Tuning Behaviors of Methane Inclusion in Isoxazole Clathrate

Sep 19, 2014 - Minjun Cha†‡, Seungjun Baek§, Wonhee Lee§, Kyuchul Shin∥, and Jae W. Lee‡§. † Department of Energy and Resources Engineeri...
0 downloads 0 Views 2MB Size
Download PDF
Article pubs.acs.org/jced

Tuning Behaviors of Methane Inclusion in Isoxazole Clathrate Hydrates Minjun Cha,†,‡ Seungjun Baek,§ Wonhee Lee,§ Kyuchul Shin,∥ and Jae W. Lee*,‡,§ †

Department of Energy and Resources Engineering, Kangwon National University, 1 Kangwondaehak-gil, Chuncheon-si, Gangwon-do 200-701, Republic of Korea ‡ Chemical Engineering Department, The City College of New York, Steinman Hall, 140th Street & Convent Avenue, New York, New York 10031, United States § Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea ∥ Department of Applied Chemistry, Kyungpook National University, 80 Daehakro, Bukgu, Daegu, 702-701, Republic of Korea S Supporting Information *

ABSTRACT: In this study, the inclusion of methane (CH4) gas in isoxazole (C3H3NO) clathrate hydrates was investigated through spectroscopic observations, such as powder X-ray diffraction (PXRD) and Raman spectroscopy. PXRD patterns of isoxazole clathrate hydrates having two different mole fractions of water were analyzed, and Raman spectroscopy was used to understand the CH4 inclusion behaviors in the hydrate cavities. Raman spectra indicated that CH4 can be captured in both small and large cavities of structure II hydrate in the C3H3NO with 34H2O system, while CH4 can be entrapped in only small cavities of structure II hydrate in the C3H3NO with 17H2O system. The PXRD result showed both clathrate hydrate samples exhibit the same cubic Fd3m structure II hydrate as expected. However, the structure II hydrate in the C3H3NO with 34H2O system includes a small amount of hexagonal ice and structure I CH4 hydrate. The phase equilibrium conditions of the binary (isoxazole + CH4) clathrate hydrate were also identified through high-pressure micro differential scanning calorimetry (MicroDSC), and the equilibrium temperatures of the binary (isoxazole + CH4) clathrate hydrate at given pressures are higher than those of the structure I CH4 hydrate.

■

INTRODUCTION

Several studies reported an interesting phenomenon for gas (methane or hydrogen) storage in THF clathrate hydrates.10,11,13,14 It was revealed that the use of THF as a hydrate former can significantly lower the hydrate formation pressure for gas storage, while the gas storage capacity in clathrate hydrate decreases due to the inclusion of THF in large (51264) cavities of structure II (sII) clathrate hydrate.10,11 To overcome the decrease of gas storage capacity, Sugahara et al.14 demonstrated that the decrease of THF concentration can induce the vacant large cavities in sII hydrates, and hydrogen molecules can be trapped inside these vacant cavities in sII hydrates through the tuning phenomenon.11−15 Similar to the THF hydrate, isoxazole17−19 can form sII hydrates without gaseous guest molecules (methane or hydrogen) at 271 K and ambient pressure. It was reported that the isoxazole hydrates

Clathrate hydrates, also known as gas hydrates, are one of the types of inclusion compounds possessing physicochemical properties of icy materials. Gas molecules having low molecular weights such as methane, ethane, carbon dioxide, nitrogen, and hydrogen as well as some organic molecules such as cyclopentane (CP) and tetrahydrofuran (THF) can be captured into the cavities formed by the hydrogen-bonded network of water molecules.1−3 Various studies associated with clathrate hydrates have received considerable attention due to their potential applications in several areas such as carbon dioxide capture and sequestration (CCS),4,5 gas storage and separation,6,7 and energy-related devices.8,9 In addition, recent hydrate-related discoveries9−16 such as the hydrogen storage in tetrahydrofuran (THF) clathrate hydrates,10−12,14,15 the tuning mechanism of clathrate hydrates for gas storage (methane or hydrogen),11−15 and the great enhancement of hydrate formation kinetics16 with the addition of liquid cyclopentane (CP) can contribute to clathrate hydrate research being considered as quite promising technologies. © XXXX American Chemical Society

Special Issue: In Honor of E. Dendy Sloan on the Occasion of His 70th Birthday Received: June 20, 2014 Accepted: September 8, 2014

A

dx.doi.org/10.1021/je500568f | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

pressurized reactors were stored at 253.15 K in an alcohol bath (Jeio Tech., RW-2025) for 1 week. After the complete hydrate conversion, the reactors were immersed into the liquid nitrogen to prevent the partial hydrate dissociation, followed by recovering the hydrate samples for the subsequent measurement. Powder X-ray diffraction (PXRD) was used to investigate the crystal structure and lattice parameter of the two binary (isoxazole + CH4) clathrate hydrates in both C3H3NO with 17H2O and C3H3NO with 34H2O systems at 93.15 K. The θ/ 2θ scan mode with a fixed time of 3 s and a step size of 0.02° for 2θ = (5−42)° for the hydrate samples was used in this study with the graphite-monochromatized CuKα1 radiation (wavelength of 0.15406 nm) at a generator voltage of 40 kV and a current of 300 mA as the light source (Rigaku D/MAX-2500). Dispersive Raman experiments (Horiba Jobin Yvon, France) with a CCD detector cooled by liquid nitrogen were conducted with an Ar-ion laser having a 514.53 nm line as an excitation source. The typical intensity of laser was about 25 mW. The THMS600G model (Linkam stage) was used to cool the samples to 93.15 K in the Raman analysis. High-pressure micro differential scanning calorimetry (MicroDSC VII, Setaram) was used to measure the phase equilibrium condition of the binary (isoxazole + CH4) clathrate hydrate system. The MicroDSC was calibrated by n-decane, water, and naphthalene with a temperature precision of 0.02 K. In addition, MicroDSC has its own uncertainty of 0.2 K in the temperature measurement. Druck DPI-104 digital pressure gauge was used to measure the pressure with a precision of 0.01 MPa. The experimental setup and procedures are presented in our previous studies, and the onset temperature from the endothermic signal is evaluated as the hydrate equilibrium condition in this study.20,21

could possess two different types of stoichiometry of C3H3NO· 17H2O and C3H3NO·34H2O.17 In the hydrate with the hydration number of 17, it was suggested that isoxazole molecules occupy essentially all of the large cavities of the sII hydrate as tetrahydrofuran molecules do in this structure. In the hydrate with the hydration number of 34, it was hypothesized that the large cavities of sII were partially occupied. However, it was shown later that the form of C3H3NO·34H2O does not exist using X-ray diffraction and NMR studies.19 Given that it has been established that the hydrate with the hydration number of 34 does not exist, our hypothesis was that by the introduction of methane gas it is possible to convert remaining ice to sII hydrate at temperatures lower than ice’s melting temperature; in other words it is possible to use the so-called “tuning effect” to increase the mole fraction of methane in the hydrate. Thus, this work aims at identifying the tuning behavior of the isoxazole clathrate hydrates and determining new equilibrium conditions through the inclusion of methane gas. We synthesized the binary (isoxazole + CH4) clathrate hydrates using two different water fractions [a mixture of x C3H3NO + (1 − x) H2O with a mole fraction, x, of 0.0556 ± 0.001 is abbreviated as “C3H3NO with 17H2O system”, while a mixture of x C3H3NO + (1 − x) H2O with a mole fraction, x, of 0.0286 ± 0.001 is abbreviated as “C3H3NO with 34H2O system”] to check the possible tuning behavior in this study. Their structures and guest distributions were investigated through spectroscopic observations of powder X-ray diffraction (PXRD) and Raman spectroscopy. Additionally, the hydrate phase equilibrium conditions for the binary (isoxazole + CH4) clathrate hydrate were determined through high-pressure micro differential scanning calorimetry (MicroDSC).

■

■

EXPERIMENTAL DETAILS Materials. Deionized (DI) water was obtained from a Millipore Direct-Q unit with a resistivity of 18 MΩ·cm−1. Methane (CH4) gas was purchased from Special Gas (Korea) with a minimum mole fraction purity of 0.9995. Isoxazole having a minimum mole fraction purity of 0.99 was supplied from Sigma-Aldrich Inc. Details of materials information are tabulated in Table 1.

RESULTS AND DISCUSSION Kaloustian et al.17 reported that isoxazole (C3H3NO) can form the well-known structure II (sII) hydrate with a decomposition temperature of 271 K through thermal analyses, but the isoxazole hydrate can contain 34 mol of water per mole of isoxazole for constructing the unit cell structure, while the THF hydrate contains 17 mol of water per mole of THF for the unit cell structure. It was then observed that the isoxazole hydrate is a typical sII clathrate hydrate with the cubic Fd3m structure and the composition of 17 mol of water per mole of isoxazole through X-ray diffraction (XRD), continuous wave nuclear magnetic resonance (NMR), and dielectric studies of the isoxazole clathrate hydrate.18,19 Prior to investigating the crystal structure and guest distributions of CH4 in the binary (isoxazole + CH4) clathrate hydrate, we synthesized two different samples containing different mole fractions of isoxazole in water (both C3H3NO with 17H2O and C3H3NO with 34H2O systems) and qualitatively analyzed the data through powder X-ray diffraction (PXRD) studies. Figure 1 shows PXRD patterns of the isoxazole clathrate hydrates both in C3H3NO with 17H2O and in C3H3NO with 34H2O systems at 93.15 K. The crystal structure and lattice parameters of the isoxazole clathrate hydrates in both C3H3NO with 17H2O and C3H3NO with 34H2O systems are analyzed by the Checkcell program (Laugier),22 and PXRD patterns of both clathrate hydrates exhibit the cubic Fd3m structure with a lattice parameter of a = 1.7144 (17) nm in the C3H3NO with 17H2O system and a lattice parameter of a = 1.7155 (13) nm in the C3H3NO with 34H2O system, respectively. These calculated lattice parameter values are in close agreement with a literature

Table 1. Details of Material Information chemical name

source

mole fraction purity

chemical structure

DI water methane isoxazole

Special Gas (Korea) Sigma-Aldrich Inc.

0.9995 0.99

H2O CH4 C3H3NO

Experimental Methods. Initially, we prepared two liquid solution samples (one mixture of x C3H3NO + (1 − x) H2O with a mole fraction, x, of 0.0556 ± 0.001, as C3H3NO with 17H2O and the other mixture of x C3H3NO + (1 − x) H2O with a mole fraction, x, of 0.0286 ± 0.001, as C3H3NO with 34H2O) by mixing DI water and isoxazole crystals at room temperature. And then, we kept our solution samples in a freezer at 223.15 K for 1 day. After 1 day, the frozen samples were ground to fine powders (∼100 μm) at liquid nitrogen conditions. Liquid nitrogen was used to cool the high-pressure reactors having each volume of 15 mL, and the fine powder samples were placed into the precooled reactors. Afterward, the reactors were flushed three times with CH4 gas to remove residual air and pressurized by CH4 gas up to 10.0 MPa. The B

dx.doi.org/10.1021/je500568f | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

induce the inclusion of gaseous guests (methane and hydrogen) in large cavities of sII hydrate by tuning mechanism.11,13,14 Thus, it might be worthwhile to identify the possible tuning behavior in the C3H3NO with 34H2O system. To check the possible tuning behavior in the C3H3NO with 34H2O system, we introduced the gaseous methane (CH4) into both C3H3NO with 17H2O and C3H3NO with 34H2O samples and analyzed the crystal structures and guest distribution of methane through PXRD and Raman spectroscopy. Figure 2 shows the PXRD patterns of the binary (isoxazole + CH4) clathrate hydrates in both C3H3NO with 17H2O and C3H3NO with 34H2O systems. The binary (isoxazole + CH4) clathrate hydrate in the C3H3NO with 17H2O system (green line in Figure 2) shows a clear crystal structure of cubic Fd3m

Figure 1. Powder X-ray diffraction patterns of the isoxazole clathrate hydrates in C3H3NO with 17H2O (green) and C3H3NO with 34H2O (pink) systems. Black tick marks and black brackets indicate the Bragg’s signals and Miller indices from the hydrate phase (structure II, cubic Fd3m). Red tick marks and red brackets indicate the Bragg’s signals and Miller indices from the hexagonal ice phase.

value of a = 1.717 nm for the isoxazole clathrate hydrate in C3H3NO·14.7H2O.18 In addition, we can clearly see the difference of a relative amount of hexagonal ice (H2O, ice Ih) phase between the two hydrate samples in Figure 1b. In the C3H3NO with 17H2O sample (black line), the peak intensity from (422) plane of cubic Fd3m structure (2θ = 25.4°) is higher than that from (011) plane of hexagonal ice (2θ = 25.8°) as shown in Figure 1b. However, in the C3H3NO with 34H2O (pink) sample, the peak intensity from (422) plane of cubic Fd3m structure (2θ = 25.4°) is lower than that from (011) plane of hexagonal ice (2θ = 25.8°). It was reported17 that isoxazole forms sII hydrate with the occupancy of only half in large cavities (51264) and the isoxazole clathrate hydrate have the composition of the C3H3NO with 34H2O system, but our PXRD results showed that the C3H3NO with 34H2O system has a significant amount of hexagonal ice phase as compared with the C3H3NO with 17H2O system, and thus; the C3H3NO with 34H2O system might not be a dominant hydrate form. However, in the recent studies, the decrease of THF concentration in sII hydrates can

Figure 2. Powder X-ray diffraction patterns of the binary (isoxazole + methane) clathrate hydrates in C3H3NO with 17H2O (green) and C3H3NO with 34H2O (pink) systems. Black tick marks and black brackets indicate the Bragg’s signals and Miller indices from the hydrate phase (structure II, cubic Fd3m). Blue tick marks and blue brackets indicate the Bragg’s signals and Miller indices from the hydrate phase (structure I, cubic Pm3n). Red tick marks and red brackets indicate the Bragg’s signals and Miller indices from the hexagonal ice phase. C

dx.doi.org/10.1021/je500568f | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

structure with a lattice parameter of a = 1.7172 (14) nm. In Figure 2b, we can see that there is an extremely small amount of hexagonal ice phase in (C3H3NO with 17H2O + CH4) hydrate around 2θ = 24.2° region for the diffraction peak from (002) plane of hexagonal ice. This implies that the isoxazole hydrate in the binary hydrate system also have the same 17H2O composition as the isoxazole hydrate even when gaseous CH4 is introduced in the system. The small amount of hexagonal ice phase in the isoxazole hydrate with 17H2O composition (green line in Figure 1a) may be due to the inhomogeneity of solution sample. Compared to the isoxazole hydrate system in the C3H3NO with 34H2O system (pink line in Figure 1a), the hexagonal ice phase in the binary (isoxazole + CH4) hydrate in the C3H3NO with 34H2O system (pink line in Figure 2a) greatly decreases, and this may be due to the partial inclusion of methane in large cavities of sII hydrate. However, there is one additional phase of cubic Pm3n structure (sI structure), implying that there can be a possible structure transition from the remaining ice to sI hydrate, because the CH4 pressure in the formation stage is 10.0 MPa (stable condition for sI hydrate) and all of ice phase in the C3H3NO with 34H2O system (pink line in Figure 1a) cannot be transformed into sII hydrate. It was roughly estimated that the phase weight fraction resulting from CH4 hydrate in the C3H3NO with 17H2O system was as 0.98 of sII hydrate phase and 0.02 of ice phase, while the phase weight fraction resulting from CH4 hydrate in the C3H3NO with 34H2O system was 0.72 of sII hydrate phase, 0.17 of ice phase, and 0.11 of sI hydrate phase (refer to Figure S1 in Supporting Information). A substantial decrease of ice phase in the binary (isoxazole + CH4) hydrate in the C3H3NO with 34H2O system is an indicator for the inclusion of methane in large cavities of sII hydrate, so-called tuning behavior. Raman spectroscopy was used to further identify the possible inclusion of methane in the hydrate structure as shown in Figures 3 and 4. In Figure 3, Raman spectra of both isoxazole (black line) and binary (isoxazole + CH4) hydrates (red line) in the C3H3NO with 17H2O system were shown. In full range spectra in Figure 3a, there is no significant difference between two hydrate samples without or with CH4 except for C−H vibration region around 2900 cm−1. The Raman signal from the inclusion of methane in small cavities of sII hydrate is observed at 2914 cm−1, and this Raman signal did not exhibit a shoulder pattern at 2904 cm−1 which is an evidence for CH4 inclusion in large cavities of sII hydrate as shown in our previous work for the binary (pyrrole + CH4) and (pyridine + CH4) clathrate hydrates.20 Isoxazole molecules are known to have a molecular size of 0.5751 nm,19 and they can occupy the large cavities of sII hydrate with almost full occupancy. Thus, we cannot observe the methane inclusion in large cavities of sII hydrate. In Figure 4, we can clearly see the Raman signal from the inclusion of methane in small cavities of sII hydrate at 2914 cm−1 and in large cavities of sII hydrate at 2904 cm−1 for the binary (isoxazole + CH4) hydrate in C3H3NO with 34H2O system. From the PXRD result of isoxazole hydrate in the C3H3NO with 34H2O system, the sII hydrate phase exists with an excess hexagonal ice phase. When CH4 gas is introduced to the isoxazole hydrate in the C3H3NO with 34H2O system, the original sII hydrate phase in the isoxazole hydrate will react with CH4 gas through the CH4 inclusion in small cavities of sII hydrate, and some portions of hexagonal ice phase may also participate the formation of sII hydrate with the introduction of

Figure 3. (A) Full range Raman spectra of isoxazole clathrate hydrate (black) and binary (isoxazole + CH4) clathrate hydrate (red) in the C3H3NO with 17H2O system, and (B) enlarged Raman spectra of the C−H vibration region.

CH4 gas. The transition of the excess ice phase into the formation of sII hydrate with the CH4 inclusion might induce the some portions of vacant large cavities in sII hydrate (refer to Figure 4), and the CH4 can be trapped in these large cavities via the tuning behavior. We obtained several Raman patterns from different sample spots as shown in Figure 5. Except for the top spectrum, all of peaks in other spectra show dominant positions for the C−H symmetric stretch in the small and large cavities of sII hydrates (please refer to black and blue lines in Figure 5). We also calculated the area ratio of Raman peaks between large and small cavities of sII hydrates, and the area ratio does not change much even though partial inhomogeneity may exist due to a small amount of sI hydrates. In other words, the PXRD result showed that the peak intensity of sI hydrate from (213) plane is much smaller than the intensity of sII hydrate from (115) plane (pink line in Figure 2). This clearly indicates that a relative amount of the sI hydrate phase in the (C3H3NO with 34H2O + CH4) hydrate is really small and most of the abundant phase in the (C3H3NO with 34H2O + CH4) hydrate is the sII hydrate with CH4 molecules encaged inside the large cavities of sII hydrate in terms of the tuning behavior (refer to Figure 6). D

dx.doi.org/10.1021/je500568f | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Figure 5. Enlarged Raman spectra of the C−H vibration region from repeated measurements of different samples in the binary (isoxazole + CH4) clathrate hydrate. The vertical black and red lines denotes CH4 occupying the small cavities of sII and sI, while the blue and green lines are for CH4 encaged in the large cavities of sII and sI. AS/AL values indicate the Raman peak area ratio between small to large cavities of sI or sII hydrate.

Figure 4. (A) Full range Raman spectra of isoxazole clathrate hydrate (black) and binary (isoxazole + CH4) clathrate hydrate (red) in the C3H3NO with 34H2O system, and (B) enlarged Raman spectra of the C−H vibration region.

Figure 6. Schematic diagram of tuning behavior in the binary (isoxazole + CH4) clathrate hydrate.

We measured the hydrate phase equilibrium conditions for the binary (pyrrole + CH4) and (pyridine + CH4) clathrate hydrates through MicroDSC.20 Moreover, we also identified that the hydrate phase equilibrium of sI CH4 hydrate from MicroDSC have close agreement with the results from CSMGem prediction.1,20 Therefore, we performed the experiments on the measurements of hydrate equilibrium conditions for the binary (isoxazole + CH4) clathrate hydrate by using MicroDSC. The hydrate equilibrium conditions for the binary (isoxazole + CH4) clathrate hydrate are plotted in Figure 7 and tabulated in Table 2 from the pressure conditions ranging from (3.0 to 9.0) MPa. These results show that the equilibrium conditions for the binary (isoxazole + CH4) clathrate hydrate at given pressures are milder than those for sI CH4 hydrate, but more severe than those for the binary (tetrahydrofuran + CH4) clathrate hydrate.22

■

CONCLUSIONS This study has investigated the water composition of isoxazole clathrate hydrate through powder X-ray diffraction studies. The result from PXRD patterns showed that the form of C3H3NO with 17H2O might be favorable in the isoxazole clathrate

Figure 7. Equilibrium pressure−temperature conditions for sI CH4 hydrate calculated by CSMGem (), binary (isoxazole + CH4) hydrates (red ●), and binary (THF + CH4)23 hydrates (blue ▲).

E

dx.doi.org/10.1021/je500568f | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

■

Table 2. Equilibrium Pressure−Temperature Conditions for the Binary (Isoxazole + CH4) Hydrate T/K 290.05 290.82 292.27 293.58 294.60 295.72 296.75

± ± ± ± ± ± ±

3.23 3.71 4.55 5.64 6.53 7.68 8.81

± ± ± ± ± ± ±

0.01 0.01 0.01 0.01 0.01 0.01 0.01

hydrate and the isoxazole hydrate with C3H3NO with 34H2O has an excess amount of hexagonal ice phase in its structure. We also identified the crystal structure and guest distribution of methane in the binary (isoxazole + CH4) clathrate in both C3H3NO with 17H2O and C3H3NO with 34H2O systems through Raman studies. Raman spectroscopy indicated that CH4 can be captured in both small and large cavities of structure II hydrate in the C3H3NO with 34H2O system through a tuning behavior, while CH4 can be entrapped in only small cavities of structure II hydrate in the C3H3NO with 17H2O system. The PXRD result also showed both clathrate hydrate samples exhibit the identical cubic Fd3m structure II hydrate as expected, but CH4 hydrate in the C3H3NO with 34H2O system have a small amount of hexagonal ice and structure I hydrate. The phase equilibrium conditions of binary (isoxazole + CH4) clathrate hydrate were determined in highpressure MicroDSC, and the dissociation temperatures of the binary (isoxazole + CH4) clathrate hydrate at given pressures are higher than those of pure CH4 hydrate. These results indicate that the binary (isoxazole + CH4) clathrate hydrate system can show the tuning phenomena of guest molecules in sII clathrate hydrates, and there can be a possible application of the isoxazole clathrate hydrate system to CH4 gas storage through the tuning mechanism.

■

ASSOCIATED CONTENT

S Supporting Information *

The Rietveld refinement of powder X-ray diffraction patterns of CH4 hydrates in both C3H3NO with 17H2O and C3H3NO with 34H2O systems. This material is available free of charge via the Internet at http://pubs.acs.org.

■

REFERENCES

(1) Sloan, E. D.; Koh, C. A. Clathrate Hydrates of Natural Gases, 3rd ed.; CRC Press: Boca Raton, FL, 2008. (2) Sloan, E. D. Fundamental principles and applications of natural gas hydrates. Nature 2003, 426, 353−359. (3) Ripmeester, J. A.; Ratcliffe, C. I.; Udachin, K. A. Encyclopedia of Supramolecular Chemistry; Marcel Dekker, Inc.: New York, 2004. (4) Lee, H.; Seo, Y.; Seo, T.-T.; Moudrakovski, I. L.; Ripmeester, J. A. Recovering Methane from Solid Methane Hydrate with Carbon Dioxide. Angew. Chem., Int. Ed. 2003, 42, 5048−5051. (5) Park, Y.; Kim, D.-Y.; Lee, J.-W.; Huh, D.-G.; Park, K.-P.; Lee, J.; Lee, H. Sequestering carbon dioxide into complex structures of naturally occurring gas hydrates. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 12690−12694. (6) Kang, S.-P.; Lee, H. Recovery of CO2 from flue gas using gas hydrate: Thermodynamic verification through phase equilibrium measurements. Environ. Sci. Technol. 2000, 34, 4397−4400. (7) Zhang, J.; Yedlapalli, P.; Lee, J. W. Thermodynamic Analysis of Hydrate-based Pre-combustion Capture of CO2. Chem. Eng. Sci. 2009, 64, 4732−4736. (8) Cha, J.-H.; Lee, W.; Lee, H. Thermal stability and ionic conductivity of the ionic clathrate hydrates incorporated with potassium hydroxide. J. Mater. Chem. 2009, 19, 6542−6547. (9) Cha, J.-H.; Lee, W.; Lee, H. Hydrogen Gas Sensor Based on Proton-Conducting Clathrate Hydrate. Angew. Chem., Int. Ed. 2009, 121, 8843−8846. (10) Florusse, L. J.; Peters, C. J.; Schoonman, J.; Hester, K. C.; Koh, C. A.; Dec, S. F.; Marsh, K. N.; Sloan, E. D. Stable low-pressure hydrogen clusters stored in a binary clathrate hydrate. Science 2004, 306, 469−471. (11) 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, 743−746. (12) Kim, D.-Y.; Lee, J.-W.; Seo, Y.-T.; Ripmeester, J. A.; Lee, H. Structural Transition and Tuning of the tert-Butylamine Hydrate. Angew. Chem., Int. Ed. 2005, 44, 7749−7752. (13) Kim, D.-Y.; Park, J.; Lee, J.-W.; Ripmeester, J. A.; Lee, H. Critical Guest Concentration and Complete Tuning Pattern Appearing in the Double Clathrate Hydrates. J. Am. Chem. Soc. 2006, 128, 15360−15361. (14) Sugahara, T.; Haag, J. C.; Prasad, P. S. R.; Warntjes, A. A.; Sloan, E. D.; Sum, A. K.; Koh, C. A. Increasing Hydrogen Storage Capacity Using Tetrahydrofuran. J. Am. Chem. Soc. 2009, 131, 14616−14617. (15) Sugahara, T.; Haag, J. C.; Warntjes, A. A.; Prasad, P. S. R.; Sloan, E. D.; Koh, C. A.; Sum, A. K. Large-Cage Occupancies of Hydrogen in Binary Clathrate Hydrates Dependent on Pressure and Guest Concentration. J. Phys. Chem. C 2010, 114, 15218−15222. (16) Zhang, J.; Lee, J. W. Enhanced Kinetics of CO2 Hydrate Formation under Static Conditions. Ind. Eng. Chem. Res. 2009, 48, 5934−5942. (17) Kaloustian, J.; Rosso, C.; Carbonnll, L. C.R. Acad. Sci. Paris, Ser. C 1972, 275, 249. (18) Sargent, D. F.; Calvert, L. D. Crystallographic Data for Some New Type II Clathrate Hydrates. J. Phys. Chem. 1966, 70, 2689−2691. (19) Gouch, S. R.; Garg, S. K.; Ripmeester, J. A.; Davidson, D. W. Isoxazole Hydrate. Can. J. Chem. 1974, 52, 3193−3195. (20) Cha, M.; Lee, H.; Lee, J. W. Thermodynamic and Spectroscopic Identification of Methane Inclusion in the Binary Heterocyclic Compound Hydrates. J. Phys. Chem. C 2013, 117, 23515−23521. (21) Cha, M.; Baek, S.; Lee, H.; Lee, J. W. Inclusion of Thiophene as a Co-Guest in Structure II Hydrate with Methane Gas. RSC Adv. 2014, 4, 26176−26180. (22) Laugier, J.; Bochu, B. Laboratoire des Materiaus et du Genie Physique, Ecole Superieure de Physique de Grenble; http://www. ccp14.ac.uk. (23) Seo, Y.-T.; Kang, S.-P.; Lee, H. Experimental Determination and Thermodynamic Modeling of Methane and Nitrogen Hydrates in the Presence of THF, Propylene Oxide, 1,4-Dioxane and Acetone. Fluid Phase Equilib. 2001, 189, 99−110.

P/MPa 0.2 0.2 0.2 0.2 0.2 0.2 0.2

Article

AUTHOR INFORMATION

Corresponding Author

*(J.W.L.) Tel.: +82-42-350-3940. Fax: +82-42-350-3910. Email: [email protected]. Address: Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea. Funding

This work (2014R1A2A2A01007076) was supported by the Midcareer Researcher Program through NRF grant funded by the Ministry of Science, ICT, and Future Planning. The authors are grateful for the partial financial support from ACS-PRF (under a grant number of 51991-ND9). This research was also made possible in part by a grant from BP/GoMRI. Notes

The authors declare no competing financial interest. F

dx.doi.org/10.1021/je500568f | J. Chem. Eng. Data XXXX, XXX, XXX−XXX