Use of organic polysulfides against corrosion by acid crudes

Abstract

Method of combating the corrosion caused by naphthenic acids to the metal walls of a refining unit, comprising the use of a polysulphide having an alkyl radical containing between 2 and 5 carbon atoms.

1 . Method of combating the corrosion caused by naphthenic acids to the metal walls of a refining unit, characterized in that it comprises the addition to the hydrocarbon stream for processing by the unit of an effective amount of one or more hydrocarbon compounds of formula  
     
       
         
         
             
             
         
       
     
     in which 
 n is an integer between 2 and 15 and  
 the symbols R 1  and R 2 , which are identical or different, are selected from a linear or branched alkyl radical containing between 2 and 5 carbon atoms, or a cycloalkyl radical containing between 3 and 5 carbon atoms, it being possible for these radicals to contain, optionally, one or more heteroatoms such as oxygen or sulphur.  
 
   
   
       2 . Method according to  claim 1 , characterized in that a compound of formula (I) is used in which R 1  and R 2  are linear or branched alkyl radicals and n is between 2 and 6.  
   
   
       3 . Method according to  claim 1 , characterized in that a compound of formula (I) is used in which the radicals R 1  and R 2  are identical.  
   
   
       4 . Method according to  claim 1 , characterized in that said one or more hydrocarbon compounds comprises a mixture of poly(di-tert-butyl sulphide)s in which the average value of n is between 2 and 6.  
   
   
       5 . Method according to  claim 1 , characterized in that the amount of compound(s) of formula (I) corresponds to a concentration, expressed by equivalent weight of sulphur relative to the weight of the hydrocarbon stream, of between 1 and 5000 ppm.  
   
   
       6 . Method according to  claim 1 , characterized in that the stream of hydrocarbons to be processed has a TAN of more than 0.2.  
   
   
       7 . Method according to  claim 1 , characterized in that it is carried out at a temperature of between 200 and 450° C.  
   
   
       8 . Method according to  claim 1 , characterized in that the hydrocarbon stream to be processed is selected from petroleum crude, the residue from atmospheric distillation, the gas-oil cuts obtained from atmospheric distillations, the gas-oil cuts obtained from vacuum distillations, the vacuum residue obtained from vacuum distillation or the distillate obtained from vacuum distillation.  
   
   
       9 . Method according to  claim 1  characterized in that the amount of compound(s) of formula (I) corresponds to a concentration, expressed by equivalent weight of sulphur relative to the weight of the hydrocarbon stream of between 5 and 500 ppm.  
   
   
       10 . Method according to  claim 1 , characterized in that the stream of hydrocarbons to be processed has a TAN of more than 1.  
   
   
       11 . Method according to  claim 1 , characterized in that it is carried out at a temperature of between 250 and 350° C.