Investigation of methane and ethane pyrolysis with highly active and durable iron-alumina catalyst to produce hydrogen and valuable nano carbons: Continuous fluidized bed tests and reaction rate analysis

Abstract

The goal of this research work was to evaluate a novel iron-alumina catalyst for methane and ethane pyrolysis with high conversion rates to H2 with a long life time to address two major issues reported with previous catalysts. Fluidized bed tests demonstrated continuous hydrogen production while collecting carbon containing fines. During the 230 h fluid bed test the methane conversion rate to hydrogen at 700 °C remained above 80% for 160 h while creating valuable nano carbons. Similarly high catalyst lifetimes with high methane conversions have not been reported before. Ethane was more active than methane for pyrolysis with 100% conversion to H2. Transmission electron microscopy and Raman analysis of the carbon showed single and multiwall nanotubes and conglomerate nano-fibers. Ethane did not impact the allotrope of carbon formed. TGA was used to create a data array that was used for kinetic analysis and reaction model parametric regressions. Ethane had a higher rate of pyrolysis that was 2.3–2.8 times that of methane. Ethane pyrolysis was found to be more sensitive to temperature with a higher activation energy of 62 kJ/mol as compared to methane at 43 kJ/mol. The frequency factor, Ai, was significantly higher for ethane at 0.73 [[kmol/m3-sec]/[N/m2]n] compared to 0.03 for methane on the same basis. Both gases had a functional partial pressure order dependence of ∼0.6 based on the regression analysis.