HYDROCARBON-SUBSTITUTED SUCCINIC ACID OR ANHYDRIDE-POLYAMINE LUBRICATING OIL ADDITIVE WITH ASYMMETRICAL MOLECULAR WEIGHT DISTRIBUTION

Abstract: There are disclosed oil-soluble alkenyl succinimides hav­ ing improved sludge dispersant and varnish inhibition proper­ ties characterized in that the alkenyl groups, e.g., polyisobute­ nyl, have a C₆₀ - C₈₀ average and have an asymmetrical molecu­ lar weight distribution with minimization of the presence of rad­ icals below C₄₀.

Description: This invention relates to an improved lubricating oil additive having both dispersant and varnish potency. More particularly, this invention relates to an improved hydrocarbon-substituted succinic acid or anhydride-polyamine reaction product, wherein the hydrocarbon substituent has a relatively narrowly defined carbon atom range. Additives comprising the reaction product of polyamines with a hydrocarbon-substituted succinic acid or anhydride compound, particularly a polyisobutenyl-substituted succinic acid or anhydride derivative, are well known in the art and are disclosed in U.S. 3,172,892, issued March 9, 1965, to LeSuer et al. Other representative disclosures are U.S. Patent 3,272,746, issued September 13, 1966 to LeSuer et al, and U.S. Patent 4,105,571, issued August 8, 1978 to Shaub et al. The prior art as represented by said U.S. Patent 3,172,892 has recognized the importance of the carbon atom range of hydrocarbon substituent in such hydrocarbon-substituted succinic acid or anhydride-polyamine reaction products which are usually polyisobutenyl succinimides, and has been further recognized that the substituent should have 50 or more carbon atoms, preferably a polyisobutenyl radical having 50 or more carbon atoms, to have desirable dispersant properties. In practice, such additives have been prepared from polyisobutenyl radicals which, although containing substantial proportions of C50 and higher radicals have also contained appreciable quantities of relatively lower molecular weight radicals, on the order of about 26 percent by weight or more of C40 and lower radicals and 20 percent of C32 and lower radicals. The preset ence of these radicals is due to the fact that polymerization of isobutene necessarily results in polyisobutenyl radicals which vary widely in their carbon atom range and normally have a symmetrical molecular weight distribution. Such products typically have an average of C54 The prior art has not fully recognized that distinct advantages are obtainable by optimizing the carbon atom range of the hydrocarbon substituent group which is linked to the succinic acid or anhydride moiety, and which product is subsequently reacted with a polyamine to make the well-known dispersant additives, which have been widely used in commercially available lubricating oil composi- tions. The present invention, which can be considered an improvement within the broad teachings of U.S. Patent 3,172,892, is based on the discovery that removal of a significant amount of hydrocarbon substituent groups below about C40, particularly polyisobutenyl groups, or at least minimization of the quantity of such relatively lower hydrocarbon substituents results in a hydrocarbon-substituted succinic acid or anhydride polyamine reaction product lubricating oil additive which exhibits excellent dispersant potency as well as significant anti-varnish properties. The present invention is further based upon the discovery that unless positive steps are taken to remove radicals of about C40 and below, particularly radicals in a 025 035 range and below, that these hydrocarbon substituents will have a definite adverse effect on the overall performance of the engine oil lubricating composition and will even promote the formation of varnish deposits on engine components. While the prior art has recognized the ineffectiveness of these relatively lower molecular weight hydrocarbon substituents as dispersants, there has been no recognition of the severe negative impact on lubricant performance caused by the promotion of varnish and deposition which will occur when significant quantities are present in the lubricating oil blend. The prior art does disclose relatively higher molecular weight alkenyl, specifically polyisobutenyl, succinimide dispersants but these are considered outside the scope of and distinct from the products of the present invention since such products have a relatively higher carbon atom range, typically a C81 5 average. Such products are disclosed in U.S. Patent 4,173,540. This patent discloses hydrocarbyl substituents having a number average molecular weight (Mn) by VPO (Vapor Pressure Osmometry) of 1200 to 5800 optimally 1300 to 4800. While such products, particularly the polyisobutenyl succinimide embodiments have a number of advantages, their viscosities are generally too high for general formulating purposes. Analysis of a typical product of average molecular weight 1141 by Gel Permeation Chromatography will show 25 weight percent radicals greater than C188 and 15 weight percent radicals below C40 with a carbon atom average of C81 5 as noted above. In accordance with the present invention, there has been discovered a lubricating oil additive exhibiting improved varnish inhibition and sludge dispersant potency consisting essentially of the reaction product of an ethylene polyamine and an aliphatic hydrocarbon-substituted succinic acid or anhydride wherein the aliphatic hydrocarbon radical substituent has an asymmetrical molecular weight distribution as indicated by an average of 60 to 80, preferably 64 to 75 carbon atoms, at least 75 weight percent of said radicals being C50 or greater and not more than 20 weight percent of said radicals being C40 and below. Embodiments where the radicals are polyisobutenyl radicals are the particularly preferred embodiment of this invention. The invention in its broadest aspects relates to those hydrocarbon-substituted succinic acid or anhydridepolyamine reaction products wherein the hydrocarbon substituent radicals, preferably polyisobutenyl, have a C average of C50 to C120 preferably C60 to Cog0, with not more than 20 weight percent of the radicals being 2/3 of the C average or less and with not more than 25 weight percent of the radicals having more than twice the C average, preferably the hydrocarbon radicals will have not more than 10 to 15 weight percent of radicals which are greater than twice the C average. These parameters broadly define products within the present invention having an asymmetrical molecular weight distribution. All these values are determined by GPC (Gel Permeation Chromatography). Thus additive D of the present invention herein below has 19.65 weight percent of radicals below 2/3 of the C average and 9.4 weight percent of the radicals were greater than twice the C average; for Additive E the corresponding values were 18.1 weight percent below 2/3 of C average and 9.7 weight percent greater than twice the C average. The hydrocarbon substituent is derived from those sources commonly employed by the prior art, that is, polyolefins, such as polyethylene, polypropylene, and polyisobutylene, the latter being preferred since it is the product commercially used and polyisobutylene is a readily available source of the succinic hydrocarbon substituent. Particularly preferred for use in the present invention are polyisobutenyl radicals having an average of about 64 to 75, such as C64-C70 or C70-C74, carbon atoms and containing about 75 to 95 weight percent or more, ideally up to 100 percent of polyisobutenyl radicals having 50 or more carbon atoms, with the amount of radicals below about C30 being not more than 10 weight percent based on the total weight of polyisobutenyl radicals in the polyisobutylene used to form the polyisobutenyl succinimide dispersants of the present invention. Preferred embodiments are illustrated by a C64 average polyisobutenyl radical having less than 10 weight percent C30 radicals and a C74 average polyisobutenyl radical having about less than 8 percent C30 radicals. Such products in which the presence of lower molecular weight polyisobutenyl radicals has been minimized can be prepared using known separation techniques. Such techniques generally comprise treatment of commercially available polyisobutylene by solvent extraction with isopropanol with associated separation and distillation methods. Such methods are known in the art and are not considered an embodiment of the present invention which resides in the recognition of the improved dispersant and anti-varnish properties based on proper selection of the carbon atom range. Polymerization under controlled conditions would also be a desired method of providing polyisobutylene, whose molecular weight distribution is controlled to provide an asymmetrical distribution in accordance with this invention. The polyamines used in the present invention are those ethylene polyamines as represented by the formula: H2N(CH2CHRNH) xH wherein x is about 1 to 10 and R is a lower C1-C8 alkyl or hydrogen. Illustrative polyamines are ethylenediamine, diethylene triamine, triethylene tetramine, tetramethylene pentamine, pentaethylene hexamine, and the like. Tetraethylene pentamine is a preferred polyamine. The formation of the hydrocarbon-substituted succinic acid or anhydride derivative is also known in the art and typically first involves a chlorination reaction to prepare a chlorinated polyisobutene, which is then reacted with maleic acid or anhydride to form the hydrocarbon-substituted succinic acid or anhydride product. Thereafter, the polyamine is reacted with the hydrocarbonsubstituted succinic acid/anhydride in a ratio of about 1:1 to about 10:1 moles of hydrocarbon-substituted succinic acid/anhydride to amine. The improved additive of the present invention is used in hydrocarbon lubricating oils including mineral lubricating oils as well as synthetic oils and mixtures thereof. Synthetic oils include diester oils, complex ester oils, silicone oils, and the like. Other conventionally used additives may be added to the oil compositions containing the additive of the present invention and these include anti-oxidants, rust inhibitors, friction modifiers, detergents, dispersants, viscosity index improvers. A typical commercial formulation will contain a number of such other addtives. The additives of the present invention will be used in normal amounts such as about 0.1 to about 10 weight percent based upon the total weight of the lubricant composition, preferably about 0.5 to 5 weight percent. The optimum concentration is a function of the nature of the particular mineral oil base stock and the type of service conditions expected. Typical mineral oils used as a base stock are those having a viscosity as measured by ASTM D445 of from about 2 to 40, preferably 5 to 20 centistokes at 990C. The present invention is illustrated by the following examples where dispersant additives were evaluated which had a variable molecular weight distribution of polyisobutenyl radicals. Each additive used was the reaction product of tetraethylene pentamine with polyisobutenyl succinic anhydride in a molar ratio of 1.4 moles of polyisobutenyl succinic anhydride per mole of amine. The polyisobutenyl succinic anhydride has been prepared from chlorinated polyisobutylene (1 chlorine atom per polymer molecule) and maleic anhydride. The products differed principally in -the molecular weight and carbon atom range of the polyisobutenyl substituent. The products are described below as Additives A, B, and C. Additive A being a type of dispersant disclosed by the prior art and Additives B and C being used and treated for purposes of comparison, to illustrate the newly discovered adverse effect of high proportions of lower molecular weight radicals in the polyisobutenyl group. The carbon atom values were obtained by Gel Permeation Chromatography (GPC). Additive A: Polyisobutenyl molecular weight (VPO)=973; weight percent nitrogen = 2,12 Average carbon atoms = 69 - 70 (polyisobutenyl radical 60 weight percent C56 and above 68 weight percent C46 and above 25 weight percent C30 and below Additive B: Polyisobutenyl molecular weight (VPO) = 595; weight percent nitrogen = 2.64 Average carbon atoms 42 - 43 (polyisobutenyl radical) 18 weight percent C55 and above 26 weight percent C48 and above 65 weight percent C42 and below Additive C: Polyisobutenyl molecular weight (VPO) = 434; weight percent nitrogen = 3.75 Average carbon atoms 29 - 33 (polyisobutenyl radical) 3 weight percent C50 and above 4 weight percent C44 and above 90 weight percent C30 and below Each of these additives were evaluated in an engine test after being blended into a conventional lubricating oil composition. The test used was the 'MS sequence VC engine Test" which was carried out in a Ford 302 cubic inch engine as described in ASTM Special Publication 315-E. This engine test is currently accepted by industry as a valid evaluation of lubricant additive performance. The blends tested each contained 6.3 weight percent of Additives A, B, and C together with 5.65 percent of a conventional additive package and 13.0 weight percent of a viscosity modifier. In the MS-VC tests, at the end of each test, various parts of the engine are graded on a merit basis wherein ten represents a perfectly clean part and lesser numbers represent increasing degrees of deposit formation. The various ratings are totalled and averaged on the basis of ten as a completely clean rating. The results of this test are set forth below, the three additives being compared with a blank run which contained only the conventional additive and viscosity modifier but no polyisobutenyl succinimide product. The conventional additive package contained overbased magnesium sulfonate, overbased barium/calcium phenate carbonate, and P2S5-treated alpha-pinene. The viscosity modifier was an ethylene-propylene copolymer viscosity index improver. The base stock was a 25 percent/75 percent by weight blend of, respectively, a paraffin lubricating oil having a kinematic viscosity of 20 cS min. at l000F. and a paraffin oil having a viscosity of 3t'cS min. at l000F. TABLE I MS ¯ VC RESULTS Bland Additive A Additive B Additive C Limit Sludge 5.8 8.8 8.4 6.5 8.7 min. Piston Skirt Varnish 5.2 8.3 7.0 5.3 7.9 min. Average Varnish 5.7 8.0 5.3 5.3 8.0 min. Oil Ring Clogging 7% 0% 14% 96% The significance of these data is seen if one compares the varnish rating and oil ring clogging data for Additives B and C with both the blank run and the blend of the present invention. It is clear that Additives B and C promoted varnish deposition and associated oil ring sticking tendencies. Further evaluations were conducted with dispersants prepared from tetraethylene pentamine and polyisobutenyl succinic anhydride which contained an asymmetrical molecular weight distribution in accordance with the present invention. These were prepared from a polyisobutylene which had been treated in accordance with conventional tech niques comprising isopropanol extraction and separation to remove the lower molecular weight species. These are identified herein as Additions D and E. The polyisobutenyl moiety of Additive D had a GPC average molecular weight of 896 and GPC analysis showed 74.95 weight percent of radicals greater than C50, 81.54 weight percent of radicals greater than C41 and 9.09 weight percent of radicals below C30; the C average was C64 The polyisobutenyl moiety of Additive E had 79.48 weight percent of radicals greater than C53, 85.27 weight percent of radicals greater than C44 and 7.17 weight percent of radicals below C31. The C average was C74 and the GPC molecular weight average was 1039. Both Additives D and E had a distinct asymmetrical molecular weight distribution as indicated by the above analysis. The sludge and varnish potency were evaluated for these two additives in the SIB (SLUDGE INHIBITION BENCH TEST) and VIB (VARNISH INHIBITION BENCH TEST) while conducting a comparative test with Additives A and C which had been evaluated above in Table I. The SIB Test employs a used crankcase mineral lu bricating oil composition having an original viscosity of about 325 SUS at 37.80C., which has been used in a taxicab that was driven generally for short trips only, thereby causing a buildup of a high concentration of sludge pre cursors. The oil that was used contained only a refined base mineral oil, a viscosity index improver, a pour point depressant and zinc dialkyldithiophosphate anti-wear additive. The oil contained no sludge dispersants. The quantity of such used oil was obtained by draining and refilling the taxicab crankcase at 1,000 - 2,000 mile intervals. The SIB Test is conducted in the following manner: The used crankcase oil is freed of sludge by centrifuging for one-half hour at about 39,000 gravities (gs). The resulting clear bright red oil is then decanted from the insoluble sludge particles thereby separated out. However, the supernatant oil still contains oil-soluble sludge precursors which under the conditions employed by this test will tend to form additional oil-insoluble deposits of sludge. The sludge inhibiting properties of the additives being tested are determined by adding to portions of the used oil a small amount of the particular additive being tested. Ten grams of each one being tested is placed in a stainless steel centrifuge tube and is heated at 137.8 degrees C for 16 hours in the presence of air. Following the heating, the tube containing the oil being tested is cooled and then centrifuged for 30 minutes at about 39,000 gs. Any deposits of new sludge that forms in this step are separated from the oil by decanting supernatent oil and then carefully washing the sludge deposits with 15 ml. of pentane to remove all remaining oils from the sludge. The weight of the new solid sludge that formed in the test, in milligrams, is determined by drying the residue and weighing it. The results are reported as milligrams of sludge per ten grams of oil, thus measuring differences as small as one part per ten thousand. The less new sludge formed, the more effective is the additive as a dispersant. In other words, if the additive is effective, it will hold at least a portion. of the new sludge that forms on heating and oxidation stably suspended in the oil so that it does not precipitate down during the centrifuging period. In the VIB Test, a test sample consisting of ten grams of lubricating oil containing the additive being evaluated-is used. The test oil is a commercial lubricating oil obtained from a taxi after two thousand miles of driving with said lubricating oil. Each sample is heat soaked overnight at about l400C and thereafter centrifuged to remove the sludge. The supernatant fluid of each sample is subjected to heat cycling from about l500C to room temperature over a period of 3.5 hours at a frequency of about two cycles per minute. During the heating phase, a gas containing a mixture of 0.7 volume percent S02, 1.4 volume percent NO and the balance air was bubbled through the test samples and during the cooling phase, water vapor was bubbled through the test samples. At the end of the test period, which testing cycle can be repeated at necessary to determine the inhibiting effect of any additive, the wall surfaces of the test flasks in which the samples were contained are visually evaluated as to the varnish inhibition. The amount of varnish imposed on the walls is rated at values of from one to seven with the higher number being the greater amount of varnish. It has been found that this test collaborates with the varnish results obtained as a consequence of carrying out MS-VC engine tests. The results of the SIB and VIB test are set forth in the table below: TABLE II Addi- tqt. % %Nitrogen Relative SIB VIB tive in oil in oil % Nitro- Rat- Rat gen inc ¯ ing A 0.5 0.0105 1.0 3.09 6.00 D 0.5 0.00835 0.8 2.63 4.25 D 0.42 0.00701 0.67 4.23 6.75 E 0.5 0.00835 0.8 3.35 5.00 E 0.36 0.00601 0.57 4.95 6.75 C 0.5 0.01875 1.79 9.64 8.50 The point of these data is that both Additives D and E of the invention exhibit significant sludge and varnish potency at relatively low levels of nitrogen. Additive D is superior at equal dispersant concentration to Additive A in both SIB and VIB ratings. Additive E is superior at equal concentration of dispersant to Additive A in varnish performance. Evaluation of Additives D and E coupled with the data presented in Table I demonstrate clearly the performance obtained with the additives of the present invention, which are characterized as having an asymmetrical molecular weight distribution. Additional SIB and VIB tests were conducted on Additives D and E of the present invention to verify the results and in this test, comparison was made with Additive A which represents a typical commercial polyisobutenyl succinimide prepared from the anhydride and tetraethylene pentamine. The data are reported in Table III below: : TABLE III Addi- % N in % Additive % Nitrogen SIB VIB tive Additive in oil in oil rat- rat ina ing D 1.64 0.5 0.0082 4.20 4 D 1.64 0.42 0.0069 5.40 6.5 E 1.64 0.5 0.0082 4.60 4.5 R 1.64 0'.36 0.0059 5.43 6.5 A 2.12 0.5 0.0106 5.00 6 A 2.12 0.5 0.0106 5.00 6 These data confirm the superior performance of the Additives D and E of the present invention at equivalent or somewhat reduced nitrogen levels which usually is viewed as a measure of the activity of a dispersant.

Claims: WHAT WE CLAIM IS: 1. A lubricating oil additive exhibiting improved varnish inhibition and sludge dispersant potency, said additive being the reaction product of an ethylene polyamine and an aliphatic hydrocarbon-substituted succinic acid or anhydride, the hydrocarbon substituents having an asymmetrical molecular weight distribution as indicated by at least 75 weight percent of said hydrocarbon radicals being C50 or greater, not more than 20 weight percent of said hydrocarbon radicals being C40 and less, and said hydrocarbon radicals having an average of from about C60 to C80. 2. The additive of claim 1 wherein the hydrocarbon radicals are polyisobutenyl radicals. 3. The additive of claims 1 or 2 wherein said hydrocarbon radicals having an average of C64 to C75. 4. The additive of claims 1-3 wherein the polyamine is tetraethylene pentamine. 5. The additive of claims 1-4 wherein the hydrocarbon radicals having an average of about C64 and contain less than 10 weight percent C30 radicals. 6. The additive of claims 1-4 wherein the hydrocarbon radicals have an average of about C74 and contain less than 8 weight percent of C30 radicals. 7. A lubricating oil composition containing a mineral lubricating oil base stock and about 0.5 to 10 weight percent of the additive of claims 1-6. 8. A lubricating oil additive exhibiting improved varnish inhibition and sludge dispersant potency, said additive being the reaction product of an ethylene polyamine and an aliphatic hydrocarbon-substituted succinic acid or anhydride wherein the hydrocarbon substituents have a C average of C50 to C120 with not more than 20 weight percent of the substituent radicals being 2/3 or less of the C average and not more than 25 weight percent of the substituent radicals bein greater than twice the C average. 9. The additive of claim 8 wherein the substituent radicals are polyisobutenyl radicals. 10. The additive of claims 8 or 9 wherein said C average is C60 to C90. 11. The additive of claims 8-10 wherein not more than 15 weight percent of the substituent radicals are greater than twice the C average.

Inventors: BROWNAWELL, DARRELL WILLIAM, GUTIERREZ, ANTONIO
Applicants: EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1981
Main classification: C10M1
IPC codes: C10M159, C08F8, C10M133, C10N40, C10N30