Kinetic Modeling of Carbon Nanotube Production and Minimization of Amorphous Carbon Overlayer Deposition in Floating Catalyst Method

A kinetic modeling of longitudinal and depth profiles of multiwall carbon nanotubes (MWCNTs) synthesis using xylene and ferrocene in a floating catalyst (FC) reactor is hereby reported. Both amorphous and arrays of carbon nanotubes (CNTs) are formed, whose ratio sharply increases along a growth window and from the bottom to top of the arrays. A model is presented for the rate of CNTs synthesis as well as the rate of amorphous carbon formation which undesirably forms on the nanotube walls and reduces nanotubes quality and synthesis efficiency. Based on the amounts of amorphous carbons and CNTs formed in the reactor, kinetic parameters of formation of these species from xylene were estimated. It is shown that, as the temperature increases, the weight ratio of amorphous carbon to CNTs shows minimum at 970 K. The ratio increases with decreasing the amount of deposited iron. Increasing pressure and carrier gas is found to have marginal effects on producing CNTs with lower amounts of amorphous carbon. Higher surface density of CNTs (number of CNTs per surface area) and their diameter, result in a significantly higher amount of amorphous carbon deposition.