Process for reducing ultra low sulfur diesel color

Abstract

The present invention is a process for preparing ultra low sulfur diesel. The steps include reacting a feedstock of petroleum crude oil with hydrogen in the presence of a hydrodesulfurization catalyst under hydrodesulfurization conditions, fractionating the reaction products, flash distilling the bottoms fraction, condensing the volatile distillate fraction as ultra low sulfur diesel, and recycling the distillation bottoms fraction for further reacting with hydrogen.

What is claimed is: 
     
         1 . A process for preparing ultra low sulfur diesel comprising the steps of:
 (a) reacting a feedstock of petroleum crude oil with hydrogen in the presence of a hydrodesulfurization catalyst under hydrodesulfurization conditions;   (b) fractionating the reaction products into a naphtha fraction, a kerosene fraction, and a first bottoms fraction;   (c) flash distilling the first bottoms fraction in a distillation column having at least one stage and a total stage efficiency of less than about 99%, thereby yielding
 (i) a volatile distillate fraction having an ASTM Color of less than or equal to 2.5 and a sulfur content less than 15 ppm and 
 (ii) a second bottoms fraction; 
   (d) condensing the volatile distillate fraction as ultra low sulfur diesel; and   (e) recycling the second bottoms fraction into the feedstock of petroleum crude oil for further reacting of the second bottoms fraction with hydrogen in the presence of the hydrodesulfurization catalyst.   
     
     
         2 . The process of  claim 1  wherein the reacting step occurs in a hydrotreater. 
     
     
         3 . The process of  claim 1  wherein the distillation column for the flash distilling step has a stage efficiency of at least about 80%. 
     
     
         4 . The process of  claim 3  wherein the distillation column for the flash distilling step has a stage efficiency in the range of about 80% to about 99%. 
     
     
         5 . The process of  claim 4  wherein the distillation column for the flash distilling step has a stage efficiency of about 95%. 
     
     
         6 . The process of  claim 1  wherein the hydrodesulfurization catalyst is a zeolite catalyst. 
     
     
         7 . The process of  claim 1  wherein the hydrodesulfurization catalyst is a nickel molybdenum catalyst. 
     
     
         8 . The process of  claim 1  wherein the hydrodesulfurization catalyst consists of more than one hydrodesulfurization catalyst. 
     
     
         9 . The process of  claim 1  wherein the hydrodesulfurization catalyst comprises palladium. 
     
     
         10 . The process of  claim 1  wherein the hydrodesulfurization catalyst comprises platinum. 
     
     
         11 . The process of  claim 1  wherein the hydrodesulfurization catalyst comprises at least a first metal component selected from Group 8, 9, and 10 (IUPAC) metals and at least a second metal component selected from Group 6 (IUPAC) metals, on a high surface area support material. 
     
     
         12 . The process of  claim 11  wherein the first metal component is selected from the group consisting of iron, cobalt, and nickel. 
     
     
         13 . The process of  claim 11  wherein the second metal component is selected from the group consisting of molybdenum and tungsten. 
     
     
         14 . The process of  claim 11  wherein the high surface area support material is alumina. 
     
     
         15 . The process of  claim 11  wherein the reacting step occurs at a temperature of 200-485 degrees Celsius. 
     
     
         16 . The process of  claim 11  wherein the reacting step occurs at a pressure of 8-200 bar. 
     
     
         17 . The process of  claim 11  wherein the reaction has a liquid hourly space velocity of 0.1-10 hr −1 . 
     
     
         18 . A process for preparing ultra low sulfur diesel comprising the steps of:
 (a) reacting a feedstock of petroleum crude oil with hydrogen in a hydrotreater in the presence of a nickel molybdenum hydrodesulfurization catalyst under hydrodesulfurization conditions of
 (i) a temperature of 200-485 degrees Celsius, 
 (ii) a pressure of 8-200 bar, and 
 (iii) a liquid hourly space velocity of 0.1-10 hr −1 ; 
   (b) fractionating the reaction products into a naphtha fraction, a kerosene fraction, and a first bottoms fraction;   (c) flash distilling the first bottoms fraction in a distillation column having at least one stage and a total stage efficiency of less than about 99%, thereby yielding
 (i) a volatile distillate fraction having an ASTM Color of less than or equal to 2.5 and a sulfur content less than 15 ppm and 
 (ii) a second bottoms fraction; 
   (d) condensing the volatile distillate fraction as ultra low sulfur diesel; and   (e) recycling the second bottoms fraction into the feedstock of petroleum crude oil for further reacting of the second bottoms fraction with hydrogen in the presence of the nickel molybdenum hydrodesulfurization catalyst.