Infrared spectroscopy on the role of surfactants during methane hydrate formation

Rauh, Florian; Pfeiffer, Jens; Mizaikoff, Boris

doi:10.1039/c7ra05242a

Cited by 11 publications

(4 citation statements)

References 52 publications

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“…Experimental IR studies of gas hydrates were undertaken by Kumar et al [21] to identify the vibrations of carbon dioxide in different hydrate cages to estimate cage occupancies. Rauh et al [22] investigated the formation of methane hydrates using experimental infrared spectroscopy and highlighted key vibrational modes of the structure. The vibrational characteristics of THF sII gas hydrates were discussed by Vlasic et al [23] using ab initio DFT computations.…”

Section: Introductionmentioning

confidence: 99%

From Infrared Spectra to Macroscopic Mechanical Properties of sH Gas Hydrates through Atomistic Calculations

2020

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The vibrational characteristics of gas hydrates are key identifying molecular features of their structure and chemical composition. Density functional theory (DFT)-based IR spectra are one of the efficient tools that can be used to distinguish the vibrational signatures of gas hydrates. In this work, ab initio DFT-based IR technique is applied to analyze the vibrational and mechanical features of structure-H (sH) gas hydrate. IR spectra of different sH hydrates are obtained at 0 K at equilibrium and under applied pressure. Information about the main vibrational modes of sH hydrates and the factors that affect them such as guest type and pressure are revealed. The obtained IR spectra of sH gas hydrates agree with experimental/computational literature values. Hydrogen bond’s vibrational frequencies are used to determine the hydrate’s Young’s modulus which confirms the role of these bonds in defining sH hydrate’s elasticity. Vibrational frequencies depend on pressure and hydrate’s O···O interatomic distance. OH vibrational frequency shifts are related to the OH covalent bond length and present an indication of sH hydrate’s hydrogen bond strength. This work presents a new route to determine mechanical properties for sH hydrate based on IR spectra and contributes to the relatively small database of gas hydrates’ physical and vibrational properties.

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Section: Introductionmentioning

confidence: 99%

From Infrared Spectra to Macroscopic Mechanical Properties of sH Gas Hydrates through Atomistic Calculations

2020

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“…The aqueous solutions considered in this work consist of deionized water with a small amount (500 ppmw) of an anionic surfactant, either SDS (sodium dodecyl sulfate) or AOT (dioctyl sulfosuccinate sodium salt, known under its commercial name: AerosolOc-Tyl), both being excellent methane hydrate promoters. 46,53 The capillary, loaded with the two aqueous and gas phases separated by a meniscus at the pressure of the experiment, is placed in a heating−cooling stage (Linkam CAP500) that allows control of its position in the two horizontal directions (over a distance of ± 2.5 cm along the axis of the capillary), under the objective of a microscope used either in the transmission mode with video-monitoring (particularly in the meniscus region) or with confocal microRaman spectroscopy to provide the Raman spectral signatures of selected crosssections within the sample. With a 532 nm incident wavelength, a grating of 600 grooves/mm, and a 50× longdistance objective, the spatial resolution is close to the micrometer in the horizontal directions, and the spectral resolution in the range of 3 cm −1 .…”

Section: Experimental Setup and Procedures�outline Of The Studymentioning

confidence: 99%

“…The air initially present in the capillary is eliminated through repeated compression and purges. The aqueous solutions considered in this work consist of deionized water with a small amount (500 ppmw) of an anionic surfactant, either SDS (sodium dodecyl sulfate) or AOT (dioctyl sulfosuccinate sodium salt, known under its commercial name: AerosolOcTyl), both being excellent methane hydrate promoters. , …”

Section: Experimental Setup and Proceduresoutline Of The Studymentioning

confidence: 99%

“…This phenomenon does not seem to be connected with the occurrence of a critical micellar concentration in the aqueous solution, 4 , 38 − 42 as hypothesized in early studies. 33 , 43 Further tentative explanations of the promoting effect involve surfactant adsorption onto hydrate crystals, 44 − 46 an increased hydrate interfacial area and a decreased adhesion between hydrate particles. Enhanced presence of the hydrate former in the bulk aqueous solution has been observed concomitant to SDS-promoted hydrate growth.…”

Section: Introductionmentioning

confidence: 99%

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Growth Kinetics and Porous Structure of Surfactant-Promoted Gas Hydrate

Samar,

Venet,

Desmedt

et al. 2024

ACS Omega

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Surfactants present in tiny amounts in the aqueous phase are known to be efficient gas hydrate promoters; yet, the promotion mechanisms are still not fully understood. Understanding and directing those mechanisms is key to the implementation of gashydrate-based applications such as gas storage and separation, secondary refrigeration or water treatment, and desalination. In this work, the growth at the water/gas interface and the porous structure of surfactant-promoted methane hydrate are observed by optical microscopy and Raman imaging in glass capillaries used as optical cells. Hollow crystals are continuously generated and expelled from the methane/water meniscus into the water or surfactant solution, where they ultimately form the skeleton of a porous medium filled with the solution. Unprecedented information is gathered over a range of scales from the molecular scale (crystal structure and cage filling) to the mesoscale (crystal morphologies, growth habits and pore sizes) and macroscale (rates and amounts of water and gas converted into hydrate and hydrate porosity). Following an early steady-state growth regime, a sudden order-of-magnitude increase of the conversion rate occurs, which is related to gaseous methane microbubbles being directly incorporated across the meniscus in the aqueous solution and later converted to methane hydrate. An assessment and comparison are made of the mechanisms and performance of two common anionic surfactants known to be efficient gas hydrate promoters, SDS (sodium dodecyl sulfate) and AOT (dioctylsulfosuccinate sodium or AerosolOcTyl). AOT provides a quicker but more limited conversion into hydrate than SDS, suggesting that it is more appropriate for continuous flow processes while SDS is better suited for gas storage applications. Raman spectra reveal that cage filling by methane of structure I methane hydrate is not affected by surfactants.

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Progress in use of surfactant in nearly static conditions in natural gas hydrate formation

Pan

Shang

et al. 2020

Front. Energy

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Infrared spectroscopy on the role of surfactants during methane hydrate formation

Abstract: Studies on the role of surfactants at a molecular level during gas hydrate formation via in situ fiberoptic infrared spectroscopy.

Cited by 11 publications

References 52 publications

From Infrared Spectra to Macroscopic Mechanical Properties of sH Gas Hydrates through Atomistic Calculations

From Infrared Spectra to Macroscopic Mechanical Properties of sH Gas Hydrates through Atomistic Calculations

Growth Kinetics and Porous Structure of Surfactant-Promoted Gas Hydrate

Progress in use of surfactant in nearly static conditions in natural gas hydrate formation

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