Abstract:
Process for catalytic steam reforming of a carbonaceous feedstock with improved resistance to sulphur poisoning and sintering characterized by contacting the feedstock with a nickel catalyst supported on magnesium aluminum spinel, MgO·xAl 2 O 3 , wherein the spinel support has a specific surface area A sp [m 2 /g] higher than 400·exp(−T c /400° C.) obtained by calcination at a temperature T c [° C.].

Description:
This application claims the benefit of the U.S. Provisional Application No. 60/113,544, filed Dec. 22, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to steam reforming of hydrocarbons by contact with a supported nickel catalyst having improved activity and resistance to sulphur poisoning. 
     In particular, the invention is directed to an improved catalyst support material of high surface spinel, optionally promoted by Group III, IV or lanthanide metals. High surface spinel carrier materials provide a much improved sulphur resistance when employing hydrocarbon feedstock with high content of sulphur compounds due to a reduced degree of sulphur coverage on the carrier surface. Thereby, retaining sufficient catalytic activity with sulphur compounds containing feedstock. 
     The surface area of the carrier depends on the calcination temperature actually employed in the preparation of the carrier. 
     SUMMARY OF THE INVENTION 
     It has been found that spinel carrier material having a specific surface higher than or equal to a certain value after calcination at a predetermined calcination temperature posses the above advantageous properties. 
     Accordingly, the invention provides a process for catalytic steam reforming of a carbonaceous feedstock with improved resistance to sulphur poisoning and sintering characterised by contacting the feedstock with a nickel catalyst supported on magnesium aluminum spinel, MgO.xAl 2 O 3 , with a specific surface area, A sp [m 2 /g], higher than expressed by the formula A sp =400·exp(−T c /400° C.) obtained by calcination at a temperature T c [° C.] where T c ≧400° C. 
     As mentioned herein before, steam reforming activity of the spinel supported nickel catalyst is further improved when promoting the catalysts by inclusion of additional metals. 
     Preferred metals are Zr, Y, W, La, Ce or a mixture of lanthanides including La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, commercially available as lanthanide concentrate. The above metal promoters are preferably included in the catalyst in a total amount of 0.01% to 10% by weight, most preferred in an amount of 0.5% to 5% by weight. The nickel content in the catalyst will be between 10% and 60% by weight, preferably between 15% and 40% by weight. 
     When operating the inventive process in industrial scale, it may be sufficient to arrange the above catalyst as top layer in a catalyst bed of a conventional nickel steam reforming catalyst. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The above and further aspects and features of the invention will become more apparent from the following description illustrating by example specific embodiments of the invention. 
     EXAMPLE 1 
     Preparation of High Surface Area Spinel 
     Preferably, the first precipitation step is conducted under an atmosphere containing no water vapour to prevent hydrolysis of the aluminum alcoxide. In practise, the precipitation can be conducted under ambient conditions as long as excessive storage under these conditions is not required. 
     A solution was prepared by dissolution of 1 kg (4.05 mole) of aluminum tri-sec-butoxide, Al(C 4 H 9 O) 3 , with stirring in a tank equipped with a condenser containing 20 kg of 1-propanol. Another solution containing 0.520 kg (2.02 mole) of magnesium nitrate hexahydrate, Mg(NO 3 ) 2 ·6H 2 O, dissolved in 1 kg of water and 10 kg of 1-propanol was rapidly added to the solution of Al(C 4 H 9 O) 3  with intense stirring and a white precipitate formed. After 30 min. the precipitate was isolated by filtration, washed with 10 kg water and dried at 110° C. Calcination at 550° C. for 4 hours yielded 0.275 kg of a pure MgAl 2 O 4  spinel with a lattice constant of 8.076 Å, a crystal size of 41 Å and a surface area of 192 m 2 /g. 
     Generally, this method can be applied using any aluminum alcoxide Al(OR) 3  precursor and any alcohol solvent (R=alkyl). 
     EXAMPLE 2 
     Preparation of High Surface Area Spinel 
     Preferably, the first precipitation step is conducted under an atmosphere containing no water vapour to prevent hydrolysis of the aluminum and magnesium alcoxide. In practise, the precipitation can be conducted under ambient conditions as long as excessive storage under these conditions is not required. 
     A solution was prepared by dissolution of 1 kg (6.18 mole) of aluminum triethoxide and 0.352 kg (3.08 mole) of magnesium ethoxide with stirring in a tank equipped with a condenser containing 30 kg of 99% ethanol. 1.5 kg of water was added to the solution with intense stirring and immediately a white precipitate formed. After 30 min. the white filtrate was collected by filtration. Upon calcination at 550° C. for 4 hours 0.423 kg of a pure MgAl 2 O 4  spinel is obtained with a lattice constant of 8.081 Å, a crystal size of 45 Å and a surface area of 183 m 2 /g. 
     Generally, this method can be applied using any alcoxides of magnesium and aluminum. The alcohol can be recovered from the aqueous filtrate by distillation—the details being dependent on the alcohol and alcoxides used. 
     EXAMPLE 3 
     Steam Reforming Activity 
     A series of nickel catalysts containing 10% to 60% by weight of nickel and containing varying contents of Zr, La, Ce, Y, or W (stabilizer), where prepared by sequential impregnations of a shaped high surface area magnesium aluminum spinel carrier by methods known in the art with nickel nitrate and ziconyl nitrate, ZrO(NO 3 ) 2 , zirconium carbonate, Zr(CO 3 ) 2 , basic zirconium carbonate, Zr(CO 3 ) x (OH) 4−2x , X&lt;2, lanthanum nitrate, La(NO 3 ) 3 , cerium nitrate, Ce(NO 3 ) 3 , yttrium nitrate, Y(NO 3 ) 3 , or ammonium decatungstate, (NH 4 ) 6 H 2 W 12 O 40 . Before the impregnation with the stabilizer, the nickel nitrate was decomposed. After drying the tablets were loaded in a reactor and activated during heating to a temperature between 500° C. and 850° C. in a hydrogenflow containing 1% steam at atmospheric pressure. 
     The steam reforming activity was determined under the following conditions: 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Catalyst sieve fraction, 
                 mm 
                 0.3-0.5 
               
               
                   
                 Catalyst amount, 
                 g 
                 0.025 
               
               
                   
                 Temperature, 
                 ° C. 
                 400-750 
               
               
                   
                 Feed gas composition, 
                 Nl/h 
               
               
                   
                 NH 4   
                 4.0 
               
               
                   
                 H 2 O 
                 16.0 
               
               
                   
                 H 2   
                 1.6 
               
               
                   
                   
               
             
          
         
       
     
     The activities obtained at 500° C. are shown in Table 1. 
     Steam reforming activity of stabilized and unstabilized catalysts, here shown with 25% by weight nickel, relative to low surface area spinel (less than 25 m 2 /g) supported nickel catalyst, R67GR obtained from Haldor Topsøe A/S, Nymøllevej 55, DK-2800 Lyngby, Denmark, at 500° C. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Stabilizer content 
                   
               
               
                   
                 Catalyst 
                 (weight %) 
                 Relative Activity 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 R67GR 
                 0 
                 100 
               
               
                   
                 Catalyst 1 
                 0 
                 142 
               
               
                   
                 Catalyst 2 
                  1.7% La 
                 149 
               
               
                   
                 Catalyst 3 
                  1.6% Y 
                 162 
               
               
                   
                 Catalyst 4 
                 0.95% Zr 
                 156 
               
               
                   
                 Catalyst 5 
                  4.4% w 
                 87 
               
               
                   
                 Catalyst 6 
                  3.1% Ce 
                 151 
               
               
                   
                   
               
             
          
         
       
     
     It is apparent from Table 1 that stabilizers Zr, L, Ce, Y have only minor influence on the steam reforming activity compared to the pure nickel catalyst. W stabilizer decreases the steam reforming activity. 
     EXAMPLE 4 
     Sulphur Poisoning Capacity 
     A series of nickel catalysts containing 10% to 60% by weight of nickel and containing varying contents of Zr, La, Ce, Y, or W (stabilizer) where prepared by sequential impregnations of a shaped high surface area magnesium aluminum spinel carrier by methods known in the art with nickel nitrate and zirconyl nitrate, ZrO(NO 3 ) 2 , zirconium carbonate, Zr(CO 3 ) 2 , basic zirconium carbonate, Zr(CO 3 )x(OH) 4−2x , x&lt;2, lanthanum nitrate, La(NO 3 ) 3 , cerium nitrate, Ce(NO 3 ) 3 , yttrium nitrate, Y(NO 3 ) 3 , or ammonium decatungstate, (NH 4 ) 6 H 2 W 12 O 4 0. Before the impregnation with the stabilizer, the nickel nitrate was decomposed. After drying the tablets were loaded in a reactor and activated during heating to a temperature between 500° C. and 850° C. in a hydrogenflow containing 1% steam at atmospheric pressure. 
     The capacity against sulphur poisoning was determined under conditions described by I. Alstrup et al. in Applied Catalysis, 1 (1981) 303-314 with dihydrogen sulphide content in the hydrogen flow between 10 ppm and 12 ppm. The sulphur poisoning capacities obtained at 550° C. are shown in Table 2. 
     Capacity against sulphur poisoning of stabilized and unstabilized catalysts, here shown with 25% by weight nickel, relative to low surface area spinel (less than 25 m 2 /g) supported nickel catalyst, R67GR obtained from Haldor Topsøe A/S, Denmark, at 500° C. 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Stabilizer content 
                 Capacity against 
               
               
                   
                 Catalyst 
                 (weight %) 
                 sulphur poisoning 
               
               
                   
                   
               
             
             
               
                   
                 R67GR 
                 0 
                 100 
               
               
                   
                 Catalyst 1 
                 0 
                 231 
               
               
                   
                 Catalyst 2 
                  1.7% La 
                 239 
               
               
                   
                 Catalyst 3 
                  1.6% Y 
                 254 
               
               
                   
                 Catalyst 4 
                 0.95% Zr 
                 231 
               
               
                   
                 Catalyst 5 
                  4.4% W 
                 219 
               
               
                   
                 Catalyst 6 
                  3.1% Ce 
                 296 
               
               
                   
                   
               
             
          
         
       
     
     It is apparent from Table 2 that catalyst based on high surface area spinel have increased capacity against sulphur poisoning compared to conventional spinel based catalyst, and only minor influence of the stabilizer on the capacity against sulphur poisoning. 
     EXAMPLE 5 
     Sintering Stability 
     A series of nickel catalysts containing 10% to 60% by weight of nickel and containing varying contents of Zr, La, Ce, Y, or W (stabilizer) where prepared by sequential impregnations of a shaped high surface area magnesium aluminum spinel carrier by methods known in the art with nickel nitrate and zirconyl nitrate, ZrO(NO 3 ) 2 , zirconium carbonate, Zr(CO 3 ) 2 , basic zirconium carbonate, Zr(CO 3 )x(OH) 4−2x , x&lt;2, lanthanum nitrate, La(NO 3 ) 3 , cerium nitrate, Ce(NO 3 ) 3 , yttrium nitrate, Y(NO 3 ) 3 , or ammonium decatungstate, (NH 4 ) 6 H 2 W 12 O 40 . Before the impregnation with the stabilizer, the nickel nitrate was decomposed. After drying the tablets were loaded in a reactor and activated during heating to a temperature between 500° C. and 850° C. in a hydrogenflow containing 1% steam at atmospheric pressure. 
     The sintering stability was determined by exposing the catalysts to a steam/hydrogen atmosphere at 30 bar, 500° C. and a steam to hydrogen ratio of 10 to 1 on a molar basis for more than 500 hours, and, subsequently, analyse the catalysts for steam reforming activity and capacity against sulphur poisoning as described in Examples 3 and 4, respectively. 
     The steam reforming activities and capacities against sulphur poisoning obtained after sintering are shown in Table 3. 
     Steam reforming activity and capacity against sulphur poisoning after sintering of stabilized and unstabilized catalysts are shown tested at 500° C. with 25% by weight nickel, compared with a low surface area spinel (less than 25 m 2 /g) supported nickel catalyst, R67GR obtained from Haldor Topsøe A/S, Denmark, at 500° C. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                   
                   
                 Capacity 
               
               
                   
                   
                 Stabilizer 
                   
                 against 
               
               
                   
                   
                 content 
                 Relative 
                 sulphur 
               
               
                   
                 Catalyst 
                 (weight %) 
                 activity 
                 poisoning 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 R67GR 
                 0 
                 100 
                 100 
               
               
                   
                 Catalyst 1 
                 0 
                 100 
                 192 
               
               
                   
                 Catalyst 2 
                  1.7% La 
                 132 
                 242 
               
               
                   
                 Catalyst 3 
                  1.6% Y 
                 129 
                 242 
               
               
                   
                 Catalyst 4 
                 0.95% Zr 
                 121 
                 217 
               
               
                   
                 Catalyst 5 
                  4.4% W 
                 79 
                 258 
               
               
                   
                 Catalyst 6 
                  3.1% Ce 
                 139 
               
               
                   
                   
               
             
          
         
       
     
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. Therefore, the present invention is to be limited not by the specific disclosure herein, but only by the appended claims.