Demulsification of Crude Oil-in-Water Emulsions Driven by Graphene Oxide Nanosheets

Seeking highly efficient, rapid,
universal, and low-cost demulsification
materials to break up the crude/heavy oil-in-water emulsion and emulsified
oily wastewater at ambient conditions has been the goal of the petroleum
industry. In this work, an amphiphilic material, graphene oxide (GO)
nanosheets, was introduced as a versatile demulsifier to break up
the oil-in-water emulsion at room temperature. It was encouraging
to find that the small oil droplets in the emulsion quickly coalesced
to form the oil phase and separated with the water within a few minutes.
The demulsification tests indicated that the residual oil in separated
water samples was as low as ∼30 mg/L, corresponding to a demulsification
efficiency over 99.9% at an optimum GO dosage. More importantly, GO
not only is useful for ordinary crude oil emulsion but also can be
used to break up the extra heavy oil emulsion. The effect of the emulsion
pH on the demulsification was also investigated. It was interesting
to find that the distribution of GO either in oil or in water phase
after demulsification was dependent on the pH value of the solution,
which was attributed to the pH-dependent amphiphilicity of GO. The
prominent demulsification ability of GO was attributed to the strong
adsorption between the GO nanosheets and molecules of asphaltenes/resins
driven by π–π interactions and/or n−π
interactions. The findings in this work indicate that the GO nanosheets
are a simple, highly efficient, and universal demulsifier to separate
the oil from the crude/heavy oil-in-water emulsions at ambient conditions,
which shows a good application prospect in the oil industry.