Molecular Cage Occupancy of Clathrate Hydrates at Infinite Dilution: Experimental Determination and Thermodynamic Significance

Seol, Jiwoong; Lee, Jun Young; Kim, Doyoun; Takeya, Satoshi; Ripmeester, John A.; Lee, Huen

doi:10.1021/jp909982n

Cited by 10 publications

(12 citation statements)

References 15 publications

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“…The cage occupancy of each guest in the small and large cages of sI and sII clathrates can be calculated through the following statistical thermodynamic equations by considering the area ratios of each guest and the number of carbons in each guest molecule: ,, where Δμ w ° is the chemical potential of the empty lattice relative to clathrate cages (Δμ w ° = μ W β – μ W H ) and θ i,J is the fractional cage occupancy of guest J in type i cage. The Δμ w ° values of 1297 J/mol for eq and 883.8 J/mol for eq were used for sI and sII clathrates, respectively. ,, The occupancy ratios of θ L,CH 4 /θ S,CH 4 and θ L,THF /θ S,CH 4 were obtained from the area ratios shown in Figure , and the composition ratio of CH 4 to CO 2 in the clathrate phase was obtained by GC measurement and the assumption of large cage occupancy . The calculated cage occupancy of each guest for the pure water and THF (5.6 mol %) solution systems is listed in Table along with the predicted values determined by CSMGem software .…”

Section: Resultsmentioning

confidence: 99%

“…The Δμ w °values of 1297 J/mol for eq 1 and 883.8 J/mol for eq 2 were used for sI and sII clathrates, respectively. 48,50,51 The occupancy ratios of θ L,CH 4 /θ S,CH 4 and θ L,THF /θ S,CH 4 were obtained from the area ratios shown in Figure 7, and the composition ratio of CH 4 to CO 2 in the clathrate phase was obtained by GC measurement and the assumption of large cage occupancy. 50 The calculated cage occupancy of each guest for the pure water and THF (5.6 mol %) solution systems is listed in Table 1 along with the predicted values determined by CSMGem software.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…48,50,51 The occupancy ratios of θ L,CH 4 /θ S,CH 4 and θ L,THF /θ S,CH 4 were obtained from the area ratios shown in Figure 7, and the composition ratio of CH 4 to CO 2 in the clathrate phase was obtained by GC measurement and the assumption of large cage occupancy. 50 The calculated cage occupancy of each guest for the pure water and THF (5.6 mol %) solution systems is listed in Table 1 along with the predicted values determined by CSMGem software. 17 For the pure water system, the estimated cage occupancy of CO 2 in the large 5 12 6 2 cages (0.669) was larger than that of CH 4 (0.311), and the cage occupancy of CO 2 in the small 5 12 cages (0.100) was much lower than that of CH 4 (0.655).…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

See 2 more Smart Citations

Clathrate-Based CO₂ Capture from Co₂-Rich Natural Gas and Biogas

Lim

Choi

Mok

et al. 2018

ACS Sustainable Chem. Eng.

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In this study, clathrate-based CO2 capture was investigated in the presence of thermodynamic promoters such as tetrahydrofuran (THF) and tetra-n-butyl ammonium chloride (TBAC) for upgrading CO2-rich natural gas and biogas. The phase equilibria, gas uptakes, gas composition measurements, and spectroscopic analyses of CH4 (50%), CO2 (50%), and promoter clathrates were examined with a primary focus on the effects of thermodynamic promoters on clathrate stability and cage filling behavior. The addition of THF and TBAC significantly enhanced the thermodynamic stability of CH4 (50%) and CO2 (50%) clathrates. 13C NMR and Raman spectroscopy clearly revealed that CO2 and CH4 are enclathrated in the clathrate cages. THF solutions demonstrated a faster growth rate of clathrates, but CO2 was less selective than CH4 in the THF clathrate phase due to the lower thermodynamic stability of the CO2 and THF clathrate compared to the CH4 and THF clathrate. TBAC solutions produced higher CO2 selectivity in the semiclathrate phase due to the presence of distorted small cages, which have a strong preference for CO2 molecules. The experimental results demonstrated that CO2 selectivity in the clathrate phase can be influenced by the thermodynamic stability, cage shape and dimension, and cage filling behavior in the presence of thermodynamic promoters, and thus, a suitable promoter and their optimum concentration should be carefully determined in designing and operating clathrate-based CO2 capture from natural gas or biogas.

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Section: Resultsmentioning

confidence: 99%

Section: ■ Experimental Sectionmentioning

confidence: 99%

Section: ■ Experimental Sectionmentioning

confidence: 99%

See 1 more Smart Citation

Clathrate-Based CO₂ Capture from Co₂-Rich Natural Gas and Biogas

Lim

Choi

Mok

et al. 2018

ACS Sustainable Chem. Eng.

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“…22 A slight increase in the mole ratio (3x/θ) can be observed with the elevated ratio of N With respect to the results described above, one would expect to understand the specific distributions of N 2 and CO 2 over different cages. In several studies, 38,39 cage occupancy ratio was realized as a simple and representative thermodynamic variable that provides the characteristic behavior of guest molecules clathrated in hydrate lattices. According to the results calculated, the cage occupancy ratios of N 2 and CO 2 molecules in both small (θ) cages and large (x) cages of the ternary hydrate are independent of the equilibrium temperature (see Figure S2 in Supporting Information).…”

Section: Occupancy Behaviors Of Guest Molecules In Cagesmentioning

confidence: 99%

Hydrate Phase Equilibrium of CH₄+N₂+CO₂ Gas Mixtures and Cage Occupancy Behaviors

Sun

Zhang

et al. 2017

Ind. Eng. Chem. Res.

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Methane, nitrogen, and carbon dioxide coexist after the injection of CO 2 /N 2 mixture into CH 4 hydrate. For a better understanding of CH 4 recovery and CO 2 sequestration by gas exchange involving N 2 , the hydrate phase equilibrium of CH 4 /N 2 /CO 2 ternary gas mixtures in pure water system was determined in a sapphire cell using the pressure-search method under isothermal conditions. The hydrate equilibrium data were analyzed with respect to the concentration of CH 4 and the ratio of N 2 /CO 2 . The cage occupancies of CH 4 , N 2 , and CO 2 were calculated by Chen−Guo hydrate model and CSMHYD program. The result revealed that the cage-specific guest distributions and preferential partitioning of guest molecules in cages were involved in the formation of mixed gas hydrates. The enthalpy of the ternary hydrates was calculated using the Clausius−Clapeyron equation. It was deduced that the enthalpy of the mixed hydrates was changed with the occupancy of CO 2 molecules in large cavities.

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“…In the case of ionic guest species, more complex intermolecular potentials of guest-host exist during the formation of the hydrate, because the guest-host interaction strongly affects the phase equilibrium, hydration number, chemical potential, cage occupancy fraction, and relative ratio of small to large cages. [15][16][17] A previous investigation showed that in artificial MH formed in Cheto and Otay clay (Na-MMT and Ca-MMT, 7.5-60 wt%) including various minerals, promotion effects on hydrate formation were found in the phase equilibrium condition. 8 As the clay concentration increased, higher promotion effects were shown.…”

Section: Broader Contextmentioning

confidence: 99%

Abnormal methane occupancy of natural gas hydrates in deep sea floor sediments

Yeon

Seol

Koh

et al. 2011

Energy Environ. Sci.

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Natural gas hydrates were recovered from near-seafloor sediments and analysed to compare two distinctive methane inclusion phenomena. We document the first observation of abnormal methane occupancy in sediment-rich NGH deposits.Natural gas hydrate (NGH) deposits in the deep sea floor are of interest to researchers because of their high potential as a next generation energy source. Among recovered NGHs, the structure I (sI) has been the most abundantly discovered hydrate worldwide. Regarding the existence of other NGH structures, Dr Ripmeester revealed that NGH samples collected from the Gulf of Mexico show sH and predicted that there are considerable sH NGH deposits in the ocean sediments. 1,2 However, we confirmed that sII and sH structures eventually transform to sI under severe conditions of continuous gaseous methane supply. 3 Marine sediments consist of a variety of geochemicals including clay minerals. Clay minerals comprise approximately 1 nm thick unit layers within micrometre-sized crystalline particles. This implies that the properties of gas hydrates confined in the clay interlayer are vastly different from those of gas hydrates in the bulk. 4 The interlayer mobile ions provide unique electrokinetic surroundings, where methane molecules are intercalated to form sI hydrate. Such heterogeneous complexity appearing in the mixed system of clay, water, light hydrocarbons, and cations are expected to strongly influence hydrate nucleation characteristics such as host water-lattice formation. Only a few studies have examined complex gas hydrate formation patterns in clay sediments, [5][6][7] with most works focusing on macroscopic identification of marine NGH sediments. In previous works, 8,9 we attempted to determine the phase behavior and cage occupancy of methane in clay sediments. Our analyses revealed that the gas hydrate formation in clays of Na-montmorillonite and Ca-montmorillonite differs greatly from that in pure gas hydrate. We also found that the interlayer cations might significantly affect the gas hydrate stability and cage occupancy of methane due to entrapment of cations in small cages.The purpose of the present investigation is to determine whether such abnormal methane occupancy significantly affects the overall stored methane amount in near-seafloor NGH. NGH samples recovered from three sites (06C, 08C, and 12C) in the East Sea (DongHae, 37 0 N and 132 0 S, 07GHP) located in the eastern part of the Korean Peninsula were tested to confirm the occurrence of abnormal methane population in marine NGH sediments. From these samples the clay-rich and NGH-rich parts were separated to characterize distinctive properties of each parts, as can be seen in the insets of Fig. 1.Solid-state 13 C MAS NMR spectroscopy was to evaluate the methane population at the recovered NGH, resulting in two peaks at À4.3 (sI-S) and À6.7 ppm (sI-L) in both clay-rich and NGH-rich parts, as shown in Fig. 1. The corresponding cage occupancy ratio, sI-L/sI-S, ranged from 3.5 to 3.9, which is quite close to the ideal ratio of ...

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Molecular Cage Occupancy of Clathrate Hydrates at Infinite Dilution: Experimental Determination and Thermodynamic Significance

Cited by 10 publications

References 15 publications

Clathrate-Based CO₂ Capture from Co₂-Rich Natural Gas and Biogas

Clathrate-Based CO₂ Capture from Co₂-Rich Natural Gas and Biogas

Hydrate Phase Equilibrium of CH₄+N₂+CO₂ Gas Mixtures and Cage Occupancy Behaviors

Abnormal methane occupancy of natural gas hydrates in deep sea floor sediments

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Molecular Cage Occupancy of Clathrate Hydrates at Infinite Dilution: Experimental Determination and Thermodynamic Significance

Cited by 10 publications

References 15 publications

Clathrate-Based CO2 Capture from Co2-Rich Natural Gas and Biogas

Clathrate-Based CO2 Capture from Co2-Rich Natural Gas and Biogas

Hydrate Phase Equilibrium of CH4+N2+CO2 Gas Mixtures and Cage Occupancy Behaviors

Abnormal methane occupancy of natural gas hydrates in deep sea floor sediments

Contact Info

Product

Resources

About

Clathrate-Based CO₂ Capture from Co₂-Rich Natural Gas and Biogas

Clathrate-Based CO₂ Capture from Co₂-Rich Natural Gas and Biogas

Hydrate Phase Equilibrium of CH₄+N₂+CO₂ Gas Mixtures and Cage Occupancy Behaviors