Process and apparatus for removal of heavy polynuclear aromatics in a hydrocracking process

Abstract

Processes and apparatuses are disclosed for removing heavy polynuclear aromatic compounds from a hydrocracked stream comprising passing at least a portion of the hydrocracked stream to a fractionation column to provide a plurality of fractionator product streams and a fractionator bottoms stream comprising unconverted hydrocarbons. A first stream and a second stream are taken from the fractionator bottoms stream. The first stream is passed through a heavy polynuclear aromatic adsorption zone to obtain a treated bottoms stream having a reduced concentration of heavy polynuclear aromatic compounds. The second stream is bypassed around the heavy polynuclear aromatic adsorption zone. Finally, the treated bottoms stream and the bypassed second stream are hydrocracked.

1 . A process of removing heavy polynuclear aromatic (HPNA) compounds from a hydrocracked stream, the process comprising:
 passing at least a portion of the hydrocracked stream to a fractionation column to provide a plurality of fractionator product streams and a fractionator bottoms stream comprising unconverted hydrocarbons;   taking a first stream from the fractionator bottoms stream;   taking a second stream from the fractionator bottoms stream;   passing the first stream through a HPNA adsorption zone to obtain a treated bottoms stream having a reduced concentration of HPNA compounds;   bypassing the second stream around the HPNA adsorption zone; and   hydrocracking the treated bottoms stream and the bypassed second stream.   
     
     
         2 . The process of  claim 1  further comprising hydrocracking a hydrocarbon feedstream in a first hydrocracking reactor, wherein the hydrocarbon feedstream is contacted with a first hydrocracking catalyst under first hydrocracking conditions in the presence of hydrogen to provide the hydrocracked stream. 
     
     
         3 . The process of  claim 2 , wherein the step of hydrocracking the treated bottoms stream and the bypassed second stream occurs in the first hydrocracking reactor. 
     
     
         4 . The process of  claim 2 , wherein the step of hydrocracking the treated bottoms stream and the bypassed second stream occurs in a second hydrocracking reactor. 
     
     
         5 . The process of  claim 1 , wherein the HPNA adsorption zone comprises an activated carbon. 
     
     
         6 . The process of  claim 2  further comprising hydrotreating the hydrocarbon feedstream in a hydrotreating reactor prior to hydrocracking the hydrocarbon feedstream in the first hydrocracking reactor. 
     
     
         7 . The process of  claim 6 , wherein the treated bottoms stream and the bypassed second stream are passed through the hydrotreating reactor prior to the step of hydrocracking. 
     
     
         8 . The process of  claim 1  further comprising:
 passing the hydrocracked stream through one or more vapor-liquid separators to provide a recycle hydrogen gas stream and at least one liquid process stream; and 
 passing the at least one liquid process stream to the fractionation column to provide the plurality of fractionator product streams and the fractionator bottoms stream. 
 
     
     
         9 . The process of  claim 1  further comprising taking a third stream from the fractionator bottoms stream and rejecting the third stream as a bleed stream. 
     
     
         10 . A process for upgrading a hydrocarbon stream, the process comprising:
 passing the hydrocarbon feedstream to a first hydrocracking reactor, the first hydrocracking reactor containing at least one bed of a first hydrocracking catalyst, wherein the hydrocarbon feedstream is contacted with the first hydrocracking catalyst under first hydrocracking conditions in the presence of hydrogen to produce a first hydrocracked effluent stream;   passing at least a portion of the first hydrocracked effluent stream to a fractionation column to provide a plurality of fractionator product streams and a fractionator bottoms stream comprising unconverted hydrocarbons;   splitting the fractionator bottoms stream to provide a first stream and a second stream;   passing the first stream through a HPNA adsorption zone to obtain a treated bottoms stream having a reduced concentration of HPNA compounds;   bypassing the second stream around the HPNA adsorption zone; and   passing the treated bottoms stream and the bypassed second stream to a second hydrocracking reactor, the second hydrocracking reactor containing at least one bed of a second hydrocracking catalyst, wherein the treated bottoms stream and the bypassed second stream are contacted with a second hydrocracking catalyst under second hydrocracking conditions in the presence of hydrogen to provide a second hydrocracked effluent stream.   
     
     
         11 . The process of  claim 10 , wherein the HPNA adsorption zone comprises an activated carbon. 
     
     
         12 . The process of  claim 10  further comprising hydrotreating the hydrocarbon feedstream in a hydrotreating reactor prior to hydrocracking the hydrocarbon feedstream in the first hydrocracking reactor. 
     
     
         13 . The process of  claim 10 , wherein the treated bottoms stream and the bypassed second stream are passed through the hydrotreating reactor prior to being passed to the second hydrocracked reactor. 
     
     
         14 . The process of  claim 10  further comprising:
 passing the first hydrocracked effluent stream through one or more vapor-liquid separators to provide a recycle hydrogen gas stream and at least one liquid process stream; 
 passing the at least one liquid process stream to the fractionation column to provide the plurality of fractionator product streams and the fractionator bottoms stream. 
 
     
     
         15 . The process of  claim 10  further comprising obtaining a third stream from the fractionator bottoms stream, the third stream being rejected as a bleed stream. 
     
     
         16 . An apparatus for removing HPNA compounds from a hydrocracked stream, the apparatus comprising:
 a fractionation column in communication with a hydrocracked effluent line to provide a plurality of fractionator product streams and a fractionator bottoms stream in a fractionator bottoms line;   a first fractionator bottoms line fluidly connected to the fractionator bottoms line;   a second fractionator bottoms line fluidly connected to the fractionator bottoms line;   a HPNA adsorption zone in downstream communication with the first fractionator bottoms line to provide a treated bottoms stream in a treated bottoms line having a reduced concentration of HPNA compounds; and   a hydrocracking reactor in communication with the treated bottoms line and the second fractionator bottoms line, the second fractionator bottoms line bypassing the HPNA adsorption zone.   
     
     
         17 . The apparatus of  claim 16 , wherein the HPNA adsorption zone comprises an activated carbon. 
     
     
         18 . The apparatus of  claim 16  further comprising a first hydrocracking reactor to provide a hydrocracked stream in the hydrocracked effluent line. 
     
     
         19 . The apparatus of  claim 16 , wherein the hydrocracking reactor is the first hydrocracking reactor. 
     
     
         20 . The apparatus of  claim 16 , wherein the hydrocracking reactor is a second hydrocracking reactor, the second hydrocracking reactor in downstream communication with the first hydrocracking reactor.