Fluid Phase Equilibria, Vol.487, 76-82, 2019
The effect of aqueous NaCl solution on methane hydrate nucleation and growth
Electrolyte solution can effectively inhibit the formation of hydrate. In this work, molecular dynamics simulations of hydrate nucleation and growth in aqueous NaCl solutions were performed to study the effect of ions on hydrate formation. We found that the electrolyte ions can inhibit hydrate formation on both the nucleation and the growth stage. Hydrates prefer nucleation in a region with low ionic concentration because the availability of water molecules in the ionized hydration layer is reduced. The slight change in orientation distribution of water around methane molecules in a NaCl solution system may be another factor to inhibit nucleation. The induction time is approximately proportional to the ionic strength, indicating that the charge has a more obvious inhibitory effect on hydrate formation. In hydrate growth stage, ions are excluded from the hydrate phase and a certain amount of free water molecules exist around the hydrate cluster. The ions near the hydrate can reduce its growth rate, causing a higher crystallinity of hydrate formed in salt solution. Finally, a dual influence of the ions on methane mass transfer was found to be that the ions increase the apparent concentration of methane to facilitate nucleation, but inhibit their diffusion at the same time. (C) 2019 Elsevier B.V. All rights reserved.