Powders of silica-oxide and mixed silica-oxide and method of preparing same

Abstract

Silica powders and mixed silica-oxide powders and methods of preparing such powders for use as catalyst supports for polymerization processes.

What is claimed is:  
     
         1 . An amorphous SiO 2  or mixed oxide silica base composition comprising: 
 (a) a non-particulate, dense, continuous network matrix; and    (b) encapsulated, less dense, non particulate regions with true macropores.    
     
     
         2 . The composition of  claim 1 , wherein the gel matrix further comprises a sheetlike microstructure.  
     
     
         3 . The composition of  claim 1 , wherein the composition has surface areas in a range of from 150 to 600 m 2 /gm.  
     
     
         4 . The composition of  claim 1 , wherein the composition has a mean mesopore diameter in a range of from 60 to about 250 Å.  
     
     
         5 . The composition of  claim 1 , wherein the composition has a measured pore volume in a range of from about 0.5 to 1.5 cc/gm.  
     
     
         6 . The composition of  claim 1 , wherein the composition has a macropore volume of at most 0.5 cc/gm.  
     
     
         7 . The composition of  claim 1 , wherein the composition is a mixed metal silica oxide selected from the group consisting of silica alumina, silica titania, silica zirconia and silica vanadia.  
     
     
         8 . Powders produced from the composition of  claim 1 .  
     
     
         9 . The powders of  claim 8 , wherein the powders are spray dried.  
     
     
         10 . The powders of  claim 8 , wherein the powders are vacuum dried.  
     
     
         11 . The spray dried powders of  claim 9 , wherein fragmentation potentials are in a range of from about 20 about 30.  
     
     
         12 . A catalyst comprising the composition of  claim 1  impregnated with a catalytic amount of at least one transition metal-containing compound.  
     
     
         13 . The catalyst of  claim 12 , wherein the at least one transition metal-containing compound is a chromium compound.  
     
     
         14 . The catalyst of  claim 12 , wherein the at least one transition metal-containing compound is present in an amount of 0.1 weight percent or greater based on the total catalyst weight.  
     
     
         15 . The catalyst of  claim 14 , wherein the at least one transition metal-containing compound is present in an amount in the range of from about 0.1 weight percent to about 10 weight percent.  
     
     
         16 . A polymerization process comprising contacting the catalyst of  claim 12  with at least one alpha-olefin under polymerization conditions.  
     
     
         17 . A method for preparing a silica gel composition which is a precursor material for a silica powder material with a microstructure comprising a non-particulate, dense, continuous, network matrix and encapsulated, less dense, non-particulate regions with true macropores, the method comprising: 
 (a) forming a first aqueous solution comprising silica ions;    (b) forming a second aqueous solution capable of neutralizing said first aqueous solution; and    (c) contacting said first and second aqueous solutions in a mixer-reactor under mixing conditions with shear forces to form the silica gel composition.    
     
     
         18 . The method according to  claim 17  further comprising aging the silica gel composition in acidic or basic conditions for up to one hour.  
     
     
         19 . The method of preparing the silica powder composition from the silica gel composition prepared by the method of  claim 17 , comprising the steps of: 
 (a) washing the silica gel with solutions of ammonium acetate, bicarbonate or nitrate;    (b) washing the silica gel composition in deionized water to further replace salts-contaminated water in the composition with fresh water; and    (c) drying the washed composition to remove substantially all water.    
     
     
         20 . The method of  claim 19 , further comprising calcining the dried composition for up to 8 hours at a maximum temperature of 450° C.  
     
     
         21 . The method according to  claim 17 , wherein said first aqueous solution is an acidic solution comprising sodium silicate and acid wherein the second aqueous solution has a pH above 8.  
     
     
         22 . The method according to  claim 17 , wherein said second aqueous solution is an ammonia based material selected from the group consisting of ammonium hydroxide; ammonium carbonate; ammonium bicarbonate and urea.  
     
     
         23 . The method according to  claim 17 , wherein said first aqueous solution is a basic solution of sodium silicate and wherein the second aqueous solution has a pH below 6.  
     
     
         24 . The method according to  claim 17 , wherein said second aqueous solution is sulfuric acid.  
     
     
         25 . The method according to  claim 17 , wherein the apparent average shear rate in said mixer-reactor is greater than about 0.5×10 4  sec −1 .  
     
     
         26 . The method according to  claim 17 , wherein said neutralization step is conducted in such a manner that the pH of the combined first aqueous solution and the neutralizing medium is controlled in the range of about 3.5 to about 11.  
     
     
         27 . The method of  claim 17 , wherein said catalyst is activated by being heated to a temperature in the range of 300° C. to 900° C. for from 2 to 16 hours.  
     
     
         28 . The method of  claim 21  further comprising the steps of: 
 (a) preparing an aqueous slurry of amorphous silica gel by continuously feeding an acidic solution comprising sodium silicate and acid to an emulsifier mixer while simultaneously and continuously feeding to said mixer an alkaline solution;  
 (b) operating said mixer with sufficient shear so that the precipitated silicate has sheets of silica in its microstructure;  
 (c) recovering said silica from said aqueous slurry using a vibrating filtration membrane to a solids content from 8 to 20 wt. %, after washing;  
 (d) drying the silica from (c);  
 (e) calcining the silica from (d);  
 (f) dispensing a chromium compound substantially uniformly onto said silica from (d) or (e) to form a catalyst having from 0.01 to 4 wt. % chromium;  
 (g) drying said catalyst; and  
 (h) activating said dry catalyst from (f) by heating to a temperature from 300° C. to 900° C. for from 2 to 16 hours.  
 
     
     
         29 . An olefin polymerization catalyst prepared by the method of  claim 17 .  
     
     
         30 . An olefin polymerization catalyst prepared by the method of  claim 28 .  
     
     
         31 . A polymerization process according to  claim 15  comprising contacting at least one mono-1-olefin having from 2 to 8 carbon atoms per molecule under polymerization reaction conditions in a polymerization reaction zone with a catalyst comprising an active catalytic component on a silica support comprising (a) a non-particulate, dense, gel matrix; and (b) encapsulated regions with true macropores.  
     
     
         32 . A process according to  claim 31 , wherein said catalytic component comprises a chromium component on the silica support.  
     
     
         33 . A process according to  claim 31 , wherein said at least one mono-1-olefin is selected from ethylene; propylene; butene-1; hexene-1 and octene-1.  
     
     
         34 . A process according to  claim 33 , wherein said at least one mono-1-olefin comprises ethylene and from 0.5 to 2 mole percent of one additional mono-1-olefin is selected from propylene; butene-1, hexene-1 and octene-1.  
     
     
         35 . A method for preparing silica alumina powder material with a microstructure comprising a non-particulate, dense continuous network matrix, encapsulated regions with true macropores, and sheets, the method comprising: 
 (a) preparing an acid aqueous solution comprising aluminum and silicon ions;    (b) preparing a basic aqueous solution comprising ammonium hydroxide;    (c) mixing the acidic aqueous solution and the basic aqueous solution in a mixer with shear forces to obtain a gel slurry with a microstructure comprising a non-particulate, dense, continuous network matrix, encapsulated regions with true macropores and sheets;    (d) maintaining the gel slurry at approximately pH 8.0 for up to one hour before washing the gel;    (e) washing the gel slurry first with aqueous acetate solution, then with water to obtain a gel conductivity below 1,000 mmhos;    (f) acidifying and concentrating the gel slurry by adding acid to the gel slurry to achieve a pH below 6.0 while gradually removing water from the gel slurry; and    (g) drying and calcining the gel slurry to form the silica-alumina powder material.