KHALED, Fethi; Giri, Binod; Farooq, Aamir(Proceedings of the Combustion Institute, Elsevier BV, 2016-10-11)[Article]
Isobutene is an important intermediate formed during the oxidation of branched alkanes. It also appears as a byproduct during the combustion of methyl-tert-butyl-ether (MTBE) which is used as octane enhancer in gasolines. To understand better the oxidation kinetics of isobutene, we have measured the rate coefficients for the reaction of OH radicals with isobutene (HCC(CH)) behind reflected shock waves over the temperature range of 830-1289K and pressures near 1.5atm. The reaction progress was followed by measuring mole fraction of OH radicals near 306.7nm using UV laser absorption technique. Three deuterated isotopes, isobutene-1-d2 (DCC(CH)), isobutene-3-d6 (HCC(CD)) and isobutene-d8 (DCC(CD)) were employed to elucidate branching ratios of the allylic and vinylic H-abstraction from isobutene by OH radicals. H-abstraction from the allylic sites was found to be dominant and constituted about 75% of the total rate in the entire temperature range of the current work. The derived three-parameter Arrhenius expressions for site-specific H- and D- abstraction rates over 830-1289K are (units:cm mol s):k3,H=6.98×106(TK)1.77exp(-136.6KT) k3,D=4.42×106(TK)1.8exp(-361.7KT) k1,H=6.25×105(TK)2.16exp(-711.6KT) k1,D=3.13×107(TK)1.67exp(-1814KT) The subscript of . k identifies the position of H or D atom in isobutene according to the IUPAC nomenclature of alkenes.
This work reports rate coefficients of the thermal unimolecular decomposition reaction of ethyl propionate (EP) behind reflected shock waves over the temperature range of 976–1300 K and pressures of 825–1875 Torr. The reaction progress was monitored by detecting CH near 10.532 μm using CO gas laser absorption. In addition, G3//MP2/aug-cc-pVDZ and master equation calculations were performed to assess the pressure- and temperature-dependence of the reaction. Our calculations revealed that CH elimination occurs via a six-centered retro-ene transition state. Our measured rate data are close to the high-pressure limit and showed no discernable temperature fall off.
Giri, Binod; KHALED, Fethi; Szőri, Milán; Viskolcz, Béla; Farooq, Aamir(Proceedings of the Combustion Institute, Elsevier BV, 2016-06-24)[Article]
Tetrahydrofuran (CHO, 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 cmmols) are recommended for combustion modeling in the temperature range 800-1350 K: . k1(T)=4.11×1040.16em0ex(TK)2.69exp(1316.80.16em0exKT)2.em0ex0.16em0ex(THF+OH→Products) . k2(T)=6.930.16em0ex×10110.16em0ex(TK)0.41exp(-106.80.16em0exKT)2.em0ex0.16em0ex(THF+OH→THF-R20.16em0ex+H2O) . k3(T)=4.120.16em0ex×1030.16em0ex(TK)3.02exp(456.90.16em0exKT)2.em0ex0.16em0ex(THF+OH→THF-R30.16em0ex+H2O) . .
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