Study On Batch Extractive Distillation With Mixed Solvents

In this paper, the technology and progress of extractive distillation were summaried. Selection and design of solvents, different configuration for extractive distillation columns, operational policies and effect of operating parameters on separation were introduced, and the current disadvantages and the development direction of extractive distillation in future were pointed out.Solvent selection is the key problem for extractive distillation. A number of binary mixed solvents for separation of benzene-cyclohexane and ethyl acetate-ethanol were examined respectively in a VLE experiment apparatus. The integrated properties of the binary mixed solvent were investigated and the experimental data were correlated by modified UNIFAC model .It was found that binary solvent is superior to single solvent, the binary mixed solvent composed of DMF and DMSO was one of the best solvents for separation of benzene-cyclohexane and ethyl acetate-ethanol. The prediction by modified UNIFAC model conformed by experiments is a rapid, accurate approach for selection for extractive distillation. In addition, the influence of temperature on solvent's selectivity was set forth by Clausius-Mosotti equation and a better solubility parameter model was set up for select a vice-solvents.A regular batch extractive distillation processes separating close boiling and azeotropic mixtures were studied experimentally, the effect of operating parameters such as reflux ratio and solvent feed rate on the separation process was investigated. All these features were illustrated, with the increase of the reflux ratio and flow rate of the solvents, the recycle rate of solvents is increased. In addition, the process was simulated perfectly . A middle-vessel batch extractive distillation process was studied experimentally and simulated by constant molar holdup model. A middle-vessel batch column has both an enriching and stripping section and thus both a distillate and bottom product. It requires a much smaller reboiler compared with regular column, as we can continually remove and recycle the extractive agent. The mathematical model is a group of stiff equations and resolved by two point implicit method, the experiment results agree well with simulation.