(225h) Reaction Kinetics and Mechanistic Studies of Nitric Oxide Removal By Combined Aqueous Persulfate and Ferrous-EDTA Systems
AIChE Annual Meeting
2013
2013 AIChE Annual Meeting
Environmental Division
Advanced Oxidation Processes I
Tuesday, November 5, 2013 - 10:15am to 10:30am
Nitrogen oxides (NOx – mainly NO2 and NO) and sulfur oxides (SOx – mainly SO2) are the most prominent acid gases emitted from the burning of fossil fuel especially from the coal fired power plants, and are responsible for widespread problems of air pollution, health hazards, acid rains etc. Of these oxides NO2 and SO2 are readily soluble in water and can be scrubbed easily from the exhaust stream but nitric oxide (NO) is very sparingly soluble in water and cannot be separated easily. It is well known that the commonly practiced methods of removing NO such as selective catalytic and non-catalytic processes 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. 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 (S2O82-) activated by temperature showed significant removal (up to 90% at 900C). Later work involving the simultaneous activation by thermal and ferrous ion showed further 10% increment in the NO removal at all temperatures. But the energy requirement for high temperature process to obtain higher removal rates could be one of the main stumbling blocks for further developments. A number of reports have suggested NO removal by iron chelating agent especially ferrous ethylenediamine tetraacetic acid (FeII-EDTA) where NO is combined with FeII-EDTA and separated from the solution. The main drawbacks this process are removal of FeII-EDTA(NO) complex and fast oxidation of FeII-EDTA to inert FeIII-EDTA and high cost of EDTA. The problem was somewhat overcome in BiodNOx process where FeII-EDTA(NO) is broken down by denitrifying bacteria and FeIII-EDTA is reduced by iron reducing bacteria and the resultant FeII-EDTA is recycled to the reactor again. But the process was impeded by the slow action of the biological process and uncertainty involving in bacteria culture and the additional cost of another unit. It is widely reported in the literature that FeIII-EDTA can also be reduced by persulfate ion (S2O82-) and sulfate radical (SO4•-) and the resulting FeII-EDTA used for the remediation of other chemical pollutants. However, to the best of our knowledge the simultaneous and synergistic application of peroxydisulfate (S2O82-) and FeII-EDTA for the removal of NO has never been studied and is the main focus of this work.
NO removal by combined aqueous persulfate and ferrous EDTA was studied in a bubble column reactor in semibatch mode. Firstly, the optimum FeII:EDTA ratio was determined for different temperatures and the 1:1 ratio was found to give the highest NO removal rates. The experiments were carried out at different temperatures and the results were compared to the thermal- and iron-activated persulfate alone removal experiments. It was shown that the combined persulfate-ferrous-EDTA system resulted in significantly higher NO removal at low temperatures, almost 30% higher than the thermal- and iron-activated systems. Also, the pH for optimal NO removal was found to be around neutral (pH 7.0). The concentrations of the ferrous, ferric ion and iron-EDTA complex species were measured by spectrophotometric methods and total iron material balance verified. Finally, kinetics and mechanistic reaction pathways for the complex process were investigated using a physicochemical mathematical model involving the use of pseudo-steady-state-approximation technique and film theory of mass transfer. The model was solved numerically using fourth order RK method in Matlab to find the theoretical concentration profile and results used to validate the experimental data. We are currently investigating the effects SO2 and the various process parameters using design of experiments (DOE) methodologies.
References
Adewuyi, Y.G., Khan, N.E. Modeling the Ultrasonic Cavitation-Enhanced Removal of Nitrogen Oxide (NO) in a Bubble Column Reactor. AIChE J. 2012, 58, 2397 - 2411. http://onlinelibrary.wiley.com/doi/10.1002/aic.12751/pdf
Khan, N.E.; Adewuyi, Y.G. Absorption and Oxidation of Nitric Oxide (NO) by Aqueous Solutions of Sodium Persulfate in a Bubble Column Reactor. Ind. Eng. Chem. Res. 2010, 49 8749-8760. http://pubs.acs.org/doi/abs/10.1021/ie100607u
Adewuyi, Y.G., Owusu, S.O. Ultrasound-induced Aqueous Removal of Nitric Oxide from Flue Gases. Effects of Sulfur Dioxide, Chloride and Chemical Oxidant. J. Phys. Chem. A. 2006. 110, 11098-11107. http://dx.doi.org/10.1021/jp0631634
Owusu, S.O; Adewuyi, Y.G. Sonochemical Removal of Nitric Oxide from Flue Gases. Ind. Eng. Chem. Res. 2006, 45, 4475-4485. http://dx.doi.org/10.1021/ie0509692
Adewuyi, Y.G.; Owusu, S.O. Aqueous Absorption and Oxidation of Nitric Oxide with Oxone for the Treatment of Tail Gases: Process Feasibility, Stoichiometry, Reaction Pathways and Absorption Rate. Ind. Eng. Chem. Res. 2003, 42, 4084-4100. http://dx.doi.org/10.1021/ie020709+
Adewuyi, Y.G.; He, X.; Shaw, H.;Lolertpihop, W. Simultaneous Absorption and Oxidation of NO and SO2 by Aqueous Solutions of Sodium Chlorite. Chem. Eng. Commun., 1999, 174, 21-51. http://dx.doi.org/10.1080/00986449908912788
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