Nitrogen oxides are noxious gas, which contributes to atmospheric pollution including particulate matter formation. Typically, most nitrogen oxides are emitted as nitric oxide. However, its low water solubility makes the treatment difficult. To enhance the solubility transition metal complexes have been tried as nitric oxide absorbents since they form stable metal nitrosyl complexes. Among many transition metal complexes, Fe(II)EDTA was studied extensively and pointed as a promising NO scavenger. However, the central Fe(II) in the complex is susceptible to oxidation by residual oxygen (5% v/v) in flue gas. As an alternative approach, an iron complex with thiol-based ligands was used in this study. The chosen ligand is 2,3-Dimercapto-1-propanesulfonic acid (shortly called DMPS), and it forms a Fe(II)(DMPS)2 complex. Fe(II)(DMPS)2 has an oxidation resistance because of the thiols in the ligand. Despite its superior oxidation resistance, Fe(II)(DMPS)2 also lose its nitric oxide binding ability as it is continuously exposed to oxygen in flue gas, so it should be regenerated. In this research, oxidized Fe(DMPS)2 was regenerated electrochemically. 1) The oxidized central Fe(III) ion is reduced to Fe(II), and 2) the oxidized S-S bond is reduced to thiols. To quantify the regeneration rate, Fe(II) ion and thiol concentration was measured with spectrophotometry with proper chromogenic reagents, respectively. Electrochemical activity of the oxidized Fe(DMPS)2 was examined with cyclic voltammetry with glassy carbon, gold, and silver electrodes. A redox couple near -0.6 V (vs Hg/HgO) and an oxidation peak at 0.7 V (vs Hg/HgO) were observed, and those peaks might be related to Fe(III)/Fe(II) or S-S/S-H redox couple. When the oxidized Fe(DMPS)2 was reduced in a two-chamber electrolysis cell, the concentration of S-H increased with time. This phenomenon implies the feasibility of the electrochemical regeneration of the oxidized Fe(DMPS)2. The provided regeneration study could resolve a critical drawback of an absorption based deNOx technology and open up a possibility of the application to practical sites.

Electrochemical regeneration of oxidized Fe(II) thiochelate based nitric oxide absorbent

2019 Fall National Meeting

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