Photooxidation for sulphur dioxide removal from flue gases

An oxygen stream doped with SO2 at flue gas concentrations was passed at room temperature and atmospheric pressure through a photochemical reactor containing an aqueous solution of a photosensitizing dye. The oxidation of SO2 to SO3 was measured while intense visible light was passed through the reactor. During the experiments the removal of SO2 from the oxygen stream via oxidation to SO3 proceeded at a steady rate. SO2 removal efficiency ranged from 10–50% and was calculated as a function of the initial SO2 concentration (1240–3400 ppm), the light intensity on the reactor surface (7.3–13.3 W cm−2), the concentration of the sensitizing dye (4.0 × 10−5–4.0 × 10−4 M) and the reactor space time (1.7–5.5 s). SO2 removal efficiency increased with increase in light intensity and reactor space time and decreased with increase in initial SO2 concentration. In the dye concentration range of 4.0 × 10−5–9.8 × 10−5 M, the SO2 removal efficiency showed an increase with increasing dye concentration. Beyond 9.8 × 10−5 M, SO2 removal efficiency decreased with increasing dye concentration. Rose Bengal was a more efficient photosensitizing dye than Methylene Blue. A mathematical expression for SO2 removal efficiency was derived from a kinetic model independent of the experiments. This expression predicted a functional dependence on dye concentration, initial SO2 concentration, light intensity and reactor space time, which is consistent with the experiments.