PHOSPHATE ESTER COMPOSITIONS IN A WEIGHT RATIO GREATER THAN 1:1 MONOALKYL TO DIALKYL PHOSPHATE USED AS LUBRICANT ADDITIVES

Abstract: Alkyl phosphate esters having a high monoalkyl content are used as lubricating additives in functional and lubricating fluids. The esters have a weight ratio of monoalkyl phosphate esters to dialkyl phosphate esters of greater than one. The alcohols from which the esters are prepared are preferably non-ethoxylated. The functional or lubricating fluids can be oil-based or aqueous based.

Description: CROSS-REFERENCE TO RELATED APPLICATIONS 5 This application claims priority from U. S. provisional patent application Serial No. 60/1 13,389 filed December 23, 1998, the disclosure of which is incorporated herein by reference. FIELD OF THE INVENTION This invention relates to the use of alkyl phosphate esters having a high monoalkyl content as lubricating additives in functional and lubricating fluids. BACKGROUND OF THE INVENTION 5 Conventional alkyl phosphate esters have been used as lubricants, anti-corrosion agents, and anti-wear agents in a variety of functional and lubricating fluids. These conventional phosphate esters were typically of approximately equal molar proportions of monoalkyl and dialkyl esters. Further, it is known that by ethoxylating the alcohol which is esterified to 0 form the phosphate ester, the performance of the ester as a lubricant is enhanced, relative to non-ethoxylated esters. SUMMARY OF THE INVENTION It has now been found that phosphate esters containing a higher 5 monoalkyl content perform as lubricants equal to or better than conventional phosphate esters and that the non-ethoxylated esters perform better than the ethoxylated esters. DETAILED DESCRIPTION OF THE INVENTION 0 The high monoalkyl content phosphate esters will find utility as lubricants or anti-wear additives in metal working fluids, motor oils, aqueous hydraulic fluids, aqueous cooling systems, aqueous metal cleaning fluids and the like in which the fluids, particularly aqueous ones, are in contact with metal and are circulated by pumps which are subject to corrosion and need lubrication and wear reduction of the metal surfaces. The high monoalkyl phosphate esters will typically be added to a fluid base, e.g. an oil base or an aqueous base, in a minor amount, e.g. typically from about 0.1% to about 25% by weight, more typically from about 0.5% to about 10% by weight and even more typically from about 1 % to about 5% by weight of the total fluid composition. The oil base will typically be a mineral (natural or synthetic) or vegetable oil, Examples of mineral oils are the natural petroleum oils, such as the aliphatic or wax base oils, the aromatic or asphalt base oils, or mixed-base oils and the petroleum derived oils such as engine oils, machine oils, cutting oils, and refined paraffin oils. Vegetable oils would be of the nondrying or soap stock variety. Aqueous fluid bases will consist essentially of water which may be of varying hardness based on the intended application of the fluid. The alkyl phosphate ester compositions are high in monoalkyl phosphates relative to dialkyl phosphates, i.e. a weight ratio of mono- to di- alkyl phosphate esters of greater than 1 :1 , typically equal to or greater than about 60:40, more typically equal to or greater than about 70:30, preferably equal to or greater than 80:20, more preferably 90:10 or greater and even more preferably greater than 95:5. The phosphate ester compositions of low residual phosphoric acid and residual alcohol content and high in monoalkyl phosphate content used in fluids of this invention are produced, for example, by the processes disclosed in US Patents 5,463,101 , 5,550,274 and 5,554,781 , as well as in EP Patent publication number EP 0 675,076 A2, especially as described in Example 18 of the EP publication. The alkyl phosphate ester salts are prepared by stirring the appropriate alkyl phosphate esters, high in monoalkyl phosphate ester content, into a solution of an appropriate base. As examples of suitable base materials for producing the salts of the alkyl phosphate esters, there may be mentioned sodium, potassium, lithium, or ammonium hydroxides and amines, such as for example, triethanolamine (TEA) and 2-amino-2- methyl-1-propanol (AMP) and the like. The salts of the monoalkyl phosphate esters may be of any suitable base:acid molar ratio salts, such as 0.8, 1 , 1.5, 1.7 salts and the like. Alkyl phosphate esters employed in forming the fluids of this invention are preferably produced from alcohols or mixtures of alcohols typically found in natural oils, for example, coconut oils, with carbon chain length of about C 8 to C 18 or tallow or rapeseed oils with chain lengths from about C 14 to C 22 and higher content of unsaturated chains. Blends of linear and branched, saturated and unsaturated alcohols are permissable. These alcohols are employed in the phosphation processes described in the aforementioned three US Patents and the EP Patent publication. As examples of such alcohols, there may be mentioned octanol, decanol, dodecanol, tetradecanol, hexadecanol and octadecanol, octadecenol (oleyl alcohol), octadecadienol, eicosanol, docosanol, docosenol or mixtures of alcohols, such as a commercially available blend of a mixture of about 0.1 % tetradecanol, 5.1 % hexadecanol, 94.4% octadecenol and 0.4% eicosanol, as HD OCENOL™ 90/95 (Emery Group, Henkel Corporation, Cincinnati, Oho). Preferably, the alcohol blends are comprised predominantly of C 16 to C 18 alcohols or C 14 to C 22 alcohols. The residual phosphoric acid or residual alcohol content of the compositions of this invention will generally be less than 8% by weight, preferably less than 6% by weight, and more preferably less than 5% by weight of each residual component. The invention is illustrated by the following illustrative, but non-limiting, examples. EXAMPLE 1 Oleyl Phosphate bv Hybrid Process An oven-dried 2 liter, five-necked, round bottom flask was equipped with paddle stirrer, pressure equalizing addition funnel, thermocouple and Claisen adapter fitted with a gas inlet and outlet through a condenser and silicone fluid bubbler. The system was flushed with argon and further dried with a heat gun. Oleyl alcohol, 876.1 g (hydroxyl number 208) was added against a positive flow of argon through the addition funnel. The funnel was then charged with 1 15% polyphosphoric acid and 159.2 g was added, with water bath cooling, over a 70 minute period with a temperature range of 35 ± 10° C. The mixture was stirred for ten minutes to ensure a uniform solution. The liquid addition funnel was quickly replaced by a screw feed powder addition funnel containing phosphoric anhydride. With continued cooling and positive argon pressure, 97.8 g was added over 60 minues, during which the temperature reached 43° C. The orange slurry was then heated to 80° C and maintained at that temperature for nineteen hours. Deionized water, 5.7 g, was added and stirring at 80° C was continued for an additional two hours. The liquor was cooled to 63° C, 2.3 g of 35% hydrogen peroxide was added, stirring continued for 30 minutes and the mixture was allowed to cool to room temperature. The weight percent nonionic components (unreacted alcohol) was 4.0% and the monoalkyl to dialkyl phosphate weight ratio, determined by 31 P nuclear magnetic resonance spectroscopy, was 77.4 to 22.1. EXAMPLE 2 Oleyl Phosphate bv Phosphoric Anhydride Process A 2 liter, five-necked flask equipped and prepared as in Example 1 was similarly charged with 1 109.9 g of oleyl alcohol (hydroxyl number 207.6) followed by 199.25 g phosphoric anhydride, added over one hour with water bath cooling. The temperature maximum was 58° C. The slurry was then warmed to 80° C over a two hour period where it was maintained for 18 hours. Deionized water, 3.87 g, was added and stirring continued at 80° C for an additional two hours. The viscous, dark liquid was then allowed to cool to 64° C, 2.59 g of 35% hydrogen peroxide was added and stirring continued for 30 minutes during which the liquor cooled to 55°C and thereafter to room temperature. The residual alcohol, as percent nonionics, was 8.2 weight percent and the monoalkyl to dialkyl phosphate weight ratio was 46.7:53.3. EXAMPLE 3 Oleyl Ethoxylate Phosphate bv Hybrid Process A 12 liter, four-necked flash equipped and prepared as in Example 1 was charged under argon atmosphere with 8810.4 g of an oleyl alcohol ethoxylate (hydroxyl number 117.0) followed by the addition of 115% polyphosphoric acid, 905.6 g, over a 30 minute period. The temperature rose to 52° C and the liquor was stirred for 150 minutes to obtain a clear solution and allow the temperature to drop to 40° C. Phosphoric anhydride, 552.9 g, was added over a 30 minute period during which the temperature rose to 52° C and continued to a maximum of 60° C. External heat was then applied to reach a temperature of 80° C in two hours, which was maintained for 10 hours. Deionized water, 20.9 g, was added and stirring at 80° C continued for two hours. The liquor was then cooled to 62°C, 35% hydrogen peroxide, 20.6 g, was added and after 30 minutes continued stirring was allowed to cool to room temperature. Analysis showed the monoalkyl to dialkyl phosphate weight ratio was 74.1 :25.9 and residual nonionics, 6.6%. PERFORMANCE EVALUATION The scar diameter in the 4-Ball Wear Test 6 is a sensitive measurement of the antiwear properties of the additive. Compositions containing 2.0 weight percent of the phosphate ester products of Examples 1 , 2, 3 and the commercial Rhodafac LB-400 reference in an oil base are compared in Table 1. The significantly lower values for the two oleyl alcohol phosphates, Examples 1 and 2, compared to the three mole ethoxylate (EO) homologs, Examples 3 and LB-400, show the superiority of the non-ethoxylated oleyl phosphates. Superimposed on this effect is the lower value for the member of each pair prepared by the proprietary Rhόne-Poulenc Hybrid Phosphation process compared to the phosphate mixture of the same alcohol prepared by the conventional phosphoric anhydride process, Examples 1 vs. 2 and 3 vs. LB-400 respectively. Table 1. Antiwear Properties of Oleyl Phosphate Derivatives 4-Ball Wear Test Wear Scar ΔT Diameter (mm) (° F) Sample Medium (a) Example 1 Oil Base 0.14 73 Example 2 Oil Base 0.22 96 Example 3 Oil Base 0.34 62 LB-400 Oil Base 0.37 80 (a) 2.0 weight percenl t additive in 105 Costal Pale Oil EXAMPLES 4-6 Effect of Oleyl Alcohol Composition Three separate commercial grades of oleyl alcohol were phosphated according to the procedure of Example 1. The compositions of all of the examples are listed in Table 2. The products of these three examples were evaluated by both the 4-Ball Wear Test and the Falex Pin and Vee Block Test (6.), with the results summarized in Table 4. Since the monoalkyl to dialkyl ratios (MAP:DAP) for all samples were very similar and the test results would not be expected to be sensitive to the variation in residual alcohol over the narrow range encountered in these experiments, the primary variable would be expected to be the alcohol composition. In the HD-Ocenol series, described in Table 3, it is seen that the numerical product designation is related to the iodine value, not a percent purity. In the specific products used, the increasing iodine values and decreasing melting points reflect a decrease in the undesirable saturated C 16 , cetyl alcohol component, and increase in the unsaturated C 18 , oleyl alcohol component. (The high iodine value for the 1 10/130 product is achieved by addition of the diene, linolenic alcohol.) The important wear scar diameters are seen in Table 4 to decrease steadily in the oil based formulations with the increasing oleyl alcohol and decreasing cetyl alcohol content of the starting material, further emphasizing the importance of the non-ethoxylated, oleyl alcohol content within this series of monoalkyl enriched phosphates. Interestingly, the 4-Ball Wear Test performance in the water based systems did not appear to be significantly affected by the change in starting material composition. The Falex Pin and Vee Test, however, showed a clear distinction, especially in the water based system where two out of three of the samples survived the maximum 4500 lb. loading without failure of the test piece. In these same two cases, the performance was notably superior in the oil based system to the commercial standard, Rhodafac LB-400. TABLE 2 TABLE 3 TABLE 4

Claims: What is claimed is: 1. A lubricating medium comprising a base fluid in a major amount and a minor amount by weight of an alkyl phosphate ester having a weight ratio of monoalkyl phosphate esters to dialkyl phosphate esters of greater than 1. 2. A lubricating medium as claimed in claim 1 wherein said alkyl phosphate ester is derived from a non-ethoxylated alcohol. 3. A lubricating medium as claimed in claim 1 wherein said amount of said alkyl phosphate ester is from about 0.1% to about 25% by weight of said lubricating medium. 4. A lubricating medium as claimed in claim 1 wherein said amount of said alkyl phosphate ester is from about 0.5% to about 10% by weight of said lubricating medium. 5. A lubricating medium as claimed in claim 1 wherein said amount of said alkyl phosphate ester is from about 1% to about 5% by weight of said lubricating medium. 6. A lubricating medium as claimed in claim 1 wherein said base fluid is an oil selected from the group consisting of mineral and vegetable oils. 7. A lubricating medium as claimed in claim 6 wherein said oil is selected from the group consisting of aliphatic or wax base oils, aromatic or asphalt base oils, mixed-base oils, and petroleum oils. 8. A lubricating medium as claimed in claim 1 wherein weight ratio of monoalkyl phosphate esters to dialkyl phosphate esters is no less than about 70:30. 9. A lubricating medium as claimed in claim 1 wherein weight ratio of monoalkyl phosphate esters to dialkyl phosphate esters is no less than about 80:20. 10. A lubricating medium as claimed in claim 1 wherein weight ratio of monoalkyl phosphate esters to dialkyl phosphate esters is no less than about 95:5. 11. A lubricating medium as claimed in claim 1 wherein said alkyl phosphate ester is derived from a mixture of alcohols comprised predominantly of C 14 to C 22 alcohols. 12. A lubricating medium as claimed in claim 1 wherein said alkyl phosphate ester is derived from a mixture of alcohols comprised predominantly of C 16 to C 18 alcohols. 13. A lubricating medium as claimed in claim 1 wherein said alkyl phosphate ester is derived from a mixture of alcohols comprised predominantly oleyl alcohol. 14. A lubricating medium as claimed in claim 1 wherein said alkyl phosphate ester is derived from a mixture of alcohols derived from the group consisting of tallow oils and rapeseed oils. 15. A lubricating medium comprising a base fluid selected from the group consisting of oil and water, and from about 0.1% to about 25% of an alkyl phosphate ester having a weight ratio of monoalkyl phosphate esters to dialkyl phosphate esters of no less than about 70:30, the alcohols from which said alkyl phosphate ester is derived being comprised predominantly of C 14 to C 22 alcohols. 16. A lubricating medium as claimed in claim 15 wherein the alcohols from which said alkyl phosphate ester is derived are non- ethoxylated. 17. A lubricating medium as claimed in claim 15 wherein the alcohol from which said alkyl phosphate ester is derived is comprised predominantly of oleyl alcohol.

Inventors: JOYE JEAN-LUC, REIERSON ROBERT LEE, WERNER JAMES J DI, JOYE, JEAN-LUC, REIERSON, ROBERT, LEE, WERNER, JAMES, J. DI
Applicants: RHODIA, RHODIA INC.
Application year: 1999
Main classification: C10M137
IPC codes: C10M101, C10M137, C10M169, C10M173, C10N30