Novel Operation Mode Of Batch Extractive Distillation

Batch extractive distillation (BED) is used to separate azeotropic mixtures or the mixtures of which the relative volatility is close to 1. Because it has both advantages of batch distillation and extractive distillation, BED has been becoming more and more important for the products of small scale and high extra value, such as the fine chemicals, pharmaceuticals and so on.In this paper, the pilot-plant experiment and the simulation of regular BED and the operation mode of BED with two reboilers are well studied by theoretical analysis and experimental method.Due to few reports on the pilot-plant experiment and the industrial application of BED, one pilot-plant experiment for the separation of ethanol and water using glycol as solvent in regular BED was in particular discussed. The effect of some key operation parameters such as the reflux ratio, the flow rate and the temperature of the solvent on the separation processes such as the purity of the distillate, the recovery yield of the solvent, etc, was also discussed.For studying the process of BED theoretically, the nonlinear stiff differential equations of the equilibrium mode describling BED are well solved by the modified two-piont implicit integration method. The simulated results and the above experimental data show good agreement. The separation process of acetone and methanol using water as solvent is well simulated and the results prove the accuracy and commonality of the model.Because of the disadvantages of regular BED, a novel operation mode of BED with two reboilers is proposed and the feasibility of the operation mode is in particular analyzed. The experimental data were compared with those under the same operation condition in regular BED. The distillate with a purity of +99.82% may still be obtained from the top of the column. The results show that there are, in new mode, more advantages such as more stability of the temperature in the reboiler, easier control of the process, more flexibility of the operation, higher yield of the distillate and recovery of the solvent, etc.