Sustainable and Continuous Flow Preparation of High-Concentration H₂O₂ by Visible-Light-Activated Molecular Oxygen Oxidation of Lower Alcohols

Abstract

H 2 O 2 is a multifunctional green oxidant, and the preparation of H 2 O 2 by photocatalysis is a kind of green and efficient method; however, the production of terminal H 2 O 2 with a high concentration of up to 10 mmol•g −1 •h −1 under visible light irradiation is a challenge. With this objective, herein, we report a strategy for the homogeneous visible light photocatalytic preparation of H 2 O 2 via the HAT (hydrogen atom transfer) process using commercially available 2-ethylanthraquinone (EAQ) as the photocatalyst. Even under intermittent conditions, the H 2 O 2 generation rate could reach up to 323.32 mM/h (526.6 mmol•g −1 •h −1 ), which represents the fastest photochemical H 2 O 2 production reaction reported. The continuous flow strategy could significantly improve the yield of H 2 O 2 by 91 times to ∼29460 mM/h. A liquid−liquid extraction device that connects with the flow reactor could realize the continuous separation of H 2 O 2 in aqueous solution of up to 11.1 wt % in 1 h with a lower EAQ loading of 0.2−0.3 mol % (∼6.2−9.3 g/L). Compared with the AO method, EAQ efficiency is significantly elevated by 10−20 times in this continuous flow photocatalysis strategy.