Polymerization process

Abstract

Polymerization processes for ethylene and at least one mono-1-olefin comonomer having from about three to eight carbon atoms per molecule in the presence of a twice-aged catalyst system comprising chromium supported on a silica-titania support and a trialkylboron compound is provided. Novel ethylene copolymers also are produced.

That which is claimed is:  
     
         1 . A polymerization process comprising contacting under slurry polymerization conditions at a temperature within a range of about 200° F. to about 226° F. (about 93° C. to about 108° C.) in an isobutane diluent: 
 a) ethylene monomer;  
 b) at least 1 mono-1-olefin comonomer having about three to eight carbon atoms per molecule;  
 c) a catalyst system comprising chromium supported on a silica-titania support, wherein said support comprises from about 1 to about 10 weight percent titanium, based on the weight on the support, wherein said catalyst system has a pore volume within a range of about 0.5 to about 1.3 ml/g, a surface area within a range about 150 to 400 m 2 /g, and said catalyst system has been activated at a temperature within a range of about 800° F. to about 1300° F. (about 427° C. to about 704° C.);  
 d) about 1 to about 6 mg/kg, based on total reactor contents, of a trialkylboron compound; and  
 e) recovering an ethylene/mono-1-olefin copolymer.  
 
     
     
         2 . A process according to  claim 1  wherein said comonomer is selected from the group consisting of propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and mixtures thereof.  
     
     
         3 . A process according to  claim 2  wherein said comonomer is 1-hexene.  
     
     
         4 . A process according to  claim 1  wherein said reactor temperature is within a range of about 210° F. to 220° F.  
     
     
         5 . A process according to  claim 1  wherein said titania of the silica-titania support is coprecipitated with the silica.  
     
     
         6 . A process according to  claim 1  wherein said catalyst system is aged twice and wherein the first aging is at a substantially neutral pH and wherein the second aging is at an alkaline pH.  
     
     
         7 . A process according to  claim 1  wherein said catalyst system is calcined at a temperature within a range of about 800° F. to about 1300° F.  
     
     
         8 . A process according to  claim 1  wherein trialkyboron cocatalyst is present in the reactor in an amount within a range of 2 to about 4 mg/kg.  
     
     
         9 . A composition comprising ethylene and a mono-1-olefin having from about 3 to about 8 carbon atoms carbon atoms per molecule, wherein said copolymer has a high load melt index (HMLI) within a range of about 10 to about 80 g/10 minutes, a density within a range of about 0.95 to 0.96 g/cc, a shear response (HLMI/MI) is within a range of about 100 to about 250, a weight swell lower than about 380%, and a die swell lower than about 43%, an ESCR of greater than about 200 hours, a M w/ M n  of greater than about 12 and the onset of melt fracture of greater than about 2000 sec −1 .  
     
     
         10 . A composition according to  claim 9  wherein said mono-1-olefin is 1-hexene.  
     
     
         11 . A composition according to  claim 9  wherein said high-load melt index is within a range of 13 to 40 grams/10 minutes.  
     
     
         12 . A composition according to  claim 9  wherein said shear response (HLMI/MI) is within a range of 125 to 175.  
     
     
         13 . A polymerization process comprising contacting under slurry polymerization conditions at a temperature within a range of about 210° F. to about 220° F. in an isobutane diluent: 
 a) ethylene monomer;  
 b) 1-hexene comonomer;  
 c) a catalyst system comprising chromium supported on a silica-titania support, where in said support comprises from 2 to 8 weight percent titanium, based on the weight on the support, wherein said catalyst system has a pore volume within a range of 0.8 to 1.2 ml/g, a surface area within a range of 250 to 350 m 2 /g, and said catalyst system has been activated at a temperature within a range of 1 100° F. to 1200° F.;  
 d) about 2 to about 4 mg/kg, based on total reactor contents, of a triethylboron cocatalyst; and  
 e) recovering an ethylene/1-hexene copolymer.  
 
     
     
         14 . A copolymer composition comprising ethylene and 1-hexene, wherein said copolymer has a high load melt index (HMLI) within a range of 15 10 to 30 g 10 minutes, a density within a range of 0.954 to 0.956 g/cc, a shear response (HLMI/MI) is within a range of 125 to 175, a weight swell lower than about 330%, and a die swell lower than about 38% an ESCR, condition A, of greater than about 1000 hours, a M w/ M n  of within a range of 15 to 22. and the onset of melt fracture of greater than about 2300 sec −1 .