US2673175A

US2673175A - Synthetic lubricating oil

Info

Publication number: US2673175A
Authority: US
Publication date: 1954-03-23
Anticipated expiration: 1971-03-23

Description

March 23, 1954 R. K. sTRATFoRD x-:r Ai. 2,673,175 SYNTHETIC LUBRICATING OIL Filed April 21, 1951 TIME-MINUTES MEA N/NG OF SYMBOLS MCL. J0 M/D-CoA/TWEA/T Louocw SIAE. m GRADE MCL 3o M/D-CONT/NEA/ cubo/v S.A.E. 3o GQADE C'WO COLUMBIA/V WEBSTEQ L/GHTEQ THAN SAE. -IO GRADE CW 30 COLUMe/A/v WEBSTEQ SAE 3o GQADE 5o//oo PFFE. D/sr (Mc/ pA QA PF/,v D/s r/LLATE 0F 5o SUS V/scoS/TY ATJOOE FROM M/D-CONT/^/ENT LoL/DOM CQUDE.

rf cza A. Stuart ZJZZL'czrn. A. Jones 5 ave labors' Patented Mar. 23, 1954 2,673,175 SYNTHETIC LUBRICATIN G OIL Reginald K. William A. Frank A.

to Standard Oil Develop poration of Delaware Stratford, Corunna, Jones, Sarnia, Stuart, Richmond, Calif., assignors ment Company, a cor- Ontario, and Ontario, Canada, and

Application April 21, 1951, Serial No. 222,172

14 Claims.

This invention relates to the manufacture of a synthetic lubricating oil of improved properties by chemical treatment of a refined mineral lubricating oil fraction.

The invention will be described hereinafter with reference to the accompanying drawing, the single ligure of which is a graphical illustration of the relative utility of various oils for the purposes of the present invention.

In the operation of internal combustion en gines, particularly at relatively low crankcase and cooling jacket temperatures, deposition of varnish on piston surfaces, oil screen and other engine parts is a serious problem. This varnish deposition which is mainly caused by the fuel and varies with the type of fuel used as well as with engine operating conditions, may be controlled by lubricants which have high solubility for oxi dized fuel combustion products and/or prevent deposition of insoluble polymerization products. It is a well-known practice to add oxidation inhibitors to oil in order to prevent lubricating cil oxidation in high temperature operation. Such inhibitors, however, generally do not lessen varnish formation from fuel products in low temperature operation and, in fact, sometimes increase the amount of varnish formation. In order to keep sludge and insoluble matter in suspension it is a common practice to use agents known as detergents in combination with inhibitors. In general, detergent additives do not increase the solvent power of the lubricant for varnish forming materials. Hence the concentrations generally used do not give effective reduction of varnish deposits.

By the present invention, the mineral lubricating oil is submitted to chemical treatment before addition of antioxidant, if the latter is required. The resulting product not only keeps suspended material in suspension but also inhibits formation of insoluble varnish. At the same time the chemical treatment gives a product of higher viscosity than the original mineral oil. Thus, by the treatment it is possible to increase the viscosity to that desired for lubricating purposes, without the necessity of adding thickeners or without employing more expensive base stocks, such as bright stocks. Products obtained by the process of the present invention have shown marked ability to prevent deposition of varnish when employed in the crankcase of a typical automobile engine, operating under conditions at which varnish formation is heavy when mineral lubricants and a deposit forming fuel are used.

"Briey, the process of the present invention involves the treatment of' a phenol extracted, hydronished mineral lubricating oil with oxygen to produce a material having a saponication number of at least 20, substantially reducing the neutralization number of the resulting product by means of a neutralizing agent, and preferably though not always necessarily adding to the neutralized product an antioxidant to prevent further oxidation. Whether or not an antioxidant is necessary is dependent on the nature of the base stock processed and the manner of oxidation.

The method of the invention may be applied generally to distillates in the viscosity range from heavy gas oil (30 seconds viscosity Saybolt at F.) to heavy lubricating oil distillates (3000 seconds Saybolt at 100 F). For example, distillates from Mid-Continent (Londen) and Colombian crudes have been found to be quite suitable.

It is considered necessary, prior to oxidation, to apply phenol extraction and mild hydrogenation to the base oil, for the purpose of obtaining a material which oxidizes rapidly without the formation of oil insoluble sludge. Dewaxing may also be applied, but this is not essential. The scope of the process is not limited however to the use of phenol extraction and mild hydrogenation as the method of preparing' a base oil suitable for oxidation. It is considered possible by proper choice of conditions to produce a suitable base stock by refining the lubricating oil distillate by means of other extracting solvents such as furfural, cresols, nitrobenzene, etc. and hydronishing or by fuming acid treatment or by treatment with silica gel or by severe hydrogenation followed by mild hydrogenation.

The solvent extracted distillate may be hydrogenated, preferably by the use of nickel, nickel on kieselguhr, platinum or palladium catalysts, but it is also possible to use sulfur resistant catalysts, such as nickel-tungsten sulldes, cobalt molybdate or alumina, molybdenum on alumina and other known hydrogenation catalysts. The dev gree of hydrogenation necessary and the hydrogenation conditions depend on the nature of the distillate being refined and the degree of extrac tion to which it has been subjected. lt is desirable but not absolutely necessary to decrease the sulfur content of the oil to 0.03% or lower and to improve the color to about 18 Robinson or better by the hydrogenation process.

The oxidation step is carried out by passing oxygen or air into the oil, preferably through a diffuser placed in the oil contained in a tall for oxidation. is .from about F., although it is possible Vto carry out the oxidation satisfactorily in the temperature range from about 200 to about 400 F. The saponication numberv is increasedLtvo approximately after an absorption utf8-10% vby weight of oxygen and to approximately 50460 aiter the absorption of 14-16% oxygen. Yields of oxidized material on the basis of mineral oil charged are generally about 99 volume percent at 20 saponiiication number and 96 volume percent at 50 'saponiication value. The exact chemical nature of the saponiiiable material cannot be defined from the data at present available.

In the present process no advantage hasbeen demonstrated for the use of metallic catalysts such as manganese naphthenate, calcium salts and other recommended oxidation catalysts. If metallic catalysts are used, extra processing steps may be necessary for their removal. As a catalyst t`o initiate oxidation, particularly when air is used as the oxidizing agent, benzoyl peroxide has been found to be effective. `Other organic peroxides appear to be useful in a similar manner, and do not reduire the extra processing steps which are required when metal catalysts are used.

Oxidation by means of air takes place much more slowly of course than with gaseous oxygen. Whereas a hydronished Mid-Continent Louden stock-was `converted by commercial oxygen at 350 F. into a material having a saponication number of -30 in 45 minutes, similar treatment of this stock at the same temperature with air required 54 hours to produce a similar result. Oxidation was accomplished by means of air at 400 F. in 16 hours, but the product was very dark in color. The addition of 1% benzoyl peroxide as catalyst in the air treatment at 300 F. produced an oxidized 'product of 43 saponiiication number in 4 hours.

Following the oxidation step, which produces an acidic product, a basic material is added to substantially reduce the acidity. yGenerally the amount oi' neutralizing agent which is addedis that which is theoretically suicient to reduce the neutralization number to 0. In actual practice a zero neutralization value has notbeen obtained by using the theoretical quantity of basic material. However, a certain degree oi acidity can be tolerated. The addition of the theoretically required amount of neutralizing agent has been formation. The preferred` those of 3 to Y tion temperature.

found to give a product which is non-corrosive to iron and babbit at temperatures up to 350 F. It is desirable to reduce the original neutralization number, as determined by ASTM Method D663-46T, o the oxidizedproduct to a value not greater than one-half the original value. In the average case the neutralization number of the product should/not be greater than about 6. However, a good product has` been obtained by oxidizing sufficiently toraise the neutralization numberto about4 21 and then treating ywith 'a neutralizing agent (butyl alcohol) in at least 4 and preferably greater than theoretical quantity even though the final neutralization number was 9.4. It appears to be necessary to reduce the neutralization number by at least half, and preferably more than half. ,Y

As neutralizing agents alcohols, such as butyl alcohol, as well as metallic bases have been used. The alcohol has the advantage of not introducing metallic constituents into the oil, and even where metal bases are used alcohol is useful for partially reducing high neutralization value in order to avoid the necessity of adding an undesirably large amount of 'metallic bases. Metallic bases, such as the oxides and hydroxides or" alkaline earth metals, are then used as neutralizing agents. These give a product which has the ability to keep solid sludge and water in suspension.

For this purpose, calcium hydroxide in combination with calcium oxide has been used, the purpose of the calcium oxide being to react Vwith the water formed by the action of calcium hydroxide. Similarly, barium hydroxide with and.

without barium oxide has been used. Magnesium hydroxide and/or oxide is also believed to be suitable. Sodium and aluminum hydroxides were not found to be satisfactory because vof a thickening action on the product.

The practice in using volatile alcohols suchw'as butyl is to heat oxidized material with 5 to 10 times as much alcohol 'as `is theoretically required for complete reduction of the neutralization value by esteriilcation. During the heating period part of the alcohol is'gradually distilled oi in order to remove water and promote esterification. Organic amines and ammonia may be employed in place oi alcohols. Any oi the aliphatic saturated alcohols of 2 8 carbon ratoms are preferred.

The practice in using metallic bases with or without prior neutralization by alcohol -is to add the calculated theoretical amount of the base to the oxidized material, and to heat preferably to about 15G-250 F. with agitation until all the neutralizing material dissolves. The Ymetallic base may be added 'gradually or all at once.

'After partial 'or complete reduction of the neutralization value by esteriiication and/or interaction with calcium hydroxide or other suitable metallic bases, final traces kof alcohol and/or low boiling oxidation products including water are removed from the oxidized material by Vacuum distillation. In the laboratory vacuum distillation has been carried out `at 5-10 mm. pressure andthe distillate taken overhead until the still temperature reaches L15G-500 F. Lower or higher pressures may be employed provided the corresponding adjustment is made in the final distilla- Exact choice o distillation conditions depends on the viscosity and boiling range of the original distillate. After vacuum distillation the yield of material which is not carried overhead is generally about 94-95 volume percent of a product v,with 50 saponication number. Yields are 96-97 volume percent of oxidized product when it has a saponication number of about 20. Aiter vacuum stripping, the oxidized and neutralized oil isn preferably ltered to remove any suspended material. When pure calcium hydroxide and pure calcium oxide are used as neutralizing agents no suspended material is formed and filtration is not necessary. ,A

Itv is considered necessary to add to theufinal product an Vantioxidant in, suilicientmamountuto reduce the tendency to further oxidation by an to 20 carbon atoms may be used;V

amount which will prevent oxygen absorption at 350 F. at a greater rate than about 1% per hour, as determined by an oxygen absorption test conducted as follows: 10 cc. of oil is placed in a closed tube fitted with an oxygen disperser, immersed in the oil. The tube is placed in a bath maintained at 350 F. and connected to a bur-ette containing oxygen. Oxygen is cirdulated through the oil at a rate of 750 inl/min. The amount of oxygen in the burette is measured at intervals and the rate of oxygen uptake plotted against A satisfactory oil shows only a slow rate of oxygen absorption which does not increase with time.

Any of the well k abl oxidant is the reaction product of a-pinene and phosphorus pentasulfide. Other suitable antioxidants are the alkaline earth metal salts of alkylated phenol sulfides and their reaction products with sulfur and suldes of phosphorus, also phenyl a-naphthylamine and 2,6di-tert.butyl 4-methylphenol. The last two are recommended for use only where the oil is not subjected to temperatures greater than 300 F.

In the :following table are given typical inspecweight percent of 50% lyst. After four hours nickel on kieselguhr cataat 250 F. and two hours at 450 F. a product was obtained in 99% yield having 0.02% sulfur content and +26 Saybolt color. I'his product was then blown with oxygen at 350 F., whereby 14 weight percent of oxygen was absorbed after 21/2 hours. A yield of 97-98 weight percent of oxidized product, based on the oil charge, was obtained of a light red color, having a saponication number of 56 and a neutralization number of 17. The viscosity had increased to 533 seconds Saybolt at 100 F.

This oxidized product was heated with volume percent of butyl alcohol in such a manner as to distill 01T approximately one-half of the alcohol over a period of 4 hours. The balance of the alcohol was then distilled off by heating the mixture to 450 F. under 10 mm. vacuum. By this treatment the neutralization value was reduced to 10. The residue from the distillation was then heated for six hours with 0.3% calcium hydroxide and 0.15% calcium oxide. After this treatment all the calcium hydroxide and calcium oxide had dissolved in the oil and the neutralization number was reduced to 6. The oil was ltered to remove any suspended undissolved material, but practically no residue was obtained on the tions of an oil after the various treatments demien The product after neutralization, when scribed above, the Original Oils being Mid-COII- blown with oxygen at 350 F., absorbed approxitinent Louden stocks which have been phenol mately 1.4 weight percent after one hour. 1.0% extracted and hydronished. of a commercial oxidation inhibitor (reaction n "Mm" I Oil Desi Vis. Sep. Neat. Anilino Oxygen Absorption nationg Tleatment (wirr f l' I No. No. reim (350 F.) MM .In Extracted hydmnished iight 150 95 nu J nu l 21s 9%111 one-naifhour,

lube distillate. A2 A1 after absorption oi l2-14% 533 04 56 17 156 4% in ono hour.

oxygen. A3 A2 refluxed with outyl alcohol. 603 80 45 6 154 1.4%in one hour.

heated with 0.5% lime at 200 F., l0 hours vacuum stripped, i filtered. A4 A3+l%reaction product a-pinene 650 82 45 6 157 0.6%inonehour.

+P B1 Extracted hydronishcd light-l 364 95 nil nil 228 7%inone-haliliour intermediate lube distillate. B2 B1 after absorption of 8-10% 620 78 23.4 7.0 195 5.5% in onehour.

Oxygen. B3 B2 heated With 0.4% lime at 200 596 S9 I 17 3.0 190 6 hours vacuum stripped, filtered. B4 B13- 511% reaction product ar-piuenc 602 89 19.5 2.4 197 0.8%inoi1el1our.

S5. C1 Mediizim grade refined distillate C2 C1 highly oxidized 547 G4. 1 68. 3 21 159 C3 C2 reliuxed with butyl alcohol, 555 70 70 10 148 heatcd with 0.5% lime at 200 F., 10 hrs. vacuum stripped, filtered. C4 Same as C3+l% commercial anti- 596 70 70 9. 4 148 oxidant.

In the following examples the preparations of some satisfactory iinished products are described in detail, including an engine test of the same, but it is to be understood that these examples are given by way of illustration only and do not limit the scope of the invention.

Example 1 g oil distillate of 165 viscosity (Say- F'., obtained from a Mid-Continent A lubricatin bolt) at 100 drogenation at 100 lbs/sq. in. pressure using 10 product of a-pinene and Pass) was then added, and the inhibited oxidized oil when blown with oxygen at 350 F. absorbed only 0.8 weight percent after 3 hours.

The product and 45 brake horsepower, at a block temperature of F. and an oil sump temperature of F., using a deposit forming fuel.

011s were rated by a demerit system,

given a rating of 0, while a rating of 10 is given to the worst condicted on that surface, with respect to the deposition of varnish on the piston surfaces., The non-oxidized oil showed a demerit of 5.5-6.5, while the oxidized and neutralized oil showed a demerit of 0.5 which is quitel satisfactory. The oil` pan and oil screen of the engine operated on the oxidized lubricant was clean and free of sludge, while the nonoxidized lubricant gave an appreciable quantity of watery sludge and the oil screen was heavily coated with varnish.

Example 2 A light lubricating oil distillate and an intermediate lubricating oil distillate, derived from a Mid-Continent Louden crude, were separately phenol extracted and dewaxed as in Example 1. These were blended to a viscosity of 364 seconds Saybolt at 100 F. and treated for four hours at 350 F. and for one hour at 450 F. with hydrogen at 100 lbs/sq. in. pressure in the presence of weight'percent of 50% nickel on kieselguhr catalyst. The hydrogenated product had a color of 23 Robinson and a sulfur content of 0.02 weight percent. When blown with oxygen at 340 F. it absorbed approximately 9 weight percent after l hour to give a 99 volume percent yield of a light red colored product having a saponication number of 23, a neutralization number of 7, and a viscosity of 628 seconds Saybolt at 100 F.

The oxidized material was heated and shaken at intervals for 6 hours at 200 F. with 0.3 weight percent calcium hydroxide and 0.1 weightrpercent calcium oxide. By this treatment the neutralization value was reduced to 3. The product was then vacuum stripped to give a 97 volume percent yield. This partially neutralized oxidized oil was then inhibited with 1.0% of the reaction product of e-pinene and P285, thereby lowering the oxygen absorption rate from 2.0% in 1 hour to 0.8% in 1 hour or 1.5% in 3 hours. The oil prepared in this manner was tested in a Chevrolet engine in the manner described in Example 1, and a sample of the unoxidized oil, also with inhibitor, was likewise tested. The unoxidized oil showed a piston varnish demerit rating, of 5.5-6.5, while the oxidized oil showed a demerit of 1.7. In this case also the engine operated on the oxidized oil and had a much cleaner crankcase and oil screen than when operated with the unoxidized oil.

It is not possible at this time to give all the exact specifications for the oil to be oxidized but, in general, it is preferable to use an oil which is low in sulfur and nitrogen. These elements, along with oxygen and other materials commonly found in trace proportions, affect the oxidation rate appreciably and, therefore, affect the final product materially. The presence of small amounts of oxidation inhibitors, natural. or synthetic, may effectively inhibit oxidation and/or cause sludge formation during oxidation. Thus in one experiment, proportions as low as 0.01% sulfur in the form of mercaptan or aliphatic disulfide causedl sludge formation in a closed static oxidation system (Sligh oxidation at 392 FJ. By extracting the same oil with a solvent (furfural or phenol) and then hydrofinishing, the same base stock was readily oxidized without sludge formation.

Hence the oil should be renned tosuch a degree that it can be oxidized readily to a saponification number of to '70 without substantial formation of sludge or oil insoluble gums. Oils of low average molecular weight, containing about 40% ofv aromatic constituents, appear to give oil insoluble gums and, in general, those of lower aromatic content appearmora suitable.. Also,

oils capableof rapid oxidation are desirable. The drawing which accompanies this specification shows the oxidation rates for hydronished oils of various origins and viscosity grades, as determined by a test in which the volume of pure oxygen absorbed at 200 C. and approximately atmospheric pressure is measured, using both4 10 cc. and cc. oil sample tubes in the tests. Oils which absorb 800 cc. of oxygen per 10 cc. of oil in a period of not more than 100 minutes are especially desirable for the purposes of this invention.

Oils treated according to the present process may be oxidized to various degrees, but those treated to a saponication number ranging lbetween 20 a-nd 30 are particularly preferred for economic reasons. This product should be neutralized to as low a final neutralization number asis practicable, but various products having neutralization numbers of 4, 7, 17, 21, reduced to 1.4, 2.4, 6 and 9.4 upon treatment with basic reagent all showed reasonably good results.

Obviously, the degree and conditions of oxidation and neutralization and the agents or combinations of agents employed for neutralization may be varied within the limits previously suggested. The iinal products may be further modified by addition of conventional modifiers such as various antioxidants, viscosity index improvers, pour point depressants, metal deactivators, detergents, thickeners, soaps (to form greases, for example), as will be obvious to those skilled in the art.

What is claimed is:

1. A lubricating oil composition prepared by contacting a solvent extracted, hydrogenated mineral lubricating oil fraction with a gas comprising free oxygen at a temperature of 20C-400 F. until a product having a saponication number of at least 20 and not more than about '70 is produced, and treating the oxidized product with a neutralizing agent until the neutralization number of the same is reduced by at least 50% of its original value, said product having the property of inhibiting sludge and varnish formation in internal combustion engines operating Vfor extended periods at low temperatures on deposit forming gasolines.

2. A product according to'claim l obtained from a lubricating oil fraction which is hyf drogenated prior to oxidation in order to reduce the sulfur content to a value not greater than 0.03% by weight, to increase the color to a value of at least 18 Robinson, and to substantially increase the oxidation rate.

3. A product according to claim 1 obtained by treatment of the oil with oxygen or a gas containing free oxygen at a temperature of 275-400 F.

4. A product according to claim 1 in which benzoyl peroxide is used as catalyst to initiate oxidation by the gas which comprises free oxygen.

5. A process which comprises treating a solvent extracted mineral base lubricating oil of low sulfur, low nitrogen, and moderately low aromatic content vwith a gas comprising oxygen at a temperature range between 200 and 400 F. for a period of time and under catalyst conditions such` that a saponication value of at least 20 and not more than '70 is reached, then treating the oxidized oil with aneutralizing agent consisting at least in part of an alcohol capable of esterifying the oxidation product,.the product after neutralization being,I heated tor remove by 9 distillation any portions which have boiling points lower than 350 F. at 10 mm. pressure.

6. A process according to claim in which the neutralizing agent is a mixture of calcium hydroxide and calcium oxide.

7. A process according to claim 5 in which the neutralization is accomplished by iirst re fluxing with butyl alcohol and then by treatment with a mixture of calcium hydroxide and calcium oxide.

8. A process which comprises contacting a phenol extracted hydrogenated lubricating oil fraction with oxygen at a temperature of 275400 F. until a product having a saponiiication number of 20 to 70 is produced, heating the oxidized product with volume percent of butyl alcohol until approximately one half of the alcohol is distilled off over a period of about l hours, iurther heating to remove the remainder of the unreaoted alcohol at a temperature of 450 F. and 10 mm. pressure, heating the product for about 6 hours in the presence of 0.3 weight percent calcium hydroxide and 0.15 Weight percent calcium oxide, and adding to the nal product 1.0 Weight percent of an oxidation inhibitor in suil'icient amount to reduce the oxygen absorption rate at 350 F. of the product to less than 1% per hour.

9. Process according to claim 8 wherein the oil is oxidized to a saponication number of about 50.

10. Process according to claim 8 wherein the oil is oxidized to a saponication number of to 30.

11. A product extracted hydrogenated mineral lubricating oil fraction with a gas containing free oxygen at a temperature of 200-400 F. until a product having a saponication number of at least 20 and not more than is produced, treating the oxidized product with a neutralizing agent until the neutralization number of the same is reduced to not more than 50% of its original value and in any case to a Value not greater than prepared by contacting a phenol 12. A product according to claim 11. to which has been added an antioxidant sufficient in amount to prevent oxygen absorption when the oil is in contact with oxygen at 350'D F. at a rate not greater than 1% per hour.

13. A product according to claim l1, prepared by partially neutralizing the oxygenated product with butyl alcohol and further neutralizing with a mixture of calcium hydroxide and calcium oxide.

14. A product prepared by extracting a lubricating oil distillate of about 165 seconds viscosity Saybolt at F., obtained from a parainic type crude oil, with phenol to give 5 an extracted oil having a viscosity index of at least 95, deyvaxing the extracted oil to a pour point of about 0 F., hydrogenating the extracted, dewaxed oil until the same contains not more than 0.02% sulfur, blowing the hydrogenated oil with oxygen at about 350 F. until about 14 weight percent of oxygen has been absorbed, heating the oxidized oil with butyl alcohol until the neutralization number is reduced by at least half and in any case until it is not greater than 10, heating the partially neutralized product with a mixture of calcium hydroxide and calcium oxide until the neutralization number was reduced to not greater than 6, and adding to the oil product a suilicient amount of an antioxidant to prevent absorption of oxygen when the oil is in contact with oxygen at 350 F. at a rate greater than l weight percent per hour.

REGINALD K. STRATFORD. WILLIAM A. JONES. FRANK A. STUART.

References Cited in the le of this patent UNTED STATES PATENTS Number Name Date 2,070,627 Shoemaker Feb. 16, 1937 2,455,337 Jones Nov. 310, 1948 2,560,650 Kronstein July 17, 1951

Claims

1. A LUBRICATING OIL COMPOSITION PREPARED BY CONTACTING A SOLVENT EXTRACTED, HYDROGENATED MINERAL LUBRICATING OIL FRACTION WITH A GAS COMPRISING FREE OXYGEN AT A TEMPERATURE OF 200-400* F. UNTIL A PRODUCT HAVING A SAPONIFICATION NUMBER OF AT LEAST 20 AND NOT MORE THAN ABOUT 70 IS PRODUCED, AND TREATING THE OXIDIZED PRODUCT WITH A NEUTRALIZING AGENT UNTIL THE NEUTRALIZATION