Off-cut Recycle for Batch and Batch Extractive Distillation Separation of a Multicomponent Azeotropic Mixture

Abstract

The influence of recycling off-cuts for the batch and batch extractive distillation separation of a four component (methanol- THF- water- toluene) waste solvent mixture of a pharmaceutical plant is studied by rigorous dynamic simulation. The evolution of the charge composition, of the amount of fresh feed and that of methanol product are determined for six consecutive productions of batch rectification. As an alternative of the traditional batch distillation, batch extractive distillation by using water as entrainer is also studied. Water feeding is applied during the heating-up phase, in order to decrease the methanol concentration in the column top, in this way reducing methanol loss with the fore-cuts. The profit of the productions is calculated on the basis of the operational and incineration costs and the price of the methanol. The influence of the volume of the first fore-cut, which is later incinerated, on the profit of the whole production process is also investigated and its optimal amount is determined for both separation methods. For the extractive process the profit of the regeneration is higher, the optimal volume of the first fore-cut is lower, which means a reduction in the air pollution caused by the incineration.