The resolution of water-in-crude oil emulsions by the addition of low molar mass demulsifiers

Abstract

We have measured the rates of demulsification of water-in-crude oil emulsions using a series of octylphenyl-polyethoxylates and sodium bis(2-ethylhexyl)sulfosuccinate (AOT) as demulsifiers. The hydrophilic—lipophilic balance (HLB) of the surfactant systems was varied systematically by changing the number of ethoxy groups in the case of the nonionic surfactants and by changing the concentration of added NaCl in the case of AOT. For all surfactants and conditions, the demulsification rate increased with surfactant concentration up to the onset of surfactant aggregation in the oil, the water, or a third, surfactant-rich phase. The highest rate reached is estimated to be close to the diffusion controlled value. Higher concentrations of the surfactants produced either a decrease in demulsification rate (“overdosing”) or a slight increase to a plateau value of the rate. Overdosing was observed for solutions where the surfactants formed aggregates in the oil phase (“hydrophobic surfactants”). “Hydrophilic surfactants” (for which aggregation occurred in the water phase) showed overdosing behavior only for cases where a high viscosity aqueous phase was produced. Higher concentrations of hydrophilic surfactants which gave low viscosity aqueous phases on demulsification gave a plateau value in the demulsification rate.