Comparison of a Pseudo-homogeneous Nonequilibrium Dynamic Model and a Three-phase Nonequilibrium Dynamic Model for Catalytic Distillation

A comparison of a pseudo-homogeneous nonequilibrium (NEQ) dynamic model and a three-phase NEQ dynamic model was studied for the simulation of both a batch catalytic distillation (CD) process and a continuous CD process for the aldol condensation of acetone. The models were implemented in gPROMS and C++. The simulation results show that most of the dynamic responses of both the batch and continuous CD columns are either close to zero order or first order; however, the responses of temperatures in and below the reaction zone of the batch CD column predicted by the pseudo-homogeneous NEQ dynamic model are highly nonlinear. The formation rate of diacetone alcohol (DAA) and the liquid phase temperatures predicted by the pseudo-homogeneous NEQ dynamic model were found to be much higher than those predicted by the three-phase NEQ dynamic model for both the CD columns. Through a comparison with the experimental data, it was found that the three-phase NEQ dynamic model can adequately describe this CD process, while the simpler pseudo-homogeneous NEQ dynamic model overly predicts the formation rate of DAA and the liquid phase temperatures because the mass- and heat-transfer resistances between the liquid and solid phases are ignored. Since the computation time for the two NEQ dynamic models is very similar, it is recommended that the three-phase NEQ dynamic model should be used in the simulation of the CD process unless it is known a priori that the CD process is kinetically controlled.