Production of low sulfur gasoline

Abstract

Systems and methods are provided for producing naphtha boiling range fractions having a reduced or minimized amount of sulfur and an increased and/or desirable octane rating and suitable for incorporation into a naphtha fuel product. A naphtha boiling range feed can be separated to form a lower boiling portion and a higher boiling portion. The lower boiling portion, containing a substantial amount of olefins, can be exposed to an acidic catalyst without the need for providing added hydrogen in the reaction environment. Additionally, during the exposure of the lower boiling portion to the acidic catalyst, a stream of light olefins (such as C 2 -C 4 olefins) can be introduced into the reaction environment. Adding such light olefins can enhance the C 5 + yield and/or improve the removal of sulfur from thiophene and methyl-thiophene compounds in the naphtha feed.

What is claimed is: 
     
         1 . A method for treating a naphtha boiling range fraction, comprising:
 separating a feedstock to form a lower boiling fraction and a higher boiling fraction, the separated lower boiling fraction comprising a naphtha boiling range fraction, the separation being performed at a separation cut point temperature of about 170° F. (77° C.) to about 270° F. (132° C.);   exposing at least a portion of the separated lower boiling fraction and a C 2 -C 4  olefin-containing stream to an acidic catalyst without providing substantial added hydrogen under effective desulfurization conditions to form at least a desulfurized naphtha boiling range effluent having a sulfur content of about 90 wppm or less, the effective desulfurization conditions including a pressure of at least about 150 psia (about 1.0 MPa); and   exposing at least a portion of the separated higher boiling fraction to a hydrotreating catalyst under effective hydrotreating conditions to form a hydrotreated effluent having a sulfur content of about 15 wppm or less.   
     
     
         2 . The method of  claim 1 , wherein a weight hourly space velocity of the C 2 -C 4  olefin-containing stream exposed to the acidic catalyst is about 0.1 hr −1  to about 1.0 hr −1 . 
     
     
         3 . The method of  claim 1 , wherein the separated lower boiling fraction has a sulfur content of about 50 wppm or less of sulfur contained in C 2 + thiophenes. 
     
     
         4 . The method of  claim 1 , wherein the separation is performed at a separation cut point temperature of about 250° F. (121° C.) or less. 
     
     
         5 . The method of  claim 1 , wherein a T95 boiling point of the separated lower boiling fraction differs from a T5 boiling point of the separated higher boiling fraction by about 40° F. (22° C.) or less. 
     
     
         6 . The method of  claim 1 , wherein the hydrodesulfurization process comprises a selective hydrodesulfurization process and wherein the separated higher boiling range fraction comprises at least about 5 wt % of olefins. 
     
     
         7 . The method of  claim 1 , wherein the effective desulfurization conditions are effective for converting at least about 60% of the sulfur-containing compounds in the separated lower boiling fraction. 
     
     
         8 . The method of  claim 1 , further comprising combining at least a portion of the desulfurized naphtha boiling range effluent and at least a portion of the hydrotreated effluent to form a naphtha boiling range product, the naphtha boiling range product having a sulfur content of about 15 wppm or less, or about 10 wppm or less. 
     
     
         9 . The method of  claim 1 , wherein the effective desulfurization conditions comprise a temperature of about 400° F. (204° C.) to about 1200° F. (649° C.); a pressure of about 150 psia (1.0 MPa) to about 750 psia (5.2 MPa); and a weight hourly space velocity of about 0.05 to about 10 hr −1 . 
     
     
         10 . The method of  claim 1 , wherein the effective desulfurization conditions comprise exposing the lower boiling portion to the acidic catalyst under fluidized bed conditions. 
     
     
         11 . The method of  claim 1 , wherein the acidic catalyst comprises a hydrogenation metal supported on an aluminosilicate molecular sieve optionally substituted with one or more heteroatoms, an silicoaluminophosphate molecular sieve optionally substituted with one or more heteroatoms, or a combination thereof. 
     
     
         12 . The method of  claim 1 , wherein the acidic catalyst comprises a molecular sieve having a 10-member ring structure, a 12-member ring structure, or a combination thereof. 
     
     
         13 . The method of  claim 1 , wherein the acidic catalyst comprises a molecular sieve having a framework structure of ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-48, MCM-22, MCM-36, MCM-49, zeolite Y, zeolite beta, mordenite, or a combination thereof. 
     
     
         14 . The method of  claim 1 , wherein exposing the at least a portion of the separated lower boiling fraction to the acidic catalyst without providing substantial added hydrogen comprises exposing the at least a portion of the separated lower boiling fraction to the acidic catalyst in the presence of a) less than about 100 SCF/bbl of added hydrogen, or less than about 50 SCF/bbl; b) a partial pressure of less than 50 psig (350 kPag) of hydrogen, or less than about 15 psig (100 kPag); or c) a combination thereof. 
     
     
         15 . The method of  claim 1 , wherein exposing the at least a portion of the separated higher boiling fraction to a hydrotreating catalyst under effective hydrotreating conditions comprises:
 exposing the at least a portion of the separated higher boiling fraction to one or more beds of the hydrotreating catalyst, the one or more beds of the hydrotreating catalyst being located downstream from a first location in a reaction system, an additional one or more beds of the hydrotreating catalyst being located upstream from the first location, the at least a portion of the separated higher boiling fraction being introduced into the reaction system at a position downstream from the first location;   determining that the one or more beds of the hydrotreating catalyst are deactivated;   modifying a position for introducing the at least a portion of the separated higher boiling fraction to a second location, the second location being upstream from the additional one or more beds of hydrotreating catalyst; and   exposing the at least a portion of the separated higher boiling fraction to the additional one or more beds of hydrotreating catalyst.   
     
     
         16 . The method of  claim 15 , wherein exposing the at least a portion of the separated higher boiling fraction to the additional one or more beds of hydrotreating catalyst further comprises exposing the at least a portion of the separated higher boiling fraction to the deactivated one or more beds of hydrotreating catalyst after said exposing to the additional one or more beds of hydrotreating catalyst. 
     
     
         17 . A naphtha boiling range composition formed according to a method comprising:
 separating a feedstock to form a lower boiling fraction and a higher boiling fraction, the separated lower boiling fraction comprising a naphtha boiling range fraction, the separation being performed at a separation cut point temperature of about 170° F. (77° C.) to about 270° F. (132° C.); and   exposing at least a portion of the separated lower boiling fraction and a C 2 -C 4  olefin-containing stream to an acidic catalyst without providing substantial added hydrogen under effective desulfurization conditions to form at least a naphtha boiling range composition having a sulfur content of about 90 wppm or less, the effective desulfurization conditions including a pressure of at least about 150 psia (about 1.0 MPa).   
     
     
         18 . A method for treating a naphtha boiling range fraction, comprising:
 separating a feedstock to form a lower boiling fraction and a higher boiling fraction, the separated lower boiling fraction comprising a naphtha boiling range fraction, the separation being performed at a separation cut point temperature of about 160° F. (71° C.) to about 300° F. (149° C.), the separated lower boiling fraction comprising at least about 10 wppm of thiophene, methyl thiophene, or a combination thereof, the separated lower boiling fraction further comprising about 50 wppm or less of sulfur contained in C 2 + thiophenes;   exposing at least a portion of the separated lower boiling fraction to an acidic catalyst without providing substantial added hydrogen under effective desulfurization conditions to form at least a desulfurized naphtha boiling range effluent having a sulfur content of about 50 wppm or less, the effective desulfurization conditions including a pressure of at least about 150 psig (about 1.0 MPag); and   exposing at least a portion of the separated higher boiling fraction to a hydrotreating catalyst under effective hydrotreating conditions to form a hydrotreated effluent having a sulfur content of about 15 wppm or less.   
     
     
         19 . The method of  claim 18 , wherein exposing at least a portion of the separated lower boiling fraction to an acidic catalyst comprises exposing the at least a portion of the separated lower boiling fraction and a C 2 -C 4  olefin stream to the acidic catalyst. 
     
     
         20 . The method of  claim 18 , wherein the separation is performed at a separation cut point temperature of about 250° F. (121° C.) or less.