Methods for producing bimodal polyolefins and impact copolymers
Provided are methods for producing bimodal polyolefins comprising the steps of contacting α-olefin monomers with a catalyst in slurry polymerization conditions in the presence of zero to minimum hydrogen to produce a high molecular weight polyolefin and contacting additional α-olefin monomers in gas phase polymerization conditions and the high molecular weight polyolefin and the catalyst to produce bimodal polyolefin having high stiffness and broad molecular weight distribution. An additional step of polymerizing the bimodal polyolefin with a comonomer in a second gas phase can provide a bimodal impact copolymer having high stiffness and broad molecular weight distribution. Among the advantages of the present methods, bimodal polyolefins can be produced in a continuous process between a slurry polymerization reactor and a gas phase polymerization reactor without a venting step in between and with minimal hydrogen in the slurry polymerization reactor.
1 . A method for producing polypropylene comprising the steps of:
polymerizing propylene monomer with a catalyst in a slurry to produce an effluent comprising a high molecular weight polypropylene having a weight average molecular weight (Mw) of between about 500 kDa and 1000 kDa and non-polymerized propylene monomer; and
reacting the catalyst and additional propylene monomer in the presence of the high molecular weight polypropylene with hydrogen in a first gas phase to produce low molecular weight polypropylene having a weight average molecular weight of between about 20 kDa to 150 kDa, wherein the produced polypropylene has a flex modulus of at least about 1500 MPa.
2 . The method of claim 1 , wherein polymerizing propylene monomer with a catalyst in a slurry is performed in a slurry polymerization reactor.
3 . The method of claim 1 , wherein reacting in the first gas phase occurs in a gas phase polymerization reactor.
4 . The method of claim 1 , wherein the low molecular weight polypropylene has a molecular weight distribution of between about 3.0 and about 40.0.
5 . The method of claim 1 , wherein the low molecular weight polypropylene has a flexural modulus between about 1500 mPa and 1900 mPa.
6 . The method of claim 1 , wherein a mole ratio of hydrogen to propylene monomer in the first gas phase is between about 0.02 to about 0.3.
7 . The method of claim 1 , further comprising the step of polymerizing the high molecular weight polypropylene and the low molecular weight polypropylene with ethylene and propylene in a second gas phase with hydrogen to produce an impact copolymer.
8 . The method of claim 7 , wherein a second effluent is drawn from the second gas phase and the second effluent comprises the impact copolymer.
9 . The method of claim 7 , wherein the impact copolymer has a melt flow rate (230° C./2.16 kg) within a range of from 5.0 g/10 min to 50 g/10 min.
10 . The method of claim 7 , wherein the impact copolymer has a Notched Izod impact, according to ASTM D256 at 21° C., between about 400 J/m and about 1000 J/m.
11 . The method of claim 1 , wherein propylene monomer is recycled to the slurry.
12 . The method of claim 1 , wherein the polypropylene has a molecular weight distribution between about 4.0 to about 20.
13 . The method of claim 1 , wherein pressure of the slurry is between about 430 psig to about 510 psig and wherein temperature of the slurry is between about 60° C. and about 80° C.
14 . The method of claim 1 , wherein pressure of the first gas phase is between about 180 psig to about 300 psig and wherein temperature of the first gas phase is between about 60° C. and about 90° C.
15 . The method of claim 1 , wherein reaction residence time in the slurry is between about 30 minutes to about 90 minutes and wherein a residence time in the first gas phase is between about 30 minutes to about 180 minutes.
16 . The method of claim 1 , wherein hydrogen is fed to the first gas phase at a flow rate of between about 1000 sccm to about 5000 sccm.
17 . The method of claim 1 , wherein the polypropylene has a melt flow rate (230° C./2.16 kg) within a range of from 5.0 g/10 min to 50 g/10 min.
18 . The method of claim 1 , wherein polypropylene has a Notched Izod impact, according to ASTM D256 at 21° C., between about 0 J/m and about 6 J/m.
19 . A method for producing polypropylene comprising the steps of:
contacting a propylene monomer with a catalyst in a slurry polymerization reactor to produce an effluent comprising a high molecular weight polypropylene and propylene monomer, the high molecular weight polypropylene having a weight average molecular weight (Mw) of between about 500 kDa and 1000 kDa; and
feeding hydrogen and the effluent into a gas phase polymerization reactor to produce low molecular weight polypropylene having a weight average molecular weight of between about 20 kDa and about 150 kDa and a flexural modulus between about 1500 mPa and 1900 mPa, wherein a mole ratio of hydrogen to propylene monomer in the gas phase is between about 0.02 to about 0.3.
20 . A method for producing bimodal polyolefin comprising the steps of:
contacting α-olefin monomers with a catalyst in slurry polymerization conditions in the presence or absence of hydrogen to produce a high molecular weight polyolefin; and
contacting additional α-olefin monomers in gas phase polymerization conditions in the presence of hydrogen and the high molecular weight polyolefin and the catalyst to produce bimodal polyolefin having a molecular weight distribution of between about 3.0 and about 40.0, a flexural modulus of at least 1500 MPa and a melt flow rate between about 50 g/10 min and about 150 g/min;
wherein a mole ratio of hydrogen to α-olefin monomers in the gas phase is between about 0.02 to about 0.3.