Examples liquid mixing Chapter

A reactor model based on solid particles in BMF may be used for situations in which there is deliberate mixing of the reacting system. An example is that of a fluid-solid system in a well-stirred tank (i.e., a CSTR)-usually referred to as a slurry reactor, since the fluid is normally a liquid (but may also include a gas phase) the system may be semibatch with respect to the solid phase, or may be continuous with respect to all phases (as considered here). Another example involves mixing of solid particles by virtue of the flow of fluid through them an important case is that of a fluidized bed, in which upward flow of fluid through the particles brings about a particular type of behavior. The treatment here is a crude approximation to this case the actual flow pattern and resulting performance in a fluidized bed are more complicated, and are dealt with further in Chapter 23. 

In the following the state of the art of microstructured mixing devices is presented. Only the mixing of miscible liquids (and gases) is considered the same micro mixers, however, can usually be used for making liquid/liquid and gas/liquid dispersions, which is outside the scope of this chapter, but certainly is worth consideration in the future. If not otherwise mentioned, liquid mixing is involved. The few examples on gas mixing are explicitly dealt with. 

At the opposite extreme, it may be required to disperse very fine particles into a highly viscous liquid. For example, the incorporation of carbon black into rubber is such an operation. Here, as with emulsification in liquid-liquid mixing, the product is stable, highly viscous and may well exhibit complex rheology. Such processes often involve surface phenomena and physical contacting only, in contrast to the mass transfer and chemical reactions described in the previous paragraph. The dispersion of fine particles in liquids is considered in detail in Chapter 6. 

We now leave pure materials and the limited but important changes they can undergo and examine mixtures. We shall consider only homogeneous mixtures, or solutions, in which the composition is uniform however small the sample. The component in smaller abundance is called the solute and that in larger abimdance is the solvent. These terms, however, are normally but not invariably reserved for solids dissolved in Kquids one liquid mixed with another is normally called simply a mixture of the two liquids. In this chapter we consider mainly nonelectrolyte solutions, where the solute is not present as ions. Examples are sucrose dissolved in water, sulfur dissolved in carbon disulfide, and a mixture of ethanol and water. Although we also consider some of the special problems of electrolyte solutions, in which the solute consists of ions that interact strongly with one another, we defer a full study until Chapter 5. The measures of concentration commonly encoimtered in physical chemistry are reviewed in Further information 3.2. 

In Chapter 7 we examined several methods for separating an analyte from potential interferents. For example, in a liquid-liquid extraction the analyte and interferent are initially present in a single liquid phase. A second, immiscible liquid phase is introduced, and the two phases are thoroughly mixed by shaking. During this process the analyte and interferents partition themselves between the two phases to different extents, affecting their separation. Despite the power of these separation techniques, there are some significant limitations. 

When two immiscible liquids are stirred together, one phase becomes dispersed as tiny droplets in the second liquid which forms a continuous phase. Liquid-liquid extraction, a process using successive mixing and settling stages (Volume 2, Chapter 13) is one important example of this type of mixing. The liquids are brought into contact with... 

Liquid-liquid extraction is carried out either (1) in a series of well-mixed vessels or stages (well-mixed tanks or in plate column), or (2) in a continuous process, such as a spray column, packed column, or rotating disk column. If the process model is to be represented with integer variables, as in a staged process, MILNP (Glanz and Stichlmair, 1997) or one of the methods described in Chapters 9 and 10 can be employed. This example focuses on optimization in which the model is composed of two first-order, steady-state differential equations (a plug flow model). A similar treatment can be applied to an axial dispersion model. 

Various catalytic systems for H202- and 02-based oxidations catalyzed by POMs have been developed. Typical examples are listed in Table 13.1. The systems can be classified into four groups according to the stmctures of POMs (1) mixed-addenda POMs, (2) transition-metal-substituted POMs, (3) POMs, and (4) lacunary POMs. In this chapter, liquid-phase homogeneous oxidations by POMs with H202 and 02 are described according to the above classification. 

The book presents some basic considerations regarding liquid surfaces. After an introduction, the liquid-solid interface phenomena is described. Following this, the colloid chemistry systems are discussed, followed by emulsion science and technology. In the last chapter, more complex application examples are described. These are examples where different concepts of surface and colloid chemistry are involved in some mixed manner. 

Optical fibres need to be free of impurities such as transition metal ions (see Chapter 8) and conventional methods of preparing silica glasses are inadequate. The sol-gel process is one way of forming fibres of sufficient purity (chemical vapour deposition. Section 3.7, is another). These processes use volatile compounds of silicon which are more easily purified, for example by fractional distillation, than silica. It is possible to produce silica fibres using a method similar to that studied in the nineteenth century, but with the geldrying time reduced from a year to a few days. Liquid silicon alkoxide (Si(OR)4), where R is methyl, ethyl, or propyl, is hydrolysed by mixing with water. 

Earlier in this chapter, we discussed isotopic fractionation during evaporation. Under appropriate conditions, where the condensed phase remains isotopically well mixed and the gas phase is removed from the system to prevent back reaction, Rayleigh distillation will occur (Box 7.2), resulting in a condensed phase that is isotopically heavy relative to the starting composition (Fig. 7.9). Isotopic fractionation can occur during both condensation and evaporation, as demonstrated by experiments (Richter el al., 2002). But it is not necessary that isotopes fractionate during evaporation or condensation. It depends on the details of the process. If evaporation occurs into a gas phase that is sufficiently dense, back reactions between gas and liquid can reduce the isotopic fractionation to near the equilibrium value, which is very small. For example, sulfur in chondrules does not show the isotopic fractionation (Tachibana and Huss, 2005) expected during evaporation from a liquid. Also, evaporation from a solid does not produce isotopic fractionation in the solid because diffusion is much too slow to equilibrate the few layers of surface atoms that are fractionated with the bulk of the material. 

Most transition metals form complexes known as carbonyls with carbon monoxide as ligands. Examples include Fe(CO)s, Fe2(CO)9, Cr(CO)6, and Rh6(CO)i6, in all of which the metal is ostensibly in the oxidation state of zero, and many mixed-ligand carbonyls such as Mn(CO)sI, CH3Mn(CO)s, and (C6H6)Mo(CO)3 are known. Such compounds have an organiclike chemistry, being essentially covalent (see Section 8.2 and Chapter 18), and the simple carbonyls such as Ni(CO)4 are volatile liquids that can be purified by fractional distillation. Of all these, however, only Ni(CO)4 (bp 43 °C) forms rapidly (and reversibly) from the elemental metal and CO gas... 

Separation of the mixed phases is accomplished by gravity settling or less commonly by centrifugation. It can be enhanced by inducing coalescence with packing or electrically, or by shortening the distance of fall to a coalesced phase. Figures 14.11(d), 18.2, and 18.3 are some examples. Chapter 18 deals with some aspects of the separation of liquid phases. 

Precipitation refers to dissolved species (such as As(V) oxyanions) in water or other liquids reacting with other dissolved species (such as Ca2+, Fe3+, or manganese cations) to form solid insoluble reaction products. Precipitation may result from evaporation, oxidation, reduction, changes in pH, or the mixing of chemicals into an aqueous solution. For example, As(V) oxyanions in acid mine drainage could flow into a nearby pond and react with Ca2+ to precipitate calcium arsenates. The resulting precipitates may settle out of the host liquid, remain suspended, or possibly form colloids. Like sorption, precipitation is an important process that affects the movement of arsenic in natural environments and in removing arsenic from contaminated water (Chapters 3 and 7). 

This reaction is an example of a heterogeneous reaction with a solid catalyst with one reactant principally in solution and another in the gas phase the gas-liquid-solid mixture has to be mixed thoroughly to promote conversion (see Chapter 5 for more detailed consideration of multiphase reactions). Compared with the examples above, the measurement of the hydrogen uptake delivers an additional signal, which can also be used for the determination of reaction parameters. 

In this chapter some results on the electrodeposition of alloys from ionic liquids are summarized. Many fundamental studies have been performed in chloroaluminate first generation ionic liquids but the number of studies employing air- and water-stable ionic liquids rather than the chloroaluminates is increasing. Currently, new ionic liquids with better electrochemical properties are being developed. For example, Abbott et al. [47] have prepared a series of ionic liquids by mixing commercially available low-cost choline chloride and MCI2 (M = Zn, Sn) or urea and demonstrated that these ILs are good media for electrodeposition for pure metals (see Chapter 4.3). It can be expected that in the near future, the electrodeposition of alloys from ILs may become available for industrial applications. Furthermore, due to their variety, their wide electrochemical and thermal windows air- and water-stable ionic liquids have unprecedented prospects for electrodeposition. 

---