Separation processes, based on the

HSCCC is attracting attention based on its high separation scale, 100% recovery of sample, and mild operating conditions. It is a chromatographic separation process based on the partition coefficients of different analytes in two immiscible solvent systems (mobile phase and stationary phase) subjected to a centrifugal acceleration field. 

Kinetic resolution. Kinetic resolution is a separation process based on the different rates of the transformation of the enantiomers into certain products under the influence of chiral reagents or catalysts. In recent years the use of enzyme-catalyzed enantio-selective hydrolysis of chiral esters has attracted much attention (3). A large rate difference in the transformation of the starting enantiomers is an important criteria for this technology to be of practical use. 

Another example in which change in the interphase transfer direction is made use of is provided by separation processes based on the dependence of selectivity and sorbability of polyfunctional ion exchangers upon the solution pH [33]. 

In the meantime, the chemical industry has developed munerous processes based on the use of adsorption. The complexity of these processes has been increasing constantly. Some of the recent ones are based on the use of chromatographic principles. This is the case for separation processes based on the simulated moving bed concept [6-8]. Initially developed for the extraction of a few... 

For a given separation problem, differences in selectivity of the two processes result therefore from both the diffusivity in, and the affinity of solutes i andj for, the membrane polymer. This is the principal difference and advantage that pervaporation has in comparison with separation processes based on the vapor-Hquid equilibrium, such as distillation. It must certainly be noted that while selectivities can be higher in pervaporation, the flux (a kinetic parameter) per unit mass transfer area will in general be lower, owing to the additional mass-transport resistance presented by the membrane. However, this can be compensated for by increasing the membrane area, which contribution to the overall process costs has became less relevant during recent years. 

Separation processes based on the formation of adducts with urea, thiourea and other substances have been described by several authors (Findlay and Weedman, 1958 Hoppe, 1964 Santhanam, 1966 McCandless, 1988 Jadhav, Chivate and Tavare, 1991, 1992 Kitamura and Tanaka, 1994). 

Flotation is a gravity separation process based on the attachment of air or gas bubbles to solid (or liquid) particles, which are then carried to the liquid... 

Separation processes based on the wettability make use of the effect that hydrophobic particles can be attached to air bubbles that transport them to the surface of the pulp, forming a froth that is collected as a concentrate. This process is known as flotation, and is an important method of solid-solid separation in the mineral industry. Various reagents are used to enhance the process. Flotation is used for the recovery of sulfides and oxides of various metals such as copper, lead, zinc, nickel, molybdenum, iron, titanium, tungsten, and tin. 

Paper electrophoresis is a separation process based on the differential migration of electrically charged molecules in an electric field. It is carried out on a strip of paper impregnated with a suitable electrolyte. Solutions of substances to be analyzed are applied on it (as in paper chromatography) and the ends of the strip are connected with the positive and negative poles,... 

Although there are many types of membranes employed in various gas separation and water purification processes, similar membrane formation processes are often employed. The phase inversion process promoted by nonsolvent addition and the thermal phase separation process based on the fundamentals discussed above are the most prevalent processes to produce membranes. In addition to References 20-22,References 25-31 " also discuss these processes, and therein applications are covered in more detail than will be attempted in this chapter. 

Solvent deasphalting. This is an extraction of the heaviest fractions of a vacuum residue or heavy distillate. The extract is used to produce the bitumen. The separation is based on the precipitation of asphaltenes and the dissolution of the oil in an alkane solvent. The solvents employed are butane or propane or a butane-propane mixture. By selecting the proper feedstock and by controlling the deasphalting parameters, notably temperature and pressure, it is possible to obtain different grades of bitumen by this process. 

Molten Salt Distillation. Hafnium tetrachloride is slightly more volatile than zirconium tetrachloride, but a separation process based on this volatility difference is impractical at atmospheric pressures because only soHd and vapor phases exist. The triple point for these systems is at about 2.7 MPa (400 psia) and 400°C so that separation of the Hquids by distillation would necessarily require a massive pressurized system (13). 

A second approach to the production of weapons material was the uranium electromagnetic separation process, based on research at the University... 

The first successflil production method for the separation of Pu from U and its fission products was the bismuth phosphate process, based on the carrying of Pu by a precipitate of BiPO (126). That process has been superseded by Hquid-Hquid extraction (qv) and ion exchange (qv). In the Hquid-Hquid... 

In the case of low temperature tar, the aqueous Hquor that accompanies the cmde tar contains between 1 and 1.5% by weight of soluble tar acids, eg, phenol, cresols, and dihydroxybenzenes. Both for the sake of economics and effluent purification, it is necessary to recover these, usually by the Lurgi Phenosolvan process based on the selective extraction of the tar acids with butyl or isobutyl acetate. The recovered phenols are separated by fractional distillation into monohydroxybenzenes, mainly phenol and cresols, and dihydroxybenzenes, mainly (9-dihydroxybenzene (catechol), methyl (9-dihydtoxybenzene, (methyl catechol), and y -dihydroxybenzene (resorcinol). The monohydric phenol fraction is added to the cmde tar acids extracted from the tar for further refining, whereas the dihydric phenol fraction is incorporated in wood-preservation creosote or sold to adhesive manufacturers. Naphthalene Oils. Naphthalene is the principal component of coke-oven tats and the only component that can be concentrated to a reasonably high content on primary distillation. Naphthalene oils from coke-oven tars distilled in a modem pipe stiU generally contain 60—65% of naphthalene. They are further upgraded by a number of methods. 

When ionic liquids are used as replacements for organic solvents in processes with nonvolatile products, downstream processing may become complicated. This may apply to many biotransformations in which the better selectivity of the biocatalyst is used to transform more complex molecules. In such cases, product isolation can be achieved by, for example, extraction with supercritical CO2 [50]. Recently, membrane processes such as pervaporation and nanofiltration have been used. The use of pervaporation for less volatile compounds such as phenylethanol has been reported by Crespo and co-workers [51]. We have developed a separation process based on nanofiltration [52, 53] which is especially well suited for isolation of nonvolatile compounds such as carbohydrates or charged compounds. It may also be used for easy recovery and/or purification of ionic liquids. 

The second method is based on selective extraction that consists of extraction into two different organic solutions. In the first step, tantalum is extracted into an organic phase. In the second step of the procedure, niobium is extracted into a separate portion of the extractant. Fig. 126 presents a flow chart of the process based on the selective extraction scheme. 

Flotation is certainly the major separation method based on the surface chemistry of mineral particles. It is, however, not the only method. Selective flocculation and agglomeration may be mentioned as other methods used commercially to a limited extent. The former is for hematite, while the latter is for coal and finely divided metallic oxide minerals. Both processes use the same principles as described for flotation to obtain selectivity. In selective flocculation, polymeric flocculants are used. The flocculants selectively adsorb on the hematite, and the hematite floes form and settle readily. Thereby separation from the sili-... 

Enrichment, Isotopic—An isotopic separation process by which the relative abundances of the isotopes of a given element are altered, thus producing a form of the element that has been enriched in one or more isotopes and depleted in others. In uranium enrichment, the percentage of uranium-235 in natural uranium can be increased from 0.7% to >90% in a gaseous diffusion process based on the different thermal velocities of the constituents of natural uranium (234U, 235U, 238U) in the molecular form UF6. 

VaporSep A family of separation processes, based on membranes which are selectively permeable to organic vapors. Developed by Membrane Technology Research, CA, in the... 

In particular, catalytic and analogous reactions in SCFs will become increasingly attractive because of the environmental legislation. To implement future processes based on the use of SCCO2 as medium for catalysis, representative data need to be provided, which describe the states present under reaction and separation conditions. Such data are crucial to prevent losses of catalysts and/or expensive ligands and to achieve the desired product purities [24]. 

Until late 1990s, purified m-xylene was produced predominantly by the HF/BF3 process developed by Mitsubishi Gas Chemical Co. The separation is based on the complex formation between m-xylene and solvent HF/BF3. However, concerns about the process operation, environment, metallurgy and safety render the process commercially unattractive due to its use of HF/BF3. These concerns led to many developments in the adsorptive separation process for m-xylene separation [3-8]. The UOP MX Sorbex process, developed by UOP and commercialized in 1998, already accounts for more than 70% of the world s m-xylene capacity. A 95% m-xylene recovery with 99.5% purity can be achieved by the MX Sorbex process. 

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