Greenhouse Gas (CHF<sub>3</sub>) Separation by Gas Hydrate Formation

Kim, Eunae; Ko, Gyeol; Seo, Yongwon

doi:10.1021/acssuschemeng.7b00821

Cited by 55 publications

(31 citation statements)

References 39 publications

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“…Kim et al measured the phase equilibrium curve of sI CH 3 F hydrate and discovered that it could form under relatively mild conditions. They also reported the three-phase equilibria of a CHF 3 +N 2 +H 2 O system with different concentrations and determined the thermodynamic stability conditions of the CHF 3 +N 2 hydrate . Recently, Kondo et al provided the phase boundary of sH hydrate formed with CH 3 F and pinacolone as guest molecules and demonstrated that the equilibrium pressure decreased significantly compared with that of simple sI CH 3 F hydrate when the temperature was below 291 K. Moreover, Ogawa et al reviewed the refrigeration system based on HFC hydrate.…”

Section: Introductionmentioning

confidence: 99%

Phase Diagrams and Spectral Characteristics of Hydrofluorocarbon Hydrates: Insights from First-Principles Thermodynamics

Sun

et al. 2021

ACS Sustainable Chem. Eng.

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Understanding the phase equilibrium conditions of hydrofluorocarbon (HFC) hydrates is significant to reduce greenhouse gas emissions and synthetic hydrates in experiments. Herein, we construct the phase diagrams of hydrates with HFCs (CH3F, CH2F2, CHF3, and CF4) as guest molecules through density functional theory and compare them with that of CH4 hydrate. At temperature and pressure that can be reproduced experimentally, the CH3F hydrate has one stable phase (the fully occupied phase 8CH3F@46H2O), and the CH2F2 hydrate has two stable phases (the large-cage fully occupied phase 6CH2F2@46H2O and the large- and small-cage fully occupied phase 8CH2F2@46H2O). The CHF3 hydrate has one stable phase (the large-cage fully occupied phase 6CHF3@46H2O), and the CF4 hydrate has one stable phase (the large-cage fully occupied phase 6CF4@46H2O). The Raman spectra and NMR chemical shifts of guest molecules are also briefly analyzed. With the increasing number of F atoms in guest molecules, the C–H symmetric stretching frequency of guest molecules in cages shows a blueshift, and the 13C NMR chemical shifts of HFCs molecules in cages shift to the positive direction. Our theoretical research shows the optimal equilibrium conditions of HFCs hydrates as refrigerants and provides theoretical guidance for the formation of HFCs hydrates in experiments.

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Section: Introductionmentioning

confidence: 99%

Phase Diagrams and Spectral Characteristics of Hydrofluorocarbon Hydrates: Insights from First-Principles Thermodynamics

Sun

et al. 2021

ACS Sustainable Chem. Eng.

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“…A more detailed description of the experimental apparatus and procedure is available in our previous papers. 7,9,14,23,24 Calculation Methods. The formation of the SF 6 + N 2 hydrate was simulated using the GROMACS source code.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…Many previous HBGS studies have focused on the equilibrium-stage separation covering phase equilibria of mixed clathrate hydrates, separation efficiency at an equilibrium state, and the equilibrium recovery ratio. ,,− ,, However, as time-dependent guest selectivity during hydrate formation and dissociation is highly related to the determination of the optimum operation time of the process, it is crucial to the process design and operation. Despite its importance, there have been just a few attempts to verify the time-dependent guest-enclathrating behaviors of HBGS, and most of them were associated with the guest partitioning of natural gas or CO 2 capture from biogas and CO 2 -rich natural gas. − There have been no previous studies on the time-dependent guest selectivity or guest-enclathrating/-releasing behaviors of SF 6 + N 2 hydrates, which are essential in designing and development of the hydrate-based SF 6 separation process.…”

Section: Introductionmentioning

confidence: 99%

Kinetic Selectivity of SF₆ during Formation and Dissociation of SF₆ + N₂ Hydrates and Its Significance in Hydrate-Based Greenhouse Gas Separation

Seo

2021

ACS Sustainable Chem. Eng.

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The time-dependent selectivity of SF6, the most potent global warming gas, in the hydrate-based gas separation process was investigated through both experimental and computational approaches. Guest-enclathrating and guest-releasing behaviors in SF6 + N2 hydrate were observed via gas chromatography, in situ Raman spectroscopy, and molecular dynamics (MD) simulations. The increasing pattern of the normalized area ratio of the Raman peak for enclathrated SF6 molecules was similar to that for enclathrated N2 during hydrate formation, and the composition of SF6 in the hydrate phase was almost constant throughout hydrate formation. MD simulations also showed that the captured SF6/N2 ratio in the hydrate structure was nearly constant over time. These results evidenced no remarkable difference in kinetic selectivity between SF6 and N2 during hydrate formation. The in situ Raman spectra and MD simulations examined during hydrate dissociation also demonstrated that SF6 was not kinetically selective in the guest-releasing process. The overall experimental and computational results indicated that none of the guest molecules in the SF6 + N2 hydrate were kinetically selective during formation and dissociation despite the superior thermodynamic selectivity of SF6. The findings of this work provide the features of guest-filling and guest-liberating behaviors during the formation and dissociation of SF6 + N2 hydrate. They will contribute to the determination of the optimal operation time for hydrate formation and thus to the development of the hydrate-based SF6 separation process.

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“…26,27,44 The formation of CH 3 radicals in the OCM process has been confirmed by Luo et al with synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) over Li/MgO catalyst. 45 In the presence of an enhanced concentration of CH 3 radicals, higher yields of VDF are achieved via Reaction (1).…”

Section: Effect Of Lanthanum Catalyst On the Combination Of Ocm And Cmentioning

confidence: 99%

“…Trifluoromethane (CHF 3 , HFC‐23) is a major carbon‐containing byproduct generated during the manufacture of CHClF 2 (HCFC‐22) . Importantly CHF 3 has a very high global warming potential – an estimated 14 800 times higher than that of CO 2 (based on a 100‐year time horizon).…”

Section: Introductionmentioning

confidence: 99%

Catalytic coupling of CH₄ with CHF₃ for the synthesis of VDF over LaOF catalyst

et al. 2018

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The oxidative coupling of methane (OCM) with CHF3 facilitates the synthesis of vinylidene fluoride (VDF). The aim is to utilize CHF3, which is otherwise considered a waste with a very high global warming potential. This study focuses on the effect of a LaOF catalyst on OCM occurring in the presence of CHF3, which engenders a promoting effect of O2 on CH4 activation. It examines the structural and phase changes of the lanthanum catalyst during the reaction and then speculates on the reaction mechanism. In combining OCM with CHF3, both the conversion of CH4 and the formation rate of VDF are almost tripled at 700°C. However, at higher temperatures, gas‐phase reactions play a dominating role in the conversion of CH4 and LaOF catalyst plays a very minor role in the reaction system at elevated temperatures. Irrespective of the reaction temperature, VDF is produced via the gas‐phase coupling of CH3 radicals with CF2. During pretreatment or during the reaction itself, La2O3 is fluorinated by CHF3 and HF, yielding the formation of surface LaOF and LaF3 species. LaF3 is a relatively inactive catalyst for CH4 conversion, whereas, in comparison LaOF appears to play a very important role in the activation of CH4 at low temperatures. The activation mechanism of CH4 at relatively low temperatures is similar with that postulated to occur during the OCM. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.

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Greenhouse Gas (CHF₃) Separation by Gas Hydrate Formation

Cited by 55 publications

References 39 publications

Phase Diagrams and Spectral Characteristics of Hydrofluorocarbon Hydrates: Insights from First-Principles Thermodynamics

Phase Diagrams and Spectral Characteristics of Hydrofluorocarbon Hydrates: Insights from First-Principles Thermodynamics

Kinetic Selectivity of SF₆ during Formation and Dissociation of SF₆ + N₂ Hydrates and Its Significance in Hydrate-Based Greenhouse Gas Separation

Catalytic coupling of CH₄ with CHF₃ for the synthesis of VDF over LaOF catalyst

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Greenhouse Gas (CHF3) Separation by Gas Hydrate Formation

Cited by 55 publications

References 39 publications

Phase Diagrams and Spectral Characteristics of Hydrofluorocarbon Hydrates: Insights from First-Principles Thermodynamics

Phase Diagrams and Spectral Characteristics of Hydrofluorocarbon Hydrates: Insights from First-Principles Thermodynamics

Kinetic Selectivity of SF6 during Formation and Dissociation of SF6 + N2 Hydrates and Its Significance in Hydrate-Based Greenhouse Gas Separation

Catalytic coupling of CH4 with CHF3 for the synthesis of VDF over LaOF catalyst

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Greenhouse Gas (CHF₃) Separation by Gas Hydrate Formation

Kinetic Selectivity of SF₆ during Formation and Dissociation of SF₆ + N₂ Hydrates and Its Significance in Hydrate-Based Greenhouse Gas Separation

Catalytic coupling of CH₄ with CHF₃ for the synthesis of VDF over LaOF catalyst