Chain-length tunable tertiary amine/SDBS CO2-switchable emulsions for heavy oil viscosity reduction and rapid demulsification

The careful design and synthesis of CO 2 stimulus-responsive surfactants are critical to the effective application of CO 2 -switchable emulsion for reducing the viscosity of heavy crude oil. In this study, a simple alternative method was proposed to construct CO 2 -responsive emulsions using a series of N, N-dimethylalkyl tertiary amines with different chain lengths as CO 2 -responsive agents, in combination with sodium dodecylbenzene sulfonate (SDBS) as emulsifiers. The stability, responsiveness, reversibility, demulsification performance and mechanism of emulsions formed with dodecane and crude oil respectively, were evaluated by interfacial tension, electrical conductivity, particle size, Zeta potential and 1 H NMR measurements. The results show that the incorporation of the amines enhanced emulsion stability by 10～20 %, with the crude oil-in-water emulsion exhibiting approximately three times greater stability than its dodecane-in-water counterpart. Remarkably, the emulsification of the crude oil resulted in a nearly 96.77 % reduction in viscosity. Moreover, the crude oil emulsions underwent rapid demulsification within minutes upon CO 2 exposure. These distinctive properties underscore the strong potential of CO 2 -responsive surfactants for viscosity reduction in heavy oil applications.