Separation-purification using

Figure 15. Hydrogen separation-purification using hydrides...

Minerals and Metals. HCl is consumed in many mining operations for ore treatment, extraction, separation, purification, and water treatment (see Mineral recovery and processing). Significant quantities are also used in the recovery ofmolybdenum (see Molybdenum and molybdenum alloys) and gold (see Gold and gold compounds). This market consumed about 36 thousand metric tons in 1993. 

Alternatives to oxychlorination have also been proposed as part of a balanced VCM plant. In the past, many vinyl chloride manufacturers used a balanced ethylene—acetylene process for a brief period prior to the commercialization of oxychlorination technology. Addition of HCl to acetylene was used instead of ethylene oxychlorination to consume the HCl made in EDC pyrolysis. Since the 1950s, the relative costs of ethylene and acetylene have made this route economically unattractive. Another alternative is HCl oxidation to chlorine, which can subsequently be used in dkect chlorination (131). The SheU-Deacon (132), Kel-Chlor (133), and MT-Chlor (134) processes, as well as a process recently developed at the University of Southern California (135) are among the available commercial HCl oxidation technologies. Each has had very limited industrial appHcation, perhaps because the equiHbrium reaction is incomplete and the mixture of HCl, O2, CI2, and water presents very challenging separation, purification, and handling requkements. HCl oxidation does not compare favorably with oxychlorination because it also requkes twice the dkect chlorination capacity for a balanced vinyl chloride plant. Consequently, it is doubtful that it will ever displace oxychlorination in the production of vinyl chloride by the balanced ethylene process. 

It is fruitless to attempt detailed study of a phenomenon whose products are not well identified. It is unfortunately frequently noted in the literature, especially in cases of column chromatography, that fractions are only identified as to the chemical operations which brought them to light. Fractions are identified, for example, only by the solvent used. Speculations as to the composition of the radioactive solutes in such solutions can seldom be really reliable, and the presence of an unexpected radioactive species is in such cases undetectable. It is also important in reading the literature to watch out for cases in which the chemical yields of the carriers have not been measured. Extensive decomposition can often occur on silica gel and alumina columns, especially when photosensitive or moisture sensitive compounds are used. For these reasons much of the information now existing in the literature must be regarded as only exploratory, awaiting the development of better analytical methods for separation, purification, identification and determination of the products —known or expected. 

Downstream purification and isolation of proteins and biomolecules is often the most expensive and challenging aspect of their production [91]. Many of the downstream separation processes used by industry today, e.g., ultraliltration, chromatography, and centrifugation, are slow, inherently batch, nonspecific, expensive, overconsume energy, and generate wastes, particularly for downstream product purification, an important cate-... 

In the broadest sense, coordination chemistry is involved in the majority of steps prior to the isolation of a pure metal because the physical properties and relative stabilities of metal compounds relate to the nature and disposition of ligands in the metal coordination spheres. This applies both to pyrometallurgy, which produces metals or intermediate products directly from the ore by use of high-temperature oxidative or reductive processes and to hydrometallurgy, which involves the processing of an ore by the dissolution, separation, purification, and precipitation of the dissolved metal by the use of aqueous solutions. 4... 

Morigami, Y., Kondo, M., Abe, J., Kita, H., and Okamoto, K. (2001) The first large-scale pervaporation plant using tubular-type module with zeolite NaA membrane separ. Purif. Tech., 25, 251-260. 

Neumann, A.W., Absolom, D.R., Francis, D.W. and van Oss C.J. (1980). Conversion tables of contact angles to surface tension For use in determining the contribution of the van der Waals attraction or repulsion to various separation processes. Separ. Purif Mech. 9, 69-163. 

Crystallization processes can be used for separation, purification, or concentration of a solute, or because a particular product needs to be used in solid form, or as a component of an analytical procedure. Common requirements for accomplishing these functions are that the crystals must be produced with a particular size distribution and having a specified shape and purity. Almost all crystallizer operating problems are defined in terms of the product not meeting one of these criteria. 

According to the vendor, liqnid-liquid extraction (LLX) provides recovery, separation, purification, and concentration of metals in one unit process. By use of the proper extractant, metals can be reduced in process or waste streams to the low parts per million (ppm) level. The metals concentrated by the process can often be reused. When appropriate, specific metals can be recovered selectively in the presence of other metals or process stream components. Alternatively, broad-spectrum metal recovery is achievable with the properly selected extractant or process. 

Alain Berthod received his PhD in 1979 from the University of Lyon. He took an assistant professor s position at the French National Center for Scientific Research (CNRS) working in electrochemistry. In 1983 he was promoted as associate professor and in 1993 as research director. He focused on the developing and the use of micellar solutions and microemulsions in chromatography. His interests lie in the separation of chiral molecules and enantiorecognition mechanisms. He has contributed to the development of the countercurrent chromatography technique that uses a sup-port-free liquid stationary phase. He was member of the editorial board of major analytical chemistry and chromatography journals. He is editor-in-chief of Separation Purification Reviews (Taylor Francis, Philadelphia, Pennsylvania). 

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