Hollow pellet

Spray-dried extract The solutions containing the drug extracts, which are sprayed through a nozzle, sink in the form of fine droplets in the current of warm air, losing their moisture and reaching the separator as dry and hollow pellets of extract which can be recognized with a hand lens. The spray-... 

Improved high water pressure performance of a gel dynamite is achieved by incorporating hollow pellets of sulfur coated with clay or wax Ref W.L. Reinhart, USP 2674526(1954) ... 

Catalyst preparation. Chloroplatinic acid, in such amounts as to obtain the desired concentration of Pt in the catalysts, was added to previously prepared w/o microemulsions. Two types of catalytic supports, y-alumina in the form of full pellets (diameter 5 mm) and 0-alumina in the form of hollow pellets (diameter 5 mm, hole 2 mm), both manufactured in Chemopetrol Litvinov, Czech Republic, were chosen for catalysts preparation. After calcination at 500 °C y-alumina had Sbet=166 m /g, pore volume 0.459 ml/g, mean pore radius 7.0 nm and water absorption capacity 40 %. After calcination at 900 °C 0-alumina showed Sbet=145 m /g, pore volume 0.445 ml/g, mean pore radius 8.1 nm and water absorption capacity 50 %. The catalysts with 0.3 and 0.1 wt. % Pt were prepared by impregnation with HaPtCle water solutions (denoted as I) or Pt microemulsions (denoted as M). The catalysts were dried 2 h at 120-160°C and calcined 2 h in air at 550 °C. Characterization of microemulsions... 

Adding chloroplatinic acid to the w/o microemulsions prepared resulted in an impregnation solution useful for the preparation of catalysts with 0.3 wt. % Pt. 0-Alumina in the form of hollow pellets is a good example for studying the effect of viscosity on Pt concentration profiles (Fig. 2). 

Rings— hollow pellets which had gas contact surfaces inside and on the outer surface for better catalytic action. It was also seen that the converter passes with these catalyst pellets were able to operate without increase in the resistance to the gas flow—thus without increase in the pressure drop on the gas side for a much longer duration. 

The catalyst surface area per unit volume, g(Ss), can be made to vary with pellet coordinate by choosing an appropriate impregnation method. Hence, this function represents not only the level of dispersion but also activity distribution. A partially impregnated (or equivalently hollow) pellet is a typical example of a pellet with a certain activity distribution. The motivation for making such a pellet becomes obvious if it is recognized that the reactant concentration becomes almost zero at some point in the pellet when the reaction is diffusion-limited. The fraction of the volume of the pellet for which the concentration is zero is not utilized at all. If this fraction is made hollow or inert, then the observed rate on a per pellet basis should be the same as the fully impregnated pellet. Let us examine this further. Suppose that a pellet is hollow or partially impregnated for a distance Li from the center. Consider a diffusion-limited, first-order reaction. The internal effectiveness factor for this hollow pellet is ... 

It has been shown in Chapter 4 that a reduction in the amount of catalyst used can be realized for diffusion-limited reactions when hollow pellets or pellets with an inert core are used. Determine whether the same is true when the reactions are eilso affected by deactivation (Lee 1980). 

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