Environ. Sci. Technol. 1997, 31, 1040-1045
Deposition of Oil-in-Water Emulsions in Sand Beds in the Presence of Cetyltrimethylammonium Bromide JAYAPRAKASH SOMA AND KYRIAKOS D. PAPADOPOULOS* Department of Chemical Engineering, Tulane University, New Orleans, Louisiana 70118
Surfactant flushing of soils contaminated with non-aqueous phase liquids (NAPLs) has shown significant potential as an effective remediation tool. However, an important aspect that has been neglected is the formation of emulsions and their eventual transport in the subsurface. In this study, the effect of the cationic surfactant cetyltrimethylammonium bromide (CTAB) in modifying the surface properties of sand and emulsion droplets and its consequence on the transport of emulsions in porous media has been investigated with the aim of determining the emulsion-mediated transport of NAPLs in the subsurface. Flow experiments in sand-packed columns were conducted to determine the deposition of hexadecane-in-water emulsions on quartz sand at various CTAB concentrations. Adsorption of CTAB influences the electrokinetic potential of sand and emulsion droplets along with the surface hydrophilicity of the sand surface, thereby influencing the deposition of emulsion droplets. Deposition is found to be a maximum at a CTAB concentration of 5 × 10-6 M, at which the sand surface is of opposite charge to that of the emulsion droplets. Below this concentration, the deposition efficiency is reduced due to the electrostatic repulsion between the negatively charged droplets and the sand. Above this concentration, the deposition is again reduced due to the surfaces of sand and droplets being positively charged. The experimental deposition efficiencies agree qualitatively with the energy barriers calculated using the DLVO theory. The results suggest that the transport of emulsions in porous media can be regulated by the adsorption of surfactants.
Introduction The use of surface-active agents to remediate soils contaminated with non-aqueous phase liquids (NAPLs) has received considerable attention in the recent years (1). Surfactants enhance the remediation process by (i) increasing the solubility of the NAPLs via micellar solubilization and by (ii) increasing the mobility of the NAPLs in the subsurface by reducing the interfacial tension between water and NAPL. Although surfactant flushing has shown potential as an effective remediation tool, an important aspect that has been neglected is the possibility of the formation of emulsions in-situ, which may have adverse effects on the transport of NAPLs in the subsurface (2). If persistent emulsions are formed, they could aid in the remediation of NAPLs if they can be transported along with the surfactant solution. However, if their mobility is restricted due to the interaction * To whom correspondence should be addressed. E-mail: pops@ che.che.tulane.edu; phone: (504)865-5826; fax: (504)865-6744.
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with the solid surfaces, it could have a detrimental effect on the remediation process. For example, in field tests of surfactant flooding, surfactants that formed persistent emulsions were found to be less efficient in extracting the NAPLs than those that did not (3). Emulsions can be formed in porous media as a result of the presence of surface-active agents, either native or externally added, or by the action of induced shear during the movement of fluids through pore throats (4). Evidence of in-situ formation of emulsions in porous media is widespread in the petroleum industry (5-9), where oil-inwater emulsions may form inadvertently in steam flooding or in chemical flooding. Sometimes emulsions are also injected deliberately to improve the sweep efficiency (9-11). In oil production, the emulsions are usually formed as a result of high velocity gradients in the reservoir rock near the well bore (12). On the other hand, in surfactant flooding for the removal of NAPLs, the tendency for emulsion formation is found to be a function of the quantity of the contaminant present and of the method and vigor of mixing (3). Recently, Pennel et al. (13) observed emulsion formation in sand column experiments of surfactant flushing of residual PCE when the pore size was small. Evidence of in-situ emulsification can also be obtained from the experiments of Churaev et al. (14), who have observed the formation of emulsions in microcapillaries at some critical flow rate when surfactants are added to the aqueous phase. Similar emulsification was also observed earlier even in the absence of surfactants, but at higher flow rates (15). Emulsions may also be formed in the subsurface by biosurfactants or by naturally occurring surfactants such as humic and fulvic acids. Biosurfactants are produced by a wide variety of microorganisms and have found uses in a number of applications such as microbial-enhanced oil recovery and oil spill cleanup (16). These biosurfactants have also shown the ability to enhance in-situ biorestoration by emulsifying organic compounds and thereby increasing the bioavailability of contaminants. Francy et al. (16) suggest that such emulsification of hydrocarbons by microorganisms in the subsurface can be an important mechanism in bioremediation of contaminated aquifers. On the other hand, naturally occurring humic substances can also act as moderate surfactants due to their ability to lower the surface tension of water and to promote foaming (17). In the presence of NAPLs in the subsurface, humic substances, can in principle aid in the formation of emulsions in-situ. Apart from emulsification, the addition of surfactants to groundwater may also affect sorption distribution coefficients and wetting characteristics of the system. Recently, it has been proposed that cationic surfactants can be used to modify the surfaces of soils to enhance the sorption of hydrophobic organic compounds to them and thus retard their migration in the subsurface environment (18, 19). Surfactants have also been observed to affect the mobilization of colloidal particles in porous media. Clayfield and Smith (20) found the extent of colloid release from a packed column to be a function of surfactant concentration and type. Litton and Olson (21) found a strong influence of sodium dodecyl sulfate on the deposition of latex particles on quartz sand and suggested that particle attachment is enhanced by uncharged, hydrophobic regions of the surfaces of latex or quartz. Ryan and Gshwend (22) studied the effect of the surfactant dodecanoic acid and natural organic matter on the mobilization of colloids from an iron oxide-coated sand and found higher colloid release rates in their presence. The retention of bacteria in sand columns is also found to decrease dramatically in the presence of surfactants (23). An undesir-
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1997 American Chemical Society
able effect of surfactant flushing for the remediation of contaminated soils is the mobilization of colloids and the ensuing reduction of permeability, which has a deleterious effect on the remediation process (24). Similar colloid mobilization and permeability reductions are observed when surfactants are used for enhanced oil recovery (25). The purpose of this study is to evaluate the effect of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) on the transport of emulsions in a model porous medium. Such a study of transport in porous media of emulsions, formed either during surfactant flooding or by other means, can help improve the remediation of subsurface sites contaminated with NAPLs. The main emphasis in this study is on the effect of surface interaction forces on the flow of emulsions in porous media. Ionic surfactants such as CTAB influence both the surface charge and the surface hydrophilicity of the interacting surfaces and can be used to control the attachment or repulsion of the oil droplets. Emulsion Flow in Porous Media. Emulsion flow in porous media can be broadly classified according to the drop sizeto-pore size ratio and the stability of the emulsion (26). Depending on pore size-to-drop size ratio, droplets can be captured in a porous medium by either straining or interception. Straining refers to the physical capture of oil droplets in pores smaller than the oil droplets and interception refers to the capture of the oil droplets by various physical forces. Soo and Radke (26) found the flow of dilute, stable emulsions in porous media to be physically similar to that of deep-bed filtration of solid particles. In a traditional filtration process, the particle-to-pore size ratio is small, and the particles are captured on the surface of the media grains due to interception rather than straining. Filtration theory only holds for initial particle deposition onto clean surfaces before deposited colloidal particles start to block favorable deposition sites. Emulsion droplets flowing through a porous medium can be attracted to the solid surfaces either by the electrostatic attraction between the oppositely charged surfaces or by hydrophobic forces (14). Electrostatic forces are known to be more important than capillary forces in the flow of fine oil-in-water emulsions through porous media (27). Chiang et al. (28) found the oil recovery in sand packs to be maximum when the charge on the oil drops was maximum. Sarbar et al. (29) reported an optimum pH and surfactant concentration at which the emulsions were stable while flowing through porous media. The deposition of emulsion oil drops in porous media was reportedly (30) higher in the presence of salt than in its absence. In a recent study on the flow of dilute, submicron emulsions through porous media, we investigated the effect of pH and ionic strength in the absence of any surfactants (31), while in the present paper we address the effect of a specific cationic surfactant on the flow of emulsions. Since this study focuses on the effect of interaction forces on emulsion droplet deposition, emulsions with drop sizes much smaller than the pore sizes were used in order to eliminate straining.
Materials and Methods Emulsions. Emulsions used in the experiments were of the oil-in-water type with the oil phase being n-hexadecane (Aldrich Chemical Co.). Water was purified by passing it through an E-pure water purification system (Barnstead) and had a resistivity of 18.1 MΩ‚cm. Emulsions were prepared by mixing n-hexadecane in aqueous surfactant solutions of CTAB (Aldrich Chemical Co.) in a high-speed rotor/stator mixer (Silverson) to form a coarse emulsion with an average diameter of ∼1 µm. These were further homogenized by passing them through a microfluidizer (Model 110T, Microfluidics Corp.) for two to four passes at 6500 psi, which produced nearly monodispersed emulsions in the size range of 0.2-0.25 µm. In all the experiments, the concentration of the oil phase was 0.1% v/v. At such dilute concentrations,
droplet-droplet encounters are infrequent, and coalescence of the emulsion droplets in the bulk phase is slow. All experiments were conducted in the presence of 1 × 10-4 M KCl as background electrolyte and at surfactant concentrations below the critical micelle concentration (cmcCTAB ) 9.2 × 10-4 M). The pH of the solutions varied from 5.8 to 6.2. Drop size analysis of the emulsions was performed by photon correlation spectroscopy using a Coulter submicron particle analyzer (Model N4MD, Coulter Electronics) at a scattering angle of 90°. Electrophoretic mobility of the oil droplets was measured by Laser Doppler Velocimetry using a Coulter DELSA 440 (Coulter Electronics). Porous Medium. The model porous medium was made of white quartz sand (-50 + 70 mesh, Aldrich Chemical Co.) packed in a Plexiglas column having an inner diameter of 2.5 cm and a length of 10 cm. The sand was thoroughly washed using concentrated hydrochloric acid. It was then rinsed in deionized water repeatedly and oven-dried at 100 °C before use. The porosity of the porous medium varied from 0.34 to 0.36. The pore size was at least an order of magnitude larger than the drop size, ensuring that the capture of droplets by straining is eliminated. To determine the electrophoretic mobility of sand at different surfactant concentrations using the Coulter DELSA 440, the sand was crushed using a mortar and a pestle and was subjected to the same cleaning procedure as used for the sand grains. The crushed sand was centrifuged, and the supernatant with particles in the range of 0.5-0.8 µm in diameter was used for mobility measurements after equilibrating it with CTAB at different concentrations. Deposition Experiments. The experimental setup, shown elsewhere (31), consisted of a packed column through which the emulsion was pumped from the bottom at a superficial velocity of 0.04 cm/s using a peristaltic pump (Masterflex Corp.). Samples were collected both at the inlet and the outlet and were analyzed for concentration and drop size distribution. The drop size distribution was measured using the Coulter N4MD submicron particle analyzer while the concentration of the oil phase was determined by measuring the turbidity of the solution (32) with a spectrophotometer (Shimadzu UV-160). Before each experiment, the column was flushed with water for 8 h to saturate the porous medium. It was then equilibrated by flushing 15 pore volumes of surfactant solution at the same concentration and ionic strength as that of the emulsion to be deposited.
Results and Discussion Drop Size Distribution. A typical drop size distribution of the emulsions used in flow experiments is shown in Figure 1. In all the experiments, the average drop diameter was between 0.2 and 0.25 µm. The polydispersivity of the emulsion is defined as the ratio of variance to squared mean value of the decay time constant of the correlation function, τ, as measured by the Coulter submicron particle analyzer (33). An emulsion is considered to have a narrow unimodal distribution if the polydispersivity factor lies between 0.01 and 0.1 and is considered to be a broad monomodal or multimodal when it lies between 0.1 and 1.0. In all the experiments in this study, the polydispersivity factor was less than 0.1, suggesting a narrow unimodal distribution of the emulsion droplets. The emulsions were found to be stable for weeks to months depending on the amount of the surfactant present in the system. No change in drop size distribution was observed after the emulsion was passed through the sand beds during the initial stages of deposition. Electrophoretic Mobilities. The electrophoretic mobilities of the emulsion droplets and the sand particles are presented in Figure 2 as a function of CTAB concentration in the presence of 1 × 10-4 M KCl as background electrolyte. The points of zero charge of the oil droplets and the sand particles are approximately at 10-6 and 10-5 M CTAB, respectively. In the
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Deposition Experiments. In the absence of repulsive interaction forces, colloid deposition rates are usually represented in terms of single collector efficiency, η0, that depend on basic collection mechanisms of particle diffusion, interception, and sedimentation (40). Single collector efficiency is defined as the ratio of the particle deposition rate to the rate at which particles approach the collector. Experimental single collector efficiencies are calculated from the observed emulsion breakthrough curves using the following expression (41):
η)-
FIGURE 1. Typical particle size distribution of the emulsion used in flow experiments. Concentration of CTAB ) 1 × 10-4 M; pH ) 5.9; background electrolyte ) 1 × 10-4 M KCl.
()
ac 4 C ln 3 (1 - )L C0
where ac is the average radius of the sand grains, is the porosity of the packed bed, L is the length of the packed column, and C/C0 is the ratio of effluent-to-influent concentrations of emulsion droplets. The single collector efficiencies, as obtained from the breakthrough curves, depend on solution chemistry as well as physical parameters such as velocity, porosity, and length of the bed. To identify the effect of colloidal interactions on the deposition of emulsion droplets, it is necessary to separate the effects of physical parameters from solution chemistry. This is usually done through the introduction of an “attachment efficiency”, R, defined as the ratio of single collector efficiency under unfavorable conditions to that of favorable conditions, i.e., the ratio of deposition in the presence of repulsive electric double layer interactions (η) to that in the absence of such interactions (η0).
R)
FIGURE 2. Electrophoretic mobilities of oil droplets and sand particles at different CTAB concentrations. absence of any surfactants, the oil drops acquire a negative charge due to the adsorption of OH- ions (31, 34-38). Below 10-6 M CTAB, the oil droplets have a negative charge due to the incomplete neutralization of the negative charges by the surfactant molecules. As the CTAB concentration is increased, the negative charge on the drops is neutralized, and the droplets become positively charged at concentrations greater than 10-6 M CTAB. Similarly, the sand particles are negatively charged at surfactant concentrations less than 10-5 M CTAB. Above 10-5 M CTAB, the electrophoretic mobilities turn positive and increase in magnitude with an increase in CTAB concentration due to an increase in adsorption of CTAB on silica with an increase in CTAB concentration. The presence of a cationic surfactant not only affects the electrophoretic mobilities of the sand grains but also renders the surface of the sand hydrophobic. This is evident from the contact angles measured through the aqueous phase, which pass through a maximum at the point of zero charge (14, 39). The surface of silica is hydrophilic both in the absence of CTAB and at CTAB concentrations greater than 10-4 M. In the range 10-610-4 M CTAB, the silica surface is hydrophobic.
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(1)
η η0
(2)
In physical terms, the attachment efficiency R is the ratio of the rate at which particles attach to a surface to the rate at which they collide with the surface. Usually, η0 is measured experimentally by performing the experiments at high ionic strengths to suppress the double-layer interactions or by performing experiments with particles that are oppositely charged to that of the porous medium (42). In this study, η0 is obtained experimentally at a CTAB concentration of 5 × 10-6 M since the sand and emulsion droplets are oppositely charged at this concentration. Experiments at high ionic strengths were not conducted to determine η0 to avoid coalescence of emulsion droplets, which occurs at high salt concentrations. Experimental attachment efficiencies are presented in Figure 3 as a function of CTAB concentration in the presence of the 1 × 10-4 M KCl as background electrolyte. As the results suggest, deposition rates are highly dependent on CTAB concentration. Attachment efficiencies are seen to decrease with an increase in CTAB concentration above 5 × 10-6 M. A decrease in the attachment efficiency of almost 2 orders of magnitude is observed with an increase in CTAB concentration, indicating the importance of colloidal interactions in the transport of emulsions through porous media. The attachment efficiency is also seen to decrease at concentrations of CTAB below 5 × 10-6 M due to the repulsive interactive energy between the negatively charged surfaces. Colloidal Interactions. Colloid deposition rates in the presence of repulsive electrostatic interactions are sensitive to the solution chemistry and the electrokinetic potentials of the particles and the collectors. According to the DLVO theory of colloidal stability, the total interaction energy between two surfaces is equal to the sum of van der Waals and electric double-layer interactions. Since the oil droplets are much smaller than the sand grains, theoretical expressions for interaction energy between a sphere and a flat surface are used here to calculate electrostatic and van der Waals interaction energies. The electrical double-layer repulsion
FIGURE 3. Experimental attachment efficiencies of oil droplets on sand surfaces as a function of CTAB concentration (background electrolyte: 1 × 10-4 M KCl). between the droplets and the sand surfaces was calculated using the expression developed by Hogg et al. (43) for interaction between a sphere and a flat plate:
Φdl )
dp ψ ψ ln (1 + e-κh) 2 p m
FIGURE 4. Total interaction energy profiles between oil drops and sand surfaces as a function of separation distance at various CTAB concentrations in the presence of 1 × 10-4 M KCl as background electrolyte.
(3)
where is the permittivity of the medium, dp is the diameter of the oil droplet, κ is the inverse Debye length, h is the separation distance between the surfaces, ψp and ψm are the surface potentials of the droplets and the sand surfaces respectively. ζ-Potentials calculated from the measured electrophoretic mobilities were used in place of surface potentials in the above equation to determine the doublelayer repulsion forces. The van der Waals energy between a sphere and a flat plate was calculated using the expression (44)
Φa ) -
Aap 6h
(4)
where A is the Hamaker constant, ap is the radius of the oil droplet, and h is the separation distance. The Hamaker constant A for the hexadecane-water-quartz system was calculated to be 0.2 × 10-20 J using (44)
A ) (xA11 - xA33)(xA22 - xA33)
(5)
where A11, A22, and A33 are the Hamaker constants for hexadecane, quartz, and water, respectively. Figure 4 shows the total interaction energy, φtot, between the oil droplets and quartz surface as a function of separation distance at different CTAB concentrations. The height of the energy barrier is seen to increase with an increase in CTAB concentration above 5 × 10-6 M. Near the surface region, where particle transport is dominated by diffusion, droplets approaching the surface of the sand grains must possess sufficient energy to overcome this barrier to attach in the primary minimum. Theoretical investigations of collision efficiencies of small Brownian particles in the presence of electric double-layer interactions show that the collision efficiencies can be represented in the Arrhenius form as (45)
(
R ) Ψ exp -
)
φmax kT
(6)
FIGURE 5. Plot of logarithm of attachment efficiencies as a function of height of the energy barrier. where the energy barrier, φmax, is the activation energy for attachment and Γ is the frequency factor, which depends on the physical and colloidal properties of the deposition system. From the above equation, the logarithm of attachment efficiency is approximately proportional to the height of the energy barrier, which is confirmed by the results shown in Figure 5. Elimelech and O’Melia (46) found that the transition from favorable to unfavorable deposition occurred at an energy barrier of ∼5 kT, which is similar to the one observed here. According to the theory, the onset of repulsive conditions occurs when the interaction energy barrier exceeds 10-15 kT (47) which shows good agreement with the trends observed experimentally. Figure 6 shows the attachment efficiencies and the exp(-φmax/kT) as a function of CTAB concentration. As can be seen, the energy barriers calculated from DLVO theory agree qualitatively with the experimental attachment efficiencies. Similar agreement with the DLVO theory was recently observed in a recent study on the adsorption of oil droplets from dilute emulsions on silica (48) as well as in earlier experiments of deposition of silicon oil from oil-in-water emulsions on cationically modified keratin
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FIGURE 6. Correlation of the experimental attachment efficiencies with energy barriers at different CTAB concentrations. Solid line represents the attachment efficiencies while the filled circles represent exp(-Omax/kT). fibers (49). Nevertheless, quantitative agreement with the DLVO theory is poor as attachment efficiencies calculated from current theories incorporating the DLVO theory are found to be many orders of magnitude smaller than those observed experimentally (42). Implications of Emulsion Transport on Soil Remediation. Past research on surfactant flushing of contaminated soil for the removal of NAPLs from the subsurface has primarily focused on two mechanisms: (i) mobilization of large NAPL volumes through the porous structure of soil in a two-phase flow pattern and (ii) micellar or microemulsion solubilization of the organic phase. However, recent experiments have demonstrated that macroemulsion transport can be an important mechanism in the removal of NAPLs by surfactant flushing, accounting for up to 30% of its removal (50). The results presented in this paper demonstrate that such emulsion transport in porous media is highly dependent on the surface chemistry of the soil and the droplets. When chemical conditions are favorable for deposition (i.e., a ) 1.0), the emulsion droplets will be practically immobilized in the soil, thereby decreasing the efficiency of cleanup of NAPLs by surfactant flushing. However, under unfavorable chemical conditions for deposition (a ) 0.001), emulsion droplets can travel significant distances in groundwater aquifers and help enhance the removal of NAPLs by surfactant flushing. Controlling the transport of emulsions in the subsurface during surfactant flushing by suitably modifying the surface characteristics of the aquifer-emulsion system can thus help improve the remediation of NAPL-contaminated soils. Surfactant selection for remediation is dependent not only on the surfactant’s interaction with the contaminants but also on its interaction with aquifer media. Field demonstrations of surfactant flushing have shown that surfactants can plug the media by changing the hydrogeological nature of the aquifer (51). Since most natural subsurface media are negatively charged, anionic surfactants are normally used in surfactant flushing as they are less adsorbing than cationic or nonionic surfactants. When anionic surfactants are used, emulsion formation will usually enhance the remediation effort until they start plugging the pores. On the other hand, if cationic surfactants are used, emulsion transport can be achieved only at certain surfactant concentrations. Cationic surfactants are being used to modify surfaces of soils and subsurface materials to promote sorption of hydrophobic organic compounds and retard their migration
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(19). In the application of cationic surfactants for in-situ modification of the soils, if NAPLs are present in the subsurface, it is likely that emulsions will be formed. The results from this study suggest that the amount of cationic surfactant determines the mobility of the emulsion droplets in the porous medium. If the objective is to contain the movement of pollutants as is the case in in-situ soil modification, emulsion transport would be detrimental to the remediation effort. In such a scenario, to inhibit the migration of the droplets, an optimum amount of surfactant is needed such that the repulsive interaction energy between the soil and the droplets is reduced. For the sand-CTAB emulsion system, a concentration of 5 × 10-6 M CTAB would be optimum in retarding the migration of oil droplets. Cationic surfactants can be used in conjunction with insitu bioremediation, wherein the surfactant can retard the migration of the hydrophobic organic compounds long enough so that a relatively slow process of biodegradation, such as reductive dehalogenation, could be effective (19). Biodegradation of constituents of NAPLs in soil has been reported to increase by the use of some surfactants, even at concentrations below the cmc (52). If NAPL emulsion droplets are retarded by attachment to the soil, then the biodegradation of NAPL constituents could be enhanced due to an increase in the available surface area for bacterial action. The flow of emulsions in porous media is a complex process due to the complexity of the emulsions themselves and due to the heterogeneity of the porous media. In this work, the flow of stable submicron emulsions of narrow size distribution through uniform porous media was studied as a first step. It was shown that the flow of such emulsions is similar to that of solid particle filtration. However, a typical surfactant flushing of subsurface contaminants might involve the flow of a polydispersed emulsion through a heterogeneous porous media. The flow of such emulsions is dependent not only on the emulsion stability and drop size to pore size ratio but also on the surface characteristics of the porous medium. In spite of the great need for experimental studies of emulsion flow through porous media, this paper is one of the very few to date. Future investigations should also address the heterogeneities encountered in real soils and sediments.
Acknowledgments Financial support for this research from the NIEHS (Grant 5-P42-ES05946-02) and the NSF (Grant OSR-9108765) is gratefully acknowledged.
Literature Cited (1) U.S. Environmental Protection Agency. Report EPA 542-K-94003. U.S. EPA: Washington, DC, 1995. (2) Ouyang, Y.; Mansell, R. S.; Rhue, R. D. Crit. Rev. Environ. Sci. Technol. 1995, 25, 269-290. (3) Fountain, J. C. In Transport and Remediation of Subsurface Contaminants; Sabatini, D.; Knox, R., Eds.; ACS Symposium Series 491; American Chemical Society: Washington, DC, 1992, pp 182-191. (4) Kokal, S. L.; Maini, B. B.; Woo, R. In Emulsions: Fundamentals and Applications in the Petroleum Industry; Schramm, L. L., Ed.; American Chemical society: Washington, DC, 1991; pp 219261. (5) Raghavan, R.; Marsden, S. S. Soc. Pet. Eng. J. 1971, 153-161. (6) Jennings, H. Y., Jr.; Johnson, E. E., Jr.; McAuliffe, C. D. J. Pet. Technol. 1974, 26, 1344-1352. (7) Willhite, G. P.; Green, D. W.; Okoye, D. M.; Looney, M. D. Soc. Pet. Eng. J. 1980, 20, 459-472. (8) Vittortos, E. Proceedings of the Joint International Technical Meeting of the Petroleum Society of the Canadian Institute of Mining and Metallurgy and the Society of Petroleum Engineers; Society of Petroleum Engineers: Richardson, TX, 1990; Paper CIM/SPE 90-107. (9) Chen, T.; Chakrabarthy, T.; Cullen, M. P.; Thomas, R. R.; Sieben, M. C. Proceedings of the Joint CIM/AOSTRA Annual Meeting; Canadian Institute of Mining and Metallurgy: Calgary, Alberta, Canada, 1991; Paper CIM/AOSTRA 91-78.
(10) Schmidt, D. P.; Soo, H.; Radke, C. J. Soc. Pet. Eng. J. 1984, 24, 351-360. (11) Decker, R. M.; Flock, D. L. J. Can. Pet. Technol. 1988, 27, 69-78. (12) Berkman, S.; Egloff, G. Emulsions and Foams; Reinhold: New York, 1941. (13) Pennell, K. D.; Pope, G. A.; Abriola, L. M. Environ. Sci. Technol. 1996, 30, 1328-1335. (14) Churaev, N. V.; Ershov, A. P.; Esipova, N. E.; Iskandarjan, G. A.; Madjarova, E. A.; Sergeeva, I. P.; Sobolev, V. D.; Svitova, T. F.; Zakharova, M. A.; Zorin, Z. M.; Poirier, J. E. Colloids Surf. 1994, 91, 97-112. (15) Zorin, Z. M.; Churaev, N. V. Adv. Colloid Interface Sci. 1992, 40, 85-108. (16) Francy, D. S.; Thomas, J. M.; Raymond, R. L.; Ward, C. H. J. Ind. Microbiol. 1991, 237-246. (17) Beckett, R. In Surface and Colloid Chemistry in Natural Waters and Water Treatment; Beckett, R., Ed.; Plenum Press, New York, 1990; pp 3-20. (18) Boyd, S. A.; Lee, J. F.; Mortland, M. M. Nature 1988, 333, 345347. (19) Westall, J. C.; Brownawell, B. J.; Wagner, J.; Chen, H. Report EPA/600/S-94/002. U.S. EPA: Washington, DC, 1994. (20) Clayfield, E. J.; Smith, A. L. Environ. Sci. Technol. 1970, 4, 413416. (21) Litton, G. M.; Olson, T. M. J. Colloid Interface Sci. 1994, 165, 522-525. (22) Ryan, J. N.; Gschwend, P. M. Environ. Sci. Technol. 1994, 28, 1717-1726. (23) Johnson, W. P.; Martin, M. J.; Gross, M. J.; Logan, B. E. Colloids Surf. 1996, 107, 263-271. (24) Abdul, A. S.; Gibson, T. L.; Rai, D. N. Ground Water 1990, 28, 920-926. (25) Muecke, T. W. J. Pet. Technol. 1979, 144-150. (26) Soo, H.; Radke, C. J. Ind. Eng. Chem. Fundam. 1984, 23, 342347. (27) Cartmill, J. C.; Dickey, P. A. Am. Assoc. Pet. Geol. Bull. 1970, 54, 2438-2443. (28) Chiang, M. Y.; Chan, K. S.; Shah, D. O. J. Can. Pet. Technol. 1978, 17, 61-68. (29) Sarbar, M; Livesey, D. B.; Wee, W.; Flock, D. L. Proceedings of the Annual Technical Meeting of the Petroleum Society of the Canadian Institute of Mining and Metallurgy; Canadian Institute of Mining and Metallurgy: Calgary, Alberta, Canada, 1987; Paper 3004. (30) Hofman, J. A. M. H.; Stein, H. N. Colloids Surf. 1991, 61, 317329. (31) Soma, J.; Papadopoulos, K. D. Colloids Surf. 1995, 101, 51-61. (32) Reddy, S. R.; Fogler, H. S. J. Colloid Interface Sci. 1981, 79, 101104.
(33) (34) (35) (36) (37) (38)
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(40) (41) (42)
(43) (44) (45) (46) (47) (48) (49) (50) (51) (52)
Coulter N4MD Reference Manual; Coulter Electronics; 1987. Taylor, A. J.; Wood, F. W. Trans. Faraday Soc. 1957, 53, 523-529. Reddy, S. R.; Fogler, H. S. J. Phys. Chem. 1980, 84, 1570-1575 Tobin, T.; Ramkrishna, D. AIChE J. 1992, 38, 1199-1205. Deshiikan, S. R.; Papadopoulos, K. D. J. Colloid Interface Sci. 1995, 174, 302-312. Marinova, K. G.; Alargova, R. G.; Denkov, N. D.; Velev, O. D.; Petsev, D. N.; Ivanov, I. B.; Borwankar, R. P. Langmuir 1996, 12, 2045-2051. Desai, F. N.; Demond, A. H.; Hayes, K. F. In Transport and Remediation of Subsurface Contaminants; Sabatini, D., Knox, R., Eds.; ACS Symposium Series 491; American Chemical Society: Washington, DC 1992; pp 133-147. Yao, K. M.; Habibian, M. T.; O’Melia, C. R. Environ. Sci. Technol. 1971, 5, 1105-1112. Elimelech, M. Science 1994, 164, 190-199. Elimelech, M.; Gregory, J.; Jia, X.; Williams, R. Particle Deposition and Aggregation: Measurement, Modeling and Simulation; Butterworth-Heinemann Ltd.: Oxford, 1995. Hogg, R.; Healy, T. W.; Fuerstenau, D. W. Trans. Faraday Soc. 1966, 62, 1638-1651. Israelachvili, J. N. Intermolecular and Surface Forces; Academic Press: London, 1985. Ruckenstein, E.; Prieve, D. C. J. Chem. Soc. Faraday Trans. 2 1973, 69, 1522-1536. Elimelech, M.; O’Melia, C. R. Environ. Sci. Technol. 1990, 24, 1528-1536. Adamczyk, Z.; Dabros, Z.; Czarnecki, T.; van de Ven, T. G. M. Adv. Colloid Interface Sci. 1983, 19, 183-252. Malmsten, M.; Lindstrom, A.; Warnheim, T. J. Colloid Interface Sci. 1996, 179, 537-543. Jachowicz, J.; Berthiaume, M. D. J. Colloid Interface Sci. 1989, 133, 118-134. Okuda, I.; McBride, J. F.; Gleyzer, S. N.; Miller, C. T. Environ. Sci. Technol. 1996, 30, 1852-1860. Nash, J. H. Report EPA/600/2-87/110. U.S. EPA: Washington, DC, 1988. Fu, M. H.; Alexander, M. Appl. Microbiol. Biotechnol. 1995, 43, 551-558.
Received for review June 20, 1996. Revised manuscript received November 19, 1996. Accepted November 26, 1996.X ES960539Q X
Abstract published in Advance ACS Abstracts, February 1, 1997.
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