Formation, of emulsions

In this section I will start with the principles of formation of emulsions and the role of the surfactants. This is followed by a section on the procedures that can be applied to select the emulsifiers. The third section will deal to the breakdown processes that may occur on storage and methods of their prevention. The last section will deal with the assessment and prediction of the long-term physical stability of EW s. 

In most cases AAyi2 TAS , which means that AG ° is positive, i.e. the formation of emulsions is nonspontaneous and the system is thermodynamically unstable. In the absence of any stabilization mechanism, the emulsion will break by flocculation, coalescence, Ostwald ripening or a combination of all these processes. This is illustrated in Fig. 3.29 which shows several paths for emulsion breakdown processes. In the presence of a stabilizer (surfactant and/or polymer), an energy barrier is created between the droplets and therefore the reversal from state II to state I becomes non-continuous as a result of the presence of these energy barriers this is illustrated in Fig. 3.30. In the presence of the above energy barriers, the system becomes kinetically stable [85]. As discussed before, the energy barrier can be created by electrostatic and/or steric repulsion which will overcome the everlasting van der Waals attraction. 

To prepare emulsions oil, water, surfactant and energy are needed [85,86]. This can be considered from a consideration of the energy required to expand the interface, AAy (where AA is the increase in interfacial area when the bulk oil with area A produces a large number of droplets with area A2 A2 A, y is the interfacial tension). Since y is positive, the energy to expand the interface is large and positive. This energy term cannot be compensated by the small entropy of dispersion TAS (which is also 

To break up a drop into smaller ones, it must be strongly deformed and this deformation increases p [87]. Surfactants play major roles in the formation of emulsions By lowering the interfacial tension, p is reduced and hence the stress needed to break up a drop is reduced (2,3) and surfactants prevent coalescence of newly formed drops. To describe emulsion formation one has to consider two main factors hydrodynamics and interfacial science. To assess emulsion formation, one usually measures the droplet size distribution using for example laser diffraction techniques. A useful average diameter d is. 

In most cases d32 (the volume/surface average or Sauter mean) is used. The width of the size distribution can be given as the variation coefficient c which is the standard 

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Rust inhibitors usually are corrosion inhibitors that have a high polar attraction toward metal surfaces and that form a tenacious, continuous film which prevents water from reaching the metal surface. Typical mst inhibitors are amine succinates and alkaline-earth sulfonates. Rust inhibitors can be used in most types of lubricating oils, but factors of selection include possible corrosion of nonferrous metals or formation of emulsions with water. Because mst inhibitors are adsorbed on metal surfaces, an oil can be depleted of its mst inhibitor. In certain cases, it is possible to correct the depletion by adding more inhibitor. 

Solvent Extraction. Solvent extraction has widespread appHcation for uranium recovery from ores. In contrast to ion exchange, which is a batch process, solvent extraction can be operated in a continuous countercurrent-fiow manner. However, solvent extraction has a large disadvantage, owing to incomplete phase separation because of solubihty and the formation of emulsions. These effects, as well as solvent losses, result in financial losses and a potential pollution problem inherent in the disposal of spent leach solutions. For leach solutions with a concentration greater than 1 g U/L, solvent extraction is preferred. For low grade solutions with <1 g U/L and carbonate leach solutions, ion exchange is preferred (23). Solvent extraction has not proven economically useful for carbonate solutions. 

When the problem is to disrupt Ughtly bonded clusters or agglomerates, a new aspect of fine grinding enters. This may be iUustrated by the breakdown of pigments to incorporate them in liquid vehicles in the making of paints, and the disruption of biological cells to release soluble produces. Purees, food pastes, pulps, and the like are processed by this type of mill. Dispersion is also associated with the formation of emulsions which are basically two-fluid systems. Syrups, sauces, milk, ointments, creams, lotions, and asphalt and water-paint emulsions are in this categoiy. 

An emulsion is a suspension of one liquid in a second, immiscible, liquid. Emulsifiers are agents that facilitate the formation of emulsions and play a role in stabilizing the emulsion so formed. There are two main types of emulsions oil in water and water in oil. Predominantly hydrophilic emulsifiers (for example, PI88) will stabilize the former predominantly hydrophobic emulsifiers (for example, P181) will stabilize the latter. 

The emulsion blocking mechanism involves formation of emulsion in the pores either by self-emulsification of water-based filtrate with the crude oil, or oil filtrate from an oil-based fluid emulsifying formation water. The emulsions are viscous and can block the pores. The remedial design is to prevent emulsification either by eliminating oil from completion fluid or by the use of demulsifiers. 

Sufficiently low viscosity and sufficient density difference from the aqueous phase to avoid the formation of emulsions. 

Probably the chief difficulty which arises is that due to the formation of emulsions between the organic and aqueous phases. This makes separation of the phases difficult and sometimes impossible. It is clearly important to select liquid exchangers having low surface activity and to use conditions which will minimise the formation of stable emulsions [see Section 6.7, consideration (3)]. 

Before working up the reaction mixture, it is recommended to test whether the reaction is complete by thin layer chromatography (Note 6). If (F)-stilbene is observed, the reaction should be interrupted immediately. The checkers found that the work-up was complicated by formation of emulsions. Small quantities of brine were used to aid separation of the phases. 

Formation of emulsions of the oil-in-water or water-in-oil type depends mainly on the hydrophilic-lipophilic balance (HLB) of the emulsifier. Phosphate esters with their various molecular structures can be adjusted to nearly every HLB value desired. Therefore they are able to meet nearly all of demands in this field. 

Altvater, M., Rietz, R., Neubeet, R., Micromixer based formation of emulsions and creams for pharmaceutical applications, in Proceedings of the 4th International Conference on Microreaction Technology, IMRET 4, pp. 467 77 (5-9 March 2000), AIChE Topical Conf Proc., Atlanta, USA. 

J.Romocki. Application ofN,N-dialkylamides to control the formation of emulsions or sludge during drilling or workover of producing oil weUs. Patent WO 9522585,1995. 

The use of SnCl2 as the redudng agent for the nitro group was not desirable because of environmental issues and difficult work-up (formation of emulsions). 

Contaminants are mobilized into solution by reason of solubility, formation of emulsion or reaction... 

The gravity flow process prevents the formation of emulsions. 

Figure 5.16 Formation of emulsion droplets, (a) Aqueous MPS solution after acid-catalysed hydrolysis and condensation, (b) Micrometre-sized emulsion droplets are rapidly formed upon addition of the base catalyst triethanolamine. (Reproduced from ref. 28, with permission.)... 

One advance in the area of LLE is the use of solid supports that facilitate the partitioning of the analyte(s) of interest. LLE extraction methods involving nonpolar matrices often suffer from the formation of emulsions, and using the solid support is a possible solution. In one study, polychlorinated biphenyls, dioxins, and furans were extracted from the lipid fraction of human blood plasma [32], using diatomaceous earth as the solid support. Long glass columns (30 cm) were packed with several layers of Chem-Elut (a Varian product) and sodium chloride. The plasma samples were diluted with water and ethanol and passed over the columns. A mixture of isopropanol and hexane (2 3) was passed over the column and the LLE was performed. It can be concluded that the LLE with the solid support is easier to perform and can be applied to other lipid heavy matrices such as milk [32]. 

The formation of emulsions may render it difficult to discern the two rather dark layers. In this case it is helpful to acidify with some dilute sulfuric acid. 

The main advantages of LLE are its simplicity and the use of simple and inexpensive equipment. However, it is not free from practical problems such as the formation of emulsions, which are sometimes difficult to break up [377]. The... 

Polarization. The development of an electrical charge when in solution (with water.) Water, alcohol, and sulfuric acid. are polar but most hydrocarbons are not. Some carboxyl groups and hydroxyl groups are polar. Polarization is important to the formation of emulsions and the actions of detergents. 

The density of crude oil is on the order of 0.85 g/cm, so if the sea surface is calm, an oil spill will initially form a slick. The slick is subject to physical processes, such as advection and turbulence, causing it to move vertically and/or horizontally. Advection tends to lead to dispersal or, if land is nearby, shoreline stranding. Turbulence promotes the formation of emulsions, called chocolate mousse, which can be transformed via weathering into tarballs. The lower-molecular-weight compounds tend to evaporate or dissolve. Some fractions of petroleum have solubilities in seawater on the order of tens of milligrams per liter. Some are also photochemically oxidized. 

If one considers a system consisting of water (with or without added electrolyte) + oil + surfactant (with or without a cosurfactant) at equilibrium, there will most likely be present more than two phases (due to the formation of emulsion or microemulsion). The determination of the interfacial tension, Yij> between the two liquid phases is, therefore, of much importance, in order to understand the forces which stabilize these emulsions or microemulsions. The interfacial tension can be measured by using a variety of methods, as described in detail in surface chemistry text-books (1-3). If the magnitude of yij is of the order of few mN/m (=dyne/ cm), then the methods generally used are Wilhelmy plate method or the drop volume (or weight) method (1-4). However, in certain systems ultra-low (or low) interfacial tensions have been reported. Since these low values are reported to be essential in order to mo-... 

Flow patterns can be altered by change of the continuous phase and, accordingly, the tendency for the formation of emulsions or cruds is altered. At one uranium refinery, the solvent is maintained in the continuous phase to produce flow patterns to reduce emulsion tendency [57]. 

Problems that can arise in the process include the formation of emulsions during extraction from the presence of surface-active impurities in the filtered broth. The effect of these can be minimized by introducing appropriate surfactants that can also reduce the accumulation of solids in the extraction equipment. In addition, other organic impurities are present that can be coextracted with the penicillin. It has been found that a number of these can be removed by adsorption onto active carbon. 

Wennersten found that the extractant system tri- -butylphosphate (TBP) in Shellsol A diluent was temperature dependent with extraction decreasing with increasing temperature. Therefore, extraction from the broth at room temperature (22°C) and water stripping at 60°C provided an efficient process (Fig. 10.9). The extraction with long-chain amines was hampered by the formation of emulsions and thus poor separation. Emulsion formation depended on the diluent with hydrocarbons, e.g., Alamine 336/Shellsol A, given the best separation. 

D.8.3. Cl Impurity. Trace amounts of chloride impurities, which may be present at levels between 0.1 and 0.5mol/kg, have significant effects on the physical properties of ionic liquids, such as viscosity and density. Increases in viscosity are of particular concern in biphasic processes because of the formation of emulsions that affect the interface between the two phases 88). 

Some research has shown that emulsions are formed when hot water or steam is used to displace oil from porous media. The formation of emulsions would adversely affect efforts to recycle the water and would likely increase the amount of treatment that the water would require before it could be discharged. 

Heat can be used to break some emulsions Changing the pH of the water can often break an emulsion The presence of acid-forming and sulfate-reducing microorganisms may enhance the formation of emulsions treat the fuel with a microbiocide Formulate fuels with a demulsifier to inhibit emulsion formation Ensure that surfactant compounds and additives... 

Table 1.2.2 Effect of Solvent on the Formation of Emulsion from Aluminum Alkoxide...

Accdg p> GerP 386687 of 1923, the neutralization of crude oil after washing with hot w is done with neutral Na sulfite, in order to avoid the formation of emulsions which occur when strong alkalies are used... 

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