Experimental Study On Batch Extractive Distillation

Owning to the predominant advantages in separating azeotropic and close- boiling point mixtures, batch extractive distillation is being paid more and more attention. In this paper the study on the whole process of batch extractive distillation was carried out in a laboratory column to investigate operations of the slop cut withdrawal and solvent recovery, and evaluate the effect of operating parameters such as reflux ratio and solvent ratio on the column performance. Then the separation of tert-butyl alcohol from aqueous solution was tested with an industrial column in the way of batch extractive distillation. Finally an improved operation mode of batch extractive distillation with a storage tank connecting to the still was proposed. In this paper, it is considered that the batch extractive distillation process has three stages, which are withdrawal of the product, withdrawal of slop cut and solvent recovery. Slop cut withdrawal and solvent recovery was studied intensively. The experiment showed that the overhead concentration rises to a primarily stable value after the solvent is introduced and keeps constant during the product withdrawing. When the slop cut is withdrawn under constant reflux ratio, the overhead concentration descends sharply at the beginning, then smoothly afterwards. In solvent recovery stage, as the concentration of solvent begins to increase, the vapor flow rate in the column decreases soon, almost to zero, and then increases rapidly accompanied with the higher top temperature. The effect of operation parameters such as solvent ratio and reflux ratio on product purity and recovery ratio was studied also. The separation of the azeotropic mixture of tert-butyl alcohol and water in an industrial scale column was tested, which produced tert-butyl alcohol of purity >99.5% by using glycol as the solvent. The phenomena of slop cut withdrawal and solvent recovery of batch extractive distillation were verified profoundly. For disadvantages of large still in volume and difficult heating control of batch extractive distillation, a storage tank connecting to the still was introduced. The experiment results indicated that the temperature of the still in the new operation mode was relatively stable, and the heating control was more easy.