Microwave (MW) irradiation is known to selectively interact with polar molecules in a homogeneously mixed liquid solution and change their relative volatilities. The phenomenon of microwave induced relative volatility change (MIRVC) can be the basis to develop novel MW-assisted separation techniques. Herein, we derived a dimensionless number ZMW based on an assumption involving molecular radiators model to explore the effect of dielectric and thermodynamic properties of the materials as well as the MW field intensity on MIRVC. Afterwards, we established a quantitative correlation between the values of ZMW and the extent of MIRVC, whose model parameters were determined by fitting the experimental data of the relative volatility measurement of various binary mixtures under MW irradiation. The correlation was employed to estimate the extent of MIRVC in experiments conducted in the previous studies. The error range between the calculated values and the experimental values was within ± 6%, indicating the validity of the proposed quantitative correlation. The established quantitative model can provide theoretical guidance for MW-enhanced separations and MW-accelerated organic reactions. Based on the quantitative model, we predicted that 200 W MW irradiation can increase the removal rate of polar impurity (methanol and water) by 11.8% – 25.4% in the purification of polyoxymethylene dimethyl esters via MW distillation; the predicted results were validated by experiments. Moreover, we employed the quantitative model to analyzing the esterification reactions of acetic acid and various alcohols under reflux conditions. The experimental results indicated that the apparent kinetic constant under MW irradiation was 2 – 3 times larger than that under conventional heating due to the equilibrium shifting caused by MIRVC.

Microwave induced relative volatility change: Quantitative modelling and applications in intensifying chemicals separation

ACS Fall 2021

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