Process for producing premium fischer-tropsch diesel and lube base oils

Abstract

A process for producing a premium Fischer-Tropsch diesel fuel which comprises (a) hydroprocessing a waxy Fischer-Tropsch feed to remove the oxygenates that are present in the feed, whereby a first Fischer-Tropsch intermediate product is produced with reduced olefins and oxygenates relative to the Fischer-Tropsch feed; (b) separating the first Fischer-Tropsch intermediate product in a separation zone into a heavy Fischer-Tropsch fraction and a light Fischer-Tropsch fraction under controlled separation conditions; (c) hydroisomerizing the heavy Fischer-Tropsch fraction to improve the cold flow properties of the heavy Fischer-Tropsch fraction and recovering an isomerized heavy Fischer-Tropsch fraction; (d) mixing the isomerized heavy Fischer-Tropsch fraction with at least a portion of the light Fischer-Tropsch fraction of (b); and (e) recovering from the blend a Fischer-Tropsch derived diesel product meeting a target value for at least one pre-selected specification for diesel fuel.

What we claim is:  
     
         1 . A process for producing a premium Fischer-Tropsch diesel fuel which comprises: 
 (a) treating a waxy Fischer-Tropsch feed recovered from a Fischer-Tropsch synthesis in a hydroprocessing zone under hydroprocessing conditions in the presence of a hydroprocessing catalyst intended to saturate the olefins and to remove the oxygenates that are present in the feed, whereby a first Fischer-Tropsch intermediate product is produced with reduced olefins and oxygenates relative to the Fischer-Tropsch feed;    (b) separating the first Fischer-Tropsch intermediate product in a separation zone into a heavy Fischer-Tropsch fraction and a light Fischer-Tropsch fraction under controlled separation conditions wherein the light Fischer-Tropsch fraction is characterized by an end boiling point falling within the boiling range of diesel, and the heavy Fischer-Tropsch fraction being characterized by a boiling range above that of the light Fischer-Tropsch fraction;    (c) contacting the heavy Fischer-Tropsch fraction with an hydroisomerization catalyst in a hydroisomerization zone under hydroisomerization conditions selected to improve the cold flow properties of the heavy Fischer-Tropsch fraction and recovering an isomerized heavy Fischer-Tropsch fraction;    (d) mixing the isomerized heavy Fischer-Tropsch fraction with at least a portion of the light Fischer-Tropsch fraction of (b); and    (e) recovering from the blend a Fischer-Tropsch derived diesel product meeting a target value for at least one pre-selected specification for diesel fuel.    
     
     
         2 . The process of  claim 1  wherein the hydroprocessing catalyst in the hydroprocessing zone may operate as either as a hydrotreating catalyst or as a hydrocracking catalyst depending on the hydroprocessing conditions selected.  
     
     
         3 . The process of  claim 1  wherein the conversion of the Fischer-Tropsch feed in the hydroprocessing zone is greater than 20 percent.  
     
     
         4 . The process of  claim 3  including the step of recycling part of the heavy Fischer-Tropsch fraction recovered in the separation zone back to the hydroprocessing zone.  
     
     
         5 . The process of  claim 1  wherein the conversion of the Fischer-Tropsch feed in the hydroprocessing zone is 20 percent or less.  
     
     
         6 . The process of  claim 5  wherein the conversion of the Fischer-Tropsch feed in the hydroprocessing zone is 5 percent or less.  
     
     
         7 . The process of  claim 5  wherein the hydroprocessing conditions include a hydrogen partial pressure of between about 200 psig to about 2000 psig, a temperature in the range of from about 400 degrees F. to about 800 degrees F., a LHSV of between about 0.5 and about 5.0.  
     
     
         8 . The process of  claim 5  wherein the hydroprocessing catalyst comprises at least one active metal selected from Group VIIIA of the Periodic Table of the Elements and at least one active metal selected from Group VIB of the Periodic Table of the Elements, said active metals being present on a refractory support.  
     
     
         9 . The process of  claim 5  further including the intermediate step of hydrofinishing the isomerized heavy Fischer-Tropsch fraction of step (c) in a hydrofinishing zone under hydrofinishing conditions prior to blending the first portion of the isomerized heavy Fischer-Tropsch fraction with the light Fischer-Tropsch fraction.  
     
     
         10 . The process of  claim 9  wherein the hydrofinishing conditions include a pressure between about 500 psig and about 2000 psig, a temperature of between about 400 degrees F. and about 650 degrees F., a LHSV between about 0.3 and about 5.0.  
     
     
         11 . The process of  claim 9  wherein a second portion of the hydrofinished and isomerized heavy Fischer-Tropsch fraction is also recovered separately as a lubricating base oil.  
     
     
         12 . The process of  claim 9  wherein the pressure in the hydroprocessing zone and in the hydrofinishing zone are substantially the same.  
     
     
         13 . The process of  claim 12  wherein the hydoisomerization zone is operated at a lower pressure than the hydroprocessing zone and the hydrofinishing zone.  
     
     
         14 . The process of  claim 1  wherein the light Fischer-Tropsch fraction has an end point falling within the range between about 450 degrees F. and about 750 degrees F.  
     
     
         15 . The process of  claim 1  wherein the isomerization catalyst in the catalytic dewaxing zone is a hydroisomerization catalyst.  
     
     
         16 . The process of  claim 15  wherein the hydroisomerization catalyst contains a molecular sieve selected from the group consisting essentially of ZSM-22, ZSM-23, SSZ-32, ZSM-35, ZSM48, SAPO-11, SAPO-31, and SAPO-41.  
     
     
         17 . The process of  claim 16  wherein the hydroisomerization catalyst contains an active metal selected from platinum, palladium, or a combination of platinum and palladium.  
     
     
         19 . The process of  claim 1  wherein the hydroisomerization conditions include a temperature of between about 400 degrees F. and about 800 degrees F., a pressure of from about 100 psig to about 2000 psig, and an liquid hourly space velocity of between about 0.2 hr 1  and about 5 hr 1 .  
     
     
         20 . The process of  claim 1  wherein the pre-selected specification for diesel fuel to which the Fischer-Tropsch diesel product is blended is the cold filter plugging point.  
     
     
         21 . The process of  claim 20  wherein the target value for the cold filter plugging point is 0 degrees C. or less.  
     
     
         22 . The process of  claim 21  wherein the target value for the cold filter plugging point is −20 degrees C. or less.  
     
     
         23 . The process of  claim 1  wherein the pre-selected specification for diesel fuel to which the Fischer-Tropsch diesel product is blended is cloud point.  
     
     
         24 . The process of  claim 23  wherein the target value for the cloud point is about −5 degrees C. or less.  
     
     
         25 . The process of  claim 24  wherein the target value for the cloud point is about −18 degrees C. or less.  
     
     
         26 . The process of  claim 1  wherein the pre-selected specification for diesel fuel to which the Fischer-Tropsch diesel product is blended is pour point.  
     
     
         27 . The process of  claim 26  wherein the target value for the pour point is about −15 degrees C. or less.  
     
     
         28 . The process of  claim 1  in which the separation zone of step (b) is divided into at least a first intermediate separation zone and a second intermediate separation zone and wherein the separation of step (b) includes the additional steps of (i) separately recovering from the first intermediate separation zone the heavy Fischer-Tropsch fraction and a mixture containing the light Fischer-Tropsch fraction and a hydrogen-rich C 4  minus fraction; (ii) feeding the mixture containing the light Fischer-Tropsch fraction and the hydrogen-rich C 4  minus fraction to the second intermediate separation zone; and (iii) recovering separately from the second intermediate separation zone the light Fischer-Tropsch fraction and the hydrogen-rich C 4  minus fraction.  
     
     
         29 . The process of  claim 28  wherein the hydrogen-rich C 4  minus fraction is recycled to the hydroprocessing zone.  
     
     
         30 . The process of  claim 28  wherein the hydrogen-rich C 4  minus fraction is sent to the hydroisomerization zone.  
     
     
         31 . The process of  claim 28  wherein the hydrogen-rich C 4  minus fraction is sent to a hydrofinishing zone.  
     
     
         32 . The process of  claim 28  wherein a stripping gas is used in the first intermediate separation zone to assist in recovering the mixture containing the light Fischer-Tropsch fraction and the hydrogen-rich C 4  minus fraction.