US3210279A - Thiophosphonate ester dispersants for lubricating oils - Google Patents

Description

United States Patent 3,210,279 THIOPHOSPHONATE ESTER DISPERSANTS FOR LUBRICA'IING OILS Joel R. Siegel, Elizabeth, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Apr. 25, 1962, Ser. No. 189,971 16 Claims. (Cl. 252-463) This invention concerns novel ashless detergents and detergents of low ash content and improved lubricating oil compositions containing them. These compositions are especially effective as crankcase lubricants for automotive gasoline engines. The ashless detergent additives of the invention are prepared by esterifying sugar alcohols with fatty acids and then reacting the esters with phosphosulfurized hydrocarbons. The detergents of low ash content are prepared by further reacting the additives with boric acid.

In the development of compounded lubricants to meet the demands of modern internal combustion engines, there has been a recognized need for crankcase lubricants that will have high detergency and that will at the same time possess satisfactory resistance to oxidation. Lubricating oils having high detergency and good oxidation resistance serve to keep the engine free of varnish, sludge and cokelike deposits and thereby promote longer engine life through reduced wear. In order that heavy duty detergent-type lubricating oils will have the ability to maintain a high degree of engine cleanliness, they must be able to disperse insoluble material that is formed during the operation of the engine either by combustion of the fuel or by oxidation of the lubricating oil or that is derived from both of these sources. Most of the detergents, dispersants and antioxidants that are in use in lubricants for heavy duty service in internal combustion engines are metallic derivatives such as alkaline earth metal sulfonates, alkaline earth metal alkyl phenol sulfides, colloidal dispersions of metallic carbonates and the like. Although such additives function quite well as sludge dispersants and detergents, they have one disadvantage in that the ash residue from the lubricant tends to accumulate in the combustion chamber of the engine where it causes pre-ignition, spark plug fouling, valve burning and similar undesirable conditions. For this reason there is a need for effective sludge dispersants and detergents that will either be ash-free or will at least be relatively low in ash-forming tendencies.

In accordance with the present invention it has been found that particularly effective ashless dispersing agents or detergents for crankcase lubricants can be prepared by esterifying sugar alcohols with aliphatic acids and then reacting the esters with phosphosulfurized hydrocarbons. These additives can be further modified by reaction with boric acid to prepare additives of very low ash content.

The sugar alcohols are hexahydric alcohols which are well known in the art. They can be prepared by reducing mono saccharides or di saccharides. The sugar alcohols also occur in nature. The most common sugar alcohols are sorbitol, mannitol and dulcitol. Also contemplated for use in this invention are the partially dehydrated sugar alcohols such as sorbitan and other hexitans. Even if one starts with sugar alcohols that have not been partially dehydrated, some dehydration can and possibly does occur during ester-ification, so that at least a portion of the product of the sugar alcohol esterification would be a hexitan ester (through the loss of one mole of water) or even a hexide ester (through the loss of two moles of water). Alternatively, the sugar alcohol can first be dehydrated to a hexitan by conventional methods, and the latter then used to esterify the fatty acid.

The conversion of the sugar alcohol to an ester of a fatty acid is conducted by the usual esterification techniques. Depending on the molar proportions of the sugar alcohol or partially dehydrated sugar alcohol and the fatty acid, a mono, di, or tri ester may be formed, as for example mannitol trilaurate, sorbitol distearate, sorbitan mono oleate, etc. Fatty acids in the range of from 6 to 20 carbon atoms may be used. Suitable acids include caproic, caprylic, undecylic, lauric, myristic, oleic, stearic, and linoleic.

The sugar alcohol ester is then further reacted with a dialkenyl thiophosphonic acid. The latter acids are prepared by treating polyolefins with P 8 Polymers of ethylene, propylene or butylene may be used. The olefin polymers have Staudinger molecular weights in the range of from about 500 to about 200,000 and contain from 2 to 6 carbon atoms per olefin monomer. Preferably, the phosphosulfurized polyolefin is prepared by reacting the polyolefin with from 5 to 30 Weight percent of a sulfide of phosphorus, and preferably with 10 to 20 weight percent of phosphorus pentasulfide. The phosphosulfurization reaction is conducted under anhydrous conditions at temperatures in the range of to about 600 F. for from about /2 to 15 hours. It is advisable to treat or blow the phosphosulfurized product with an inert gas such as nitrogen for a period of from 10 minutes to 2 hours to aid in reducing hydrogen sulfide evolution and its corresponding odor. The preparation of phosphosulfurized hydrocarbons and the use of catalysts in the phosphosulfurization reaction are more fully described in U.S. Patent 2,875,188.

The reaction of the sugar alcohol ester and the phos phosulfurized polyolefin is preferably conducted at temperatures in the range of about 200 to 240 F. using reaction times of about 9 to 15 hours. Mole ratios of phosphosulfurized polyolefin to sugar alcohol ester may range from about 1:2 to about 3:1. The preferred ratio is about 1:1.

The products of the reaction of the sugar alcohol esters with the phosphosulfurized polyolefins may be employed in weight concentrations of from about 0.2 to 5 percent in lubricating oils to impart detergency sludge dispersancy and antioxidant properties. Greater dispersant potency and potency life may be obtained by further converting these materials to the borate esters. This may be done by heating the products with equivalent weights of boric acid (preferably orthoboric acid) in the presence of a refluxing Water-entraining agent such as hexane, xylene, benzene, or toluene until about one equivalent or mole of water produced by esterification is removed. If orthoboric acid is used there will actually be 2 moles of water formed, one resulting from dehydration of the acid to metaboric acid, and the second resulting from the esterification reaction. The final products obtained may be added in weight concentrations of from 0.5 to 5 percent to lubricating oil compositions to impart antioxidant and sludge dispersing properties.

While, as indicated, it is preferred that the further reaction of the reaction products of phosphosulfurized hydrocarbons and sugar alcohol esters with boric acid be conducted on a mole-per-mole basis, other ratios Within the range of 1:3 to 3.1, ester product to boric acid, are within the contemplation of the invention. In any case there must be available at least one free hydroxyl group in the ester-phosphosulfurized-hydrocarbon product to react with the boric acid. Thus when further reaction with boric acid is contemplated it may be preferable to start with a mono or diester of a sugar alcohol, such as sorbitan mono-oleate or manitol distearate, for

example. Reaction temperatures in the boric acid esterification step are preferably in the range of about 150 to 275 F. Reaction times may vary in the range of about 2 to 20 hours, lower temperatures requiring relatively longer reaction times than higher temperatures.

The additives of this invention may be used not only as the sole detergents in a lubricating oil composition, wherein they function as low-temperature-sludge dispersants and as antioxidants, but they may also be employed as boosters for conventional detergents, wherein the latter are used in concentrations in the range of about 0.5 to 5 weight percent. When the conventional detergents are metals-containing materials it is possible, by utilizing the additives of the present invention in combination therewith, to obtain added detergency without materially increasing the total ash-forming properties of the composition. Such metals-containing detergents or combination detergent-inhibitors include the alkaline earth metal salts of alkylated phenols or of alkylated phenol sulfides, as for example nonyl phenol sulfide, the so-called basic alkaline earth metal sulfonates, and dispersions of barium carbonate or calcium carbonate in mineral oils containing various surfactants such as phosphosulfurized polyoleiin, for example.

The sulfonates are well known in the art and are the oil-soluble alkaline earth metal salts of high molecular weight sulfonic acids obtained by sulfonating either natural or synthetic hydrocarbons.

Specific examples of suitable sulfonates include calcium petroleum sulfonate, barium petroleum sulfonate, calcium di-C alkyl benzene sulfonate (C group from tripropylene), and barium C alkyl benzene sulfonate (C group from tetraisobutylene). The sulfonates may be of either the neutral type or of the over-based or high alkalinity type, containing metal base in excess of that required for simple neutralization, wherein the excess metal base has been neutralized with carbon dioxide.

Metal salts of alkyl phenols and of alkyl phenol sulfides are also Well known in the art. Metal salts of alkyl phenols having alkyl groups of from 5 to 20 carbon atoms are usually preferred, and the metal used to form the phenate is preferably an alkaline earth metal, e.g., calcium or barium although the salts such as those of aluminum, cobalt, lead or tin are sometimes used. A specific example is the barium salt of the alkylation prodnot of phenol with tripropylene. Metal salts of the corresponding alkyl phenol sulfides may also be used. The latter are the thioethers and polysulfides of alkyl phenols, i.e. compounds in which the alkyl groups are joined by one or more divalent sulfur atoms. The alkyl phenols can be converted to phenol sulfides by reaction with sulfur dichloride. If sulfur monochloride is used, the resulting products are primarily alkyl phenol disulfides.

Other detergent additives include the reaction products of phosphosulfurized hydrocarbons with alkaline earth metal oxides or hydroxides can be prepared by first treating a hydrocarbon with the phosphorus sulfide and then reacting the product with an alkaline earth hydroxide or oxide, for example barium hydroxide, preferably in the presence of an alkyl phenol or an alkyl phenol sulfide and also preferably in the presence of carbon dioxide. The preparation of phosphosulfurized hydrocarbons has been described above.

The dispersants of this invention may also be used in conjunction with ashless detergents such as high molecular weight polymeric dispersants made with one or more polar monomers, such as vinyl acetate, vinyl pyrrolidone, methacrylates, fumarates and maleates. These dispersants have molecular weights in the range of about 500 to 50,000. One example is a copolymer of 65 to 85 weight percent of mixed C C fumarates, to 20 weight percent of vinyl acetate, and 5 to 15 percent of N-vinyl pyrrolidone. Another example is the copolymer derived by reaction of mixed tallow fumarates and C serve to illustrate this EXAMPLE 1 A phosphosulfurized hydrocarbon was prepared by reacting parts by weight of a polyisobutene having an average Staudinger molecular weight of about 830 with 15 parts by weight of P 8 for about 10 hours at about 450 F. The product was then diluted with 30 weight percent of light mineral oil for ease of handling. The 70 weight percent concentrate analyzed 2.45 weight percent phosphorus and 4.24 weight per cent sulfur.

EXAMPLE 2 A mixture of 1320 grams of the 70 weight percent con centrate of phosphosulfurized polybutene of Example 1 and 979 grams of sorbitan trioleate, which was obtained as a commercial product, was stirred and heated at about 240 F. for 12 hours using a purge stream of nitrogen. The syrup-like product had the following inspections:

Gravity, API -1 19.1 Viscosity at 210 F., centistokes 57.1 Viscosity at 100 F., centistokes 978 Phosphorus, wt. percent 1.47 Sulfur, wt. percent 2.48

The hydrogen sulfide that was evolved during the react1on was trapped in an ammoniacal solution of cadmium chloride. From the weight of cadmium sulfide that was precipitated it was determined that the reaction product was largely the oxygen ester, or thionophosphate, of sorbitan trioleate. The reaction may be envisaged by the following equation:

R=polyisobutene component R'=sorbitan trioleate component EXAMPLE 3 In the manner of Example 2, a mixture of 1321 grams of the 70 weight percent concentrate of phosphosulfurized hydrocarbon of Example 1 and 429 grams of sorbitan mono-oleate, purchased commercially, was reacted for 12 hours at 240 F. To an appropriately sized, roundbottom, four-necked flask equipped with a thermometer, stirrer, condenser and water trap, 1749 grams of the above product, containing 400 grams of oil, was added, followed by 250 ml. of toluene. Then, over a period of about one hour, 61.8 grams of orthoboric acid was added in increments to the stirred refluxing mixture. The incremental addition of orthoboric acid was necessary to avoid excessive foaming. The mixture was refluxed for a total of about 3 hours, the stopping point being determined by the lack of additional water being riven off. In this instance the total amount of water collected was 31.5 ml. The mixture was filtered hot, after which the solvent was removed from the filtrate under vacuum, giving approximately 1600 grams of product in the form of a thick viscous brown syrupy liquid. The borate had the following analysis:

Wt. percent Phosphorus 1.80 Boron 0.53 Sulfur 2.75 Active ingredient 79.5

EXAMPLE 4 In the manner of Example 2, phosphosulfurized polybutene is reacted with mannitol distearate on an equimolar basis at 230 F. for 14 hours.

EXAMPLE 5 In the manner of Example 3, the product of Example 4 is further reacted with orthoboric acid on an equimolar basis in the presence of xylene as the refluxing waterentraining agent.

EXAMPLE 6 The materal of Example 2 was compared with a commercially available detergent inhibitor in a soluble sludge dispersancy test. The test was conducted as follows. A mixture is prepared consisting of ml. of a neutral mineral lubricating oil of 150 SSU viscosity at 100 F. (in which the additive to be tested is incorporated), 10 ml. of a petroleum naphtha (boiling range 3t)0400 E), and ml. of a solution of crankcase sludge in chloroform (prepared in the ratio of 87 grams of sludge to 1275 grams of CHCl The mixture is placed in a crystallizing dish and evaporated on the steam bath for one hour. Then the mixture is centrifuged and 5 ml. of the supernatant liquid is dissolved in 35 ml. of the petroleum naphtha and filtered through a regular grade of laboratory filter paper. The light transmission of the filtrate is then measured and compared With a standard consisting of 10 ml. of the neutral mineral oil and 10 ml. of the petroleum naphtha. Light transmission may be meaured by a standard instrument such as the Lumetron photoelectric colorimeter.

The results of the tests are shown in Table I as percent of light transmission. The lower the value in the table, the more sludge is dispersed and hence the more potent the additive is.

Table I .Results of sludge dispersancy test Wt. Percent Percent Detergent-Inhibitor Used Cone. Light Transmission 3. 5 10 Product of Example 2 0. 5 5

Percent Phosphosulfurized polyisobutene 27.0 Alkyl phenol (248 average molecular weight) 11.7 Barium oxide 10.6 Carbon dioxide 2.5 Mineral Oil 48.2

EXAMPLE 7 The product of Example 2 was employed as a booster detergent in a low temperature engine test, in which conditions were intended to simulate stop-and-go driving. A six-cylinder Ford engine was used, charged with 4 quarts of the oil under test, and run for atotal of 242 hours, under the conditions given in Table II, the cycles being repeated until the end of the test.

At the end of the first 66 hours, and every 44 hours thereafter, the engine was inspected by removing the oil pan, the rocker arm cover, and the push rod chamber cover, and various parts including the oil screen, the oil pan, the crankshaft, the push rod chamber, the push rod chamber cover, the rocker arm cover, and the rocker arm assembly, were rated for sludge deposition, using a merit system in which 10 represents a clean part and zero a part covered with the maximum amount of sludge possible.

The test oil was an SAE- lubricating oil containing 3.5 weight percent of a commercial detergent inhibitor and 0.5 weight percent of the sorbitan trioleate-phosphosulfurized hydrocarbon product of Example 2. The test results obtained are shown in Table III.

Table 111 Hours on Test Percent Oil Screen Merit Rating Plugging EXAMPLE 8 in Table IV. It will be seen that the latter additive was more effective than the additive of Example 2.

Table IV Hours on Test Percent Oil Screen Merit Rating Plugging EXAMPLE 9 Table v.

Table V Hours on Test Percent Oil Screen Merit Rating Plugging The lubricating oil containing 0.5% of the booster detergent of Example 2 gave 17% higher merit rating than the commercial, premium grade motor oil after 198 hours of test.

EXAMPLE 10 In the prior art it was known to react phosphosulfurizcd polyisobutene with other reagents, e.g. amines. For a direct comparison with the compositions of the present invention, a sample of the phosphosulfurized polyisobutene of Example 1 was reacted with an equimolar proportion of a high-molecular-weight amine known as Primene 8lR, and the product was added in 0.5% concentration, in place of the product of Example 2, to the same SAE-20 lubricating oil containing 3.5 wt. percent commercial detergent inhibitor as was tested with results shown in Table III. The results of the engine test on the oil containing 0.5% of the above-described amine-treated phosphosulfurized polyisobutene are given in Table VI.

At the end of the test the merit rating with this oil was 14% lower than was shown with the oil containing the composition of the present invention. The significance of the difference of 14% is remarkable because only 0.5% of the booster detergent was used in each oil and the only difference between the two booster detergents was in the finishing treatment of the phosphosulfurized polyisobutene.

The lubricating oil base stocks to which the dispersant additives of this invention may be added include not only mineral lubricating oils but various synthetic oils. The mineral lubricating oils may be of any preferred type including those derived from the ordinary parafiinic, naph thenic, asphaltic or mixed base mineral crude oils by suitable refining methods. Synthetic hydrocarbon lubricating oils may also be employed. Other synthetic oils include dibasic acid esters such as di-2-ethyl hexyl sebacate, carbonate esters, glycol esters such as C oxo acid diesters of tetraethylene glycol, and complex esters as for example the complex ester formed by the reaction of 1 mole of sebacic acid with 2 moles of tetraethylene glycol and 2 moles of 2-ethyl hexanoic acid.

Also, although the additives of this invention are primarily intended for use in lubricating oils designed for automotive crankcases, they may also be employed in other hydrocarbon oil compositions including turbine oils, various industrial oils, hydraulic fluids, transmission fluids and the like.

The oil compositions of the invention may also contain, in addition to the detergent, such additives as viscosity index improvers, e.g. polymethacrylates, olefin polymers, etc., antioxidants such as phenyl-alpha-amine, bis phenols, etc., pour point depressants, dyes, and other additives for improving the properties of the compositions.

It is to be understood that the examples presented herein are intended to be merely illustrative of the invention and not as limiting it in any manner; nor is the invention to be limited by any theory regarding its operability. The scope of the invention is to 'be determined by the appended claims,- v

What is claimed is:

1. An improved lubricating oil composition comprising a lubricating oil to which has been added from 0.2 to 5.0 weight percent of the reaction product of (a) a phosphosulfurized polyolefin and (b) an ester of a fatty acid of from 6 to 20 carbon atoms and a sugar alcohol selected from the group consisting of hexitols, hexitans, and hexides; wherein said polyolefin has a molecular weight in the range of from about 500 to about 200,000 and is derived from an olefin monomer having from 2 to 6 carbon atoms; said (a) and (b) being reacted in a mole ratio of (a):(b) in the range of from about 1:2 to about 3:1.

2. An improved lubricating oil composition as defined in claim 1 wherein said reaction product has at least one free hydroxyl group and said reaction product has been further reacted with boric acid in a mole ratio in the range of from about 1:3 to about 3:1.

3. Lubricating oil composition as defined by claim 1 wherein said ester is sorbitan mono-oleate.

4. Lubricating oil composition as defined by claim 1 wherein said ester is sorbitan trioleate.

5. Lubricating oil composition as defined by claim 1 wherein said ester is mannitol distearate.

6. As a new composition of matter the reaction product of (a) a phosphosulfurized polyolefin and (b) an ester of a fatty acid of from 6 to 20 carbon atoms and a sugar alcohol selected from the group consisting of hexitols, hexitans and hexides; wherein said polyolefin has a molecular weight in the range of from about 500 to about 200,000 and is derived from an olefin monomer having from 2 to 6 carbon atoms; said (a) and (b) being reacted in a mole ratio of (a): (b) in the range of from about 1:2 to about 3:1.

'7. Composition of matter as defined by claim 6 Wherein said ester comprises sorbitan mono-oleate.

8. Composition of matter as defined 'by claim 6 wherein said ester comprises sorbitan trioleate.

9. As a new composition of matter the reaction product of (a) the composition of claim 6 and (b) boric acid; wherein the mole ratios of (a) (b) are from about 1:3 to about 3:1 and wherein the composition of claim 6 has at least one free hydroxyl group.

10. Composition of matter as defined by claim 9 wherein said ester comprises sorbitan mono-oleate.

11. A process for the preparation of a new composition of matter which comprises reacting about equal molar proportions of (a) a phosphosulfurized polyolefin and (b) an ester of a fatty acid of from 6 to 20 carbon atoms and a sugar alcohol selected from the group consisting of hexitols, hexitans, and hexides; wherein said polyolefin has a molecular weight in the range of about 500 to about 200,000 and is derived from an olefin monomer having from 2 to 6 carbon atoms; the reaction being carried out at a temperature of about 200 to 240 F. for a time of about 9 to 15 hours.

12. The composition prepared by the process of claim 11.

13. An improved lubricating oil composition comprising a lubricating oil to which has been added from 0.2 to 5.0 weight percent of the composition of claim ll.

14. A process for the preparation of a new composition of matter which comprises (1) reacting (a) a phosphosulfurized polyolefin and (b) an ester of a fatty acid of from 6 to 20 carbonatoms and a sugar alcohol selected from the group consisting of hexitols, hexitans, and hexides; wherein said polyolefin has a molecular weight in the range of about 500 to about 200,000 and is derived from an olefin monomer having from 2 to 6 carbon atoms; the reaction being carried out at a temperature of about 200 to 240 F. for a time of about 9 to 15 hours; said (a) and (b) being reacted in a mole ratio of (a) (b) such that the reaction product has at least one free hydroxyl group; (2) reacting about equal molar proportions of said reaction product and boric acid; the reaction being carried out at a temperature about 150 to 275 F. for a time of about 2 to 20 hours.

15. The composition prepared by the process of claim 14.

16. An improved lubricating oil composition comprising a lubricating oil to which has been added from 0.2 to 5.0 weight percent of the composition of claim 14.

References Cited by the Examiner UNITED STATES PATENTS 2,768,954 10/56 Fields 25246.6 2,795,548 6/57 Thomas et al. 252.-49.6 2,898,299 8/59 Lowe 252-466 3,002,925 10/61 Sabol et al. 25232.7

DANIEL E. WYMAN, Primary Examiner.

Claims (2)

1. AN IMPROVED LUBRICATING OIL COMPOSITION COMPRISING A LUBRICATING OIL TO WHICH HAS BEEN ADDED FROM 0.2 TO 5.0 WEIGHT PERCENT OF THE REACTION PRODUCT OF (A) A PHOSPHOSULFURIZED POLYOLEFIN AND (B) AN ESTER OF A FATTY ACID OF FROM 6 TO 20 CARBON ATOMS AND ASUGAR ALCOHOL SELECTED FROM THE GROUP CONSISTING OF HEXITOLS, HEXITANS, AND HEXIDES; WHEREIN SAID POLYOLEFIN HAS A MOLECULAR WEIGHT IN THE RANGE OF FROM ABOUT 500 TO ABOUT 200,000 AND IS DERIVED FROM AN OLEFIN MONOMER HAVING FROM 2 TO 6 CARBON ATOMS; SAID (A) AND (B) BEING REACTED IN A MOLE RATIO OF (A):(B) IN THE RANGE OF FROM ABOUT 1:2 TO ABOUT 3:1.

2. AN IMPROVED LUBRICATING OIL COMPOSITION AS DEFINED IN CLAIM 1 WHEREIN SAID REACTION PRODUCT HAS AT LEAST ONE FREE HYDROXYL GROUP AND SAID REACTION PRODUCT HAS BEEN FURTHER REACTED WITH BORIC ACID IN A MOLE RATIO IN THE RANGE OF FROM ABOUT 1:3 TO ABOUT 3:1.