Initial Observations of Ketene in Flow Reactor Kinetic Studies

Variable Pressure Flow Reactor (VPFR) experiments were conducted for ethene/methane mixtures utilizing both FTIR analyses of extracted gas samples and in situ line-of-sight far-UV absorption measurements. In situ observations of ketene prompted the re-evaluation of the presence of ketene in previous acetaldehyde oxidation and pyrolysis experiments in the VPFR. In these experiments only extractive sampling (with FTIR analysis) had been used and ketene had not been observed. In reconsidering the previously obtained FTIR spectra, ketene is shown to be not only present, but also present in levels on the order of other important acetaldehyde reaction intermediates, such as CH₂O, H₂, and C₂H₄. Through a comparison of the results of the in situ and extractive ketene diagnostics, it has been shown that significant losses of ketene can occur in sample handling and that the principal ketene loss mechanism appears to be surface dominated. It is likely that this difficulty in ketene sampling, common to many experimental systems, has led to the omission of important ketene pathways in many kinetic models.