US2757139A - Synthetic lubricating composition - Google Patents

Description

United States Patent 2,757,139 SYNTHETIC LUBRICATING COIVIPOSITION No Drawing. Application November 30, 1953,

Serial No. 395,322 4 Claims. (11. 252-56) This invention relates to synthetic lubricating compositions. Particularly the invention relates to synthetic lubricating compositions which have outstanding lubricating characteristics at both high and low temperatures which make them desirable for the lubrication of jet engines. More particularly the instant invention relates to branched chain alcohol esters of monobasic acids of a specific type.

In recent efforts to obtain superior lubricants for use in jet engines which operate at extremely high'altitudes, there have been developed entirely new synthetic materials with lubricating properties. In general, these new synthetic lubricants have viscosity properties that are outstanding at both low and high temperatures, especially when compared to mineral lubricating oils.

L For use in the lubricating of aircraft engines, particularly of the turbo-jet or turbo-prop type, a lubricant must meet very stringent viscosity properties. At low temperatures experienced at high altitudes, the lubricant must be sufficiently labile to flow through the circulatory l system of the engine and allow movement of the lubricated surfaces without undue power requirement. A lubricant having an ASTM pour point below about +35 F. has been found generally satisfactory in this respect for general use. At high temperaures a lubricating oil must have suflicient body or thickness to furnish and maintain a lubricating film. It has been found that a lubricant that is satisfactory in this respect will have a viscosity at 210 vent undue lubricant loss, due to volatility, and to insure against explosion hazards at the high temperatures sometimes encountered, a lubricating oil should have a flash point in excess of about 300 F. These requisites are inherent in the term lubricating composition, as used in this application, and the materials of this invention are limited to those having properties within these ranges. In general, the preferred materials, as contemplated herein, and as the contemplated preferred embodiment hereof, will have ASTM pour points below about 25 F., ASTM flash points above about 375 F., and viscosities within a range of 2.6 to 13 centistokes at 210 F.

The materials of the instant invention cover only a limited number of the large class of esters of monobasic acids. They may be said to have the general formula RCOOR' wherein R and R are selected from the group consisting of alkyl groups having from about 8 to 18 carbon atoms in a straight chain configuration, and alkyl groups of a branched chain configuration containing from about 12 to about 28 carbon atoms and which contain one major side chain of from 4 'to- 14 carbon atoms. A further limitation exists in that R and R may not be both branched or both straight. i

It will be seen from the above that only a limited number of aliphatic monocarboxylic acids and alcohols may be used inthe preparation of the esters of this invention.

F. of between about 2 and 60 centistokes. To pre-' If R is of straight chain configuration, that is if R is derived from an aliphatic alcohol having from about 8 to 18 carbon atoms in a straight chain, then operable alcohols include the following: n-octanol, decanol, do.- decanol, lauryl alcohol, Lorol alcohols, cetyl alcohol, etc.

When R is of straight chain configuration, then R or the acid radical, must contain from 12 to 28 carbon atoms in branched chain configuration having one major side chain of from 4 to 14 carbon atoms. Operable acids include: 2-butyl octanoic acid, C12-C2s acids prepared by the oxidation of petroleum, C12-C2s acids prepared by alkali fusion of alcohols, ClZ-C28 acids prepared as a product from Guerbet alcohols.

When R is of branched chain configuration, then R is of straight chain structure containing from 8-18 carbon atoms and the acid used may be selected from the following; caprylic acid, capric acid, pelargonic acid, lauric acid, coconut fatty acids, myristic acid, palmitic acid, stearic acid, oleic acid.

Of the listed operable acids, particularly preferred are the mixture of acids described as coconut fatty acids. This mixture of acids is prepared from coconut oil by a process comprising the saponification of coconut oil followed by acidification to recover the acids of the various mixtures obtainable, the mixture having an average chain length of about 12.5 is preferred.

When R is of branched chain configuration and R is straight chain, then in order to be included in the limitations of the formula above, that is, to have from 12 to 28 carbon atoms with one major side chain of from 4 to 14 carbon atoms, the alcohols used to form the esters of this invention are prepared by one of two specific processes as follows:

I. Dimerization of alcohols by Guerbet reaction. Higher molecular weight alcohols having but one major side chain are produced from primary or secondary alcohols by an alkaline condensation known as the Guerbet reaction. This reaction requires the presence of a methylene group adjacent to the carbinol (hydroxylated carbon) group. The sodium alcoholate of the reacting alcohol is generally used as a catalyst. However, metallic sodium has also been used since the sodium is converted to the alcoholate at the beginning of the reaction. Other alkaline agents such as sodium soaps, sodium borate, sodium alkyl borate, etc., may also be used, but are considered to be less satisfactory.

When relatively low concentrations of sodium alcoholate are used for the Guerbet reaction, that is, from 10 to 20 moles of alcohol per mole of alcoholate, water is eliminated according to the following equation:

R RCHzCHzHCHzOH 320 The reaction is not so easily described when high concentrations of sodium alcoholate are used. Furthermore, the higher alcoholate concentrations produce higher yields of sodium salts of the acid. By the use of dehydrogenation catalyst such as copper, zinc, nickel, etc., however, there is a tendency to reduce the amount of salts produced while maintaining or improving the conversion to higher alcohols.

After condensation, the higher alcohols and unreacted alcohols may be distilled from the reaction mixture by distillation under reduced pressure .or at atmospheric pressure for relatively low molecular weight alcohols. Steam distillation may also be used. In most cases, however, it is desirable to remove the salts of the fatty acids by extraction prior to distillation of the alcohols.

Satisfactory operation conditions for condensation of a primary alcohol by the Guerbet reaction are as follows:

Although the above conditions are favorable for the Guerbetization of alcohols in the range of C6 to C14 it is possible for these conditions to be altered considerably. The alcohols may be condensed in the presence of an entraining agent for removal of water. Pressure may be desirable for alcohols boiling below the condensation temperatures. The temperature and time of reaction may be varied by use of different concentrations of caustic.

An example of the reaction described above is set out in detail below.

To a one gallon nickel reactor fitted with a large bore 30-inch condenser, there was charged 2340 g. (18 moles) Cs alcohol 72 g. (1.8 mole) of flake NaOH 18 g. copper powder The mixture was heated with agitation and little or no cooling was applied to the condenser. Formation of the sodium alcoholate took place with the liberation of 1.8 moles of water during about one-half hour at a pot temperature of 170-188 C. Heating and agitation were continued to 13 hours during which time the pot temperature rose to 206 C. The water from the condensation reaction was collected and the hydrogen which was liberated by the caustic fusion reaction was measured. The reaction product was removed from the reaction mixture while still hot by use of a vacuum.

The hot product was poured into approximately four liters of water, thus preventing the solidification of the alcoholate or of the sodium salts. After allowing to cool, the mixture was transferred to a 12 liter separatory funnel which was equipped with an agitator. Approximately two liters of water and two liters of petroleum ether were used in the transfer. After agitation, the aqueous layer was removed and the supernatent layer, alcohols and petroleum ether, was given a second wash with two liters of water.

The aqueous layers from the two washes were combined and extracted with one liter of petroleum ether. The total aqueous portion was acidified in the presence of one-half liter of petroleum ether and the acid extract was evaporated to obtain the yield of crude acids.

The two petroleum ether extracts of the alcohols were evaporated, leaving crude alcohol being a mixture of the unreacted alcohol and the dimerized alcohols. The unreacted alcohols were then distilled off in a short path still.

II. Dimerization of aldehyde by aldol condensation.- Aldehydes possessing a methylene group adjacent to the carbonyl group readily condense in the presence of an alkali or an acid to yield a beta-hydroxy aldehyde which is designated as an aldol product. This aldol product may be readily dehydrated to yield an unsaturated aldehyde which in turn may be hydrogenated to yield a saturated primary alcohol having twice as many carbon atoms as the aldehyde starting material. This reaction may be depicted as follows:

OH R acid or I 2: -H2O RCHZCHO RCHQCHO --1-k1- RCHzCH- HCHO a at Such alcohols in general are the same as those prepared by the Guerbet reaction, when the alcohol of the same aldehyde is used. However, during the aldol condensation, small amounts of alcohols and acids may also be produced under some conditions, as shown by the following typical 20 mm. distillation data on a product obtained by dehydrating and hydrogenating the aldol condensation product prepared from Ca ()xo aldehyde in the presence of sodamide.

Fraction Initial, to 225 F. (Alcohol) 225230 F. (Intermediate) Acids. sum-3r. Bottoms (C16 Alcohol).

Trap-light hydrocarbons If in the formula above, R is of branched chain configuration, having one major side chain of from 4 to 14 carbon atoms, then the acid used to formulate the ester is prepared from the alcohols as described above, i. e., by alkali fusion of C12 to C28 Guerbet dimerized or aldolized alcohols. In this case the esterifying alcohol may be any primary straight chain alcohol having from 8 to 18 carbon atoms, or mixtures thereof such as was described above.

In order to more explicitly describe the instant invention, the following detailed examples are given. It is understood, of course, that these examples are of an illustrative nature only, and are not to be considered as limiting the inventive concept.

EXAMPLE 1 A mixture of 121.2 g. (0.5 mole) of C16 Guerbet alcohol (dimer of branched Cs Oxo alcohol obtained by oxonation of propylene-butylene copolymer), 115.0 g. (0.525 mole) of coconut fatty acids, 1.2 g. NaHSO4 cata lyst and 75 g. of toluene was refluxed at 140 C. to 161 C. for 90 minutes during which time 9.0 cc. of water was collected. This material was diluted with 200 g. of hexane and washed twice with 150 cc. portions of 2% NazCOa. Three 100 cc. portions of water were used to remove the alkali. The material was then distilled. The monoester boiling mainly at 185 C.-195 C. at 0.05 mm. weighed 188 g. (83% yield) and had the properties set out in Table I.

EXAMPLE 2 Following the procedure outlined in Example 1 above, a normal Ca alcohol was dimerized by the Guerbet re action and used to esterify the same coconut oil fatty acids of Example 1. Data on this ester are set out in Table I below.

EXAMPLE 3 C26 Guerbet alcohol (95.5 g., 0.25 mole) prepared by dimerizing branched C13 Oxo alcohol (obtained by oxonation of a C12 olefin fraction containing mainly tetrapropylene) was refluxed with coconut fatty acids (57.3 g.,

0.262 mole) and 75 g. of toluene in the presence of 0.8 g. NaHSOt. The material was heated for 4 hours at C. to C. during which time 4.1 cc. of water was collected. The mixture was diluted with 300 g. Varsolhexane mixture, washed thrice with 100 cc. of 2% NazCOa solution and twice with 100 cc. of water. The material was distilled. The monoester fraction boiling mainly at 235 C. at 0.1 mm. weighed 126 g. (86.5% yield) and had the properties set out in Table I below.

EXAMPLE 4 To illustrate the lubricating nature of the ester of Example 1, it was blended with 7.0 wt. percent of a polymeric methacrylate ester having about 9 carbon atoms in the side chains. This material is commercially available as a viscosity index improver. The standard inspections on the blend are set out in Table I below.

EXAMPLE 5 A synthetic ester lubricating oil comparable to that of Example 1 above was prepared by esterifying the coconut fatty acids with a C16 Oxo alcohol. This alcohol was prepared by oxonafing a C15 polypropylene fractionin the Oxo process. The" preparation was as follows:

A mixture of 440* g. (2.2 moles) or C16 ()xo alcohol;

To summarizebriefly, the instantinvention relates. to

lubricating characteristics at high and low temperatures which comprises ester materials of the formula 438 g. (2 moles) of coconut fatty acids, 4 g. of NAHS04 5 RCOOR catalyst and 100 g. toluene was refluxed at 114 C. to H 165 C. for a period of one hour during which time wherein R and'R are selected from the group of ali- 37 cc. of water were collected '(theory' is 38 ecu). This phatio monobasic acids having from about 81w 18 carbon mix re was dflu l im. 255 {01.116119 w h d: atoms in straight chain configuration, or substantially with 100 cc. of NazCOs and three roo'ee. portions of Straight chained, and branched chain primarymonohydric water. The material-"was t hendistilled. The monoester alcohols containing from about 12 to about 28 carbon boiled over the range 187 205 C. at 0.08 atoms which contains one major side chain of from 4 to EXAMPLE 6 14 carbon atoms. When'R is branched, R must be straight, and vice versa.

The Cu; Oxo alcohol as was used in Example 5 above 15 The synthetic lubricating compositions according to was used in this example to esterify a C13 0x0 acid prethis invention may be used as such, or they may be pared by oxidation of a C13 Oxo alcohol via alkali fusion. blended with other lubricants, either natural mineral The C13 Oxo alcohol was prepared by the oxonation of a oils, or other synthetic lubricants. They are completely C12 polypropylene fraction in the 0x0 process. The compatible with the various additive materials known to ester was prepared as follows: the lubrication art, and such materials as viscosity index C16 0x0 alcohol (121 g., 0.5 mole), C13 Oxo acid improvers, pour point depressants, detergent inhibitors, (113 g., 0.53 mole), NaHSOt (1.2 g.) and toluene (75 foxidation inhibitors, extreme pressure agents, and the like,

g.) were heated to 162 C. for 4 hours. The water colmay be blended with these materials to enhance special lected was 8.3 cc. After washing the ester with 2% characteristics. The synthetic lubricants of invention may NazCOs and water it was distilled. The fraction boiling be blended with any of the commonly used grease makat mainly 200-2l0 C. at 0.1 mm. had the properties ing soaps to form solid or semi-solid lubricants. set out in Table I below. What is claimed is:

l. A lubricating composition having an ASTM pour EXAMPLE 7 point below about +35 R, an ASTM flash point above In this example the C16 Guerbet alcohol, prepared a about 375 F., and a viscosity at 210 F. of about 2 to described in P 1 above, Was used to ri y h 13 centistokes which comprises an ester of the formula C13 Oxo acid of Example 6 above. This preparation RCOOR, was the same as described in Example 6. The product, distilling largely at 190 -200 C. at 0.05 mm., had the wherein R and R are alkyl groups selected from the class properties as set out in Table I below. consisting of alkyl radicals having a straight chain con- Table 1 PROPERTIES OF SYNTHETIC LUBRICANTS [Comparison of 0x0 versus Guerbet alcohol derived monoesters] Hydrogen Viscosity, Cs. F. ASTM Slope 210/ Combustion Pour Flash Test, mgs. Ex. N o. Ester V. I Point, Point,

F. F. 210 100 0 100 F. 0 F. -40 F. Total Varnish Deposit C 1 Guerbet Coconate 3. 51 15. 11 293 2, 623 128 60 425 O. 736 0. 732 0. 727 5. 5 1 8 n-Cls Guerbet Coconate 3.13 11.67 140 viscous 148 10 420 0. 711 0. 696 Cu Guerbet Coconate 6. 30 39. 30 1, 657 25, 057 118 70 +430 0. 713 O. 708 0. 700 6. 7 1. 9 C Guerbet Coconate +7% Acryloid 747 1. 7. 25 31. 84 593 viscous 164 425 0. 578 0. 595 O10 OX0 Coconate 4. 12 18. 77 568 Solid 142 25 430 0. 714 0. 740 3. 4 0. 7 Cu OX0 G11 Oxoate 4. 72 27. 92 1, 630 37, 100 93 ---65 425 0. 767 0. 782 0. 778 l. 7 0. 9 Ci Guerbet C1; 0xoate 3. 98 22. 07 1, 028 19, 611 74 -75 395 0. 792 0. 797 O. 792 5. 6 1. 4

1 5 gm. sample placed in a tared beailker and ignited. Total incombustible material reported varnish and carbon. Carbon removed mechanically and beaker re-weighed to obtain varms 1 Made from n-C; alcohol.

Examination of the data of Table I above points out the superiority of the esters of the invention over similar esters having an equal number of carbon atoms. It is shown by the data above that the Guerbet esters are superior to the 0x0 esters by virtue of the lower pour points, better low temperature viscosities, and a downwardcurvature when viscosity is plotted on the ASTM chart against temperature. All of the Guerbet esters have decreasing ASTM slopes whereas the 0x0 esters show increasing slopes in the lower temperature regions. This downward curvature of the slope indiactes much better properties at temperatures where viscosity increase is very material.

With 7.0% of a commercially available polymethacrylate viscosity index improver, the C16 Guerbet ester is thickened to the point at which its low temperature viscosity nears the low temperature viscosity of the C16 0x0 ester. The formerester is then far superior in high temperature characteristics, as well as in pour point, viscosity index, and ASTM slope.

figuration and containing from about 8 to about 18 carbon atoms and alkyl radicals containing from about 12 to about 28 carbon atoms in a configuration such that there is present one major side chain containing from about 4 to about 14 carbon atoms, and wherein one of said alkyl groups has a branched chain configuration and the other alkyl group has a straight chain configuration. 2. A lubricating composition having an ASTM pour point below about +35 R, an ASTM flash point above about 375 F., and a viscosity at 210 F. of about 2 to 13 centistokes which comprises an ester of the formula RCOOR wherein R is the alkyl radical of an aliphatic monobasic acid having from about 8 to about 18 carbon atoms in straight chain configuration and wherein R is the alkyl radical of a branched chain primary monohydric alcohol containing from about 12 to about 28 carbon atoms and which contains one major side chain of from 4 to 14 carbon atoms.

3. A synthetic lubricating composition according to from 4 to 14 carbon atoms and wherein R is the alkyl claim '2 wherein R contains an average of 12.5 carbon radical of a primary aliphatic monohydric alcohol conatoms. taining about 8 to 18 carbon atoms in straight chain con- 4. A lubricating composition having an ASTM pour figuration.

point below about +35 R, an ASTM flash point above 5 about 375 F., and a viscosity at 210 F. of about 2 to References Cited in the file 9 this Patent 13 centistokes which comprises an ester of the formula Structural Guides f Synthgtic Lubricant Develop- RCOOR' ments, I. & E. Chem., vol. 42, No. 12, December 1950,

2417 rti t. wherein R is the alkyl radical of a branched chain ali- 10 page pe Hen Aliphatic Esters, I. & E. Chem, vol. 45, No. 8, phatic monobasic acid containing from about 12 to about August 1953 page 1768 pertinent 28 carbon atoms and containing one major side chain of

Claims (1)

1. A LUBRICATING COMPOSITION HAVING AN ASTM POUR POINT BELOW ABOUT +35* F., AN ASTM FLASH POINT ABOVE ABOUT 375* F., AND A VISCOSITY AT 210* F. OF ABOUT 2 TO 13 CENTISTOKES WHICH COMPRISES AN ESTER OF THE FORMULA