Improved Catalyst Shapes

Modem catalysts are now supplied in a variety of shapes, all with the same composition. These allow longer continuous operation, at a lower pressure drop, by distributing the dust to prevent the formation of a crast. Shapes are available as rings of various diameters, often with fluted surfaces (ribs) and simple fluted extradates. Use of any shaped catalyst can also offer more than 30% reduction in pressure drop and, often, increased activity to allow more operating flexibility. The best combination of shapes to be used in particular plants is recommended by catalyst suppliers. 

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Another approach to improving access to the catalyst interior and, therefore, the metal uptake capacity is to modify the catalyst shape, which can decrease the effective diffusion length without compromise on reactor... 

Zeolite catalysts are frequently applied after treatments that tend to increase their stability and also to further enhance surface acidity and shape selectivity effects. These treatments, such as steam dealumination, can cause a decrease in the framework A1 content and the release of aluminum-containing species from the framework. This can contribute to the stability of the framework, but extraframework species can also contain additional catalyticaUy active acid sites. These particles can also narrow the size of the zeolite charmels or of their mouths, so improving the shape selectivity effects. Extra-framework material (EF) can also... 

In addition, in order to improve the shape selectivity of adsorbents and catalysts, besides adjustment of pore size, the external surface of zeolites also needs to be modified to deactivate the adsorption sites and catalytically active sites present on the external surface which shows no shape selectivity. The external surface modification is especially important for small-particle and nano-sized zeolites. 

In essence, diluting the catalyst bed with appropriate size of inert particles increases liquid holdup, improves catalyst wetting, and reduces liquid backmix-ing. The selection of diluent size depends on several factors such as the length and inner diameter of the reactor, the size, shape and amount of catalyst, and the fiow rate of reactants. Therefore, there is a lot of research interest to determine the appropriate size of the diluent for various sizes of small-scale reactors to overcome their limitations. 

If a solid-supported catalyst is reaction rate limited, then changing size, shape, or pore structure will not improve catalyst performance. In this case, the only way to improve catalyst performance is to alter the chemical composition of the catalyst. 

The high load technology was developed not only thanks to process improvements, but also to a new catalyst shape and formulation. 

Shape-selective is also an important application of the molecular sieves. Modification of the zeolite in order to enhance its catalytic selectivity and stability has become an important process in the catalyst preparation. Y. Sugi et al prepared the La203 modified H-ZSM-5 zeolites by using the impregnation technology, and examined their activity to improve the shape-selectivity in the alkylation and related reactions of mononuclear aromatic hydrocarbons. The results show that La20s modification enhances the selectivity, and no... 

The new catalyst shapes that were under development gave some compensation for these disadvantages. Higher activity, particularly at lower temperature, could help to avoid carbon formation. Carefully optimized shapes also gave a lower pressure drop and provided better heat transfer within the tubes to decrease the temperature of the tube wall. The use of manaiuite tubes also helped to improve operation. 

The detailed study of chemical composition, stmcture, surface, shape and sizes of particles of fine-dispersed zeolite powder by EPMA will provide useful recommendations to improve the technology of producing alkanes and alkyl benzenes catalysts. 

MW fraction increases the melt flow, thus improving the processability but at the cost of toughness, stiffness, and stress crack resistance. In addition, the improvement in performance through narrowing the MWD is restricted by the catalyst, the process hardware, and the process control limitations. Dow has developed a reactor grade HDPE of optimized breadth, peak, and shape of MWD... 

To improve the yield of mono- and dimethylamines, a shape selective catalyst has been tried. Carhogenic sieves are microporous materials (similar to zeolites), which have catalytic as well as shape selective properties. Comhining the amorphous aluminum silicate catalyst (used for producing the amines) with carhogenic sieves gave higher yeilds of the more valuable MMA and DMA. ... 

Although cracking also occurs on chlorine-treated clays and amorphous silica-aluminas, the application of zeolites has resulted in a significant improvement in gasoline yield. The finite size of the zeolite micropores prohibits the formation of large condensed aromatic molecules. This beneficial shape-selectivity improves the carbon efficiency of the process and also the lifetime of the catalyst. 

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