Experimental Investigation on Yield Stress of Water-in-Heavy Crude Oil Emulsions in Order to Improve Pipeline Flow

An experimental study on yield stress of water-in-heavy crude oil emulsions has been carried out by using a HAAKE RS6000 Rheometer with a vane-type rotor. Several factors such as oil volume fraction, shear rate, temperature, and emulsifying agent on the yield stress of emulsions were investigated. Zero shear viscosity of heavy crude oil was 6000 mPas at 30°C, with a density 955 kg/m³. This study shows that the yield stress increases linearly with the increasing shear rate, and displays an exponential decay with increasing the temperature and oil volume fraction. Although the addition of emulsifying agent enhanced the stability of the emulsion, to some extent it also increased the yield stress, especially for the emulsions with high oil volume fractions. Therefore, to reduce the start-up force for the pipeline transport of water-in-heavy crude oil emulsions, the starting rate should be decreased, temperature increased, or oil volume fraction increased. These results are helpful to improve the transportation of water-in-heavy crude oil in pipeline.      

Effect of Water Fraction on Rheological Properties of Waxy Crude Oil Emulsions

This article discusses the effect of water fraction on the rheological properties of waxy crude oil emulsions including gel point, yield stress, viscosity, and thixotropy. The experimental results reveal that the rheological behaviors of the w/o emulsion samples all intensify with the increase of water volume fraction within 60%. Of more significance is that a correlation for w/o emulsions between yield stress and water volume fraction is put forward with an average relative error of 6.75%. In addition, some mainstream viscosity prediction models of w/o emulsions are evaluated, and Elgibaly model is the best-fit for the emulsions in this study.     

Experimental Investigation of Rheological and Morphological Properties of Water in Crude Oil Emulsions Stabilized by a Lipophilic Surfactant

Rheological behavior of two crude oils and their surfactant-stabilized emulsions with initial droplet sizes ranging from 0.5 to 75 µm were investigated at various temperatures under steady and dynamic shear testing conditions. In order to evaluate the morphology and Stability of emulsions, microscopic analysis was carried out over three months and average diameter and size distribution of dispersed droplets were determined. The water content and surfactant concentration ranged from 10 to 60% vol/vol and 0.1 to 10% wt/vol, respectively. The results indicated that the rheological properties and the physical structure and stability of emulsions were significantly influenced by the water content and surfactant concentration. The crude oils behaved as Newtonian fluids over a wide range of shear rates, whereas the emulsions behaved as non-Newtonian fluids, indicating shear-thinning effects over the entire range of shear rates. The viscosity, storage modulus and degree of elasticity were found to be significantly increased with the increase in water content and surfactant concentration. The maximum viscosity was observed at the point close to the phase inversion point where the emulsion system changes from water-in-oil emulsion to oil-in-water emulsion. The results also indicated that the rheological properties of crude oils and their emulsions are significantly temperature-dependent.     

Factors in the Single-Step Bulk Process Preparation of a Triple Janus Emulsion

Some factors in the preparation of triple Janus emulsions in a single-step bulk process were investigated using optical microscopy. The emulsions consisted of water, O.097 weight fraction, a commercial surfactant, Tween 80, 0.03 weight fraction, a vegetable oil (VO), 0.18 weight fraction, and a silicone oil (SO), 0.72 weight fraction. A surprising connection was found between the state of the compounds prior to mixing and the final morphology as well as stability of the emulsion. Separately adding the compounds or with the surfactant dissolved in the vegetable oil, prior to mixing, did not result in a Janus emulsion. Instead, simpler emulsions with limited stability were attained even with prolonged mixing. Storing the compounds together without mixing for two days followed by mixing resulted in a Janus emulsion in which the (VO + SO)/W/VO drops were more sparsely populated with Janus drops, and emulsion stability was limited. Finally, preparing the emulsion from the aqueous surfactant solution and the two oils gave a (VO + SO)/W/VO/SO emulsion with the W drops heavily populated by Janus drops and with improved stability.      

Cinnamoyl Alginate Microspheres: Effect of UV-Treatment on Release of FITC-Dextran

Cinnamoyl alginate microspheres were prepared using the water droplets of W/O emulsions as a template. Cinnamoyl alginates having variable content of the cinnamoyl group were prepared by a condensation reaction. The photo-dimerization degree of the cinnamoyl group increased as the molar ratio of pyranose unit/cinnamoyl group increased from 1:0.043 to 1:0.18. The air/water interfacial activity of cinnamoyl alginate also increased with increasing the molar ratio. Aqueous solution of cinnamoyl alginate was dispersed in mineral oil to obtain W/O emulsion. UV light (254 nm, 6 W) was irradiated to the emulsion to dimerize the cinnamoyl groups, and CaCl₂ was added to the emulsion to cross-link the cinnamoyl alginate. The surface of UV-treated microspheres was rougher than that of UV-untreated microspheres, possibly due to the photo-dimerization-induced tension on the alginate chains. The release degrees for 24 hours of fluorescein isothiocyanate-dextran (FITC-dextran; MW 4000) from UV-treated microspheres were markedly higher than those from UV-untreated ones. This is possibly due to the intramolecular dimerization of cinnamoyl group. The UV irradiation-induced percentage increase in the maximum release degree was greater as the content of cinnamoyl group was higher.     

Comparison of the Rheological Behavior of Solutions and Formulated Oil-in-Water Emulsions Containing Carboxymethylcellulose (CMC)

In this study, it was aimed to compare the rheological properties of carboxymethylcellulose (CMC) in aqueous solutions and their corresponding emulsions containing 0.05, 0.1, 0.25, and 0.5% CMC in the aqueous phase. Samples with 0.05 and 0.1% CMC showed Newtonian behavior, but shear-thinning behavior was observed in CMC solutions and emulsions with increasing CMC concentrations to 0.25% and 0.5%. Rheological behavior of all samples were modeled by Power law (R ² = 0.986–197) and Casson models (R ² = 0.968–1). According to the Ostwald–de Waele model, the consistency index of all samples was increased and the flow behavior index decreased with increasing CMC concentration. Comparison of our data with four predicting models (Einstein, Larson, Pal, and Dougherty-Krieger equations) showed that the viscosity of continuous phase controls the viscosity of emulsions with high CMC concentrations and these models are not applicable for such situations. Addition of CMC increased the emulsion stability of O/W emulsions. This stability was increased with increasing CMC concentrations.     

Influence of Interfacial Rheological Properties on Stability of Asphaltene-Stabilized Emulsions

A series of oscillating droplet measurements have been performed on asphaltenes at the oil/water interface, in order to correlate the interfacial rheological behavior to their ability to stabilize emulsions. In the concentration sweep, the elastic modulus goes through a maximum around an asphaltene concentration of 0.05–0.10 g/l. This behavior was not in good correspondence with emulsion stability, which increased consistently from low to high concentrations. The decrease above 0.10 g/l was most likely an effect of diffusion of asphaltenes in the bulk to the interface, which became more significant at higher bulk concentrations. The rheology data as a function of concentration has been fitted to Butler's surface equation of state and the Lucassen–van den Tempel model. A decent correlation was found between emulsion stability and elasticity for both the effect of solvent aromaticity and pH. The elastic modulus displayed a gradual increase when xylene was mixed with heptane as the solvent, as was seen with emulsion stability. This was not caused by a significant increase of the adsorbed amount of asphaltene at the interface, as shown by a quartz crystal microbalance (QCM), but a more efficient reorganization of the already adsorbed asphaltenes. The ability asphaltenes displayed in stabilizing emulsions was significantly increased at both low and high pH, according to a previous study. The elastic modulus, on the other hand, only showed a very weak increase at pH 2, but a better correlation with emulsion stability above pH 8. From this it would appear that the dissociation of acid groups in the asphaltene structure at high pH has a bigger impact on the interfacial activity than the protonation of bases at low pH, while their effect on emulsion stability was the same.      

Characterization of Optical Properties in Water-in-Oil Emulsion

There have been few studies on the factors that determine the overall appearance of emulsions. Optical properties are quite important in determining the perceived quality of emulsion-based products. The overall appearance of an emulsion is determined by the way that it interacts with electromagnetic radiation in the visible region of the spectrum, for example, reflection, transmission, adsorption, and scattering. These interactions are principally determined by the characteristics of emulsion droplets (size, concentration, and refractive index). The present study aims at characterizing the optical properties and rheological behaviors of water-in-oil emulsions, especially macroemulsions. There is a decrease in the absorbance spectra as increasing glycerin ratio in aqueous phase because the difference of refractive index between oil phase and aqueous phase decreased, which improved the transparency of water-in-oil emulsion. The absorbance of linear and branched surfactant emulsions were smaller than that of alkyl modified branched surfactant emulsion. Moreover the transparency of emulsions prepared with linear and branched surfactants was much clearer than that of alkyl modified branched surfactant emulsion. The absorbance spectra also showed that low polar oil attributed to the more transparent emulsion, compared with high polar or nonpolar oil. However, these kinds of oils were not helpful to prepare transparent emulsion because the appearance of these emulsions was translucent or opaque, even if polyols in aqueous phase was 30 wt%.     

Influence of Mixing Speed in Liquid Crystal Formation and Rheology of O/W Emulsions Containing Vegetable Oils

The process parameters are important in the development of emulsions containing liquid crystals. Thus, we studied the influence of the mixing speed in microscopic and rheological features. Oil-in-water emulsions using vegetable oils and nonionic surfactant were developed employing gradual raise of the mixing speed. It decreased the liquid crystal formation and the density values, and increased apparent viscosity values. The most suitable mixing speed was 600 rpm, since it allowed the attainment of emulsion with better performance and presence of lamellar liquid crystals. However, all emulsions were stable in these experimental conditions and presented pseudoplastic behavior and tixotropy.     

Synergetic Effect of Reactive Surfactants and Clay Particles on Stabilization of Nonaqueous Oil-in-Oil (o/o) Emulsions

Although surfactants and particles are often used together in stabilization of aqueous emulsions, the contribution of each species to such stabilization at the oil-water interface is poorly understood. The situation becomes more complicated if we consider the nonaqueous oil-oil interface, i.e, the stabilization of nonaqueous oil-in-oil (o/o) emulsions by solid particles and reactive surfactants which, to our knowledge, has not been studied before. We have prepared Pickering nonaqueous simple (o/o) emulsions stabilized by a combination of kaolinite particles and a nonionic polymerizable surfactant Noigen RN10 (polyoxyethylene alkylphenyl ether). Different pairs of immiscible oils were used which gave different emulsion stabilities. Using kaolinite with equal volumes of paraffin oil/formamide system gave no stable emulsions at all concentrations while the addition of Noigen RN10 enhanced the emulsion stability. In contrast, addition of Noigen RN10 surfactant to silicon oil-in-glycerin emulsions stabilized by kaolinite resulted in destabilization of the system at all concentrations. For all systems studied here, no phase inversion in simple emulsion was observed by altering the volume fraction of the dispersed phase as compared to the known water-based simple Pickering emulsions.      

Physical and Rheological Characteristics of Emulsion Model Structures Containing Iranian Tragacanth Gum and Oleic Acid

The physical and rheological properties of oil in water model emulsion systems containing Iranian tragacanth gum (TG) (0.5, 1 g/100 ml emulsions), whey protein isolate (WPI) (2, 4 g/100 ml emulsions), and oleic acid (5, 10 ml/100 ml emulsions) were investigated for droplet-size distribution, creaming index, and rheological properties of emulsions. The shear-thinning behavior of all dispersions was modeled using power law, Cross, and Ellis models. The power law model described the flow behavior of dispersions for its lowest standard error (0.29) and highest determination coefficient (R²) (0.99). Rheological investigation showed that both loss (G″) and storage (G′) modules increased as gum and oil content increased. Delta degree was 0.1 and increased as frequency increased, indicating that liquid-like viscose behavior dominated solid-like elastic behavior. Droplet-size distribution was measured by light scattering and microscopic observations revealed a flocculated system. Gum, WPI, and oil contents decreased the emulsion creaming index with gum concentration having the greatest effect.     

Electrocoagulation of Crude Oil From Oil-In-Water Emulsions Using a Rectangular Cell with a Horizontal Aluminium Wire Gauze Anode

Separation of crude oil from oil-in-water emulsions in a square batch electrocoagulation cell, using an aluminum screen as the sacrificial anode was studied, the cathode was a rectangular aluminum plate placed on the cell bottom below the anode. The oil separation efficiency was insensitive to the sodium chloride electrolyte concentration. Increasing current density increased the rate of oil separation from the emulsion. Also it was found that increasing the number of screens per stack at the same current intensity, does not affect the efficiency of oil separation. The removal doesn't depend on the initial pH in the range of pH ～3?8.     

Foam Flooding with Ultra-Low Interfacial Tension to Enhance Heavy Oil Recovery

Severe viscous fingering during water flooding of heavy oil leaves a large amount of oil untouched in the reservoir. Improving sweep efficiency is vital for increasing heavy oil recovery. Previous researches have proved that foam flooding can increase the sweep efficiency and oil recovery. The polymers could make the foam more stable and have better plugging capacity, but the interfacial tension (IFT) of oil and water increase which could decrease the displacement efficiency of the heavy oil. In view of the deficiency of conventional foam flooding, it is necessary to research the ultra-low interfacial tension foam which could improve macro-swept volume and micro-displacement efficiency in heavy oil reservoir. In this paper a novel foam agent is developed by the combination of surfactant and additives to lower the IFT of oil and water. The operating parameters including foam injections modes and gas liquid ratio were investigated by core flooding experiments. Field test performance shows that oil production per day increased from 85.6 to 125.7 t, water cut declined from 92.1 to 83.6% after 3 months injection. This study provides a novel method to improve heavy oil recovery with an ultra-low interfacial tension foam flooding system.     

Effects of Salts Containing Mono-, Di-, and Trivalent Ions on Electrical and Rheological Properties of Oil-Water Interface in Presence of Cationic Surfactant: Importance in the Stability of Oil-in-Water Emulsions

Many industrial applications of oil-in-water emulsions involve salts containing ions of different valence. The properties of the oil-water interface (e.g., interfacial tension, zeta potential and interfacial shear viscosity) are strongly influenced by the presence of these salts. This work investigates the role of NaCl, CaCl₂ and AlCl₃ on these properties of the hexane-water interface in presence of a cationic surfactant, viz., hexadecyltrimethylammonium bromide. Addition of salt enhanced the adsorption of surfactant molecules at the hexane-water interface, which increased the interfacial charge density, and consequently, the zeta potential. Interfacial shear viscosity significantly decreased in the presence of salt. The effectiveness of salt at a given concentration was in the sequence: AlCl₃ > CaCl₂ > NaCl. The hexane-in-water emulsions coarsened with time due to the coalescence of hexane droplets. The increase in droplet size with time was analyzed by a model based on the frequency of rupture of the thin aqueous film. The rate constants for coalescence were determined. The rate of coalescence increased in presence of salt.      

Removal of Mercury by Emulsion Liquid Membranes: Studies on Emulsion Stability and Scale Up

Emulsion liquid membranes (ELM) have received significant attention in the separation of various metal ions from industrial wastewater. Still efforts are needed to get the desired level of stability to overcome the hindrance in the application of ELM at industrial scale. In this paper, the effects of various parameters such as emulsification speed, concentration of cosurfactant, surfactant, carrier and impeller speed during extraction on the stability of an emulsion liquid membrane are studied. Dispersion destabilization of w/o emulsion is checked by Turbiscan. Drop size distribution and photomicrographs of the emulsions are also analyzed to evaluate stability of the emulsion. Instability of emulsion liquid membrane during extraction process is measured in terms of membrane breakage. A stable emulsion is used for the extraction of mercury from aqueous solution in small scale as well as in large scale.     

Application of a Laser Diffraction Method for Determination of Stability of Dispersion Systems in Food and Chemical Industry

Laser diffraction was used for determination of particle size of various emulsions. Mean particle size, fractions' number, and dispersion coefficients of tested systems are presented. Stability of greasing emulsions in relation to their pH was also tested. It was found out that determination of droplet size distribution in fat emulsions allows prediction of their properties (stability). The parameter may be helpful in selection of appropriate production process parameters, composition, and control of marketed emulsion systems during their storage. The purpose of the study was to determine applicability of a laser diffraction method for evaluation of stability of selected dispersion systems in food and chemical industry.     

Multi-Walled Carbon Nanotubes as a Cosurfactant for Highly Concentrated Emulsions

The role of multi-wall carbon nanotubes (MWCNT) as a solid surfactant in highly concentrated water-in-oil emulsions was investigated. MWCNT were dispersed in the oil phase. These suspensions are viscoplastic fluids with the yield stress increasing by more than 1000 times with addition of 2% MWCNT, which demonstrates intensive “structurizing” ability. After emulsion preparation, MWCNT were concentrated at the interface, stabilizing emulsions. The dependence of the inversion point on MWCNT concentration was found. Emulsions containing up to 94 wt% of the aqueous phase can be prepared only when MWCNT is combined with conventional surfactant. Rheological properties of such compositions were measured. It was established that emulsions stabilized by a combined surfactant were more stable in comparison to conventional surfactant stabilized emulsion.     

Effects of a Novel Organic Alkali on the Interfacial Tension and Emulsification Behaviors Between Crude Oil and Water

Experiments have been carried out to investigate the interfacial tension (IFT) and emulsification behaviors between Shengli crude oil and a novel organic alkali (OA). The dynamic IFT and minimum IFT are adopted to characterize the IFT behaviors; the microscopic method, Turbiscan stability index, separated water rate, and laser particle size analysis method are used to show the emulsification behaviors. The dynamic and minimum IFT both decrease continuously with the increase of OA concentration whether surfactant is added or not; because of the synergy of OA and surfactant, the minimum IFT will be reduced to the ultralow value. The synergy is also crucial for the crude oil emulsification. When OA and surfactant are used together, owing to the mosaic and cross-multiple adsorption of OA, surfactant and in situ soap at the interfacial film, the oil can be emulsified more easily, the quantity of emulsified droplets is higher, and the emulsion is more stable with OA concentration increases. The relationship of the minimum IFT and emulsification is investigated; it indicates that the emulsion stability improves, the degree of dispersed homogeneity of oil droplets increases, and the median diameter of emulsified oil droplets decreases with the decline of the minimum IFT.