The paper presents the results of the study of phase equilibrium in the system formed in the reaction of cyclohexene oxidation (cyclohexene + water + cyclohexanone + solvent). Pure N-methyl-2-pyrrolidone or binary mixture acetonitrile + N-methyl-2-pyrrolidone was considered as a solvent. The method of studying was mathematical modeling on the base of the nonrandom two-liquid model. Thermodynamic-topological analysis was used to analyze the structure of the vaporliquid equilibrium diagram. The mixture separation flowsheets were proposed and parameters of column work were determined using simulation in Aspen Plus V.10.0. The possibility of isolation of the target component (cyclohexanone) without the use of special separation methods was proved. The results obtained showed the prospects of replacement of pure acetonitrile or previously proposed dimethylsulfoxide and dimethylacetamide by solvents considered.