(388d) Continuous Biphasic Microreactor for Production of Hydrogen Peroxide Via Non-Thermal Atmospheric Pressure Plasma

Hydrogen peroxide (H₂O₂) represents an attractive green oxidant due to its high active oxygen content and its clean reduction product (i.e., water). Nevertheless, state of the art production of H₂O₂ comprises catalytic cycles of oxidation and hydrogenation in the presence of an organic substrate (anthraquinone).¹ This process is viable only at an economy of scale, with highly concentrated H₂O₂ requiring special handling for the downstream distribution and storage. Therefore, plasma-assisted production of diluted H₂O₂ can embody an alternative route for localized production, allowing for minimization of waste (only water is produced) and energy demand (electric energy is the only energy source).²

In this work, a novel biphasic non-thermal atmospheric pressure plasma microreactor is presented and characterized with respect to its H₂O₂ production. The system features a continuous biphasic stream of helium and water (whose flow rates are regulated by a gas flow controller and a syringe pump, respectively) that passes through a modular plasma region which can be adjusted by changing the reactor geometry. The micro-dimension of the reactor allows for low applied voltage and in turn low power input even for sinusoidal high-voltage signals. The production of H₂O₂ is assessed in relation to varying ratios of gas and liquid flow rate, reactor geometry and power input.

Most importantly, the effect of gas and liquid flow rate in the system is two-fold: on the one hand, high gas flow rate enhances the stability of the plasma and the production of excited species. On the other hand, high gas-to-liquid flow rate ratio has proven to intensify the interfacial area between the two phases with direct effect on the H₂O₂ concentration. In fact, H₂O₂ is expected to be forming on the gas-liquid interface, where recombination of OH radicals formed in gas phase takes place.^3,4 CFD calculations help capturing the different flow patterns linked to the varying flow rates. The effect of all operating parameters on the performance of the reactor is also discussed.

References

1. Strukul, Giorgio, ed. Catalytic oxidations with hydrogen peroxide as oxidant. Vol. 9. Springer Science & Business Media, 2013.
2. Locke, Bruce R., and Kai-Yuan Shih. "Review of the methods to form hydrogen peroxide in electrical discharge plasma with liquid water." Plasma Sources Science and Technology 20, no. 3 (2011): 034006.
3. Zhou, Renwu, Rusen Zhou, Peiyu Wang, Yubin Xian, Anne Mai-Prochnow, Xinpei Lu, P. J. Cullen, Kostya Ken Ostrikov, and Kateryna Bazaka. "Plasma-activated water: generation, origin of reactive species and biological applications." Journal of Physics D: Applied Physics 53, no. 30 (2020): 303001.
4. Wang, Huihui, Robert J. Wandell, Kosuke Tachibana, Jan Voráč, and Bruce R. Locke. "The influence of liquid conductivity on electrical breakdown and hydrogen peroxide production in a nanosecond pulsed plasma discharge generated in a water-film plasma reactor." Journal of Physics D: Applied Physics 52, no. 7 (2018): 075201.