Study On The Separation Process Of Methanol+acetonitrile+benzene System

The separation of ternary azeotropic system is very difficult due to the morecomplex force relationship between components. The solvents selected by the methodfor binary systems separation are not fittable, so the separation by add extra solvents isnot easy. In this paper, the separation of methanol+acetonitrile+benzene was studied.The feed was waste liquid from a pharmaceutical factory which contain methanol、acetonitrile and benzene, the mass fraction was70%、20%and10%separately.The distillation curves and distillation region characteristics were analysed andstudied, the application of distillation curves are summarized.A series of isobaric VLE data of methanol-acetonitrile-benzene system wereinvestigated by double circulating still at101.3kPa. Distillation curve ofmethanol-acetonitrile-benzene was drawn with VLE data obtained from experiment.After observation and analysis of the trend and destination of the distillation curve, wefound that the ternary azeotropic point neither the highest nor the lowest. The distillationregion was divided into three parts, and the destination of each part are different.With methanol as solvent was put forward to change the region of the mixture, sothe top product could be methanol-benzene and the bottom product was methanol-acetonitrile, the ternary system became to two ternary system which can be separated bypressure swing distillation.According to the lab experiments, we proved the method was possible, andoptimized the solvent ratio and reflux ratio of the preliminary separation column, theresult is that solvent rato was2and the reflux ratio was6are better.Chemical software was pulled in to optimize the operation parameters of columns,obtained optimized conditions as follows:1) Preliminary column: theoretical plate number was28; feed stage was16; solventstage was3; solvent ratio was1; reflux ratio was1.2) The second low pressure methanol column: the pressure was30kPa; theoreticalplate number was16; feed stage was6; reflux ratio was3. Benzene column: the pressurewas200kPa; theoretical plate number was14; feed stage was8; reflux ratio was4.3) The first low pressure methanol column: the pressure was30kPa; theoreticalplate number was12; feed stage was8; reflux ratio was2. Acetonitr column:the pressurewas200kPa; theoretical plate number was8; feed stage was6; reflux ratio was2.