Gas-solid fluidization of cohesive powders

Fine and ultrafine powders (down to nanoparticles) have recently received growing inter- est in both industrial and academic sectors due to their very distinctive features, mainly coming from their very small primary particle size and very large surface-to-volume ratio. Indeed, due to these characteristics, they can provide better contact efficiency and higher reaction rates per unit volume of reactor than traditional materials in the case of gas/solid and solid/solid reactions. They have been used to produce a large variety of materials, such as catalysts, sorbents, cosmetics, etc. Therefore, the interest in using this type of granular materials in a variety of industrial processes raises many questions about how they can be handled. Therefore, the interest in using this type of granular materials in a variety of industrial processes raises many questions on how they can be handled and processed (e.g. mix- ing, transporting and modifying the surface properties) in large-scale applications. With reference to this point, among all the available techniques for continuously handling and dispersing granular solids, gas fluidization is one of the most efficient, mainly due to the large gas-solid contact area. The aim of this work is to provide a critical review of experimental/theoretical research and latest progress in the science and technology of gas fluidization of fine/ultrafine particles, thus deeply covering the current international state-of-the-art. In particular, the challenges linked to the extensive use of these powders have been discussed, highlighting and explain- ing the fundamental aspects needed to comprehend the complexity of the process and provide possible answers/solutions.