Catalyst carriers

Abstract

The selectivity and activity of a silver-based olefin epoxidation catalyst is found to be a function of the pore size distribution in the alumina carrier on which it is deposited. Specifically it is found advantageous to provide a carrier which has a minimum of very large pores, (greater than 10 micrometers) and a water absorption of 35 to 55% and a surface area of at least 1.0 m 2 /g. A method of making such carriers is also described.

1 . A carrier for a catalyst which comprises at least 95% alpha alumina with a surface area of from 1.0 to 2.6 m 2 /g and a water absorption of from 35 to 55%, wherein the pores are distributed such that at least 80% of the pore volume is in the form of pores having pore diameters from 0.2 to 10 micrometers and pores with diameters less than 0.2 micrometers represent from 0 to 10% of the total pore volume of the carrier.  
     
     
         2 . A carrier according to  claim 1  in which pores with diameters between 0.2 and 10 micrometers provide a pore volume of at least 0.27 mL/g of the carrier.  
     
     
         3 . A carrier according to  claim 1  in which the pore volume is up to 0.56 mL/g.  
     
     
         4 . A carrier according to  claim 1  wherein the surface area is from 1.6 to 2.2 m 2 /g.  
     
     
         5 . A carrier according to  claim 1  wherein the pores are distributed such that pores with pore diameters greater than 10 micrometers represent less than 20% of the total pore volume.  
     
     
         6 . A carrier according to  claim 1  which further comprises from 0.2 to 0.8% of an amorphous silica compound.  
     
     
         7 - 11 . (canceled)  
     
     
         12 . A catalyst carrier for which comprises at least 95% alpha alumina with a surface area of from 1.0 to 2.6 m 2 /g and a water absorption of from 35 to 55%, wherein the pores are distributed such that pores having pore diameters from 0.2 to 10 micrometers provide a pore volume of 0.3 to 0.56 mL/g of the carrier.  
     
     
         13 . A catalyst carrier formed by a method comprising: 
 forming a mixture comprising:    a) from 50 to 90% by weight of a first particulate alpha alumina having an average particle size (d 50 ) of from 10 to 90 micrometers;    b) from 10 to 50% by weight, based on the total alpha alumina weight, of a second particulate alpha alumina having an average particle size (d 50 ) of from 2 to 6 micrometers;    c) from 2 to 5% by weight of an alumina hydrate;    d) from 0.2 to 0.8% of an amorphous silica compound, measured as silica; and    e) from 0.05 to 0.3% of an alkali metal compound measured as the alkali metal oxide;    all percentages being based on the total alpha alumina content of the mixture;    forming the mixture into particles; and    firing the particles at a temperature of from 1250 to 1470° C. to form the carrier.    
     
     
         14 . A carrier according to  claim 13  wherein the alumina hydrate is boehmite.  
     
     
         15 . A carrier according to  claim 13  wherein the mixture comprises up to 20% by weight of pore formers in the form of organic burnout material.  
     
     
         16 . A carrier according to  claim 13  in which the mixture is compounded with from 10 to 25% based on the mixture weight of extrusion aids and pore formers and sufficient water to render the mixture extrudable, and then extruded to form pellets which are then dried and fired to produce the carrier.