Hydrogen and carbon produced by fluidized bed catalytic methane decomposition

Abstract

Natural gas or methane-rich gas resources (e.g. digestion biogas) are major fuel sources for heat and power generation. CH4 is furthermore used in petrochemical and chemical reactions (reforming, ammonia, methanol, urea, among others). In these thermal applications, the transformation of methane will release greenhouse gases, as CO2 together with mostly thermal NOx from its combustion. The development of alternative CH4 utilization techniques is important. The Catalytic Methane Decomposition (CMD) operates at near-zero GHG emissions and produces 2 valuable products:CH4→C+2H2∆Hr=74.8kJ/mol20°C,85.5kJ/mol650°CHydrogen can help to partly decarbonize the fossil fuel applications either as a mix with natural gas (Hydrogen Enriched Natural Gas), or applied in fuel cells and industrial thermal processes, such as cement or steel production. The carbon product can be used as a filler or additive. Although different catalysts for the CMD process have been assessed, their high cost and low CH4 decomposition efficiencies are drawbacks. The present research investigates the use of a cheap and efficient catalyst. Fluidized bed CMD experiments using a 12 wt%Fe/Al2O3 catalyst were performed, and CH4 conversion yields of over 80% are obtained at 650 to 700 °C. The carbon formed is of a CNT nature but partly deposits within the catalyst bed, leading to a progressive reduction in H2 yield. Although the CNT can be continuously removed from the bed, a partial thermal regeneration of the catalyst is required. A three-step process was tested and developed. The very low CO2 emission and competitive cost for both H2 and CNT will be proven.