The gaseous oxidation of aliphatic alcohols. I. Ethyl alcohol: the products formed in the early stages

Abstract

A detailed analytical investigation has been made of the reactions occurring during the early stages of the oxidation of ethyl alcohol (ethanol) in the temperature region 270 to 370° C. During an induction period the alcohol is converted quantitatively into acetaldehyde until a critical concentration of this intermediate has accumulated. The pressure then begins to rise autocatalytically, and methanol, formaldehyde and carbon monoxide become detectable; evidence is presented to show that these compounds arise from the further oxidation of acetaldehyde. The amount of ethanol consumed and of acetaldehyde formed at the end of the induction period are largely independent of the initial reactant pressures, except at low pressures of the alcohol. A study of the effect of added acetaldehyde shows that the minimum quantity required to eliminate the induction period is the same as that normally present at the end of the induction period. Hydrogen peroxide is the only product, other than acetaldehyde, detected during the induction period. Under optimum surface conditions the yields of hydrogen peroxide are equivalent to those of the aldehyde. A moderate increase in surface shortens the induction period, but a further increase retards reaction. In vessels of large surface: volume ratio, the yields of hydrogen peroxide are much reduced, while in a potassium chloride-coated vessel peroxides are invariably absent; in each case, the other products are unchanged. The mechanisms of the chain-initiating and propagating reactions are considered and the role of the surface in initiating and terminating chains is discussed.