Design of distillation columns with external side reactors

Previous work presented a quantitative economic comparison between a reactive distillation process and a conventional multiunit process for systems in which relative volatilities are temperature dependent. A fundamental difference between these two flowsheets is the ability in the conventional process to adjust reactor temperature and distillation column temperatures completely independently, which is not possible in the reactive distillation process. If the temperature required for reasonable reaction kinetics is not in the same range as that in which vapor-liquid phase equilibrium permits the use of distillation, reactive distillation becomes unattractive. This paper explores a third alternative process that can overcome the problem of reaction/distillation temperature mismatch. The column is operated at its optimum temperature (and pressure). Several liquid trap-out trays collect all the liquid coming down from upper trays. These liquids are pumped to external reactors operating at their optimum temperatures (and pressures). Reactor effluents are returned to the column. Results show that this external-reactor/column configuration has much better steady-state economics than either reactive distillation or the conventional process when there is a mismatch between optimum reaction and distillation temperatures.