US2846391A - Process for sodium soap-salt thickened lubricating greases containing sodium phosphate - Google Patents

Description

United States Patent Arnold J. Morway, Clark Township, Union County, N. J assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application June 14, 1952 Serial No. 293,671

1 Claim. (Cl. 252-18) The present invention relates to improvements in lubricating greases and methods for their production. More specifically it relates to an improved process for preparing lubricating greases which are stable at high temperatures and under operating conditions where high rates of shear are involved. It has particular application to lubricating greases which are used in anti-friction bearings such as ball and roller bearings.

In the prior art a lubricating grease which has given satisfactory results over a long period of time is based primarily upon the sodium soap of rapeseed oil, prepared, for example, as described in United States Patent No. 2,265,791, issued December 9, 1941. While various improvements have been made from time to time sodium soap greases of this particular type have held an eminent position in the lubricating field because of their excellent long life performance under adverse operating conditions.

According to the present invention it has been found possible to improve the prior art products by incorporating therein certain stabilizing ingredients such as the salts of oxygen acids of phosphorus, especially sodium phosphate.

It has previously been suggested that sodium phosphate is a desirable additive for lubricating greases. S0- dium or potassium silicate, borate or carbonate has been used in an analogous manner. The present invention, however, is based on the discovery that a superior product may be prepared by processing it in a particular manner so as to incorporate the phosphate or analogous salt into the grease either as an element of a complex soap-salt system or, at any rate, in such a manner that no detectable crystals of salt are found.

Essentially the process of the present invention involves saponifying a suitable fatty oil, preferably rapeseed oil, or mixtures of fatty acids and glycerine, etc. at a moderate temperature in the presence of a portion only of the lubricating oil which is eventually to be used in the grease. Thereafter the saponified mixture is heated to a relatively very high temperature, i. e. 475 to 575 F., to cause the glycerine released upon saponification to react with the saponifying agent, for example, according to the Cannizzaro reaction. The glycerine apparently is converted to acrolein which in turn undergoes a reaction which results in a low molecular weight salt product. The exact mechanism by which this reaction occurs is not known, but it may be postulated that dehydration of the glycerine occurs, and that the resulting acrolein or a dimer thereof reacts with the excess alkali, for example, by the Cannizzaro reaction and/ or by the alkali fusion reaction to form low molecular weight salts. An excess of the saponifying agent, preferably an alkali metal hydroxide and especially sodium hydroxide, is used above the quantity required for saponification of the fat or fatty acid and reaction with the glycerine or decomposition products thereof. This excess alkali is reacted Patented Aug. 5, 1958 with the acid of phosphorus at a high temperature, at least 425 F. and preferably above 450 F. In fact, it is desirable to operate at a temperature of at least 475 to 500 F. or slightly higher for best results.

The process described above results in the incorporation of the phosphate salt into the soap in such a manner that no salt crystals can be detected in the finished grease product even with a high power microscope. It is believed that a complex of salt and soap which includes the phosphate is formed in this manner but in any case there are no perceptible salt crystals. The product is substantially different from that obtained when preformed phosphate, for example trisodium phosphate, is simply added to the grease as described in the above mentioned application.

A preferred product made according to the present invention will consist of about 65 to by weight of lubricating oil, preferably a mineral base oil. The soap content of the grease is between 10 and 35% by weight, preferably of soda soap, and the phosphate content is from about "0.5 to about 3%. Conventional additives may be employed such as 0.25 to 2% of a phenyl naphthylamine as antioxidant and a similar quantity of an oil soluble sulfonate to give further protection against rust where that is of major importance. For best performance in the presence of various non-ferrous metals 0.1 to 1% of a good metal deactivator may be used, for example di-salicylal-propylene-diamine.

Ordinarily the grease of the present invention will be prepared initially with a relatively high soap content. It may be oiled back subsequently by adding 75 to of its weight of lubricating oil. Thereafter the oiled back product is stabilized against oil separation and against mechanical breakdown in service by subjecting the composition to high rates of shear in a mechanical worker, homogenizer or mill. Suitably homogenized grease may contain as little as6% soap. This particular aspect of the process forms no part of the present invention. Ordinarily, mineral base oils are preferred throughout but the invention also contemplates the use of synthetic esters, polyglycols and other synthetic oils which are well known to those skilled in the art. As a rule the saponification step at least should be carried out in the presence of an inert material such as mineral base oil to which the synthetic oil, if employed, may be added later. It is also desirable, ordinarily, to saponify the fatty oil in the presence of a relatively small part of the total oil used, usually not more than half and preferably somewhat less than half, for example about a third of the total lubricating oil content. Additional oil, of mineral or synthetic type, is added to the concentrate thus formed.

The invention will be more clearly understood by reference to the following specific examples.

EXAMPLE I A composition was prepared of the following ingredi ents:

Ingredients: Weight, percent Rapeseed oil 22.00

Ortho phosphoric acid +1.33

.3 The grease was prepared by the following procedure. Rapeseed oil, about one-third of the mineral oil, and

of the product of Examples I and II are listed in the following table:

Table I Grease Example I Example II Regular Commercial Prod. Lubricant Appearance:

Structure Short fiber Short fiber Short fiber. Light yellow Light yellow Dark brown.

Color Penetrations 77 F., mmJlO:

Unworked Worked strokes- Worked 100,000 strokes Dropping Point Color Stability, 3 weeks at 250F Ultimate Hardness, nun/10. After Gaulin Homogenization.

Norma-Hofiman Oxidation, Hours to 5 'p. s. i. g. Spindle Life, Hours, 10,000 R. P. M., 250

520+ 6 500+. Excellent Lt. yellow Excellent Lt. yellow Poor Dark, consider- (no crusts). (no crusts). ably harder. 0 300 171.

Rapid Rapid Rapid. Immediate Immediate.

1 Greases in which trisodium phosphate has been added as Such have given excessive high torque and high temperatures in the spindle test when run at ambient temperatures (-90 F.). The grease of invention (Ex.

I) gave desirable low torque and temperature rise similar to the prior art commercial lubricant which has'au excellent reputation for this reason. In this case a special spindle was used which ordinarily gives shorter grease life than standard test spindles. The test life of over 1,700 hours with this spindle is considered to be an outstanding performance.

the sodium sulfonate concentrate were charged to a fire heated grease kettle and warmed to about 150 F. This temperature should be between and 200 F., the narrower limits of and F. being preferred. When this temperature range was reached a 50% aqueous solution of sodium hydroxide was added in quantitics suflicient to saponify the rapeseed oil, react with the glycerine, and still leave an excess sufficient to react with the proportions of the acid of phosphorus mentioned above, that is 1.33%, though quantities of 0.5 to 3% or so of the acid may be used.

After adding the saponifying agent heating was con tinued and the temperature was raised to about 300 F. By this time saponification was substantially complete and the water content of the grease was quite fully evaporated. At this point, therefore, the balance of the mineral oil was added slowly with continued stirring.

Thereafter the temperature was raised to about 425 F. where foaming commenced, indicating a breakdown of the glycerine into acrolein or related products and reaction with the sodium hydroxide. Heating was continued until a temperature of about 500 F. was reached whereupon the foam subsided and the product became relatively clear.

At this temperature the ortho phosphoric acid was slowly added as the temperature was allowed to drop by turning off the heat. The acid was completely added before the temperature dropped to 475 F. Thereafter cooling of the grease continued while stirring was maintained and the oxidation inhibitor and the metal deactivator were added when the temperature dropped to about 250 F. The product was further cooled to 200 F. and an excellent grease of smooth consistency resulted. This product was finished by homogenizing in a Manton-Gaulin homogcnizer operating at a high shear rate.

EXAMPLE II The product of Example I was diluted by adding an equal weight of mineral base lubricating oil of about 50 S. S. U. viscosity at 210 F. and a viscosity index of about 60. The oil and grease were mixed together and homogenized by passing the mixture twice through the Manton-Gaulin homogenizer at a pressure of 3,000 p. s.:i. g. The resulting product was smooth and almost transparent with a light yellow color. The properties iii) Various modifications may be made in process and product as will be self-evident to those skilled in the art. The preferred temperature ranges for the process are those listed above but they may be varied in some degree and cooling of the grease may be accomplished in various ways known to the art. Various conventional additives such as anti-oxidants, thickeners, viscosity index improving agents, pour point depressants, and 'the like may be present as will be obvious to those skilled in the art.

What is claimed is:

In a method of preparing a grease stable at high temperatures wherein a grease-forming mixture of rapeseed oil, sodium hydroxide and an inert mineral lubricating oil is heated after saponification and dehydration to-a temperature in the range of 475 to 575 F. to cause the glycerine released by saponification and decomposition products of the-glycerine to react with said sodiumhydroxidc; the improved method of incorporatingtrisodium phosphate into said grease which comprises maintaining in the reactants an excess of said sodium hydroxide above the quantity required for saponification and reaction with the glycerine and decomposition products thereof, adding to the reactionmixture at a temperature above 450 F. before appreciably cooling the grease in the range of 0.5 to 3.0 weight percent of orthophosphoric acid, forming thereby from the acid and excess alkali trisodium phosphate in such a form that no detectable crystals of the salt exist.

References Cited in the file of this patent UNITED STATES PATENTS 2,265,791 Zimmcr ct al Dec. 9, 1941 2,360,631 Zimmer et a1. Oct. 17, 1944 2,413,121 Swenson Dec. 24, 1946 2,417,428 McLennan Mar. 18, 1947 2,417,429 McLennan Mar. 18, 1947 2,417,430 McLennan Mar. 18, 1947 2,417,431 McLennan Mar. 18, '1947 2,417,432. McLennan Mar. 18, 1947 2,417,433 'McLennan Mar. 18, 1947 2,468,098 Morway Apr. 26, 1949 2,468,099 Morway Apr. 26, 1949 2,513,680 Schott July 4, 1950 2,595,161 Morway et al. Apr. 29, 1952 OTHER REFERENCES Inst. Spokesman, '14, No.12, 7 (1951).