Fat crystals and water-in-oil emulsion stability

Products such as cosmetics, pharmaceuticals, and crude oil often exist as water-in-oil (W/O) emulsions during their processing or in final form. In many cases, their dispersed aqueous phase is encased in a crystal network and/or by interfacially-adsorbed (‘Pickering’) particles [paraffins, triacylglycerols, polymers, etc.] that promote emulsion kinetic stability by hindering droplet–droplet contact, coalescence and macroscopic phase separation. In processed foods, important questions remain regarding whether a continuous phase fat crystal network or Pickering crystal provides better stabilization. This review explores the following factors related to crystal-stabilized W/O emulsions: i) the key properties dictating fat crystal spatial distribution (at the interface or in the continuous phase); ii) how temperature and freeze–thaw emulsion destabilization are intimately linked with fat crystal spatial distribution, and; iii) why oil-soluble surfactant interactions with the continuous oil phase influence fat crystal wettability and emulsifier efficacy. It is shown that these parameters strongly govern W/O emulsion formation and stability.     

Oilfield solids and water-in-oil emulsion stability

Model water-in-hydrocarbon emulsions consisting of toluene, heptane, water, asphaltenes, and native solids were used to investigate the role of native solids in the stability of oilfield emulsions. The solids were recovered from an oil-sands bitumen, a wellhead emulsion, and a refinery slop oil. The solids were clay platelets and fell into two size categories: (1) fine solids 50 to 500 nm in diameter and (2) coarse solids 1 to 10 microm in diameter. Emulsions stabilized by fine solids and asphaltenes were most stable at a 2:1 fractional area ratio of asphaltenes to solids. It appears that when the asphaltene surface coverage is high, insufficient solids remain to make an effective barrier. When the solids coverage is high, insufficient asphaltenes remain on the interface to immobilize the solids. Treatments that weaken the interface, such as toluene dilution, are recommended for emulsions stabilized by fine solids. Emulsions stabilized by coarse solids were unstable at low solids concentrations but became very stable at solids concentrations greater than 10 kg/m(3). At low concentrations, these solids may act as bridges between water droplets and promote coalescence. At high concentrations, layers of coarse solids may become trapped between water droplets and prevent coalescence. Treatments that flocculate the solids, such as heptane dilution, are recommended for emulsions stabilized by high concentrations of coarse solids. It is possible that emulsions containing both types of solids may require more than one treatment, or even process step, for effective water resolution.     

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%.     

Separation of water-in-oil emulsion with microfiber glass coalescing bed

Water-in-oil emulsion separation through a fibrous media bed is a complex and challenging process in industries. In this article, we used a vertical column separator to investigate the effects of the height and porosity of the fiber bed, the structure arrangement (the mixed or the layered fibrous bed), the superficial velocity of the water-in-oil emulsion through the bed, and the influent water content of the emulsion on water removal. Four kinds of glass microfibers (GF1-GF4) with mean diameters of 0.6, 2.6, 4.6, and 8.0?µm, respectively, acted as the coalescence medium and composed the fibrous bed with different structure types. The separation efficiency could reach 97.1% with a relatively low pressure drop under the optimal bed structure and operational conditions. It also showed that the mixed bed had higher separation performance compared to the layered fibrous bed.     

Effect and optimization of bed properties on water-in-oil emulsion separation

Water-in-oil emulsion separation through a fibrous media bed is a complex process in industries. In this article, in order to select the optimal fibrous material for the separation of water-oil emulsion, three types of commercial fibers as fibrous beds were used to separate water from diesel oil. Based on the principle of orthogonal experimental design, a series of experiments were performed to investigate the effect of such parameters as bed porosity (0.77-0.89), bed length (100-400?mm) and settlement length (120-480?mm) on the separation efficiency and the superficial velocity, and then three parameters were optimized to achieve good separation performance. The experiment showed that the separation efficiency could reach 77% and the flow velocity could reach 30?m/h under the optimal bed structure and stable working conditions. The results of this paper could provide basic designing reference for the industrial application of fibrous bed coalescer.     

Demulsification of water-in-oil emulsion by wetting coalescence materials in stirred- and packed-columns

Demulsification of emulsified water-in-oil droplets was developed using wetting coalescence materials. Demulsification tests were carried out using conventional stirred- and packed-columns. Of the four kinds of natural fibers and two kinds of inorganic materials tested, natural fiber A, selected from shaves of a wood showed the best performance in demulsification. The demulsification efficiency can exceed 97% when demulsification conditions are optimized. The packed-column showed much better performance both in terms of demulsification efficiency and repeated use of the recovered oil phase for extracting cadmium in a simulated wastewater. Operating variables that govern the demulsification efficiency were investigated.     

Investigation of wax deposition and effective diffusion coefficient in water-in-oil emulsion system

As pipeline transportation is widely used in the petroleum industry, the problem of wax deposition is a severe threat to the safety of oil and gas transportation. In addition, the mechanism of wax deposition is very complicated due to the presence of water phase. This paper tries to clarify the effects of water fraction, temperature difference and experimental period on the wax deposition process in water-in-oil emulsion system by a series of static cold finger experiments. The experimental results reveal that the average diffusion rates decrease with increased water fraction, longer experimental period and reduced temperature difference. Furthermore, on the basis of wax deposition experiments in cold finger apparatus and radial temperature distribution simulations via Fluent, the influence of water phase on heat transfer occurring in the wax molecular diffusion process is revealed, and relationship between mass transfer and heat transfer is investigated. Additionally, the effective diffusion coefficient of wax molecules is calculated on the basis of experimental and simulation results. The calculated effective diffusion coefficients using this approach are significantly lower than the calculated results from conventional methods. This explains the remarkable disparity with previous works due to underestimating the influence of dispersed water.     

Macroporous polymer thin film prepared from temporarily stabilized water-in-oil emulsion

We report a simple and convenient method for fabricating ordered porous structure in a polymeric thin film. A temporarily stabilized water-in-oil emulsion, where aqueous droplets were dispersed in the medium of polymer-organic solvent solution, was utilized for the preparation of porous structure. The water-in-oil emulsion was simply prepared by sonicating the mixture of water and polymer-organic solvent solution without any colloid stabilizer. The growth of aqueous droplets was profoundly retarded by dissolving a small amount of sucrose, selectively soluble in the dispersed phase. The prepared emulsion was recovered onto a substrate through dip-coating and subsequently air-dried to get a well-ordered porous polymer film. The polymer content in the polymer solution phase and the compositional ratio of the aqueous phase to the polymer solution phase was optimized to fabricate well-ordered structures.     

Dehydration efficiency of high-frequency pulsed DC electrical fields on water-in-oil emulsion

The influence of several operational variables on the electrostatic separation of water-in-oil emulsions is investigated in a Perspex cell equipped with a high-frequency pulsed DC generator using conductivity technique. The ascending and the descending periods of the observed conductivity vs. time curves were fit to the sigmoid and power function, respectively, which revealed the model parameters that were used to quantify dehydration efficiency (DE). Experiment results show that DE increases with decreasing inter-electrode distance, and at a given inter-electrode distance, DE increases with decreasing frequency. Furthermore, at a given pulse interval, DE increases with increasing pulse duration.     

Effects of petroleum resins on asphaltene aggregation and water-in-oil emulsion formation

Asphaltenes from four crude oils were fractionated by precipitation in mixtures of heptane and toluene. Solubility profiles generated in the presence of resins (1:1 mass ratio) indicated the onset of asphaltene precipitation occurred at lower toluene volume fractions (0.1–0.2) than without resins. Small-angle neutron scattering (SANS) was performed on solutions of asphaltene fractions in mixtures of heptane and toluene with added resins to determine aggregate sizes. Water-in-oil emulsions of asphaltene–resin solutions were prepared and separated by a centrifuge method to determine the vol.% water resolved. In general, the addition of resins to asphaltenes reduced the aggregate size by disrupting the π–π and polar bonding interactions between asphaltene monomers. Interaction of resins with asphaltenic aggregates rendered the aggregates less interfacially active and thus reduced emulsion stability. The smallest aggregate sizes observed and the weakest emulsion stability at high resin to asphaltene (R/A) ratios presumably corresponded to asphaltenic monomers or small oligomers strongly interacting with resin molecules. It was often observed that, in the absence of resins, the more polar or higher molecular weight asphaltenes were insoluble in solutions of heptane and toluene. The addition of resins dissolved these insolubles and aggregate size by SANS increased until the solubility limit was reached. This corresponded approximately to the point of maximum emulsion stability. Asphaltene chemistry plays a vital role in dictating emulsion stability. The most polar species typically required significantly higher resin concentrations to disrupt asphaltene interactions and completely destabilize emulsions. Aggregation and film formation are likely driven by polar heteroatom interactions, such as hydrogen bonding, which allow asphaltenes to absorb, consolidate, and form cohesive films at the oil–water interface.     

Synthesis of Fe3O4/PAM superparamagnetic nano-hydrogels in water-in-oil emulsion

Abstract

In this study, the nano-sized water droplets (NWDs) in water-in-oil (W/O) emulsion were employed as mini-reactors, in which Fe₃O₄/PAM magnetic nano-hydrogels (MNHs) were obtained based on the coprecipitation and inverse emulsion polymerization. In addition, compound nonionic surfactant was used as the stabilizer of W/O emulsion. The test results showed that Fe₃O₄/PAM MNHs were quasi-sphere particles with a diameter of about 50–380?nm and had superparamagnetism. The percentage of PAM coating Fe₃O₄ was about 81%. The saturation magnetization of the Fe₃O₄/PAM MNHs was 21.6?emu/g (Fe₃O₄/AM (wt/wt)?=?16.63%). The W/O emulsion containing Fe₃O₄/PAM MNHs (E-2) changed from fluid to solidlike in an external magnetic field. As current intensified or shear rate increased, the shear stress of E-2 increased.     

A visible coalescence of droplets on hydrophobic and hydrophilic fibers in water-in-oil emulsion

The droplets’ coalescence is instantaneous and rather complex in emulsion. The theoretical analysis of this process was presented by a former research, while visible experiments to verify these are still scarce. This work aims to show and analyze the visible water droplets’ coalescence on hydrophobic bamboo charcoal fibers and hydrophilic glass fibers in water-in-oil emulsion. An experimental setup with microscope and high-speed camera was designed and established to record the water droplets’ coalescence. The water droplets’ collision coalescence on bamboo charcoal fibers was observed, and the diameters of water droplets detaching from the fibers with different angles were measured. The angle between the fiber and the flow velocity can affect the diameters of water droplets detaching from the bamboo charcoal fibers, and cross-fibers can the enormously increase water diameters compared with single fiber. Meanwhile, the water droplets’ collision coalescence on glass fibers was observed and the result shows that the collision coalescence also occurred on the hydrophilic glass fibers when the droplet diameter was small. In addition, other factors, including flow velocity and droplets’ diameter for the coalescence on the hydrophilic glass fibers were investigated.     

Time-dependent nucleation of methane hydrate in a water-in-oil emulsion: effect of water redistribution

Nucleation is a key step in preventing gas hydrate formation during oil and gas production. Oil can sharply affect the hydrate nucleation with changing the activity of nucleation centers (mainly at the water–oil interface) over time. The spontaneous emulsification of water-in-oil emulsions in the course of aging can lead to a decrease in the size of water drops and, consequently, facilitate the hydrate nucleation and alter hydrate mitigation during the shut-in period     

Selective collection of inorganic iron(III) colloids in water with oxine-impregnated water-in-oil emulsion

An oxine-impregnated emulsion was prepared by dissolving 100 mg of oxine and 0.3 ml of non-ionic surfactant (Span-80) in 10 ml of toluene and mixing with 3 ml of 1 mol l(-1) hydrochloric acid by sonication (20 kHz). The water-in-oil emulsion was injected into 50 ml of water sample (containing iron(III) at the ppb level, pH 4-7) and dispersed by stirring for 10 min as numerous small globules (0.1-0.5 mm in diameter). The iron diffused through the toluene layer into the small droplets of hydrochloric acid. The emulsion was separated by flotation and heated to segregate the aqueous (hydrochloric acid) and organic (toluene) phases. The iron in the aqueous phase was determined by graphite-furnace atomic absorption spectrometry (GFAAS). Hydrated iron(III) oxide having particle sizes of larger than 1 mum did not penetrate into the emulsion. Other iron species which were not incorporated into the emulsion include humic complexes and hybrid particles of hydrated iron(III) oxide and humic substances. This discrimination can be attributed to the surfactant layer at the oil-water interfaces and gentle stirring of the solution. The conventional liquid-liquid extraction, however, did not offer such a selectivity, because all iron(III) species were simultaneously extracted into the organic phase with vigorous shaking. The unique property of the emulsion method has been applied to the separation and determination of inorganic dissolved iron species in river water.     

Microdroplet size prediction in microfluidic systems via artificial neural network modeling for water-in-oil emulsion formulation

In this paper, an experimental study and modeling by artificial neural networks were carried out to predict the generated microdroplet dimensionless size in a microfluidic system in order to formulate a water-in-oil emulsion. The various parameters that affect the size of microdroplets (flow rates, viscosities, surface tensions of both the two phases and the diameter of the microchannel) are studied and further grouped into dimensionless numbers; we used these numbers as input to the neural network and the dimensionless length as output. The better neural network architecture has 10 neurons in the hidden layer with a mean square error of 1.4 10^?6 and a determination’s coefficient near 1 value. The relative importance of inputs on the size of the microdroplets has been determined using the Garson algorithm and the results are in good agreement with other works.     

A water-in-oil emulsion containing Kelex-100 for the speciation analysis of trace heavy metals in water

A water-in-oil (w/o) emulsion containing Kelex-100 (7-dodecenyl-8-quinolinol) and Span-80 (sorbitan monooleate, non-ionic surfactant) was ultrasonically prepared from 1.0 mol l⁻¹ hydrochloric acid and a (1 + 3) mixture of toluene and n-heptane. The resulting emulsion was gradually injected into water sample and dispersed as numerous tiny globules (0.01-0.1 mm in diameter). Dissolved inorganic species (free metal species) of heavy metals (e.g., Fe, Co, Cu, Cd, and Pb) were selectively transported through the oil layer into the internal aqueous phase of the emulsion, leaving other species, such as humic complexes and suspended particles (larger than 1 μm), in the sample solution. After collecting the dispersed emulsion globules, they were demulsified and the heavy metals in the segregated aqueous phase were determined by graphite-furnace atomic absorption spectrometry. The emulsion-based separation method allowed the selective collection of free metal species with a high concentration factor of 100, whereas the conventional solvent extraction did not offer such discrimination. This unique property of the emulsion method was successfully applied to the selective determination of free species of heavy metals in fresh water samples.     

Biocompatible water-in-oil emulsion as a model to study ascorbic acid effect on lipid oxidation

A biocompatible water-in-oil (W/O) emulsion has been used as a model to study the effect of ascorbic acid (AA) on the oxidation of the oil (glycerol trioleate, GTO) continuous phase. The model system consisted of 3 wt % water dispersed in GTO containing 0.5 wt % sodium oleate (NaO)/oleic acid (OA) mixture (NaO/OA = 20/80 mol/mol %) as a stabilizer. To study the ascorbic acid effect on GTO light-promoted oxidation, we added aqueous solutions of ascorbic acid to GTO in place of distilled water. Results obtained as peroxide values show that ascorbic acid activity depends on its concentration and it is affected by the characteristics of the W/O interface. In the presence of ascorbyl palmitate (AP) or sorbitan trioleate (Span 85) in the continuous phase, ascorbic acid activity increases in the first few hours of oxidation. The effect of ascorbic acid has been related to emulsion structure by calculating characteristic parameters of the droplet size distributions by means of optical microscopy.     

The effects of anionic surfactants on the conductivity of a water-in-oil emulsion in a dielectric hydrophobic capillary

The effect of anionic surfactants on the conductivity of a water-in-crude oil emulsion in a laminar flow inside a dielectric hydrophobic capillary is experimentally investigated in an alternating electric field with strengths ranging from 4 to 10 kV/cm and a frequency of 50 Hz. Conductivity is analyzed as a function of aqueous phase concentration, electric field strength, and surfactant concentration in the dispersed phase.     

Orientation of anthracene molecules in naphthalene and tetracene molecules in anthracene single crystals

The orientation of isolated anthracene and tetracene molecules in naphthalene and anthracene single crystals, respectively, was determined using electron spin resonance. The result indicates only small deviations of less than 60° from that of a molecule in a substitutional position.