Synthesis of hydrogen peroxide by underwater bubbling multi-mode discharge

Hydrogen peroxide(H 2 O 2 ) is an efficient and environmentally friendly oxidant, which is widely used in the synthesis of caprolactam, papermaking, printing and dyeing, textile, etc. Represented by the anthraquinone method, various traditional H 2 O 2 preparation methods have defects such as complex production process, high cost of raw materials and organic pollution. In this study, an underwater bubbling discharge reactor was designed for H 2 O 2 synthesis with water as the only raw materials. The reactor consists of a coaxial needle and quartz tube with a small hole at the bottom, and glow discharge mode or glow/spark mixed discharge mode (shown as a glow discharge at the middle of the high-voltage needle electrode and a spark discharge at the needle tip) can be realized using argon as working gas, which depends on whether the high voltage needle electrode is covered by the dielectric tube. The characteristics of the two discharge mode were researched and compared through the waveforms of voltage and current, and the optical emission spectra. The experimental results show that during one voltage pulse period, the mixed discharge mode is composed of a high-intensity breakdown discharge and several low-intensity breakdown discharges, the magnitude of the current is ampere level, whereas the glow discharge mode is only composed of many low-intensity breakdown discharges, and the current is all in the milliampere level. Meanwhile, the total electric power of the mixed mode discharge mode is always greater than that of the glow discharge mode. The emission spectra of the two discharge modes are both composed of Ar (4p-4s) and OH radicals emission lines, accompanied by a very small amount of N 2 (C-B) impurity, proving that OH radicals is the key particle in the synthesis of hydrogen peroxide. The concentration of hydrogen peroxide generated in the mixed discharge mode and glow discharge mode are 4.486mg/L and 3.287mg/L, respectively, for 60 seconds discharge duration. Considered the total electric power, the mixed discharge mode is more suitable for emergency preparation, while the glow discharge mode is suitable for the preparation of large amounts of H 2 O 2 . This research fully reflects the high-efficiency and environmentally friendly characteristics of low-temperature plasma, and provides an idea for the development of new H 2 O 2 preparation methods.