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Liu L, Guan D, Lu Y, Sun M, Liu Y, Zhao J, Yang L. A Molecular Dynamics Study on Xe/Kr Separation Mechanisms Using Crystal Growth Method. ACS OMEGA 2024; 9:25822-25831. [PMID: 38911791 PMCID: PMC11191100 DOI: 10.1021/acsomega.4c00108] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/04/2024] [Revised: 03/31/2024] [Accepted: 05/23/2024] [Indexed: 06/25/2024]
Abstract
The separation of xenon/krypton gas mixtures is a valuable but challenging endeavor in the gas industry due to their similar physical characteristics and closely sized molecules. To address this, we investigated the effectiveness of the hydrate-based gas separation method for mixed Xe-Kr gas via molecular dynamics (MD) simulations. The formation process of hydrates facilitates the encapsulation of guest molecules within hydrate cages, offering a potential strategy for gas separation. Higher temperatures and pressures are advantageous for accelerating the hydrate growth rate. The final occupancy of guest molecules and empty cages within 512, 51264, and all hydrate cages were thoroughly examined. An increase in the pressure and temperature enhanced the occupancy rates of Xe in both 512 and 51264 cages, whereas elevated pressure alone improved the occupancy of Kr in 51264 cages. However, the impact of temperature and pressure on Kr occupancy within 512 cages was found to be minimal. Elevated temperature and pressure resulted in a reduced occupancy of empty cages. Predominantly, 51264 cages were occupied by Xe, whereas Kr showed a propensity to occupy the 512 cages. With increasing simulated pressure, the final occupancy of Xe molecules in all cages rose from 0.37 to 0.41 for simulations at 260 K, while the final occupancy of empty cages decreased from 0.24 to 0.2.
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Affiliation(s)
- Liangliang Liu
- Shenyang
Aircraft Design Institute Shenyang 110042, China
| | - Dawei Guan
- Key
Laboratory of Ocean Energy Utilization and Energy Conservation of
Ministry of Education, Dalian University
of Technology, Dalian 116024, China
| | - Yi Lu
- Shenyang
Aircraft Design Institute Shenyang 110042, China
| | - Mingrui Sun
- Key
Laboratory of Ocean Energy Utilization and Energy Conservation of
Ministry of Education, Dalian University
of Technology, Dalian 116024, China
| | - Yu Liu
- Key
Laboratory of Ocean Energy Utilization and Energy Conservation of
Ministry of Education, Dalian University
of Technology, Dalian 116024, China
| | - Jiafei Zhao
- Key
Laboratory of Ocean Energy Utilization and Energy Conservation of
Ministry of Education, Dalian University
of Technology, Dalian 116024, China
| | - Lei Yang
- Key
Laboratory of Ocean Energy Utilization and Energy Conservation of
Ministry of Education, Dalian University
of Technology, Dalian 116024, China
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2
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Li K, Chen B, Yang M, Song Y, Sum AK. Methane hydrate phase equilibrium considering dissolved methane concentrations and interfacial geometries from molecular simulations. J Chem Phys 2023; 159:244505. [PMID: 38153154 DOI: 10.1063/5.0174705] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Accepted: 12/05/2023] [Indexed: 12/29/2023] Open
Abstract
Natural gas hydrates, mainly existing in permafrost and on the seabed, are expected to be a new energy source with great potential. The exploitation technology of natural gas hydrates is one of the main focuses of hydrate-related studies. In this study, a large-size liquid aqueous solution wrapping a methane hydrate system was established and molecular dynamics simulations were used to investigate the phase equilibrium conditions of methane hydrate at different methane concentrations and interfacial geometries. It is found that the methane concentration of a solution significantly affects the phase equilibrium of methane hydrates. Different methane concentrations at the same temperature and pressure can lead to hydrate formation or decomposition. At the same temperature and pressure, in a system reaching equilibrium, the size of spherical hydrate clusters is coupled to the solution concentration, which is proportional to the Laplace pressure at the solid-liquid interface. Lower solution concentrations reduce the phase equilibrium temperature of methane hydrates at the same pressure; as the concentration increases, the phase equilibrium temperature gradually approaches the actual phase equilibrium temperature. In addition, the interfacial geometry of hydrates affects the thermodynamic stability of hydrates. The spherical hydrate particles have the highest stability for the same volume. Through this study, we provide a stronger foundation to understand the principles driving hydrate formation/dissociation relevant to the exploitation of methane hydrates.
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Affiliation(s)
- Kehan Li
- Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education, Dalian University of Technology, Dalian, China
- Phases to Flow Laboratory, Chemical & Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, USA
| | - Bingbing Chen
- Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education, Dalian University of Technology, Dalian, China
| | - Mingjun Yang
- Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education, Dalian University of Technology, Dalian, China
| | - Yongchen Song
- Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education, Dalian University of Technology, Dalian, China
| | - Amadeu K Sum
- Phases to Flow Laboratory, Chemical & Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, USA
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3
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Guerra A, Mathews S, Su JT, Marić M, Servio P, Rey AD. Molecular dynamics predictions of transport properties for carbon dioxide hydrates under pre-nucleation conditions using TIP4P/Ice water and EPM2, TraPPE, and Zhang carbon dioxide potentials. J Mol Liq 2023. [DOI: 10.1016/j.molliq.2023.121674] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/30/2023]
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4
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Cao P. Structural Stability Evolutions of CH4 and CO2 Hydrate-Sand Nanoparticle Systems. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.121041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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5
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Wang L, Hall K, Zhang Z, Kusalik PG. Mixed Hydrate Nucleation: Molecular Mechanisms and Cage Structures. J Phys Chem B 2022; 126:7015-7026. [PMID: 36047925 DOI: 10.1021/acs.jpcb.2c03223] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The molecular-level details of the formation of mixed gas hydrates remain elusive despite their significance for a variety of scientific and industrial applications. In this study, extensive molecular simulations have been performed to examine the behavior of CH4/H2S mixed hydrate nucleation utilizing two different simulation setups varying in compositions and temperatures. The observed behavior exhibits similar phenomenology across the various systems once differences in nucleation rates and guest uptake are accounted for. We find that CH4 is always enriched in the hydrate phase while the aqueous phase is enriched in H2S. Even with H2S as a minor component (i.e., 10% mole fraction), the system can mirror the overall nucleation kinetics of pure H2S hydrate systems with CH4-dominant nuclei. Through analyses of cages and their transitions, nonstandard cages, particularly those with 12 faces (e.g., 51062), have been found to be key intermediate cage types in the early stage of nucleation. Additionally, we present previously unreported cage types comprising heptagonal faces (e.g., 596271) as having a significant role in the early-stage gas hydrate structural transitions.
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Affiliation(s)
- Lei Wang
- Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, T2N 1N4 Alberta, Canada
| | - Kyle Hall
- Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, T2N 1N4 Alberta, Canada
| | - Zhengcai Zhang
- Laboratory for Marine Mineral Resources, Pilot National Laboratory for Marine Science and Technology, Qingdao 266071, China
| | - Peter G Kusalik
- Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, T2N 1N4 Alberta, Canada
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6
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Guerra A, Mathews S, Marić M, Servio P, Rey AD. All-Atom Molecular Dynamics of Pure Water-Methane Gas Hydrate Systems under Pre-Nucleation Conditions: A Direct Comparison between Experiments and Simulations of Transport Properties for the Tip4p/Ice Water Model. MOLECULES (BASEL, SWITZERLAND) 2022; 27:molecules27155019. [PMID: 35956968 PMCID: PMC9370622 DOI: 10.3390/molecules27155019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/12/2022] [Revised: 07/29/2022] [Accepted: 08/02/2022] [Indexed: 11/24/2022]
Abstract
(1) Background: New technologies involving gas hydrates under pre-nucleation conditions such as gas separations and storage have become more prominent. This has necessitated the characterization and modeling of the transport properties of such systems. (2) Methodology: This work explored methane hydrate systems under pre-nucleation conditions. All-atom molecular dynamics simulations were used to quantify the performance of the TIP4P/2005 and TIP4P/Ice water models to predict the viscosity, diffusivity, and thermal conductivity using various formulations. (3) Results: Molecular simulation equilibrium was robustly demonstrated using various measures. The Green–Kubo estimation of viscosity outperformed other formulations when combined with TIP4P/Ice, and the same combination outperformed all TIP4P/2005 formulations. The Green–Kubo TIP4P/Ice estimation of viscosity overestimates (by 84% on average) the viscosity of methane hydrate systems under pre-nucleation conditions across all pressures considered (0–5 MPag). The presence of methane was found to increase the average number of hydrogen bonds over time (6.7–7.8%). TIP4P/Ice methane systems were also found to have 16–19% longer hydrogen bond lifetimes over pure water systems. (4) Conclusion: An inherent limitation in the current water force field for its application in the context of transport properties estimations for methane gas hydrate systems. A re-parametrization of the current force field is suggested as a starting point. Until then, this work may serve as a characterization of the deviance in viscosity prediction.
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Li J, Lu J, Wang Z. Non-equilibrium decomposition dynamics and fluctuation-dissipation analysis of structure I methane hydrate in confined space. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.119980] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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8
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Liu Y, Sun J, Chen C, Li W, Qin Y, Wang Y. Molecular insights into gas hydrate formation in the presence of graphene oxide solid surfaces. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.119309] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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9
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Molecular insights into the heterogeneous crystal growth of tetrahydrofuran hydrate: Kinetic and interfacial properties. J Mol Graph Model 2022; 115:108205. [DOI: 10.1016/j.jmgm.2022.108205] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2022] [Revised: 04/17/2022] [Accepted: 04/23/2022] [Indexed: 11/22/2022]
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10
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Mileo PGM, Rogge SMJ, Houlleberghs M, Breynaert E, Martens JA, Van Speybroeck V. Interfacial study of clathrates confined in reversed silica pores. JOURNAL OF MATERIALS CHEMISTRY. A 2021; 9:21835-21844. [PMID: 34707871 PMCID: PMC8491980 DOI: 10.1039/d1ta03105h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Accepted: 08/22/2021] [Indexed: 05/08/2023]
Abstract
Storing methane in clathrates is one of the most promising alternatives for transporting natural gas (NG) as it offers similar gas densities to liquefied and compressed NG while offering lower safety risks. However, the practical use of clathrates is limited given the extremely low temperatures and high pressures necessary to form these structures. Therefore, it has been suggested to confine clathrates in nanoporous materials, as this can facilitate clathrate's formation conditions while preserving its CH4 volumetric storage. Yet, the choice of nanoporous materials to be employed as the clathrate growing platform is still rather arbitrary. Herein, we tackle this challenge in a systematic way by computationally exploring the stability of clathrates confined in alkyl-grafted silica materials with different pore sizes, ligand densities and ligand types. Based on our findings, we are able to propose key design criteria for nanoporous materials favoring the stability of a neighbouring clathrate phase, namely large pore sizes, high ligand densities, and smooth pore walls. We hope that the atomistic insight provided in this work will guide and facilitate the development of new nanomaterials designed to promote the formation of clathrates.
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Affiliation(s)
- Paulo G M Mileo
- Center for Molecular Modeling (CMM), Ghent University Technologiepark 46 B-9052 Zwijnaarde Belgium
| | - Sven M J Rogge
- Center for Molecular Modeling (CMM), Ghent University Technologiepark 46 B-9052 Zwijnaarde Belgium
| | - Maarten Houlleberghs
- Center for Surface Chemistry and Catalysis, Katholieke Universiteit Leuven Celestijnenlaan 200F 3001 Heverlee Belgium
| | - Eric Breynaert
- Center for Surface Chemistry and Catalysis, Katholieke Universiteit Leuven Celestijnenlaan 200F 3001 Heverlee Belgium
| | - Johan A Martens
- Center for Surface Chemistry and Catalysis, Katholieke Universiteit Leuven Celestijnenlaan 200F 3001 Heverlee Belgium
| | - Veronique Van Speybroeck
- Center for Molecular Modeling (CMM), Ghent University Technologiepark 46 B-9052 Zwijnaarde Belgium
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11
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Cao P, Li T, Ning F, Wu J. Mechanical Instability of Methane Hydrate-Mineral Interface Systems. ACS APPLIED MATERIALS & INTERFACES 2021; 13:46043-46054. [PMID: 34520161 DOI: 10.1021/acsami.1c08114] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Massive methane hydrates occur on sediment matrices in nature. Therefore, sediment-based methane hydrate systems play an essential role in the society and hydrate community, including energy resources, global climate changes, and geohazards. However, a fundamental understanding of mechanical properties of methane hydrate-mineral interface systems is largely limited due to insufficient experimental techniques. Herein, by using large-scale molecular simulations, we show that the mechanical properties of methane hydrate-mineral (silica, kaolinite, and Wyoming-type montmorillonite) interface systems are strongly dictated by the chemical components of sedimentary minerals that determine interfacial microstructures between methane hydrates and minerals. The tensile strengths of hydrate-mineral systems are found to decrease following the order of Wyoming-type montmorillonite- > silica- > kaolinite-based methane hydrate systems, all of which show a brittle failure at the interface between methane hydrates and minerals under tension. In contrast, upon compression, methane hydrates decompose into water and methane molecules, resulting from a large strain-induced mechanical instability. In particular, the failure of Wyoming-type montmorillonite-based methane hydrate systems under compression is characterized by a sudden decrease in the compressive stress at a strain of around 0.23, distinguishing it from those of silica- and kaolinite-based methane hydrate systems under compression. Our findings thus provide a molecular insight into the potential mechanisms of mechanical instability of gas hydrate-bearing sediment systems on Earth.
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Affiliation(s)
- Pinqiang Cao
- Faculty of Engineering, China University of Geosciences, Wuhan, Hubei 430074, China
- Department of Civil & Environmental Engineering, The George Washington University, Washington, District of Columbia 20052, United States
- Department of Physics, Jiujiang Research Institute, Research Institute for Biomimetics and Soft Matter, Fujian Provincial Key Laboratory for Soft Functional Materials Research, Xiamen University, Xiamen, Fujian 361005, China
- School of Resource and Environmental Engineering, Wuhan University of Science and Technology, Wuhan, Hubei 430081, China
| | - Tianshu Li
- Department of Civil & Environmental Engineering, The George Washington University, Washington, District of Columbia 20052, United States
| | - Fulong Ning
- Faculty of Engineering, China University of Geosciences, Wuhan, Hubei 430074, China
| | - Jianyang Wu
- Department of Physics, Jiujiang Research Institute, Research Institute for Biomimetics and Soft Matter, Fujian Provincial Key Laboratory for Soft Functional Materials Research, Xiamen University, Xiamen, Fujian 361005, China
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12
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Zhang L, Zhuang Q, Wen Z, Zhang P, Ma W, Wu Q, Yun H. Spatial state distribution and phase transition of non-uniform water in soils: Implications for engineering and environmental sciences. Adv Colloid Interface Sci 2021; 294:102465. [PMID: 34126567 DOI: 10.1016/j.cis.2021.102465] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2021] [Revised: 06/04/2021] [Accepted: 06/06/2021] [Indexed: 10/21/2022]
Abstract
The physical behaviors of water in the interface are the fundamental to discovering the engineering properties and environmental effects of aqueous porous media (e.g., soils). The pore water pressure (PWP) is a key parameter to characterize the pore water state (PWS) and its phase transition in the micro interface. Traditionally, the water in the interface is frequently believed to be uniform, negative in pressure and tensile based on macroscopic tests and Gibbs interface model. However, the water in the interface is a non-uniform and compressible fluid (part of tensile and part of compressed), forming a spatial profile of density and PWP depending on its distance from the substrate interface. Herein, we introduced the static and dynamic theory methods of non-uniform water based on diffuse interface model to analyze non-uniform water state dynamics and water density and PWP. Based on the theory of non-uniform water, we gave a clear stress analysis on soil water and developed the concepts of PWS, PWP and matric potential in classical soil mechanics. In addition, the phase transition theory of non-uniform water is also examined. In nature, the generalized Clausius-Clapeyron equation (GCCE) is consistent with Clapeyron equation. Therefore, a unified interpretation is proposed to justify the use of GCCE to represent frozen soil water dynamics. Furthermore, the PWP description of non-uniform water can be well verified by some experiments focusing on property variations in the interface area, including the spatial water density profile and unfrozen water content variations with decreasing temperature and other factors. In turn, PWP spatial distribution of non-uniform water and its states can well explain some key phenomena on phase transition during ice or hydrate formation, including the discrepancies of phase transition under a wide range of conditions.
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13
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Liu N, Zhu H, Zhou J, Yang L, Liu D. Molecular dynamics simulations on formation of CO2 hydrate in the presence of metal particles. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2021.115793] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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14
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Reduced phase stability and faster formation/dissociation kinetics in confined methane hydrate. Proc Natl Acad Sci U S A 2021; 118:2024025118. [PMID: 33850020 DOI: 10.1073/pnas.2024025118] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The mechanisms involved in the formation/dissociation of methane hydrate confined at the nanometer scale are unraveled using advanced molecular modeling techniques combined with a mesoscale thermodynamic approach. Using atom-scale simulations probing coexistence upon confinement and free energy calculations, phase stability of confined methane hydrate is shown to be restricted to a narrower temperature and pressure domain than its bulk counterpart. The melting point depression at a given pressure, which is consistent with available experimental data, is shown to be quantitatively described using the Gibbs-Thomson formalism if used with accurate estimates for the pore/liquid and pore/hydrate interfacial tensions. The metastability barrier upon hydrate formation and dissociation is found to decrease upon confinement, therefore providing a molecular-scale picture for the faster kinetics observed in experiments on confined gas hydrates. By considering different formation mechanisms-bulk homogeneous nucleation, external surface nucleation, and confined nucleation within the porosity-we identify a cross-over in the nucleation process; the critical nucleus formed in the pore corresponds either to a hemispherical cap or to a bridge nucleus depending on temperature, contact angle, and pore size. Using the classical nucleation theory, for both mechanisms, the typical induction time is shown to scale with the pore volume to surface ratio and hence the pore size. These findings for the critical nucleus and nucleation rate associated with such complex transitions provide a means to rationalize and predict methane hydrate formation in any porous media from simple thermodynamic data.
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15
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Mineralogical and structural characterization of the sediments of Krishna Godavari and Mahanadi Basin and their influences on hydrate formation kinetics. ADV POWDER TECHNOL 2021. [DOI: 10.1016/j.apt.2021.02.026] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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16
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Observation of the Main Natural Parameters Influencing the Formation of Gas Hydrates. ENERGIES 2021. [DOI: 10.3390/en14071803] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Chemical composition in seawater of marine sediments, as well as the physical properties and chemical composition of soils, influence the phase behavior of natural gas hydrate by disturbing the hydrogen bond network in the water-rich phase before hydrate formation. In this article, some marine sediments samples, collected in National Antarctic Museum in Trieste, were analyzed and properties such as pH, conductivity, salinity, and concentration of main elements of water present in the sediments are reported. The results, obtained by inductively coupled plasma-mass spectrometry (ICP-MS) and ion chromatography (IC) analysis, show that the more abundant cation is sodium and, present in smaller quantities, but not negligible, are calcium, potassium, and magnesium, while the more abundant anion is chloride and sulfate is also appreciable. These results were successively used to determine the thermodynamic parameters and the effect on salinity of water on hydrates’ formation. Then, hydrate formation was experimentally tested using a small-scale apparatus, in the presence of two different porous media: a pure silica sand and a silica-based natural sand, coming from the Mediterranean seafloor. The results proved how the presence of further compounds, rather than silicon, as well as the heterogeneous grainsize and porosity, made this sand a weak thermodynamic and a strong kinetic inhibitor for the hydrate formation process.
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17
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H-bonding behavior of ethylene oxide within the clathrate hydrates revisited: Experiment and theory. Chem Phys Lett 2020. [DOI: 10.1016/j.cplett.2020.137728] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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18
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Cuadrado-Collados C, Mouchaham G, Daemen L, Cheng Y, Ramirez-Cuesta A, Aggarwal H, Missyul A, Eddaoudi M, Belmabkhout Y, Silvestre-Albero J. Quest for an Optimal Methane Hydrate Formation in the Pores of Hydrolytically Stable Metal–Organic Frameworks. J Am Chem Soc 2020; 142:13391-13397. [DOI: 10.1021/jacs.0c01459] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Carlos Cuadrado-Collados
- Laboratorio de Materiales Avanzados, Departamento de Quı́mica Inorgánica-IUMA, Universidad de Alicante, E-03690 San Vicente del Raspeig, Spain
| | - Georges Mouchaham
- Functional Materials Design, Discovery & Development Research Group, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Luke Daemen
- Spallation Neutron Source, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831, United States
| | - Yongqiang Cheng
- Spallation Neutron Source, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831, United States
| | - Anibal Ramirez-Cuesta
- Spallation Neutron Source, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831, United States
| | - Himanshu Aggarwal
- Functional Materials Design, Discovery & Development Research Group, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
| | | | - Mohamed Eddaoudi
- Functional Materials Design, Discovery & Development Research Group, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Youssef Belmabkhout
- Functional Materials Design, Discovery & Development Research Group, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
- Chemical and Biochemical Sciences, Green Process Engineering, Mohamed VI Polytechnic University, Lot 660 − Hay Moulay Rachid, 43150 Ben Guerir, Morocco
| | - Joaquin Silvestre-Albero
- Laboratorio de Materiales Avanzados, Departamento de Quı́mica Inorgánica-IUMA, Universidad de Alicante, E-03690 San Vicente del Raspeig, Spain
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19
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Yu KB, Yazaydin AO. Does Confinement Enable Methane Hydrate Growth at Low Pressures? Insights from Molecular Dynamics Simulations. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2020; 124:11015-11022. [PMID: 32582402 PMCID: PMC7304911 DOI: 10.1021/acs.jpcc.0c02246] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2020] [Revised: 04/30/2020] [Indexed: 05/23/2023]
Abstract
Natural methane hydrates are estimated to be the largest source of unexploited hydrocarbon fuel. The ideal conditions for methane hydrate formation are low temperatures and high pressures. On the other hand, recent experimental studies suggest that porous materials, thanks to their confinement effects, can enable methane hydrate formation at milder conditions, although there has not been a consensus on this. A number of studies have investigated methane hydrate growth in confinement by employing molecular simulations; however, these were carried out at either very high pressures or very low temperatures. Therefore, the effects of confinement on methane hydrate growth at milder conditions have not yet been elaborated by molecular simulations. In order to address this, we carried out a systematic study by performing molecular dynamics (MD) simulations of methane water systems. Using a direct phase coexistence approach, microsecond-scale MD simulations in the isobaric-isothermal (NPT) ensemble were performed in order to study the behavior of methane hydrates in the bulk and in confined nanospaces of hydroxylated silica pores at external pressures ranging from 1 to 100 bar and a simulation temperature corresponding to a 2 °C experimental temperature. We validated the combination of the TIP4P/ice water and TraPPE-UA methane models in order to correctly predict the behavior of methane hydrates in accordance to their phase equilibria. We also demonstrated that the dispersion corrections applied to short-range interactions lead to artificially induced hydrate growth. We observed that in the confinement of a hydroxylated silica pore, a convex-shaped methane nanobuble forms, and methane hydrate growth primarily takes place in the center of the pore rather than the surfaces where a thin water layer exists. Most importantly, our study showed that in the nanopores methane hydrate growth can indeed take place at pressures which would be too low for the growth of methane hydrates in the bulk.
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20
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He Z, Zhang K, Jiang J. Formation of CH 4 Hydrate in a Mesoporous Metal-Organic Framework MIL-101: Mechanistic Insights from Microsecond Molecular Dynamics Simulations. J Phys Chem Lett 2019; 10:7002-7008. [PMID: 31657572 DOI: 10.1021/acs.jpclett.9b02808] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The formation of CH4 hydrate in a mesoporous metal-organic framework MIL-101 is investigated by microsecond molecular dynamics simulations. CH4 hydrate is observed to form preferentially in the outer space of MIL-101 cavities rather than inside the cavities; only when the hydrate formation is nearly complete in the outer space can stable hydrate form in MIL-101 cavities. The underlying reason is revealed to be the easy dissociation of small hydrate clusters formed in the nanospace of the cavities, because of the diffusion of CH4 molecules out of the cavities into the outer space. Compared with dry MIL-101, the CH4 storage capacity of H2O-saturated MIL-101 is drastically reduced as the cavities are occupied by H2O. When oversaturated with H2O, however, extra H2O molecules in the outer space of the cavities can form considerable CH4 hydrate, significantly promoting CH4 storage capacity. This study provides important mechanistic insights into the formation mechanism and process of CH4 hydrate in MIL-101 and will facilitate the design of emerging materials for energy storage.
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Affiliation(s)
- Zhongjin He
- Department of Chemical and Biomolecular Engineering , National University of Singapore , 117576 , Singapore
- National Center for International Research on Deep Earth Drilling and Resource Development, Faculty of Engineering , China University of Geosciences , Wuhan , Hubei 430074 , China
| | - Kang Zhang
- Department of Chemical and Biomolecular Engineering , National University of Singapore , 117576 , Singapore
| | - Jianwen Jiang
- Department of Chemical and Biomolecular Engineering , National University of Singapore , 117576 , Singapore
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21
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Liang S, Hall KW, Laaksonen A, Zhang Z, Kusalik PG. Characterizing key features in the formation of ice and gas hydrate systems. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2019; 377:20180167. [PMID: 30982452 PMCID: PMC6501917 DOI: 10.1098/rsta.2018.0167] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 02/26/2019] [Indexed: 05/16/2023]
Abstract
Crystallization in liquids is critical to a range of important processes occurring in physics, chemistry and life sciences. In this article, we review our efforts towards understanding the crystallization mechanisms, where we focus on theoretical modelling and molecular simulations applied to ice and gas hydrate systems. We discuss the order parameters used to characterize molecular ordering processes and how different order parameters offer different perspectives of the underlying mechanisms of crystallization. With extensive simulations of water and gas hydrate systems, we have revealed unexpected defective structures and demonstrated their important roles in crystallization processes. Nucleation of gas hydrates can in most cases be characterized to take place in a two-step mechanism where the nucleation occurs via intermediate metastable precursors, which gradually reorganizes to a stable crystalline phase. We have examined the potential energy landscapes explored by systems during nucleation, and have shown that these landscapes are rugged and funnel-shaped. These insights provide a new framework for understanding nucleation phenomena that has not been addressed in classical nucleation theory. This article is part of the theme issue 'The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets'.
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Affiliation(s)
- Shuai Liang
- Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangdong Key Laboratory of New and Renewable Energy Research and Development, Guangzhou, People's Republic of China
| | - Kyle Wm. Hall
- Department of Chemistry, Temple University, Philadelphia, PA, USA
| | - Aatto Laaksonen
- Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm, Sweden
- Department of Chemistry-Ångström Laboratory, Uppsala University, 75121 Uppsala, Sweden
- Centre of Advanced Research in Bionanoconjugates and Biopolymers, Petru Poni Institute of Macromolecular Chemistry, Aleea Grigore Ghica-Voda, 41A, 700487 Iasi, Romania
| | - Zhengcai Zhang
- Department of Chemistry, University of Calgary, Calgary, Canada
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22
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Yan K, Li X, Chen Z, Zhang Y, Xu C, Xia Z. Methane hydrate formation and dissociation behaviors in montmorillonite. Chin J Chem Eng 2019. [DOI: 10.1016/j.cjche.2018.11.025] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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23
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Energy and Environmental Analysis of Membrane-Based CH4-CO2 Replacement Processes in Natural Gas Hydrates. ENERGIES 2019. [DOI: 10.3390/en12050850] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Natural gas hydrates are the largest reservoir of natural gas worldwide. This paper proposes and analyzes the CH4-CO2 replacement in the hydrate phase and pure methane collection through the use of membrane-based separation. The investigation uses a 1 L lab reactor, in which the CH4 hydrates are formed in a quartz sand matrix partially saturated with water. CH4 is subsequently dissociated with a CO2 stream supplied within the sediment inside the reactor. An energy and environmental analysis was carried out to prove the sustainability of the process. Results show that the process energy consumption constitutes 4.75% of the energy stored in the recovered methane. The carbon footprint of the CH4-CO2 exchange process is calculated as a balance of the CO2 produced in the process and the CO2 stored in system. Results provide an estimated negative value, equal to 0.004 moles sequestrated, thus proving the environmental benefit of the exchange process.
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24
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Hou J, Bai D, Zhou W. Methane Hydrate Nucleation within Elastic Confined Spaces: Suitable Spacing and Elasticity Can Accelerate the Nucleation. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:10889-10896. [PMID: 30157653 DOI: 10.1021/acs.langmuir.8b02387] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Elastic materials are candidates for process intensification of gas storage by forming gas hydrate. In this work, molecular dynamics simulations of hydrate nucleation in elastic silica double layers were performed to study the effect of elastic confined spaces on hydrate formation. It is found that in narrow confined spaces, hexagonal rings dominated the hydrogen bond network of water molecules established rapidly by a multisite nucleation mechanism. With molecules added, a bilayer water structure was formed finally because elastic space can adapt the volume expansion. In medium and wide confined spaces, hydrates were formed from a series of "pseudo cages" which are considered as precursors of complete hydrate cages. Moreover, the induction time for nucleation was a minimum when the elasticity of the silica layer changes: nucleation is fastest in the weak-elastic system. When the elasticity increases, it becomes hard to adapt the volume expansion during nucleation and also difficult to nucleate in very weak-elastic systems because of the fluctuation of the layers.
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Affiliation(s)
- Jingpeng Hou
- Department of Chemistry, School of Science/Key Laboratory of Cosmetic, China National Light Industry , Beijing Technology and Business University , Beijing 100048 , PR China
| | - Dongsheng Bai
- Department of Chemistry, School of Science/Key Laboratory of Cosmetic, China National Light Industry , Beijing Technology and Business University , Beijing 100048 , PR China
| | - Wei Zhou
- Department of Chemistry, School of Science/Key Laboratory of Cosmetic, China National Light Industry , Beijing Technology and Business University , Beijing 100048 , PR China
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25
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Warrier P, Khan MN, Srivastava V, Maupin CM, Koh CA. Overview: Nucleation of clathrate hydrates. J Chem Phys 2018; 145:211705. [PMID: 28799342 DOI: 10.1063/1.4968590] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Molecular level knowledge of nucleation and growth of clathrate hydrates is of importance for advancing fundamental understanding on the nature of water and hydrophobic hydrate formers, and their interactions that result in the formation of ice-like solids at temperatures higher than the ice-point. The stochastic nature and the inability to probe the small length and time scales associated with the nucleation process make it very difficult to experimentally determine the molecular level changes that lead to the nucleation event. Conversely, for this reason, there have been increasing efforts to obtain this information using molecular simulations. Accurate knowledge of how and when hydrate structures nucleate will be tremendously beneficial for the development of sustainable hydrate management strategies in oil and gas flowlines, as well as for their application in energy storage and recovery, gas separation, carbon sequestration, seawater desalination, and refrigeration. This article reviews various aspects of hydrate nucleation. First, properties of supercooled water and ice nucleation are reviewed briefly due to their apparent similarity to hydrates. Hydrate nucleation is then reviewed starting from macroscopic observations as obtained from experiments in laboratories and operations in industries, followed by various hydrate nucleation hypotheses and hydrate nucleation driving force calculations based on the classical nucleation theory. Finally, molecular simulations on hydrate nucleation are discussed in detail followed by potential future research directions.
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Affiliation(s)
- Pramod Warrier
- Center for Hydrate Research, Chemical and Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, USA
| | - M Naveed Khan
- Center for Hydrate Research, Chemical and Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, USA
| | - Vishal Srivastava
- Center for Hydrate Research, Chemical and Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, USA
| | - C Mark Maupin
- Center for Hydrate Research, Chemical and Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, USA
| | - Carolyn A Koh
- Center for Hydrate Research, Chemical and Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, USA
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26
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He Z, Linga P, Jiang J. CH 4 Hydrate Formation between Silica and Graphite Surfaces: Insights from Microsecond Molecular Dynamics Simulations. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:11956-11967. [PMID: 28991480 DOI: 10.1021/acs.langmuir.7b02711] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Microsecond simulations have been performed to investigate CH4 hydrate formation from gas/water two-phase systems between silica and graphite surfaces, respectively. The hydrophilic silica and hydrophobic graphite surfaces exhibit substantially different effects on CH4 hydrate formation. The graphite surface adsorbs CH4 molecules to form a nanobubble with a flat or negative curvature, resulting in a low aqueous CH4 concentration, and hydrate nucleation does not occur during 2.5 μs simulation. Moreover, an ordered interfacial water bilayer forms between the nanobubble and graphite surface thus preventing their direct contact. In contrast, the hydroxylated-silica surface prefers to be hydrated by water, with a cylindrical nanobubble formed in the solution, leading to a high aqueous CH4 concentration and hydrate nucleation in the bulk region; during hydrate growth, the nanobubble is gradually covered by hydrate solid and separated from the water phase, hence slowing growth. The silanol groups on the silica surface can form strong hydrogen bonds with water, and hydrate cages need to match the arrangements of silanols to form more hydrogen bonds. At the end of the simulation, the hydrate solid is separated from the silica surface by liquid water, with only several cages forming hydrogen bonds with the silica surface, mainly due to the low CH4 aqueous concentrations near the surface. To further explore hydrate formation between graphite surfaces, CH4/water homogeneous solution systems are also simulated. CH4 molecules in the solution are adsorbed onto graphite and hydrate nucleation occurs in the bulk region. During hydrate growth, the adsorbed CH4 molecules are gradually converted into hydrate solid. It is found that the hydrate-like ordering of interfacial water induced by graphite promotes the contact between hydrate solid and graphite. We reveal that the ability of silanol groups on silica to form strong hydrogen bonds to stabilize incipient hydrate solid, as well as the ability of graphite to adsorb CH4 molecules and induce hydrate-like ordering of the interfacial water, are the key factors to affect CH4 hydrate formation between silica and graphite surfaces.
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Affiliation(s)
- Zhongjin He
- Department of Chemical and Biomolecular Engineering, National University of Singapore , Singapore 117576, Singapore
| | - Praveen Linga
- Department of Chemical and Biomolecular Engineering, National University of Singapore , Singapore 117576, Singapore
| | - Jianwen Jiang
- Department of Chemical and Biomolecular Engineering, National University of Singapore , Singapore 117576, Singapore
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27
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Zhang P, Wu Q, Mu C. Influence of temperature on methane hydrate formation. Sci Rep 2017; 7:7904. [PMID: 28801566 PMCID: PMC5554230 DOI: 10.1038/s41598-017-08430-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2017] [Accepted: 07/11/2017] [Indexed: 11/09/2022] Open
Abstract
During gas hydrate formation process, a phase transition of liquid water exists naturally, implying that temperature has an important influence on hydrate formation. In this study, methane hydrate was formed within the same media. The experimental system was kept at 1.45, 6.49, and 12.91 °C respectively, and then different pressurization modes were applied in steps. We proposed a new indicator, namely the slope of the gas flow rates against time (dν g /dt), to represent the intrinsic driving force for hydrate formation. The driving force was calculated as a fixed value at the different stages of formation, including initial nucleation/growth, secondary nucleation/growth, and decay. The amounts of gas consumed at each stage were also calculated. The results show that the driving force during each stage follows an inverse relation with temperature, whereas the amount of consumed gas is proportional to temperature. This opposite trend indicates that the influences of temperature on the specific formation processes and final amounts of gas contained in hydrate should be considered separately. Our results also suggest that the specific ambient temperature under which hydrate is formed should be taken into consideration, when explaining the formation of different configurations and saturations of gas hydrates in natural reservoirs.
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Affiliation(s)
- Peng Zhang
- State Key Laboratory of Frozen Soil Engineering, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 73000, China
| | - Qingbai Wu
- State Key Laboratory of Frozen Soil Engineering, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 73000, China.
| | - Cuicui Mu
- Key Laboratory of Western China's Environmental Systems (Ministry of Education), College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, 730000, China
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28
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Maşlakcı Z, Devlin JP, Uras-Aytemiz N. NH 3 as unique non-classical content-former within clathrate hydrates. J Chem Phys 2017. [PMID: 28641420 DOI: 10.1063/1.4985668] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
High quality FTIR spectra of aerosols of NH3-THF and NH3-TMO binary clathrate hydrates (CHs) have been measured. Our recently developed all-vapor sub-second approach to clathrate-hydrate formation combined with computational studies has been used to identify vibrational spectroscopic signatures of NH3 within the gas hydrates. The present study shows that there are three distinct NH3 types, namely, classical small-cage NH3, nonclassical small-cage NH3, and NH3 within the hydrate network. The network ammonia does not directly trigger the non-classical CH structure. Rather, the ammonia within the network structure perturbs the water bonding, introducing orientational defects that are stabilized by small and/or large cage guest molecules through H-bonding. This unusual behavior of NH3 within CHs opens a possibility for catalytic action of NH3 during CH-formation. Furthermore, impacts over time of the small-cage NH3-replacement molecules CO2 and CH4 on the structure and composition of the ternary CHs have been noted.
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Affiliation(s)
- Zafer Maşlakcı
- Department of Chemistry, Karabuk University, 78050 Karabuk, Turkey
| | - J Paul Devlin
- Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, USA
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29
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Smirnov KS. A modeling study of methane hydrate decomposition in contact with the external surface of zeolites. Phys Chem Chem Phys 2017; 19:23095-23105. [DOI: 10.1039/c7cp01985h] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Methane hydrate dissociates on the external surface of siliceous zeolites with methane absorbed by the solid and water forming a liquid-like phase.
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Affiliation(s)
- Konstantin S. Smirnov
- Laboratoire de Spectrochimie Infrarouge et Raman
- UMR 8516 CNRS – Université de Lille
- Sciences et Technologies
- 59655 Villeneuve d'Ascq
- France
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30
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Mokshin AV, Galimzyanov BN. Kinetics of crystalline nuclei growth in glassy systems. Phys Chem Chem Phys 2017; 19:11340-11353. [DOI: 10.1039/c7cp00879a] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This work reports results for crystalline nuclei growth in glassy systems. The crystal growth laws rescaled onto the waiting times of critically-sized nuclei follow a unified dependence. The scaled crystal growth rate characteristics as functions of reduced temperature follow unified power-law dependencies.
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Affiliation(s)
- Anatolii V. Mokshin
- Institute of Physics
- Kazan Federal University
- 420008 Kazan
- Russia
- L. D. Landau Institute for Theoretical Physics
| | - Bulat N. Galimzyanov
- Institute of Physics
- Kazan Federal University
- 420008 Kazan
- Russia
- L. D. Landau Institute for Theoretical Physics
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31
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Hall KW, Carpendale S, Kusalik PG. Evidence from mixed hydrate nucleation for a funnel model of crystallization. Proc Natl Acad Sci U S A 2016; 113:12041-12046. [PMID: 27790987 PMCID: PMC5087014 DOI: 10.1073/pnas.1610437113] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The molecular-level details of crystallization remain unclear for many systems. Previous work has speculated on the phenomenological similarities between molecular crystallization and protein folding. Here we demonstrate that molecular crystallization can involve funnel-shaped potential energy landscapes through a detailed analysis of mixed gas hydrate nucleation, a prototypical multicomponent crystallization process. Through this, we contribute both: (i) a powerful conceptual framework for exploring and rationalizing molecular crystallization, and (ii) an explanation of phenomenological similarities between protein folding and crystallization. Such funnel-shaped potential energy landscapes may be typical of broad classes of molecular ordering processes, and can provide a new perspective for both studying and understanding these processes.
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Affiliation(s)
- Kyle Wm Hall
- Department of Chemistry, University of Calgary, Calgary, AB, Canada T2N 1N4
| | - Sheelagh Carpendale
- Department of Computer Science, University of Calgary, Calgary, AB, Canada T2N 1N4
| | - Peter G Kusalik
- Department of Chemistry, University of Calgary, Calgary, AB, Canada T2N 1N4;
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32
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Yan KF, Li XS, Chen ZY, Xia ZM, Xu CG, Zhang Z. Molecular Dynamics Simulation of the Crystal Nucleation and Growth Behavior of Methane Hydrate in the Presence of the Surface and Nanopores of Porous Sediment. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:7975-7984. [PMID: 27398713 DOI: 10.1021/acs.langmuir.6b01601] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The behavior of hydrate formation in porous sediment has been widely studied because of its importance in the investigation of reservoirs and in the drilling of natural gas hydrate. However, it is difficult to understand the hydrate nucleation and growth mechanism on the surface and in the nanopores of porous media by experimental and numerical simulation methods. In this work, molecular dynamics simulations of the nucleation and growth of CH4 hydrate in the presence of the surface and nanopores of clay are carried out. The molecular configurations and microstructure properties are analyzed for systems containing one H2O hydrate layer (System A), three H2O hydrate layers (System B), and six H2O hydrate layers (System C) in both clay and the bulk solution. It is found that hydrate formation is more complex in porous media than in the pure bulk solution and that there is cooperativity between hydrate growth and molecular diffusion in clay nanopores. The hydroxylated edge sites of the clay surface could serve as a source of CH4 molecules to facilitate hydrate nucleation. The diffusion velocity of molecules is influenced by the growth of the hydrate that forms a block in the throats of the clay nanopore. Comparing hydrate growth in different clay pore sizes reveals that the pore size plays an important role in hydrate growth and molecular diffusion in clay. This simulation study provides the microscopic mechanism of hydrate nucleation and growth in porous media, which can be favorable for the investigation of the formation of natural gas hydrate in sediments.
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Affiliation(s)
- Ke-Feng Yan
- Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences , Guangzhou 510640, China
- Guangdong Key Laboratory of New and Renewable Energy Research and Development , Guangzhou 510640, China
| | - Xiao-Sen Li
- Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences , Guangzhou 510640, China
- Guangdong Key Laboratory of New and Renewable Energy Research and Development , Guangzhou 510640, China
| | - Zhao-Yang Chen
- Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences , Guangzhou 510640, China
- Guangdong Key Laboratory of New and Renewable Energy Research and Development , Guangzhou 510640, China
| | - Zhi-Ming Xia
- Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences , Guangzhou 510640, China
- Guangdong Key Laboratory of New and Renewable Energy Research and Development , Guangzhou 510640, China
| | - Chun-Gang Xu
- Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences , Guangzhou 510640, China
- Guangdong Key Laboratory of New and Renewable Energy Research and Development , Guangzhou 510640, China
| | - Zhiqiang Zhang
- College of Mining Engineering, Taiyuan University of Technology , Taiyuan 030024, China
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33
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Yagasaki T, Matsumoto M, Tanaka H. Effects of thermodynamic inhibitors on the dissociation of methane hydrate: a molecular dynamics study. Phys Chem Chem Phys 2015; 17:32347-57. [PMID: 26587576 DOI: 10.1039/c5cp03008k] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We investigate the effects of methanol and NaCl, which are known as thermodynamic hydrate inhibitors, on the dissociation kinetics of methane hydrate in aqueous solutions by using molecular dynamics simulations. It is shown that the dissociation rate is not constant but changes with time. The dissociation rate in the initial stage is increased by methanol whereas it is decreased by NaCl. This difference arises from the opposite effects of the two thermodynamic inhibitors on the hydration free energy of methane. The dissociation rate of methane hydrate is increased by the formation of methane bubbles in the aqueous phase because the bubbles absorb surrounding methane molecules. It is found that both methanol and NaCl facilitate the bubble formation. However, their mechanisms are completely different from each other. The presence of ions enhances the hydrophobic interactions between methane molecules. In addition, the ions in the solution cause a highly non-uniform distribution of dissolved methane molecules. These two effects result in the easy formation of bubbles in the NaCl solution. In contrast, methanol assists the bubble formation because of its amphiphilic character.
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Affiliation(s)
- Takuma Yagasaki
- Department of Chemistry, Faculty of Science, Okayama University, Okayama, 700-8530, Japan
| | - Masakazu Matsumoto
- Department of Chemistry, Faculty of Science, Okayama University, Okayama, 700-8530, Japan
| | - Hideki Tanaka
- Department of Chemistry, Faculty of Science, Okayama University, Okayama, 700-8530, Japan and Research Center of New Functional Materials for Energy Production, Storage and Transport, Okayama, 700-8530, Japan.
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34
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Gillan MJ, Alfè D, Manby FR. Energy benchmarks for methane-water systems from quantum Monte Carlo and second-order Møller-Plesset calculations. J Chem Phys 2015; 143:102812. [PMID: 26374005 DOI: 10.1063/1.4926444] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The quantum Monte Carlo (QMC) technique is used to generate accurate energy benchmarks for methane-water clusters containing a single methane monomer and up to 20 water monomers. The benchmarks for each type of cluster are computed for a set of geometries drawn from molecular dynamics simulations. The accuracy of QMC is expected to be comparable with that of coupled-cluster calculations, and this is confirmed by comparisons for the CH4-H2O dimer. The benchmarks are used to assess the accuracy of the second-order Møller-Plesset (MP2) approximation close to the complete basis-set limit. A recently developed embedded many-body technique is shown to give an efficient procedure for computing basis-set converged MP2 energies for the large clusters. It is found that MP2 values for the methane binding energies and the cohesive energies of the water clusters without methane are in close agreement with the QMC benchmarks, but the agreement is aided by partial cancelation between 2-body and beyond-2-body errors of MP2. The embedding approach allows MP2 to be applied without loss of accuracy to the methane hydrate crystal, and it is shown that the resulting methane binding energy and the cohesive energy of the water lattice agree almost exactly with recently reported QMC values.
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Affiliation(s)
- M J Gillan
- London Centre for Nanotechnology, University College London, Gordon St., London WC1H 0AH, United Kingdom
| | - D Alfè
- London Centre for Nanotechnology, University College London, Gordon St., London WC1H 0AH, United Kingdom
| | - F R Manby
- Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom
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35
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Yagasaki T, Matsumoto M, Tanaka H. Adsorption Mechanism of Inhibitor and Guest Molecules on the Surface of Gas Hydrates. J Am Chem Soc 2015; 137:12079-85. [DOI: 10.1021/jacs.5b07417] [Citation(s) in RCA: 104] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Takuma Yagasaki
- Department
of Chemistry, Faculty of Science, Okayama University, Okayama, 700-8530, Japan
| | - Masakazu Matsumoto
- Department
of Chemistry, Faculty of Science, Okayama University, Okayama, 700-8530, Japan
| | - Hideki Tanaka
- Department
of Chemistry, Faculty of Science, Okayama University, Okayama, 700-8530, Japan
- Research Center of New Functional Materials for Energy Production, Storage and Transport, Okayama, 700-8530, Japan
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36
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Yi L, Liang D, Liang S, Zhou X. Molecular dynamics study of CH4-CO2mixed hydrate dissociation. ASIA-PAC J CHEM ENG 2015. [DOI: 10.1002/apj.1919] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Lizhi Yi
- Key Laboratory of Gas Hydrate; Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences; Guangzhou 510640 China
- Guangzhou Center for Gas Hydrate Research; Chinese Academy of Sciences; Guangzhou 510640 China
| | - Deqing Liang
- Key Laboratory of Gas Hydrate; Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences; Guangzhou 510640 China
- Guangzhou Center for Gas Hydrate Research; Chinese Academy of Sciences; Guangzhou 510640 China
| | - Shuai Liang
- Key Laboratory of Gas Hydrate; Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences; Guangzhou 510640 China
- Guangzhou Center for Gas Hydrate Research; Chinese Academy of Sciences; Guangzhou 510640 China
| | - Xuebing Zhou
- Key Laboratory of Gas Hydrate; Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences; Guangzhou 510640 China
- Guangzhou Center for Gas Hydrate Research; Chinese Academy of Sciences; Guangzhou 510640 China
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37
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Abstract
Understanding the nucleation and crystal growth of gas hydrates near mineral surfaces and in confinement are critical to the methane recovery from gas hydrate reservoirs. In this work, through molecular dynamics simulation studies, we present an exploration of the nucleation behavior of methane hydrates near model hydroxylated silica surfaces. Our simulation results indicate that the nucleation of methane hydrates can initiate from the silica surfaces despite of the structural mismatch of the two solid phases. A layer of intermediate half-cage structures was observed between the gas hydrate and silica surfaces, apparently helping to minimize the free energy penalty. These results have important implications to our understanding of the effects of solid surfaces on hydrate nucleation processes.
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Affiliation(s)
- Shuai Liang
- Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou, China
| | - Peter G. Kusalik
- Department of Chemistry, University of Calgary, Calgary, Alberta, Canada
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38
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Bai D, Chen G, Zhang X, Sum AK, Wang W. How Properties of Solid Surfaces Modulate the Nucleation of Gas Hydrate. Sci Rep 2015; 5:12747. [PMID: 26227239 PMCID: PMC4521183 DOI: 10.1038/srep12747] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2015] [Accepted: 07/07/2015] [Indexed: 11/09/2022] Open
Abstract
Molecular dynamics simulations were performed for CO2 dissolved in water near silica surfaces to investigate how the hydrophilicity and crystallinity of solid surfaces modulate the local structure of adjacent molecules and the nucleation of CO2 hydrates. Our simulations reveal that the hydrophilicity of solid surfaces can change the local structure of water molecules and gas distribution near liquid-solid interfaces, and thus alter the mechanism and dynamics of gas hydrate nucleation. Interestingly, we find that hydrate nucleation tends to occur more easily on relatively less hydrophilic surfaces. Different from surface hydrophilicity, surface crystallinity shows a weak effect on the local structure of adjacent water molecules and on gas hydrate nucleation. At the initial stage of gas hydrate growth, however, the structuring of molecules induced by crystalline surfaces are more ordered than that induced by amorphous solid surfaces.
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Affiliation(s)
- Dongsheng Bai
- 1] Department of Chemistry, School of Science, Beijing Technology and Business University, Beijing, 100048, P. R. China [2] Division of Molecular and Materials Simulation, State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing, 100029, P. R. China
| | - Guangjin Chen
- State Key Laboratory of Heavy Oil Processing, School of Chemical Engineering, China University of Petroleum, Beijing, 102249, P. R. China
| | - Xianren Zhang
- Division of Molecular and Materials Simulation, State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing, 100029, P. R. China
| | - Amadeu K Sum
- Center for Hydrate Research, Department of Chemical &Biological Engineering, Colorado School of Mines, Golden, CO 80401, U.S.A
| | - Wenchuan Wang
- Division of Molecular and Materials Simulation, State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing, 100029, P. R. China
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Liang S, Kusalik PG. Communication: Structural interconversions between principal clathrate hydrate structures. J Chem Phys 2015; 143:011102. [DOI: 10.1063/1.4923465] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Affiliation(s)
- Shuai Liang
- Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou, China
| | - Peter G. Kusalik
- Department of Chemistry, University of Calgary, Calgary, Alberta T2N 1N4, Canada
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Michalis VK, Costandy J, Tsimpanogiannis IN, Stubos AK, Economou IG. Prediction of the phase equilibria of methane hydrates using the direct phase coexistence methodology. J Chem Phys 2015; 142:044501. [DOI: 10.1063/1.4905572] [Citation(s) in RCA: 90] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Vasileios K. Michalis
- Chemical Engineering Program, Texas A&M University at Qatar, P.O. Box 23847, Doha, Qatar
| | - Joseph Costandy
- Chemical Engineering Program, Texas A&M University at Qatar, P.O. Box 23847, Doha, Qatar
| | - Ioannis N. Tsimpanogiannis
- Environmental Research Laboratory, National Center for Scientific Research NCSR “Demokritos,” Aghia Paraskevi, Attiki GR-15310, Greece
| | - Athanassios K. Stubos
- Environmental Research Laboratory, National Center for Scientific Research NCSR “Demokritos,” Aghia Paraskevi, Attiki GR-15310, Greece
| | - Ioannis G. Economou
- Chemical Engineering Program, Texas A&M University at Qatar, P.O. Box 23847, Doha, Qatar
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42
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Perspectives on molecular simulation of clathrate hydrates: Progress, prospects and challenges. Chem Eng Sci 2015. [DOI: 10.1016/j.ces.2014.07.047] [Citation(s) in RCA: 144] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Devlin JP, Balcı FM, Maşlakcı Z, Uras-Aytemiz N. CO2 and C2H2 in cold nanodroplets of oxygenated organic molecules and water. J Chem Phys 2014; 141:18C506. [PMID: 25399171 DOI: 10.1063/1.4895549] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Recent demonstrations of subsecond and microsecond timescales for formation of clathrate hydrate nanocrystals hint at future methods of control of environmental and industrial gases such as CO2 and methane. Combined results from cold-chamber and supersonic-nozzle [A. S. Bhabhe, "Experimental study of condensation and freezing in a supersonic nozzle," Ph.D. thesis (Ohio State University, 2012), Chap. 7] experiments indicate extremely rapid encagement of components of all-vapor pre-mixtures. The extreme rates are derived from (a) the all-vapor premixing of the gas-hydrate components and (b) catalytic activity of certain oxygenated organic large-cage guests. Premixing presents no obvious barrier to large-scale conditions of formation. Further, from sequential efforts of the groups of Trout and Buch, a credible defect-based model of the catalysis mechanism exists for guidance. Since the catalyst-generated defects are both mobile and abundant, it is often unnecessary for a high percentage of the cages to be occupied by a molecular catalyst. Droplets represent the liquid phase that bridges the premixed vapor and clathrate hydrate phases but few data exist for the droplets themselves. Here we describe a focused computational and FTIR spectroscopic effort to characterize the aerosol droplets of the all-vapor cold-chamber methodology. Computational data for CO2 and C2H2, hetero-dimerized with each of the organic catalysts and water, closely match spectroscopic redshift patterns in both magnitude and direction. Though vibrational frequency shifts are an order of magnitude greater for the acetylene stretch mode, both CO2 and C2H2 experience redshift values that increase from that for an 80% water-methanol solvent through the solvent series to approximately doubled values for tetrahydrofuran and trimethylene oxide (TMO) droplets. The TMO solvent properties extend to a 50 mol.% solution of CO2, more than an order of magnitude greater than for the water-methanol solvent mixture. The impressive agreement between heterodimer and experimental shift values throughout the two series encourages speculation concerning local droplet structures while the stable shift patterns appear to be useful indicators of the gas solubilities.
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Affiliation(s)
- J Paul Devlin
- Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, USA
| | - F Mine Balcı
- Department of Chemistry, Suleyman Demirel University, 32260 Isparta, Turkey
| | - Zafer Maşlakcı
- Department of Polymer Engineering, Karabuk University, 78050 Karabuk, Turkey
| | - Nevin Uras-Aytemiz
- Department of Polymer Engineering, Karabuk University, 78050 Karabuk, Turkey
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44
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Barnes BC, Knott BC, Beckham GT, Wu DT, Sum AK. Reaction coordinate of incipient methane clathrate hydrate nucleation. J Phys Chem B 2014; 118:13236-43. [PMID: 25347748 DOI: 10.1021/jp507959q] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Nucleation from solution is a ubiquitous phenomenon with relevance to myriad scientific disciplines, including pharmaceuticals, biomineralization, and disease. One prominent example is the nucleation of clathrate hydrates, multicomponent crystalline inclusion compounds relevant to the energy industry where they block pipelines and also constitute a potential vast energy resource. Despite their importance, the molecular mechanism of incipient hydrate formation remains unknown. Herein, we employ advanced molecular simulation tools (pB histogram, equilibrium path sampling) to provide a statistical-mechanical basis for extracting physical insight into the molecular steps by which clathrates form. Through testing the Mutually Coordinated Guest (MCG) order parameter, we demonstrate that both guest (methane) and host (water) structuring are crucial to accurately describe the nucleation of hydrates and determine a critical nucleus size of MCG-1 = 16 at 255 K and 500 bar. Equipped with a validated (and novel) reaction coordinate, subsequent equilibrium path sampling simulations yield the free energy barrier and nucleation rate. The resulting quantitative nucleation process is described by the MCG clustering mechanism. This constitutes a significant advance in the field of hydrates research, as the fitness of a molecular descriptor has never been statistically verified. More broadly, this work has significance to a wide range of multicomponent nucleation contexts wherein the formation mechanism depends on contributions from both solute and solvent.
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Affiliation(s)
- Brian C Barnes
- Center for Hydrate Research, Chemical & Biological Engineering Department, Colorado School of Mines , Golden, Colorado 80401, United States
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Yi L, Liang D, Zhou X, Li D, Wang J. Molecular dynamics simulations of carbon dioxide hydrate growth in electrolyte solutions of NaCl and MgCl2. Mol Phys 2014. [DOI: 10.1080/00268976.2014.932454] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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46
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Molecular dynamics simulation of the intercalation behaviors of methane hydrate in montmorillonite. J Mol Model 2014; 20:2311. [PMID: 24906646 DOI: 10.1007/s00894-014-2311-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2014] [Accepted: 05/19/2014] [Indexed: 10/25/2022]
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47
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Barnes BC, Beckham GT, Wu DT, Sum AK. Two-component order parameter for quantifying clathrate hydrate nucleation and growth. J Chem Phys 2014; 140:164506. [PMID: 24784286 DOI: 10.1063/1.4871898] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Methane clathrate hydrate nucleation and growth is investigated via analysis of molecular dynamics simulations using a new order parameter. This order parameter (OP), named the Mutually Coordinated Guest (MCG) OP, quantifies the appearance and connectivity of molecular clusters composed of guests separated by water clusters. It is the first two-component OP used for quantifying hydrate nucleation and growth. The algorithm for calculating the MCG OP is described in detail. Its physical motivation and advantages compared to existing methods are discussed.
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Affiliation(s)
- Brian C Barnes
- Center for Hydrate Research, Chemical and Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, USA
| | - Gregg T Beckham
- National Renewable Energy Laboratory, Golden, Colorado 80401, USA
| | - David T Wu
- Center for Hydrate Research, Chemical and Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, USA
| | - Amadeu K Sum
- Center for Hydrate Research, Chemical and Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, USA
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Agarwal V, Peters B. Solute Precipitate Nucleation: A Review of Theory and Simulation Advances. ADVANCES IN CHEMICAL PHYSICS 2014. [DOI: 10.1002/9781118755815.ch03] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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49
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Nguyen AH, Molinero V. Cross-nucleation between clathrate hydrate polymorphs: Assessing the role of stability, growth rate, and structure matching. J Chem Phys 2014; 140:084506. [DOI: 10.1063/1.4866143] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
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Chari VD, Prasad PSR, Murthy SR. Structural stability of methane hydrates in porous medium: Raman spectroscopic study. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2013; 120:636-641. [PMID: 24239388 DOI: 10.1016/j.saa.2013.10.080] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Revised: 10/11/2013] [Accepted: 10/17/2013] [Indexed: 06/02/2023]
Abstract
Thermal and temporal stability of the methane hydrates (MH) at ambient pressure, synthesised in a spherical silica (solid and hollow, with average diameter of 70 μm) matrix, are investigated by the Raman spectroscopy. Identical Raman spectroscopic spectral features for all the synthesized hydrate samples indicate structural resemblance irrespective of matrix. It is observed that the growth of hydrates in hollow silica matrix is homogeneous, while that with solid grain is highly heterogeneous. Temporal and thermal stability of MH depends on the silica matrix. Appearance of the Raman signatures characteristic of MH, in hollow silica, indicates that the hydrates are stable over several hours (upon preserving at 153 K and 0.1 MPa) and until ∼273 K at 0.1 MPa. However, MH in solid silica matrix is highly unstable under similar P, T conditions and they are readily dissociated within 2 h. The thermal stability of these samples at 0.1 MPa is also significantly lower.
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Affiliation(s)
- Vangala Dhanunjana Chari
- Gas Hydrates Division, National Geophysical Research Institute (CSIR-NGRI), Council of Scientific and Industrial Research, Hyderabad 500007, India; Department of Physics, Osmania University, Hyderabad 500007, India
| | - Pinnelli S R Prasad
- Gas Hydrates Division, National Geophysical Research Institute (CSIR-NGRI), Council of Scientific and Industrial Research, Hyderabad 500007, India.
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