Synthetic industrial oils made with "tri-synthetic" base stocks

Abstract

This invention describes a blend of three base stock fluids, a PAO, an alkylated aromatic and a aromatic ester that synergistically improve the solvency for industrial lubricant additives such as oxidation and rust inhibitors, extreme-pressure/antiwear agents, metal deactivators and the like. The blend also has excellent hydrolytic stability plus improved dispersancy and resistance to deposit formation without degrading demulsibility.

Description

FIELD OF INVENTION

[0001] The present invention relates to lubricant base stock blends. More particularly, the present invention is directed toward base stocks having unexpectedly improved resistance to deposit formation, improved solubility for lubricant additives, degradation products and enhanced demulsibility.

BACKGROUND OF INVENTION

[0002] Synthetic lubricant base stocks prepared by oligomerizing one or more alpha olefins are well known commercially available materials that have low pour points and high viscosity indices. Lube products employing these poly-alpha-olefins (PAO's) typically are combined with a more polar co-base stock such as alkylated aromatic fluids or polyol esters or certain dispersant additives such as polyalkylene type additives.

[0003] The inclusion of alkylated aromatic base fluids such as alkylated naphthalene in PAO base fluids provides the fluid blend with improved hydrolytic stability but there remains a need to provide the blend with improved dispersancy.

[0004] The inclusion of polyalkylene type additives in PAO base fluids provides enhanced dispersancy but these additives form stable emulsions with water and degrade the hydrolytic stability of compositions employing them thereby limiting the use of the blend to applications where water ingress is not a problem.

[0005] The inclusion of polyol esters in PAO base fluids provides good dispersancy but poor hydrolytic stability.

[0006] Therefore, one object of the present invention is to provide a lubricant product of improved dispersancy along with good demulsibility and hydrolytic stability.

SUMMARY OF INVENTION

[0007] Briefly stated the present invention is a synergistic combination of synthetic fluids useful as lubricant base stock blend and comprising about 10 wt % or more of a PAO fluid; about 1 wt % or more of an alkylated aromatic fluid and about 1 wt % or more of an aromatic ester.

[0008] In a preferred embodiment the lubricant base stock comprises:

[0009] from about 10 wt % to about 98 wt % of a PAO fluid;

[0010] from about 1 wt % to about 59 wt % of an alkylated aromatic; and

[0011] from about 1 wt % to about 75 wt % of an aromatic ester,

[0012] all amounts based on the weight of the blend.

[0013] Advantageous features of the invention will become apparent from the detailed description that follows.

BRIEF DESCRIPTION OF DRAWINGS

[0014] FIG. 1 is a graphic comparison of the storage stability of a commercial lubricant composition with one using a base stock of the invention.

[0015] FIG. 2 graphically illustrates the deposit control property of a base stock of the invention.

[0016] FIG. 3 graphically compares the water demulsibility of a commercial composition with one using a base stock of the invention.

[0017] FIG. 4 graphically compares the oxidative and hydrolytic stability of two base stocks formulations of the invention with two others.

DETAILED DESCRIPTION OF INVENTION

[0018] Applicant has discovered that a blend of three lubricant fluids, viz a PAO, an alkylated aromatic and an aromatic ester has improved solvency for lube additives such as oxidation and rust inhibitors, metal passivators and the like. The blend also has improved hydrolytic stability, dispersancy and resistance to deposit formation without degrading demulsibility making the blend useful in a wide range of industrial applications. Indeed, fully formulated lubricant compositions employing the base stock of the present invention are especially suitable for use in applications where there is the potential for water of moisture ingress such as oils used in combined cycle turbines, paper machinery, rod mills and the like.

[0019] The blended base stock of the invention includes at least about 10 wt % of a PAO fluid. In general, the blend will comprise from about 10 wt % to about 98 wt % of the PAO fluid, based on the total weight of the blend. Preferably, the blend will comprise from 60 wt % to 95 wt %, and more preferably from 80 wt % to 85 wt %.

[0020] PAO fluids and their preparation are well known in the art. Those PAO's suitable in the practice of the present invention may be derived from C2 to about C32 alpha olefins with C8 to about C16 alpha olefins being preferred. Typically the PAO will have a viscosity in the range of about 3 cSt to about 300 cSt at 100° C. The preferred PAO a viscosity will, of course, depend upon factors such as the nature and amount of the other components used in the blend and the intended end use for the lubricant base stock blend.

[0021] The base stock blend of the present invention also includes a alkylated aromatic compound such as alkylated benzene, naphthalene, anthracene, biphenyl and the like. Like the PAO's, alkylated aromatics and their method of preparation are well known in the art. Suitable alkylated aromatics are those having one or more short chain alkyl groups of from 1 to about 8 carbon atoms. The preferred alkyl aromatics will have viscosities in the range of about 3 cSt to about 300 cSt at 100° C. The alkylated aromatics will comprise about 1 to about 59 wt % of the total blend, preferably about 5 wt % to about 35 wt % and more preferably about 10 wt %.

[0022] The base stock of the present invention also includes an aromatic ester fluid. Common lubricant grade aromatic esters such as phthalate esters, mono- and diesters, polyol ester and ester with tails contain S, N and O suitable in the blend of this invention are commercial available materials typically formed by reacting an organic acid or anhydride with straight or branched alcohols. Such esters have viscosities in the range of about 4 cSt to about 30 cSt at 100° C. In general, the amount of aromatic ester employed in the base stock blend will be about 1 wt % to about 75 wt %, and preferably from about 2 wt % to about 25 wt % of the total blend, with about 5 wt % to 8 wt % being more preferred.

[0023] An advantageous feature of the base stock blend of the present invention is its ability to solubilize additives such as heterocyclic rust inhibitors, antioxidants, antiwear agents, corrosion inhibitors and the like. Among the antioxidants suitable for use in the base stock blend specific mention is made of aminic and phenolic type antioxidants. Suitable antiwear agents include alkylated triphenyl phosphates, phosphorophites, diorganodithiocarbamates and the like.

[0024] The following examples and comparative examples further illustrate the many advantageous of the instant invention.

EXAMPLES

Example 1

[0025] A base stock according to the present invention comprising 84 wt % of a PAO (6 cSt at 100° C.) 10 wt % of an alkyl aromatic (alkylated naphthalene) fluid (5 cSt at 100° C.) and 6 wt % of an ester fluid (diisooctylphthalate) was used in preparing a fully formulated lubricant composition (Formulation A) by blending the base stock with the following additives:

[0026] (1) 0.4 wt % hindered phenolic and diphenyl amine type antioxidants and 1:1 ratio;

[0027] (2) 1.5 wt % butylated triphenyl phosphate type antiwear agent; and

[0028] (3) 0.1 wt % of an ashless rust inhibitor.

[0029] The composition was maintained at 100° C. for 16 weeks without any evidence of haze or floc. Haze or floc, of course, is indicative of additive insolubility.

[0030] In contrast, a commercially available composition comprising a 6 cSt at 100° C. PAO, 20 wt % diisodecylphthalate ester and substantially the same amounts of similar type additives of Formulation A after six weeks displayed a trace of haze and moderate floccing.

[0031] FIG. 1 graphically presents the results of the tests and illustrates the improved solubility that the base stock of the invention has for lubricant additives.

Example 2

[0032] The deposit control of the base stock of the invention was compared to a commercially available lubricant composition (Comparative 2) by subjecting Formulation A of Example 1 and Comparative 2 to the Cincinnati Machine Thermal Test A. The Comparative 2 composition has a PAO base fluid, typical additives and 1.0 wt % of a dispersant. The results of the text are graphically shown in FIG. 2. As can be seen under the text conditions Formulation A exhibited excellent low deposit formation. Moreover, when the test was modified by raising the test temperature from 275° F. to 350° F. at the end of 168 hours visual inspection of the samples showed that the Formulation A had far less deposit formation.

Example 3

[0033] Formulation A of Example 1 and a commercial lubricant composition (Comparative 3) were subjected to the ASTM-D 1401 demulsibility test. Comparative 3 was a PAO based lubricant containing 1.0 wt % of a polyalkylene dispersant. The results of the tests are shown in FIG. 3.

[0034] As can be seen, Formulation A with the base stock of the invention showed complete water separation within 10 minutes. Formulation A, of course, did not contain a demulsfier additive.

Example 4

[0035] This example compares the oxidative and hydroytic stability, as determined by ASTM D 943 TOST life test, of two base stocks of the invention (A and B) with two other base stock (C and D). Base stock A comprised 80 wt % PAO (6 cSt at 100° C.); 10 wt % of an alkylated naphthalene (5 cSt at 100° C.) and 6 wt % an ester fluid (diisooctylphthalate). Base stock B differed from A in that the ester was a 50:50 mixture of ditridicyl phthalate and terephtalate ester.

[0036] Base stock C and D used the same PAO as A and B. The alkylated aromatic fluid of C was the same as in A and B while the ester of D was a trimellitatte ester.

[0037] The results of the tests are shown in FIG. 4.

[0038] As can be seen A and B display 30% longer life than C.

Claims

1. A lubricant base stock blend comprising:

about 10 wt % or more of a polyalpha olefin (PAO) fluid;

about 1 wt % or more of an akylated aromatic fluid; and

about 1 wt % or more of an aromatic ester;

all amounts based on the weight of the blend.

2. The blend of claim 1 comprising:

from about 10 wt % to about 98 wt % of a PAO fluid;

from about 1 wt % to about 59 wt % of an alkylated aromatic fluid; and

from about 1 wt % to about 75 wt % of an aromatic ester.

3. The blend of claim 2 wherein the PAO comprise from about 80 to 85 wt %.

4. The blend of claim 2 wherein the alkylated aromatic comprises about 10 wt %.

5. The blend of claim 2 wherein the ester comprises from about 5 to about 8 wt %.

6. The blend of claim 1 or 2 wherein the alkylated aromatic is an alkylated naphthalene having 1 or more alkyl group of from 1 to about 8 carbon atoms.

7. The blend of claim 1 or 3 wherein the aromatic ester is the product of an aromatic acid or acid anhydride and a straight or branched aliphatic alcohol of from 3 to 18 carbon atoms.

8. The ester of claim 7 wherein the aromatic acid or anhyride is phthalic acid or anhydride.

9. A lubricant composition comprising:

a major amount of a lubricant base stock blend; and

an effective amount of at least one lubricant additive selected from the group consisting of antioxidants, rust inhibitors, extreme pressure agents, and metal deactivators;

the base stock blend comprising about 10 wt % or more of a polyalpha olefin fluid;

about 1 wt % or more of an alkylated aromatic fluid; and

about 1 wt % or more of an aromatic ester,

the amounts in the blend being based on the weight of the blend.

10. The composition of claim 9 wherein the blend comprises:

from about 10 wt % to about 98 wt % of a PAO fluid;

from about 1 wt % to about 59 wt % of an alkylated aromatic fluid; and

from about 1 wt % to about 75 wt % of an aromatic ester.