PhD abstract

The aim of this work is to develop and to characterize a wire-cylinder reactor using corona discharge with dielectric barrier technology, for the treatment of nitrogen oxides contained in a gas mixture (N2:O2:CO2:H2O:C3H6:NO) simulating an auto exhaust. We were particularly interested in the qualification of physical, hydrodynamics, electrical and chemical properties of the impulsional reactor and in the understanding of its global behavior. First, we characterized the electrical behavior of the reactor depending on various operating parameters like gas flow, gap, mixture temperature, dielectric material or high voltage electrode material. Then, we analyzed the gas mixture after the plasma treatment with a GC-MS and a gas analyzer in order to carry out a mass balance on NOx and VOC. The oxidation of the nitrous oxide in nitric oxide, the trapping of NOx by water (formation of nitric acid) and the formation of various hydrocarbons by-products (essentially aldehydes and R-NOx) showed the major role of oxidation phenomenon due to the oxygen atoms formed by the dissociation of O2 and CO2. The isotopic substitution of the molecular oxygen with labeled 18O allowed us to identify the origin of oxygen atoms in the different by-products, wich can be produced from O2, CO2 or H2O, and to determine the reactional pathways. The determination of the isotopic distribution of R-NOx demonstrated the role of energy density on the formation of NOx through the discharge. Finally, we proposed a model of the reactor as a cascade of continuous stirred tank reactors with an impulsional feeding of oxygen atoms. Simulation results showed a good agreement between experimental and modeling. Once validated, this model allowed us to understand the main mechanisms governing the behavior of the wire-cylinder reactor.