Experimental Kinetic Study of the Reactions of Hydroxyl Radicals With Three Oxymethylene Ethers and With 1,3,5-Trioxane, Tetrahydrofuran, and Tetrahydrofuran-d8

Abstract

Polyoxymethylene dimethyl ethers, CH₃O(CH₂O)_nCH₃ with n ≥ 1 (abbreviated in the literature also as OME-n, PODEn, POMDMEn, or OMDMEn) are currently discussed as renewable fuels. Despite fuel + OH reactions are crucial for the combustion chemistry and atmospheric degradation of fuels, experimental kinetic data on OME-n + OH do not exist in the literature for n > 1; only estimated or theoretically calculated values are available. In the present work, we present an experimental kinetic study of the reactions OH + OME-2 and OH + OME-3. For verification and comparison, identical experiments were also performed on the somewhat better-known reactions of OH with OME-1 and with the cyclic ethers 1,3,5-trioxane (TRI, C₃H₆O₃) and tetrahydrofuran (THF, C₄H₈O) as well as its perdeuterated isotopologue (THF-d8, C₄D₈O). Rate coefficients were determined as a function of temperature and pressure in slow-flow reactors with the pulsed laser photolysis/laser-induced fluorescence technique. The experiments were performed at temperatures between 250 and 520 K and pressures ranging from 0.2 to 5 bar (OME-2), 0.2 to 10 bar (OME-3), 0.2 to 0.9 bar (OME-1, TRI), and 0.2 to 0.8 bar (THF, THF-d8) with helium as bath gas. No significant pressure dependence of the rate coefficients was observed. The generally very weak temperature dependences are parameterized in Arrhenius form. Structural influences on reactivity are discussed and compared with predictions from structure-reactivity relationships.