Efficient Encapsulation of a Water-Soluble Molecule into Lipid Vesicles Using W/O/W Multiple Emulsions via Solvent Evaporation

We developed a novel method for preparing lipid vesicles with high entrapment efficiency and controlled size using water‐in‐oil‐in‐water (W/O/W) multiple emulsions as vesicle templates. Preparation consists of three steps. First, a water‐in‐oil (W/O) emulsion containing to‐be‐entrapped hydrophilic molecules in the water phase and vesicle‐forming lipids in the oil phase was formulated by sonication. Second, this W/O emulsion was introduced into a microchannel emulsification device to prepare a W/O/W multiple emulsion. In this step, sodium caseinate was used as the external emulsifier. Finally, organic solvent in the oil phase was removed by simple evaporation under ambient conditions to afford lipid vesicles. The diameter of the prepared vesicles reflected the water droplet size of the primary W/O emulsions, indicating that vesicle size could be controlled by the primary W/O emulsification process. Furthermore, high entrapment yields for hydrophilic molecules (exceeding 80 % for calcein) were obtained. The resulting vesicles had a multilamellar vesicular structure, as confirmed by transmission electron microscopy.     

Comparison of fuel properties and emission characteristics of two- and three-phase emulsions prepared by ultrasonically vibrating and mechanically homogenizing emulsification methods

Emulsions have long been considered as an alternative fuel for combustion equipment in order to achieve better fuel economy and pollution reduction. While a mechanical homogenizing method is frequently used to prepare emulsions, the use of an ultrasonic emulsification method to do so is still rather limited, and is mostly applied to two-phase emulsions only. Hence, two-phase W/O and three-phase O/W/O emulsions, prepared by a mechanical homogenizer and an ultrasonic vibrator, respectively, were prepared and used as engine fuel. The emulsion properties, engine performance, and engine emission characteristics between these two emulsification methods were measured and compared. The potential of the ultrasonic emulsification method was also evaluated. The experimental results show that the emulsions prepared by the ultrasonic vibrator appeared to have more favorable emulsification characteristics such as smaller dispersed water droplets that were distributed more uniformly in the continuous oil phase, lower separation rate of water droplets from the continuous phase of diesel fuel and thus a lower separating rate of the dispersed water droplets from the emulsion, larger emulsion stability, and larger emulsion viscosity than the emulsions produced using a mechanical homogenizer. In addition, a larger content of water was emulsified when the emulsion was prepared using the ultrasonic vibrator than the mechanical homogenizer. The emulsions prepared by the ultrasonic vibrator also had a lower fuel consumption rate, lower bsfc, and significantly lower CO emission while at the same time having a larger black smoke opacity. When comparing the two-phase W/O and the three-phase O/W/O emulsions prepared by either the ultrasonic vibrator or the mechanical homogenizer, the two-phase W/O emulsions appeared to have a lower fuel consumption rate, bsfc, CO, and a lower black smoke opacity than the three-phase O/W/O emulsions, regardless of whether they were prepared by ultrasonic vibrator or mechanical homogenizer.     

Effects of Curcumin on the Oxidative Stability of Oils Depending on Type of Matrix,Photosensitizers, and Temperature

The photosensitizing activity of curcumin was tested in corn oil and oil‐in‐water (O/W) emulsion systems under visible light irradiation. In addition, the antioxidative/prooxidative properties of curcumin were evaluated in corn oil at 100 °C and in O/W emulsion at room temperature under riboflavin photosensitization or at 60 °C in the dark. Curcumin acted as a photosensitizer in corn oil and O/W emulsions . The oxidative stability of corn oil samples containing curcumin (0–5.0 mmol/kg oil) were not significantly different (p > 0.05) at 100 °C, implying curcumin did not act as an antioxidant nor a prooxidant in corn oil. However, curcumin inhibited lipid oxidation in O/W emulsions under riboflavin photosensitization at room temperature and 60 °C in the dark. The photosensitization and antioxidant abilities of curcumin were greatly influenced by matrix types and presence of riboflavin. Therefore, antioxidative or prooxidative characteristics of curcumin should be evaluated considering matrix type including bulk oil or O/W emulsions and presence of visible light irradiation.     

重质油包水乳液破乳过程及降黏强化机制

重质油包水（W/O）乳液普遍存在于石油开采与加工过程中,因其高黏度、高密度、强界面稳定特性,导致重质油包水乳液分离困难,生产成本增加。为了提高重质W/O乳液的分离效率,本文探究了温度与甲苯加入量对重质油黏度的影响规律。在此基础上,研究了上述降黏过程与脱水率之间的协同机制。采用自制的TJU-3破乳剂对重质W/O乳液进行破乳,通过调整破乳剂在乳液中的浓度和破乳温度得到了最佳工艺条件。利用分子模拟的方法构建了重质油平均分子模型并计算了SARA四组分在不同甲苯含量的重质油中的扩散系数,分析了甲苯添加量对重质油中SARA四组分相互作用的影响规律,研究了沥青质分子和TJU-3破乳剂分子在油水界面的运移过程。结果表明：重质油的黏度降低到1500mPa·s时,可实现在1h内完全破乳;黏度降低到50mPa·s时可实现在20min内完全破乳。当破乳剂在乳液中的浓度为400mg/L时,乳液的脱水率最高;破乳温度为60℃时,破乳速度最快。SARA四组分中胶质的扩散系数增大最显著,是重质油的黏度能被甲苯迅速降低的主要原因。TJU-3分子能够破坏沥青质界面膜,进而实现破乳。该协同机制和工艺条件可为石油工业中重质W...     

分子氧化及光电催化氧化对石油Pickering乳液的破乳研究进展

石油开采、集输、加工过程中会面临复杂的工况条件,原油中的天然表面活性剂与人工添加乳化剂以及纳微米固体颗粒共同形成石油Pickering乳液,使得油水体系呈稳定的水包油（O/W）、油包水（W/O）或多重乳化状态。油水乳状液作为注水采油的主要产物,其高效破乳是石油工业链条中的普遍需求。目前对于石油Pickering的破乳仍然借鉴普通油水乳液的方法,而对于成因复杂的油水乳状液,以去除成膜乳化剂为目标的氧化破乳法比传统破乳法的效果更佳。为此,本文基于高效的氧化破乳机制,介绍了石油Pickering乳液的特点及危害,与非氧化反应类型的传统化学破乳法进行对比,综述了分子氧化、光催化氧化、电化学氧化三类技术对于不同来源及特征的油水乳状液的破乳进展。通过对每种方法的机理过程、应用实例、优缺点等方面详细分析,总结了分子氧化、光催化氧化、电化学氧化在石油Pickering乳液破乳中的局限性,并对今后如何实现石油Pickering乳液精准破乳提出展望。     

Emulsification characteristics of three- and two-phase emulsions prepared by the ultrasonic emulsification method

Diesel engines exhausting gaseous emission and particulate matter have long been regarded as one of the major air pollution sources, particularly in metropolitan areas, and have been a source of serious public concern for a long time. The emulsification method is one of the potentially effective techniques to reduce emission pollution from diesel engines. Ultrasonic waves are a kind of sound waves with a frequency larger than 20 kHz, and they cannot be detected by the human ear. The phenomena of cavitation and hot spots produced by the rather violent action of ultrasonic waves can cause rapid chemical and physical reactions. This allows immiscible liquids to be well stirred with each other by means of ultrasonics. An ultrasonically vibrating machine that provides ultrasonic waves of a 40-kHz frequency was employed to prepare two- and three- phase emulsions in this experimental study. The fuel properties and the emulsion stability of the diesel emulsions were measured and analyzed. Experimental results show that the ultrasonic emulsification method successfully prepared two- and three-phase emulsions with tiny dispersed-phase droplets that are very evenly distributed in the outer oil or water phase. The ultrasonic processing time, quantity and HLB of the emulsifying agent were noted to have determinative influences on the formation of the emulsion and the fuel properties. A longer ultrasonic processing time caused less un-emulsified diesel fuel, smaller sizes and a more even distribution of dispersed-phase droplets in the outer oil phase and larger emulsion viscosity. However, a longer ultrasonic processing time also produced a larger temperature rise in the emulsion, leading to the deterioration of the emulsion stability. The O/W emulsion was found to have the lowest percentage of separation and thus the highest emulsion stability among the O/W/O, O/W and W/O emulsions. In addition, in comparison with the W/O emulsion, the O/W emulsion was shown to have a smaller size and a more even distribution of the dispersed-phase droplets. It also had a lesser rise in emulsion temperature when the ultrasonic processing time increased. The control of the ultrasonic processing time is important to successfully prepare the three-phase O/W/O emulsion. Too long a vibration time at the second-stage of emulsification is shown to cause the dispersed-phase pellets to contract and congregate with the inner-phase droplets. The three-phase emulsion structure then finally disappears and transforms into a two-phase emulsion. The addition of 2% by volume of the emulsifier mixture of Span80 and Tween80 with a HLB = 8, as suggested by this study for the preparation of stable two- and three-phase emulsions, were observed to have the lowest percentage of separation of the W/O and O/W/O emulsions. For preparing a stable O/W emulsion, the proportion of the emulsifier could be as low as 1.5% by volume. The percentage of separation of the O/W/O emulsion was lower and less influenced by the change in emulsion temperature than was the W/O emulsion with the same water content. However, the O/W/O emulsion was found to have a larger viscosity and a more significant variation of its viscosity, depending on the ultrasonic processing time, than the W/O emulsion.     

The effect of shear and oil/water ratio on the required hydrophile-lipophile balance for emulsification

Required hydrophile-lipophile balance (HLB) values were examined in terms of the nature of kerosene-water, both oil-in-water (O/W) and water-in-oil (W/O), emulsions formed using Span 80/Tween 80 surfactant blends. Both the nature of the emulsification method and the oil/water ratio were critical in determining the resulting emulsion type. Both high- and low-shear conditions were investigated. Under high shear, low internal phase emulsions formed using the surfactant mixtures that corresponded to the required HLB values for emulsification involving kerosene (6 for W/O and 14 for O/W). However, at low shear, high internal phase (concentrated) emulsions resulted. Furthermore, depending on the oil/water ratio, some of the high internal phase emulsions were opposite to the type expected, given the HLB of the surfactant blend used. From these results, it appears that the emulsification technique (applied shear and oil/water ratio) used can be of greater importance in determining the final emulsion type than the HLB values of the surfactants themselves.     

高亲水性纳米二氧化硅颗粒稳定Pickering乳液

用未修饰的高亲水性纳米二氧化硅颗粒(SiO2 NPs)在其等电点附近制备Pickering乳液。结果表明,等电点(pH 2.7)条件下SiO2 NPs借助高能均质与油水界面剧烈混合,并在范德华引力的驱动下以弱吸附的状态在界面处负载,从而稳定得到O/W型Pickering乳液。增加SiO2 NPs的浓度或减小油相体积分数可提高单位油滴界面的颗粒负载率,增大连续相黏度并促进乳液液滴之间形成三维网络结构从而提高乳液稳定性。通过调节连续相的pH以促进SiO2 NPs表面的硅烷醇发生质子化与去质子化的转变,实现乳液多次pH响应循环。     

SiO2改性聚丙烯纤维棉对油水乳状液的高效分离

近年来,基于特殊润湿性理论制备表面具有微纳米粗糙结构的多孔材料成为油水分离领域研究的重点。为了满足不同环境下对不同形式油-水乳状液高效高通量分离的需求,该研究利用纳米SiO2颗粒对聚丙烯（PP）纤维棉有针对性地亲（疏）水改性,构建了系列不同润湿性和粗糙度的PP纤维棉,探究了不同孔隙度和表面能的PP纤维棉对W/O及O/W型乳状液的分离性能,结果表明,经过亲（疏）水改性后的PP纤维棉对水/正己烷和水/甲苯乳状液的分离效率都高于99.5%,通量高于700 L/(m2·h),并针对不同形式油-水乳状液阐释其相应的分离机制,为后续油-水乳状液分离材料的科学设计和可控制备提供了理论依据。     

Stability of vitamin A in oil-in-water-in-oil-type multiple emulsions

The stabilityof vitamin A was studied in thee different emulsions: oil-in-water (O/W), water-in-oil (W/O), and oil-in-water-in-oil (O/W/O). The stability of retinol (vitamin A alcohol) in the O/W/O emulsion was the highest among the thee types of emulsions; remaining percentages at 50°C after 4 wk in the O/W/O, W/O, and O/W emulsions were 56.9, 45.7, and 32.3, respectively. With increasing peroxide value of O/W and W/O emulsifiers, the remaining percentage of vitamin A palmitate and retinol in the emulsions decreased significantly, indicating that peroxides in the formulae accelerate the decomposition of vitamin A. Organophilic clay mineral (an oil gelling agent and a W/O emulsifier) also affected the stability of retinol; synthesized saponite was better than naturally occurring bentonite for retinol stability. The stability of retinol in the O/W/O emulsion increased with increasing inner oil phase ratio (φ_i), whereas in O/W it was unaffected by φ_i. Encapsulation percent of retinol in the O/W/O emulsion, the ratio of retinol in the inner oil phase to the total amount in the emulsion, increased with increasing φ_i. The remaining percent of retinol in the O/W/O emulsion was in excellent agreement with encapsulation percent, suggesting that retinol in the inner oil phase is more stable than that in the outer oil phase. Addition of antioxidants (tert-butylhydroxytoluene, sodium ascorbate, and EDTA) to the O/W/O emulsion improved the stability of retinol up to 77.1% at 50°C after 4 wk. We conclude that the O/W/O emulsion is a useful formula to stabilize vitamin A.     

Preparation of water-in-oil and ethanol-in-oil emulsions by membrane emulsification

In this work, water-in-oil emulsions (W/O) and ethanol-in-oil emulsions (E/O) emulsions were prepared successfully by membrane emulsification. The emulsifiers selected were PGPR and MO-750 for the W/O and E/O emulsions, respectively. For W/O emulsions prepared with an oil pre-filled membrane, the dispersed flux was lower and the droplet size sharper than that obtained with a water pre-filled membrane. On the contrary, for E/O emulsions prepared with the membrane pre-filled with oil, the dispersed phase (ethanol) rapidly pushed out the oil from the membrane pores. Therefore, the pre-treatment of the membrane had almost no effect on the dispersed phase flux and on the droplet size. The droplet size distribution of the E/O emulsion was close to that obtained with a classical homogenizer. The dispersed phase fluxes were high and no fouling was observed for our experimental conditions (1.6 l emulsion, 10 wt% ethanol). These results confirm that membrane emulsification could be an interesting alternative for the preparation of E/O emulsions for the purpose of biodiesel fuels, considering the scale-up ability of membranes and their potentiality for industrial processes.     

Influence of clay addition on the properties of olive oil in water emulsions

The behaviour of olive oil-in-water emulsions (O/W) was studied in the presence of smectite particles. The distribution of these particles in the emulsions and the effect of their interaction with the surfactant on the stability of the emulsions were investigated. Whereas the variation of surfactant and/or clay content did not seem to affect the nature of the emulsion, it had a significant influence on emulsion stability. This observation led to two main assumptions on the distribution of clay particles within the emulsion, either exclusively in the continuous phase, or also at the oil-water interface.In the absence of clay, the variation of surfactant concentration (from 0 to 17% (w/w)) allowed to distinguish 3 domains. In the first concentration domain (0–4.2%) emulsions stability increased with the content of surfactant. Within the second domain (4.2–8.5% (w/w)), a slight decrease in stability was observed due to flocculation by depletion. For surfactant concentrations equal or higher than 8.5% (3rd domain), emulsion stability increased sharply, probably due to the development of interactions between surfactant molecules as they came closer to their gelling concentration. The effect of clay addition to the aqueous phase (up to 10% (w/w)) on the physicochemical properties of the studied emulsions was assessed from stability, drop size, interfacial tension, rheological and acido-basic analyses. A model based on the location of clay particles either in the bulk or at the interface could be proposed, in which clay particles would interact with surfactant molecules in the bulk phase, and form a mechanical barrier around the oil droplets, thus increasing emulsion stability.     

Predicting the Viscosity of Non‐Newtonian Water‐in‐Oil Emulsions Based on the Lederer Model

The accurate prediction of the viscosity of emulsions is highly important for oil well exploitation. Commonly used models for predicting the viscosity of water‐in‐oil (W/O) emulsions composed by two or three factors cannot always fit well the viscosity of W/O emulsions, especially in the case of non‐Newtonian W/O emulsions. An innovative and comprehensive method for predicting the viscosity of such emulsions was developed based on the Lederer, Arrhenius, and Einstein models, using experimental data. Compared with the commonly applied W/O emulsion viscosity models, the proposed method considers more factors, including temperature, volume fraction of water, shear rate, and viscosity of the continuous (oil) and dispersed phase (water). Numerous published data points were collected from the literature to verify the accuracy and reliability of the method. The calculation results prove the high accuracy of the model.     

The fuel properties of three-phase emulsions as an alternative fuel for diesel engines

Diesel engines are employed as the major propulsion power for in-land and marine transportation vehicles primarily because of their rigid structure, low breakdown rate, high thermal efficiency and high fuel economy. It is expected that diesel engines will be widely used in the foreseeable future. However, the pollutants emitted from diesel engines (in particular nitrogen oxides and particulate matter) are detrimental to the health of living beings and ecological environment have been recognized as the major air pollution source in metropolitan areas and have thus attracted much research interest. Although diesel oil emulsion has been considered as a possible approach to reduce diesel engine pollutants, previous relevant applications were restricted to two-phase emulsions. Three-phase emulsions such as oil-in-water-in-oil briefly denoted as O/W/O emulsions and water-in-oil-in-water, denoted as W/O/W, have not been used as an alternative fuel for any combustion equipment. Studies on the properties of three-phase emulsion as fuel have not been found in the literatures. The emulsification properties of an O/W/O three-phase diesel fuel emulsion were investigated in this experimental study. The results show that the mean drop size of the O/W/O emulsion was reduced significantly with increasing homogenizing machine revolution speed. An increase in inner phase proportion of the O/W/O emulsion resulted in increasing the emulsion viscosity. The viscosity of O/W/O emulsion is greater than that for water-in-oil (denoted briefly as W/O emulsion) for the same water content. More stable emulsion turbidity appeared for three-phase O/W/O diesel emulsions added with emulsifier with HLB values ranging from 6 to 8. In addition, three-phase O/W/O emulsions with greater water content will form a larger number of liquid droplets, leading to a faster formation rate and greater emulsion turbidity at the beginning but a faster descending rate of emulsion turbidity afterwards. The potential for using O/W/O emulsions as an alternative fuel for diesel engines was also evaluated.     

A novel method for preparing oil-in-water-in-oil type multiple emulsions using organophilic montmorillonite clay mineral

A stable formula using oil-in-water-in-oil (O/W/O) type multiple emulsions was investigated. The components consisted of hydrophilic nonionic surfactant (HCO-60), organophilic montmorillonite, and lipophilic nonionic surfactant (DIS-14). O/W/O emulsions were prepared by a double-step procedure in which an O/W emulsion was prepared in the first step, and then the O/W emulsion was “re-emulsified” in an oil phase with organophilic montmorillonite. The diameter of the innermost oil droplets decreased with increasing HCO-60 content (0.1–3%), while the viscosity showed a maximum at 1% of HCO-60, indicating that the yiel of re-emulsification is highest at this condition. Viscosity of the O/W/O emulsion increased with increasing organophilic montmorillonite and DIS-14. According to the results of a phase ratio study, viscosity and stability of the O/W/O emulsion decreased at high weight fraction of inner oil phase (0.4–0.5), indicating that the excess amount of inner oil phase is absorbed by the outer oil phase. These results revealed that the weight fraction of inner oil phase should be kept below 0.3 for a stable O/W/O emulsion. A similar study on the weight fraction of O/W phase [фO/W)/O] suggested that the O/W/O emulsion is stable at ϕ(O/W)/O=0.65–0.70.     

Engine performance and emission characteristics of three-phase diesel emulsions prepared by an ultrasonic emulsification method

The emulsification method is a potential technique for reducing pollutant emissions from combustion equipment primarily due to occurrence of micro-explosion to enhance burning. In this study, an ultrasonic emulsification method was applied to prepare two-phase water-in-oil (W/O) and three-phase oil-in-water-in-oil (O/W/O) emulsions. The engine performance and the pollutant emission characteristics of a diesel engine were measured and analyzed. A rather violent ultrasonic wave may result in the phenomena of cavitations and hot spots, which in turn promotes fast chemical and physical reactions. Various kinds of liquid, which are immiscible with each other, may thus become highly mixed so that an emulsion is formed. This study first used an ultrasonic oscillating bath to produce ultrasonic waves by which two- and three-phase emulsions were prepared. The experimental results show that the emulsions prepared by the ultrasonic vibrating method have much finer and better-distributed droplets. The use of these emulsions as an engine fuel produced lower NO emission, lower soot concentration and lower black smoke opacity, while creating a larger brake specific fuel consumption (bsfc) and a larger CO emission compared with that of an engine using neat diesel fuel. However, the variations in the concentrations of CO₂ and O₂ emissions between the emulsions and neat diesel fuel were not significant. In a comparison with the characteristics of the two-phase W/O emulsion, the three-phase O/W/O emulsion was found to have a larger CO emission, larger soot particles and larger bsfc while producing a lower brake thermal efficiency and a lower black smoke opacity.     

三元复合驱中原油乳化作用研究

通过乳状液稳定实验考察了大庆油田碱-表面活性剂-聚合物三元复合驱过程乳状液的形成机理、乳状液类型及稳定性。结果表明,大庆原油与碱反应1d时,测得其浓相体积分数为25%,所形成的乳状液为O/W型乳状液,而随着原油与碱作用时间的增加,其浓相体积分数达到40%以上,形成W/O型乳状液,且乳状液稳定性随作用时间增加而增强。大庆原油与水溶性表面活性剂ORS-41溶液作用时,所形成的乳状液为O/W型,且乳状液的稳定性与原油和ORS-41作用时间的长短关系较小。原油与NaOH和ORS-41混合溶液作用时,形成上层为W/O型乳状液,下层为O/W型乳状液的混合体系。     

Characterization of a double emulsion system (oil-in-water-in-oil emulsion) with low solid fats: Microstructure

A double emulsion system [oil-in-water-in-oil (O/W/O)] with 16.3% (w/w) water and 83% (w/w) oil was prepared and stabilized using a novel method of mixing two oil-in-water (O/W) emulsions together. The first emulsion consisted of 85% (w/w) liquid canola oil, 14.4%(w/w) water, 0.5% (w/w) sodium caseinate, and 0.1% (w/w) lecithin and the second emulsion contained 73% (w/w) canola oil, 8% (w/w) palm-cotton stearin (50∶50), 0.2% (w/w) lecithin, 18.2% (w/w) water, and 0.6% (w/w) sodium caseinate. Mixing the two emulsions (50∶50) by weight produced a product with 79% (w/w) liquid canola oil and 4% (w/w) palm-cotton stearin. The two O/W emulsions were prepared separately at 50°C, mixed together at 45°C for 2–5 min, and then supercooled in a −5°C ice/salt bath while mixing at low shear rates (2,000–3,000 rpm). Under supercooling conditions the fat globules in the second emulsion (containing liquid oil and stearin) began to break down as a result of fat crystal growth and shearing action and release plastic fat. During this stage, the continuous aqueous phase underwent a phase transition and the emulsion viscosity dropped from 37,000–50,000 to 250 cP. The released plastic fat continued to harden as the temperature dropped and stabilized the first O/W emulsion (containing only liquid oil). The low shear rate mixing was stopped when the temperature dropped below 15°C and before the O/W/O emulsion hardens. Microstructural analysis of the first emulsion before and after supercooling showed essentially intact fat globules. The microstructure of the second emulsion before supercooling showed the same intact globules as the first emulsion, but after supercooling, an amorphous mass with only a few intact globules was seen. By mixing the two emulsions together and supercooling, a stable O/W/O emulsion was formed with plastic fat as the continuous phase and the first O/W emulsion as the dispersed phase.     

高频脉冲电场作用下乳状液液滴动力学模型

基于乳状液中液滴在电场中的受力情况的分析,建立了W/O乳状液中液滴振荡固有频率公式,从理论角度分析和解释了高频脉冲电场对W/O乳状液的破乳机理,从力学的角度分析了最佳频率存在的理论基础,并推导出了最佳频率的计算公式。该固有频率与液滴尺寸、界面张力、黏度、温度、密度等有关。为了验证最佳频率公式的可靠性,用正辛烷乳状液进行了室内实验。实验结果表明,理论最佳频率公式的预测结果与实验测得的最佳频率结果吻合,经修正后与白油实验结果也非常接近。     

Destabilization‐Enhanced Centrifugation of Metalworking Oil‐in‐Water Emulsions: Effect of Demulsifying Agents

The effect of a commercial flocculant (Alpacon® WS009) and two coagulant salts (CaCl₂ and AlCl₃) on the stability of metalworking oil‐in‐water (O/W) emulsions was examined. Two O/W emulsions were tested: a fresh emulsion, prepared in the laboratory from a commercial concentrate, and a waste metalworking emulsion, provided by a local waste management company, with initial oil concentrations of 32900 and 16900 mg/L, respectively. The emulsion stability was studied at different demulsifier concentrations, temperatures and pH through centrifugation tests, zeta potential and multiple light scattering measurements. Emulsion breakdown is explained by electrostatic repulsion of oil droplets and steric interactions. The former was observed for the laboratory emulsion, while the latter was observed for the waste emulsion. Aluminum chloride was the only effective agent for demulsifying both emulsions.