(80f) Nitric Oxide Removal By Aqueous Persulfate Activated By Temperature and Fe (II) in a Bubble Column Reactor: Reaction Kinetics and Mechanistic Modeling

The combustion of fossil fuel (e.g., in coal-fired plants) releases a large amount of NO_x (mainly NO and NO₂) and SO₂ into the atmosphere.  Both NO_x and SO₂ contribute to the formation of ground-level ozone, urban photochemical smog, acid rain, eutrophication, respiratory and cardiovascular diseases. Currently, available control technologies popularly used for NO_x abatement include selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR) with urea injection or ammonia injection (thermal deNO_x), flue gas recirculation (FGR) and low-NO_x burners (LNB). It is well known that these commonly practiced methods of removing NO have high capital costs and undesirable problems of high temperatures and handling of harmful chemicals, and alternative cost-effective and environmentally friendlier processes are of ardent interest. Aqueous scrubbing with chemical agents either to oxidize insoluble NO into a more soluble NO₂ or form a complex with NO, which can be subsequently removed, provides alternative treatment techniques. Various chemicals including water-soluble ferrous-chelating agents (e.g., Fe(II)EDTA) and oxidants such as hydrogen peroxide (H₂O₂), chlorine dioxide (ClO₂), sodium chlorite (NaClO₂), potassium permanganate (KMnO₄), sodium hypochlorite and  yellow phosphorous have been studied for their effectiveness in removing NO_x by aqueous wet scrubbing. The mechanism of SO₂ removal in the wet scrubbing method is not a novel idea, whereas the mechanism of NO removal has unknown areas to be developed. With the number of wet flue gas desulfurization (FGD) scrubbers scheduled to be constructed in response to the Clean Air Interstate Rule (CAIR) issued by EPA on March 10, 2005, it is desirable to develop cost-effective, wet-scrubber-based technologies, especially those capable of providing simultaneous multipollutant (SO₂, NO_X, and Hg⁰ and Hg²⁺) control. Such technologies could make wet-FGD scrubber more cost-effective and could obviate the need for installation of additional costly control equipment such as SCR system.

It is also well known that suitable oxidizing agents can increase the solubility of NO significantly in water and our group’s previous studies involved detailed experimental and mechanistic studies of the removal of NO by aqueous oxidizing agents, of which, peroxydisulfate or persulfate (S₂O₈^2-) activated by temperature showed significant removal (up to 90% at 90 ⁰C).  In this work, the chemistry and effects of temperature and Fe²⁺ activated persulfate on the fractional conversion of NO were determined via experimental and modeling studies in a bubble column reactor operated in the semibatch mode. In addition, mechanistic reaction pathways were proposed and a detailed physicochemical mathematical model utilizing the pseudo-steady-state-approximation technique  (PSSA) and film theory of mass transfer was developed.  The model was solved numerically using fourth order RK method in Matlab to find the theoretical concentration profile and model results used to validate and correlate the experimental data; and kinetic rate constants, and the activation energies for the NO_x-persulfate-Fe²⁺reacting systems were estimated.

References

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