WO1996012780A2

WO1996012780A2 - Lube oil antioxidants

Info

Publication number: WO1996012780A2
Application number: PCT/US1995/013789
Authority: WO
Inventors: David G. L. Holt; Manuel A. Francisco
Original assignee: Exxon Research And Engineering Company
Priority date: 1994-10-25
Filing date: 1995-10-25
Publication date: 1996-05-02
Also published as: WO1996012780A3

Abstract

The present invention provides for lubricating oil compositions comprising the synergistic combination of a synthetic lube base stock, an aminic antioxidant, a phenolic antioxidant and an antioxidancy enhancing amount of oil soluble or oil dispersible multiring aromatics such as 2, 3 and 4 ring multiring aromatics in a minor amount, typically less than 25 wt.%, but more preferably at least about 4.0 wt.%. The present invention also provides for a method of enhancing the antioxidancy of the synthetic lube base stock containing an aminic and a phenolic antioxidant by addition of the aforementioned multiring aromatics. The invention has utility in lube applications.

Description

LUBE OIL ANTIOXIDANTS

Field of the Invention

The present invention relates to lube oil antioxidants.

Background of the Invention

Changes in engine design are causing greater stress to be placed on the thermal stability of conventional lubricants. As a result there is a need for formulations that can provide enhanced levels of oxidative liability and thermal performance. The present invention addresses these needs.

Summary of the Invention

The present invention provides for lubricating oil compositions, comprising a synergistic combination of a synthetic base stock of lubricating viscosity, an aminic antioxidant and phenolic antioxidant system or package and a minor, antioxidancy enhancing amount of oil soluble or oil dispersible multiring aromatics.

The present invention also provides for a method of enhancing the antioxidancy of an engine lubricating system with a synthetic oil base stock containing an aminic antioxidant and a phenolic antioxidant additive, comprising combining a synthetic oil base stock, an aminic and phenolic antioxidant and an antioxidancy enhancing amount of an oil soluble or oil dispersible multiring aromatic to enhance the oxidative stability of the oil.

The present invention may suitably comprise, consist, or consist essentially of the elements disclosed herein and may be practiced in the absence of any limitation not disclosed herein as requi ed. Detailed Description of the Invention

The present invention provides for a method of enhancing the thermal and oxidative stability of a synthetic oil of lubricating viscosity, particularly polymerized alpha-olefins (PAOs), hydrocracked base stocks and wax isomerized base stock formulated with combined aminic and phenolic antioxidant, by adding multiring aromatics thereto. The present invention also provides for compositions containing these synthetic base stocks formulated with a combination of aminic and phenolic antioxidants and a thermal and oxidative stability enhancing combination of multiring aromatic compounds. The multiring aromatic additives used in the present invention may be used as part of a fully formulated oil, alone, or as part of an additive package.

The starting materials may be made by means known in the art or purchased commercially.

The base oil thus is a synthetic base stock such as PAOs, hydrocracked base stocks, isomerized base stocks, preferably of lubricating viscosity. Preferred are isomerized base stocks.

In the present invention the base stock is typically present in a major amount to a minor amount of each additive, and usually to a major amount in comparison to all additives in combination. The term "minor amount" is intended to mean an amount less than 50% by weight of the composition. The term "major amount" is intended to mean more than 50% by weight of the composition.

Wax isomerates are the fraction remaining following dewaxing an isoinerate formed from isomerizing wax in the presence of a suitable catalyst under iso erization conditions. The wax which is isomerized may originate from any number of sources. Synthetic waxes from Fischer-Tropsch processes may be used, as may be waxes recovered from the solvent or autorefrigerative dewaxing of conventional hydrocarbon oils, or mixtures of these waxes. Waxes from dewaxing conventional hydrocarbon oils are commonly called slack waxes and usually contain an appreciable amount of oil. The oil content of these slack waxes can range anywhere from 0 to 45% or more, but usually from 5 to 30% oil. The isomerization process is known in the art. Typically, by way of example, isomerization is conducted over a catalyst containing a hydrogenating metal component, typically one from Group VI, or Group VIII, or mixtures thereof, preferably Group VIII, more preferably noble Group VIII, and most preferably platinum on a halogenated refractory metal oxide support. The catalyst typically contains from 0.1 to 5.0 wt%, preferably 0.1 to 1.0 wt%, and most preferably from 0.2 to 0.8 wt% metal. The halogenated metal oxide support is typically an alumina (e.g. gamma or eta) containing chlorides (typically from 0.1 to 2 wt%, preferably 0.5 to 1.5 wt%) and fluorides (typically 0.1 to 10 wt%, preferably 0.3 to 0.8 wt%). Isomerization is typically conducted under conditions of temperatures between about 270* to 400'C (preferably between 300^* to 360^*C), at pressures of from 500 to 3000 psi H2 (preferably 1000-1500 psi H2), at hydrogen gas rates of from 1000 to 10,000 SCF/bbl , and at a space velocity in the range of from 0.1 to 10 v/v/hr, preferably from 1 to 2 v/v/hr. Following isomerization, the iso erate may undergo hydrogenation to stabilize the oil and remove residual aromatics, and thus are also known as "hydroisomerized" base stocks. The resulting product may then be fractionated into a lubes cut and fuels cut, the lubes cut being identified as that fraction boiling in the 330^*C+ range, preferably the 370'C+ range, or even higher. This lubes fraction is then dewaxed to reduce the pour point typically to between about -15^* to about -24*C. The term "isomerized" base stocks is used herein to include the term "hydroisomerized" base stocks. The resulting base oil of lubricating viscosity is typically essentially free of aromatics. PAOs are polymerized alpha olefins, suitable for the applications disclosed herein and are known in the art. Suitable hydrocracked base stocks used for the disclosed applications are also known in the art.

In order to enhance oxidative and thermal stability of the base stock it is typically formulated with a combination of aminic and phenolic antioxidants, typically oil soluble or dispersible antioxidants, such as diphenyl amine and hindered phenols, to produce the formulated oil (referred to herein as "formulated" oil or "base stock formulated with" additives). Often these are alkylated. Such formulations are commercially available. It is the synergistic combination of these formulations with multiring aromatic additives that provides enhanced anti-oxidation performance in the present invention. This benefit is even more unexpected given that such base stocks are typically processed to contain very low, if any, amounts on a weight percent basis, of multiring aromatics. Surprisingly, applicants have found that addition back of these aromatics to the base stock formulated with aminic and hindered phenolic antioxidants in combination enhances the stability of the formulation and can boost the anti-oxidative performance above that of the formulated oil alone.

Any combination of aminic and phenolic antioxidant additive of the type suitable for lube formulations may be used, for example, oil soluble or dispersible, preferably alkylated, aminic and phenolic antioxidants, such as sulfurized hindered phenols and diphenyl amines or phenyl alpha naphthamines (PAMA). The compositional ranges for these types of antioxidants are known in the art.

In the present invention the synergistic effect of addition of the multiring aromatics is to be expected over the range of weight percents at which aminic antioxidant and phenolic antioxidant additives are typically present in the synthetic oils. The multiring aromatics are required to be present in a minor amount sufficient to enhance the antioxidancy, i.e. the oxidative and thermal stability, of the oil at operating conditions. Typically for lube applications the minor amount is less than 25 wt%, more preferably at least about 4.0 wt%, more preferably at least about 4.5 wt%, up to a minor amount of less than 25 wt%. The multiring aromatics are required to be hydrocarbon, preferably oil soluble or dispersible, preferably two, three or four ring multiring aromatics. Unsubstituted and alkyl substituted multiring aromatics and mixtures thereof may be used. Representative examples include phenanthrenes, napthalenes, anthracenes, and pyrenes.

Solubility or dispersibility of the multiring aromatics in the formulated oil may be achieved using suitable surfactants or dispersants. These are known in the art and include neutral or overbased calcium sulfonate detergents, magnesium sulfonates, calcium and magnesium salicylates, calcium phenates and PIBSA-PAM dispersants.

As used herein the term hydrocarbon or oil "soluble" and "dispersible" means that the material is soluble or stably dispersible in hydrocarbons, preferably oils of lubricating viscosity that are liquid at temperatures found in the environments at which oils are typically used. The term "stably dispersible" means that the material is capable of being dispersed in the hydrocarbon or oil to an extent that allows it to function in its intended manner. Thus, for example, a lube oil antioxidant is hydrocarbon or oil soluble or dispersible if it is capable of being dissolved, dispersed or otherwise suspended in a lubricating oil in a manner sufficient to allow the oil to function as a lubricant.

The present invention also permits the use of other additives in the formulations. These other additives include such conventional additive types as viscosity modifiers,extreme pressure agents, corrosion-inhibiting agents, pour point depressants, color stabilizing agents, anti-foam agents, and other such additive materials known generally to those skilled in the art. Thus, for example, a commercially available isomerized base stock may contain a commercially available mono-functional olefin viscosity index improver, a neutral or overbased blend of calcium sulfonate detergent, PIBSA-PAM dispersant, ZDDP antiwear agents, in addition to the aminic and phenolic antioxidant system or package.

The formulated oils containing the antioxidancy enhancing multiring aromatics additionally are suitable for essentially any application in which oxidation protection is desired. When used as additive concentrates the multiring aromatics in combination with the aminic and phenolic antioxidant are present in a suitable carrier fluid. Other lube additives as mentioned previously may also be present.

It is expected that similar benefits could be obtained in fuels.

The present invention may be further understood with reference to the following examples.

Example 1

Catalyzed Differential Scanning Calorimetry ("CDSC") tests were performed to determine the synergistic effect of adding a multiring aromatic compound to a lubricating oil formulation having the characteristics described below. In the cDSC test, the sample was heated at a programmed rate of in pure oxygen under pressure to a specified temperature of 210^*C in the presence of a 2000 ppm of a lead (lead carboxylate) and 500 ppm of iron (iron naphthenate) catalyst and held at the specified temperature. The time at which oxidation commenced ("induction time") was measured. The longer the induction time, the more stable (i.e. the greater the antioxidancy of) the oil.

Table 1 shows the cDSC results for a wax hydroisomerized base stock containing specific additives typically used as antioxidants. Run (d) demonstrates the enhanced synergistic effect of adding multiring aromatics to a lube oil containing the combination of diphenyl amine and sulfurized hindered phenol antioxidant. TABLE 1

Lube Oil Formulation cDSC Induction Time (mini

(a) Base stock * + copper 0

(b) Base stock + copper + 0

4.5 wt% phenanthrene

(c) Base stock + diphenyl- 3.6 amine and sulfurized hindered phenol antioxidants

(d) Base stock + diphenyl amine 6.5 sulfurized hindered phenol antioxidants + 4.5 wt% phenanthrene

* Base stock is a commercially available wax isomerized base oil. The copper, diphenyl amine and sulfurized hindered phenol additives are commercially available antioxidants.

Claims

CLAIMS :

1. An internal combustion engine lubricating oil composition, comprising: a synergistic combination of a synthetic base stock of lubricating viscosity, an aminic antioxidant, a phenolic antioxidant and an antioxidancy enhancing amount of less than 25 wt% of oil soluble or oil dispersible multiring aromatics, selected from the group consisting of 2, 3 and 4 ring multiring aromatics.

2. The composition of claim 1 wherein the multiring aromatic is present a minor amount of at least about 4.0 wt%.

3. The composition of claim 1 wherein the multiring aromatic is present in a minor amount of at least about 4.5 wt%.

4. The composition of claim 1 wherein the multiring aromatic is selected from the group consisting of unsubstituted and alkyl substituted phenanthrenes, naphthalenes, anthracenes and pyrenes.

5. The composition of claim 1 wherein the synthetic base stock is selected from the group consisting of isomerized base stocks, hydrocracked base stocks and polymerized alpha olefin base stocks.

6. The composition of claim 1, further comprising at least one agent selected from the group consisting of a dispersant and a detergent.

7. The composition of claim 1, further comprising at least one additive selected from the group consisting of antiwear agents, viscosity modifiers, extreme pressure agents, antifoam agents, pour point depressants, and color stabilizing agents.

8. A method of enhancing the antioxidancy of a synthetic engine lubricating oil containing an aminic antioxidant and a phenolic antioxidant comprising: combining a synthetic lubricating oil containing an aminic antioxidant and a phenolic antioxidant with an antioxidancy enhancing amount of less than 25 wt% of an oil soluble or oil dispersible multiring aromatic selected from the group consisting of 2, 3 and 4 ring multiring aromatics to enhance the oxidative stability of the oil .