NONCATALYTIC PARTIAL OXIDATION OF METHANE INTO SYNGAS OVER A WIDE TEMPERATURE RANGE

Abstract

Noncatalytic partial oxidation of methane has been studied over a wide temperature range from 823 to 1531 K using two flow reactors. Highly diluted fuel-rich CH₄/O₂/N₂ mixtures were reacted in uncoated tubular flow reactors at 1.2 atm. Residence time was varied from 1 to 164 s. Major and minor products of the partial oxidation were measured using a gas chromatograph. Kinetic modeling was performed to simulate experiments and key rate-controlling reactions were revealed by sensitivity analysis. It was found that chain-branching reaction H + O₂ = OH + O, recombination CH₃ + CH₃ (+M) = C₂H₆ (+M), and methyl radical oxidation CH₃ + O₂ = CH₂O + OH govern the overall rate of the process at short residence times. Recent measurements of these rate constants were analyzed and appropriate modifications in the detailed reaction mechanism were proposed. The model was adjusted to reproduce the measurements accurately at short residence times. At longer residence times, a significant impact of the heterogeneous reactions leading to inhibition of the overall process was observed. The model developed in the present study correctly reproduced temporal profiles and final compositions of the products over the entire range of temperatures and the initial mixture compositions.

Keywords:

• methane
• partial oxidation
• reaction mechanisms
• syngas
• reforming

The experimental work was performed in the Research Laboratory of Alinta Ltd. of Western Australia. Part of this work has been financially supported by the European Government via the “Safekinex” Project EVG1-CT-2002-00072. Curtin University of Technology is gratefully acknowledged for the award of the C.Y. O'Connor Fellowship to A.A. Konnov, which made this joint work possible.

Notes

^a The falloff behavior of this reaction is expressed in the form used by Baulch et al. (1992) and others.

^b All other species have efficiencies equal to unity.