Skeletal iron catalyst having improved attrition resistance and product selectivity in slurry-phase synthesis processes

Abstract

Particulate skeletal iron catalyst is provided which contain at least about 50 wt. % iron with the remainder being a minor portion of a suitable non-ferrous metal and having characteristics of 0.062-1.0 mm particle size (62-1000 micron), 20-100 m 2 /g surface area, and 10-40 nm average pore diameter. Such skeletal iron catalysts are prepared and utilized for producing synthetic hydrocarbon products from CO and H 2 feeds by Fischer-Tropsch synthesis process. Iron powder is mixed with non-ferrous metal powder selected from aluminum, antimony, silicon, tin or zinc powder to provide 20-80 wt. % initial iron content and melted together to form an iron alloy, then cooled to room temperature and pulverized to provide 0.1-10 mm iron alloy catalyst precursor particles. The iron alloy precursor particles are treated with NaOH or KOH caustic solution at 30-95° C. temperature to extract and/or leach out most of the non-ferrous metal portion, and then screened and treated by drying and reducing with hydrogen so as to provide smaller sized skeletal iron catalyst material. Such skeletal iron catalyst is utilized with CO+H 2 feedstream for Fischer-Tropsch reactions in either a fixed bed or slurry bed type reactor at 180-500° C. temperature, 0.5-5.0 mPa pressure, and gas hourly space velocity of 0.5-3.0 L/g Fe/hr to produce desired hydrocarbon products.

1 . A particulate skeletal iron catalyst comprising at least about 50 wt. % iron with the remainder being non-ferrous metal selected from the group consisting of aluminum, antimony, nickel, tin and zinc, and a non-ferrous promotor metal selected from the group consisting of calcium, copper, chromium, magnesium and potassium, which non-ferrous metals have been substantially removed from the catalyst by a chemical extraction and/or leaching step and thereby providing iron alloy particles having a skeletal type structure of mainly iron, said catalyst having particle size smaller than 10 mm, surface area of 20-100 m 2 /g, and average pore diameter of 10-40 nm.  
     
     
         2 . The skeletal iron catalyst of  claim 1 , wherein said catalyst contains 60-90 wt. % iron, has surface area of 25-80 m2/g., and particle size of 0.02-5 mm (20-5000 microns).  
     
     
         3 . A method for preparing a skeletal iron catalyst useful for Fischer-Tropsch synthesis processes, comprising the steps of: 
 a) providing a catalyst precursor metal alloy by mixing iron powder together with non-ferrous metal powder selected from aluminum, antimony, silicon, tin and zinc sufficient to provide iron content of 20-80 wt. % and 0.01-5.0 wt. % non-ferrous promotor metal powder selected from calcium, chromium, copper, magnesium and potassium; heating said mixed metal powders together under inert gas protection, while stirring said metal powders uniformly and melting the metal powders to form precursor iron alloy material, then cooling the melted iron alloy to room temperature and pulverizing the resulting iron alloy to provide skeletal iron catalyst precursor particles having 0.1-10 mm particle size;    b) contacting said skeletal iron alloy catalyst precursor particles with NaOH or KOH caustic solution having 10-50% concentration under inert argon, helium or hydrogen atmosphere, and heating the mixture to 30-95° C. temperature while maintaining reaction condition for 2-150 minutes and extracting and/or leaching out a major portion of the non-ferrous metal from the iron alloy precursor particles so as to provide a skeletal iron structure, then washing said particles with ion-free water until pH=7, displacing the water with alcohol, and placing the resulting skeletal iron catalyst particles in ethanol; and    c) treating said skeletal iron catalyst particles by drying and reducing with hydrogen at high space velocity at 100-500° C. temperature for 2-12 hours, then transferring the treated skeletal iron catalyst into water-free ethanol or liquid paraffin for storage.    
     
     
         4 . The skeletal iron catalyst preparation method of  claim 3 , wherein step (b) is treating said skeletal iron catalyst precursor particles by adding sufficient said NaOH or KOH caustic solution into a stirred container under hydrogen atmosphere and heating the solution to 30-95° C. temperature, then adding the iron alloy precursor particles into the caustic solution at suitable periodic time intervals, while maintaining the reaction condition for 5-150 minutes for extracting and /or leaching out a major portion of the non-ferrous metal from the iron alloy precursor particles, then washing the iron alloy precursor particles with deionized water until pH=7, displacing the water with alcohol, and placing the resulting skeletal iron alloy catalyst particles in ethanol.  
     
     
         5 . The skeletal iron catalyst preparation method of  claim 3 , wherein step (b) is mixing said iron alloy precursor particles with solid sodium hydroxide (NaOH) powder at weight ratio of the sodium hydroxide to the iron alloy particles of 5-10:1, then adding deionized water dropwise to wet the mixture to provide a paste but not a fluid state while stirring so that reaction proceeds under a wet paste state; after the reaction has proceeded 5-30 minutes while gas release gradually decreases, adding to said paste mixture fresh NaOH or KOH 10-50% concentration solution and maintaining for 2-60 minutes at 50-95° C. temperature; then washing the iron alloy particles with deionized water to pH=7, displacing water with water-free ethanol and storing in ethanol.  
     
     
         6 . The skeletal iron catalyst preparation method of  claim 3 , wherein step (b) includes placing said iron alloy precursor particles in a stirred container, spraying the particles with a 40-60% concentration NaOH or KOH solution, maintaining reaction in a wet but not fluid state for 5-30 minutes, adding NaOH or KOH caustic solution of 10-50% concentration and maintaining for 2-60 minutes at 50-90° C. temperature, then washing the iron alloy particles with deionized water to pH=7, then displacing the water with water-free ethanol and storing in ethanol.  
     
     
         7 . The catalyst preparation method of  claim 3 , wherein said mixed metal powders are iron, aluminum and copper having an initial respective weight ratio of 33:66:1.  
     
     
         14 . (Amended) The skeletal iron catalyst of  claim 1 , wherein the catalyst particle size after Fischer-Tropsch synthesis reaction is 0.025-1.0 mm. (25-1000 microns).  
     
     
         15 . The catalyst preparation method of  claim 3 , wherein the step (b) catalyst precursor metal alloy extraction and/or leaching temperature is 50-95° C., and the treated skeletal iron catalyst particle size is 0.062-3.0 mm. (62-3000 microns).  
     
     
         16 . The skeletal iron catalyst preparation method of  claim 3 , wherein said non-ferrous metal powder is aluminum and said promotor metal powder is copper.  
     
     
         17 . The skeletal iron catalyst preparation method of  claim 3 , wherein said metal powder mixture is heated and melted in an electric induction furnace during magnetic stirring.  
     
     
         18 . The skeletal iron catalyst preparation method of  claim 3 , wherein the iron alloy catalyst particle extracting/leaching temperature is 65-95° C., particle size is 30-50 microns, and relative separation of the catalyst in F-T synthesis product liquid slurry is 20-25 % of the initial height in the product liquid slurry.  
     
     
         19 . A method for preparing a skeletal iron catalyst particularly useful for Fischer-Tropsch synthesis processes, comprising the steps of: 
 a) providing a catalyst precursor metal alloy by mixing iron powder together with aluminum powder sufficient to provide iron content of 20-80 wt. % and 0.01-5.0 wt. % copper powder, heating said mixed metal powders together in an electric induction furnace under inert gas protection, while mixing said metal powders uniformly by magnetic stirring and melting the metal powders to form precursor iron alloy material, then cooling the melted precursor iron alloy to room temperature and pulverizing the resulting iron alloy to provide skeletal iron catalyst precursor particles having 0.1-10 mm particle size;    b) contacting said skeletal iron alloy catalyst precursor particles with NaOH or KOH caustic solution having 10-50% concentration under inert hydrogen atmosphere by adding sufficient NaOH or KOH caustic solution having 10-50% concentration into a stirred container under the hydrogen atmosphere and heating the solution to 30-95° C. temperature, then adding the iron alloy precursor particles into the caustic solution at suitable periodic time intervals, while maintaining the reaction condition for 2-150 minutes and extracting and/or leaching out a major portion of the non-ferrous metal from the iron alloy precursor particles so as to provide a skeletal iron structure having particle size smaller than 10 mm, then washing said skeletal iron particles with ion-free water until pH=7, displacing the water with alcohol, and placing the resulting skeletal iron catalyst particles in ethanol; and    c) treating the skeletal iron catalyst particles by drying and reducing with hydrogen at high space velocity at 200-500° C. temperature for 2-12 hours, then transferring the treated skeletal iron catalyst into water-free ethanol or liquid paraffin for storage.