Formation and dissociation behaviors of SF6 hydrates in the presence of a surfactant and an antifoaming agent for hydrate-based greenhouse gas (SF6) separation

Ko, Gyeol; Seo, Yongwon

doi:10.1016/j.cej.2020.125973

Cited by 34 publications

(12 citation statements)

References 42 publications

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“…The results indicate that both SF 6 and HFC134a molecules were enclathrated into the large cages (5 12 6 4 ) of the structure II-unit lattice after the hydrate began crystallizing, while there is no band corresponding to SF 6 and HFC134a occupying the residual small cages (5 12 ). These results are in good agreement with the reference data. ,,, As shown in Figure , the structure II (sII) of the SF 6 /HFC134a hydrate in the various concentrations of NaCl solutions remains unchanged, as evidenced by the lack of variation in the peak positions at 761 and 835 cm –1 during the hydrate formation process. Both pure SF 6 and HFC134a hydrate are known to form structure II. , Thus, it was confirmed that the addition of salt and gas blending did not change the structure of the SF 6 and HFC134a hydrates.…”

Section: Resultsmentioning

confidence: 99%

“…A higher than permissible limit concentration of the residual gas in water will require a secondary separation system for dissolved gas removal . On the basis of these considerations, sulfur hexafluoride (SF 6 ) has been selected as a target gas molecule for hydrate-based desalination because it has a low solubility in water (∼0.004% at 25 °C) and can form gas hydrates at low pressures. − …”

Section: Introductionmentioning

confidence: 99%

“…SF 6 is widely used in a variety of industries as an electrical insulating gas and etching reagent, including in semiconductor production and liquid-crystalline display development. , However, SF 6 is a potent greenhouse gas responsible for global warming (23 800 times more potent than CO 2 ) and has a long lifetime in the atmosphere (3200 years). , Moreover, the hydrate of SF 6 is known to have an intrinsically low formation rate. , The slow kinetics of hydrates has been considered the main factor hindering the commercialization of hydrate-based desalination technology. ,, To improve hydrate kinetics, surface-active agents have been utilized as additives to enhance the hydrate growth rate. ,, The relevant industries, however, do not prefer adding surface-active agents as they affect the feasibility and economics of the water purification process.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Salinity on Hydrate Phase Equilibrium and Kinetics of SF₆, HFC134a, and Their Mixture

et al. 2021

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In this study, the effects of salinity on the equilibrium and kinetics of sulfur hexafluoride (SF6), 1,1,1,2-tetrafluoroethane (HFC134a), and their mixture were evaluated to analyze their potential applications to hydrate-based desalination. The equilibrium pressure of the mixture gas (SF6/HFC134a) was lower than that of pure SF6 gas but higher than that of pure HFC134a gas. The thermodynamic effects of various concentrations (0, 3.5, 5, and 8 wt %) of NaCl on the gas hydrates were evaluated. Experiments were performed on the formation kinetics in the presence of NaCl solution at the same experimental temperature and pressure (274.15 K and 0.70 MPa). The hydrate growth rates decreased with increasing NaCl concentration. The rates also declined with time, associated with the inhibition of mass transfer between the gas and the liquid. During hydrate formation, the vapor compositions of the mixture gas were analyzed by in situ Raman spectroscopy and the results were consistent with those obtained by gas chromatography. Furthermore, an in situ Raman spectroscopic analysis demonstrated that the SF6 and HFC134a molecules occupy only the large cage (51264) of the structure II (sII) hydrate during SF6/HFC134a formation and the addition of salt did not change the structure of the SF6 and HFC134a hydrates. The hydrate phase behavior and kinetic results of this study can serve as foundational data for hydrate-based desalination technology and fluorinated gases separation and recovery processes.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of Salinity on Hydrate Phase Equilibrium and Kinetics of SF₆, HFC134a, and Their Mixture

et al. 2021

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“…After multiple heating–cooling cycles for a complete conversion of LMGS solution to gas hydrates, the temperature was raised at a rate of 0.5 K/min to detect the endothermic heat flow from the dissociation of formed gas hydrates. More detailed descriptions of the experimental setup and measurement procedure are available in our prior works. − …”

Section: Experimental Sectionmentioning

confidence: 99%

Complex Phase Behaviors and Structural Coexistence of Natural Gas Hydrates Containing Large-Molecule Guest Substances

Lee

Mok

et al. 2021

Energy Fuels

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The complex phase behaviors and structural coexistence of natural gas hydrates (NGHs) that contain large-molecule guest substances (LMGSs) were examined for their significance in the exploration and exploitation of NGHs as well as natural gas storage and transportation. Methylcyclopentane (MCP) and 2,2-dimethylbutane [neohexane (NH)] were chosen as LMGSs, and the simplest composition of NGHs and natural gas was simulated by a gas mixture of CH4 (90%) + C2H6 (10%). The coexistence of structure II (sII) and structure H (sH) hydrates in the CH4 + C2H6 + LMGS + water mixtures was revealed by 13C nuclear magnetic resonance (NMR) and powder X-ray diffraction (PXRD). CH4 and LMGSs were captured in sH, whereas CH4 and C2H6 were enclathrated in sII. Endothermic heat flow curves, which were obtained by a differential scanning calorimeter (DSC), and pressure (P)–temperature (T) traces exhibited two-step dissociation of formed gas hydrates (sH dissociation followed by sII dissociation). The experimental results for the PXRD patterns, 13C NMR spectra, phase equilibria, DSC heating curves, and P–T traces clearly demonstrated that the CH4 (90%) + C2H6 (10%) + LMGS + water mixtures formed both sII hydrates and sH hydrates and that the final hydrate structure at equilibrium dissociation points was sII.

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“…Clathrate hydrates are prospective materials for storage, capture, and separation of energy and greenhouse gases such as hydrogen, methane, carbon dioxide, sulfur hexafluoride, and nitrous oxide. − In particular, hydrate-based carbon capture and sequestration are of considerable interest to the hydrate field, and much research has been focused on carbon dioxide sequestration accompanying subsea natural gas production − and hydrate-based gas separation (HBGS) for carbon capture from syngas or flue gases. − Carbon dioxide can form a simple sI hydrate under moderate temperature and pressure conditions (for example, temperatures below 273 K at pressures of about 1.2 MPa) . In many research reports on HBGS, thermodynamic promoters such as THF, propane, or quaternary ammonium salts were used to moderate the harsh conditions for hydrate formation.…”

Section: Introductionmentioning

confidence: 99%

Incorporation of Ammonium Fluoride and Methanol in Carbon Dioxide Clathrate Hydrates and Their Significance for Hydrate-Based Gas Separation

Kim

Lee

Shin

et al. 2021

Ind. Eng. Chem. Res.

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Methanol is known as one of few small molecules that cannot stabilize a solid clathrate hydrate host lattice as a guest molecule in a simple hydrate phase. Recently, it was discovered that water−NH 4 F solutions can form clathrates consisting of solid solutions of water and NH 4 F, which have the same structure as the canonical clathrate hydrates. These doped phases were found to be able to incorporate strongly hydrophilic guests such as methanol. As the next step in testing the utility of these novel hydrates, we prepared NH 4 F-doped clathrates with simple CO 2 and binary CO 2 + methanol guest molecules and characterized these by powder X-ray diffraction (PXRD), Raman spectroscopy, and molecular dynamics (MD) simulations. From the PXRD analysis, it was confirmed that CO 2 interacts more strongly with the NH 4 F-doped 5 12 cages than the 5 12 cages without dopants. The MD simulations supported the PXRD results by demonstrating a strong interaction between the O atom of CO 2 and the dopant NH 4 + in the small cages. The incorporation of methanol into the CO 2 + methanol clathrates was confirmed by PXRD analysis. With low concentrations of methanol, this guest shows a preference for the 5 12 cages and may serve as a site blocker for the 5 12 cage that normally would be occupied by small molecules such as CH 4 and N 2 in hydrate-based gas separation (HGBS) processes. Phase boundary conditions for hydrate stability in CO 2 −NH 4 F−CH 3 OH− water were obtained, and it was determined that a solution of 5 mol % NH 4 F and 2.2 mol % CH 3 OH is a reasonable choice for operating an HBGS process. The present findings provide insight into the potential of the NH 4 F-doped hydrate lattice, aided by quantities of catalytic methanol, for use in HBGS processes.

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Formation and dissociation behaviors of SF6 hydrates in the presence of a surfactant and an antifoaming agent for hydrate-based greenhouse gas (SF6) separation

Cited by 34 publications

References 42 publications

Effects of Salinity on Hydrate Phase Equilibrium and Kinetics of SF₆, HFC134a, and Their Mixture

Effects of Salinity on Hydrate Phase Equilibrium and Kinetics of SF₆, HFC134a, and Their Mixture

Complex Phase Behaviors and Structural Coexistence of Natural Gas Hydrates Containing Large-Molecule Guest Substances

Incorporation of Ammonium Fluoride and Methanol in Carbon Dioxide Clathrate Hydrates and Their Significance for Hydrate-Based Gas Separation

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Formation and dissociation behaviors of SF6 hydrates in the presence of a surfactant and an antifoaming agent for hydrate-based greenhouse gas (SF6) separation

Cited by 34 publications

References 42 publications

Effects of Salinity on Hydrate Phase Equilibrium and Kinetics of SF6, HFC134a, and Their Mixture

Effects of Salinity on Hydrate Phase Equilibrium and Kinetics of SF6, HFC134a, and Their Mixture

Complex Phase Behaviors and Structural Coexistence of Natural Gas Hydrates Containing Large-Molecule Guest Substances

Incorporation of Ammonium Fluoride and Methanol in Carbon Dioxide Clathrate Hydrates and Their Significance for Hydrate-Based Gas Separation

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Product

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Effects of Salinity on Hydrate Phase Equilibrium and Kinetics of SF₆, HFC134a, and Their Mixture

Effects of Salinity on Hydrate Phase Equilibrium and Kinetics of SF₆, HFC134a, and Their Mixture