Bulk catalyst density

The units on the rate constants reported by DeMaria et al. indicate that they are based on pseudo homogeneous rate expressions (i.e., the product of a catalyst bulk density and a reaction rate per unit mass of catalyst). It may be assumed that these relations pertain to the intrinsic reaction kinetics in the absence of any heat or mass transfer limitations. 

Assuming a catalyst density at flowing conditions in the standpipe of about 90% of the catalyst bulk density, the amount of excess gas above minimum fluidization that is entrained with the catalyst into the standpipe may be calculated. Sufficient aeration should be added to sustain minimum fluidization along the length of the standpipe. 

The latter equation is used to calculate the pressure drop through the bed and is named the Ergun equation [4]. The ps is the catalyst bulk density [kg/nfi), and / is a friction factor (—) for the packing. Ergun proposed the following parameterization for the friction factor ... 

Total Molar Feed Mass Flow Rate Inlet Pressure Inlet Temperature Catalyst Bed Diameter Catalyst Bed Length Catalyst Bulk Density Catalyst Particle Diameter... 

The new generation of fixed bed catalysts made fi om activated base metals (Metalyst ) is best described as an extremely durable collection of empty eggshells composed of high surface area activated metal. This technology offers an increase in volumetric activity at lower catalyst bulk densities without the presence of expensive, but not utilized, materials. In other words, the amount of metal in the reactor is reduced by as much as 40 to 77% leading to a more effective use of metal (1). In this paper, the effectiveness of this catalyst technology will be compared to others for the hydrogenation of various compounds (2, 3,4). 

The use of these and various other units for the space time requires the use of correspondingly altered units for the catalytic rate constant. The rate constant can now include the mass of the catalyst, and also be dependent on catalyst bulk-density, active site surface-density, porosity and accessible surface area. Catalyst properties in terms of these quantities must be known in detail before valid comparisons between competing catalysts can be made. 

Citral (Alfa Aesar, 97%) hydrogenation was carried out in a pressurized reactor working in a special mode, in which small amounts of the liquid phase initially introduced in the reactor were constantly pumped out from the reactor, whereas the supported Pd-ionic liquid catalyst remained in the reactor. The initial liquid phase volume was 325 ml. The catalyst bulk density was changed during the reaction via pumping out the liquid phase from the reactor with a rate of 1 g/min. Such procedure allows efficient investigation of consecutive reactions... 

The ot,j are negative for reactants and positive for reaction products. The units of Rj depend on the nature of the reaction. If the reaction is homogeneous the units could be kmol/m s but for a reaction catalyzed by a solid preference would be given to kmol/kg cat s, multiplied by the catalyst bulk density in the reactor. 

Medium size capacity 15,000 barrels/day = 2390 gasoil/day Catalyst silica-alumina zeolite catalyst or molecular sieves 20-80 p Total catalyst inventory 250 tons Amount in regenerator 100 tons Catalyst bulk densities... 

The terms in this equation have the dimensions kmol hr. The reaction rate terms takes into account that the reaction in the ensemble bubble and interchange zone really only takes place in the interchange zone, which has a volume and in which one assumes that the catalyst bulk density b the same as that in the emulsion phase, p,. According to Partridge and Rowe s experimental correlation VJVc = 1.17/(0.17 -1- a). Also, p, = Pa/(1 — / ) when the fraction of the... 

Figure 13.1.10 shows the effects of bulk density of 400 cpi catalysts on warmup characteristics after engine aging. To examine the effects of heat mass of catalysts, 4, 6, and 8 mil catalysts are used. As catalyst bulk density increase, inlet gas temperature at 50% conversion efficiency (T5o%) increases, and conversion efficency during the initial 3 min (rj min) decreases in the HC, CO, and NO warm-up tests. Consequently, reducing the heat mass of catalysts presumably improves warm-up characteristics. 

The rate constant must be measured in gas volume per particle volume for a proper conversion, so the conversion from the mass particle based kmt requires the molar volume of the gas. In addition it is also assumed that the particle is isothermal so in practice conversion of intrinsic rate to effective rate requires fitting of the rate constant. Most important is, however, that the effective energy of activation is half the intrinsic value and that the rate is inversely proportional to the equivalent particle diameter. At reactor conditions the catalyst bulk density must be used for a comparison of the activity of different catalyst particles as shown in Figure 3.3. 

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