REACTOR SYSTEM FOR MULTIMODAL POLYETHYLENE POLYMERIZATION

Abstract

The present invention relates to a process for producing a multimodal polyethylene composition in the reactor system according to the invention, comprising; (a) polymerizing ethylene in an inert hydrocarbon medium in the first reactor in the presence of a catalyst system, selected from Ziegler-Natta catalyst or metallocene, and hydrogen in an amount of 0.1-95% by mol with respect to the total gas present in the vapor phase in the first reactor to obtain a low molecular weight polyethylene or a medium molecular weight polyethylene; (b) removing in the hydrogen removal unit 98.0 to 99.8% by weight of the hydrogen comprised in a slurry mixture obtained from the first reactor at a pressure in the range of 103-145 kPa (abs) and transferring the obtained residual mixture to the second reactor; (c) polymerizing ethylene and optionally C.sub.4 to C.sub.12 α-olefin comonomer in the second reactor in the presence of a catalyst system, selected from Ziegler-Natta catalyst or metallocene, and in the presence of hydrogen in an amount obtained in step (b) to obtain a first high molecular weight polyethylene or a first ultra high molecular weight polyethylene in the form of a homopolymer or a copolymer and transferring a resultant mixture to the third reactor; and (d) polymerizing ethylene, and optionally α-olefin comonomer in the third reactor in the presence of a catalyst system, selected from Ziegler-Natta catalyst or metallocene, and hydrogen, wherein the amount of hydrogen in the third reactor is in a range of 1-70% by mol, preferably 1-60% by mol with respect to the total gas present in the vapor phase in the third reactor or optionally substantial absence of hydrogen to obtain a second high molecular weight polyethylene or a second ultra high molecular weight polyethylene homopolymer or copolymer; and a multimodal polyethylene composition obtainable this way.

Claims

1. A reactor system for a multimodal polyethylene polymerization process, comprising; (a) a first reactor; (b) a hydrogen removal unit arranged between the first reactor and a second reactor comprising at least one vessel connected with a depressurization equipment, preferably selected from vacuum pump, compressor, blower, ejector or a combination thereof, the depressurization equipment allowing to adjust an operating pressure to a pressure in a range of 100-200 kPa (abs); (c) the second reactor; and (d) a third reactor.

2. The reactor system according to claim 1, wherein the depressurization equipment allows to adjust the operating pressure in the hydrogen removal unit to a pressure in the range of 103-145 kPa (abs), preferably 104-130 kPa (abs), most preferably 105 to 115 kPa (abs).

3. The reactor system according to claim 1, wherein the hydrogen removal unit further contains a stripping column for the separation of hydrogen and a liquid diluent.

4. A process for producing a multimodal polyethylene composition in the reactor system according to claim 1, comprising; (a) polymerizing ethylene in an inert hydrocarbon medium in the first reactor in the presence of a catalyst system, selected from Ziegler-Natta catalyst or metallocene, and hydrogen in an amount of 0.1-95% by mol with respect to the total gas present in the vapor phase in the first reactor to obtain a low molecular weight polyethylene or a medium molecular weight polyethylene; (b) removing in the hydrogen removal unit 98.0 to 99.8% by weight of the hydrogen comprised in a slurry mixture obtained from the first reactor at a pressure in the range of 103-145 kPa (abs) and transferring the obtained residual mixture to the second reactor; (c) polymerizing ethylene and optionally C.sub.4 to C.sub.12 α-olefin comonomer in the second reactor in the presence of a catalyst system, selected from Ziegler-Natta catalyst or metallocene, and in the presence of hydrogen in an amount obtained in step (b) to obtain a first high molecular weight polyethylene or a first ultra high molecular weight polyethylene in the form of a homopolymer or a copolymer and transferring a resultant mixture to the third reactor; and (d) polymerizing ethylene, and optionally α-olefin comonomer in the third reactor in the presence of a catalyst system, selected from Ziegler-Natta catalyst or metallocene, and hydrogen, wherein the amount of hydrogen in the third reactor is in a range of 1-70% by mol, preferably 1-60% by mol with respect to the total gas present in the vapor phase in the third reactor or optionally substantial absence of hydrogen to obtain a second high molecular weight polyethylene or a second ultra high molecular weight polyethylene homopolymer or copolymer.

5. The process according to claim 4, wherein the removing is removing of 98.0-99.7% of the hydrogen, more preferable 98.0-99.5%, and most preferred 98.0 to 99.1%.

6. The process according to claim 4, wherein the operation pressure in the hydrogen removal unit is in the range of 103-145 kPa (abs), more preferably 104-130 kPa (abs), and most preferred 105 to 115 kPa (abs).

7. A multimodal polyethylene composition obtainable by a process according to claim 4, comprising; (A) 30 to 65 parts by weight of the low molecular weight polyethylene or the medium molecular weight polyethylene; (B) 5 to 40 parts by weight of the first high molecular weight polyethylene or the first ultra high molecular weight polyethylene; and (C) 10 to 60 parts by weight of the second high molecular weight polyethylene or the second ultra high molecular weight polyethylene copolymer.

8. The multimodal polyethylene composition according to claim 7, wherein the multimodal polyethylene composition has a weight average molecular weight from 80,000 to 5,000,000 g/mol, preferably 150,000 to 3,000,000 g/mol, measured by Gel Permeation Chromatography.

9. The multimodal polyethylene composition according to claim 7 wherein the multimodal polyethylene composition has a number average molecular weight from 5,000 to 100,000 g/mol, preferably 5,000 to 80,000 g/mol measured by Gel Permeation Chromatography.

10. The multimodal polyethylene composition according to claim 7 wherein the multimodal polyethylene composition has a Z average molecular weight from 700,000 to 10,000,000 g/mol, preferably 700,000 to 8,000,000 g/mol, measured by Gel Permeation Chromatography.

11. The polyethylene composition according to claim 7 wherein the multimodal polyethylene composition has a density 0.930 to 0.965 g/cm.sup.3 according to ASTM D 1505 and/or a melt flow index MI.sub.5 from 0.01 to 60 g/10 min, and/or MI.sub.21 from 0.05 to 800 g/10 min and/or an intrinsic viscosity from 1.0 to 30, preferably 1.5 to 30 measured according to ISO1628-3.

Description

EXPERIMENTAL AND EXAMPLES

[0076] The medium or high density polyethylene preparation was carried out in three reactors in series. Ethylene, hydrogen, hexane, catalyst and TEA (triethyl aluminum) co-catalyst were fed into a first reactor in the amounts shown in Table 1. A commercial available Ziegler-Natta catalyst was used. The suitable catalyst preparation is for example described in the Hungarian patent application number 0800771R. The polymerization in first reactor was carried out to make a low or medium molecular weight polyethylene. All of polymerized slurry polymer from first reactor was then transferred to a hydrogen removal unit to remove unreacted gas and some of hexane from polymer. The operating pressure in the hydrogen removal unit was be varied in a range of 100 to 115 kPa (abs) where residual hydrogen was removed more than 98% by weight but not more than 99.8% by weight from hexane before transferring to a second polymerization reactor. Some fresh hexane, ethylene and/or comonomer were fed into second reactor to produce first high molecular weight polyethylene (HMW1). All of polymerized polymer from second reactor was fed into the third reactor which produce second high molecular weight polyethylene (HMW2). Ethylene, comonomer, hexane and/or hydrogen were fed into the third reactor.

Comparative Example 1 (CE1)

[0077] A homopolymer was produced in first reactor to obtain a low molecular weight portion before transferring such polymer to hydrogen removal unit. Reactant mixture was introduced into the hydrogen removal unit to separate the unreacted mixture from the polymer. Residual hydrogen was removed 97.6% by weight when hydrogen removal unit was operated at pressure of 150 kPa (abs). The low molecular weight polymer was then transferred to the second reactor to produce a first high molecular weight polymer. Final, produced polymer from second reactor was transferred to the third reactor to create a second high molecular weight polymer. In third, a copolymerization was carried out by feeding 1-butene as a comonomer.

Example 1 (E1)

[0078] Example 1 was carried out in the same manner as Comparative Example 1 except that the hydrogen removal unit was operated at pressure of 115 kPa (abs). The residual of hydrogen from first reactor was removed 98.0% by weight. Characteristic properties of these multimodal polymers are shown in Table 2. As it can be seen, an improvement of stiffness-impact balance was observed when the percentage of removed hydrogen residual increased compared with the properties of Comparative Example 1.

Example 2 (E2)

[0079] Example 2 was carried out in the same manner as Comparative Example 1 except that the hydrogen removal unit was operated at pressure of 105 kPa (abs). The residual hydrogen from the first reactor was removed to an extend of 99.1% by weight. The operational of hydrogen removal unit under this pressure leads to an expansion of a polymer properties range. As seen in Table 2, a final melt flow rate of E2 was lower than a final melt flow rate of CE1 resulted in an improvement of Charpy impact while still maintained the flexural modulus.

Comparative Example 2 (CE2)

[0080] Comparative Example 2 was carried out in the same manner as Comparative Example 1 except that the hydrogen removal unit was operated at pressure of 102 kPa (abs). The residual of hydrogen from first reactor was removed to an extend of 99.9% by weight. The operational of hydrogen removal unit under this pressure leads to an expansion of a polymer properties range. As seen in Table 2, the final melt flow rate and a density of CE2 were quite similar to a final melt flow rate and a density of E2. A decay of Charpy impact was showed in CE2 compared to E2.

Comparative Example 3 (CE3)

[0081] A homopolymer was produced in a first reactor to obtain a low molecular weight portion before transferring the polymer to a hydrogen removal unit. Reactant mixture was introduced into the hydrogen removal unit to separate the unreacted mixture from the polymer. Hydrogen residual was removed to an extend of 97.9% by weight when hydrogen removal unit was operated at pressure of 150 kPa (abs). The low molecular weight polymer was then transferred to a second reactor to produce a first high molecular weight polymer. In the second reactor, a copolymerization was carried out by feeding 1-butene as a comonomer. Finally, in-situ bimodal copolymer from second reactor was transferred to a third reactor to create a second high molecular weight copolymer portion. Characteristic properties of this multimodal polymers is shown in Table 2. A significant improvement in Charpy impact at room temperature could be obtained by decreasing a density of final polymer when co-polymer was produced in both the second and the third reactor.

Example 3 (E3)

[0082] Example 3 was carried out in the same manner as Comparative Example 3 except that the hydrogen removal unit was operated at pressure of 105 kPa. The residual of hydrogen from first reactor was removed to an extend of 98.8% by weight. The polymer obtained by this process operation had a melt flow rate of 0.195 g/10 min (5 kg loading) lower than such value obtained from CE3. As seen in Table 2, it revealed an improvement of stiffness-impact balance when the percentage of removed hydrogen residual increases compared with the properties of Comparative Example 3.

Example 4 (E4)

[0083] A homopolymer was produced in the first reactor to obtain a medium molecular weight portion before transferring such polymer to hydrogen removal unit. The hydrogen removal unit was operated at pressure of 105 kPa (abs) to separate the unreacted mixture from the polymer. The residual of hydrogen from first reactor was removed to an extend of 98.9% by weight. The medium molecular weight polymer was then transferred to the second reactor to produce a first ultra high molecular weight polymer. Finally, produced polymer from second reactor was transferred to the third reactor to create a second ultra high molecular weight polymer. The second and third reactors are operated under hydrogen depleted polyethylene polymerization. The processable in-situ ultra high molecular weight polyethylene is produced by this process operation leads to an excellent improvement of Charpy impact strength while still maintained the flexural modulus. The conventional UHMWPE with very high IV was known that it was unable to measured MI.sub.21. The inventive example E4 with IV of 9 dl/g show good melt flow ability beyond the known art.

Comparative Example 4 (CE4)

[0084] A homopolymer was produced in first reactor to obtain a low molecular weight portion before transferring such polymer to hydrogen removal unit. Reactant mixture was introduced into the hydrogen removal unit to separate the unreacted mixture from the polymer. Residual hydrogen was removed 97.6% by weight when hydrogen removal unit was operated at pressure of 150 kPa (abs). The low molecular weight polymer was then transferred to the second reactor to produce a first high molecular weight polymer. Final, produced polymer from second reactor was transferred to the third reactor to create a second high molecular weight polymer. In third, a copolymerization was carried out by feeding 1-butene as a comonomer. As seen in Table 2 and 3, the final melt flow rate of CE4 were quite similar to a final melt flow rate of E5. A decay of charpy impact and flexural modulus were showed in CE4 compared to E5, even it showed lower density of E5.

Example 5 (E5)

[0085] Example 5 was carried out in the same manner as Comparative Example 4 except that the hydrogen removal unit was operated at pressure of 115 kPa (abs). The residual of hydrogen from first reactor was removed to an extend of 98.5% by weight. The polymer obtained by this process operation had a melt flow rate of 48 g/10 min (5 kg loading) lower than such value obtained from CE3. As seen in Table 2, it revealed an improvement of stiffness-impact balance when the percentage of removed hydrogen residual increases compared with the properties of Comparative Example 4.

Example 6 (E6)

[0086] Example 6 was carried out in the same manner as Example 4 except that the comonomer feeding in the third ultra high molecular weight polyethylene. The polymer produced by this process leads to an excellent improvement of Charpy impact strength while still maintained the flexural modulus. As shown in table 2, the inventive example 6 with IV of 23 dl/g show the high impact strength (one notched impact without break) and flexural modulus as compared to comparative samples, however, the melt flow index is unmeasurable due to high viscosity and high Mw.

TABLE-US-00001 TABLE 1 CE1 E1 E2 CE2 CE3 E3 E4 CE4 E5 E6 W.sub.A, % 55 55 55 55 45 45 30 50 50 30 W.sub.B, % 20 20 20 20 25 25 30 10 10 30 W.sub.C, % 25 25 25 25 30 30 40 40 40 40 First reactor Polymerization type Homo Homo Homo Homo Homo Homo Homo Homo Homo Homo Temperature, ° C. 80 80 80 80 80 80 80 80 80 80 Total pressure, kPa 800 800 800 800 800 800 800 800 800 800 Ethylene, g 1,100.72 1,100.70 1,100.86 1,100.74 900.30 900.30 540.50 725.21 725.57 485.70 Hydrogen, g 1.62 1.62 1.55 1.55 2.97 2.99 1.34 1.13 1.13 1.23 Hydrogen removal unit Pressure, kPa (abs) 150 115 105 102 150 105 105 150 115 105 Hydrogen remove, % 97.6 98.0 99.1 99.9 97.9 98.8 98.9 97.7 98.5 98.3 Second reactor Polymerization type Homo Homo Homo Homo Copo Copo Homo Copo Copo Homo Temperature, ° C. 70 70 70 70 70 70 70 80 80 70 Total pressure, kPa 250 250 250 250 250 250 400 300 300 400 Ethylene, g 400.52 400.81 400.35 400.06 500.17 500.31 540.36 145.35 145.21 485.78 Hydrogen, g 0 0 0 0 0 0 0 0 0 0 1-butene, g 0 0 0 0 18.84 18.91 0 8 8 0 Third reactor Polymerization type Copo Copo Copo Copo Copo Copo Homo Copo Copo Copo Temperature, ° C. 70 70 70 70 70 70 80 80 80 70 Total pressure, kPa 400 400 400 400 400 400 600 600 600 600 Ethylene, g 500.74 500.11 500.30 500.63 600.02 601.19 720.60 580.53 580.46 647.54 Hydrogen, g 0 0.001 0.001 0.001 0 0.001 0 0.59 1.37 0 1-butene, g 35.05 30.01 30.03 30.04 60.01 60.04 0 27 27 20.60 W.sub.A means percent by weight of Polymer in the first reactor W.sub.B means percent by weight of Polymer in the second reactor W.sub.C means percent by weight of Polymer in the third reactor

TABLE-US-00002 TABLE 2 CE1 E1 E2 CE2 CE3 Powder MI.sub.5, g/10 min 0.474 0.372 0.240 0.242 0.275 MI.sub.21, g/10 min 13.83 10.80 7.38 7.23 6.40 Density, g/cm.sup.3 0.9565 0.9578 0.9555 0.9567 0.9441 IV, dl/g — — — — — Mw 276,413 244,279 291,295 319,487 252,160 Mn 8,877 8,724 8,843 8,472 8,016 Mz 2,788,607 2,370,678 3,401,041 4,135,007 1,638,224 PDI 31 28 33 38 31 Pellet MI.sub.5, g/10 min 0.436 0.410 0.232 0.199 0.298 MI.sub.21, g/10 min 14.46 11.68 7.876 6.696 7.485 Density, g/cm.sup.3 0.9577 0.9574 0.9568 0.9566 0.9442 IV, dl/g 2.97 3.03 3.52 3.64 3.12 % Crystallinity, 64.70 67.24 64.78 66.16 57.49 % Charpy, 23 ° C., 23.5 29.9 35.3 30.5 47.9 kj/m.sup.2 Flexural 1,130 1,210. 1,123 1,123 727 modulus, MPa E3 E4 CE4 E5 E6 Powder MI.sub.5, g/10 min 0.200 — 54.80 48.07 NA MI.sub.21, g/10 min 4.81 0.145 641 653 NA Density, g/cm.sup.3 0.9438 0.9534 0.9606 0.9590 0.9409 IV, dl/g — 9.00 1.07 1.06 23 Mw 306,468 868,813 77,334 91,752 1,269,336 Mn 7,637 24,107 5,400 6,035 23,450 Mz 2,643,953 5,112,060 667,276 1,027,956 5,262,195 PDI 40 36 14 15 54.13 Pellet MI.sub.5, g/10 min 0.195 — 60.62 55.47 — MI.sub.21, g/10 min 4.604 — 713.1 752.2 — Density, g/cm.sup.3 0.9440 — 0.9608 0.9594 — IV, dl/g 3.37 9.00 1.0 1.1 23 % Crystallinity, 54.05 68.23 69.52 65.64 58.20 % Charpy, 23 ° C., 50.9 84.4 1.5 1.8 85.41 kj/m.sup.2 Flexural 785 1,109 1,147 1,196 890 modulus, MPa The features disclosed in the foregoing description and in the claims may, both separately and in any combination, be material for realizing the invention in diverse forms thereof.