Removal of polynuclear aromatics from severely hydrotreated base stocks

1. A method for making lubricant base stock, comprising:

performing solvent deasphalting, under effective solvent deasphalting conditions on a feedstock having a T5 boiling point of 370° C. or more and a T50 of 510° C. or more, the effective solvent deasphalting conditions producing a yield of deasphalted oil of 40 wt % or more of the feedstock;

hydroprocessing at least a portion of the deasphalted oil under first effective hydroprocessing conditions to form a hydroprocessed effluent, the at least a portion of the deasphalted oil having an aromatics content of 60 wt % or more, the hydroprocessed effluent comprising a sulfur content of 300 wppm or less, a nitrogen content of 100 wppm or less, or a combination thereof;

separating, from the hydroprocessed effluent, at least a fuels boiling range fraction, a first fraction comprising polynuclear aromatics and having a T5 distillation point of at least 370° C., and a second fraction having T5 distillation point of at least 370° C., the second fraction having a higher kinematic viscosity at 100° C. than the first fraction;

hydroprocessing at least a portion of the first fraction under second effective hydroprocessing conditions, the second effective hydroprocessing conditions comprising catalytic dewaxing conditions, to form a twice-hydroprocessed effluent comprising a 370° C.+ portion having a first kinematic viscosity at 100° C.; and

i) exposing the at least a portion of the first fraction, prior to the hydroprocessing under second effective hydroprocessing conditions, to an adsorbent under aromatic adsorbent conditions to form an adsorbent effluent having a reduced content of polynuclear aromatics relative to the at least a portion of the first fraction prior to the exposing; ii) exposing at least a portion of the twice-hydroprocessed effluent, during or after the hydroprocessing under second effective hydroprocessing conditions, to an adsorbent under aromatic adsorbent conditions to form an adsorbent effluent having a reduced content of polynuclear aromatics relative to the at least a portion of the twice-hydroprocessed effluent prior to the exposing; or iii) a combination of i) and ii); and further comprising separating a third fraction and a fourth fraction from the at least a portion of the twice-hydroprocessed effluent, the fourth fraction having a higher kinematic viscosity at 100° C. than the third fraction and adding a diluent stream to the twice-hydroprocessed effluent or the at least a portion of the twice-hydroprocessed effluent prior to separating the third fraction and the fourth fraction.

2. The method of claim 1 , wherein after the exposing, the at least a portion of the twice-hydroprocessed effluent has a Saybolt color that is greater than the Saybolt color of the at least a portion of the twice-hydroprocessed effluent prior to the exposing by 2 or more; or wherein after the exposing, the at least a portion of the first fraction has a Saybolt color that is greater than the Saybolt color of the at least a portion of the first fraction prior to the exposing by 2 or more; or a combination thereof.

3. The method of claim 1 , wherein the at least a portion of the twice-hydroprocessed effluent is exposed to the adsorbent after the hydroprocessing under second effective hydroprocessing conditions, and

wherein the at least a portion of the twice-hydroprocessed effluent has a Saybolt color of 16 or less after the hydroprocessing under second effective hydroprocessing conditions and prior to the exposing.

4. The method of claim 1 , wherein performing solvent deasphalting comprises performing solvent deasphalting using a C 4+ solvent.

5. The method of claim 1 , wherein the second effective hydroprocessing conditions further comprise hydrotreating conditions, hydrocracking conditions, and aromatic saturation conditions.

6. The method of claim 1 , wherein the diluent stream comprises at least a portion of the fuels boiling range fraction, at least a portion of the third fraction, or a combination thereof.

7. The method of claim 1 , further comprising adding a diluent stream to the first fraction, or adding a diluent stream to the at least a portion of the first fraction prior to the exposing, or a combination thereof.

8. The method of claim 1 , wherein i) the exposing the at least a portion of the first fraction, ii) the exposing at least a portion of the twice-hydroprocessed effluent, or iii) a combination of i) and ii) to an adsorbent under aromatic adsorbent conditions comprises exposing to an adsorbent comprising one or more of activated carbon, hydroxyl-modified activated carbon, attapulgus clay, an adsorbent clay, silica or alumina with greater than 10 m 2 /g BET surface area, porous polymer, porous resin, diatomaceous earth, and zeolite.

9. The method of claim 1 , wherein

a) the at least a portion of the twice-hydroprocessed effluent comprises a viscosity of 10 cP to 13 cP at 150° C. and the aromatic adsorbent conditions comprise an exposure temperature of 120° C. to 160° C.;

b) the at least a portion of the twice-hydroprocessed effluent comprises a viscosity of 13 cP to 15 cP at 150° C. and the aromatic adsorbent conditions comprise an exposure temperature of 160° C. to 200° C.; or

c) the at least a portion of the twice-hydroprocessed effluent comprises a viscosity of 8 cP to 10 cP at 150° C. and the aromatic adsorbent conditions comprise an exposure temperature of 80° C. to 120° C.

10. The method of claim 1 , wherein the first effective hydroprocessing conditions comprise ebullated bed processing conditions, slurry hydroprocessing conditions, or a combination thereof.

11. The method of claim 1 , wherein the first hydroprocessing conditions further comprise first aromatic saturation conditions, the first aromatic saturation conditions comprising exposing the at least a portion of the deasphalted oil to a hydrocracking catalyst and a demetallization catalyst, the at least a portion of the deasphalted oil being exposed to the demetallization catalyst after exposing the at least a portion of the deasphalted oil to the hydrocracking catalyst.

12. The method of claim 1 , wherein the adsorbent effluent has a reduced content of polynuclear aromatics comprising six or more rings relative to the at least a portion of the twice-hydroprocessed effluent prior to the exposing.

13. The method of claim 1 , i) wherein after the exposing and the hydroprocessing under second effective hydroprocessing conditions, the at least a portion of the twice-hydroprocessed effluent has a Saybolt color of 15 or more, or ii) wherein after the hydroprocessing under second effective hydroprocessing conditions and prior to the exposing, the at least a portion of the twice-hydroprocessed effluent has a Saybolt color of 14 or less, or iii) a combination of i) and ii).

14. A method for making lubricant base stock, comprising:

performing solvent deasphalting, under effective solvent deasphalting conditions on a feedstock having a T5 boiling point of 370° C. or more and a T50 of 510° C. or more, the effective solvent deasphalting conditions producing a yield of deasphalted oil of 40 wt % or more of the feedstock;

hydroprocessing at least a portion of the deasphalted oil under first effective hydroprocessing conditions to form a hydroprocessed effluent, the at least a portion of the deasphalted oil having an aromatics content of 60 wt % or more, the hydroprocessed effluent comprising a sulfur content of 300 wppm or less, a nitrogen content of 100 wppm or less, or a combination thereof;

separating, from the hydroprocessed effluent, at least a fuels boiling range fraction, a first fraction comprising polynuclear aromatics and having a T5 distillation point of at least 370° C., and a second fraction having a T5 distillation point of at least 370° C., the second fraction having a higher kinematic viscosity at 100° C. than the first fraction;

hydroprocessing at least a portion of the first fraction under second effective hydroprocessing conditions, the second effective hydroprocessing conditions comprising catalytic dewaxing conditions, to form a twice-hydroprocessed effluent comprising a 370° C.+ portion having a first kinematic viscosity at 100° C.; and

i) exposing the at least a portion of the first fraction, prior to the hydroprocessing under second effective hydroprocessing conditions, to an adsorbent under aromatic adsorbent conditions to form an adsorbent effluent having a reduced content of polynuclear aromatics relative to the at least a portion of the first fraction prior to the exposing, ii) exposing at least a portion of the twice-hydroprocessed effluent, during or after the hydroprocessing under second effective hydroprocessing conditions, to an adsorbent under aromatic adsorbent conditions to form an adsorbent effluent having a reduced content of polynuclear aromatics relative to the at least a portion of the twice-hydroprocessed effluent prior to the exposing; or iii) a combination of i) and ii); and further comprising hydroprocessing at least a portion of the second fraction under third effective hydroprocessing conditions, the third effective hydroprocessing conditions comprising catalytic dewaxing conditions, to form a second twice-hydroprocessed effluent comprising a 370° C.+ portion having a second kinematic viscosity at 100° C.;

separating from at least a portion of the second twice-hydroprocessed effluent a fifth fraction and a sixth fraction, the sixth fraction having a higher kinematic viscosity at 100° C. than the fifth fraction; and

exposing; at least a portion of the fifth fraction to an adsorbent under aromatic adsorbent conditions to form an effluent having a reduced content of polynuclear aromatics relative to the at least a portion of the fifth fraction.

15. A method for making lubricant base stock, comprising: performing solvent deasphalting, under effective solvent deasphalting conditions on a feedstock having a T5 boiling point of 370° C. or more and a T50 of 510° C. or more, the effective solvent deasphalting conditions producing a yield of deasphalted oil of 40 wt % or more of the feedstock;

hydroprocessing at least a portion of the deasphalted oil under first effective hydroprocessing conditions to form a hydroprocessed effluent, the at least a portion of the deasphalted oil having an aromatics content of 60 wt % or more, the hydroprocessed effluent comprising a sulfur content of 300 wppm or less, a nitrogen content of 100 wppm or less, or a combination thereof;

separating, from the hydroprocessed effluent, at least a fuels boiling range fraction, a first fraction comprising polynuclear aromatics and having a T5 distillation point of at least 370° C., and a second fraction having a T5 distillation point of at least 370° C., the second fraction having a higher kinematic viscosity at 100° C. than the first fraction;

hydroprocessing at least a portion of the first fraction under second effective hydroprocessing conditions, the second effective hydroprocessing conditions comprising catalytic dewaxing conditions, to form a twice-hydroprocessed effluent comprising a 370° C.+ portion having a first kinematic viscosity at 100° C.; and

i) exposing the at least a portion of the first fraction, prior to the hydroprocessing under second effective hydroprocessing conditions to an adsorbent under aromatic adsorbent conditions to form an adsorbent effluent having a reduced content of polynuclear aromatics relative to the at least a portion of the first fraction prior to the exposing; ii) exposing at least a portion of the twice-hydroprocessed effluent, during or after the hydroprocessing under second effective hydroprocessing conditions, to an adsorbent under aromatic adsorbent conditions to form an adsorbent effluent having a reduced content of polynuclear aromatics relative to the at least a portion of the twice-hydroprocessed effluent prior to the exposing; or iii) a combination of i) and ii); and wherein separating the hydroprocessed effluent further comprises forming an additional fraction having a T5 distillation point of at least 370° C., the method further comprising:

hydroprocessing at least a portion of the additional fraction under third effective hydroprocessing conditions, the third effective hydroprocessing conditions comprising catalytic dewaxing conditions, to form a third catalytically dewaxed effluent comprising a 370° C.+ portion having a kinematic viscosity at 100° C. of 3.5 cSt or more.

16. A method for making lubricant base stock, comprising:

performing solvent deasphalting, under effective solvent deasphalting conditions on a feedstock having a T5 boiling point of 370° C. or more and a T50 of 510° C. or more, the effective solvent deasphalting conditions producing a yield of deasphalted oil of 40 wt % or more of the feedstock;

hydroprocessing at least a portion of the deasphalted oil under first effective hydroprocessing conditions to form a hydroprocessed effluent, the at least a portion of the deasphalted oil having an aromatics content of 60 wt % or more, the hydroprocessed effluent comprising a sulfur content of 300 wppm or less, a nitrogen content of 100 wppm or less, or a combination thereof;

separating, from the hydroprocessed effluent, at least a fuels boiling range fraction, a first fraction comprising 6+ ring aromatics and having a T5-distillation point of at least 370° C., and a second fraction having a T5-distillation point of at least 370° C., the second fraction having a higher kinematic viscosity at 100° C. than the first fraction;

hydroprocessing at least a portion of the second fraction under second effective hydroprocessing conditions, the second effective hydroprocessing conditions comprising catalytic dewaxing conditions, to form a twice-hydroprocessed effluent comprising a 370° C.+ portion having a kinematic viscosity at 100° C. of 16 cSt or greater; and

i) exposing the at least a portion of the second fraction, prior to the hydroprocessing under second effective hydroprocessing conditions, to an adsorbent under aromatic adsorbent conditions to form an adsorbent effluent having a reduced content of polynuclear aromatics relative to the at least a portion of the second fraction prior to the exposing; ii) exposing at least a portion of the twice-hydroprocessed effluent, during or after the hydroprocessing under second effective hydroprocessing conditions, to an adsorbent under aromatic adsorbent conditions to form an adsorbent effluent having a reduced content of polynuclear aromatics relative to the at least a portion of the twice-hydroprocessed effluent prior to the exposing; or iii) a combination of i) and ii); and further comprising adding a diluent stream to the at least a portion of the twice-hydroprocessed effluent prior to the exposing at least a portion of the twice-hydroprocessed effluent to an adsorbent, the diluent stream comprising at least a portion of the fuels boiling range fraction, at least a portion of the first fraction, or a combination thereof.

17. The method of claim 16 , wherein prior to the exposing, the at least a portion of the twice-hydroprocessed effluent has a turbidity of 2 NTU or more.

18. The method of claim 16 , wherein the adsorbent effluent has a reduced content of polynuclear aromatics comprising six or more rings relative to the at least a portion of the twice-hydroprocessed effluent prior to the exposing.