Feasibility of kinetically controlled reactive distillation
For some time, there has been an interest in reactive distillation as an alternative to conventional reactor-separator processes because it has the potential for lower capital and energy costs as well as improved conversions and selectivities. However, it is not true that all processes using reactor-separators can be given up in favor of reactive distillation. This is due to the constraints that develop because of the complex interaction between distillation and reaction in the same device. It is very important then to determine when reactive distillation is a good process concept.
We have developed systematic feasibility methods that can be used to address this issue and decide at the conceptual design stage if there is an incentive for process alternatives based on reactive distillation. Knowledge of a reaction rate model and thermodynamic information comprising phase and chemical equilibrium is the required input. Two approaches are considered. In the first approach, a detailed reactive column model is used to map out the feasible product compositions for reactive distillation. However, this method is practically limited to ternary systems. In the second approach, feasible products are predicted with a model in which a column section is represented by a cocurrent series of isobaric flash reactors. Bifurcation methods provide a global view of the “direct” and “indirect” sharp split products from a continuous column as a function of the production rate, the catalyst concentration and the liquid holdup. In addition, this feasibility method generates the column configuration, if any, that provides the desired product, e.g., a single-feed or a double-feed column; fully reactive columns or columns with both reactive and non-reactive sections. This method is applicable for any number of components and reactions.