Polymeric surfactants and emerging alternatives used in the demulsification of produced water: a review

Stable emulsions are frequently encountered in oil production and cause a series of environmental and operational issues. Chemical demulsification is widely used for the separation of oil from water or removal of water from oil. The chemicals used in the demulsification process have a strong affinity to the oil-water interface. This review presents the various types of chemical demulsifiers used for the demulsification of water-in-oil and oil-in-water emulsions. The review covers the relevant properties of polymeric surfactants such as polyether, dendrimers, and natural biodegradable polymeric surfactants. In addition, emerging alternatives like nanoparticles-based demulsifiers and ionic liquids are also reviewed. The factors affecting the demulsification efficiency of these demulsifiers and structure-property relationships are discussed. Copolymers with high hydrophilic content and molecular weight are more efficient demulsifiers. Similarly, the position isomerism (same carbon skeleton and functional groups but a different location of functional groups) strongly affects the HLB and demulsification performance. Generally, dendrimers show better performance compared to linear polymeric surfactants due to their relatively higher interfacial activity, better penetrability, and a larger number of reactive terminal groups. Techniques used to evaluate the performance of demulsifiers are also covered. The review also highlights the current developments and future prospects of chemical demulsifiers.