This paper presents a novel method for the process synthesis and optimisation, the so called Mixed Integer Non Linear Programming (MINLP). The speciality of this tool is that not only the operating parameters but also the structure of the process are simultaneously optimised. A necessary condition for this kind of optimisation is the definition of an appropriate superstructure, that contains all physically relevant processes including the optimal one. Therefore, it is advantageous to determine these superstructures based on the information relating to thermodynamic equilibrium. The methodology for the development of superstructures and the results of the optimisation are presented for several examples concerned with distillation, extractive distillation, azeotropic distillation, and reactive distillation.