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

The fluidization behaviors of different types of multi-walled carbon nanotubes (MWCNTs) were investigated in a fluidized bed with a 0.14 m-ID x 2.4 m-height Plexiglas column. Four types of MWCNTs were used as the bed materials: (i) N refers to the NC7000 (TM) prepared by Nanocyl (R), (ii) S-f refers to the agglomerate by which fine entangled MWCNTs were agglomerated by strong cohesive force such as van der Waals force, (iii) S-c refers to the coarse entangled MWCNTs with a shape such as a single particle, (iv) S-mix refers to the binary mixture of Se and S-c physically mixed in a 1:1 volumetric ratio. For N and S-f, the fluidization behavior with superficial gas velocity is similar to that of Geldart's group A particles. In the bubbling fluidization of N and S-f no bubbles were observed. The minimum fluidizing gas velocity and bed expansion ratio of S-f was higher than those of N. The fluidization behavior of S-c was similar to that shown by the results from Geldart's group B with a wide size distribution. For the binary mixture, S-f and S-c are the flotsam and jetsam, respectively. The fluidization behavior of Smix was divided into four regions with decreasing superficial gas velocity. S-c and S-f were not mixed sufficiently at high velocity due to the high bed expansion ratio of S-f. As the superficial gas velocity was decreased, S-c gradually became defluidized. When S-c, had a fixed bed at the bottom, S-f showed particulate fluidization at the top. At this point, S-c and S-f were completely segregated. The variation in the pressure drop across the beds at the superficial gas velocity was similar to that for the S-c; however, the bed expansion was similar to that for the S-f. (C) 2015 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.