Aircraft turbine oil base stock and method of making

Abstract

Provided is a polyol ester base stock composition with reduced odor and volatility. The polyol ester back stock composition does not include C5 acid. More particularly, the polyol ester base stock includes the reaction product of: (a) a polyol represented by the formula R(OH) n wherein R is an aliphatic or a cyclo-aliphatic hydrocarbyl group and n is at least 2, and (b) a mixture of monocarboxylic acids comprising at least one linear acid selected from the group consisting of between C6 to C10 acids and at least one branched C6 acid, wherein the amount of C6 to C10 acids is at least 55 wt. % and the amount of the at least one branched C6 acid is 45 wt. % or less, based upon the total amount of said mixture of monocarboxylic acids. The polyol ester base stock is particularly suited for aviation turbine oils.

1 . A polyol ester base stock comprising the reaction product of:
 (a) a polyol represented by the formula R(OH) n  wherein R is an aliphatic or a cyclo-aliphatic hydrocarbyl group and n is at least 2, and   (b) a mixture of monocarboxylic acids comprising at least one linear acid selected from the group consisting of between C6 to C10 acids and optionally at least one branched C6 acid, wherein the amount of C6 to C10 acids is at least 55 wt. % and the amount of the optional at least one branched C6 acid is 45 wt. % or less, based upon the total amount of said mixture of monocarboxylic acids, and wherein the mixture of monocarboxylic acids is substantially free of C5 acid.   
     
     
         2 . The base stock of  claim 1 , wherein the hydrocarbyl group of the polyol includes from 2 to 20 carbon atoms. 
     
     
         3 . The base stock of  claim 1 , wherein the hydrocarbyl group includes a substituent selected from the group consisting of chlorine, nitrogen, oxygen and combinations thereof. 
     
     
         4 . The base stock of  claim 1 , wherein the polyol is selected from the group consisting of 2-ethyl-1,3-hexanediol, 2-propyl-3,3-heptanediol, 2-butyl-1,3-butanediol, 2,4-dimethyl-1,3-butanediol, neopentyl glycol, 2,2-dimethylol butane, trimethylol ethane, trimethylol propane, trimethylol butane, mono-pentaerythritol, technical grade pentaerythritol, di-pentaerythritol, tri-pentaerythritol, ethylene glycol, propylene glycol, polyalkylene glycols and combinations thereof. 
     
     
         5 . The base stock of  claim 4 , wherein the polyalkylene glycol is selected from the group consisting of polyethylene glycols, polypropylene glycols, polybutylene glycols and combinations thereof. 
     
     
         6 . The base stock of  claim 1 , wherein the polyol comprises at least di-pentaerythritol. 
     
     
         7 . The base stock of  claim 1 , wherein said at least one C6 to C10 linear acid is selected from the group consisting of hexanoic acid, heptanoic acid, caprylic acid, pelargonic acid and capric acid. 
     
     
         8 . The base stock of  claim 1 , wherein said at least one C6 branched acid is selected from the group consisting of: 2-methylpentanoic, 4-methylpentoic acid, and combinations thereof. 
     
     
         9 . The base stock of  claim 1 , wherein said polyol comprises technical pentaerythritol in an amount between about 50 to 100 weight %, based on the total polyol, and di-pentaerythritol in an amount between about 0 to 50 weight %, based on the total polyol. 
     
     
         10 . The base stock of  claim 1  including a linear C6 acid ranging from 20 to 70 wt. % of the total amount of said mixture of monocarboxylic acids. 
     
     
         11 . The base stock of  claim 1  including a linear C7 acid ranging from 16 to 40 wt. % of the total amount of said mixture of monocarboxylic acids. 
     
     
         12 . The base stock of  claim 1  including a linear C8-C10 acid ranging from 14 to 25 wt. % of the total amount of said mixture of monocarboxylic acids. 
     
     
         13 . The base stock of  claim 1 , wherein the base stock has a viscosity of at least 4 cSt at 100 degree C., a viscosity of less than 11,000 cSt at −40 degree C., a viscosity index of at least 120, and a pour point of at least as low as −54 degree C. 
     
     
         14 . An aircraft turbine oil comprising from 70 to 95 wt % of a polyol ester base stock and from 1 to 15 wt. % of a lubricant additive package, wherein the polyol ester base stock comprises the reaction product of:
 (a) a polyol represented by the formula R(OH) n  wherein R is an aliphatic or a cyclo-aliphatic hydrocarbyl group and n is at least 2, and   (b) a mixture of monocarboxylic acids comprising at least one linear acid selected from the group consisting of between C6 to C10 acids and at least one branched C6 acid, wherein the amount of C6 to C10 acids is at least 55 wt. % and the amount of the at least one branched C6 acid is 45 wt. % or less, based upon the total amount of said mixture of monocarboxylic acids, and wherein the mixture of monocarboxylic acids is substantially free of C5 acid.   
     
     
         15 . The turbine oil of  claim 14 , wherein the lubricant additive package comprises at least one additive selected from the group consisting of viscosity index improvers, corrosion inhibitors, antioxidants, dispersants, anti-emulsifying agents, color stabilizers, detergents and rust inhibitors, and pour point depressants. 
     
     
         16 . The turbine oil of  claim 14 , wherein turbine oil comprises a blend of the polyol ester base stock and at least one additional base stock selected from the group consisting of: mineral oils, highly refined mineral oils, poly alpha olefins, polyalkylene glycols, phosphate ester, silicone oils, diesters and polyol ester. 
     
     
         17 . The turbine oil of  claim 14 , wherein the turbine oil has an evaporative weight loss at 204° C. for 6.5 hours per ASTM D972 of less than 3.2 wt. %. 
     
     
         18 . The turbine oil of  claim 14 , wherein the turbine oil has a TGA-simulated Noack volatility of less than 3.1 wt. %. 
     
     
         19 . The turbine oil of  claim 14 , wherein the turbine oil has a GC-simulated distillation at 10% weight loss temperature of greater than 800 deg. F. 
     
     
         20 . The turbine oil of  claim 14 , wherein the turbine oil has a reduced odor during use in an aircraft turbine relative to a comparable aircraft turbine oil including a C5 acid in the mixture of monocarboxylic acids. 
     
     
         21 . The turbine oil of  claim 14 , wherein the turbine oil meets military specification MIL-L-23699G with a viscosity at 210 degree F. (99 degree C.) of at least 5.0 cSt and at −40 degree C. of no more than 13,000 cSt, and a pour point of less than at least −65 degree F. (−54 degree C.). 
     
     
         22 . A method of making a polyol base stock comprising:
 esterifying reaction mixture of a polyol represented by the formula R(OH) n  wherein R is an aliphatic or a cyclo-aliphatic hydrocarbyl group and n is at least 2 and an excess mixture of monocarboxylic acids comprising at least one linear acid selected from the group consisting of between C6 to C10 acids and optionally at least one branched C6 acid, wherein the amount of C6 to C10 acids is at least 55 wt. % and the amount of the optional at least one branched C6 acid is 45 wt. % or less, based upon the total amount of said mixture of monocarboxylic acids, and wherein the mixture of monocarboxylic acids is substantially free of C5 acid,   wherein the esterification occurs with or without a sulfonic acid, phosphorus acid, sulfonic acid, para-toluene sulfuric acid or titanium, zirconium or tin-based catalyst, at a temperature in the range between about 140 to 250 degree C. and a pressure in the range between about 30 mm Hg to 760 mm Hg.   
     
     
         23 . The method of  claim 22  further comprising the step of adding an adsorbent to said reaction mixture following esterification. 
     
     
         24 . The method of  claim 23 , wherein said adsorbent is at least one material selected from the group consisting of alumina, silica gel, activated carbon, zeolites, clay and filter aid. 
     
     
         25 . The method of  claim 22  further comprising the steps of:
 adding water and base to simultaneously neutralize the residual organic and mineral acids and/or hydrolyze said catalyst; 
 removing of said water used in the hydrolysis step by heat and vacuum in a flash step; 
 filtering of solids from said ester mixture containing the bulk of the excess acids used in the esterification reaction; 
 removing excess acids by steam stripping or any other distillation method; and 
 removing any residual solids from the stripped ester in a final filtration. 
 
     
     
         26 . The method of  claim 22  wherein said at least one C6 to C10 linear acid is selected from the group consisting of: hexanoic acid, heptanoic acid, caprylic acid, pelargonic acid and capric acid. 
     
     
         27 . The method of  claim 22  wherein said at least one C6 branched acid is selected from the group consisting of: 2-methylpentanoic, 4-methylpentoic acid, and combinations thereof. 
     
     
         28 . The method of  claim 22 , wherein said polyol comprises technical pentaerythritol in an amount between about 50 to 100 weight %, based on the total polyol, and di-pentaerythritol in an amount between about 0 to 50 weight %, based on the total polyol. 
     
     
         29 . A method of reducing volatility and odor of an aircraft turbine oil comprising:
 providing to an aircraft turbine an aircraft turbine oil comprising from 70 to 95 wt % of a polyol ester base stock and from 1 to 15 wt. % of a lubricant additive package, wherein the polyol ester base stock comprises the reaction product of:   
       a) a polyol represented by the formula R(OH) n  wherein R is an aliphatic or a cyclo-aliphatic hydrocarbyl group and n is at least 2, and 
       b) a mixture of monocarboxylic acids comprising at least one linear acid selected from the group consisting of between C6 to C10 acids and optionally at least one branched C6 acid, wherein the amount of C6 to C10 acids is at least 55 wt. % and the amount of the optional at least one branched C6 acid is 45 wt. % or less, based upon the total amount of said mixture of monocarboxylic acids, and wherein the mixture of monocarboxylic acids is substantially free of C5 acid,
  wherein the turbine oil has an evaporative weight loss at 204° C. for 6.5 hours per ASTM D972 of less than 3.2 wt. %, a TGA-simulated Noack volatility of less than 3.1 wt. % and a GC-simulated distillation at 10% weight loss temperature of greater than 800 deg. F., and reduced odor during use in an aircraft turbine relative to a comparable aircraft turbine oil including a C5 acid in the reaction mixture. 
 
     
     
         30 . The method of  claim 29  wherein the lubricant additive package comprises at least one additive selected from the group consisting of viscosity index improvers, corrosion inhibitors, antioxidants, dispersants, anti-emulsifying agents, color stabilizers, detergents and rust inhibitors, and pour point depressants.