Patent Publication Number: US-6043178-A

Title: Midbarrel hydrocracking catalyst and preparation thereof

Description:
FIELD OF THE INVENTION 
     The present invention relates to a midbarrel hydrocracking catalyst, more particularly, to a hydrocracking catalyst of improved activity, selectivity and stability for producing middle distillates from vacuum gas oil and the like, especially of improved resistance to nitrogenous matter present in the feed material. 
     BACKGROUND OF THE INVENTION 
     Petroleum refiners usually employ hydrocracking process to produce desirable products such as turbine fuel, diesel fuel and other middle distillate products in the presence of a suitable hydrocracking catalyst. In recent years, since the vacuum gas oil becomes heavier in density and worse in quality, the hydrocracking catalysts are required to possess high activity, selectivity and stability for producing middle distillates from vacuum gas oil and the like, and especially to possess high resistance to various catalytic poison, in particular nitrogenous matter present in the feed material. Unfortunately, the prior art hydrocracking catalysts are suitable for processing a feed material with a nitrogenous matter level of no more than 10×10 -4  % by weight (calculated as nitrogen), and when the nitrogen level of the feed material increases, the hydrocracking catalyst deactivates rapidly, in order to keep the productivity of the hydrocracking process constant, the operation temperature should be increased, which incurs more operation expense. 
     Each of U.S. Pat. Nos. 4,517,033, 4,517,074, 4,563,434, 4,576,711, 4,664,776, 4,672,048 and 4,762,813 disclosed a midbarrel hydrocracking catalyst, which comprises a molecular sieve, an amorphous aluminosilicate, an alumina and hydrogenation metal components, wherein said molecular sieve is LZ-10,LZ-210, modified LZ-210 or USY. Of the molecular sieves, LZ-10 is obtained by further hydrothermally treating USY, and LZ-210 is prepared by treating NH 4  NaY molecular sieve with ammonium fluorosilicate in the presence of a buffer solution. However, when LZ-10 is used to prepare a midbarrel hydrocracking catalyst, the result catalyst achieves good selectivity to middle distillates but relatively low activity; while when LZ-210, modified LZ-210 or USY is used, the resulting catalyst possesses high activity but low selectivity to middle distillates. 
     It is known that the resistance of the hydrocracking catalyst containing a molecular sieve to nitrogenous matter can be improved by strengthening the resistance of said molecular sieve to nitrogenous matter. A known effective technique to strengthen the resistance of a molecular sieve to nitrogenous matter is treating NH 4  NaY molecular sieve with fluorosilicate salts or fluorosilic acid in the presence of a buffer solution, but such a treating process provides molecular sieve with relatively low activity and resistance to nitrogenous matter. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the invention is to provide a hydrocracking catalyst of improved activity, selectivity and stability for producing middle distillates from vacuum gas oil and the like, especially of improved resistance to nitrogenous matter, the catalyst of the present invention comprises: 
     10-75% by weight of a Y-type molecular sieve; 
     10-25% by weight of a small pore alumina; 
     0-40% by weight of an amorphous aluminosilicate; 
     0-35% by weight of a large pore alumina; 
     12-32% by weight of a Group VIB metal oxide; and 
     3-8% by weight of a Group VIII metal oxide; 
     wherein the Y-type molecular sieve is a high silica Y-type molecular sieve of a Na 2  O content of no more than 0.2% by weight, a SiO 2  to Al 2  O 3  molar ratio of 6-40, a relative crystallinity of more than 80% and a unit cell size of 2.426-2.444 nm, designated as USSSY. 
     Another object of the present invention is to provide a process for preparing a high silica Y-type molecular sieve USSSY of a Na 2  O content of no more than 0.2% by weight, a SiO 2  to Al 2  O 3  molar ratio of 6-40, a relative crystallinity of more than 80% and a unit cell size of 2.426-2.444 nm, said process comprises treating a low sodium and high silica Y molecular sieve of a Na 2  O content of no more than 0.2% by weight, a SiO 2  to Al 2  O 3  molar ratio of 6-40, a relative crystallinity of more than 95% and a unit cell size of 2.444-2.455 nm at 500-700° C. under a steam pressure of 0.05-0.2 MPa for 0.5-2 hours. 
     A still another object of the present invention is to provide a preparation process for a hydrocracking catalyst of improved activity, selectivity and stability for producing middle distillates from vacuum gas oil and the like, the process of the present invention comprises: 
     adding dilute nitric acid to a small pore alumina and comulling to form an adhesive; and 
     mixing a USSSY, an adhesive, a Group VIB element salt or oxide and/or a Group VIII element salt or oxide, and optionally a large pore alumina and an amorphous aluminosilicate, and kneading, then drying at 100° C.-150° C. for 3-6 hours, finally calcining at 450-650° C. for 3-6 hours to give a catalyst; or 
     mixing a USSSY, an adhesive, and optionally a large pore alumina and an amorphous aluminosilicate, kneading, drying at 100-150° C. for 3-5 hours, calcining at 450-650° C. for 3-5 hours to give a support, impregnating said support with an aqueous solution containing a Group VIB element and/or a Group VIII element, then drying at 100-150° C. for 3-6 hours and finally calcining at 450-650° C. for 3-6 hours to give a catalyst. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The inventors carried out extensive investigation on catalyst systems applied in the hydrocracking process and found that a high silica Y-type molecular sieve of a Na 2  O content of no more than 0.2% by weight, a SiO 2  to Al 2  O 3  molar ratio of 6-40, a relative crystallinity of more than 80% and a unit cell size of 2.426-2.444 nm possesses improved activity, selectivity and superior resistance to nitrogenous matter under hydrocracking process conditions, and that when such a molecular sieve is used to prepare a hydrocracking catalyst, the resulting catalyst achieves unexpectedly improved activity and selectivity for producing middle distillates from vacuum gas oil and the like, in addition to improved resistance to nitrogenous matter present in the feed material. 
     The hydrocracking catalyst of the present invention comprises a Y-type molecular sieve, a small pore alumina, a Group VIB element oxide and/or a Group VIII element oxide, and optionally an amorphous aluminosilicate and a large pore alumina. 
     The Y-type molecular sieve used in the present invention is a high silica Y-type molecular sieve of a Na 2  O content of no more than 0.2% by weight, a SiO 2  to Al 2  O 3  molar ratio of 6-40, a relative crystallinity of more than 80% and a unit cell size of 2.426-2.444 nm, and is designated as a molecular sieve USSSY. Such a USSSY is included in the present catalyst at a level of 10-75% by weight. 
     The USSSY can be preferably prepared from a Y molecular sieve of a Na 2  O content of no more than 0.2% by weight, a SiO 2  to Al 2  O 3  molar ratio of 6-40, a relative crystallinity of more than 95% and a unit cell size of 2.444-2.455 nm, by hydrothermally treating said Y molecular sieve at 500-700° C. under a steam pressure of 0.05-0.2 MPa for 0.5-2 hours. Said Y molecular sieve is one preferably prepared by treating a NaY and/or NH 4  NaY in the absence of any pH regulating agent, detailed as in, for example, Chinese Patent Application No. CN90102645.X 
     The process for preparing the low-sodium-high-silica Y-type molecular sieve is identical with that disclosed in CN90102645.X, and comprises the steps of: 
     (1) mixing the raw material Y type molecular sieve (NH 4  NaY or NaY) with water to give a slurry having a concentration of 5-30 g of the raw material Y type molecular sieve per 100 ml of the slurry and heating the slurry to a reaction temperature of 50-120° C.; 
     (2) allowing to react by adding generally at an adequately slow rate of 30 g max., preferably 5-25 g, of crystalline ammonium hexafluorosilicate or equivalent aqueous solution thereof per 100 g Y type molecular sieve/hour. 
     (3) continuously stirring the mixture within 0.1-24 hours after completion of the addition of ammonium hexafluorosilicate while maintaining the reaction temperature at 50-120° C.; 
     (4) separating the product from the reaction mixture; 
     (5) washing with water, filtering and drying the isolated low-sodium-high-silica Y type molecular sieve and sodium ammonium fluoroaluminate crystal to give the end product. 
     The small pore alumina used in the present invention, commercially available from, for example, No. 3 Refinery of Fushun, P.R. China, is of a pseudoboehmite phase. Its pore volume is 0.40-0.60ml/g, surface area 180-340 m 2  /g, alumina trihydrate content less than 3% by weight. Said small pore alumina is present in the present catalyst at a level of 10-25% by weight. 
     The amorphous aluminosilicate used herein is present in the catalyst at a level of 0-40% by weight. Its SiO 2  content is 10-90% by weight, pore volume 0-56-1.08 ml/g, surface area 220-460 m 2  /g. It can be prepared by conventional process, such as depositing SiO 2  upon porous Al 2  O 3  to give an amorphous aluminosilicate cogel or graft copolymer, or by depositing Al 2  O 3  upon porous SiO 2  to give said cogel or graft copolymer according to U.S. Pat. No. 4,517,073. Such an amorphous aluminosilicate is also available from for example No. 3 refinery of Fushun, P.R. China. When there is no amorphous aluminosilicate present in the present catalyst, the catalyst will become more suitable for producing light oils, but still possess high resistance to nitrogenous matter. 
     The large pore alumina used in the invention, commercially available from for example No. 3 Refmery of Fushun, P.R. China, possesses a pore volume of 0.8-1.1 ml/g, a surface area of 230-400m 2  /g, an alumina trihydrate content of less than 2% by weight. Its content in the present catalyst is 0-35% by weight. 
     The hydrogenation metals used in the present invention are a Group VIB element and/or a Group VIII element of the periodic table of elements, their contents in oxide form in the catalyst are 12-32% by weight and 3-8% by weight respectively. The Group VIB elements are preferably W and/or Mo, and the Group VIII elements are preferably Ni and/or Co, the metals can be used in combination or singly. 
     To produce the present catalyst, one can first prepare an adhesive by comulling a mixture of a small pore alumina and a nitric acid solution, then mechanically mix the hydrogenation metal oxides and/or insoluble salts thereof, a molecular sieve, an adhesive, and optionally a large pore alumina and an amorphous aluminosilicate, or alternatively, impregnate a support prepared from a mixture of a molecular sieve, an adhesive, and optionally an amorphous aluminosilicate and a large pore alumina with a solution of soluble salts of said hydrogenation elements, and knead, then dry at 100-150° C. for 3-6 hours and finally calcining at 450-650° C. for 3-6 hours to give the catalyst. Said support can be prepared by kneading said mixture, then drying at 100-150° C. for 3-5 hours, and finally calcining at 450-650° C. for 3-5 hours. Said metal oxide can be, for example, MoO 3 , WO 3 , NiO, CoO and Co 2  O 3  etc., said insoluble salts can be, for example, NiCO 3 , CoCO 3  etc. Said soluble salts can be, for example, Ni(NO 3 ) 2 , Co(NO 3 ) 2 , (NH 4 ) 2  MoO 4  and (NH 4 ) 2  W 4  O 13 . Soluble acid of th corresponding element can also be used. 
     The present catalyst can be moulded into any form suitable for hydrocracking process before putting into use. The operation temperature for the catalyst is preferably 300-400° C., the hydrogen partial pressure is preferably 5-20 MPa. 
     By utilizing a USSSY, the molecular sieve of improved activity, selectivity and improved resistance to nitrogenous matter, the present catalyst can achieve improved activity, selectivity and stability for producing middle distillates from vacuum gas oil and the like, even at a nitrogenous matter level of up to 30×10 -4  % by weight (calculated as nitrogen, and the same below) of a feed material. 
    
    
     The present invention will be described in more detail by way of the nonlimiting examples below. 
     EXAMPLE 1 
     A low sodium and high silica Y molecular sieve is prepared according to CN 90102645.X. The said Y molecular sieve is treated at 600° C. under a steam pressure of 0.1 MPa for 1 hour to give USSSY-1. 
     EXAMPLE 2 
     The Y molecular sieve prepared as in Example 1 is treated at 500° C. under a steam pressure of 0.05 MPa for 1 hour to give USSSY-2. 
     EXAMPLE 3 
     The Y molecular sieve prepared as in Example 1 is treated at 550° C. under a steam pressure of 0.2 MPa for 1 hour to give USSSY-3. 
     The properties of USSSYs prepared in Example 1 to Example 3 are shown in Table 1. 
     
                       TABLE 1                                                     
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Properties of USSSYs                                                      
               USSSY-1    USSSY-2  USSSY-3                                
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molar ratio of SiO.sub.2 to Al.sub.2 O.sub.3                              
               10.01       10.05    9.99                                  
  unit cell size, nm                        2.440    2.438     2.439      
                                    relative crystallinity, %             
                                       99       110       103             
  Na.sub.2 O content, % by weight                0.05     0.2             
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                                   0.05                                   
 
    
     EXAMPLE 4 
     440 ml of 0.2N HNO 3  solution is added to 75.4 g of a small pore alumina Al 2  O 3  of a pore volume of 0.47 ml/g and a surface area of 280 m 2  /g (available from No. 3 Refinery of Fushun, P.R. China). This mixture is mulled to give an is adhesive (the same in all examples.) 180.5 g of USSSY-1, 100.8 g of H 2  WO 4 , 82.8 g of Ni(NO 3 ) 2 .-6H 2  O and the prepared adhesive are subjected to comulling in a grinder into a paste which is then extruded. The extrudate is allowed to dry, then further dried at 110° C. for 3 hours, and finally calcined in the stream of air at 500° C. for 5 hours to give Catalyst A. 
     EXAMPLE 5 
     80.8 g of USSSY-2, 40.7 g of an amorphous aluminasilicate of a pore volume of 0.64 m 1  /g and a surface area of 310 m 2  /g, 40.7 g of large pore Al 2  O 3  of a surface area of 350 m 2  /g and a pore volume of 0.90 ml/g (available from No. 3 Refinery of Fushun) and 105.5 g of adhesive prepared as in Example 4 are subjected to comulling in a grinder into a paste which is then extruded. After being dried, the extrudate are calcined at 600° C. for 5 hours to give a carrier. The carrier obtained is impregnated with a mixture of an aqueous solution of ammonium metatungstate and nickelous nitrate, dried at 110° C. for 3 hours and finally calcined at 500° C. for 4.5 hours to give Catalyst B. 
     EXAMPLE 6 
     A mixture of 40.9 g of USSSY-3, 88.2 g of large poreAl 2  O 3  of a pore volume of 0.90 ml/g and a surface area of 350 m 2  /g, 105.0 g of H 2  WO 4 , 88.2 g of Ni(NO 3 ) 2  -6H 2  O and 220.5 adhesive prepared as in Example 4 is extruded, dried at 110° C. for 5 hours and finally calcined at 500° C. for 6 hours to give Catalyst C. 
     EXAMPLE 7 
     A mixture of 80 g of USSSY-3, 19.2 g of a large pore Al 2  O 3 , 48g of an amorphous aluminosilicate and 40g of adhesive prepared as in Example 4 is extruded, dried at 110° C. for 5 hours and calcined at 650° C. for 3 hours. The carrier thus obtained is impregnated with a mixture solution of ammonium metatungstate and nickelous nitrate which contains 54.07 g of WO 3  /100 ml and 9.38 g of NiO/100 ml respectively, dried at 110° C. for 6 hours and calcined at 500° C. for 6 hours to give Catalyst D. 
     EXAMPLE 8 
     Catalyst E is prepared in the same procedures as in Example 7 except that the large poreAl 2  O 3  is not used. 
     Compositions of catalysts of Example 4 to Example 8 are as follows: 
     
                       TABLE 2                                                     
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Catalyst Compositions                                                     
  Catalyst        A       B     C    D    E                               
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composition, % by weight                                                  
              48.8    28.6   13.0  40   40                                
  USSSY                                                                   
  small pore Al.sub.2 O.sub.3   20.4  14.4 21.0   20    20                
  large pore Al.sub.2 O.sub.3   --  11.2 28.0   16    --                  
  amorphous aluminosilicate     --  16.8  --  24    40                    
  WO.sub.3                       25.1  24.1 31.0 24.06  20.91             
  NiO                            5.6  4.9  7.0   3.62  7.23               
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     COMPARATIVE EXAMPLE 1 
     A mixture of 15 g of MoO 3 , 20 g of Ni(NO 3 ) 2  -6H 2  O, 59.9 g of a USY molecular sieve available from No. 3 Refinery of Fushun, P.R. China and 66.7 g of an adhesive prepared as in Example 4 is comulled in a grinder into a paste, which is then extruded, dried at 105° C. for 3 hours and calcined at 500° C. for 4 hours to give comparative Catalyst A&#39;. 
     COMPARATIVE EXAMPLE 2 
     Comparative Catalyst B&#39; is prepared according to the procedures as described in U.S. Pat. No. 3,897,327. 
     COMPARATIVE EXAMPLE 3 
     Comparative Catalyst C&#39; is prepared according to the procedures as described in U.S. Pat. No. 4,664,776. 
     Compositions of comparative catalysts are as follows: 
     
                       TABLE 3                                                     
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Compositions of Comparative Catalysts                                     
    Catalyst           A&#39;        B&#39;    C&#39;                                 
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composition, % by weight USSSY                                            
                   60        16     40                                    
  small pore A1.sub.2 O.sub.3                  20     20    20            
  large pore A1.sub.2 O.sub.3                  --   36    16              
  amorphous aluminosilicate                    --   28    24              
  WO.sub.3                                   15(Mo.sub.3)   20.87 23.0    
                                     NiO                                  
                                           5     6.0   3.5                
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     EXAMPLE 9 
     Evaluation of Catalytic Activity 
     Catalysts are evaluated by a single-stage once-through operation in a 200 ml small scale reactor. Vacuum gas oil is pre-treated by hydrorefining to remove hetero-atoms, hydrogenate aromatics, and to keep nitrogen and sulphur at certain levels. The sulphur level is finally controlled at about 0.3% by weight (if necessary, CS 2  can be injected) before contacting the catalyst. The properties of the pre-treated vacuum gas oil to be used as feed material are as follows: 
     
                       TABLE 4                                                     
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Properties of the Vacuum Gas Oil                                          
  Pre-treated Vacuum Gas Oil NO.                                          
                     1         2     3                                    
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density (D.sub.4.sup.20), g/cm.sup.3                                      
                 0.9176    0.8732  0.8792                                 
  distillation range, ° C.                                         
  initial point                      262     272     280                  
  50%                                427     425     391                  
  95%                                512     502     457                  
  dry point                          520     --    470                    
  sulfur, 10.sup.-4 w %        34    41     34                            
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     (1) Comparison between A and A&#39; 
     Activities of Catalyst A and A&#39; are evaluated for comparison, using pre-treated vacuum gas oil 1 as feed material. Process conditions and results are as follows: 
     
                       TABLE 5                                                     
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Catalyst               A        A&#39;                                        
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reaction conditions                                                       
  H2 partial pressute, MPa                 7.8      7.8                   
  hydrocracking temperature, ° C.     375      375                 
  volume space velocity, h.sup.-1       1.81      1.34                    
  H.sub.2 /oil ratio, v/v               1500:1   1500:1                   
  nitrogen level of feed material, 10.sup.-4 % by weight    25.8     3.8  
                                 product distribution, % by weight        
                                 C1-C4                                 -- 
                                    5.9                                   
  C5-65° C.                           3.2      4.5                 
  65-177° C.                       32.3     27.8                   
  177-340° C.                         35.8     33.4                
  &gt;340° C.                            26.8     30.2                
  &lt;340° C.                            71.3     65.7                
  product properties                                                      
  65-177° C. naphtha                                               
  density(D.sub.4.sup.20), g/cm.sup.3                 0.7570   0.7579     
                                 aromatic potential content, % by weight  
                                      65       52                         
  177-340° C. diesel oil                                           
  density(D.sub.4.sup.20), g/cm.sup.3         0.8249   0.8254             
  hexadecane value                            47.1     47.1               
  solidification point, ° C.           &lt;26      &lt;-30               
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     As shown in Table 5, Catalyst A of the invention possesses higher activity and resistance to nitrogen. Furthermore, less gas and a naphtha of higher aromatic potential are produced in the presence of Catalyst A of the invention. 
     (2) Activity Evaluation for Catalyst A, B and C 
     Catalysts A, B and C. are evaluated using pre-treated vacuum gas oil 2 as the feed material under the same operation conditions: hydrogen partial pressure, 14.7 MPa; H 2  /oil ratio, 1500:1 (v/v); volume space velocity, 1.5h -1  ; nitrogen level, 18×10 -4  % by weight. Results are as follows: 
     
                       TABLE 6                                                     
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Evaluation of Catalysts A, B and C                                        
  Catalyst           A         B     C                                    
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reaction temp., ° C.                                               
                 374       370     355                                    
  product distribution, % by weight                                       
  &lt;65° C.                      3.7    5.6  1.8                     
  65-180° C.                  50.8   46.2 26.6                     
  180-320° C.                 29.78  32.7 31.4                     
  yield                               93.6   94.7 99.8                    
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     As shown in Table 6, under various operation temperature, the catalysts of the invention achieve high activities and produce acceptable products. 
     (3) Test on Selectivities of Catalysts D, E, B&#39; and C&#39; to Middle Distillates. 
     Operation conditions and results for this test are shown in Table 7 and 8, respectively. 
     
                       TABLE 7                                                     
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Operation Conditions                                                      
                          Pre-treated Vacuum                              
                          gas oil 3, 18 × 10.sup.-4 %               
  Feed Material           by weight of N                                  
______________________________________                                    
conversion of fractions with b.P. less than                               
                      60                                                  
  350° C., % by weight                                             
  H.sub.2 partial pressure, MPa            14.7                           
  volume space velocity, h.sup.-1          1.5                            
  H.sub.2 /oil ratio, v/v                  1500:1                         
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                       TABLE 8                                                     
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Evaluation Results                                                        
                            Selectivityto middle                          
  Catalyst       Reaction Temp, ° C.   distillates*                
______________________________________                                    
D         358                 76.2                                        
  E                 360                    75.8                           
    B&#39;         371                    76.4                                
   C&#39;            358                    74.7                              
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 *selectivity to middle distillates = (weight of 132-350° C.       
 fractions)/(weight of 60-350° C. fractions)                       
 
    
     As shown in Table 8, when selectivity of the catalyst of the invention to middle distillates is equal to that of Catalyst B&#39;, the reaction temperature with the catalyst of the invention can be decreased by 13-15° C. At the same reaction temperature, selectivity of Catalyst E is increased by 1.1% by weight compared with Catalyst C&#39;. 
     EXAMPLE 10 
     Catalyst A is evaluated under different pressures. Pre-treated vacuum gas oil 2 is used and the results are shown in Table 9. 
     
                       TABLE 9                                                     
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Evaluation of Catalyst A Under Various Pressures                          
H.sub.2 partial pressure, MPa                                             
               9.8       7.84      6.37                                   
  reaction temp, ° C.               365       365        368       
                                    N content in feed material      8.5   
                                       13.5       17.1                    
  10-4% by weight                                                         
  density of the product oil 0.7655  0.7844  0.7909                       
  (D.sub.4.sup.20), g/cm.sup.3                                            
  product distribution, %                                                 
  by weight                                                               
  &lt;65° C.                       4.6       3.5        3.1           
  65-180° C.                    36.0      27.9       25.1          
  180-350° C.                   32.4      32.8       33.8          
  &gt;350° C.                      24.8      30.7       36.4          
  properties of the product                                               
  6514 180° C. naphtha                                             
  PNA          52.2/43.1/4.7  46.7/45.6/7.7  47.0/43.5/9.5                
  aromatic potential content,   45.3  50.9  50.7                          
  % by weight                                                             
  180-350° C. diesel oil                                           
  Solidification point, .sub.-- ° C.  -- -16   -12                 
  diesel index   --         70.8       64.7                               
  BMCI value of &gt;350° C.         9.1       10.7       8.5          
  tail oil                                                                
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     As shown in Table 9, desirable products can be produced under middle pressure even when nitrogen content in feed material is relatively high. 
     EXAMPLE 11 
     Stability Tests of the Catalysts 
     (1) Stability Test of Catalyst A 
     Stability of Catalyst A is tested for 2100 hours under 7.8 MPa using pre-treated vacuum gas oil 1 with a nitrogen content in the range of 20-30×10 -4  % by weight. When 60% conversion of fractions with a b.P. less than 320° C. is kept constant, the reaction temperature is only increased by 3° C. and the increase rate of temperature is 0.034° C./day, which indicates that catalyst of the invention has relatively high activity and stability even when nitrogen content is high. 
     (2) Stability Test of Catalyst D 
     Stability of Catalyst D prepared in Example 8 is tested for 5212 hours under the same operation conditions as those in (3) of Example 9. The reaction temperature is only increased by 5° C. during the whole operation, which means that the catalyst of the invention possesses good stability.