Separation/purification methods precipitation processes

Energetic compounds can be collected for reuse by processing to reject binder, impurities, and other inert components. Explosives such as high-blast explosive (HBX), HMX, research department explosive (RDX, or hexahydro-l,3,5-trinitro-l,3,5-triazine), tetryl, TNT, NG, and NC are dissolved or suspended by steaming, high-pressure water jet cutting, or solvent extraction. Filtration, selective extraction/precipitation, vacuum evaporation, and other purification methods then separate the explosives from the binders and impurities, such as metal fragments and decomposition products. 

Although precipitation constitutes the concluding part of the hydrometallurgical process flowsheet, the process is also put to use as a purification step in order to separate impurities. The different methods of precipitation are shown in Figure 5.25. The crystallization process is probably the simplest method to remove metals from solutions as compounds. No reagents are added, and the process simply involves the complete dissolution of the metal salt at a suitable temperature and pressure to obtain as high a metal content as possible. As the temperature is raised or lowered, depending on the particular system, the solubility of the metal salt in solution is exceeded and the salt precipitates or crystallizes... 

Another method of preparation is as follows 1 33 parts of fluorescein are dissolved in 5 parts of ether and treated with 25 parts of selenium chloride in the same solvent. A yellowish-red precipitate separates, and after long stirring at the ordinary temperature the ether is distilled off. The residue is stirred with water, the mixture filtered and the residue now dissolved in sodium hydroxide. After further filtration the filtrate is treated with hydrochloric acid, which precipitates seleno-fluorescei n. Further purification is effected by solution in alkali and reprecipitation. A reddish-brown powder is obtained, soluble with fluorescence in alcohol, but insoluble in water. In concentrated sulphuric acid it dissolves to give an orange solution. Its alkali salts are very soluble in wrater, giving red solutions. This process may also be applied to phthalins, which are obtained by the reduction of phthaleins and their halogen derivatives. If the selenium chloride is replaced by the oxychloride similar products are obtained.2 In place of the phthalins specified in the patents quoted, their O-acetyl compounds or O-acetyl compounds of the phthaleins may be used in indifferent solvents. The products are different from those obtained by the action of selenium on fluoresceins in aqueous alkali solutions.3... 

It is often desirable to go through a postlysis separation/concentration step prior to chromatography. Concentration methods involve the use of ammonium acetate and polyethylene glycol precipitation to further remove host proteins and small nucleic acids. These methods also reduce the volume of the sample (or the process streams) prior to chromatographic purification. The separation may also involve centrifugation and filtration to remove cell debris. 

Precipitation is used as a separation step during the early stages of a purification process, usually followed by chromatographic separations, and also as a concentration method prior to an analysis or to a subsequent purification step. 

Purity, safety, potency, and cost-effectiveness are some of the main factors that should be considered when designing an expression method and, more importantly, when defining the purification processes. The purification of antibodies was most likely initiated with the separation of proteins, mainly paraproteins, several decades ago. A plethora of protocols have now been described involving precipitation with a variety of chemical agents, electrophoretic separation, membrane methodologies, and liquid chromatography. The latter probably represents the most popular technique because of the ease of implementation, the capability to play on the selectivity, and the... 

Purification can also be achieved in other ways, through precipitation with salts, crystallization, and through aqueous two-phase extraction. Some of these methods are associated with substantial capital cost, low throughput, low yields, or waste issues. Fractional precipitation, one of the oldest protein separation technologies, can be surprisingly effective to separate a compound of interest from a complex broth. For instance, the process of fractional solvent precipitation of blood plasma components has been used since World War II. 

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