emulsion stability investigation

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Petroleum Science and Technology, 23: 649667, 2005Copyright Taylor & Francis, Inc.ISSN 1091-6466 print/1532-2459 onlineDOI: 10.1081/LFT-200033001

UNITED ARAB EMIRATES UNIVERSITY

Water-in-Crude Oil Emulsion Stability Investigation

Mamdouh T. Ghannam

Department of Chemical and Petroleum Engineering, College of Engineering,United Arab Emirates University, Al-Ain, United Arab Emirates

Abstract: The water-in-crude oil emulsion has great importance in the oilindustry. The stability of water-in-crude oil emulsion is investigated over awide range of parameters. These parameters are water concentration (1050%),surfactant concentration (0.11%), mixing speed (5002,000rpm), salt concentra-

tion (05%), polymer concentration (01,000ppm), and temperature (1340

C).The physical properties of water-in-crude oil emulsion in terms of density,viscosity, and interfacial tension are measured by Pycnometer, Ostwaldviscometer, and spinning drop tensiometer, respectively. The stability of water-in-crude oil emulsion is studied for each case in details. This investigation showsthat the presence of the emulsifying agent is necessary for stable emulsion, andstability gradually decreases with water concentration. The presence of 5% NaClor 1,000ppm of Alcoflood polymer provides 100% stable emulsion. Emulsionstability reduces with temperature. Impeller type has a strong effect on theemulsion stability. S-curved blade impeller provides 100% stable emulsion for

more than 2 days.

Keywords: Alcoflood polymer; Mixing; Salt; Surfactant; Water-in-crude oilemulsion.

INTRODUCTION

When water is present in an immiscible dispersed droplets phase within

the continuous crude oil phase it usually leads to the formation of

Received October 20, 2003; Accepted December 10, 2003Correspondence: Mamdouh T. Ghannam, Department of Chemical and

Petroleum Engineering, College of Engineering, United Arab EmiratesUniversity, P.O. 17555, Al-Ain, United Arab Emirates; Fax: 9713 7624262;E-mail: [email protected]


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water-in-crude oil emulsion (W/O emulsion). W/O emulsion is ofgreat interest in several industrial and environmental applications. Some

examples of these applications are crude oil spillage (Mingyuan et al.,1992), pipeline transportation of water in heavy crude oil (Pilehvari et al.,1988), the crude oil production from an oil field generally associated withdifferent proportions of water (Carcoana, 1992), and crude oil-polymeremulsion production during enhanced oil recovery stage (Ghannam, 2003).There are several other important industrial processes that involve theproduction of stable emulsions, such as food industry (e.g., mayonnaise),detergency (e.g., removal of oil deposits), pharmacy (e.g., drug emulsions),cosmetics (e.g., skin creams), and agricultural sprays (e.g., pesticides).

Surface active material plays important roles in the formation ofW/O emulsion. The first function for the surface active material is tolower the interfacial tension between water and crude oil (i.e., formationof W/O emulsion). The second function is to stabilize the presence ofthe water droplets phase within the oil phase, therefore, preventing thecoalescence mechanism of the water phase (Sherman, 1983). Surfaceactive material accumulates at the interfacial film between water dropletsand crude oil to stabilize the water droplets and consequently stabilizethe emulsion.

W/O emulsion stability can be characterized through the conditionsthat avoid the coalescence mechanism of small water droplets, thedroplet size range is 110 m. Whereas the coalescence will producelarger water droplets and eventually will lead to unstable W/O emulsion.The size of water droplets in W/O emulsions has been studied by lightand electron microscopy (Mikula, 1992). Norwegian crude oil formedemulsion with water droplets size range of 1030m (Sjoblom et al.,1990), however, the average water droplet size of water in the North Seacrude oil emulsion is about 10m (Thompson et al., 1985).

In general, an emulsifying agent plays an important characteristic to

stabilize the W/O emulsion. Surface active materials and particles thatare available in a crude oil behave as emulsifying agents to prevent waterseparation from a given W/O emulsion. If the concentration of surfaceactive materials is reasonably high, the coalescence of water droplets willbe avoided (Bobra, 1990; Canevari, 1987; Christopher, 1993; Eley et al.,1976; Fingas et al., 1995; Mackay, 1987).

The present study is aiming to investigate the effect of variousfactors on the stability behavior of W/O emulsion. These factors arethe water concentration, mixer speed, salt concentration, surfactant

concentration, polymer concentration, and temperature.

EXPERIMENTAL WORK

The main purpose of this study is to investigate the stability of W/Oemulsion. Several parameters will be investigated in this study. W/O


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emulsion is prepared by high speed mixing of gradually adding certainamounts of water into crude oil containing 1% surfactant material.

250 mL of W/O emulsion was prepared in a mixing container usinga laboratory high-speed mixer. Several mixer speeds of different timesare covered to prepare the W/O emulsion. The prepared samples ofemulsion were placed into graduated glass cone-containers to measurethe amount of water separated over 48hours.

Crude oil from Bu-Hasa oil fieldUnited Arab Emirates is used inall of the W/O emulsion investigation. The physical properties of theemployed crude oil are given in Table 1.

Nonionic surfactant of Triton X-100 (iso-Octylphenoxypolyethoxy

ethanol from BDH Middle East L.L.C.United Arab Emirates) wasemployed as an emulsifying agent in the concentration range of 01% byvolume.

Alcoflood polymer material of AF1235 (from Ciba SpecialtyChemicals, Bradford, West Yorks, England) was used to preparepolymer aqueous solution with two different concentrations of 500 and1,000 ppm. This polymer solution is used to form an emulsion withcrude oil to study the effect of polymer presence on W/O emulsionstability behavior. Alcoflood polymer of AF1235 is high molecular

weight polyacrylamide copolymer with bulk density of 800kg/m3 andintrinsic viscosity of 12.

Zeiss optical microscope is used to examine the emulsioncharacteristics, droplets distribution, and water-crude oil dropletsinteraction of W/O emulsion. The computer image analyzer system(CIAS) from Kontron ElektronikGermany consists of a high-resolutionvideocamera mounted on an optical polarizing microscope, an imageprocessor, a Pentium PC, a high-resolution image monitor. In addition,the CIAS has a powerful facility to enhance the captured image in terms

of sharpening, edge detection, threshold function, transition filter, chordsizing, and dilation.

The physical properties of W/O emulsion are necessary toinvestigate to provide some insight about the water droplets phase withinthe continuous phase of crude oil. These properties are density, viscosity,and interfacial tension between crude oil and water. Pycnometer is usedto measure density, Ostwald viscometer is employed to measure emulsionviscosity of Newtonian behavior, and spinning drop tensiometer is

Table 1. Physical properties of Bu-Hasa crude oil

Density @ 25C, kg/m3 827Dynamic viscosity @ 25C, mPas 4.79Asphaltene content, wt% 0.42Sulphur content, wt% 1.33


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Table 2. Physical properties of W/O emulsions

Density Viscosity IFT

W/O emulsion Kg/m3 mPas mN/m

10/90 833 41 43520/80 849 37 43530/70 874 32 43540/60 893 27 43550/50 908 23 435

used for interfacial tension (IFT) measurements. However, for non-Newtonian emulsion behavior RheoStress RS100 rheometer is used toinvestigate the viscosity behavior of W/O emulsion in the presence of500 and 1,000ppm Alcoflood polymer material of AF1235. Tables 24show all the physical properties of all the prepared W/O emulsions.

RESULTS AND DISCUSSION

The water-in-crude oil emulsion has great importance in the oil industry,such as in heavy crude oil transportation, presence of water withinthe produced crude oil, and presence of Alcoflood polymer solutionwithin crude oil. The stability of W/O emulsion is investigated underthe influence of numerous parameters and conditions. These parametersand conditions are the water concentration, surfactant concentration,mixing speed, salt concentration, Alcoflood polymer concentration, andtemperature.

Water Concentration

Wide range of water concentration is covered in this study over therange of 1050% by volume. Figure 1 shows the percentage of the watercontent within the W/O emulsion versus elapsed time for two samples

Table 3. Physical properties of W/O emulsion in presence of salt

NaCl Density Viscosity IFTW/O emulsion Conc.% Kg/m3 mPas mN/m

10/90 1 840 51 6110/90 5 849 55 33550/50 1 916 24 6150/50 5 930 28 335


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Table 4. Physical properties of W/O emulsion in presence of Triton X-100

Triton X-100 Density Viscosity IFT

W/O emulsion % Kg/m3 mPas mN/m

10/90 01 841 365 13102 845 371 12905 851 378 11910 862 390 110

50/50 01 910 25 13102 914 24 12905 917 23 11910 925 22 110

of water concentration of 10 and 50% W/O emulsions. These samplesare prepared with no surfactant and mixing speed of 2,000 rpm for30min of mixing period. Figure 1 shows that the percentage of watercontent within both emulsions drops very significantly over 15min only.The water content drops from almost 100% at 1min to 16% and 4%after 15 min for the 10% and 50% water concentration, respectively.

These samples show strong unstable behavior of water within W/Oemulsion. This conclusion can be attributed to the absence of emulsifyingagents within the emulsion. These samples are prepared without anyaddition of surfactant materials. Also, this type of crude oil has a verylimited amount of asphaltene content (i.e., 0.42 wt.%). Several studies

Figure 1. Emulsion behavior without surfactant.


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reported the importance of asphaltenes in W/O emulsions. Brandvikand Daling (1991) reported that the presence of asphaltene within the

crude oil enhances strongly the stability of W/O emulsion. Sjoblomet al. (1990) found that very unstable W/O emulsions are produced ifasphaltene content of the original crude oil is removed.

Figure 2 shows the stability behavior of water content versus elapsedtime when 1% by volume of Triton X-100 surfactant was added as anemulsifier for wide range of water concentrations over 20 to 50% byvolume. Surfactant material accumulates at the interfacial film betweenwater droplets dispersed phase and crude oil continuous phase. This roleof surfactant stabilizes the water droplets and avoiding the coalescencemechanism of water droplets phase (Sherman, 1983). Therefore, thestability of W/O emulsion is strongly enhanced by the addition ofTriton X-100, as can be concluded from Figure 2. For 20% waterconcentration, the percentage of water content drops slightly from 100%at 10min to 95% after 2 days. Therefore, the function of the TritonX-100 is to help in the formation of W/O emulsion, stabilize thewater droplet dispersed phase for longer time, and delay the coalescenceand separation mechanism of water. Figure 2 shows that when waterconcentration increases for the same conditions of mixing speed andsurfactant concentration, the percentage of water content decreasesgradually with elapsed time. This can be attributed to the coalescencemechanism that enhances gradually when more water is added. In thecase of water concentration of 50% by volume, the percentage of watercontent gradually decreases from 98.4% at a 10min period to 24% after2 days. Table 5 reports the amount of water separated as a function of

Figure 2. Effect of water concentration on W/O emulsion.


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Table 5. Water separation performance

Reduction % of water content

Water concentration % 1 hr 5 hr 48 hr

20 0 0 530 0.667 167 1640 2.5 14 66550 6 228 768

reduction percentage of water content in W/O emulsion. It shows thatthe reduction percentage in water content of W/O emulsion increasesslightly with water concentration at the beginning of the separationprocess. However, it increases significantly with time. After 48hr, only5% of water content is separated in the case of 20% water concentration,however, 76.8% of water content is separated in the case of 50% of waterconcentration.

Effect of Surfactant Concentration

The presence of surfactant material in W/O emulsion promotesand stabilizes the water-in-crude oil emulsion. Surfactant moleculessurround the water droplets with a certain arrangement. The polarhydrophilic portion of the surfactant molecules resides within theaqueous phase, whereas the hydrophobic end resides within the crudeoil phase. Mackay et al. (1973) found that the water droplets areencapsulated with surfactant molecules to prevent coalescence of thewater droplets. Figure 3 shows the effect of Triton X-100 on the stabilityperformance of W/O emulsion for 50% water concentration overthe surfactant concentration of 0.1 to 1.0% by volume. It shows thatthe stability performance increases with surfactant concentration. Thiscan be attributed to the ability of more surfactant molecules to encap-sulate more of the water droplets to avoid the coalescence mechanism.Although the stability performance enhanced with surfactant concen-tration, however, the W/O emulsion is not stable over time. This issue

will be addressed later in this study. Figure 4 shows the same effectfor 10% water concentration. It shows again, the more the addition ofsurfactant the better stability is reported up to 0.2% by volume, whichcan be explained due to a lower amount of water available (i.e., 10%only). The stability of water performance of 96% is achieved for a timeperiod of 5hr in comparison with much less performance and a shorterperiod in the case of 50% water concentration.


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Figure 3. Effect of surfactant concentration on 50% W/O emulsion.

Mixing Speed Effect

Mechanical mixing is one of the well-known methods to form W/Oemulsions from two immiscible phases. Adding the dispersed phase veryslowly to the continuous phase during the mixing process usually offers

Figure 4. Effect of surfactant concentration on 10% W/O emulsion.


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a big advantage for the emulsification process. The interface between thedispersed and continuous phases is deformed to form droplets.

At the beginning of the emulsification process, the droplets aremostly too large. During the mixing process, these large droplets arebroken down into smaller ones due to the disruption process of thelarge droplets. Droplets must be deformed to achieve their disruption,the deformation behavior is opposed by the high Laplace pressure. Thepressure drop, P, between the concave side and the convex side of acurved interface is given by:

P= 2/R (1)

where is the interfacial tension between crude oil and water, and Ris the droplet radius. To break down the large droplet diameter, sucha pressure must be externally supplied over the droplet radius. Therequired pressure gradients are supplied by agitation. Eq. (1) shows thatthe smaller the droplet, the more amount of agitation should be supplied.

Figure 5 shows the percentage of the water content within theemulsion versus elapsed time for 50% W/O emulsion in the presenceof 1% surfactant. A wide range of mixing speed is investigated over

the range of 500 to 2000rpm for 30min of mixing period. Figure 5shows that the more rpm supplied, the more stability is achieved.It is clear that by increasing the mixing speed, the droplet diameterdecreases significantly and consequently enhances the emulsion stability.However, Figure 5 shows a gradual reduction of water content within

Figure 5. Effect of mixing speed on 50% W/O emulsion.


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the emulsion over time due to the coalescence mechanism between thewater droplets.

After the formation of W/O emulsion, droplets may recombinetogether through a flocculation process followed by coalescence to formbigger droplets in which the emulsion stability will be negatively affected.During the emulsion preparation, it is difficult to predict whether ornot and how fast the coalescence will occur. When water and crude oilare agitated within a vessel until the emulsion is formed, the surfactantconcentration is consumed due to the generation of a new dropletsurface area. Therefore, the water droplet size often increases slowly,which results in a change in the initial droplet size distribution. This

process usually leads to the complete separation of the emulsion into twoimmiscible water and crude oil phases. The enhancement of the watercontent percentage will be investigated in this study in a later section.

Salt Effect

It is necessary sometimes to form W/O emulsions with salty water,especially for a heavy crude oil pipeline transportation situation, since

saline water is available and much cheaper than fresh water at oilindustry facilities. Therefore, it is important to investigate the role andthe effect of sodium chloride on the stability of W/O emulsion. Figures 6and 7 show the effect of NaCl concentration on the stability of 50 and10% W/O emulsions, respectively. One percent NaCl slightly increases

Figure 6. Behavior of 50% W/O emulsion in the presence of NaCl.


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Figure 7. Behavior of 10% W/O emulsion in the presence of NaCl.

the water content within the W/O emulsion for both concentrations.

However, the addition of 5% NaCl strongly improves the presence ofwater content within the emulsion. The presence of 5% NaCl in bothemulsions, 50 and 10% W/O emulsions, enhances the stability of W/Oemulsion to reach 100% for the whole period of the test.

The same experiment was exactly repeated for 50% W/O emulsion(with the conditions of 5% NaCl, 2,000 rpm, and 30 min of mixingperiod), but without Triton X-100. Although, this sample has 5%of NaCl concentration, however, it separated completely into waterand crude oil phases within a few minutes. First, these results clearly

showed that the emulsifying performance of Triton X-100 is enhancedsignificantly in the presence of NaCl. Second, the addition of NaCllowers the IFT between crude oil and water significantly, which enhancesthe stability of W/O emulsion. Third, increasing the ionic strengthmay reduce the electrostatic attraction between the water dropletsand therefore prevents flocculation and coalescence of these droplets.Therefore, the role of NaCl strongly enhances the stability performanceof W/O emulsion and reaches to 100% stability after 48hr for 5% NaClconcentration. The improvement performance for the presence of NaCl

within W/O emulsion can be calculated using Eq. (2) as:

Improvement % = S5%NaCl S0%NaCl100/S0%NaCl (2)

where S is the H2O content percent. The results of improvementpercent for the presence of NaCl for 10 and 50% W/O emulsions arelisted in Table 6.


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Table 6. Improvement percentage for the presence of NaCl

Improvement percent

Time, min 10% W/O emulsion 50% W/O emulsion

10 412 04120 846 08130 1182 33360 1667 690

120 2429 1810180 2429 2040240 3000 2400

300 3000 30531,440 3000 230672,880 3000 35091

Table 6 shows that the improvement percent increases with time forboth emulsions. The presence of NaCl is more effective in the first threehr for the 10% W/O emulsion, whereas, it reports higher improvementfor the 50% W/O emulsion after five hr.

Polymer Effect

Alcoflood polymer of AF1235, water soluble polymer powder, is usedextensively in the enhanced oil recovery stage to extract some of thetrapped oil in the well. Alcoflood polymers provide superior handlingcharacteristics and solubility to enhance injection properties throughreservoir permeability. The main objectives of using Alcoflood polymers

are to improve mobility ratio, sweep efficiency, and increase recovery andoil production rates. Therefore, it is necessary to study the role and effectof the presence of AF1235 in the aqueous phase on the stability of W/Oemulsion. This study covers two different concentrations of aqueoussolution of 500 and 1,000 ppm. The viscosity behavior of AF1235

aqueous solutions is studied using RheoStress RS100 from Haakeof cone and plate sensor (cone diameter is 35mm, cone tip gap is0.137mm, and cone angle is 4). Figure 8 shows the viscosity behaviorof AF1235 aqueous solution versus shear rate for 500 and 1,000ppm

polymer concentration. The viscosity of the aqueous phase of AF1235is a strong function of shear rate and polymer concentration. Viscosityof the aqueous solution of the AF1235 is gradually decreasing withshear rate showing shear thinning of non-Newtonian behavior for theconcentrations of 500 and 1,000 ppm. Figure 9 shows the water contentpercent versus elapsed time for 50% W/O emulsion in the presence ofa different concentration of AF1235. Figure 9 shows clearly that the


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Figure 8. Viscosity behavior of AF1235.

AF1235 strongly enhances the stability of W/O emulsion. The more

Alcoflood polymer material is added, the more stable the emulsionwill be. The 1,000 ppm of AF1235 provides almost 100% stabilityfor 50% W/O emulsion. Figure 8 shows that the viscosity of theAlcoflood aqueous phase increases strongly with polymer concentration.The stability of W/O emulsion enhances significantly due to the largeincrease of viscosity of the aqueous phase (Dalgleish, 1996).

Figure 9. Behavior of 50% W/O emulsion in the presence of AF1235.


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Polymer, in general, does not have the same ability to lower theIFT between crude oil and water as the surfactant materials. Nonionic

polymer provides a layer on the droplet surface, in which the W/Oemulsion will be stabilized by a steric repulsion mechanism. Biopolymermaterials introduce significant viscosity modification or gelation phase,which strongly stabilizing W/O emulsion. Employing water solublepolymers is a very efficient technique to avoid coalescence due to theincrease of aqueous phase viscosity. Therefore, the droplets have lowerkinetic energy, in which the collisions mechanism between water dropletswill be less probable (Reichman and Garti, 1991).

Temperature Effect

Temperature plays an important role in the emulsion preparation and itsstability. Temperature influences many variables such as viscosity of eachphase and solubility of the nonionic surfactant in either phase. Therefore,it is necessary to study the effect of temperature on the W/O emulsionstability. Figure 10 shows the effect of temperature on the stability ofW/O emulsion over the temperature range of 1340C. After one hr ofemulsion preparation, temperature shows a significant influence on theemulsion stability. It shows that the higher temperature slightly reducesthe emulsion stability. Although, the solubilization of crude oil in theaqueous surfactant solution increases, the viscosity of either phase willreduce significantly with temperature. Therefore, the droplets of waterphase will acquire more kinetic energy in which the collisions between

Figure 10. Effect of temperature on 50% W/O emulsion.


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droplets of water phase will be more common. The collision mechanismbetween water droplets is enhanced with temperature, therefore, the

interaction between these mechanisms improves the separation betweenthe crude oil and water phases, (i.e., lower stability).

Enhancement of Stability Behavior

It is necessary to improve the W/O emulsion stability performance. Thepresence of 5% NaCl or 1,000ppm of AF1235 enhances the stability ofW/O emulsion to almost 100% over 48hr. However, all other samples

suffer a significant drawback in the stability behavior. It is importantfor this study to investigate the effect of mixer impeller as well. Theimpeller with a helical shape diameter of 1.2cm was used in all previousemulsions. S-curved blade impeller with a diameter of 2.8cm is used toinvestigate the stability of 50% W/O emulsion with conditions of 1%Triton X-100, 2,000rpm mixing speed, and for a wide range of mixingtime (10 to 50min). The 50% W/O emulsion was selected because itshowed the lowest stability behavior among all samples. Table 7 showsthe stability results as a function of the elapsed time over the time

range of 048hr for the S-curved blade impeller mixer. First of all, it isvery necessary to mention that no water was separated from any testedsample over the recorded time. Therefore, the stability of W/O emulsionreaches 100% for all samples (no water was separated). However, overthe time, depending upon the mixing period of 10 to 50min, a lightbrown emulsion layer formed underneath the main emulsion layer. Thelight brown layer increases slightly with time. Therefore, one can saythis technique achieves stable emulsion for the mentioned conditionsover 48hr with no water separated. The values listed in Table 7 are

Table 7. Stability performance percent using S-curved blade impeller

Mixing period, min

Elapsed time, min 10 20 30 40 50

10 100 100 100 100 10020 100 100 100 100 10030 975 985 99 100 100

60 965 975 98 100 100120 95 955 97 100 100180 92 93 95 100 100240 905 91 94 100 100300 885 885 925 100 100

1440 655 665 675 68 1002880 64 65 66 68 685


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Table 8. Average diameter of the water droplet

Mixing period, min 10 20 30 40 50

Dsv m 115 110 103 96 88

for the stability of the main emulsion w.r.t. the light brown emulsion.The growth percent of the light brown layer can be obtained from thesubtraction of 100 minus the listed value in Table 7.

The computer image analyzer system is used to observe the W/Oemulsions prepared with a different time of mixing, 1050min. Severalimages were analyzed for each sample over the first 5hr of elapsed time.For each sample, the image analyzer shows that the average diameter ofthe water droplets within W/O emulsion does not change significantlywith elapsed time. The Sautor mean droplet diameter Dsv, Eq. (3), ismeasured for these emulsions.

Dsv =

NiD3i /

NiD2i (3)

where Ni is the number of droplets and Di droplet diameter. Table 8 lists

the average diameter of the water droplets within W/O emulsion for eachmixing period.

Figure 11 shows some examples of water droplets distribution withindifferent W/O emulsions for different mixing periods with the conditionsof 2,000rpm, 1% Triton X-100, and 50% water concentration. Table 8and Figure 11 show that the water droplets average diameter decreasesgradually with time of mixing. The droplets average diameters are 11.5,10.3, and 8.8m for a mixing period of 10, 30, and 50min, respectively.The degree of emulsion stability enhances significantly by decreasing the

droplet diameter. Therefore, for the same mixing speed, the more mixingtime supplied the more stable the emulsion will be.

CONCLUSIONS

From the investigation of W/O emulsion behavior, the following pointsare found:

1. The W/O emulsions show strong unstable behavior of water withinthe emulsion due to the absence of an emulsifying agent.

2. The stability of W/O emulsion enhances significantly by the additionof Triton X-100.

3. Stability of W/O emulsion gradually decreases with waterconcentration.


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Figure 11. Photomicrograph for 50% W/O emulsion.


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4. Stability of W/O emulsion enhances with Triton X-100 concentration.Concentrations of 0.2% and 1.0% of Triton X-100 achieved better

performance for 10 and 50% W/O emulsions, respectively.5. Mixing speed improves the W/O emulsion stability, the more rpmsupplied the more stability of the W/O emulsion is achieved.

6. The role of NaCl strongly enhances the stability performance of W/Oemulsion and reaches to 100% stability for 5% NaCl concentration.

7. The presence of AF1235 strongly enhances the stability of W/Oemulsion.

8. High temperature reduces the W/O emulsion stability.9. The stability of W/O emulsion reaches 100% by using S-curved blade

impeller.

ACKNOWLEDGMENT

The author is very grateful to the financial support from the United ArabEmirates University under the grant # 01-02-7-11/04.

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emulsion stability investigation

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