Reactive Double Dividing-Wall Distillation Columns: Structure And Performance

The separations of quaternary reversible reactions with the most unfavorable ranking of relative volatilities (i.e., the two reactants are the lightest and heaviest components and the two products in between) require a reactive distillation column, followed by one or two conventional distillation columns. The multiple-column structure reflects not only a high energy intensity in the reaction operation and separation operation involved but also a great potential of process intensification in process development. With reference to a two-column system involving a reactive distillation column with an external recycle and a conventional distillation column (ER-RDC + CDC), a kind of reactive double dividing-wall distillation column (R-DDWDC) is derived via careful coordination and mass and thermal coupling between the ER-RDC and CDC. Closely dependent upon the magnitude of the reaction thermal effect, the left dividing wall is located either at the top or at the bottom. In addition to allowing the mass and thermal coupling between the ER-RDC and CDC, it facilitates primarily the reaction operation in the reactive section. The right dividing wall is located at the middle to fully strengthen the mass and thermal coupling not only between the ER-RDC and CDC but also between the separation operations included. The derived R-DDWDC features essentially the greatest degree of process intensification and becomes consequently the most thermodynamically efficient scheme in the separations of quaternary reversible reactions with the most unfavorable ranking of relative volatilities. The derived R-DDWDC is evaluated in terms of two examples, involving, respectively, the separations of ideal exothermic and endothermic quaternary reversible reactions with the most unfavorable ranking of relative volatilities. The derived R-DDWDC is found to be much more energy efficient than the ER-RDC + CDC, the reactive single dividing-wall distillation column, and those R-DDWDCs with different configurations. These outcomes demonstrate that the derived R-DDWDC is a much competitive alternative for the separations of quaternary reversible reactions with the most unfavorable ranking of relative volatilities. They also highlight the feasibility and effectiveness of the proposed strategy for process synthesis and design, that is, when the reaction processed is exothermic, the optimum R-DDWDC must come from one of R-DDWDC2 and R-DDWDC4; otherwise, the R-DDWDC4 remains to be the only possibility.