Fluidization behaviors of different types of multi-walled carbon nanotubes in gas–solid fluidized beds

Abstract

The fluidization behaviors of different types of multi-walled carbon nanotubes (MWCNTs) were investigated in a fluidized bed with a 0.14m-ID×2.4m-height Plexiglas column. Four types of MWCNTs were used as the bed materials: (i) N refers to the NC7000™ prepared by Nanocyl®, (ii) Sf refers to the agglomerate by which fine entangled MWCNTs were agglomerated by strong cohesive force such as van der Waals force, (iii) Sc refers to the coarse entangled MWCNTs with a shape such as a single particle, (iv) Smix refers to the binary mixture of Sf and Sc physically mixed in a 1:1 volumetric ratio. For N and Sf, the fluidization behavior with superficial gas velocity is similar to that of Geldart's group A particles. In the bubbling fluidization of N and Sf, no bubbles were observed. The minimum fluidizing gas velocity and bed expansion ratio of Sf was higher than those of N. The fluidization behavior of Sc was similar to that shown by the results from Geldart's group B with a wide size distribution. For the binary mixture, Sf and Sc are the flotsam and jetsam, respectively. The fluidization behavior of Smix was divided into four regions with decreasing superficial gas velocity. Sc and Sf were not mixed sufficiently at high velocity due to the high bed expansion ratio of Sf. As the superficial gas velocity was decreased, Sc gradually became defluidized. When Sc had a fixed bed at the bottom, Sf showed particulate fluidization at the top. At this point, Sc and Sf were completely segregated. The variation in the pressure drop across the beds at the superficial gas velocity was similar to that for the Sc; however, the bed expansion was similar to that for the Sf.