Hydrogen produced from renewable energy sources is of great interest as an alternative to fossil fuels and as a means for power generation via fuel cells. The aqueous fraction of bio-oil can be effectively reformed to hydrogen-rich streams in the presence of active catalytic materials. In this paper, we present the experimental work carried out in a fixed bed reactor for the reforming of bio-oil. The performance of the reactor was studied at various conditions and compared to the values theoretically predicted by thermodynamic equilibrium. The effect of reaction temperature, steam-to-carbon ratio in the feed, and space velocity was investigated in the presence of a commercial nickel catalyst. Runs were conducted with acetic acid, acetone, and ethylene glycol, representative model compounds of bio-oil, and the aqueous phase of a real bio-oil derived from beech wood. The results of the selected model compounds show that all can be effectively reformed with hydrogen yields up to 90% at reaction temperatures higher than 600 °C and steam-to-carbon ratios higher than 3. The reforming of the aqueous fraction of bio-oil proved to be more difficult, with the hydrogen yield fluctuating at about 60%. The most serious problem encountered in these experiments is coking. The formation of carbonaceous deposits in the upper part of the catalyst zone limits the reforming time and necessitates frequent regeneration of the catalyst.

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A microkinetic model for oxidative coupling of methane (OCM) has been developed that comprises a reaction network of 39 gas-phase and 26 catalytic elementary steps. It has been implemented in a heterogeneous reactor model that explicitly accounts for the interactions between gas phase and surface species. Concentration gradients arising from mass transport limitations are found to develop inside the catalyst pellet for all intermediates (i.e., surface and gas-phase) even under an intrinsic kinetics regime for the molecules and clearly affect the C 2 selectivity. Special attention has been devoted to the reduction of the number of adjustable parameters in the model and the a priori determination of thermodynamic as well as kinetic parameters. A contribution analysis is conducted in order to elucidate the complex reaction pathways in OCM that lead to the desired products. Apart from the methyl radicals that couple to an extent of almost 70% in the void space between the pellets, the catalyst pellet accounts for the majority of molecules and radicals conversion, which are produced on the surface and further interact either in the catalyst pores or with other surface species. Almost 95% of CH 4 consumption and more than half of the C 2 H 6 production take place inside the catalyst pellet. A similar analysis is applied to understand the effect of various textural properties of catalysts on the performance of OCM, for example, increasing the catalyst porosity is found beneficial for the C 2 yield, as long as a sufficient CH 4 activation takes place, so that the coupling pathway is promoted over the heterogeneous oxidation of CH 3 •.

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