Continuous vacuum evaporation crystallization

A Kryslai type of vacuum evaporator-crystallizer B Forced-circulation pump C Slurry-redrculation pump D Mother-liquor recycle pump E Mother-liquor tank F Continuous or batch centrifuge G Slurry concentrator H Drier conveyor I Rotary drier J Dried-product conveyor K Vacuum condenser-ejector unit... 

The reaction mixture is diluted with 250 ml of water, the mixture is transferred to a 2 liter flask using methanol as a wash liquid, and the organic solvents are distilled at 20-25 mm using a rotary vacuum evaporator. The product separates as a solid and distillation is continued until most of the residual toluene has been removed. The solid is collected on a 90 cm, medium porosity, fritted glass Buchner funnel and washed well with cold water. After the material has been sucked dry, it is covered with a little cold methanol, the mixture is stirred to break up lumps, and the slurry is kept for 5 min. The vacuum is reapplied, the solid is rinsed with a little methanol followed by ether, and the material is air-dried to give 9.1 g (85%), mp 207-213° after sintering at ca. 198°. Reported mp 212-213°. The crude material contains 1.0-1.5% of unreduced starting material as shown by the UV spectrum. Further purification may be effected by crystallization from methanol. 

In most commercial processes, borax is obtained from lake brines, tincal and colemanite. The primary salt constituents of brine are sodium chloride, sodium sulfate, sodium carbonate and potassium chloride. The percent composition of borax as Na2B40 in brine is generally in the range 1.5 to 1.6%. Borax is separated from these salts by various physical and chemical processes. The brine solution (mixed with mother liquor) is subject to evaporation and crystahzation for the continuous removal of NaCl, Na2C03 and Na2S04, respectively. The hot liquor consists of concentrated solution of potassium salts and borate components of the brine. The insoluble solid particles are filtered out and the liquor is cooled rapidly in continuous vacuum crystallizers under controlled conditions of temperatures and concentrations to crystallize KCl. Cystallization of borax along with KCl from the concentrated liquor must not occur at this stage. KCl is separated from the hquor by filtration. Bicarbonate then is added to the liquor to prevent any formation of sodium... 

Spray some drops of coffee into a vacuum chamber, and they, too, boil until they freeze. Even after they are frozen, the water molecules continue to evaporate into the vacuum until all that is left to be seen are little crystals of coffee solids. This is how freeze-dried coffee is made. The low temperature of this process tends to keep the chemical structure of the coffee solids from changing. When hot water is added, much of the original flavor of the coffee is retained. 

Hexamine is manufactured from anhydrous ammonia (NH3) and a 45% solution of methanol-free formaldehyde (HCH=0). These raw materials, plus recycle mother liquor, are charged continuously at carefully controlled rates to a high-velocity reactor, since the reaction is exothermic. The reactor effluent is discharged into a vacuum evaporator that also serves to crystallize the product, and the hexamine crystals are washed, dried, and screened. Typically, the yield of hexamine is on the order of 96%. 

A stream of a saturated brine suspension of crystals is continuously withdrawn from each evaporator-crystallizer, and the salt crystals separated on a continuous rotary filter with return of the brine to the evaporator. Much of the salt may be marketed in moist condition, or it may be passed through a drier moving countercurrently to heated air to give vacuum salt of typically 99.8-99.9% purity [21]. 

The industrial crystallization process examined is outlined in Figure l.The filtered fermentation broth was fed to the vacuum evaporator and concentrated to 28 g/dl then the pH was adjusted within the range of 1.7 to 2.0 with sulfuric acid. When this solution was cooled continuously through a two-stage crystallizer whose temperature were 40 and 25 C, the pillar form crystals of the sulfate salt of l phenylalanine formed and were easily separated by centrifugation. 

However, salt obtained by evaporation of seawater had a number of drawbacks the purity was limited, mainly due to the high content of inclusions of mother liquor that entrained impurities. Hence, industrial techniques have developed over the time for the industrial crystallization of salt, resulting in the modern continuous vacuum crystallization apparatus. 

---