Fluidization of nanoparticles agglomerates enhanced by supercritical carbon dioxide

The present work focuses on the study of fluidization of nanoparticle agglomerates with SC-CO2 at different temperatures (308-320 K) and pressures (7.7-14.4 MPa). These conditions allow this work to be carried out in a wide range of densities, varying from 200 to 800 kg/m(3). Three materials with different bulk densities were tested: aluminum oxide (Al2O3, 40 kg/m3), titanium oxide (TiO2, 90 kg/m(3)) and magnetite (Fe3O4, 840 kg/m(3)). With regards to fluidization, two different behavior patterns were detected, according to the variation of the minimum fluidization velocity (u(mf)) in accordance with carbon dioxide density. At high densities (> 500 kg/m(3)) only fluid particle interactions controlled the process, therefore, the same behavior of u(mf) vs density was found for the three materials. Meanwhile at low densities (< 500 kg/m(3)) both fluid-particle and particle-particle interactions affect the fluidization process. Moreover, minimum fluidization velocity values were compared with other fluidization enhancing techniques reported in literature for titanium dioxide and aluminum oxide particles: pulsed gas flow, microjets and acoustic fields. Regarding the fluidization of titanium oxide, the supercritical fluid method achieved minimum fluidization velocities of between 10 and 100 times lower, depending on the selected density, with respect to pulsed gas flow and acoustic fields. While comparing with acoustic fields, both methods accomplished similar values (0.02-0.180 cm/s) for the fluidization of aluminum oxide. (c) 2017 Elsevier B.V. All rights reserved.