Coalescence Of Oil Drops Research Articles

Coalescence of oil drops and films on micropillared substrates enabled by enhanced water drainage through pillar gaps.

Collecting or removing oil drops dispersed in water is essential in a range of industrial processes including oil recovery and oil spill cleanup. However, it is by no means easy to induce merging of oil drops with another body of oil due to slow drainage of the intervening water film. Here, we report immediate coalescence of oil drops with oil films that lie on micropillar arrays as immersed in various aqueous solutions. In addition to experimental demonstrations, we theoretically construct a regime map to predict whether the drop will bounce off or coalesce with the oil film, which is determined by the oil film thickness, geometry of the pillar array and liquid properties. Good agreement between theory and experiment indicates that micropillar arrays provide additional drainage paths of the intervening film, which helps drop-film coalescence. Our results suggest potential implications of utilizing oil-laden microporous structures to achieve efficient demulsification of oil drops in contaminated water.

Demulsification of Oil-in-Water (O/W) Emulsion in Bidirectional Pulsed Electric Field.

The research about electric demulsification of oil-in-water (O/W) emulsion is not enough at present, especially compared with that about electric demulsification of water-in-oil (W/O) emulsion. As an easy and novel method, a bidirectional pulsed electric field (BPEF) was investigated to demulsify the O/W emulsion in this work. Here we report that BPEF could actuate O/W emulsion to form rotational flow and drove oil droplets to form oil-droplet chains and to coalescence. In order to interpret the mutual attraction and coalescence of oil drops in BPEF, we put forward the hypothesis that charges on an oil drop surface would redistribute in BPEF, and we built the charge redistribution model according to the adsorption phenomenon of oil droplets. The behavior of oil drops in BPEF could be successfully explained in terms of the hypothesis and the model. The charge redistribution on an oil droplet surface could be evaluated by the two parameters we proposed. An amended potential redistribution formula of an oil drop surface was also obtained according to the model. The O/W emulsions were successfully demulsified by BPEF in the experiments. It showed that BPEF could be a significant method for electric demulsification of O/W emulsions.

Coalescence of oil drops on the skeleton of a porous medium in filtering a water-oil mixture

Two mathematical models of filtration coalescence of oil drops when a water-oil mixture moves through a porous material are proposed. In the first model, coalescence is interpreted as the process of sorption, i.e., the accumulation of the oil phase on the pore surface up to a definite critical value above which the larger drops involved by a filtration flow stall. The second model assumes that the motion of the sorbed oil and the entire mixture obeys the generalized Darcy laws.

Preparation and stabilization of simple and multiple emulsions using a microporous glass membrane

A microporous glass membrane with a narrow range of pore sizes was used for the preparation of simple and water-oil-water (W/O/W) type emulsions using egg yolk phospholipids and soybean oil. Simple oil-in-water (O/W) and water-in-oil (W/O) emulsions and a W/O/W type emulsion were successfully prepared using the membranes without any coalescence of oil drops or breakdown of the emulsions. The simple and W/O/W emulsions were stable for at least 6 weeks when stored at 5°C. The particle size distribution of the emulsion depended on the pore size of the membrane. These results indicate that the technique would be valuable for the production of stable simple and multiple emulsions for food uses as well as for intravenous fat and/or drug carriers.

London-vdW and EDL Effects in the Coalescence of Oil Drops

Visual observations of coalescence of n-hexadecane oil drops (70-140 μm in diameter) suspended inside an aqueous phase of varying pH are reported. The oil drops are produced in situ and confined inside the aqueous-phase-filled fine capillary (100-160 μm i.d.). Rapid, spontaneous coalescence was observed at low pH (⩽2.5) as soon as two drops were very carefully brought into apparent contact. At very high pH (⩾13.0), coalescence was observed some time after the drops made contact. No coalescence was observed at intermediate pH 5.2, 7.1, and 10.9. The "coalescence times" at pH 2.2 and 2.4 were less than 0.033 s. At pH 3.2, 12, and 13.1 the coalescence times were 8, 20, and 1.8 s, respectively. The coalescence time in the acidic solution of a certain pH was distinctly lower than that in the basic solution of equivalent pOH. The coalescence tendency increased with an increase in the acidity or basicity of the aqueous phase. Also, in strongly basic or acidic media, freshly formed drops were more susceptible to coalescence. Visual observations of collision interactions are qualitatively described. When two drops were made to collide, coalescence was rapid at all pH at which coalescence was previously observed for the stationary drops. Almost no coalescence was observed at the intermediate pH's 5.2, 7.1, and 10.9, even after repeated collisions between the drops. The relative velocity of the collision interactions ranged from 100 to 2100 μm/s. The observed phenomena are explained on the basis of the London-van der Waals and electrical double layer forces, which are important either in stabilizing the thin liquid film formed between the approaching drops or in drawing the two interfaces close enough to thin the liquid film to the "critical rupture thickness range." In this range, it is believed that thin liquid film properties control the rupture process.

Behaviour of Crude Oil Under Fresh-Water Ice

Abstract Experiments were carried out in a cold room at −15 °C to investigate the behaviour of Norman Wells crude oil under fresh water ice. The crude, when injected in water under the ice, separates into droplets and rises to the ice-water interface, where the oil droplets coalesce to form a slick. The spreading of oil under ice is complicated by the coalescence of oil drops at the ice-water interface, and the spreading process is found to be different from that of oil on water or on ice. If sufficient turbulence exists in the water, both oil-in-water and water-in-oil emulsions are formed. An oil lens sandwiched between the ice acts as an insulating layer and thus increases the temperatures drop cross the ice. Introduction The discovery of oil in commercial quantities in Northern Canada could lead to the construction of oil pipelines to the southern markets. Such pipelines would cross many rivers and streams that are subjected to ice conditions of varying seasonal length. It is conceivable that oil spills under ice-covered rivers may result from such pipeline crossings, The spills can be large, such as those caused by a major pipeline fracture, or they can be small, such as those developing through holes of a few centimeters diameter in the pipe. In addition, accidents involving oil tankers, storage tanks and tank trucks may also result in oil spills in ice-covered rivers. Although results on oil pollution research are published in an increasing number, available information on the behaviour of oil spilled under ice is limited. The only systematic study reported in the literature is by Wolf and Hoult(1). They investigated the effects of crude and diesel oils on the porous substructure of Arctic sea ice and found that the oil, when injected under the ice, was pocketed below the ice surface. They also reported that as freezing continued, more ice formed beneath the oil and that the oil acted as an insulating layer impeding the flow of heat- However, in order to assess the effect of an oil spill under ice-covered rivers and to help in developing clean-up techniques for such an oil spill, more must be understood about the behaviour of oil under ice, The present work investigates the behaviour of crude oil under fresh-water ice, Parts of the work were presented at the 1975 Conference on Prevention and Control of Oil Pollution(2). Experimental A circular aluminum basin, 150 cm in diameter and 70 cm deep was installed in a cold room where the temperature was maintained at −15 ±2 °C. Heating tapes were glued to the outside of the tank and covered with 10 cm of polystyrene insulation. The heating tapes were connected to variacs set at very low power to cancel out the bottom and side heat losses. This arrangement resulted in one-dimensional freezing in the basin, A stirrer was mounted on the side of the basin and a circular boom installed to prevent the oil from rising up the tank walls.

The flocculation of aqueous sols of a graphitized carbon black by a potential-determining electrolyte

Recent work on the film thinning behavior during the coalescence of oil drops in water is summarized. In the experimental work, color movies were taken of the light interference patterns produced by the thin film of water trapped between the rising drop and the bulk oil phase. The drops were relatively small (0.2–0.32 cm diam.); sufficient KCl was added to minimize double layer repulsion. Concentrations of 10 −6 –10 −2 g l −1 of sodium lauryl sulfate were used. The oils used were toluene, anisole, cyclohexanol and a mixture of anisole and cyclohexane. Five different patterns of film behavior were observed. The mechanisms to explain these patterns are based on concepts of dynamic immobility (when the distribution of surfactant along the interface gives an interfacial tension gradient that every-where balances the interfacial shear stress) and of steric immobility. The mechanisms include rapid approach (when both interfaces are mobile), dimple formation (when the interfacial tension gradient exceeds the interfacial shear stress), even drainage (when the interfaces are dynamically or sterically immobile) and uneven drainage (when there is local mobility). Reasons for uneven drainage are discussed. The different theoretical models developed to describe film thinning are reviewed. The emphasis is on the assumptions and the relationship between the equations describing flow in the film and those describing surface behavior. The predictions of the different models are compared but the emphasis is on the success of more recent models based on the above mentioned mechanisms to describe symmetrical film drainage.

The stability of emulsions

Recent work on the film thinning behavior during the coalescence of oil drops in water is summarized. In the experimental work, color movies were taken of the light interference patterns produced by the thin film of water trapped between the rising drop and the bulk oil phase. The drops were relatively small (0.2–0.32 cm diam.); sufficient KCl was added to minimize double layer repulsion. Concentrations of 10−6–10−2 g l−1 of sodium lauryl sulfate were used. The oils used were toluene, anisole, cyclohexanol and a mixture of anisole and cyclohexane.