Reactor selection particle size

Long-Term Stability of the S/O Aerosol Nanoparticle Reactor with Five Randomly Selected Particle Size Distributions atlfum = 850 °C and Qpr =10 cm /min Over 5 Months. 

Microlevel. The starting point in multiphase reactor selection is the determination of the best particle size (catalyst particles, bubbles, and droplets). The size of catalyst particles should be such that utilization of the catalyst is as high as possible. A measure of catalyst utilization is the effectiveness factor q (see Sections 3.4.1 and 5.4.3) that is inversely related to the Thiele modulus (Eqn. 5.4-78). Generally, the effectiveness factor for Thiele moduli less than 0.5 are sufficiently high, exceeding 0.9. For the reaction under consideration, the particles size should be so small that these limits are met. 

We have presented a general reaction-diffusion model for porous catalyst particles in stirred semibatch reactors applied to three-phase processes. The model was solved numerically for small and large catalyst particles to elucidate the role of internal and external mass transfer limitations. The case studies (citral and sugar hydrogenation) revealed that both internal and external resistances can considerably affect the rate and selectivity of the process. In order to obtain the best possible performance of industrial reactors, it is necessary to use this kind of simulation approach, which helps to optimize the process parameters, such as temperature, hydrogen pressure, catalyst particle size and the stirring conditions. 

Lower catalyst effectiveness and selectivity owing to the large catalyst particle size used in this reactor type. 

Fourth, the PtC species is further chlorinated to form Pt4 + species which are strongly bound to the surface. This process leads to a completely new spatial distribution of platinum. After reduction there is an entirely new distribution of platinum particle sizes. One caveat is that metal is lost as volatile species and removed from the reactor. Operating conditions must be selected with care. 

The catalyst bed length for the demonstration test was set at the likely length for a commercial plant. For the demonstration unit, the internal diameter was selected to be about 10 cm, which is significantly larger than catalyst particle size to minimize wall effects. In addition, heat transfer along the reactor wall would also be negligible. 

The particle size distribution of various latices, prepared via the above monomer emulsion addition technique, was determined with the aid of an ultracentrifuge. It was found to be invariably of the log-normal type, as shown in Figure 6, independent of the way the particles are formed. This illustrates that the agglomeration of particles during latex preparation, when the initial reactor charge contained more than 15% of the anionic emulsifier, is a random and not a selective process. 

Several length-scales have to be considered in a number of applications. For example, in a typical monolith reactor used as automobile exhaust catalytic converter the reactor length and diameter are on the order of decimeters, the monolith channel dimension is on the order of 1 mm, the thickness of the catalytic washcoat layer is on the order of tens of micrometers, the dimension of the pores in the washcoat is on the order of 1 pm, the diameter of active noble metal catalyst particles can be on the order of nanometers, and the reacting molecules are on the order of angstroms cf. Fig. 1. The modeling of such reactors is a typical multiscale problem (Hoebink and Marin, 1998). Electron microscopy accompanied by other techniques can provide information on particle size, shape, and chemical composition. Local composition and particle size of dispersed nanoparticles in the porous structure of the catalyst affect catalytic activity and selectivity (Bell, 2003). 

A.A. Khassin, T.M. Yurieva, V.N. Parmon, Fischer Tropsch Synthesis over Cohalt Containing Catalysts in Slurry Reactor. Effect of the Metallic Co Particle Size on the Selectivity, React. Kinet. Catal. Lett. 64 (1998) 55 62. 

The yields of the main products vary, as indicated in Table 2. The relative amounts depend on the purity and particle size of the silicon and the copper catalyst, the amount and nature of the additives, the temperature profile and flow velocity in the reactor, and the history of the particular contact mass. A major consideration is to maximize the selectivity for the desired Me2 SiCl2 over MeSiCb, which is often obtained in more than useful amounts. Early in the reaction, selectivity for Me2SiCl2 is high as the silicon becomes largely consumed, this selectivity decreases. The by-products MesSiCl and MeSiHCb are both usefiil in further processing. 

Figure 16 is constructed for = 10 m and = 0.50. The highest STY is obtained for the TBR using the smallest particles possible. The pressure drop is approximately 5 bar, which is close to what can be accepted. Both pressure drop and STYy decrease fast with increasing particle size, and for the 2-mm particles the STYy has dropped below the highest STYy that can be reached with the washcoated MR. For both reactors the selectivity decreases with increasing catalyst thickness. Selectivity is higher for the MR. The diffusion... 

Entrainment may be defined as the carryover of ejected particles, while selective entrainment of finer or less dense particles is often referred to as elutriation. In most industrial processes, neither entrainment nor elutriation are desirable, which is in sharp contrast to this particular application. Consequently, there is very little research aimed specifically at enhancing the selective removal of less dense material from fluidised beds. Most research on entrainment is based on dimensional analysis applied to experimental data either with no or very limited consideration of the underlying physics Predictions made from these correlations are limited to very simple geometries. They may vary widely even for reactor airangements close to the experimental conditions they are based on, and are often completely unreliable when conditions are markedly different. In several intemal studies they have been found inadequate for entrainment and elutriation predictions in the fluidised bed system under investigation. The problem is too complex to be adequately represented by a small number of ordinary equations that would simply require substitution of a few parameters to obtain the rales of entrainment of the different particle size ftactions. 

The performance targets, such as reactivity of the reaction mixture, selectivity, extension of a production campaign or reproducibility, are controlled by quite a number of parameters. The most important parameters are temperature, pressure, catalyst and promoters, poisons and inhibitors, silicon composition and structure, particle size distribution of solids, dust removal from fluidized-bed reactor, homogeneity of fluidized-bed and the purity of chloromethane. 

Liquid distribution in trickle bed reactors has been mainly discussed from the aspect of flow channels between particles [6, 7]. However, since most of the commercial catalysts are extrudates, an effect of the particle orientation on liquid distribution is much more important than flow channel, which relates to mass flow rate and a particle size. Shaped catalysts have a higher volume activity than cylindrical catalysts when an effect of diffusion on the reaction rate is large [8]. Therefore, the shaped catalysts have been commonly used for hydrodemetallation of residue. However, since an effect of liquid distribution on the catalyst performance is important in large-scale commercial reactors, catalyst shape should be carefully selected to maximize the effectiveness of the catalyst usage in a commercial application. 

Reactor selectivity for the formation of para-products raises with decreasing particle size. 

Many reported microreactors use micropacked beds for gas-liquid-solid reactions. One advantage of micropacked beds is the commercial availability of active and selective catalysts, for example, for hydrogenation reactions. Furthermore, the particle sizes of these catalysts, which are typically used in suspension reactors, are in the micrometer range and well suited for the use in microchannels. However, proper design of the reactor is required to maintain an acceptable pressure drop. 

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