Thermodynamics Research Center / ThermoML | Fluid Phase Equilibria

ABSTRACT

In order to study the soluting-effect of ionic liquids on carbohydrates in aqueous solutions and to better understanding of its molecular mechanism, systematic investigations on the vapor-liquid (VLE) equilibria and solid-liquid equilibria (SLE) of ternary ionic liquid + carbohydrate + water systems were carried out at various temperatures. The ionic liquids 1-butyl-3-methylimidazolium bromide ([Bmim] [Br]) and 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim][HSO4]) with different hydrophilicity and seven carbohydrates including monosaccharides (L-(+)-arabinose, D-(+)-xylose, D-(+)-glucose and D-(-)-fructose), disaccharides (maltose and sucrose), and a polyol (maltitol) were selected. The water activity data showed that the hydrophilicity of the investigated solutes obey the following order: [Bmim] [HSO4] greater than [Bmim][Br] greater than or equal to carbohydrates. In these systems, the more hydrophilic solutes [Bmim][Br] and [Bmim][HSO4] acted as soluting-out agent and precipitated the sugars from the aqueous solutions. The negative deviations of the constant water activity lines from the linear isopiestic relation for [Bmim] [HSO4]/carbohydrate systems were somewhat larger than [Bmim][Br]/carbohydrate systems. The order of these deviations was agreement with the obtained soluting-out coefficients from the SLE experiments.