Crystallization crystal size control

Jhung, S.H., Lee, J.H., and Chang, J. (2008) Crystal size control of transition metal ion-incorporated aluminophos-phate molecular sieves effect of ramping rate in the syntheses. Micropor. Mesopor. Mater., 112, 178-185. 

Kitamura M, Yamamoto M, Yoshinaga Y, Masuoka H. Crystal size control of sulfathiazole using high pressure carbon dioxide. J Cryst Growth 1997 178 378-386. 

During the freezing process, the cold accumulator loop can be used as a thermal flying wheel which results, when operated shelf by shelf, in an almost instantaneous freezing effect on the product. This high freezing rate capability is mostly used in ice crystal size control. 

Uses O/w emulsifier, wetting agent, dispersant, solubilizer for personal care, topical pharmaceuticals, household, and Industrial applies. emulsifier for fIre-resIst. hydraulic fluids, water-misc. cutting fluids solubilizer, emulsifier for flavors, vitamin oils emulsion stabilizer for dietary supplements provides dryness in ice cream flavor/color dispersant in pickles, yeast defoamers antifoam for beet sugar prod. crystal size control agent In salt Regulatory USP/NF, EP compliance FDA 21CFR 172.515,172.840 Properties Yel. brn. liq. sol. in water, at low levels in cottonseed oil vise. 460 cps HLB 15.0... 

Madsen C and Jacobsen C J FI 1999 Nanosized zeolite crystals—convenient control of crystal size distribution by confined space synthesis Chem. Commun. 673-4... 

Sodium fluoride is normally manufactured by the reaction of hydrofluoric acid and soda ash (sodium carbonate), or caustic soda (sodium hydroxide). Control of pH is essential and proper agitation necessary to obtain the desired crystal size. The crystals are centrifuged, dried, sized, and packaged. Reactors are usually constmcted of carbon brick and lead-lined steel, with process lines of stainless, plastic or plastic-lined steel diaphragm, plug cock, or butterfly valves are preferred. 

Optimizing the Cr layer also controls the crystal size and morphology. It was reported in 1986 (89,90) that the Cr underlayer thickness has a great influence on the coercivity of the Co—Ni—Cr layer. In most of the Hterature it can be found that with increasing Cr thickness the increases. Under ideal conditions and the right material combinations coercivities above 240 kA/m have been prepared. 

In order to make an efficient Y202 Eu ", it is necessary to start with weU-purifted yttrium and europium oxides or a weU-purifted coprecipitated oxide. Very small amounts of impurity ions, particularly other rare-earth ions, decrease the efficiency of this phosphor. Ce " is one of the most troublesome ions because it competes for the uv absorption and should be present at no more than about one part per million. Once purified, if not already coprecipitated, the oxides are dissolved in hydrochloric or nitric acid and then precipitated with oxaflc acid. This precipitate is then calcined, and fired at around 800°C to decompose the oxalate and form the oxide. EinaHy the oxide is fired usually in air at temperatures of 1500—1550°C in order to produce a good crystal stmcture and an efficient phosphor. This phosphor does not need to be further processed but may be milled for particle size control and/or screened to remove agglomerates which later show up as dark specks in the coating. 

Nickel Phosphate. Tri nickel orthophosphate [14396-43-17, Ni2(P0 2 7H20, exists as apple-green plates which decompose upon heating. It is prepared by the reaction of nickel carbonate and hot dilute phosphoric acid. Nickel phosphate is an additive to control the crystal size of ziac phosphate ia coaversioa coatiags which are appHed to steel prior to its being paiated (see Metal surface treatments). 

The ammonium perchlorate solution is spray-dried to the desired crystal size at air temperatures below 150°C and crystal temperatures of about 110°C. This procedure provides a pure product having a controlled grain size. Prior mechanical and thermal treatment affects the isothermal... 

Control of supersaturation is an important factor in obtaining crystal size distributions of desired characteristics, and it would be useful to have a model relating rate of cooling or evaporation or addition of diluent required to maintain a specified supersaturation in the crystallizer. Contrast this to the uncontrolled situation of natural cooling in which the heat transfer rate is given by... 

Thermally efficient calcination of lime dolomite and clay can be carried out in a multicompartmeut fluidized bed (Fig. 17-27). Fuels are burned in a fluidized bed of the product to produce the required heat. Bunker C oil, natural gas, and coal are used in commercial units. Temperature control is accurate enough to permit production of hme of very high availability with close control of slaking characteristics. Also, half calcination or dolomite is an accepted practice. The requirement of large crystal size for the hmestoue limits apphcatiou. SmaU-sized crystals in the hmestoue result in low yields due to high dust losses. 

In some crystalhzation apphcations it is desirable to increase the solids content of the shiny within the body above the natural consis-tencw, which is that developed by equilibrium cooling of the incoming feed solution to the final temperature. This can be done by withdrawing a stream of mother liquor from the baffle zone, thereby thickening the shiny within the growing zone of the crystallizer. This mother liquor is also available for removal of fine ciystals for size control of the product. 

Crystallization generally involves the evaporation and subsequent cooling of a solution to the point of supersaturation, whereupon the formation of crystals takes place. Modern technology often focus on the control of crystal size, since product demands frequently are rigorous in this regard. The process of crystallization is often conducted in evaporators. As in the evaporation of salt and in the recovery of salt and glycerin in soap manufacturing, salt separators are used to remove crystallized materials as rapidly as it settles. 

In the present case the state variables are most conveniently chosen as crystal size, moments of the distribution and solution concentration (which, as shown above, give rise to ordinary rather than partial differential equations, equations 7.14-7.18) while the control is solution temperature. The performance measure adopted is to maximize the terminal size of the S-crystals (i.e. those originating as added seeds those from nuclei being A -crystals )... 

Estimate the maximum product crystal size and determine a simple controlled cooling curve (Jones, 1972, 1974 Mullin and Jones, 1974). 

In this case, the co-solvent dosage rate is programmed in order to control the transient level of supersaturation in an effort to improve on the product crystal size distribution from simply dumping in all the solvent at the start of the batch. An experimental crystallizer within which a programmed microcomputer determines the set point of a variable speed-dosing pump is shown in Figure 7.7. Controlled co-solvent dosing improves the product crystal size, with a consequent increase in the filterability of the product. These process concepts are developed further in Chapter 9. 

The size of crystals produced in the gas-liquid system varied from 10 to 100 pm by controlling the level of supersaturation, while the liquid-liquid system produced crystals of 5—30 pm. The wide variation of crystal size is due to the marked sensitivity of the nucleation rate on the level of supersaturation, while the impurity content is another variable that can affect the crystal formation. 

Crystallization process control is desirable from a number of standpoints. The primary objective is often to meet customer requirements by achieving consistent product quality to a desired specification of crystal size, size distribution and purity. Secondly, process requirements often dictate maintenance of stable crystallizer operation, the avoidance of fines and encrustation, and the minimization of subsequent downstream processing. 

Beckmann, J.R. and Randolph, A.D., 1977. Crystal size distribution and dynamics in a classified crystallizer. Part II. Simulated control of crystal size distribution. American Institution of Chemical Engineers Journal, 23, 510-520. 

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