Separation of heterogeneous mixtures

The four principal methods for the separation of heterogeneous mixtures are... 

Microfiltration. Microfiltration is a pressure-driven membrane filtration process and has already been discussed in Chapter 8 for the separation of heterogeneous mixtures. Microfiltration retains particles down to a size of around 0.05 xm. Salts and large molecules pass through the membrane but particles of the size of bacteria and fat globules are rejected. A pressure difference of 0.5 to 4 bar is used across the membrane. Typical applications include ... 

Capillary electrophoresis has become extremely important in several application areas (a) enantiomeric separations can be achieved by the simple addition of a chiral additive to the run buffer (b) rapid and distinctive profiles for different isoform groups can be obtained by reversed-charge CE separations of heterogeneous mixtures and (c) inorganic and organic ion determination has improved significantly with new detection systems. 

Plotting residue curves maps (RCM) allows the designer to anticipate problems by the separation of nonideal mixtures, namely when dealing with homogeneous and heterogeneous azeotropes. By reactor selection, it may foresee problems incurred by the recycle of some reactants. 

A suspension is a type of heterogeneous mixture. Suspension particles settle out over time Q, and can be separated from the mixture by filtration... 

Chromatography is a physico-chemical method of separation of components within mixtures, liquid or gaseous, in the same vein as distillation, crystallization, or the fractionated extraction. The applications of this procedure are therefore numerous since many of heterogeneous mixtures, or those in solid form, can be dissolved by a suitable solvent (which becomes, of course, a supplementary component of the mixture). 

A homogeneous mixture is called a solution. Air is a solution consisting of a mixture of gases. Wine is a complex liquid solution. Brass is a solid solution of copper and zinc. Sand in water and iced tea with ice cubes are examples of heterogeneous mixtures. Fleterogeneous mixtures usually can be separated into two or more homogeneous mixtures or pure substances (for example, the ice cubes can be separated from the tea). 

Heterogeneous means different kinds in Latin. In a heterogeneous mixture, the different parts of the mixture have different properties. A heterogeneous mixture can be separated mechanically into its component parts. Some examples of heterogeneous mixtures are gasoline, the air we breathe, blood, and mayonnaise. 

Which technique—distillation, crystallization, or filtration— is most useful for separating a heterogeneous mixture composed of a solid and a liquid ... 

The preparation of enantiomerically pure compounds can be realized by methods of separation of racemic mixtures into enantiomers, by asymmetric S5mthesis using chiral auxiliaries, or better by using chiral homogeneous or heterogeneous catalysts. Below will be considered only the last two methods. 

This book contains many publications which represent analyses of the steps of elaboration of effective heterogeneous enantioselective hydrogenation catalysts, of their significant role in the theory of catalysis, and of their role in the practice of asymmetric catalysis. In addition to reviewing the first works on catal Tic hydrogenation of C=C double bond in prochiral compounds on metal catalysts supported on chiral carriers, which admittedly have only historical interest, the Chapters 1-3 review data on asymmetric adsorption of enantiomers and separation of racemic mixtures on organic and inorganic adsorbents. 

Theoretical models for the dieleetrie properties of heterogeneous mixtures [for instance, Eq. (20), or extensions of this model] are commonly applied in order to explain or predict the dieleetrie behavior also of emulsions (106, 158). However, in the present theories a homogeneous distribution of the dispersed phase is required. This requirement is rarely fulfilled in a real emulsion system where the inherent instability makes the emulsions go through different stages on the way towards complete phase separation. Proeesses like sedimentation, flocculation, and coalescence continuously alter the state of the system (Fig. 36). These processes also influence the dielectric properties (159—162). Thus, the dielectric properties of one given sample may vary considerably over a period of time (160), depending on the emulsion rate. 

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