588
Langmuir 1996, 12, 588-590
Aqueous Phase Microemulsions Employing N-Methyl-N-D-glucalkanamide Surfactants with Chlorinated Hydrocarbons Eliana Arenas,† Jimmie R. Baran, Jr.,† Gary A. Pope,‡ William H. Wade,*,† and Vinitha Weerasooriya† Departments of Chemistry and Petroleum Engineering, The University of Texas, Austin, Texas 78712 Received May 10, 1995. In Final Form: July 31, 1995
Figure 1. Structures of a linear N-methyl-N-D-glucalkanamide (R ) C7-C10 and C12) (left) and a branched N-methyl-N-D-gluca2-butyloctanamide (right).
Introduction Recently, our laboratory has turned its attention to the application of the knowledge gained about surfactants for enhanced oil recovery (EOR) to the development of surfactants for enhanced aquifer remediation (SEAR).1-5 We have found that anionic surfactants are successful in aiding in the pump and treat method of remediation by enhancing the solubilization of contaminants in aquifers. One of the major contaminants of aquifers is chlorocarbons. These chlorinated hydrocarbons or DNAPLs (dense nonaqueous phase liquids) are excellent solvents for surfactants. This combined with the fact that aquifer temperatures are generally 25 °C or lower, has made it difficult to identify surfactants suitable for forming water continuous microemulsions. We have succeeded in finding anionic surfactants that, during salinity scans, produce classical Winsor I S III S II phase behavior with tetrachloroethylene (PCE), carbon tetrachloride, and trichloroethylene (TCE).1-3 But, we have also identified a list of six other commonly used chlorocarbons that failed to produce Winsor type III phase behavior with these or any other anionic surfactants.3,5 We have also failed to identify any anionic surfactant that will function without electrolyte. In the recent patent literature, Proctor and Gamble teaches of the synthesis of glucamine-based surfactants6 (see Figure 1), wherein an amide linkage is formed between methylglucamine and a variety of carboxylic acids. The reaction goes with high yield and little or no side reactions. Since these surfactants are extremely hydrophilic they were thought to be good candidates for formation of chlorocarbon-in-water microemulsions. The linear C7C10 and C12 acyl analogues from the patent6 were synthesized as well as a branched C12 species, derived from the Guerbet carboxylic acid starting material, based on previous studies showing that Guerbet tail branching can be advantageous.7 Various combinations of these surfactants succeeded in producing Winsor type I and Winsor type III behavior at room temperature with all the chlorinated hydrocarbons on the previous list,3,5 as well as producing this behavior with little or no added electrolyte. Several were successfully subjected to Winsor I S III S II phase transitions, † ‡
Department of Chemistry. Department of Petroleum Engineering.
(1) Baran, J. R., Jr.; Pope, G. A.; Wade,W. H.; Weerasooriya, V. Langmuir 1994, 10, 1146. (2) Baran, J. R., Jr.; Pope, G. A.; Wade,W. H.; Weerasooriya,V.; Yapa, A. Environ. Sci. Technol. 1994, 28, 1361. (3) Baran, J. R., Jr.; Pope, G. A.; Wade,W. H.; Weerasooriya, V.; Yapa, A. J. Colloid Interface Sci. 1994, 168, 67. (4) Baran, J. R., Jr.; Pope, G. A.; Schultz, C.; Wade,W. H.; Weerasooriya, V. Submitted for publication. (5) Baran, J. R., Jr.; Pope, G. A.; Schultz, C.; Wade,W. H.; Weerasooriya, V.; Yapa, A. Submitted for publication. (6) Connor, D. S.; Scheibel, J. J.; Kao, J.-N. U.S. Patent 5,338,487, 1994. (7) Sunwoo, C.; Wade, W. H. J. Dispersion Sci. Technol. 1992, 13, 491.
0743-7463/96/2412-0588$12.00/0
but this will be the subject of an upcoming publication. This report will focus on aqueous phase (type I) microemulsions near the I/III transition. In particular, surfactant formulations which produce type I systems at 0 and 0.1 wt % NaCl but give type III systems at 0.5 wt % NaCl are discussed. Experimental Section 1H-
13C-NMR
and spectra were run on a General Electric QE300 FT-NMR. Low-resolution chemical ionization mass spectra were run on a Finnigan TSQ-70 spectrometer, using methane as the reagent gas. High-resolution chemical ionization mass spectra were run on a Fisons VG-ZAB spectrometer, using methane as the reagent gas. Chemicals. The aqueous phase as constituted contained just surfactant or surfactant and NaCl at 0.10 or 0.50 wt % in distilled H2O. The nonaqueous phases used were perchloroethylene (PCE), 1,2-C6H4Cl2 (DCB), and 1,1,1-C2H3Cl3 (TCA) (Aldrich), CH2Cl2, CHCl3, and CCl4 (EM Science), trichloroethylene (TCE) (Fisher), 1,2-C2H4Cl2 (MCB Manufacturing), and 1,1,2,2-C2H2Cl4 (Eastman) and were obtained as reagent grade and used without further purification. The linear N-methyl-N-D-glucalkanamide surfactants were synthesized by reacting the methyl ester of the carboxylic acid with methylglucamine in the presence of sodium carbonate.6 An example of this method is described below for N-methyl-N-Dglucanonanamide. Synthesis of N-Methyl-N-D-glucanonanamide. In a threeneck 100 mL round bottom flask, equipped with a mechanical stirrer, a distillation head, and a N2 inlet, 58.5 g (0.3 mol) of N-methyl-D-glucamine (MEG, Aldrich), 51.6 g (0.3 mol) of methyl nonanoate and 47.0 g of Na2CO3 (Fisher, 30% by total weight of the reactants) were mixed. The reaction flask was then heated to 150 °C with an oil bath. The reaction was considered complete when no further methanol was distilled out of the system (approximately 2 h). The reaction mixture was removed from the oil bath and allowed to cool to room temperature. The solid that was formed dissolved in CH2Cl2, and the solution was then neutralized with formic acid. The cloudy solution was warmed and filtered through a fine glass frit. The filtrate was cooled, and a white solid formed. The solid was removed via filtration and dried in a vacuum oven overnight. The solid was then recrystallized from CH2Cl2 to yield 60.0 g (57%) of N-methylN-D-glucanonanamide (mp 86-88 °C). The Guerbet-branched surfactants could not be produced by this method, and an alternate synthetic route via the acid chloride was undertaken. The synthesis of N-methyl-N-D-gluca-2-butyloctanamide is given below. 2-Butyloctanoyl Chloride. In a three-neck 500 mL round bottom flask equipped with a mechanical stirrer, a N2 inlet, and a cooling condenser 30.0 g (0.15 mol) of Isofol12 acid (2butyloctanoic acid, Condea, Inc.) was mixed with 50.0 g (0.42 mol) of thionyl chloride (Aldrich) and refluxed at 85 °C for 1 h. The contents were quickly transferred to a one-neck flask, and the excess thionyl chloride was removed via distillation. A quantitative yield of 32.8 g of the product was recovered. The product was identified by 1H- and 13C-NMR and used without further purification. N-Methyl-N-D-gluca-2-butyloctanamide. In a three-neck 500 mL round bottom flask equipped with a mechanical stirrer
© 1996 American Chemical Society
Notes
Langmuir, Vol. 12, No. 2, 1996 589 Table 1. Surfactant System Compositions
chlorocarbon
EACN3,5
surfactant mixturea
PCE CCl4 TCA TCE 1,2-DCB 1,2-DCE CHCl3 CH2Cl2 1,1,2,2-TCE
2.9 -0.06 -2.5 -3.8 -4.9 -12.1 -13.7 -13.8 -22.2
A12G/A9 (3/2) A12G/A9 (42/58) A12G/A9 (34/66) A12G/A9 (1/3) A12G/A9 (27/73) A12G/A9 (1/4) (4%) A9/A7 (1/4) (4%) A9 A9/A7 (1/9) (8%)
a Surfactant concentration is 2 wt % of the aqueous phase, unless otherwise noted. The numbers in parentheses are weight ratios.
and a dropping funnel, 9.8 g (0.05 mol) of MEG was dissolved in 50 mL of 5% NaCl solution. The mixture was cooled to 0 °C, and 10.9 g (0.05 mol) of 2-butyloctanoyl chloride (from above) was slowly added to the stirred solution. After 10 min 50 mL of 1 N NaOH was added to neutralize the HCl produced in the reaction. The mixture was stirred for 2 h at 0 °C and then filtered. The filter cake was washed several times with cold water, and the white solid was then dried in a vacuum oven overnight. The solid was then recrystallized from CH2Cl2 to yield 10.0 g (53%) of N-methyl-N-D-gluca-2-butyloctanamide (mp 106-108 °C). 1H-NMR (CDCl , ppm): 0.87 (t, 3H), 0.89 (t, 3H), 1.25 (m, 3 12H), 1.44 (m, 2H), 1.57 (m, 2H), 1.77 (s, 5H), 2.66 (m, 1H), 3.15 (s, 3H), 3.65 (m, 8H). 13C-NMR (CDCl3, ppm): 13.82, 13.92, 22.49, 22.71, 27.40, 29.32, 29.59, 31.58, 32.42, 32.75, 37.57, 41.45, 51.76, 63.70, 69.76, 71.53, 72.28, 72.83, 178.74. MS (CI) (m/e): 378 (100), 362 (6.05), 298 (3.01), 256 (6.82), 154 (10.46). HRMS (CI): mass calculated, 378.285563; mass found, 378.285457. Formulation of Equilibrium Microemulsion Systems. Equal volumes (2 cm3) of aqueous and nonaqueous phases (WOR ) 1) were placed in calibrated pipettes. 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 overnight to several days. Equilibration was done at 25 °C. In all studies total surfactant concentration was constant at 2 wt % of the aqueous phase, unless otherwise noted.
Results and Discussion As noted earlier, we have chosen to address those systems that produce a Winsor type I system at 0% and 0.10% NaCl and a Winsor type III system at 0.50% NaCl. The surfactant system compositions identified for each of the chlorocarbons studied are summarized in Table 1. The notation used in Table 1 is defined so that A refers to the surfactant being a glucamine followed by a number, which represents the length of the acyl chain as shown in Figure 1. Therefore, the abbreviation A9 represents N-methylN-D-glucanonanamide, while A12 represents N-methylN-D-glucadodecanamide. The A12G denotes the N-methylN-D-gluca-2-butyloctanamide. In Table 1, the surfactant compositions are given for the entire spectrum of chlorocarbons studied. In addition, the equivalent alkane carbon numbers (EACN) are shown.3,5 EACN began as a scheme for classifying alkanes by their number of carbon atoms, and techniques were developed to assign equivalent numbers to other types of hydrocarbons. It is possible to assign EACNs to any fluid that is immiscible in water. The arrangement in Table 1 is in the order of increasing negative EACN values which is synonymous with increasing solvency. Table 2 contains the solubilization parameter, σ, at the three salinities for the corresponding surfactant solutions from Table 1. The solubilization parameter for a type I system is defined as the volume of oil dissolved in water divided by the weight of surfactant (cm3/g). For a type III system, there are two solubilization parameters, σo and σw. σo is defined as the volume of oil dissolved in the middle phase divided by the weight of surfactant. σw is
Figure 2. Mole fraction for A12G versus EACN from ref 3 for various chlorocarbons. Table 2. Solubilization Parameters for the Systems in Table 1 chlorocarbon
σ0% (cm3/g)
σ0.1% (cm3/g)
σo,0.5% (cm3/g)
σw,0.5% (cm3/g)
PCE CCl4 TCA TCE 1,2-DCB 1,2-DCE CHCl3 CH2Cl2 1,1,2,2-TCE
1.25 2.00 2.25 3.50 0.50 0.25 1.00 2.50 0.63
1.00 0.75 1.00 3.50 1.00 0.25 1.13 2.50 0.63
1.75 1.50 1.50 3.00 2.25 0.50 1.25 2.75 0.63
0.75 4.25 4.25 4.00 3.00 1.38 1.75 2.50 0.75
defined as the volume of water dissolved in the middle phase divided by the weight of surfactant. It was expected that the solubilization parameters would be small, since we had shown earlier with sulfosuccinates that short hydrophobes produce small solubilization parameters.1-3 Generally, it has been noted that as one approaches the type III region of a system, the solubilization parameter increases.2 In the present systems that is true also, except when going from 0% to 0.1% NaCl. In comparing these two values, one notes that the solubilization parameter shows no definite trend. There is no apparent explanation for this anomaly, except that operating at 0% NaCl is new territory and may not be governed by the same rules that apply to systems containing an electrolyte. Similar to anionic systems, an equation used to predict the behavior of nonionic systems has been elucidated for alkylphenol ethoxylates.8,9 With HLBMIX as the dependent variable,
HLBMIX ) a - k(EACN) + f[A] + b[S] + c(T - 28 °C) (1) where a, k, f, b, and c are constants whose values differ depending on whether one is interested in the type I/III boundary, the optimal system, or the type III/II boundary.8 The HLB of a mixture of two surfactants having different HLBs is given by
HLBMIX ) X1HLB1 + X2HLB2
(2)
or (8) Graciaa, A.; Barakat, Y.; Schechter, R. S.; Wade, W. H.; Yiv, S. J. Colloid Interface Sci. 1982, 89, 217. (9) Bourrel, M.; Salager, J. L.; Schechter, R. S.; Wade, W. H. J. Colloid Interface Sci. 1980, 75, 451.
590
Langmuir, Vol. 12, No. 2, 1996
HLBMIX ) HLB2 + X1(HLB1 - HLB2)
Notes
(3)
where X1 and X2 are the mole fractions of surfactants 1 and 2, respectively.8 Even though it is not possible to assign an HLB value to each of these surfactants, one can see from eq 3 that the HLBMIX value should be a linear function of the mole fraction. This permits a linear relationship to be developed between HLBMIX and (EACN) by combining (3) with (1).8,9 A plot of surfactant mole fraction versus the EACN of the oil phase was constructed to check the validity of these equations. This is shown in Figure 2. Obviously, the relationship is not linear, and we are currently exploring the validity of (1) for the class of surfactants used here. Nevertheless, in Table 1, one notes that as the EACN decreases, the weight fraction of A12G decreases and that of A9 increases. Since the HLB of
A12G is undoubtedly greater than that of A9, both because of the larger number of carbon atoms in A12G and the branching of A12G,10 then the HLBMIX is decreasing with decreasing EACN as qualitatively expected. In summary, we have finally identified a class of nonionic surfactants that will produce aqueous phase microemulsions with no electrolyte and Winsor III middle phase microemulsions. Acknowledgment. We wish to thank the State of Texas’s Advanced Technology Program for Grant 379 and Condea, Inc. for chemical samples. LA950360D (10) Graciaa, A.; Barakat, Y.; El-Emary, M.; Fortney, L.; Schechter, R. S.; Wade, W. H.; Yiv, S. J. Colloid Interface Sci. 1982, 89, 209.
