Optimization Of Reactor And Reaction Condition In Direct Synthesis Of H₂O₂ Through Hydrogen-Oxygen Plasma

Hydrogen peroxide (H2O2) is widely used in chemical synthesis, textile bleaching, environmental protection, aerospace and military fields as an important green oxidant. H2/O2 plasma method is a new way that can synthesize high purity and concentrated H2O2.In this paper, the effects of plasma reactor structure and reaction conditions on the synthesis of H2O2 were studied in detail.Effects of reactor structure such as outer diameter of the high voltage electrode, thickness of high voltage electrode dielectric, length of discharge zone, material of high voltage electrode and conductivity of grounding electrode on synthesis of H2O2 through H2/O2 plasma were investigated. The mechanism of how the reactor structure affect the reaction result was also studied. The optimized outer diameter of high voltage electrode, thickness of high voltage electrode dielectric and length of discharge zone were about 4.0 mm,1.0 mm and 250 mm, respectively. The optimized material of high voltage electrode was Ni powder, and conductivity of grounding electrode was about 1200 ?s/cm. It is also summarized that the optimized discharge current was about 30 mA.Reaction conditions such as temperature of circulating-cooling water and residence time of raw gas were investigated. The optimum temperature of circulating-cooling water was about 24? and the optimum residence time of raw gas was in the range of 1-2 seconds. Temperature of circulating-cooling water influences the reaction results mainly through changing the active species of H2/O2 plasma; Residence time of raw gas affect the reaction results mainly via altering the electron density and average electron energy of H2/O2 plasma.Effect of adding gaseous oxide molecules such as CO, CO2 and H2 on synthesis of H2O2 was studied in detail. The promotion effect of H2O to synthesis of H2O2 was significant, but the effects of CO and CO2 were weak. In the condition of 18 ml/min H2O flow rate,12.8 kHz discharge frequency,40 W discharge power,210 ml/min H2 flow rate,9.3 ml/min O2 flow rate,4? circulating-cooling water temperature,60 minutes reaction time, the conversion of O2 increased from 43.5% to 83.7%, the selectivity of H2O2 increased from 73.5% to 73.6%, the yield of H2O2 increased from 32.0% to 61.6%, compared with the condition of non H2O. The results of oscilloscope, optical emission spectra and literatures show that, H2O molecules can not only increase the electron density to promote the activation of H2 and O2, but also accelerate some radical reaction to synthesize H2O2. These two reasons result in improved H2O2 yield.