4+TBAB+H2O+NaCl for wNaCl=0.03 and 0.10 and wTBAB=0.05 and 0.20 in an aqueous solution at a P and T range of 1.65–20.71MPa and 281.19–296.38K, respectively. This is not yet available in the open literature. It is observed that NaCl inhibits the semiclathrate hydrate formation of CH4 in TBAB for wNaCl=0.03 and 0.10 in wTBAB=0.20 in the system. However, a promotion effect is observed for wNaCl=0.03 in wTBAB=0.05. This study calls for more detailed investigations on the effect of salts on semiclathrate hydrate systems, which may find potential use in engineering applications.

Equilibrium Conditions for Semiclathrate Hydrates Formed with CO2, N2, or CH4 in the Presence of Tri-n-butylphosphine Oxide

We measured the thermodynamic stability conditions for the N2, CO2, or CH4 semiclathrate hydrate formed from the aqueous solution of tri-n-butylphosphine oxide (TBPO) at 26 wt %, corresponding to the stoichiometric composition for TBPO·34.5H2O. The measurements were performed in the temperature range 283.71–300.34 K and pressure range 0.35–19.43 MPa with the use of an isochoric equilibrium step-heating pressure-search method. The results showed that the presence of TBPO made these semiclathrate hydrates much more stable than the corresponding pure N2, CO2, and CH4 hydrates. At a given temperature, the semiclathrate hydrate of 26 wt % TBPO solution + CH4 was more stable than that of 26 wt % TBPO solution + CO2, which in turn was more stable than that of 26 wt % TBPO solution + N2. We analyzed the phase equilibrium data using the Clausius–Clapeyron equation and found that, in the pressure range 0–20 MPa, the mean dissociation enthalpies for the semiclathrate hydrate systems of 26 wt % TBPO solution + N2, 26 wt % TBPO solution + CO2, and 26 wt % TBPO solution + CH4 were 177.75, 206.23, and 159.00 kJ·mol–1, respectively.

Characterization of tetra-n-butylphosphonium bromide semiclathrate hydrate by crystal structure analysis

The crystal structure of the semiclathrate hydrate of tetra-n-butylphosphonium bromide is reported, and the thermophysical property is characterized by comparison with an analogous hydrate.

Enhanced Selectivity of the Separation of CO2from N2during Crystallization of Semi-Clathrates from Quaternary Ammonium Solutions

CO2 mitigation is crucial environmental problem and a societal challenge for this century. CO2 capture and sequestration is a route to solve a part of the problem, especially for the industries in which the gases to be treated are well localized. CO2 capture by using hydrate is a process in which the cost of the separation is due to compression of gases to reach the gas hydrate formation conditions. Under pressure, the water and gas forms a solid that encapsulates preferentially CO2 . The gas hydrate formation requires high pressures and low temperatures, which explains the use of thermodynamic promoters to decrease the operative pressure. Quaternary ammoniums salts represent an interesting family of components because of their thermodynamic effect, but also because they can generate crystals that are easily handled. In this work, we have made experiments concerning the equilibrium of (CO2 , N2 ) in presence of Tetra-n-Butyl Ammonium Bromide (TBAB) which form a semi-clathrate hydrate. We propose equilibrium data (pressure, temperature) in presence of TBAB at different concentrations and we compare them to the literature. We have also measured the composition of the hydrate phase in equilibrium with the gas phase at different CO2 concentrations. We observe that the selectivity of the separation is dramatically increased in comparison to the selectivity of the pure water gas clathrate hydrate. We observe also a benefice on the operative pressure which can be dropped down to the atmospheric pressure.

Experimental and Modeling Study on Phase Equilibria of Semiclathrate Hydrates of Tetra-n-butyl Ammonium Bromide + CH4, CO2, N2, or Gas Mixtures

Tetra-n-butyl ammonium bromide (TBAB) is most-widely used as a hydrate promoter in the separation of flue gases and CO2 sequestration. Because of the complicacy of semiclathrate hydrate formed by TBAB aqueous solution and gases, few researchers have investigated the thermodynamic modeling of phase equilibria of semiclathrate hydrates. In this work, the CH4–N2 hydrate dissociation conditions were determined in TBAB solution first, and then a thermodynamic model for gas hydrate proposed by Chen and Guo was extended for semiclathrate hydrates of gas mixtures in TBAB aqueous solution. The Patel-Teja equation of state (PT EoS) was used for calculation of the fugacity of the gas phase. To evaluate the activity of water and activity coefficients of TBAB in TBAB aqueous solution, a correlation on the basis of existing osmotic coefficient and activity coefficient values is employed. For modeling the hydrate phase, parameters for sII hydrates proposed in the Chen–Guo hydrate model were used to calculate the fugacit...

Phase equilibria for the ionic semiclathrate hydrate formed with tetrabutylphosphonium chloride plus CO2, CH4, or N2

This paper presents the phase equilibrium conditions for the semiclathrate hydrates in the systems of (CO2, CH4 or N2+tetrabutylphosphonium chloride+water). The experiments were performed by isochoric method within the range of temperature from (283.0 to 291.8)K and pressure from (0.19 to 5.02)MPa with mass fraction of tetrabutylphosphonium chloride aqueous solution 0.36. The presence of tetrabutylphosphonium chloride increases the phase equilibrium temperatures of CO2, CH4 or N2 hydrates by at least 8K at a given pressure. The gas separation performance in tetrabutylphosphonium chloride hydrate systems was compared with that in other semiclathrate hydrate systems, based on the measured phase equilibrium conditions.

Hydrate phase equilibria data and hydrogen storage capacity measurement of the system H2 + tetrabutylammonium hydroxide + H2O

The possibility of hydrogen storage in mixed semi-clathrate hydrates formed from hydrogen+tetrabutylammonium hydroxide (TBAOH)+water was studied using high pressure differential scanning calorimetry (DSC) and isochoric reactor experiments (p–V–T). The phase diagram of the system TBAOH+water was first investigated, confirming the existence of one congruent melting hydrate and one non-congruent melting hydrate. Secondly, the effect of hydrogen pressure was studied under the range from 0 to 40MPa, and salt mole fractions from 0.0083 to 0.0244. (p, T) equilibrium data for hydrate dissociation in the system H2+TBAOH+water were determined. These results showed that hydrogen has a strong stabilizing effect on the non-congruent TBAOH hydrate structure, dissociation temperatures being increased by about 8K under a pressure of 40MPa. This effect was attributed to hydrogen enclathration into the TBAOH hydrate structure. Hydrogen pressure revealed to have much less effect on the stability of the congruent melting TBAOH hydrate, the increase in dissociation temperatures being of the order of 1K at 40MPa, therefore indicating an absence of H2 enclathration. A volumetric measurement of hydrogen storage capacity of hydrate was performed. The amount of gas entrapped in the hydrate phase was measured to be 0.35–0.47wt% over the pressure range 10–20MPa.

Phase equilibrium conditions for simulated landfill gas hydrate formation in aqueous solutions of tetrabutylammonium nitrate

Hydrate phase equilibrium conditions for the simulated landfill gas (LFG) of methane and carbon dioxide (50mol% methane, 50mol% carbon dioxide) were investigated with the pressure range of (1.90 to 13.83)MPa and temperature range of (280.0 to 288.3)K at (0.050, 0.170, 0.340, and 0.394) mass fraction (w) of tetrabutylammonium nitrate (TBANO3). The phase boundary between liquid–vapor–hydrate (L–V–H) phases and liquid–vapor (L–V) phases was determined by employing an isochoric pressure-search method. The phase equilibrium data measured showed that TBANO3 appeared a remarkable promotion effect at wTBANO3=0.394, corresponding to TBANO3·26H2O, but inhibition effect at wTBANO3=(0.050, or 0.170) on the semiclathrate hydrate formation. In addition, the application of TBANO3 at 0.340 mass fraction, corresponding to TBANO3·32H2O, displayed promotion effect at lower pressures (below 6.38MPa) and inhibition effect at higher pressures (above 6.38MPa).