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Title: Atomistic modeling of structure II gas hydrate mechanics: Compressibility and equations of state

Abstract

This work uses density functional theory (DFT) to investigate the poorly characterized structure II gas hydrates, for various guests (empty, propane, butane, ethane-methane, propane-methane), at the atomistic scale to determine key structure and mechanical properties such as equilibrium lattice volume and bulk modulus. Several equations of state (EOS) for solids (Murnaghan, Birch-Murnaghan, Vinet, Liu) were fitted to energy-volume curves resulting from structure optimization simulations. These EOS, which can be used to characterize the compressional behaviour of gas hydrates, were evaluated in terms of their robustness. The three-parameter Vinet EOS was found to perform just as well if not better than the four-parameter Liu EOS, over the pressure range in this study. As expected, the Murnaghan EOS proved to be the least robust. Furthermore, the equilibrium lattice volumes were found to increase with guest size, with double-guest hydrates showing a larger increase than single-guest hydrates, which has significant implications for the widely used van der Waals and Platteeuw thermodynamic model for gas hydrates. Also, hydrogen bonds prove to be the most likely factor contributing to the resistance of gas hydrates to compression; bulk modulus was found to increase linearly with hydrogen bond density, resulting in a relationship that could be usedmore » predictively to determine the bulk modulus of various structure II gas hydrates. Taken together, these results fill a long existing gap in the material chemical physics of these important clathrates.« less

Authors:
; ;  [1]
  1. Department of Chemical Engineering, McGill University, Montreal H3A 0C5 (Canada)
Publication Date:
OSTI Identifier:
22611395
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Advances; Journal Volume: 6; Journal Issue: 8; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; BUTANE; CHEMICAL PHYSICS; COMPRESSIBILITY; COMPRESSION; DENSITY FUNCTIONAL METHOD; EQUATIONS OF STATE; EQUILIBRIUM; ETHANE; GAS HYDRATES; HYDROGEN; METHANE; OPTIMIZATION; PRESSURE RANGE; SIMULATION; SOLIDS; THERMODYNAMIC MODEL; VAN DER WAALS FORCES

Citation Formats

Vlasic, Thomas M., Servio, Phillip, and Rey, Alejandro D., E-mail: alejandro.rey@mcgill.ca. Atomistic modeling of structure II gas hydrate mechanics: Compressibility and equations of state. United States: N. p., 2016. Web. doi:10.1063/1.4961728.
Vlasic, Thomas M., Servio, Phillip, & Rey, Alejandro D., E-mail: alejandro.rey@mcgill.ca. Atomistic modeling of structure II gas hydrate mechanics: Compressibility and equations of state. United States. doi:10.1063/1.4961728.
Vlasic, Thomas M., Servio, Phillip, and Rey, Alejandro D., E-mail: alejandro.rey@mcgill.ca. 2016. "Atomistic modeling of structure II gas hydrate mechanics: Compressibility and equations of state". United States. doi:10.1063/1.4961728.
@article{osti_22611395,
title = {Atomistic modeling of structure II gas hydrate mechanics: Compressibility and equations of state},
author = {Vlasic, Thomas M. and Servio, Phillip and Rey, Alejandro D., E-mail: alejandro.rey@mcgill.ca},
abstractNote = {This work uses density functional theory (DFT) to investigate the poorly characterized structure II gas hydrates, for various guests (empty, propane, butane, ethane-methane, propane-methane), at the atomistic scale to determine key structure and mechanical properties such as equilibrium lattice volume and bulk modulus. Several equations of state (EOS) for solids (Murnaghan, Birch-Murnaghan, Vinet, Liu) were fitted to energy-volume curves resulting from structure optimization simulations. These EOS, which can be used to characterize the compressional behaviour of gas hydrates, were evaluated in terms of their robustness. The three-parameter Vinet EOS was found to perform just as well if not better than the four-parameter Liu EOS, over the pressure range in this study. As expected, the Murnaghan EOS proved to be the least robust. Furthermore, the equilibrium lattice volumes were found to increase with guest size, with double-guest hydrates showing a larger increase than single-guest hydrates, which has significant implications for the widely used van der Waals and Platteeuw thermodynamic model for gas hydrates. Also, hydrogen bonds prove to be the most likely factor contributing to the resistance of gas hydrates to compression; bulk modulus was found to increase linearly with hydrogen bond density, resulting in a relationship that could be used predictively to determine the bulk modulus of various structure II gas hydrates. Taken together, these results fill a long existing gap in the material chemical physics of these important clathrates.},
doi = {10.1063/1.4961728},
journal = {AIP Advances},
number = 8,
volume = 6,
place = {United States},
year = 2016,
month = 8
}
  • The study of gas hydrates is of particular interest to the natural gas and petroleum industry because they may block transmission lines, plug blow out preventers, jeopardize the foundation of deepwater platforms and pipelines, cause tubing and casing collapse and foul process heat exchangers, valve and expander. Hydrates can be prevented by reducing the water content of the hydrocarbon mixture or by heating or insulating the pipelines. However, a more common alternative is to add a water soluble inhibitor to lower the hydrate forming temperature. Methanol, ethanol, ethylene glycol (EG), diethylene glycol (DEG), and salts are examples of good inhibitors.more » The information given in this work is just a set of guidelines to illustrate how equations of state, when properly calibrated to selected experimental data, can help the processing engineer to find the optimum inhibition scheme to avoid natural gas hydrate formation.« less
  • No abstract prepared.
  • The modeling of the complex thermochemistry that takes place in the wake of a detonation or shock propagation in an energetic material requires accurate equations of state (EOS) for the resulting chemical species under conditions of high temperature and pressure. Nitrous Acid (HONO or HNO{sub 2}) has been shown to be an important post-detonation product on short and intermediate time scales for many energetic compounds. Given that its EOS has not been determined so far, either experimentally or theoretically, we develop an accurate force field to model both conformers (i.e. cis and trans) of HONO, and compute the EOS usingmore » classical molecular dynamics simulations. We then show that this EOS can be very well represented within a thermodynamics theory framework previously applied to other polar fluids.« less
  • This paper describes an integrated experimental and computational framework for developing 3-D structural models for humic acids (HAs). This approach combines experimental characterization, computer assisted structure elucidation (CASE), and atomistic simulations to generate all 3-D structural models or a representative sample of these models consistent with the analytical data and bulk thermodynamic/structural properties of HAs. To illustrate this methodology, structural data derived from elemental analysis, diffuse reflectance FT-IR spectroscopy, 1-D/2-D {sup 1}H and {sup 13}C solution NMR spectroscopy, and electrospray ionization quadrupole time-of-flight mass spectrometry (ESI QqTOF MS) are employed as input to the CASE program SIGNATURE to generate allmore » 3-D structural models for Chelsea soil humic acid (HA). These models are subsequently used as starting 3-D structures to carry out constant temperature-constant pressure molecular dynamics simulations to estimate their bulk densities and Hildebrand solubility parameters. Surprisingly, only a few model isomers are found to exhibit molecular compositions and bulk thermodynamic properties consistent with the experimental data. The simulated {sup 13}C NMR spectrum of an equimolar mixture of these model isomers compares favorably with the measured spectrum of Chelsea soil HA.« less
  • This paper describes an integrated experimental and computational framework for developing 3-D structural models for humic acids (HAs). This approach combines experimental characterization, computer assisted structure elucidation (CASE), and atomistic simulations to generate all 3-D structural models or a representative sample of these models consistent with the analytical data and bulk thermodynamic/structural properties of HAs. To illustrate this methodology, structural data derived from elemental analysis, diffuse reflectance FT-IR spectroscopy, 1-D/2-D | 1H and 13C solution NMR spectroscopy, and electrospray ionization quadrupole time-of-flight mass spectrometry (ESI QqTOF MS) are employed as input to the CASE program SIGNATURE to generate all 3-Dmore » structural models for Chelsea soil humic acid (HA). These models are subsequently used as starting 3-D structures to carry out constant temperature-constant pressure molecular dynamics simulations to estimate their bulk densities and Hildebrand solubility parameters. Surprisingly, only a few model isomers are found to exhibit molecular compositions and bulk thermodynamic properties consistent with the experimental data. The simulated 13C NMR spectrum of * Corresponding author phone: (626)395-2730; fax: (626)585-0918; e-mail: diallo@wag.caltech.edu and mdiallo@howard.edu. Present address: Materials and Process Simulation Center,BeckmanInstitute 139-74, California Institute of Technology, Pasadena, CA 91125. † California Institute of Technology. ‡ Howard University. § University of Toronto. Pacific Northwest National Laboratory. ^ Sandia National Laboratories. # The Ohio State University. ã xxxx American Chemical Society PAGE EST: 11 10.1021/es0259638 CCC: $25.00 Published on Web 00/00/0000 an equimolar mixture of these model isomers compares favorably with the measured spectrum of Chelsea soil HA.« less