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Co-gasification of biomass, namely, switchgrass, with coal and fluid coke was performed to investigate the availability of the gasification catalysts to the mixed feedstock, especially alkali and alkaline earth elements, naturally present on switchgrass. Rates of CO 2 gasification of the single and mixed materials were measured at temperatures between 750 and 950 °C and atmospheric pressure by thermogravimetry. High interparticle mobility of the catalysts is indicated by a prompt and lasting effect on the mixed feed gasification rate when compared with the separate rates. The switchgrass−coal mixtures show a deactivation (antagonism), attributed to sequestration of the mobile alkali elements by reaction with aluminosilicate minerals in coal to form inactive alkali aluminosilicates, such as KAlSi 3 O 8 and KAlSiO 4 . Remaining catalytic activity is evident when excess alkali is present in the feed mixture to satisfy the stoichiometric requirements of these deactivation reactions. In co-gasification of switchgrass with fluid coke, which has little interfering inorganic matter, a synergism is noted in the gasification of the mixed feed. The results document the effects of fuel mixture, composition of the coal or coke ash, and the gasification temperature on this behavior.

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The kinetics of K 2 CO 3 -catalyzed CO 2 gasification of ash-free coal was investigated with a thermogravimetric analyzer and compared to raw coal and uncatalyzed ash-free coal. At 750 °C, the gasification of ash-free coal dry mixed with 20 wt % K 2 CO 3 was approximately 3 and 60 times faster than the raw coal and ash-free coal without catalyst, respectively. Increasing the amount of catalyst from 20 to 45 wt % increased the gasification rate 3-fold. The gasification rate of ash-free coal containing potassium catalyst strongly depended upon the pretreatment (i.e., heating gas atmosphere and heating time) because it directly affected the degree of catalyst reduction. The catalytic gasification behavior could only be predicted with the extended random pore model, whereas the random pore model and integrated model were essentially equal for fitting the gasification rate for raw and ash-free coal. The activation energy for the catalyzed ash-free coal gasification was approximately 100 kJ mol −1 larger than for raw coal and the uncatalyzed ash-free coal. This increase might be due to the energy required for the potassium (i.e., catalyst) transfer to a new carbon site or caused by the pyrolysis process, because the formed char might have different properties.

In the present work, the influence of reaction and mass transfer on the fluidized-bed methanation have been investigated by both experiments and modeling. By applying spatially resolved gas concentration and temperature measurements in a bench-scale fluidizedbed reactor, it was shown that most of the reaction proceeds in the first 20 mm while the temperature increases by 74 K in the first 2 mm of the bed. A CO conversion of practically 100% is achieved. The experimental data indicate that the measured gas composition represents mainly the dense phase and that mass transfer between bubble and dense phase is the dominant effect in the upper part of the bed. A fluidized-bed model is proposed based on the two-phase model approach, hydrodynamic correlations from the literature and kinetic parameters previously determined. Although it was not possible to reproduce all measured phenomena within the methanation reactor, this first attempt to model the fluidized bed provides a better understanding of the behavior of the reactor and the reactions.

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