Hypothesis: Mixed clays (e.g. montmorillonite, illite and kaolinite) are ubiquitous in hydrate-bearing sediments under seafloor, and their surfaces inevitably affect the formation of natural gas hydrates therein. Nevertheless, the actual effects of clay surfaces on hydrate formation remain elusive.
Experiments: Systematic molecular dynamics simulations have been performed to investigate CH4 hydrate formation in mixed clay nanopores of montmorillonite, illite and kaolinite, to examine the effects of surface property and layer charges of mixed clays.
Findings: Simulation results indicate that the surfaces of mixed clays affect CH4 hydrate formation in the nanopores by changing the CH4 concentration (xCH4) and ion concentration (xions) in the middle region of the nanopores via surface adsorption for CH4, H2O and ions. Specifically, the surfaces of montmorillonite and illite, the siloxane and gibbsite surfaces of kaolinite show different affinities for adsorbing CH4, H2O and ions, which can significantly affect the xCH4 and xions in the interfacial and middle regions of the nanopores. Moreover, hydrate growth shows certain surface preference. These molecular insights into the effect of mixed clay surfaces on CH4 hydrate formation can help to understand the formation mechanism of natural gas hydrate in marine sediments.
Keywords: Hydrate formation; Layercharge; Methane hydrate; Mixedclays; Molecular dynamics simulation; Surface property.
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