Book Description
Abstract: "Batch distillation has received renewed interest as the market for small volume, high value, specialty chemicals has increased. While batch distillation is more flexible than continuous distillation because the same equipment can be used for several products and operating conditions, batch distillation can be less flexible when azeotropes are present in the mixture to be separated. Azeotropes can form batch distillation regions where the types of feasible separations can be more limited than in continuous distillation. New types of batch column configurations, such as the middle vessel column, can help in the separation of azeotropic mixtures. We show how insights developed for continuous distillation can identify the feasible products and possible column profiles for such a column. We compare extractive distillation using the middle vessel column and a batch rectifying column. While both can often theoretically recover 100% of the pure components from a binary azeotropic mixture, the middle vessel has the benefits of a finite size still pot which is made possible by 'steering' the still composition versus time. We also investigate the operation of the extractive middle vessel column by looking at the sensitivity of a profit function to some of the operational parameters. In order to separate azeotropic mixtures in general, a sequence of batch columns must normally be used. A tool for finding the basic, continuous and batch distillation regions for any mixture is developed in order to synthesize such sequences. This tool, given an initial still composition, can determine the possible products at total reflux and reboil and infinite number of trays for a variety of batch column configurations. We then show how to use such a tool in the synthesis of all possible batch column sequences."
