In this contribution, the application of the computer-aided modeling and simulation environment ProMoT/Diva to the modeling of (reactive) distillation processes is presented. The main focus is on the description of the underlying modeling concept, together with some implications of this concept for the modeling of distillation processes. One important point of the modeling concept and the subsequent design of the knowledge base of ProMoT is the decomposition of individual process units into physically meaningful, finer grained modeling entities on different hierarchical levels. The hierarchical levels considered thus far are the process unit level, the phase level, and the storage level. This contribution focuses mainly on the definition of the modeling entities on the phase level, which are important for the modeling of (reactive) distillation processes. Furthermore, the design of the object-oriented knowledge base of ProMoT that contains these modeling entities is illustrated.