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Reactive or catalytic distillation technology combines chemical synthesis steps with separations by distillation. This combination can lead to intensified, high-efficiency process systems with significant green engineering attributes. New applications and understanding have prompted growth in the use of reactive distillation for a variety of chemical syntheses, especially esterifications and etherifications involving oxygenated hydrocarbons. We describe several applications and the potential and tradeoffs for reactive distillation technology in the context of green engineering principles.

Fast and accurate distillation design requires a model that significantly reduces the problem size while accurately approximating a full-order distillation column model. This collocation model builds on the concepts of past collocation models for design of complex real-world separation systems. Two variable transformations make this method unique. Polynomials cannot accurately fit trajectories which flatten out. In columns, flat sections occur in the middle of large column sections or where concentrations go to 0 or 1. With an exponential transformation of the tray number which maps zero to an infinite number of trays onto the range 0−1, four collocation trays can accurately simulate a large column section. With a hyperbolic tangent transformation of the mole fractions, the model can simulate columns which reach high purities. Furthermore, this model uses multiple collocation elements for a column section, which is more accurate than a single high-order collocation section.

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We present applications for a collocation method for modeling distillation columns that we developed in a companion paper. We discuss implementation of the model, including discussion of the ASCEND system, which enables us to create complex models with simple building blocks and interactively learn to solve them. We first investigate applying the model to compute minimum reflux for a given separation task, exactly solving nonsharp and approximately solving sharp split minimum reflux problems. We next illustrate the use of the collocation model to optimize the design a single column capable of carrying out a prescribed set of separation tasks. The optimization picks the best column diameter and total number of trays. It also picks the feed tray for each of the prescribed separations.