Thermodynamics of clouding process in 1-butanol + water mixtures in the presence and absence of sugars

Abstract

This paper deals with liquid-liquid equilibrium of binary {1-butanol + water} and ternary {1-butanol + aqueous sugar solutions} systems in both water-rich and butanol-rich environments. Immiscibility region of 1-butanol-water system is expanded by addition of sugars, and this effect becomes stronger by increasing hydrophilicity and molality of sugars. The soluting-out ability of sugars follows the order maltitol ≈ maltose > sucrose > D-(+)-glucose > D-(−)-fructose > xylitol > D-(+)-xylose. The experimental cloud point data were successfully correlated by Setschenow's equation. Thermodynamic functions and relative contributions of entropy and enthalpy to Gibbs free energy of clouding were calculated. From the obtained results, the clouding process of 1-butanol in water mixtures is more spontaneous than that of water in 1-butanol ones. The presence of sugars, in both water-rich and alcohol-rich environments, leads to a more spontaneous liquid-liquid demixing process. The clouding process in the water-rich region is entropy-driven, while in the butanol-rich region is enthalpy-driven.