No abstract

No abstract

No abstract

No abstract

No abstract

-This work focuses on the fluidization of three types of TiO 2 powders: Anatase (99% TiO 2 ), Rutile 1 (95% TiO 2 and 5% Al) and Rutile 2 (96.5% TiO 2 and 3.5% Al and Si); the average diameters of the powders are 204 nm, 159 nm and 167 nm, respectively. These powders belong to group C of the Geldart classification and are characterized as cohesive powders with a non-free flow and a difficult fluidization. The fluidization of the powders was carried out in a glass column of 103 mm inner diameter and 1500 mm height. The experiments and analysis performed included measurements of the physical properties of the powders such as the particle size, density, specific surface area and the flow properties of the powders like the Hausner's index, the angle of repose, the angle of slide, consolidation and shearing (via shear cell testing). The results obtained with the nanometric TiO 2 powders show a more complex behavior than the micronic powders; with a low strength value (Hausner index, angle of repose and angle of slide), the TiO 2 powders have a free flow or intermediate-flow and a non-free-flow for higher strength intensities (consolidation and shearing). This behavior is related to the structure of the nanometric particles in the packed bed; the evolution of this structure is made up of individualized and spherical agglomerate shapes and is not perturbed by stresses of low intensities. Indeed, the latter seems to modify the structure of the powder (group C of Geldart classification) to acquire a behavior typical of group A, B or D in the Geldart classification. With high stress values, the individualized agglomerates are disintegrated and the powder is reduced to a more compact structure. The fluidization of TiO 2 powders seems to evolve in a more homogeneous way than the micronic powders. This behavior is related to the initial structure being made up of stable agglomerates. Thus, this fluidization is made by agglomerates with a gas velocity of 3×10 6 to 4.6×10 6 times the gas velocity for fluidizing the primary particles.A numerical approach based on a force balance in agglomerating fluidized beds was developed in order to estimate the agglomerates sizes.

The gas-phase catalytic dehydration of glycerol to acrolein was carried out in a Two-Zone Fluidized-Bed Reactor (TZFBR) using a 20 wt. % phosphotungstic acid (H3PW12O40) catalyst supported on CARIACT-Q10 commercial silica. In the first step, a hydrodynamic study of the reactor was performed. A quality of fluidization of more than 80% was obtained. In the second step, the mechanical stability of the catalyst was studied. It was found that only the external layer of active phase is eliminated under the conditions of operation whereas the global composition of the catalyst was not significantly affected after 44 h of fluidization. Finally, in a third step, the influence of the main operating parameters on the overall catalytic performances (glycerol/oxygen molar ratio and relative volumes of the reaction and regeneration zones) was investigated, showing notably the importance of the O2/glycerol ratio, resulting in an inverse trend between conversion and selectivity. Increasing O2/glycerol ratio led to higher conversion (lower coke deposit as shown by TGA analysis), but to the detriment of the selectivity to acrolein, supposedly due to the presence of O2 in the reaction zone causing the degradation of glycerol and acrolein.

Cement powder particles of micronic size tend to form agglomerates due to the influence of interparticle forces (Van der Waals forces). The formation of agglomerates results in an increased air-void in the solid structure (aerated powder) requiring an increase in water demand to sustain the feasibility of the structure. Consequently, if the compound formed is not stabilized, it would have low mechanical strength that may result in cracking of hardened cement. In this study, the results of cement powder consolidation and its flow properties show that its behaviour is controlled by internal forces (Van der Waals) and external forces (elastic and plastic). These forces have a direct influence on the powder structure, leading to a variable packing behaviour (void reduction). Consolidated cement powder shows a decrease in the void structure leading to a more efficient material. This study intends to determine the impact of interaction forces between cement particles during consolidation.