Oxidation of propionaldehyde in KCl-coated vessels

Abstract

The rate of oxidation of C₂H₅CHO at 440°C in vessels freshly coated with KCl is higher than in boric-acid-coated vessels, and is highly erratic. The rate decreases considerably as the vessel is aged by repeated runs, and reasonable reproducibility can eventually be obtained. In contrast to boric-acid-coated vessels, the reaction is not autocatalytic, consistent with the low H₂O₂ concentration, which indicates that H₂O₂ is destroyed at the surface with considerable efficiency. The lower initial rate in KCl-coated vessels indicates that HO₂ is also destroyed at the surface with considerable efficiency, and a computer treatment has enabled lower-limit estimates of both surface velocity constants to be made. The yields of CH₃CHO, which are small in boric-acid-coated vessels, are much higher than expected in fresh KCl-coated-vessels, and decrease as the rate decreases due to ageing of the surface. The high yield is attributed to a heterogeneous reaction forming both C₂H₄ and CH₃CHO in almost equal proportions, and which, even in the aged vessel, contributes about 45 % to the rate.