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Issue 14, 2018
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Formation of a nanobubble and its effect on the structural ordering of water in a CH4–N2–CO2–H2O mixture

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Abstract

The replacement of methane (CH4) from its hydrate by a mixture of nitrogen (N2) and carbon dioxide (CO2) involves the dissociation of methane hydrate leading to the formation of a CH4–N2–CO2–H2O mixture that can significantly influence the subsequent steps of the replacement process. In the present work, we study the evolution of dissolved gas molecules in this mixture by applying classical molecular dynamics simulations. Our study shows that a higher CO2 : N2 ratio in the mixture enhances the formation of nanobubbles composed of N2, CH4 and CO2 molecules. To understand how the CO2 : N2 ratio affects nanobubble nucleation, the distribution of molecules in the bubble formed is examined. It is observed that unlike N2 and CH4, the density of CO2 in the bubble reaches a maximum at the surface of the bubble. The accumulation of CO2 molecules at the surface makes the bubble more stable by decreasing the excess pressure inside the bubble as well as surface tension at its interface with water. It is found that a frequent exchange of gas molecules takes place between the bubble and the surrounding liquid and an increase in concentration of CO2 in the mixture leads to a decrease in the number of such exchanges. The effect of nanobubbles on the structural ordering of water molecules is examined by determining the number of water rings formed per unit volume in the mixture. The role of nanobubbles in water structuring is correlated to the dynamic nature of the bubble arising from the exchange of gas molecules between the bubble and the liquid.

Graphical abstract: Formation of a nanobubble and its effect on the structural ordering of water in a CH4–N2–CO2–H2O mixture

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Publication details

The article was received on 25 Nov 2017, accepted on 27 Feb 2018 and first published on 27 Feb 2018


Article type: Paper
DOI: 10.1039/C7CP07934F
Citation: Phys. Chem. Chem. Phys., 2018,20, 9157-9166
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    Formation of a nanobubble and its effect on the structural ordering of water in a CH4–N2–CO2–H2O mixture

    S. P. Kaur, K. S. Sujith and C. N. Ramachandran, Phys. Chem. Chem. Phys., 2018, 20, 9157
    DOI: 10.1039/C7CP07934F

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