Reactive distillation has been established fur different processes, for example, the production of MTBE and TAME. Numerous publications have shown experimental and theoretical results of such etherification processes, The present paper deals with a theoretical background fur an esterification process. The investigations will be carried out with the quaternary system consisting of n-butanol, butyl acetate, acetic acid and water. For this system, not often used in literature, the chemical equilibrium constant and a suitable reaction kinetic has to be found. The different singular points will be checked and the kind of singularity will be determined. Residue curve maps will show the shape of simulations from different starting points. The differences between a simple distillation process and a reactive distillation process will be demonstrated.