Kinetics of metal oxide-catalyzed CO2 gasification of coal in a fluidized-bed reactor for solar thermochemical process

Metal oxide-catalyzed CO2 gasification of coal was examined in a small-scale fluidized-bed reactor at 1073-1223 K and at atmospheric pressure, for the purpose of converting solar high-temperature heat to chemical fuels. The metal oxide powder of In2O3, ZnO, or Fe2O3 in the grain sizes of 4-9 mum was simply mixed with the ground bituminous coal (grain size < 300 mum) and the catalytic effects of the metal oxide on the Boudouard reaction (C-CO2 reaction) in the coal gasification were kinetically studied. The initial coal gasification rate followed the homogeneous or shrinking core model. Gasification activity followed the order of In2O3 > ZnO > Fe2O3 at high temperatures above 1123 K while the order changed to In2O3 > Fe2O3 > ZnO at lower temperatures. The comparison on the Arrhenius parameters for the catalytic and noncatalytic gasification suggests that the gas species of In2O(g) and Zn(g) are the intermediates to react with CO2 in the cases of the In2O3- and ZnO-catalyzed gasifications, respectively. High-temperature separation of used ZnO catalyst from the remaining coal ash by Zn evaporation was demonstrated at 1423 K.