ACETONE-CHLOROFORM-n-BUTANOL MIXTURE SEPARATION BY THE EXTRACTIVE DISTILLATION IN SCHEMES OF TWO-OUTLET COLUMNS

Abstract

Extractive distillation of acetone-chloroform-n-butanol mixture with dimethylformamide in two-outlet column schemes is considered. Optimal parameters according to the total energy consumption criterion in the column boilers of the three extractive distillation schemes for this mixture separation are determined. Calculations were carried out in a design-verification version at 1000 kg/hr of the initial mixture with the concentrations of acetone, chloroform and n-butanol 71.3, 14.7 and 14.0% wt., respectively. Dimethylformamide concentration in the entrainer flow was set to 99.99 wt%. The main component concentration in the product stream was 99.9 wt% for chloroform and 99.5 wt%. for acetone and n-butanol. The parameters to be optimized were: the number of plates in the columns, the temperature and flow rate of dimethylformamide, reflux ratios, distillate flow rates and the position of the feed plates in the columns. The optimum location of the entrainer feed plate was found additionally in the extractive distillation column. Separation product concentrations served as the constraints of the optimization. The optimization was carried out in Aspen Plus with the use of a combination of Sensitivity Analysis and sequential quadratic programming (SQP). It is established that scheme P5 has the lowest energy consumption. In the first column of this scheme, n-butanol is separated, and then the azeotrope-forming components (acetone and chloroform) are separated by the extractive distillation subsystem. Energy consumptions for two other schemes (P1 and P2), in which dimethylformamide is used in the first column of the sequence, are significantly higher than for scheme P5 - by 69.1% and by 49.3%, respectively. The data obtained will be used: to synthesize and optimize the extractive distillation schemes including the subsystems with coupled thermal and material flows to separate the acetone-chloroform-n-butanol mixture; to estimate the energy efficiency of those schemes and to obtain the criterion for estimating the energy efficiency of systems with coupled thermal and material flows in the extractive distillation of multicomponent mixtures.