US2298080A - Lubricating oil for diesel engines - Google Patents

Description

Patented Oct. 6, 1942 LUBRICATING OIL FOR DIESEL ENGINES Philip 8-. Clarke, Palos Verdes Estates, and

Marcellus T. Flaxman. Inglewood, Calif., assignors to UnionOil Company of California, Los Angeles, Calif., a corporation of California No Drawing. Application November 19, 1940, Serial No. 366,236

14 Claims.

This invention relates primarily to lubricating oils for internal combustion engines, especially Diesel engines and the like. The particular object is to produce a lubricating oil especially adapted for use in breaking-in Diesel engines under circumstances where moisture is present and may interfere with the retention of additives such as soaps used in the oil, or cause emulsification. Another object of the invention is to produce such an oil having high detergent characteristics whereby to eliminate or prevent the formation and deposition of gummy, resinous and varnish-like materials in Diesel engines or other varnish-like materials in Diesel engines or other er objects are to produce such lubricants which will have high film strengths, and to produce such lubricants wherein the additive materials are adapted to use in the so-called highly paraffinic lubricating oils, such as typical Eastern or paraflin base oils of the Pennsylvania type, and the highly solvent-treated oils of high viscosity index.

Briefly, the invention resides primarily in mineral lubricating oils, especially those of high viscosity index, containing small proportions of oilsoluble salts or soaps of phosphonic acids produced by phosphorizing and oxidizing highly paraflinic mineral lubricating oil fractions, such as the high viscosity index oils mentioned, and also containing oil-soluble esters of acidic materials produced by the oxidation of highly paraflinic petroleum fractions typified by paraffin wax. In addition to esters from the oxidation acids from parafiin wax, esters of acids of other highly parafiinic petroleum fractions of sufficiently high molecular weight to produce oil-soluble materials of suficiently high boiling point to retain them in an engine during use, may be used, for example, those of petrolatum and those of the high viscosity index mineral lubricating oils mentioned. V

The invention especially includes such mineral lubricating oils for use in breaking-in Diesel ngines and the like to avoid emulsification or soap separation in the presence of water, wherein the described phosphonic acid soap (especially an alkaline earth metal soap) is present in proportions in the order of about to about 1.5%, or within limits of about 0.25% and about 3%, and the ester of the synthetic acids from the oxidation of parafiinic fractions is present in percentages in the order of about /2% to about 1.5%, or within limits of about 0.1% and about 3%. For example, about 1% of a calcium phosphonic acid soap has been employed with about 1% of the methyl ester of oxidation acids from parafiin wax.

These materials may be used also in low viscosity index or naphthenic base oils, at least for some purposes.

The term detergent designates the property of removing or materially retarding the accumulation of resinous, gummy and varnish-like or carbonaceous materials which otherwise tend to deposit upon or around piston rings and valve stems and cause sticking thereof or otherwise accumulate in internal combustion engines.

The term viscosity index (V. I) is a term well-known in the petroleum industry to indicate whether an oil is a paraffin base or a naphthenic base oil, a paraflinic base oil being assigned an index of and certain naphthenic base oils assigned an index of 0. The term is de--v fined by Dean and Davis in Chemical and Metallurgical Engineering, volume 36, 1929, page 618.

The composition of the present invention has the important advantages that the phosphonic soap imparts good detergent properties to the oil, and at the same time is not conducive to the formation of corrosive acids in internal combustion engines during use. These phosphonates do not appear to possess any catalytic influence toward the formation of corrosive acids by oxidation'or the like, but on the other hand possess neutralizing characteristics or at least a tendency to maintain non-corrosive conditions insofar as eilects on highly corrosion-sensitive alloy bearings such as copper-lead or cadmium-silver bearings and the like are concerned. This effect may be due to the fact that the metal element of the salt or soap may combine with any corrosive acids that might form in the engine, and thereby liberate the non-corrosive phosphonic acids which in turn appear to exert corrosion-inhibiting influences kindred to corrosion-inhibiting influences exerted by the phosphonic salts or soaps themselves. Or possibly, there is no decomposition of the-phosphonic salts or soaps and they maintaintheir original form which continuously exerts said influences tending to inhibit development of corrosive conditions.

The composition of the present invention has the further advantage in that the esters of the oxidation acids from paraffinic petroleum frac tions serve to prevent the emulsification of the soaped oil in the presence of water which sometimes gets into the lubricating oil in internal combustion engines and apparently often happens especially in breaking-in lines in engine factories. In other words, these esters possess high demulsibility characteristics in the presence of the phosphonic soaps described. These esters therefore also act to overcome any tendency which might otherwise exist for the phosphonic soaps to precipitate out in the presence of moisture.

An example of suitable esters whichmay be employed is the methyl ester of the synthetic acids produced by the oxidation of parafiin wax having, for example, a melting point of around 120 F. to 125 F. Such materials may have saponification numbers varying from 105 to 150 or 170. These materials will have boiling points high enough so that they will not volatilize from lubricating oil in the crank case of an internal combustion engine during use. Other appropriate boiling point esters may be employed such as ethyl esters or butyl, propyl or amyl esters and kindred lower aliphatic alcohol esters.

Similarly, other parafflnic petroleum .fractions.

such as petrolatum and the highly paraflinic mineral lubricating oils may be used for oxidation to form the acids, and possibly for some instances the well-refined so-called spray oils of high unsulfonatable residue. The method of oxidation and production of such acids and,their esters is well known in the arts and is not here described. While these esters have been known in the lubricating industry as additives for the improvement of oiliness, film strength and the like, it apparently has never been recognized that they would have functions which they exert in the present combination.

With respect to the phosphonic acid soaps, the phosphonic acids are preferably obtained by phosphorizing mineral lubricating oil fractions of the so-called highly parafilnic character or of high viscosity index, and then oxidizing these phosphorized materials to produce phosphonic acids, which in turn are more or less readily convertible into appropriate salts or soaps such as calcium soaps. Although such lubricating oils are preferred for production of the phosphonic acids, other parafllnic mineral oil frac-' tions may sometimes be used.

According to the best modern authorities on the constitution of mineral lubricating oils of the high viscosity index type, the molecules are in fact not primarily aliphatic or chain compounds but are mixed or complex molecules containing aromatic or naphthenic rings protected by aliphatic or parafiinic side chains which may in themselves be straight chains or branched chains. Or such oils may be mixtures of molecules wherein aromatic or benzene rings are protected by aliphatic chains and wherein naphthenic rings also are protected by aliphatic chains. This is presumably the character of lubricating oil fractions designated by the term highly paraflinic or parafinic. On phosphorizing these materials, the phosphorus grouping apparently enters more readily to replace a hydrogen atom connected to one of the carbons of the aliphatic chain. This phosphorus grouping apparently may be connected either to an end carbon of the chain portion of the molecule or to an intermediate carbon of said chain portion, and the phosphorus grouping of the resultant phosphonic acids apparently has the arrangement:

However, while there seems to be ample evidence that this is the structure, we nevertheless do not wish to be bound in all events by this .theory. It is possible also that a portion of the total phosphorus may be attached to naphthenic rings or to aromatic rings, when such are present.

In phosphorizing mineral lubricating oils, preparatory to oxidizing the phosphorized materials to yield the phosphonic acids, diiferent'procedures may be employed. According to one pro cedure the oil itself is heated to incipient "cracking or decomposition and yellow phosphorous lumps are added with heating at appropriate temperatures such as up to about 600 F. until the phosphorizing reaction is complete. (Yellow phosphorus is the commercial term for white phosphorus which ordinarily contains small quantities of red phosphorus sufllcient to give it a yellow color.) In this instance, a nitrogen, carbon dioxide, or other inert atmosphere may be employed for safety purposes. According to another operation the mineral oil is first chlorinated to facilitate subsequent phosphorization. This may be done by bubbling chlorine gas therethrough until the weight is increased by chlorine addition to an extent of perhaps 10% but'preierably less. Only 2% has been used in these examples. This material after a suitable washing is then phosphorized by heating for appropriate periods to incipient cracking" or decomposition with addition of yellow phosphorus lumps until suitable phosphorization is produced. In this case lower temperatures such as a maximum of about'475" F. will sufiice. Following phosphorization for an appropriate time, for example one to three hours, thecharge is cooled to about 200 F. for example, and air then passed therethrough at a slow enough rate to prevent temperature rise much above 250 F. When the oxidation reaction ceases to promote temperature increase, further air-blowing may or may not be resorted to, but it continued for the purpose of insuring sufllcient or further oxidation the air-blowing may be extended for a suitable time, for example about on hour, at a higher temperature, for example at about 300 F. In all cases, air-blowing should be carried out in a manner to attain sufficient oxidation of the phosphorus in the phosphinated oil, but should not be severe enough to oxidize more than minute quantities of the unohosphorized oil molecules. Formation of carboxylic acids byoxidation of the oil hydrocarbons is to be avoided as far as possible.

When suitable oxidation of the original ph0sphorized material has been accomplished in order to insure production of the desired phosphonic acids, the charge is then mingled with a suitable alkaline earth metal hydroxide, such as calcium hydroxide, in the presence of diluting quantities of water, and the batch heated at a temperature around or somewhat above the boiling point of water for a time to efiect saponification or conversion of the phosphonic acids into the calcium or other soap or, salt, which material after filtering and washing is ready for; incorporation in an appropriate mineral lubricating oil such as a high viscosity index oil herein described, which oil may be of the same type as that which is phosphorized.

One specific method for the preparation of calcium phosphonates as herein described was as follows:

A paraflinic oil which was a highly solvent-refined lubricating oil of S. A. E. 20 grade having 89 V. I., was heated to 300 F. and four five per cent by weight additions (20% total) of yellow phosphorus were made while heating from 300 F. to

400 F. The oils were heated at all times in a nitrogen atmosphere. Heating, was then continued until the temperature reached the boiling point of the oil (600 to 650 F.) and the temperature of the oil was held at that point for one-half to one hour. The respective oil was then cooled to 200 F. and a stream of air was passed through the oil at a rate slow enough to prevent temperature rise above 250 1*. After air-blowing caused no further evolution of heat, the oil was cooled, washed free of water-soluble acids, and the calcium soap was prepared by heating the resulting phosphonic acids with calcium hydroxide at 300 F. for one-half hour. The batch was filtered at 300 F, for removal of solids. This resulted in about 4% of soap in about 96% unmodified oil.

Another method which was employed is as follows:

Nine quarts of said S. A. E. 20 grade oil having a V. I. of 89, were chlorinated at 150-170 F. by bubbling a rapid stream of chlorine through the oil. The process was continued until 2.0% of chlorine had been absorbed, as judged by the increase in weight of the charge. The chlorinated oil was then heated and stirred with 2% of yellow phosphorus. The temperature was raised to 475 F. and held at that point for three hours. (In another instance the temperature was raised to about 625 F. which insured removal from the product of the trace of chlorine retained when a temperature of only 475 F. was used.)

1 The total charge was cooled to 200 F. and a rapid stream of air passed through the oil until heat evolution ceased (approximately minutes), the temperature being held in the meantime to a degree below 210 F. by use of cooling water. The charge was then filtered through a filter precoated with a fine diatomaceous earth. A small sample was then water washed, and the acid number found to be 8.05. The total charge was then again air-blown for one hour at 200- 210 F. to insure complete oxidation of the phosphorus, after which the acid number of a small, water-washed sample was found to be 8.25. The whole charge was then washed with an equal volume of water, and the wash drawn oil.

The charge was then heated and stirred for one hour with 200 grams of calcium hydroxide and 300 ml. of water at 200 F. The water was evaporated off by final heating to 230 F. The charge was cooled, 200 ml. of ethyl alcohol was added to insure complete saponificatlon, and the heating and stirring was continued for one hour until the temperature reached 300 F. The total charge was then filtered as above. The filtered oil tested as follows:

Soap number 8.4 mg. KOH/g. oil

Per cent phosphorus 0.25% Sulfate ash 1.36% Soap number, calc. from ash 11.4 mg. KOH/g. oil Soap number, calc. from phosphorus 9.0

This signified about 10% soap in about 90% unmodified oil.

The various salts or soaps produced by methods herein given may be readily incorporated into suitable mineral lubricating oils by mere agitation with slight warming if required. Ordinarily about 1% to 1.5% of the salt will be employed in the oil. However, as conditions vary percentages perhaps as low at 0.25% to 0.5% may be used and higher percentages up to 2% or perhaps 3% may be employed. Larger percentages are of doubtful practical value and merely increase the cost, but unless very large do not materially increase the viscosity of the product Iii over that of the original mineral lubricating oil.

v A lubricating base oil particularly desired for additions of these soaps thereto is one of highly paramnic type produced by modern dewaxing and heavy solvent-refining treatments to yield a viscosity index of from about 75 (or to 100 or higher, e. g. about V. I. as in the examples above. v

To such an oil with the'indicated additions of the mentioned phosphonic soap, there will be added the desired or necessary proportion of a previously described ester of synthetic acids produced by the oxidation of paraflinic mineral oil fractions such as those from the oxidation of parafiin wax. As has been indicated, these percentages will range from about 0.1% to perhaps as high as 3%, an average desirable proportion perhaps being 1% to 1.5% of the phosphonate and 1% to 1.5% of said esters. The esters of the other alcohols than methyl alcohol, as previously indicated, may be used. A specific example will be about 1% of the calcium soap of the described phosphonic acid and about 1% of the methyl ester described. In on instance, soap showing 0.25% calcium sulfate ash, and representing about 1.5% of soap produced from a lubricating oil, was used with-about 1% of the described methyl ester.

When employing a lubricating oil composition containing both of these additive materials, as where breaking-in Diesel engines in the factories before delivery, these oils exhibit an adequately high degree of detergency, are not corrosive, and exhibit a high degree of demulsibility characteristic where either very small or substantial proportions of water get into the system. The esters here function to maintain an unstable system in the presence of water by controlling interfacial tension so that emulsification is avoided both where large amounts of water are present and also where very small amounts of water are present.

In connection with oils of this type a further advantage is found in the fact that these phosphonic acid soaps do not precipitate from the oils or from oil concentrates even after long standing in storage or in the laboratory. In other words, they do not cloud. There is no gelling tendency, and the soaps are sufiiciently soluble in the high viscosity index oil described that concentrates containing as high as 10% soap or even more may be prepared and shipped or stored.

The phosphonic acids which have been produced by the above described methods have contained 16 or more carbon atoms per molecule.

To insure adequate oil-solubility of their soaps such acids should contain at least about 10 carbon atoms per molecule. In blending the phosphonates with the oils, the soap addition has generally'been based on the sulfate ash produced.

It may vary from calcium sulfate ash of about 0.1% to about 0.6%. This will vary the soap content in the finished oil from about 0.25% to about 3%, the lower the molecular weight of the acids (lower number of carbons per molecule) the greater will be the calcium content and the higher the calcium sulfate ash test. Ordinarily, in the order of about 0.75% to 1.5% of the soap will be adequate.

In addition to using calcium soaps it will be appropriate, at least for some uses to employ magnesium .soaps or barium soaps, i. .e. the

alkaline earth metal soaps including strontium soaps. However, we prefer for practical Diesel engine purposes the calcium soaps here described, and in general. we prefer to employ around 1%.or 1.5% of soaps from those acids produced from lubricating oil fractions of the type indicated.

While the proportions of the phosphonic soaps and the esters are not necessarily critical, nevertheless large enough proportions are employed to impart the characteristics desired. For example, as little as 0.1% of the ester exerts a distinctly beneficial eflect, and as little as 0.2% of a calcium phosphonate exhibits desirable detergent and anti-corrosive eifects. On the other hand, proportions between about 0.5% and 1.5%, or in the order of about 1%, of each of the additives is preferred. As larger proportions are employed no great advantage is found, and in the case of the esters larger proportions are in general to be avoided for the reason that the esters tend to reduce the detergent value of the phosphonic soaps. For these reasons it appears that 3% is approximately the practical upper limit for each additive and probably for most Purposes about 1.5% will be the practical upper limit.

The general range of materials for the production of the esters has been indicated. As to the phosphonic acids, in addition to the preferred use of highly paraillnic lubricating oil fractions as indicated, it may be suitable, at least for some uses, to employ other paraflinic mineral oil fractions such as paraflin waxes, petrolatum, spray oil fractions and the like from which it has been indicated that suitable acids might be prepared by oxidation for the preparation of the desired esters.

The lubricating oils produced by addition of these additives in the proportions indicated are normally liquid oils without appreciable increase in viscosity over that of the original base oil employed.

We claim:

1. A lubricating oil for breaking-in internal combustion engines comprising mineral lubricating oil of high viscosity index containing a minor proportion of esters of lower aliphatic alcohols from synthetic acids produced by the oxidation of paraflln wax, and a minor proportion of the calcium soap of phosphonic acids prepared from high viscosity index mineral lubricating oils.

2. An oil according to claim 1 wherein each of the additives is present in proportions between about 0.1% and about 3%.

3. A lubricating oil for internal combustion engines comprising high viscosity index mineral lubricating oil containing a minor proportion of oil-soluble alkaline earth metal soaps of phosphonic acids prepared by phosphorizing and oxidizing paraiiinic mineral lubricating oils. and a minor proportion of lower aliphatic alcohol esters of synthetic acids from the oxidation of hi hly paraiilnic mineral oil fractions.

4. Lubricating 011 according to claim 3 wherein each additive is present in the order of about 0.5% to about 1.5%.

5. Mineral lubricating oil according to claim 1 wherein the additives are present in proportions between about 0.5% and 1.5%.

6. Mineral lubricating oil according to claim 3 wherein each additive is present in proportions between about 0.1% and 1.5%.

7. Lubricating oil for breaking-in internal combustion engines comprising mineral lubricating oil containing a small proportion of an alkaline earth metal soap of phosphonic acids produced by phosphorizlng and then oxidizing highly parai'llnic mineral oil fractions, and a small proportion. of a lower aliphatic alcohol ester of synthetic acids from the oxidation of highly paraillnic mineral oil fractions.

8. Lubricating oil according to claim 7 wherein the ester is the methyl ester of acids from parafiin wax.

9. Lubricating oil according to claim 7 wherein each additive is present in proportions between about 0.1% and about 3%.

10. Mineral lubricating 011 according to claim 1 wherein the ester is the methyl ester.

11. Lubricating oil according to claim 3 wherein the ester is the methyl ester.

12. Mineral lubricating oil according to claim 3 wherein the ester is the methyl ester from the oxidation of paraflln wax having a melting point in the order of F.

13. Lubricating oil according to claim 3 wherein the phosphonic soap is the calcium soap