Sonochemical removal of nitric oxide from flue gases

The absorption of nitric oxide (NO) into water with simultaneous oxidation induced by ultrasonic irradiation at a fixed frequency of 20 kHz has been studied in a bubble column reactor at about room temperature. Factors studied include the flow rate of flue gas, intensity of ultrasound, and effect of sulfur dioxide (SO2) on the fractional conversion of NO. The concentration of NO in the inlet gas studied ranged from 50 to 1040 ppm, while that of SO2 ranged from about 52 to 4930 ppm. The fractional conversions of NO were found to range from 60% to 85%, while complete removal of SO2 was observed for all the inlet gas concentrations studied. In addition, the presence of low to moderate concentrations of SO2 in the inlet gas stream was found to enhance NO removal. Also, increasing the ultrasonic intensity was observed to improve NO removal. Sonochemical oxidation pathways leading to nitrite, nitrate, and sulfate formation are discussed. The results of this study suggest the feasibility of developing an innovative, cost-effective, and low-temperature aqueous sonochemical scrubber to provide an environmentally conscious method for the control of NOx and SO2. This should reduce or eliminate chemical usage, resulting in minimal sludge and disposal problems and associated costs.