AN INDIRECT ELECTROCHEMICAL PROCESS FOR THE REMOVAL OF NOX FROM INDUSTRIAL-WASTE GASES

The development of a new electrochemical process for the absorption of NOx from industrial waste gases is described. Conversion of NO was pe rformed by an indirect outer cell process using dithionite as the redo x mediator and Fe-(II)EDTA as the complexing agent. The absorption pro cess, involving complex formation with Fe-(II)EDTA in the absence and presence of dithionite, was investigated using a packed bubble column. In semibatch experiments the dependence of different system parameter s on the degree of NO conversion was studied: concentration of dithion ite and Fe(II)EDTA, gas flow rate, oxygen content, and temperature. Th e reaction products in the gas phase and in the liquid phase were anal yzed using gas chromatography and ion chromatograghy, respectively. Th is analysis proved that, instead of N-2 or N2O, ammonia and amidosulfo nic acid are the main reaction products in the solution. The kinetics and the conditions for the regeneration of dithionite by electrochemic al reduction of sulfite were studied on RDE and by experiments in a di vided cell. For the dithionite production a current efficiency of abou t 80% was found in 0.2 M Na2SO4 at pH 5.6. By combining the chemical N O absorption in a gas/liquid contactor with the electrochemical regene ration of dithionite in a divided plate and frame cell a degree of NO conversion better than 90% under continuous operation can be obtained.