DYNAMIC BEHAVIOR OF REACTIVE DISTILLATION COLUMNS. EQUILIBRIUM SYSTEMS

This paper deals with the dynamic behavior of simultaneous reaction-separation systems which operate at or near the chemical equilibrium in the liquid phase. The process under study comprises a whole set of “instantaneous”, and very fast reversible reactions where the difference in volatilities favors both the progress of reaction and product separation. The main aim of our study is to gain a deeper understanding of the dynamic behavior of distillation columns by using a model that is simple and efficient, yet informative. This kind of model is outstanding for synthesis and design of control schemes which require a careful modelling and understanding of process response to different changes in the environment. We use a suitable transformation of variables (after Barbosa and Doherty, 1988b) in order to define a new set of state variables; as a result, the balance equations become identical to those for conventional distillation. Also, an efficient physicochemical algorithm that can handle both the original and new state variables is used. Thus, a composition-holdup dynamic model is simulated in the “transformed field” using a stage-by-stage approach. To further reduce computational time, the transformed problem has also been solved by means of a reduction procedure based on approximating by orthogonal polynomials the transformed composition and flow profiles in the column. The performance of the two proposed methods are compared by using the top section of a quaternary reactive column. The results obtained shown that reactive distillation dynamics has certain peculiarities derived from superimposing reaction and separation phenomena.