Photochemical removal of NO(2) by using 172-nm Xe(2) excimer lamp in N(2) or air at atmospheric pressure

Ozone Catalytic Oxidation for Gaseous Dimethyl Sulfide Removal by Using Vacuum-Ultra-Violet Lamp and Impregnated Activated Carbon

Gaseous sulfur compounds are emitted from many facilities, such as wastewater facilities or biomass power plants, due to the decay of organic compounds. Gaseous dimethyl sulfide removal by ozone catalytic oxidation was investigated in this study. A Vacuum-Ultra-Violet (VUV) xenon excimer lamp of 172 nm was used for ozone generation without NOx generation, and activated carbon impregnated with iodic acid and H2SO4 was utilized as a catalyst. Performance assessment of dimethyl sulfide removal ability was carried out by a dynamic adsorption experiment. Empty-Bed-Contact-Time (EBCT), superficial velocity, concentration of dimethyl sulfide, temperature and humidity were set at 0.48 s, 0.15 m/s, 3.0 ppm, 25 °C and 45%, respectively. Without ozone addition, the adsorption capacity of impregnated activated carbon was 0.01 kg/kg. When ozone of 7.5 ppm was added, the adsorption capacity of impregnated activated carbon was increased to 0.15 kg/kg. Methane sulfonic acid, a reaction product of dimethyl sulfide and ozone, was detected from the activated carbon. The results suggest that the VUV and activated carbon impregnated with iodic acid and H2SO4 are workable for ozone catalytic oxidation for gas treatments.

Efficient removal of benzene in air at atmospheric pressure using a side-on type 172 nm Xe2 excimer lamp

The photochemical removal of benzene was studied in air at atmospheric pressure using a side-on type 172 nm Xe₂ excimer lamp with a wide irradiation area. After 1.5 min photoirradiation, C₆H₆ (1000 ppm) in air was completely converted to HCOOH, CO, and CO₂ at a total flow rate of 1000 mL/min. The initial decomposition rate of C₆H₆ was determined to be 1.18 min^-1. By using a flow system, C₆H₆ (200 ppm) was completely removed at a total flow rate of 250 mL/min. The conversion of C₆H₆ and the energy efficiency in the removal of C₆H₆ changed in the 31-100% and 0.48-1.2 g/kWh range, respectively, depending on the flow rate, the O₂ concentration, and the chamber volume. On the basis of kinetic model simulation, dominant reaction pathways were discussed. Results show that the O(³P) + C₆H₆ reaction plays a significant role in the initial stage of the C₆H₆ decomposition. Important experimental parameters required for further improvement of the C₆H₆ removal apparatus using a 172 excimer lamp were discussed based on model calculations.

Novel Process of Simultaneous Removal of Nitric Oxide and Sulfur Dioxide Using a Vacuum Ultraviolet (VUV)-Activated O2/H2O/H2O2 System in A Wet VUV-Spraying Reactor

A novel process for NO and SO₂ simultaneous removal using a vacuum ultraviolet (VUV, with 185 nm wavelength)-activated O₂/H₂O/H₂O₂ system in a wet VUV-spraying reactor was developed. The influence of different process variables on NO and SO₂ removal was evaluated. Active species (O₃ and ·OH) and liquid products (SO₃^2-, NO₂^-, SO₄^2-, and NO₃^-) were analyzed. The chemistry and routes of NO and SO₂ removal were investigated. The oxidation removal system exhibits excellent simultaneous removal capacity for NO and SO₂, and a maximum removal of 96.8% for NO and complete SO₂ removal were obtained under optimized conditions. SO₂ reaches 100% removal efficiency under most of test conditions. NO removal is obviously affected by several process variables. Increasing VUV power, H₂O₂ concentration, solution pH, liquid-to-gas ratio, and O₂ concentration greatly enhances NO removal. Increasing NO and SO₂ concentration obviously reduces NO removal. Temperature has a dual impact on NO removal, which has an optimal temperature of 318 K. Sulfuric acid and nitric acid are the main removal products of NO and SO₂. NO removals by oxidation of O₃, O·, and ·OH are the primary routes. NO removals by H₂O₂ oxidation and VUV photolysis are the complementary routes. A potential scaled-up removal process was also proposed initially.

The use of vacuum ultraviolet irradiation to oxidize SO₂ and NOx for simultaneous desulfurization and denitrification

A simple and efficient method for simultaneous desulfurization and denitrification via vacuum ultraviolet (VUV) irradiation and with no additional chemicals is presented. The simultaneous removal of 90% SO2 and 96% NOx (NO+NO2) was achieved from the simulated flue gas under the irradiation from a low-pressure mercury lamp with main wavelengths of 185 and 254 nm, respectively. The composition, flow rate, and temperature of the simulated flue gas, as well as the VUV light intensity, were evaluated as the factors impacting on the efficiency of SO2 and NOx removal. The OH, HO2, O, and O3 produced from the photolysis of H2O and O2 were concluded as the major reactive oxygen species that oxidized SO2 and NOx. The additional OH and HO2 generated through the reactions of NO+HO2 and SO2+OH/HO2 improved treatment efficiency, while the oxidation products of NOx, e.g., NO2, HNO2, HNO3, and HNO4, consumed massive reactive oxygen species (such as O, OH, and HO2) and thereby reducing the removal efficiencies. The main reaction products were characterized as H2SO4 and HNO3 by ion chromatography, which could be used as chemical or fertilizer raw materials.