Detailed Product Analysis during Low- and Intermediate-Temperature Oxidation of Ethylcyclohexane

Abstract

An experimental study of the oxidation of ethylcyclohexane has been performed in a jet-stirred reactor with online gas chromatography, under quasi-atmospheric pressure (800 Torr), at temperatures ranging from 500 to 1100 K (low- and intermediate-temperature zone including the negative temperature coefficient area), at a residence time of 2 s, and for three equivalence ratios (0.25, 1, and 2). Ethylcyclohexane displays important low-temperature reactivity with a well-marked negative temperature coefficient behavior. In addition to 47 products with a mass lower than ethylcyclohexane which have been quantified, many species with a C(8)H(14)O formula (molecular weight of 126) were detected by GC-MS and 7 of them were quantified. These molecules are cyclic ethers, ketones, and aldehydes with the same carbon skeleton as the reactant. Experiments were also carried on under the same conditions for two other C(8) hydrocarbons, n-octane and 1-octene, showing that the reactivity of ethylcyclohexane is close to that of the alkene and lower than that of the alkane. Simulations using a detailed kinetic model of the literature allow a good prediction of the global reactivity and of the main hydrocarbon products for temperatures above 800 K. The main reaction channels leading to the observed reaction products at both low (below 800 K) and intermediate temperature (above 800 K) are discussed.

Progress in Understanding Low‐Temperature Organic Compound Oxidation Using a Jet‐Stirred Reactor

“…This is illustrated in Fig. , which shows the cyclic ethers and unsaturated ketone (oct‐7‐en‐3‐one) formed from ethyl‐cyclohexane.…”

“…More recently, not only oxolanes but also oxiranes, oxetanes, and tetrahydropyrans have been observed upon low‐temperature oxidation of propane, n ‐butane , hexane isomers , n ‐heptane , n ‐decane, and n ‐hexadecane. Cyclic ether formation was also observed with other types of fuels: naphthenes , olefins , and esters.…”

“…This study allowed the existing set of mass spectra concerning cyclic ethers to be completed and rules for the fragmentation of these species in electronic impact mass spectrometry to be derived. These rules were useful for the identification of cyclic ethers formed during the low‐temperature oxidation of fuels having more complex structure than n ‐alkanes, such as methyl esters (methyl decanoate and methyl palmitate, branched isomers of hexane , hexene isomers, and ethyl‐cyclohexane.…”

“…As far as naphthenic compounds are concerned, bicyclic ethers are observed except those corresponding to oxetanes (four‐membered ring ethers) because this type of species is unstable and opens through a concerted mechanism to yield unsaturated ketones. This is illustrated in Fig.…”

Experimental and modeling study of 1-octene jet-stirred reactor oxidation

“…However, the current mechanism lacks of low-temperature reactions related to ethyl-cyclohexane and ethyl-cyclohexenes, for which very few papers can be found in the literature. Although recent experimental, theoretical and modeling studies of ethylcyclohexane oxidation were recently published [43][44][45] and detailed kinetic models are available for the high-temperature oxidation and pyrolysis of this molecule [45], there is still no validated model for its low-temperature oxidation. As a result, the production of ethylcyclohexenes is largely overpredicted at temperatures below 800 K; by contrast, the predictions at high temperatures are close to the experimental data.…”