Enhancing oil–solid and oil–water separation in heavy oil recovery by CO2-responsive surfactants

Interfacial properties are of critical importance to various separation applications. In heavy oil recovery, for example, a low oil–water interfacial tension (IFT) benefits the separation of heavy oil from their host rocks, which becomes problematic in the later stage of oil–water separation. CO₂-responsive surfactants were investigated to enhance the overall heavy oil recovery by switching their interfacial activity to the desired state in each stage. The surfactants at interfacially active state greatly enhanced the separation of heavy oil from hosting solids, as demonstrated by measuring contact angle and oil liberation using a custom-designed on-line visualization system. Meanwhile, the resulting heavy oil-in-water emulsions could also be easily demulsified by the bubbling of CO₂ gas, which switched off the interfacial activity of the surfactants. Furthermore, CO₂-responsive surfactants could be partially recycled in process water to improve sustainability, making CO₂-responsive surfactants to be promising chemical aids in heavy oil production and many other vital industries.