Modelling of the Flame Synthesis of Single-walled Carbon Nanotubes in Non-premixed Flames with Aerosol Catalyst

Abstract

The use of aerosol catalyst in the flame synthesis of carbon nanotube (CNT) is known to yield single-walled CNT (SWCNT) that is useful for various applications. Modelling works are needed to optimize operating conditions for SWCNT growth but are unavailable. Therefore, a baseline model for the aerosol-catalyst system in flames is developed and the effect of oxygen on SWCNT growth is investigated. A baseline flame model for a normal diffusion flame with 24% oxygen concentration at the inlet is established via Computational Fluid Dynamic simulation. A dispersed phase model (DPM) is employed to simulate the entrainment of catalyst particles. The flame model is coupled with a published CNT growth rate model to predict the CNT growth rate at each particle. Inlet oxygen concentration is varied from 19% to 27% to study the effect of oxygen on SWCNT growth. Satisfactory validation of the baseline flame shape and temperature is established. Results show that particle 3 for the baseline case yields the highest CNT length compared to other particles due to the suitable path for the synthesis. The particles are classified based on the shortest time residence, moderate and longest time residence. Increasing oxygen concentration from 19% to 27% results in a 30% decrease in CNT length for particle 3 for each inlet condition due to lower carbon precursor and composition in the flame. Furthermore, the results showed that regardless of burner operating conditions, high SWCNT growth is consistently predicted between 120-140 mm HAB, which indicates the existence of an optimum range of species concentration for SWCNT growth in aerosol-based flame synthesis. Thus, it can be inferred that SWCNT growth in the aerosol–based method is highly dependent on carbon source and moderately dependent on temperature.