Separation methods Table

Next, characteristic properties of components are listed to select appropriate separation method (Table 3.7). Because the trace components belong to different chemical families, we eliminate gas-phase catalytic oxidation or hydrogenation. More specific chemical-based techniques remain. A first one is reversible chemical absorption. As solvents we may enumerate liquid redox systems (chelated iron), caustic washing solutions, amines or special formulations, as Selexol . Since H2S and C02 both have an add character, we may expect that a certain amount of C02 will pass in the off-gas stream. Dry chemical treatment could also be used, as reaction of H2S with iron-sponge or impregnated wood chips. 

In order to select the separation method. Table 7.15 lists some characteristic properties of components. Chemical absorption is not feasible, because all the trace... 

Table 4. Characteristic Properties for Liquid Separation Methods ...

The special case involving the removal of a low (2—3 mol %) mole fraction impurity at high (>99 mol%) recovery is called purification separation. Purification separation typically results in one product of very high purity. It may or may not be desirable to recover the impurity in the other product. The separation methods appHcable to purification separation include equiUbrium adsorption, molecular sieve adsorption, chemical absorption, and catalytic conversion. Physical absorption is not included in this Hst as this method typically caimot achieve extremely high purities. Table 8 presents a Hst of the gas—vapor separation methods with their corresponding characteristic properties. The considerations for gas—vapor methods are as follows (26—44). 

Separation and Purification of Isomers. 1-Butene and isobutylene caimot be economically separated into pure components by conventional distHlation because they are close boiling isomers (see Table 1 and Eig. 1). 2-Butene can be separated from the other two isomers by simple distHlation. There are four types of separation methods avaHable (/) selective removal of isobutylene by polymeriza tion and separation of 1-butene (2) use of addition reactions with alcohol, acids, or water to selectively produce pure isobutylene and 1-butene (3) selective extraction of isobutylene with a Hquid solvent, usuaHy an acid and (4) physical separation of isobutylene from 1-butene by absorbents. The first two methods take advantage of the reactivity of isobutylene. Eor example, isobutylene reacts about 1000 times faster than 1-butene. Some 1-butene also reacts and gets separated with isobutylene, but recovery of high purity is possible. The choice of a particular method depends on the product slate requirements of the manufacturer. In any case, 2-butene is first separated from the other two isomers by simple distHlation. 

The choice of room airflow pattern and air supply method is subject to study in each separate case. Table 8.9 presents, however, some guidelines for air distribution methods most commonly applied for various cases. 

Iron was present as Fe " in the calcined precursors. For all the catalysts the reduction procedure described in Sec. 2.1 resulted in incomplete reduction of the Fe to metallic iron. This is in agreement with the findings of previous authors [6,11]. The individual percentage reductions of Fe to Fe°, as determined by the separate gravimetric and volumetric measurements (Sec. 2.2), are shown in Table 1. The values are calculated on the assumption that all the Fe is reduced to Fe prior to the onset of reduction to Fe°. There is good agreement between the two methods. Table 1 also records the actual Fe/(Fe + Mg) ratio in the catalysts as determined by atomic absorption spectroscopy (AAS) on the calcined precursors. 

TABLE 9.1. Rhodium catalysed hydroformylation of 1-octene using a variety of separation methods and catalyst systems compared with results from homogeneous... 

The metallurgical results obtained are presented in Table 23.12. The results indicated that good separation efficiency can be achieved using a heat starch separation method. The zircon collector used in this test programme (CES3) was a mixture of primary and secondary amines. 

The feed composition and relative volatilities of adjacent components by using different separation methods are given in Table 30. 

Crystal structures are available for many (N)4Co-amino acid complexes (Table I). Many of the diastereomers (AS, AS) in the bis-en series have been resolved using classic crystallization (usually via bromocamphor sulfonate, arsenyl-, or antimonyl-tartrate salts) or ion exchange methods (Table II). Reversed-phase ion-pair HPLC, using aryl phosphate or aryl/alkyl sulfonate ion pairing reagents in MeOH/ H20 eluent, has allowed diastereomer separations to be carried out on analytical amounts (28) (Table II). 

The classification of separation techniques as shown in Table 3.2 is concise and easy to remember but it is also simplistic because it appears to imply that only one factor is involved in each technique. In practice, the effectiveness of any method is a composite of many factors, the one indicated in the table usually being the most significant. Some of the developments in separation procedures exploit this range of factors involved in any separation technique by using conditions or reagents designed to minimize one or maximize another. As a consequence, the techniques and instrumentation of separation methods are constantly changing but the fundamental principles remain the same and need to be understood in order to appreciate the usefulness and limitations of any particular technique. 

Normal-phase liquid chromatography is thus a steric-selective separation method. The molecular properties of steric isomers are not easily obtained and the molecular properties of optical isomers estimated by computational chemical calculation are the same. Therefore, the development of prediction methods for retention times in normal-phase liquid chromatography is difficult compared with reversed-phase liquid chromatography, where the hydrophobicity of the molecule is the predominant determinant of retention differences. When the molecular structure is known, the separation conditions in normal-phase LC can be estimated from Table 1.1, and from the solvent selectivity. A small-scale thin-layer liquid chromatographic separation is often a good tool to find a suitable eluent. When a silica gel column is used, the formation of a monolayer of water on the surface of the silica gel is an important technique. A water-saturated very non-polar solvent should be used as the base solvent, such as water-saturated w-hexane or isooctane. 

The factors in Table 2 were selected from the chiral separation methods for propranolol, praziquantel, and warfarin. All factors were quantitative and their extreme levels situated symmetrically around the nominal. 

The factors in Table 3 were selected from a non-aqueous chiral separation method for timolol. One qualitative factor (1), i.e., the type of CE equipment, was examined. Two HPCE systems, A and B, with different software versions for equipment control, data acquisition, and handling were compared. Six quantitative factors ((2) till (7)), for which the extreme levels usually were situated symmetrically around the nominal, also were... 

The applied designs in the robusmess testing of the chiral separation methods of propranolol, praziquantel, and warfarin,and of timoloP concern PB designs, i.e., one with 12 (Table 6) and one with 8 (Table 7) experiments. 

Validation is the process of proving that a method is acceptable for its intended purpose. It is important to note that it is the method not the results that is validated. The most important aspect of any analytical method is the quality of the data it ultimately produces. The development and validation of a new analytical method may therefore be an iterative process. Results of validation studies may indicate that a change in the procedure is necessary, which may then require revalidation. Before a method is routinely used, it must be validated. There are a number of criteria for validating an analytical method, as different performance characteristics will require different validation criteria. Therefore, it is necessary to understand what the general definitions and schemes mean in the case of the validation of CE methods (Table 1). Validation in CE has been reviewed in references 1 and 2. The validation of calibrations for analytical separation techniques in general has been outlined in reference 3. The approach to the validation of CE method is similar to that employed for HPLC methods. Individual differences will be discussed under each validation characteristic. 

The lanthanide group of elements (Table 11.7) is very difficult to separate by traditional methods because of their similar chemical properties. The techniques originally used, like the precious metals, included laborious multiple fractional recrystallizations and fractional precipitation, both of which required many recycle streams to achieve reasonably pure products. Such techniques were unable to cope with the demands for significant quantities of certain pure compounds required by the electronics industry hence, other separation methods were developed. Resin ion exchange was the first of these... 

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