Particles size distribution control

Modified ball mill configuration, particle size distribution control, improved grinding media and linings, high-pressure roller press for clinker pre-grinding, high-efficiency classifiers, roller mills... 

Numerous microporous crystallines with various structure types have been successfully synthesized by using microwave irradiation in the last decade. Compared with conventional hydrothermal synthesis, microwave synthesis has many advantages, such as narrow particle-size distribution, controllable morphology, broader parent mixture composition, and short crystallization time. It can be expected that microwave synthesis will play an important role in the rapid, energy-saving, and continuous production of microporous compounds. 

A cascade of grinding mills (Fig. 7.11 B) produces a considerably smaller particle size distribution. Control is, however, more complex than with the single-pass procedure. 

A wide variety of reactor processes have been reported in the literature and especially in patents. Most reactor designs are aimed at narrowing particle size distributions, controlling copolymer composition and/or particle morphologies, or reducing wall fouling and particle aggregation. 

To produce crystals with a mean diameter X and a narrow particle size distribution, control of the seed number is necessary. A crystal size density distribution, i. e., a balance for the number of crystals in each size... 

The RDX particle size distribution must be carefully controlled to produce castable slurries of RDX and TNT having acceptable viscosity. Several classes of RDX are produced to satisfy requirements for the various pressed and cast RDX-based compositions. A continuous process for medium-scale production of RDX has been developed by Biazzi based on the Woolwich process (79,151—154). 

Bubble size control is achieved by controlling particle size distribution or by increasing gas velocity. The data as to whether internal baffles also lower bubble size are contradictory. (Internals are commonly used in fluidized beds for heat exchange, control of soflds hackmixing, and other purposes.)... 

However, in the case of mini- and microemulsions, processing methods reduce the size of the monomer droplets close to the size of the micelle, leading to significant particle nucleation in the monomer droplets (17). Intense agitation, cosurfactant, and dilution are used to reduce monomer droplet size. Additives like cetyl alcohol are used to retard the diffusion of monomer from the droplets to the micelles, in order to further promote monomer droplet nucleation (18). The benefits of miniemulsions include faster reaction rates (19), improved shear stabiHty, and the control of particle size distributions to produce high soHds latices (20). 

The batch process is similar to the semibatch process except that most or all of the ingredients are added at the beginning of the reaction. Heat generation during a pure batch process makes reactor temperature control difficult, especially for high soHds latices. Seed, usually at 5—10% soHds, is routinely made via a batch process to produce a uniform particle-size distribution. Most kinetic studies and models are based on batch processes (69). 

The most commonly measured pigment properties ate elemental analysis, impurity content, crystal stmcture, particle size and shape, particle size distribution, density, and surface area. These parameters are measured so that pigments producers can better control production, and set up meaningful physical and chemical pigments specifications. Measurements of these properties ate not specific only to pigments. The techniques appHed are commonly used to characterize powders and soHd materials and the measutiag methods have been standardized ia various iadustries. 

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. 

Any refractory material that does not decompose or vaporize can be used for melt spraying. Particles do not coalesce within the spray. The temperature of the particles and the extent to which they melt depend on the flame temperature, which can be controlled by the fueLoxidizer ratio or electrical input, gas flow rate, residence time of the particle in the heat zone, the particle-size distribution of the powders, and the melting point and thermal conductivity of the particle. Quenching rates are very high, and the time required for the molten particle to soHdify after impingement is typically to... 

In the second process, a small particle-size latex is prepared and treated so that a limited and controlled degree of particle agglomeration occurs. The agglomerated latex is then concentrated as before but, because of the particle-size distribution obtained, the soHds may be raised to ca 70 wt %. Two methods exist for agglomeration of latices, ie, chemical and freeze agglomeration (45,46). 

Tantalum Compounds. Potassium heptafluorotantalate [16924-00-8] K TaF, is the most important tantalum compound produced at plant scale. This compound is used in large quantities for tantalum metal production. The fluorotantalate is prepared by adding potassium salts such as KCl and KF to the hot aqueous tantalum solution produced by the solvent extraction process. The mixture is then allowed to cool under strictiy controlled conditions to get a crystalline mass having a reproducible particle size distribution. To prevent the formation of oxyfluorides, it is necessary to start with reaction mixtures having an excess of about 5% HF on a wt/wt basis. The acid is added directiy to the reaction mixture or together with the aqueous solution of the potassium compound. Potassium heptafluorotantalate is produced either in a batch process where the quantity of output is about 300—500 kg K TaFy, or by a continuously operated process (28). 

Continuous emulsion copolymerization processes for vinyl acetate and vinyl acetate—ethylene copolymer have been reported (59—64). CycHc variations in the number of particles, conversion, and particle-size distribution have been studied. Control of these variations based on on-line measurements and the use of preformed latex seed particles has been discussed (61,62). 

Stricter control of particle size distribution improves powder handling (qv) and transport through the system, and appHcation efficiency. It also reduces blinding of the final filter (69). Additives have been developed which improve the triboelectric charging characteristics (70). 

Preparation of Dispersion. The reduction process is a two-phase reaction between soluble reducing agent and insoluble dye particles, and therefore the rate of reduction is influenced by the particle size distribution of the dye dispersion. The smaller the particle size the greater the surface area and hence the more rapid the reduction process. However, if the particles are too small, migration will occur in continuous dyeing. It is therefore extremely important to control the size and range of particle size and this is a closely guarded piece of dyestuff manufacturers know-how. 

For dust-control work, it is recommended that a preliminary quah-tative examination of the dust first be made without a detailed particle count. A visual estimate of particle-size distribution will often provide sufficient guidance for a preliminaiy assessment of reqmrements for collection eqmpment. 

Crystallizers with Fines Removal In Example 3, the product was from a forced-circulation crystallizer of the MSMPR type. In many cases, the product produced by such machines is too small for commercial use therefore, a separation baffle is added within the crystallizer to permit the removal of unwanted fine crystalline material from the magma, thereby controlling the population density in the machine so as to produce a coarser ciystal product. When this is done, the product sample plots on a graph of In n versus L as shown in hne P, Fig. 18-62. The line of steepest ope, line F, represents the particle-size distribution of the fine material, and samples which show this distribution can be taken from the liquid leaving the fines-separation baffle. The product crystals have a slope of lower value, and typically there should be little or no material present smaller than Lj, the size which the baffle is designed to separate. The effective nucleation rate for the product material is the intersection of the extension of line P to zero size. 

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