EP0075478B1

EP0075478B1 - Borated hydroxyl-containing composition and lubricants containing same

Info

Publication number: EP0075478B1
Application number: EP82304950A
Authority: EP
Inventors: Andrew Gene Horodysky
Original assignee: Mobil Oil Corp; ExxonMobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1981-09-22
Filing date: 1982-09-21
Publication date: 1987-07-29
Also published as: AU8801682A; ZA825972B; ATE28661T1; NZ201613A; EP0075478A3; JPS5865792A; BR8205535A; JPH0328478B2; EP0075478A2; DE3276869D1; AU553247B2; CA1198726A

Abstract

Multifunctional additives are provided for fuel and lubricant compositions. The additives are borated hydrocarbyl vicinal diols, made by reacting the diol with a boron-containing compound such as boric acid or trialkyl borate.

Description

The invention relates to lubricant compositions containing borated linear hydrocarbyl vicinal termainal diols to reduce friction and fuel consumption in internal combustion engines.
According to the invention, there is provided a lubricant composition comprising a lubricant and from 0.1 to 10% by weight of a borated linear hydrocarbyl vicinal terminal diol containing from 14 to 20 carbon atoms.
Alcohols are well known for their lubricity properties when formulated into lubricating oils and fortheir water-scavenging characteristics when blended into fuels. Vicinal hydroxyl-containing alkyl carboxylates such as glycerol monooleate have also found widespread use as lubricity additives. U.S. Patent 2,788,326 describes such esters as glycerol monoleates, as minor components of lubricating oil compositions. U.S. Patent 3,235,498 describes, among others, that same ester as an additive to other oils. U.S. Patent 2,443,578 teaches esters wherein the free hydroxyl group is found in the acid portion as for example in tartaric acid.
The above patents, as well as numerous others, are directed to the use of such esters as additives. Other patents, such as U.S. Patents 2,798,083; 2,820,014; 3,115,519; 3,282,971; and 3,309,318 as well as an article by R. R. Barnes et al, entitled "Synthetic Ester Lubricants" in Lubrication Engineering, August, 1975, pp. 454-457, teach lubricants prepared from polyhydric alcohols and acid containing no hydroxyl groups other than those associated with the acid function.
So far as is known, no effort has been made to employ borated hydrocarbyl vicinal diols as lubricant additives. It is recognised that borated hydrocarbyl and borated aliphatic diols are known for other uses. For example, U.S. Patent 3,740,358 teaches a phenol-aldehyde foamable composition containing a boron compound, e.g. a material formed by reacting boric acid or boric oxide with such aliphatic hydroxyl-containing compound.
It has now been found that boration of these linear long-chain alkyl terminal vicinal diols significantly improves friction-reducing properties and imparts an anti-oxidant component to these novel compositions. In addition to the friction-reducing properties described, the alkyl terminal vicinal diol borate esters possess much improved solubility characteristics, especially in synthetic fluids, over those of the non-borated derivatives. These borates are non-corrosive to copper, possess anti-oxidant and potential anti-fatigue characteristics. Furthermore, the compositions also have significantly greater friction reducing properties, higher viscosity indices and good low temperature characteristics and solubility characteristics when used in low additive concentrations-than do other known additives.
The hydrocarbyl vicinal terminal diols contemplated for use in this invention are linear hydrocarbyl diols having vicinal terminal hydroxyls. They have the formula:
wherein R is a linear hydrocarbyl group containing 14 to 20 carbon atoms. As used herein, "hydrocarbyl" includes, but is not limited to tetradecyl, pentadecyl, hexadecyl, octadecyl, eicosyl and the like. R can be saturated or unsaturated with linear saturated members being preferred to maximize friction reduction.
The vicinal terminal diols can be synthesized using several methods known to the art such as that described in J. Am. Chem. Soc., 68,1504 (1946) which involves the hydroxylation of 1-olefins with peracids. Vicinal terminal diols can also be prepared by the peroxytrifluoroacetic acid method for the hydroxylation of olefins as described in J. Am. Chem. Soc., 76, 3472 (1954). Similar procedures can be found in U.S. Patents 2,411,762; 2,457,329; and 2,455,892.
The diols can also be prepared via catalytic epoxidation of an appropriate olefin followed by hydrolysis to form the appropriate vicinal diol.
The borated vicinal terminal diols contain 14 to 20 carbon atoms. Above a carbon number of 20, solubility constraints become significant. Preferred are the C₁₄―C₁₇ hydrocarbyl groups in which solubility, frictional characteristics and other properties are maximized.
Among the diols contemplated for reaction with the boron compound are 1,2-tetradecanediol, 1,2-pentadecanediol, 1,2-hexadecanediol, 1,2-octadecanediol, 1,2-mixed Cis-C18-alkanediols and mixtures thereof.
The boronated compound used in this invention can be made using a single diol or two or more diols. A mixture of diols can contain from about 5% to about 95% by weight of any one diol, the other diol or diols being selected such that it or they together comprise from about 95% to about 5% by weight of the mixture. Such mixtures are often preferred to the single diol.
Reaction with the boron compound of the formula
where R is a C, to C₆ alkyl, x is 0 to 3

and y is 0 to 3, the sum of x and y being 3, can be performed in the presence of an alcoholic solvent, such as butanol or pentanol, or a hydrocarbon solvent such as benzene, toluene or xylene, or mixtures of such solvents. Reaction temperatures of 90°C to 260°C or more can be used, but 110 to 200°C is preferred. Reaction times can be 1 to 24 hours and more. Up to a stoichiometric amount of boric acid can be used, or an excess thereof can be used to produce a drivative containing from about 0.1 % to about 10% of boron. At least 5 to 10% of the available hydroxyl groups of the diol should be borated to derive substantial beneficial effect. Conversely, a stoichiometric excess or boric acid (more than an equivalent amount of boronating agent compared to diol hydroxyl groups) can also be charged to the reaction medium resulting in a product containing the stated amount of boron. The boronated diols can also be borated with a trialkyl borate such as tributyl borate, often in the presence of boric acid. Preferred reaction temperatures for boration with the borate will range from 180°C to 280°C. Times can be from 2 to 12 hours, or more.

As disclosed hereinabove, the borated esters are used with lubricating oils to the extent of from 0.1 % to 10% by weight of the total composition. Furthermore, other additives, such as detergents, anti-oxidants, anti-wear agents may be present. These can include phenates, sulfonates, succinimides, zinc dithiophosphates, polymers, calcium and magnesium salts.
The lubricants contemplated for use with the esters herein disclosed include mineral and synthetic hydrocarbon oils of lubricating viscosity mixtures of mineral oils and synthetic oils and greases from any of these, including mixtures. The synthetic hydrocarbon oils include long-chain alkanes such as cetanes and olefin polymers such as oligomers of hexane, octene, decene, and dodecene, etc. These vicinal diols are especially effective in synthetic oils formulated using mixtures of synthetic hydrocarbon olefin oligomers and lesser amounts of hydrocarbyl carboxylate ester fluids. The other synthetic oils, which can be used alone with the borated compounds of this invention, or which can be mixed with a mineral or synthetic hydrocarbon oil, include (1) fully esterified ester oils, with no free hydroxyls, such as pentaerythritol esters of monocarboxylic acids having 2 to 20 carbon atoms, trimethylolpropane esters of monocarboxylic acids having 2 to 20 carbon atoms, (2) polyacetals and (3) siloxane fluids. Especially useful among the synthetic esters are those made from polycarboxylic acids and monohydric alcohols. More preferred are the ester fluids made by fully esterifying pentaerythritol, or mixtures thereof with di- and tripentaerythritol, with an aliphatic monocarboxylic acid containing from 1 to 20 carbon atoms, or mixtures of such acids.
A wide variety of thickening agents can be used in the greases of this invention. Included among the thickening agents are alkali and alkaline earth metal soaps of fatty acids and fatty materials having from 12 to 30 carbon atoms per molecule. The metals are typified by sodium, lithium, calcium and barium. Fatty materials are illustrated by stearic acid, hydroxystearic acid, stearin, cottonseed oil acids, oleic acid, palmitic acid, myristic acid and hydrogenated fish oils.
Other thickening agents include salt and salt-soap complexes as calcium stearate-acetate (U.S. Patent No. 2,197,263), barium stearate acetate (U.S. Patent No. 2,564,561), calcium stearate-caprylateacetate complexes (U.S. Patent No. 2,999,065), calcium caprylate-acetate (U.S. Patent No. 2,999,066), and calcium salts and soaps of low-, intermediate- and high-molecular weight acids and of nut oil acids.
Another group of thickening agents comprises substituted ureas, phthalocyanines, indanthrene, pigments such as perylimides, pyromellitdiimides, and ammeline.
The preferred thickening gelling agents employed in the grease compositions are essentially hydrophobic clays. Such thickening agents can be prepared from clays which are initially hydrophilic in character, but which have been converted into a hydrophobic condition by the introduction of long chain hydrocarbon radicals into the surface of the clay particles; prior to their use as a component of a grease composition, as, for example, by being subjected to a preliminary treatment with an organic cationic surface active agent, such as an onium compound. Typical onium compounds are tetraalkylammonium chlorides, such as dimethyl dioctadecyl ammonium chloride, dimethyl dibenzyl ammonium chloride and mixtures thereof. This method of conversion, being well known to those skilled in the art, is believed to require no further discussion, and does not form a part of the present invention. More specifically, the clays which are useful as starting materials in forming the thickening agents to be employed in the grease compositions, can comprise the naturally occurring chemically unmodified clays. These clays are crystalline complex silicates, the exact composition of which is not subject to precise description, since they vary widely from one natural source to another. These clays can be described as complex inorganic silicates such as aluminum silicates, magnesium silicates, barium silicates, and the like, containing, in addition to the silicate lattice, varying amounts of cation-exchangeable groups such as sodium. Hydrophilic clays which are particularly useful for conversion to desired thickening agents include montmorillonite clays, such as bentonite, attapulgite, hectorite, illite, saponite, sepiolite, biotite, vermiculite, zeolite clays, and the like. The thickening agent is employed in an amount from 0.5 to 30, and preferably from 3 percent to 15, percent by weight of the total grease composition.
In all reactions decribed hereinabove, a solvent is preferred. Solvents that can be used include the hydrocarbon solvents, such as toluene, benzene, xylene, and the like, alcohol solvents such as propanol, butanol, pentanol and the like, as well as mixtures of hydrocarbon solvents or alcohol solvents and mixtures of hydrocarbon and alcohol solvents.

Example 1

1,2-Hexadecanediol Borate

86 g of 1,2-hexadecanediol and 200 g toluene solvent was charged to a 1 liter reactor equipped with agitator, heater and Dean-Stark tube with condenser. The contents were heated up to 80-90°C to dissolve the diol and approximately 11 g boric acid was added. The mixture was heated up to 155°C until water evolution stopped over a period of about 4 hours. Approximately 9 ml water was removed by azeotropic distillation. The solvent was removed by vacuum distillation and the product was filtered at 100°C through diatomaceous earth. The product became waxy after cooling.
It is believed that the borated product included the following structures:
where R= C14H29

Example 2

1,2-Mixed C,₅-C_ls Alkanediol Borate (High Boron Content)

Approximately 155 g of 1,2-mixed C₁₅―C₁₈ alkanediols and 130 g of toluene were charged to a 1 liter reactor, equipped as described in Example 1 and with provision for providing a nitrogen atmosphere. The contents were heated up to 65°C and 34 g of boric acid was added. The mixture was heated up to 160°C over a period of 4 1/2 hours until water evolution stopped. The solvent was removed by vacuum distillation and the product was filtered hot through diatomaceous earth, yielding a white waxy solid after cooling.

Example 3

1,2-Mixed C₁₅―C₁₈ Alkanediol Borate

Approximately 265 g of 1,2-mixed C₁₅―C₁₈ alkanediols and 200 g of toluene were charged to a 1 liter reactor equipped as described in Example 2. The contents were heated to 70°C and 42 g of boric acid was added. The mixture was heated up to 155°C over a period of 5 hours until water evolution stopped. The solvent was removed by vacuum distillation and the product was filtered at 100°C through diatomaceous earth.
The products of the Examples were blended into a fully formulated 5W-20 synthetic automotive engine oil containing other additives, such as detergent, dispersant, anti-oxidant and the like additives and evaluated using the Low Velocity Friction Apparatus (LVFA) test.

Evaluation of Products

The compounds were evaluated as friction modifiers in accordance with the following test.

Low Velocity Friction apparatus

Description

The Low Velocity Friction Apparatus (LVFA) is used to measure the friction of test lubricants under various loads, temperatures, and sliding speeds. The LVFA consists of a flat SAE 1020 steel surface (diam. 3.8 cm.) which is attached to a drive shaft and rotated over a stationary, raised, narrow ringed SAE 1020 steel surface of 51.6 mm² (area 0.08 in.²). Both surfaces are submerged in the test lubricant. Friction between the steel surfaces is measured as a function of the sliding speed at a lubricant temperature of 121°C. The friction between the rubbing surfaces is measured using a torque arm-strain gauge system. The strain gauge output, which is calibrated to be equal to the coefficient of friction, is fed to the Y axis of an X-Y plotter. The speed signal from the tachometer-generator is fed to the X-axis. To minimise external friction, the piston is supported by an air bearing. The normal force loading the rubbing surfaces is regulated by air pressure on the bottom of the piston. The drive system consists of an infinitely variable- speed hydraulic transmission driven by a 373W (1/2 HP) electric motor. To vary the sliding speed, the output speed of the transmission is regulated by a lever-cam motor arrangement.

Procedure

The rubbing surfaces and 12-13 ml of test lubricant are placed on the LVFA. A 1756 kPa (240 psig) load is applied, and the sliding speed is maintained at 12.2 m/s (40 fpm) at ambient temperature for a few minutes. A plot of coefficients of friction (U_k) over the range of sliding speeds, 1.5 to 12.2 m/s (5 to 40 fpm, 25-195 rpm), is obtained. A minimum of three measurements is obtained for each test lubricant. Then, the test lubricant and specimens are heated to 121°C, another set of measurements is obtained, and the system is run for 50 minutes at 121°C, 240 psi and 12.2 m/s (40 fpm) sliding speed. Afterward, measurements of U_k vs. speed are taken at 1756, 2170, 2859 and 3549 kPa (240, 300, 400, and 500 psig). Freshly polished steel specimens are used for each run. The surface of the steel is parallel ground to .1 to .2 µm (4-8 microinches).
The data obtained are shown in Table 1. The data in Table 1 are reported as percent reduction in coefficient of friction at two speeds. The friction reducing ester additives were evaluated in a fully formulated 5W-20 synthetic lubricating oil comprising an additive package including anti-oxidant, detergent and dispersant. The oil had the following general characteristics:

Viscosity 100°C - 6.8 mm²/s
Viscosity 40°C - 36.9 mm²/s
Viscosity Index - 143

The results clearly show the borated hydrocarbyl vicinal diol to be a fare superior friction reducer. For example, the use of only 1/2% of Example 5, borated 1,2-mixed C₁₅―C₁₈ alkanediols reduces the coefficient of friction by 40%/28%.
The products of this invention were tested in a catalytic oxidation test for lubricants, using as the base oil a 200" solvent paraffinic neutral mineral oil. The test lubricant composition is subjected to a stream of air bubbled through the composition at a rate of 5 liters per hour at 163°C for 40 hours. Present in the composition are metals commonly used as materials of engine construction, namely:

a. 100.6 cm² (15.6 sq. in.) of sand-blasted iron wire,
b. 5.03 cm² (0.78 sq. in.) of polished copper wire,
c. 5.61 cm² (0.87 sq. in.) of polished aluminum wire, and
d. 1.08 cm² (0.167 sq. in.) of polished lead surface.

Inhibitors for oil are rated on the basis of prevention of oil deterioration as measured by the increase in acid formation or neutralization number (NN) and kinematic viscosity (KV) occasioned by the oxidation. The results of the tests are reported in Table 2.
The results clearly show the effectiveness of the borates at controlling viscosity increase and neutralization number increase under somewhat severe oxidation conditions.

Claims

1. A lubricant composition comprising a lubricant and from 0.1 to 10% by weight of a borated linear hydrocarbyl vicinal terminal diol containing from 14 to 20 carbon atoms.

2. A composition according to claim 1, wherein the diol is 1,2-tetradecanediol, 1,2-pentadecanediol, 1,2-hexadecanediol, 1,2-octadecanediol or 1,2-eicosanediol.

3. A composition according to claim 1 or claim 2, wherein the diol is 1,2-mixed C₁₅―C₁₈ alkanediols.

4. A composition according to claim 1, wherein the hydrocarbyl group contains from 14 to 17 carbon atoms.

5. A composition according to any one of claims 1 to 4, wherein the diol is a mixture of diols containing from 5 to 95% by weight of one diol.

6. A composition according to any one of claims 1 to 5, wherein the diol has been borated with a compound of the formula:

wherein R is a C_l-C₆ alkyl group, x is 0 to 3, y is 0 to 3, and the sum of x and y is 3.

7. A composition according to claim 6, wherein the compound is boric acid.

8. A composition according to any one of claims 1 to 7, wherein at least 5 to 10% of the available hydroxyl groups of the diol have been borated.

9. A composition according to any one of claims 1 to 8, wherein the borated diol contains from 0.1 to 10% by weight of boron.

10. A composition according to any one of claims 1 to 9, wherein the lubricant comprises a mineral lubricating oil, a synthetic lubricating oil, a mixture thereof or a grease prepared therefrom.