Research

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14 pages, 4022 KiB

Open AccessArticle

Advances in the Study of Gas Hydrates by Dielectric Spectroscopy

by Ivan Lunev, Bulat Kamaliev, Valery Shtyrlin, Yuri Gusev, Airat Kiiamov, Yulia Zaripova, Artur Galiullin, Abdolreza Farhadian, Mikhail Varfolomeev and Malcolm Kelland

Molecules 2021, 26(15), 4459; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26154459 - 24 Jul 2021

Viewed by 2225

Abstract

The influence of kinetic hydrate inhibitors on the process of natural gas hydrate nucleation was studied using the method of dielectric spectroscopy. The processes of gas hydrate formation and decomposition were monitored using the temperature dependence of the real component of the dielectric [...] Read more.

The influence of kinetic hydrate inhibitors on the process of natural gas hydrate nucleation was studied using the method of dielectric spectroscopy. The processes of gas hydrate formation and decomposition were monitored using the temperature dependence of the real component of the dielectric constant ε′(T). Analysis of the relaxation times τ and activation energy ΔE of the dielectric relaxation process revealed the inhibitor was involved in hydrogen bonding and the disruption of the local structures of water molecules. Full article

(This article belongs to the Special Issue Gas Hydrates: Formation, Structures, and Properties)

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8 pages, 761 KiB

Open AccessArticle

Carbon Isotope Fractionation during the Formation of CO₂ Hydrate and Equilibrium Pressures of ¹²CO₂ and ¹³CO₂ Hydrates

by Hiromi Kimura, Go Fuseya, Satoshi Takeya and Akihiro Hachikubo

Molecules 2021, 26(14), 4215; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26144215 - 11 Jul 2021

Cited by 5 | Viewed by 2172

Abstract

Knowledge of carbon isotope fractionation is needed in order to discuss the formation and dissociation of naturally occurring CO₂ hydrates. We investigated carbon isotope fractionation during CO₂ hydrate formation and measured the three-phase equilibria of ¹²CO₂–H₂O [...] Read more.

Knowledge of carbon isotope fractionation is needed in order to discuss the formation and dissociation of naturally occurring CO₂ hydrates. We investigated carbon isotope fractionation during CO₂ hydrate formation and measured the three-phase equilibria of ¹²CO₂–H₂O and ¹³CO₂–H₂O systems. From a crystal structure viewpoint, the difference in the Raman spectra of hydrate-bound ¹²CO₂ and ¹³CO₂ was revealed, although their unit cell size was similar. The δ¹³C of hydrate-bound CO₂ was lower than that of the residual CO₂ (1.0–1.5‰) in a formation temperature ranging between 226 K and 278 K. The results show that the small difference between equilibrium pressures of ~0.01 MPa in ¹²CO₂ and ¹³CO₂ hydrates causes carbon isotope fractionation of ~1‰. However, the difference between equilibrium pressures in the ¹²CO₂–H₂O and ¹³CO₂–H₂O systems was smaller than the standard uncertainties of measurement; more accurate pressure measurement is required for quantitative discussion. Full article

(This article belongs to the Special Issue Gas Hydrates: Formation, Structures, and Properties)

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20 pages, 1729 KiB

Open AccessArticle

Rapid Gas Hydrate Formation—Evaluation of Three Reactor Concepts and Feasibility Study

by Florian Filarsky, Julian Wieser and Heyko Juergen Schultz

Molecules 2021, 26(12), 3615; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26123615 - 12 Jun 2021

Cited by 11 | Viewed by 2306

Abstract

Gas hydrates show great potential with regard to various technical applications, such as gas conditioning, separation and storage. Hence, there has been an increased interest in applied gas hydrate research worldwide in recent years. This paper describes the development of an energetically promising, [...] Read more.

Gas hydrates show great potential with regard to various technical applications, such as gas conditioning, separation and storage. Hence, there has been an increased interest in applied gas hydrate research worldwide in recent years. This paper describes the development of an energetically promising, highly attractive rapid gas hydrate production process that enables the instantaneous conditioning and storage of gases in the form of solid hydrates, as an alternative to costly established processes, such as, for example, cryogenic demethanization. In the first step of the investigations, three different reactor concepts for rapid hydrate formation were evaluated. It could be shown that coupled spraying with stirring provided the fastest hydrate formation and highest gas uptakes in the hydrate phase. In the second step, extensive experimental series were executed, using various different gas compositions on the example of synthetic natural gas mixtures containing methane, ethane and propane. Methane is eliminated from the gas phase and stored in gas hydrates. The experiments were conducted under moderate conditions (8 bar(g), 9–14 °C), using tetrahydrofuran as a thermodynamic promoter in a stoichiometric concentration of 5.56 mole%. High storage capacities, formation rates and separation efficiencies were achieved at moderate operation conditions supported by rough economic considerations, successfully showing the feasibility of this innovative concept. An adapted McCabe-Thiele diagram was created to approximately determine the necessary theoretical separation stage numbers for high purity gas separation requirements. Full article

(This article belongs to the Special Issue Gas Hydrates: Formation, Structures, and Properties)

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18 pages, 5606 KiB

Open AccessArticle

Influence of Gas Supply Changes on the Formation Process of Complex Mixed Gas Hydrates

by Mengdi Pan and Judith M. Schicks

Molecules 2021, 26(10), 3039; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26103039 - 19 May 2021

Cited by 5 | Viewed by 2113

Abstract

Natural gas hydrate occurrences contain predominantly methane; however, there are increasing reports of complex mixed gas hydrates and coexisting hydrate phases. Changes in the feed gas composition due to the preferred incorporation of certain components into the hydrate phase and an inadequate gas [...] Read more.

Natural gas hydrate occurrences contain predominantly methane; however, there are increasing reports of complex mixed gas hydrates and coexisting hydrate phases. Changes in the feed gas composition due to the preferred incorporation of certain components into the hydrate phase and an inadequate gas supply is often assumed to be the cause of coexisting hydrate phases. This could also be the case for the gas hydrate system in Qilian Mountain permafrost (QMP), which is mainly controlled by pores and fractures with complex gas compositions. This study is dedicated to the experimental investigations on the formation process of mixed gas hydrates based on the reservoir conditions in QMP. Hydrates were synthesized from water and a gas mixture under different gas supply conditions to study the effects on the hydrate formation process. In situ Raman spectroscopic measurements and microscopic observations were applied to record changes in both gas and hydrate phase over the whole formation process. The results demonstrated the effects of gas flow on the composition of the resulting hydrate phase, indicating a competitive enclathration of guest molecules into the hydrate lattice depending on their properties. Another observation was that despite significant changes in the gas composition, no coexisting hydrate phases were formed. Full article

(This article belongs to the Special Issue Gas Hydrates: Formation, Structures, and Properties)

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15 pages, 3947 KiB

Open AccessArticle

Kinetic Behavior of Quaternary Ammonium Hydroxides in Mixed Methane and Carbon Dioxide Hydrates

by Muhammad Saad Khan, Cornelius Borecho Bavoh, Khor Siak Foo, Azmi Mohd Shariff, Zamzila Kassim, Nurzatil Aqmar Bt Othman, Bhajan Lal, Iqbal Ahmed, Mohammad Azizur Rahman and Sina Rezaei Gomari

Molecules 2021, 26(2), 275; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26020275 - 07 Jan 2021

Cited by 13 | Viewed by 2642

Abstract

This study evaluates the kinetic hydrate inhibition (KHI) performance of four quaternary ammonium hydroxides (QAH) on mixed CH₄ + CO₂ hydrate systems. The studied QAHs are; tetraethylammonium hydroxide (TEAOH), tetrabutylammonium hydroxide (TBAOH), tetramethylammonium hydroxide (TMAOH), and tetrapropylammonium hydroxide (TPrAOH). The test [...] Read more.

This study evaluates the kinetic hydrate inhibition (KHI) performance of four quaternary ammonium hydroxides (QAH) on mixed CH₄ + CO₂ hydrate systems. The studied QAHs are; tetraethylammonium hydroxide (TEAOH), tetrabutylammonium hydroxide (TBAOH), tetramethylammonium hydroxide (TMAOH), and tetrapropylammonium hydroxide (TPrAOH). The test was performed in a high-pressure hydrate reactor at temperatures of 274.0 K and 277.0 K, and a concentration of 1 wt.% using the isochoric cooling method. The kinetics results suggest that all the QAHs potentially delayed mixed CH₄ + CO₂ hydrates formation due to their steric hindrance abilities. The presence of QAHs reduced hydrate formation risk than the conventional hydrate inhibitor, PVP, at higher subcooling conditions. The findings indicate that increasing QAHs alkyl chain lengths increase their kinetic hydrate inhibition efficacies due to better surface adsorption abilities. QAHs with longer chain lengths have lesser amounts of solute particles to prevent hydrate formation. The outcomes of this study contribute significantly to current efforts to control gas hydrate formation in offshore petroleum pipelines. Full article

(This article belongs to the Special Issue Gas Hydrates: Formation, Structures, and Properties)

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27 pages, 2616 KiB

Open AccessArticle

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

by Shaden M. Daghash, Phillip Servio and Alejandro D. Rey

Molecules 2020, 25(23), 5568; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25235568 - 27 Nov 2020

Cited by 11 | Viewed by 2534

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Gas Hydrates: Formation, Structures, and Properties)

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14 pages, 1727 KiB

Open AccessArticle

Rheology Impact of Various Hydrophilic-Hydrophobic Balance (HLB) Index Non-Ionic Surfactants on Cyclopentane Hydrates

by Khor Siak Foo, Cornelius Borecho Bavoh, Bhajan Lal and Azmi Mohd Shariff

Molecules 2020, 25(16), 3725; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25163725 - 15 Aug 2020

Cited by 16 | Viewed by 3252

Abstract

In this study, series of non-ionic surfactants from Span and Tween are evaluated for their ability to affect the viscosity profile of cyclopentane hydrate slurry. The surfactants; Span 20, Span 40, Span 80, Tween 20, Tween 40 and Tween 80 were selected and [...] Read more.

In this study, series of non-ionic surfactants from Span and Tween are evaluated for their ability to affect the viscosity profile of cyclopentane hydrate slurry. The surfactants; Span 20, Span 40, Span 80, Tween 20, Tween 40 and Tween 80 were selected and tested to provide different hydrophilic–hydrophobic balance values and allow evaluation their solubility impact on hydrate formation and growth time. The study was performed by using a HAAKE ViscotesterTM 500 at 2 °C and a surfactant concentration ranging from 0.1 wt%–1 wt%. The solubility characteristic of the non-ionic surfactants changed the hydrate slurry in different ways with surfactants type and varying concentration. The rheological measurement suggested that oil-soluble Span surfactants was generally inhibitive to hydrate formation by extending the hydrate induction time. However, an opposite effect was observed for the Tween surfactants. On the other hand, both Span and Tween demonstrated promoting effect to accelerate hydrate growth time of cyclopentane hydrate formation. The average hydrate crystallization growth time of the blank sample was reduced by 86% and 68% by Tween and Span surfactants at 1 wt%, respectively. The findings in this study are useful to understand the rheological behavior of surfactants in hydrate slurry. Full article

(This article belongs to the Special Issue Gas Hydrates: Formation, Structures, and Properties)

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Review

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21 pages, 64580 KiB

Open AccessReview

Numerical Simulation on the Dissociation, Formation, and Recovery of Gas Hydrates on Microscale Approach

by Mar’atus Sholihah and Wu-Yang Sean

Molecules 2021, 26(16), 5021; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26165021 - 19 Aug 2021

Cited by 6 | Viewed by 3350

Abstract

Investigations into the structures of gas hydrates, the mechanisms of formation, and dissociation with modern instruments on the experimental aspects, including Raman, X-ray, XRD, X-CT, MRI, and pore networks, and numerical analyses, including CFD, LBM, and MD, were carried out. The gas hydrate [...] Read more.

Investigations into the structures of gas hydrates, the mechanisms of formation, and dissociation with modern instruments on the experimental aspects, including Raman, X-ray, XRD, X-CT, MRI, and pore networks, and numerical analyses, including CFD, LBM, and MD, were carried out. The gas hydrate characteristics for dissociation and formation are multi-phase and multi-component complexes. Therefore, it was important to carry out a comprehensive investigation to improve the concept of mechanisms involved in microscale porous media, emphasizing micro-modeling experiments, 3D imaging, and pore network modeling. This article reviewed the studies, carried out to date, regarding conditions surrounding hydrate dissociation, hydrate formation, and hydrate recovery, especially at the pore-scale phase in numerical simulations. The purpose of visualizing pores in microscale sediments is to obtain a robust analysis to apply the gas hydrate exploitation technique. The observed parameters, including temperature, pressure, concentration, porosity, saturation rate, and permeability, etc., present an interrelationship, to achieve an accurate production process method and recovery of gas hydrates. Full article

(This article belongs to the Special Issue Gas Hydrates: Formation, Structures, and Properties)

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8 pages, 1504 KiB

Open AccessReview

Hydrocarbon Hydrate Flow Assurance History as a Guide to a Conceptual Model

by E. Dendy Sloan

Molecules 2021, 26(15), 4476; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26154476 - 24 Jul 2021

Cited by 8 | Viewed by 2120

Abstract

This work reviews major hydrocarbon hydrate advances in flowline applications of 25 international hydrate organizations. After a review of hydrate history and the current state-of-the-art, four conclusions were drawn: (1) engineers must take risks and cannot always afford the luxury to await scientific [...] Read more.

This work reviews major hydrocarbon hydrate advances in flowline applications of 25 international hydrate organizations. After a review of hydrate history and the current state-of-the-art, four conclusions were drawn: (1) engineers must take risks and cannot always afford the luxury to await scientific developments, (2) industry is more likely than academia to suggest hydrate needs and solutions, (3) the best hydrate blockage prevention practices are evolving and (4) a stepwise conceptual model can be proposed for a transient restart flowline hydrate blockage. Full article

(This article belongs to the Special Issue Gas Hydrates: Formation, Structures, and Properties)

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22 pages, 2140 KiB

Open AccessFeature PaperReview

Brief Overview of Ice Nucleation

by Nobuo Maeda

Molecules 2021, 26(2), 392; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26020392 - 13 Jan 2021

Cited by 20 | Viewed by 8108

Abstract

The nucleation of ice is vital in cloud physics and impacts on a broad range of matters from the cryopreservation of food, tissues, organs, and stem cells to the prevention of icing on aircraft wings, bridge cables, wind turbines, and other structures. Ice [...] Read more.

The nucleation of ice is vital in cloud physics and impacts on a broad range of matters from the cryopreservation of food, tissues, organs, and stem cells to the prevention of icing on aircraft wings, bridge cables, wind turbines, and other structures. Ice nucleation thus has broad implications in medicine, food engineering, mineralogy, biology, and other fields. Nowadays, the growing threat of global warming has led to intense research activities on the feasibility of artificially modifying clouds to shift the Earth’s radiation balance. For these reasons, nucleation of ice has been extensively studied over many decades and rightfully so. It is thus not quite possible to cover the whole subject of ice nucleation in a single review. Rather, this feature article provides a brief overview of ice nucleation that focuses on several major outstanding fundamental issues. The author’s wish is to aid early researchers in ice nucleation and those who wish to get into the field of ice nucleation from other disciplines by concisely summarizing the outstanding issues in this important field. Two unresolved challenges stood out from the review, namely the lack of a molecular-level picture of ice nucleation at an interface and the limitations of classical nucleation theory. Full article

(This article belongs to the Special Issue Gas Hydrates: Formation, Structures, and Properties)

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