Removal Of Nitrogen Oxides From Flue Gases By Complexation And Electrochemical Method

As the atmosphere pollution caused by nitrogen oxides from flue gases is getting worse day after day,more attention should be paid to the importance and urgency of controlling it.The electrochemical treatment applied in denitrification of flue gases has a lot of advantages.But it is still in the preliminary study stage in our country.So this research of flue gas denitrification by electrochemical methode is very necessary.A new process for removal of nitrogen oxides from waste gases is proposed consisting of nitric oxide absorption and electrochemical treatment.In nitric oxide absorption step,nitric oxide is absorbed by Fe(II)EDTA solution to form ferric-nitrosyl complex which would be deoxidized by hyposulphite.In electrochemical step,the hyposulphite would be regenerated by electrochemical reduction on the cathode electrode.On the opposite side,I2 would be regenerated from I-by electro-oxidation on the anode to remove S02 from flue gases.The electro-reduction and electro-oxidation behavior of ferric-nitrosyl complex on platinum electrode and graphite electrode were investigated as the main task of this work to provide a theoretic basis of removal of nitrogen oxides from flue gases by complexation and electrochemical method.The reversibility of NO absorbed by Fe(II)EDTA reaction and the electrochemical reduction behavior of Fe(II)EDTA(NO)on a flake of Pt electrode had been respectively investigated by UV-Vis spectrometry and the measurement of cyclic voltammetry and in situ FTIR technique.It is found that,the absorption between Fe(?)EDTA and NO temporarily is a reversible process.The product of Fe(?)EDTA(NO)can slowly and automatically gets decomposed into Fe(?)EDTA and N20.The electro-reduction and electro-oxidation of Fe(?)EDTA/Fe(?)EDTA occur respectively at the cathode potential-0.12V(vs.SCE)and at the reversed anode potential-0.05V(vs.SCE).The direct conversion of coordinated NO by electrochemical reduction takes place at the potential range of 0?-0.40V(vs.SCE)with N2O22-as its product.As the cathode potential polarlized to-0.80V(vs.SCE),the formed N2O22-is electro-deoxidized into NH2OH.Meanwhile the electro-reduction of N20 also occurs at this potential scale.What's more,the N20 takes an advanced conversion while the potential is in the range of-0.85?-1.40V(vs.SCE).The complex electrochemical oxidation behavior of Fe(?)EDTA(NO)on a flake of Pt electrode had been investigated by the measurement of cyclic voltammetry and in situ FTIR technique.It is found that the electro-redoxidation of Fe(?)EDTA/Fe(?)EDTA also respectively occur at-0.05V/-0.12V(vs.SCE)in the solution of Fe(?)EDTA(NO).The direct conversion of coordinated NO by electrochemical oxidation takes place at the potential of 0.80V(vs.SCE)with NO2-as its product.It is confirmed that a new electro-oxidation of coordinated NO or a further electro-oxidation of NO2-formed in the former electro-oxidation of coordinated NO arises along with the anode degradation of excessive EDTA during the positive sweep at 1.00V(vs.SCE).The electrochemical reduction and electrochemical oxidation behavior of Fe(?)EDTA(NO)on a flake of graphite electrode had been researched by the measurement of cyclic voltammeatry,scanning electron microscope(SEM)and energy-dispersive X-ray spectroscopy(EDX).The result comes out that The electrochemical reduction and electrochemical oxidation of Fe(III)EDTA/Fe(II)EDTA occur respectively at the cathode potential-0.12V(vs.SCE)and at the reversed anode potential-0.01 V(vs.SCE).The direct conversion of coordinated NO by electrochemical reduction takes place at the potential range of-0.40-0.10V(vs.SCE).As the cathode potential polarlized to-0.80V(vs.SCE),the products of the former electro-reduction of NO and the N20 both take an advanced reduction.As the results showed by the cyclic voltammetry of Fe(?)EDTA solution with larger concentrations of 0.015M and 0.02M by electro-reduction and the EDX analysis of graphite electrode by electro-reduction at a constant potential-1.30V(vs.SCE)that iron deposition indistinctively does arise along with the water decomposition when the potential is negative to-1.10V(vs.SCE).By this results token,the iron deposition also occurs on the graphite electrode which has taken an electro-reduction in the Fe(?)EDTA(NO)solution.What's more,the reduction products of coordination NO and N20 take an advanced reduction as the cathode potential negatived to the range of-1.15V?-1.40V(vs.SCE).Durring the positive polarization,direct electrochemical oxidation of coordinated NO takes place at the potential range of 0.50V?1.00V(vs.SCE)along with the anode degradation of EDTA.When the potential is positive to 1.00V(vs.SCE),the coordinated NO or the oxides formed in the former electro-oxidation of coordinated NO may take an advanced electrochemical oxidation.