Opposite effects of gas flow rate on the rate of formation of carbon during the pyrolysis of ethane and acetylene on a nickel mesh catalyst

Abstract

The importance of mass transfer in the formation of carbon on a nickel catalyst during the pyrolysis of ethane and acetylene was investigated. This included the formation of a composite of carbon fibre and amorphous carbon, using a non-porous nickel mesh catalyst in a tubular reactor at 750 °C. Increases in the gas flow rate through the Ni mesh decreased the formation of carbon during the pyrolysis of ethane. On the contrary, a similar increase in gas flow rate increased the formation of carbon during the pyrolysis of acetylene. Characterisation of the carbon products by SEM, TEM, TGA and FT-Raman spectroscopy also showed the opposite effects of gas flow rate on the type and structure of carbon formed on the nickel catalyst. These results can be explained by considering the relative ease with which various C-containing radicals and H radicals desorb from the nickel surface as the mass transfer resistance for radicals is decreased with increasing gas flow rate.