Catalysts equivalent diameter

Tab. 3.3.1 Physical properties of the packed porous particles. The relaxation times were determined at a Larmor frequency of 300 MHz for protons of water adsorbed into saturated catalyst pellets (average error 2%). The equivalent diameter is defined by 6 Vp/Ap where Vp and Ap are volume and external surface of the particles, respectively.

Catalyst Apparent density of particle or pellet (g/cm3) Equivalent diameter (m2/g) K (cm3/g) total... 

During the R D of the upflow type catalyst cooler, using catalyst CRC-1 (pp = 1,700 kg/m), the influence of vertical heat transfer tubes on bed density was investigated by LPEC in a dt 0.36 m cold test model, with 0.04 m o.d. tubes and 0.08-0.2 m shell side equivalent diameters. The gas velocities and solid mass velocities were 1.0—1.6 m/s and 70-180 t/(m2 h), respectively. Average bed density was correlated by the equation... 

Catalyst Type Pore Volume (cm3/g) Surface Area (m2/g) Equivalent Diameter (mm)... 

Cylindrical pellets of four industrial and laboratory prepared catalysts with mono- and bidisperse pore structure were tested. Selected pellets have different pore-size distribution with most frequent pore radii (rmax) in the range 8 - 2500 nm. Their textural properties were determined by mercury porosimetry and helium pycnometry (AutoPore III, AccuPyc 1330, Micromeritics, USA). Description, textural properties of catalysts pellets, diameters of (equivalent) spheres, 2R, (with the same volume to geometric surface ratio) and column void fractions, a, (calculated from the column volume and volume of packed pellets) are summarized in Table 1. Cylindrical brass pellets with the same height and diameter as porous catalysts were used as nonporous packing. 

This practical apparent rate equation for the Girdler (G3-b) catalyst of particle size 0.62 cm equivalent diameter (1/4" x 1/4" pellets) is given by ... 

The equivalent diameter of 6.2 nm observed in the new catalyst is probably an overestimate, due to the existence of particles that are hyperdispersed on the support and that have not been taken into account in these calculations. 

To minimize the complications arising from a change in the total number of moles within the catalyst particles, they restricted their studies to feeds containing less than 17% ethylene. They used continuous-flow reactors operating at steady state to obtain the data reported in Table P12.12. The pressure was 1 atm. Two forms of catalyst were used in their studies (1) granular particles (100 to 150 Tyler mesh equivalent diameter = 0.13 mm) and (2) spherical pellets (1.27 cm diameter) fabricated by compressing unreduced granular particles in a steel mold. 

Only four of the above particle size definitions are of general interest for applications in packed beds and fluidized beds. They are the sieve diameter, d, the volume diameter, d, the surface diameter, (f, and the surface-volume diameter, d. The most relevant diameter for application in a fluidized bed is the surface-volume diameter, 4v For applications in catalytic reactors with diflferent isometric catalyst shapes. Rase (1990) suggested that we use the equivalent diameters summarized in Table 1. 

Equivalent) diameter of catalyst particle dp Length of tubes... 

The catalysts for ammonia synthesis are porous particles with weenie and interlaced micro-pores. The active sites playing the role of surface catalysis are distributed on the internal surfaces formed by these micro-pores. The internal surface area of ammonia synthesis after reduction is about 10m -g -15m -g , and the external surface area is only 0.1 m g F So, the surface area playing the role of surface catalysis mainly is internal surface. The equivalent diameter of catalyst particles used in industrial ammonia reactor is between 1.5 mm and 13 mm, and the inhibition effect of diflfusion should be considered in real ammonia synthesis rates. When designing industrial reactor, the resistance of external diffusion can be neglected by increasing contact between gas flow and external sm-face of catalysts. The catalytic reaction processes for ammonia synthesis pertain to considerable internal diffusion process in most cases. 

Bingchen Zhu et al obtained the surface equivalent diameter d g = 1.92 mm, and the shape coefficient is 0.487 for ammonia s3mthesis catalyst A301 with size of 3.3-4.7 mm. 

Catalyst size/mm Apparent equivalent diameter/mm Diminishable volume catalyst/%... 

The friction factor / in (11.9.1.A-d) is that of Ergun [1952] the equivalent diameter of the catalyst rings is calculated according to Brauer [1957] and the porosity of the bed is calculated according to Reichelt and Blasz [1971]. 

Sometimes catalyst pores not covered by the liquid film are not filled with liquid due to evaporation phenomena caused by an excess of heat of reaction. If both reactants A and B have an appreciable vapor pressure at the working conditions, they can react as gaseous reactants after diffusing inside the catalyst pores. In this case inter-particle diffusion resistance is strongly reduced (at least 10 times) and the reaction rate can be very fast. These last phenomena are not significant in Slurry Reactors where the catalyst particles are always completely wetted and are much smaller - 0.1 mm (equivalent diameter) instead of 10-50 mm as in TBRs. 

TABLE 6.3. 6-10 mm Ammonia Synthesis Catalyst Average-Particle Equivalent Diameter... 

A fluidized bed reactor contains catalyst particles with a mean diameter of 500 pm and a density of 2.5 g/cm3. The reactor feed has properties equivalent to 35° API distillate at 400°F. Determine the range of superficial velocities over which the bed will be in a fluidized state. 

In general, TPR measurements are interpreted on a qualitative basis as in the example discussed above. Attempts to calculate activation energies of reduction by means of Expression (2-7) can only be undertaken if the TPR pattern represents a single, well-defined process. This requires, for example, that all catalyst particles are equivalent. In a supported catalyst, all particles should have the same morphology and all atoms of the supported phase should be affected by the support in the same way, otherwise the TPR pattern would represent a combination of different reduction reactions. Such strict conditions are seldom obeyed in supported catalysts but are more easily met in unsupported particles. As an example we discuss the TPR work by Wimmers et al. [8] on the reduction of unsupported Fe203 particles (diameter approximately 300 nm). Such research is of interest with regard to the synthesis of ammonia and the Fischer-Tropsch process, both of which are carried out over unsupported iron catalysts. 

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