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

Abstract

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.

Liquid-liquid equilibrium for the quaternary system propionic acid + n-propanol + n-propyl propionate + water at 293.15, 313.15 and 333.15 K

“…For example, one can use the advantage of the phase splitting by coupling the distillation column with a liquid-liquid separator [4]. For this reason the majority of recent papers on n-propyl propionate production include the discussion of the splitting in propionic acid + n-propanol + n-propyl propionate + water system [1,[4][5][6][7][8][9][10]. Nevertheless the available experimental data sets on LLE were presented for binary sub-systems and for ternary n-propanol + water + n-propyl propionate system only [11].…”

A helicopter view of microwave application to chemical processes: reactions, separations, and equipment concepts

“…In this context, Altman et al (2010) experimentally explored the effect of microwaves on the separation of binary mixtures by comparison with conventional thermodynamic equilibrium experiments. Although the effects of electromagnetic radiation on boiling and evaporation have been studied for more than Brought to you by | University of California Authenticated Download Date | 1/5/15 5:27 AM 30 years, the underlying physics are not yet universally agreed upon.…”

“…Different explanations put forward include the surface hydrodynamic instabilities (Courville et al 1991, Stuerga and Lallemant 1993a,b, 1994, superheating (Chemat and Esveld 2001), nonequilibrium conditions at the evaporating interface , and pressure increase at the interface ). According to Altman et al (2010), conventional vapor-liquid equilibrium (VLE) experiments were performed using binary mixtures of the components involved in the esterification synthesis of n-propyl propionate from propanol and propionic acid. VLE experiments were carried out under microwave heating as well to investigate the potential changes in phase composition compared to conventional VLE (Altman et al 2010).…”

“…According to Altman et al (2010), conventional vapor-liquid equilibrium (VLE) experiments were performed using binary mixtures of the components involved in the esterification synthesis of n-propyl propionate from propanol and propionic acid. VLE experiments were carried out under microwave heating as well to investigate the potential changes in phase composition compared to conventional VLE (Altman et al 2010). The reason for such a composition change can be one of the effects mentioned above or the different interaction of microwaves with the binary components according to their dielectric properties.…”

Reactive Distillation

“…Worth mentioning are the ideas to introduce energy into the chemical process equipment through alternative energy forms such as microwaves or high-gravity fields. Because microwave irradiation can improve both reaction and separation performance, the application of microwave irradiation could reduce the required column size for a given separation and reaction efficiency [111]. The use of high-gravity fields can increase the achievable throughputs and interphase mass transfer rates [112].…”