Method for improving thermal-oxidative stability and elastomer compatibility

Abstract

A method for improving thermo-oxidative stability and elastomer compatibility in an apparatus lubricated with a lubricating oil by using as the lubricating oil a formulated oil including a lubricating oil base stock. The lubricating oil base stock includes a di-alkylated aromatic base stock of the formula: (R 1 )—(R 2 )—(R 1 ) wherein each R 1 is the same or different and represents a C 10 -C 30 alkyl group; R 2 represents an aromatic moiety. The di-alkylated aromatic base stock includes at least 44 wt % dialkylate product. Thermo-oxidative stability and elastomer compatibility are improved as compared to thermo-oxidative stability and elastomer compatibility achieved using a lubricating oil base stock other than the di-alkylated aromatic base stock. A lubricating oil including the di-alkylated base stock of the above formula, and the di-alkylated aromatic base stock of the above formula.

What is claimed is: 
     
         1 . A method for improving thermo-oxidative stability and elastomer compatibility in an apparatus lubricated with a lubricating oil by using as the lubricating oil a formulated oil comprising a lubricating oil base stock; wherein the lubricating oil base stock comprises a di-alkylated aromatic base stock of the formula:
   (R 1 )—(R 2 )—(R 1 )
   wherein each R 1  is the same or different and represents a C 10 -C 30  alkyl group; R 2  represents an aromatic moiety; wherein branching characteristics of the alkyl groups have a total methyl number (“TMN”) determined by C 13  NMR spectroscopy of from 1.0 to 2.1 or have a branching index (“BI”) of from −1.0 to 0.1, wherein TMN is calculated by dividing the sum of integrated areas for all methyl groups by the total integration area for all aliphatic carbons and multiplying the result by the averaged chain length carbon number, and wherein BI is TMN minus 2 (two terminal methyl carbons); wherein the di-alkylated aromatic base stock comprises at least 44 wt % dialkylate product; and wherein thermo-oxidative stability and elastomer compatibility are improved as compared to thermo-oxidative stability and elastomer compatibility achieved using a lubricating oil base stock other than the di-alkylated aromatic base stock.   
     
     
         2 . The method of  claim 1  wherein, in the di-alkylated aromatic base stock, R 2  is naphthalene, and each R 1  is a C 10 -C 20  linear alkyl group, a C 10 -C 20  branched alkyl group; or mixtures of such groups. 
     
     
         3 . The method of  claim 1  wherein, in the di-alkylated aromatic base stock, branching characteristics of the alkyl groups have a total methyl number (“TMN”) determined by C 13  NMR spectroscopy of from 1.1 to 2.0 or have a branching index (“BI”) of from −0.99 to 0.099. 
     
     
         4 . The method of  claim 1  wherein the di-alkylated aromatic base stock comprises di-C 10  alkyl naphthalene, di-C 12  alkyl naphthalene, di-C 14  alkyl naphthalene, di-C 16  alkyl naphthalene, di-C 18  alkyl naphthalene, or mixtures thereof. 
     
     
         5 . The method of  claim 1  wherein the di-alkylated aromatic base stock comprises at least 90 wt. % dialkylate product and no more than 5 wt. % monoalkylate, trialkylate and higher polyalkylate product, and is present in an amount from 15 weight percent to 95 weight percent, based on the total weight of the lubricating oil. 
     
     
         6 . The method of  claim 1  wherein the lubricating oil further comprises a Group I, II, III, IV or V base oil stock. 
     
     
         7 . The method of  claim 1  wherein the lubricating oil further comprises a poly alpha olefin (PAO) or gas-to-liquid (GTL) oil base stock. 
     
     
         8 . The method of  claim 1  wherein the lubricating oil further comprises one or more of a viscosity improver, antioxidant, detergent, dispersant, pour point depressant, corrosion inhibitor, metal deactivator, seal compatibility additive, anti-foam agent, inhibitor, and anti-rust additive. 
     
     
         9 . A lubricating oil comprising a lubricating oil base stock; wherein the lubricating oil base stock comprises a di-alkylated aromatic base stock of the formula:
   (R 1 )—(R 2 )—(R 1 )
   wherein each R 1  is the same or different and represents a C 10 -C 30  alkyl group; R 2  represents an aromatic moiety; wherein branching characteristics of the alkyl groups have a total methyl number (“TMN”) determined by C 13  NMR spectroscopy of from 1.0 to 2.1 or have a branching index (“BI”) of from −1.0 to 0.1, wherein TMN is calculated by dividing the sum of integrated areas for all methyl groups by the total integration area for all aliphatic carbons and multiplying the result by the averaged chain length carbon number, and wherein BI is TMN minus 2 (two terminal methyl carbons); wherein the di-alkylated aromatic base stock comprises at least 44 wt % dialkylate product; and wherein thermo-oxidative stability and elastomer compatibility are improved as compared to thermo-oxidative stability and elastomer compatibility achieved using a lubricating oil base stock other than the di-alkylated aromatic base stock.   
     
     
         10 . The lubricating oil of  claim 9  wherein, in the di-alkylated aromatic base stock, R 2  is naphthalene, and each R 1  is a C 10 -C 20  linear alkyl group, a C 10 -C 20  branched alkyl group; or mixtures of such groups. 
     
     
         11 . The lubricating oil of  claim 9  wherein, in the di-alkylated aromatic base stock, branching characteristics of the alkyl groups have a total methyl number (“TMN”) determined by C 13  NMR spectroscopy of from 0.99 to 2.0 or have a branching index (“BI”) of from −0.99 to 0.099. 
     
     
         12 . The lubricating oil of  claim 9  wherein the di-alkylated aromatic base stock comprises di-C 10  alkyl naphthalene, di-C 12  alkyl naphthalene, di-C 14  alkyl naphthalene, di-C 16  alkyl naphthalene, di-C 18  alkyl naphthalene, or mixtures thereof. 
     
     
         13 . The lubricating oil of  claim 9  wherein the di-alkylated aromatic base stock comprises at least 90 wt. % dialkylate product and no more than 5 wt. % monoalkylate, trialkylate and higher polyalkylate product, and is present in an amount from 15 weight percent to 95 weight percent, based on the total weight of the lubricating oil. 
     
     
         14 . The lubricating oil of  claim 9  wherein the lubricating oil further comprises a Group I, II, III, IV or V base oil stock. 
     
     
         15 . The lubricating oil of  claim 9  wherein the lubricating oil further comprises a poly alpha olefin (PAO) or gas-to-liquid (GTL) oil base stock. 
     
     
         16 . The lubricating oil of  claim 9  wherein the lubricating oil further comprises one or more of a viscosity improver, antioxidant, detergent, dispersant, pour point depressant, corrosion inhibitor, metal deactivator, seal compatibility additive, anti-foam agent, inhibitor, and anti-rust additive. 
     
     
         17 . A di-alkylated aromatic base stock of the formula:
   (R 1 )—(R 2 )—(R 1 )
   wherein each R 1  is the same or different and represents a C 10 -C 30  alkyl group; R 2  represents an aromatic moiety; wherein branching characteristics of the alkyl groups have a total methyl number (“TMN”) determined by C 13  NMR spectroscopy of from 1.0 to 2.1 or have a branching index (“BI”) of from −1.0 to 0.1, wherein TMN is calculated by dividing the sum of integrated areas for all methyl groups by the total integration area for all aliphatic carbons and multiplying the result by the averaged chain length carbon number, wherein the di-alkylated aromatic base stock comprises at least 44 wt % dialkylate product; and wherein BI is TMN minus 2 (two terminal methyl carbons); and wherein thermo-oxidative stability and elastomer compatibility are improved as compared to thermo-oxidative stability and elastomer compatibility achieved using a lubricating oil base stock other than the di-alkylated aromatic base stock.   
     
     
         18 . The di-alkylated aromatic base stock of  claim 17  wherein R 2  is naphthalene, and each R 1  is a C 10 -C 20  linear alkyl group, a C 10 -C 20  branched alkyl group; or mixtures of such groups. 
     
     
         19 . The di-alkylated aromatic base stock of  claim 17  wherein branching characteristics of the alkyl groups have a total methyl number (“TMN”) determined by C 13  NMR spectroscopy of from 0.99 to 2.0 or have a branching index (“BI”) of from −0.99 to 0.099. 
     
     
         20 . The di-alkylated aromatic base stock of  claim 17  comprising di-C 10  alkyl naphthalene, di-C 12  alkyl naphthalene, di-C 14  alkyl naphthalene, di-C 16  alkyl naphthalene, di-C 18  alkyl naphthalene, or mixtures thereof. 
     
     
         21 . The method of  claim 8  wherein the lubricating oil comprises a di-alkylated aromatic base stock, a salicylate, sulfonate or phenate based detergent, an ashless antioxidant, a succinimide based dispersant, a zinc dialkyldithiophosphate (ZDDP), a friction modifier, a corrosion inhibitor, and a defoamant. 
     
     
         22 . The lubricating oil of  claim 16  which comprises a di-alkylated aromatic base stock, a salicylate, sulfonate or phenate based detergent, an ashless antioxidant, a succinimide based dispersant, a zinc dialkyldithiophosphate (ZDDP), a friction modifier, a corrosion inhibitor, and a defoamant. 
     
     
         23 . The di-alkylated aromatic base stock of  claim 17  further comprising a salicylate, sulfonate or phenate based detergent, an ashless antioxidant, a succinimide based dispersant, a zinc dialkyldithiophosphate (ZDDP), a friction modifier, a corrosion inhibitor, and a defoamant.