Separation/purification methods solvent extraction processes

Purification or refining of rare earths. The separation of rare earths from thorium can be performed in different ways depending on the production scale. Small laboratory-scale methods used first the fractional crystalhzation of nitrates, followed by the fractional thermal decomposition of nitrates. Pilot-scale separation can be achieved by ion exchange. Large commercial-scale separation is based only on the solvent-extraction process of an aqueous nitrate solution with n-tributyl phosphate (TBP) dissolved in kerosene. 

The recovery system may affect the amount of product recovered, the convenience of the subsequent purification steps and the quality of the final product. Cell separation from the fermentation broth is the preliminary step of the recovery method. In order to recover the PHA granules, it is necessary to rupture the bacterial cell and remove the protein layer that coats the PHA granules. Alternatively, the PHA has to be selectively dissolved in a suitable solvent. Generally, two methods are usually utilized for the recoveiy and purification of PHAs from cell biomass, which include PHA solubilization or non-polymer cellular material (NPCM) dissolution. The majority of the PHA recovery method is performed using a solvent extraction process mainly by chloroform and methanol. Modifying the cell wall s permeability and then PHA dissolution in the solvent are the mechanisms for PHA extraction. 

Extraction is a method used to separate the desired product from impurities. This process is used in product purification and results from an unequal distribution of solute between two immiscible solvents. This process, then, makes use of differences is solubilities to separate components in what is called a work-up. 

Extraction of Essential Oils from Plants. Essential oils are aromatic substances widely used in the perfume industry, the pharmaceutical sector, and the food and human nutrition field. They are mixtures of more than 200 compounds that can be grouped basically into two fractions a volatile fraction, which constitutes 90-95% of the whole oil, and a nonvolatile residue, which constitutes the remaining 5-10%. The isolation, concentration, and purification of essential oils have been important processes for many years, as a consequence of the widespread use of these compounds. The common methods used are mainly based on solvent extraction and steam distillation. SFE has been used for the extraction of essential oils from plants, in an attempt to avoid the drawbacks linked to conventional techniques (57). Such is the case with the extraction of flavor and fragrance compounds, such as those from rose (58), rosemary (59), peppermint (60), eucalyptus (61), and guajava (62). The on-line coupling of the extraction and separation ietermi-nation steps (by SFE-GC-FID) has been proposed successfully for the analysis of herbs (63) and for vetiver essential oil (64). 

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. 

The establishment of a nuclear power industry based on fission reactors involves the production of a number of materials that have only recently acquired commercial importance, notably uranium, thorium, zirconium, and heavy water, and on the operation of a number of novel chemical engineering processes, inciuding isotope separation, separation of metals by solvent extraction, and the separation and purification of intensely radioactive materials on a large scale. This text is concerned primarily with methods for producing the special materials used in nuclear fission reactors and with processes for separating isotopes and reclaiming radioactive fuel discharged from nuclear reactors. 

The biological activity of molecules such as proteins, cells, and viruses can easily be destroyed by processing conditions that do not conform to their natural environment. Therefore, traditional separation processes such as distillation or solvent extraction are seldom used to isolate them. Affinity adsorption is one of the most effective methods for the direct isolation and purification of biomolecules from complex mixtures (Camperi et al., 2003). It is based on recognition between a pair of molecules determined by the steric structure (three-dimensional arrangement of its atoms) of the molecules. When molecules have complementary steric structures, they can interact to maximize the hydrogen bonds and electrostatic interactions. Affinity adsorption allows a separation with high specificity and purity. 

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