Process Scheme for the Production of Optimal Quality Distillate for Olefin Production

Abstract

Systems and processes for hydrotreating, splitting, and extracting a gasoil feed to produce a saturate-rich feedstock for olefin pyrolysis are provided. A gasoil feed is provided to a hydrotreating section to produce an ultralow sulfur distillate (ULSD) stream. The ULSD stream is provided to a splitter section to produce a light distillate stream and a heavy bottom stream. The light distillate stream is provided to an extraction section to produce an aromatic-rich extract phase and a saturate-rich raffinate phase. The raffinate phase is mixed with the heavy bottom stream to produce an olefin pyrolysis feedstock having a reduced BMCI as compared to the gasoil feed stream and the ULSD stream.

What is claimed is: 
     
         1 . A system, comprising:
 a hydrotreating section operable to hydrotreat a gasoil feed with a hydrotreating catalyst in the presence of hydrogen to produce an ultralow sulfur distillate (ULSD) stream comprising less than 10 parts-per-million weight (ppmw) sulfur and less than 10 ppmw nitrogen;   a separation section operable to separate the ULSD stream into a light distillate stream and a heavy bottom stream, wherein aromatics in the light distillate stream comprise at least 50% by weight monoaromatics and the aromatics in the heavy bottom stream comprise no more than 15% by weight monoaromatics; and   an extraction section operable to extract an extract phase and a raffinate phase from the light distillate stream, the raffinate phase comprising at least 50% by weight saturated hydrocarbons and no more than 15% by weight aromatics.   
     
     
         2 . The system of  claim 1 , wherein the light distillate stream has a true boiling point (TPB) in the range of 140° C. to about 300° C. 
     
     
         3 . The system of  claim 1 , wherein the heavy bottom stream has a true boiling point (TPB) in the range of 300° C. to about 400° C. 
     
     
         4 . The system of  claim 1 , comprising a mixing apparatus operable to mix the raffinate phase with the heavy bottom stream to produce the feedstock for olefin pyrolysis, wherein a Bureau of Mines Correlation Index (BMCI) of the feedstock for olefin pyrolysis is less than the BMCI of the gasoil feed and the BMCI of the ULSD stream. 
     
     
         5 . The system of  claim 1 , wherein the gasoil feed has a true boiling point (TPB) in the range of about 140° C. to about 400° C. 
     
     
         6 . The system of  claim 1 , wherein the hydrotreating catalyst is a heterogeneous fixed bed catalyst comprising at least one Group VIII metal and at least one Group VIB metal. 
     
     
         7 . The system of  claim 6 , wherein the at least one Group VIII metal is selected from the group consisting of iron, cobalt and nickel and at least one Group VIB metal is selected from the group consisting of molybdenum and tungsten. 
     
     
         8 . The system of  claim 1 , wherein the separation section comprises a tray distillation column. 
     
     
         9 . The system of  claim 1 , wherein the extraction section comprising a liquid-liquid extraction (LLE) column, secondary re-extract column, an extract and raffinate wash column, a distillation column, and a solvent recovery column 
     
     
         10 . The system of  claim 9 , wherein the liquid-liquid extraction (LLE) column comprises a first solvent and a second solvent. 
     
     
         11 . The system of  claim 10 , wherein the first solvent comprises N-Methyl-2-pyrrolidone (NMP) or dimethyl sulfoxide (DMSO). 
     
     
         12 . The system of  claim 10 , wherein the second solvent comprises paraffinic light naphtha or C6 and C7 hydrocarbons. 
     
     
         13 . The system of  claim 1 , wherein the extract phase comprises at least 50% by weight aromatics.