Methods of Separation

Relative displacement differs for each of the various forces that can be applied its magnitude depends on how different components respond to these forces. Details are provided in Chapter 3. The origin and nature of bulk (flow) displacement will be described in Chapter 4. 

Our emphasis in this book is not so much on the subtleties that distinguish one historical name from another, or one result from another. The basic classification of methods described in Chapter 7, for example, is founded on the arrangements of the fundamental forces and flows that give rise to separation and ultimately determine their efficacy. It is the belief of this author that this approach is ultimately the most lasting one it will 

1( ) Use a parenthetical expression like those shown in Eqs. 1.1-1.3 to represent the separation of five components (a, by c, d, e) into three regions, one containing all of (and nothing more than) components a and d and a second all of (and only) c and e. 

2( ) For a binary solution in equilibrium with its vapor in accordance with Raoult s law, show that the vapor/liquid separation factor is given by the ratio of pure component vapor pressures. 

4( ) Calculate the entropy change, in calories/degree, that accompanies the separation of four components from one another in an ideal solution containing one mole of each. When separated, each component occupies one-quarter of the original volume. Deduce from your results whether or not the separation is thermodynamically spontaneous. 

Nuclear reaction Optimal energy range (MeV) Thick target yields at EOB (MBq/pAh) Major impurities at EOB %) 

Several methods have been published for the separation of Tc from irradiated Mo03 target (Nickles et al. 1993 a, b Rosch et al. 1994). In an online method, a well-focused, vertical 11-MeV proton beam was used for irradiation (Nickles et al. 1993 a). The Mo03 target was melted by the beam and kept at 800 °C, under continuous surface temperature control. Ninety-five percent of the radiotechnetium, heated out simultaneously, was collected on a cooled quartz tube. One milligram of Mo03 also was evaporated and adsorbed on the surface, from which the Tc was separated and purified by a wet chemistry method. 

An alternate method is described in (Nickles et al. 1993b). A Mo foil (0.1 mm thick) was used for irradiation and the radiotechnetium was extracted by an electrochemical etching procedure. With the obtained Tc-pertechnetate, Tc-teboroxime was prepared, which was used for the first preliminary human investigation with this Tc-la-beled pharmaceutical (Nickles et al. 1993 b). Another PET study with Tc-2-methoxy isobutyl isonitrile was also reported (Stone et al. 1994). 

Browne E, Firestone RB (1986) Table of radioactive isotopes. Wiley, New York Denzler F, Rdsch F, Qaim SM (1995) Excitation functions of a-particle induced nuclear reactions on highly enriched Mo comparative evaluation of production routes for Tc. Radiochim Acta 68 13-20 

Fafibender M, Novgorodov AF, Rdsch F, Qaim SM (1995) Excitation functions of Nb( He,xn) Tc processes from threshold up to 35 MeV possibility of production of Tc in high radiochemical purity using a thermochromatographic separation technique. Radiochim Acta 65 215-224 

---

Eliminate extraneous materials for separation. The third option is to eliminate extraneous materials added to the process to carry out separation. The most obvious example would be addition of a solvent, either organic or aqueous. Also, acids or alkalis are sometimes used to precipitate other materials from solution. If these extraneous materials used for separation can be recycled with a high efficiency, there is not a major problem. Sometimes, however, they cannot. If this is the case, then waste is created by discharge of that material. To reduce this waste, alternative methods of separation are needed, such as use of evaporation instead of precipitation. 

Bag filters. Bag filters, as discussed in Chap. 3 and illustrated in Fig. 3.66, are probably the most common method of separating particulate materials from gases. A cloth or felt filter material is used that is impervious to the particles. Bag filters are suitable for use in very high dust load conditions. They have an extremely high efficiency, but they suflFer from the disadvantage that the pressure drop across them may be high. ... 

Graham showed that the rate of diffusion of different gases through a porous diaphragm was inversely proportional to the square roots of their densities this is the basis of a method of separation of gases, and has been applied successfully to the separation of hydrogen and deuterium. 

Originally, general methods of separation were based on small differences in the solubilities of their salts, for examples the nitrates, and a laborious series of fractional crystallisations had to be carried out to obtain the pure salts. In a few cases, individual lanthanides could be separated because they yielded oxidation states other than three. Thus the commonest lanthanide, cerium, exhibits oxidation states of h-3 and -t-4 hence oxidation of a mixture of lanthanide salts in alkaline solution with chlorine yields the soluble chlorates(I) of all the -1-3 lanthanides (which are not oxidised) but gives a precipitate of cerium(IV) hydroxide, Ce(OH)4, since this is too weak a base to form a chlorate(I). In some cases also, preferential reduction to the metal by sodium amalgam could be used to separate out individual lanthanides. 

The various types of Chromatographic Separation have been developed partly to avoid the above disadvantages, but (more particularly) to provide methods of separation on a micro-scale. Three methods are described below ... 

Special methods are available for particular classes of compounds, Hinsberg s method of separating primary, secondary and tertiary amines (p. 249)-... 

Only those mixtures in which the neutral substance is insoluble in water will be considered. The method of separation consists in extracting the mixture with aqueous sodium hydroxide solution, whereby the acidic component dissolves in the form of its sodium salt, while the neutral component remains undissolved and can thus be separated. 

An alternative method of separation consists in treating the dry residue several times with a warm mixture of benzene and ether. The residual solid (about 20 g.) is moderately pure succinic acid, m.p. 183-184°. Upon evaporating the benzene - ether extract, and recrystallising the residue from chloroform or from benzene, about 70 g. of glutaric acid, m.p. 95-96°, are obtained. 

In connexion with the above chemical methods of separation, it is important to note that sufficient of the extracting reagent must be used to remove completely the component which it dissolves or with which it reacts. 

A method of separation that uses a semi-permeable membrane. 

Gel filtration chromatography (GFC) is the name used to describe this method of separation in the biochemical literature. Under this heading, the method is primarily applied to aqueous solutions of solutes of biological origin. 

Another method of separating petrolatum from residua is by centrifuge dewaxing. In this process, the reduced cmde oil is dissolved in naphtha and chilled to —18° C or lower, which causes the wax to separate. The mixture is then fed to a battery of centrifuges where the wax is separated from the Hquid. However, the centrifuge method has been largely displaced by solvent dewaxing methods as well as more modem methods of wax removal. Similar use is... 

Other Separation Techniques. Under some circumstances, distillation is not the best method of separation. Among these instances are the following when relative volatiHty is <1.05 when <1% of a stream is removed, as in gas drying (adsorption or absorption) or C2H2 removal (reaction or absorption) when thermodynamic efficiency of distillation is <5% and when a high boiling point pushes thermal stabiHty limits. A variety of other... 

Dilution with water reverses the reaction, and heating the solution Hberates sulfur dioxide. Upon being added to a solution of teUurides, teUurium forms colored polyteUurides. Unlike selenium, teUurium is not soluble in aqueous sodium sulfite. This difference offers a method of separating the two elements. Like selenium, teUurium is soluble in hot alkaline solutions except for ammonium hydroxide solutions. Cooling reverses the reaction. Because teUurium forms solutions of anions, Te , and cations, Te" ", teUurium films can be deposited on inert electrodes of either sign. 

Bromine can function as a solvent. One of the very few metal bromides that has significant solubiUty in bromine is cesium bromide, 19.3 g/100 g of solution, thus providing a method of separating cesium bromide from the other alkah bromides (12). Aluminum bromide also is reported to have significant solubiUty in bromine but the pubUshed solubiUty values are not in good agreement (13). Bromine serves as the solvent in some brominations of organic compounds, such as 1,2-diphenylethane (14). 

Distillation is a method of separation that is based on the difference in composition between a Hquid mixture and the vapor formed from it. This composition difference arises from the dissimilar effective vapor pressures, or volatihties, of the components of the Hquid mixture. When such dissimilarity does not exist, as at an a2eotropic point, separation by simple distillation is not possible. Distillation as normally practiced involves condensation of the vaporized material, usually in multiple vaporization/condensation operations, and thus differs from evaporation (qv), which is usually appHed to separation of a Hquid from a soHd but which can be appHed to simple Hquid concentration operations. 

Method of separation Rotor type Centrifuge type Manner of liquid discharge Manner of solids discharge or removal Centrifuge speed for solids discharge Capacity ... 

The use of polymers in various areas of ehemisti y allows to improve the eharaeteristies of known methods of separation, eoneentration, and identifieation of many inorganie and organie substanees. One of the ai eas of interesting applieations is the modifieation of properties and reaetivity of various reagents. The reason for these modifieations is the formation of neutral pariieles of adduets, whieh ar e stabilized by eleetrostatie and hydrophobie interaetions. 

Since centrifuges are subject to the hazards inherent in all rotating equipment, the designer should first consider whether other, safer methods of separation (such as decanters or static filters) can be used. If it is determined that a... 

Although the traditional method of separating the diastereomeric compounds generated in a resolution procedure is fractional crystallization, chromatographic procedures are now common and convenient. Diastereomeric compounds exhibit different adsorption... 

In the case of the free jet, the solution for the Aaberg exhaust system can be found by solving the Laplace equation by the method of separation of variables and assuming that there is no fluid flow through the surface of the workbench. At the edge of the jet, which is assumed to be at 0—0, the stream function is given by Eq. (10.113). This gives rise to... 

Tobacco and its alkaloids have long ceased to have any therapeutic importance, but their extensive use as insecticides and the demand for nicotine for the manufacture of nicotinic acid have stimulated interest in processes of extraction and methods of estimation. On the latter subject there is a voluminous literature, of which critical resumes have been published by various authors.Recent work on this subject has been specially concerned with (1) the development of miero- and semi-miero-methods suitable for estimating nieotine in tobacco smoke and the distribution of nieotine on sprayed garden produce, in treated soils and in tobaeeo leaves,(2) the study of conditions necessary to ensure satisfactory results in using particular processes, " and (3) methods of separation and estimation of nicotine, nomicotine and anabasine in mixtures of these bases. ) In the United States and in Russia considerable interest is being shown in the cultivation of types of tobacco rich in nicotine, in finding new industrial uses for tobacco and its alkaloids, and in possible by-products from tobacco plants such as citric and malic acids, i " Surveys of information on tobacco alkaloids have been published by Jackson, i Marion and Spath and Kuffner. ... 

Preparation. The mother liquors from strychnine manufacture are concentrated and the alkaloids precipitated as neutral oxalates. The precipitate is dried and extracted with dry alcohol in which the strychnine salt is the more soluble. The less soluble salt dissolved in water is decolorised with charcoal, the alkaloid regenerated with ammonia and purified by crystallisation as the sulphate. According to Saunders, pure brucine may be obtained by slow crystallisation from a solution of the pure hydrochloride in alcoholic ammonia. A method of separation depending on the greater solubility in water of strychnine hydriodide was employed by Shenstone, whilst others have made use of the sparing solubility of strychnine chromate for the removal of small quantities of this alkaloid from brucine. For a large scale process see Schwyzer. ... 

Crystallization continues to be the most widely used method of separating or resolving enantiomers (optical resolutions). The manufacture of chemicals and pharmaceuticals as purified optical isomers, or enantiomers, has taken on a pivotal importance in the pharmaceutical, agricultural and fine chemicals industries over the past 15-20 years. Crystallization has been and continues to be the most widely used method of separating or resolving enantiomers (optical resolutions), and is particularly well suited to separations at large scale in manufacturing processes (Jacques etal., 1981 Roth etai, 1988 Wood, 1997 Cains, 1999). 

Modern Methods of Separation, Identification, and Structure Determination... 

---