Effect of Compressed CO2 On the Solubility of Inorganic Salt in Reverse Micelle

Effect of Compressed CO₂ on the Solubility of Inorganic Salt in Reverse Micelle

 

Jianchao Zhang, Rui Zhang*, Yu Cang, Lixiao Liu, Tao Li, Xuhong Guo*

State Key Laboratory of Chemical Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China.

*Corresponding authors. Tel.: +86-21-64253491; E-mail: r.zhang@ecust.edu.cn

guoxuhong@ecust.edu.cn

Abstract: Reverse micelles are thermodynamically stable surfactant aggregates with polar cores, which are formed spontaneously as certain types of surfactants dissolve in nonpolar solvents. It's well known that a small amount of salt can reduce critical micelle concentration (CMC) of surfactant at normal pressure. However, the work about the compressed CO₂ can enhance the solubility of inorganic salt obviously in reverse micelles has not been reported before.

In this work, the phase behavior of compressed CO₂ on sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in octane with different concentration of inorganic salt was studied. It was found that the suitable pressure which can form one phase region increases with the decreasing of salt concentration at high salt concentration range (Figure 1). Different inorganic salts with valence state have been used to examine the effect of metal ion on the AOT-octane-inorganic salt-water-CO₂-quintuple system. It was found that compressed CO₂ can dissolve higher concentration of NaCl than that of CaCl₂ at the same W0, which is defined by water to AOT molar ratio. For example, thanks to compressed CO₂, the maximum concentration value of NaCl and CaCl₂ aqueous solution with the W₀ at 30 which can be dissolved is 5.0mol/L and 2.5 mol/L, respectively. The main reason is probably the divalent ion can reduce the thickness of electric double layer more effective than monovalent ion do. The clear point pressure increases with the W0 increasing at the same salt concentration. In other words, the area of one phase of quintuple system turns to smaller with the increasing of W₀. This work will provide the valuable suggestion for the application of surfactant under the inorganic salt condition.

Keywords: compressed CO₂, solubility, inorganic salt, reverse micelle

Figure 1. The phase diagram of AOT-octane-inorganic salt-water-CO₂ quintuple system at 303.2K.