Classification of Separation Techniques

A number of unit operations have as fundamental purpose the separation of two or more components within a system. Mixtures and multiphase fluids previously mentioned are varied in the materials processing industries and include solutions, suspensions, dispersions, and solid blends. The components within these systems may include any of the three common states of matter (i.e., solid, liquid, or gas), and so different combinations are possible. There are many criteria used to determine the most suitable strategy to 

Two possible classifications of separation techniques based on the above criteria are given in Tables 8.1 and 8.2. 

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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. 

Table 4.1 Classification of separation techniques TKCHNiyUI PHASE SYSTEM ...

TABLE 8.1 Classification of Separation Techniques Based on Diffusion Properties... 

Figure 5.2 — Classification of (bio)chemical flow-through sensors based on integrated reaction, separation and detection according to the type of separation technique involved.

Separation of the components, or solutes, of a sample results from differences in their rates of adsorption, solution, or reaction with the mobile and stationary phases. In the light of these observations distinguishing the numerous chromatographic techniques only on the basis of specification of the physical states of the stationary and mobile phases is inadequate, and a more adequate classification of these techniques must additionally also take into account (i) the nature of the separation e.g. adsorption, and (ii) the configuration of the system e.g. columnar. Table 4.4 gives a system of classification which incorporates these considerations. 

These are arbitrary classifications of chromatographic techniques, and some types of chromatography are considered together as a separate technique, such as gas chromatography for gas-solid and gas-liquid chromatography. In every case, successive equilibria are at work that determine to what extent the analyte stays behind or moves along with the eluent (mobile phase). In column chromatography, the column may be packed with small particles that act as the stationary phase... 

A convenient classification of chromatographic techniques can be made in terms of the physical state of the phases employed in the separation process (Fig. 3) If the mobile phase is a gas, the separation techniques are known as gas-liquid chromatography (GLC) or gas-solid chromatography (GSC) when the stationary phase is a liquid or solid, respectively. GLC is the more popular separation mode and is often simply referred to as GC. If the mobile phase is a supercritical fluid, the separation technique is known as supercritical fluid chromatography (SFC) whether the stationary phase is an... 

The classification of methods for studying electrode kinetics is based on the criterion of whether the electrical potential or the current density is controlled. The other variable, which is then a function of time, is determined by the electrode process. Obviously, for a steady-state process, these two quantities are interdependent and further classification is unnecessary. Techniques employing a small periodic perturbation of the system by current or potential oscillations with a small amplitude will be classified separately. 

TABLE 5.1 Classification and Examples of Two-Dimensional Liquid-Phase Separation Techniques... 

Each chapter presents several detailed studies illustrating the application of various optimization techniques. The following matrix shows the classification of the examples with respect to specific techniques. Truly optimal design of process plants cannot be performed by considering each unit operation separately. Hence, in Chapter 15 we discuss the optimization of large-scale plants, including those represented by flowsheet simulators. 

In a chromatographic separation procedure the parameters of the chromatographic system (stationary phase, flow, temperature, etc.) have to be selected respectively optimized with respect to some criterion (resolution, time, etc.). In gas chromatography retention data series are published and used for the sttidy of solvent/solute interaction, prediction of the retention behaviour, activity coefficients, and other relevant information usable for optimization and classification. Several clKmometrk techniques of data anal s have been employed, e.g. PCA, numerical taxonomic methods, information theory, and j ttern recognition. 

So, clustering techniques have been used for classification. Piepponen et al. applied a hierarchical cluster analysis (CLUSTAN) to the classification of food oils (groundnut, soya, sunflower and maize) by their fatty acid composition. The dendrogram of the distances shows four weU-separated clusters. Some suspect commercial samples of sunflower oil fall near the cluster of soya oils, so far from the clainud class that they cannot be consider i genuine. 

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