Process for selective cascade deasphalting

Abstract

The invention describes a process for the deasphalting of a heavy feedstock by liquid/liquid extraction, said process comprising at least two stages of deasphalting in series carried out on the feedstock to be treated making it possible to separate at least one fraction of asphalt, at least one fraction of heavy deasphalted oil, referred to as heavy DAO and at least one fraction of light deasphalted oil, referred to as light DAO, at least one of said stages of deasphalting being carried out by means of a mixture of at least one polar solvent and at least one apolar solvent, said stages of deasphalting being implemented under the subcritical conditions of the mixture of solvents used.

1 . Process for the deasphalting of a heavy feedstock by liquid/liquid extraction, said process comprising at least two stages of deasphalting in series carried out on the feedstock to be treated, making it possible to separate at least one fraction of asphalt, at least one fraction of heavy deasphalted oil, referred to as heavy DAO and at least one fraction of light deasphalted oil, referred to as light DAO, at least one of said stages of deasphalting being carried out by means of a mixture of at least one polar solvent and at least one apolar solvent, the proportions of said polar solvent and said apolar solvent in the mixture of solvents being adjusted according to the properties of the feedstock treated and according to the desired yield of asphalt and/or the quality of the deasphalted oil, said stages of deasphalting being implemented under the subcritical conditions of the mixture of solvents used. 
     
     
         2 . Process according to  claim 1  comprising at least:
 a) a first stage of deasphalting comprising bringing the feedstock into contact with a mixture of at least one polar solvent and at least one apolar solvent, the proportions of said polar solvent and said apolar solvent being adjusted so as to obtain at least one fraction of asphalt phase and one fraction of complete deasphalted oil phase referred to as complete DAO; and 
 b) a second stage of deasphalting comprising bringing at least a part of the deasphalted oil phase originating from stage a) into contact with either an apolar solvent, or a mixture of at least one polar solvent and at least one apolar solvent, the proportions of said polar solvent and said apolar solvent in the mixture being adjusted so as to obtain at least one fraction of light deasphalted oil and one fraction of heavy deasphalted oil, 
 
       said stages of deasphalting being implemented under the subcritical conditions of the apolar solvent or of the mixture of solvents used. 
     
     
         3 . Process according to  claim 2 , in which the deasphalted oil phase originating from stage a) is previously subjected to at least one stage of separation in which the deasphalted oil is separated from the mixture of solvents or at least one stage of separation in which the complete deasphalted oil referred to as complete DAO is separated only from the apolar solvent. 
     
     
         4 . Process according to  claim 2 , in which the deasphalted oil phase originating from stage a) is previously subjected to at least two successive stages of separation in which the polar and apolar solvents are separated individually. 
     
     
         5 . Process according to  claim 3  in which the deasphalted oil separated from the solvents is sent into at least one stripping column before being sent into the second stage of deasphalting. 
     
     
         6 . Process according to  claim 1  comprising at least:
 a) a first stage of deasphalting comprising bringing the feedstock into contact with either an apolar solvent, or a mixture of at least one polar solvent and at least one apolar solvent, the proportions of said polar solvent and said apolar solvent in the mixture being adjusted so as to obtain at least one fraction of light deasphalted oil phase and an effluent comprising an oil phase and an asphalt phase; and 
 b) a second stage of deasphalting comprising bringing at least a part of the effluent originating from stage a) into contact with a mixture of at least one polar solvent and at least one apolar solvent, the proportions of said polar solvent and said apolar solvent being adjusted so as to obtain at least one fraction of asphalt phase and one fraction of heavy deasphalted oil phase, 
 
       said stages of deasphalting being implemented under the subcritical conditions of the apolar solvent or of the mixture of solvents used. 
     
     
         7 . Process according to  claim 6 , in which the effluent originating from stage a) is previously subjected to at least one stage of separation in which the effluent is separated from the apolar solvent or from the mixture of solvents or at least one stage of separation in which said effluent is separated only from the apolar solvent contained in the mixture of solvents. 
     
     
         8 . Process according to  claim 6 , in which the effluent originating from stage a) is previously subjected to at least two stages of separation in which the polar and apolar solvents are individually separated. 
     
     
         9 . Process according to  claim 7  in which the effluent separated from the solvents is sent into at least one stripping column before being sent into the second stage of deasphalting. 
     
     
         10 . Process according to  claim 1  in which the proportion of polar solvent in the mixture of polar solvent and apolar solvent in at least one of the stages of deasphalting is comprised between 0.1 and 99.9% volume. 
     
     
         11 . Process according to  claim 1  in which the polar solvent used is selected from the pure aromatic or naphthene-aromatic solvents, the polar solvents comprising hetero-elements, or a mixture thereof or cuts rich in aromatics such as cuts originating from FCC (Fluid Catalytic Cracking) or originating from the petrochemical units of refineries, cuts derived from coal, biomass or biomass/coal mixture. 
     
     
         12 . Process according to  claim 1  in which the apolar solvent used comprises a solvent made up of saturated hydrocarbon(s) comprising a carbon number greater than or equal to 2, preferably comprised between 2 and 9. 
     
     
         13 . Process according to  claim 1  in which the feedstock is selected from the feedstocks of petroleum origin of crude oil type, atmospheric residue, vacuum residue type originating from so-called conventional crude, heavy crude or extra heavy crude, a residual fraction originating from any pre-treatment or conversion process such as hydrocracking, hydrotreatment, thermal cracking, hydroconversion of one of these crudes or of one of these atmospheric residues or one of these vacuum residues, a residual fraction originating from the direct liquefaction of ligno-cellulosic biomass alone or in a mixture with coal and/or a fraction of residual petroleum. 
     
     
         14 . Process according to  claim 3  in which, when the recycled solvents are in a mixture, the apolar/polar proportion is verified on-line and readjusted as needed via makeup tanks individually containing the polar and apolar solvents. 
     
     
         15 . Process according to  claim 3  in which, when the solvents are separated individually, said solvents are individually recycled into said respective makeup tanks.