The pandemic has created a huge demand for disinfectants worldwide. Developing a facile, quick, small footprint, and continuous synthetic device for disinfectants is highly desired. Hydrogen peroxide (H₂O₂), a wildly-used disinfectant, is greener and less corrosive than chlorine-based disinfectants. The commercial synthesis of H₂O₂ is achieved by the batch-wise air oxidation of hydroquinone along with the extraction of the peroxide, into the aqueous phase. Typically, the anthraquinone is first hydrogenated in an organic solvent, then the hydroquinone is treated with O₂ to produce H₂O₂ and to regenerate the quinone. 2-ethylanthraquinone is the most common anthraquinone that has been used for H₂O₂ production because of its high solubility in solvent mixtures. Also, Pd is the most active to catalyze the hydrogenation of anthraquinone. However, using the Pd as heterogeneous catalysts still has several disadvantages, including the overhydrogenation of anthraquinone and the separation of a heterogeneous catalyst. To address these problems, we develop facile continuous-flow hydrogenation of 2-ethylanthraquinone in a flow reactor. H₂, serving as a reducing agent, is produced in-situ by water electrolysis, and the pressure of H₂, as well as the flow rate of the reactant, can be precisely controlled. After the hydrogenation, the reaction solution is directly mixed with air and water for oxidation and extraction of produced H₂O₂. No separation of the Pd catalyst is needed because the catalyst is well-packed in the reaction column. The anthraquinone can be recycled for continuous production and atom economy. By tuning the H₂ pressure and the flow rate of the reaction solution, we can greatly suppress the overhydrogenation of 2-ethylanthraquinone and achieve a high yield and purity of H₂O₂. In this presentation, we will discuss the details of this set-up including reduction reaction kinetics vs. hydrogen pressure, temperature, and residence time; oxidation and extraction kinetics, catalyst lifetime (Pd and anthraquinone) in flow, and the concentration ranges of peroxide possible with this technique. In addition, we will discuss the performance of H₂O₂ production with various anthraquinone derivatives and solvents.

Mengqi Shen

Columbia University

Appearances