Abstract
The reactions of heptanone isomers, namely diisopropyl ketone (DIPK, k1), isopropyl propyl ketone (IPPK, k2), and dipropyl ketone (DPK, k3), with OH radicals play a crucial role in predicting their combustion behavior. We conducted the first high-temperature measurements of these reactions over the temperature range of 876 to 1328 K at pressures near 1 bar. The determined overall rate coefficients may be described as (unit of cm3molecule−1s−1):k1=2.13×10−10e(−2684T)k2=2.42×10−10e(−2733T)k3=2.84×10−10e(−2808T)Over the investigated high temperature range, all three reactions exhibit a positive temperature dependence, with activation energies ranging 5.3 to 5.6 kcal mol−1. We did not observe discernible pressure dependence within the pressure range of 0.66 to 1.66 bar. At 1250 K, DPK reacts with OH radicals 11 % faster than IPPK and 21 % faster than DIPK. Interestingly, compared to heptane, which reacts twice as fast, the presence of the C=O group significantly hinders the reactivity of the normal chain heptanone (DPK) towards OH radicals. Furthermore, the rate coefficients of OH + DIPK reaction in literature models underestimate the measured activation energy and overpredict the overall rate coefficients. To enhance the accuracy of SAR prediction for OH + ketone reactions, a multiplicative factor of 0.6 - 0.75 is suggested. Additionally, this study provides a site-specific expression for the tertiary CH bonds adjacent to the C=O bond in ketone molecules, expanding the applicability of the NNN (next-nearest-neighbor) prediction scheme to encompass larger branched ketones.
Published Version
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