Acetone and methanol are organic solvents widely used in industry. Acetone with methanol forms a homogeneous minimum-boiling azeotrope which is not separable by conventional distillation processes. A common method for its separation is the extractive distillation in the presence of a selective solvent (such as water). In this paper, the use of an ionic liquid (1-ethyl-3-methylimidazolium trifluoro methanesulfonate [Emim][triflate]) for acetone–methanol separation by extractive distillation was designed. The aim of the design calculation was to obtain acetone with the purity of 99.5 mol % and methanol with the purity of above 99.0 mol %. Calculations were carried out in a proprietary program constructed in Matlab® by solving a set of material balances at individual theoretical stages of the distillation column combined with the vapor–liquid equilibrium (VLE) of the ternary system acetone–methanol–[Emim][triflate]. For the description of VLE of the above mentioned system, the NRTL equation was used. Several optimization cycles were done resulting in optimal parameters of the extractive distillation column (number of theoretical stages, solvent consumption, reflux ratio and position of the feed stage) in regard to the required purity of products (acetone and methanol). Regeneration of ionic liquid was provided by evaporation at the low pressure of 20 kPa. The heat and cooling consumption duties of the designed separation process were analyzed. Regeneration of the ionic liquid is energy-demanding compared to the separation of acetone–methanol in an extractive distillation column. The heat consumption is only 11 % of the heat used up by the whole separation process.