Emulsions separation, breaking

Less stable parts of the sludge can be treated by holding in tanks for extended periods of time to allow the weaker emulsion to break and separate a clean product. The mote stable sludges can be broken by mechanical action in filters or centrifuges, by recycle to the furnace for redistillation, or by redistillation in auxiliary units. Chemical attack via oxidation or complexing agents that break the emulsion has also been employed. 

Oiling out Continued coalescence of lipid emulsion particles, resulting in irreversible separation of the emulsion (or breaking of the emulsion). 

Ice cream emulsion has a very characteristic degree of stability. The air bubbles should remain dispersed, but as soon it melts in the mouth, the emulsion should break. This leads to the sensation of taste, which is very essential to enjoy its specialness. The sensation of taste on the surface of the tongue is known to be related to molecular shape and physicochemical properties. As soon as these molecules are separated from the emulsion, the taste sensation is recorded in the brain. Therefore, the various components must stay in the same phase after the breakup of the emulsion. Emulsifiers that are generally used have low HLB values (for W/O), and have been found to have considerable effect on the structure of the ice cream. 

Chemical Any agent added to an emulsion that causes or enhances the rate of breaking of the emulsion (separation into its constituent liquid phases). Demulsifiers can act by any of a number of different mechanisms, which usually include enhancing the rate of droplet coalescence. 

Oil-Water Versus Water-Oil Emulsions. If oil and water are vigorously shaken, they form a dispersion of water droplets in oil and oil droplets in water. When shaking is stopped the phases start to separate small water drops fall toward the interface, and oil drops rise. The emulsion quickly breaks. Adding an emulsifier to the system changes the outcome after standing, one phase becomes continuous, while the other remains dispersed. The nature of the emulsion is determined by the emulsifier. As a general rule, the continuous phase is the one in which the emulsifier is soluble. Thus sodium stearate promotes an oil-in-water (o/w) emulsion, while zinc distearate promotes a water-in-oil (w/o) emulsion. Several qualitative theories have been advanced to explain this empirical mle. 

Breaking The process in which an emulsion separates, the formerly dispersed phase becoming a continuous phase, separate from the original continuous phase. 

The basic principle involves the preparation of an epoxy emulsion just prior to use. Previously, in preemulsifying the epoxy resins and the curing agents, and packaging them separately, the emulsions would break and separate into phases, in the package, or upon mixing. 

Observations were made on the appearance of the emulsions and were used to classify the emulsions. All of the stable emulsions appeared to be stable and remained intact over 7 days in the laboratory. All of the mesostable emulsions broke after a few days in water, free oil, and emulsion. The time for these emulsions to break down varied from about 1 to 3 days. The emulsion portion of these breakdown emulsions appears to be somewhat stable, although separate studies on this portion have not been performed because of the difliculty in separating these portions from the oil and water. All entrained water appeared to have larger suspended water droplets. The appearance of nonstable water in oil was just that the oil appeared to be unchanged and a water layer was clearly visible. 

This chapter has covered different physical phenomena and processes, ranging from bulk-fluid dynamics to microscopic interdroplet surface chemistry. All of these topics play a role in the electrostatic separation of W/O emulsions and the development and construction of an optimal, compact electrostatic coalescer. In some areas, such as turbulent droplet break-up, the understanding is well developed. In other fields there are still many questions to be answered. It is interesting to note that various authors have performed experimental assessments of W/O emulsion separation by using electrostatic fields. There is agreement on some as-... 

In lab-scale SWE, separation of the compounds from the aqueous extract obtained is the critical stage. A liquid-liquid extraction technique often causes emulsion and breaking this can be very difficult. It has been found that solid phase extraction is a better technique for the removal of compounds from the aqueous environment of SWE when comp>ared with liquid-liquid extraction (Rovio et al., 1999 Ozel et al., 2003). Headspace solid phase microextraction with GC-MS may be another alternative (Deng et al., 2005). 

In some respects the mechanism of SPE is similar to that of LLE where an extractive organic solvent is added to the aqueous sample solution and the vessel is agitated vigorously to create a temporary emulsion. The emulsion consists of very small spherical solvent droplets suspended in the aqueous phase. The interfacial contact area between the two phases must be quite large in order to promote rapid mass transfer of the analytes from the aqueous to the organic phase. To complete the desired extraction, a finite amount of time is required for the emulsion to break and the phases coalesce into separate layers. The lower layer is carefully drawn off to complete the separation. 

Macro- and miniemulsions are thermodynamically unstable. If not stabilized, the droplets tend to fiocculate, coalesce, sediment or cream [2-4]. Other instabilities, such as Ostwald ripening and phase inversion, are also known. At worst, an emulsion will break, i.e. the two phases will separate completely. A product becoming unstable will lose its quality within a short period of time and thus cannot be commercialized. Therefore, even in natural emulsion-based products, amphiphilic molecules are found (e.g. lecithin and proteins in egg yolk and milk and artificial surfactants and emulsifiers in cosmetics and chemical products. They adsorb at the droplets interfaces and stabilize them against flocculation and coalescence. Adsorption and stabilization mechanisms depend on the molecular structure of a surfactant or an emulsifier as depicted in Figure 20.1. Stabilization mechanisms are summarized in... 

Stability of Acid-in-Diesel Emulsions. Al-Anazi et al. [14] showed that acid-in-diesel emulsion is stable for more than three days at room temperature. However, at high temperatures it breaks down and an aqueous (acidic) phase was noted at the bottom of the test tube. Figure 4 depicts the volume of the separated aqueous phase as a function of time at 96 °C. The aqueous phase first appears after 85 minutes. The volume of separated acid gradually increases until complete phase separation occurs after nearly 220 minutes. In the presence of reservoir rock, the aqueous phase appears after approximately 20 minutes, and complete phase separation takes place after an hour. These results indicate lower emulsion stability in the presence of calcite. The acid reaction with the carbonate rock produces water (which causes the pH to rise) and calcium chloride. It appears from these results that the surfactant moves away from the acid-diesel interface as the pH or ionic strength increases, which causes the emulsion to break. 

Stability, or permanence, of the emulsion is of the utmost importance in liquid extraction, since it is necessary to separate the phases at each extraction stage. Stable emulsions, those which do not settle and coalesce rapidly, must be avoided. For an emulsion to break, or separate into its phases in bulk, both sedimentation and coalescence of the dispersed phase must occur. 

In addition to gravity separation, the emulsion must be collected and held in the treater for a certain retention time so that the emulsion will break. In horizontal flow treaters, the emulsion collects... 

Emulsified oil contains a Hquid film so that it will not separate by gravity without first breaking the emulsion. This is achieved by adding surfactants, emulsion breaking polymers or coagulants. After the emulsion is broken, the conventional technologies described above are appHcable. 

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