A shock tube study of C4-C6 straight chain alkenes + OH reactions

Alkenes are known to be good octane boosters and they are major components of commercial fuels. Detailed theoretical calculations and direct kinetic measurements of elementary reactions of alkenes with combustion radicals are scarce for C4 alkenes and they are practically absent for C5 and larger alkenes. The overall rate coefficients for the reaction of OH radical with 1-butene (CH2CHCH2CH3, kI), 1-pentene (CH2CHCH2CH2-CH3, kII), cis/trans 2-pentene (CH3CHCHCH2CH3, kIII and kIV), 1-hexene (CH2CHCH2CH2CH2CH3, kV) and cis/trans 2-hexene (CH3CHCHCH2CH2CH3, kVI and kVII) were measured behind reflected shock waves over the temperature range of 833-1377 K and pressures near 1.5 atm. The reaction progress was followed by measuring mole fraction of OH radicals near 306.7 nm using UV laser absorption technique. It is found that the rate coefficients of OH + trans-2-alkenes are larger than those of OH + cis-2-alkenes, followed by OH + 1-alkenes. The derived Arrhenius expressions for the overall rate coefficients (in cm3.mol−1.s−1) are:kI=(4.83±0.03)104.T2.72±0.01.exp(940.8±2.9cal/molRT)(946K−1256K)kII=(5.66±0.54)10−1.T4.14±0.80.exp(4334±227cal/molRT)(875K−1379K)kIII=(3.25±0.12)104.T2.76±0.5.exp(1962±83cal/molRT)(877K−1336K)kIV=(3.42±0.09)104.T2.76±0.5.exp(1995±59cal/molRT)(833K−1265K)kV=(7.65±0.58)10−4.T5±1.exp(5840±175cal/molRT)(836K−1387K)kVI=(2.58±0.06)106.T2.17±0.37.exp(1461±55cal/molRT)(891K−1357K)kVII=(3.08±0.05)106.T2.18±0.37.exp(1317±38cal/molRT)(881K−1377K)