Application of Buffer-Based Ionic Liquid in the Separation of 1,4-Dioxane from Its Azeotropic Aqueous Solution

We have found that the ionic liquid (IL) [TMA] [EPPS] could induce liquid-liquid phase splitting in the aqueous solution of 1,4-dioxane at ambient conditions. This IL is composed of tetramethylammonium (TMA) as a cation and a biological buffer, 4-(2-hydroxyethyl)-1-piperazinepropanesulfonic acid (EPPS), as an anion. The efficiency of this buffer-based IL for separating 1,4-dioxane from its aqueous solution has been evaluated on the basis of the liquid-liquid equilibrium (LLE) and solid-liquid-liquid equilibrium (SLLE) data of 1,4-dioane + water + [TMA] [EPPS] at 298.15 K and under atmospheric pressure. The experimental LLE phase boundary data were correlated with an empirical equation and the effective excluded volume (EEV) model, respectively. The consistency of the LLE tie-line data was confirmed by using the Othmer-Tobias model. The binary interaction parameters of the NRTL model for each pair were obtained by correlating the experimental LLE and SLLE tie-line data. By using [TMA] [EPPS] as an auxiliary agent, the maximum concentrations of 1,4-dioxane (97.8 wt %) in the organic-rich phase is greater than the azeotropic compositions (87.82 wt %) of the corresponding aqueous system. It clearly indicates that [TMA] [EPPS] can be served as a high efficiency, noncorrosive, and biocompatible green agent for recovering high purity of 1,4-dioxane from its aqueous solution.