Separation spray crystallization

Although spray-crystallized dextrose-maltose (EMDEX , J. Rettenmaier Sohne GmbH Co. KG, Germany) and compressible sugars are coprocessed, they are commonly considered as single components and are listed as such in the United States Pharmacopeia, while the third edition of the Handbook of Pharmaceutical Excipients has listed SMCC as a separate excipient (58). 

Solvents are important ingredients of emulsifiable concentrates and of solution formulations. When the formulation is to be used on crops, it is critical that the solvent be nonphytotoxic. The solvent must have a high level of solvent power if an EC is being formulated. Because most toxicants are insoluble in water, the solvent must also be water insoluble. Otherwise, when the EC is added to water in the spray tank, the solvent will mix with the water and leave the toxicant behind as a crystalline precipitate. The carrying power of the solvent, i.e., the amount of pesticide it will hold in solution, is important in the storage stability of formulations. If near its saturation point at ordinary temperatures, it may exceed this at low temperature with the result that solvent and pesticide may separate, causing crystal formation and phase separation (Terriere, 1982). 

There are two commercial solvent crystaUi2ation processes. The Emersol Process, patented in 1942 by Emery Industries, uses methanol as solvent and the Armour-Texaco Process, patented in 1948, uses acetone as solvent. The fatty acids to be separated are dissolved in the solvent and cooled, usually in a double-pipe chiller. Internal scrapers rotating at low rpm remove the crystals from the chilled surface. The slurry is then separated by means of a rotary vacuum filter. The filter cake is sprayed with cold solvent to remove free Hquid acids, and the solvents are removed by flash evaporation and steam stripping and recovered for reuse (10). 

Complete descriptions of the particle beam, its operation, its experimental setup, and its utility in protein structural studies have been previously described. (8, 12). Relevant PB dimensions include a 25 pm diameter fused silica capillary for production of the aerosol spray, a 22 cm length desolvation chamber to remove solvent, a single stage momentum separator, and a nozzle-substrate distance of 5 mm. Particle beam deposits ranged in size from 20 pm to 100 pm in diameter, and averaged approximately 50 pm. Deposit were made onto a water insoluble calcium fluoride (CaFj) window (25 mm dia. x 2 mm) from International Crystal Laboratories (Garfield, NJ). 

Trona may be recovered from the deposit by conventional dry, or solution mining depending on the nature and accessibility of the source [19]. Fractional crystallization of solutions of trona [20] or the sodium carbonate-rich brines separates the sodium carbonate for recovery. Sodium carbonate has also been produced from trona in a spray drier [21]. 

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