Emulsification with surfactant mixture

Emulsification with caustic is possible with oils that have a fairly high total acid number (TAN). Below about 1.5 mg KOH/gm oil, the oils either will not emulsify or will form water-in-oil emulsions. The rate of emulsification with caustic is much faster than emulsification with surfactant mixtures, which is a characteristic property for emulsions generated via the agent-in-oil procedure (1 ). 

The emulsification properties of the crude oil must be determined. Some crude oils can be emulsified with surfactant mixtures, others with caustic. Some crudes, such as Hasley Canyon (Table III), are difficult to emulsify. Experiments can be performed to determine if in situ emulsification is feasible, or if an emulsion must be injected. If in situ emulsification is feasible, loss of chemicals to reservoir rock is a problem to be addressed. If in situ emulsification is employed in conjunction with steam, it must be determined if chemicals are most effective when injected with the flowing steam or when chemical/steam injections are alternated. Relative permeabilities of the injected fluids should be determined. All of this information is needed to calculate the economics of scale-up to a specific field situation. 

Different methods are used in microemulsion formation a low-energy emulsification method by dilution of an oil surfactant mixture with water and dilution of a water-surfactant mixture with oil and mixing all the components together in the final composition. These methods involve the spontaneous formation of microemulsions and the order of ingredient addition may determine the formation of the microemulsion. Such applications have been performed with lutein and lutein esters. ... 

The point at which, supposedly, 50% of the acid species is transformed in salt corresponds to the half-neutrahzation, i.e., when half the alkahne required to reach the equivalence point has been added. This position corresponds to a buffer zone in which the variation of pH is small with respect to the amoimt of added neutralization solution (Fig. 14 left plot). Hence, in this region a very slight variation of pH can produce a very large variation of neutralization (Fig. 14 right plot), i.e., a considerable alteration of the relative proportion of AH and A . Far away from this pH, the opposite occurs. Consequently, the pH could be used to carry out a formulation scan, but the scale is far from hnear and the variation of pH does not render the variation of the characteristic parameter of the actual surfactant mixture that is at interface [77,78]. The appropriate understanding of the behavior of this kind of acid-salt mixture is particularly important in enhanced oil recovery by alkaline flooding [79,80] and emulsification processes that make use of the acids contained in the crude oils [81-83]. 

An oil has an HLB of 10 for O/W emulsification. Calculate the percentages of Ci2H25(OC2H4)2OH and Ci2H25(OC2H4)gOH that should be used in attempting to emulsify this oil with a mixture of these two surfactants. 

Data on the preparation of alkyd emulsions by the phase inversion technique were presented in [211]. This technique is accomplished by adding water to an alkyd/surfactant mixture under formation of a stable emulsion. The determination of surfactant s solubility in water and alkyd phases allows to calculate the quantity of water required for phase inversion. Effective emulsifiers are ethoxylated sulphates (2-3 EO groups) of C12 - Ch and C16 - Cig higher alcohols. With these surfactants, the emulsification becomes less dependent on the temperature than with nonionic surfactants. 

Several procedures may be applied to enhance the efficiency of emulsification when producing nano-emulsions One should optimise the efficiency of agitation by increasing 6 and decreasing the dissipation time. The emulsion is preferably prepared at high volume faction of the disperse phase and diluted afterwards. However, very high rj) may result in coalescence during emulsification. Addition of more surfactant creates a smaller and possibly diminishes recoalescence. A surfactant mixture that shows a reduction in y compared with the individual components can be used. If possible, the surfactant is dissolved in the disperse phase rather than the continuous phase this often leads to smaller droplets. 

A study of the phase behavior of water/oil/surfactant systems demonstrated that emulsification can be achieved by three different low energy emulsification methods (A and B as schematically shown in Fig. 2.8). Method A stepwise addition of oil to a water surfactant mixture. Method B stepwise addition of water to a solution of the surfactant in oil. Method C mixing all the components in the final composition, pre-equilibrating the samples prior to emulsification. In these studies, the system water/Brij 30 (polyoxyethlene lauryl ether with an average of 4 moles of ethylene oxide)/decane Wcis chosen as a model to obtain 0/W emulsions. The results showed that nanoemulsions with droplet sizes of the order of 50 nm were formed only when water was added to mixtures of surfactant and oil (method B) whereby inversion from W/0 emulsion to 0/W nanoemulsion occurred. 

Figure 8.9 Shift of optimum emulsification peak by addition of lauryl alcohol (emulsions contain 30 % oil phase, 65 % deionized water, and 5 % surfactant mixtures. Surfactant mixtures consist of hydrophilic Tween 20 and lipophilic Span 20 at ratios and corresponding HLB values indicated by abscissa). Dotted lines represent data for pure mineral oil systems. Solid lines represent data for oil mixture consisting of 8 parts mineral oil and 2 parts lauryl alcohol. O mean droplet size A solubilization limit. From Lin et al [44] with permission.

Examples of different emulsification routes based on the PIT method and the corresponding droplet sizes obtained are shown in Fig. 12. In this example [7,115], the emulsification of a polar oil, cetyl isononanoate, was performed with a surfactant mixture consisting of a long-chain ethoxylated alcohol (Cis/igEz) and glyceryl monostearate (GMS) nonionic surfactants. It was shown that in order to obtain nanometer-size droplets in the system studied, either a liquid crystalline phase or a bicontinuous microemulsion should be formed during emulsification [7]. 

Cross-linked xylan-based microparticles are produced by the emulsification of an alkaline solution of xylan with a lipophilic phase formed by a mixture of chloroform and cyclohexane by using 5% (w/v) sorbitan triesterate as the surfactant. Subsequently, the cross-linking reaction is carried out for 30 minutes with 5% (w/v) terephthaloyl chloride in order to yield a hard and rigid polymeric shell (Nagashima et al., 2008). 

Chen [8] studied mixtures of the pure surfactants Ci2(EO)4 and sodium dodecyl sulfate (SDS) at 30 °C. At this temperature the former is a liquid which does not dissolve in water (see Fig. 3), and the latter is a solid. The SDS was doubly recrystallized from ethanol to remove n-dodecanol and other impurities. The solubility of SDS in pure Ci2(EO)4 at 30 °C was found to be approximately 9 wt. %. When small drops of an 8 wt. % mixture were injected into water at 30 °C, complete dissolution was observed, the time required being a linear function of the square root of initial drop radius. For instance, a drop having an initial radius of 70 (xm required approximately 100 s to dissolve, significantly more than the 16 s cited above for a slightly larger drop of pure Ci2(EO)6. Behavior was similar to that of nonionic mixtures below their cloud points discussed previously in that most of the drop dissolved rapidly, but the final small volume dissolved rather slowly with some observable emulsification. 

Bai [2] performed similar drop dissolution experiments with sodium oleate (NaOl) and Ci2(EO)4. For drops initially containing 7 and lOwt. % NaOl (particle size < 38 jim) the behavior was similar to that described above for drops having 8 wt. % SDS. However for drops with 15 and 17 wt. % NaOl dissolution was faster—comparable to that of the pure nonionics—and neither a surfactant-rich liquid immiscible with water nor emulsification was seen. Instead a concentrated liquid crystalline phase transformed directly into a micellar solution, as seen for the pure nonionics and nonionic mixtures well below their cloud points. 

Figure 9.10 Emulsion switching for a hexadecane-water 2 1 (v/v) mixture containing switchable surfactant, after carbon dioxide treatment and 10 min shaking and (A) 5 min wait period, (B) 30 min wait period and (C) 24 h wait period. (D) After subsequent treatment with argon to turn off emulsification. [Reprinted with permission from Science 2006, 313, 958-960. Copyright 2006 American Association for the Advancement of Science.]...

When a surfactant-water or surfactant-brine mixture is carefully contacted with oil in the absence of flow, bulk diffusion and, in some cases, adsorption-desorption or phase transformation kinetics dictate the way in which the equilibrium state is approached and the time required to reach it. Nonequilibrium behavior in such systems is of interest in connection with certain enhanced oil recovery processes where surfactant-brine mixtures are injected into underground formations to diplace globules of oil trapped in the porous rock structure. Indications exist that recovery efficiency can be affected by the extent of equilibration between phases and by the type of nonequilibrium phenomena which occur (J ). In detergency also, the rate and manner of oily soil removal by solubilization and "complexing" or "emulsification" mechanisms are controlled by diffusion and phase transformation kinetics (2-2). 

After describing the experimental technique in the next section, we report our observations of intermediate phase formation and spontaneous emulsification in three parts corresponding to three types of equilibrium phase behavior found when equal volumes of oil and the surfactant-alcohol-brine mixtures are equilibrated. The three types are well known (8-9) and, in order of increasing salinity, are a "lower" phase, oil-in-water microemulsion in equilibrium with excess oil, a "surfactant" or "middle" phase, probably of varying structure, in equilibrium with both excess oil and excess brine, and an "upper" phase, water-inoil microemulsion in equilibrium with excess brine. 

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