Designing high ionicity ionic liquids based on 1-ethyl-3-methylimidazolium ethyl sulphate for effective azeotrope breaking

Separation of alkanols and alkanes is a complex process in the production of oxygenated additives and fuels due their close boiling points and azeotrope formation. In this work, liquid–liquid extraction of ethanol from n-heptane + ethanol mixtures using high ionicity ionic liquids (HIILs) as extraction solvents is studied. Three different HIILs, with different ionicities were prepared through the addition of different amounts of ammonium thiocyanate inorganic salt to 1-ethyl-3-methylimidazolium ethyl sulphate ionic liquid, and used. Liquid–liquid equilibria of ternary mixtures of n-heptane + ethanol + 3 different HIILs were experimentally measured at 298.15 K and 0.1 MPa. Modelling of the experimental tie lines and binodal curves was performed by using the non-random two-liquid (NRTL) activity coefficient model; each HIIL (IL + salt) was treated as a pseudo-component. Both the selectivity and the distribution coefficient were used in the assessment of the extraction solvent feasibility and a correlation of these parameters with the ionicity of the HIILs was established. A comparison between the different HIILs and the neat ionic liquid is also made.