Droplet Crystallization in Water-in-Crude Oil Emulsions: Influence of Salinity and Droplet Size (original) (raw)
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Kinetics of Crystallization of Aqueous Droplets in Water-in-Crude Oil Emulsions at Low Temperatures
Energy & Fuels, 2018
This study focused on the examination of the isothermal crystallization of aqueous droplets in water-in-crude oil emulsions with water concentrations in the range of 5 to 20 wt%. Experiments were carried out using differential scanning calorimetry (DSC) with temperatures ranging from −36 °C to −41 °C. The experimental results were approximated using a mathematical kinetic model including the effect of self-acceleration. The rate of crystallization increases with decreasing temperature, and the final accepted degree of crystallinity also increases along with a decrease in temperature. Correlation was observed between the kinetics of isothermal and non-isothermal crystallization. Furthermore, the complete crystallization in the isothermal process is reached at
Applied Sciences, 2019
In this work, the evolution of dispersed droplets in a water-in-oil (W/O) emulsion during formation, storage, and destabilization was observed using a calorimetry technique. The emulsion was prepared by dispersing drop by drop an aqueous phase into an oil continuous phase at room temperature using a rotor-stator homogenizer. The evolution of droplets during (1) preparation; (2) storage; and (3) destabilization was observed using differential scanning calorimetry (DSC). The samples were gently cooled-down below its solid-liquid equilibrium temperature then heated back above the melting point to determine its freezing temperature. The energy released during the process was recorded in order to get information about the water droplet dispersion state. The mean droplet size distribution of the sample emulsion was correlated to its freezing temperature and the morphology was followed by optical microscopy. The results indicated that the calorimetry technique is so far a very good techniq...
Journal of the American Oil Chemists' Society, 2008
The objective of this research was to systematically study the effect of processing conditions on the crystallization behavior and destabilization mechanisms of oil-in-water emulsions. The effect of crystallization temperature (T c) and homogenization conditions on both thermal behavior and destabilization mechanisms were analyzed. Results show that the crystallization of lipids present in the emulsions was inhibited when compared with bulk lipids as evidenced by a lower onset and peak temperature (T on and T p , respectively) in differential scanning calorimetry crystallization exotherms. The smaller the droplet size in the emulsion, the more significant the inhibition (lower T on and T p). Lower values of T on and T p were not necessarily indicators of emulsion stability. Homogenization conditions not only affected the T on and T p of crystallization but also the crystallization profile of the samples. Lipids present in emulsions with small droplets were crystallized and melted in a less fractionated manner when compared to lipids in bigger droplets or even to the bulk lipids. The amount of lipid crystallized as evidenced by enthalpy values, did not have a direct relationship with the emulsions stability. Although enthalpy values increased as T c decreased, the destabilization kinetics did not follow the same tendency as evidenced by back scattering measurements.
Crystal Comets: Dewetting During Emulsion Droplet Crystallization
Australian Journal of Chemistry, 2005
Liquid oil emulsion droplets can violently dewet their own solid crystals during crystallization as a result of surfactant adsorption. The crystal shape formed is a function of the relative rates of dewetting and crystallization as controlled by surfactant adsorption, cooling rate, and lipid purity. For negligible dewetting rates, crystals nucleate and grow within the droplet. At similar crystallization and dewetting rates, the droplet is propelled around the continuous phase on a crystalline 'comet tail' much larger than the original droplet. Rapid dewetting causes the ejection of small discrete crystals across the droplet's oil-water interface.
Coalescence of Water Droplets in Crude Oil Emulsions: Analytical Solution
Chemical Engineering & Technology, 2010
In petroleum refineries, water is used in desalting units to remove the salt contained in crude oil. Typically, 7 % of the volume of hot crude oil is water, forming a water-and-oil emulsion. The emulsion flows between two electrodes and is subjected to an electric field. The electrical forces promote the coalescence of small droplets of water dispersed in crude oil, and these form bigger droplets. This paper calculates the forces acting on the droplets, highlighting particularly the mechanisms proposed for droplet-droplet coalescence under the influence of an applied electric field. Moreover, a model is developed in order to calculate the displacement speed of the droplets and the time between droplet collisions. Thus, it is possible to simulate and optimize the process by changing the operational variables (temperature, electrical field, and water quantity). The main advantage of this study is to show that it is feasible to increase the volume of water recycled in desalting processes, thus reducing the use of freshwater and the generation of liquid effluents in refineries.
Thermal properties of non-crystallizable oil-in-water highly concentrated emulsions
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011
In this work, a differential-scanning-calorimetry (DSC) technique is applied to studying the thermal properties of highly concentrated oil-in-water (O/W) emulsions of two immiscible liquids (castor oil and water) with high viscosity ratios (3400/1 for O/W), similar densities (0.974/1 for O/W) and stabilized by a non-ionic surfactant. A low-energy mixing process was used to produce highly concentrated emulsions (typically more than 90% O/W) with different mean droplet sizes, dependent on the emulsification time. The oil is non-crystallizable, thus only very thin water-surfactant films and water-surfactant solutions at the Plateau border and node regions between the compressed oil droplets crystallize under freezing. We show that the DSC technique is able to reveal the influence of interfacial energy phenomena (i.e., surface-to-volume effects) on the supercooling degree and on the apparent specific heat capacities of the concentrated emulsions.
Colloids and Surfaces A-physicochemical and Engineering Aspects, 2003
Confectionery coating fat (CCF ) emulsions (40 wt.%) were prepared by mixing liquid fat with solutions (1 Á/4 wt.%) of selected polymeric and small molecule surfactants, and homogenizing to a mean particle diameter of 0.719/0.05 mm. Aliquots of the emulsions were temperature cycled (40 to (/10 to 40 8C at 1.5 8C min (1 ) four times in a differential scanning calorimeter. The stable emulsion droplets crystallized at 0 Á/6 8C (depending on the type of emulsifier) while the non-emulsified fat crystallized at Â/15 8C. The ratio of the enthalpies at these temperatures was used to calculate the proportion of the emulsion that had destabilized after each thermal cycle. All of the small molecule-stabilized emulsions largely destabilized after one cycle. The caseinate-stabilized emulsions were relatively resistant to several thermal cycles unless ethanol (30 wt.%) was added or the pH lowered to 5, in both cases they destabilized during the first cycle. When a small molecule surfactant was added to displace the caseinate from the interface, there was a sharp reduction in stability at the surfactant to protein molar ratio R !/25. Whey protein-stabilized emulsions were partly unstable to freeze Á/thaw even following a thermal pretreatment to denature the proteins. Cryo-SEM confirmed the destabilization of the emulsions was due to partial coalescence. #
Prediction of the Amount of Ice Formation in the Water Dispersed Phase of a W/O Emulsion
2016
This paper deals with investigation of the effect of solute concentration on the amount of ice formation from some materials such as pure water, NaCl and glycerol solutions were dispersed into a W/O emulsion system. The investigations were carried out by inserting sample emulsions into a steady cooling-heating program at constant heating rate, ሶ ܶ = 2.5 K/min from T = (20 to-60)oC, that considered all the water have frozen, then heated back to the initial temperature, T = 20oC to bring about the frozen one to the liquid state using differential scanning calorimetry (DSC-131 evoSetaram, France). The proportion of ice formed, P was then calculated from the recorded thermogram, at which the melting signal is related to the total amount of water frozen. The way the droplets frozen during cooling process is described from the thermodynamics ice/solution phase diagram completed by the curves that give the freezing conditions. The results indicated that the proportion of ice formed calcula...
Coalescence dynamics in oil-in-water emulsions at elevated temperatures
Scientific Reports
Emulsion stability in a flow field is an extremely important issue relevant for many daily-life applications such as separation processes, food manufacturing, oil recovery etc. Microfluidic studies can provide micro-scale insight of the emulsion behavior but have primarily focussed on droplet breakup rather than on droplet coalescence. The crucial impact of certain conditions such as increased pressure or elevated temperature frequently used in industrial processes is completely overlooked in such micro-scale studies. In this work, we investigate droplet coalescence in flowing oil-in-water emulsions subjected to higher than room temperatures namely between 20 to 70 ^{\circ }$$ ∘ C. We use a specifically designed lab-on-a-chip application for this purpose. Coalescence frequency is observed to increase with increasing temperature. We associate with this observation the change in viscosity at higher temperatures triggering a stronger perturbation in the thin aqueous film separating t...