Application of microfluidics to control product selectivity during non-catalytic oxidation of naphthenic-aromatic hydrocarbons

Abstract

Liquid phase oxidation of a simple naphthenic-aromatic hydrocarbon was studied in a microreactor over low temperatures. The goal was to investigate how local oxygen availability could be controlled during oxidation and how it affected both oxidation rate and product selectivity. A microfluidic reactor provides a unique opportunity to exactly manipulate local oxygen availability by changing the hydrodynamics of the reactor in a Taylor flow region. Ketone-to-alcohol selectivity in the microreactor was increased by an order of magnitude from less than 1 : 1 to 14 : 1 by increasing oxygen availability in the liquid phase at a near constant conversion, oxygen partial pressure, and temperature. Similar oxidation experiments were conducted in semi-batch and batch reactors and the results were compared to the microreactor experiment. The higher ketone selectivity in the microreactor could be explained in terms of the oxidation of the alcohol and/or alkoxy radicals formed. It was observed that the selectivity to alcohols and addition products increased at lower oxygen availabilities. In addition to selectivity, the oxygen mass transfer coefficient to the liquid phase was also calculated based on the microreactor geometry and hydrodynamics.