Effective Electroregeneration of the Oxidized Iron(II) Thiochelate Absorbent in the Wet NOX Absorption Process

Abstract

ABSTRACT: The ever-increasing air pollution has brought the treatment of nitrogen oxides (NOX) to the forefront of flue gas purification. Wet absorption achieves outstanding NOX removal efficiency, but it suffers from an oxidative deactivation of the NOX absorbent, iron(II) thiochelate, by the residual O2 in flue gases. To address this critical issue, we demonstrate a regeneration process to electrochemically reduce the oxidized iron thiochelate into the original form to effectively bind nitric oxide (NO). A series of voltammetric techniques were adopted to define the redox potentials of Fe(III)/ Fe(II) thiochelate, represented as 2,3-dimercapto-1-propanesulfonate (DMPS). The electrochemical reduction of the oxidized iron thiochelate led to the transformations of disulfide (S-S) to a thiol (R-SH) and Fe(III) to Fe(II). Both the rate and Faradaic efficiency of electroregeneration could be enhanced through the adsorption between iron(II) thiochelate and a copper catalyst as revealed by X-ray photoelectron spectroscopy. At an optimal condition, recovery efficiencies of 99.8 and 96.1% for thiol and Fe(II) concentrations were obtained, respectively, on a Cu electrode at -1.3 V vs Ag/AgCl, thereby restoring 97.9% of NO absorption capacity. Our findings offer routes to complement the wet scrubbing NOX treatment technology while preventing the abuse of chemical absorbents.