Environ. Sci. Technol. 1994, 28, 1361-1366
Microemulsion Formation with Chlorinated Hydrocarbons of Differing Polarity Jimmle R. Baran, Jr.,t Gary A. Pope? William H. Wade,'it Vinitha Weerasoorlya,t and Anusha Yapat Departments of Chemistry and Petroleum Engineering, The Unlversity of Texas, Austin, Texas 78712 Type 111
Winsor Type I (o/w), Type I1 (w/o), and Type I11 (middle phase) microemulsions have been produced for water and CC4, water and trichloroethylene (TCE), and water and 1,Pdichlorobenzene (DCB) with anionic surfactants and appropriate electrolytes. Attempts at producing classical phase behavior with several more polar chlorinated hydrocarbons were unsuccessful. These results are compared to those obtained previously with PCE. All studies were done at 25 "C. The experimental data presented are electrolyte concentration and solubilization parameter for optimum formulations and salinity window for the Type I11 Dhase region. The addition of surfactants to aquifers contaminated with species such as chlorinated hydrocarbons has been shown to potentially improve remediation efficiency by the pump and treat method (1-6). The surfactant increases the "solubility" of the organic in the pumped water by micellar solubilization and/or encapsulation in microemulsiondrops by orders of magnitude varying from 101 to 104. Alternatively, the low interfacial tensions associated with many microemulsions can allow bulk mobilization of the chlorinated hydrocarbons. Both possibilities permit one to apply the general principles that have been developed for surfactant enhanced oil recovery to aquifer remediation. Researchers (7),who developed the systematics of microemulsionproduction for enhanced oil recovery, have been forced to design surfactantsfor a wide range of system conditions-salinities ranging from 0.1 to 30 wt % , the presence of divalent ions, temperatures ranging from 30 to 100 "C, crude oils which are best modeled by alkanes varying from hexane to dodecane, the addition of various cosurfactants to eliminate high viscosity liquid crystal phases, and variations in water-to-oil ratio (WOR) ranging from 0.1 to 10. The usual systematic approach is to hold constant all variables except one and to scan the one over an appropriate range of values. The most commonly chosen variable is electrolyte concentration. The surfactant is selected so that at low salinity an aqueous continuous microemulsion (o/w, Winsor Type I) is formed in equilibrium with excess oil. With increased salinity more and more oil is solubilized, but a t a critical salinity, SI, this Type I system converts to a Winsor Type 111,which is a microemulsionexisting in equilibrium with excessaqueous and oil phases. Just beyond SI,the microemulsioncontains mostly aqueous phase. As salinity increases, oil incorporated in the microemulsion increases, and the aqueous phase decreasesuntil one arrives at a defined salinity called the optimum salinity, S*, where equal volumes of aqueous and oleic phases are incorporated in the microemulsion. More globally one refers to this whole system as an optimum formulation. Continuing to still higher elec-
* Author to whom correspondence should be addressed. t
Department of Chemistry. Department of Petroleum Engineering.
0013-938X/94/0928-1381$04.50/0
0 1994 American Chemlcai Soclety
Type II
2 54
0
2
4
SI
6 S '
a
10
12
s2
Figure 1. Typical phase behavior and measured parameters for a properlydesigned chlorocarbon/water/surfactant systemfor a variation in electrolyte concentration.
trolyte concentration, the oil-to-water ratio in the microemulsion continues to increase until one reaches a second critical salinity, SZ,where the system reverts to a twophase oil continuous microemulsion (w/o, Winsor Type 11) system in equilibrium with excess aqueous phase. Further increases in salinity lead to ever reduced solubilization of water in oil. Such behavior is shown for a hypothetical system in Figure 1. The data recorded from such scans consist of the optimum salinity, S*; the salinity window, AS = SZ- SI, and the solubilization parameter, u*, for the optimum state. In general, the solubilization parameter u is the volume of water or oil encapsulated in a w/o or o/w system, respectively, per gram of surfactant added and is the measure of surfactant efficiency of solubilization. Since the scans described above are done in graduated, sealed pipets and since 6's are relatively large, increases in phase volumes can be read directly from the pipets and divided by the total weight of surfactant, which is constant from tube to tube. u* by the definition of the optimum state is simply one-half the volume of the middle phase divided by the weight of surfactant. u*'s are of additional importance because Chun-Huh has proposed (8, 9) and we have repeatedly verified (10-13)an inverse relationship between u and interfacial tension between the microemulsion and the excess phases. Potentially, the same type of systematic studies could be fruitfully applied to chlorinated hydrocarbons in a variety of toxic spill remediation processes. If one wants to purposely mobilize a chlorocarbon, one would design Winsor Type I11 systems, because of their low interfacial tensions (see Figure 1) y, but carefully avoid Type I1 Environ. Scl. Technol.. Vol. 28, No. 7, 1994
1361
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Table 1. Experimental Parameters for 2% MA-100,Electrolyte and Oil Phase As Noted
cc4
PCE S* (wt %)
NaCl CaCll
u*
4.1 2.4
(mL/g) 2.4 1.0
AS (wt %)
S* (wt %)
2.8 5.6
2.48 0.16
systems since the chlorocarbons would be a near-infinite chemical potential sink for surfactant. If, on the other hand, one wishes to simply solubilize but not mobilize, Type I systems must be designed to be sufficiently far from the VI11 boundary so that interfacial tensions are sufficientlyhigh to prevent mobilization. One notices the reciprocal relationship between y and u in Figure 1. Over time, a wide variety of chlorinated hydrocarbons have been used for cleaning processes or are good model compounds for microemulsion study. These have included: CzC14 (PCE), CC4, CzHC13 (TCE), 1,2-C&C1z (DCB),CHzClz, CHC13,1,2-CzH4Cl~,and 1,1,2,2-CzHzC14. Our initial studies (14) focused on PCE, since it is one of the most ubiquitous solvents. In the present study, we had hoped to report on the phase behavior of the rest of the above molecules using the same suite of surfactants as with PCE. For reasons which will become obvious later, we have only been able to study CC4,TCE, and DCB. The reason for our failure with the remaining chlorocarbons will also be discussed later. The previous study on tetrachloroethylene (PCE) demonstrated that the systematics used to study hydrocarbonlwaterlanionic surfactant systems (15-29)could be extended to include PCE as the oil phase. The results from that study showed that more hydrophilic surfactants were needed to form typical Winsor Type I (o/w), Type I1 (w/o), and Type 111(middle phase) microemulsionswith PCE as compared to typical hydrocarbons, such as octane. It was determined that sodium dihexyl sulfosuccinate (MA-loo), being a twin-tailed surfactant, possessed considerable tolerance to variations in system conditions undergoing classical I I11 I1 phase behavior by itself or was needed to varying extents as a cosurfactant with all other surfactant species studied. In the study contained herein, these same anionic surfactant systems are applied to other highly chlorinated hydrocarbons to obtain a more global view of using surfactants to assist in the remediation of sites contaminated with dense nonaqueous-phase liquids (DNAPLs). Studies concentrated on Winsor I11 formulations having significant volumes of DNAPL and aqueous electrolyte incorporated in the middle phase microemulsion. S*,u*, and AS, for Winsor Type I11 formulations using trichloroethylene (TCE),carbon tetrachloride (Ccld, and 1,2-dichlorobenzene (DCB) are reported. The other organicsstudied (CHzClz,CHCl3,1,2-C2H4Clz,and 1,1,2,2CzHzC14) appeared to be sufficiently polar so that the surfactants preferentially solubilized into the chlorocarbon rather than water, with no subsequent micelle formation. Studies of these latter four species will be reported in a subsequent publication dealing with DNAPL mixing rules for microemulsion formulations.
--
Experimental Section
Chemicals. The aqueous phase as originally formed contained NaCl in distilled H2O adjusted to a variety of salinities in wt % units. CC14, CHzC12, and CHCl3 (EM 1362 Envlron. Sci. Technol., Vol. 28, No. 7, 1994
u*
(mL/g) 3.3 2.65
TCE A S (wt %)
S* (wt %)
0.77 0.10
1.31
u*
(mL/g) 4.65
A S (wt %)
0.42
Science); TCE (Fisher); 1,2-CzH4Clz (MCB Manufacturing); 1,1,2,2-CzHzC14(Eastman); and DCB (Aldrich) were obtained as reagent grade and used without further purification. Surfactant mixtures of AEROSOL MA (American Cyanamid) [MA is 80% active as received. It was further purified in this laboratory to 100% active and as such is designated as MA-100.1, sodium dihexyl sulfosuccinate, were prepared in various weight ratios with a series of Guerbet ethoxy (EO) and propoxy (PO) sulfates reported on earlier (10). Their formulas were as follows: C14GA(EO),S04Na ( x = 1.6 and 2.9), C14EX(E0)&04Na, C16EX(EO),S04Na (y = 0, 2, 4, 6, 8, and lo), and C&X(PO),S04Na ( z = 2.6,4, and 6.5). GA refers to the common twin-tailed Guerbet alcohol hydrophobe, and EX refers to Exxon, USA's version which has an additional internal branching in both tails. The c14 surfactants were synthesized in-house, while the CIS species were obtained from Alkaril Chemical. Formulation of Equilibrium Systems. Surfactants and NaCl were always predissolved in the aqueous phase, and all systems, as initially constituted, contained equal volumes of aqueous and oleic phases (WOR = 1). All systems were shaken multiple times, and sufficient time was allowed for the initially formed unstable macroemulsions to decay to thermodynamically stable microemulsion systems. Depending upon the system in question, these times varied from hours to weeks. Equilibration was done at 25 "C. In all studies, the total surfactant concentration was held constant at 2 wt % of the aqueous phase. Results and Discussion
Phase Behavior Parameters with MA-100. Carbon Tetrachloride. Using MA-100 (MA)as the sole surfactant, S* = 2.48 wt % NaC1, u* = 3.30 mL/g, and A S = 0.77 wt % NaC1. In comparing these values to those for PCE (see Table l),the S* for C C 4is approximately 1.6 wt % lower than for PCE, while u* is about 0.9 mL/g greater and A S is about one-fourth that of PCE. Table 1also reproduces the same values with CaC12 replacing NaCl as the electrolyte. Similar to what was demonstrated previously by comparison of PCE to octane (14), C C 4 is a more strongly interacting solvent for surfactants than either octane or PCE. This is evidenced by the lower value of S* for CC14 compared to PCE. Interestingly, the optimum solubilization parameter actually increases by changing from PCE to CC4, also indicating the better solvency of CC4. The decrease in A S was expected, since the optimum solubilization parameter and the salinity window are inversely related (19, 20). The same trends are apparent in changing the electrolyte from NaCl to CaC12. They mimic those reported for PCE (14). Trichloroethylene (TCE). Using MA as the only surfactant, S* = 1.31 wt % NaCl, u* = 4.65 mL/g, and A S = 0.42 wt % NaCl (see Table 1). Again a noticeable drop in S* is observed for TCE versus cc4. This once again demonstrates the increased solvent strength that TCE
0
0.1
1 0
'
'
'
I
2
'
'
1
'
'
'
1
8
4
'
'
'
1
8
'
'--t
Flgure 2. S" vs EON for C,eEX(E0)$04Na/MA-100 at 25 OC for systems as noted.
has versus CC14. The optimum solubilization parameter increased in going from CC14 to TCE, while the salinity window decreased as expected. No data could be obtained for CaC12 as the sole electrolyte. One notes that, in changing the electrolyte from NaCl to CaC12 in both PCE and CC4,S* drops 2.32.4 wt % With TCE, in effect, the optimum salinity drops to a "negative" value. Various ratios of CaCldNaCl have been investigated with the MA/TCE system. In a 1/1w/w mixture of CaCldNaCl, S* = 0.55 wt %, u* = 3.2 mL/g, and AS = 0.1 wt % Above a critical Ca2+concentration, a Type I11 system vanishes and a I I1transition occurs. At this point, we would like to introduce a new term to be used in these studies, the switching salinity, denoted by Ss.We define the switching salinity as the point a t which the system changes from a Winsor type I system to a Winsor type I1 system without going through a Winsor type I11 system, due to the fact that the salinity window goes to zero. 1,2-Dichlorobenzene (DCB). DCB does not form a Type I11system with only MA; therefore no comparisons can be made to the other oils. Only Winsor Type I1 systems were found by combining DCB with MA. C16EX(PO)J304Na/MA and ClsEX(EO)fi04Na/ MA Systems. Guerbet alcohol ethoxy and propoxy sulfates were studied in 50/50 and 70/30 weight fractions of Guerbet to MA and were formulated at 2 wt % total surfactant concentration in the aqueous phase. These are the same ratios previously used with PCE (14). Carbon Tetrachloride. When incorporating ethoxylated surfactants, the addition of EO increases S* exponentially, but slower than with PCE. Surfactants with six or less EOs are more lipophilic than MA. The EO10 species is more hydrophilic relative to MA, and the EO8 species has an HLB similar to MA, ie.,the 50/50 and 70/30 lines cross near EOa. The optimum salinity vs EON (average number of EO units/molecule) data is presented in Figure 2. Here, we have plotted log S* vs EON to show the optimum salinity data. One notices immediately that both the 50/50 and 70/30 mixtures of CI~/MA surfactants with C C 4show that the number of EOs affects S* less than it affects S* for PCE (the net overall change of S* between EO0 and E010 is less). But, the rate of change is the same (i.e.,the slopes
.
-
4
6 EON
8
10
12
Figure 3. Optimum solubilization parameter vs EONfor 50/50 systems with electrolyte and oil phase as noted at 25 OC.
10
EON
.
2
are the same). The values of the slopes were found to be 0.041 for the 50/50mixture and 0.083 for the 70/30mixture. These are almost identical to the slopes found for PCE (0.044 and 0.082). The slope would be expected to increase by increasing the amount of EO in the surfactant mixture. The spacing between these lines remains constant when varying the surfactant system (between 50/50 and 70/30); therefore, we believe that the spacing is a measure of the polarity of the chlorocarbons. Thus, we find that PCE is less polar than CC4. Increasing the concentration of the EO surfactants to greater than 70% only led to complex phase behavior; therefore, the two data points obtained for PCE and C c 4 were used to linearly extrapolate to obtain data for the pure Guerbet species (100/0). The average slope of a log S* vs EON plot for the pure Guerbet species with PCE and CCl4 was found to be 0.180. This compares to a value of 0.15 for the slope obtained from a plot of log S* vs EON for octane (10). The data obtained for the propoxylated (PO) surfactants was minimal and, therefore, not included in Figure 2. A 50/50 mix of (POMMA and a 50/50 mixture of (PO)6.5/ MA produced middle phases with essentially the same S* (0.96 and 0.97 wt '36 NaC1, respectively). These values are very similar to the EO0 species, which was the general trend exhibited earlier with PCE. This leads one to believe that almost all of the propoxy groups reside in the oleic phase. The u*'s are also very similar (24.8 and 22.0 mL/ g), while the windows are almost identical (0.3 and 0.18 wt % ). The u*'s for the PO species, just as was found with PCE, show that by adding structural length with PO the solubilization parameters are significantly enhanced as compared to the EO0 species. The S* for the 50/50 system of (PO)Z.~/MA is 1.50 f 0.01 wt '36 NaCl and for the 70/30 system with the same surfactants is 0.49 f 0.01 wt % NaC1. Ssfor the 70/30 systems of (P0)dMA and (PO)6.5/ MA are 0.51 f 0.01 wt % NaCl and 0.49 f 0.01 wt % NaC1, respectively. The optimum solubilization parameters for the EO, species show the same complexity that was noted for PCE (see Figure 3). There is asteady increase in the u*'s of the 50/50 mixtures with a maximum at EO6 and a minimum at EO8 superimposed on the trend. This is due to the complex relationship between the increasing salinity reducing u* with the increasing structural length increasing u*. Increasing the GuerbetlMA ratio to 70/30 results in an increase of the solubilization parameter by only Environ. Sci. Technol., VoI. 28, No. 7, 1994
1363
35 30 S’ Iwt.
03
i
L
1
0.2
0
15
10
0
2
6
4
8
10
EON
Figure 4. Salinity window vs EON for 50/50 systems with electrolyte and oil phase as noted at 25 OC.
approximately 10%. This is in stark contrast to the data obtained for PCE (14). Upon increasing the Guerbet/MA ratio from 50/50 to 70/30 with PCE, the solubilization parameter increases by a factor of 2-3. We presume this trend occurs due to the increased solvency of CC14 over PCE. Changing the electrolyte causes an increase in u* as is similar to that seen earlier for PCE (14). The salinity windows of the systems show a great deal of complexity also, but decrease overall as more EO is added (see Figure 4 ) (15). Trichloroethylene (TCE). Figure 2 displays the S* data for 50/50 mixtures of EOJMA systems. No 70/30 data could be acquired for TCE, due to AS going to zero as the amount of the EO surfactant was increased. In general, the data shows an increase in S* as EON increases. This increase is less than the overall increase in S* seen with Cc4. But, once again, the rate of change is the same as that for the 50/50mixtures with PCE and cc4. The slope of the TCE data was found to be 0.04. The data for TCE are found at lower salinities than either PCE or CCb, indicating an increase in polarity by changing the oil phase to TCE. The spacing between CC14 and TCE is greater than that found between C c 4 and PCE, indicating that PCE and CC14 are closer in polarity than CCl4 and TCE. The optimum solubilization parameters again show the complexity seen in all previous oils (Figure 3). There is an overall increase in u* as EON increases. A maximum lies at EO6, while a minimum is at EOs. The salinity windows show a decrease with increasing EON as is expected (Figure 4). 1,2-Dichlorobenzene (DCB). Only two surfactant systems produced Type I11phase behavior with DCB at room temperature. 50/50 mixtures with EO6/MA and EO$MA resulted in middle phases (see Figure 2). The EOo/MA surfactant system did not produce a stable aqueous-phase microemulsion at room temperature, the E02/MA and E04/MA systems produced liquid crystals at room temperature, and the EOto/MA system produced a precipitated surfactant. These data are plotted in Figure 2. The slope of this line is found to be 0.041, once again comparing favorably with those of the other oils studied here. The data points are found in between those of CC14 and TCE, indicating the increased polarity of DCB over ccl4. The optimum solubilization parameter data shows a decrease in going from EO6to EO8 (see Figure 3). One can only assume that the entire curve would mimic those for the previously discussed oils, if the data could be obtained. 1364 Environ. Scl. Technol., Vol. 28, No. 7, 1994
04
05
06 07 OB Mole Fraction of Guerbet
09
1
Figure 5. Optimum salinity and optimum solubilization parameter vs Guerbet mole fraction at 25 OC, with NaCl as electrolyte. (0)S” (0) S‘ (E0)2.8; (0) S’ (EOh.6. (0)a’ (EOk; u* (E0h.e; (e)r e (EOh.6.
The salinity windows generally decreasedwith increasing EON as is expected (see Figure 4). Placing the systems in a 40 OC temperature bath led to the EOdMA system producing a middle-phase system: S* = 1.63 w t % NaC1, u* = 10.4 mL/g, and A S = 0.14 wt % NaC1. No changes in the other systems were detected at this elevated temperature. C I ~ E X ( E O ) ~ S O ~ N ~ and / M AC14GA(EO)304Na/ MA Systems. Only CC4 formed classical phase behavior, due to the salinity window approaching zero with TCE and DCB. In Figure 5, one notices that S* increases as EON increases and decreases as more of the C14 species is added. This is similar to that seen with the cl6 species and with PCE. For E04, S* is 2.5 wt % . The E02.9 and EOl.6 species have slopes that are the same due to the fact that they both are Guerbet alcohol derivatives, while the EO4 species is an EXXAL (EX) derivative. As expected, there is an increase in u* as EON increases and as the amount of c14 is increased. The EO4 species has a u* = 12.4 mL/g. Again, one notices the data for the EOz.9 and EO1.6 species have equivalent slopes, while the slope of the EO4species is different, due to the difference in structure of the hydrophobic end of the molecule. AS decreases with increasing EON, as expected. For EO4, AS = 0.2 wt %. Phase Behavior with “Nonclassical” Chlorocarbons. All the other oils originally envisaged for this study (CHZC12, CHC13, 1,2-CzH4Clz,and 1,1,2,2-CzHzCl4) only produced Winsor Type I1 systems. Winsor Type I and Type 111 systems were not produced with these oils due to their inability to form stable aqueous or middlephase microemulsionswith these surfactant systems. Since Winsor Type I systems are of interest for solubilization mechanisms and Type I11 systems are of interest for sufficient lowering of interfacial tension for mobilization of DNAPLs, these systems are preferred. Microemulsion systems that will produce Winsor Type I and I11 systems will require extremely hydrophilic surfactants, such as those reported recently (30). Current studies in our laboratory show that these oils will show classical phasebehavior studies with a new class of surfactants being prepared in-house. We believe that the large behavioral range of the various oils (from no microemulsion formation to S*’s mimicking those of hydrocarbons) is due to the wide range of polarities
of the DNAPLs. The less polar the DNAPL, the more the system appears to follow classical Winsor-type phase behavior. A correlation between the polarities of the solvents and the phase behavior is presently under investigation in our laboratory. That study will contain a mixing rule for chlorocarbons, wherein we will be able to predict the properties of the intractable species of this study. Conclusions
The less polar chlorocarbons in this study ( C c 4 and TCE) produced classical Winsor-type phase behavior with the anionic surfactants studied, much like the previous study on PCE. As the oil phase becomes more polar in going from PCE to CC14 to TCE, optimum salinities decrease and optimum solubilization parameters increase. The relative change in optimum salinity over the EO range studied was found to be the same for all three of these oils. The plotting of these data on a log S*vs EON graph shows the lines for all three oils to be parallel, with an average slope of 0.042 for the 50/50 mixtures and 0.083 for the 70/3Qmixtures. The spacing between the lines is indicative of the difference in the polarities of the three oils. The lines remain parallel (although their slopes increase) as you increase the amount of ethoxylated Guerbet surfactant in the system. The spacing remains constant as you increase the amount of ethoxylated Guerbet surfactant present in the system. In general, we were unable to achieve extremelylow optimum salinities (4wt 76 NaC1) due to the salinity window going to zero for these systems. The more polar species demonstrated nonclassical phase behavior. Except for a few DCB systems, all the more polar chlorocarbons mentioned earlier produced only Winsor Type I1 systems. Since we were least interested in Type I1 systems as they can be near infinite sinks for the surfactant, further work with these pure oils combined with anionic surfactants was stopped. From the point of view of toxic spill remediation, we have now identified anionic surfactants which greatly enhance the solubility of C2C14, CC4, CZHCl3, and CeH4Clz in water in the presence of significant concentrations of sodium and calcium ion. Acknowledgments
The authors thank the U.S. EPA Kerr Environmental Research Laboratory for Grant CR-818647-01 and the State of Texas’ Advanced Technology Program for Grant 379. Although the research described in this article has been supported by the US. Environmental Protection Agency (through CR-818647-01) and has not been subjected to the Agency’s administrative review, it does not necessarily reflect the views of the Agency, and no official endorsement should be inferred. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. All research projects funded by the U.S.Environmental Protection Agency that make conclusions or recommendations based on environmentally related measurements are required to participate in the Agency Quality Assurance Program. This project was conducted under an approval Quality Assurance Project Plan, and the procedures therein specified were used. Information on the plan and documentation of the quality assurance activities and results are available from the Principal Investigator.
Literature Cited West, C. C.; Harwell, J. H. Surfactants and Subsurface Remediation. Enuiron. Sci. Technol. 1992, 26 (12),2324. Fountain, J. C. Field Test of Surfactant Flooding: Mobility Controlof Dense Non-AqueousPhase Liquids.In Transport and Remediation of Subsurface Contaminants; Sabatini, D. A., Knox, R. C., Eds.; American Chemical Society Symposium Series 491;ACS: Washington, DC, 1992. Kueper, B. H.; Redman, R. C.; Reitsma Starr, S.; Mah, M. A Field Experiment to Study the Behavior of Tetrachloroethylene Belowthe Water Table: Spatial Distribution of Residual and Pooled DNAPL. Ground Water 1993,31 (5), 756. Nash, J. H. Field Studies of In-Situ Soil Washing;EPA/ 600/2-87/110; U.S. Environmental Protection Agency: Cincinnati, OH, 1987. Abdul, A. S.;Gibson,T. L. Enuiron. Sci. Technol. 1991,25, 665-671. Harwell,J. H. In Transport and Remediation of Subsurface Contaminants; Sabatini, D. A., Knox, R. C., Eds.; ACS Symposium Series 491;American Chemical Society: Washington, DC, 1992;pp 124-132. A comprehensive review of this work can be found in: Bourrel, M.; Schechter, R. S. Microemulsions and Related Systems; Marcel Dekker, Inc.: New York, 1988; Vol. 30, Surfactant Science Series, Chapters 4-6. Huh, C. Interfacial Tensions and Solubilizing Ability of a MicroemulsionPhase that Co-existswith Oil and Brine. J. Colloid Interface Sci. 1979, 71, 408. Israelachvili, J. Physical Principles of Surfactant SelfAssociation into Micelles, Bilayers, Vesicles and Microemulsion Drops. In Surfactants in Solution; Mittal, K. L., Bothorel, P., Eds.; Plenum Press: New York, 1986;Vol. 4, P 3. Sunwoo, C.; Wade, W. H. Optimal Surfactant Structures for Cosurfactant-Free Microemulsion Systems I. C I and ~ C14 Guerbet Alcohol Hydrophobes. J. Dispersion Sci. Technol. 1992, 13, 491. Lalanne-Cassou, C.; Schechter, R. S.; Wade, W. H. Microemulsion Formation with Alkyl Vinylidene Sulfonates. ?’repr.-Am. Chem. SOC.,Diu. Pet. Chem. 1984,29, 1187; J.Dispersion Sci. Technol. 1986, 7 (4),479. Schechter, R. S.;Wade, W. H.; Weerasooriya, U.; Weerasooriya, V.; Yiv, S. Synthesis and Performance of IsomerFree SecondaryAlkane SulfonateSurfactants. J.Dispersion Sci. Technol. 1985, 6 (2))223. Abe, M.; Schechter, R. S.; Selliah, R. D.; Sheikh, B.; Wade, W. H. Phase Behavior of Branched Tail Ethoxylated Carboxylate Surfactant/Electrolyte/Alkane Systems. J. Dispersion Sci. Technol. 1987, 8, 157. Baran, J. R., Jr.; Pope, G. A.; Wade, W. H.; Weerasooriya, V. Phase Behavior Studies of Water/Perchloroethylene/ Anionic Surfactant System. Langmuir, in press. Cash, R. L.; Cayias, J. L.; Fournier, G. R.; Jacobson, J. K.; LeGear, C. A.; Schares, T.; Schechter, R. S.; Wade, W. H. Low Interfacial Tension Variables. SOC.Pet. Eng. J. 1977, 17, 122. Salager, J. L.; Vasquez, E.; Morgan, J.C.; Schechter, R. S.; Wade, W. H. Optimum Formulation of Surfactant-OilWater Systems for Minimum Interfacial Tension or Phase Behavior. Soc.Pet. Eng. J. 1979, 19, 107. Vasquez, E.; Salager, J. L.; El-Emary, M.; Koukounis, C.; Schechter,R. S.;Wade, W. H. Interfacial Tension and Phase Behavior of Pure Surfactant Systems. Solution Chem. Surfactants 1979, 2, 801. Salager, J. L.; Bourrel, M.; Schechter, R. S.; Wade, W. H. Mixing Rules for Optimum Phase Behavior Formulations of Surfactant/Oil/Water Systems. SOC.Pet. Eng. J. 1979, 19, 271. Graciaa, A.; Schechter, R. S.; Wade, W. H.; Yiv, S. H.; Barakat, Y. Emulsion Stability and Phase Behavior for Ethoxylated Nonyl Phenol Surfactants. J.Colloidlnterface sci. 1982, 89, 217. Graciaa, A.; Fortnoy, L.; Schechter, R. S.; Wade, W. H.; Environ. Sci. Technol., Voi. 28, No. 7, 1994
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Yiv, S. Criteria for Structuring Surfactants to Maximize Solubilization of Oil and Water I: Commercial Nonionics. Soc. Pet. Eng. J. 1982, 22, 743. (21) Barakat, Y.; Fortney, L. N.; Schechter, R. S.; Wade, W. H.; Yiv S. H. Criteria for Structuring Surfactants to Maximize Solubilization of Oil and Water II: Alkyl Benzene Sodium Sulfonates. J. Colloid Interface Sci. 1983, 92 (2), 561. (22) Abe, M.; Schechter, D.; Schechter , R. S.; Wade, W. H.; Weerasooriya, U.; Yiv, S. Microemulsion Formation with Branched Tail Polyoxyethylene Sulfonate Surfactants. J. Colloid Interface Sci. 1986, 114 (2), 343. (23) Lalanne-Cassou, C.; Carmona, I.; Fortney, L.; Samii, A.;
Schechter, R. S.; Wade, W. H.; Weerasooriya, U.; Weerasooriya, V.; Yiv, S. Minimizing Cosolvent Requirements for Microemulsion Formed with Binary Surfactant Mixtures. J. Dispersion Sci. Technol. 1987, 8 (2), 137. (24) Healy, R. N.; Reed, R. L. Immisicible Microemulsion Flooding. Soc. Pet. Eng. J. 1977, 17, 129. (25) Healy, R. N.; Reed, R. L. Multiphase Microemulsion Systems. Soc. Pet. Eng. J. 1976, 16, 147.
1366 Environ. Sci. Technol., Vol. 28, No. 7, 1994
(26) Puerto, M. C.; Reed, R. L. A Three-Parameter Representation of Surfactant-Oil-Brine Interaction. SOC.Pet. Eng. J. 1982, 23, 669. (27) Salter, S. J. The Influence of Type and Amount of Alcohol
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Received for review December 9, 1993. Revised manuscript received March 28, 1994. Accepted April 8, 1994."
Abstract published in Advance ACS Abstracts, May 15, 1994.
