A parametric study of the large scale production of multi-walled carbon nanotubes by fluidized bed catalytic chemical vapor deposition

A parametric study investigating the impact of temperature, run duration, total pressure, and composition of the gaseous phase on the catalytic growth of multi-walled carbon nanotubes (MWCNT) has been performed. MWCNTs have been produced very selectively on the multi-gram scale by catalytic chemical vapor deposition from ethylene in a fluidized bed reactor. The kinetics of MWCNTs growth is fast and, with the catalyst used, no induction period has been observed. The kinetic law is of positive order in ethylene concentration and the process is limited by internal diffusion in the porosity of the catalyst. The formation of MWCNTs in the macroporosity of the catalyst induces an explosion of the catalyst grains. Such a process, thanks to the absence of temperature gradient and to the efficient mixing of the grains allows a uniform and selective treatment of the catalyst powder leading to very high selectivity towards MWCNTs formation. High purity MWCNTs have been obtained after catalyst dissolution. Depending on the temperature of production, the specific surface area of this material ranged between 95 and 455 m2/g.