Phase Behavior of Tetrabutylammonium Salt/Oil/Water/Inorganic Salt Four-Component Systems

The phase behavior of four-component systems composed of tetrabutylammonium halide (TBAX; X = Cl, Br, or I), nonpolar benzene, water, and sodium halide (NaX) has been examined in detail. According to their constituents, compositions, and temperatures, the four-component systems afforded from single- to four-phase states. There were at least three kinds of liquid phases: a TBAX-rich phase (M), an aqueous solution phase (W), and an oil solution phase (O). In the M phase, TBAX was assumed to form aggregates, like microemulsions, while, in the latter two solution phases, TBAX was present without any aggregated form. When these three liquid phases coexisted, an O-M-W three-liquid-phase equilibrium state occurred. Depending on the temperature and NaX concentration in the W phase, the system changed its state from the O-M-W to the O-M or M-W two-liquid-phase. In some cases, a solid TBAX phase (Q) or solid NaX phase (S) coexisted with these liquid phases. In the presence of excess sodium halide, an O-M-W-S four-p...