A rigorous rate-based modeling approach to reactive distillation equipment is presented in detail. This approach has succeeded from the three-year project "Reactive Distillation" initiated by SUSTECH and supported by the EU in the frame of the BRITE-EURAM program. As a result, a steady-state rate-based simulator DESIGNER has been created and tested with industrially important reactive distillations. First, a thorough description of the model development, including process hydrodynamics and kinetics, is given. The general structure of DESIGNER is highlighted. Furthermore, numerical problems, simulation issues, and validation of the developed simulator are discussed, whereas several industrially important applications are demonstrated. The main advantages of DESIGNER are the direct account of mass and heat transport (rate-based approach), multicomponent mass-transport description via the Maxwell-Stefan equations, consideration of a large spectrum of reactions (homogeneous and heterogeneous; slow, moderate, and fast; equilibrium and kinetically controlled), reaction account in both bulk and film phases, availability of different hydrodynamic models, and a large choice of hydrodynamic and mass-transfer correlations for various types of column internals (trays, random and structured packings, catalytic packings). Particular attention is devoted to the mass-transfer model, including the reaction in the film region, to the catalyst efficiency determination based on the mass transfer inside the catalyst and to the hydrodynamic models for reactive trays. (C) 2004 American Institute of Chemical Engineers.