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The investigation of CH4 hydrates holds considerable importance in addressing energy, environmental, and resource-related challenges. The storage and transportation of CH4 have garnered widespread interest, prompting the utilization of the all-atom MD simulation method to examine the growth of CH4 hydrates above freezing point. Specifically, this study simulated the hydrate growth process of CH4 aqueous solution with structure I CH4 hydrate as a seed, under the conditions of 275 K and 10 MPa. The simulation was conducted utilizing Gromacs version 2019.6 with a total duration time of 100 ns. The TIP4P/Ice water model was employed to characterize water, while the gaff force field was utilized to describe CH4. Visualization was performed using VMD software. The CHILL + tool was employed to quantify the water molecules number present in various states, including hydrate, hexagonal ice, cubic ice, liquid water, and the interface between solid and liquid phases. Order parameters were utilized to analyze the phase transition of water. Throughout the simulation, the F3 order parameter decreases from 0.055 to 0.025, while the F4 order parameter increases from 0.225 to 0.625. This change is attributed to the transition of the solution state from liquid to solid, as evidenced by alterations in the quantity of cages formed by water molecules and the distribution of water molecules across distinct phase states, substantiating the formation of hydrates alongside a concomitant decrease in energy. Furthermore, the variation in the total count of h-bonds within the system serves as a reliable indicator of the phase transition from liquid to solid. This phenomenon occurs due to the ability of every liquid water molecules to establish 3 ~ 4 h-bonds with neighboring water molecules, whereas solid water molecules are capable of forming 4 h-bonds with adjacent water molecules. However, the resultant hydrate structure does not align precisely with the idealized CH4 hydrate structure, as evidenced by the presence of liquid water molecules observed following the completion of the simulation. Examining the growth process of CH4 hydrates above their freezing point holds practical importance for the storage and transportation of CH4.

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Investigating the Growth Process of CH4 Hydrate Using Molecular Dynamics Simulation Above Water Freezing Point

  • 会议论文

  • 发表日期：

    2025年

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  • Xian-wu Jing,
  • You-quan Liu,
  • Xin Huang,
  • Ziyi Fu,
  • Long Xian

摘要

The investigation of CH4 hydrates holds considerable importance in addressing energy, environmental, and resource-related challenges. The storage and transportation of CH4 have garnered widespread interest, prompting the utilization of the all-atom MD simulation method to examine the growth of CH4 hydrates above freezing point. Specifically, this study simulated the hydrate growth process of CH4 aqueous solution with structure I CH4 hydrate as a seed, under the conditions of 275 K and 10 MPa. The simulation was conducted utilizing Gromacs version 2019.6 with a total duration time of 100 ns. The TIP4P/Ice water model was employed to characterize water, while the gaff force field was utilized to describe CH4. Visualization was performed using VMD software. The CHILL + tool was employed to quantify the water molecules number present in various states, including hydrate, hexagonal ice, cubic ice, liquid water, and the interface between solid and liquid phases. Order parameters were utilized to analyze the phase transition of water. Throughout the simulation, the F3 order parameter decreases from 0.055 to 0.025, while the F4 order parameter increases from 0.225 to 0.625. This change is attributed to the transition of the solution state from liquid to solid, as evidenced by alterations in the quantity of cages formed by water molecules and the distribution of water molecules across distinct phase states, substantiating the formation of hydrates alongside a concomitant decrease in energy. Furthermore, the variation in the total count of h-bonds within the system serves as a reliable indicator of the phase transition from liquid to solid. This phenomenon occurs due to the ability of every liquid water molecules to establish 3 ~ 4 h-bonds with neighboring water molecules, whereas solid water molecules are capable of forming 4 h-bonds with adjacent water molecules. However, the resultant hydrate structure does not align precisely with the idealized CH4 hydrate structure, as evidenced by the presence of liquid water molecules observed following the completion of the simulation. Examining the growth process of CH4 hydrates above their freezing point holds practical importance for the storage and transportation of CH4.