Role of quenching of metastable states in acetaldehyde decomposition by a non-equilibrium nitrogen plasma at sub-atmospheric pressure

• Published in: Journal of physics. D, Applied physics Applied physics, 2013-03, Vol.46 (10), p.105202-1-16
• Main Authors: Faider, W, Pasquiers, S, Blin-Simiand, N, Magne, L
• Format: Article
• Language: English
• Subjects: acetaldehyde; Electric discharges; environmental application; Exact sciences and technology; nitrogen metastable states; photo-triggered discharge; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; plasma kinetic; Plasma kinetic equations; Plasma properties; Sub-atmospheric pressure non-thermal plasmas
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/46/10/105202

A photo-triggered discharge is used to study the decomposition processes of acetaldehyde in a high-pressure (460 mbar) nitrogen plasma, for a concentration of CH3CHO ranging from 500 up to 5000 ppm. Results of chromatographic measurements are compared with predictions of a self-consistent discharge and plasma kinetic model, for the primary molecule and for a number of detected by-products: H2, CH4, C2H2, C2H4, C2H6, CO and CH3COCH3. The main by-products are H2, CH4 and CO. It is proposed that CH3CHO mainly decomposes owing to quenching collisions of metastable states of the nitrogen molecule. The estimated coefficients for the quenching of is 4.2 × 10−11 cm3 s−1, assuming that the coefficient for the singlet states equals the one previously known for the quenching of N2(a′) by ethene, i.e. 4.0 × 10−10 cm3 s−1. A value of 6.5 × 10−11 cm3 s−1 constitutes a maximum for and a minimum for N2(a′). The most probable exit routes (and the branching ratios) for the dissociation process of CH3CHO are CH3 + HCO (45%), CH4 + CO (30%), CH2CO + H2 (17%) and CH3CO + H (8%), as regards . For singlet states, a break of the double C = O bond occurs and the branching ratios are 15% for both exit channels producing C2H2 and C2H4 together with the oxygen atom. The model predictions for concentration values of C2H6 and CH3COCH3 are in good accordance with measurements, supporting the proposed dissociation pathways that lead to the production of methyl and acetyl radicals.