Operation and control of batch extractive distillation for the separation of mixtures with minimum-boiling azeotrope

Batch distillation is commonly used in the fine chemicals, specialty polymer, biochemical, pharmaceutical, and food industries. For separating mixtures with minimum-boiling azeotrope, a heavy entrainer is frequently added to the top section of the batch column to aid in the separation. This process is called batch extractive distillation. Most of the papers in open literature have only studied the first operating step of the batch extractive distillation which is the recovery of the light component without mentioning the later steps for the recovery of the other component and entrainer. In this paper, two real chemical systems, one separating acetone and methanol using water as entrainer and the other separating isopropyl alcohol (IPA) and water using dimethyl sulfoxide (DMSO) as entrainer, are studied for the feasible operation of the complete batch distillation sequence. The operating variables, including the pre-load amount with the mixture, continuous feed rate of the entrainer, and reflux ratio at each operating step are determined in the operating sequence. The constant reflux ratio and constant entrainer feed rate operating policy and another policy to allow these two operating variables to be varied will be compared in order to further improve the batch operation. All dynamic simulations that are performed directly mimic industrial situations from an empty column using a rigorous dynamic simulator, Aspen Dynamics™.