Propane dissociation in a non-thermal high-pressure nitrogen plasma

The removal and the conversion processes of propane in N-2/C3H8 mixtures (concentration of hydrocarbon molecules up to 5500 ppm) energized by a photo-triggered discharge (homogeneous plasma) are studied at 460 mbar total pressure, both experimentally and theoretically. A self-consistent 0D discharge and kinetic model is used to interpret chromatographic measurements of propane and some by-products' concentrations (hydrogen and hydrocarbons with two or three carbon atoms). It is suggested, from the comparison between measurements and model predictions, that quenching processes of nitrogen metastable states by C3H8 lead to the dissociation of the hydrocarbon molecule, and are the most important processes for the removal of propane. Such a result is obtained using the quenching coefficient value previously determined by Callear and Wood (1971 Trans. Faraday Soc. 67 272) for the A (3)Sigma(+)(u) state, whereas the coefficient for collisions of the singlet states with C3H8 is estimated to be 3.0 x 10(-10) cm(3) s(-1) in order to explain the measured propane disappearance in the N-2/C3H8 mixture excited by the photo-triggered discharge. The hydrogen molecule is the measured most populated by-product and, also from the comparison between experimental results and model predictions, the most probable dissociation products of propane appear to be H-2 and C3H6. The propene molecule is also efficiently dissociated by the quenching processes of N-2 states, and probably leads to the production of hydrogen atoms and methyl radicals with equivalent probabilities. The kinetic model predicts that the carbon atom is distributed amongst numerous molecules, including HCN, CH4, C2H2, C2H4, C2H6 and C3H6.