Water-continuous phases

Fig. 9.3 Sauter mean diameter < 32 calculated from drop size measurements at single nozzles of liquid systems (a) toluene (dispersed phase d) water (continuous phase c) and (b) butanol d) water (c), is dependent on the mean velocity Vjv of the dispersed phase in the nozzle. (From Ref. 5.)... 

From experiments, equations have been derived that enable calculation of the minimum velocity in the nozzle, the nozzle velocity, and the Sauter diameter at the drop size minimum. They provide the basis for the correct design of a sieve tray [3,4]. Figure 9.4a shows the geometric design of sieve trays and their arrangement in an extraction column. Let us again consider toluene-phenol-water as the liquid system. The water continuous phase flows across the tray and down to the lower tray through a downcomer. The toluene must coalesce into a continuous layer below each tray and reaches... 

The function of all water-treating equipment is to cause oil droplets, which exist in the water continuous phase, to float to the surface of the water. These droplets are subjected to continuous dispersion and coalescence during the trip up the wellbore through surface chokes, flowlines, control valves and process equipment. When energy is put into the system at a high rate, drops are dispersed to smaller sizes. When the energy input rate is low, small droplets collide and join together in the process of coalescence. 

Gravity separation. Most commonly used water treating equipment relies on gravity to separate oil droplets and the water continuous phase. Oil droplets, being lighter than the volume of water they displace, have a buoyant force exerted upon them. This is resisted by a drag force caused by their vertical movement through the water. When the two forces are equal, a constant velocity is reached that can be computed from Stokes Law ... 

Solution of this equation requires a determination of surface tension. The surface tension of an oil droplet in a water continuous phase normally is between 1 and 50 dynes/cm. It is not possible to predict the value without lab measurements in the produced water Small amounts of impurities in pro duced water can lower surface tension significantly from what might lie measured in synthetic water. As these impure ties change with time, so will surface tension. In the absence of data, it is recommended that a maximum diameter of between 250 and 500 microns be used for design... 

Figure 2.4 (Upper) White-light (polarized) photomicrograph, in reflected mode, of an suspension with a significant emulsified oil content. With polarized light, the clays (C) appear bright, but the oil droplets cannot be seen at all. (Lower) In this reflected-light photomicrograph, of the same field of view as above, the fluorescence mode shows bright oil droplets in a dark water-continuous phase. In this photograph the clays cannot be seen. From Mikula [66], Copyright 1992, American Chemical Society.

System water (continuous phase)-ethyl malonate (dispersion phase, 1 g/50cc water (0.08 wt%), surface tension 11.2mN/m, viscosity 2.0 mPa s, density 1.055 g/cm3). 

Equilibrium with Aqueous Phases. The formation and properties of reverse micelle and microemulsion phases in equilibrium with a second predominantly water continuous phase is of practical interest for extraction processes. Figure 7 compares apparent hydrodynamic diameters observed in the ethane/AOT/water system at 37 C for values of 1, 3 and 16. In single phase systems at W - 1 (a) and 3 (b) the apparent hydrodynamic diameter decreases with increased pressure due to decreased micelle-micelle interactions as the solvent power increases. In contrast for a system with an overall W - 16 (c), where a second aqueous phase exists, hydrodynamic diameter increases continuously with pressure. 

A general pattern of microemulsion phase behavior exists for systems containing comparable amounts of water and a pure hydrocarbon or hydrocarbon mixture together with a few percent surfactant. For somewhat hydrophilic conditions, the surfactant films tend to bend in such a way as to form a water-continuous phase, and an oil in water microemulsion coexists with excess oil. Drops in the microemulsion are spherical with diameters of order 10 nm. Both drop size and solubilization expressed as (VJVX the ratio of oil to surfactant volume in the microemulsion, increase as the system becomes less hydrophilic. At the same time interfacial tension between the microemulsion and oil phases decreases. Just the opposite occurs for somewhat lipophilic conditions. That is, a water in oil microemulsion coexists with excess water with drop size and solubilization of water (VJV,) increasing and interfacial tension decreasing as the system becomes less lipophilic. When the hydrophilic and lipophilic properties of the surfactant films are nearly balanced, a bicontinuous microemulsion phase coexists with both excess oil and excess water. For a balanced film (VJV,) and (VJV ) in the microemulsion are nearly equal, as are 7, 0 and... 

There is a type of melt-dispersion technology, which actually represents a combination of melt-dispersion and emulsification technique. Namely, a melt (dispersed phase) is fed into a vessel containing water (continuous phase) wherein mechanical stirring is used for dispersing it thus, mixing is performed simultaneously with cooling (Figure 25.2). 

For verification of adequacy of suggested method for disperse phase particles sizes calculation experimental investigation of emulsification process in turbulent flows limited by impenetrable wall of divergent-convergent design in hexane-water (continuous phase) system was carried out (see 2.2.7). Six-sectional tubular apparatus differ in canal geometry were used (Table 2.1). 

The distribution coefficients of PAN and CAS indicators between microemulsion droplets and the water-continuous phase in O/W microemulsions constituted of anionic, cationic, and nonionic surfactants have been measured in order to investigate the mechanism of enhanced sensitivity of reactions in O/W microemulsion [31]. From Table 2 one can see that the distribution coefficients of PAN and CAS indicators in all O/W microemulsions are larger than those in micelles with the same surfactants. Thus, we can conclude from these results that the reason for higher sensitivity in microemulsions is that a microemulsion has greater solubilization capacity for indicators or complexes. 

It was found that the formation brine could not be completely eliminated from the heavy crude oil. Because of some limitations in the emulsion-breaking process, about 1% of this concentrated brine remained in the oil as a W/O emulsion. The brine droplets that were of very small size, typieally less than 2 pm, did not join the water continuous phase during preparation of the commercial emulsion, but remained as droplets encapsulated inside the oil drops. It is also possible that the proximity of the A /B" transition region could have promoted the formation of a multiple... 

ORIGINS OF THE FORMATION OF SURFACTANT LIQUID CRYSTALS - WATER-CONTINUOUS PHASES... 

There is a vast body of data concerning the influence of third components on surfactant liquid crystals. Because of the potentially great complexity of the inherent mesophase behaviour, this array of data can appear to be enormously difficult to rationalize. However, if we consider the simple concepts described above (micelle formation, micelle shape/packing constraints, volume fractions and the nature of intermicel-lar interactions), then a reasonably simplified picture emerges, at least for the water-continuous phases. This present section does not attempt to be comprehensive - it simply reports selected examples of behaviour to illustrate the general concepts. The simplest way to show the changes in mesophase behaviour is to employ ternary phase diagrams. The reader should recall that the important factors are (i) the behaviour as a function of surfactant/additive ratio, and (ii) the volume... 

For surfactants having small polar groups and bulky chains, there can be extensive effects with the addition of oils. Alone with water, the surfactants form reversed micelles and/or reversed mesophases. Large volumes of oil can be incorporated into these systems because of the possibility of swelling the alkyl chain regions in these oil-continuous phases (L2, H2 and V2). While extensive research has been carried out in this area, it appears to be much more complex than for the water-continuous phases. Each different surfactant type can show individual behaviour according to the curvature properties of the surfactant layer. 

The emulsion structure is obtained by adding energy to the mixture of water, surfactant and oil. The energy is necessary to increase the interface area. Droplets tend to form. Oil in water (OAV) emulsions are formed when the oil droplets are dispersed in a water continuous phase. Water in oil (W/0) emulsions have a continuous oil phase with water droplets inside (Figure 2.14). The droplet diameter range from 0.02 pm for very fine emulsion to 50 pm and more for coarse emulsions. The emulsion structure is not stable. With time, the droplets fiise by coalescence. Creaming or sedimentation... 

These considerations apply to the tension between an oil-continuous and a water-continuous phase. The interface is covered by a surfactant monolayer and hence is relatively thin. However, attraction between micelles or droplets can canse separation into, for example, two water-continuous phases, one having a higher concentration of aggregates than the other. In this case the interface can be mueh thicker (e.g., on the order of a few droplet diameters) and interfacial tension can be low. In the limiting case of near criticality between the phases, the tension approaches zero and interfacial thickness becomes very large. 

---