Separation processes high-purity materials

Crystallization — The process of forming solid crystals from solution, melted or polycrystalline phase. Used to separate solid and liquid phase or preparing high purity materials. Crystallization from solution is the most common example of solid-liquid separation. In the process, the solid crystals are formed from supersaturated solution (the solution that contains more soluble molecules, ions etc. that it would under equilibrium conditions). Usually the supersaturated solution is obtained either by cooling the solution, evaporating the solvent, pH change, or adding another solvent. The crystallization process can be induced electrochemically (- electro deposition, electro crystallization). The most common ex-... 

The advantage of the Amoco process is that high-purity terephthalic acid is produced in one step. The solubility of terephthalic acid in acetic acid is low its separation with high purity by crystallization is therefore relatively easy. However, the corrosive nature of the acids and the relatively drastic conditions make it necessary to use special material of construction for the reactors. 

Precipitation from supercritical fluids is of interest not only in relation to the production of uniform particles. The thermodynamics of dilute mixtures in the vicinity of the solvent s critical point (more specifically, the phenomenon known as retrograde solubility, whereby solubility decreases with temperature near the solvent s critical point) has been cleverly exploited by Chlmowitz and coworkers (12-13) and later by Johnston et al. (14). These researchers implemented an elegant process based on retrograde solubility for the separation of physical solid mixtures which gives rise to high purity materials. 

The separation of organic mixtures into groups of components of similar chemical type was one of the earliest applications of solvent extraction. In this chapter the term solvent is used to define the extractant phase that may contain either an extractant in a diluent or an organic compound that can itself act as an extractant. Using this technique, a solvent that preferentially dissolves aromatic compounds can be used to remove aromatics from kerosene to produce a better quality fuel. In the same way, solvent extraction can be used to produce high-purity aromatic extracts from catalytic reformates, aromatics that are essentially raw materials in the production of products such as polystyrene, nylon, and Terylene. These features have made solvent extraction a standard technique in the oil-refining and petrochemical industries. The extraction of organic compounds, however, is not confined to these industries. Other examples in this chapter include the production of pharmaceuticals and environmental processes. 

Solvent extraction is a frequently employed technique in isotope dilution analysis. It gives very clean separations, resulting in high-purity samples. It has the disadvantage of requiring further chemical processing to determine the mass of material isolated and the specific activity. 

Ganzi, G.C. (1988) Electrodeionization for high purity water production, in New Membrane Materials and Processes for Separation, 84 (eds K.K. Sirkar and... 

SuperLig materials have been used to recover at high purity Rh, Pt, and Pd from spent catalyst [36]. These individual elements can be recovered at purity levels of > 99.9%. The separation and recovery of rhodium is particularly difficult because of the similarity of its chemical properties to those of the remaining platinum metals. An MRT process has been developed that is effective for rhodium separations and recovery. This process is used commercially for rhodium production. An example of rhodium separation and recovery is given in Table 8. Another case of precious metal... 

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