Fluidized Bed Synthesis of Carbon Nanotubes: Reaction Mechanism, Rate Controlling Step and Overall Rate of Reaction

Carbon nanotubes have been synthesized from acetylene and methane in a fluidized bed by using ferrocene as the catalyst dispersed over carbon black support material. The agglomerate size of carbon black, loading of catalyst, total gas flow rate, partial pressure of reactant gas, temperature of synthesis, and time of synthesis have been varied to understand their effects on the yield of carbon nanotubes. A reaction mechanism consisting of eleven steps and the rate equations for these steps have been proposed. Formation of carbon molecules on the catalyst surface was found to be the rate controlling step in the temperature range of 700-807 degrees C, with an activation energy 47 kJ mol 21, while diffusion through pores in the carbon black was found to be the rate controlling step in the temperature range of 807-1000 degrees C with an activation energy of 7.6 kJ mol(-1). A continuous deactivation of the catalyst, represented by an exponential decay, was observed. The products have been characterized by thermogravimetry, electron microscopy, and Raman spectroscopy. (C) 2014 American Institute of Chemical Engineers