Preparing synthesis gas using hydrotalcite- derived nickel catalysts

Abstract

There is provided is a process for preparation of synthesis gas, i.e. mixtures containing dihydrogen and oxides of carbon, from feedstocks containing methane and/or higher hydrocarbons having from about 2 to about 12 carbon atoms by an initial catalytic treatment of feedstock to provide a methane-containing gaseous mixture substantially free of compounds having 2 or more carbon atoms, and reforming the gaseous mixture at elevated temperatures using nickel-containing catalytic materials that are unusually active under mild conditions of conversion and resistant to deactivation. The process consists fundamentally in converting the higher hydrocarbon compounds to form a methane-containing gaseous mixture substantially free of compounds having 2 or more carbon atoms in an initial conversion zone containing a catalyst while controlling temperatures within the initial conversion zone to temperatures in a range of temperature downward from about 500° C. to about 300° C., and reforming the methane-containing gaseous mixture with steam and/or carbon dioxide in a subsequent zone containing catalyst at elevated temperatures and pressure sufficient to form synthesis gas.

Having described the invention, that which is claimed is:  
     
         1 . A process for preparation of synthesis gas containing dihydrogen and oxides of carbon from feedstocks containing methane and/or higher hydrocarbons having from about 2 to about 12 carbon atoms which comprises the steps of 
 (A) feeding a stream comprising one or more hydrocarbon compounds having up to about 12 carbon atoms, and steam and/or carbon dioxide into an initial conversion zone containing a catalyst,    (B) controlling temperatures within the initial conversion zone to temperatures in a range of temperature downward from about 500° C. to about 300° C.,    (C) converting the higher hydrocarbon compounds in the presence of the initial conversion zone catalyst to form a methane-containing gaseous mixture substantially free of compounds having 2 or more carbon atoms, and    (D) reforming the methane-containing gaseous mixture with steam and/or carbon dioxide in a subsequent zone containing catalyst at elevated temperatures and pressure sufficient to form synthesis gas,    wherein the catalyst comprises mixtures formed by heat treating a nickel containing hydrotalcite compound to temperatures in a temperature range upward from about 400° C.    
     
     
         2 . The process according to  claim 1  wherein the reforming is carried out at temperatures in a range of temperature upward from about 600° C.  
     
     
         3 . The process according to  claim 1  wherein the stream feeding into the initial conversion zone is derived from a source of natural gas, and the amount of steam is sufficient to provide a ratio of steam to carbon in a range upward from about 0.25.  
     
     
         4 . The process according to  claim 1  wherein the stream feeding into the initial conversion zone comprises naphthas with a final boiling point up to about 200° C., and the amount of steam is sufficient to provide a ratio of steam to carbon in a range upward from about 1.5.  
     
     
         5 . The process according to  claim 1  wherein the catalysts comprise compositions formed by heat treating to a temperature of at least about 700° C., a nickel containing hydrotalcite compound having formula  
       [M 2+   (1−x) M x   3+ (OH) 2 ] x+ (A x/n   n− ). m H 2 O,  
       where M 2+  is Ni 2+  ion or a mixture of Ni 2+  ion and another metal ion having a valence of 2+; M 3+  is a metal ion having a valence of 3+; x is a number greater than about 0.25 to about 0.50; A n−  is an anion having a negative charge of n; and m is 0 or a positive number.  
     
     
         6 . The process according to  claim 5  wherein the heat treating is to a temperature of at least 800° C., and wherein the reforming step (D) is carried out at temperatures in a range of temperature upward from about 650° C. to about 1100° C.  
     
     
         7 . The process according to  claim 6  wherein the catalyst comprises nickel at an amount of from about 5 to 75 percent based upon the weight of the catalyst.  
     
     
         8 . The process according to  claim 7  wherein the stream feeding into the initial conversion zone is derived from a source of natural gas, and the amount of steam is sufficient to provide a ratio of steam to carbon in a range upward from about 0.25.  
     
     
         9 . The process according to  claim 7  wherein the stream feeding into the initial conversion zone comprises naphthas with a final boiling point up to about 200° C., and the amount of steam is sufficient to provide a ratio of steam to carbon in a range upward from about 1.5.  
     
     
         10 . The process according to  claim 6  wherein M 2+  is at least Ni 2+  and Mg 2+ ; and where M 3+  is at least one of Al 3+ , Ga 3+ , Ni 3+ , Co 3+ , Fe 3+ , Mn 3+ , Cr 3+ , V 3+ , Ti 3+ , La 3+  or In 3+ .  
     
     
         11 . The process according to  claim 10  wherein M 3+  is Al 3+ .  
     
     
         12 . The process according to  claim 6  wherein M 2+  is a mixture of Ni 2+  and Mg 2+ ; M 3+  is Al 3+ ; and A is carbonate.  
     
     
         13 . The process according to  claim 12  wherein the heat treating is to a temperature of at least 800° C., and wherein the reforming step (D) is carried out at temperatures in a range of temperature upward from about 650° C. to about 1100° C.  
     
     
         14 . The process according to  claim 13  wherein the catalyst comprises nickel at an amount of from about 5 to 75 percent based upon the weight of the catalyst.  
     
     
         15 . The process according to  claim 14  wherein the stream feeding into the initial conversion zone is derived from a source of natural gas, and the amount of steam is sufficient to provide a ratio of steam to carbon in a range upward from about 0.25.  
     
     
         16 . The process according to  claim 14  wherein the stream feeding into the initial conversion zone comprises naphthas with a final boiling point up to about 200° C., and the amount of steam is sufficient to provide a ratio of steam to carbon in a range upward from about 1.5.  
     
     
         17 . The process according to  claim 1  wherein the catalyst compositions comprise (a) M 2+ O, (b) M 2+ Al 2 O 4  spinel and (c) a hybrid phase comprising (i) a M 2+ O component and (ii) a M 2+ Al 2 O 4  spinel component in the same catalyst crystallite and joined through an epitaxial interface, said epitaxial interface being an area in the crystallite where crystalline species of both components (i) and (ii) coexist and form a well defined interface, and wherein M 2+  is Ni 2+  or a mixture of Ni 2+  plus another metal ion or plus other metal ions.  
     
     
         18 . The process according to  claim 17  wherein M 2+  is Ni 2+  or a mixture of Ni 2+  and Mg 2+ .  
     
     
         19 . The process according to  claim 17  wherein the catalyst contains metal particles of about 1 to about 1000 nanometers in size and containing at least nickel in the zero oxidation state.  
     
     
         20 . The process according to  claim 1  wherein the reforming catalyst comprises metal particles of about 1 to about 1000 nanometers in size and comprising at least nickel in the zero oxidation state, the external surface area of the metal particles being mostly surrounded by spinel crystallites, the spinel crystallites comprising M 2   3+ O 3  or M 2+ M 2   3+ O 4  or a mixture thereof where M 2+  is a metal in the 2+ oxidation state, and M 3+  is a metal in the 3+ oxidation state.  
     
     
         21 . A process for preparation of synthesis gas containing dihydrogen and oxides of carbon from feedstocks containing methane and/or higher hydrocarbons which comprises the steps of 
 (A) feeding a stream comprising one or more hydrocarbon compounds having up to 12 carbon atoms, and stream and/or carbon dioxide into an initial conversion zone containing catalyst for initial conversions,    (B) controlling temperatures within the initial conversion zone to temperatures in a range of temperature downward from 500° C. to 300° C.,    (C) converting the higher hydrocarbon compounds in the presence of the initial conversion zone catalyst to form a methane-containing gaseous mixture substantially free of compounds having 2 or more carbon atoms, but optionally contains hydrogen sulfide, and    (D) reforming the methane-containing gaseous mixture with steam and/or carbon dioxide in a subsequent zone containing reforming catalyst at temperatures in a range of temperature upward from 600° C. to 1100° C. whereby a synthesis gas containing dihydrogen and oxides of carbon is formed, and    wherein the catalyst for initial conversions used in step (A) and the reforming catalyst used in step (D) comprises mixtures formed by heat treating the same or different nickel containing hydrotalcite precursor compound to temperatures in a temperature range upward from 650° C. to 1050° C. thereby forming catalytic materials resistant to deactivation and coking in the presence of sulfur-containing compounds, and wherein the catalytic materials comprise (a) M 2+ O, (b) M 2+ Al 2 O 4  spinel and (c) a hybrid phase comprising (i) a M 2+ O component and (ii) a M 2+ Al 2 O 4  spinel component in the same catalyst crystallite and joined through an epitaxial interface, said epitaxial interface being an area in the crystalline where crystalline species of both components (i) and (ii) coexist and form a well defined interface, and wherein M 2+  is Ni 2+  or a mixture of Ni 2+  plus another metal ion or plus other metal ions.    
     
     
         22 . The process according to  claim 21  wherein the crystallites comprising the hybrid phase are 5 to 400 nanometers in size.  
     
     
         23 . The process according to  claim 21  wherein the stream feeding into the initial conversion zone comprises a natural gas composition and steam an amount sufficient to provide a ratio of steam to carbon in a range from 0.2 to 2.0.  
     
     
         24 . The process according to  claim 21  wherein the stream feeding into the initial conversion zone comprises naphthas with a final boiling point up to 200° C. and steam an amount sufficient to provide a ratio of steam to carbon in a range from 1.5 to 10.  
     
     
         25 . The process according to  claim 21  wherein at least one of the nickel-containing hydrotalcite precursor compounds is represented by  
       {M 2+   (1−x) M x   3+ (OH) 2 } x+ (A x/n   n− ).mH 2 O, 
       where M 2+  is Ni 2+  ion or a mixture of Ni 2+  ion and another metal ion having a valence of 2+; M 3+  is a metal ion having a valence of 3+, x is a number greater than 0.25 to 0.50; A n−  is an anion having a negative charge of n; and m is 0 or a positive number.  
     
     
         26 . The process according to  claim 25  wherein M 2+  is a mixture of Ni 2+  and Mg 2− ; M 3+  is Al 3+ ; and A is carbonate.  
     
     
         27 . The process according to  claim 26  wherein the catalytic material used in step (A) and the reforming catalyst used in step (D) comprises nickel at an amount of from 5 to 75 percent based upon the weight of the catalyst.  
     
     
         28 . The process according to  claim 21  wherein at least one of the nickel-containing hydrotalcite precursor compounds is represented by {Ni 4 Al 2 (OH) 12 }CO 3 .4H 2 O.  
     
     
         29 . The process according to  claim 21  wherein at least one of the nickel-containing hydrotalcite precursor compounds is represented by {Ni 2 Mg 2 Al 2 (OH) 12 }CO 3 .4H 2 O.  
     
     
         30 . The process according to  claim 21  wherein at least one of the nickel-containing hydrotalcite precursor compounds is represented by {NiMg 5 Al 2 (OH) 16 }CO 3 .4H 2 O.  
     
     
         31 . The process according to  claim 21  wherein at least one of the nickel-containing hydrotalcite precursor compounds is represented by {NiMg 3 Al 2 (OH) 12 }CO 3 .4H 2 O.