Nitrogen fixed into HNO3 by pulsed high voltage discharge

By applying pulsed high voltage discharge to a needle-mesh reactor that using seven acupuncture needles as discharge electrode and stainless steel wire mesh as ground electrode, nitrogen from bubbling gas could be fixed into NO2− and NO3− with equivalent mol H+ produced in the liquid phase and a small amount of NO and NO2 yielded in the gas phase. The HNO2 was originally formed and then converted into HNO3. The ·OH and H2O2 stimulated the conversion reaction from HNO2 to HNO3, which caused HNO2 concentration increased in the first 12 min and then decreased until lower than its detection limit. The concentration of HNO3 still increased with discharge time. After 36 min, HNO3 was the only and ultimate product in the liquid. The total yield of HNO2 and HNO3 could be affected by processing parameters such as electric factors of peak voltage and frequency, mesh size of ground electrode and content of nitrogen in N2/O2 bubbling. Increasing peak voltage or frequency, the total yield of HNO2 and HNO3 increased. Gas composition had a heavy impact on the fixation efficiency that obtained its maximum value at an oxygen content of 66.7% with bubbling O2/N2 gas. At the end of the 36 min discharge, the HNO3 concentration with bubbling air was 2.215 mmol L−1 at an applied voltage of 25 kV, pulse repetition frequency of 140 Hz and ground electrode mesh of 20 × 20. The energy yield was about 1.22 g (HNO3)/kWh.

► Nitrogen in bubbling is fixed to NO2− and NO3− with equivalent mol H+ by discharge.
► The HNO2 is originally produced and then converted into ultimate product of HNO3.
► Increasing peak voltage or frequency, the total yield of HNO2 and HNO3 increases.
► The fixation rate obtains a maximum value at 33.3% of nitrogen in bubbling O2/N2.
► The energy yield is 1.2 g(HNO3)/kWh at 52.5 W by peak voltage of 25 kV with 140 Hz.