Demulsification of water-in-heavy oil emulsions by oxygen-enriched non-ionic demulsifier: Synthesis, characterization and mechanisms

Separation of water-in-heavy oil (W/HO) emulsions is a critical issue in petroleum industry (especially for the thickened oils and natural bitumen) due to its high viscosity and rigid interfacial film formed by natural stabilizers (e.g., asphaltenes). Herein, two different strategies have been proposed to enhance the demulsification of the W/HO emulsions from the aspects of interfacial reconstruction and bulk oil phase property regulation. Firstly, to break the rigid interfacial film at the oil–water interface, a novel demulsifier (TJU-3, Mn: 6131 g/mol) has been successfully designed, introducing high content of carboxyl groups and ester groups to the molecules. The chemical groups, molecular structure, content of oxygen-containing groups, solubility, turbidity and phase distribution rules of TJU-3 have been instrumentally determined. It was observed that TJU-3 performed well in breaking the W/HO emulsions with faster rate (reaching 100% dehydration in less 25 min) and no “tailing phenomenon” compared with other commercial demulsifiers. Secondly, to facilitate the diffusion of demulsifer molecules from bulk oil phase to oil–water interface which promote the demulsification rate, the effect of oil viscosity on the demulsification efficiency has been investigated. Results showed that, after working with demulsifiers, when only one single method (heating or dilution at ambient conditions) was used, the dehydration rate of W/HO emulsions is limited (no more than 50%). When combining demulsifiers with diluents at slight heating conditions, a complete dehydration (∼100%) of W/HO emulsions was obtained, which was optimized at 60 ℃, 400 ppm. This synergistic effect was mainly contributed to the fact that viscosity reduction weakens the obstruction of the demulsifier diffusion and increases the average kinetic energy of the thermal movement of demulsifiers. This work would provide insights for developing new low-carbon demulsification separation method for petroleum production.