Hydrogenation of polynuclear aromatic compounds

Abstract

A process for reducing the polynuclear aromatics (PNA) content of a sulfur-containing hydrocarbon stream. The process includes contacting the sulfur-containing hydrocarbon stream with a dearomatization composition comprising a promoter metal component and zinc oxide. The dearomatization composition has enhanced resistance to sulfur poisoning and is also effective to remove sulfur from the hydrocarbon stream.

1 . A process for removing polynuclear aromatics (PNA) from a low-sulfur hydrocarbon-containing stream containing less than about 500 ppmw sulfur, said process comprising: contacting said low-sulfur stream with a dearomatization composition comprising a promoter metal component and zinc oxide under dearomatization conditions sufficient to reduce the PNA content of said low-sulfur stream by at least about 25 percent by weight thereby providing a PNA-reduced stream, wherein the sulfur content of said PNA-reduced stream is at least about 5 percent by weight less than the sulfur content of said low-sulfur stream. 
   
   
       2 . The process of  claim 1  further comprising using a desulfurization system to remove sulfur from an initial hydrocarbon-containing stream to thereby produce said low-sulfur stream, wherein the sulfur content of said low-sulfur stream is at least about 50 percent by weight less than the sulfur content of said initial hydrocarbon-containing stream. 
   
   
       3 . The process of  claim 2  wherein said desulfurization system employs a regenerable sorbent comprising a reduced-valence promoter metal component and zinc oxide to remove sulfur from said initial hydrocarbon-containing stream. 
   
   
       4 . The process of  claim 3  wherein said desulfurization system includes a fluidized bed reactor for contacting said initial hydrocarbon-containing stream with said regenerable sorbent. 
   
   
       5 . The process of  claim 1  wherein said dearomatization composition is pre-treated with citric acid and/or tartaric acid prior to said contacting with said low-sulfur stream. 
   
   
       6 . The process of  claim 1  wherein said dearomatization composition is subjected to reduction prior to said contacting with said low-sulfur stream. 
   
   
       7 . The process of  claim 1  wherein said promoter metal component comprises a promoter metal selected from the group consisting of nickel, cobalt, iron, manganese, tungsten, silver, gold, copper, platinum, zinc, ruthenium, molybdenum, antimony, vanadium, iridium, chromium, palladium, and combinations thereof. 
   
   
       8 . The process of  claim 7  wherein said dearomatization composition contains at least about 20 percent by weight of said zinc oxide. 
   
   
       9 . The process of  claim 8  wherein said contacting with said low-sulfur stream converts at least a portion of said zinc oxide to zinc sulfide. 
   
   
       10 . The process of  claim 9  wherein said dearomatization composition contains at least about 10 percent by weight nickel. 
   
   
       11 . The process of  claim 1  wherein said promoter metal component is a substitutional solid metal solution of the formula Ni A Zn B , wherein A and B are each in the range of from 0.01 to 0.99. 
   
   
       12 . The process of  claim 11  wherein A is in the range of from about 0.70 to about 0.97 and B is in the range of from about 0.03 to about 0.30. 
   
   
       13 . The process of  claim 1  wherein said dearomatization composition contains an aluminate. 
   
   
       14 . The process of  claim 13  wherein said aluminate contains nickel and/or zinc. 
   
   
       15 . The process of  claim 13  wherein said aluminate is nickel-zinc aluminate. 
   
   
       16 . The process of  claim 1  wherein said dearomatization composition contains perlite. 
   
   
       17 . The process of  claim 1  wherein the cetane number of said PNA-reduced stream is at least about 5 percent greater than the cetane number of said low-sulfur stream. 
   
   
       18 . The process of  claim 1  wherein the PNA content of said PNA-reduced stream is at least about 50 percent by weight less than the PNA content of said low-sulfur stream, wherein the sulfur content of said PNA-reduced stream is at least about 25 percent by weight less than the sulfur content of said low-sulfur stream, wherein the cetane number of said PNA-reduced stream is at least about 10 percent greater than the cetane number of said low-sulfur stream. 
   
   
       19 . The process of  claim 1  wherein said low-sulfur stream has a cetane number of at least about 20. 
   
   
       20 . The process of  claim 1  wherein said low-sulfur stream has a cetane number in the range of from about 20 to about 40, wherein said PNA-reduced stream has a cetane number in the range of from about 35 to about 60. 
   
   
       21 . The process of  claim 1  wherein said low-sulfur stream has a PNA content of at least about 5 percent by weight. 
   
   
       22 . The process of  claim 1  wherein said low-sulfur stream has a PNA content in the range of from about 10 to about 70 percent by weight, wherein said PNA-reduced stream has a PNA content less than about 7.5 percent by weight. 
   
   
       23 . The process of  claim 1  wherein said low-sulfur stream contains in the range of from about 5 to about 400 ppmw sulfur, wherein said PNA-reduced stream contains less than about 10 ppmw sulfur. 
   
   
       24 . The process of  claim 1  wherein said low-sulfur stream is a middle distillate stream having a mid-boiling point of at least about 350° F. 
   
   
       25 . The process of  claim 24  wherein said middle distillate stream has a boiling range of from about 300 to about 750° F., an API gravity in the range of from about 20 to about 50, and a minimum flashpoint of at least about 80° F. 
   
   
       26 . The process of  claim 1  wherein said low-sulfur stream is selected from the group consisting of diesel fuel, jet fuel, kerosene, light cycle oil, and mixtures thereof. 
   
   
       27 . The process of  claim 1  wherein said low-sulfur stream consists essentially of diesel fuel having a boiling range of 375 to 700° F., a mid-boiling point of at least 500° F., an API gravity in the range of from 30 to 38, and a minimum flashpoint of at least 100° F. 
   
   
       28 . The process of  claim 1  wherein said contacting is carried out for an activity-maintaining time period of at least 12 hours without regeneration of said dearomatization composition, wherein during said activity-maintaining time period the reduction in the PNA content of said low-sulfur stream is maintained at 25 percent by weight or more. 
   
   
       29 . The process of  claim 28  wherein during said activity-maintaining time period the reduction in the sulfur content of said low-sulfur stream is maintained at 50 percent by weight or more. 
   
   
       30 . The process of  claim 28  wherein said activity-maintaining time period is at least 36 hours. 
   
   
       31 . The process of  claim 28  wherein after said activity-maintaining time period said dearomatization composition is deactivated, wherein said process further comprises regenerating the deactivated dearomatization composition by contacting the deactivated dearomatization composition with an oxygen-containing regeneration stream. 
   
   
       32 . The process of  claim 31  wherein said deactivated dearomatization composition contains zinc sulfide, wherein said regeneration converts at least a portion of said zinc sulfide to zinc oxide. 
   
   
       33 . The process of  claim 1  wherein said contacting takes place in a fixed bed reactor and/or moving bed reactor. 
   
   
       34 . The process of  claim 1  wherein said dearomatization composition is in the form of solid particles having an average minimum diameter of at least about 0.0625 inches. 
   
   
       35 . The process of  claim 1  wherein said dearomatization conditions include a temperature in the range of from about 500 to about 800° F., a pressure in the range of from about 200 to about 2,000 psia, a weight hourly space velocity in the range of from about 0.1 to about 5 hr −1 , and a hydrogen flow rate in the range of from about 1,000 to about 5,000 scf/bbl. 
   
   
       36 . A process for treating an initial hydrocarbon-containing stream having a sulfur content of at least about 500 ppmw and a polynuclear aromatics (PNA) content of at least about 5 percent by weight, said process comprising:
 (a) contacting said initial stream with a catalyst and/or sorbent composition in a first zone under desulfurization conditions sufficient to reduce the sulfur content of said initial stream by at least about 25 percent by weight, thereby producing a sulfur-reduced stream having a sulfur content of less than about 500 ppmw and a PNA content of at least about 5 percent by weight; and   (b) contacting at least a portion of said sulfur-reduced stream with a dearomatization composition comprising nickel and zinc oxide in a second zone, thereby producing a PNA-reduced stream having a PNA content at least about 25 percent by weight less than the PNA content of said sulfur-reduced stream.   
   
   
       37 . The process of  claim 36  wherein step (a) is carried out in a fluidized bed reactor and step (b) is carried out in a fixed and/or moving bed reactor. 
   
   
       38 . The process of  claim 36  wherein said catalyst and/or sorbent is a regenerable sorbent comprising a reduced-valence promoter metal component and zinc oxide. 
   
   
       39 . The process of  claim 36  wherein said dearomatization composition comprises at least about 10 percent by weight nickel and at least about 20 percent by weight zinc oxide. 
   
   
       40 . The process of  claim 36  wherein said dearomatization composition has been pretreated with an acid prior to said contacting of step (b). 
   
   
       41 . The process of  claim 36  wherein said initial stream is a middle distillate stream having a mid-boiling point of at least about 350° F. 
   
   
       42 . The process of  claim 36  wherein said initial stream is diesel fuel. 
   
   
       43 . The process of  claim 36  wherein the sulfur content of said PNA-reduced stream is at least about 5 percent by weight less than the sulfur content of said sulfur-reduced stream. 
   
   
       44 . The process of  claim 36  wherein the PNA content of said PNA-reduced stream is less than about 10 percent by weight. 
   
   
       45 . The process of  claim 36  wherein the sulfur content of said sulfur-reduced stream is at least about 50 percent less than the sulfur content of said initial stream. 
   
   
       46 . The process of  claim 45  wherein the PNA content of said PNA-reduced stream is at least about 50 percent by weight less than the PNA content of said sulfur-reduced stream. 
   
   
       47 . The process of  claim 46  wherein the PNA content of said PNA-reduced stream is less than about 7.5 percent by weight, wherein the PNA content of said sulfur-reduced stream is in the range of from about 10 to abut 60 percent by weight.