Characterisation of liquid-liquid interfaces related to offshore produced water treatment - interfacial activity of model Components

Abstract

Produced water is one of the biggest environmental challenges in gas and crude oil production, and the stability of oil in water emulsions makes separation during treatments difficult.The objective of this work is to find out how interfacial active compounds contribute to the stability of oil/water emulsions. A model naphthenic acid dissolved in model oil was used together with a synthetic aqueous brine of different pH values in order to mimic produced water conditions. The experiment was conducted with a model oil (xylene) containing a model naphthenic acid (4-Heptyl benzoic acid) with concentrations ranging from 0,01M to 0,2M while the pH values of the aqueous phase ranged from 2 to 10. The results showed that interfacial tension decreased as the surface age increased because the model naphthenic acid migrates from the oil bulk to the interface. Interfacial tension also decreased with increasing concentration of the model naphthenic acid. The study showed also dilatational elasticity modulus was found to increase with the model acid concentration up to a certain concentration level depending on the aqueous phase composition. The diffusion coefficient was calculated using the Ward and Tordai equation .A slight decrease in the diffusion coefficient as the concentration of the naphthenic acid increased was observed. Furthermore, an increase in diffusion coefficient with increasing pH was observed in both the short and long time approaches. This trend was observed for concentration values of under 0.1M, thereafter a mixed result was observed. This study showed that both pH change on the aqueous phase and presence of surfactants on the oil phase impact the interfacial properties and behavior.