Block copolymer penetration into an asphaltene film as a mechanism for water-in-crude oil emulsion break-up

Abstract

During crude oil extraction, asphaltene-stabilized water-in-oil emulsions are formed and make the dewatering a challenging task. Demulsifiers (surface active agents), are typically used to destabilize the emulsion and facilitate the coalescence of water droplets. The demulsification mechanism of asphaltene-stabilized water-in-toluene emulsions by an ethylene oxide-propylene oxide-ethylene oxide (EO37─PO56─EO37) based block copolymer was studied. The performance of the demulsifier was assessed by bottle tests and the interfacial properties were determined by means of interfacial tension, Langmuir trough and contact angle measurements. From bottle tests experiments, the demulsifier showed the best performance at 3.85 µM in the water phase. A concentration dependent disruption of an asphaltene monolayer onto an aqueous polymeric surfactant subphase, was observed by means of Langmuir trough experiments. An interesting breakpoint was found at 0.154 µM aqueous polymeric surfactant concentration in the surface pressure-area isotherm, which is attributed to the formation of a new phase. Contact angle measurements of drops of aqueous polymeric surfactant solution onto asphaltene films showed that, at increasing polymeric surfactant concentration, the contact angle diminished to a threshold value. A direct interaction of block copolymer with asphaltene is proposed as a mechanism to account for the destabilization of water-in-oil emulsions.