Emulsions mechanical agitation

A (macro)emulsion is formed when two immiscible Hquids, usually water and a hydrophobic organic solvent, an oil, are mechanically agitated (5) so that one Hquid forms droplets in the other one. A microemulsion, on the other hand, forms spontaneously because of the self-association of added amphiphilic molecules. During the emulsification agitation both Hquids form droplets, and with no stabilization, two emulsion layers are formed, one with oil droplets in water (o /w) and one of water in oil (w/o). However, if not stabilized the droplets separate into two phases when the agitation ceases. If an emulsifier (a stabilizing compound) is added to the two immiscible Hquids, one of them becomes continuous and the other one remains in droplet form. 

Emulsion polymerisation represents the next stage in development from the suspension technique and is a versatile and widely used method of polymerisation. In this technique droplets of monomer are dispersed in water with the aid of an emulsifying agent, usually a synthetic detergent. The detergent forms small micelles 10-100 /im in size, which is much smaller than the droplets that can be formed by mechanical agitation in suspension polymerisation. These micelles contain a small quantity of monomer, the rest of the monomer being suspended in the water without the aid of any surfactant. 

In the coacervation process, the core substance is first added to a homogeneous solution of the selected solvent and polymer. Mechanical agitation is used to disperse the immiscible core to create tiny droplets suspended in solution (i.e., an emulsion). The coacervation or phase separation phenomenon is then induced by several means, such as changing the temperature and/or acidity of the polymer solution or adding salts, nonsolvents, or incompatible (immiscible) polymers to... 

Mechanical agitation of the cream - a process called whipping - creates a metastable foam (i.e. it contains much air). Further whipping causes this foam to collapse some water separates out, and the major product is yellow butter. Incidentally, butter is a different form of colloid from milk, since its dispersed medium is water droplets and its dispersal phase is oil (milk is an oil-in-water colloid). Forming butter from milk is a simple example of emulsion inversion. 

Emulsions are mixture of two (or more) immiscible substances. Everyday common examples are milk, butter (fats, water, salts), margarine, mayonnaise, skin creams, and others. In butter and margarine, the continuous phase consists of lipids. These lipids surround the water droplets (water-in-oil emulsion). All technical emulsions are prepared by some kind of mechanical agitation or mixing. Remarkably, the natural product, milk, is made by organisms without any agitation inside the mammary glands. 

An emulsion can be defined as a system in which an immiscible liquid (e.g., citrus oil) is dispersed as droplets in another immiscible liquid (water) by mechanical agitation (2 ). 

In conclusion, it is possible to prepare concentrated gas-inwater emulsions using various surfactant mixtures. The artificial, surfactant-stabilized microbubbles produced apparently undergo a cyclical process of microbubble formation/coalescence/fission/dis-appearance, where the end of each cycle is characterized by a collapse of the gas microbubbles into large micellar structures — only to re-emerge soon after as newly formed, gas microbubbles. This cyclical microbubble process is promoted by prior mechanical agitation of, and hence entrapment of macroscopic gas bubbles in, these saturated surfactant solutions. 

One final complication in emulsions must be mentioned. It seems unlikely that true equilibrium is ever reached in forming an emulsion with a solid emulsifier. Shaking or other forms of mechanical agitation are necessary to bring the solid to the interface, but they are much too coarse physical operations to produce equilibrium. The globules are divided up and also reunited by the shocks, and the solid particles are violently driven in and out of the interface, so that the distribution of solid in the interface is partly an accidental effect of the means used to agitate the mixture. 

Since mixing and good heat transfer are of vital importance in viscous polymerization reactions, a mechanically agitated continuous stirred-tank reactor is widely used in polymerization processes. Solution polymerization, emulsion polymerization, and solid-catalyzed olefin polymerization are all carried out in a mechanically agitated slurry reactor. 

Liquid-liquid systems with mechanical agitation are widely employed by the chemical industry to carry out chemical reactions like nitration, alkylation, and polymerization to prepare emulsions and to perform a variety of extraction, washing, and other operations involving transfer of material from one liquid phase to another. The literature on these systems is limited, and the many different liquids used by different investigators make it difficult to compare the published studies. As in the... 

Another parameter that influences the overall properties of the bulk emulsion is the physical state of the lipid droplets in an emulsion (17, 19, 28-31). Crystallization of lipid droplets in emulsions can be either beneficial or detrimental to product quality. Margarine and butter, the most common water-in-oil emulsions in the food industry, are prepared by a controlled destabilization of oil-in-water emulsions containing partly crystalline droplets. The stability of dairy cream to mechanical agitation and temperature cycling depends on the nature and extent of crystallization in milk-fat globules. It should be noted that because the density of the phases can change as crystallization occurs, the rate at which milkfat droplets cream can be altered as droplets solidify. Emulsion manufacturers should therefore understand which factors influence the crystallization and melting of emulsified substances, and be aware of the effect that droplet phase transitions can have on the properties of emulsions. 

Following emulsification, the emulsion is dispersed by mechanical agitation into the external feed phase containing the solute to be extracted. The efficiency of this extraction process is dependent on several parameters as discussed below. 

So far we have looked at the flow of emulsions in porous media in this section we discuss some aspects of in situ emulsification in porous media that have received little attention. Some evidence suggests strongly that emulsions can be produced in the reservoir rock itself. A discussion on the formation of oil-field emulsions was given by Berkman and Egloff (50). They concluded that emulsions could be formed within the porous rock near the well bore where the velocity gradients (i.e., shear rates) were very high. Emulsions could also be formed as a result of mechanical agitation, for... 

Many operations in chemical engineering require the contact of two liquid phases between which mass and heat transfer with reaction occurs. Examples are hydrometallurgical solvent extraction, nitrations and halogenations of hydrocarbons, hydrodesulfurization of crude stocks, emulsion polymerizations, hydrocarbon fermentations for single-cell proteins, glycerolysis of fats, and phase-transfer catalytic reactions. A most common method of bringing about the contact of the two phases is to disperse droplets of one within the other by mechanical agitation. 

Gas-to-liquid mass transfer is a transport phenomenon that involves the transfer of a component (or multiple components) between gas and liquid phases. Gas-liquid contactors, such as gas-liquid absorption/ stripping columns, gas-liquid-solid fluidized beds, airlift reactors, gas bubble reactors, and trickle-bed reactors (TBRs) are frequently encountered in chemical industry. Gas-to-liquid mass transfer is also applied in environmental control systems, e.g., aeration in wastewater treatment where oxygen is transferred from air to water, trickle-bed filters, and scrubbers for the removal of volatile organic compounds. In addition, gas-to-liquid mass transfer is an important factor in gas-liquid emulsion polymerization, and the rate of polymerization could, thus, be enhanced significantly by mechanical agitation. 

More often a mechanical agitator is required to form the emulsion of the two immiscible liquids at each stage. One common design is the mixer-settler (shown above). The two liquid phases are fed to the tank where the mixer imparts mechanical energy and thus disperses one of the phases as fine droplets in the second phases (usually continuous). This state of mixtures is called an emulsion. 

Many studies have been reported about the methods of emulsification of hydrocarbons, such as emulsification by surface-active agents, by mechanical agitation, or by biological methods. For the most favorable configurations between oil droplets and cells for growth, the biologically active emulsion of hydrocarbon was proposed. Munk (1969) indicated that the larger the amount of lipid a cell contained, the faster it incorporated hydrocarbon. Mimura et al. (1970) studied the characteristic phenomena of emulsification in hydrocarbon fermentation, and... 

In areas such as miscible liquid blending, the formation of emulsions, solid dispersions such as paints, and dry powder mixing, it is understandable, therefore, that several criteria have been developed to assess mixture quality . It is unfortunate that of the many definitions presently available for mixture quality, in solid or liquid mixtures, none is universally applicable. In the case of powder mixing, further details may be found in Chapter 2, while for liquid mixing more information is presented in Chapters 8 and 10 for mechanically agitated vessels. Chapter 9 for Jet mixers and Chapter 12 for in-line static mixers. 

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