Bubble powder effect

Figure 14 Fluidisation behaviour of a Group B powder effect of gas flow on bubbles in a two-dimensional fluidised bed, (i) lower gas velocity, (ii) higher gas velocity. A max. stable bubble size is never achieved... 

Slurry Reactors. Slurry reactors are commonly used in situations where it is necessary to contact a liquid reactant or a solution containing the reactant with a solid catalyst. To facilitate mass transfer and effective catalyst utilization, the catalyst is usually suspended in powdered or in granular form. This type of reactor has been used where one of the reactants is normally a gas at the reaction conditions and the second reactant is a liquid, e.g., in the hydrogenation of various oils. The reactant gas is bubbled through the liquid, dissolves, and then diffuses to the catalyst surface. Obviously mass transfer limitations can be quite significant in those instances where three phases (the solid catalyst, and the liquid and gaseous reactants) are present and necessary to proceed rapidly from reactants to products. 

The erosion effects of cavitation on solid surfaces have been extensively investigated both in terms of surface erosion [68] and corrosion [69]. The consequences of these effects on metal reactivity are important since passivating coatings are frequently present on a metal surface (e. g. oxides, carbonates and hydroxides) and can be removed by the impacts caused by collapsing cavitation bubbles. An illustration can be found with the activation of nickel powder and the determination of the change in its surface composition under the influence of cavitation by Auger spectroscopy (Fig. 3.6) [70]. 

Fung A.S., Hamdullahpur F, (1993) Effect of bubble coalescence on entrainment in gas fluidized beds. Powder Technology. 77, pp 251-265 Zenz F.A. et al (1958) A Theoretical-Empirical Approach to the Mechanism of Particle Entrainment from Fluidized Beds. American InstitiUe of Chemical Engineering Journal, 4, pp. 472-479... 

Finally, we studied the effect of liquid dispersion on catalyst performance by comparing the performance of the powder catalyst in a bubble column reactor with the HyperCat-FT system. As shown in Figure 6, the CO conversion is much lower for a low Peclet number (bubble colunm reactor with a back-mixed liquid phase) as opposed to a higher Peclet number for the HyperCat system. The tests were conducted under the same process conditions and Damkohler number. The change in Peclet number did not change the liquid product... 

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