Nobutake Suzuki

Radiation chemical reactions in NOx and SO2 removals from flue gas

Abstract For the purpose of elucidation of radiation chemical reactions of No x and SO 2 removals in irradiation of flue gas, the reactions of NO x and SO 2 were studied under irradiation with electron beams in various systems ranging from a simple system (NO-nitrogen) to the complex (NO-SO 2 -water vapour-oxygen-nitrogen) which was close to the composition of an flue gas. Reaction mechanisms of NO x and SO 2 were changed markedly by oxygen and water vapour. In nitrogen, NO was decomposed to oxygen and nitrogenthrough reactions with N atom and NO 2 was also decomposed to NO, dinitrogen oxide, oxygen and nitrogen. The decompositions were retarded markedly in the presence of oxygen, and an oxidation of NO and a reduction of NO 2 became predominant reactions. In the moist mixture of oxygen and nitrogen, fast oxidation of NO took place through the reactions with O, OH and HO 2 radicals, leading to the formation of NO 2 , followed by oxidation of NO 2 to produce HNO 3 . The SO 2 was also oxidized to H 2 SO 4 through the reactions with O and OH radicals in the moist mixture. An addition of ammonia enhanced markedly the NO x and SO 2 removals in the moist mixture. Reactions of NO and SO 2 with NH 2 radical took place in irradiation of the moist mixture containing ammonia in addition to the oxidations of No and NO 2 . The HNO 3 and H 2 SO 4 produced through the oxidations were converted to solid NH 4 NO 3 and (NH 4 ) 2 SO 4 and some parts of SO 2 itself reacted with ammonia, leading to the SO 2 removal.

The radiation-induced degradation of azo dyes in aqueous solutions

Abstract The aqueous solutions of Acid Red 265, Acid Red 37, Reactive Red 8, Reactive Red 3, Direct Red 79 and Direct Blue 78 were easily decolored by gamma radiation. For the oxygen- and nitrogen-saturated solutions, the degree of decoloration, the change of pH, the TOC reduction, the COD reduction and the amount of carbon dioxide formed were measured as functions of dose. After decoloration, the dye molecules are degraded to the lower molecular weight compounds, mainly, such as organic acids, and finally to carbon dioxide. The degradation reaction is promoted markedly by oxygen.

Radiation treatment of exhaust gases. IV. Oxidation of NO in the moist mixture of O2 and N2

Abstract A NO-H2O-O2-N2 gaseous mixture was irradiated by electron beams of 1.5 MeV at various reaction conditions. The decrease in [NO] was much larger for the moist mixture than for the dry mixture. The NO was easily oxidized to NO2 and finally to HNO3 in the moist mixture. The rate of NO consumption in the mixture increased with increasing H2O- and O2-concentrations and with lowering irradiation temperature from 150 to 100°C. The G(-NO) obtained in lower dose was 7.5 in the moist mixture of NO(100–500 ppm), H2O(8.4%), O2(11.4%) and N2(80.2%) at 120°C. The formed HNO3 reacted with NO to form NO2.

Decoloration and degradation of an anthraquinone dye aqueous solution in flow system using an electron accelerator

Abstract A study on the decoloration and degradation of a commercial anthraquinone dye (Acid Blue 40) was carried out by electron-beam irradiation. Experiments were done in a flow system using a five-stage, dual-tube bubbling column reactor. The oxygen contents of the gas bubbled into the inner tubes of the columns were varied from 0 to 100%. The inlet dye concentration, the solution feed rate and the dose rate were also varied from 50 to 100 ppm, 1.5 to 101/min and 0.1 to 0.15 Mrad/s, respectively. The degree of decoloration and degradation of aromatic rings increased with the oxygen content and became close to those for pure oxygen bubbling system at about 25% of oxygen content. The amount of degraded aromatic rings was proportional to that of consumed oxygen. The rate expression of the decoloration and degradation of the dye and the oxygen consumption were derived according to a reaction scheme.

The radiation-induced degradation of anthraquinone dyes in aqueous solutions

Abstract The aqueous solutions of Acid Blue 40, Acid Green 25, Reactive Blue 4, and Reactive Blue 2 were easily decolored by gamma radiation in the presence of oxygen. The decoloration reaction was promoted by addition of hydrogen peroxide and nitrous oxide. In the nitrogen-saturated Acid Blue 40 solution, new absorption bands appeared at 460–490 nm with the disappearance of the band at 610 nm and became more distinct by addition of alcohols. Such phenomena were not observed in the oxygen-saturated solution. In the presence of enough oxygen, the dye molecules after decoloration were degraded to lower molecular weight compounds, mainly organic acids, and finally to carbon dioxide.

The degradation of an azo dye in aqueous solutions by high-intensity electron-beam irradiation

Abstract A study of the degradation of Acid Red 265 (azo dye) in aqueous solutions by high-intensity electron- irradiation was carried out in a flow system. For the oxygen-saturated solutions (oxygen bubbled during irradiation), the change of absorption spectra, the degree of decoloration at 542 nm, the reduction in optical density at 230 nm, the change of pH, and the amount of dissolved oxygen were measured as functions of dose under various conditions (dye concentration, dose rate, solution flow rate, and oxygen flow rate). The decoloration scheme in the flow system by electron beam irradiation was similar to that in the batch system by gamma radiation. Oxygen was not necessary for the destruction of the chromophore but was absolutely essential for the destruction of substituted aromatic rings in the dye molecule. For the purpose of the destruction of the skeleton of the Acid Red 265 molecules, it was necessary to keep the concentration of dissolved oxygen above at about 30 ppm (in mass) in the case of the 60 ppm dye solution.

Oxygen gas dosimeter for flow systems

Abstract Oxygen was used as a high dose gas phase dosimeter by measuring the concentration of ozone formed with electron beam irradiation in a flow system. The formed ozone was measured by an ultraviolet absorption ozone detector. A part of the formed ozone was decomposed during irradiation. The decomposition of ozone is mainly caused by radical reactions of OH and HO 2 with ozone, and the rate of decomposition can be estimated easily by computer calculations. It is therefore possible to use this method as a gas phase dosimeter with a correction for the decomposition. The dose rate obtained by this method was in good agreement with that of the nitrous oxide dosimeter.

Enhancement of removal of SO2 and NOx by powdery materials in radiation treatment of exhaust gases

Abstract We studied the effect of powdery silica on radiation removal of SO 2 and NOx from mixtures of SO 2 , NOx, water vapour, oxygen and nitrogen under irradiation by electron beams of 1.5 MeV at 120°C. The SO 2 and NOx concentrations decreased when powdery silica was fed without irradiation. Decrements of SO 2 and NOx concentrations were markedly enhanced when powdery silica was fed together with the irradiation. The enhancement of SO 2 - and NOx-removal is attributed to the adsorption of SO 2 and NO on the water-covered surface of powdery silica, and the effective removal of NO 2 due to the reaction with water adsorbed on the surface of powdery silica. The results obtained show that the addition of powdery silica under irradiation is an effective method of enhancing the removal of SO 2 and NOx.

Radiation treatment of exhaust gases. V. Effect of NH3 on the removal of NO in the moist mixture of O2 and N2

Abstract NO was irradiated by electron beams of 1.5 MeV in the NH3-containing mixture of H2O, O2 and N2. The NO removal was larger in the mixture with NH3 than without NH3. The rate of NO removal in the mixture with NH3 increased with the concentrations of NH3 to 600 ppm, H2O to 4.4%, and O2 to 3.0%, leveling off above those concentrations. The rate decreased with increasing irradiation temperature. NO2, HNO3, N2O and small amounts of NH4NO3 were found as products in irradiation of the mixture with NH3. Formation of NO2 and HNO3 was markedly supressed, and N2O formation was enhanced by the addition of NH3. The solid NH4NO3 was found below about 70°C. NO removal is considered to be brought about not only by the oxidation of NO with O atom, OH and HO2 radicals, but also by reduction with NH2 radical.

Radiation treatment of exhaust gases. VII. NO decomposition in NO-N2 and NO-rare gas mixtures.:NO Decomposition in NO-N 2 and NO-Rare Gas Mixtures

The NO decomposition by electron beam irradiation was studied in the NO-N2 and NO-rare gas mixtures. The NO decomposition yields, G (−NO) at low doses in the case of the 500 ppm NO initial concentration were 4.04.4 and 1.2 for the NO-N2, NO-He and NO-Ar mixtures respectively. A small amount of NO2 was formed by irradiation of these mixtures. The NO decomposition is mainly attributable to the attacks of N and N4 + (or N2 +), formed by the radiolysis of N2on NO in the NO-N2 mixtureand to the attacks of R+ and R*, formed by the radiolysis of a rare gas (R)on NO in the NO-rare gas mixture. The NO decomposition in the NO-N2 mixture was depressed markedly by the addition of a small amount of O2. This may be mainly attributable to scavenging of N and N4 + (or N2 +) by O2.