US2694683A - Lubricating grease containing pectic acid salt - Google Patents

Description

United States Patent LUBRICATING GREASE CONTAINING PECTIC ACID SALT Arnold J. Morway, Rahway, and Louis A. Mikeska, Westfield, N. J., assignors to Standard Oil Development Company, a corporation of Delaware N0 Drawing. Application December 24, 1952, Serial No. 327,902

15 Claims. (Cl. 252-41) The present invention relates to improved lubricating greases. More specifically, the invention is concerned with lubricating greases having high dropping points and high structural stability to mechanical working over long periods of time at relatively low thickener concentrations. In its broadest aspect, the invention pertains to greases thickened with a soap-type grease thickener which contains a substantial proportion of a metal salt of pectic acid, preferably in the form of a complex with the metal salt of a low molecular weight carboxylic acid.

Prior to the present invention, greases having desirably high dropping points and high mechanical stability to Working have been prepared by using the alkali or alkaline earth metal soaps of combinations of high and low molecular weight carboxylic acids: It is also known that these greases require soap contents of at least to exhibit the desired structural stability and freedom from oil separation. As the soap thickeners are diluted with lubricating oil, i. e. as the soap concentration of the grease decreases, the dropping point is materially lowered and semi-fluid products of poor structural stability result.

It has now been found that greases having excellent high dropping points and highly desirable structure and stability characteristics at much reduced soap requirements may be obtained by incorporating into the grease thickener at least a substantial proportion of a metal salt, particularly an alkali metal salt, of pectic acid. Preferably, this pectic acid salt forms all or part of the high molecular weight fatty acid soap constituent of a thickener of the high molecular weight-low molecular weight complex soap type discussed above.

Pectic acid may be derived from pectin which is a plentiful and inexpensive mucilaginous vegetable carbohydrate present in the cellular tissue of most fruits. The jellying tendency of fruit juices is due to the presence of pectin. Pectic acid is present in pectin partly as a polymer and partly in the form of a calcium and magnesium salt. In the preparation of pectic acid from pectin, the latter is hydrolyzed either enzymatically or by careful hydrolysis with dilute alkali or alkali carbonate. The calcium is removed by precipitation with oxalic acid, the albuminous substances by means of tannic acid. The pectic acid may then be purified by repeated dissolution in water with subsequent precipitation with alcohol. The free pectic acid is a tetra basic acid with two free carboxyl groups, the two others being linked as esters with methyl alcohol; it may be regarded as triacetyl-arabino-galacto-tetra galacturonic acid dimethyl ester. It yields on hydrolysis galacturonic acid (about 65%); d-arabinose (11.7%); d-galactose (13.1%); methyl alcohol (6.5%) and acetic acid (13%).

Some of the advantages of the invention may be realized by using metal salts, particularly alkali metal salts of pectic acid as the sole or essentially sole thickener. Salt concentrations of about 2-15 should be used in this case. However, in accordance with the preferred embodiment of this invention, the pectic acid salt is present in the grease in the form of a complex with a salt, preferably an alkali metal salt, of a low molecular weight carboxylic acid. In many cases, it may be desirable to incorporate into the complex a soap of a hi h molecular weight fatty acid other than pectic acid. Thickeners of this type may contain about 10-75 Wt. percent, preferably about 25-50 wt. per cent, of pectic acid salt. The low molecular weight acid salts and total high molecular weight acid salt and soaps may be present in equi-molecular proportions. low molecular weight acid may be present in smaller However, the

or larger proportions, mol ratios of 1:1 to 3:1 of low to total high molecular weight acids being preferred.

The total complex thickener content may vary within the wide range of about 2-40 wt. per cent of the finished grease. It is however a particular advantage of the present invention that excellent greases having high dropping points and high structural stability to mechanical working may be obtained by using substantially less than 10 wt. per cent and even as little as 2.5 wt. per cent of a pectic acid salt containing thickener. Complex thickener concentrations of about 5-10 wt. per cent are, therefore, preferred for most purposes.

The low molecular weight acids to be combined with the pectic acid to form the complex thickener of the invention may be any aliphatic carboxylic acid having 1-5 carbon atoms per molecule, such as formic, acetic, propionic, butyric, valeric, furoic, acrylic acids, etc. The preferred low molecular weight acids are formic and acetic acids. High molecular weight fatty acids which may be used together with pectic acid and the low molecular weight acids here specified include saturated or unsaturated fatty acids having 10-30 carbon atoms per molecule, such as hydrogenated fish oil acids, stearic acid, oleic acid, behenic acids, etc., saturated acids having 18-22 carbon atoms per molecule being preferred.

Metal bases suitable for the formation of complex thickeners in accordance with the invention include the hydroxides and carbonates of alkali, alkaline earth and certain other metals, for example lithium, sodium, potassium, calcium, barium and aluminum. However, alkali metal bases, particularly the hydroxides of sodium and lithium, which form complexes of satisfactory water solubility and temperature characteristics, are preferred.

Regarding lubricating oil bases suitable for the greases of the invention, all types of mineral lubricating oils as well as synthetic oils including diesters, complex esters, formals and hydrocarbon polymers having lubricating oil characteristics may be used.

Greases in accordance with the invention may be prepared by preforming the pectic acid salt or salt or soap complex with other acids and incorporating the same in the lubricating oil by mechanical mixing. The preformed salt or complex may be prepared by neutralizing the pectic acid or mixtures thereof with the other acids to be used by means of substantially stoichiometric amounts of the desired metal base preferably in aqueous solution, recovering the complex formed and compounding the same with the lubricating oil at grease-making conditions.

However, the preferred method of the invention involves formation of the salt or salt or soap complex in situ in the lubricating oil in the course of the greasemaking process. For this purpose the pectic acid and other high molecular weight fatty acids, if any, may be charged to a reaction zone and heated together with a p rtion of the lubricating oil to about l70 F. Thereafter the low molecular Weight acid may be added and the mixture neutralized, preferably with a slight stoichiometric excess of an aqueous solution of the metal base of about 30-50% concentration. Sufficient metal base should be used to give the grease a free alkalinity of about 0.1-1 as NaOH.

The mixture may then be dehydrated at temperatures of about 250350 F. When dehydration is substantially complete, further lubricating oil may be added and heating continued to about 450550 F. Thereafter, the grease may be cooled. When temperatures below 300 F. are reached other conventional additives, such as antioxidants, particularly amino compounds, extreme pressure agents containing sulfur, halogen and/or phosphorus, etc. may be added in any conventional manner.

The invention will be further illustrated by the following specific examples.

EXAMPLE I Ingredients: Wt. Percent Pectic acid- 10.00 Hydrofol acids 54 1 10.00 Acetic acid (glacial) 4.00 Sodium hydroxide 6.50 Phenyl alpha-naph'thylamine 1.00

flydrogenated fish oil acids corresponding in degree of saturation to commercial stearic acid.

Blend of naphthenic-type mineral oil distillates having -a viscosity of 50 S. S. -U. at 210 F 68.50

Preparation The pectic acid (.brown powder), Hydrofol acid and about /2 of the mineral .oil were charged to a grease kettle and warmed to 150 At this temperature the acetic acid was charged followed immediately by a 40% aqueous solution of sodium hydroxide. Heating was continued and at 300 F., when the soap mass .inthe kettle was fairly .dry, the balance of the mineral oil was added. The mixture was further heated to 500-5,15 F. At this temperature heating was discontinued and .the mass cooled to 250 R, where the phenyl alpha-naphthylarninewasadded and the greasefurther cooled to 200 F.

Inspection of the grease showed'the formation of some small specks. vHowever, on Gaulin homogenization of the grease at higher rates of shear these specks were removed, resulting in an exccllent smooth uniform very hard product.

Properties Percent alkalinity as NaQH 0.91 Penetrations, 77 F. mm./ 10:

Unworked 96 Worked 60 strokes 1103 Dropping point, "LF 500+ Water washingtest, percent loss None Norma Hoifmann 0xidation Test, hours to 5 -p. s. i.

drop in Oz pressure 235 EXAMPLE II The grease of Example I was diluted with 100% additional mineral oil by mixing together at 80 F. and then Gaulin homogenizing. The mineral oil employed was a solvent extracted parafiinic-type oil, having low volatility, high viscosity index, and good oxidation resistance with a viscosity of S. .S. U. at 210 F. It is not possible to employ this type of mineral oil exclusively as a grease base due to the poor solubility or colloidal dispersibility of the thickener in this less polar mineral oil. Ingredients: Wt. Percent 45 Pectic acid grease Base of Example I 50.00 Additional mineral oil 50.00

or w Pectic acid 5.00 Hydrofol acid 54 5.00 Acetic acid 2.00 NaOH 3.25 Naphthenic-type original oil 34.25 Paraffinic-type additional oil 49.50 Phenyl alpha-naphthylamine 1.00

EXAMPLE III The above grease was again diluted with 100% additional parafiinic mineral oil, similarly as in Example II. Ingredients: Wt. Percent Pectic acid grease Base of Example I 25.00 Additional mineral oil 75.00

or Pectic acid 2.50 Hydrofol acid 54 2.50 Acetic acid 1.00 NaOH 1.62 Phenyl alpha-naphthylamine 1.00 Naphthenic-type original oil 17.13 Paraffinic-type additional oil 74.25

Properties Example II Example III Appearance Excellent... Smgoth But- Dropplng Point, F 500+ 488. Penetrations, 77 F. min/l0: 80

Unworked Worked 6O Strokes. Worked 67,000 Strokes. Water Was ing Test, Percent Loss.. Norma Hoffman Oxidation Test, Hours 108 185.

to 5 p. s. 1. Drop in 03 Pressure.

It will be noted that even the grease of Example HI, the 'total thickener content 'of which is only about 7 wt. percent, has excellent high temperature and structural stability characteristics.

Excellent greases in which Hydrofol or other high molecular weight saturated acids alone are employed in combination with low molecular weight acids, i. e. acetic acid can be prepared by similar formulations and manufacturing methods. However, as the concentration of the thickener falls below 10.0%, the greases become quite soft and lack structural stability to mechanical working. Such greases, therefore, have limited applications in industry.

The invention is not limited to the specific figures of the foregoing examples. The relative proportions of the grease constituents may be varied within the limits indicated above to obtain greases of different consistency and varying characteristics.

What is claimed'is:

1. A lubricating grease comprising about 60-98 wt. percent lubricating oil and about 240 -wt. percent ot a grease thickener containing about 1075 wt. percent,=based on thickener, of an alkali metal salt of pectic acid, the remainder of said thickener comprising an alkali metal soap of a high molecular weight fatty acid having 18 -22 carbon atoms and an alkali metal salt of a low moleculer weight-carboxylic .acid having 1-5 carbon atoms, the mol ratio of low molecularweight acid salt to high molecular weight fatty soap plus pectic acid soap being 1-3.

2. A-grease as-claimed in claim '1 which contains about 5-10 wt. percent of said thickener, the latter containing about 25-50 Wt. percent of said pectic acid salt.

3. A grease as claimed 'in 'claim 1 in which said high molecular weight fatty acid soap is the sodium soap of hydrogenated fishoil-acids and said low molecular weight carboxylic acid salt is sodium acetate.

4. 'The method of preparing lubricating greases which comprises heating a lubricating oil containing substantial proportions of pectic acid to about 130-170 F, adding 'a substantial proportion of a low molecular weight carboxylic acid, neutralizing the mixture with sufiicient alkali metal hydroxide to give the mixture a free alkalinity of about 0.11% calculated as Na'OH, dehydrating the mixture at temperatures of about 250- 350 F., further heating the mixture to about 450- 550 F. and cooling the mixture.

'5. The method of claim 4 in which said lubricating oil contains additionally a substantial proportion 'of a high molecular weight fatty acid having 1822 carbon atoms.

6. The method of claim 4 in which said hydroxide is sodium hydroxide.

7. The method of claim 4 in which said lubricating oil is a naphthenic oil and said cooled mixture is diluted with a paraffinic lubricating oil.

8. A lubricating grease comprising about -95 wt. of mineral lubricating oil, about 1 wt. of an oxidation inhibitor and about 4-9 wt. of a grease thickener consisting of about 4042 wt. of the sodium salt of pectic acid, about 4042 wt. of the sodium soap of hydrogenated fish oil acids and about 16-20 wt. of sodium acetate.

9. A lubricating grease comprising a major proportion of a lubricating oil and about 2 to 40 wt. based on total grease, of a metal soap thickener containing at least about 10% of its weight of pectic acid metal salt, said metal being selected from the group consisting of alkali and alkaline earth metals and aluminum.

10. A lubricating grease comprising a major proportion of a lubricating oil and about 2 to 40 wt. based on total grease, of a thickener comprising at least about 10% of its weight of pectic acid metal salt and a metal salt of a low molecular weight carboxylic acid, the mol ratio of said last-named salt to said first-named salt being between 1:1 and 3:1 and the said metal being selected from the group consisting of alkali and alkaline earth metals and aluminum.

11. A lubricating grease comprising a major proportion of a lubricating oil and 2 to 40 wt. based on total grease, of a metal soap thickener containing about 10 to 75% of its weight of pectic acid metal salt, said metal being selected from the group consisting of alkali and alkaline earth metals and aluminum.

12. A lubricating grease comprising a major proportion of a lubricating oil and about 2 to 40 wt. based on total grease, of a thickener containing at least about 14. A grease as in claim 13 in which said high molecuof its weight of a metal salt of pectic acid, at least lar weight fatty acid has 10 to carbon atoms. about 25% of its weight of a grease thickening metal 15. A grease as in claim 12 in which said low molecusoap of a high molecular weight fatty acid and a metal lar weight acid has 1 to 5 carbon atoms. salt of a low molecular weight carboxylic acid, the mol 5 ratio of said last-names salt to total amount ofdsglap and References Cited in the file of this patent pectic acid salt being etween 1:1 and 3:1 an e said metal being selected from the group consisting of alkali UNITED STATES PATENTS and alkaline earth metal and aluminum. Number Name Date 13. A grease as in claim 12 wherein said total amount 0 2,44 ,720 Roehner et a1. May 18, 1948 consists of 10 to of pectic acid salt and 25 to 2,487,379 Roehllel 6t 1949 of said high molecular weight fatty acid soap.

Claims (1)

1. A LUBRICATING GREASE COMPRISING ABOUT 60-98 WT. PERCENT LUBRICATING OIL AND ABOUT 2-40 WT. PERCENT OF A GREASE THICKENERCONTAINING ABOUT 10-75 WT. PERCENT, BASED ON THICKENER, OF AN ALKALI METAL SALT OF PECTIC ACID, THE REMAINDER OF SAID THICKENER COMPRISING AN ALKALI METAL SOAP OF A HIGH MOLECULAR WEIGHT FATTY ACID HAVING 18-22 CARBON ATOMS AND AN ALKALI METAL SALT OF A LOW MOLECULER WEIGHT CARBOXYLIC ACID HAVING 1-5 CARBON ATOMS, THE MOL RATIO OF LOW MOLECULAR WEIGHT ACID SALT TO HIGH MOLECULAR WEIGHT FATTY SOAP PLUS PECTIC ACID SOAP BEING 1-3.