5808
Ind. Eng. Chem. Res. 2010, 49, 5808–5815
Stability and Performance Study of Water-in-Oil-in-Water Emulsion: Extraction of Aromatic Amines Jaydeep M. Barad Department of Chemical Engineering, S. V. National Institute of Technology, Surat-395 007, Gujarat, India
Mousumi Chakraborty and Hans-Jo¨rg Bart* Department of Mechanical and Process Engineering, UniVersity of Kaiserslautern, 67663 Kaiserslautern, Germany
One of the major obstacles to the application of emulsion liquid membranes to industrial separations is the stability of emulsion globules. Stability of emulsion is affected by two phenomenasglobule rupture and osmotic swell. Interfacial shear between the continuous and membrane phase causes the liquid membrane to thin and, in some cases, rupture, thereby affecting separation. Destabilization phenomena affecting the homogeneity of dispersions are emulsion globule migration (creaming, sedimentation) and size variation or aggregation (coalescence, flocculation). In the present study, the stability of an emulsion liquid membrane is studied by varying different parameters, for example, internal acid phase and surfactant concentration and stirrer speed for emulsification. Dispersion destabilization of the emulsion is detected by Turbiscan. Properties such as interfacial tension, drop size distribution, photomicrographs, and zeta potential are also analyzed to evaluate emulsion stability. A stable emulsion is used for the removal of aromatic amines from aqueous solutions. An advancing reaction front model considering competitive transport of aromatic amines has been proposed to simulate data. The simulated curves are found to be in good agreement with the experimental data. Introduction Aromatic amines such as aniline and its derivatives are an important class of environmental water pollutants.1 They are widely used in the manufacture of azo dyes, rubbers, plastics cosmetics, pharmaceuticals, and pesticides. Hence, aromatic amines constitute a group of priority water pollutants which are present at high concentrations in groundwater, and soils nearby many industrial contaminated zones have to be effectively removed.2,3Several attempts have been made either to treat such types of effluents for facilitating easy disposal or to recover the chemicals and recycle the process water. Traditional method of purification such as, distillation, liquid extraction, and absorption are still in use; however, industries are looking for competing alternative technologies which may overcome some of the inherent disadvantages of the traditional processes. The liquid membrane (LM) separation technique provides a potentially powerful technique for affecting a diverse number of separation operations. Aromatic amines had been successfully removed from wastewater by a number of researchers using emulsion liquid membranes (ELMs).4,5 Devulapalli and Jones6 separated 99.5% of the aniline within 4 min in a standard Rushton stirred tank using kerosene and sorbitan monooleate (span 80) as the membrane phase and hydrochloric acid as the internal phase. Datta et al.7 also studied the removal of aniline from an aqueous solution in a mixed flow reactor. The maximum removal of aniline obtained in this study was 98.53%. Although all of them achieved 98-99% separation efficiency, the problem that inhibits the application of this technology in industrial equipment is the loss of extraction efficiencies that often occur in these systems due to lack of stability of the emulsion globules. The breakdown of water-in-oil-in-water (w/ o/w) type dispersions is described through several possible * To whom correspondence should be addressed. Tel.: +49 6312052414. E-mail:
[email protected].
mechanisms8 which include (i) coalescence of the internal aqueous droplets into larger internal droplets, (ii) coalescence of the emulsion globules suspended in the external continuous phase, (iii) expulsion of the internal droplets following rupture of the thin membrane film during interaction of the internal and external continuous phases, and (iv) swelling or contraction due to water permeation through the oil membrane by diffusion in the case of w/o/w emulsions. The first study on stability was performed experimentally by Hochhauser and Cussler.9 They used 0.l M sodium dichromate solution as the internal phase and water as the external bulk phase with span 80 as the surfactant dissolved in an organic membrane phase. The solubility of dichromate found in the external water phase was due to the rupture of the membranes. They observed a rapid breakage during an initial period with no further breakage at longer times. Martin and Davies10 along with their mass transfer studies on the extraction of copper from an aqueous solution also performed a stability study using sulfuric acid as the encapsulated phase. Their study revealed that the emulsion breakup was dependent on factors like the operation conditions in the mixing device, size of the subdrops, type of surfactant used, and impeller speed. Breakage was also found to increase linearly with time. This was however in contrast to the findings of Kondo et al.11 and Takahasi et al.;12 all measured the stability of double emulsions using a tracer technique. The effects of variables like tracer or salt concentration, agitation time, size of the emulsion drops, concentration of the emulsifying agent, and pH of the internal droplets on breakage were studied in the above investigations. Shere and Cheung13 measured the stability of ELMs as a function of time using NaOH as a tracer and span 80 as the surfactant. Stroeve et al.14 used this approach on the study of Taylor15 who was the first to study both experimentally and theoretically the deformation and breakup of a drop of a Newtonian liquid suspended in another immiscible Newtonian liquid undergoing simple shear and plane hyperbolic flows. Similar studies had
10.1021/ie901698u 2010 American Chemical Society Published on Web 05/11/2010
Ind. Eng. Chem. Res., Vol. 49, No. 12, 2010
5809
Figure 1. BS profile at different internal phase acid concentrations.
been conducted experimentally by Grace et al.16 Bart et al.17 found that osmotic swelling can create a breakdown of membrane stability and revealed the water transport mechanism has its origin in reversed micelles dissolved in the LM.18,19 Goto
et al.20 and Kasaini et al.21 also used the tracer technique to study emulsion stability. Mengual et al.22 proposed physical models for the surface flux in the backscattered spot light and the diffuse reflectance measurement performed with the Tur-
5810
Ind. Eng. Chem. Res., Vol. 49, No. 12, 2010
A stable emulsion comprising n-heptane as the membrane phase with span 80 as the surfactant and dilute hydrochloric acid as the internal phase is used for the removal of aromatic amines from a synthetic binary feed mixture as well as from industrial wastewater. An advancing reaction front model considering competitive transport of aromatic amines has been proposed to simulate solute transport data. Experimental Procedure
Figure 2. Effect of surfactant concentration on interfacial tension and the mean diameter of the internal droplets.
Figure 3. Effect of surfactant concentration on internal droplet size distribution (log-normal).
biscan MA 1000 optical analyzer. Yan et al.23 monitored osmotic swelling behavior over a long period of time (up to about 4 h) for a w/o/w system. The osmotic pressure difference between the internal and external aqueous phases was induced by creating a concentration difference of D-glucose between the two aqueous phases. Chakraborty et al.24 found that the leakage phenomena, which reflect the stability, are influenced by pH of the feed phase, speed of agitation, emulsion drops size per unit specific interfacial area, surfactant concentration, pH in inner aqueous phase, and the presence of different tracers. Chakraborty and Bart25 also found that the dispersed drop sizes as well as internal droplets sizes define the interfacial contact area and are important in determining efficiency of extraction and stability of the liquid membrane. Liu et al.26 found that the main destabilization mechanism of the nanoemulsion systems was Ostwald ripening. They also observed that the effect of flocculation can be reduced or eliminated by improving the negative surface charges on the droplets through tuning the pH of the systems. There still exists some scope for better insight to study, monitor, and predict the emulsion stability. In the present study, Turbiscan has been used to monitor emulsions and dispersions in the kinetic studies of emulsion stability. Properties such as interfacial tension, drop size distribution, photomicrographs and zeta potential are also analyzed to evaluate emulsion stability.
Chemicals. Span 80 (sorbitan monooleate) as surfactant, n-heptane as membrane phase, and hydrochloric acid (all purity greater than 0.99 mass fractions) as internal phase are used for ELMs preparation. Aniline and 4-chloro aniline (supplied by Glaxo India, Ltd.) are used to prepare a synthetic feed mixture. Common effluent treatment plant (Palsana, India) wastewater (more than 200 numbers of dying houses) is used as industrial wastewater. Nessler reagent (supplied by Finar chemicals) is used to detect ammonical nitrogen in industrial wastewater. Apparatus and Procedure. The internal phase (1 N HCl) and membrane phase (n-heptane and span 80) are emulsified using an ultraturax T25 homogenizer (IKA, Germany), a high speed mechanical stirrer, with speed variation from 6500 to 24000 rpm. Emulsion stability is checked varying different parameters, and the stable emulsion is then dispersed in the feed phase. The agitation speed of the mixer is controlled by a speed controller and monitored by a tachometer. Samples of about 2 mL are withdrawn from the extractor at different intervals of time and are filtered through a sintered glass plug to separate emulsion and feed phase and then analyzed. The concentrations of aromatic amines in feed phase are measured at characteristic wavelengths using a Hach (Germany) make UV-vis spectrophotometer. Measurement of Physical Properties of the Emulsion. Interfacial tensions are measured by the Du Nou¨y ring method with a tensiometer. The lower phases are hydrochloric acid solutions (inner phase) in all cases at different concentrations. The concentration of surfactant (span 80) in n-heptane (membrane phase) is varied in the upper phase. Oil and water phases are equilibrated before the interfacial tension measurements. Emulsion stability is analyzed using transmission and backscattering (BS) profiles, scanning the emulsion sample by light rays of 880 nm wavelength using Turbiscan classic MA 2000 (Formulaction, France). Dispersed drop size measurements are carried out within a few minutes after preparation of the emulsion. Samples (1 mL) are taken and diluted in an aqueous phase (3 mL). To improve the optical transparency of the dispersed emulsion, most of the emulsion drops are adsorbed by contacting the drop with filter paper, leaving few emulsion drops on the glass slide. The photomicrographs are taken using Diastar Microscope and Photostar camera system (Cambridge Instruments, USA). Internal droplets size and drop size distribution of the (w/o) emulsion are measured by an acoustic and electroacoustic spectrometer (model DT1200, Dispersion Technology, Inc., USA). Colloidal silica solution (Silica Ludox, wt fraction 10%) having a mean particle diameter 28 ( 5 nm was used for calibration. The zeta-potential measurements were performed using the electrophoretic light scattering method (ELS-8000, Photal Otsuka Electronics Co. Ltd., Osaka, Japan). Mathematical Model. The model has been derived from the advancing front model of Ho et al.27 and neglects the externalphase mass-transfer resistance and the effect of membrane breakage. Following the work of Chakraborty et al.28,29 the
Ind. Eng. Chem. Res., Vol. 49, No. 12, 2010
5811
advancing front model in dimensionless form can be written as ∂g 1 ∂ 2 ∂g ) η 2 ∂η ∂τ ∂η (1 - φ)η
( )
∂g' β ∂ 2 ∂g' ) η ∂τ (1 - φ)η2 ∂η ∂η
(
)
(1)
at (χ < η < 1, τ > 0) (2)
τ ) 0,
g ) 0,
g' ) 0 (η e 1)
(3)
η ) χ,
g ) 0,
g' ) 0 (τ g 0)
(4)
η ) 1 then g ) CDh,
g' ) CD′ h' at (τ g 0)
(5)
Here eq 1 gives the solute balance for aniline and eq 2 for 4-chloroaniline, respectively. The material balance equations in the external phase are then dh ∂g ) -E η)1 dτ ∂η
(6)
dh' ∂g' ) -Eβ η)1 dτ ∂η
(7)
τ ) 0,
h ) 1,
h' ) 1
(8)
The material balance equation at the reaction front is as follows: -
1 ∂g dχ β ∂g' ) + dτ φm ∂η η)χ φm' ∂η η)χ τ ) 0,
χ)1
(9) (10)
The coupled eqs 1, 2, 6, 7, and 9 were solved by numerical computation using an implicit finite difference technique. Distribution coefficients are calculated by a linear regression method. A central difference scheme has been used for integration along the dimensionless radial distance. The grid sizes in τ and χ directions have been chosen by trial and error to obtain good convergence. The diffusivity values of the aniline and 4-chloroaniline in the membrane phase is determined by the correlation of Wilke and Chang30 and found to be 5.976 × 10-10 and 5.466 × 10-10 m2/s, respectively. The Sauter mean diameter is found to be 0.1 cm.31 Results and Discussion It has been found from the literature that more than 90-99% recovery of aromatic amine is possible within 20 min of residence time.5-7 The BS profile of any sample scanned from the bottom (0 mm) to the top of the vial (∼60 mm) during the period of 20 min shows that the top part of the emulsion sample has shown some changes probably due to the release of bubbles. However, the middle and the bottom part of the sample have not changed noticeable. Effect of Internal Phase Acid Concentration. At a surfactant concentration at 5.0% w/v, an S value (ratio of the volume of the surfactant solution to that of the internal phase in emulsion) at 0.5, and an ultraturax speed at 6500 rpm the internal phase acid concentration is varied from (0.1-1.0 N). It is found from Figure 1 that with variation in the concentrations of the internal phase (0.1-1.0 N) the BS increases. It indicates that the emulsion has become denser with an increase in internal phase acid concentration. Actually the size of the emulsion globule increases with an increase in internal phase acid concentration due to swelling which decreases emulsion stability.
Figure 4. BS profile at different surfactant concentration.
Then the migration velocity of emulsions is calculated from the clarification front obtained from transmission profiles. Emulsions with 0.1 and 0.5 N internal phase acid concentration
5812
Ind. Eng. Chem. Res., Vol. 49, No. 12, 2010
Figure 5. BS profile at different stirrer speeds.
Ind. Eng. Chem. Res., Vol. 49, No. 12, 2010
5813
Figure 6. Photomicrograph of emulsions prepared at (a) 6500, (b) 9500, and (c) 13500 rpm.
show better stability (migration rates, 0.248 and 0.276 mm/min) than the emulsion with 1.0 N internal phase acid concentration (migration rate, 0.321 mm/min). Inspite of the slight instability problem, internal phase acid concentration is kept at 1.0 N because a high H+ concentration increases the capacity of the internal phase as a sink for amine compounds. Effect of Surfactant Concentration. Figure 2 shows that interfacial tension decreases with increasing surfactant concentration, and there is no change of interfacial tension when the surfactant concentration reaches its optimum value; that is, the critical micelle concentration (CMC) of span 80 in n-heptane is 3.16 × 10-4 mol/L (0.135 g/L).32 It is observed that the surfactant concentration in the membrane phase significantly affects the emulsion stability. With increasing surfactant concentration, interfacial film strength will increase and enhance resistance to coalescence. The droplet size distribution and mean droplet diameters of emulsions with different surfactant concentrations are presented in Figures 2and 3. Emulsions containing low surfactant concentrations (0.5% w/v) are not very stable and result in phase separation within a short period of time. The droplet size distribution becomes narrow, and the mean droplets diameter declines from about 3.13 to 1.96 µm as the surfactant concentration increases from 1.0 to 4.0% w/v and then again increases slightly with surfactant concentration due to the creaming effect. Therefore, in the remainder of the experiments the surfactant volume was kept at 5.0% w/v to provide a stable emulsion with a narrow drop size distribution (Figure 3). The BS profile (Figure 4) indicates that the sizes of the emulsion globules have been increased with an increase in surfactant concentration. When the surfactant concentration is 5.0% w/v and higher than what is due to the creaming effect and high viscosity of the emulsion, a rapid swelling of internal droplets occurs which results in an increase in globule sizes. Effect of Stirrer Speed. Keeping other parameters constant, emulsions are prepared at 6500, 9500, and 13500 rpm of ultraturax. The percent BS at 6500 rpm is higher than that at 9500 rpm, but both emulsions are found stable (Figure 5). The emulsion prepared at 13 500 rpm stirrer speed is found unstable as the BS profile is moving upward with time. The migration velocity of the clarification front of the 13 500 rpm emulsion is also very high (1.24 mm/min). Actually with increasing stirrer speed, the diameter of the internal droplets will decrease and population density will increase which leads to flocculation and coalescences of an emulsion. From the microphotograph (Figure 6) and internal droplet size distribution (Figure 7), it is found that diameters of the droplets in dispersed emulsions are in the range of 10-110 µm and those of the internal droplets are in the range of 0.001-10 µm. However, the dispersed emulsion drops prepared at 6500 rpm contain a relatively less number of internal droplets (Figure 6a) than those prepared at 9500 rpm (Figure 6b). Distefano et al.33 found that the number and size of internal droplets in multiple emulsions are a function of the
Figure 7. Effect of stirrer speed on internal droplet size distribution (lognormal and cumulative).
Figure 8. Zeta potential as a function of pH with 5.0% (w/v) surfactants concentration.
agitation rate used to prepare the emulsion. From Figure 7, which shows log-normal as well as cumulative internal droplet size distribution, it has been observed that emulsions prepared using 6500 and 9500 rpm result in a narrow size distribution having internal droplets mean diameters of 2.08 and 1.17 µm. In contrast, the emulsion prepared at 13 500 rpm yields broader droplet size distribution with a lower mean diameter of 0.042 µm. Long-Term Stability. For molecules and particles that are small enough, a high zeta potential will confer stability, that is, the solution or dispersion will resist aggregation. When the potential is low, attraction exceeds repulsion and the dispersion will break and flocculate. So, colloids with high zeta potential (negative or positive) are electrically stabilized, while colloids with low zeta potentials tend to coagulate or flocculate. Here droplets of the emulsions are found to be negatively charged, as shown in Figure 8. The zeta potential of the emulsion is approximately -8.8 mv at pH 6.8 (water as internal phase).
5814
Ind. Eng. Chem. Res., Vol. 49, No. 12, 2010
the residence time, the better is the solute recovery. But longer residence time increases water transport, which ultimately diminishes the solute enrichment in the internal phase. Swelling and globule rupture can be controlled by proper selection of emulsion composition and parameters during the emulsification process. This paper describes the stability behavior of emulsions under a wide variety of operating conditions such as internal acid phase and surfactant concentration and stirrer speed for emulsification. From this study it has been found that a uniformly distributed stable emulsion can be obtained by selecting optimum conditions which will provide a higher mass transfer rate and high extraction efficiency for the removal of aromatic amines from the binary feed mixture as well as from industrial wastewater. Acknowledgment The authors wish to acknowledge the Alexander von Humboldt-Stiftung Foundation, Germany, for financial support. Figure 9. Variation of external phase aniline and 4-chloroaniline concentrations with time.
Liu et al.26 suggested that negative charges on the droplets come from the adsorption of hydroxyl ions at the o/w interface, and the ethylene oxide (EO) group of span 80 creates hydrogen bonds with the hydroxyl ions to give more negative surface charges. The zeta potential is strongly dependent on the pH of the system. The absolute value of the zeta potential is reduced with the decrease of pH. At pH 3.8, the zeta potential is close to zero, after which the droplets become positive charged (+16.8 mv at pH 1.0) with 1 N HCl as the internal phase. With 1 N NaOH as the internal phase, the absolute value of the zeta potential increases to -18.2 mv at pH 12. Low zeta potential value,+ 16.8 mv (below +20 mv), indicates instability of emulsion particularly when we are considering longterm stability. Abu-Nemeh and Peteghem34 studied the aging of the membrane phase and found span 80 in the presence of water and traces of hydroxyl ions or hydrogen ions undergoes hydrolysis but up to 20 min of residence time no significant changes of emulsion properties have been observed. Extraction of Aromatic Amines. Using optimum conditions (internal acid concentration, 1.0 N; span 80 concentration, 5.0% (w/v); and 6500 rpm) a stable emulsion is prepared, which is used for the removal of aniline and 4-chloroaniline mixtures (100 ppm each) from aqueous solutions. The values of S (ratio of the volume of the surfactant solution to that of the internal phase in emulsion) and K (ratio of the volume of the feed phase to that of the emulsion) are fixed at 0.5 and 8, respectively. It is found that 94% recovery (maximum) of aniline is possible, along with 89% 4-chloroaniline within 20 min of residence time (Figure 9). Figure 9 shows that initially experimental and simulated data superimpose, but with time, a deviation is observed because of a slight membrane breakage problem only. Membrane breakage starts initially and continues to progress with time. Common effluent treatment plant wastewater has been treated with stable ELMs and significant reduction (98%) of ammonical nitrogen has been observed. Conclusions Emulsions become unstable due to osmotic swelling and globule rapture, thereby affecting mass balances and final concentrations of the solute in the external phases. Residence time is the key parameter of the ELM process. The longer is
Nomenclature C, C′ ) aromatic amines (aniline and 4-chloroaniline) concentrations in saturated zone of emulsion globule, mol/L Cio ) initial internal reagent concentration in internal phase, mol/L Ci ) internal reagent concentration in internal phase, mol/L Ce, Ce′ ) aromatic amines concentration in external phase, mol/L Ceo, Ceo ′ ) initial aromatic amines concentration in external phase, mol/L D, D′ ) diffusivity of aromatic amines in saturated zone of emulsion globules, m2/s V ) total volume of emulsion phase, L Ve ) volume of external phase, L CD, C D′ ) distribution coefficients of the solutes (aniline and 4-chloroaniline) between membrane and external phase r ) radial coordinate in emulsion globules, m. R ) radius of emulsion globules, m Rf ) reaction front position, m t ) time, s. ELM ) emulsion liquid membrane K ) ratio of the volume of the feed phase to that of the emulsion PSD ) particle size distribution S ) ratio of the volume of the surfactant solution to that of the internal phase in emulsion BS ) back scattering Variables
C C' , g' ) Ceo Ceo ′ Ce′ Ce , h' ) h) Ceo Ceo ′ Ci Ci′ m) , m' ) Ceo Ceo ′
g)
Greek Letters η ) r/R, χ ) Rf/R, E ) 3V/Ve, τ ) D t/R2, β ) D′/D φ ) volume fraction of internal aqueous phase in the emulsion
Literature Cited (1) Asthana, A.; Bose, D.; Durgbanshi, A.; Sanghi, S. K.; Kok, W. T. Determination of aromatic amines in water samples by capillary electrophoresis with electrochemical and fluorescence detection. J. Chromatogr. A 2000, 895, 197.
Ind. Eng. Chem. Res., Vol. 49, No. 12, 2010 (2) Pinheiro, H. M.; Touraud, E.; Thomas, O. Aromatic amines from azo dye reduction: status review with enphasis on direct UV spectrophotometric detection in textile industry waste waters. Dyes Pigm. 2004, 61, 121. (3) Shengquan, Y.; Huang, F. Separation of carcinogenic amines in dyestuff plant waste water treatment. Desalination 2007, 206, 78. (4) Teramoto, M. H.; Takihana, M.; Shibutani, T.; Yuasa, Y. M.; Teranishi, H. Extraction of amine by w/o/w emulsion system. J. Chem. Eng. Jpn. 1981, 14, 122. (5) Braid, R. S.; Bunge, A. L.; Noble, R. D. Batch extraction of amines using emulsion liquid membranes importance of reaction reversibility. AIChE J. 1987, 33, 43. (6) Devulapalli, R.; Jones, F. Separation of aniline from aqueous solutions using emulsion liquid membranes. J. Hazard. Mater. 1999, 70, 157. (7) Datta, S.; Bhattacharya, P. K.; Velma, N. Removal of aniline from aqueous solution in a mixed flow reactor using emulsion liquid membrane. J. Membr. Sci. 2003, 226, 185. (8) Hou, W.; Papadopoulos, K. D. Stability of water-in-oil-in-water type globules. Chem. Eng. Sci. 1996, 51, 5043. (9) Hochhauser, A. M.; Cussler, E. L. Concentrating chromium with liquid surfactant membranes. AIChE Symp. Ser. 1975, 71, 136. (10) Martin, T. P.; Davies, G. A. The extraction of copper from dilute aqueous solutions using a liquid membrane process. Hydrometallurgy 1977, 2, 315. (11) Kondo, K.; Kita, K.; Koida, I.; Irie, J.; Nakashio, F. Extraction of copper with liquid surfactant membranes containing benzoylacetone. J. Chem. Eng. Jpn. 1979, 12, 203. (12) Takahasi, K.; Ohtsubo, F.; Takeuchi, H. A study of the stability of (w/o)/w-type emulsions using a tracer technique. J. Chem. Eng. Jpn. 1981, 14, 416. (13) Shere, A. J.; Cheung, H. M. Effect of preparation parameters on leakage in liquid surfactant membrane systems. Sep. Sci. Technol. 1988, 23, 687. (14) Stroeve, P.; Prabodh, P. V.; Elias, T.; Ulbrecht, J. J. Stability of double emulsion droplets in shear flow. 53rd Annual Meeting of the Society of Rheology, Louisville, KY, October, 1981, 11. (15) Taylor, G. I. The formation of emulsions in definable fields of flow. Proc. R. Soc. London, Ser. A 1934, 146, 501. (16) Grace, H. P. Dispersion phenomena in high-viscosity immiscible fluid systems and application of static mixers as dispersion devices in such systems. Chem. Eng. Commun. 1982, 14, 225. (17) Bart, H. J.; Draxler, J.; Marr, R. Residence time selection in liquid membrane permeation for copper recovery. Hydrometallurgy 1988, 19, 351. (18) Bart, H. J.; Jungling, H.; Ramaseder, N.; Marr, R. Water and solute solubilization and transport in emulsion liquid membranes. J. Membr. Sci. 1995, 102, 103. (19) Abou-Nemeh, I.; Bart, H. J. Microstructures in the system water/ D2EHPA/span-80/n-dodecane. Langmuir 1998, 14, 4451.
5815
(20) Goto, M.; Matsumoto, M.; Kondo, K.; Nakashio, F. Development of new surfactant for liquid surfactant membrane process. J. Chem. Eng. Jpn. 1987, 20, 157. (21) Kasaini, H.; Nakashio, F.; Goto, M. Application of emulsion liquid membranes to recover cobalt ions from a dual-component sulphate solution containing nickel ions. J. Membr. Sci. 1998, 146, 159. (22) Mengual, O.; Meunier, G.; Cayre, I.; Puech, K.; Snabre, P. Characterisation of instability of concentrated dispersions by a new optical analyser: the TURBISCAN MA 1000. Colloids Surf., A 1999, 152, 111. (23) Yan, J.; Pal, R. Osmotic sweling behaviour of globules of W/O/W emulsion liquid membranes. J. Membr. Sci. 2001, 190, 79. (24) Chakraborty, M.; Bhattacharya, C.; Datta, S. Study of the stability of (w/o)/w-type emulsion during the extraction of nickel (II) via emulsion liquid membrane. Sep. Sci. Technol. 2004, 39, 1. (25) Chakraborty, M.; Bart, H. J. Emulsion liquid membranes:Role of internal droplet size distribution on toluene/n-heptane separation. Colloids Surf., A 2006, 272, 15. (26) Liu, W.; Sun, D.; Li, C.; Liu, Q.; Xu, J. Formation and stability of paraffin oil-in-water nanoemulsions prepared by the emulsion inversion point method. J. Colloid Interface Sci. 2006, 303, 557. (27) Ho, W. S.; Hatton, T. A.; Lightfoot, E. N.; Li, N. N. Liquid surfactant membranes: A diffusion controlled model. AIChE J. 1982, 28, 662. (28) Chakraborty, M.; Bhattacharya, C.; Datta, S. Mathematical modeling of simultaneous copper (II) and nickel (II) extraction from wastewater by emulsion liquid membranes. Sep. Sci. Technol. 2003, 38, 2081. (29) Chakraborty, M.; Bhattacharya, C.; Datta, S. Effect of drop size distribution on mass transfer analysis of the extraction of nickel(II) by emulsion liquid membrane. Colloids Surf., A 2003, 224, 65. (30) Reid, R. C.; Prausnitz, J. M.; Sherwood, T. K. The Properties of Gases and Liquids, 4th ed.; McGrawHill: New York, 1988. (31) Ohtake, T.; Hano, T.; Takagi, K.; Nakashio, F. Effect of viscosity on drop diameter of w/o emulsion dispersed in a stirred tank. J. Chem. Eng. Jpn. 1987, 20, 443. (32) Valenzuela, F.; Salinas, C.; Basualto, C.; Hagar, J. S.; Tapia, C. Influence of nonionic surfactant compound on coupled transport of copper(II) through a liquid membrane. J. Chil. Chem. Soc. 2003, 48 (http://www. scielo.cl/scielo.php?pid)S071797072003000100014&script)sci_arttext). (33) Distefano, F. V.; Shaffer, O. M.; El-Aasser, M. S.; Vanderhoff, J. W. Multiple oil-in-water-in-oil emulsions of extremely fine droplet size. J. Colloid Interface Sci. 1983, 92, 269. (34) Abou-Nemeh, I.; van Peteghem, A. P. Some aspects of emulsion instability on using sorbitan monooleate (span 80) as a surfactant in liquid emulsion membranes. Chem. Ing.Tech. 1990, 62, 420.
ReceiVed for reView October 29, 2009 ReVised manuscript receiVed April 20, 2010 Accepted April 27, 2010 IE901698U
