The experiments reported here demonstrate that during propene autoxidation, some propene oxide is formed via the oxidation of the primary product, acetaldehyde. Propene oxide selectivity from a flow reactor can be further enhanced by recycling the acetaldehyde produced by the reaction of propene and oxygen, giving an eventual stabilisation of the acetaldehyde concentration in the reactor and no net production of the aldehyde. Propene oxide yield during acetaldehyde co-oxidation experiments can be maximised by lowering the temperature to ensure that all acetyl radicals add oxygen to give the acetylperoxy radical, an efficient epoxidising agent.

Recycling acetaldehyde gives an increase in the overall rate of reaction at a given temperature, or conversely allows a lower temperature to be used for a given rate of reaction, giving a further increase in epoxide selectivity (Stark and Waddington, 1995).