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Effect of micropores diffusion on kinetics of CH4 decomposition over a wood-derived carbon catalyst

Dufour A., Cembrzynski T., Ouartassi B., Broust F., Fierro V., Zoulalian A.. 2009. Applied Catalysis. A, General, 360 : p. 120-125.

In order to optimise hydrogen production from biomass gasification, catalytic conversion of methane contained in a surrogate biomass syngas (CH4 14%; CO 19%; CO2 14%; H2 16%; H2O 30%; N2 7%) is investigated over a fixed bed of porous wood char as a function of temperature (800-1000 8C) and space time (1.6-6.2 min g L_1). Determination of Thiele modulus evidences a change of kinetic regime from chemically- to diffusion-controlled when the temperature increases; this finding is particularly relevant when porous chars having an average pore width of 1 nm are used as catalysts. Mass diffusion transfers are accounted for by a model introducing an internal effectiveness factor. Knudsen diffusion in micropores is shown to limit the conversion rate of methane per unit mass of catalyst, and explains why such a rate is not proportional to the BET surface area, especially when the latter is higher than typically 300 m2/g. It is concluded that diffusion limitations in micropores should be taken into account, otherwise underestimated activation energy and intrinsic kinetic constant are obtained in some experimental conditions. (Résumé d'auteur)

Mots-clés : gazéification; charbon de bois; biomasse; hydrogène

Thématique : Technologie des produits forestiers; Sources d'énergie renouvelable

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