Characterization and phase behavior of the surfactant ionic liquid tributylmethylphosphonium dodecylsulfate for enhanced oil recovery

Surface active ionic liquids have been gaining attention in the literature. A range of applications such as nanoparticle preparation, solubilization or reaction in microemulsion, and Enhanced Oil Recovery have centered the uses of these new surfactants. In this work the surface active ionic liquid tributylmethylphosphonium dodecylsulfate has been synthesized and characterized for the first time. By introducing a phosphonium cation, instead of the commonly used sodium, a room temperature surfactant ionic liquid has been obtained. Thus, the production of an anionic surfactant which is easy to handle has been achieved. Relevant physical and thermal properties such as density, viscosity, refractive index, melting point and thermal decomposition have been measured. The aggregation in aqueous solutions has been evaluated by means of surface tension and electrical conductivity, with calculation of critical parameters such as the critical micelle concentration, surface excess concentration, degree of ionization of micelles, or the Thermodynamic functions of micellization. The results have been compared with the classical surfactant sodium dodecylsulfate and other surface-active ionic liquids based on the dodecylsulfate anion. With the application of Enhanced Oil Recovery in mind, the phase behavior and interfacial tension of ternary mixtures with brine and n-dodecane have been evaluated. The system is Winsor type III over a wide range of salinity and temperature conditions. Optimal salinity was found at ∼8 wt% NaCl, with interfacial tension about 0.1 mN m−1. The interfacial tensions obtained with crude oil significantly improve previous results found with other ionic liquids or even with ionic liquids in combination with alkalis. [Display omitted] •A new SAIL, [P4441][DS], has been synthesized and characterized.•[P4441][DS] shows better capacity to reduce water/air interfacial tension than SDS.•Winsor type III phase behavior with water or brine and n-dodecane obtained.•Optimal salinity of ∼8 wt% NaCl leads to minimum interfacial tension of ∼0.08 mN m−1.