Hydrogen peroxide production using ambient pressure microplasmas

Abstract Hydrogen peroxide (H2O2) is an important chemical compound in industry and applications of H2O2 are ubiq-uitous and range from disinfection up to a wide array of commercial processes, such as an oxidant for the epoxidation of propene to propene oxide, a major bulk material in the chemical industry [1] or as precursor reac-tant in catalytic processes. H2O2 also plays an important role in environmental processes such as waste water abatement to control sulfides and nitrous oxides levels in water and in novel medical therapies to treat wounds and stimulate wound healing. This work has the goal to un-derstand and improve the production of H2O2 in an ambi-ent pressure microplasma. In contrast to established methods in industry, this plasma approach can improve the overall cost-effectiveness of the production process by eliminating expensive transport and handling costs and is especially suitable for explosive gas mixtures. The H2O2 production yield in a parallel plate capacitive coupled RF glow discharge and a kHz AC dielectric bar-rier discharge (DBD), both operating at ambient pressures and close to room temperatures (350K ± 50K) have been investigated using different gas mixtures (He-H2O and He-H2/O2 mixtures). The challenge is to strongly dissoci-ate H2O or H2/O2 while simultaneously guiding the re-combination of the dissociation products to H2O2. The former would be favoured at higher gas temperatures (Tg), which in return would lead to thermal dissociation of the produced peroxide. Similar as for the production of O3, H2O2 is also formed in 3-body reactions: both the DBD and the RF glow discharge have a large Te and a small Tg at atmospheric pressure, which are required to produce H2O2. This work aims to understand the requirements of an efficient and stable low temperature gas discharge for producing hydrogen peroxide from either water or hydro-gen oxygen mixtures (potentially with added inert gases). Electrical discharges have been successfully used by var-ious groups for this purpose [2-4], however mostly in a multi phase environment. Our first results show a similar energy and production efficiency of peroxide using either of the gas mixtures in both of our reactor types, thus eliminating the need for expensive and potentially explosive H2/O2 mixtures. The experiments indicate a strong dependence of the produc-tion efficiency on the dissipated power and size of the plasma which indicate a strong dependence on gas tem-perature and residence time (figure 1). This is also sup-ported by the observation that pulsed operational modes in both reactors improve the efficiency. Plasma conditions which influence H2O2 production will be discussed in detail.