Lubricant formulations and methods of lubricating a combustion system to achieve improved emmisions catalyst durability

Abstract

Different zinc dialkyldithiophosphate (ZDDPs) exhibit different volatilities and have different effects on automotive emissions control catalysts. The ZDDPs and their respective decomposition fragments that have low volatility will have a correspondingly lower detrimental effect on combustion emissions control systems, because there are simply fewer phosphorous atoms that will pass through the combustion system to reach the emissions control system. Specifically, it has been discovered that ZDDPs that contain a significant fraction of MIBC ZDDP exhibit significantly lower volatility than other ZDDPs.

1 . A lubricant composition comprising::
 (a) a base oil; and   (b) an additive composition comprising a zinc dialkyldithiophosphate component;
 wherein the lubricant has a phosphorous content of less than about 800 ppm; 
 wherein the lubricant has a TEOST MHT-4 test yield of less than about 30 mg of deposit; and 
 wherein the TEOST MHT-4 volatile fraction has a phosphorous content of less than 100 ppm. 
   
     
     
         2 . The lubricant composition as described in  claim 1 , wherein the TEOST MHT-4 test yield is less than about 25 mg. 
     
     
         3 . The lubricant composition as described in  claim 1 , further wherein the TEOST MHT-4 volatile fraction has a phosphorous content of less than 65 ppm. 
     
     
         4 . The lubricant composition as described in  claim 3 , further wherein the TEOST MHT-4 volatile fraction has a phosphorous content of less than 40 ppm. 
     
     
         5 . The lubricant composition as described in  claim 1 , wherein substantially all of the phosphorous in the lubricant is originated in the zinc dialkyldithiophosphate additive component. 
     
     
         6 . A lubricant composition as described in  claim 1 ,
 wherein a phosphorous retention value of the lubricant composition is greater than about 85% after oil aging based on an initial phosphorous amount in the lubricant composition.   
     
     
         7 . A lubricant composition as described in  claim 6 , wherein the phosphorous retention value is greater than about 87%. 
     
     
         8 . The lubricant composition as described in  claim 1 , wherein the zinc dialkyldithiophosphate comprises substantially all methylisobutylcarbanol zinc dialkyldithiophosphate. 
     
     
         9 . The lubricant composition as described in  claim 1 , wherein the zinc dialkyldithiophosphate comprises at least 90% methylisobutylcarbanol zinc dialkyldithiophosphate. 
     
     
         10 . The lubricant composition as described in  claim 1 , wherein the zinc dialkyldithiophosphate comprises at least 80% methylisobutylcarbanol zinc dialkyldithiophosphate. 
     
     
         11 . The lubricant composition as described in  claim 1 , wherein the zinc dialkyldithiophosphate comprises at least 50% methylisobutylcarbanol zinc dialkyldithiophosphate. 
     
     
         12 . A method of evaluating a zinc dialkyldithiophosphate additive for use in an engine lubricant formulation that has reduced catalyst poisoning effects in a combustion emissions control system, the method comprising the steps of:
 providing a lubricant that comprises a zinc dialkyldithiophosphate additive component;   performing a TEOST MHT-4 test using the lubricant;   collecting the trapped volatiles resulting from the TEOST MHT-4 test; and   analyzing the trapped volatiles to determine the amount of phosphorous in the trapped volatiles.   
     
     
         13 . The method described in  claim 12 , wherein the analyzing step comprises analyzing the trapped volatiles using ICP analysis. 
     
     
         14 . The method described in  claim 12 , further comprising the step of selecting the particular zinc dialkyldithiophosphate additive component that results in the least amount of phosphorous in the trapped volatiles. 
     
     
         15 . A lubricant composition comprising:
 (a) a base oil; and   (b) an additive composition comprising a zinc dialkyldithiophosphate component;   wherein the lubricant has a phosphorous content of less than about 800 ppm;   wherein the trapped volatiles resulting from the TEOST MHT-4 test using ICP analysis results in a phosphorous content of about 60 ppm or less.   
     
     
         16 . The lubricant composition as described in  claim 15 ;
 wherein the ICP analysis results in a phosphorous content of about 40 ppm or less.