AbstractThe thermal behavior of acetaldehyde, at pressures of the order of 100 microns, has been investigated, up to 750°C, in a quartz reactor connected to a TOF Bendix mass spectrometer. In those conditions, no methane formation has been observed. Two important processes are the formation of acetylene and water, possibly by unimolecular decomposition of acetaldehyde, and the formation of ethylene and water, probably by decomposition of ethanol, a secundary product. The primary step of acetaldehyde decomposition is discussed, as well as the overall order of the reaction. At the low pressures used in this work, data are consistent with a first order reaction, rather than 3/2 or 2, and an activation energy of 57 kcal/m is proposed.