Phase Equilibrium Conditions for Clathrate Hydrates of Tetra-n

Lin , W.; Delahaye , A.; Fournaison , L. Phase Equilibrium and Dissociation Enthalpy for Semi-Clathrate Hydrate of CO2 + TBAB Fluid Phase Equilib. 200...
0 downloads 0 Views 457KB Size
Download PDF
Article pubs.acs.org/jced

Phase Equilibrium Conditions for Clathrate Hydrates of Tetra-nbutylammonium Bromide (TBAB) and Xenon Yusuke Jin,* Masato Kida, and Jiro Nagao* Production Technology Team, Methane Hydrate Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 2-17-2-1, Tsukisamu-Higashi, Toyohira-Ku, Sapporo, 062-8517, Japan S Supporting Information *

ABSTRACT: Phase equilibrium pressure−temperature (pT) conditions for the xenon (Xe)−tetra-n-butylammonium bromide (TBAB)−water system were characterized by an isochoric method in the pressure range from (0.05 to 0.3) MPa using TBAB solutions with mole fractions ranging from (0.0029 to 0.0137). The phase equilibrium pT conditions in the system appeared at a lower pressure and higher temperature than in the pure Xe hydrate. Furthermore, under atmospheric pressure, the dissociation temperature in the Xe−TBAB− water system shifted to a higher region than in the pure TBAB hydrate. In the experimental TBAB concentration range, the powder X-ray diffraction patterns of the Xe−TBAB−water system revealed that the TBAB clathrate hydrate is TBAB·38H2O.

1. INTRODUCTION Gas clathrate hydrates (gas hydrates) are currently of interest as a gas storage medium.1−3 They are crystals consisting of gas and water molecules in which gas molecules are stored in cages formed by water molecules.4 Gas hydrates can store high volumes of gas: 170 times the volume of a guest gas molecule is stored in a unit of gas hydrate under theoretically ideal conditions. However, gas hydrates are typically stable only at high pressures and low temperatures. On the other hand, peralkyl ammonium salts also form a clathrate hydrate crystal with water molecules under atmospheric conditions.4−6 Tetra-n-butylammonium bromide (TBAB), a well-known peralkyl ammonium salt, forms five clathrate hydrates with different hydration numbers of 24, 26, 32, 36, and 38.7,8 The crystallographic features of the five TBAB clathrate hydrates (TBAB hydrates hereafter) are listed in Table 1. The TBAB− water system preferentially forms two of the five TBAB hydrates.9 The two TBAB hydrates have hydration numbers of TBAB·26H2O and TBAB·38H2O and are often referred to as type A and type B TBAB hydrates, respectively.9 In the TBAB·38H2O hydrate, the tetra-n-butylammonium cation is located at the center of four cages, and two empty cages (pentagonal dodecahedron cages, 512) exist.8 Shimada et al.10 recently suggested that TBAB hydrates can encage gas molecules. Hydrogen sulfide (H2S), which is 0.46 nm in diameter, can also be separated from mixed gas using TBAB hydrates.11,12 In these experiments, TBAB hydrates were found to be crystallized by encaging H2S molecules in their two empty cages. Furthermore, H2S molecules can be stored in the empty cages of TBAB hydrates under pressure conditions that are milder than those for the pure H2S hydrate. For example, at 292 K, the H2S hydrate is stable above approximately 0.7 MPa,4 whereas the TBAB hydrate enclosing H2S in a water solution containing 0.0029 mole fraction, xTBAB, of TBAB (TBAB solution (xTBAB = 0.0029)) is stable above 0.15 MPa.13 © 2012 American Chemical Society

Therefore, TBAB hydrates show potential as a gas storage medium. Other gas species that have been encaged in a 512 cage are H2, N2, CH4, and CO2,14−24 whose diameters are approximately (0.27, 0.41, 0.44, and 0.51) nm, respectively. Further, the dissociation pressure−temperature (pT) conditions of the TBAB hydrate enclosing gas molecules also shift to conditions milder than those for pure gas hydrates such as H2S. Moreover, the TBAB hydrate slurry using a low mole fraction of TBAB solution (∼xTBAB = 0.014) is of interest as a refrigerant medium.25 Although the dissociation enthalpy of the pure TBAB hydrate (∼200 kJ·kg−1) is lower than that of ice (333 kJ·kg−1), the dissociation enthalpy of the TBAB hydrate enclosing gas is higher than that of the pure TBAB hydrate. By using CO2, a dissociation enthalpy of 300 kJ·kg−1 can be achieved.16,23 Therefore, a slurry of TBAB hydrate enclosing gas can be applied to an air-conditioning system. The xenon (Xe) molecule is spherical and has a diameter of approximately 0.46 nm, which is approximately the same as the van der Waals diameter of the tetrahedral CH4 molecule. Because the phase equilibrium pT conditions for pure Xe hydrate are very low,26 the Xe−TBAB−water system is expected to show very low dissociation pressure conditions. Therefore, knowledge of Xe−TBAB−water systems having low pressure dissociation conditions may enable suitable applications using clathrate hydrates. In this paper, we report the TBAB solution−TBAB hydrate−vapor three-phase equilibrium for Xe−TBAB−water systems at low TBAB solution concentrations (xTBAB = 0.0029, 0.0062, and 0.0137), which are 0.05, 0.10, and 0.20, respectively, in units of the mass fraction of TBAB; we also examine the crystal structures of the TBAB hydrate when pressurized by Xe. Received: March 7, 2012 Accepted: May 9, 2012 Published: May 11, 2012 1829

dx.doi.org/10.1021/je300299b | J. Chem. Eng. Data 2012, 57, 1829−1833

Journal of Chemical & Engineering Data

Article

Table 1. Crystallographic Properties of Tetra-n-butylammonium Bromide (TBAB) Clathrate Hydrates7,8 unit cell clathrate hydrate

crystal system

space group

a/nm

b/nm

c/nm

β/°

ref

TBAB·24H2O TBAB·26H2O TBAB·32H2O TBAB·36H2O TBAB·38H2O

monoclinic tetragonal tetragonal orthorhombic orthorhombic

C2/m P4/mmm P4/m Pmmm Pmma

2.85 2.39 3.34 2.13 2.11

1.69

1.65 5.08 1.27 1.21 1.20

125

7 7 7 7 8

2. EXPERIMENTAL METHODS A schematic of the measurement apparatus for the Xe−TBAB− water system at equilibrium is shown in Figure 1. Our pressure

1.29 1.26

the sample temperature. The pressure of the inner vessel was measured using a pressure transducer (AP-13S, KEYENCE Co.). The uncertainty of the pressure measurements was ± 0.005 MPa with a confidence level of approximately 95 %. Temperature and pressure data for the inner vessel were collected using a data logger (JULIUS, INR-900X, HEOKI E. E. Co.). The equilibrium pT conditions in the Xe−TBAB−water system were measured as follows. We poured 70 cm3 of TBAB aqueous solution having a designated concentration into the pressure vessel. After air was eliminated from the vessel by a vacuum pump, we pressurized it with Xe gas and cooled the TBAB solution by stirring. The stirring rate was maintained at approximately 1000 r·min−1 during the measurement. Crystallization was identified not only by observing the pressure decrease but also visually through the optical windows, as shown in Figure 1. After crystal formation, the temperature was increased stepwise in 0.5 K increments. During the temperature-ramping test, when the pressure condition was above the phase equilibrium conditions for the Xe−TBAB−water system, the system pressure was almost constant (arrow A in Figure S1 of the Supporting Information, SI). On the other hand, when the pressure was lower than the phase equilibrium conditions for the system, the system pressure increased owing to hydrate dissociation, keeping the system in phase equilibrium (arrow B in Figure S1, SI). When sufficient time had elapsed after the increase in system pressure due to hydrate dissociation, if the existence of crystals was also visually confirmed, the pT condition could be identified as the phase equilibrium conditions of the Xe−TBAB−water system (filled circles in Figure S1, SI). Otherwise, because the existence of crystals was not visually confirmed, the pT condition could not be identified as the phase equilibrium condition in the system (open square in Figure S1, SI). At each temperature step, we maintained the temperature for (6 to 8) h after the pressure increase. After the system pressure became nearly constant and hydrate crystals were visually confirmed, the equilibrium pressure of the Xe− TBAB−water system was determined at a given temperature. We collected the TBAB solution−TBAB hydrate−vapor threephase equilibrium data for the Xe−TBAB−water systems at various TBAB concentrations (xTBAB = 0.0029, 0.0062, and 0.0137). For crystallographic analysis, we prepared samples using the pressure vessel shown in Figure 1. After crystallization in the vessel, crystals were separated from the mixture in the vessel by filtration in a cold room at 278 K. Next, the separated crystals were quenched in liquid nitrogen. Crystallographic analysis was performed by powder X-ray diffraction (PXRD). PXRD profiles of samples were obtained using an X-ray diffraction apparatus (Rint-2500; Rigaku Co.) with Cu Kα radiation. The voltage and current of the X-ray source were 40 kV and 249 mA, respectively. The powdered samples were introduced into a quartz glass capillary cell (2.0 mm diameter, 0.01 mm thickness,

Figure 1. Configuration of the pressure vessel.

vessel was made of SUS316 stainless steel and equipped with two optical quartz windows and a fin for stirring the solution. The inner volume of the pressure vessel was approximately 120 cm3. The vessel's temperature was controlled by a thermal jacket connected to a circulating thermostat (HAAKE, N8); the operating temperature range was (253 to 303) K. The sample temperature was maintained within ± 0.1 K by the circulating thermostat and measured using a thermocouple (type T, CHINO Co.). For precision temperature measurement, the thermocouple was connected to a cold-junction compensation device (ZEROCON, ZC-114, Coper Electronics Co., Ltd.), which can establish a reference temperature of 273.15 K by using an ice−water slurry. The temperature measurements were reproducible within ± 0.02 K. Therefore, the expanded uncertainty of the obtained equilibrium temperature was estimated to be ± 0.1 K with a confidence level of approximately 95 %, considering the uncertainty in controlling 1830

dx.doi.org/10.1021/je300299b | J. Chem. Eng. Data 2012, 57, 1829−1833

Journal of Chemical & Engineering Data

Article

the literature, confirming the reliability of our experimental setup. The obtained pT conditions for the Xe−TBAB−water system at various TBAB concentrations are also plotted in Figure 2. The pT data at each TBAB concentration are listed in Table 3. The equilibrium pT conditions of the Xe−TBAB−

10 mm length) and maintained below approximately 220 K by blowing cooled dry nitrogen gas during the PXRD measurement. The PXRD profiles were acquired using a step of 0.02° with a counting time of 1.2 s·step−1 and 16 to 24 data acquisitions. In the experiment, ReagentPlus grade TBAB with 99 % purity was used (Sigma-Aldrich Co., Inc.). Water purified by ultrafiltration, reverse osmosis, deionization, and distillation was obtained from Lonza Ltd. Research grade Xe gas with 99.995 % purity was used (AIR WATER Inc., Osaka, Japan). All of these materials were used without further purification.

Table 3. Equilibrium Pressure−Temperature Conditions of the Xe−TBAB−Water Systems xTBAB = 0.0029

3. RESULTS AND DISCUSSION First, to confirm the reliability of our experimental setup and procedures and the accuracy of the obtained data, we measured the phase equilibrium pT conditions for a pure Xe−water system; these conditions are listed in Table 2 and plotted in Table 2. Equilibrium Pressure−Temperature Conditions of the Xe−Water System Ta/K

pb/MPa

274.5 276.3 278.2 279.6 280.5

0.175 0.210 0.253 0.291 0.317

xTBAB = 0.0062

xTBAB = 0.0137

Ta/K

pb/MPa

Ta/K

pb/MPa

Ta/K

pb/MPa

275.7 276.2 276.7 277.2 277.7 278.2 278.7 279.2 279.7 280.2 280.7 281.2 281.7 282.2

0.108 0.113 0.118 0.125 0.132 0.139 0.150 0.160 0.170 0.182 0.196 0.210 0.224 0.240

280.2 280.7 281.2 281.7 282.2 282.7 283.2 283.7 284.2 284.7 285.2

0.092 0.103 0.114 0.126 0.141 0.155 0.172 0.192 0.212 0.236 0.257

283.7 284.2 284.7 285.2 285.7 286.2 286.7 287.2

0.079 0.097 0.112 0.135 0.159 0.186 0.216 0.260

a

The expanded uncertainty of equilibrium temperature was estimated to be ± 0.1 K with a confidence level of approximately 95 %. b Uncertainties of pressure measurements were estimated to be ± 0.005 MPa with a confidence level of approximately 95 %.

a

The expanded uncertainty of equilibrium temperature was estimated to be ± 0.1 K with a confidence level of approximately 95 %. b Uncertainties of pressure measurements were estimated to be ± 0.005 MPa with a confidence level of approximately 95 %.

water system are milder than those of pure Xe hydrate. In comparison with the Xe−water system, for example, the equilibrium pressure in the Xe−TBAB−water system with TBAB solution (xTBAB = 0.0062) decreased from approximately (0.50 to 0.24) MPa at 284.7 K. In the CH4−TBAB−water and N2−TBAB−water systems (xTBAB = 0.0062), the decreases in equilibrium pressure at 285 K were approximately (7.5 and 50) MPa, respectively.4,15,17−20 The equilibrium pressure decreases significantly when the gas species that form the hydrate have a higher equilibrium pressure. In addition, the equilibrium pressure at the same temperature decreased with increasing TBAB concentration, as in other gas−TBAB−water systems.13−24 Figure 3 shows PXRD profiles of the TBAB hydrates and TBAB. TBAB·26H2O and TBAB·38H2O hydrates (Figure 3b,e) were prepared from aqueous solutions of the stoichiometric compositions for TBAB solutions (xTBAB = 0.0370 and 0.0256), respectively, at 253 K under atmospheric conditions. As shown in Figure 3b,e, the PXRD profiles of the pure TBAB·26H2O and TBAB·38H2O hydrates differ. In particular, the diffraction patterns differ in the 2θ region below 12°. In the pure TBAB·38H2O hydrate (Figure 3e), three unique peaks were observed at approximately 6.8°, 8.3°, and 10.8°, respectively. On the other hand, the pure TBAB·26H2O hydrate had two unique peaks at approximately 5.2° and 8.0°, respectively. Samples I and II (Figure 3c,d) were prepared from TBAB solutions (xTBAB = 0.0062 and 0.0137), respectively, at 279.2 K and a Xe pressure of 0.25 MPa. The PXRD profiles of samples I and II showed the three peaks at 6.8°, 8.3°, and 10.8° that appeared for the pure TBAB·38H2O hydrate (Figure 3e). In addition, the two peaks at 5.2° and 8.0° that appeared for the pure TBAB·26H2O hydrate did not appear in Figure 3c,d.

Figure 2. A Xe hydrate formed at 278.2 K and 0.3 MPa. Data from the literature for pure Xe hydrate26 are also plotted in Figure 2. Our experimental data agreed well with those from

Figure 2. Equilibrium pressure−temperature conditions of Xe hydrate and Xe−TBAB−water system. □, Xe hydrate (present study); solid line, Xe hydrate (Shimada et al.26); ●, Xe−TBAB−water system (xTBAB = 0.0029); ○, Xe−TBAB−water system (xTBAB = 0.0062); ■, Xe−TBAB−water system (xTBAB = 0.0137). Dotted line, vapor pressure of Xe;27 ◊, critical point of Xe (289.7 K and 5.84 MPa);27 dashed spaced line, vapor pressure of water.27 Uncertainties of equilibrium temperature and pressure were estimated to be ± 0.1 K and ± 0.005 MPa, respectively, with a confidence level of approximately 95 %. 1831

dx.doi.org/10.1021/je300299b | J. Chem. Eng. Data 2012, 57, 1829−1833

Journal of Chemical & Engineering Data

Article

in the H2S−TBAB−water system.13,14 The phase stabilization may be affected by the solubility of guest molecules in the salt solution.

4. CONCLUSIONS We characterized the phase equilibrium pT conditions for the Xe−TBAB−water system at pressures of (0.05 to 0.3) MPa. The measured dissociation pT conditions for TBAB hydrate enclosing Xe shifted to high temperature with increasing TBAB concentration, as in other gas−TBAB−water systems. The PXRD profiles of the Xe−TBAB−water system showed that the TBAB hydrate is TBAB·38H2O below a 0.0137 mole fraction of TBAB in water solution. Furthermore, the dissociation temperature under atmospheric pressure is higher than that for the pure TBAB hydrate. This increase in the dissociation temperature is considered to be caused by the capture of guest molecules.

■

ASSOCIATED CONTENT

S Supporting Information *

Schematic illustrating how the phase equilibrium conditions are determined in this study. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*Tel.: +81-11-857-8526. Fax: +81-11-857-8417. E-mail address: [email protected] (Y.J.) and [email protected] (J.N.). Funding

This work was supported by funding from the Research Consortium for Methane Hydrate Resources in Japan (MH21 Research Consortium), planned by the Ministry of Economy, Trade and Industry (METI), Japan. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank Drs. H. Narita, T. Ebinuma, Y. Konno, H. Ohno, H. Oyama, and S. Takeya of AIST for valuable discussions. They also thank Ms. J. Hayashi of AIST for experimental support.

Figure 3. Measured PXRD profiles. (a) TBAB. (b) TBAB·26H2O hydrate prepared in TBAB solution (xTBAB = 0.0370). (c) Sample I, prepared in TBAB solution (xTBAB = 0.0062) pressurized by Xe. (d) Sample II, prepared in TBAB solution (xTBAB = 0.0137) pressurized by Xe. (e) TBAB·38H2O hydrate prepared in TBAB solution (xTBAB = 0.0256). Miller index of each peak of the pure TBAB·38H2O hydrate was assigned using crystal information8 and the RIETAN-2000 program.28

■

REFERENCES

(1) Lee, H.; Lee, J. W.; Kim, D. Y.; Park, J.; Seo, Y. T.; Zeng, H.; Moudrakovski, I. L.; Ratcliffe, C. I.; Ripmeester, J. A. Tuning Clathrate Hydrates for Hydrogen Storage. Nature 2005, 434, 743. (2) Strobel, T. A.; Koh, C. A.; Sloan, E. D. Hydrogen Storage Properties of Clathrate Hydrate Materials. Fluid Phase Equilib. 2007, 261, 382−389. (3) Wang, W.; Bray, C. L.; Adams, D. J.; Cooper, A. I. Methane Storage in Dry Water Gas Hydrates. J. Am. Chem. Soc. 2008, 130 (35), 11608−11609. (4) Sloan, E. D.; Koh, C. A. Clathrate Hydrates of Natural Gases, 3rd ed.; CRC Press: New York, 2007. (5) Jeffrey, G. A. Water Structure in Organic Hydrates. Acc. Chem. Res. 1969, 2, 344−352. (6) Aladko, L. S.; Dyadin, Y. A.; Rodionova, T. V.; Terekhova, I. S. Effect of Size and Shape of Cations and Anions on Clathrate Formation in the System: Halogenides of Quaterly Ammonium Bases and Water. J. Mol. Liq. 2003, 106, 229−238. (7) Gaponenko, L.; Solodovnikov, S. F.; Dyadin, Y. A.; Aladko, L. S.; Polyanskaya, T. N. Crystallographic Study of Tetra-n-butylammonium Bromide Polydrates. J. Struct. Chem. 1984, 25, 157−159.

Therefore, the clathrate hydrate in the Xe−TBAB−water system at TBAB concentrations below xTBAB = 0.0137 was TBAB·38H2O hydrate. The pressure response to temperature shown in Figure 2 indicates that TBAB·38H2O hydrate captured Xe in the empty cages. In the pure TBAB hydrate formed under atmospheric conditions, TBAB·38H2O hydrate produced from TBAB solution (xTBAB = 0.0137) dissociates above approximately 282 K at atmospheric pressure.9 On the other hand, TBAB·38H2O hydrate enclosing Xe is stable below approximately 284.5 K, as shown in Figure 2. The differential dissociation temperature between TBAB·38H2O hydrates with and without enclosed Xe is approximately 2.5 K. The TBAB hydrate clearly exhibits phase stabilization during Xe capture. Guest molecules captured in empty cages would enable phase stabilization of the TBAB hydrate. This phase stabilization seems to be absent in the H2−TBAB−water system but present 1832

dx.doi.org/10.1021/je300299b | J. Chem. Eng. Data 2012, 57, 1829−1833

Journal of Chemical & Engineering Data

Article

(8) Shimada, W.; Shiro, M.; Kondo, H.; Takeya, S.; Oyama, H.; Ebinuma, T.; Narita, H. Tetra-n-butyl Ammonium Bromide−Water (1/38). Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 2005, C61, 065−066. (9) Oyama, H.; Shimada, W.; Ebinuma, T.; Kamata, Y.; Takeya, S.; Uchida, T.; Nagao, J.; Narita, H. Phase Diagram, Latent Heat, and Specific Heat of TBAB Semiclathrate Hydrate Crystals. Fluid Phase Equilib. 2005, 234, 131−135. (10) Shimada, W.; Ebinuma, T.; Oyama, H.; Kamata, Y.; Takeya, S.; Uchida, T.; Nagao, J.; Narita, H. Separation of Gas Molecule using Tetra-n-butyl Ammonium Bromide Semi-clathrate Hydrate Crystals. Jpn. J. Appl. Phys. 2003, 42, L129−L131. (11) Kamata, Y.; Oyama, H.; Shimada, W.; Ebinuma, T.; Takeya, S.; Uchida, T.; Nagao, J.; Narita, H. Gas Separation Method Using Tetran-butyl Ammonium Bromide Semi-Clathrate Hydrate. Jpn. J. Appl. Phys. 2004, 43, 362−365. (12) Kamata, Y.; Yamakoshi, Y.; Ebinuma, T.; Oyama, H.; Shimada, W.; Narita, H. Hydrogen Sulfide Separation Using Tetra-n-butyl Ammonium Bromide Semi-clathrate (TBAB) Hydrate. Energy Fuels 2005, 19 (4), 1717−1722. (13) Mohammadi, A. H.; Richon, D. Phase Equilibria of SemiClathrate Hydrates of Tetra-n-butylammonium Bromide + Hydrogen Sulfide and Tetra-n-butylammonium Bromide + Methane. J. Chem. Eng. Data 2010, 55, 982−984. (14) Hashimoto, S.; Sugahara, T.; Moritoko, M.; Sato, H.; Ohgaki, K. Thermodynamic Stability of Hydrogen + Tetra-n-Butyl Ammonium Bromide Mixed Gas Hydrate in Nonstoichiometric Aqueous Solutions. Chem. Eng. Sci. 2008, 63, 1092−1097. (15) Arjmandi, M.; Chapoy, A.; Tohidi, B. Equilibrium Data of Hydrogen, Methane, Nitrogen, Carbon Dioxide, and Natural Gas in Semi-Clathrate Hydrates of Tetrabutyl Ammonium Bromide. J. Chem. Eng. Data 2007, 52, 2153−2158. (16) Deschamps, J.; Dalmazzone, D. Dissociation Enthalpies and Phase Equilibrium for TBAB Semi-Clathrate Hydrates of N2, CO2, N2 + CO2 and CH4 + CO2. J. Therm. Anal. Calorim. 2009, 98, 113−118. (17) Mohammadi, A. H.; Eslamimanesh, A.; Belandria, V.; Richon, D. Phase Equilibria of Semiclathrate Hydrates of CO2, N2, CH4, or H2 + Tetra-n-butylammonium Bromide Aqueous Solution. J. Chem. Eng. Data 2011, 56, 3855−3865. (18) Li, D. L.; Du, J. W.; Fan, S. S.; Liang, D. Q.; Li, X. S.; Huang, N. S. Clathrate Dissociation Conditions for Methane + Tetra-n-butyl Ammonium Bromide (TBAB) + Water. J. Chem. Eng. Data 2007, 52, 1916−1918. (19) Sun, Z. G.; Sun, L. Equilibrium Conditions of Semi-Clathrate Hydrate Dissociation for Methane + Tetra-n-butyl Ammonium Bromide. J. Chem. Eng. Data 2010, 55, 3538−3541. (20) Acosta, H. Y.; Bishnoi, P. R.; Clarke, M. A. Experimental Measurements of the Thermodynamic Equilibrium Conditions of Tetra-n-butylammonium Bromide Semiclathrates Formed from Synthetic Landfill Gases. J. Chem. Eng. Data 2011, 56, 69−73. (21) Lee, S.; Park, S.; Lee, Y.; Lee, J.; Lee, H.; Seo, Y. Guest Gas Enclathration in Semiclathrates of Tetra-n-butylammonium Bromide: Stability Condition and Spectroscopic Analysis. Langmuir 2011, 27, 10597−10603. (22) Nguyen, H. D.; Fabien, C.; Jean-Michel, H. CO2 Capture by Hydrate Crystallization−A Potential Solution for Gas Emission of Steelmaking Industry. Energy Convers. Manage. 2007, 48, 1313−1322. (23) Lin, W.; Delahaye, A.; Fournaison, L. Phase Equilibrium and Dissociation Enthalpy for Semi-Clathrate Hydrate of CO2 + TBAB. Fluid Phase Equilib. 2008, 264, 220−227. (24) Li, S.; Fan, S.; Wang, J.; Lang, X.; Wang, Y. Semiclathrate Hydrate Phase Equilibria for CO2 in the Presence of Tetra-n-butyl Ammonium Halide (Bromide, Chloride, or Fluoride). J. Chem. Eng. Data 2010, 55, 3212−3215. (25) Ogushi, H.; Takao, S. Air-Conditioning Using Clathrate Hydrate Slurry. JFE Tech. Rep. 2004, 3, 1−5. (26) Shimada, N.; Sugahara, K.; Sugahara, T.; Ohgaki, K. Phase Transition from Structure-H to Structure-I in the Methylcyclohexane + Xenon Hydrate System. Fluid Phase Equilib. 2003, 205, 17−23.

(27) Lemmon, E. W.; McLinden, M. O.; Friend, D. G. Thermophysical Properties of Fluid Systems. In NIST Chemistry WebBook, NIST Standard Reference Database Number 69; Linstrom, P. J., Mallard, W. G., Eds.; National Institute of Standards and Technology: Gaithersburg, MD; http://webbook.nist.gov (retrieved March 27, 2012). (28) Izumi, F.; Ikeda, T. A Rietveld-analysis Program RIETAN-98 and its Applications to Zeolites. Mater. Sci. Forum 2000, 321−324, 198−203.

1833

dx.doi.org/10.1021/je300299b | J. Chem. Eng. Data 2012, 57, 1829−1833