Water in-oil-emulsion stabilized

Our goal is to develop a property-performance relationship for different types of demulsifiers. The important interfacial properties governing water-in-oil emulsion stability are shear viscosity, dynamic tension and dilational elasticity. We have studied the relative importance of these parameters in demulsification. In this paper, some of the results of our study are presented. In particular, we have found that to be effective, a demulsifier must lower the dynamic interfacial tension gradient and its ability to do so depends on the rate of unclustering of the ethylene oxide groups at the oil-water interface. 

We have restricted fliis presentation to involve only oil-continuous emulsions. The reason for excluding water-continuous systems is that the OAV emulsions are usually stabilized by means of ionic surfactants (or surfactant mixtures) and consequently the electric double-layer effects can be very large. The electrode polarization will normally also be very strong in many 0/W systems. For the TDS technique water-in-oil emulsions stabilized by means of non-ionie surfactants are very good model systems. 

MF Fingas, B Fieldhouse, JVMullin. Studies of water-in-oil emulsions stability and oil properties. Proceedings of the Twenty—First Arctic and Marine Oil Spill Program Technical Seminar, Ottawa, ON, 1998, pp 1—25. 

In our work we have attempted to determine the relationship between interfacial layer properties and water-in-oil emulsion stability. For this objective, physico-chemical properties of surfactants (stabilizing agents), properties of emulsified hydrocarbon films and rheological properties of interfacial layers must be studied. The results of the study may lead to recommendations for preparing high-stability systems for commercial well-drilling. 

The chapter next dealt with the rheology of emulsions stabilized by polymeric surfactants. The factors affecting the rheology of emulsions were briefly discussed. This was followed by a section on interfacial rheology and its correlation with emulsion stability. The bulk rheology of oil-in-water and water-in-oil emulsions stabilized by polymeric surfactants was described. Both steady-state and viscoelastic investigations were described. These emulsions show a transition from predominantly viscous to predominantly elastic response as the frequency of oscillation exceeds a critical value. This allows one to obtain... 

Ortiz, D. P. Baydaka, E.N. Yarranton H.W.(2010). Effect of surfactants on interfacial films and stability of water-in-oil emulsions stabilized by asphaltenes. Journal off Colloid and Interface Sdence,doi 10.1016/j.jcis.2010.08.032 Pryanto, S., Mansoori, G.A., Suwono, A., (2001). Measurement of property relationships of nano-structure micelles and coacervates of asphaltene in a pure solvent. Chemical Engineering Science, 56, 6933-6939... 

Ortiz, D., Baydak, E., Yarranton, H. (2010). Effect of surfactants on interfacial films and stability of water-in-oil emulsions stabilized by asphaltenes. Journal of Colloid and Interface Science Vol.351 542-555... 

Yan, M. Gray, J. Masliyah, (2001) On water-in-oil emulsions stabilized by fine solids. 

Sherman [36] reported that the viscosity of water-in-oil emulsions stabilized with nonionic surfactants falls with time. Refer to Fig. 38. This phenomenon is controlled by the increase in the particle size caused by coalescence. The flocculation and coalescence rates will cause either the increase or decrease of the viscosity on aging [37]. 

Liu, G.J., Yang, H.S., and Zhou, J.Y. (2005b) Preparation of magnetic microspheres from water-in-oil emulsion stabilized by block copolymer dispersant. Biomacromolecules, 6,1280-1288. 

Opawale FO, Burgess DJ. 1998. Influence of interfacial properties of lipophitic surfactant on water-in-oil emulsion stability. J Colloid Interface Sci 197 142-150. 

Sztukowski, D.M. and Yarranton, H.W. (2005) Oilfield solids and water-in-oil emulsion stability. Journal of Colloid and Interface Science, 285, 821-833. 

T. Jiang, G. Hirasaki, C. Miller, K. Moran and M. Fleury. Diluted bitumen water-in-oil emulsion stability and characterization by nuclear magnetic resonance (NMR) measurements. Energy Fuels 21, 2007, 1325-1336. 

Particles that are small relative to emulsion drop size are also expected to have an effect on emulsion properties in systems stabilized by surfactants when present in only small amounts (say a sufficient number of particles to give 10% coverage of droplet surfaces). We reported elsewhere [40] on a preliminary smdy of the ways in which the stability to flocculation and coalescence of water-in-oil emulsions stabilized by the anionic surfactant Aerosol OT are modified by polystyrene latex particles. There is evidence that the particles bridge droplets to give weak floes, which slow down droplet coalescence. 

The class I FruA isolated from rabbit muscle aldolase (RAMA) is the aldolase employed for preparative synthesis in the widest sense, owing to its commercial availability and useful specific activity of 20 U mg . Its operative stability in solution is limiting, but the more robust homologous enzyme from Staphylococcus carnosus has been cloned for overexpression [87], which offers unusual stability for synthetic purposes. Recently, it was shown that less polar substrates may be converted as highly concentrated water-in-oil emulsions [88]. 

Pigments are generally labile as free molecules and the natural and simplest way to stabilize their function is to form micelles (oil-in-water or water-in-oil emulsions, depending on the major dispersion media). 

The viscosity function of the natural gums is utilized in both oil in water and water in oil emulsions. Often the gums are referred to as emulsifying agents. They are considered not so much as emulsifiers, but rather as emulsion protectors or stabilizers. To a large extent, the function is to increase the viscosity of the aqueous phase so that it approaches, or slightly exceeds, that of the oil hence, there is less tendency for the two phases, once emulsified, to separate by mechanical slippage. 

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]. 

Water-in-oil macroemulsions have been proposed as a method for producing viscous drive fluids that can maintain effective mobility control while displacing moderately viscous oils. For example, the use of water-in-oil and oil-in-water macroemulsions have been evaluated as drive fluids to improve oil recovery of viscous oils. Such emulsions have been created by addition of sodium hydroxide to acidic crude oils from Canada and Venezuela. In this study, the emulsions were stabilized by soap films created by saponification of acidic hydrocarbon components in the crude oil by sodium hydroxide. These soap films reduced the oil/water interfacial tension, acting as surfactants to stabilize the water-in-oil emulsion. It is well known, therefore, that the stability of such emulsions substantially depends on the use of sodium hydroxide (i.e., caustic) for producing a soap film to reduce the oil/water interfacial tension. 

Crude oils contain various amounts of indigenous surface-active agents that stabilize water-in-oil emulsions. Therefore crude oils may stabilize such emulsions. It has been shown that the effectiveness of a dispersant is dependent on both the dispersant type and the specific crude oil [309]. However, there is no apparent correlation between the degree of emulsion-forming tendency of the crude oil, which is a function of the indigenous surfactant content, and the effectiveness of the dispersant. In general, indigenous surfactants in crude oil reduce the effectiveness of the dispersant, but to an unpredictable level. 

Surfactants are used to stabilize water-in-oil emulsions and to promote rapid return of injected fluids and a faster return of the well to hydrocarbon production. Although they are expensive, water-soluble fluorochemicals have been shown to be effective in this application (97,98). 

The two main assumptions underlying the derivation of Eq. (5) are (1) thermodynamic equilibrium and (2) conditions of constant temperature and pressure. These assumptions, especially assumption number 1, however, are often violated in food systems. Most foods are nonequilibrium systems. The complex nature of food systems (i.e., multicomponent and multiphase) lends itself readily to conditions of nonequilibrium. Many food systems, such as baked products, are not in equilibrium because they experience various physical, chemical, and microbiological changes over time. Other food products, such as butter (a water-in-oil emulsion) and mayonnaise (an oil-in-water emulsion), are produced as nonequilibrium systems, stabilized by the use of emulsifying agents. Some food products violate the assumption of equilibrium because they exhibit hysteresis (the final c/w value is dependent on the path taken, e.g., desorption or adsorption) or delayed crystallization (i.e., lactose crystallization in ice cream and powdered milk). In the case of hysteresis, the final c/w value should be independent of the path taken and should only be dependent on temperature, pressure, and composition (i.e.,... 

P. Poulin, W. Essafl, and J. Bibette On the Colloidal Stability of Water-in-Oil Emulsions. A Self-Consistent Field Approach. J. Chem. Phys. B 103,5157 (1999). 

The first kinetics measurements about coalescence were reported by Kabalnov and Weers in water-in-oil emulsions [40]. These authors measured the characteristic time at which the layer of free water formed at the bottom of the emulsions corresponded approximately to half of the volume of the dispersed phase. This time was assumed to be equal to t. By measuring r at different temperatures, the activation energy was deduced from an Arrhenius plot. Kabalnov and Weers were able to obtain the activation energy for a water-in-octane emulsion at 50%, stabilized by the nonionic surfactant C12E5 (pentaethylene glycol mono n-dodecyl ether), above the phase inversion temperature (PIT), and found a value of 47 kgTr, Tr being the room temperature. 

M.P. Aronson and M.F. Petko Highly Concentrated Water-in-Oil Emulsions Influence of Electrolyte on Their Properties and Stability. J. Colloid Interface Sci. 159, 134(1993). 

Figure 5. fVater-in-oil emulsion stabilized by a surfactant (upper left.) and oil-in-water emulsion stabilized by a surfactant (lower right.) (6)... 

Powders often have a stabilizing effect on emulsions [548], To understand the responsible effect we have to remember that a particle assumes a stable position in the liquid-liquid interface if the contact angle is not zero (see section 7.2.2). Upon coalescence of two drops the solid particles would have to desorb from the interface. This is energetically unfavorable. A common example of the stabilizing contribution of solid particles are margarine and butter. Both are water-in-oil emulsions. The water droplets are stabilized by small fat crystals. 

Whether, upon stabilizing with powders, an oil-in-water or a water-in-oil emulsion is formed depends largely on the contact angle. Also the effect of additional surfactants can often be explained by their influence on the contact angle. 

The most common agents to stabilize an emulsion are surfactants. Different effects contribute to the stabilization of emulsions. Steric repulsion between those parts of the surfactant, which are in the continuous phase, is an important effect. For a water-in-oil emulsion the hydrocarbon chains are hindered in their thermal movements if two water drops approach each other too closely. For an oil-in-water emulsion there is an additional effect the hydrophilic head groups have to be dehydrated to come into close contact. The resulting hydration repulsion stabilizes the emulsion. 

---