Acid-Neutralizing of Marine Cylinder Lubricants: Effects of Nonionic

marine cylinder lubricants (MCLs) formulated with an overbased sulfonate and a series of different .... deformation could be observed at the boundary ...
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Acid-Neutralizing of Marine Cylinder Lubricants: Effects of Nonionic Surfactants Rong C. Wu,† Curt B. Campbell,‡ and Kyriakos D. Papadopoulos*,† Department of Chemical Engineering, Tulane University, New Orleans, Louisiana 70118, and Chevron Chemical Company, Oronite Global Technology, 100 Chevron Way, Richmond, California 94802

The neutralization reaction between a concentrated sulfuric acid droplet and a series of model marine cylinder lubricants (MCLs) formulated with an overbased sulfonate and a series of different nonionic surfactants was studied using a capillary video-microscope technique at room temperature and a phase transfer neutralization rate test at several temperatures up to 55 °C. The model MCLs were characterized using dynamic light scattering and transmission electron microscopy. On the basis of the observations, a mechanism is proposed for the neutralization reaction which involves the initial formation of a mixed reverse micelle system between the overbased sulfonate and the nonionic surfactant followed by the neutralization reaction at the aqueous acid/oil interface to form calcium sulfate crystals. The rate of the neutralization reaction is enhanced by the presence of the nonionic surfactants in the model MCLs and is consistent with the formation of the mixed micelle systems which makes the basic core (CaCO3/Ca(OH)2) of the overbased sulfonate more accessible to the aqueous acid due to the increased size and flexibility of the overbased sulfonate reverse micelle. Introduction Marine crosshead diesel engines (Figure 1) operate on fuel oil containing high levels of sulfur (2-5%).1 A consequence of sulfur in fuels is that, upon combustion, corrosive acids, mainly sulfuric, are formed2 which can attack the metal surfaces in the combustion chamber leading to corrosive wear of the cylinder liners and/or piston rings. The piston and cylinders in crosshead engines are lubricated by an injection system which provides lubricant through the cylinder liner during each piston stroke such that the lubricant is only used once.1 The lubricants used in crosshead engines are of the general class called marine cylinder lubricants (MCLs), and one of their most important functions is to neutralize the acids formed during combustion and thus help prevent corrosive wear.3 The corrosive-wear problem in crosshead engines is particularly important, and over the years, a large number of studies have been reported on various aspects of this problem ranging from the mechanism of sulfuric acid formation and metal corrosion4 to means of controlling corrosive wear.5 Commercial MCLs are typically formulated with overbased detergent additives, and it is these detergent additives which provide a source of oil-soluble base to neutralize the acids formed during combustion. To date, the most effective commercially viable means of controlling corrosive wear in crosshead diesel engines is to use MCLs containing very high-treat levels of detergent additives.6 Improving the ability of MCLs to effectively neutralize encroaching acid in the lubrication layer is hence very important to MCLs quality.3,7,8 The overbased detergents used to formulate MCLs are normally group-II metal (usually calcium or magnesium) organometallic colloid complexes, most notably sulfonates, salicylates, and phenates. When these com* Corresponding author. E-mail: [email protected]. † Tulane University. ‡ Chevron Chemical Co.

Figure 1. Cylinder lubricant system in marine diesel engine.

plexes contain a large excess of base, they are commonly referred to as overbased detergents. The generally accepted structure of these overbased sulfonates and salicylates is that of reverse micelles,7,9-12 with a mixed metal hydroxide/carbonate core stabilized by an outer alkyl-aryl shell which makes the detergent oil soluble. The overbased phenates appear to have a polymeric structure.13,14 The surfactants used in detergent sulfonates are alkylaromatic sulfonic acids while in detergent salicylates they are alkylsalicylic acids, and for detergent phenates they are both sulfurized and nonsulfurized alkylphenols. The calcium carbonate core of a typical overbased sulfonate reverse micelle has a diameter of between 4 and 14 nm and, together with the stabilizing surfactant layer, an overall diameter of between 8 and 18 nm.15 Overbased sulfonates may also contain between 5 and 15 wt % of metal non-carbonate

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(mainly hydroxylic) base, which surrounds the carbonate core.14,16 Unlike commonly studied reverse micelles, which are dynamic structures and have very short relaxation times,17 the surrounding alkyl-aryl sulfonyl groups in overbased sulfonates are tightly bonded chemically to the mineral core, which causes the micelles to remain stable even after being separated from their original medium and redispersed in model solvent systems.10,11 The basicity of an additive or an oil is expressed in terms of the total base number (TBN), which is defined as the milligrams of KOH that have the equivalent acid-neutralizing ability as that of the base present in 1 g of the sample. The addition of nonionic surfactants to lubricating oils has been reported to modify the properties of lubrication oils,18 and there are some studies of the use of nonionic surfactants in lubricants to accelerate their acid neutralization.19 Several researches have shown that the solution properties of micelle systems change by introducing some nonionic surfactants to an anionic or cationic surfactant micellar system.20,21 In these mixed surfactant systems, two kinds of micelles may coexist (one rich in anionic/cationic surfactant and the other rich in nonionic surfactant). In a study on the mixed surfactant system with poly(oxyethylene) (POE) nonionic surfactants, it has been reported that the mixed micelles form more easily when a long alkyl chain and/ or a short POE chain are present in nonionic surfactant.20 The effective solubilization volume in the mixed micelles was found to be larger than that of the pure surfactant micelles, due to the increase in the radius of the mixed micelles.21 Solubilization capacity of water in cationic/anionic mixed reverse micellar systems has also been found to increase significantly with the presence of nonionic surfactants.22 In a previous study we reported on the use of our capillary video-microscopy technique to rank MCL.23 We proposed that the neutralization reaction occurs in the basic core of the overbased reverse micelles and that the “solubilization” of acid and water by the reverse micelles could be an important step in the neutralization reaction. In this paper, a model MCL was made with a commercial overbased sulfonate, and nonionic surfactants were added to form a mixed surfactant system. Direct visualization, together with particle size analysis, allows us to determine the most likely mechanism of acid neutralization, elucidating the special role of nonionic surfactants. Materials and Methods Materials. The detergent used was a commercial overbased calcium carbonate alkylbenzenesulfonate (C20-24C6H5 based) provided by Chevron Chemical Co., Oronite Additives Division, with a TBN value of 325 and Ca and S weight percents of 12.9 and 1.9, respectively. The UCON and Plurafac nonionic surfactants were obtained from Union Carbide Corp. and BASF Corp., respectively. Their basic structure and MW are shown in Table 1. The overbased sulfonate was dissolved in dodecane (anhydrous, 99+%, Aldrich Inc.) to produce the model oil with a TBN of about 75. To eliminate solid particles the model oil was purified initially by centrifugation at 5000 rpm and subsequently by filtration through syringe filters (Gelman acrodisc, HT Tuffryn, 0.2 µm pore size). The final TBN of the purified model oil was determined titrametrically using the ASTM D-2896 method by Chevron. Sulfuric acid was obtained

Table 1. Nonionic Surfactants Used in the Study nonionic surfactant

chem structure

MW

Plurafac LF-1200 Plurafac LF-3140 Plurafac LF-4030 Plurafac LF-7000 UCON LB-65

alkoxylated alcohol alkoxylated alcohol alkoxylated alcohol alkoxylated alcohol polyalkylene glycol [(C4H9)(OCH2CH(CH3))xOH] polyalkylene glycol polyalkylene glycol polyalkylene glycol polyalkylene glycol

470 570 560 920 340

UCON LB-165 UCON LB-385 UCON LB-625 UCON LB-1715

740 1200 1550 2490

Figure 2. Static phase-transfer acid neutralization experiments.

with a concentration of 98 wt % from Aldrich, Inc., and was diluted to produce a 9.4 mol/L stock solution. Water was deionized and ultrafiltered by means of a Barnstead E-pure system. Microcapillaries and micropipets were pulled from Microcaps (Drummond Scientific) using a Narashige PB-7 puller. Methods. The capillary video-microscopy technique for studying the neutralization reaction is the same as described in detail elsewhere.23,24 A specially pulled micropipet (i.d. 30-40 µm) was used to inject a sulfuric acid droplet into the model oil-filled microcapillary with an inner diameter of 80-100 µm. The fate of the droplet and the surrounding oil phase were monitored visually. To successfully produce an acid droplet, which did not wet and spread on the wall of an oil-filled capillary, both the internal wall of the microcapillary and the external surface of the injection micropipet were hydrophobically treated.24 The microscopic experiments were carried out at ambient temperature. To assess the effects of nonionic surfactants at high temperatures, a simple static phase-transfer acid neutralizing experimental method was designed, as shown in Figure 2. Higher temperature was achieved and controlled by a water bath. Sulfuric acid (10 mL), with pH around 2.0, and 2 mL of model lubricant were separately preheated in the water bath before introduction into a preheated 20 mL vial. After careful addition of the oil phase to the acid phase and with care not to mix the two phases, the time-dependent pH in the aqueous bulk phase was measured by means of a pH electrode (Orion Ross 8103) and recorded by a pH meter (Orion 720 A). The amount of base in the oil phase was excessively more than the amount of sulfuric acid in the water phase. Special care was taken to make sure that the pH electrode was in the same depth in all experiments. Dynamic light scattering was carried out using a BI-200SM Goniometer (Brookhaven Instruments Corp., Holtsville, NY). A BI-9000 correlator (Brookhaven Instruments Corp., Holtsville, NY) was used to process the signal. TEM measurements were performed by a Chevron laboratory. Results and Discussions Neutralization Rate Test. Visualization experiments were performed by injecting a sulfuric acid

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Figure 3. Neutralization reaction in HOB sulfonate model lubricant containing 1.5 wt % UCON LB-65 (50 vol % sulfuric acid droplet in oil): (a) 0 min; (b) 2 min; (c) 10 min; (d) 16 min; (e) 20 min. Table 2. Model Oil Neutralization Ability Measurement model oil E1 E2 E3 E4 E5 E6 E7 E8 E9 E10

nonionic surfactant (2 wt %) none Plurafac LF-1200 Plurafac LF-3140 Plurafac LF-4030 Plurafac LF-7000 UCON LB-65 UCON LB-165 UCON LB-385 UCON LB-625 UCON LB-1715

time to break (min) >120 13 25 44 27 8 22 62 56 72

droplet into an oil-filled microcapillary at room temperature. Figure 3 shows what is typically observed when a sulfuric acid droplet is injected in a model MCL. Immediately after injection of acid (Figure 3a), the droplet showed a nonspherical shape, probably due to its rigidity arising from the formation of solid reaction products on the oil-acid interface. If one views the droplet as an ellipse, the semimajor axis was controlled in all experiments to ensure all droplets had the same size. A short time later (2 min; Figure 3b), a small deformation could be observed at the boundary of the droplet. At the same time, the formation of tiny needlelike crystals was observed, which were deposited on the droplet surface. The crystals are believed to be hydrated calcium sulfate, the expected product from the neutralization of sulfuric acid by the calcium carbonate (and/ or hydroxide) present in the overbased sulfonate detergent. As the reaction progressed, there were increasingly more crystals formed on the surface of the droplet, and after 10 min (Figure 3c), the droplet became very dark due to the solids covering its surface. The droplet remained stable for about 16 min (Figure 3d) and then began to break down in structure. This break-down phenomenon consisted of crystals spreading into the oil phase, with the remaining liquid of the acid droplet clinging to the crystals. After 20 min (Figure 3e), the process seemed to be complete and only well-shaped crystals could be visualized. For different model oils, this process was basically the same, but there was significant difference in the time needed for the droplet to begin to break down, which was used as a measure of the rate of neutralization ability of each model oil. Table 2 compares the break-down time for the model oils containing different nonionic surfactants. It is apparent that the presence of nonionic surfactants can significantly decrease this break-down time which we

Table 3. Effect of Nonionic Surfactant Concentration on the Rate of Neutralization in HOB Sulfonate Model Lubricant (TBN ) 74 with UCON LB-65) concn (wt %)

time to break (min)

concn (wt %)

time to break (min)

none 0.5 1.0

>60 >60 24

1.5 3.0 4.9

15 9 5

Figure 4. Intermediate phase formation at high nonionic surfactant concentration in the neutralization reaction of HOB sulfonate model lubricant containing 5 wt % UCON LB-65 (50 vol % sulfuric acid droplet in oil).

interpret as an increased rate of acid neutralization of the oils. Table 3 shows the effect of the concentration of the nonionic surfactant UCON LB-65 on the model oil’s rate of neutralization. It should be pointed out that, at high concentration of UCON LB-65, a new phase formed at the oil-acid interface immediately upon contact of the sulfuric acid drop with the model oil, as shown in Figure 4. After acid injection into the oil, a brighter “ring” was observed to form and grow around the acid droplet, which was comparable to the intermediate phase observed in similar contacting experiments on the dynamic behavior of alcohol drops in dilute solutions of an amine oxide surfactant.25 The crystals were observed to appear in this intermediate phase, and the droplet began to break up after only 5 min. The new phase here could be the product of the spontaneous emulsification of the acid drop in a mixed surfactant system. The formation and role of this phase in the neutralization reaction are not very clear at this time. Neutralization Rate Test at High Temperatures. To study the behavior of model lubricant at high temperatures, static phase-transfer acid neutralizing

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Figure 5. Effect of temperature on the rate of neutralization of the model lubricant: (a) oil E-6 at various temperatures; (b) four model oils at various temperatures.

experiments were designed which involved delicately depositing the model oil onto acid so as to avoid mixing and maintain a planar oil-acid interface. Although there must be a pH gradient in the acid phase near the interface, no such gradient was observed in the bulk acid. We also assume that the volume rate of change in the acid phase can be neglected. On the basis of these two assumptions, by measuring the time-dependent pH value in the bulk acid, we can calculate how much of the acid has been consumed at time t by the following:

reacted acid % ) (1 - 10-(pH (t) - pH (t)0))) × 100% Furthermore, we can find the half time of the acid, t1/2, when 50% of acid has been consumed from the reacted acid % vs time curve. This t1/2 can be considered as another measure of the rate of neutralization of model lubricant. Experiments were performed at four temperatures: room temperature (25 °C); 35 °C; 45 °C; 55 °C. Figure 5a shows experimental results for model oil E-6 as a function of temperature which indicate that, at higher temperature, the neutralization reaction is faster. Although the highest temperature studied here (55 °C) is much lower than the typical temperatures encountered in an actual crosshead engine (between 180 and 250 °C), it is reasonable to expect that the rate of acid

Figure 6. Measurements on size distribution of reverse micelles in HOB sulfonate model lubricant: (a) dynamic light scattering; (b) transmission electron microscopy.

neutralization will continue to increase with temperature. In Figure 5b, the time needed to have 50% acid reacted (t1/2) is compared for the four model lubricants. The t1/2 decreases with the temperature, though in a nonlinear way. It is interesting to note that the higher the temperature, the smaller the differences among different nonionic surfactants in their capacity to increase the neutralization ability of the model lubricating oil. Characterization of the Mixed Surfactant System. Changes in the size distribution of the particles in the model lubricant can be indicative of the size of the reverse micelles in the mixed surfactant system. Two techniques, dynamic light scattering (DLS) and transmission electron microscopy (TEM), were used to measure the size distribution in the model oil without nonionic surfactant. Figure 6a shows the intensity vs the diameter of particles in DLS measurements. There were two size ranges of particles present in the lubricant. One was in the range of 7-10 nm, which is believed to represent the overbased reverse micelles, while the other was in the order of 100 nm, which may be due to impurities or large calcium carbonate particles in the oil. Figure 6b shows the size distribution based

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Figure 8. Mechanism of neutralization reaction in model lubricant: (a) without nonionic surfactant; (b) with nonionic surfactant.

Figure 7. Changes in size distribution of reverse micelles in HOB sulfonate model lubricant: (a) effect of nonionic concentration (UCON LB-65, TBN ) 74); (b) effect of TBN (dilution effect, no nonionic surfactant).

on a TEM image analysis on 60 particles, and most particles were around 7-9 nm. Figure 7a further shows the effect of nonionic surfactant concentration on the size distribution of particles in three model oils with 0, 1.0, and 2.0 wt % nonionic surfactant (UCON LB-65), respectively. By addition of the nonionic surfactant, the size of reverse micelles increases to 10-12 nm (1 wt %) and then up to 14-15 nm (2 wt % of UCON LB-65). From this observation, we conclude that the added nonionic surfactants join the overbased reverse micelles to form larger, mixed reverse micelles. The dilution effects on reverse micellar size distribution in the model lubricating oil without nonionic surfactant were also studied using DLS measurements by adding pure solvent (dodecane), thus producing four model oils. The results are shown in Figure 7b where the extent of dilution is reflected by the oil’s TBN. In

all four samples, the size of reverse micelles was around 10 nm without significant variation. The size analysis on these four oils supports the notion that overbased reverse micelles are not dynamic structures13 and justifies the formulation of model lubricants by simply redisolving the purified overbased detergents into an appropriate solvent. Effects of Nonionic Surfactant. The mechanism of the acid neutralization reaction in lubricating oils is the key to understanding the role of nonionic surfactants, and several papers have addressed this issue and proposed possible mechanisms.16,26 In our previous paper,23 we proposed a mechanism, which is redrawn in Figure 8a. The mechanism envisions that the detergent CaCO3-containing reverse micelles in the bulk oil approach and collide with the oil-acid interface by Brownian motion. A successful (sticky) collision results in the “adsorption” of the reverse micelles on the interface followed by the formation of channels between the reverse micelles and the bulk aqueous phase, through which mass transfer can occur. The acid is then transferred into the core of the reverse micelles and reacts with the calcium carbonate. In another paper,27 we further found that the “adsorption” of overbased reverse micelles to the interface is the rate-controlling step within this interfacial neutralization reaction mechanism. According to our particle size measurements (Figures 6 and 7a) on the model oils containing nonionic surfactants, the latter can promote the formation of larger mixed reverse micelles. The mechanism of acid neutralization in the case of the overbased sulfonate with a nonionic surfactant present is illustrated in Figure 8b: the enlarged reverse micelles will have more space to accommodate the water and acid upon sticking to the interface, which may increase the transport rate of acid and water into the mineral core. The nonionic surfactants may also lower the hydrophobicity of the reverse micelles,28 which could provide a more polar environ-

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ment for the acid to interact with the reverse micelle. Additionally, when the hydrophilic heads of nonionic surfactants are exposed to the acid, hydrogen bonds will form between the surfactant oxygen groups (such as poly(oxypropylene)) and the aqueous phase. These factors will facilitate the transport of acid and water into the alkaline core and may thus further explain the enhanced neutralization ability of model lubricants with additional nonionic surfactants. As it is known that the addition of low molecular weight alcohols to overbased sulfonates reduces the rigidity of the reverse micelles;12 nonionic surfactants may also serve a similar function and make the alkyl-aryl sulfonic acid surfactant tails more flexible and thus the access of acid to the basic core more feasible. Finally, considering the neutralization rate results for the model oils shown in Table 2, it is reasonable that mixed reverse micelles are easier to form for certain nonionic surfactants than others and that this is a function of the degree of hydrophilicity of the nonionic as well as its molecular weight. For example, it has been observed that mixed micelle systems involving nonionic surfactants are more easily formed with nonionics having different poly(oxyethylene) chain lengths.20 Acknowledgment We thank Chevron Chemical Co., Oronite Division, for its support of this work. Financial support was also provided by the Louisiana Board of Regents under Grant LEQSF-RD-B-14. Literature Cited (1) Wilbur, C. T.; Wight, D. A. Pounder’s Marine Diesel Engines, 6th ed.; Butterworths: London, 1984; Chapters 6-12. (2) Broeze, J. J.; Wilson, A. Proc. Automob. Div., Inst. Mech. Eng. 1948-49, 128. Mitsutake, S.; Ono, S.; Maekawa, K.; Takahashi F.; Deguchi A. Lubrication of Cylinder Liners and Piston Rings in Low-speed Marine Diesel Engines; Mitsubishi Juko Giho 1987, 24, 87. (3) Mortier, R. M.; Orszulik, S. T. Chemistry and Technology of Lubricants; Blackie Academic & Professional: London, 1997; Chapter 10. (4) Van Helden, A. K. A Physico-Chemical Model of Corrosive Wear in Low-speed Diesel Engines. CIMAC (International Congress on Combustion Engines), Warsaw, June 8-11, 1987. Shott F. H.; MacDonald, A. G. The Influence of Acid Strength on the Corrosive Wear of Grey Cast Irons in Oil-sulphuric Acid Mixtures. Wear 1988, 122, 343. Vinogradov, T. L. Moisture Corrosion in Operating Cylinders of Marine Diesel Engines. Tr. TsNIIMF (Proceedings of the Scientific Research Institute of the Maritime Fleet) 1967, 81, 54. Forsund, K. Wear in Cylinder Liners. Wear 1957, 1, 104. (5) McGeehan, J. A.; Kulkarni, A. V. SAE International Fuels and Lubricants Meeting and Exposition, Toronto, Ontario, November 2-5, 1987, No. 872029. Groth, K.; Behrens, R. Motortech. Z. 1990, 51, 468. Inouye, K.; Mitou, T. Acid Neutralization Capacity of Overbased Detergents. Nisseki Rev. 1988, 30, 197. (6) Van Der Horst, G. W.; Hold, E. E. ASME Diesel and Gas Symposium, Jan 1983. (7) Genfaremo, N.; Liu, C. S. Crankcase Engine Oil Additives. Lubrication 1986, 76, 1. (8) Porter, M. R. In Recent Developments in the Technology of Surfactants; Porter, M. R., Ed.; Elsevier Science Publishers Ltd.: London, 1990; p 163. (9) Krasin, V. P.; Voinova, L. A.; Lashkhi, V. L.; Arslanov, M. G. Khim. Effect of the Dimensions of Detergent Micelles on Their

Effectiveness in Motor Oils. Tekhnol. Topl. Masel. 1989, 3, 37. Martin, J.; Belin, M.; Manosot, J. L. EXAFS of Calcium in Overbased Micelles. J. Phys. Colloq. 1986, 47, 887. Martin, J. M.; Manosot, J. L.; Hallouis, M. Ultramicro 1989, 30, 321. Inoue, K.; Watanabe, H. Micelle Formation of Detergent-Dispersant Additives in Nonaqueous Solutions. J. Jpn. Petrol. Inst. 1981, 24, 92. (10) Mansot, J. L.; Hallouis, M.; Martin, J. M. Colloidal Antiwear Additives 1. Colloids Surf. A 1993a, 71, 123-134. (11) Mansot, J. L.; Hallouis, M.; Martin, J. M. Colloidal Antiwear Additives 2. Colloids Surf. A 1993b, 75, 25-31. (12) Jao, T. C.; Kreuz, K. L. Rigidity of Alkylaryl Sulfonate Micelles Monitored by Intrinsic Fluorescence Probes. J. Colloid Interface Sci. 1988, 126, 622. (13) Hori, T.; Jinnai, H.; Ueda, S. Bull. Jpn. Petrol. Inst. 1974, 16, 1. (14) Marsh, J. F. Colloidal lubricant additives. Chem. Ind. 1987, 470. (15) Lewis, J. F. Mechanism of Action of Overbased Additives in Hydrocarbon Media. Ph.D. Thesis, University of East Angila, 1991. Arndt, E. R.; Kreuz, K. L. Characterization of Calcium Alkylaryl Sulfonates Containing Encapsulated Solids. J. Colloid Interface Sci. 1988, 123, 230-237. (16) Papke, B. L. Neutralization of Basic Oil-soluble Calcium Sulfonates by Carboxylic Acids. Tribol. Trans. 1988, 31, 420-426. (17) Eicke, H.-F.; Zinsli, P. E. Nanosecond Spectroscopic Investigations of Molecular Processes in W/O Microemulsions. J. Colloid Interface Sci. 1978, 65, 131-140. (18) Zoleski. U.S. Patent 4,358,386, 1982. Zoleski. U.S. Patent 4,358,387, 1982. Zoleski. U.S. Patent 4,438,005, 1982. (19) Kokai. Japan Patent 5-239458, 1983. Lowe. U.S. Patent 3,856,687, 1974. (20) Abe, M.; Tsubaki, N.; Ogino, K. Solution Properties of Mixed surfactant System V. J. Colloid Interface Sci. 1985, 107, 503-508. Abe, M.; Tsubaki, N.; Ogino, K. Solution Properties of Mixed Surfactant Systems IV. Colloid Polym. Sci. 1984, 262, 584588. Ogino, K.; Tsubaki, N.; Abe, M. Solution Properties of Mixed Surfactant Systems VI. J. Colloid Interface Sci. 1985, 107, 509513. (21) Tokuoka, Y.; Uchiyama, H.; Abe, M. Solubilization of Some Synthetic Perfumes by Anionic-Nonionic Mixed Surfactant Systems. J. Phys. Chem. 1994, 98, 6167-6171. Ogino, K.; Kakihara, T.; Uchlyama H.; Abe, M. Solution Properties of Mixed Surfactant System: Sodium Dodecyl Sulfate and Alkyl Polyoxyethylene Ether System. J. Am. Oil Chem. Soc. 1988, 65, 405-410. (22) Seedher, N.; Manik, M. Solubilization in Mixed Surfactant Reverse Micellar Systems. J. Surf. Sci. Technol. 1993, 9, 81-86. (23) Wu, R. C.; Campbell, C. B.; Papadopoulos, K. D. Visualization Test for Neutralization of Acids by Marine Cylinder Lubricants. AIChE J. 1999, 45, 2011-2018. (24) Hou, W.; Papadopoulos, K. D. W1/O/W2 and O1/W/O2 Globules Stabilized with Span 80 and Tween 80. Colloids Surf. 1997, 125, 181. (25) Rang, M. J.; Lim, J. C.; Miller, C. A.; Thunig, C.; Hoffmann, H. H. Dynamic Behavior of Alcohol Drops in Dilute Solutions of an Amine Oxide Surfactant. J. Colloid Interface Sci. 1995, 175, 440-447. (26) Roman, J.-P. New method of measurement in thin film of the neutralization ability of marine lubricants for low-speed diesel engines. Int. Congr. Combust. Engines 1998, 4, 913-925. (27) Wu, R. C.; Campbell, C. B.; Papadopoulos, K. D. AcidNeutralizing of Marine Cylinder Lubricants: Measurements and Effects of Dispersants. AIChE J. 2000, 46, 1471-1477. (28) Yamada, Y.; Kuboi R.; Komasawa, I. Increased Activity of Chromobacterium viscosum Lipase in Aerosol OT Reverse Micelles in the Presence of Nonionic Surfactants. Biotechnol. Prog. 1993, 9, 468-472.

Received for review January 12, 2000 Revised manuscript received June 26, 2000 Accepted June 29, 2000 IE000039C