PERFLUORO(7-METHYLBICYCLO[4.3.0]NONANE) PURIFICATION FROM CLOSE-BOILING IMPURITIES BY HETEROASEOTROPIC DISTILLATION METHOD

The process of distillation purification of the constituent of an industrial mixture of products of electrochemical fluorination of naphthalene – perfluorinated cycloalkanes, is considered. As an investigation object, in the present work, perfluoro(7-methylbicyclo[4.3.0]nonane) (MBCN) is considered. The last one is a close-boiling impurity in the production of perfluorodecalin, and has its own commercial value, that leads to purity requirements for the MBCN – not less than 0.998 mass fraction. According to the experimental data, the distillation purification of MBCN fractions with component content above 0.950 mass fraction is not effective and requires the use of special separation methods. The heteroazeotropic distillation was used to intensify the separation process. Acetone (Ac) and dimethylformamide (DMF) were considered as heteroazeotropic agents. All experiments were performed at atmospheric pressure on a semicommercial distillation column with an efficiency of 85 theoretical separation stages. The content of the MBCN in all initial fractions of the investigated samples of the reaction mixture ranged from 0.950 to 0.975 mass fraction, the mixture itself was taken directly from industry. According to experimental data, the separation factor of the initial mixture during distillation with no additional substances is close to 1. The adding of DMF and Ac makes it possible to significantly intensify the process, while Ac shows greater efficiency. Ac allowed to obtain a fraction of MBCN with purity higher than 0.998 mass fraction in one separation cycle, the degree of recovery was more than 0.80 by weight. The paper presents data on the distribution of components (target products, identified and unidentified impurities; the nomenclature of the latter is unknown because of the lack of relevant scientific studies and difficulties during their concentration and purifying) between the distillate and bottom product fractions; recovery ratio; separation factor; liquid-liquid phase equilibrium in the Ac-MBCN system and characteristics of the Ac-MBCN heteroazeotrope.