Catalyst composition for selective hydrogenation with improved characteristics

Abstract

This invention relates to heterogeneous catalysts useful for selective hydrogenation of unsaturated hydrocarbons, comprising palladium and optionally a promoter, supported on a substrate, having an uncoated BET surface area of ≦9 m 2 /g, the surface being coated with an ionic liquid. Also described are methods of making the catalysts and methods of selective hydrogenation of acetylene and/or dienes in front-end mixed olefin feed streams.

What is claimed: 
     
         1 . A catalyst comprising palladium supported on a substrate, said catalyst further comprising at least one ionic liquid, wherein said substrate has a BET surface area of less than 9 m 2 /g prior to the addition of said at least one ionic liquid. 
     
     
         2 . The catalyst of  claim 1 , wherein said BET surface area is preferably within a range of 2 to 8 m 2 /g, and more preferably within a range of 3 to 5 m 2 /g. 
     
     
         3 . The catalyst of  claim 1 , wherein the palladium-supported catalyst further comprises a promoter selected from the group consisting of Ag, Au, Zn, Sn, Cd, Pb, Cu, Bi, K, Ga, and mixtures thereof. 
     
     
         4 . The catalyst of  claim 3 , wherein the promoter comprises Ag. 
     
     
         5 . The catalyst of  claim 1 , having a Pd loading of 10 to 1000 ppm. 
     
     
         6 . The catalyst of  claim 3 , having a ratio of Pd:promoter of 1:5-3:1. 
     
     
         7 . The catalyst of  claim 1 , wherein the ionic liquid comprises a compound of the formula:
   [A] n   + [Y] n   − ,   wherein:   n=1 or 2;   [Y] n   −  is selected from the group consisting of tetrafluoroborate ([BF 4 ] − ) hexafluorophosphate ([PF 6 ] − ), dicyanamide ([N(CN) 2 ] − ), halides (Cl − , Br − , F − , I − ), hexafluoroantimonate ([SbF 6 ] − ), nitrate ([NO 3 ] − ), nitrite ([NO 2 ] − ), anionic metal complexes such as for example [CuCl 4 ] 2− , [PdCl 4 ] 2−  or [AuCl 4 ] − , acetate ([CH 3 COO] − ), trifluoracetate ([F 3 CCOO] − ), hexafluoroarsenate ([AsF 6 ] − ), sulfate ([SO 4 ]2 − ), hydrogen sulfate ([R′—SO 4 ] − ), alkyl sulfate ([R′—SO 4 ] − ), tosylate ([C 7 H 7 SO 3 ] − ), triflate ([CF 3 SO 3 ] − ), nonaflate ([C 4 F 9 SO 3 ] − ), triperfluoroethylene trifluorophosphate ([PF 3 (C 2 F 5 ) 3 ] − ), tricyanomethide ([C(CN) 3 ] − ), tetracyanoborate ([B(CN) 4 ] − , thiocyanate ([SCN] − ), carbonate ([CO 3 ] 2   − ), carboxylate ([R′—COO] − ), sulfonate ([R′SO 3 ] − ), dialkylphosphate ([R′PO 4 R″] − ), alkyl phosphonate ([R′HPO 3 ] − ) and bissulfonylimide ([(R′-SO 2 ) 2 N] − ), such as bis(trifluormethylsulfonyl)imide,   wherein R′ and R″ are the same or different, and each represent a linear or branched 1 to 12 carbon atom-containing aliphatic or alicyclic alkyl group or a C 5 -C 18 -aryl, C 5 -C 18 -aryl-C 1 -C 6 -alkyl or C 1 -C 6 -alkyl-C 5 -C 18 -aryl group that can be substituted with halogen atoms;   [A] +  is selected from the group consisting of quaternary ammonium cations with the formula [NR 1 R 2 R 3 R] + , phosphonium cations with the formula [PR 1 R 2 R 3 R] + , sulfonium cations with the formula [SR 1 R 2 R] + , guadinium cations with the formula   
       
         
           
           
               
               
           
         
         imidazolium cations with the formula 
       
       
         
           
           
               
               
           
         
         wherein the imidazole core can also be substituted with one or more groups selected from C 1 -C 6 -alkyl, C 1 -C 6 -alkoxy, C 1 -C 6 -aminoalkyl, C 5 -C 12 -aryl and C 5 -C 12 -aryl-C 1 -C 6 -alkyl groups, pyridinium cations with the formula 
       
       
         
           
           
               
               
           
         
         wherein the pyridine core can also be substituted with one or more groups selected from C 1 -C 6 -alkyl, C 1 -C 6 -alkoxy, C 1 -C 6 -aminoalkyl, C 5 -C 12 -aryl and C 5 -C 12 -aryl-C 1 -C 6 -alkyl groups, pyrazolium cations with the formula 
       
       
         
           
           
               
               
           
         
         wherein the pyrazole core can also be substituted with one or more groups selected from C 1 -C 6 -alkyl, C 1 -C 6 -alkoxy, C 1 -C 6 -aminoalkyl, C 5 -C 12 -aryl or C 5 -C 12 -aryl-C 1 -C 6 -alkyl groups, and triazolium cations with the formula 
       
       
         
           
           
               
               
           
         
         wherein the triazole core can also be substituted with one or more groups selected from C 1 -C 6 -alkyl, C 1 -C 6 -alkoxy, C 1 -C 6 -aminoalkyl, C 5 -C 12 -aryl or C 5 -C 12 -aryl-C 1 -C 6 -alkyl groups, 
         wherein R 1 , R 2 , R 3  are selected independently from each other from the group consisting of: hydrogen; linear or branched, saturated or unsaturated, aliphatic or alicyclic alkyl groups with 1 to 20 carbon atoms; heteroaryl groups with 3 to 8 carbon atoms and at least one hetero atom selected from N, O and S, wherein the heteroaryl group can be substituted with one or more groups selected from C 1 -C 6 -alkyl groups and halogen atoms; heteroaryl-C 1 -C 6 -alkyl groups with 3 to 8 carbon atoms and at least one hetero atom selected from N, O and S in the heteroaryl moiety, wherein the heteroaryl moiety can be substituted with at least one group selected from C 1 -C 6 -alkyl groups and halogen atoms; polyethers with the formula [—CH 2 CH 2 O] n R a  with n=1 to 50,000, wherein R a  is selected from the group consisting of linear or branched, saturated or unsaturated, aliphatic or alicyclic alkyl groups with 1 to 20 carbon atoms; aryl groups with 5 to 12 carbon atoms, which may be substituted with one or more C 1 -C 6 -alkyl groups and/or halogen atoms; aryl-C 1 -C 6 -alkyl groups with 5 to 12 carbon atoms in the aryl moiety, which may be substituted with one or more C 1 -C 6 -alkyl groups and/or halogen atoms, and 
         wherein R is selected from the group consisting of: linear or branched, saturated or unsaturated, aliphatic or alicyclic alkyl groups with 1 to 20 carbon atoms; heteroaryl-C 1 -C 6 -alkyl groups with 4 to 8 carbon atoms and at least one hetero atom selected from N, O and S in the heteroaryl moiety, which can be substituted with one or more C 1 -C 6 -alkyl groups and/or halogen atoms; and aryl-C 1 -C 6 -alkyl groups with 4 to 12 carbon atoms in the aryl moiety, which may be substituted with one or more C 1 -C 6 -alkyl groups and/or halogen atoms. 
       
     
     
         8 . The catalyst of  claim 7 , wherein the ionic liquid comprises one or more selected from the group consisting of 1-butyl-3-methylimidazolium triflate, 1-ethyl-3-methylpyridinium ethylsulfate, 1-butyl-1-methylpyrrolidinium triflate, 1-butyl-2,3-dimethylimidazolium triflate, 1-butyl-3-methylimidazolium tricyanomethane, 1-butyl-3-methylimidazolium methylsulfate, 1-butyl-3-methylimidazolium octylsulfate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium ethylsulfate, 1-ethyl-3-methylimidazolium methylphosphonate, 1-ethyl-3-methylimidazolium triflate, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpyrrolidinium tetracyanoborate, 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium tricyanomethane, 1-ethyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium tetracyanoborate, 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, 1-methyl-3-octylimidazolium triflate, ethyldimethyl-(2-methoxyethyl)ammonium tris(pentafluoroethyl)trifluorophosphate, tributylmethylammonium dicyanamide, tricyclohexyltetradecylphosphonium tris(pentafluoroethyl)trifluorophosphate, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and mixtures thereof. 
     
     
         9 . The catalyst of  claim 7 , wherein [A] n   +  is selected from the group consisting of 1-butyl-1-methylpyrrolidinium, 1-butyl-2,3-dimethylimidazolium, 1-butyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium, 1-ethyl-3-methylpyridinium, 1-methyl-3-octylimidazolium, ethyldimethyl-(2-methoxyethyl)ammonium, tributylmethylammonium, tricyclohexyltetradecylphosphonium, and mixtures thereof, and wherein [Y] n   −  is selected from the group consisting of bis(trifluoromethylsulfonyl)imide, dicyanamide, ethylsulfate, methylphosphonate, methylsulfate, octylsulfate, tetracyanoborate, tetrafluoroborate, tricyanomethane, triflate, tris(pentafluoroethyl)trifluorophosphate, and mixtures thereof. 
     
     
         10 . The catalyst of  claim 1 , having an ionic liquid loading of 0.01% to 10% by weight, and more preferably of 0.1% to 5% by weight. 
     
     
         11 . The catalyst of  claim 1 , having a cleanup temperature of less than 80° C. and an operating window of greater than 25° C. when tested with a simulated de-ethanizer feed containing 0.35 mol % acetylene, 20 mol % hydrogen, 0.02 mol % CO, 45 mol % ethylene, and balance methane being passed over a 25 ml catalyst bed at 500 psig (35.5 bar) in total pressure and 7000 h −1  in Gas Hourly Space Velocity (GHSV), while the bed temperature is gradually increased from about 35° C., the “clean up temperature” is defined as the temperature at which the outlet reaches <25 ppm acetylene, the runaway temperature is defined as the temperature at which the outlet ethane concentration is >2% and the operation window is defined as the difference between the runaway temperature and the clean up temperature. 
     
     
         12 . The catalyst of  claim 1 , wherein the integral pore volume of the catalyst without the presence of said at least one ionic liquid is in the range of 0.005 to 0.07 ml/g, preferably in the range of 0.007 to 0.04 ml/g and more preferably within a range of 0.009 to 0.02 ml/g. 
     
     
         13 . The catalyst of  claim 1 , having a selectivity of >25% at clean up temperature, when tested with a simulated de-ethanizer feed containing 0.35 mol % acetylene, 20 mol % hydrogen, 0.02 mol % CO, 45 mol % ethylene, and balance methane being passed over a 25 ml catalyst bed at 500 psig (35.5 bar) in total pressure and 7000 h −1  in Gas Hourly Space Velocity (GHSV), while the bed temperature is gradually increased from about 35° C., the “clean up temperature” being defined as the temperature at which the outlet reaches <25 ppm acetylene. 
     
     
         14 . A method of making a coated catalyst, comprising the steps of:
 (a) providing a catalyst having a BET surface area less than or equal to 9 m 2 /g and comprising palladium supported on a substrate and optionally further comprising a promoter;   (b) coating the catalyst in (a) with a mixture of an ionic liquid and a solution agent; and   (c) removing the solution agent during or after the coating in (b).   
     
     
         15 . The process of  claim 14 , further comprising the step of reducing the catalyst before step (b) or after step (c). 
     
     
         16 . The process of  claim 14 , wherein step (b) comprises a fluidized bed coating or an impregnation with a solution or suspension. 
     
     
         17 . A method of selective hydrogenation of acetylene in front-end mixed olefin feed streams, comprising catalyzing said hydrogenation with a catalyst comprising palladium supported on a substrate, the catalyst having an uncoated BET surface area of less than 9 m 2 /g, said catalyst further comprising at least one ionic liquid. 
     
     
         18 . The method of  claim 17 , wherein the selective hydrogenation occurs in a gas phase. 
     
     
         19 . The method of  claim 17 , wherein the selective hydrogenation occurs in a liquid phase.