Effect of micropores diffusion on kinetics of CH4 decomposition over a wood-derived carbon catalyst
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.
| Main Authors: | , , , , , |
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| Format: | article biblioteca |
| Language: | eng |
| Subjects: | K50 - Technologie des produits forestiers, P06 - Sources d'énergie renouvelable, hydrogène, biomasse, charbon de bois, gazéification, http://aims.fao.org/aos/agrovoc/c_3724, http://aims.fao.org/aos/agrovoc/c_926, http://aims.fao.org/aos/agrovoc/c_1503, http://aims.fao.org/aos/agrovoc/c_34000, |
| Online Access: | http://agritrop.cirad.fr/548997/ http://agritrop.cirad.fr/548997/1/document_548997.pdf |
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