Abstract
Aqueous phase reforming of sorbitol was carried out in a 1.7 m long, 320 μm ID microchannel reactor with a 5 μm Pt-based washcoated catalyst layer, combined with nitrogen stripping. The performance of this microchannel reactor is correlated to the mass transfer properties, reaction kinetics, hydrogen selectivity and product distribution. Mass transfer does not affect the rate of sorbitol consumption, which is limited by the kinetics of the reforming reaction. Mass transfer significantly affects the hydrogen selectivity and the product distribution. The rapid consumption of hydrogen in side reactions at the catalyst surface is prevented by a fast mass transfer of hydrogen from the catalyst site to the gas phase in the microchannel reactor. This results in a decrease of the concentration of hydrogen at the catalyst surface, which was found to enhance the desired reforming reaction rate at the expense of the undesired hydrogen consuming reactions. Compared to a fixed bed reactor, the selectivity to hydrogen in the microchannel reactor was increased by a factor of 2. The yield of side products (mainly C3 and heavier hydrodeoxygenated species) was suppressed while the yield of hydrogen was increased from 1.4 to 4 moles per mole of sorbitol fed.
Highlights
The decentralized conversion of biomass to hydrogen is an attractive alternative to feed highly efficient polymer electrolyte membrane (PEM) fuel cells for power generation.[1]
SÀ1 a Liquid–solid mass transfer coefficient estimated from correlations of Wakao et al.[31] for the fixed bed reactor and Kreutzer et al.[24] for the microchannel. b Thiele modulus calculated assuming the first order reaction as f = L(k/De)0.5, where L = particle diameter/6 for the bulk catalyst, L = coating thickness for the washcoated microchannel, and De is the effective diffusivity coefficient. c Reaction rate constant estimated from experimental data. d Reaction rate constant approximated using the kinetic model of Brahme and Doralswamy.[32,33] e Solid–gas mass transfer coefficient estimated from correlations of Kreutzer et al.[24] for the microchannel
The Pt-based washcoated microchannel reactor for aqueous phase reforming of sorbitol, combined with nitrogen stripping, has excellent mass transfer from the catalyst active site to the inert gas phase, which aided the rapid removal of hydrogen from the catalyst surface and limited its availability to participate in undesired hydrogenation reactions
Summary
The decentralized conversion of biomass to hydrogen is an attractive alternative to feed highly efficient polymer electrolyte membrane (PEM) fuel cells for power generation.[1]. Rearrangement reactions may occur given the high functionality of the intermediate products and the combined catalytic effect of the active metal, the support and the liquid medium. These reactions represent an overall consumption of hydrogen and result in the formation of a significant amount of liquid phase water-soluble oxygenated products, and eventually alkanes.[10,11,12] The complexity of this
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