In-situ characterization of RF field induced reactions by Raman spectroscopy — I. Urethane formation kinetics and mechanisms

Abstract

The effects of radiofrequency (RF) electromagnetic field on the kinetics and mechanism of a series of secondary alcohol and phenylisocyanate reactions were studied by in-situ Raman spectroscopy. The urethane reaction rates under intense RF fields increased significantly. A 2-propanol and phenylisocyanate reaction under an RF field of 6.3 kV/cm could reach 90 percent conversion in less than 150 seconds, yet it took more than 30 min without the exposure to an RF field. The maximum reaction rate of such a reaction system increased from 0.4 to 1.6 percent per second when the RF field intensity increased from 1.6 to 6.3 kV/cm. Reaction kinetics simulation based on a simple kinetic model was employed to analyze the mechanisms of these reactions. The simulation results suggest that an intense RF field has no direct influence on urethane reaction mechanism and kinetic parameters. The main effect of an RF field on pure urethane reactions is the dielectric heating effect. Although the heat generated during the reaction due to the systems' dielectric loss is small, an intense RF field creates high initial heating rates, which induces high heat generation of these exothermic reaction (urethane) systems, and results in high reaction temperatures (from 20°C to 160°C in about 45 seconds for a 2-propanol and phenylisocyanate reaction under an RF field of 6.3 kV/cm).