Optimisation of a Batch Extractive Distillation Process with Off-Cut Recycle

Abstract

The recovery of methanol from an industrial waste solvent mixture (acetone (A) – methanol (B) – THF (C)–water (D) – toluene (E)) by a batch (BD) and batch extractive distillation (BED) process was simulated and optimised. For both processes a production cycle consists of six consecutive batches. The first fore- cut is incinerated; the second fore-cut, the after-cut and the hold-up are recycled to the next batch in order to decrease the loss of methanol. The optimization of both processes was performed by a genetic algorithm (GA) coupled with a professional flow-sheet simulator performing the dynamic simulation. The optimization of the batches was performed consecutively, with the objective function being the profit of the actual batch. The optimization variables were the reflux ratios of the steps (fore-cuts, main cut), duration of fore-cut withdrawals and for the BED the flow rate and duration of entrainer (water) feeding. The effects of the recycling of the off-cuts on the charge composition and on the optimal values of the parameters were studied, and the optimised BD and BED processes were compared.