Continuous Three-Phase Distillation: A Process for Separating Thermally Unstable Substances

In this work, the use of heteroazeotropic distillation for separation of thermally unstable substances is discussed. A new process has been developed and analysed, which makes use of the fact that the boiling temperature of a heteroazeotrope is always lower that that of its constituents. Three-phase distillation is characterized by the fact that two liquid phases and a vapour phase coexist in the entire column which ensures low temperatures in the entire apparatus. The process is an alternative or addition to state of the art processes like vacuum distillation. Experiments were carried out in a continuous laboratory scale distillation column equipped with structured gauze wired packing. The experiments prove the feasibility and operability of the new process and provide a sound data base for the development and the validation of process models. It is shown that the process can be successfully modelled using an equilibrium stage approach that accounts for the presence of two liquid phases. Convergence of the simulation model is not trivial. The homotopy continuation method was used for solving the model equations.