| A nonequilibrium cell model for reactive distillation is developed. In the new model, trays or packed sections are divided into stages that are subsequently split up into nonequilibrium cells. This approach allows for easy modeling of flow patterns on distillation trays and maldistribution in packed columns, by adoption of appropriate cell linking patterns.; In the nonequilibrium cell, thermodynamic equilibrium is assumed only at the vapor-liquid interface. The bulk phases of both vapor and liquid are assumed to be perfectly mixed, and the resistance to mass transfer is located in two films next to the phase boundary. Mass transfer rates are calculated from the Maxwell-Stefan equations.; The Dusty Fluid Model is used for description of mass transfer and reaction in systems with heterogeneous catalysts.; Using the nonequilibrium. model for several example problems, it is shown that efficiencies in the reactive distillation process can be influenced by the reaction. Thus, the prediction of efficiencies becomes problematic, and the use of efficiencies and equilibrium models should be avoided.; In addition, it is shown that the reactive distillation process is much more sensitive to the design than normal distillation processes, emphasizing the need to take column design into account in the model calculations.; Furthermore multiple steady states have been found with both NEQ and EQ models, but not all of these may be realizable due to flooding. In addition, the realizable window of multiple steady states is smaller if transfer resistances are accounted for.; For packed columns with systems with highly nonlinear interactions between the reaction rate and the temperature, it is very important to approximate the column concentration and temperature profiles as accurately as possible. Failure to do so may lead to significant deviations in column performance.; The influence of maldistribution in packed columns is often ambiguous. In some cases, choosing a different maldistribution pattern may lead to substantially different column behavior. For reactive systems, maldistribution is found to influence the process through both the loss of interfacial area and changes in residence times and residence time distribution. |
