WO1999036387A1

WO1999036387A1 - Biodegradable high hydroxyl synthetic ester base stocks and lubricants formed therefrom

Info

Publication number: WO1999036387A1
Application number: PCT/US1999/000581
Authority: WO
Inventors: Thomas H. Henry; Richard H. Schlosberg; Carolyn B. Duncan
Original assignee: Exxon Chemical Patents Inc.
Priority date: 1998-01-13
Filing date: 1999-01-11
Publication date: 1999-07-22
Also published as: AU2315799A

Abstract

A biodegradable lubricant which is prepared from: at least one biodegradable synthetic ester base stock with a branched or linear alcohol having the general formula R(OH)n, wherein R is an aliphatic or cyclo-aliphatic group having from about 2 to 20 carbon atoms and n is at least 2; and at least one branched or linear mono-carboxylic acid which has a carbon number in the range between about C5 to C20; wherein the synthetic ester composition has between 2-50 % unconverted hydroxyl groups, based on the total amount of hydroxyl groups in the branched or linear alcohol; wherein the ester base stock exhibits the following properties: at least 25 % biodegradation in 28 days as measured by the Modified Sturm test; and a pour point of less than -25 °C; and an additive package.

Description

BIODEGRADABLE HIGH HYDROXYL SYNTHETIC ESTER BASE STOCKS AND LUBRICANTS FORMED THEREFROM

The present invention relates generally to the use of high hydroxyl synthetic esters to improve the biodegradable properties of an otherwise unacceptably poor biodegradable fully esterified synthetic ester of the same reactants. Furthermore, these unique high hydroxyl esters exhibit a unique and wholly unexpected synergistic biodegradable affect when they are blended with otherwise poor biodegradable base stocks.

These biodegradable high hydroxyl synthetic esters or blends of esters are particularly useful in the formation of biodegradable lubricants in two-cycle engine oils, catapult oils, hydraulic fluids, drilling fluids, water turbine oils, greases, compressor oils, gear oils, and other industrial and engine applications where biodegradability is needed or desired.

BACKGROUND OF THE INVENTION

The interest in developing biodegradable lubricants for use in applications which result in the dispersion of such lubricants into waterways, such as rivers, oceans and lakes, has generated substantial interest by both the environmental community and lubricant manufacturers.

Base stocks for biodegradable lubricant applications (e.g., two-cycle engine oils, catapult oils, hydraulic fluids, drilling fluids, water turbine oils, greases, gear oils and compressor oils) should typically meet five criteria: (1) solubility with dispersants and other additives such as polyamides; (2) good cold flow properties (such as, less than -40°C pour point; less than 7500 cps at -25°C); (3) sufficient biodegradability to off-set the low biodegradability of any dispersants and/or other additives to the formulated lubricant; (4) good lubricity without the aid of wear additives; and (5) high flash point (greater than 260°C, flash and fire points by COC (Cleveland Open Cup) as measured by ASTM test number D-92).

The Organization for Economic Cooperation and Development (OECD) issued draft test guidelines for degradation and accumulation testing in December 1979. The Expert Group recommended that the following tests should be used to determine the "ready biodegradability" of organic chemicals: Modified OECD Screening Test, Modified MITI Test (I), Closed Bottle Test, Modified Sturm Test and the Modified AFNOR Test. The Group also recommended that the following "pass levels" of biodegradation, obtained within 28 days, may be regarded as good evidence of "ready biodegradability": (Dissolved Organic Carbon (DOC)) 70%; (Biological Oxygen Demand (BOD)) 60%; (Total Organic Carbon (TOD)) 60%; (C0₂) 60%; and (DOC) 70%, respectively, for the tests listed above. Therefore, the "pass level" of biodegradation, obtained within 28 days, using the Modified Sturm Test is at least (CO₂) 60%.

Since the main purpose in setting the test duration at 28 days was to allow sufficient time for adaptation of the micro-organisms to the chemical (lag phase), this should not allow compounds which degrade slowly, after a relatively short adaptation period, to pass the test. A check on the rate of biodegradation therefore should be made. The "pass level" of biodegradation (60%) must be reached within 10 days of the start of biodegradation. Biodegradation is considered to have begun when 10% of the theoretical C0₂ has evolved. That is, a readily biodegradable fluid should have at least a 60% yield of CO₂ within 28 days, and this level must be reached within 10 days of biodegradation exceeding 10%. This is known as the "10-Day Window."

The OECD guideline for testing the "ready biodegradability" of chemicals under the Modified Sturm test (OECD 301B, adopted May 12, 1981, and which is incorporated herein by reference) involves the measurement of the amount of CO₂ produced by the test compound which is measured and expressed as a percent of the theoretical CO₂ (TC0₂) it should have produced calculated from the carbon content of the test compound. Biodegradability is therefore expressed as a percentage of TCO₂. The Modified Sturm test is run by spiking a chemically defined liquid medium, essentially free of other organic carbon sources, with the test material and inoculated with sewage micro-organisms. The CO₂ released is trapped as BaCO₃. After reference to suitable blank controls, the total amount of CO₂ produced by the test compound is determined for the test period and calculated as the percentage of total CO₂ that the test material could have theoretically produced based on carbon composition. See G. van der Waal and D. Kenbeek, "Testing, Application, and Future Development of Environmentally Friendly Ester Based Fluids", Journal of Synthetic Lubrication, Vol. 10, Issue No. 1, April 1993, pp. 67-83, which is incorporated herein by reference. One base stock in current use today is rapeseed oil (i.e., a triglyceride of fatty acids, e.g., 7 % saturated C₁₂ to C₁₈ acids, 50% oleic acid, 36% linoleic acid and 7% linolenic acid, having the following properties: a viscosity at 40°C of 47.8 cSt, a pour point of 0°C, a flash point of 162°C and a biodegradability of 85% by the Modified Sturm test. Although it has very good biodegradability, its use in biodegradable lubricant applications is limited due to its poor low temperature properties and poor stability.

Unless they are sufficiently low in molecular weight, esters synthesized from both linear acids and linear alcohols tend to have poor low temperature properties. Even when synthesized from linear acids and highly branched alcohols, such as polyol esters of linear acids, high viscosity esters with good low temperature properties can be difficult to achieve. In addition, pentaerythritol esters of linear acids exhibit poor solubility with dispersants such as polyamides, and trimethylolpropane esters of low molecular weight (i.e., having a carbon number less than 14) linear acids do not provide sufficient lubricity. This lower quality of lubricity is also seen with adipate esters of branched alcohols. Since low molecular weight linear esters also have low viscosities, some degree of branching is required to build viscosity while maintaining good cold flow properties. When both the alcohol and acid portions of the ester are highly branched, however, such as with the case of polyol esters of highly branched oxo acids, the resulting molecule tends to exhibit poor biodegradation as measured by the Modified Sturm test (OECD Test No. 301B).

In an article by Randies and Wright, "Environmentally Considerate Ester Lubricants for the Automotive and Engineering Industries", Journal of Synthetic Lubrication, Vol. 9-2, pp. 145-161, it was stated that the main features which slow or reduce microbial breakdown are the extent of branching, which reduces β- oxidation, and the degree to which ester hydrolysis is inhibited. The negative effect on biodegradability due to branching along the carbon chain is further discussed in a book by R.D. Swisher, "Surfactant Biodegradation", Marcel Dekker, Inc., Second Edition, 1987, pp. 415-417. In his book, Swisher stated that "The results clearly showed increased resistance to biodegradation with increased branching... Although the effect of a single methyl branch in an otherwise linear molecule is barely noticeable, increased resistance [to biodegradation] with increased branching is generally observed, and resistance becomes exceptionally great when quaternary branching occurs at all chain ends in the molecule." The negative effect of alkyl branching on biodegradability was also discussed in an article by N.S. Battersby, S.E. Pack , and R.J. Watkinson, "A Correlation Between the Biodegradability of Oil Products in the CEC-L-33-T-82 and Modified Sturm Tests", Chemosphere, 24(12), pp. 1989-2000 (1992).

Initially, the poor biodegradation of branched polyol esters was believed to be a consequence of the branching and, to a lesser extent, to the insolubility of the molecule in water. However, recent work by the present inventors has shown that the non-biodegradability of these branched esters is more a function of steric hindrance than of the micro-organism's inability to breakdown the tertiary and quaternary carbons. Thus, by relieving the steric hindrance around the ester linkage(s), biodegradation can more readily occur with branched esters.

Branched synthetic polyol esters have been used extensively in non- biodegradable applications, such as refrigeration lubricant applications, and have proven to be quite effective if 3,5,5-trimethylhexanoic acid is incorporated into the molecule at 25 molar percent or greater. However, trimethylhexanoic acid is not biodegradable as determined by the Modified Sturm test (OECD 30 IB), and the incorporation of 3,5,5-trimethylhexanoic acid, even at 25 molar percent, would drastically lower the biodegradation of the polyol ester due to the quaternary carbons contained therein.

Likewise, incorporation of trialkyl acetic acids (i.e., neo acids) into a polyol ester produces very useful refrigeration lubricants. These acids do not, however, biodegrade as determined by the Modified Sturm test (OECD 30 IB) and cannot be used to produce polyol esters for biodegradable applications. Polyol esters of all branched acids can be used as refrigeration oils as well. However, they do not rapidly biodegrade as determined by the Modified Sturm Test (OECD 301B) and, therefore, are not desirable for use in biodegradable applications.

Although polyol esters made from purely linear C₅ and C₁₀ acids for refrigeration applications would be biodegradable under the Modified Sturm test, they would not work as a lubricant in hydraulic or two-cycle engine applications because the viscosities would be too low and wear additives would be needed. It is extremely difficult to develop a lubricant base stock which is capable of exhibiting all of the various properties required for biodegradable lubricant applications, i.e., high viscosity, low pour point, oxidative stability and biodegradability as measured by the Modified Sturm test.

U.S. Patent No. 4,826,633 (Carr et al.), which issued on May 2, 1989, discloses a synthetic ester lubricant base stock formed by reacting at least one of trimethylolpropane and monopentaerythritol with a mixture of aliphatic mono- carboxylic acids. The mixture of acids includes straight-chain acids having from 5 to 10 carbon atoms and an iso-acid having from 6 to 10 carbon atoms, preferably iso-nonanoic acid (i.e., 3,5,5-trimethylhexanoic acid). This base stock is mixed with a conventional ester lubricant additive package to form a lubricant having a viscosity at 99°C (210°F) of at least 5.0 centistokes and a pour point of at least as low as -54°C (-65°F). This lubricant is particularly useful in gas turbine engines. The Carr et al. patent differs from the present invention for two reasons. Firstly, it preferably uses as its branched acid 3,5,5-trimethylhexanoic acid which contains a quaternary carbon in every acid molecule. The incorporation of quaternary carbons within the 3,5,5-trimethylhexanoic acid inhibits biodegradation of the polyol ester product. Also, since the lubricant according to Carr et al. exhibits high stability, as measured by a high pressure differential scanning calorimeter (HPDSC), i.e., about 35 to 65 minutes, the micro-organisms cannot pull them apart. Conversely, the lubricant according to the present invention is low in stability, i.e., it has a HPDSC reading of about 12-17 minutes. The lower stability allows the micro-organisms to attack the carbon-to-carbon bonds about the polyol structure and effectively cause the ester to biodegrade. One reason that the lubricant of the present invention is lower is stability is the fact that no more than 10% of the branched acids used to form the lubricant's ester base stock contain a quaternary carbon.

In addition to the role of steric hindrance having a major (inhibiting) effect on the rate of biodegradation of a synthetic ester molecule, the present inventors have discovered that there is also a role of phase behavior (i.e., ester solubility) on the rate of biodegradation. Since it is believed that in an aqueous system the biodegradability largely takes place in the aqueous phase, the greater the water solubility of a synthetic ester the higher its concentration in water and, all other things being equal, the greater the rate of biodegradation. For synthetic ester systems the present inventors have discovered through experimentation that a high hydroxyl has higher water solubility than does a full synthetic ester formed from the same components. The present inventors have discovered that the high hydroxyl ester of the present invention will be higher in oxygen content and lower in molecular weight, both of which typically result in greater solubility in water and, thus, result in an ester base stock which exhibits a greater degree of biodegradability than fully esterified esters. Due to enhanced biodegradability, such high hydroxyl esters are capable of utilizing 3,5,5-trimethyl hexanoic acid to enhance thermal and oxidative stability, while still maintaining a high degree of biodegradation versus fully esterified ester using 3,5,5-trimethyl hexanoic acid.

Therefore, the present inventors have discovered that biodegradable lubricants using biodegradable base stocks with good cold flow properties, good solubility with dispersants, and good lubricity can be achieved using base stocks of high hydroxyl esters or blends thereof with other base stocks. Lubricants formed using biodegradable high hydroxyl ester provide the following cumulative advantages over lubricants formed from fully esterified base stocks: (1) increased water solubility; (2) leaving some free hydroxyl groups reduced steric hindrance around the quaternary carbon of polyols, thus increasing the molecules' biodegradability; and (3) increased thermal and oxidative stability.

In summary, lubricant formulators who use esters with high hydroxyl numbers should see increased biodegradability for those ester with free hydroxyl groups over those that are completely esterified.

SUMMARY OF THE INVENTION

A biodegradable high hydroxyl base stock which preferably comprises the reaction product of: a branched or linear alcohol having the general formula R(OH)_n, wherein R is an aliphatic or cyclo-aliphatic group having from about 2 to 20 carbon atoms and n is at least 2; and at least one branched or linear mono- carboxylic acid which has a carbon number in the range between about C₅ to C₂₀; wherein the synthetic ester composition has between about 2-50%, preferably between about 5-35% unconverted hydroxyl groups, based on the total amount of hydroxyl groups in the branched or linear alcohol; wherein the ester exhibits the following properties: at least 25% biodegradation in 28 days as measured by the Modified Sturm test; and a pour point of less than -25°C.

Preferably, the branched or linear alcohol of the high hydroxyl ester is present in an excess of about 10 to 35 equivalent percent for the amount of the branched acid or branched/linear mixed acids used. Between about 60 to 90% of the hydroxyl groups from the branched or linear alcohol are converted upon the esterification of the branched or linear alcohol with the acid. The resultant synthetic polyol ester composition according to the present invention exhibits a thermal/oxidative stability measured by HPDSC at 220°C, 3.445 MPa air and 0.5 wt. % Vanlube® 81 antioxidant (i.e., dioctyl diphenyl amine) of greater than 10 minutes, preferably greater than 100 minutes.

Linear acids may be present in an amount of between about 0 to 100 wt. % based on the total amount of the branched mono-carboxylic acid. The linear acid is any linear saturated alkyl carboxylic acid having a carbon number in the range between about C₂ to C₁₂, preferable a commercially available C810 linear acid.

This novel synthetic polyol ester composition exhibits between about 20 to

200 % or greater thermal/oxidative stability as measured by high pressure differential scanning calorimetry versus a fully esterified composition which is also formed from the same branched or linear alcohol and the branched mono- carboxylic acid which have less than 10% unconverted hydroxyl groups, based on the total amount of hydroxyl groups in the branched or linear alcohol. The fully esterified synthetic polyol ester composition of the present invention typically has a hydroxyl number which is greater than 5, preferably in the range between about 5 to 150, more preferably between about 5 to 100, and most preferably between about 10 to 80. The present invention also includes a lubricant which is prepared from at least one synthetic polyol ester composition having unconverted hydroxyl groups as set forth immediately above and a lubricant additive package. Additionally, a solvent may also be added to the lubricant, wherein the lubricant comprises about 60-99% by weight of the synthetic polyol ester composition, about 1 to 20% by weight the additive package, and about 0 to 20% by weight of the solvent.

Still other lubricants can be formed according to the present invention by blending this unique biodegradable high hydroxyl ester base stock with at least one additional base stock selected from the group consisting of: mineral oils, highly refined mineral oils, poly alpha olefins, polyalkylene glycols, phosphate esters, silicone oils, diesters and polyol esters. The high hydroxyl ester base stock is blended with the additional base stocks in an amount between about 1 to 50 wt. %, based on the total blended base stock, preferably 1 to 25 wt. %, and most preferably 1 to 15 wt. %.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The biodegradable polyol ester composition of the present invention is preferably formed by reacting a polyhydroxyl compound with at least one branched or linear acid. In the polyol ester composition, the polyol is preferably present in an excess of about 10 to 35 equivalent percent or more for the amount of acid used. The composition of the feed polyol is adjusted so as to provide the desired composition of the product ester.

The acid is preferably a highly branched acid such that the unconverted hydroxyl groups which are bonded to the resultant ester composition act similarly to an antioxidant such that it transfers a hydrogen atom to the unstable carbon radical which is produced when the ester molecule is under thermal stress, thereby effecting a "healing" of the radical (i.e., convert the carbon radical to a stable alcohol and oxygen). These unconverted hydroxyl groups which act as internal antioxidants, can substantially reduce or, in some instances, eliminate the need for the addition of costly antioxidants to the polyol ester composition. Moreover, esters having unconverted hydroxyl groups bonded thereto demonstrate substantially enhanced thermal/oxidative stability versus esters having similar amounts of antioxidants admixed therewith.

Alternatively, when increased levels of biodegradation are required for a particular application, linear acids can be used either alone or in an mixture with the branched acids. When linear and branched acids are used in a mixture it is preferable that they be mixed in a ratio of between about 1 :99 to 80:20 and thereafter reacted with the branched or linear alcohol as set forth immediately above. However, the same molar excess of alcohol used in the all branched or all linear case is also required in the mixed acids case such that the synthetic ester composition formed by reacting the alcohol and the mixed acids still has between about 2-50%, preferably about 5-35%, unconverted hydroxyl groups, based on the total amount of hydroxyl groups in the alcohol.

The esterification reaction is preferably conducted, with or without a catalyst, at a temperature in the range between about 140 to 250°C and a pressure in the range between about 30 mm Hg to 760 mm Hg (3.999 to 101.308 kPa) for about 0.1 to 12 hours, preferably 2 to 8 hours. The stoichiometry in the reactor is variable, with the capability of vacuum stripping excess acid to generate the preferred final composition.

If the esterification reaction is conducted under catalytic conditions, then the preferred esterification catalysts are titanium, zirconium and tin catalysts such as titanium, zirconium and tin alcoholates, carboxylates and chelates. Selected acid catalysts may also be used in this esterification process. See U.S. Patent Nos. 5,324,853 (Jones et al.), which issued on June 28, 1994, and 3,056,818 (Werber), which issued on October 2, 1962, both of which are incorporated herein by reference. ALCOHOLS

Among the alcohols which can be reacted with either the branched acid or branched and linear acid mixture are, by way of example, polyols (i.e., polyhydroxyl compounds) represented by the general formula: R(OH)_n wherein R is any aliphatic or cyclo-aliphatic hydrocarbyl group (preferably an alkyl) and n is at least 2. The hydrocarbyl group may contain from about 2 to about 20 or more carbon atoms, and the hydrocarbyl group may also contain substituents such as chlorine, nitrogen and/or oxygen atoms. The polyhydroxyl compounds generally may contain one or more oxyalkylene groups and, thus, the polyhydroxyl compounds include compounds such as polyetherpolyols. The number of carbon atoms (i.e., carbon number, wherein the term carbon number as used throughout this application refers to the total number of carbon atoms in either the acid or alcohol as the case may be) and number of hydroxy groups (i.e., hydroxyl number) contained in the polyhydroxyl compound used to form the carboxylic esters may vary over a wide range.

The following alcohols are particularly useful as polyols: neopentyl glycol, 2,2-dimethylol butane, trimethylol ethane, trimethylol propane, trimethylol butane, mono-pentaerythritol, technical grade pentaerythritol, di-pentaerythritol, tri-pentaerythritol, ethylene glycol, propylene glycol and polyalkylene glycols (e.g., polyethylene glycols, polypropylene glycols, 1 ,4-butanediol, sorbitol, glycerol and the like, 2-methylpropanediol, polybutylene glycols, etc., and blends thereof such as a polymerized mixture of ethylene glycol and propylene glycol). The most preferred alcohols are technical grade (e.g., approximately 88% mono-, 10% di- and 1-2% tri-pentaerythritol) pentaerythritol, monopentaerythritol, di- pentaerythritol, neopentyl glycol and trimethylol propane.

BRANCHED ACIDS

The branched acid is preferably a mono-carboxylic acid which has a carbon number in the range between about C₅ to C₁₃, more preferably about C₇ to C₁₀ wherein methyl or ethyl branches are preferred. The mono-carboxylic acid is preferably at least one acid selected from the group consisting of: 2,2- dimethyl propionic acid (neopentanoic acid), neoheptanoic acid, neooctanoic acid, neononanoic acid, neodecanoic acid, 2-ethyl hexanoic acid (2EH), 3,5,5-trimethyl hexanoic acid (TMH), isoheptanoic acid, isooctanoic acid, isononanoic acid, oleic acid and isodecanoic acid. One especially preferred branched acid is 3,5,5- trimethyl hexanoic acid. The term "neo" as used herein refers to a trialkyl acetic acid, i.e., an acid which is triply substituted at the alpha carbon with alkyl groups. These alkyl groups are equal to or greater than CH₃ as shown in the general structure set forth herebelow:

Ri O

I I I

R₂ - C-C -OH

R₃ Alpha Carbon

wherein R_]5 R₂, and R₃ are greater than or equal to CH₃ and not equal to hydrogen.

3,5,5-trimethyl hexanoic acid has the structure set forth herebelow:

CH₃ CH₃ O I I II

C H₃-C-C H₂-C H-C H₂-C-OH

CH₃

LINEAR ACIDS

The preferred mono- and /or di-carboxylic linear acids are any linear saturated alkyl carboxylic acid having a carbon number in the range between about C₂ to C₁₈, preferably C₂ to C₁₂.

Some examples of linear acids include acetic, propionic, pentanoic, heptanoic, octanoic, nonanoic, and decanoic acids. Selected diacids include any C₂ to C₁₂ diacids, e.g., adipic, azelaic, sebacic and dodecanedioic acids. The process of synthesizing polyol ester compositions having significant unconverted hydroxyl groups according to the present invention typically follows the below equation:

R(OH)„ + R'COOH → R(OH)_n + R(OOCR')_n + R(OOCR')„.,OH

+ R(OOCR')_n.₂(OH)₂ + R(OOCR')_n.,(OH), (Eq. 1)

wherein n is an integer having a value of at least 2, R is any aliphatic or cyclo- aliphatic hydrocarbyl group containing from about 2 to about 20 or more carbon atoms and, optionally, substituents such as chlorine, nitrogen and/or oxygen atoms, and R' is any branched aliphatic hydrocarbyl group having a carbon number in the range between about C₄ to C₁₂, more preferably about C₆ to C₉, wherein methyl or ethyl branches are preferred, and (i) is an integer having a value of between about 0 to n.

The biodegradable high hydroxyl reaction product from Equation 1 above can either be used by itself as a lubricant base stock or in admixture with other base stocks, such as mineral oils, highly refined mineral oils, poly alpha olefins (PAO), polyalkylene glycols (PAG), phosphate esters, silicone oils, diesters and polyol esters. When blended with other base stocks, the partial ester composition according to the present invention is preferably present in an amount of from about 1 to 50 wt. %, based on the total blended base stock, more preferably between about 1 to 25 wt. %, and most preferably between about 1 to 15 wt. %.

One preferred additional base stock is selected from the group consisting of: biodegradable synthetic ester base stocks which comprise the reaction product of: a branched or linear alcohol having the general formula R(OH)_n, wherein R is an aliphatic or cyclo-aliphatic group having from about 2 to 20 carbon atoms and n is at least 2; and mixed acids comprising about 30 to 80 molar % of a linear acid having a carbon number in the range between about C₅ to C₁₂, and about 20 to 70 molar % of at least one branched acid having a carbon number in the range between about C₅ to C₁₃; wherein the ester base stock exhibits the following properties: at least 60% biodegradation in 28 days as measured by the Modified Sturm test; a pour point of less than -25°C; and a viscosity of less than 7500 cps at -25°C.

The polyol ester composition according to the present invention can be used in the formulation of various lubricants, such as, crankcase engine oils (i.e., passenger car motor oils, heavy duty diesel motor oils, and passenger car diesel oils), two-cycle engine oils, catapult oil, hydraulic fluids, drilling fluids, aircraft and other turbine oils, greases, compressor oils, gear oils, functional fluids and other industrial and engine lubrication applications. The lubricating oils contemplated for use with the polyol ester compositions of the present invention include both mineral and synthetic hydrocarbon oils of lubricating viscosity and mixtures thereof with other synthetic oils. The synthetic hydrocarbon oils include long chain alkanes such as cetanes and olefin polymers such as oligomers of hexene, octene, decene, and dodecene, etc. The other synthetic oils include (1) fully esterified ester oils, with no free hydroxyls, such as pentaerythritol esters of monocarboxylic acids having 2 to 20 carbon atoms, trimethylol propane 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 tri- pentaerythritol, with an aliphatic monocarboxylic acid containing from 1 to 20 carbon atoms, or mixtures of such acids.

In some of the lubricant formulations set forth above a solvent be employed depending upon the specific application. Solvents that can be used include the hydrocarbon solvents, such as toluene, benzene, xylene, and the like. The formulated lubricant according to the present invention preferably comprises about 60-99% by weight of at least one polyol ester composition of the present invention, about 1 to 20% by weight lubricant additive package, and about 0 to 20% by weight of a solvent.

BIODEGRADABLE LUBRICANTS

The high hydroxyl ester base stock of the present invention can be used in the formulation of biodegradable lubricants together with selected lubricant additives. The additives listed below are typically used in such amounts so as to provide their normal attendant functions. Typical amounts for individual components are also set forth below. The preferred biodegradable lubricant contains approximately 80% or greater by weight of the base stock and 20% by weight of any combination of the following additives:

(Broad) (Preferred)

Wt.% Wt.%

Viscosity Index Improver 1-12 1-4

Corrosion Inhibitor 0.01-3 0.01-1.5

Oxidation Inhibitor 0.01-5 0.01-1.5

Dispersant 0.1-10 0.1-5

Lube Oil Flow Improver 0.01-2 0.01-1.5

Detergents and Rust Inhibitors 0.01-6 0.01-3

Pour Point Depressant 0.01-1.5 0.01-1.5

Antifoaming Agents 0.001-0.1 0.001-0.01

Antiwear Agents 0.001-5 0.001-1.5

Seal Swellant 0.1-8 0.1-4

Friction Modifiers 0.01-3 0.01-1.5

Biodegradable Synthetic Ester Base Stock >80% >80%

BIODEGRADABLE TWO-CYCLE ENGINE OILS

The biodegradable high hydroxyl ester base stock can be used in the formulation of biodegradable two-cycle engine oils together with selected lubricant additives. The preferred biodegradable two-cycle engine oil is typically formulated using the biodegradable high hydroxyl esterbase stock formed according to the present invention together with any conventional two-cycle engine oil additive package. The additives listed below are typically used in such amounts so as to provide their normal attendant functions. The additive package may include, but is not limited to, viscosity index improvers, corrosion inhibitors, oxidation inhibitors, coupling agents, dispersants, extreme pressure agents, color stabilizers, surfactants, diluents, detergents and rust inhibitors, pour point depressants, antifoaming agents, and antiwear agents.

The biodegradable two-cycle engine oil according to the present invention can employ typically about 75 to 85% base stock, about 1 to 5% solvent, with the remainder comprising an additive package.

Examples of the above additives for use in biodegradable lubricants are set forth in the following documents which are incorporated herein by reference: U.S.

Patent No. 5,663,063 (Davis), which issued on May 5, 1987; U.S. Patent No.

5,330,667 (Tiffany, III et al), which issued on July 19, 1994; U.S. Patent No. 4,740,321 (Davis et al.), which issued on April 26, 1988; U.S. Patent No.

5,321,172 (Alexander et al), which issued on June 14, 1994; and U.S. Patent No.

5,049,291 (Miyaji et al.), which issued on September 17, 1991.

BIODEGRADABLE CATAPULT OILS

Catapults are instruments used on aircraft carriers at sea to eject the aircraft off of the carrier. The biodegradably high hydroxyl ester base stock can be used in the formulation of biodegradable catapult oils together with selected lubricant additives. The preferred biodegradable catapult oil is typically formulated using the biodegradable high hydroxyl ester base stock formed according to the present invention together with any conventional catapult oil additive package. The additives listed below are typically used in such amounts so as to provide their normal attendant functions. The additive package may include, but is not limited to, viscosity index improvers, corrosion inhibitors, oxidation inhibitors, extreme pressure agents, color stabilizers, detergents and rust inhibitors, antifoaming agents, antiwear agents, and friction modifiers.

The biodegradable catapult oil according to the present invention can employ typically about 90 to 99% base stock, with the remainder comprising an additive package.

Biodegradable catapult oils preferably include conventional corrosion inhibitors and rust inhibitors. If desired, the catapult oils may contain other conventional additives such as antifoam agents, antiwear agents, other antioxidants, extreme pressure agents, friction modifiers and other hydrolytic stabilizers. These additives are disclosed in Klamann, "Lubricants and Related Products", Verlag Chemie, Deerfield Beach, FL, 1984, which is incorporated herein by reference.

BIODEGRADABLE HYDRAULIC FLUIDS

The branched synthetic ester base stock can be used in the formulation of biodegradable hydraulic fluids together with selected lubricant additives. The preferred biodegradable hydraulic fluids are typically formulated using the biodegradable high hydroxyl ester base stock formed according to the present invention together with any conventional hydraulic fluid additive package. The additives listed below are typically used in such amounts so as to provide their normal attendant functions. The additive package may include, but is not limited to, viscosity index improvers, corrosion inhibitors, boundary lubrication agents, demulsifϊers, pour point depressants, and antifoaming agents.

The biodegradable hydraulic fluid according to the present invention can employ typically about 90 to 99% base stock, with the remainder comprising an additive package.

Other additives are disclosed in U.S. Patent No. 4,783,274 (Jokinen et al.), which issued on November 8, 1988, and which is incorporated herein by reference.

BIODEGRADABLE DRILLING FLUIDS The branched synthetic ester base stock can be used in the formulation of biodegradable drilling fluids together with selected lubricant additives. The preferred biodegradable drilling fluids are typically formulated using the biodegradable high hydroxyl ester base stock formed according to the present invention together with any conventional drilling fluid additive package. The additives listed below are typically used in such amounts so as to provide their normal attendant functions. The additive package may include, but is not limited to, viscosity index improvers, corrosion inhibitors, wettinging agents, water loss improving agents, bactericides, and drill bit lubricants. The biodegradable drilling fluid according to the present invention can employ typically about 60 to 90% base stock and about 5 to 25% solvent, with the remainder comprising an additive package. See U.S. Patent No. 4,382,002

(Walker et al), which issued on May 3, 1983, and which is incorporated herein by reference.

Suitable hydrocarbon solvents include: mineral oils, particularly those paraffin base oils of good oxidation stability with a boiling range of from 200- 400°C such as Mentor 28®, sold by Exxon Chemical Americas, Houston, Texas; diesel and gas oils; and heavy aromatic naphtha.

BIODEGRADABLE WATER TURBINE OILS

The branched synthetic ester base stock can be used in the formulation of biodegradable water turbine oils together with selected lubricant additives. The preferred biodegradable water turbine oil is typically formulated using the biodegradable high hydroxyl ester base stock formed according to the present invention together with any conventional water turbine oil additive package. The additives listed below are typically used in such amounts so as to provide their normal attendant functions. The additive package may include, but is not limited to, viscosity index improvers, corrosion inhibitors, oxidation inhibitors, thickeners, dispersants, anti-emulsifying agents, color stabilizers, detergents and rust inhibitors, and pour point depressants.

The biodegradable water turbine oil according to the present invention can employ typically about 65 to 75% base stock and about 5 to 30% solvent, with the remainder comprising an additive package, typically in the range between about

0.01 to about 5.0 weight percent each, based on the total weight of the composition.

BIODEGRADABLE GREASES

The branched synthetic ester base stock can be used in the formulation of biodegradable greases together with selected lubricant additives. The main ingredient found in greases is the thickening agent or gellant and differences in grease formulations have often involved this ingredient. Besides, the thickener or gellants, other properties and characteristics of greases can be influenced by the particular lubricating base stock and the various additives that can be used. The preferred biodegradable greases are typically formulated using the biodegradable high hydroxyl ester base stock formed according to the present invention together with any conventional grease additive package. The additives listed below are typically used in such amounts so as to provide their normal attendant functions. The additive package may include, but is not limited to, viscosity index improvers, oxidation inhibitors, extreme pressure agents, detergents and rust inhibitors, pour point depressants, metal deactivators, antiwear agents, and thickeners or gellants.

The biodegradable grease according to the present invention can employ typically about 80 to 95% base stock and about 5 to 20% thickening agent or gellant, with the remainder comprising an additive package.

Typically thickening agents used in grease formulations include the alkali metal soaps, clays, polymers, asbestos, carbon black, silica gels, polyureas and aluminum complexes. Soap thickened greases are the most popular with lithium and calcium soaps being most common. Simple soap greases are formed from the alkali metal salts of long chain fatty acids with lithium 12-hydroxystearate, the predominant one formed from 12-hydroxystearic acid, lithium hydroxide monohydrate and mineral oil. Complex soap greases are also in common use and comprise metal salts of a mixture of organic acids. One typical complex soap grease found in use today is a complex lithium soap grease prepared from 12- hydroxystearic acid, lithium hydroxide monohydrate, azelaic acid and mineral oil. The lithium soaps are described and exemplified in may patents including U.S. Patent No. 3,758,407 (Halting), which issued on September 11, 1973; U.S. Patent No. 3,791,973 (Gilani), which issued on February 12, 1974; and U.S. Patent No. 3,929,651 (Murray), which issued on December 30, 1975, all of which are incorporated herein by reference together with U.S. Patent No. 4,392,967 (Alexander), which issued on July 12, 1983.

A description of the additives used in greases may be found in Boner, "Modern Lubricating Greases", 1976, Chapter 5, which is incorporated herein by reference, as well as additives listed above in the other biodegradable products. BIODEGRADABLE COMPRESSOR OILS

The branched synthetic ester base stock can be used in the formulation of biodegradable compressor oils together with selected lubricant additives. The preferred biodegradable compressor oil is typically formulated using the biodegradable high hydroxyl ester base stock formed according to the present invention together with any conventional compressor oil additive package. The additives listed below are typically used in such amounts so as to provide their normal attendant functions. The additive package may include, but is not limited to, oxidation inhibitors, additive solubilizers, rust inhibitors/metal passivators, demulsifying agents, and antiwear agents.

The biodegradable compressor oil according to the present invention can employ typically about 80 to 99% base stock and about 1 to 15% solvent, with the remainder comprising an additive package.

The additives for compressor oils are also set forth in U.S. Patent No. 5,156,759 (Culpon, Jr.), which issued on October 20, 1992, and which is incorporated herein by reference.

EXAMPLE 1 The following comparative data in Table 1 shows that the biodegradable high hydroxyl ester according to the present invention has a higher oxygen content and lower molecular weight than their full ester counterparts, both of which typically result in greater solubility in water and enhanced biodegradability.

TABLE 1 ESTER MOL. WT. % OXYGEN

Trimethylolpropane/iso-C₈ acid full ester 512 18.75

Trimethylolpropane/iso-C₈ acid (diester) 386 20.7

Trimethylolpropane/iso-C₈ acid (monoester) 260 24.6

Trimethylolpropane/iso-C₈ acid w/25% OH «425 20.4

Table 2 below demonstrates the biodegradability of the esters set forth in Table 1, wherein only the high hydroxyl ester exhibits any acceptable level of biodegradability. TABLE 2

ESTER % BIODEGRADABILITY*

Trimethylolpropane/iso-C₈ acid full ester 13.33

Trimethylolpropane/iso-C₈ acid (diester) >44 Trimethylolpropane/iso-C₈ acid (monoester) »44

Trimethylolpropane/iso-C₈ acid w/OH #70 44.18

* % Biodegradability was determined using the Modified Sturm Test.

EXAMPLE 2

The following examples demonstrate that blends with high hydroxyl ester and other polyolester base stocks result in a synergistic effect wherein the combined product is biodegradable. The examples set forth in Table 3 below compare the blended base stocks with Sample 1 (i.e., a trimethylolpropane/iso-C₈ acid ester having a hydroxyl number of 70), Sample 2 (i.e., rapeseed oil), Sample 3 (i.e., technical grade pentaerythritol with a 45:55 mixture of iso-C₈ and C810 acids, and Sample 4 (i.e., a full trimethylolpropane/iso-C₈ acid ester).

As demonstrated below, the blending of Samples 1 and 3 clearly resulted in a blended product which exceeded 60% biodegradation threshold as measured by the Mofidied Sturm Test for a product, i.e., Sample 1, which would not have otherwise satisfied the 60% level.

TABLE 3

ESTER % BIODEGRADABILITY*

Sample 1 44.18

Sample 2 76.03

Sample 3 92.90

Sample 4 13.33

Blend of Samples 1 and 3 (ratio of20:80) 65.36

* % Biodegradability was determined using the Modified Sturm Test.

EXAMPLE 3 The data set forth below in Table 4 demonstrate that polyol ester compositions having unconverted hydroxyl groups which are formed from polyols and branched acids in accordance with the present invention exhibit internal antioxidant properties.

Table 4

HPDSC

Sample Hydroxyl Decomposition

Number Ester Number Time, Min.

1 TechPE/TMH greater than 50 468 with 0.5% V-81

2 TechPE/TMH greater than 50 58.3 with no V-81

3 TechPE/L9 less than 5 16.9 with 0.5% V-81

4 Tech PE/TMH less than 5 148 with 0.5% V-81

5 Tech PE/TMH less than 5 3.14 with no V-81

V-81 is dioctyl diphenyl amine.

TechPE is technical grade pentaerythritol (i.e., 88% mono-, 10% di- and 1-2% tri- pentaerythritol). TMH is 3,5,5-trimethyl hexanoic acid. L9 is blend of 62-70 mole % linear C₉ acid and 30-38 mole % branched C₉ acid.

The results in Table 4 above demonstrate that polyol esters with unconverted hydroxyl groups (i.e., sample numbers 1 and 2) greatly enhance the oxidative induction time of the lubricant formulation versus conventional polyol esters which do not have any significant amount of free or unconverted hydroxyl groups. Moreover, combining these unique polyol esters with an antioxidant such as V-81 significantly extends the time required for decomposition (see sample no. 1). Although the time for decomposition was reduced when this polyol ester did not include any added antioxidant, it still took approximately 3/ times longer to decompose versus a conventional C₉ acid polyol ester which had an antioxidant additive (i.e., 58.3 minutes (sample 2) versus 16.9 minutes (sample 3)). Furthermore, Samples 4 and 5 demonstrate that decomposition of the polyol ester compositions having a hydroxyl number less than 5 occurs much more rapidly compared to polyol ester compositions of the same acid and polyol having a hydroxyl number greater than 50 (e.g., Samples 1 and 2) regardless of whether or not an antioxidant is admixed with the respective polyol ester composition. This clearly demonstrates that synthesizing a polyol ester composition having unconverted hydroxyl groups disposed about the carbon chain of the polyol ester provide enhanced thermal/oxidative stability to the resultant product, as measured by HPDSC. Finally, a comparison of Sample Nos. 2 and 5, wherein no antioxidant was used, clearly establishes the antioxidant properties of the polyol ester of technical grade pentaerythritol and 3,5,5-trimethyl hexanoic acid having substantial amounts of unconverted hydroxyl group bonded which has an HPDSC of 58.3 minutes versus the same polyol ester with little or no unconverted hydroxyl groups which has an HPDSC of 3.14 minutes.

Claims

WHAT IS CLAIMED IS

1. A biodegradable high hydroxyl synthetic ester base stock which comprises the reaction product of: a branched or linear alcohol having the general formula R(OH)_n, wherein

R is an aliphatic or cyclo-aliphatic group having from about 2 to 20 carbon atoms and n is at least 2; and at least one branched or linear mono-carboxylic acid which has a carbon number in the range between about C₅ to C₂₀; wherein said synthetic ester composition has between 2-50% unconverted hydroxyl groups, based on the total amount of hydroxyl groups in said branched or linear alcohol; wherein said ester base stock exhibits the following properties: at least

25% biodegradation in 28 days as measured by the Modified Sturm test; and a pour point of less than -25°C

The synthetic ester composition according to claim 1 wherein between about 50 to 90 of the hydroxyl groups from said branched or linear alcohol are converted upon the esterification of said branched or linear alcohol with said branched or linear mono-carboxylic acid.

The synthetic ester composition according to claim 1 wherein said synthetic ester composition has a hydroxyl number in the range between about 5 to 150.

4. The synthetic ester composition according to claim 3 wherein said synthetic ester composition has a hydroxyl number in the range between about 5 to 100.

5. The synthetic ester composition according to claim 4 wherein said synthetic ester composition has a hydroxyl number in the range between about 10 to 80.

6. The synthetic ester composition according to claim 1 wherein said branched acids are any mono-carboxylic acid which have a carbon number in the range between about C₅ to C₁₀.

7. The synthetic ester composition according to claim 1 wherein said branched or linear alcohol is selected from the group consisting of: neopentyl glycol, 2,2-dimethylol butane, trimethylol ethane, trimethylol propane, trimethylol butane, mono-pentaerythritol, technical grade pentaerythritol, di-pentaerythritol, tri-pentaerythritol, ethylene glycol, propylene glycol, polyalkylene glycols, 1 ,4-butanediol, sorbitol, glycerol, and 2-methylpropanediol.

8. The synthetic ester composition according to claim 1 wherein said branched acid is at least one acid selected from the group consisting of: 2,2-dimethyl propionic acid, neoheptanoic acid, neooctanoic acid, neononanoic acid, neodecanoic acid, 2-ethyl hexanoic acid, 3,5,5-trimethyl hexanoic acid, isoheptanoic acid, isooctanoic acid, isononanoic acid, oleic acid and isodecanoic acid.

9. The synthetic ester composition according to claim 1 wherein said linear acid is at least one acid selected from the group consisting of: acetic acid, propionic acid, pentanoic acid, heptanoic acid, octanoic acid, nonanoic acid, and decanoic acid.

10. The synthetic ester composition according to claim 1 wherein said linear acid is at least one diacid selected from the group consisting of: C₂ to C₁₂ diacids.

11. A biodegradable lubricant which is prepared from at least one biodegradable synthetic ester base stock which comprises the reaction product of: a branched or linear alcohol having the general formula R(OH)_n, wherein R is an aliphatic or cyclo-aliphatic group having from about 2 to 20 carbon atoms and n is at least 2; and at least one branched or linear mono-carboxylic acid which has a carbon number in the range between about C₅ to C₁₃; wherein said synthetic ester composition has between 2-50% unconverted hydroxyl groups, based on the total amount of hydroxyl groups in said branched or linear alcohol; wherein said ester base stock exhibits the following properties: at least 25% biodegradation in 28 days as measured by the Modified Sturm test; a pour point of less than -25°C; and a viscosity of less than 7500 cps at -25°C; and a lubricant additive package.

12. The biodegradable lubricant according to claim 11 wherein said additive package comprises additives selected from the group consisting of: viscosity index improvers, corrosion inhibitors, oxidation inhibitors, dispersants, lube oil flow improvers, detergents and rust inhibitors, pour point depressants, anti-foaming agents, antiwear agents, seal swellants, and friction modifiers.

13. The biodegradable lubricant according to claim 11 wherein said biodegradable lubricant is selected from the group consisting of: catapult oils, hydraulic fluids, drilling fluids, water turbine oil, gear oil, grease, compressor oil, and two-cycle engine oil.

14. The use of the biodegradable high hydroxyl synthetic ester base stock according to claim 1 as a catapult oil, hydraulic fluid, drilling fluid, water turbine oil, gear oil, grease, compressor oil or two-cycle engine oil.