Methanol oxidation in a flow reactor: Implications for the branching ratio of the CH₃OH+OH reaction

Abstract

The oxidation of methanol in a flow reactor has been studied experimentally under diluted, fuel-lean conditions at 650-1350 K, over a wide range of O 2 concentrations (1%-16%), and with and without the presence of nitric oxide. The reaction is initiated above 900 K, with the oxidation rate decreasing slightly with the increasing O 2 concentration. Addition of NO results in a mutually promoted oxidation of CH 3 OH and NO in the 750-1100 K range. The experimental results are interpreted in terms of a revised chemical kinetic model. Owing to the high sensitivity of the mutual sensitization of CH 3 OH and NO oxidation to the partitioning of CH 3 O and CH 2 OH, the CH 3 OH + OH branching fraction could be estimated as α = 0.10 ± 0.05 at 990 K. Combined with low-temperature measurements, this value implies a branching fraction that is largely independent of temperature. It is in good agreement with recent theoretical estimates, but considerably lower than values employed in previous modeling studies. Modeling predictions with the present chemical kinetic model is in quantitative agreement with experimental results below 1100 K, but at higher temperatures and high O 2 concentration the model underpredicts the oxidation rate.

Experimental and Kinetic Modeling Study of Methanol Ignition and Oxidation at High Pressure

“…Some CO 2 is also produced directly from the formyl radical by the reaction with HO 2 under fuel-rich conditions at 20 bar, and from CO, with HOCO as an intermediate species, under stoichiometric and fuel-lean conditions. The main reaction pathways under the present conditions are consistent with those reported for atmospheric pressure [13][14][15]. Unlike unsaturated fuels such as ethylene [45], the high pressure does not introduce additional oxidation pathways for methanol because addition reactions of OH and O 2 are not important.…”

“…These reactions yield hydroxymethyl and methoxy radicals, with the former radical being predominant. As expected [13][14][15], the hydroxymethyl radical mainly react with oxygen (R18), while methoxy undergoes thermal decomposition (R19). However, due to the larger value of k 27 in the present work, compared to previous modeling studies, the reaction of CH 3 O with O 2 (R27) becomes competitive under lean conditions.…”

“…The mechanism used in the present study is based on the atmospheric pressure methanol schemes by the authors [14,15], drawing also on previous high pressure work on oxidation of CO and CH 4 [18,20,21]. The methanol subset has been updated with results from recent theoretical work [22][23][24] and from ab initio calculations and RRKM analysis made as part of the present work on reactions of CH 2 OH and CH 3 O (dissociation, isomerization, reaction with O 2 ).…”

“…Laboratory experiments allow more controlled conditions compared to tests in engines; methanol oxidation has been studied in flames [6][7][8], stirred reactors [9], static reactors [10,11], flow reactors [12][13][14][15], Rapid Compression Machines [16], and shock tubes [17]. Of these studies, only three have been carried out at elevated pressures, i.e.…”

The effect of oxygen and volatile combustibles on the sulphation of gaseous KCl

“…The oxidation subsets were compiled and validated against a broad range of CO 2 and O 2 concentrations by Glarborg and Bendtsen [15]. Their mechanism is based mostly on work by previous authors on oxidation of CO/H 2 [32], CH 2 O [33], CH 3 OH [34], and C 2 -C 3 hydrocarbons [35][36][37][38][39]. Mech B is compiled in the present work and has never been validated as whole, although the subsets are validated for their individual use.…”