Batch average particle size

The rate of polymerization with styrene-type monomers is directly proportional to the number of particles formed. In batch reactors most of the particles are nucleated early in the reaction and the number formed depends on the emulsifier available to stabilize these small particles. In a CSTR operating at steady-state the rate of nucleation of new particles depends on the concentration of free emulsifier, i.e. the emulsifier not adsorbed on other surfaces. Since the average particle size in a CSTR is larger than the average size at the end of the batch nucleation period, fewer particles are formed in a CSTR than if the same recipe were used in a batch reactor. Since rate is proportional to the number of particles for styrene-type monomers, the rate per unit volume in a CSTR will be less than the interval-two rate in a batch reactor. In fact, the maximum CSTR rate will be about 60 to 70 percent the batch rate for such monomers. Monomers for which the rate is not as strongly dependent on the number of particles will display less of a difference between batch and continuous reactors. Also, continuous reactors with a particle seed in the feed may be capable of higher rates. 

In a batch thickener, an aqueous sludge containing 35% by volume of solids (SG = 1.6), with an average particle size of 50 pm, is allowed to settle. The sludge is fed to the settler at a rate of 1000 gpm, and the clear liquid overflows the top. Estimate the minimum tank diameter required for this separation. 

The counterparts of dissolving particles are the processes of precipitation and crystallization the description and simulation of which involve several additional aspects however. First of all, the interest in commercial operations often relates to the average particle size and the particle size distribution at the completion of the (batch) operation. In precipitation reactors, particle sizes strongly depend on the (variations in the) local concentrations of the reactants, this dependence being quite complicated because of the nonlinear interactions of fluctuations in velocities, reactant concentrations, and temperature. 

A series of runs were made on this mill, and grind times were measured to achieve a 3 micron average particle size for batch sizes ranging from 4.5 to 20 gallons. The mill used 1/8 inch stainless steel media and operated at 360 RPM, with the pump rate set at 2 gpm (see Table VIl). 

Experimentally, kjp and A are adjusted until a best fit between computer and experimental a vs. t curves is obtained. The agreement between the model and data can be judged from Figure 3. Although the predicted and experimental curves vary by only 1% decomposed, model constants obtained from samples having different average particle size vary by 10%. Thus, the model accounts for the effect of particle size to within 10%. Moreover, it is possible to predict the experimental o (0mixture vs. t curve for a mixture of batches of material with different size distributions. Thus,... 

From the standpoint of the user, reproducible averages are desirable. For example, the pack -bed permeability depends on the square of the particle size. Therefore a 10% shift in the average particle size would result in a 20% change in column backpressure. Such a large difference is unacceptable. Figure 4.3 shows the particle size distribution of several batches of Symmetry silica. One can see that today s sizing techniques can give quite reproducible results. 

In any materials process, it is essential that the starting powders be well characterized. This is especially true for tape casting. The important parameters to monitor in all powder lots are the average particle size and distribution, surface area, and trace-impurity level. The powder density in weight per unit volume is also an essential property that must be considered when formulating a batch for tape casting. 

Using these methods, both the composition and the microstructure can be varied. It is the combination of these attributes - control over microstmeture at a number of different length scales and over composition, simultaneously - that is extremely important to the performance of the electrocatalyst powder in an MEA. The spray-based manufacturing approach can relatively independently vary three main characteristics of the powder batch a) particle size (from an average size... 

Particle formation in a steady-state CSTR, however, depends on the amount of free emulsifier within the CSTR and, thus, in the effluent stream. The average particle size will be larger than that of the particles in a batch reactor at the end of the nucleation period. Also these larger particles will be saturated with... 

Early commercial catalysts were supplied to a strict specificatioa The average particle size was usually in the range 10-100 pm with an activity exceeding 1000 g polypropylene per gram of catalyst and an isotactic index exceeding 88%. Continuous, rather than batch, operation was possible with the new, externally formed eatalyst but the efficiency was still low and the polypropylene still contained unacceptably high levels of both catalyst residues and atactic polymer. 

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