Process Intensification of Reactive Distillation for the Synthesis of n-Propyl Propionate: The Effects of Microwave Radiation on Molecular Separation and Esterification Reaction

An envisioned reactive distillation (RD) process for the esterification reaction of n-propyl propionate (ProPro) from 1-propanol (ProOH) and propionic acid (ProAc) using microwave irradiation (MW) (f = 2.45 GHz) is studied. In this frame, the fundamental research performed is divided in two parts comparing reaction conditions and equilibrium curves under MW and conventional heating, looking for possible improvement in process efficiency. For the test system, the use of microwaves does not improve the conversion of the esterification reaction catalyzed by selected zeolite catalysts possibly because microwaves are dissipated in the liquid phase before they interact with the zeolites. Concerning molecular separation, however, it was found that when the vapor−liquid interface is exposed to microwaves, the system can be disturbed from conventional equilibrium conditions and a positive deviation in phase composition can be achieved, as the vapor phase becomes richer in the component with the lower boiling temperature; the extent of separation improvement depends on the boiling points and the dielectric properties of the mixture components. This finding may have significant practical impact as it implies smaller columns with a lower number trays for a given separation efficiency, compared to conventional designs involving heat exchange in the reboiler and the condenser only. It is stressed, though, that the effect is present only when the vapor−liquid interface is exposed to microwaves; no effect is observed when solely the bulk liquid volume is irradiated.