Integrated method for producing middle distillate with a recycling loop in hydrotreatment

Abstract

Method of treating petroleum feedstocks comprising the hydrotreatment of said feedstocks followed by hydrocracking of at least one part of the hydrotreatment effluent. Cooling and separating the hydrocracking effluent into a hydrogen-rich gas efflux and a liquid efflux. Fractionating the liquid effluent into converted hydrocarbon products having boiling points lower than 340° C. and an unconverted liquid fraction having a boiling point higher than 340° C. Hydrotreating a diesel-fuel-type liquid hydrocarbon feedstock and separating the effluent into a hydrogen-rich gas efflux and a liquid efflux. Fractionating the liquid efflux into at least one light gas fraction, a naphtha fraction, and a middle distillate fraction having a boiling point higher than 150° C. and compressing the gas efflux in a hydrogen makeup compressor supplying the hydrotreatment and hydrocracking steps comprising at least 2 stages, with said gas efflux being injected and compressed in an intermediate stage of said compressor before being recycled upstream.

1 . A hydrocracking method for treating hydrocarbon feedstocks containing at least 20% by volume and preferably at least 80% by volume of compounds boiling above 340° C., said method comprising:
 a) hydrotreatment of said feedstocks in the presence of hydrogen and at least one hydrotreatment catalyst, at a temperature of between 200 and 450° C., under a pressure of between 2 and 18 MPa, at a volumetric flow rate of between 0.1 and 6 h −1 , and with an amount of hydrogen introduced such that the volumetric ratio of liter of hydrogen/liter of hydrocarbon is between 100 and 2,000 L/L, 
 b) hydrocracking of at least one part of the effluent obtained from step a), with the hydrocracking step b) being carried out, in the presence of hydrogen and at least one hydrocracking catalyst, at a temperature of between 250 and 480° C., under a pressure of between 2 and 25 MPa, at a volumetric flow rate of between 0.1 and 6 h −1 , and with an amount of hydrogen introduced such that the volumetric ratio of liter of hydrogen/liter of hydrocarbon is between 100 and 2,000 L/L, 
 c) passing into at least one heat exchanger of at least said effluent obtained from step b) in which said effluent is cooled by exchanging the liquid hydrocarbon feedstock entering into step f) in at least one exchanger, 
 d) gas/liquid separation of the cooled effluent obtained from step c) to produce at least one hydrogen-rich gas efflux and at least one liquid efflux, 
 e) fractionation of said liquid effluent obtained from step d) into at least one fraction comprising the converted hydrocarbon products having boiling points lower than 340° C. and an unconverted liquid fraction having a boiling point higher than 340° C., 
 f) hydrotreatment of a liquid hydrocarbon feedstock comprising at least 95% by weight of compounds boiling at a boiling point of between 150 and 400° C., preheated in advance in step c), with said step f) being carried out in the presence of hydrogen and at least one hydrotreatment catalyst, at a temperature of between 200 and 390° C., under a pressure of between 2 and 16 MPa, at a volumetric flow rate of between 0.2 and 5 h −1 , and with an amount of hydrogen introduced such that the volumetric ratio of liter of hydrogen/liter of hydrocarbon is between 100 and 2,000 L/L, 
 g) gas/liquid separation of the effluent obtained from step f) for producing at least one hydrogen-rich gas efflux and at least one liquid efflux, 
 h) fractionation of the liquid effluent obtained from step g) making possible the separation of at least one light gas fraction, a naphtha fraction, and a middle distillate fraction having a boiling point higher than 150° C., 
 i) compression of the hydrogen-rich gas effluent obtained from step g) in a hydrogen makeup compressor supplying steps a), b) and f) and comprising n stages, with n being an integer that is greater than or equal to 2, with said hydrogen-rich gas effluent being injected and compressed in an intermediate stage of said compressor before being recycled upstream from step f), 
 j) hydrocracking of at least one part of the liquid fraction having a boiling point higher than 340° C. that is unconverted during the first hydrocracking step b) and obtained from the fractionation step e), with said second hydrocracking step j) being carried out in the presence of hydrogen and at least one hydrocracking catalyst, at a temperature of between 250 and 480° C., under a pressure of between 2 and 25 MPa, at a volumetric flow rate of between 0.1 and 6 h-1, and with an amount of hydrogen introduced such that the volumetric ratio of liter of hydrogen/liter of hydrocarbon is between 100 and 2,000 L/L. 
 
     
     
         2 . Method according to  claim 1 , in which the hydrocarbon feedstocks treated in said method and sent into step a) are selected from among the hydrocarbon feedstocks containing at least 80% by volume of compounds boiling between 340-580° C. 
     
     
         3 . Method according to  claim 1 , in which the hydrocarbon feedstocks treated in said method and sent into step a) are selected from among the vacuum distillates (DSV) selected from among the diesel fuels obtained from direct distillation of crude or conversion units and the distillates coming from the desulfurization or hydroconversion of atmospheric residues and/or vacuum residues, deasphalted oils, and the feedstocks obtained from biomass or else any mixture of the feedstocks cited above. 
     
     
         4 . Method according to  claim 1 , in which the hydrocracking catalyst(s) used in step b) comprise(s) at least one metal of group VIII selected from among iron, cobalt, nickel, ruthenium, rhodium, palladium and platinum, and/or at least one metal of group VIB selected from among chromium, molybdenum, and tungsten, by itself or in a mixture, and a zeolite selected from among the USY zeolites, by itself or in combination, with other zeolites from among the following zeolites: beta, ZSM-12, IZM-2, ZSM-22, ZSM-23, SAPO-11, ZSM-48, ZBM-30, by themselves or in a mixture. 
     
     
         5 . Method according to  claim 1 , in which at least one part of the effluent obtained from the hydrotreatment step a) and/or at least one part of the effluent obtained from the second hydrocracking step j) is/are cooled by passing into at least one exchanger of said step c) by exchanging the liquid hydrocarbon feedstock entering into step f), mixed with a stream of makeup and recycling hydrogen obtained from step i) and supplying step f), in the same exchanger or in different exchangers. 
     
     
         6 . Method according to  claim 1 , in which said step c) is implemented in a number of heat exchangers of between 1 and 10. 
     
     
         7 . Method according to  claim 1 , in which said liquid hydrocarbon feedstock treated in the hydrotreatment step f) is selected from among the diesel fuel obtained from atmospheric fractionation of crude oil, the Light Vacuum Gasoil Oil (LVGO) according to English terminology or light vacuum distillate, and the liquid hydrocarbon feedstocks obtained from a coking unit (coking according to English terminology), preferably coker diesel fuel, from a visbreaking unit (visbreaking according to English terminology), a steam-cracking unit (steam cracking according to English terminology) and/or from a catalytic cracking unit (Fluid Catalytic Cracking according to English terminology), preferably the LCO (light cycle oil) or light diesel fuels obtained from a catalytic cracking unit, and a diesel fuel feedstock obtained from biomass conversion. 
     
     
         8 . Method according to  claim 1 , in which the hydrotreatment step f) according to the invention is carried out at a temperature of between 230 and 350° C., in a very preferred manner between 250 and 350° C., under a pressure of between 5 and 16 MPa, at a volumetric flow rate of between 0.2 and 4 h −1 , and with an amount of hydrogen introduced such that the volumetric ratio of liter of hydrogen/liter of hydrocarbon is between 300 and 1,500 L/L. 
     
     
         9 . Method according to  claim 1 , in which the compressor of step i) comprises a number of stages n of between 2 and 4. 
     
     
         10 . Method according to  claim 9 , in which said compressor comprises 3 stages. 
     
     
         11 . Method according to  claim 1 , in which the hydrotreatment step a) and the hydrocracking step b) are supplied by hydrogen coming from the outlet of the last compression stage of said step i), and the hydrotreatment step f) is supplied by the outlet of an intermediate compression stage of said step i). 
     
     
         12 . Method according to  claim 10 , where n is equal to 3, wherein the hydrogen coming from the outlet of the second compression stage which supplies the hydrotreatment step f is mixed with the liquid hydrocarbon feedstock entering into said step f). 
     
     
         13 . Method according to  claim 10 , in which said hydrogen-rich gas effluent obtained from step g) is injected between the first and second compression stages and compressed in the second compression stage. 
     
     
         14 . Method according to  claim 10 , in which said hydrogen-rich gas effluent obtained from step g) is mixed with the makeup hydrogen at the intake between the first and second compression stages and then compressed by the second stage, before being recycled upstream from the hydrotreatment step f).