Methods and systems to improve light olefin yield and feedstock utilization from c5 raffinate streams

Abstract

Systems and methods for producing light olefins from a natural gas liquid (NGL) or other C5 stream are provided. The method may include supplying a NGL or other C5 stream to a reverse isomerization unit to produce a n-pentane enriched NGL stream and supplying the n-pentane enriched NGL stream to a liquid furnace to produce a pyrolyzed product stream. The method may also include separating the C2 hydrocarbons, the C3 hydrocarbons, the C4 hydrocarbons, the C5 hydrocarbons, and the C6+ hydrocarbons in the pyrolyzed product stream in a separation train and supplying the separated C5 hydrocarbons, or a portion thereof, to a hydrogenation reactor to produce a saturated C5 hydrocarbon stream, followed by recycling the saturated C5 hydrocarbon stream to the reverse isomerization unit.

What is claimed is: 
     
         1 . A method for producing light olefins from a natural gas liquid stream, the method comprising:
 supplying a natural gas liquid (NGL) stream to a reverse isomerization unit to produce a n-pentane enriched NGL stream;   supplying the n-pentane enriched NGL stream to a liquid furnace to produce a pyrolyzed product stream, the pyrolyzed product stream comprising C2 hydrocarbons, C3 hydrocarbons, C4 hydrocarbons, C5 hydrocarbons, and C6+ hydrocarbons;   separating the C2 hydrocarbons, the C3 hydrocarbons, the C4 hydrocarbons, the C5 hydrocarbons, and the C6+ hydrocarbons in the pyrolyzed product stream in a separation train;   supplying the separated C5 hydrocarbons, or a portion thereof, to a first hydrogenation reactor to produce a saturated C5 hydrocarbon stream; and   recycling the saturated C5 hydrocarbon stream to the reverse isomerization unit.   
     
     
         2 . The method according to  claim 1 , wherein recycling the saturated C5 hydrocarbon stream to the reverse isomerization unit increases an ethylene and/or a propylene yield at the liquid furnace. 
     
     
         3 . The method according to  claim 1 , wherein the NGL stream is formed from the combination of a fresh natural gas liquid feed and the saturated C5 hydrocarbon stream produced at the first hydrogenation reactor. 
     
     
         4 . The method according to  claim 1 , further comprising:
 supplying the separated C4 hydrocarbons, or a portion thereof, to a second hydrogenation reactor to produce a saturated C4 hydrocarbon stream;   recycling the saturated C4 hydrocarbon stream to the reverse isomerization unit.   
     
     
         5 . The method according to  claim 1 , further comprising:
 supplying the separated C4 hydrocarbons, or a portion thereof, to the first hydrogenation reactor to produce a combined saturated C4 hydrocarbon and saturated C5 hydrocarbon stream; and   recycling the combined saturated C4 and C5 hydrocarbon stream to the reverse isomerization unit.   
     
     
         6 . The method according to  claim 5 , wherein the NGL stream is formed from the combination of a fresh natural gas liquid feed and the combined saturated C4 and C5 hydrocarbon stream produced at the first hydrogenation reactor. 
     
     
         7 . The method according to  claim 4 , wherein the NGL stream is formed from the combination of a fresh natural gas liquid feed, the saturated C5 hydrocarbon stream produced at the first hydrogenation reactor, and the saturated C4 hydrocarbon stream produced at the second hydrogenation reactor. 
     
     
         8 . The method according to  claim 1 , further comprising:
 supplying the C4 hydrocarbons separated from the pyrolyzed product stream to a butadiene and but-1-ene processing unit to produce a butadiene stream, a butene-1 stream, and a C4 raffinate stream;   supplying the C4 raffinate stream to the first hydrogenation reactor or the second hydrogenation reactor to produce a saturated C4 hydrocarbon stream; and   supplying the saturated C4 hydrocarbon stream to the reverse isomerization unit.   
     
     
         9 . The method according to  claim 8 , further comprising:
 separating, at a debutanizer unit, C4 hydrocarbons from the pyrolyzed product stream, or a portion thereof, to produce a separated C4 hydrocarbon stream; and   supplying the separated C4 hydrocarbon stream to the butadiene and but-1-ene processing unit.   
     
     
         10 . The method according to  claim 1 , further comprising:
 supplying the pyrolyzed product stream to a product recovery section of the separation train operable to separate propylene and ethylene from the pyrolyzed product stream to produce a C4+ hydrocarbon stream;   supplying the C4+ hydrocarbon stream to a debutanizer to produce a separated C4 hydrocarbon stream and a C5+ hydrocarbon stream;   supplying the C5+ hydrocarbon stream to a depentanizer to produce a separated C5 hydrocarbon stream and a C6+ hydrocarbon stream; and   supplying the separated C5 hydrocarbon stream to the first hydrogenation reactor.   
     
     
         11 . The method according to  claim 1 , further comprising:
 supplying the C5+ hydrocarbon stream or the separated C5 hydrocarbon stream to a gas hydro treatment reactor prior to supplying the C5 hydrocarbon stream to the first hydrogenation reactor.   
     
     
         12 . A system for producing light olefins from a natural gas liquid stream, the system comprising:
 a reverse isomerization unit operable to receive a natural gas liquid (NGL) stream, the reverse isomerization unit further operable to isomerize the NGL stream to produce a n-pentane enriched NGL stream;   a liquid furnace operable to receive the n-pentane enriched NGL stream, the liquid furnace further operable to pyrolyze the n-pentane enriched NGL stream to produce a pyrolyzed product stream, the pyrolyzed product stream comprising C2 hydrocarbons, C3 hydrocarbons, C4 hydrocarbons, C5 hydrocarbons, and C6+ hydrocarbons;   a separation train operable to separate the C2 hydrocarbons, the C3 hydrocarbons, the C4 hydrocarbons, the C5 hydrocarbons, and the C6+ hydrocarbons in the pyrolyzed product stream; and   a first hydrogenation reactor operable to receive the separated C5 hydrocarbons, or a portion thereof, the first hydrogenation reactor further operable to hydrogenate the separated C5 hydrocarbons, or a portion thereof, to produce a saturated C5 hydrocarbon stream;   the reverse isomerization unit further operable to receive the saturated C5 hydrocarbon stream.   
     
     
         13 . The system according to  claim 12 , wherein the separation train comprises:
 a product recovery section configured to receive the pyrolyzed product stream produced by the liquid furnace, the product recovery section further configured to separate propylene and ethylene from the pyrolyzed product stream to produce a C4+ hydrocarbon stream;   a debutanizer configured to receive the C4+ hydrocarbon stream produced by the product recovery section, the debutanizer further configured to debutanize the C4+ hydrocarbon stream to produce a separated C4 hydrocarbon stream and a C5+ hydrocarbon stream; and   a depentanizer configured to receive the C5+ hydrocarbon stream produced by the debutanizer, the depentanizer further configured to depentenize the C5+ hydrocarbon stream to produce a separated C5 hydrocarbon stream and a C6+ hydrocarbon stream;   wherein the first hydrogenation reactor is operable to receive the separated C5 hydrocarbon stream produced by the depentanizer.   
     
     
         14 . The system according to  claim 12 , further comprising:
 a gas hydro treatment reactor configured to receive the C5+ hydrocarbon stream produced by the debutanizer or the separated C5 hydrocarbon stream produced by the depentanizer prior to supplying the C5 hydrocarbon stream to the first hydrogenation reactor.   
     
     
         15 . The system according to  claim 12 , wherein the reverse isomerization unit is operated at a temperature of from about 240° C. to about 440° C. and at a pressure of from about 15 bar to about 30 bar.