Search

Abstract: NO can be removed from exhaust gas streams by using a basic solution of cobalt ethylenediamine (H2NCH2CH2NH2). The cobalt ethylenediamine acts as a homogeneous catalyst to oxidize NO into soluble nitrogen dioxide and realize the oxidation and absorption of nitric oxide simultaneously. The dissolved oxygen in equilibrium with the residual oxygen in the exhaust gas stream acts as the oxidant. SO2 can also be removed by the Co(en)3 3+ (en stands for ethylenediamine) solution. A double-stirred reactor with a plane gas–liquid interface that was planar to close approximation was used to measure the absorption rates of NO into the Co(en)3 3+ solutions. The experiments demonstrate that the gas–liquid reaction becomes gas film controlling as the cobalt ethylenediamine concentration exceeds 0.03moll−1 when there is 1200ppm SO2 in the gas phase. The NO absorption rate decreases as SO2 concentration increases. Oxygen in the gas phase accelerates the NO absorption rate into the cobalt ethylenediamine solution. The optimal temperature for nitric oxide absorption is 50°C. The NO absorption rate increases as the pH of the Co(en)3 3+ solutions rises. [Copyright &y& Elsevier]

The wet ammonia desulfurization process can be retrofitted for combined removal of SO2 and NO from the flue gases by adding soluble cobalt(II) salt into the aqueous ammonia solution. Activated carbon is used to catalyze the reduction of hexamminecobalt(III) to hexamminecobalt(II) to maintain the capability of removing NO of the hexamminecobalt solution. The effects of temperature, pH, activated carbon particle size, and superficial liquid flow velocity on hexamminecobalt(III) conversion have been investigated. An apparent activation energy is obtained. According to the experimental results, the catalytic reduction reaction rate increases with temperature. The batch reactor experiments show that the best pH range lies in between 3.5 and 6.5. In a fixed-bed reactor, superficial liquid flow velocity obviously affects the reaction and a high yield of cobalt(II) is obtained at a pH value lower than 9.0. The experiments manifest that the hexamminecobalt solution coupled with catalytic regeneration of hexamminecobalt(II) can maintain a high nitric oxide removal efficiency during a period of time. [Copyright &y& Elsevier]

Aqueous ammonia solution can be used to remove NO from waste gas streams by adding soluble cobalt(II) salt into aqueous ammonia solution. The hexamminecobalt(II) cations can not only bind nitric oxide but also activate oxygen molecules in aqueous solutions. Nitric oxide is absorbed and oxidized simultaneously in the same reactor. Nitric oxide can be turned into nitrite and nitrate. Activated carbon is used to catalyze the reduction of hexamminecobalt (III) to hexamminecobalt (II) to maintain the capability of removing NO with the hexamminecobalt solution. The influences of temperature and activated carbon particle size on the conversion of hexamminecobalt (III) are investigated. According to the experimental results, the catalytic reduction reaction rate increased with temperature. The influence of particle size of AC on the reduction of hexamminecobalt (III) in fixed bed reactor was very little. Oxygen in the gas phase was beneficial to the absorption of NO into the hexamminecobalt solution. The experiments performe manifestly that the hexamminecobalt solution coupled with catalytic regeneration of hexamminecobalt (II) was able to maintain a high nitric oxide removal efficiency for a long time. This method may have a bright promise in application.