Title: Synthesis of Distillation-Based Separation Systems
Abstract: This tutorial paper is a review of recent advances in the synthesis of ideal and nonideal distillation-based separation systems. We start by showing that the space of alternative separation processes is enormous. We discuss simple methods to classify a mixture either as nearly ideal or as nonideal, in which case it displays azeotropic and possibly liquid/liquid behavior. For nearly ideal mixtures, insights based on marginal vapor flows permit the development of a simple screening criterion computed using only relative volatilities and component feed flowrates to find the better column sequences from among the many possible. This criterion explains several of the traditional heuristics. We ask how one can invent alternative structures to separate nonideal mixtures. We present and illustrate an approach with three examples: separating n-butanol and water; separating acetone, chloroform, and benzene; and separating n-pentane, acetone, methanol, and water. We find that these processes always contain recycles because we are unable to obtain the sharp separations possible for ideal mixtures. Next, we explore more advanced methods to assess the behavior of complex mixtures. We discuss two algorithms to find all azeotropes for a mixture: we also discuss the problem of finding the regions for liquid/ liquid behavior. Example problems are included to highlight the need to estimate the entire set of products that can be reached for a given feed when using a particular type of separation unit. We show that readily computed distillation curves and pinch point curves allow us to identify the entire reachable region for simple and extractive distillation for ternary mixtures. This analysis proves that finite reflux often permits increased separation; we can compute exactly how far we can cross so-called “distillation boundaries.” For extractive distillation, we illustrate how to find minimum solvent rates, minimum reflux ratios, and, interestingly, maximum reflux ratios.
Publication Year: 1996
Publication Date: 1996-01-01
Language: en
Type: book-chapter
Indexed In: ['crossref']
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Cited By Count: 53
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