Lubricant compositions stabilized with styrenated phenolic antioxidant

Abstract

Compositions are disclosed that comprise a lubricant, at least a first antioxidant and an optional second antioxidant, the first antioxidant being a styrenated phenolic antioxidant and the optional second antioxidant a secondary diarylamine for synergistic antioxidant action. Also disclosed is a method of increasing the oxidation stability of lubricating oils comprising: adding thereto at least a first antioxidant and, optionally, a second antioxidant, the first antioxidant being a styrenated phenolic antioxidant and the optional second antioxidant a secondary diarylamine.

1 . A composition comprising: (a) at least one lubricating oil comprising one or more Group I, Group II, Group III, Group IV or synthetic lubricating base stocks of varying viscosity grades; (b) at least a first antioxidant comprising one or more hindered phenolics having the general formula: 
       
         
           
           
               
               
           
         
       
       or an isomer or isomeric mixture thereof wherein R 1  and R 2  are independent and hydrogen or styryl groups represented by formula (IA): 
       
         
           
           
               
               
           
         
       
       wherein n is an integer of from 0 to 5 and the α-position on the styryl group is optionally substituted with a hydrocarbyl group having from 1 to about 8 carbon atoms; and R 3  is hydrogen or a hydrocarbyl group; and (c) an optional second antioxidant comprising one or more secondary diarylamines having the general formula: (R 4 ) a —Ar 1 —NH—Ar 2 —(R 5 ) b  wherein Ar 1  and Ar 2  are independent and comprise one or more aromatic hydrocarbons, and R 4  and R 5  are independent and comprise one or more hydrogen or hydrocarbyl groups, and a and b are independent and integers from 0 to 3, with the proviso that (a+b) is not greater than 4. 
     
     
         2 . A composition of  claim 1  further comprising at least one additional additive comprising one or more dispersants, detergents, rust inhibitors, metal deactivators, antiwear agents, antifoamants, friction modifiers, seal swell agents, demulsifiers, viscosity index improvers, and pour point depressants. 
     
     
         3 . A composition of  claim 1  wherein the lubricant is suitable for use in a high temperature and iron catalyzed environment. 
     
     
         4 . A composition of  claim 3  wherein the lubricant is a grease. 
     
     
         5 . A method of increasing the oxidation stability of a lubricating oil comprising one or more Group I, Group II, Group III, Group IV or synthetic lubricating base stocks of varying viscosity grades comprising adding thereto a composition comprising from about 0.01 to about 10 weight percent of a first antioxidant and from about 0.01 to about 10 weight percent of a second antioxidant, the first antioxidant comprising one or more hindered phenolics having the general formula: 
       
         
           
           
               
               
           
         
       
       or an isomer or isomeric mixture thereof wherein R 1  and R 2  are independent and hydrogen or styryl groups represented by formula (IA): 
       
         
           
           
               
               
           
         
       
       wherein n is an integer of from 0 to 5 and the α-position on the styryl group is optionally substituted with a hydrocarbyl group having from 1 to about 8 carbon atoms; and R 3  is hydrogen or a hydrocarbyl group and the second antioxidant comprising one or more secondary diarylamines having the general formula: (R 4 ) a —Ar 1 —NH—Ar 2 —(R 5 ) b  wherein Ar 1  and Ar 2  are independent and comprise one or more aromatic hydrocarbons, and R 4  and R 5  are independent and comprise one or more hydrogen or hydrocarbyl groups, and a and b are independent and integers from 0 to 3, with the proviso that (a+b) is not greater than 4. 
     
     
         6 . The method of  claim 5  wherein the content ratio of the first antioxidant to the second antioxidant is from 1:99 to 99:1. 
     
     
         7 . The method of  claim 5  further comprising one or more dispersants, detergents, rust inhibitors, metal deactivators, antiwear agents, antifoamants, friction modifiers, seal swell agents, demulsifiers, viscosity index improvers, and pour point depressants. 
     
     
         8 . A method of  claim 5  wherein the composition comprises about 600 ppm or less of phosphorus.