Method for marking hydrocarbons with anthraquinone imines

Abstract

A method for invisibly marking a liquid petroleum hydrocarbon. The method comprises adding to the liquid petroleum hydrocarbon at least one dye having formula (I) wherein R 1 , R 2 , R 3 and R 4 independently are aryl or aromatic heterocyclic; and wherein the dye has an absorption maximum in the range from 710 nm to 900 nm.

1 . A method for invisibly marking a liquid petroleum hydrocarbon; said method comprising adding to said liquid petroleum hydrocarbon at least one dye having formula (I)  
       
         
           
           
               
               
           
         
       
       wherein R 1 , R 2 , R 3  and R 4  independently are aryl or aromatic heterocyclic; and wherein said at least one dye has an absorption maximum in the range from 710 nm to 900 nm:  
     
     
         2 . The method of  claim 1  in which the liquid petroleum hydrocarbon is selected from the group consisting of lubricating oil, hydraulic fluid, brake fluid, gasoline, diesel fuel, kerosene, jet fuel and heating oil.  
     
     
         3 . The method of  claim 1  in which R 1 , R 2 , R 3  and R 4  are the same aryl or aromatic heterocyclic group.  
     
     
         4 . The method of  claim 3  in which R 1 , R 2 , R 3  and R 4  are phenyl or substituted phenyl.  
     
     
         5 . The method of  claim 1  in which each dye is present in an amount from 0.01 ppm to 5 ppm.  
     
     
         6 . The method of  claim 5  in which said dye having formula (I) has an absorption maximum in the range from 750 nm to 900 nm.  
     
     
         7 . The method of  claim 6  further comprising at least one visible dye in an amount from 0.1 ppm to 2 ppm.  
     
     
         8 . The method of  claim 7  in which each dye having formula (I) is present in an amount from 0.01 ppm to 2 ppm, and each visible dye is present in an amount from 0.2 ppm to 2 ppm.  
     
     
         9 . The method of  claim 8  in which R 1 , R 2 , R 3  and R 4  are phenyl or substituted phenyl.  
     
     
         10 . The method of  claim 9  in which the liquid petroleum hydrocarbon is selected from the group consisting of lubricating oil, hydraulic fluid, brake fluid, gasoline, diesel fuel, kerosene, jet fuel and heating oil.