Hydrate Formation and Decomposition of CH4 and N2 in Ordered

Apr 28, 2015 - The use of hydrate formation in porous media is an effective method for gas storage and separation. The equilibrium isotherms of CH4 an...
1 downloads 15 Views 988KB Size
Download PDF
Article pubs.acs.org/jced

Hydrate Formation and Decomposition of CH4 and N2 in Ordered Mesoporous Carbon CMK‑3 in the Presence of Tetrahydrofuran Qiaobei Dong,† Yan Sun,*,† Wei Su,‡ and Jia Liu§ †

Department of Chemistry, School of Science, and ‡School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, P. R. China § College of Engineering, Peking University, Beijing 100087, P. R. China ABSTRACT: The use of hydrate formation in porous media is an effective method for gas storage and separation. The equilibrium isotherms of CH4 and N 2 in CMK-3, a mesoporous carbon material, were measured under different tetrahydrofuran (THF) concentrations and temperatures. The higher is the temperature required, the greater is the formation pressure needed, but the presence of THF significantly reduces the hydrate formation pressure. When THF exists, both CH4 and N2 form structure II (sII) hydrate; however, the amount of hydrate generation is lower than the theoretical value. As the operating pressure increases, some of the sII CH4 hydrate may transform into structure I (sI) and the amount of hydrate generation increases. The desorption isotherms showed that the gas hydrate decomposed completely when the operating pressure was below the hydrate decomposition pressure. In addition, it is feasible to separate gas mixtures via hydrate formation using the different gas hydrate formation pressures.

1. INTRODUCTION

hydrate formation pressures, and what changes will happen to the structure of hydrates after adding the promoter. Hydrates have also been found to be useful for gas separation and have the potential to consume lower amounts of energy than current separation methods. Separation is achieved by using the difference in phase equilibria of each component of the gas mixture to form hydrates. Song et al.14 separated CO2 from simulated fuel gas using hydrates in porous media. The formation pressures of gas hydrates in porous media are higher than those in pure water because of the resistance to gas diffusion through the pores. Thus, more energy consumption is needed to compress the gas. Researchers found that promoters, such as THF, cyclopentane, propane, and isobutene could reduce the gas hydrate formation pressure and promote the gas hydrate formation rate.15 Yang et al. separated CO2 from a fuel gas in porous media by adding THF and SDS promoters.16 The separation of CH4 and N2 has always been a difficult problem in the adsorption field. Hydrate separation in the nanometer space is a new attempt which reduces gas hydrate formation pressures by adding THF, combining with pressure swing adsorption to separate CH4 and N2 at same time. Sun et al. found that THF significantly reduced the gas hydrate formation pressure in the separation of CH4 and N2,17 but, there are few reports about the hydrate generation of experimental and theoretical value. Hence, this paper examines the sorption and desorption equilibrium of CH4 and N2

Gas hydrates (or clathrate hydrates) have very unique properties and are being applied in areas such as the storage of natural gas. Currently, natural gas is typically stored on-board vehicles using compression. However, this requires pressure of 20 MPa which induces safety issues and increases the cost of the fuel. Natural gas hydrate (NGH) storage has attracted great attention as a promising new storage method.1,2 In theory, NGHs can safely store 150 V/V to 200 V/V of natural gas in a very small space. In addition, NGHs are slow to decompose and easy to store; thus, NGH storage is much safer than the compression method. The core issue in NGH technology is the rapid formation of hydrates. Currently studies of gas hydrate formation are mainly focused on pure water systems. However, hydrate formation is slow in pure water and the rate of conversion almost never achieves 100 %.3 In addition, the hydrates do not completely decompose when the pressure is decreased.4 To solve this problem, some researchers have used porous media to make water molecules scatter on the surfaces of the materials, which increases the contact area of the gas and water, by this way to accelerate gas hydrate formation.5−10 Zhou et al. have reported that using water-wetted carbon can promote the rate of natural gas hydrate formation, reduce the storage pressure, and save costs.11−13 In addition, the hydrates are easy to decompose, besides the filling and releasing rates are also improved. However, some problems still need to be studied. For example, how to choose appropriate promoters to further reduce the © 2015 American Chemical Society

Received: October 30, 2014 Accepted: April 20, 2015 Published: April 28, 2015 1318

DOI: 10.1021/je500993h J. Chem. Eng. Data 2015, 60, 1318−1323

Journal of Chemical & Engineering Data

Article

Figure 1. High-pressure adsorption apparatus: V1−2, V4−5, V7−9, cutoff valves; V3, V6, metering valves; M1, M2, pressure gauges; M3, pressure transducer.

connection pipelines were evacuated. Then, a certain amount of gas was fed into the reference cell and the pressure was recorded. After that, the reference and adsorption cells were connected by opening V5 and V7, and the pressure was recorded. Since the gas is inhaled by the sample, the amount of gas in the free space is less than it was before the two cells were connected. This difference is the sorption amount and is calculated using the constitutional equation of authentic gas (pV = nZRT). The calculation process was reported in a previous publication.3 The compressibility factor (Z) was determined from the Virial equation. To avoid any loss of moisture, the adsorption cell containing the wet sample was placed in a chamber with a constant temperature of −30 °C for 4 h before the system was evacuated. The purity of helium, nitrogen, and methane was higher than 99.999 %. The gases were supplied by Tianjin Liufang Co., Ltd., China. The AR-grade THF was obtained from Aladdin Chemistry Co., Ltd., China.

hydrates in ordered mesoporous carbon CMK-3 under the different THF concentrations and temperatures, to provide basic data support for natural gas storage and gas mixture separation.

2. EXPERIMENTAL SECTION 2.1. Materials. Mesoporous silica material, SBA-15, with two-dimensional ordered channels was synthesized under acidic conditions. A nonionic oligomeric alkyl-ethylene oxide surfactant (Plouronic P123, Aladdin Reagent Co., Ltd., China) was used as the structure-directing agent, and TEOS (tetraethyl orthosilicate, AR, Tianjin Liyuan Chemical Co., Ltd., China) was used as the silica source. The SBA-15 was then used as the template and sucrose (AR, Tianjin Guangfu Science and Technology Development Co., Ltd., China) was used as the carbon source for preparing the CMK-3. The SBA-15 and sucrose were carbonized twice to give CMK-3. The specific preparation process was reported in previous publications.10,18 THF was dissolved in deionized water to form THF solutions with concentrations of 1.8 mol % to 12.6 mol %. The desired THF solution was then slowly added to the CMK3 by mechanical mixing to prepare the wet sample. 2.2. Apparatus. The sorption equilibria of CH4 and N2 in porous media were collected using the high-pressure apparatus which is shown in Figure 1. The reference cell was placed inside a temperature-controlled water bath in order to ensure a constant temperature Tr which was usually close to room temperature. The volume of the reference cell was determined by a drip method. The pressure in the reference cell was measured using a pressure transmitter (model PAA-23/8465.1200, Keller Druckmesstechnik, Switzerland). The maximum pressure of the pressure transmitter is 20 MPa, with an accuracy of 0.05 %. The wet sample was placed in the adsorption cell, and the temperature of the cell was maintained at a constant temperature. The volume of the adsorption cell was determined using helium at Tr. The calculation of sorption amount from the p−V−T readings before and after opening V5 and V7 was as follows: first, the reference cell, adsorption cell, and

3. RESULTS AND DISCUSSION 3.1. Characterizations of CMK-3. The CMK-3 was characterized using N2 adsorption isotherms at 77 K and the results are shown in Figure 2a. The specific surface area of the CMK-3 calculated from the BET equation is 936 m2/g. The total pore volume determined from the amount of N2 adsorbed at a relative pressure of 0.99 is 0.96 mL/g. The pore size distribution determined from the Barrett−Joyner−Halenda equation is shown in Figure 2b. The CMK-3 sample shows a very narrow pore size distribution with diameters in the range of 2 nm to 6 nm, and an average pore size of 3.5 nm. SEM and TEM images and the XRD patterns of the CMK-3 were reported in a previous publication.10 3.2. Equilibrium Isotherms of CH4 and N2. 3.2.1. Effect of THF Concentration on the Equilibrium Isotherms of CH4 and N2. The water content in the wet sample is denoted as Rw which is the mass ratio of the amount of water to the amount of CMK-3. Previously, it has been shown that the maximum amount of gas is fixed by the wet sample when the holes are exactly filled with water.19 That is, the optimal Rw = ρV/m, where ρ is the density of the water, V is the pore volume of 1319

DOI: 10.1021/je500993h J. Chem. Eng. Data 2015, 60, 1318−1323

Journal of Chemical & Engineering Data

Article

Figure 3. Sorption and desorption isotherms of CH4 without THF at 275.15 K.

Figure 2. (a) Nitrogen adsorption isotherm of CMK-3 at 77 K; (b) pore size distribution in the CMK-3.

CMK-3, and m is the mass of CMK-3. Because ρ = 1.0 g/mL, V is 1.0 mL/g, so, enough deionized water to make Rw = 1 was added to CMK-3. The concentration of THF is expressed as the molar amount of THF per total molar amount of water and THF which is designated as C (mol %). The amount adsorbed is very low at low pressure because the adsorption potential is weak when the pores are filled with water. As the pressures increased, significant inflection points appeared in the isotherms revealing that hydrates began to form and the storage mechanism was changed.6 The sorption amount increased with the increasing pressure. For example, at a THF concentration of 8.2 mol %, CH4 and N2 formed hydrates when the pressures were 0.4 and 1.3 MPa, respectively. The suction volume of the gases rose sharply at the inflection point due to the formation of gas hydrates. The maximum adsorption of CH4 and N2 gas were 53.6 % and 14.6 % respectively of the initial CH4 and N2 present when the pressure was 10 MPa. In the desorption stage, when the operating pressure is lower than the decomposition pressure, hydrates will decompose in great quantities, and the equilibrium isotherms drop sharply, until the hydrates decompose completely. Such conditions are very suitable for natural gas storage. The sorption and desorption isotherms do not overlap, due to the difference between hydrate formation and decomposition pressure. The CH4 sorption/desorption curves for the wet CMK-3 without any THF is shown in Figure 3; thus, THF can reduce the formation pressure of hydrate significantly. The formation curves are presumably due to pure sI formation without sII hydrate former at present. The equilibrium isotherms of CH4 and N2 in the wet CMK-3 with different THF concentrations are shown in Figure 4. In the range of experiment pressures (0−10 MPa), N2 cannot generate hydrate without THF. The effect of THF concentration on hydrate formation pressure is summarized in Figure 5.

Figure 4. Sorption and desorption isotherms of N2 and CH4 at different THF concentrations under 275.15 K: (A) 1.8, (B) 3.5, (C) 5.1, (D) 6.7, (E) 8.2, (F) 9.7, (G) 11.1, (H) 12.6 mol %.

As shown in Figure 5, CH4 and N2 hydrate formation pressures are different under the same THF concentration. Using the difference between CH4 and N2 hydrate formation pressure is suitable for gas separation when the THF concentration is below 12.6 mol %. Therefore, under the different operating pressures, people can choose the CMK-3 in 1320

DOI: 10.1021/je500993h J. Chem. Eng. Data 2015, 60, 1318−1323

Journal of Chemical & Engineering Data

Article

Table 1. State Data of Desorption Isotherm Drop at Different Temperatures under THF Concentration of 8.2 mol % (a) CH4

(b) CH4

Figure 5. Effect of THF concentration on the gas hydrate formation pressure at 275.15 K. (c) N2

which different THF concentrations aqueous solution was preadsorbed to achieve the separation of CH4 and N2. 3.2.2. Effect of Temperature on the Equilibrium Isotherms of N2 and CH4. The equilibrium isotherms of CH4 and N2 in the wet sample were measured at different temperatures with a THF concentration of 8.2 mol %. The results are shown in Figure 6. The higher is the temperature, the greater is the formation pressure, which shows that the rise of temperature is against the hydrate formation. 3.3. Decomposition Enthalpy of CH4 and N2 Hydrate. The CH4 and N2 decomposition enthalpy can be calculated by the decomposition pressures at points a, b, and c on CH4 and N2 desorption isotherms under different temperatures. The two plummets on the CH4 desorption isotherms indicate that the hydrate structure has changed. The decomposition enthalpy can be determined through the Clausius−Clapeyron equation: ⎡ d ln f ⎤ −ΔH = −R ⎢ ⎥ ⎣ d(1/T ) ⎦n

(1)

∫0

Φ

ln f

275 277 279 281 275 277 279 281 275 277 279 281

3.18 3.96 4.94 6.20 0.38 0.57 0.86 1.27 1.58 2.41 3.60 5.45

0.9262 0.9124 0.8956 0.8752 0.9872 0.9837 0.9780 0.9704 0.9942 0.9917 0.9883 0.9851

14.8957 15.1000 15.3026 15.5068 12.8350 13.2369 13.6425 14.0245 14.2671 14.6868 15.0958 15.4962

aqueous solution. The sI hydrate formation enthalpy is −60.9 kJ/mol.21 The decomposition enthalpy of CH4 hydrate at point a is 65.88 kJ/mol, which can be calculated from the slope of line 3, which is quite close to the transition enthalpy from sII into sI hydrate whose value is close to the formation enthalpy difference of type II and type I. This may prove that part of the sII hydrates transformed into sI hydrates. The decomposition enthalpy of N2 hydrate at point c is 129.74 kJ/mol, which is also quite close to the decomposition enthalpy of sII hydrate in pure water (130 kJ/mol). The sII hydrates being formed by N2 is also very reasonable. 3.4. The Calculation of the Amount of CH4 and N2 Fixed. According to the molar ratio of sI (CH4/H2O = 8:46) and sII (CH4/THF/H2O = 16:8:136) hydrate,22 the amount of CH4 theoretically fixed is calculated when H2O is completely

p

(z − 1) dp /p

p/MPa

Figure 7. Plot of ln f−1/T at different temperatures (1) CH4 b; (2) N2 c; (3) CH4 a.

where f is the fugacity (MPa), T is the temperature (K), and R is the gas constant (8.314 J·mol−1·K−1), because f = p × Φ and ln Φ =

T/K

(2)

where Φ is the fugacity coefficient and z is the compressibility factor. The gas inflection pressure, fugacity coefficient Φ, and ln f under different temperatures and a THF concentration of 8.2 mol % are shown in Table 1. The plot of ln f versus 1/T is shown in Figure 7. The decomposition enthalpy of CH4 at point b is 127.55 kJ/mol, which can be calculated from the slope of line 1 and is quite close to the decomposition enthalpy of sII hydrate in pure water (130 kJ/mol).20 Therefore, the two values are in reasonable agreement. The sII hydrates being formed by CH4 is very reasonable in porous media that has adsorbed THF in

Figure 6. Sorption and desorption isotherms of N2 and CH4 at different temperatures: (I) 277.15, (J) 279.15, (K) 281.15 K. 1321

DOI: 10.1021/je500993h J. Chem. Eng. Data 2015, 60, 1318−1323

Journal of Chemical & Engineering Data

Article

used to form the hydrate, and the amount of CH 4 experimentally fixed is read out when the pressure is 10 MPa from the sorption isotherms shown in Figure 4. The amounts of CH4 theoretically and experimentally fixed under different THF concentrations are listed in Table 2.

Table 3. Amount of N2 Theoretically (theor) and Experimentally (exp) Fixed under Different THF Concentrations THF concn mol·% 1.8 3.5 5.1 6.7 8.2 9.7 11.1 12.6

Table 2. Amount of CH4 Theoretically (theor) and Experimentally (exp) Fixed under Different THF Concentrations THF concn mol % 1.8 3.5 5.1 6.7 8.2 9.7 11.1 12.6

exp fixed −1

sII theor fixed

mmol·g

mmol·g

6.38 6.58 7.56 8.66 9.33 9.55 9.60 9.62

6.54

−1

sI theor fixed mmol·g−1 9.66

exp fixed mmol·g 1.63 2.03 2.06 3.14 3.16 3.20 3.22 3.60

−1

sII theor fixed mmol·g−1 6.54

4. CONCLUSIONS Through the study of equilibrium isotherms of CH4 and N2 in CMK-3 in the presence of THF, it is found that gas hydrates are more difficult to generate with the increase of temperature, but THF can obviously reduce the formation pressure in the hole, that is, people can store gas using the hydrate method at a relatively lower pressure. Besides, it can be seen from the equilibrium isotherms that when the pressure is lower than the hydrate decomposition pressure, gas hydrate can decompose completely and release gas, which is also beneficial to gas storage. This study also calculated the enthalpy change at the decomposition point of the desorption isotherms of CH4 and N2 and found that the enthalpy was similar to that of sII hydrate, which also proved that CH4 and N2 can both form sII hydrate in the presence of THF, but the hydrate generation is relatively lower than the theoretical value; through studies of the equilibrium of CH4 with different THF concentrations, it can be inferred that a portion of sII CH4 hydrates may changed into sI. In addition, according to the difference of hydrate formation pressures, it is feasible to separate CH4 and N2 via hydrate formation in the lower operating pressure with the presence of THF.

According to the molar ratio of sI hydrate (CH4/H2O = 8:46) and sII hydrate (CH4/THF/H2O = 16:8:136), the amount of CH4 theoretically fixed by sI hydrate is 9.66 mmol per gram of water, and that fixed by sII hydrate is 6.54 mmol per gram of water. The lower amount of CH4 theoretically fixed in sII hydrate is due to the existence of THF hydrate. THF occupies the big cavities in lattice structures, while CH4 occupies small cavities when they form sII hydrate of 16CH4· 8THF·136H2O. However, CH4 occupies both big and small cavities in sI hydrate of 8CH4·46H2O. The amount of CH4 experimentally fixed at 10 MPa can be read from sorption isotherms, which are shown in Figure 4. The theoretical and experimental values are listed in Table 2. The amounts of CH4 experimentally fixed are all between the theoretical calculation of sI and sII hydrate except the THF concentration of 1.8 mol % (the exception is due to insufficient THF). This shows that part of sII hydrate may transform into sI hydrate. This assumption can also be demonstrated by desorption isotherms (as shown in Figure 4) in which methane amounts plummet two times. As it is shown in Table 2, along with the increase of THF concentration, the final ratio of sI to sII also increased. THF, as a promoter, makes gas hydrates form easily at lower pressure. According to the structure of 16CH4·8THF·136H2O, in theory, all the water can be used to form sII hydrate when the THF concentration reaches 5.9 mol %. But in practice, a greater amount of THF may be needed. Therefore, a higher THF concentration is conducive to the formation of sII hydrates, and this beneficial effect also works at higher pressure at which the sI hydrate forms; therefore we concluded that the final ratio of sI to sII also increased along with the increase of THF concentration. But this beneficial effect also has a limit; therefore we can find that the values of experimentally fixed CH4 tend to be close when the THF concentration is higher than 9.7 mol %. N2 can form sII hydrate whether the THF exists or not.23,24 In the same way, the amounts of N2 experimentally and theoretically fixed under different THF concentrations when the pressure is 10 MPa are listed in Table 3. As can be seen from Table 3, there is a big gap between the amount of N2 experimentally fixed and that theoretically fixed. The specific reasons require further research.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +86-022-27406301. Fax: +86-022-27406301. Funding

This work was supported by the National Natural Science Foundation of China (NO.21206108), (NO.21406004) and Tianjin Municipal Science and Technology Commission (NO. 14JCYBJC21200). Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Gudmundsson, J.; Borrehaug, A. Natural gas hydrateAn alternative to liquefied natural gas. Pet. Rev. 1996, 50 (592), 232−5. (2) Lozano-Castello, D.; Alcaniz-Monge, J.; De la Casa-Lillo, M.; Cazorla-Amorós, D.; Linares-Solano, A. Advances in the study of methane storage in porous carbonaceous materials. Fuel 2002, 81 (14), 1777−1803. (3) Sloan Jr, E. D.; Koh, C. Clathrate Hydrates of Natural Gases. CRC Press: 2007. (4) Gudmundsson, J.; Parlaktuna, M. In Storage of natural gas hydrate at refrigerated conditions. AIChE Spring National Meeting, New Orleans: 1992; p 27.

1322

DOI: 10.1021/je500993h J. Chem. Eng. Data 2015, 60, 1318−1323

Journal of Chemical & Engineering Data

Article

(5) Zhou, L.; Sun, Y.; Zhou, Y. Enhancement of the methane storage on activated carbon by preadsorbed water. AIChE J. 2002, 48 (10), 2412−2416. (6) Zhou, Y.; Wang, Y.; Chen, H.; Zhou, L. Methane storage in wet activated carbon: Studies on the charging/discharging process. Carbon 2005, 43 (9), 2007−2012. (7) Sun, Y.; Wang, Y.; Zhang, Y.; Zhou, Y.; Zhou, L. CO2 sorption in activated carbon in the presence of water. Chem. Phys. Lett. 2007, 437 (1), 14−16. (8) Sun, Y.; Liu, X.-W.; Su, W.; Zhou, Y.; Zhou, L. Studies on ordered mesoporous materials for potential environmental and clean energy applications. Appl. Surf. Sci. 2007, 253 (13), 5650−5655. (9) Liu, J.; Zhou, Y.; Sun, Y.; Su, W.; Zhou, L. Methane storage in wet carbon of tailored pore sizes. Carbon 2011, 49 (12), 3731−3736. (10) Liu, X.; Zhou, L.; Li, J.; Sun, Y.; Su, W.; Zhou, Y. Methane sorption on ordered mesoporous carbon in the presence of water. Carbon 2006, 44 (8), 1386−1392. (11) Zhou, L.; Liu, J.; Su, W.; Sun, Y.; Zhou, Y. Progress in studies of natural gas storage with wet adsorbents. Energy Fuels 2010, 24 (7), 3789−3795. (12) Zhou, L.; Liu, X.; Sun, Y.; Li, J.; Zhou, Y. Methane sorption in ordered mesoporous silica SBA-15 in the presence of water. J. Phys. Chem. B 2005, 109 (48), 22710−22714. (13) Zhou, Y.; Dai, M.; Zhou, L.; Sun, Y.; Su, W. Storage of methane on wet activated carbon: Influence of pore size distribution. Carbon 2004, 42 (8), 1855−1858. (14) Song, Y.; Wang, X.; Yang, M.; Jiang, L.; Liu, Y.; Dou, B.; Zhao, J.; Wang, S. Study of selected factors affecting hydrate-based carbon dioxide separation from simulated fuel gas in porous media. Energy Fuels 2013, 27 (6), 3341−3348. (15) Sabil, K. M.; Witkamp, G.-J.; Peters, C. J. Phase equilibria in ternary (carbon dioxide + tetrahydrofuran + water) system in hydrateforming region: Effects of carbon dioxide concentration and the occurrence of pseudo-retrograde hydrate phenomenon. J. Chem. Thermodyn. 2010, 42 (1), 8−16. (16) Yang, M.; Liu, W.; Song, Y.; Ruan, X.; Wang, X.; Zhao, J.; Jiang, L.; Li, Q. Effects of additive mixture (THF/SDS) on the thermodynamic and kinetic properties of CO2/H2 hydrate in porous media. Ind. Eng. Chem. Res. 2013, 52 (13), 4911−4918. (17) Sun, Q.; Guo, X.; Liu, A.; Dong, J.; Liu, B.; Zhang, J.; Chen, G. Experiment on the separation of air-mixed coal bed methane in THF solution by hydrate formation. Energy Fuels 2012, 26 (7), 4507−4513. (18) Liu, X.; Zhou, L.; Fu, X.; Sun, Y.; Su, W.; Zhou, Y. Adsorption and regeneration study of the mesoporous adsorbent SBA-15 adapted to the capture/separation of CO2 and CH4. Chem. Eng. Sci. 2007, 62 (4), 1101−1110. (19) Zhou, L.; Sun, Y.; Su, W.; Zhou, Y. Natural gas storage in wet active carbonsA Report on research progress. Chin. J. Chem. Eng. 2005, 6, 020. (20) Carrol, J. J.; Du, J.; Jianfen, D. The correlations of the hydrates formation conditions of natural gas components. Nat. Gas Ind. 2002, 22 (2), 66−71. (21) Platteeuw, J. C.; von der Waals, J. H. Thermodynamic properties of gas hydrates. Mol. Phys. 1958, 1, 91−96. (22) Sharma, D.; Sowjanya, Y.; Chari, V. D.; Prasad, P. Methane storage in mixed hydrates with tetrahydrofuran. Indian J. Chem. Technol. 2014, 21, 114−119. (23) Davidson, D. W.; Handa, Y. P.; Ratcliffe, C. I. The ability of small molecules to form clathrate hydrates of structure II. Nature 1984, 311 (8), 142−143. (24) Davidson, D. W.; Handa, Y. P.; Ratcliffe, C. I. Crystallographic studies of clathrate hydrate. Mol. Cryst. Liq. Cryst. 1986, 141 (1), 141− 149.

1323

DOI: 10.1021/je500993h J. Chem. Eng. Data 2015, 60, 1318−1323