Ketohydroperoxides and Korcek mechanism identified during the oxidation of dipropyl ether in a JSR by high-resolution mass spectrometry

Abstract

International audienceWith the growing interest for biomass-derived fuels the understanding of the combustion chemistry of ethers becomes of major scientific importance. Ethers usually develop strong cool flames at relatively low temperatures. Very complex processes occur there, with the formation of peroxidized intermediates such as ketohydroperoxides and highly oxidized molecules. Such chemicals are relatively unstable and difficult to analyze.We studied the low-temperature oxidation of dipropyl ether in a jet-stirred reactor. The experimental conditions were selected to maximize the production of ketohydroperoxides, based on the kinetic model of Serinyel et al. (2019). We oxidized 5000 ppm of dipropyl ether at 1 bar, T = 520–530 K, an equivalence ratio of 0.5, and at a residence time of 1 s. Analyses were performed on solubilized products of dipropyl ether oxidation in cooled acetonitrile. The samples were analyzed using soft HESI electrospray ionization (+/-) and an Orbitrap mass spectrometer (resolution: 140,000, mass accuracy RO2 QOOH; QOOH + O2 OOQOOH HOOQ’OOH followed by HOOQ’OOH + O2 (HOO)2Q’OO (i) (HOO)2POOH → OH + (HOO)2P=O (i.e., C6H12O6) and (ii) (HOO)2POOH + O2 → (HOO)3POO (HOO)3P’OOH → OH + (HOO)3P=O (i.e., C6H12O8).The so-called Korcek mechanism through which ketohydroperoxides are transformed into stable products, namely propanoic acid here, was also observed. Hydrogen–Deuterium exchange reactions using D2O served to confirm the presence of –OH groups in the products