Molecular-Level Study on Decomposition Kinetics of CO2-CH4 Hydrates

YC Li and SF Song and NJ Liao and HH Chen and HY Yao and BH Shi and J Gong, ENERGY & FUELS, 38, 12875-12887 (2024).

DOI: 10.1021/acs.energyfuels.4c01796

With the escalating global demand for energy, the disparity in the supply of oil and gas continues to widen, prompting the exploration of alternative extraction methods. Current technologies for extracting natural gas from hydrate deposits face numerous challenges, including high costs, low efficiency, and environmental concerns. The mechanism and kinetics of CO2-CH4 hydrate decomposition remain unclear. This study focuses on elucidating the decomposition kinetics of CO2-CH4 hydrates. Moreover, the influences of CO2-CH4 hydrate configuration on the decomposition process are explored. Interface mass-transfer phenomena, alongside water cage occupancy, are scrutinized as integral factors affecting decomposition kinetics. Microscopic decomposition kinetics of CO2-CH4 hydrates by depressurization at various temperatures are analyzed through molecular dynamic simulations. Additionally, we employ the four-body structural order parameter, fixed number of molecules, and radial distribution function to support our analysis. Our simulations delve into the interface mass transfer of CO2-CH4 hydrates during depressurization processes, shedding light on the intricate dynamics at play. Our results reveal rapid decomposition of the outer layers of hydrate phases, with the liquid phase posing a hindrance to decomposition. Furthermore, we observe that water cage occupancy significantly influences the stability and decomposition kinetics of CO2-CH4 hydrates. Increased CO2 occupancy intensifies interaction energy with water cages, consequently reducing the stability of mixed hydrates. Also, the higher proportion of empty cavities, the more prone the CO2-CH4 hydrate is to decomposition. Overall, our findings contribute to a deeper understanding of the microscopic-scale decomposition mechanisms of CO2-CH4 hydrates, thus advancing techniques for CO2 replacement of CH4 hydrates and offering insights into the development of novel energy sources.

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