Growth Kinetics of Carbon Nanotubes in a Fluidized Bed Reactor: A Langmuir–Hinshelwood Approach

For the economical mass production of carbon nanotubes (CNTs) using a fluidized bed reactor (FBR), reactor design is essential. Here, we identified the rate law and the rate-limiting step for CNT synthesis in an FBR using the Langmuir–Hinshelwood (L–H) approach. To determine initial growth rate of CNTs, we plotted growth curves and decided to gather the initial growth rate data from 2 min growth periods. We then obtained the initial growth rate of CNT at various partial pressure of C₂H₄. By formulating rate laws for adsorption, surface reaction, and CNT growth, and comparing them with the initial growth rate data, we concluded that the surface reaction is the rate-limiting step. The rate law was determined to be r_S = k_S·P_C2H4/1 + K_A·P_C2H4. Additionally, we tested the validity of the underlying assumption of the L-H approach by employing Thiele modulus, which suggested that the reaction rate is much slower than the diffusion rate.