Patent Publication Number: US-6043199-A

Title: Corrosion inhibiting additive combination for turbine oils

Description:
This application is a Continuation-In-Part of U.S. Ser. No. 08/918,827 filed Aug. 26, 1997 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to turbine oils, particularly aviation turbine oils containing additives exhibiting enhanced corrosion resistance. 
     RELATED ART 
     While the use of polyol ester base stocks produces turbine lubricating oils which possess outstanding thermal stability, a satisfactory level of oxidation stability and corrosion resistance can be achieved only by the use of additives. 
     To this end, a wide assortment of different additives have been proposed and utilized. 
     U.S. Pat. No. 3,790,478 describes a lubricant for aviation turbines comprising hindered esters as base stock and containing alkylated diphenyl amines, and an alkylated phenyl naphthylamine as anti oxidants, a copper passivator, dispersant polymers and a neutral organic phosphate as load carrying additive. The lubricant may also contain hydrolytic stabilizers and lead corrosion inhibitors, e.g., a C 1  -C 20  alkyl gallate, neopentyl glycol disebacate, sebacic acid or quinizarin. 
     U.S. Pat. No. 3,790,481 is similar to U.S. Pat. No. 3,790,478 in being directed to an aviation turbine oil and also recites the presence of lead corrosion inhibitors selected from the group consisting of C 1  -C 20  alkyl gallate, neopentyl glycol, disebacate, sebacic acid, and quinizarin. 
     U.S. Pat. No. 3,585,137 is directed to a synthetic ester aviation turbine oil containing an anthranilamide type metal passivator, antioxidants, phosphate esters, dimer acids. A formulation is disclosed containing p,p&#39;dioctyldiphenylamine, phenothiazine, sebacic acid, benzotriazole, a mixture of phosphate esters and, in other examples, various other additive ingredient. In all cases, however, sebacie acid is indicated as present in the formulation. 
     U.S. Pat. No. 3,912,640 teaches a gas turbine lubricant comprising a base stock of a blend of carboxylate ester and low viscosity mineral oil and various additives including anti oxidants such as phenothiazines or derivatives thereof and secondary diaryl amines. Methylene linked hindered bisphenol may be substituted for a portion of the phenothiazine material. Additional additives present in the examples include benzotriazole, sebacic acid, tricresyl phosphate. Benzotriazole, tolyltriazole, N,N&#39;-disalicylidene dialkyl amines and sebacic acid are identified as well known metal deactivators. They can be present in the formulations in amounts of from about 0.005 to about 1.0 wt %. See also GB 1,420,824. 
     WO 95/29214 discloses a synthetic ester based lubricant for helicopter transmissions comprising a synthetic ester base stock, an antioxidant, a neutral organic phosphate, a dicarboxylic acid component, a monocarboxylic acid component, a triazole and a phosphorus containing extreme pressure additive. 
     WO 94/10270 discloses a synthetic ester based aviation turbine oil containing saturated or unsaturated dicarboxylic acids, e.g., sebacic acid, in combination with a triazole derivative and specified monocarboxylic acids or an ester thereof The combination is reported as being particularly effective in inhibiting corrosion. 
     U.S. Pat. No. 5,397,487 is directed to lubricating oils having enhanced rust inhibitor capability containing a minor synergistic rust inhibiting amount of a combination of two additives, the first being a material of the Mobilad C 603 type, reported in the &#39;487 patent as being a succinic anhydride amine derivative of the formula: ##STR1## where R 1  and R 2  are each independently alkyl or alkenyl of from 1 to 20 carbons, and a second material of the Lubrizol LZ 859 type, reported in U.S. Pat. No. 5,397,487 as being a mixture of about 74.5 wt % unreacted tetrapropenyl succinic acid of the formula ##STR2## and about 25.5 wt % of a partially esterified tetrapropenyl succinic acid of the formula ##STR3## 
     The patents recite that the lubricant can be natural oil or synthetic oil based, synthetic oils including synthetic ester. The lubricants are described as useful in automotive applications, e.g., engine oils, transmission oils, aviation piston engines, turbines and the like. The lubricant can contain other additives which include dispersants, anti-wear agents, anti-oxidants, corrosion inhibitors, detergents, pour point depressants, extreme pressure additives, viscosity index improvers, friction modifiers and the like. Specifics of these other additives were not provided and there were no examples presented employing such other additives. 
     U.S. Pat. No. 5,225,094 is directed to enhancing the rust inhibition capability of a lubricating oil having an average ring number per mole of less than 1.5 by the addition thereto of at least about 0.06 wt % of an oil soluble rust inhibitor which is a succinic anhydride amine. Data in the patent shows that for the base oil tested, which was a slack wax isomerate, an additive such as LZ 859 (as described in U.S. Pat. No. 5,397,4987, above) was ineffective in preventing rust. 
     U.S. Pat. No. 5,227,082 is directed to a lubricating oil of enhanced rust resistance comprising a lube oil base stock and a synergistic mixture of (1) a rust inhibiting amount of a rust inhibitor comprising a succinic acid derivative and a partially esterified alkyl succinic acid and (2) a pyridine derivative wherein the weight ratio of (2) to (1) is greater than zero and less than about 0.06. 
     U.S. Pat. No. 5,599,779 is directed to a synergistic rust inhibiting composition consisting of (a) N-acylsarcosine compound, (b) dicarboxylic acid having 6 to 48 carbon atoms and (c) an amine selected from primary, secondary or tertiary amines or imidazoline compounds. The primary, secondary, or tertiary amine is described as being one selected from the group of compounds of the formula: ##STR4## wherein R 1 , R 2 , R 3  are independently selected from hydrogen, alkyl having up to 14 carbons, hydroxyalkyl, cycloalkyl, or polyalkyleneoxy groups. 
     It would be highly desirable if the corrosion inhibiting performance of synthetic ester based aviation turbine oils could be improved employing a combination of readily available additives. 
    
    
     DESCRIPTION OF THE INVENTION 
     The present invention is a synthetic ester based turbine oil of enhanced corrosion inhibiting capacity comprising a major amount of a synthetic ester oil base stock and a minor amount of a corrosion inhibiting additive comprising a combination of as a first component one or more dicarboxylic acids such as sebacic acid, azelaic acid, dioleic acid (known as dimer acids) and a second component selected from (a) linear or branched alkyl or alkenyl succinic acid/anhydride ester or hemi ester or hydroxylated derivatives of such esters or hemi esters, or (b) linear or branched alkyl or alkenyl substituted succinimides or amino substituted succinimides. The formulation containing the combination employing component (a) being marked by the absence of pyridene derivatives of the formula ##STR5## wherein R 1 , R 2 , R 3  are independently an alkyl group containing from 1 to 3 carbon atoms, preferably marked by the absence of any pyridene or derivative of pyridene. 
     The diesters that can be used as base oils for the improved turbo oil of the present invention are formed by esterification of linear or branched C 6  -C 15  aliphatic alcohols with one of such dibasic acids as adipic, sebacic, or azelaic acids. Examples of diesters are di-2-ethylhexyl sebacate and dioctyl adipate. 
     The synthetic polyol ester which can be used as the base oil is formed by the esterification of an aliphatic polyol with carboxylic acid. The aliphatic polyol contains from 4 to 15 carbon atoms and has from 2 to 8 esterifiable hydroxyl groups. Examples of polyol are trimethylolpropane, pentaeiythritol, dipentaerytlritol, neopentyl glycol, tripentaeiytritol and mixtures thereof. 
     The carboxylic acid reactant used to produce the synthetic polyol ester base oil is selected from aliphatic monocarboxylic acid or a mixture of aliphatic monocarboxylic acid and aliphatic dicarboxylic acid. The carboxylic acid contains from 4 to 12 carbon atoms and includes the straight and branched chain aliphatic acids, and mixtures of monocarboxylic acids may be used. 
     The preferred polyol ester base oil is one prepared from technical pentaerythritol and a mixture of C 4  -C 12  carboxylic acids. Technical penta- erythfritol is a mixture which includes about 85 to 92% monopentaetydiritol and 8 to 15% dipentaerythritol. A typical commercial technical pentaerydiritol contains about 88% monopentaerythritol having the formula ##STR6## and about 12% of dipentaetythutol having the formula ##STR7## The technical pentaetytlritol may also contain some tri and tetra pentaeiythiitol that is normally formed as by-products during the manufacture of technical pentaetydiritol. 
     The preparation of esters from alcohols and carboxylic acids can be accomplished using conventional methods and techniques known and familiar to those skilled in the art. In general, technical pentaerytliritol is heated with the desired carboxylic acid mixture optionally in the presence of a catalyst. 
     Generally, a slight excess of acid is employed to force the reaction to completion. Water is removed during the reaction and any excess acid is then stripped from the reaction mixture. The esters of technical pentaerythritol may be used without further purification or may be further purified using conventional techniques such as distillation. 
     For the purposes of this specification and the following claims, the term &#34;technical pentaerytritol ester&#34; is understood as meaning the polyol ester base oil prepared from technical pentaerytiritol and a mixture of C 4  -C 12  carboxylic acids. 
     The dibasic carboxylic acid comprising one component of the combination additive added to the base stock to enhance the corrosion inhibiting performance of the lubricant is a C 6  to C 40  total carbon number dicarboxylic acid or mixture of such acids, preferably a C 6  to C 36  dicarboxylic acid, more preferably C 6  to C 14  dicarboylic acid or mixture thereof. The dicarboxylic acids can be any n-alkyl, branched alkyl, aryl, or alkyl substituted aryl dicarboxylic acid or mixture thereof having a total number of carbons within the above recited ranges. Preferred dicarboxylic acids are selected from the group consisting of the commercially available di-oleic acids known as &#34;dimer acids&#34;, sebacic acid, azelaic acid and mixtures thereof. These acids are added to the turbo oil formulations in an amount in the range of 100 to 1000 ppm, preferably 200 to 500 ppm, more preferably 200 to 400 ppm. 
     The second component of the corrosion inhibiting additive combination is (a) linear or branched alkyl or alkenyl succinic acid/anhydride ester or hemi ester or hydroxylated derivatives of such esters or hemi-ester, said material having the structural formula: ##STR8## wherein R 3  is a C 8  -C 16  linear or branched alkyl or alkenyl, R 4  and R 5  are or different and are hydrogen, C 1  -C 4  alkyl or C 2  -C 4  alkenyl or ##STR9## where n can be an integer from zero to 5, preferably R 3  is C 10-12  branched alkenyl, R 4  is H and R 5  is ##STR10## and n and m are each 1, (commercial materials such as Lubrizol 859 from the Lubrizol Corporation or Parabar 302 from Exxon Chemical Company being representative of such materials) or (b) reaction product of linear or branched alkyl or alkenyl substituted succinic anhydride with substituted amino-imidazolines resulting in what are believed to be linear or branched alkyl or alkenyl substituted succininide or amine substituted succinimides, which are believed to be of the structural formula: ##STR11## and mixtures thereof, wherein R 6 , R 8 , R 9  and R 10  are the same or different and are H or a C 1  -C 16 , linear or branched alkyl or alkenyl wherein at least one of R 6 , R 8 , R 9  or R 10  is hydrocarbyl, preferably at least one of R 6 , R 8 , R 9  or R 10  is a C 10  -C 14  hydrocarbyl, more preferably a C 12  hydrocarbyl, e.g., tetra propenyl, and R 7  is C 8  -C 20 , preferably C 16  -C 18 , linear or branched alkyl or alkenyl and x is 2 to 10, preferably 2 and y is 0 or 1, preferably 0. Commercially available material known as Mobilad C-603 from Mobil Chemical Company and Hitec 536 from Ethyl are believed to be examples of such materials. 
     This second component is added to the turbo oil formulation in an amount in the range 100 to 1000 ppm, preferably 300 to 1000 ppm, more preferably 300 to 500 ppm. 
     When the combination which is employed is the combination of one or more dicarboxylic acids and a second component selected from linear or branched alkyl or alkenyl succinic acid/anhydride ester or hemi ester or hydroxylated derivatives of such esters or hemi esters the combination is employed in the turbine oil in the absence of any pyridine derivative(s) of the formula ##STR12## wherein R 1 , R 2 , R 3  are independently an alkyl group containing from 1 to 3 carbon atoms. 
     The turbine oil of the present invention may also contain any of the other, typical additives which are usually or preferably present in such fully formulated products except where as it has been otherwise indicated above. Thus, a fully formulated turbine oil may contain one or more of the following classes of additives: antioxidants, antiwear agents, extreme pressure additives, antifoamants, detergents, hydrolytic stabilizers, metal deactivators, other rust inhibitors, etc. Total amounts of such other additives can be in the range 0.5 to 15 wt % preferably 2 to 10 wt %, most preferably 3 to 8 wt %. 
     Antioxidants which can be used include aryl amines, e.g. phenylnaphthylamines and dialkyl diphenyl amines and mixtures thereof, hindered phenols, phenothiazines, and their derivatives. 
     The antioxidants are typically used in an amount in the range 1 to 5 wt %. 
     Antiwear/extreme pressure additives include hydrocarbyl phosphate esters, particularly trihydrocarbyl phosphate esters in which the hydrocarbyl radical is an aryl or alkaryl radical or mixture thereof. Particular antiwear/extreme pressure additives include tricresyl phosphate, triaryl phosphate and mixtures thereof. Other or additional anti wear/extreme pressure additives may also be used. 
     The antiwear/extreme pressure additives are typically used in an amount in the range 0 to 4 wt %, preferably 1 to 3 wt %. 
     Industry standard corrosive inhibitors may also be included in the turbo oil. Such known corrosion inhibitors include the various triazols, for example, tolyltriazol, 1,2,4 benzotriazol, 1,2,3 benzotriazol, carboxy benzotriazole, allylated benzotriazol. 
     The standard corrosion inhibitor additive can be used in an amount in the range 0.02 to 0.5 wt %, preferably 0.05 to 0.25 wt %. 
     Other rust inhibitors common to the industry include the various hydrocarbyl amine phosphates and/or amine phosphates. 
     As previously indicated, other additives can also be employed including hydrolytic stabilizers pour point depressants, anti foaming agents, viscosity and viscosity index improver, etc. 
     The invention is further described by reference to the following non-limiting examples and comparative examples. 
     Base Formulation 1 is a Tech-PE polyol ester additized with tricresylphosphate, arylamine antioxidants, benzotriazole derivative copper deactivator, amine phosphate and alkyl amine components. To this base formulation individual corrosion inhibitors were added and D665A rust results were obtained as shown in Table 1. Values reported are percent rust in the D665A rust test. A passing result requires that no rust be present. 
     Additive combination of sebacic acid with alternatively Hitec 536, Mobilad-C603 or Parabar 302 are reported in Table 2. At lower concentrations the additive combinations show improvement over the base case in Table 1. With the combination of 200 ppm sebacic acid and 300 ppm of the other corrosion inhibitor, passing results are obtained which are not achievable via a single corrosion inhibitor. It is desirable to limit the concentration of dicarboxylic acid component because higher levels of acidity can catalyze polyol ester hydrolysis. By using the combination of corrosion inhibitors total acidity is reduced while anti-corrosion performance equal to or exceeding that achieved with high concentrations of acid are obtained. 
     Table 3 shows additive combinations in Base Formulation 2. Base Formulation 2 differs from Base Formulation 1 only in that the antioxidant treat rate is somewhat higher. Again combination of corrosion inhibitors at certain concentrations are more effective than either inhibitor used alone. 
     Table 4 gives the base line results for single corrosion inhibitors in base Formulation 3. Base Formulation 3 is similar to Base Formulation 2 except that an alternate antioxidant is substituted at the same treat rate. Sebacic acid is much more efficient alone than the longer chain dicarboxylic acid Empol 1022, a mixture of dimers and trimers of C 18  unsaturated dicarboxylic fatty acids. 
     Table 5 provides results for Base Formulation 3 with a combination of corrosion inhibitors. Passing results are achieved for 400 ppm sebacic acid with 1000 ppm of the second corrosion inhibitor. 
     
                       TABLE 1                                                     
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BASE FORMULATION #1                                                       
  PLUS ONE CORROSION INHIBITOR                                            
  AVERAGE     CONCENTRATION, ppm                                          
D665 - % Rust                                                             
          Sebacic Acid                                                    
                    Hitec 536                                             
                             Mobilad-C603                                 
                                      PAR-302                             
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73        --                                                              
  50  50                                                                  
  16 100                                                                  
  18 200                                                                  
   2 500                                                                  
  90   50                                                                 
  65    50                                                                
  45     50                                                               
  80  100                                                                 
  80   100                                                                
  75    100                                                               
  80  200                                                                 
  70   200                                                                
  45    200                                                               
  20  500                                                                 
  10   500                                                                
  25    500                                                               
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                       TABLE 2                                                     
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BASE FORMULATION #1                                                       
  PLUS COMBINATION OF CORROSION INHIBITORS                                
  AVERAGE     CONCENTRATION, ppm                                          
D665 - % Rust                                                             
          Sebacic Acid                                                    
                    Hitec 536                                             
                             Mobilad-C603                                 
                                      PAR-302                             
______________________________________                                    
60         50        50                                                   
  90  50   50                                                             
  70  50    50                                                            
  50 100 100                                                              
  30 100  100                                                             
  15 100   100                                                            
   5 200 200                                                              
   1 200 300                                                              
  Pass 200  300                                                           
  Pass 200   300                                                          
   7 300 100                                                              
   5 300 200                                                              
   3 300 300                                                              
  13 100 200                                                              
  10 100 300                                                              
   5 200 200                                                              
  35 100 100                                                              
  12 150 150                                                              
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                       TABLE 3                                                     
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BASE FORMULATION #2                                                       
  PLUS COMBINATION OF CORROSION INHIBITORS                                
    AVERAGE    CONCENTRATION, ppm                                         
D665 - % Rust                                                             
           Sebacic Acid                                                   
                       Hitec 536                                          
                                Mobilad-C603                              
______________________________________                                    
5           50         100                                                
  6  50 200                                                               
  Pass  50 300                                                            
  Pass  50 500                                                            
  Pass 400 300                                                            
  Pass 400 500                                                            
  5 200  300                                                              
  1 400  300                                                              
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                       TABLE 4                                                     
______________________________________                                    
BASE FORMULATION #3                                                       
  PLUS ONE CORROSION INHIBITOR                                            
  AVERAGE     CONCENTRATION, ppm                                          
D665 - % Rust                                                             
          Sebacic Acid                                                    
                    Empol 1022                                            
                              H-536 Mobilad C603                          
______________________________________                                    
50        (None)                                                          
  60  100                                                                 
  65  200                                                                 
  50  500                                                                 
  45  1000                                                                
  15 100                                                                  
   3 200                                                                  
   1 500                                                                  
   1 1000                                                                 
  40   300                                                                
  10   500                                                                
  35    300                                                               
   7    500                                                               
   1   1000                                                               
   1    1000                                                              
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                       TABLE 5                                                     
______________________________________                                    
BASE FORMULATION #3                                                       
  PLUS COMBINATION OF CORROSION INHIBITORS                                
  AVERAGE     CONCENTRATION, ppm                                          
D65 - % Rust                                                              
          Sebacic Acid                                                    
                    H-536   Mobilad C603                                  
                                     PAR-302                              
______________________________________                                    
30        200       100                                                   
  1 200 500                                                               
  1 400 500                                                               
  10  200  100                                                            
  2 200  300                                                              
  1 200  500                                                              
  5 400  100                                                              
  2 400  300                                                              
  1 400  500                                                              
  15  200   100                                                           
  1 200   300                                                             
  5 200   500                                                             
  1 400   100                                                             
  1 400   300                                                             
  1 400   500                                                             
  10  200 300                                                             
  7 400 500                                                               
  1 600 500                                                               
  B/L 600 1000                                                            
  Pass 400 1000                                                           
  1 600  500                                                              
  Pass 600  1000                                                          
  3 400  500                                                              
  Pass 400  1000                                                          
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     When considering the data in these Tables, one needs to bear several factors in mind. Rust tests are highly variable. Thus, for those skilled in the art, it is the trend in rust results with increasing additive concentration which is most important. When all of the data are examined, it is clear that none of the additives alone are able to provide passing results. Combinations of rust inhibitors, however, are able to achieve passing results at concentration levels which do not have harmful secondary effects. 
     Even when the test results are not a pass, the combination of rust inhibitors provides an improved rust rating than either additive alone. This trend clearly indicates a synergistic interaction of the combined corrosion inhibitors.