Ignition of Mixtures of Aliphatic Aldehydes with Oxygen, Initiated by an Adsorbed Peroxide Compound
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Ignition of Mixtures of Aliphatic Aldehydes with Oxygen, Initiated by an Adsorbed Peroxide Compound A. S. Martirosyana,*, S. V. Tsarukyana, and I. A. Vardanyana aNalbandyan
Institute of Chemical Physics, National Academy of Sciences of Armenia, Yerevan, 0014 Armenia *e-mail: [email protected] Received November 13, 2019; revised November 13, 2019; accepted February 11, 2020
Abstract—Based on a joint review and discussion of data on the ignition of aldehyde–oxygen mixtures, initiated by an adsorbed peroxide compound upon heating, and on the heterogeneous interaction between RO2 peroxide radicals and an aldehyde, it is concluded that the constant temperature Ti of ignition in one range of changes in the amount of peroxide compound is due to the limited number of active centers on its surface because of its saturation with heterogeneous radical reactions. Keywords: ignition, aldehyde, surface, peroxide, peroxide radicals DOI: 10.1134/S0036024420100192
INTRODUCTION It was found in [1–6] that the nature of a surface on which RCO3H peroxyacid is adsorbed affects the temperature of ignition (Ti) of CH3CHO and C2H5CHO– oxygen mixtures in quartz reactors treated with different substances (KCl and H3BO3) upon heating. This effect manifests in a drop in Ti, in some cases down to room temperature. At the same time, it was found that Ti does not depend on the amount of the adsorbed peroxide compound in one range of its changes, which was inexplicable. However, recent studies [7–13] allow us to shed light on this phenomenon and make some refinements regarding the mechanism of this process. This is especially true with respect to experimental evidence of the possibility of heterogeneous interaction between an aldehyde and CH3O2 and C2H5O2 radicals [7, 10–12], and to the discovery of a correlation between the rate of interaction between peroxide radicals and an aldehyde and the Ti of aldehyde–oxygen mixtures on surfaces treated with KCl and H3BO3 [11, 12], testifying to the heterogeneous nature of ignition initiation. The aim of this work was therefore to clarify some features of the ignition of aldehyde–oxygen mixtures [1–6], initiated by an adsorbed peroxide compound that generates radicals upon heating. EXPERIMENTAL A typical pattern of ignition (Fig. 1) was studied using a mixture of C2H5CHO + O2 + C2H5CO3Hads and the heterogeneous radical decomposition of C2H5CO3H, which resulted in the formation of perox-
ide radicals from an amount of peroxyacid based on experimental data [6]. As is seen from Fig. 1, several characteristic regions of ignition (AB, BC, CD, and DE) can be distinguished, depending on the amounts (N) of adsorbed C2H5CO3H. Region AB is characterized by a sharp drop in the temperature of ignition when small amounts of peroxyacid are used. Region BC is characterized by the constancy of Ti. Then there is another sharp drop in Ti at high feeds of peroxyacid. Curve 1' shows the dependence of the yield in the volume of peroxide radicals formed during the heterogeneous radical decomposition of pero
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