Figure 5 b) Agglomerate size distributions of Aerosil R974 in conventional and jet assisted fluidized beds.
A paper by Jose Quevedo and Robert Pfeffer titled In Situ Measurements of Gas Fluidized Nanoagglomerates was just published on the web and will also be published in an upcoming issue of Industrial & Engineering Chemical Research.
The paper explores the in-process measurement of nanoparticle aggregates in a fluidized bed. Real-time, in-process particle system measurement with FBRM (Focused Beam Reflectance Measurement) and PVM (Particle Video Microscopy) show significant differences in the density and mean size of the aggregates formed in conventional fluid beds and microjet assisted fluid bed.
The authors report:
“Nanoparticles cannot be fluidized as individual particles but instead fluidize in the form of large (mean size about 100-400 μm), highly porous (internal porosity greater than 98%), hierarchical fractal structured agglomerates. Many nanopowders are very difficult to fluidize because of the large cohesive forces between the particles due to their very small size and high surface area…
In situ agglomerate size measurements and imaging of fluidized nanoagglomerates were achieved by reducing the electrostatic charge in the bed and using the FBRM and PVM probes from Lasentec.”
Electrostatic charges were reduced by bubbling the fluidizing gas through an alcohol-water mixture. This dramatically reduced adhesion of particles to surfaces and greatly improved the quality of the on-line measurements in this dry fluidized bed.
In Situ Measurements of Gas Fluidized Nanoagglomerates
Jose A. Quevedo† and Robert Pfeffer*‡
Otto York Department of Chemical, Biological and Pharmaceutical Engineering, New Jersey Institute of Technology, Newark, New Jersey 07102
Ind. Eng. Chem. Res., Article ASAP
Publication Date (Web): March 2, 2010
Publication is Copyright © 2010 American Chemical Society
† Current address: Shell Global Solutions, P.O. Box 38000, 1030BN Amsterdam, The Netherlands.
‡ Current address: Department of Chemical Engineering, Arizona State University, Tempe, AZ 85287.