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Existing methods for synthesizing thermally-integrated distillation sequences fail frequently when applied to nonideal and azeotropic systems, because increasing the column pressures often introduces new azeotropes and distillation boundaries into the mixture, which make some separation tasks infeasible. A new thermal integration procedure is presented that combines a bifurcation and residue-curve map analysis with the methods of Andrecovich and Westerberg. The procedure is demonstrated with two commercially important separations: ethanol-water-ethylene glycol and methanol-acetone-water. Energy savings of 65% and 40%, respectively, over the optimized nonintegrated sequences are possible.

Many industrial processes depend on efficient separation methods for azeotropic or other close‐boiling or low relative volatility mixtures. Whereas ordinary distillation is either uneconomical or impossible in these cases, the addition of specially chosen separating agents can generally facilitate the separation. Four of the five principal techniques employed are discussed: extractive or homogeneous azeotropic distillation, where the liquid separating agent is completely miscible; heterogeneous azeotropic distillation, where the agent, known as the entrainer, forms one or more azeotropes but causes immiscibility; distillation in the presence of ionic salts, which alters the relative volatilities of the components; and pressure‐swing distillation, where a series of columns operate at different pressures. Residue curve maps, material balance lines, and column sequences are given for several commercially important systems. Methods for evaluating total annualized costs are also discussed as are models for determining feasible separating agents.

Many industrial processes depend on efficient methods for separating azeotropic, close‐boiling, or other low relative volatility mixtures. Ordinary distillation is typically either uneconomical or impossible in these cases. However, by adding specially chosen separating agents, the separation can generally be accomplished. The principal distillation‐based techniques employed for separating such mixtures are discussed: extractive or homogeneous azeotropic distillation, where a completely miscible liquid separating agent is added to alter the relative volatilities; heterogeneous azeotropic distillation, where the agent, known as the entrainer, forms one or more azeotropes and causes immiscibility; distillation in the presence of ionic salts that alter the relative volatilities of the components; and pressure‐swing distillation, wherein some azeotropes can be circumvented using a series of columns operating at different pressures. Residue curve maps, material balance lines, and column sequences are given for several example systems. Methods for identifying feasible separating agents are also discussed.