No abstract

The characteristics of ion-exchange resins provide the basis for many processes of practical interest involving both sorption separations and catalytic reactions. The optimal design and operation of these processes require a proper understanding of the equilibrium behavior of multicomponent liquid mixtures in contact with cross-linked polymeric resins, in terms of both the amount and composition of the sorbed mixture. For this, a model which describes the equilibrium between a polymer phase, described through the extended Flory−Huggins theory, and a liquid phase, which does not contain the polymer, has been developed. This has then been coupled with a kinetic model describing the catalytic reaction inside the resin particles. The model has been validated through an appropriate experimental analysis involving both equilibrium partitioning and reactive experiments, for the case of a highly cross-linked sulfonated resin in the presence of various mixtures of the components involved in the esterification of ethanol with acetic acid. The results indicate the ability of the resin not only to catalyze the esterification reaction but also to shift the corresponding equilibrium conversion, due to its swelling capability. This approach is believed to apply to a wide class of reactions catalyzed by polymeric resins, and it is suitable for the optimal design of the corresponding processes.

Reactive chromatography, i.e., coupling chemical reaction and selective sorption, allows us to drive the chemical reaction beyond equilibrium and to separate its products. Chromatographic reactors exhibit a complex dynamical behavior, whose analysis is the objective of this work. The synthesis of ethyl acetate and water from ethanol and acetic acid on a commercial polystyrene−divinylbenzene acidic resin is considered. The results of experiments run in a laboratory-scale chromatographic reactor are reported. Experimental data are in good agreement with the results obtained using a fully predictive equilibrium dispersive model. This exploits an accurate description of both the multicomponent sorption equilibria on the resin, based on the extended Flory−Huggins model, and the kinetics of the heterogeneously catalyzed chemical reaction. The chromatographic reactor exhibits a rather rich dynamical behavior, which is a consequence of the dual role, as a catalyst and as a selective sorbent, played by the resin. In particular, it is characterized by the development of composition fronts traveling along the fixed bed column at well-defined propagation velocities. By interpreting the obtained results in terms of these classical nonlinear chromatography concepts, a deep insight into the dynamical behavior of the chromatographic reactor can be achieved. These findings can be usefully summarized in a master plot which allows us to identify the different dynamic regimes in the operating parameter space.

A new tool for the design of multicomponent distillation columns is presented, which is based on analytical solutions of a suitable mathematical model. The assumptions on which it is built are (i) a large number of stages, which makes it possible to apply a continuous description of the column instead of the usual stage-by-stage equations; (ii) constant molar overflow; (iii) constant relative volatility; and (iv) attainment of vapor−liquid equilibrium everywhere along the column. The resulting model equations are solved in the frame of Equilibrium Theory, which was originally developed to describe chromatographic processes. Through this approach explicit results may be obtained and both the steady state and the dynamic behavior of high-purity columns can be analyzed. In particular, this work focuses on the former, thus obtaining the following results:  (i) a complete picture of the different separation regions in the operating parameter plane spanned by the flow-rate ratios in the rectifying and stripping section; (ii) the evaluation of the optimal operating conditions corresponding to each different separation regime, together with the proof that these are equivalent to the Underwood minimum reflux conditions; (iii) the explanation of well-known features of multicomponent distillation such as pinch conditions and nonlinear behavior. Numerical examples of binary and multicomponent separations are presented and discussed.