Simultaneous and Continuous Production of Carbon Nanotubes and Hydrogen by Catalytic CH4 Decomposition in a Pressurized Fluidized-Bed Reactor

The optimal operating conditions for a fluidized-bed reactor (FBR) capable of simultaneous and continuous production of both hydrogen and carbon materials via direct decomposition of methane, employing a transition-metal-based catalyst, were determined. The nickel-based catalyst was synthesized via the sol–gel method and the catalyst particles, classified as Geldart group B, were used in the FBR. As the first step, the optimal reaction temperature and flow rate for the catalysis were determined by using a lab-scale FBR with an internal diameter of 28 mm. Using the data obtained in the lab-scale FBR experiments, the appropriate operating conditions were established for a bench-scale FBR with an internal diameter of 76.2 mm. The system was operated in a continuous manner, in which hydrogen and solid carbon with catalyst particles were simultaneously and continuously discharged and the catalyst was periodically fed into the reactor. Approximately 5 h stable operation and performance were confirmed at an average temperature of 710 °C and a pressure of 2 bar in the fluidized bed. The maximum carbon production rate observed was 5 kg/day, and the hydrogen production rate was 1.66 kg/day with the bench-scale reactor. The quality of the carbon products, in the form of multiwalled carbon nanotubes, was characterized and evaluated using transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy.