Kinetics of glyoxal oxidation by nitric acid in a capillary microreactor

Aiming at solving the problems of long operation periods, low selectivity, and low safety in the traditional batch reactor, a method of oxidation reaction of glyoxal with nitric acid through a continuous flow microreactor is proposed, with high selectivity. The method utilizes the excellent performance of mass and heat transfer in the microreactor, to improve the reaction efficiency, selectivity, and safety. The effects of the mixing performance, the molar ratio of reactants, temperature, residence time, and mass fraction of nitric acid on the oxidation of glyoxal with nitric acid are investigated, and the optimum reaction conditions are determined. The glyoxylic acid yield can reach 81.6% while the selectivity is 92.4% with the set residence time of only 7.9 min at 68 ℃ (the molar ratio of nitric acid to glyoxal is 1.4, sodium nitrite to glyoxal is 0.15, hydrochloric acid to glyoxal is 0.2, and the mass concentration of nitric acid is 35%). The apparent kinetic model of the oxidation reaction of glyoxal with nitric acid in a microchannel reactor is established. By precisely controlling the reaction temperature and residence time of the continuous flow microreactor system, the apparent reaction rate constants, pre-exponential factor, and activation energy of glyoxal oxidation to glyoxylic acid by nitric acid are obtained. This work paves the way for the promotion of the synthesis of glyoxylic acid in a microreactor by the continuous flow chemistry system.