Demulsification of water-in-oil emulsions by permeation through Shirasu-porous-glass (SPG) membranes

To investigate the effect of the droplet/pore size ratio on membrane demulsification, water-in-oil (W/O) emulsions with uniform-sized droplets was demulsified by permeation through Shirasu-porous-glass (SPG) membranes with a narrow pore size distribution at mean droplet/pore diameter ratios of 0.52–5.75. At transmembrane pressures above a critical pressure, the water droplets larger than the membrane pore size were demulsified, where the SPG membrane acted as a coalescer because the hydrophilic membrane surface had a high affinity for the water droplets. By contrast, at transmembrane pressures below the critical pressure, the larger water droplets were all retained by the membrane due to the sieving effect of the uniform-sized pores. When a W/O emulsion with a mean droplet diameter of 2.30 μm was allowed to permeate through a membrane with a mean pore diameter of 0.86 μm, the demulsification efficiency increased with increasing transmembrane pressure, to a maximum value of 91% at a transmembrane pressure of 392 kPa, and then decreased, while the transmembrane flux increased almost linearly with increasing transmembrane pressure. The demulsification efficiency was higher for higher water phase content and lower concentration of the surfactant, tetraglycerin condensed ricinoleic acid ester, in the emulsions due to the reduction of the emulsion stability.     

Effects of pH and salt concentration on oil-in-water emulsions stabilized solely by nanocomposite microgel particles

Aqueous dispersions of lightly cross-linked poly(4-vinylpyridine)/silica nanocomposite microgel particles are used as a sole emulsifier of methyl myristate and water (1:1 by volume) at various pH values and salt concentrations at 20 degrees C. These particles become swollen at low pH with the hydrodynamic diameter increasing from 250 nm at pH 8.8 to 630 nm at pH 2.7. For batch emulsions prepared at pH 3.4, oil-in-water (o/w) emulsions are formed that are stable to coalescence but exhibit creaming. Below pH 3.3, however, these emulsions are very unstable to coalescence and rapid phase separation occurs just after homogenization (pH-dependent). The pH for 50% ionization of the pyridine groups in the particles in the bulk (pK(a)) was determined to be 3.4 by acid titration measurements of the aqueous dispersion. Thus, the charged swollen particles no longer adsorb at the oil-water interface. For continuous emulsions (prepared at high pH with the pH then decreased abruptly or progressively), demulsification takes place rapidly below pH 3.3, implying that particles adsorbed at the oil-water interface can become charged (protonated) and detached from the interface in situ (pH-responsive). Furthermore, at a fixed pH of 4.0, addition of sodium chloride to the aqueous dispersion increases the degree of ionization of the particles and batch emulsions are significantly unstable to coalescence at a salt concentration of 0.24 mol kg(-1). The degree of ionization of such microgel particles is a critical factor in controlling the coalescence stability of o/w emulsions stabilized by them.     

Materials based on solid-stabilized emulsions

Solid-stabilized emulsions are obtained by shearing a mixture of oil, water, and solid colloidal particles. In this article, we present a large variety of materials, resulting from a limited coalescence process. Direct (o/w), inverse (w/o), and multiple (w/o/w) emulsions that are surfactant-free and monodisperse were produced in a very wide droplet size range, from micrometers to centimeters. These materials exhibit original properties compared with surfactant-stabilized emulsions: outstanding stability with respect to coalescence and unusual rheological behavior. For such systems, the elastic storage modulus G' is not controlled by interfacial tension but by the interfacial elasticity resulting from the strong adhesion between the solid particles adsorbed at the oil-water interface. Due to the wide accessible droplet size range, concentrated emulsions can be extremely fluid while emulsions with low droplet volume fraction can behave as solids.     

Effect of Emulsification Method on the Properties of Lecithin‐ and PGPR‐Stabilized Water‐in‐Oil‐Emulsions

Water‐in‐oil (w/o) emulsions were prepared with phosphatidylcholine‐depleted lecithin or polyglycerol polyricinoleate (PGPR) as emulsifying agents. The effect of different laboratory emulsification devices and the effect of sodium chloride on particle size distribution, coalescence stability, and water droplet sedimentation were investigated. The properties of lecithin‐stabilized w/o emulsions were found to depend more strongly on the emulsifying method than those prepared with PGPR. The rotor‐stator system was not suitable for preparing stable w/o emulsions with lecithin. Whereas the addition of salt was essential to achieve coalescence‐stable emulsions prepared with PGPR, the presence of NaCl favored the coalescence of water droplets and phase separation in emulsions containing lecithin.     

Demulsification of water-in-oil emulsion by using porous glass membrane

The hydrophilic porous glass membranes were used to demulsify water-in-oil emulsion, and demulsification efficiency can reach more than 96.2%. Effects of pore size of the membrane, transmembrane pressure and volumetric ratio of oil phase to internal aqueous phase in the emulsion on demulsification were investigated. It was found that pore size of membrane and transmembrane pressure can significantly affect demulsification efficiency. The smaller the pore size of the membrane, the better the demulsification efficiency. However, smaller pore size of the membrane has to be exerted a greater transmembrane pressure in order to make internal aqueous phase enter the membrane pore. Correspondingly, effect of transmembrane pressure on permeation flux of the droplets was also studied. In addition, recovered-oil phase by the demulsification were reused five times to extract cadmium from simulated aqueous waste. The results indicated that the extracting efficiency could arrive at 96.5%.     

Behaviour of formula emulsions containing hydrolysed whey protein and various lecithins

Formula emulsion systems are used as enteral, sports and health products. In some formulas addition of hydrolysed protein is necessary to guarantee ease of digestion and hypoallergenicity. In the low fat emulsion model an increase in the content of lecithin (phospholipid mixture) was required, in consideration of the advice of the Food and Nutrition Board (USA) for choline supplementation. The individual and interactive effects of whey protein isolate (WPI) or hydrolysate (WPH) (3.7 and 4.9% w/w), unmodified deoiled or hydrolysed lecithin (0.48 or 0.7% w/w) and carbohydrate in the form of maltodextrin with dextrose equivalent (DE) 18.5 or glucose syrup with DE 34 (11% w/w) on the properties of formula emulsions with 4% v/w sunflower oil, were investigated using a full factorial design. The emulsions were characterised by particle size distribution, coalescence stability, creaming rate, and also surface protein and lecithin concentration. WPI-containing emulsions proved to be stable against coalescence and showed only little creaming after 1 and 7 days standing. There was a significant increase in the mean droplet size and a significant deterioration of coalescence and creaming stability when WPH instead of WPI was used as the protein source, due to the lower number of large peptides and lower surface activity of the WPH. Increasing the WPH concentration led to an increase in oil droplet size and further deterioration of the stability of the emulsions. The starch hydrolysate and lecithin also significantly influenced the emulsion properties. Their influence was less strong when the emulsion contained WPI. Under the conditions used WPH-based emulsions were more stable, in terms of creaming and coalescence, when a low level of protein was used in conjunction with hydrolysed lecithin and glucose syrup. Oil droplets in emulsions containing unmodified lecithin in either the continuous or disperse phase and WPH in the continuous phase were very sensitive to coalescence. The addition of starch hydrolysates (DE 18.5) induced intensive flocculation and phase separation in these emulsions.     

Demulsification by increasing the gravitational force acting upon the dispersed phase owing to the adsorption/absorption of the magnetite particles

Demulsification using a magnetic demulsifier is commonly used to separate emulsions using an external magnetic field. However, this study presents a new demulsification method based on the increased weight of the dispersed phase due to the adsorption/absorption of the magnetite particles by the droplets. Micron-sized bare magnetite particles were used as the demulsifier in this method which does not necessarily need to apply a surface-active additive and the magnetic field for the demulsification. Magnetic responsivity of the demulsifier can only be used for the recovery of the demulsifier. The demulsification experiments were performed using the oil-in-water and water-in-oil emulsions. The effect of temperature, wettability, demulsifier dosage and activity, sedimentation rate and particles size were investigated. The results showed that the proposed method can remarkably improve the efficiency and speed of the demulsification, and has a great potential to be considered for the commercialization.     

Filtration of deformable emulsion droplets

Oil-in-water (o/w) emulsions of different droplet size were filtered on membranes of various pore sizes to investigate the growth and behaviour of o/w filter cakes. The cake desorptivity S and the filter membrane resistance R were measured at various filtration pressures P. The variation of S with P shows that filter cake oil droplets of radius a are effectively rigid for P < gamma/a and fully deformable for P > gamma/a, where gamma is the oil-water interfacial tension. For the largest P, when S became P-independent, the filter cake remained water-permeable as expected from theory.     

Performance of a rotating membrane emulsifier for production of coarse droplets

A versatile and high capacity membrane emulsification system which utilises a rotating membrane for the precision manufacture of oil-in-water (o/w) emulsions is investigated. The o/w emulsions produced used a low viscosity paraffin wax as the dispersed phase, Tween 20 or sodium dodecyl sulphate (SDS) as the emulsifier and carbomer as the stabiliser, respectively. The ability to generate coarse monodisperse emulsions was demonstrated with droplets of average diameter 80–570 μm and coefficient of variation ranging from 9.8% to 33.6%. The effects of key process parameters on the droplet size and distribution are discussed, including requirements for future developments of the membrane.     

Water in oil (w/o) and double (w/o/w) emulsions prepared with spans: microstructure,stability, and rheology

The objective was to analyze the microstructure, stability, and rheology of model emulsions prepared with distilled water, refined sunflower oil, and different Spans (20, 40, 60, and 80) as emulsifiers. The effects of the water content and Span 60 concentration were studied. The lowest water contents led to w/o emulsions, whereas higher percentages gave w/o/w emulsions. Microscopy analysis showed that w/o/w emulsions of higher water contents had a lower number of internal water droplets. W/o emulsions were destabilized by coalescence and sedimentation, whereas creaming was observed in unstable w/o/w emulsions. In the last ones, the creaming stability decreased with increasing water content and enhanced with higher Span 60 concentration; the same effect was observed in their viscoelasticity: They were from unstable liquids to stable gels. Solid Spans (40 and 60) produced more consistent w/o/w emulsions at low water contents and more stable systems at high water percentages in comparison with liquid Spans (20 and 80).     

Fabrication of core/shell hybrid organic–inorganic polymer microspheres via Pickering emulsion polymerization using laponite nanoparticles

Oil-in-water (o/w) emulsions of styrene, as monomer oil in water, were achieved successfully via Pickering emulsification with laponite nanoparticles as the sole inorganic stabilizers. The formed emulsions showed excellent stability not only against droplets coalescence (before polymerization) but also against microparticles coagulation (after polymerization). Generally, the number of composite polystyrene microparticles (PS) increased and their sizes decreased with the content of solid nanoparticles used in stabilizing the precursor o/w emulsions. This is consistent with the formation of rigid layer(s) of the inorganic nanoparticles around the PS microparticles thus a better stability was achieved. The composite microparticles were characterized using various techniques such as surface charge, stability, transmission electron microscope (TEM), scanning electron microscope (SEM) and Fourier transform infra-red (FT-IR). Coating films of the prepared latexes were applied to flat glass surfaces and showed reasonable adhesion compared to PS latex particles prepared with conventional surfactants. The effect of employed conditions on the features of the resulting emulsions in terms of stability and particle size has been discussed.     

Studies of Kinetics of Coalescence of Water‐in‐Furrial Crude Oil Emulsions by Confocal Microscopy

The kinetic of coalescence of water in Furrial crude oil emulsions (W/O) during the initial stage of demulsification process is showed through of high‐resolution image micrographics by using a confocal microscope. Furrial crude oil from Monagas state is a crude oil extra heavy with severe flocculation/aggregation problems. The kinetic of the initial stage in the coalescence process is critical and of great importance in the definition of the foreword behavior. This information allowed us to characterize the demulsification rate process in a Furrial crude oil. Total W/O emulsion separation was achieved about of 2 hours at 80ºC. The initial fast coalescence is characterized by a short binary coalescence time, which is followed by a large binary coalescence time. Our results demonstrate that the initial coalescence rate determinate the time necessary to achieve a total separation.     

Further Investigation into the Stability of Water-in-Crude Oil Emulsions Formed in Burgan Oilfield: Effect of Toluene,Resins to Asphaltenes Ratio,and Surfactant

Factors controlling the formation and stabilization of water-in-crude oil (w/o) emulsions in oil fields are of great concern to the petroleum industry for the economic development of underground oil reservoirs. Controlling and minimizing the formation of w/o emulsions and demulsification of water from emulsions are also important for environmental development. Because of its importance, the mechanisms, formation, and stability of w/o emulsions have received considerable attention. This article deals with some of the factors responsible for the formation and stabilization of w/o emulsions formed in Burgan oil field in Kuwait. Some of the factors investigated in this study are the naturally occurred surface active components of crude oils such as asphaltenes and resins. Stability of emulsion samples with resins to asphaltenes ratio (R/A) contents of 3, 5, 9, 12, and 20 has been studied. It was found that Emulsion tightness is correlated with resins to asphaltene content of the sample. As the R/content increases the emulsion becomes unstable. The effect of additives such as toluene and dodecyle benzene sulfonic acid (DBSA) on the stability of various emulsion samples collected from oil field are also reported. A 2 wt% of DBSA was found to resolve all the water from emulsion samples collected from Burgan oilfield.     

Microgels as stimuli-responsive stabilizers for emulsions

Temperature- and pH-sensitive microgels from cross-linked poly(N-isopropylacrylamide)-co-methacrylic acid are utilized for emulsion stabilization. The pH- and temperature-dependent stability of the prepared emulsion was characterized. Stable emulsions are obtained at high pH and room temperature. Emulsions with polar oils, like 1-octanol, can be broken by either addition of acid or an increase of temperature, whereas emulsions with unpolar oils do not break upon these stimuli. However, complete phase separation, independent of oil polarity, can be achieved by successive acid addition and heating. This procedure also offers a way to recover and recycle the microgel from the sample. Interfacial dilatational rheology data correlate with the stimuli sensitivity of the emulsion, and a strong dependence of the interfacial elastic and loss moduli on pH and temperature was found. The influence of the preparation method on the type of emulsion is demonstrated. The mean droplet size of the emulsions is characterized by means of flow particle image analysis. The type of emulsion [water in oil (w/o) or oil in water (o/w)] depends on the preparation technique as well as on the microgel content. Emulsification with high shear rates allows preparation of both w/o and o/w emulsions, whereas with low shear rates o/w emulsions are the preferred type. The emulsions are stable at high pH and low temperature, but instable at low pH and high temperature. Therefore, we conclude that poly(N-isopropylacrylamide)-co-methacrylic acid microgels can be used as stimuli-sensitive stabilizers for emulsions. This offers a new and unique way to control emulsion stability.     

A Videomicroscopic Investigation of Coupled Reversible Flocculation and Coalescence at Singlet-Doublet Equilibrium in an O/W Emulsion of Low Density Contrast

Video enhanced microscopy (VEM) enables direct investigation of dilute emulsions. A practical and effective preparative technique utilizes microslides, which are flat, rectangular microcapillaries made from borosilicate glass. Experimental difficulties due to droplet sedimentation and droplet-microslide wall interaction can be drastically reduced, even eliminated, by the use of low density contrast emulsions, i.e. emulsions where the densities of the dispersed and continuous phases are not very different. The dichlorodecane (DCD)-in-water emulsion is an example of such a system. This system.can as such be used for measurement of the time of the elementary act of coalescence, calculated from the evolution in the droplet size distribution. The developing distributions can be determined through automated VEM.

In this paper we discuss the perspective for elaboration of a standard method for the determination of an averaged time for the elementary act of coalescence. The experimental basis is automated measurement of the time dependence of the droplet size distribution, as applied to dilute DCD/w emulsions at singlet-doublet equilibrium.     

Emulsion stabilization and inversion using a pH- and temperature-sensitive amphiphilic copolymer

We describe how a versatile amphiphilic diblock copolymer can form oil-in-water (o/w) or water-in-oil (w/o) emulsions depending on pH and temperature. At high pH and temperature, this copolymer is mostly hydrophobic and forms w/o emulsions. Its spontaneous curvature is greatly increased upon pH and/or temperature lowering (due to protonation and/or hydration, respectively), which allows the formation of o/w emulsions. Conductivity measurements and confocal fluorescence micrographs evidence the two kinds of structures obtained over a wide range of pH and temperature. We also show how the emulsion type can be reversibly switched along a temperature scan under stirring. The lower stability of the w/o emulsions as compared to the o/w ones is attributed to a lack of electrostatic repulsion. The importance of the copolymer architecture and conformation with regards to droplet stability is discussed.     

The effect of brine salinity on water-in-oil emulsion stability through droplet size distribution analysis: A case study

Water-in-oil emulsion usually forms during waterflooding in some heavy oil reservoirs. The composition and salinity of the injected water critically affect the w/o emulsion droplet size distribution, which control the emulsion stability and emulsion flow in porous media. The aim of the present work is to assess the effect of different sea water salinities on w/o emulsion stability through microscopic imaging. Therefore, w/o emulsions were prepared with different sea water samples, which were synthesized to resemble Persian Gulf, Mediterranean, Red Sea, and North Sea water samples. The results showed that log-normal distribution function predicts very well the experimental data to track the emulsion droplet size distribution, and then it was used for the emulsion stability analysis. It was found that among the four emulsion samples, North Sea emulsion with the lowest NaCl and TDS concentration of 24.12?g/L and 34.44?g/L remained stable up to almost 24 hours, while Red sea emulsion with the highest NaCl and TDS concentration of 32.39?g/L and 41?g/L became unstable after 6-hour period. This indicated that as the brine concentration increases, the w/o emulsion droplets would be larger due to the higher rate of aggregation and coalescence, and the emulsion stability decreases.     

Synthesis and evaluation of some polymeric surfactants for treating crude oil—Part II. Destabilization of naturally occurring water‐in‐oil emulsions by polyalkylphenol formaldehyde amine resins

In the present work, three polymeric surfactants were prepared and used as demulsifiers; polyalkyl phenol formaldehyde monoethanol amine ethoxylate, eo, 136(D1), polyalkyl phenol formaldehyde diethanol amine ethoxylate, eo, 37(D2) and polyalkyl phenol formaldehyde triethanol amine ethoxylate, eo, 21.5(D3). Their demulsification potency in breaking water‐in‐crude oil emulsions was investigated. In this respect, two naturally occurring Egyptian water‐in‐oil (w/o) emulsions, one of them was waxy and the other was asphaltenic, were used in order to study the demulsification power of these compounds. The data revealed that, the resolution of water from waxy crude emulsion was easier than asphaltenic crude emulsion. The demulsification efficiency increases with increasing demulsifier concentration, contact time and temperature. The interfacial tension (IFT) at the crude oil–water interface was measured, it was found that the concentration of demulsifiers required to cause a minimum IFT are always less than these indicating a maximum demulsification efficiency. All the results were discussed in relation to emulsifier chemical structure and crude oil composition. Copyright © 2002 John Wiley & Sons, Ltd.     

Structure of nanofibrillated cellulose layers at the o/w interface

The nature of layers formed by cellulose nanofibrils that had been surface modified (hydrophobized) at the oil/water (o/w) interface was investigated. The aim of the study was to clarify the mechanism underlying the excellent ability of these nanoparticles to stabilize emulsions. Layers of hydrophobized nanofibrillated cellulose spread at the o/w interface were deposited on glass slides by the Langmuir-Blodgett deposition technique. Overall evaluation of layer structures was performed by image analysis based on a Quadtree decomposition of images obtained from a flatbed scanner. A more detailed characterization of the layer structures was performed by Atomic Force Microscopy (AFM), and Field-Emission Scanning Electron Microscopy (FE-SEM). The results show that nanofibrils that were able to stabilize emulsions occur as single, dispersed fibrils or form large, network-like aggregates at the o/w interface. Fibrils that were insufficiently hydrophobized and therefore did not stabilize emulsions were only partially deposited and formed small, compact aggregates. We conclude that it is likely that the network formation is the main mechanism by which the fibrils prevent coalescence of emulsion droplets.     

Silica particle-stabilized emulsions of silicone oil and water: aspects of emulsification

A study of the emulsification of silicone oil and water in the presence of partially hydrophobic, monodisperse silica nanoparticles is described. Emulsification involves the fragmentation of bulk liquids and the resulting large drops and the coalescence of some of those drops. The influence of particle concentration, oil/water ratio, and emulsification time on the relative extents of fragmentation and coalescence during the formation of emulsions, prepared using either batch or continuous methods, has been investigated. For batch emulsions, the average drop diameter decreases with increasing particle concentration as the extent of limited coalescence is reduced. Increasing the oil volume fraction in the emulsion at fixed aqueous particle concentration results in an increase in the average drop diameter together with a dramatic lowering of the uniformity of the drop size distribution as coalescence becomes increasingly significant until catastrophic phase inversion occurs. For low oil volume fractions (phi(o)), fragmentation dominates during emulsification since the mean drop size decreases with emulsification time. For higher phi(o) close to conditions of phase inversion, coalescence becomes more prevalent and the drop size increases with time with stable multiple emulsions forming as a result.