US2798083A - Synthetic ester lubricants - Google Patents

Description

States Patent?) 2,798,083 Ice Patented July 2, 1957 SYNTHETIC ESTER LUBRICANTS No Drawing. Application February 3, 1954, Serial No. 408,016

3 Claims. (Cl. 260-4106) This invention relates to synthetic ester lubricants and their preparation and is particularly concerned with the diesters of substituted propanediols.

The hydrocarbon lubricating oils are widely used but suiter from certain disadvantages which limit their use for certain applications. In particular, hydrocarbon oils undergo marked viscosity changes with changes in tem-' perature and have relatively high pour points when they have a usable viscosity at high temperatures. Furthermore, the hydrocarbon oils suitor oxidation or other thermal decomposition at high temperatures. When hydrocarbon lubricating oils having a low pour point are used, they usually contain a considerable amount of volatile material which is lost at high temperatures and thus greatly affects the lubricating power of the oil.

Because of these inherent disadvantages, the hydrocarbon lubricating oils are not suitable for use in such critical applications as lubrication of turbo-jet aircraft engines and aircraft instruments. In recent years, a number of synthetic lubricants have been proposed to overcome some or all of these disadvantages. In general these synthetic lubricating oils are of ester type and they are characterized by lower changes in viscosity with changing temperature, low pour point, high oxidative stability and low volatility.

It is an object of this invention to provide a new class of synthetic ester lubricants which are not subject to many of the disadvantages inherent in hydrocarbon lubricating oils.

It is another object of this invention to provide a new method for making synthetic lubricating oils which were not known heretofore.

Another object of this invention is to provide a highly efiective group of new compounds which have a low viscosity slope, a low pour point, a high oxidative stability I and low volatility.

Another object of the invention is to provide hitherto unknown diesters of 2,2 dimethyl 3 isopropyl 1,3 propanediols which have particular utility as synthetic lubricants.

Other object will be apparent from the description and claims which follow.

These and other objects are attained by means of this invention as described in detail hereinafter with particular reference to certain preferred embodiments thereof. The

compounds embodying this invention are synthetic lubricants comprising acyl diesters of the formula:

wherein each R is a straight or branched chain alkyl or alkoxy alkyl group at least one of which contains at least 8 carbon atoms, and R is either hydrogen or a lower alkyl radical. The simple diesters embodying the invention are prepared by reacting one molar proportion of a propanediol of the formula:

with 2 molar proportions of a monocarboxylic acid of the.

formula:

RCOOH wherein R is a straight or branched chain alkyl or alkyl alkoxy group containing at least 8 carbon atoms. The

esters thus. obtained are characterized by having a lowis reacted with a monocarboxylic acid containing at least 9 carbon atoms in order to fully esterify the diol. Another typical lubricant embodying the invention .is prepared by reacting 2,2-dimethyl-3-isopropyl-1,3-propanediol with a monocarboxylic acid of the same type. In practicing the invention, the monocarboxylie acid can be any acid of the formula:

wherein R is a straight or branched chain alkyl or alkoxy alkyl group containing at least 8 carbon atoms. The acids employed are thus aliphatic acids, and can be fatty acids of the acetic acid series or branched chain derivatives. thereof or they can be acids which contain an ether linkage inthe chain. A particularly suitable group of acids are the branched chain 0x0 acids which are prepared by the reaction of carbon monoxide and hydrogen on the olefins obtainable from petroleum and oxidation of the resulting aldehydes. These oxo acids have a highly branched structure and are derived from such materials as propylene trimers, propylene tetramers, isobutylene trimers, isobutylene. tetramers, the C7 olefins and similar well known olefins. Thus, for example, suitable acids are fatty acids such as pelargonic acid, lauric acid,

myristic acid, palmitic acid, stearic acid and the like; and the branched-chain 0x0 acids such as decylic acid derived from propylene trimers, tridecylic acid derived from propylene tetramer or from isobutylene trimer, or 'similar well known branched chain 0x0 acids, as well as any of the other well known aliphatic acids containing at least 9 carbon atoms. Similarly, the alkoxy alkyl acids containing at least 9 carbon atoms are also suitable. In the case of the mixed esters described hereinafter, such acids can be used with a lower acid containing as low as 6 carbon atoms.

The diester lubricants embodying this invention can be used alone, particularly in applications where it is undesirable to employ additives which would leave a residue or which might decompose or be volatile at elevated temperatures. to employ propanediol esters as defined herein in conjunction with such additives as antioxidants, anticorrosion agents, pour point depressors, viscosity improvers, or extreme pressure additives. The synthetic lubricants embodying the invention can also be used in the formulation of greases by the usual methods, as well as being used in admixture with a hydrocarbon lubricating oil, another synthetic ester lubricant, mineral oil, or any of the other well known lubricating materials.

By varying the nature of the acid used to esterify the diol, a variety of products having a wide range of viscosity and pour points can be obtained. In most cases, the acid employed will contain from 10 to about 22 carbon atoms although the synthetic fatty acids having chain. lengths of as much as 30 carbon atoms. or more can be used in some cases, particularly where a low pour point is not necessary.

These lubricants are readily prepared by heating 2 molar equivalents of the desired acid as defined herein with one molar equivalent of the propanediol of. the formula:

The conditions under which the esterification is effected can be varied in accordance with well-known practice for effecting esterification of an alcohol with an acid. In most cases, it is desirable to heat the mixture of the acid and the propanediol to a temperature of about 150-200 C. for a time sufficient to cause evolution of 2' molar equivalents of water. If desired this water can be removed as formed, but this is not necessary in practicing the invention. When the water is removed, an entraining solvent such as xylene or Stoddard solvent can be used or the water can be distilled off without the use of a solvent. When esterification is substantially complete, the diesters obtained are washed with an alkaline material to remove unreacted acid and are then distilled at reduced pressure.

The viscosity and pour point characteristics of the diesters embodying this invention are illustrated in Table I for typical synthetic ester lubricants prepared as described herein and a comparison is made with the properties of a typical hydrocarbon oil. out in the table was determined by ASTM method D-88 44 and the pour point data by a modification of ASTM method D-97-47.

Table I Kinematic Viscosity in Centistokes Pour Lubricant Point,

F. 100 F. 210 F.

Typical hydrocarbon oil l3. 2. 6 -30 2,2,4-Trimethyl-l,3-pentancdiol di caprate 13. 2 3. 0 65 2,2-Din1ethylpropanedlo1 dipelargonate 7. 8 2. 3 below 85 The caprate" diester set out in the table was the ester of the C acid derived from propylene trimer by oxida: tion of the corresponding oxo aldehyde and is a branched chain corresponding in chemical composition to the caprate diester. As can be seen from the table, the lubricants prepared by means of this invention have excellent viscosity and pour point characteristics.

'A particularly useful class of synthetic lubricants is prepared by esterifying a propanediol as defined herein with a mixture of two or more acids. The acids employed can be mixtures of straight and branched chain The viscosity data set In some cases, however, it may be desirable I acids, mixtures of acids having the same number of car atoms in the molecule provided that at least one of such acids and preferably both acids contain at least 9 carbon atoms. Similarly, the lubricants embodying this invention can be mere mechanical mixtures of two or more esters as described herein. In most cases, however, the mixed esters prepared by esterifying one molar proportion of the propanediol with two molar proportions of a mixture of acids are preferred.

By the use of mixtures of acids with one or more of the propanediols as herein defined, the pour points and viscosity characteristics of the diesters can be made in any predetermined range. Thus, for example, if 2,2-dimethyl-1,3-propanediol is esterified with a mixture of three acids RICOOH, RzCOOH- and RsCGOH wherein each R is an alkyl group of at least 8 carbon'atoms, the resulting mixed product will contain the following esters: Similar mixtures are obtained using the propanediol, 2,2-

Similar mixtures are obtained using the propanediol, 2,2- dimethyl-3-isopropyl-1,3-propanediol, and the number of ester components is doubled when a mixture of propanediols is employed.

It is often desirable to be able to prepare a lubricant with a particular set of values for the pour point and viscosity characteristics. Thus, for example, lubricants for use in aircraft instruments should be light lubricants having viscosities in the range of 48 centistokes at F., whereas the medium lubricants having viscosities in the range of 10-15 centistokes at 100 F. are useful in turbojet engines, and the heavy lubricants having viscosities of 15-25 centistokes at 100 F. are useful for high temperature applications.

Typical examples of synthetic dicster lubricants prepared by reacting typical propanediols with mixtures of acids having the same number of carbon atoms in the molecule are set out in Table II:

The decanoate diesters set out in Table II were prepared by esterifying the respective diols with a mixture of C10 branched chain acids, and tridecanoate diesters were prepared by esterifying the respective diols with a ture of C13 branched chain acids.

Another highly useful group of lubricants are those prepared by esterifying a propanediol with a mixture of acids having diflerent numbers of carbon atoms but in which at least one of the acids contains 9 carbon atoms. Typical examples of these lubricants are set out in Table III. Mixed ester A was prepared by esterifying 2,2-dimethyl-1,3-propanediol with a mixture of equal parts by weight of a branched chain iso-octanoic acid mixture and a mixture of. branched chain decanoic acids. Mixed ester B was prepared by esterifying the same propanediol with a mixture of equal parts by weight of Z-ethyl hexanoic acid, a mixture of branched chain decanoic acids, and a mixture of branched chain tridecanoic acids. Mixed ester C was prepared by esterifying 2,2-dimethyl-3-isopropyl- 1,3-propanediol with a mixture of equal parts by Weight of Z-ethylhexoic acid, a mixture of branched chain isooctanoic acids, and a mixture of branched chain decanoic acids.

The diester lubricants embodying this invention are characterized by a high degree of thermal stability and resistance to oxidation. Thus, the ester compositions as described herein can be refluxed at atmospheric pressure for 24 hours at a pot temperature of 335 C. and in the presence of air. After this prolonged heating period, the weight loss is usually less than about 1.0% which indicates the low content of volatile material in the diester and its chemical stability, since very little of the lubricant is decomposed to volatile decomposition products. Furthermore, the color of the lubricant is substantially unchanged following this test and there is no free acid present.

Thus, by means of this invention, a highly useful class of synthetic diester lubricants is provided. The improved physical characteristics make these materials eminently suitable for use as lubricating oils in the applications Where hydrocarbon lubricating oils are now used, and particularly in high temperature applications where hydrocarbon lubricating oils are completely unsuitable. Because of their low pour point and high oxidative and thermal stability, it is usually not necessary to employ additives with these diester lubricants which means that they can be used very successfully in jet aircraft and similar applications where the presence of a residue is undesirable. The straight chain fatty acid diesters are completely suitable, but the branched chain diesters are preferably prepared due to the modification of the physical properties by the presence of the branched chain. The effect of the branched chain is particularly noticeable in the viscosity characteristics of the product. Thus, the branched chain diesters prepared by use of the oxo acids remain fluid for higher molecular weights than is the case with the straight chain diesters. The mixed esters are particularly desirable because they can be prepared to any desired characteristics.

The invention has been described in considerable detail with particular reference to certain preferred embodiments thereof but it will be understood that variations and modifications can be elfected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A synthetic lubricant comprising a diester of the formula O OH: CH-CHs O wherein each R is a member of the group consisting of straight and branched chain alkyl groups, one R containing 421 carbon atoms and the other R containing 82l carbon atoms.

2. A synthetic lubricant comprising an acyl diester of 2,2-dimethyl-3-isopropyl-1,3-propanedio1 wherein each acyl group contains 921 carbon atoms.

3. A synthetic lubricant comprising 2,2-dimethyl-3- isopropyl-1,3-propanediol dipelargonate.

References Cited in the file of this patent UNITED STATES PATENTS 2,492,955 Ballard et al. Jan. 3, 1950 2,499,983 Beavers Mar. 7, 1950 2,520,733 Morris et al. Aug. 29, 1950 2,563,609 Mutuszak Aug. 7, 1951 2,705,724 Cottle Apr. 5, 1955 OTHER REFERENCES Oil and Gas Journal, 51, No. 43 (1953), pages 74-77.

Petroleum (London), 17, No. 147 (1954), pages 122-126.

Ind. and Eng. Chem., vol. 45, No. 8, pages 1766-1775.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,798,083 July 2, 1957 Alan Bell et al.

It is hereby certified that error appears .in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read 'as corrected below.

Column 6, line 29, fair "9-21" read 9-22 Signed and sealed this 10th day of September 1957.,

1 meat:

KAR AXLINE ROBERT c. WATSON

Claims (1)

1. A SYNTHETIC LUBRICANT COMPRISING A DIESTER OF THE FORMULA