Understanding the effect of transport phenomena in deep-injection floating catalyst chemical vapor deposition carbon nanotube synthesis

We explore deep injection (DI) floating catalyst chemical vapor deposition (FCCVD) for carbon nanotube (CNT) growth, focusing on momentum and heat transport effects. By systematically changing process gas composition, we study the effects of gas physical properties on reactor productivity while preserving other process parameters. DI causes a colder jet to penetrate deep into the reactor, creating an axial recirculation near the reactor walls. We find nitrogen and argon are interchangeable due to similar transport properties. Increasing the helium fraction in the process gas lowers jet momentum, reducing its length and recirculation size; beyond a certain level, the changes in reactor flow pattern cause a productivity drop. Increasing hydrogen fraction affects the flow and thermal profiles similarly; but productivity decreased further due to the chemical effects of hydrogen, preventing the formation of active species. Computational fluid dynamics simulations suggest that high productivity of DI reactor is associated with the colder jet meeting hotter recirculating gases, creating local conditions for catalyst formation in the presence of activated carbon precursors at the jet/recirculation interface. Under optimum conditions, we achieve ∼13 % methane conversion, >90 % CNT selectivity, and ∼430 mg/h productivity, among the highest results reported so far. This work provides valuable insights for designing efficient CNT reactors.