The solubility curve and density curve of 1-butyl-3-methylimidazolium tetrafluoroborate-water-sodium carbonate system ([Bmim]BF4-H2O-Na2CO3) were measured with the turbidity titration method at 30℃ under atmospheric pressure and were correlated with empirical equations.The liquid-liquid equilibrium data of the system were measured with the turbidity-density method and the phase diagram was constructed.As shown by experimental results, one phase of the aqueous two-phase system was composed mainly of water and ionic liquid whereas the sodium carbonate concentration was very low, the other phase was composed mainly of water and sodium carbonate whereas the ionic liquid concentration was very low.The system could be used for extraction and separation.It could also be used for primary separation and recovery of ionic liquids from aqueous solution.Othmer-Tobias and Bancroft equations were used for correlation of the liquid-liquid equilibrium data, but the result was not satisfactory.The maximum relative error was about 94.99%, and the maximum average relative error was about 15.69%.A new method for the correlation by using Othmer-Tobias and solubility equations was proposed.The maximum relative error was about 4.52%, and the maximum average relative error was about 2.77%.The calculated results were in good agreement with experimental data.The method could be used for correlation of liquid-liquid equilibrium for the system with a low content of one component.
