Electrolyte and pH effect on emulsion stability of water-in-petroleum oils

Abstract

The stability of water-in-Guanipa crude emulsion was studied as a function of pH and the electrolyte concentration of mono- and polyvalent metal chlorides in the initial aqueous phase. The natural crude showed a medium to strong i.r. absorbance from silicon groups indicating that emulsion stability is supported by the oil content of dispersed mineral fines. Emulsion stability was found to be strongly dependent on pH of the initial aqueous phase, emulsion breakdown occurring at 10 < pH < 13.5. Whether base was introduced before or after emulsion formation was found to affect appreciably the extent of emulsion collapse within the stability gap boundaries. An emulsion stability gap was also observed at 10 −2 < N < 2.5 × 10 −1 of polyvalent metal chlorides concentration in the initial aqueous phase. The electrolyte threshold concentration for emulsion breakdown corresponded to its concentration at the isoelectric point of aqueous silica sol. The results indicate that the electrolyte and pH affect the emulsion stability of water-in-petroleum oil through their action on the coagulation of the mineral colloids. The data point to the absorption of positive metal or negative hydroxyl ions on the gel resulting in a deflocculation of the newly charged aggregates.