Study On Batch Extractive Ditillation For Separating Minimum Boiling Azeotropes

The technology of batch extractive distillation was sum up. Selection and design of solvents, different configuration of extractive distillation columns, operational policies as well as effect of operating parameters on separation were introduced, and then the current issues and disadvantages for batch extractive distillation were put forward.The separating process of ethyl acetate-ethanol was studied in a batch extractive distillation column with a middle vessel. The effects of liquid hold-up in the middle vessel, temperature of liquid hold-up in the middle vessel, flux of extractive solvent on the separation of minimum boiling azeotrope of ethyl acetate-ethanol by batch extractive distillation with N,N -dimethylformamide (DMF) were investigated. The experimental results show that the purity of product will be obviously increased due to a fitting liquid holdup in the middle vessel, the fitting liquid reflux in the middle vessel, and a fitting temperature of liquid hold-up in the middle vessel. With the flux of solvent increased, relative volatility of ethyl acetate and ethanol is increased, but the charge of distillation column is also increased.A number of ternary mixed solvents [N-methyl-2-pyrrolidone (NMP) + DMF + dimethyl sulfoxide(DMSO)] and binary mixed solvents(DMF+DMSO) for separation of ethyl acetate-ethanol or cyclohexane-benzene were examined in a vapor-liquid equilibrium experiment apparatus. Experimental result showed that the binary mixed solvents were superior to the single solvents, there are the best solvent composition for effectual separation. In addition, performance of the ternary mixed solvents and binary mixed solvents lie on their composition.The process of a batch extractive distillation with a middle vessel and a regular batch extractive distillation with ternary mixed solvent for separating close boiling and azeotropic mixtures were simulated. The mathematical models for them were resolved by two point implicit method, the experiment results agree well with simulation.