CO2 responsive emulsions stabilized with fatty acid soaps in NaCl brine

Abstract

Similar to the responsive behaviors of emulsions under salt-free conditions, precise control of emulsification and demulsification is also required in some applications under saline conditions, especially in crude oil production and transport. So far, few studies have focused on the preparation of the responsive emulsions under saline conditions. In this study, CO2 responsive emulsions were prepared in the presence of NaCl using a fatty acid soap M-DA as stabilizer. M-DA complex was synthesized through electrostatic interactions between dimeric acid (DA) and Jeffamine (M1000). The droplet size and morphology of the oil–brine emulsions were characterized by dynamic light scattering and transmission electron microscopy, respectively. The oil–brine emulsion maintains high stability under air but completely separates into two phases upon exposure to CO2. NaCl plays a significant role in the CO2-induced demulsification, including salting-out effect and screening of electrostatic repulsion. It is worth noting that in the absence of NaCl, the emulsion remained stable after CO2 bubbling. CO2 responsive emulsions can also be prepared in the presence of other salts, or with other fatty acid soaps, which presents more interesting possibilities for preparation of CO2 responsive emulsions under saline conditions.