Direct measurements of the reaction OH + CH₂O → HCO + H₂O at high temperatures

Abstract

The reaction of hydroxyl [OH] radicals with formaldehyde [CH 2 O] was studied at temperatures ranging from 934 K to 1670 K behind reflected shock waves at an average total pressure of 1.6 atm. OH radicals were produced by shock-heating tert-butyl hydroperoxide [(CH 3 ) 3 CO OH], while 1,3,5-trioxane [(CH 2 O) 3 ] was used in the preshock mixtures to generate reproducible levels of CH 2 O. OH concentration time-histories were inferred from laser absorption using the well-characterized R 1 (5) line of the OH A-X (0, 0) band near 306.7 nm. Detailed error analyses, taking into account both experimental and mechanism-induced contributions, yielded uncertainty estimates of ±25% at 1595 K and ±15% at 1229 K for the rate of the reaction between CH 2 O and OH. These uncertainties are substantially lower than the factor of two uncertainty currently used for this reaction at high temperatures. The rate constants were fit with the recent low-temperature measurements of Sivakumaran et al. (Phys Chem Chem Phys 2003,5,4821-4827) to the three-parameter form shown below; this fit reconciles experimental data on the title reaction at low, intermediate, and high temperatures (200-1670 K).The reaction of OH with CH 2 O was also studied using quantum chemical methods at the CCSD(T) level of theory using the 6-311++G(d,p) basis set. The transition state for the H-atom metathesis reaction was located, and reaction rate coefficients were calculated. Reasonable agreement with the experimental measurements was obtained.

Chemical Kinetics in Support of Syngas Turbine Combustion

“…The recommended rate constants [79,80] are within a factor of 2 of those suggested by Tsang and Hampson [81].…”

High‐temperature shock tube study of the reactions CH3 + OH → products and CH3OH + Ar → products

“…Preshock mixture samples were analyzed in a gas chromatograph using a flame ionization detector to check the possible decomposition of TBHP in the gas phase in the mixing chamber. These measurements show that less than 0.30 ppm TBHP decomposed to form acetone [11], and this has no discernible effect on our rate coefficient determination.…”

“…Further details of the shock tube setup are available elsewhere [2,11,12]. Incident shock velocity measurements were made using five PZT pressure transducers and four programmable timer counters, and linearly extrapolated to the endwall.…”

“…The diagnostic system has been described in detail elsewhere [11,12]. A 532-nm solid-state laser was used to pump a tunable ring-dye laser cavity generating visible light at ∼614 nm.…”

“…Since GC analyses of the preshock reactant mixtures show that TBHP does not decompose in the gas phase in the mixing tank, the measurement of OH behind the reflected shock is an accurate indicator of the concentration of TBHP in the shock tube. In the kinetic modeling, an initial TBHP concentration that resulted in the measured peak OH yield was used; the approach is described in greater detail elsewhere [11].…”