Hydroprocessing configuration for low sulfur diesel

Abstract

Methods are provided for producing low sulfur diesel fuels by performing multi-stage hydroprocessing at low pressure on a distillate feed. A feedstock suitable for forming a diesel fuel product is hydrotreated at a hydrogen partial pressure of 500 psig or less in at least two reaction stages. In order to provide improved desulfurization and/or aromatic saturation activity in the final stage, the stages are configured so that the highest hydrogen pressure and/or highest hydrogen purity are delivered to the last hydrotreatment stage.

What is claimed is: 
     
         1 . A method for producing low sulfur distillate products, comprising:
 exposing a feedstock having a sulfur content of at least about 1500 wppm and a first content of polyaromatic hydrocarbons to hydrotreating catalyst in the presence of a recycled hydrogen treat gas stream in at least a first reaction stage under first effective hydrotreating conditions to produce an intermediate effluent comprising at least a gas phase fraction and a liquid fraction;   separating the liquid fraction from the gas phase fraction, the separated liquid fraction having a sulfur content of at least about 250 wppm;   scrubbing the gas phase fraction to remove at least a portion of H 2 S, NH 3 , or a combination thereof from the gas phase fraction;   compressing the scrubbed gas phase fraction;   exposing the separated liquid effluent to a second hydrotreating catalyst in the presence of the compressed gas phase fraction and a fresh hydrogen treat gas stream under second effective hydrotreating conditions to produce hydrotreated effluent; and   separating the hydrotreated effluent to form at least a diesel boiling range product and a second gas phase fraction, the diesel boiling range product having a sulfur content of 25 wppm or less and a polyaromatic hydrocarbon content of about 7 wt % or less,   wherein the recycled hydrogen treat gas stream comprises at least a portion of the second gas phase fraction.   
     
     
         2 . The method of  claim 1 , wherein the effective hydrotreating conditions comprise a hydrogen partial pressure from about 300 psig (2.1 MPa) to about 800 psig (5.5 MPa), a temperature of from about 500° F. (260° C.) to about 800° F. (427° C.), and a space velocity of from about 0.3 hr −1  to about 5.0 hr −1 . 
     
     
         3 . The method of  claim 1 , wherein the effective hydrotreating conditions include a treat gas rate that provides an amount of hydrogen from about two times to about five times the hydrogen consumed during the hydrotreating. 
     
     
         4 . The method of  claim 1 , wherein the sulfur content of the diesel boiling range product is about 10 wppm or less. 
     
     
         5 . The method of  claim 1 , wherein the sulfur content of the separated liquid fraction is at least about 500 wppm. 
     
     
         6 . The method of  claim 1 , wherein the fresh hydrogen treat gas stream comprises at least about 80 wt % of hydrogen. 
     
     
         7 . The method of  claim 1 , wherein the at least a first reaction stage comprises a plurality of reaction stages, the intermediate effluent comprising an effluent produced after exposure to hydrotreating catalyst in each of the plurality of reaction stages. 
     
     
         8 . The method of  claim 7 , wherein the second hydrotreating catalyst is the same as a hydrotreating catalyst in at least one of the plurality of reaction stages. 
     
     
         9 . The method of  claim 1 , wherein separating the liquid fraction from the gas phase fraction comprises performing a flash separation on the intermediate effluent. 
     
     
         10 . The method of  claim 1 , wherein the diesel boiling range product has a polyaromatic hydrocarbon content of about 6.5 wt % or less. 
     
     
         11 . The method of  claim 1 , wherein the hydrogen partial pressure is about 500 psig (3.4 MPag) or less.