(689b) Adiabatic Operation of Chromatographic Fixed-Bed and SMB Reactors

In reactive chromatography, chemical reactions and chromatographic separation of the products are carried out simultaneously in a single unit operation. The aim of the method is to increase conversion of the reactants and product purity. Typical applications are esterification of carboxylic acids, such as synthesis on methyl acetate, ethyl acetate.

A characteristic feature of reactive chromatography processes is their transient behavior. When carried out batchwise in a single column unit, pulses of reactants are eluted through the reactor. In a continuous simulated moving bed reactor, periodic switching of the inlet and outlet ports in the direction of fluid flow generates a periodic, quasi-steady state with moving concentration fronts in each column.

Owing to the dynamic nature of the process, there is continuous generation or consumption of heat due to enthalpies of adsorption, chemical reaction, and mixing. Scale-up of the process is accomplished by increasing the column diameter, which eventually renders the system nearly adiabatic.

In this work, we demonstrate how thermal effects can significantly affect performance of liquid phase chromatographic reactors under adiabatic conditions. Experimental results for exothermic reactions (esterification of acetic acid ethanol and methanol) catalyzed by an acidic ion exchange resins are presented in both fixed-bed and simulated moving-bed reactors. In addition, the influence of adsorption and mixing enthalpies on the thermal behavior of the reactor are illustrated with data from non-reactive experiments. Numerical simulations are presented to further elucidate the coupling between concentration and temperature waves in the reactor.

It is shown that the conversion of an exothermic reaction under adiabatic conditions may be either higher or lower than under isothermal conditions, depending on the residence time and reaction rate. The results also indicate that, similar to adiabatic gas¬-solid reactors, the solid phase to fluid phase heat capacity ratio affects the propagation velocity of the thermal waves.