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10 pages, 10188 KB

Open AccessArticle

Morphological Study of Tetra-n-Butylammonium Bromide Semi-Clathrate Hydrate in Confined Space

by Lijuan Gu and Hailong Lu

Crystals 2024, 14(5), 408; https://doi.org/10.3390/cryst14050408 - 26 Apr 2024

Cited by 1 | Viewed by 1433

Tetra-n-butylammonium Bromide (TBAB) finds extensive use in diverse applications. An in-depth investigation into the effects of the formation conditions on TBAB hydrate is necessary to optimize the application process. This work focuses on examining the influence of the mass concentration of TBAB solution [...] Read more.

Tetra-n-butylammonium Bromide (TBAB) finds extensive use in diverse applications. An in-depth investigation into the effects of the formation conditions on TBAB hydrate is necessary to optimize the application process. This work focuses on examining the influence of the mass concentration of TBAB solution and the cooling rate on TBAB hydrate formation through optical microscopy and Raman spectroscopy. The TBAB hydrate formation process occurs in a confined space created by an optical sheet with a 0.03 mm deep groove. Four TBAB solutions of 13. 8 wt%, 18 wt%, 32 wt%, and 40 wt% are investigated, and the supercooling required for hydrate nucleation increases with concentration at a cooling rate of 0.5 K/min. Notably, Type A TBAB hydrate preferentially forms in all of the solutions, although type B hydrate is thermodynamically stable in the two dilute solutions. At a larger cooling rate of 2 K/min, two distinct crystal growth patterns are observed: one controlled by mass transfer and the other regulated by heat transfer. Increasing the cooling rate not only alters the optical morphology, but also reduces the supercooling due to a decrease in the Gibbs free energy barrier caused by a larger temperature gradient. This is beneficial for practical applications as it helps to alleviate the supercooling degree. Full article

(This article belongs to the Section Materials for Energy Applications)

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14 pages, 5404 KB

Open AccessArticle

Selective CO₂ Capture from CO₂/N₂ Gas Mixtures Utilizing Tetrabutylammonium Fluoride Hydrates

by Hyeonjin Kim and Yun-Ho Ahn

Molecules 2024, 29(6), 1284; https://doi.org/10.3390/molecules29061284 - 14 Mar 2024

Cited by 5 | Viewed by 2083

Abstract

Gas hydrates, a type of inclusion compound capable of trapping gas molecules within a lattice structure composed of water molecules, are gaining attention as an environmentally benign gas storage or separation platform. In general, the formation of gas hydrates from water requires high-pressure [...] Read more.

Gas hydrates, a type of inclusion compound capable of trapping gas molecules within a lattice structure composed of water molecules, are gaining attention as an environmentally benign gas storage or separation platform. In general, the formation of gas hydrates from water requires high-pressure and low-temperature conditions, resulting in significant energy consumption. In this study, tetrabutylammonium fluoride (TBAF) was utilized as a thermodynamic promoter forming a semi-clathrate-type hydrate, enabling gas capture or separation at room temperature. Those TBAF hydrate systems were explored to check their capability of CO₂ separation from flue gas, the mixture of CO₂ and N₂ gases. The formation rates and gas storage capacities of TBAF hydrates were systematically investigated under various concentrations of CO₂, and they presented selective CO₂ capture behavior during the hydrate formation process. The maximum gas storage capacities were achieved at 2.36 and 2.38 mmol/mol for TBAF·29.7 H₂O and TBAF·32.8 H₂O hydrate, respectively, after the complete enclathration of the feed gas of CO₂ (80%) + N₂ (20%). This study provides sufficient data to support the feasibility of TBAF hydrate systems to be applied to CO₂ separation from CO₂/N₂ gas mixtures based on their CO₂ selectivity. Full article

(This article belongs to the Section Nanochemistry)

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12 pages, 2929 KB

Open AccessArticle

The Adhesion Strength of Semi-Clathrate Hydrate to Different Solid Surfaces

by Zhen Xu, Lei Zheng, Zhen Dong, Aixian Liu, Yiwei Wang, Qiang Sun, Jianyi Chen and Xuqiang Guo

Processes 2023, 11(9), 2720; https://doi.org/10.3390/pr11092720 - 12 Sep 2023

Cited by 2 | Viewed by 1333

Abstract

The adhesion between a hydrate and a pipe wall is the main cause of hydrate deposition and blockage. In this study, the adhesion strength of semi-clathrate hydrate (tetrabutylammonium bromide hydrate) to four kinds of solid surfaces (E235B carbon steel, E355CC low alloy steel, [...] Read more.

The adhesion between a hydrate and a pipe wall is the main cause of hydrate deposition and blockage. In this study, the adhesion strength of semi-clathrate hydrate (tetrabutylammonium bromide hydrate) to four kinds of solid surfaces (E235B carbon steel, E355CC low alloy steel, SUS304 stainless steel, and polytetrafluoroethylene) was measured. This investigation reveals that the adhesion strength of the hydrate to a solid surface is negatively correlated with the wettability of the solid surface, which suggests that hydrophobic materials effectively reduced the hydrate adhesion to the pipe wall. The surface roughness showed different effects on the adhesion of the hydrate to hydrophilic or hydrophobic surfaces. To be specific, when the surface roughness increased from 3.2 µm to 12.5 µm, the hydrate adhesion strength to the hydrophilic surface of SUS304 increased by 123.6%, whereas the hydrate adhesion strength to the hydrophobic surface of polytetrafluoroethylene only increased by 21.5%. This study shows that low wettability and low surface roughness effectively reduce the critical rate required to remove hydrate deposition, which achieves the self-removal of hydrates. At the same time, it was found that the adhesion strength of the hydrate to surfaces increases with increasing subcooling. This investigation holds significant theoretical implications for designing self-cleaning surfaces for oil and gas pipes. Full article

(This article belongs to the Section Chemical Processes and Systems)

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11 pages, 1583 KB

Open AccessArticle

Study of the Effect of Tetrabutylammonium Halide Aqueous Solutions on the Gas Storage of Methane and Carbon Dioxide

by Parisa Naeiji, Tom K. Woo, Ryo Ohmura and Saman Alavi

Energies 2023, 16(13), 5001; https://doi.org/10.3390/en16135001 - 28 Jun 2023

Viewed by 1623

Abstract

In this study, the effect of tetrabutylammonium halide aqueous solutions on the gas storage of CH₄ and CO₂ gases were studied with molecular dynamics (MD) simulations. The results show that the surface tension and the gas molecules adsorbed at the interface [...] Read more.

In this study, the effect of tetrabutylammonium halide aqueous solutions on the gas storage of CH₄ and CO₂ gases were studied with molecular dynamics (MD) simulations. The results show that the surface tension and the gas molecules adsorbed at the interface decreases and increases, respectively, in the presence of TBAX (X: Br, Cl, F) in the aqueous phase compared to pure water at similar gas pressures. Both of these factors may facilitate gas uptake into cages during semi-clathrate hydrate formation. CO₂ showed a stronger intermolecular interaction with the water molecules since it was preferentially adsorbed at the interface, leading to a higher surface density as compared to CH₄. Moreover, the relative increase in CH₄ adsorption on the surface was because of the hydrophobic interactions between the CH₄ molecules and the n-alkyl chains of the cation. The counter-ions of TBAXs can affect their surface activity. TBAX salts enhance the tetrahedral ordering of water molecules at the interface compared to the bulk, leading to a potential mechanism for forming semi-clathrate hydrates. Full article

(This article belongs to the Special Issue Recent Advances in Gas Hydrate Research Related to the Flow, Storage and Transport of Gases)

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17 pages, 1378 KB

Open AccessReview

Hydrogen Hydrate Promoters for Gas Storage—A Review

by Tinku Saikia, Shirish Patil and Abdullah Sultan

Energies 2023, 16(6), 2667; https://doi.org/10.3390/en16062667 - 13 Mar 2023

Cited by 18 | Viewed by 5336

Abstract

Clathrate and semi-clathrate hydrates have recently been gaining major interest as hydrogen storage material. The benefits of hydrates, such as reversible formation and dissociation, their environmentally friendly nature, economical costs, and lower fire risk, make them one of the most promising hydrogen storage [...] Read more.

Clathrate and semi-clathrate hydrates have recently been gaining major interest as hydrogen storage material. The benefits of hydrates, such as reversible formation and dissociation, their environmentally friendly nature, economical costs, and lower fire risk, make them one of the most promising hydrogen storage materials. One of the major challenges when storing hydrogen in hydrate crystals is the extreme pressure and temperature conditions required for the formation of hydrogen hydrates. Solving the problems of extreme pressure and temperature through the use of promoter molecules would make these materials a promising storage medium with high potential. Through the use of efficient, economical, and green promoter molecules, hydrogen hydrate can be used to store large amounts of hydrogen economically and safely. This review aims to present a comprehensive summary of the different hydrate promoters that have been tested specifically in terms of hydrogen storage. The hydrate promoters are classed according to the structure of the hydrate crystals they form, i.e., sI, sII, sH, and semi-clathrate hydrate. This review article provides summarized information for readers about the different promoters tested and their benefits and shortcomings. Full article

(This article belongs to the Section I1: Fuel)

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12 pages, 5434 KB

Open AccessArticle

Intermolecular Interaction of Tetrabutylammonium and Tetrabutylphosphonium Salt Hydrates by Low-Frequency Raman Observation

by Yasuhiro Miwa, Tomoki Nagahama, Harumi Sato, Atsushi Tani and Kei Takeya

Molecules 2022, 27(15), 4743; https://doi.org/10.3390/molecules27154743 - 25 Jul 2022

Cited by 5 | Viewed by 2990

Abstract

Semi-clathrate hydrates are attractive heat storage materials because the equilibrium temperatures, located above 0 °C in most cases, can be changed by selecting guest cations and anions. The equilibrium temperatures are influenced by the size and hydrophilicity of guest ions, hydration number, crystal [...] Read more.

Semi-clathrate hydrates are attractive heat storage materials because the equilibrium temperatures, located above 0 °C in most cases, can be changed by selecting guest cations and anions. The equilibrium temperatures are influenced by the size and hydrophilicity of guest ions, hydration number, crystal structure, and so on. This indicates that intermolecular and/or interionic interaction in the semi-clathrate hydrates may be related to the variation of the equilibrium temperatures. Therefore, intermolecular and/or interionic interaction in semi-clathrate hydrates with quaternary onium salts was directly observed using low-frequency Raman spectroscopy, a type of terahertz spectroscopy. The results show that Raman peak positions were mostly correlated with the equilibrium temperatures: in the semi-clathrate hydrates with higher equilibrium temperatures, Raman peaks around 65 cm⁻¹ appeared at a higher wavenumber and the other Raman peaks at around 200 cm⁻¹ appeared at a lower wavenumber. Low-frequency Raman observation is a valuable tool with which to study the equilibrium temperatures in semi-clathrate hydrates. Full article

(This article belongs to the Special Issue Aquaphotomics - Exploring Water Molecular Systems in Nature)

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13 pages, 2125 KB

Open AccessArticle

Hydrogen Intramolecular Stretch Redshift in the Electrostatic Environment of Type II Clathrate Hydrates from Schrödinger Equation Treatment

by Christian J. Burnham, Zdenek Futera, Zlatko Bacic and Niall J. English

Appl. Sci. 2020, 10(23), 8504; https://doi.org/10.3390/app10238504 - 28 Nov 2020

Cited by 1 | Viewed by 2226

Abstract

The one-dimensional Schrödinger equation, applied to the H₂ intramolecular stretch coordinate in singly to quadruply occupied large cages in extended Type II (sII) hydrogen clathrate hydrate, was solved numerically herein via potential-energy scans from classical molecular dynamics (MD), employing bespoke force-matched H [...] Read more.

The one-dimensional Schrödinger equation, applied to the H₂ intramolecular stretch coordinate in singly to quadruply occupied large cages in extended Type II (sII) hydrogen clathrate hydrate, was solved numerically herein via potential-energy scans from classical molecular dynamics (MD), employing bespoke force-matched H₂–water potential. For both occupation cases, the resultant H–H stretch spectra were redshifted by ~350 cm⁻¹ vis-à-vis their classically sampled counterparts, yielding semi-quantitative agreement with experimental Raman spectra. In addition, ab initio MD was carried out systematically for different cage occupations in the extended sII hydrate to assess the effect of differing intra-cage intrinsic electric field milieux on H–H stretch frequencies; we suggest that spatial heterogeneity of the electrostatic environment is responsible for some degree of peak splitting. Full article

(This article belongs to the Special Issue Hydrogen Storage in Gas Hydrates)

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12 pages, 1253 KB

Open AccessArticle

Design of Ecological CO₂ Enrichment System for Greenhouse Production using TBAB + CO₂ Semi-Clathrate Hydrate

by Satoshi Takeya, Sanehiro Muromachi, Tatsuo Maekawa, Yoshitaka Yamamoto, Hiroko Mimachi, Takahiro Kinoshita, Tetsuro Murayama, Hiroki Umeda, Dong-Hyuk Ahn, Yasunaga Iwasaki, Hidenori Hashimoto, Tsutomu Yamaguchi, Katsunori Okaya and Seiji Matsuo

Energies 2017, 10(7), 927; https://doi.org/10.3390/en10070927 - 4 Jul 2017

Cited by 27 | Viewed by 6601

Abstract

This paper proposes an innovative CO₂ enrichment system for crop production under a controlled greenhouse environment by means of tetra-n-butylammonium bromide (TBAB) + CO₂ semi-clathrate hydrate (SC). In this system, CO₂ is captured directly from exhaust gas from [...] Read more.

This paper proposes an innovative CO₂ enrichment system for crop production under a controlled greenhouse environment by means of tetra-n-butylammonium bromide (TBAB) + CO₂ semi-clathrate hydrate (SC). In this system, CO₂ is captured directly from exhaust gas from a combustion heater at night, which can be used for stimulating photosynthesis of crops in greenhouses during daytime. Although the gas capacity of TBAB + CO₂ SC is less than that of CO₂ gas hydrate, it is shown that TBAB + CO₂ SC can store CO₂ for CO₂ enrichment in crop production even under moderate pressure conditions (<1.0 MPa) at 283 K. Full article

(This article belongs to the Special Issue Methane Hydrate Research and Development)

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