Shock-tube study of acetaldehyde pyrolysis

The high temperature pyrolysis of acetaldehyde was studied behind reflected shock waves using a single-pulse (reaction time between 1.5 and 2.9 ms), time-resolved IR-absorption (3.39 mu m) and UV-absorption (200 nm) methods. The studies were done using mixtures, 5.0% CH3CHO, 4.0% CH3CHO and 2.0% CH3CHO diluted with Ar, in the temperature range 1000 - 1700 K at total pressures between 1.2 and 3.0 atm. From a computer-simulation study, a 58-reaction mechanism that could explain all our data was constructed. The rate constant expressions of reactions (1) - (11) at high temperatures in the CH3CHO pyrolysis were discussed. It was found that, under our experimental conditions, reactions (1), (3) and (4) played an important role as the initiation reaction and reactions (6) and (8) also played a role in the CH3CHO pyrolysis. CH3CHO -> CH3 + CHO (1) CH3CHO -> CH3CO + H (2) CH3CHO -> CH4 + CO (3) CH3CHO -> CH2CO + H-2 (4) CH3CHO + H -> CH3CO + H-2 (5) CH3CHO + H -> CH2CHO + H-2 (6) CH3CHO + CH3 -> CH3CO + CH4 (7) CH3CHO + CH3 -> CH2CHO + CH4 (8) CH3CO -> CH3 + CO (9) CH3CO -> CH2CO + H (10) CH2CHO -> CH2CO + H (11).