Homogeneous azeotropic distillation. 2. Design procedure for sequences of columns

A graphical procedure based on residue-curve maps and distillation-line maps is developed for the synthesis of sequences of distillation columns for homogeneous azeotropic distillation. The feasibility of separation is determined by the overlap of product operation leaves defined as the feasible region containing all column profiles that lead to a desired product specification, which need not be a precise composition. Column sections may be constrained to operate within a subregion of the composition space, in which case the limit of operation is defined as a section boundary. Section boundaries for node-type and saddle-type products are established, and it is shown that they do not always coincide with simple-distillation or distillation-line boundaries. When the distillation line (or residue curve) and pinch-point curve from a desired product terminate at different nodes in the composition space, then distillation sequences using complex column arrangements can be proposed.