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Special Issue "Gas Hydrates: Formation, Structures, and Properties"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Physical Chemistry".

Deadline for manuscript submissions: closed (15 June 2021).

Special Issue Editors

Dr. Nobuo Maeda
E-Mail Website
Guest Editor
Department of Civil & Environmental Engineering, University of Alberta, Edmonton, AB, Canada
Interests: emulsions; nanobubbles and nanodroplets; phase transitions; nucleation
Dr. Zhiyuan Wang
E-Mail Website
Co-Guest Editor
School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, China
Interests: Hydrate formation and deposition; hydrate inhibition; phase transition; hydrate slurry rheology; natural gas hydrate recovering
Special Issues, Collections and Topics in MDPI journals
Dr. Xiaodong Shen
E-Mail Website
Co-Guest Editor
Chengdu University of Technology, Chengdu, China
Interests: gas hydrates; surfaces and interfaces; nucleation; growth; mass transfer

Special Issue Information

Dear Colleagues,

Interest and research on gas hydrates have been rising considerably in recent years. Flow assurance of oil and natural gas pipelines, exploitation of natural methane hydrate sedimetns, gas separation and storage, desalination and refrigeration have been researched extensively. Much progress has been made to date, however, several basic physical properties of gas hydrates still remain unknown, which include electromagnetic properties such as dielectric functions, phase diagrams and polymorphism at ultrahigh pressures, surface and interfacial specific free energies. Therefore, authors are invited to submit manuscripts to this Molecules Special Issue, “Gas Hydrates: Formation, Structures, and Properties”, in which all aspects related to gas hydates, such as hydrate formation and deposition, phase transition, structures, physical properties, hydrate inhibition, slurry rheology, and other fields about gas hydrates are discussed.

Dr. Nobuo Maeda
Prof. Dr. Zhiyuan Wang
Dr. Xiaodong Shen
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Gas Hydrate Structures
  • Gas Hydrate Properties
  • Gas Hydrate Formation
  • Gas Hydrate Deposition
  • Gas Hydrate Phase Transition
  • Gas Hydrate Inhibition
  • Gas Hydrate Slurry Rheology

Published Papers (10 papers)

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Research

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Article
Advances in the Study of Gas Hydrates by Dielectric Spectroscopy
Molecules 2021, 26(15), 4459; https://doi.org/10.3390/molecules26154459 - 24 Jul 2021
Viewed by 698
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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Article
Carbon Isotope Fractionation during the Formation of CO2 Hydrate and Equilibrium Pressures of 12CO2 and 13CO2 Hydrates
Molecules 2021, 26(14), 4215; https://doi.org/10.3390/molecules26144215 - 11 Jul 2021
Cited by 1 | Viewed by 645
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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Article
Rapid Gas Hydrate Formation—Evaluation of Three Reactor Concepts and Feasibility Study
Molecules 2021, 26(12), 3615; https://doi.org/10.3390/molecules26123615 - 12 Jun 2021
Cited by 1 | Viewed by 719
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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Article
Influence of Gas Supply Changes on the Formation Process of Complex Mixed Gas Hydrates
Molecules 2021, 26(10), 3039; https://doi.org/10.3390/molecules26103039 - 19 May 2021
Viewed by 710
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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Article
Kinetic Behavior of Quaternary Ammonium Hydroxides in Mixed Methane and Carbon Dioxide Hydrates
Molecules 2021, 26(2), 275; https://doi.org/10.3390/molecules26020275 - 07 Jan 2021
Cited by 4 | Viewed by 1073
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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Article
From Infrared Spectra to Macroscopic Mechanical Properties of sH Gas Hydrates through Atomistic Calculations
Molecules 2020, 25(23), 5568; https://doi.org/10.3390/molecules25235568 - 27 Nov 2020
Cited by 1 | Viewed by 813
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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Article
Rheology Impact of Various Hydrophilic-Hydrophobic Balance (HLB) Index Non-Ionic Surfactants on Cyclopentane Hydrates
Molecules 2020, 25(16), 3725; https://doi.org/10.3390/molecules25163725 - 15 Aug 2020
Cited by 3 | Viewed by 873
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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Review
Numerical Simulation on the Dissociation, Formation, and Recovery of Gas Hydrates on Microscale Approach
Molecules 2021, 26(16), 5021; https://doi.org/10.3390/molecules26165021 - 19 Aug 2021
Cited by 1 | Viewed by 525
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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Review
Hydrocarbon Hydrate Flow Assurance History as a Guide to a Conceptual Model
Molecules 2021, 26(15), 4476; https://doi.org/10.3390/molecules26154476 - 24 Jul 2021
Cited by 1 | Viewed by 616
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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Review
Brief Overview of Ice Nucleation
Molecules 2021, 26(2), 392; https://doi.org/10.3390/molecules26020392 - 13 Jan 2021
Cited by 2 | Viewed by 2735
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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