A shock tube kinetic study on the branching ratio of methanol + OH reaction

Methanol (CHOH) is the simplest alcohol and is considered to be a future fuel, produced by solar-driven reduction of carbon dioxide. The reaction of methanol and hydroxyl radicals is important in both combustion and atmospheric systems because this reaction is the dominant consumption pathway for methanol oxida- tion. Hydrogen abstraction at the CH or OH site of CH OH leads to different radical intermediates. The relative importance of these two channels is critical for combustion modeling as the subsequent chemistries of the product radicals (CHO and CHOH) are markedly different. In this work, we measured overall rate coefficients for the reaction of methanol (CHOH), methanol-d (CD OH) and methanol-d (CH DOH) with OH radicals over the temperature range of 900 -1300 K and pressures near 1.3 atm by employing shock tube/UV laser absorption technique. Combining our results with literature data, we recommend following three-parameter Arrhenius expressions (cm molecule s ): k1 (CH3OH + OH ) = 3.25 × 10 (T/300 K) exp(297.8K/T) 210 - 1344 K k2 (CDOH + OH ) = 4.69 × 10 (T/300 K) exp (-59.8K/T)293 - 1287 K Using our measured total rate coefficients, we determined site-specific H-abstraction rate coefficients and hence, branching ratios of the two abstraction channels. Our results show that abstraction at the CH site is the dominant channel, contributing more than 80% throughout our temperature range. Our calculated site-specific rate coefficients (per H atom) over 900-1300K are given by (cm molecule s ): k (CH2OH channel) = 2.55 × 10 exp (-2287.1 K/T ) k (CH3O channel) = 4.30 × 10 exp (-3463.2 K/T )