Acetaldehyde autoignition temperature

Catalysts such as iron oxides cause isomeriza tion of the ethylene oxide to acetaldehyde with the evolution of heat. The acetaldehyde has a much lower autoignition temperature in air than does ethylene oxide, and the two effects may lead to hot-spot ignition (190,191). 

These materials are very easily autoxidised and often have a low autoignition temperature. It is reported that many of the less volatile liquid aldehydes will eventually inflame if left exposed to air on an absorbent surface. The mechanism is undoubtedly similar to that giving rise to easy ignition in the air-oxidation of acetaldehyde and propionaldehyde initial formation of a peroxy-acid which catalyses the further oxidation[l]. Autoignition temperatures of lower aldehydes are much reduced by pressure, but appear to depend little on oxygen content. The effect is worst in the presence of free liquid, in which initial oxidation appears to occur, possibly catalysed by iron, followed by ignition of the vapour phase [2], An acetaldehyde/rust mix exploded at room temperature on increasing the air pressure to 7 bar. 

The qualitative agreement of the autoignition values with relative thermal stability can be illustrated with the compounds acetone and acetaldehyde. Acetone has an autoignition temperature of 538°C, whereas the value for acetaldehyde is... 

Autoignition temperatures of these aldehydes reflect the same pattern, as presented in Table 5.2. Flammability of an aldehyde decreases with substitution in the alkyl group. Acetaldehyde is extremely flammable, with flash point (closed cup) —38°C (-36.4°F) and vapor pressure 750 torr, while its chloro-substituted product, chloroacetalde-hyde, is a combustible liquid with a flash point of 87.8°C (190.04°F) and a vapor pressure of 100 torr. 

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