Catalyst Precursor Particles, Their Preparation and Use

Abstract

A method for preparing a catalyst precursor for an olefin polymerization catalyst involves the use of aqueous or alcoholic solutions of a chromium salt and of boric acid and aluminium carboxylate for deposition onto an inorganic support material, such as a silica xerogel. The chromium salt, aluminium carboxylate and boric acid are sufficiently soluble for deposition from a single solution to be effective. The catalyst precursor can be activated by calcination to form a catalyst for homo- or co-polymerisation of α-olefins which has productivity and melt flow index for the resulting polymer or copolymer which is comparable to results obtained with catalysts prepared by prior art organometallic routes. The activation of the catalyst precursor gives reduced levels of toxic or noxious fumes during activation compared to use of organometallic sources of chromium or aluminium.

1 .- 19 . (canceled) 
     
     
         20 . A method for polymerisation of one or more C 2  to C 8  α-alkenes comprising:
 A) preparing a catalyst precursor by
 i) providing an inorganic support material which is a silica xerogel comprising at least 90% by weight of SiO 2 , 
 ii) depositing a chromium salt onto the inorganic support material from a first solution comprising a chromium salt in a solvent which is water, C1 to C4 aliphatic alcohol, or a mixture thereof, 
 iii) depositing an aluminum carboxylate and boric acid onto the inorganic support material from a second solution comprising an aluminum carboxylate and boric acid in a solvent which is water, C1 to C4 aliphatic alcohol, or a mixture thereof, and 
 iv) removing solvent to form the catalyst precursor comprising chromium salt, aluminum carboxylate and boric acid, 
 
 B) heating the catalyst precursor in a non-reducing atmosphere at a temperature from 200 to 1200° C. for a time period from 30 minutes to 15 hours to form an activated catalyst, wherein the catalyst precursor comprises a silica xerogel comprising at least 90% by weight of SiO 2  carrying a chromium salt, aluminum carboxylate and boric acid, and 
 C) polymerising the one or more C 2  to C 8  α-alkenes in the presence of the activated catalyst. 
 
     
     
         21 . The method of  claim 20  wherein the catalyst precursor comprises the chromium salt, aluminum carboxylate and boric acid within a pore structure of the inorganic support material. 
     
     
         22 . The method of  claim 21  wherein the aluminum carboxylate is aluminum acetate. 
     
     
         23 . The method of  claim 22  wherein the chromium salt is selected from the group consisting of chromium carboxylate, chromium sulfate and chromium chloride. 
     
     
         24 . The method of  claim 23  wherein the chromium salt is chromium carboxylate. 
     
     
         25 . The method of  claim 24  wherein the chromium salt is chromium acetate. 
     
     
         26 . The method of  claim 20  wherein the aluminum carboxylate is aluminum acetate. 
     
     
         27 . The method of  claim 26  wherein the chromium salt is selected from the group consisting of chromium carboxylate, chromium sulfate and chromium chloride. 
     
     
         28 . The method of  claim 27  wherein the chromium salt is chromium carboxylate. 
     
     
         29 . The method of  claim 28  wherein the chromium salt is chromium acetate. 
     
     
         30 . The method of  claim 20  wherein the inorganic support material is in the form of particles having a weight mean particle diameter from 1 to 300 micrometres. 
     
     
         31 . The method of  claim 20  wherein the catalyst precursor comprises, as carried material, from 0.01 to 3% by weight of chromium expressed as the element, from 0.1 to 8% of aluminum expressed as the element and from 0.005 to 2% of boron expressed as the element.