Compositions with improved varnish control properties

Abstract

A method for improving varnish control in a mechanical device requiring hydraulic fluids, turbine oils, industrial fluids, circulating oils, or combinations thereof. The method involves supplying the mechanical device with a lubricating composition including a Group III lubricating oil base stock. The Group III lubricating oil base stock has a viscosity from 3.8 to 8.5 mm 2 /s at 100° C., a viscosity index greater than 120, a sulfur content less than 0.0003 weight percent, and an aromatic hydrocarbon content less than 0.2 weight percent, based on the total weight of the Group III lubricating oil base stock. Varnish reduction properties are improved as compared to varnish reduction properties achieved using a lubricating composition containing a different Group III lubricating oil base stock. The disclosure also provides lubricating compositions used in the method.

What is claimed is: 
     
         1 . A method for improving varnish control in a mechanical device requiring hydraulic fluids, turbine oils, industrial fluids, circulating oils, or combinations thereof, said method comprising:
 supplying the mechanical device with a lubricating composition comprising a Group III lubricating oil base stock;   wherein the Group III lubricating oil base stock has a viscosity from 3.8 to 8.5 mm 2 /s at 100° C., a viscosity index greater than 120, a sulfur content less than 0.0003 weight percent, and an aromatic hydrocarbon content less than 0.2 weight percent, based on the total weight of the Group III lubricating oil base stock; and   wherein varnish reduction properties are improved as compared to varnish reduction properties achieved using a lubricating composition containing a different Group III lubricating oil base stock.   
     
     
         2 . The method of  claim 1  wherein the Group III lubricating oil base stock has a viscosity from 4.0 to 8.3 mm 2 /s at 100° C., a viscosity index greater than 125, a sulfur content less than 0.0002 weight percent, and an aromatic hydrocarbon content less than 0.18 weight percent, based on the total weight of the Group III lubricating oil base stock. 
     
     
         3 . The method of  claim 1  wherein the Group III lubricating oil base stock contains consecutive carbon numbers, and is a Gas-to-Liquids (GTL) oil base stock or a Fischer-Tropsch wax derived oil base stock. 
     
     
         4 . The method of  claim 1  wherein the Group III lubricating oil base stock is produced from natural gas and subsequent wax isomerization. 
     
     
         5 . The method of  claim 1  wherein the lubricating composition further comprises (i) a Group II co-base stock; wherein the Group II co-base stock has a viscosity from 6.5 to 11.0 mm 2 /s at 40° C., is isoparaffinic, and is produced from natural gas and subsequent wax isomerization; or (ii) a heavy Group II base stock having a viscosity from 10.0 to 13.0 mm 2 /s at 100° C., a viscosity index greater than 90, a sulfur content less than 0.001 weight percent, and saturates content greater than 99%. 
     
     
         6 . The method of  claim 1  wherein the Group III lubricating oil base stock is present in an amount from 80 weight percent to 99 weight percent, based on the total weight of the lubricating composition. 
     
     
         7 . The method of  claim 1  wherein the lubricating composition further comprises at least one of a viscosity index improver, an antiwear agent, an antifoam, a metal deactivator, a solubility improver, and a demulsifier. 
     
     
         8 . The method of  claim 1  wherein the lubricating composition further comprises at least one of a dispersant, an antioxidant, a corrosion inhibitor, and a co-base stock. 
     
     
         9 . The method of  claim 1  wherein the improved varnish reduction properties are rated according to a Coordinating Research Council (CRC) rating scale, the sulfur content is determined according to ASTM D2622, and the aromatic hydrocarbon content is determined according to ASTM D7419. 
     
     
         10 . The method of  claim 1  wherein the mechanical device is a hydraulic system or a turbine system. 
     
     
         11 . A lubricating composition comprising:
 a Group III lubricating oil base stock, wherein the Group III lubricating oil base stock has a viscosity from 3.8 to 8.5 mm 2 /s at 100° C., a viscosity index greater than 120, a sulfur content less than 0.0003 weight percent, and an aromatic hydrocarbon content less than 0.2 weight percent, based on the total weight of the Group III lubricating oil base stock; and   optionally one or more of an antiwear additive, viscosity index improver, antioxidant, dispersant, pour point depressant, corrosion inhibitor, metal deactivator, seal compatibility additive, antifoam agent, co-base stock, pour point depressant, seal compatibility additive, solubility improver, and antirust additive;   wherein, in a mechanical device supplied with the lubricating composition, varnish reduction properties are improved as compared to varnish reduction properties achieved using a lubricating composition containing a different Group III lubricating oil base stock.   
     
     
         12 . The lubricating composition of  claim 11  which is a hydraulic fluid, turbine oil, industrial fluid, circulating oil, or combination thereof. 
     
     
         13 . The lubricating composition of  claim 11  wherein the Group III lubricating oil base stock has a viscosity from 4.0 to 8.3 mm 2 /s at 100° C., a viscosity index greater than 125, a sulfur content less than 0.0002 weight percent, and an aromatic hydrocarbon content less than 0.18 weight percent, based on the total weight of the Group III lubricating oil base stock. 
     
     
         14 . The lubricating composition of  claim 11  wherein the Group III lubricating oil base stock contains consecutive carbon numbers, and is a Gas-to-Liquids (GTL) oil base stock or a Fischer-Tropsch wax derived oil base stock. 
     
     
         15 . The lubricating composition of  claim 11  wherein the Group III lubricating oil base stock is produced from natural gas and subsequent wax isomerization. 
     
     
         16 . The lubricating composition of  claim 11  further comprising (i) a Group II co-base stock; wherein the Group II co-base stock has a viscosity from 6.5 to 11.0 mm 2 /S at 40° C., is isoparaffinic, and is produced from natural gas and subsequent wax isomerization; or (ii) a heavy Group II base stock having a viscosity from 10.0 to 13.0 mm 2 /s at 100° C., a viscosity index greater than 90, a sulfur content less than 0.001 weight percent, and saturates content greater than 99%. 
     
     
         17 . The lubricating composition of  claim 11  wherein Group III lubricating oil base stock is present in an amount from 80 weight percent to 99 weight percent, based on the total weight of the lubricating composition. 
     
     
         18 . The lubricating composition of  claim 11  wherein the improved varnish reduction properties are rated according to a Coordinating Research Council (CRC) rating scale, the sulfur content is determined according to ASTM D2622, and the aromatic hydrocarbon content is determined according to ASTM D7419. 
     
     
         19 . The lubricating composition of  claim 11  further comprising a dispersant, an antioxidant, a corrosion inhibitor, an antiwear agent, an antifoam, a metal deactivator, a solubility improver, or combinations thereof. 
     
     
         20 . The lubricating composition of  claim 11  wherein the mechanical device is a hydraulic system or a turbine system.