Performance of a Batch Reactive Distillation System versus a Plug Flow Reactor
Consider the reaction sequence: , where is the lightest component and is the heaviest component. We assume that the desired product is component . This Demonstration compares the performances (yield and selectivity) of a plug-flow reactor (PFR) and a batch reactive distillation (BRD) system. It is found that the BRD system is superior to the PFR as far as yield and selectivity are concerned. This makes using BRD systems very attractive for such a reaction scheme and component volatilities. In order to make the calculations, the distillate rate policy is specified so that the distillate rate is proportional to the still's molar hold-up. In addition, we suppose that the reaction is taking place only in the still and that the distillate mole fraction of component is 100%. The method of Doherty and coworkers is slightly modified by taking a small time step (0.01) and choosing the constraint instead of equation (11) in their paper (see the Details section).
The first and second Damköhler numbers are defined as the dimensionless ratios of the characteristic liquid residence time to the characteristic reaction time. For example, the first Damköhler number for the BRD system is given by , where is the rate constant of the first reaction, and and are the initial molar holdup in the reactor (the still) and the initial distillate rate, respectively.
S. B. Gadewar, M. F. Malone and M. F. Doherty, "Selectivity Targets for Batch Reactive Distillation," Ind. Eng. Chem. Res., 39(6), 2000 pp. 1565-1575.