Precipitation-micronization

The dissolution profiles of PGSS-felodipine/PEG 4000 co-precipitates, along with starting felodipine and its physical mixture with PEG 4000 (1 4), are presented in Figure 9.8-15. The amount of felodipine dissolved in 1 h from felodipine/PEG 4000 co-precipitates micronized at pre-expansion pressures of 175, 190 and 195 bar is 13.5-, 10-, and 8-times higher than that of original felodipine. 

Even with proper operation of the reactor and regenerator cyclones, catalyst particles smaller than 20 microns still escape from both of these vessels. The catalyst fines from the reactor collect in the fractionator bottoms slurry product storage tank. The recoverable catalyst fines exiting the regenerator are removed by the electrostatic precipitator or lost to the environment. Catalyst losses are related to ... 

The sacrificial core approach entails depositing a coating on the surface of particles by either the controlled surface precipitation of inorganic molecular precursors from solution or by direct surface reactions [2,3,5,6,8,9,33-35,38], followed by removal of the core by thermal or chemical means. Using this approach, micron-size hollow capsules of yttrium compounds [2], silica spheres [38], and monodisperse hollow silica nanoparticles [3,35] have been generated. 

There is an upper limit of about 23 microns in size. This may be due to the fact that the precipitation was accomplished at 90 C., or from the fact that rare earth oxalates tend to form very small particles during precipitation which then grow via Ostwald ripening and agglomeration to form larger ones. Nevertheless, it is clearly evident that when the oxalate is heated at elevated temperature ( 900 °C), the oxide produced retains the same PSD characteristics of the original precipitate. 

Particles, which are built up from crystals at the time of precipitation and usually range from 0.1 to 5 microns. 

Vandegrift, the originator of this figure, cautions that in the region below 0.5 microns the data are rather sparse. ESP stands for electrostatic precipitator. 

CaC03 precipitation is clearly visible in Figure 14.14, which is a TEM image of halloysite cross-sections. Halloysite has >90% of the tubular form with outer diameter 50 5nm and inner diameter of the lumen 15 nm. The length of the initial halloysite is less than 1 micron, which results in a substantially short diffusion path length. The calculated value of the free inner space indicates the ability to load a maximum 14 3 % of the total volume ofthe halloysite. The entrapment efficiency of 5 % by volume was estimated. 

Airborne particles, bacteria, fungi spores and allergens will be removed by air filtration, which is often cheaper and more effective than electrostatic precipitators and ionizers. A disposable, high-efficiency filter capable of removing at least 95 percent of particles with size down to 0.3 micron will be installed. A washable coarse filter that removes fifty percent of particles larger than 10 microns will be used as a pre-filter to extend the life of the high efficiency filter by at least a third. An inexpensive sensor will be included to indicate when filter replacement is necessary. 

Ground calcium carbonate, extracted from the earth, is present in practically every country in the world in varying quantities in the form of limestone, marble, dolomite or chalk. Following the extraction, GCC needs to be ground. Dry grinding, the cheaper alternative, is often limited to a minimum particle size of 2- 3 microns. Wet grinding, more expensive, is used for fine and ultra fine material or when the final product must be a slurry (paper or paint application). Precipitated calcium carbonate is produced by chemical reaction between... 

The TSS has less potential for maximum emission control as the WGS and electrostatic precipitator (ESP). While all three technologies were designed to meet NSPS/ MACT, only the WGS and ESP can meet more stringent requirements. TSS performance can typically achieve d50 grade efficiency down to 2 microns. Most reported performance values result in emissions of 0.4-0.8 Ib/Mlb coke. Future PM2 5 regulations are a concern for TSS applications. By definition, TSS units cannot effectively remove small particles due to the cyclonic operation. 

If reaction is allowed to proceed until the termination stage is reached, the terminal thickness of many CD films is typically several hundred nanometers, although it may reach a micron or more in some cases. This terminal thickness depends to a large extent on the deposition parameters. To take an extreme case, addition of sulphide to a solution of Cd ions will give an immediate precipitate of CdS, but no (or at most an extremely thin) deposit on the walls of the deposition vessel, which may thicken somewhat with time, but will not be visible (which means a terminal thickness less than ca. 20 nm). For a normal CD reaction, if precipitation occurs homogeneously in solution, then that precipitate is lost for film... 

A triethanolamine/ammonia bath has been used for CdSe [19]. While this system resulted in thick films for CdS (up to a few microns), CdSe films deposited under the same conditions, only using selenosulphate instead of thiomea, were thinner [although films of 500 nm were obtained at 30°C that did not show signs of satuation (of thickness) after 25 hr—the longest time measmed]. Ethylenedi-amine has also been used as a complex for Cd, with both precipitates and films formed [86]. In this case, the emphasis was on the precipitates, and no characterization was carried out on the films. 

Micronization with supercritical fluids - Crystallization - Rapid expansion - Gas anti-solvent Recrystallization - Precipitation with compressed anti-solvent - Solution-enhanced dispersion - Particles from gas-saturated solutions 80 - 300 fine particles and powders from various products and of designed properties... 

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