Spray-dried Fe/Al2O3 as a carbon carrier for COx-free hydrogen production via methane cracking in a fluidized bed process

Abstract

Herein, we report the production of COx-free hydrogen from catalytic methane cracking. Spherical, porous and fluidizable catalyst has been produced by spray-drying of 10 wt-% Fe2O3 and 90 wt-% Al2O3. This material can accommodate the deposited solid carbon from the methane cracking reaction in its pores. In fluidized bed experiments, the kinetics of reduction of the catalyst with methane were determined. A high activation energy of 313 kJ mol−1 for the reduction of the intermediate spinel phase (FeAl2O4) to metallic iron indicates the need for high temperatures for the reduction step. The subsequent cracking of methane could be well described by applying a simple backmixed flow model. The reaction order with respect to methane concentration in the gas was nc = 0.63 and the apparent activation energy at T > 800 °C wasEa,c,T>800°C = 21.5 kJ mol−1 andEa,c,T<800°C = 128.1 kJ mol−1 at T < 800 °C. This is indicative of mass transfer limitations at temperatures greater than 800 °C. The activity of the bed material for methane cracking was found to decrease linearly with an increasing amount of carbon deposited on its surface. When the carbon deposited on the bed material was limited to below 10 wt-%, mechanical and structural stability of the spherical particles was maintained. Likewise, bed expansion and particle break-up were observed when more than 10 wt-% carbon was deposited. These results confirm the principal suitability of the developed material as a carbon carrier, and the obtained kinetic data can be useful for design and scale-up considerations of this fluidized bed methane cracking process.