Study of a photocatalytic oxidation and wet absorption combined process for removal of nitrogen oxides

A two-stage process incorporating photocatalytic oxidation (PCO) and wet absorption was developed in this study for the treatment of nitrogen oxides (NOx). At first, nitric oxide was converted to nitrogen dioxide by PCO. Then the nitrogen oxides were absorbed effectively in a wet scrubber by using sulfite solution as an absorbent. The experimental results showed that the removal efficiency of NOx by this combined process could reach 75%, when the inlet concentration of nitrogen oxides was 240 ppm (200 ppm NO). It was also observed that NOx removal efficiency had a maximum value when the absorbent concentration (Na2SO3) was 2 wt%. The addition of Na2S2O3 could effectively retard the excessive oxidation of sulfite by oxygen. 0.5 wt.% Na2S2O3 was considered the suitable inhibitor concentration. The main products of this combined process were nitrite and nitrate.