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An efficient, robust, ODE-based formulation of the continuation problem is presented for the automatic construction of all branches of the pinch point curves in any homogeneous distillation system (even highly nonideal ones) that can be represented using an activity coefficient model, with any number of components and for any adiabatic, nonreactive column configuration. Constant molar overflow is assumed. The curve is parametrized by reflux ratio, making it particularly applicable to distillation design and synthesis. Naturally, it can be used to find pinch point locations at a given finite reflux, as this is simply a subset of the pinch point curve. The method can also automatically locate all N-component azeotropes very efficiently (orders of magnitude faster than commercial process simulators). It has the additional advantage of being solvable using tools already available in typical mathematical software packages. A computer implementation of the proposed method is available.

The vapor recompression (VRC) distillation scheme is examined and compared with conventional distillation in an analysis spanning fundamental thermodynamics, high-level calculations, and rigorous simulation. The purpose of this article is three-fold: first, it provides greater insight into VRC distillation. Second, it provides a process synthesis tool to rapidly assess whether VRC is likely to be more thermodynamically favorable than conventional distillation for a given split. Third, it may be used to determine if VRC can be implemented practically. The tool presented in the article is consolidated in the form of a single chart, for which only the top and bottom product temperatures are required to determine the outcome. Using this chart, first-pass estimates can be obtained with no calculations whatsoever. The tool, which appears to be the first of its kind in this context, is validated with examples and rigorous simulation.

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