Iron Catalyzed Methane Pyrolysis in a Stratified Fluidized Bed Reactor

Abstract

Methane pyrolysis at 950 °C and 1 atm was investigated on iron containing catalysts derived from a magnetite (Fe3O4) ore in a semibatch fluidized bed reactor. The magnetite particulates (∼10-50 μm) were observed to undergo reduction and fragmentation to approximately 100 nm iron-iron carbide catalysts in 100% methane as the fluidized bed reactor was heated to 950 °C at high gas flow rates. After prereduction, the flow rate was decreased to a weight hourly space velocity (WHSV) of 3.5 h-1, and the activity was observed to increase at 950 °C to a maximum methane conversion of approximately 90% (turnover frequency ∼ 0.3 s-1). At maximum activity, the C/Fe ratio was approximately 2. With increasing time on stream, the catalyst activity and particle density decreased. As solid carbon was deposited on the iron containing catalyst, the semibatch fluidized bed volume, C/Fe, and void fraction increased at a constant WHSV. The graphitic carbon product accumulated in and around the catalyst particles with increasing time, consistent with the observed decrease in activity as access of methane to the catalyst surface was limited by diffusion through an increasingly impermeable graphite barrier. The C/Fe mass ratio of the deactivated catalyst particles was observed to be approximately 5.