Oils, emulsion formation

M. Fingas. Water-in-oil emulsion formation A review of physics and mathematical modelling. Spill Sci Technol Bull, 2(l) 55-59, March 1995. 

Fig. 14 Mechanism of droplet formation by flow instabilities between immiscible fluids (a) T-junction droplet generator and (b) photomicrograph of water-in-oil emulsion formation (Reprinted from [146] with permission. Copyright 2001 by the American Physical Society), (c) Flow focusing configuration, and (d) formation of the water-ln-oll droplets (Reproduced from [147] by permission of The Royal Society of Chemistry)...

Emulsification Emulsification is considered the second most important weathering process after a marine spill by which water is dispersed into oil in the form of small droplets. The mechanism of water-in-oil emulsion formation is not yet fully understood, but it probably starts with sea energy forcing the entry of small water droplets, about 10 to 25 /rm in size, into the oil. Emulsions of many types contain about 70% water. In general, water-in-oil emulsion can be categorized into four types (1) unstable oil simply does not hold water (2) entrained water droplets are simply held in the oil by viscosity to form an unstable emulsion, and it breaks down into water and oil within minutes or a few hours at most (3) semistable or meso-stable the small droplets of water are stabilized to a certain extent by a combination of the viscosity of the oil and interfacial action of asphaltenes and resins. For this to happen, the asphaltenes or resin content of the oU must be at least 3% by weight. The viscosity of meso-stable emulsions is 20 to 80 times... 

By January 1, 1978, 3,500 m of water and 2,000,000 m of air were injected. By this same date, the water-air ratio was 1.7 x 10 3 ta /tn . During the period of time when water and air were bdng alternately injected into the well 833, its wellhead pressure rose only a little. However, during the same time, as a result of re-pressurizing of the petroliferous bed through water and air injection, the producing wells started to yield a stable water-oil emulsion. Formation of this emulsion made the processing of the produced crude difficult so that further combined injection of water and air had to be stopped. 

Emulsion formation meehanisms are not the reverse of demulsification mechanisms. Cmde-oil emulsion formation may involve one or more meehanisms based on the process of immiseible phases interaeting, in time, with energy. To date, the detailed mechanisms are not yet understood completely, especially for petroleum emulsions. 

Kilpatrick, P. K Spiecker, P. M. Gawrys, K. L. Trail, C. B. (2003 b). Effects of Petroleum Resins on Asphaltenes Aggregation and Water-in-Oil Emulsion Formation. Colloids and Surfaces, 220,9-27... 

Petroleum Resins on Asphaltene Aggregation and Water-in-Oil Emulsion Formation. Colloids and Surfaces A-Physicochemical and Engineering Aspects, 220, 9-27. 

The cleaning process proceeds by one of three primary mechanisms solubilization, emulsification, and roll-up [229]. In solubilization the oily phase partitions into surfactant micelles that desorb from the solid surface and diffuse into the bulk. As mentioned above, there is a body of theoretical work on solubilization [146, 147] and numerous experimental studies by a variety of spectroscopic techniques [143-145,230]. Emulsification involves the formation and removal of an emulsion at the oil-water interface the removal step may involve hydrodynamic as well as surface chemical forces. Emulsion formation is covered in Chapter XIV. In roll-up the surfactant reduces the contact angle of the liquid soil or the surface free energy of a solid particle aiding its detachment and subsequent removal by hydrodynamic forces. Adam and Stevenson s beautiful photographs illustrate roll-up of lanoline on wood fibers [231]. In order to achieve roll-up, one requires the surface free energies for soil detachment illustrated in Fig. XIII-14 to obey... 

Because of the zwitterion formation, mutual buffering action, and the presence of strongly acid components, soybean phosphoHpids have an overall pH of about 6.6 and react as slightly acidic in dispersions-in-water or in solutions-in-solvents. Further acidification brings soybean phosphoHpids to an overall isoelectric point of about pH 3.5. The alcohol-soluble fraction tends to favor oil-in-water emulsions and the alcohol-insoluble phosphoHpids tend to promote water-in-oil emulsions. 

The multiple emulsion technique includes three steps 1) preparation of a primary oil-in-water emulsion in which the oil dispersed phase is constituted of CH2CI2 and the aqueous continuous phase is a mixture of 2% v/v acetic acid solution methanol (4/1, v/v) containing chitosan (1.6%) and Tween (1.6, w/v) 2) multiple emulsion formation with mineral oil (oily outer phase) containing Span 20 (2%, w/v) 3) evaporation of aqueous solvents under reduced pressure. Details can be found in various publications [208,209]. Chemical cross-linking is an option of this method enzymatic cross-linking can also be performed [210]. Physical cross-linking may take place to a certain extent if chitosan is exposed to high temperature. 

A solids-stabilized water-in-oil emulsion may be used either as a drive fluid for displacing hydrocarbons from the formation or to produce a barrier for diverting the flow of fluids in the formation. The solid particles may be formation solid particles or nonformation solid particles, obtained from outside the formation (e.g., clays, quartz, feldspar, gypsum, coal dust, asphaltenes, polymers) [228,229]. 

Solidifiers, or gelling agents, solidify oil, requiring a large amount of agent to solidify oil— ranging from 16% to more than 200% by weight. Emulsion breakers prevent or reverse the formation of water-in-oil emulsions. 

Compositions of a N,N-dialkylamide of a fatty acid in a hydrocarbon solvent and a mutual oil-water solvent are useful for the prevention of sludge formation or emulsion formation during the drilling or workover of producing oil wells [1526,1528,1529]. 

H.-Y. Lee, M. J. McCarthy, S. R. Dungan 1998, (Experimental characterization of emulsion formation and coalescence by nuclear magnetic resonance restricted diffusion techniques), J. Am. Oil Chem. Soc. 75, 463. 

Foamed cement slurries have been used to provide a low density cement slurry to reduce permeability damage to highly sensitive formations through reduced fluid loss (29). Glass microspheres have also been used to substantially reduce cement slurry density (30, 31). Other additives which reduce cement slurry density to a lesser extent include bentonite, fly ash, silicates, perlite, gilsonite, diatomaceous earth, and oil emulsions (see citations in reference 29). 

Fluid loss additives are used are used to reduce the rate of fluid loss from the fracture to the formation and to naturally occurring macro- and micro-fractures within the formation. Silica flour (73,74), oil-soluble resins (75), diesel oil emulsions (5% by volume) (74) have also been used. 

H. Kunieda, Y. Fukui, H. Uchiyama, and C. Solans Spontaneous Formation of Highly Concentrated Water-in-Oil Emulsions (Gel-Emulsions). Langmuir 12,2136 (1996). 

However, oil and water can be dispersed with the help of suitable emulsifiers (surfactants) to give emulsions (Sjoblom et al., 2008 Birdi, 2008). This is a well-known fact with emulsions found in the home, such as mayonnaise, the basic reason being that the interfacial tension (IFT) between oil and water is around 50 mN/m, which is high, and which leads to the formation of large oil drops. On the other hand, the addition of suitable emulsifiers reduces IFT to very low values (even much less than 1 mN/m). Emulsion formation means that oil drops remain dispersed for a given length of time (even up to many years). The stability and the characteristics of these emulsions are related to the areas of their applications. 

The stability of any emulsion is dependent on needs and the application area. In some cases, the emulsion need to be stable for longer time than in other cases. As in the case of hair cream, the emulsion should destabilize as soon as it is applied to the hair, as otherwise, the hair will be white with emulsion droplets. On the other hand, any emulsion used in spraying on plants needs to be stable for longer time. Further, if one needs to clean oil spills on oceans, the emulsion formation then needs to be destabilized. 

This brief review has attempted to discuss some of the important phenomena in which surfactant mixtures can be involved. Mechanistic aspects of surfactant interactions and some mathematical models to describe the processes have been outlined. The application of these principles to practical problems has been considered. For example, enhancement of solubilization or surface tension depression using mixtures has been discussed. However, in many cases, the various processes in which surfactants interact generally cannot be considered by themselves, because they occur simultaneously. The surfactant technologist can use this to advantage to accomplish certain objectives. For example, the enhancement of mixed micelle formation can lead to a reduced tendency for surfactant precipitation, reduced adsorption, and a reduced tendency for coacervate formation. The solution to a particular practical problem involving surfactants is rarely obvious because often the surfactants are involved in multiple steps in a process and optimization of a number of simultaneous properties may be involved. An example of this is detergency, where adsorption, solubilization, foaming, emulsion formation, and other phenomena are all important. In enhanced oil recovery. 

There s another example of water-in-oil compartmentation, which can circumvent this problem water-in-oil emulsions. These can be prepared by adding to the oil a small amount of aqueous surfactant solution, with the formation of more or less spherical aggregates (water bubbles) having dimensions in the range of 20-100 p,m in diameter. These systems are generally not thermodynamically stable, and tend to de-nfix with time. However, they can be long-lived enough to permit the observation of chemical reactions and a kinetic study. 

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