Enhanced Simultaneous Photocatalytic Removal of SO2 and CO2 Using Powder and Coated Zeolites-Supported TiO2 Under Concentrated Sunlight Irradiation

Single-step process for simultaneous removal of gaseous pollutants is more advantageous than multi-steps one. In this study, the efficiency of a novel synthetic zeolite (Ze) prepared from stone cutting sludge and a natural zeolite (clinoptilolite, Cp) as the supports of TiO2 photocatalyst were examined for the separate and simultaneous removal of SO2 and CO2 under solar irradiation using a parabolic trough collector (PTC). The composites exhibited a higher efficiency than raw zeolites and TiO2 for the removal of both gases. The maximum removal of SO2 by TiO2-Ze and TiO2-Cp under sunlight was 41.9 % and 56.2 % that enhanced to 53.4 % and 78.8 %, respectively in the presence of CO2. Correspondingly, it was 61.8 % and 68.7 % for single CO2 removal that increased to 74.2 % and 79.0 % in the binary gas stream. This behavior could be due to the enhanced simultaneous SO2 oxidation and CO2 reduction. The performance of coated composite for SO2 was higher than of powder one (54.3% vs. 41.9%) and for CO2 removal was almost close together (58.9% vs. 61.2%). This work promises the application of photocatalytic co-removal of SO2 and CO2 by using synthetic and natural zeolite under solar irradiation.

Comparison of various chemical compounds for the removal of SO2 and NOx with wet scrubbing for marine diesel engines

Seawater, NaOH, NaClO, NaClO2, H2O2, and KMnO4 were used as scrubbing liquids to react with SOx and NOx separately in a customized wet scrubber. The absorption of SO2 in the aqueous phase was influenced by three factors: pH, ionic concentration, and oxidation potential. For NOx removal, the effectiveness of various chemical compounds can be ranked from least to most effective as follows: seawater, NaOH, H2O2 < NaClO < KMnO4 < NaClO2. This effectiveness was influenced by the chemical compound’s ability to oxidize NO to NO2, absorb the NO2 that was formed, and retaining the nitrogen in the aqueous phase. High oxidation potential promoted the oxidation of NO to NO2 but hindered the absorption of NO2. NaClO2 was superior compared to NaClO in all three categories of oxidizing, absorption and retention. NaClO could not retain a significant amount of NO2 which it absorbed in the aqueous phase. The pH around 8 provided a good balance between oxidation versus absorption/retention and reactant utilization for the chlorine-based oxidants. KMnO4 had the lowest reactant consumption rate; only half a mole was consumed for every mole of NO removed, compared to around 2–3 mol of chlorite or 3–5 mol of hypochlorite.

Comparison of various chemical compounds for the removal of SO2 and NOx with wet scrubbing for marine diesel engines.

Seawater, NaOH, NaClO, NaClO2, H2O2 and KMnO4 were used as scrubbing liquids to react with SOx and NOx separately in a customized wet scrubber. The absorption of SO2 in the aqueous phase was influenced by three factors: pH, ionic concentration and oxidation potential. For NOx removal, the effectiveness of various chemical compounds can be ranked from least to most effective as follows: Seawater, NaOH, H2O2 < NaClO < KMnO4 < NaClO2. This effectiveness was influenced by the chemical compound’s ability to oxidize NO to NO2, absorb the NO2 that was formed and retaining the nitrogen in the aqueous phase. High oxidation potential promoted the oxidation of NO to NO2 but hindered the absorption of NO2. NaClO2 was superior compared to NaClO in all three categories of oxidizing, absorption and retention. NaClO could not retain a significant amount of NO2 which it absorbed in the aqueous phase. The pH around 8 provided a good balance between oxidation versus absorption/retention and reactant utilization for the chlorine-based oxidants. KMnO4 had the lowest reactant consumption rate; only half a mole was consumed for every mole of NO removed, compared to around 2–3 moles of chlorite or 3–5 moles of hypochlorite.