EP0709447A1

EP0709447A1 - Multiring aromatics for enhanced deposit control

Info

Publication number: EP0709447A1
Application number: EP95307523A
Authority: EP
Inventors: David Gary Lawton Holt; Manuel A. Francisco
Original assignee: Exxon Research and Engineering Co
Current assignee: Infineum USA LP
Priority date: 1994-10-25
Filing date: 1995-10-24
Publication date: 1996-05-01

Abstract

The present invention provides for lubricating oil compositions, and method of making same, comprising the synergistic combination of a synthetic lube base stock, a copper containing antioxidant and a deposit control enhancing amount of an oil soluble or oil dispersible multiring aromatic compound, typically 2, 3 and 4 ring multiring aromatics. Typically these are added in a minor amount of less than 25 wt%. The invention has utility in lube applications.

Description

The present invention relates to novel deposit control additives for lube oils.
Changes in engine design are causing greater stress to be placed on the oxidative stability of conventional lubricants, resulting in a need for formulations having enhanced performance levels. Copper antioxidants are common additives, however they degrade and form deposits at higher temperatures. It would be desirable to provide additives and formulations that address the need to retard deposit formation and extend the life of copper antioxidants.
The present invention provides for lubricating oil compositions, comprising a synergistic combination of a synthetic base stock, a copper containing antioxidant and a deposit control enhancing amount of an oil soluble or oil dispersible multiring aromatic compound.
The present invention also provides for a method of controlling deposit formation in an engine lubricating system, comprising adding a deposit control enhancing amount of an oil soluble or oil dispersible multiring aromatic compound to a synthetic base stock of lubricating viscosity formulated with a copper containing antioxidant.
The present invention may suitably comprise, consist or consist essentially of the elements disclosed herein and may be practiced in the absence of any element not specifically disclosed herein as required.
It has been discovered that multiring aromatic compounds when added to a synthetic base stock, such as a polymerized alpha olefin (PAO), a hydrocracked base stock or an isomerized base stock formulated with copper containing antioxidants can provide enhanced deposit control. Thus the present invention provides for novel lube oil compositions containing a synthetic base stock formulated with copper containing antioxidants in synergistic combination with a deposit controlling amount of multiring aromatics and the method of using them to provide enhanced enhanced antioxidancy.
The starting materials disclosed herein may be obtained from commercial sources or formulated using art recognized procedures.
In formulated oils containing copper containing antioxidants, these compounds are generally present in a hydrocarbon, preferably oil, soluble or dispersible form. Representative examples include copper naphthenates, oleates, stearates, and polyisobutylene succinic anhydride ("PIBSA") compounds, although other known copper containing antioxidants also may be used. In addition, the base stock optionally may be formulated to contain a cobalt containing compound as an antioxidant. These are also commercially available. The cobalt containing compounds also are typically present in a hydrocarbon, preferably oil, soluble or dispersible form. Representative examples include cobalt naphthenates, stearates and acetyl acetonates. Such antioxidants are also commercially available. The ranges in which these types of antioxidants are added to lube oils are known in the art. Thus it is the synergistic combination of multiring aromatics when added to these formulated oils that is provided for in the present invention. The result is even more unexpected since the 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 the introduction of these aromatics into a base stock formulated with copper containing antioxidants enhances the deposit control performance of these formulated oils.
Unexpectedly applicants have found that the addition of multiring aromatics to copper containing antioxidant-formulated synthetic base stocks described herein can boost deposit control performance above that of the oil formulated with a copper containing antioxidant alone.
The base oil is required to be a synthetic base stock, preferably of lubricating viscosity. Wax isomerates, PAOs and hydrocracked base stocks are representative examples. Preferred are isomerized base stocks. Isomerized base stocks are the fraction remaining following dewaxing the isomerate formed from isomerizing wax in the presence of a suitable catalyst under isomerization 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 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 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 isomerate may undergo hydrogenation to stabilize the oil and remove residual aromatics and are thus 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°C to about -24°C. The term "isomerized" base stocks is used herein to include "hydroisomerized" base stocks. It should be noted that the resulting base oil is essentially free of aromatics. PAOs are polymerized alpha olefins, i.e., polymerized oligomers of the types suitably used for lube applications. Suitable hydrocracked base stocks are also known in the art.
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.
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 copper containing antioxidant additives are typically added to the basestock.
The multiring aromatics used to enhance the antioxidancy of the synthetic oils according to the present invention are hydrocarbon, preferably oil, soluble or dispersible. 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 hydrocarbons or 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 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 multiring aromatics should be present in an amount sufficient to enhance deposit control in the oil. For lube applications the minor amount is less than about 25 wt% based on the total weight of the lubricant composition. Typically the multiring aromatic additive is present in an amount from 0.5 to 25 wt%, preferably from 1.0 to 15 wt.%, more preferably from 2.0 to 10 wt.%. Most preferably the amount of the additive is at least 4.0 wt.%, for example 4.5 wt.%. The multiring aromatics are oil soluble or dispersible, preferably two, three and four ring multiring aromatics. Both unsubstituted and alkyl substituted multiring aromatics and mixtures thereof may be used. Representative examples include phenanthrene, naphthalenes, anthracenes, pyrenes; both unsubsituted and alkyl versions thereof are suitable.
The present invention also permits the use of other additives and agents in the oil compositions. 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 of formulating lubricants. Thus, for example, a commercially available synthetic base stock may be formulated to contain a commercially available monofunctional viscosity index improver, a neutral and/or overbased blend of calcium sulfonated detergent, nonylphenyl sulfide, and borated PIBSA-PAM dispersant, in addition to a copper containing antioxidant such as copper PIBSA.
The formulated oils containing the antioxidancy enhancing multiring aromatic additives are suitable for essentially any lube application in which oxidation protection is desired and in which the formulated oil without the multiring aromatics additives could be used. It is expected that similar benefits could be obtained in fuels.
The present invention may be demonstrated by reference to the following examples.

Example 1 -- Inclined Panel Deposit Test

The effect of the presence of multiring aromatic compounds in a lube oil formulated with copper containing antioxidants was evaluated using the Inclined Panel Deposit Test (IPDT) . The beneficial and synergistic effect on engine deposit control of adding multiring aromatics to base oils formulated to contain copper containing antioxidants can be determined by measuring the buildup of deposits during the course of tests that simulates conditions of engine operation. The beneficial effect of addition of multiring aromatics is evidenced by smaller amounts of deposit formation on a relative scale.
The IPDT is a bench test that simulates piston deposit formation during engine operation. 35 ml of oil was heated to 150°C and run down a metal panel heated to 308°C at a 2 degree angle. The oil was then pumped through a sump back onto the panel. The oil was exposed to a synthetic blow-by gas throughout the 2 hour duration of the test. The panel was then cooled, washed with heptane and rated. The rating figure (demerit) value indicates the amount of deposit on formation on the plate. A higher number (greater demerit) indicates a greater deposit formation, with 10 being the highest and zero the lowest.

Table 1 indicates the IPDT results for a commercially available hydroisomerized base stock formulated with a copper antioxidant and a copper antioxidant in combination with a cobalt antioxidant as baselines. Runs 2 and 4 demonstrate the enhanced synergistic effect of adding phenanthrene as the multiring aromatic to copper and copper-cobalt antioxidant additive formulations.

TABLE 1

FORMULATED OIL	IPDT RESULTS (DEMERITS)
(1) Hydroisomerized base stock formulated with copper antioxidant*	5.7
(2) Hydroisomerized base stock formulated with copper antioxidant* + 4.5 wt% phenanthrene	3.3
(3) Hydroisomerized base stock formulated with copper antioxidant* and cobalt antioxidant **	4.7
(4) Hydroisomerized base stock formulated with copper antioxidant* and cobalt antioxidant* a 4.5 wt% phenanthrene	3.2

* in the form of commercially available copper PIBSA
** in the form of commercially available cobalt naphthenate

Claims

A lubricating oil composition, comprising: a synergistic combination of a synthetic base stock of lubricating viscosity, a copper containing antioxidant and a deposit control enhancing amount of less than about 25 wt% of an oil soluble or oil dispersible multiring aromatic compound, selected from 2, 3 and 4 ring multiring aromatics and mixtures thereof.
The composition of claim 1 wherein the multiring aromatic is present in a minor amount of at least about 4.0 wt%.
The composition of claim 1 or 2 wherein the multiring aromatic is selected from unsubstituted and alkyl substituted phenanthrenes, naphthalenes, anthracenes and pyrenes.
The composition of any preceding claim further comprising a cobalt containing antioxidant.
The composition of any preceding claim wherein the synthetic base stock is selected from isomerized base stocks, hydrocracked base stocks and polymerized alpha-olefin base stocks.
The composition of any preceding claim further comprising at least one agent selected from a dispersant and a detergent.
The composition of any preceding claim further comprising at least one additive selected from antiwear agents, viscosity modifiers, extreme pressure agents, antifoam agents, pour point depressants, and color stabilizing agents.
A method of enhancing the antioxidancy of a synthetic oil containing an aminic antioxidant and a phenolic antioxidant additive, comprising: combining a synthetic oil containing an aminic antioxidant, a phenolic antioxidant and 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 and mixtures thereof to enhance the oxidative stability of the oil.
Use of an oil-soluble or oil-dispersible multiring aromatic compound containing 2, 3 or 4 aromatic rings or a mixture of two or more rings thereof to enhance the deposit control of a lubricating oil composition comprising a synthetic base stock and a copper-containing antioxidant.