Influences Of Pressure On The Dynamics And Controllability Of Reactive Distillation Columns

Reactive distillation column is an example of process intensificationwhich combines reaction operation and separation operation into one unit,leading to the reduction of both capital investment and operating cost. Toexploit the full potentials of the reactive distillation column is the mainwork of the reactive distillation research.Operating pressure is one of the most important variables for theconventional distillation column and the reactive distillation column. Inthe case of conventional distillation columns, operating pressure isusually determined according to the temperature levels of the given coldand hot utilities (to guarantee sufficiently large temperature driving forcesin the condenser and reboiler simultaneously). In the case of reactivedistillation columns, the above method can not be used because thetemperature region must be matched between reaction operation andseparation operation. Moreover, their intricate interactions are needed tobe considered. The operating pressure can still adjust to maximize thethermodynamic efficiency of reactive distillation columns. The impact of operating pressure has long been ignored. The currentwork attempts to examine the influences of operating pressure on thedynamics and controllability of the reactive distillation columns involvingkinetically controlled exothermic reactions. Three reactive distillationsystems, including an ideal reactive distillation column performing ahypothetical exothermic reaction,(A+B kfkbC+D)?, and two real onesproducing respectively methyl acetate from acetic acid and methanol andmethyl tertiary butyl ether (MTBE) from isobutylene and methanol, areselected as representative examples for this kind of reactive distillationcolumns and thoroughly studied in this work. The results confirm that forthe reactive distillation column involving a kinetically controlledexothermic reaction, operating pressure can present non-monotonicinfluences on process dynamics and operation. While the enhancement ofoperating pressure benefits process dynamics and controllability in thelower part of its feasible region (which is confined by the temperaturelevels of the available cold and hot utilities), it turns to deteriorate processdynamics and controllability in the higher part of its feasible region. Theintricate behavior of such kind of reactive distillation columns isessentially governed by the conflicting effects of operating pressure onreaction rate and chemical equilibrium constant and determines actually afavorable region of operating pressure for process dynamics andoperation. Since the region may/may not coincide with the one in terms of process synthesis and design, operating pressure can therefore serve asan important decision variable to trade-off process design and operation,rendering the resultant process design with balanced steady-stateperformance and process dynamics and controllability.