An experimental and theoretical kinetic study of the reaction of OH radicals with tetrahydrofuran

Tetrahydrofuran (C4H8O, THF) and its alkylated derivatives of the cyclic ether family are considered to be promising future biofuels. They appear as important intermediates during the low-temperature oxidation of conventional hydrocarbon fuels and of heavy biofuels such as long-chain fatty acid methyl esters. The reaction of tetrahydrofuran with OH radicals was investigated in a shock tube, over a temperature range of 800-1340 K and at pressures near 1.5 bar. Hydroxyl radicals were generated by the rapid thermal decomposition of tert-butyl hydroperoxide, and a UV laser absorption technique was used to monitor the mole fraction of OH radicals. High-level CCSD(T)/cc-pV(D,T)Z//MP2/aug-cc-pVDZ quantum chemical calculations were performed to explore the chemistry of the THF + OH reaction system. Our calculations reveal that the THF + OH (R1) reaction proceeds via either direct or indirect H-abstraction from various sites, leading to the formation of tetrahydrofuran-2-yl (THF-R2) or tetrahydrofuran-3-yl (THF-R3) radicals and water. Theoretical kinetic analysis revealed that both channels are important under conditions relevant to combustion. To our knowledge, this is the first direct experimental and theoretical kinetic study of the reaction of tetrahydrofuran with OH radicals at high temperatures. The following theoretical rate expressions (in units of cm3mol−1s−1) are recommended for combustion modeling in the temperature range 800-1350 K: k1(T)=4.11×104(TK)2.69exp(1316.8KT)(THF+OH→Products)k2(T)=6.93×1011(TK)0.41exp(−106.8KT)(THF+OH→THF-R2+H2O)k3(T)=4.12×103(TK)3.02exp(456.9KT)(THF+OH→THF-R3+H2O)