Experimental characterization of emulsion formation and coalescence by nuclear magnetic resonance restricted diffusion techniques

Nuclear magnetic resonance (NMR) is explored as a technique for noninvasively monitoring emulsion droplet formation and destabilization. The method makes use of the fact that the diffusion of oil molecules within oil-in-water emulsion droplets results in attenuation of a coherent magnetic signal that emanates from those molecules. If oil diffusion is limited by the size of the droplet, the shape of a plot of attenuation over time is directly affected by the droplet radius. We use this approach to determine noninvasively the effect of surfactant type, surfactant concentration, pH, and ionic strength on droplet sizes within a 40 wt% octane and water emulsion, stabilized by Tween 20 or β-lactoglobulin (β-Lg). We find that addition of the low-molecular-weight Tween 20 forms finer emulsion droplets than does addition of the protein, and that the Tween 20 emulsion is sensitive to surfactant concentration below a threshold “saturation” concentration. The droplet sizes in β-Lg-containing emulsions increase as pH increases above the isoelectric point and as ionic strength increases. The fact that the NMR technique does not mistake clusters of droplets for single large droplets makes the analysis of these effects unambiguous. We further extend the use of NMR diffusion techniques to monitor the effect of surfactant type, surfactant concentration, and convection on the rate of droplet coalescence. The ability of NMR methods to distinguish between large single droplets and droplet clusters makes it well-suited to monitor coalescence processes independently from flocculation.     

Influence of Coagulant Salt Addition on the Treatment of Oil‐in‐Water Emulsions by Centrifugation,Ultrafiltration, and Vacuum Evaporation

Abstract

Droplet size is a key factor in the treatment of oil‐in‐water (O/W) emulsions, because of its influence on emulsion properties. The addition of a coagulant salt generally causes emulsion destabilization, increasing the droplet size, and enhancing coalescence between oil droplets, which helps its further treatment. The influence of CaCl₂ addition on droplet size distribution of a commercial O/W emulsion used in machining processes was studied in order to facilitate oil removal and to improve its further treatment by centrifugation, ultrafiltration (UF) and vacuum evaporation. The critical coagulation concentration (CCC) was observed at a CaCl₂ concentration of 0.05 M. The quality of the final aqueous effluent, expressed as its chemical oxygen demand (COD) value, was compared for all treatments. The highest COD values were obtained for centrifugation, while the COD of the UF permeate was approximately constant for all UF trials. The best effluent quality was obtained by vacuum evaporation. A combination of these techniques should be appropriate for most industrial treatments of O/W emulsions, depending on the subsequent use of the resulting aqueous effluent.     

Edible oil-in-water emulsions stabilized by hydrophile–lipophile balanced sucrose ester

Conventional emulsions are mostly stabilized by surfactants and for stabilization of oil-in-water emulsions the surfactants should be hydrophilic or with HLB numbers larger than seven. In this work, we report that edible oil-in-water emulsions can also be stabilized by surfactants with an HLB value close to seven. With edible sucrose ester C-1807 (HLB no. = 7) as emulsifier and three edible oils (canola oil, olive oil, soybean oil), edible oil-in-water emulsions can be stabilized by C-1807 at concentrations beyond its critical aggregation concentration (CAC). Although monomeric C-1807 behaves as an inferior emulsifier, they assemble to form multilamellar vesicles in water at concentrations higher than the CAC giving a viscoelastic/gel-like aqueous phase which is partly responsible for emulsion stabilization. Specifically, at 2 wt%, high internal phase emulsions (HIPEs) with ϕ_o = 0.75 can be obtained, which are stable against cooling–heating cycles between 5 and 30°C during storage. The vesicles disperse in the aqueous lamellae surrounding the oil droplets, which together with the viscoelastic/gel-like continuous phase prevents them from flocculation and coalescence.     

Coalescence of Water Droplets in Crude Oil Emulsions: Analytical Solution

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.     

De-emulsification of 2-ethyl-1-hexanol/water emulsion using oil-wet narrow channel combined with low-speed rotation

Low-speed rotation of disc in an internal circulation of a novel de-emulsification with rotation-dise horizental contactor (RHC-D) realized de-emulsification for O/W emulsions due to repeated coalescence in oil-wet narrow channels at a low rotation speed. For three emulsions included ethanol/water/2-ethyl-1-hexanol, ethanol/water/2-ethyl-1-hexanol/SDS (Sodium Dodecyl Sulfonate) and 2-ethyl-1-hexanol/water/SDS emulsion, deemulsification ratios of oil phase could reach 1, 1 and 0.67 respectively at 170 r·min^-1, and de-emulsification ratios increased obviously after agitating 10 min. De-emulsification experiment in the seam indicated that oil droplet sizes in O/W emulsion became larger after de-emulsification. The main de-emulsification mechanism in RHCD was the coalescence of oil droplets in oil-wet narrow channels. With increase of the rotation speed, oil droplets dispersed better in the aqueous phase. However, de-emulsification effect enhanced due to the increase of the coalescence rate at a bit higher rotation speed. In addition, internal circulation made those O/W emulsions to be broken repeatedly, consequently de-emulsification ratio increased. Repeated de-emulsification through internal circulation might make continuous extraction of ethanol come true at a low rotation speed.     

A coalescer for soybean oil emulsions

A simple device was designed, consisting of alternate layers of absorbant cotton supported on fiberglass that accelerated the coalescence of oil droplets from an emulsion of soybean oil in aqueous isopropyl alcohol. Separation was generally complete in 90 min or less. The mention of firm names or trade products does not imply that they are endorsed or recommended by the US Department of Agriculture over other firms or similar products not mentioned.     

Vergleich des Koaleszenzverhaltens ruhender und umströmter Wasser‐in‐Öl‐in‐Wasser‐Einzeltropfen

Phase inversion of a water‐in‐oil emulsion to a water‐in‐oil‐in‐water double emulsion is practically used for liquid/liquid separation. For successful separation in the water leg the coalescence of the internal droplets with the surrounding continuous water phase is decisive. The determination of this coalescence phenomenon is applied for the process design. Therefore, single water‐in‐oil‐in‐water drops are investigated under static and dynamic conditions by means of high speed imaging. The influence of physical and geometrical parameters on the coalescence time and partial coalescence is determined.     

Synthesis and characterization of chitosan droplet particles by ionic gelation and phase coacervation

The present study focused on formation of chitosan (CS) droplets particles/microcapsules by ionic gelation method with sodium dodecylsulfate (SDS) for encapsulating linseed oil as active substance. Chitosan droplet particles with four alternate layers of CS and SDS were developed from oil in water emulsion using SDS as an anionic emulsifier. The process was optimized by zeta potential measurements to avoid overcharging of particles by excess addition of CS. The drying process promoted coalescence of CS droplet particles to form a functional coating and to protect the core substance against influence of environmental conditions. The functional coating formed by the particles was characterized by scanning electron microscopy, wetting measurements, and atomic force microscopy and surface roughness. Atomic force microscopy and surface roughness analyses indicated that smooth surface with more hydrophobic groups on the surface of functional coating was obtained after CS addition and it was due to film forming ability of CS chains in the system.     

Production of oil-containing crosslinked poly(vinyl alcohol) microcapsules by phase separation: Effect of process parameters on the capsule size distribution

Oil-containing poly(vinyl alcohol) (PVA) microcapsules in the size range of 5–20 μm were prepared by the simple coacervation of PVA followed by chemical crosslinking of the coacervated PVA membrane with glutaraldehyde. Coacervation of the aqueous polymer solution was achieved by the addition of a phase separation inducer (e.g., sodium sulfate). PVA of different grades (e.g., molecular weight and degree of hydrolysis) was utilized both as stabilizer and wall-forming material. Dispersion of the oil phase in the aqueous PVA solution was effected by a homogenizer. The effects of the various process parameters, such as the agitation speed, the type and concentration of PVA, the volume ratio of the internal oil phase to the external aqueous phase, the viscosity of the oil phase as well as the electrolyte concentration in the aqueous solution, on the stability and the size distribution of the emulsion droplets and microcapsules were experimentally investigated. It was shown that high agitation rates and low interfacial tension (e.g., high PVA concentrations) resulted in a significant reduction of the size of the emulsion droplets and microcapsules. On the other hand, as the viscosity and the amount of the dispersed oil phase increased, the capsule size increased. Finally, it was found that the concentration of the electrolyte significantly affected the stability of the (o/w) emulsion, the size and concentration of coacervated PVA colloidal aggregates, as well as the morphology of the polymer wall membrane formed by the adsorption of the polymer-rich phase to the oil/water interface. © 1996 John Wiley & Sons, Inc.     

Effectiveness of Polyoxyethylene Nonionic Emulsifiers in Emulsification Processes Using Disc Systems

Additives such as emulsifiers and stabilizers (viscosity enhancers or polymers) are needed to stabilize emulsion systems against coalescence and creaming. A way to reduce emulsifier input by determining the effectiveness of different emulsifiers is described. Only disc systems with optimized configuration are applied for emulsification. Polysorbates are taken as an example for emulsifiers. The viscosity was increased with pectin as a viscosity enhancer to allow higher energy inputs by the disc systems and, therefore, to improve droplet disruption. The attainable mean diameters of oil droplets stabilized only by pectin were compared with the resulting mean diameters of oil droplets of emulsions containing polysorbates. Polysorbate 20, the emulsifier with the highest water solubility of all here described emulsifiers, proved to be the most effective in decreasing the mean diameter of the disperse phase when using disc systems. An optimal emulsifier concentration of 2 wt‐% for emulsions at low viscosities is observed for all polysorbates and for the whole range of oil concentration.     

利用受限空间装置从低浓度水包油乳状液中分离油相的研究(英文)

A miniature process for separating the oil phase from dilute oil/water emulsion is developed.This process applies a confined space apparatus,which is a thin flow channel made of two parallel plastic plates.The space between the two plates is rather narrow to improve the collisions between oil droplets and the plate surface.Oil droplets have an affinity for the plate surface and thus are captured,and then coalesce onto the surface.The droplet size distribution of the residual emulsion resulted from the separation process is remarkably changed.The oil layer on the plate weakens the further separation of oil droplets from the emulsion.Three types of plate materials,polypropylene(PP),polytetrafluoroethylene(PTFE) and nylon 66,were used.It is found that PP is the best in terms of the oil separation efficiency and nylon 66 is the poorest.The interaction between droplets in the emulsion and plate surface is indicated by the spreading coefficient of oil droplet on the plate in aqueous environment,and the influences of formed oil layer and plate material on the separation efficiency are discussed.     

Flocculation and Separation of Oil Droplets in Ultrasonic Standing Wave Field

A new method for breaking oil in water emulsion based on flocculation of droplets in high intensity ultrasonic standing wave field was developed in this study and the effect of initial droplets size, type of disperse phase as well as the time of sonication and the height of emulsion in the chamber on the extent of interdroplet interactions were investigated. The results showed that type of disperse phase affects the efficiency of separation process through controlling the initial size of droplets. For the two types of disperse phase in question the efficiency of separation was calculated to be 42.7% for canola oil/water emulsion and 37% for sunflower oil/water emulsion. The time of sonication was found to have a positive contribution to the percent of flocculation and coalescence, so that the largest aggregates were formed after 30 minutes treatment. Also, the optimum height of emulsion in the treatment chamber was determined to be λ/4 at which the strongest flocculation and highest percent of coalescence took place. Increasing the height of emulsion did not significantly influence the course of aggregation and separation.     

Poly(methyl methacrylate) multihollow particles by water in oil in water emulsion polymerization

Multihollow‐structured poly(methyl methacrylate) (PMMA) particles were produced employing the water in oil in water (W/O/W) emulsion polymerization technique where sorbitan monooleate was used as a primary surfactant and sodium laurylsulfate and Glucopen, a polypeptide derivative, were used as secondary surfactants. Vinyl acetate was copolymerized to improve the wettability of the particles. The agitation speed and concentration of the urethane acrylate employed as a reactive viscosity enhancer played a crucial role in determining the morphology and average size of the PMMA multihollow particles. In high agitation speed the multihollow particles displayed a small size and narrow size distribution resulting from efficient droplet breakup. Especially when the urethane acrylate was incorporated, PMMA multihollow particles with a smooth and clear surface were achieved. This was believed to be because the urethane acrylate increased the viscosity of the monomer mixture and helped to form the stable W/O/W emulsion droplets that restricted droplet coalescence during polymerization. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 38–44, 2000     

Influence of Oil Properties on Bed Coalescence Efficiency

Abstract

Bed coalescence efficiency of oil separation from formation water was studied on model systems involving 10 real samples of crude oil and its fractions of different characteristics. Oil components were varied and all other parameters were kept constant, and high mineralization water served as the continuous phase. All experiments were realized on a commercial WO/O4 two-stage bed coalescer. Temperature, oil content, and fluid velocity were kept constant for all samples. Model emulsion was dispersed by constant stirring during the experiment to obtain primarily droplets of 20 μm diameter. Correlations for predicting the coalescence efficiency as a function of some physical and chemical oil properties are presented. The investigated oil components ensured a wide span of viscosity, density, and interfacial tension. The influences of mean molecular weight, neutralization number, as well as the contents of n-alkenes, NSO, and aromatics on coalescence efficiency were analyzed. On the basis of the empirical dependences of coalescence efficiency on individual parameters obtained by regression analysis of the data, a general mathematical model was established.     

Stabilisation of emulsion droplets by fine powders

Finely divided solids can stabilize emulsion droplets provided the solids are partially wetted by both the disperse liquid phase and the continuous liquid phase. The stabilisation of oil/water emulsions by finely divided solids in the presence of suitable organics has been related to the three phase (solid/oil/water) contact line. Schulman and Leja (1954a) and Taubman and Koretskii (1965) provide evidence that O/W emulsions are formed when the contact angle is less than 90° but inversion occurs to W/O emulsions when the contact angle exceeds 90°. We present a thermodynamic study of emulsion stabilization by finely divided solids, which is an extension of an earlier theory by Van der Minne (1928) who neglected interactions among the particles and droplets and also entropy effects due to Brownian motion. Only stable W/O emulsions are considered here. The starting point of the theory is an expression for the Helmholtz free energy associated with the oil/water interfaces stabilized by finely divided solids in the presence of surfactants. By minimising this free energy, it is shown that in a stable emulsion almost all the solid particles are adsorbed at the oil/water interface of the oil drops. This accounts for the experimental result that the average size of oil droplets decreases with increase in the concentration of solids. A particular example of emulsion stabilization by solids occurs in the hot water extraction process on the Athabasca oil sands. Both clay particles and anionic surfactants act as stabilizers of the bitumen droplets suspended in an aqueous alkaline environment.     

Effects of sand and process water pH on toluene diluted heavy oil in water emulsions in turbulent flow

The presence of sand in heavy oil production is known to enhance oil recovery. Sand can also be detrimental depending on the properties of the sand–water interface. In this process, the water soluble material interacts with both sand and oil droplets and affects emulsion stability. The formation and stability of heavy oil‐in‐water emulsions during turbulent flow using batch process stirred‐tank mixing of oil, sand, and water were investigated at three pH. Size distributions were measured by laser diffraction. High‐speed video photomicrography was used to observe the process during mixing. Results showed that the presence of sand enhanced formation of stable, fine emulsion at basic pH 8.5. When the pH of the water was reduced below 6.5 both sand and droplets surface properties changed, the emulsions became less stable and coalescence was apparent. The sand grains acted as coalescers at low pH and enhanced breakage at high pH. © Her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources, 2008 AIChE J, 2009     

Influence of soybean protein isolates-phosphatidycholine interaction on the stability on oil-in-water emulsions

Soybean protein isolates and phospholipids present specific surface properties with synergistic or antagonistic effects on emulsion stability. Oil-in-water emulsions (25∶75 w/w) were prepared using native and denatured soybean isolates (NSI and DSI, respectively) with the addition of phosphatidylcholine (PC) (protein/PC ratio 100∶1 to 10∶1). The effect of ionic strength was also studied by adding sodium chloride (0–100 mM) to the aqueous phase. Analysis of NSI/PC and DSI/PC emulsions showed that the creaming rate diminished upon addition of PC, with the creamed phase showing more stability than those of the control systems. In DSI/PC systems, the coalescence process was partially controlled, as evidenced by a decrease in the size of oil droplets. Both systems were altered by the presence of sodium chloride, with an increase in the creaming rate attributable to flocculation and the coalescence of droplets. Under these conditions, DSI/PC emulsions exhibited a stronger protein-phospholipid interaction than those of NSI/PC.     

海藻酸辛酰胺的制备及其协同氨基SiO2纳米粒稳定液体石蜡/水乳液的研究

以辛胺为疏水改性剂,采用酰化法制得具有两亲性的海藻酸辛酰胺(ACA)。将ACA与采用修正Stber法制备的氨基二氧化硅(SiO_2-NH_2)纳米粒混合,在超声的作用下制得O/W型Pickering乳液。通过FT-IR,~1H NMR和荧光光谱对ACA的结构和性能进行表征。并采用激光粒度和Zeta电位分析仪、接触角测量仪和光学显微镜探究了ACA,SiO_2-NH_2及其协同水分散体系的胶体性能和相应的Pickering乳液的形貌。结果表明:ACA的取代度为0.29,在0.15 mol/L Na Cl水溶液中的临界聚集浓度(cac)为0.42 g/L,表现出较强的两亲性能。ACA通过静电作用力成功地吸附于SiO_2-NH_2纳米粒上,使水动力学粒径只有155 nm的SiO_2-NH_2纳米粒增长至386 nm,Zeta电位由+22.2 mV转变为-30.7 mV,在水溶液中能够表现出良好的稳定性。吸附于SiO_2-NH_2纳米粒表面的ACA可以抑制无机纳米粒的聚沉,而游离的ACA形成的胶束结构的疏水内腔能够增溶油滴,减少小油滴的聚并。光学显微镜中出现了粒径较大的Pickering乳液液滴和粒径较小的传统乳液液滴共存的现象,当ACA质量浓度在0.5 cac~1.0 cac时,2种乳液共存现象最为显著。     

Stability of high internal phase emulsions with sole cationic surfactant and its tailoring morphology of porous polymers based on the emulsions

Stable w/o high internal phase emulsion (HIPE) using cetyltrimethylammonium bromide (CTAB) as the sole surfactant was prepared with long time further mixing of the emulsion after the addition of aqueous phase was completed, although it was generally considered the emulsion would be unstable according to Bancroft rule. The delta backscattering data of these emulsions showed that the further mixing enhanced the stability of the HIPE significantly, because a dram partial of monomers was initiated in the period of preparing the emulsion, which reduced the diffusion of CTAB from the oil phase to aqueous phase and increased the viscosity of the continuous phase. In addition, the morphology of polyHIPEs based on this type HIPEs was tailored. Increasing aqueous phase fraction resulted in the increase of pore volume which could be up to 24.0 ml/g. Increasing the polymerization temperature led to an increase in average void and interconnect diameter in the resulting porous materials. Additionally, the presence of additives, PEG and ethanol, in the aqueous phase was found to increase the average void diameter remarkably. The interconnect diameter of the materials could be controlled at constant pore volume by tuning PEG and ethanol concentration in the aqueous phase. It was suggested that coalescence was the dominant effect in determining the morphology of the polyHIPEs prepared in the presence of PEG, and Ostwald ripening was the major role in tailoring the morphology of the porous materials with ethanol.     

Improving the Oxidative Stability of Krill Oil-in-Water Emulsions

A positively charged protein (fish gelatin) or a negatively charged protein species (heat-treated milk protein–carbohydrate mixture) was added to a primary krill oil (KO) emulsion stabilized by the phospholipids inherent in KO, with the aim of improving the oxidative stability of KO-in-water emulsions at pH 8.0 (10 % KO). The positively charged fish gelatin deposited on the primary interface of the oil droplets in the primary KO-in-water emulsion improved the oxidative stability of the KO-in-water emulsion as evidenced by the higher eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) remaining and lower propanal produced after accelerated oxidation (40 °C, 25 days). The addition of the negatively charged heat-treated milk protein–carbohydrate mixture containing Maillard reaction products (MRP) to the bulk phase of the emulsion also enhanced the oxidative stability of the KO-in-water emulsion. The addition of MRP to the aqueous phase of phospholipids stabilized emulsion droplets offered more protection to EPA and DHA of the KO emulsions compared to the formation of an additional layer at the interface of the KO emulsion droplet. This suggests that interventions based on addition of antioxidant species to the formulation were more effective for arresting oxidation than increasing the thickness of the droplet interface. The addition of proteins into KO containing emulsion formulations is a promising strategy for protecting omega-3 marine phospholipids against oxidation.