Iron Catalyst Chemistry in Modeling a High-Pressure Carbon Monoxide Nanotube Reactor

Abstract

The high-pressure carbon monoxide (HiPco) technique for producing single-wall carbon nanotubes (SWNTs) is analyzed with the use of a chemical reaction model coupled with flow properties calculated along streamlines, calculated by the FLUENT code for pure carbon monoxide. Cold iron pentacarbonyl, diluted in CO at about 30 atmospheres, is injected into a conical mixing zone, where hot CO is also introduced via three jets at 30 degrees with respect to the axis. Hot CO decomposes the Fe(CO)5 to release atomic Fe. Then iron nucleates and forms clusters that catalyze the formation of SWNTs by a disproportionation reaction (Boudouard) of CO on Fe-containing clusters. Alternative nucleation rates are estimated from the theory of hard sphere collision dynamics with an activation energy barrier. The rate coefficient for carbon nanotube growth is estimated from activation energies in the literature. The calculated growth was found be about an order of magnitude greater than measured, regardless of the nucleation rate. A study of cluster formation in an incubation zone prior to injection into the reactor shows that direct dimer formation from Fe atoms is not as important as formation via an exchange reaction of Fe with CO in FeCO.

Structure and Properties of Fe4 with Different Coverage by C and CO

“…6 However, the growth mechanisms are not well understood. Chemical reaction models 7,8 with reaction rates derived from literature predicted a growth rate, which is ∼1 order of magnitude higher than the measured one, regardless of the nucleation rate.…”

Simulation and modeling of carbon nanotube synthesis: current trends and investigations

“…The dissociation and evaporation rates of atoms from small metal clusters have a significant effect on CO 2 production. Further, the HiPco technique for producing SWCNTs with the use of a chemical reaction model coupled with the FLUENT code was also analyzed [2] . Iyuke et al [3] used the LangmuirHinshelwood mechanism to study the catalytic graphitization of carbon to CNTs from C 2 H 2 and graphite using the catalytic CVD (CCVD) method.…”

“…The chemical kinetics models of Scott et al [1,2] are able to predict the growth rate of CNTs and iron cluster formation. However, the simulation overpredicted the amount of SWCNTs and carbon dioxide produced, which may be related to the assumed rate coefficients for the formation of SWCNTs.…”

Bipolar diffusion charging characteristics of single-wall carbon nanotube aerosol particles

“…As reported by the manufacturer, CS nanotubes had a mean diameter of 1.4 nm and lengths of nanotubes that exceeded 5 m. Aqueous dispersions of CS particles (435 mg l −1 ) were prepared in deionized water without the aid of any surfactants. CN nanotubes (CNI, Houston, TX) were produced by the high pressure CO disproportionation process (HiPCOீ) (Scott et al, 2003), and were subsequently purified by the manufacturer using acid treatment to remove metal contaminants (Gorelik, Nikolaev, & Arepalli, 2000). CN was hydrophobic in nature, therefore a trace concentration of Triton-X surfactant (0.05% v/v) was used to disperse them in water.…”