Chemical Adsorption of Nitrogen Dioxide with an Activated Carbon Adsorption System

Nitrogen dioxide (NO_2) is a pollutant that directly harm the human respiratory system, lead to inflammation, as well as to form the secondary aerosol pollutants. The main NO_2 sources, combustion or thermal processes, were well controlled. However, the metal etching operation in semiconductor industry emits flue gases with reddish-brown NO_2 fume that leads to visibility reduction, acidic odor, as well as negative effects on human health. In this study, a stream of flue gases with low NO_2 (230 ± 10 ppm) and NO (50 ppm) concentrations were conducted to pass through an activated carbon-packed fixed bed for analyzing the adsorptive conversion behavior of NO_2 by the activated carbon (AC) at room temperature. The repeated adsorption test was carried out by washing the regenerated waste carbon with a caustic solution and water and drying. Results propose that at the beginning of adsorption, nitrogen dioxide combined with carbon to form NO and desorbed from carbon surface. The net adsorptive conversion removal capacity of NO_2 by the virgin AC and regenerated AC was 224 and 155 mg g^(-1) AC, respectively. Regeneration restored around 70-75% of effective surface area, pore volume, and adsorptive conversion capacity of the virgin AC. Leached caustic solution obtained from the carbon regeneration contained only nitrate and the phenomena indicates the adsorbed -C_2(ONO_2) hydrolyzed following the equation 2 -C_2(ONO_2) + H_2O → 3 -C* + -C(O) + 2 HNO_3, where -C* denotes active site on the carbon surface.