Dynamics and Control of Reactive Distillation under Multiple Steady States Based on a Nonlinear Wave Theory

Reactive distillation, which combines reaction and distillation in a single vessel, is receiving increasing attention because of its great potential for use in process intensification. The superposition of reaction and separation in a single processing unit can introduce new patterns of dynamic behavior such as multiplicity and oscillation. Acetic acid was effectively recovered from its dilute aqueous solution in the form of methyl acetate by reactive distillation. The reactive distillation column converting the acetic acid to the methyl acetate was highly nonlinear and showed steady-state multiplicity under certain conditions. The dynamic behavior of the column under multiple steady states was demonstrated to be well explained by nonlinear wave propagation theory. If the maximum conversion was obtained under the condition where the multiplicity appears, then a conventional control scheme could not deal with the control difficulty due to the multiplicity. A profile position control scheme based on wave propagation theory was proposed for the control of the column under multiple steady states, and the performance of the proposed controller was compared with that of conventional controllers. The proposed control scheme using profile positions as controlled variables was shown to give an excellent performance for the control of the reaction conversion and product purity in the reactive distillation.