Oxidation of Dibenzyl Ether with Nitric Acid to Benzaldehyde in Continuous-flow Microreactors

As an important chemical, benzaldehyde (BzH) can be synthesized by oxidizing dibenzyl ether (DBE) with nitric acid (HNO3). This is an environmentally friendly and chlorine-free production process, but it has problems such as intense in-situ gas generation, low space-time yield and safety issues. This study developed a safe and efficient continuous-flow synthesis method using a packed-bed microreactor. Five critical parameters including reaction residence time, glass bead particle size, temperature, oxidant concentration, and initiator dosage were systematically investigated. Under optimal conditions (T = 85℃, d = 104.5 μm, HNO3 eq = 3 and NaNO2 eq = 0.009), the conversion of DBE and the yield of BzH reached 80.11% and 96.35% after 17.92 min. The space-time yield was twice that of capillary microreactor and 40 times that of batch reactor. The reasons for in-situ gas production in capillary microreactors and its negative impacts were explored. A kinetic model was developed, providing significant theoretical insights and practical value for better understanding the oxidation process and optimizing the process parameters.