Hydrocarbon Conversion Process

Abstract

A process is provided to produce an ultra low sulfur diesel with less than about 10 ppm sulfur using a two-phase or liquid-phase continuous reaction zone to convert a diesel boiling range distillate preferably obtained from a mild hydrocracking unit. In one aspect, the diesel boiling range distillate is introduced to the liquid-phase continuous reaction zone over-saturated with hydrogen in an amount effective so that the liquid phase remains substantially saturated with hydrogen throughout the reaction zone as the reactions proceed.

1 . A process to produce low sulfur diesel comprising:
 (a) converting a hydrocarbonaceous feedstock in a hydrodesulfurization zone containing at least a hydrodesulfurization catalyst operating at conditions effective to produce a hydrodesulfurization zone effluent having a reduced concentration of sulfur;   (b) separating the hydrodesulfurization zone effluent in a fractionating zone into at least a diesel boiling range distillate having a reduced concentration of sulfur;   (c) dissolving hydrogen in the diesel boiling range distillate, the hydrogen in a form that is available for consumption in a liquid-phase continuous reaction zone; and   (d) reacting the diesel boiling range distillate in a liquid-phase continuous reaction zone having a hydrodesulfurization catalyst using the hydrogen dissolved in the distillate at conditions effective to produce a liquid-phase reaction effluent having the low sulfur diesel with an improved cetane number over the diesel boiling range distillate.   
     
     
         2 . The process of  claim 1 , wherein the liquid-phase reaction zone comprises one or more liquid-phase continuous reactors and an amount of hydrogen dissolved in the diesel boiling range distillate before entering each reactor effective to provide the reduction of the sulfur content in the distillate to less than about 10 ppm and an increase in cetane number of the distillate to greater than about 40. 
     
     
         3 . The process of  claim 1 , wherein the diesel boiling range distillate is over-saturated with hydrogen that is available for consumption in the liquid-phase continuous reaction zone. 
     
     
         4 . The process of  claim 3 , wherein the diesel boiling range distillate is up to about 1000 percent saturated with hydrogen. 
     
     
         5 . The process of  claim 3 , wherein the liquid-phase continuous reaction zone has a substantially constant amount of dissolved hydrogen throughout the reaction zone effective to produce a substantially constant reaction rate. 
     
     
         6 . The process of  claim 5 , wherein a reaction rate in the liquid-phase reaction zone remains substantially constant because consumed hydrogen in the liquid phase is replaced with hydrogen from a vapor phase. 
     
     
         7 . The process of  claim 6 , wherein the reaction proceeds in the liquid-phase reaction zone without additional sources of hydrogen external to the liquid-phase reaction zone. 
     
     
         8 . The process of  claim 1 , wherein the hydrocarbonaceous feedstock boils in the range from about 315° C. (600° F.) to about 565° C. (1050° F.). 
     
     
         9 . The process of  claim 1 , wherein the liquid-phase continuous reaction zone is operated at conditions effective to provide an effluent with a sulfur content below about 10 ppm and a centane number from about 40 to about 60. 
     
     
         10 . The process of  claim 9 , wherein the conditions of the liquid-phase reaction zone include a temperature from about 315° C. (600° F.) to about 371° C. (700° F.), a pressure from about 2.1 MPa (300 psig) to about 13.8 MPa (2000 psig), a liquid hourly space velocity from about 0.5 hr −1  to about 10 hr −1 , and about 100 to about 1000 percent saturated hydrogen. 
     
     
         11 . The process of  claim 10 , wherein about 300 SCF/B to about 400 SCF/B hydrogen is supplied to provide the hydrogen dissolved in the diesel boiling range distillate. 
     
     
         12 . A process to produce ultra low sulfur diesel comprising:
 (a) reacting a hydrocarbonaceous feedstock in a hydrotreating zone containing a hydrotreating catalyst at conditions effective to produce a hydrotreating zone effluent having less than about 2000 ppm sulfur;   (b) reacting the hydrotreating zone effluent in a hydrocracking zone containing at least a hydrocracking catalyst to produce a hydrocracking zone effluent;   (c) separating the hydrocracking zone effluent in a fractionation zone into at least a diesel boiling range distillate;   (d) reacting the diesel boiling range distillate in a liquid-phase continuous reaction zone having a hydrotreating catalyst at conditions effective to produce the ultra low sulfur diesel having less than 10 ppm sulfur and a cetane number greater than about 40; and.   (e) wherein the diesel boiling range distillate is over-saturated with hydrogen in an amount effective so that the liquid phase continuous reaction zone has a substantially constant level of dissolved hydrogen.   
     
     
         13 . The process of  claim 12 , wherein the hydrocarbonaceous feedstock includes at least 50 percent hydrocarbons with a boiling range above about 371° C. (700° F.). 
     
     
         14 . The process of  claim 12 , wherein the diesel boiling range distillate is up to about 1000 percent saturated with hydrogen. 
     
     
         15 . The process of  claim 12 , wherein the liquid-phase continuous reaction zone is operated at a temperature from about 315° C. (600° F.) to about 400° C. (750° F.), a pressure from about 2.1 MPa (300 psig) to about 13.8 MPa (2000 psig), and a liquid hourly space velocity from about 0.5 hr −1  to about 10 hr −1 . 
     
     
         16 . The process of  claim 15 , wherein the liquid-phase continuous reaction zone has a substantially constant amount of dissolved hydrogen throughout the reaction zone, and the amount of over-saturated hydrogen in the distillate being reduced as the hydrogen is consumed in the liquid-phase continuous reaction zone. 
     
     
         17 . The process of  claim 16 , wherein the hydrotreating zone is operated at a temperature from about 260° C. (500° F.) to about 482° C. (900° F.), a pressure from about 3.4 MPa (500 psig) to about 17.2 MPa (2500 psig), and a liquid hourly space velocity from about 0.5 hr −1  to about 5 hr −1  and wherein the hydrocracking zone is operated at a temperature from about 260° C. (500° F.) to about 482° C. (900° F.), a pressure from about 3.4 MPa (500 psig) to about 17.2 MPa (2500 psig), and a liquid hourly space velocity from about 0.5 hr −1  to about 5 hr −1 . 
     
     
         18 . A processing unit to produce ultra low sulfur diesel comprising:
 (a) a first reaction zone containing at least a hydrotreating catalyst and a hydrocracking catalyst operating effective to convert a hydrocarbonaceous feedstock into a first reaction zone effluent having a sulfur content greater than 10 ppm;   (b) a fractionation zone effective to separate the first reaction zone effluent into at least a diesel boiling range distillate having greater than 10 ppm sulfur;   (d) a liquid-phase continuous reaction zone containing a hydrotreating catalyst operating effective to convert the diesel boiling range distillate into the ultra low sulfur diesel having less than 10 ppm sulfur; and   (d) wherein the diesel boiling range distillate is over-saturated with hydrogen so that the liquid phase contains a substantially constant level of dissolved hydrogen as the hydrogen is consumed in the liquid-phase continuous reaction zone and the liquid-phase continuous reaction zone operates without a hydrogen gas compressor.   
     
     
         19 . The processing unit of  claim 18 , wherein the diesel boiling range distillate is up to about 1000 percent saturated with hydrogen. 
     
     
         20 . The processing unit of  claim 19 , wherein the liquid-phase continuous reaction zone includes a plurality of serial liquid-phase continuous reactors and wherein a feed stream to each of the liquid-phase continuous reactors is over-saturated with hydrogen so that the liquid phase in each reactor contains a substantially constant level of dissolved hydrogen as the hydrogen is consumed.