The Attainable Region (AR) was defined by Horn for reactor systems. The definition can however be broadened to include distillation processes. In this context we define the Attainable Region for a distillation column as the set of all possible outputs (and corresponding inputs) for a given feed, distillate composition and VLE thermodynamic model. The fundamental processes considered are VLE based separation and mixing.

We consider the variables of the AR to be composition and a variable that we call “kappa” that arises naturally from the system equations and is analogous to residence time in reacting systems. The kappa variable includes energy and number of stages in a single variable.

We will develop the theory and demonstrate it by considering various examples. We will show that we can find the AR for binary disitllation systems and most importantly that both the optimal structure and operating conditions come out from the solution of the AR. This allows us to determine targets for performance to which we can compare conventional columns to see what room for improvement there is in the performance of these. Furthermore, the solution also gives us insight into the way in which the operation of these conventional systems should be changed in order to get closer to the target performance.