Multi-stage hydrocracker with kerosene recycle

Abstract

This invention relates to a multi-stage process for hydroprocessing gas oils. Preferably, each stage possesses at least one hydrocracking zone. The second stage and any subsequent stages possess an environment having a low heteroatom content. Light products, such as naphtha, kerosene and diesel, may be recycled from fractionation (along with light products from other sources) to the second stage (or a subsequent stage) in order to produce a larger yield of lighter products, such as gas and naphtha. Subsequent zones are maintained at a lower pressure than that of the first zone, thereby reducing operating expenses.

What is claimed is:  
     
         1 . A method for hydroprocessing a hydrocarbon feedstock, the method employing multiple hydroprocessing zones within a single reaction loop and 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 to produce a vapor stream and a liquid stream as effluent;    (b) removing the vapor stream of step (a), which comprises hydrogen, hydrogen sulfide and light hydrocarbonaceous gases overhead;    (c) combining the liquid stream of step (b) with the liquid effluent from other hydroprocessing zones;    (d) passing the liquid stream of step (c), which comprises hydrocarbonaceous compounds boiling in approximately the same range of the hydrocarbonaceous feedstock, to fractionation;    (e) separating the liquid stream of step (d), in fractionation, into gas, naphtha, kerosene and diesel fractions, in addition to the bottoms fraction;    (f) passing the bottoms fraction of step (e) to further processing or recycling to one or more of the other hydroprocessing zones of step (c);    (g) passing one or more of the naphtha, kerosene and diesel fractions to further processing as products or recycling one or more of the fractions to one or more of the other hydroprocessing zones of step (c), the kerosene, naphtha or diesel fractions being in combination with kerosene, naphtha or diesel fractions from other sources, said hydroprocessing zone or zones being maintained at hydroprocessing conditions and at lower pressure than the first hydroprocessing zone, and possessing an environment substantially free of H 2 S, NH 3 , or other heteroatom contaminants;    (h) passing the effluent of step (g) to fractionation;    (i) recovering in fractionation an increased amount of gas and naphtha, and a decreased amount of kerosene, in the fractionation stage of step (h) than in the fractionation step of step (e).    
     
     
         2 . The process of  claim 1 , wherein the pressure in the subsequent zone or zones of  claim 1 , step (g), are at least 100 psi lower than the pressure in the initial zone.  
     
     
         3 . The process of  claim 2 , wherein the pressure in the subsequent zone or zones of  claim 1  is from 500 to 1000 psig lower than the pressure in the initial zone.  
     
     
         4 . The process of  claim 1 , wherein at least one bed in each hydroprocessing zone contains hydrocracking catalyst.  
     
     
         5 . The process of  claim 1 , wherein the hydroprocessing conditions of  claim 1 , step (a), and  claim 1 , step (g), 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).  
     
     
         6 . The process of  claim 5 , wherein the hydroprocessing conditions of  claim 1 , step (a), and  claim 1 , step (g), 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).  
     
     
         7 . The process of  claim 1 , wherein the feed to  claim 1 , step (a), comprises hydrocarbons boiling above 392° F.(200° C.).  
     
     
         8 . The process of  claim 7 , wherein the feed is selected from the group consisting of vacuum gas oil, heavy atmospheric gas oil, delayed coker gas oil, visbreaker gas oil, demetallized oils, FCC light cycle oil, vacuum residua deasphalted oil, Fischer-Tropsch streams, and FCC streams.  
     
     
         9 . The process of  claim 1 , wherein the hydroprocessing catalysts of the first hydroprocessing zone of  claim 1 , step (a), and the hydroprocessing zone of  claim 1 , step (g), comprise a cracking component and a hydrogenation component.  
     
     
         10 . The process of  claim 9 , wherein the hydrogenation component is selected from Group VI, Group VII or Group VIII metals.  
     
     
         11 . The process of  claim 10 , wherein the hydrogenation component is selected from the group consisting of Ni, Mo, W, Pt and Pd or combinations thereof.  
     
     
         12 . The process of  claim 10 , wherein the Group VI, Group VII or Group VIII metals may exist as either sulfides or oxides.  
     
     
         13 . The process of  claim 10 , wherein the hydrogenation component comprises 5 to 40 wt % of the catalyst.  
     
     
         14 . The process of  claim 11 , wherein noble metals comprise from about 0.1 wt % to about 2 wt % of the catalyst.  
     
     
         15 . The process of  claim 9 , wherein the cracking component may be amorphous or zeolitic.  
     
     
         16 . The process of  claim 15 , wherein the zeolitic component is selected from the group consisting of Y, USY, REX, and REY zeolites.  
     
     
         17 . The process of  claim 1 , step (i), wherein an increased amount of naphtha boiling in the range of 170-350° F. is recovered.