Vapor-liquid Equilibria For Mixtures Containing Acetonitrile, Water And Ionic Liquid

The investigation of phase behavior plays an important role in the production of chemical industry and design of process. To apply ionic liquids (ILs) to the separation of water+ acetonitrile, a static vapor liquid equilibrium (VLE) device of constant temperature is used to measure the VLE data of three binary and three ternary systems in this work. The binary systems are acetonitrile+1-butyl-3-methylimidazolium chloride ([C4mim][Cl]), acetonitrile +1-butyl-3-methylimidazolium fluoroborate ([C4mim][BF4]), acetonitrile+ 1-hexyl-3-methylimidazolium chloride ([C6mim][Cl]), and the ternary ones are acetonitrile+ water+[C4mim][Cl], acetonitrile+water+[C4mim][BF4] and acetonitrile+water+ [C6mim][Cl]. The experimental data were correlated and predicted by the NRTL equation. The effect of the IL mixtures on the activity coefficients of acetonitrile was also observed initially. The results indicate that acetonitrile and any of the three ILs can form a negative deviation system, and acetonitrile+[C4mim][BF4] exhibits lower saturated vapor pressures than the other two binary systems. For both the binary and ternary systems, there is a highly linear relationship between the logarithm of pressure lnp and the reciprocal of temperature 1/T at a given composition. Furthermore, the relationship can also satisfactorily correlate the VLE data of acetonitrile+IL mixture, which molar ratios of [C4mim][BF4] to [C6mim][Cl] is 1:1 or 4:1. The binary interaction parameters between acetonitrile and the three ILs were obtained by fitting the NRTL equation to the VLE data. The average absolute relative deviations (AARDs) of the vapor pressures are 1.65% for acetonitrile+[C4mim][Cl],1.84% for acetonitrile+[C4mim][BF4], and 1.40% for acetonitrile+[C6mim][Cl]. It is found that the NRTL model can successfully be used for the binary systems. In addtion, we predicted the VLE data of three ternary systems with the optimized parameters. As is observed, the order of the influence of the ILs on the separation efficiency of water+acetonitrile is [C4mim][Cl]> [C6mim][Cl]> [C4mim][BF4]. As a result, we should prefer to the ILs consisting of the anion of chlorine in screening ILs. For a given anion, the shorter alkyl chain in a cation has higher saparation efficiency. Finally, according to the experimental results, the molar ratio of the IL mixtures influences the activity coefficient of acetonitrile negligibly. It confirmed that the activity coefficient of acetonitrile greatly depends on the interations between acetonitrile and IL mixture.