(180c) Clathrate Hydrate-Water Interfacial Dynamic Behaviors with the Precipitation of Metal Naphthenate

Gas hydrates are inclusion compounds of small guest molecules enclathrated in cages of hydrogen-bonded water molecules under high pressure and low temperature. The submarine oil pipeline has such a preferable condition for gas hydrate formation, and the unexpected formation of clathrate hydrates has been a significant problem in the petroleum industry. This work reveals the adhesion behaviors between clathrate hydrate particles and an aqueous phase with naphthenate precipitation at a water-oil interface. Naphthenic acid, one of the components included in a crude oil, reduces the adhesion force between tetrahydrofuran (THF) hydrate particle and aqueous phase by reducing the interfacial tension. Naphthenic acid molecules react with metal ions in the aqueous phase at weak basic conditions (pH ≈ 11) and make a precipitation of metal naphthenate at a water-oil interface. The precipitated naphthenate layer pushes up the hydrate particle and hinders the contact between the hydrate particle and the aqueous phase. Over 0.1 wt % of naphthenic acid in the oil phase, the metal naphthenate layer is able to cover the water-oil interface completely and inhibit the further growth of hydrate particles. This result demonstrates that the risk of hydrate plugging in the submarine oil pipeline could be decreased with the crude oil of high acidity.