Catalyst body

Preferential deposition of weaMy adsorbed dissolved components on the outer surface of the catalyst body is a similar phenomenon but can occur after impregnation during removal of the solvent. When the impregnated particle is heated, the Hquid phase expands and coats the exterior surfaces with dissolved species as the solvent evaporates. In particularly severe cases, the entire outer surface of the catalyst can become completely coated with a soHd that blocks access to the underlying pore stmcture. 

One goal of catalyst designers is to constmct bench-scale reactors that allow determination of performance data truly indicative of performance in a full-scale commercial reactor. This has been accompHshed in a number of areas, but in general, larger pilot-scale reactors are preferred because they can be more fully instmmented and can provide better engineering data for ultimate scale-up. In reactor selection thought must be given to parameters such as space velocity, linear velocity, and the number of catalyst bodies per reactor diameter in order to properly model heat- and mass-transfer effects. 

The shape of the catalyst body influences the mass transport characteristics as well as the pressure drop in a catalyst bed, as the following example shows. If one... 

The Thiele modulus is related to the concentration dependence in a catalyst body by the following equations representing the ratios of the hyperbolic cosines ... 

Two kinds of poison distributions must be distinguished. One distribution is that along the catalyst bed, the other one is within the porous system of the catalyst. It may be reasonably anticipated that under most conditions there will be a gradient of contaminant concentration which decreases in the direction from inlet to outlet also that there will be a decreasing concentration of contaminants from the outer confines of each separate catalyst body inwards into the pore system. The contaminant distribution will, however, differ for different types of catalysts and contaminants. 

The activity of bulk iron oxide catalysts used in non-oxidative dehydrogenations decays under the process conditions imposed. Phase transformations leading to mechanical deterioration of the catalyst bodies, migration of the potassium promoter in the catalyst pellets and through the reactor and carbon deposition, resulting in covering of active sites or pore plugging are possible causes of the observed deactivation [1,2]. 

In addition to chemical composition, particle morphology, and texture, the preparation of industrially relevant catalysts requires the consideration of the process conditions at an early stage of the catalyst development because the macroscopic shape of a catalyst body in the micro- to millimeter scale depends on the reactor operation (Figure 4.2.1). Generally, shaping of catalysts for chemical synthesis... 

Beale AM, Jacques SDM, Bergwerff JA, Barnes P, Weckhuysen BM. Tomographic energy dispersive diffraction imaging as a tool to profile in three dimensions the distribution and composition of metal oxide species in catalyst bodies. Angew Chem Int Ed. 2007 46 8832. 

Catalyst bodies can also be made of knitted threads or woven in fabrics, felts, etc. (5-7) (Figure 5). A wide variety of materials have been considered for such catalysfs, buf mosf affenfion has been given to glass, sintered metal, and carbon fibers. 

In the trickle-bed reactor the gaseous and liquid reactants flow co-currently downward over a packed bed of catalyst. The liquid phase must be distributed such that an even wetting of the catalyst is obtained. Uneven wetting may lead to local hot spots and runaways. The gas phase is the continuous phase. High gas flow rates are used in order to obtain a sufficient heat removal (or supply) rate. Since the liquid covers the catalyst particles, reactant diffusion is much slower than in gas phase operation. The nature of the packed bed requires catalyst bodies of a few millimeters, so the catalyst effectiveness is restricted. 

Yasuyoshi, K. Kunihiko, K. Masao, O. Catalyst body for combustion Japan Patent 59136140, Aug 4, 1984. 

Fig. 6-1 Various shaped catalyst bodies (BASF, Ludwigshafen, Germany)...

Shaped catalyst bodies with optimized geometries (e.g., wagonwheels, honeycombs) offer lower resistance to gas flow and lower the pressure loss in reactors. The mechanical and thermal stabihty of catalysts and supports is being improved. New support materials such as magnesite, silicon carbide, and zircon (ZrSi04) ceramics with modified pore structures offer new possibilities. Meso- and macropores can be incorporated into solids to accelerate transport processes, and the question of porosity will increasingly be the subject of interest. 

By this invention metal-modified silica-based catalysts are produced in such a way that the metal-modified, spheroidal, silica particles of uniform size become closely packed, thus having a porosity in the interstices which is of a uniform size and distribution throughout the catalyst body. A further advantage of the catalysts of this invention is that the pores, being between particles which are already closely packed, resist further collapse when the catalysts are subjected to the elevated temperatures required in catalytic reactions. 

Fig. S.27 Simulated effectiveness factor of a ring-shaped catalyst body plotted versus the Thiele modulus for MTBE synthesis ([32], reprinted from Chem. Eng. Technol., Vol 21, Sundmacher, Kiinne and Kunz, Pages 494-498, Copyright 1998, with permission from Wiley-VCH)...

Figure 12.5 Schematic of common metal (oxide) nanoparticle distributions within an oxide support catalyst body.

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