Phase boundary curves in toluene, 1-butanol, and aqueous sodium alkylbenzenesulfonate systems

Abstract

Miscibility relationships in systems containing toluene, 1-butanol, water, and sodium alkylbenzenesulfonates are reported. The sulfonates studied included benzene, p-toluene, p-ethylbenzene, 2,4,6-trimethylbenzene, p-cymene, and 2,5-diisopropylbenzene. In a triangular representation with a constant ratio of 1 mol of sulfonate/kg of water as one component, the phase boundary curves are fairly symmetrical with respect to the alcohol apex for S/sub AC/ (number of alkyl carbons on benzene ring of benzene sulfonate) less than 3, but highly asymmetrical for S/sub AC/ greater than 3. The amount of 1-butanol required to produce miscibility decreases with the increasing S/sub AC/ in the aqueous-rich region (> 40% aqueous solution) but increases in the toluene-rich region (> 80% toluene) when S/sub AC/ = 4 and 6. One system, containing sodium 2,5-diisopropylbenzenesulfonate, was studied at eight aqueous solution concentrations at 25/sup 0/C from 0.25 to 3.0 mol of sulfonate/kg of water. Phase relationships for limiting three-component systems were also determined. Under the boundary curves of the system containing 0.50, 1.0, and 1.5 m aqueous solutions, regions with three liquid phases in equilibrium were observed at 25/sup 0/C. The regions of the three coexisting liquid phases varied with changing temperature and composition. Opalescence can be seen at several compositions, especiallymore » near the S-shape sector of the phase boundary curves, an observation which, along with low interfacial tension between phases, suggests proximity of critical end points.« less