Targeted hydrogenation hydrocracking

Abstract

This invention is directed to a process scheme in which a partial conversion hydrocracking (HCR) unit, preferably preceded by a hydrotreating unit, feeds unconverted oil to a FCC (fluid catalytic cracking ) unit. Most refineries run the FCC unit at the full capacity for optimal asset utilization. During shutdowns of Residue Desulfurization unit(s) which feed an FCC unit, it is desirable to reduce the conversion in the FCC feed hydrocracker. In this way, the feed to FCC unit is maximized. Jet and Diesel products that conform to specifications may be produced during low conversion HCR operation. Furthermore, undesirable over-saturation of the unconverted oil (UCO) from the HCR unit feeding the FCC unit can be avoided. Excess hydrogen consumption can also be avoided. Normally, further aromatic saturation of the middle distillate products from a low conversion HCR is achieved in a separate, post treatment, unit.

1 . A method for hydroprocessing a hydrocarbon feedstock, said method employing multiple hydroprocessing zones within a single reaction loop, each zone having one or more catalyst beds, comprising the following steps:
 (a) passing a hydrocarbonaceous feedstock to a first hydroprocessing zone having one or more beds containing hydroprocessing catalyst, the hydroprocessing zone being maintained at hydroprocessing conditions, wherein the feedstock is contacted with catalyst and hydrogen;   (b) passing the effluent of step (a) directly to a hot high pressure separator, wherein the effluent is separated to produce a vapor stream comprising hydrogen, hydrocarbonaceous compounds boiling at a temperature below the boiling range of the hydrocarbonaceous feedstock, hydrogen sulfide and ammonia and a liquid stream comprising hydrocarbonaceous compounds boiling approximately in the range of said hydrocarbonaceous feedstock;   (c) passing the vapor stream of step (b) after cooling and partial condensation, to a second hot high pressure separator where it is flashed, thereby producing an overhead vapor stream and a liquid stream, wherein the liquid stream, which comprises hydrotreated hydrocarbons in the middle distillate range, is passed to a second hydroprocessing zone;   (d) passing the overhead vapor stream from the hot high pressure separator of step (c), after cooling and contact with water, said vapor stream comprising hydrogen, ammonia, hydrogen sulfide, light gases and naphtha, to a cold high pressure separator, where hydrogen, hydrogen sulfide, and light hydrocarbonaceous gases are removed overhead, ammonia is removed from the cold high pressure separator as ammonium bisulfide in the sour water stripper, and naphtha and middle distillates are passed to fractionation;   (e) passing the liquid stream from the hot high pressure separator of step (b) to a hot low pressure separator, where it is flashed to produce an overhead stream comprising gases and a liquid stream comprising unconverted oil;   (f) passing the liquid stream of step (e) which comprises unconverted oil, to a steam stripper, where a vapor stream is removed overhead and a liquid stream, which comprises stripped unconverted oil, is recovered.   
   
   
       2 . The process of  claim 1 , wherein at least a portion of the stripped unconverted oil of step (f) is passed to a fluid catalytic cracking unit as feed. 
   
   
       3 . The process of  claim 1 , wherein at least a portion of the stripped unconverted oil of step (f) is combined with the liquid effluent of step (c) to form a liquid stream which is passed to the second hydroprocessing zone. 
   
   
       4 . The process of  claim 1 , wherein the second hydroprocessing zone contains at least one bed of hydroprocessing catalyst suitable for aromatic saturation and ring opening. 
   
   
       5 . The process of  claim 4 , wherein the liquid stream is contacted under hydroprocessing conditions with the hydroprocessing catalyst, in the presence of hydrogen to produce middle distillate products. 
   
   
       6 . The process of  claim 1 , wherein the hydroprocessing conditions of step (a) comprise a reaction temperature of from 400° F.-950° F. (204° C.-510° C., a reaction pressure in the range from 500 to 5000 psig (3.5-34.5 MPa), an LHSV in the range from 0.1 to 15 hr-1 (v/v), and hydrogen consumption in the range from 500 to 2500 scf per barrel of liquid hydrocarbon feed (89.1-445 m 3  H 2 /m 3  feed). 
   
   
       7 . The process of  claim 6 , wherein the hydroprocessing conditions of step 1(a) preferably comprise a temperature in the range from 650° F.-850° F. (343° C.-454° C., reaction pressure in the range from 1500-3500 psig (10.4-24.2 MPa), LHSV in the range from 0.25 to 2.5 hr-1, and hydrogen consumption in the range from 500 to 2500 scf per barrel of liquid hydrocarbon feed (89.1-445 m 3  H 2 /m 3  feed). 
   
   
       8 . The process of  claim 1 , wherein the hydroprocessing conditions of step 1(e) comprise a reaction temperature of from 400° F.-950° F. (204° C.-510° C., a reaction pressure in the range from 500 to 5000 psig (3.5-34.5 MPa), an LHSV in the range from 0.1 to 15 hr-1 (v/v), and hydrogen consumption in the range from 500 to 2500 scf per barrel of liquid hydrocarbon feed (89.1-445 m 3  H 2 /m 3  feed). 
   
   
       9 . The process of  claim 9 , wherein the hydroprocessing conditions of step 1(e) preferably comprise a temperature in the range from 650 m 3  H 2 /m 3  feed F.-850 m 3  H 2 /m 3  feed F. (343° C.-454° C., reaction pressure in the range from 1500-3500 psig (10.4-24.2 MPa), LHSV in the range from 0.25 to 2.5 hr-1, and hydrogen consumption in the range from 500 to 2500 scf per barrel of liquid hydrocarbon feed (89.1-445 m 3  H 2 /m 3  feed). 
   
   
       10 . The process of  claim 1 , wherein the feed to step 1(a) comprises hydrocarbons boiling in the range from 500° F. to 1500° F. 
   
   
       11 . The process of  claim 1 , wherein the feed is selected from the group consisting of vacuum gas oil, heavy atmospheric gas oil, delayed coker gas oil, visbreaker gas oil, FCC light cycle oil, and deasphalted oil. 
   
   
       12 . The process of  claim 1 , wherein the hydroprocessing catalyst comprises both a cracking component and a hydrogenation component. 
   
   
       13 . The process of  claim 12 , wherein the hydrogenation component is selected from the group consisting of Ni, Mo, W, Pt and Pd or combinations thereof. 
   
   
       14 . The process of  claim 3 , wherein the cracking component may be amorphous or zeolitic. 
   
   
       15 . The process of  claim 11 , wherein the zeolitic component is selected from the group consisting of Y, USY, REX, and REY zeolites. 
   
   
       16 . The process of  claim 1 , wherein the middle distillate products produced do not require additional treatment to meet product specifications. 
   
   
       17 . The process of  claim 16 , wherein the sulfur content of jet fuel is less than 10 ppm, the smoke point is greater than 24 mm, the sulfur content of diesel is less than 10 ppm, and the cetane index is greater than 50. 
   
   
       18 . The process of  claim 1 , in which smaller amounts of hydrogen are used than in single stage once-through hydrocracking. 
   
   
       19 . The process of  claim 18 , wherein the amount of hydrogen used is 160 SCF per barrel lower than the amount used in single stage once-through hydrocracking at 60% conversion, 100 SCF per barrel lower than the amount used in single stage once-through hydrocracking at 40% conversion, and 50 SCF per barrel lower than the amount used in single stage once-through hydrocracking at 30% conversion. 
   
   
       20 . The process of  claim 1 , wherein the hydrotreating occurs in the first reaction zone and hydrocracking occurs in the second reaction zone.