High temperature stability lubricant composition containing short chain acids and method for making the same

Abstract

This invention generally relates to a high temperature stable polyol ester lubricant composition containing short chain carboxylic esters and a process for making the same. The polyol ester lubricant compositions are preferably formed from pentaerythritol and a mixture of C 2 to C 10 carboxylic acids in which (1) from 95 to 80 mole %, based on total acids, are C 5 to C 10 carboxylic acid, and (2) from 5 to 20 mole %, based on total acids, are at least one C 2 to C 4 carboxylic acid The polyol ester lubricant compositions of the present invention, specifically those using at least one C 2 to C 4 carboxylic acid, are useful as base stock for high temperature application such as Aviation Turbine Oils and exhibit enhanced anti-deposition and oxidation stability compared with the base polyol ester compositions while maintaining a good viscosity index.

We claim:  
     
         1 . A lubricant composition, comprising: a mixed polyol ester, wherein the carboxylic acid portion of the ester, comprises: 
 (a) 5-20 mole % of short chain acids; and,    (b) 80-95 mole % of a C 5-10  aliphatic carboxylic acid;    and the alcohol portion of the ester, comprises: an aliphatic polyol.    
     
     
         2 . A lubricant composition according to  claim 1 , wherein the carboxylic acid portion of the ester, comprises: 
 (a) 5-20 mole % of a C 2-4  carboxylic acid;    (b1) 30-70 mole % of a C 5  carboxylic acid;    (b2) 0-15 mole % of an i-C 9  carboxylic acid; and    (b3) 10-60 mole % of C 7-10  carboxylic acids.    
     
     
         3 . A lubricant composition according to  claim 2 , wherein the carboxylic acid portion of the ester, comprises: 
 (a) 10-20 mole % of a C 2-4  carboxylic acid;    (b1) 30-60 mole % of a C 5  carboxylic acid;    (b2) 0-10 mole % of an i-C 9  carboxylic acid; and    (b3) 10-55 mole % of linear C 7-10  carboxylic acids.    
     
     
         4 . A lubricant composition according to  claim 3 , wherein the carboxylic acid portion of the ester, comprises: 
 (a) 10-15 mole % of a C 2-4  carboxylic acid;    (b1) 30-60 mole % of valeric acid;    (b2) 0-10 mole % of 3,3,5-trimethylhexanoic acid; and    (b3) 10-55 mole % of a mixture of n-heptanoic acid, n-octanoic acid, and n-decanoic acid.    
     
     
         5 . A lubricant composition according to  claim 1 , wherein the aliphatic polyol, comprises: 4-7 carbon atoms and 2-4 esterifiable hydroxyl groups.  
     
     
         6 . A lubricant composition according to  claim 5 , wherein the aliphatic polyol is selected from neopentyl glycol, 2,2-dimethylol butane, trimethylol ethane, trimethylol propane, trimethylol butane, mono-pentaerythritol, technical grade pentaerythritol, dipentaerythritol, tri-pentaerythritol, ethylene glycol, propylene glycol and polyalkylene glycols.  
     
     
         7 . A lubricant composition according to  claim 6 , wherein the aliphatic polyol is selected from trimethylolpropane, technical grade pentaerythritol, monopentaerythritol, dipentaerythritol, neopentyl glycol, and tripentaerythritol.  
     
     
         8 . A lubricant composition according to  claim 7 , wherein the aliphatic polyol is selected from technical grade pentaerythritol, trimethylolpropane, and neopentyl glycol.  
     
     
         9 . A lubricant composition according to  claim 8 , wherein the aliphatic polyol is technical grade pentaerythritol.  
     
     
         10 . A lubricant composition according to  claim 1 , wherein mixed polyol ester is formed by esterifying a mixture of the short chain C 2-4  carboxylic acids and the C 7-10  carboxylic acids.  
     
     
         11 . A lubricant composition according to  claim 1  having an inclined panel rating at 580° F. of less than 4.00.  
     
     
         12 . A lubricant composition according to  claim 1  having an inclined panel rating at 590° F. of less than 5.00.  
     
     
         13 . A lubricant composition according to  claim 1  further comprising 0.5 to 15 wt % of a lubricant additive package.  
     
     
         14 . A process for preparing a mixed polyol ester, comprising: 
 (i) contacting 5-20 mole % of short chain C 2-4  carboxylic acids with 80-95 mole % of a C 5-10  aliphatic carboxylic acid; and,    (ii) esterifying the resulting mixture with an aliphatic polyol.    
     
     
         15 . A process for preparing a mixed polyol ester, comprising: 
 (i) esterifying a short chain C 2-4  carboxylic acid with an aliphatic polyol; and,    (ii) contacting the esterification mixture with a C 5-10  aliphatic carboxylic acid;    wherein the resulting ester is a mixed ester and the carboxylic acid portion of the ester, comprises: (a) 5-20 mole % of short chain C 2-4  carboxylic acids; and, (b) 8095 mole % of a C 5-10  aliphatic carboxylic acid.    
     
     
         16 . A process for preparing a mixed polyol ester, comprising: 
 (i) esterifying a C 5-10  aliphatic carboxylic acid with an aliphatic polyol; and,    (ii) contacting the esterification mixture with short chain C 2-4  carboxylic acids;    wherein the resulting ester is a mixed ester and the carboxylic acid portion of the ester, comprises: (a) 5-20 mole % of short chain C 2-4  carboxylic acids; and, (b) 8095 mole % of a C 5-10  aliphatic carboxylic acid.    
     
     
         17 . A method of lubricating a turbine engine comprising operating the engine and lubricating the engine with a lubricant composition as claimed in  claim 1 .  
     
     
         18 . The use of the lubricant composition as defined in  claim 1  for enhancing the thermal and oxidative stability of a lubricating oil.