Separations examples

Electrodriven Separation Techniques encompass a wide range of analytical procedures based on several distinct physical and chemical principles, usually acting together to perform the requh ed separation. Example of electrophoretic-based techniques includes capillary zone electrophoresis (CZE), capillary isotachophoresis (CITP), and capillary gel electrophoresis (CGE) (45-47). Some other electrodriven separation techniques are based not only on electrophoretic principles but rather on chromatographic principles as well. Examples of the latter are micellar... 

Some detergents and surfactants are used as emulsifying agents. An emulsifier keeps oil droplets and water droplets from joining together, so a thick mixture of oil and water will not separate. Examples of emulsions are mayonnaise, butter, cream, homogenized milk, and salad dressings. 

Weatherley (1998) has discussed all the relevant aspects of the separation of low molecular weight biologically produced molecules by solvent extraction. A high degree of selectivity can be realized by careful selection of the solvent. Problems associated with the rheology of the broth, the presence of surfactants and solid materials needs to be recognized. There is a scope to consider intensified electrostatic contact for broth dispersion and separation. Examples covered in this treatise include penicillin G and cA-dihydrodiols. 

The viscosity of an emulsion can be of crucial importance for its stability, especially the viscosity of the external phase. A high viscosity reduces creaming and also lessens the tendency of particles to coalescence and produce phase separation. Examples of the widely used viscosity-imparting agents are alginates, bentonite, carboxymethylcellulose, polyvinyl pyrrolidone, hydroxypropylcellulose, and carbomer. 

TABLE 5.2 Two-Dimensional Liquid Separation Examples with Comprehensive Sampling... 

A selection from the large number of template reactions published following the original report by Curtis will now be described. Schiff-base and related condensations have figured prominently in these reactions. For ease of presentation, it is convenient to separate examples involving non-Schiff-base condensation from those involving Schiff-base formation. The next two subsections are devoted to descriptions of examples from each of these respective types. 

Based on the theory, the separation of enantiomers requires a chiral additive to the CE separation buffer, while diastereomers can also be separated without the chiral selector. The majority of chiral CE separations are based on simple or chemically modified cyclodextrins. However, also other additives such as chiral crown ethers, linear oligo- and polysaccharides, macrocyclic antibiotics, chiral calixarenes, chiral ion-pairing agents, and chiral surfactants can be used. Eew non-chiral separation examples for the separation of diastereomers can be found. 

In a dehydration reaction (Scheme 12.4), the IR band of the formamide carbonyl group at 1684 cm in (7) decreased and eventually converted to the isonitrile band at 2150 cm in (8) (Fig. 12.8). In a separate example (Scheme 12.5), the conversion of the IR band from the carbonate carbonyl group in (9) to the IR band of the carbamide carbonyl group in (10) can be monitored to assure the reaction completion (Fig. 12.9). Based on FTIR analysis, the reaction time course can be analyzed by integrating peak areas of the IR bands from the starting resin and the product. From the point of view of kinetics, the side reaction product formation can be excluded if the pseudo first order rates of the starting material consumption and the product formation are identical. 

Figure 12-4 Membrane reactor in wJiicIi a cataJyst promotes reaction in the membrane and maintains reactants and products separate. Examples sliown are CH4 oxidation to syngas and C2H6 reduction to C2H4. Tlie membrane eliminates N2 from the syngas and produces C2H4 beyond equilibrium by removing H2 in these apphcations.

Even though NP chromatography is not common in peptide and protein separations, examples of applications for the analysis of peptides produced by the cleavage of membrane proteins are reported in the literature [122],... 

We chose to organize the discussion of catalyst encapsulation by separating examples into catalyst type as opposed to encapsulation method. As previously, we do not intend to present a comprehensive treatment of the literature and discuss only examples we consider particularly illustrative. 

TABLE 1— Liquid capacity constraint—Vertical separator example... 

Surfactant (water treatment) A compound that reduces surface tension between immiscible substances, like oil and water, which prevents them from separating. Examples include detergents and emulsifiers (compare with emulsification). 

The results of the second interlaboratory study of PCN analytical methods using environmental matrices, undertaken by the US National Institute of Standards and Technology (NIST), should provide an indication of the comparability of published environmental PCN data and show where additional method enhancements are needed. Further method development efforts in the analysis of PCNs, and other complex mixtures are likely to focus on improving efficiencies by optimizing run times and separation. Examples may include time-of-flight mass spectrometry and multidimensional GC. New methods, such as isotope ratio mass spectrometry, may contribute to further source apportionment of complex mixtures [88]. 

Figure 11.2 Shape of relaxation maps (coordinates of transitions a, p, and y in a graph In (frequency) - reciprocal temperature). Left polymers having their a and p transitions well separated (example polycarbonate, amine-crosslinked epoxy). Right polymers with close a and p transitions (example polystyrene, unsaturated polyester).

Somewhat similar are the so-called adductive crystallization processes, often (wrongly) called extractive crystallization, where reactions of complex/ adduct formation are used to separate compounds that are otherwise difficult to separate. Examples of adductive crystallization include separation of p- and m-cresols (137), separation of o- and p - n i troch I oro ben zcn cs (138), separation of quinaldine and isoquinoline (139), separation of nonaromatic compounds from naphtha-cracking raffinate (140), and separation of p-cresol from 2,6-xylenol (141). Other examples of reactive crystallization/precipitation reported in the literature are listed in Table 5. 

In a separate example, the 4-phenyl-l,2,3,5-dithiadiazolium cation in the presence of [S3N3] gave 4-phenyl-1,2,3,5-dithiadiazolylium-l,3,5,2,4,6-trithiatriazinide 16. Ab initio calculations show that the ionic charges of the two rings are... 

Many foods are composed of colloidally dispersed phases. The colloidal properties have a great bearing on their texture, appearance, and stability against separation. Examples suspensions (chocolate), emulsions (milk), foams (ice-cream), and gels (mayonnaise). 

When appropriate material systems are not available for model experiments, accurate simulation of the working conditions of an industrial plant on a laboratory- or bench-scale may not be possible. Under such conditions, experiments on differently sized equipment are customarily performed before extrapolation of the results to the full-scale operation. Sometimes this expensive and basically unreliable procedure can be replaced by a well-planned experimental strategy. Namely, the process in question can be either divided up into parts which are then investigated separately (Example 9 Drag resistance of a ship s hull after Froude) or certain similarity criteria can be deliberately abandoned and then their effect on the entire process checked (Example 41/2 Simultaneous mass and heat transfer in a catalytic fixed bed reactor after Damkohler). 

A set of measurements with the three magic angles allows one to determine the three scattering components with different time dependencies separately. Examples are presented in the next section. The following pieces of information become accessible in this way ... 

Membranes are used to separate gaseous mixtures or liquid mixtures. Membrane modules can be tubular, spiral-wound, or plate and frame configurations. Membrane materials are usually proprietary plastic films, ceramic or metal tubes, or gels with hole size, thickness, chemical properties, ion potential, and so on appropriate for the separation. Examples of the kinds of separation that can be accomplished are separation of one gas from a gas mixture, separation of proteins from a solution, dialysis of blood of patients with kidney disease, and separation of electrolytes from non electrolytes. 

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