Catalysts particle size distribution

In summary the advantage of using neutrons for catalyst particle-size-distribution function measurements, is that, unlike X-rays, they can be applied to catalysts dispersed on high-electron-density supports such as a-Al203. This is because the technique of contrast matching to mask-out one component of the scattering is much more versatile with neutrons than with X-rays. In part this is due to the ready availability of suitable deuteriated solvents. 

Figure 6 Catalyst particle size distribution of the Pd catalysts (Under % by volume is the percentage of particles of the sample less than the indicated diameter). 

Table 2 Catalyst Particle Size Distribution and Filtration Rate... 

Catalyst Particle Size Distribution, microns Filtration Time ... 

The catalyst particle size distribution was measured via the method of laser diffraction on a Shimadzu Sald-7101 instrument. 

Among the assumptions made above, the weakest was to consider that all catalyst particles had the same size, since it is now known that industrial catalysts have a distribution of particle sizes. Defining the catalyst particle size distribution (in volume) as ndv) such that... 

Macrokinetic processes for slurry systems are sketched on Table 7. The main points are the characteristics of the three phase dispersion (fluid holdups, interfacial areas, bubbles and catalyst particles size distributions), the state of macromixing of fluids which can be defined through the concept of residence time distribution, the state of micromixing of fluids which for the gas phase shall determine the degree of coalescence of bubbles, the heat transfer between the reactor and the environment. 

Metallocene catalysts need to be supported to be used in gas phase reactors, such as Union Carbide s fluidized-bed Unipol process, or BASF s stined-bed Novolen process. For these processes, it is necessary to have a free flowing catalyst powder which will form polymer particles with adequate size distribution, avoiding the formation of fine powder or particle agglomerates. In other words, good replication of the catalyst particle size distribution is essential for the efficient performance of these reactors. 

Fluidized-bed reaction systems are not normally shut down for changing catalyst. Fresh catalyst is periodically added to manage catalyst activity and particle size distribution. The ALMA process includes faciUties for adding back both catalyst fines and fresh catalyst to the reactor. 

Of the three worldwide manufacturers of poly(ethylene oxide) resins. Union Carbide Corp. offers the broadest range of products. The primary quaUty control measure for these resins is the concentrated aqueous solution viscosity, which is related to molecular weight. Specifications for Polyox are summarized in Table 4. Additional product specifications frequendy include moisture content, particle size distribution, and residual catalyst by-product level. 

In many chemical processes the catalyst particle size is important. The smaller the aluminum chloride particles, the faster it dissolves in reaction solvents. Particle-size distribution is controlled in the manufacturer s screening process. Typical properties of a commercial powder are shown in Table 2. 

Analysis of a method of maximizing the usefiilness of smaH pilot units in achieving similitude is described in Reference 67. The pilot unit should be designed to produce fully developed large bubbles or slugs as rapidly as possible above the inlet. UsuaHy, the basic reaction conditions of feed composition, temperature, pressure, and catalyst activity are kept constant. Constant catalyst activity usuaHy requires use of the same particle size distribution and therefore constant minimum fluidization velocity which is usuaHy much less than the superficial gas velocity. Mass transport from the bubble by diffusion may be less than by convective exchange between the bubble and the surrounding emulsion phase. 

New templated polymer support materials have been developed for use as re versed-phase packing materials. Pore size and particle size have not usually been precisely controlled by conventional suspension polymerization. A templated polymerization is used to obtain controllable pore size and particle-size distribution. In this technique, hydrophilic monomers and divinylbenzene are formulated and filled into pores in templated silica material, at room temperature. After polymerization, the templated silica material is removed by base hydrolysis. The surface of the polymer may be modified in various ways to obtain the desired functionality. The particles are useful in chromatography, adsorption, and ion exchange and as polymeric supports of catalysts (39,40). 

Figure 3-10. Particle size distribution of a typical FCC catalyst.

The tests that reflect physical properties of the catalyst are surface area, average bulk density, pore volume, and particle size distribution. 

Once the unit is running well, it is often assumed that the aeration system is sized properly, but changes in the catalyst physical properties and/or catalyst circulation rate may require a different purge rate. It should be noted that aeration rate is directly proportional to catalyst circulation rate. Trends of the E-cat properties can indicate changes in the particle size distribution, which may require changes in the aeration rate. Restriction orifices could be oversized, undersized, or plugged with catalyst, resulting in over-aeration, under-aeration, or no aeration. All these phenomena cause low pressure buildup and low slide valve differential. 

Plot the physical properties of the equilibrium catalyst. The plotted properties will include particle size distribution and apparent bulk density. The graph confirms any changes in catalyst properties. 

Have the lab analyze the lost catalyst for particle size distribution. The analysis will provide clues as to the sources and causes of the losses. 

In [53], segregated catalyst and polymer particles act as micro reactors where the polymerization process takes place. Each particle is an individual reactor with its own energy and material balance. During polymerization, the catalyst particles undergo a change in volume by a factor of 10 -10, thereby generating the corresponding polymer particles. The particle size distributions of catalyst and polymer are the same. 

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