Production of broad molecular weight polyethylene

Abstract

Broad molecular weight polyethylene and polyethylene having a bimodal molecular weight profile can be produced with chromium oxide based catalyst systems employing alkyl silanols. The systems may also comprise various organoaluminum compounds. Catalyst activity and molecular weight of the resulting polyethylene may also be tuned using the present invention.

1 . A supported chromium catalyst comprising: 
 chromium oxide,    a silica-containing support comprising silica selected from the group consisting of silica having: 
 (a) a pore volume of about 1.1-1.8 cm 3 /g and a surface area of about 245-375 m 2 /g;  
 (b) a pore volume of about 2.4-3.7 cm 3 /g and a surface area of about 410-620 m 2 /g; and  
 (c) a pore volume of about 0.9-1.4 cm 3 /g and a surface area of about 390-590 m 2 /g; and,  
   an alkyl silanol,    wherein said supported chromium catalyst is activated at 400-860° C., prior to the addition of said alkyl silanol.    
     
     
         2 . The catalyst of  claim 1  further comprising titanium tetraisopropoxide.  
     
     
         3 . The catalyst of  claim 1  further comprising an organoaluminum compound.  
     
     
         4 . The catalyst of  claim 3  wherein said activated chromium catalyst is treated first with said alkyl silanol and then with said organoaluminum compound.  
     
     
         5 . The catalyst of  claim 3  wherein said silica has a pore volume of about 2.4-3.7 cm 3 /g and a surface area of about 410-620 m 2 /g and said organoaluminum compound is an alkyl aluminum alkoxide compound.  
     
     
         6 . The catalyst of  claim 3  wherein said silica has a pore volume of about 1.1-1.8 cm 3 /g and a surface area of about 245-375 m 2 /g, and said organoaluminum compound is an alkyl aluminum alkoxide compound.  
     
     
         7 . The catalyst of  claim 3  wherein said organoaluminum compound is added in-situ.  
     
     
         8 . The catalyst of  claim 3  further comprising at least a second chromium-based compound.  
     
     
         9 . The catalyst of  claim 8  wherein said second chromium-based compound is a chromium oxide on silica or an organoaluminum-reduced chromium oxide on silica.  
     
     
         10 . The catalyst of  claim 3  wherein said alkyl silanol or said organoaluminum compound or both said alkyl silanol and said organoaluminum compound are added in-situ.  
     
     
         11 . The catalyst of  claim 10  wherein said alkyl silanol and said organoaluminum compound are pre-mixed prior to said in-situ addition.  
     
     
         12 . The catalyst of  claim 3  wherein said organoaluminum compound is an alkyl aluminum alkoxide compound.  
     
     
         13 . The catalyst of  claim 12  wherein said alkyl aluminum alkoxide compound is diethyl aluminum ethoxide.  
     
     
         14 . The catalyst of  claim 12  formed by the in situ addition of said alkyl aluminum alkoxide compound.  
     
     
         15 . The catalyst of  claim 14  wherein said alkyl aluminum alkoxide compound is diethyl aluminum ethoxide.  
     
     
         16 . The catalyst of  claim 3  wherein said organoaluminum compound is an alkyl aluminum compound.  
     
     
         17 . The catalyst of  claim 16  wherein said alkyl aluminum compound is selected from the group consisting of triethyl aluminum, tri-isobutyl aluminum, and tri-n-hexyl aluminum.  
     
     
         18 . The catalyst of  claim 17  formed by the in situ addition of said alkyl aluminum compound.  
     
     
         19 . The catalyst of  claim 17  wherein said alkyl aluminum compound is tri-isobutyl aluminum.  
     
     
         20 . The catalyst of  claim 1  wherein said supported chromium catalyst is activated at 600-860° C.  
     
     
         21 . The catalyst of  claim 1  wherein said alkyl silanol is triphenyl silanol  
     
     
         22 . A supported chromium catalyst comprising: 
 chromium oxide,    a silica-containing support comprising silica selected from the group consisting of silica having: 
 (a) a pore volume of about 1.1-1.8 cm 3 /g and a surface area of about 245-375 m 2 /g;  
 (b) a pore volume of about 2.4-3.7 cm 3 /g and a surface area of about 410-620 m 2 /g; and  
 (c) a pore volume of about 0.9-1.4 cm 3 /g and a surface area of about 390-590 m 2 /g; and,  
   an organoaluminum compound,    wherein said supported chromium catalyst is activated at 400-860° C.    
     
     
         23 . The catalyst of  claim 22  wherein said organoaluminum compound is diethyl aluminum triethylsiloxide.  
     
     
         24 . The catalyst of  claim 22  further comprising titanium tetraisopropoxide.  
     
     
         25 . A supported chromium catalyst comprising: 
 chromium oxide,    a silica-containing support comprising silica selected from the group consisting of silica having: 
 (a) a pore volume of about 1.1-1.8 cm 3 /g and a surface area of about 245-375 m 2 /g;  
 (b) a pore volume of about 2.4-3.7 cm 3 /g and a surface area of about 410-620 m 2 /g; and  
 (c) a pore volume of about 0.9-1.4 cm 3 /g and a surface area of about 390-590 m 2 /g;  
   wherein said supported chromium catalyst is activated at 400-860° C.; and,    a second chromium-based compound comprising silylchromate on silica treated with an organoaluminum compound.    
     
     
         26 . The catalyst of  claim 25  wherein said chromium oxide catalyst component is treated with an organoaluminum compound after activation.  
     
     
         27 . The catalyst of  claim 25  further comprising titanium tetraisopropoxide.  
     
     
         28 . A process for producing an ethylene polymer comprising the steps of: 
 contacting ethylene under polymerization conditions with a catalyst system, said catalyst system comprising chromium oxide, an alkyl silanol compound, and a silica-containing support comprising silica selected from the group consisting of silica having: 
 (a) a pore volume of about 1.1-1.8 cm 3 /g and a surface area of about 245-375 m 2 /g;  
 (b) a pore volume of about 2.4-3.7 cm 3 /g and a surface area of about 410-620 m 2 /g; and  
 (c) a pore volume of about 0.9-1.4 cm 3 /g and a surface area of about 390-590 m 2 /g; and,  
   controlling one or more of catalyst activity, polymer Mz/Mw, polymer Mw/Mn, and polymer density of the resulting ethylene polymer by varying the level of addition of said alkyl silanol.    
     
     
         29 . The process of  claim 28  wherein said polymer Mw/Mn is controlled to greater than about 15 and said polymer Mz/Mw is controlled to greater than about 5.  
     
     
         30 . The process of  claim 28  wherein said catalyst system further comprises an organoaluminum compound.  
     
     
         31 . The process of  claim 30  wherein said catalyst system further comprises at least a second chromium-based catalyst.  
     
     
         32 . The process of  claim 31  wherein said second chromium-based compound is a chromium oxide on silica or an organoaluminum-reduced chromium oxide on silica.  
     
     
         33 . The process of  claim 30  wherein said organoaluminum compound is an alkyl aluminum alkoxide.  
     
     
         34 . The process of  claim 33  wherein said alkyl aluminum alkoxide comprises diethylaluminum ethoxide.  
     
     
         35 . The process of  claim 30  wherein said organoaluminum compound is an alkyl aluminum compound.  
     
     
         36 . The process of  claim 35  wherein said alkyl aluminum compound is selected from the group consisting of triethyl aluminum, tri-isobutyl aluminum, and tri-n-hexyl aluminum.  
     
     
         37 . The process of  claim 28  wherein said catalyst system further comprises titanium tetraisopropoxide.  
     
     
         38 . A process for producing an ethylene polymer comprising the steps of: 
 contacting ethylene under polymerization conditions with a catalyst system, said catalyst system comprising chromium oxide,    a silica-containing support comprising silica selected from the group consisting of silica having: 
 (a) a pore volume of about 1.1-1.8 cm 3 /g and a surface area of about 245-375 m 2 /g;  
 (b) a pore volume of about 2.4-3.7 cm 3 /g and a surface area of about 410-620 m 2 /g, and  
 (c) a pore volume of about 0.9-1.4 cm 3 /g and a surface area of about 390-590 m 2 /g;  
   wherein said supported chromium catalyst is activated at 400-860° C.; and,    a second chromium-based compound comprising silylchromate on silica treated with an organoaluminum compound; and,    controlling one or more of polymer molecular weight, polymer Mz/Mw, polymer Mw/Mn, and distribution of comonomer incorporation by varying the relative amount of each of said chromium oxide and said second chromium-based compound.    
     
     
         39 . The process of  claim 38  wherein said chromium oxide catalyst component is treated with an organoaluminum compound after activation.  
     
     
         40 . The process of  claim 38  wherein said catalyst system further comprises titanium tetraisopropoxide.  
     
     
         41 . An ethylene polymer having a density of 0.918-0.970 g/cm 3  and a flow index (I 21 ) of 1-500 and produced by the process of  claim 28 .  
     
     
         42 . An ethylene polymer having a density of 0.918-0.970 g/cm 3  and a flow index (I 21 ) of 1-500 and produced by the process of  claim 30 .  
     
     
         43 . An ethylene polymer having a density of 0.918-0.970 g/cm 3  and a flow index (I 21 ) of 1-500 and produced by the process of  claim 31 .  
     
     
         44 . An ethylene polymer having a density of 0.918-0.970 g/cm 3  and a flow index (I 21 ) of 1-500 and produced by the process of  claim 32 .  
     
     
         45 . An ethylene polymer having a density of 0.918-0.970 g/cm 3  and a flow index (I 21 ) of 1-500 and produced by the process of  claim 38.