Process for the production of vinyl acetate

Abstract

A process for the production of vinyl acetate which comprises contacting ethylene, acetic acid and an oxygen-containing gas with a supported palladium catalyst prepared by a process comprising the steps of (a) impregnating a catalyst support with a palladium compound, (b) converting the palladium compound to substantially metallic palladium, and (c) sintering the supported palladium at a temperature of greater than 500° C.

We claim:  
     
       1. A process for the production of vinyl acetate which process comprises contacting ethylene, acetic acid and an oxygen-containing gas with a supported palladium catalyst prepared by a process comprising the steps: (a) impregnating a catalyst support with a palladium compound, (b) converting the palladium compound to substantially metallic palladium, and (c) sintering the supported palladium at a temperature of greater than 500° C.  in the range of from  650  to  1000 ° C. in the presence of a gas consisting essentially of a reducing gas, an inert gas or a mixture thereof. 
     
     
       2. A process as claimed in  claim 1  wherein the catalyst support is impregnated with a palladium compound in a solvent selected from water, carboxylic acid, benzene, toluene, alcohol, nitriles, tetrohydrofuran or a chlorinated solvent. 
     
     
       3. A process as claimed in  claim 2  wherein the solvent is water and/or acetic acid. 
     
     
       4. A process as claimed in  claim 1  wherein the palladium compound is palladium acetate, sulphate, nitrate, chloride or a halogen-containing palladium salt. 
     
     
       5. A process as claimed in  claim 4  wherein the palladium compound is palladium acetate. 
     
     
       6. A process as claimed in  claim 1  in which step (b) is carried out by contacting the palladium compound with a liquid or gaseous reducing agent selected from the group consisting of aqueous hydrazine, formaldehyde, sodium formate, alcohol, carbon monoxide, carbon dioxide, hydrogen and ethylene. 
     
     
       7. A process as claimed in  claim 1  wherein step (c) is carried out at a temperature in the range of from 650 to 1000° C. 
     
     
       8. A process as claimed in  claim 1  wherein in step (c) the reducing gas is selected from the group consisting of hydrogen and carbon monoxide and the inert gas is selected from the group consisting of nitrogen, carbon dioxide and helium. 
     
     
       9. A process as claimed in  claim 1  wherein the palladium catalyst comprises at least 0.5% by weight palladium based upon the total weight of the catalyst. 
     
     
       10. A process as claimed in  claim 1  wherein the catalyst support comprises porous silica, alumina, silica/alumina, titania, zirconia or carbon. 
     
     
       11. A process as claimed in  claim 1  wherein the palladium  support is additionally impregnated in step (a) with gold, copper,  and/or nickel,  compounds, and is optionally additionally impregnated with one or more salts of Group I, II, Lanthanide or transition metals. 
     
     
       12. A process as claimed in  claim 1  wherein the ethylene, acetic acid and oxygen-containing gas is contacted with the catalyst at a temperature in the range of 145 to 195° C. and a pressure of from 1 to 20 atmospheres. 
     
     
       13. A process as claimed in  claim 4  in which step (b) is carried out by contacting the palladium compound with a liquid or gaseous reducing agent selected from the group consisting of aqueous hydrazine, formaldehyde, sodium formate, alcohol, carbon monoxide, carbon dioxide, hydrogen and ethylene. 
     
     
       14. A process as claimed in  claim 4  wherein step (c) is carried out at a temperature in the range of from 650 to 1000° C. 
     
     
       15. A process as claimed in  claim 6  wherein step (c) is carried out at a temperature in the range of from 650 to 1000° C. 
     
     
       16. A process as claimed in  claim 7  wherein in step (c) the reducing gas is selected from the group consisting of hydrogen and carbon monoxide and the inert gas is selected from the group consisting of nitrogen, carbon dioxide and helium. 
     
     
       17. A process as claimed in claim  14   4 wherein in step (c) the reducing gas is selected from the group consisting of hydrogen and carbon monoxide and the inert gas is selected from the group consisting of nitrogen, carbon dioxide and helium. 
     
     
       18. A process as claimed in  claim 1  wherein the time for the sintering step (c) is between 1 and 24 hours. 
     
     
       19. A process as claimed in  claim 7  wherein the time for the sintering step (c) is between 1 and 24 hours. 
     
     
       20. A process as claimed in  claim 8  wherein the time for the sintering step (c) is between 1 and 24 hours. 
     
     
       21. A process as claimed in  claim 16  wherein the time for the sintering step (c) is between 1 and 24 hours. 
     
     
       22. A process as claimed in  claim 9  wherein the palladium catalyst comprises up to 10% by weight based upon the total weight of the catalyst. 
     
     
       23. A process as claimed in  claim 4  wherein the catalyst support is additionally impregnated in step (a) with gold, copper,  and/or nickel,  compounds, and is optionally additionally impregnated with one or more salts of Group I, II, Lanthanide or transition metals. 
     
     
       24. A process as claimed in  claim 22  wherein the catalyst support is additionally impregnated in step (a) with gold, copper,  and/or nickel,  compounds, and is optionally additionally impregnated with one or more salts of Group I, II, Lanthanide or transition metals. 
     
     
       25. A process as claimed in  claim 1  in which the sintering step (c) causes palladium metal particle growth from 3-4 nm in diameter to 8-15 nm in diameter. 
     
     
       26. A process as claimed in  claim 7  in which the sintering step (c) causes palladium metal particle growth from 3-4 nm in diameter to 8-15 nm in diameter. 
     
     
       27. A process as claimed in  claim 8  in which the sintering step (c) causes palladium metal particle growth from 3-4 nm in diameter to 8-15 nm in diameter. 
     
     
       28. A process as claimed in  claim 11  in which the sintering step (c) causes palladium metal particle growth from 3-4 nm in diameter to 8-15 nm in diameter. 
     
     
       29. A process as claimed in  claim 18  in which the sintering step (c) causes palladium metal particle growth from 3-4 nm in diameter to 8-15 nm in diameter. 
     
     
       30. A process as claimed in  claim 21  in which the sintering step (c) causes palladium metal particle growth from 3-4 nm in diameter to 8-15 nm in diameter. 
     
     
       31. A process as claimed in  claim 22  in which the sintering step (c) causes palladium metal particle growth from 3-4 nm in diameter to 8-15 nm in diameter. 
     
     
       32. A process for the production of vinyl acetate which process comprises contacting ethylene, acetic acid and an oxygen-containing gas with a supported palladium catalyst prepared by a process comprising the steps: (a) impregnating a catalyst support with ( i ) a palladium compound, and  ( ii ) gold, copper,  and/or nickel,  compounds and ( iii ) one or more salts of Group I, II, Lanthanide or transition metals, (b) converting the palladium compound to substantially metallic palladium, and (c) sintering the supported palladium at a temperature of greater than 500° C.  in the range of from  650 ° C. to  1000 ° C. for a time of between 1 and 24 hours in the presence of a gas consisting essentially of a reducing gas, an inert gas or a mixture thereof wherein the reducing gas is selected from the group consisting of hydrogen and carbon monoxide and the inert gas is selected from the group consisting of nitrogen, carbon dioxide and helium. 
     
     
       33. A process as claimed in  claim 32  wherein step (c) is carried out at a temperature in the range of form 650 to 1000° C. 
     
     
       34. A process as claimed in  claim 32  in which the sintering step (c) causes palladium metal particle growth from 3-4 nm in diameter to 8-15 nm in diameter. 
     
     
       35. A process as claimed in  claim 32  wherein the ethylene, acetic acid and oxygen containing gas are contact  contacted with the supported palladium catalyst at a temperature in the range of 145 to 195° C. and a pressure of from 1 to 20 atmospheres. 
     
     
       36. A process as claimed in  claim 34  wherein the ethylene, acetic acid and oxygen containing gas are contact  contacted with the supported palladium catalyst at a temperature in the range of 145 to 195° C. and a pressure of from 1 to 20 atmospheres.