Optimization of Heterogeneous Batch Extractive Distillation

Abstract

Heterogeneous extractive batch distillation of the chloroform – methanol minimum boiling temperature azeotropic mixture is studied with water as a heterogeneous entrainer. The continuous feeding of water allows recovering 99%molar chloroform after condensation of the saddle binary heteroazeotrope water –chloroform. Unlike a homogeneous process, the reflux composition is different from the heteroazeotrope water – chloroform in the vapor overhead. Besides, the distillate recovery is improved by refluxing a portion a of the chloroform-rich distillate phase along with the water-rich entrainer phase. A genetic algorithm is coupled to a constant molar overflow model to study seven operation policies. Optimization parameters are the entrainer flowrate FE/V, the portion aT3 of distillate-rich phase refluxed to the column during chloroform distillation, the reflux policy RT5 during methanol distillation. The optimization maximizes a profit function, penalized with recovery yields constraints whereas purity targets are used as Task ending events. All optimized solutions achieve higher than 90%molar recovery yield and 99%molar purity for both products chloroform and methanol. Results are confirmed by rigorous simulation showing the good performance of coupling simplified model and genetic algorithm as a first approach. The two piece-wise parameter values operation policies for all three parameters increases profit by 41.8% and reduces total time by 43.8% compared to single value parameter policy. The parameter influence study ranks RT5 first, aT3 second and FE/V last. Keeping FE/V constant and using two piece-wise aT3 and RT5 value operation is recommended to increase profit.