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 waterchloroform. 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 α 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 F E /V, the portion α T3 of distillate-rich phase refluxed to the column during chloroform distillation, the reflux policy R T5 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 yields 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 R T5 first, α T3 second and F E /V last. Keeping F E /V constant and using two piece-wise α T3 and R T5 value operation is recommended to increase profit.

Review of extractive distillation. Process design, operation, optimization and control

“…If capital costs are not taken into account, for example, if the equipment already exists, the energy consumption per overall product flow rate can be minimized (e. g. De Figueirêdo et al, 2011;You et al, 2015a,b) or the profit maximized (Barreto et al, 2011b). The purity specifications are usually set as constraints, either explicitly in the optimization method, or incorporated into the model (Barreto et al, 2011b).…”

From batch to continuous extractive distillation using thermodynamic insight: Class 1.0–2 with a heavy entrainer

“…Therefore, either A or B are possible distillates of the extractive distillation process. As explained in [4], there is a maximum value (F E /V) max,A,Rf to recover component A and no entrainer limit restriction applies to recover component B at infinite reflux [6][7] (See [SN extr,A ] and [SN extr,B ] range in Figure 2a). …”

Optimization of decanter temperature in separating partially miscible homoazeotrope to reduce cost and energy consumption

“…Wu et al further applied dividing‐wall distillation to separate the binary system with the same entrainer to save energy. Barreto et al optimized the separation process of chloroform/methanol azeotrope with water as the heterogeneous entrainer and the optimum solutions achieve over 90 mol% recovery yields. For the batch heteroazeotropic distillation, the continuous feeding of the entrainer (named later as heterogeneous batch extractive distillation) was suggested and studied by Modla et al , then by Donis et al .…”