The Gas Phase Oxidation of Acetaldehyde Reaction Mechanism and Kinetics

The mechanism of the low temperature oxidation of gaseous acetaldehyde was investigated in the temperature range of ۱ ۵۰-۴۰۰?°C. The minor, intermediate and major products were identified and measured quantitatively by sampling directly into the ionization chamber of an MS۱۰-C۲ mass spectrometer from the reactor. The formation of H۲O, CO, CO۲, HCOOH, H۲, HCHO, CH۳COOH and CH۳OH as the major products, the presence of H۲O۲, (CH۳)۲C۰, (CH۳CO)۲O۲, (CH۳CO)۲ and CH۴ as the minor products, the production of the unstable product CH۳OOH and the existence of peracetic acid as a degenerate branching intermediate were confirmed. The exprimental results led to a proposed degenrate branched chain mechanism for the gas-phase oxidation of acetaldehyde. This paper attempts to explain the kinetics in the region of lower slow combustion (at ۱۵۰?°C), cool flames, and upper slow combustion (at ۴۰۰?°C) with an initial total pressure between ۴ to ۱۲ cm., Hg. The major products detected were (in order of concentrations): H۲O > CO > CO۲ > H۲ > CH۳COOH > HCHO > HCOOH The reaction orders obtained were ۰.۳۸ with respect to oxygen pressure and ۱.۸۵ with respect to acetadehyde pressure for maximum rate. The reaction rate was found to be independent of the total pressure. In temperature range of ۱ ۵۰-۲۵۰?°C, the reaction was accompanied by a pressure decrease, while in ۲۷۵-۴۰۰?°C, a pressure increase was observed. The low activation energies of ۵۳.۵۰ KJ mole-۱ (in ۱۵۰-۲۵۰?°C region) and ۵۷ KJ mole-۱. (in ۲۷۵-۴۰۰?°C region) indicate that the reaction is a degenerate branching chain type for which the net-branching factor is correlated with the acetaldehyde pressure and the activation energy as f = K [PCH۳CHO]۰.۸exp[-E/RT]. The kinetics data obtained by the mass spectrometer were analyzed by computer programing and the results were presented by the appropriate kinetics plots.

کلیدواژه ها:

Combustion ، Thermal Oxidation ، Degenerate Branching ، Organic Fuels ، Induction Period