Effect of Number of Fractionating Trays on Reactive Distillation Performance

Sneesby et al. recently suggested that adding trays in the stripping and rectifying sections of a reacti®e distillation column can degrade performance. This effect, if true, is not only counterintuiti®e, but ®ery disturbing because it suggests that the design of reacti®e distillation columns cannot use conser®ati®e estimates of tray numbers, that is, we cannot simply add excess trays, as in con®entional distillation. The problem is compounded by the uncertainty in ®apor liquid equilibrium data and tray efficiencies. This implies that de®eloping reacti®e distillation columns would require extensi®e experimental work at the pilot-plant and plant stages to find the numbers of stages offering the best performance. Such a scenario would mean long and expensi®e de®elopment programs. This article explores the effect of the number of trays in the rectifying andror ( ) stripping sections of reacti®e catalytic distillation columns. Three reacti®e distillation systems are used: an ideal hypothetical system, the ETBE system, and the methyl acetate system. Contrary to the published results, it is demonstrated that additional trays do not degrade performance. Two degrees of freedom a®ailable in all cases must be carefully chosen for fair comparisons.