PROCESS FOR THE PREPARATION OF POLYETHYLENES

Abstract

The present invention relates to a process for the production of a polyethylene by polymerisation of a reaction mixture comprising ethylene in the presence a catalyst system and an antistatic agent according to formula I: (I) wherein R1, R2 and R3 stand for a moiety according to formula II or a hydrocarbon moiety having 1 to 20 carbon atoms (II) wherein each of R4, R5 and R6 may be the same or different, and wherein each of R4, R5 and R6 is a hydrocarbon moiety having 1 to 10 carbon atoms, and wherein at least one of R1, R2 and R3 is a moiety according to formula II. Such process allows for the reduction of sheeting in the polymerisation reactor without compromising the polymerisation reaction kinetics.

##STR00001##

Claims

1. Process for the production of a polyethylene by polymerisation of a reaction mixture comprising ethylene in the presence a catalyst system and an antistatic agent according to formula I: ##STR00006## wherein R1, R2 and R3 stand for a moiety according to formula II or a hydrocarbon moiety having 1 to 20 carbon atoms ##STR00007## wherein each of R4, R5 and R6 is the same or different, and wherein each of R4, R5 and R6 is a hydrocarbon moiety having 1 to 10 carbon atoms, and wherein at least one of R1, R2 and R3 is a moiety according to formula II.

2. Process according to claim 1, wherein the process is a solution-based polymerisation process, a slurry-based polymerisation process, or a gas-phase polymerisation process.

3. Process according to claim 1, wherein the catalyst system is a metallocene-type catalyst system.

4. Process according to claim 3 wherein the metallocene-type catalyst system comprises a metallocene complex according to formula III: ##STR00008## wherein: Z is ZrX.sub.2, HfX.sub.2, or TiX.sub.2, wherein X is a halogen, an alkyl, an aryl, or an aralkyl; R2 is a bridging moiety containing at least one sp2 hybridised carbon atom; each of R1, R1′, R3, R3′, R4, R4′, R5 and R5′ is independently hydrogen or a hydrocarbon moiety comprising 1-20 carbon atoms.

5. Process according to claim 4, wherein in the metallocene complex according to formula III, R4 with R5 and R4′ and R5′ are fused to form a complex according to formula IV: ##STR00009## wherein: R2 is a bridging moiety containing at least one sp2 hybridised carbon atom; each of R4, R4′, R7 and R7′ is independently hydrogen or a moiety comprising 1-10 carbon atoms, wherein R4, R4′, R7 and R7′ are the same; each of R5, R5′, R6 and R6′ is independently hydrogen or a moiety comprising 1-10 carbon atoms, wherein R5, R5′, R6 and R6′ are the same; and Z is ZrX.sub.2, HfX.sub.2, or TiX.sub.2, wherein X is a halogen, an alkyl, an aryl or an aralkyl.

6. Process according to claim 4, wherein the bridging moiety R2 is a substituted or unsubstituted methylene, 1,2-phenylene or 2,2′-biphenylene moiety.

7. Process according to claim 3, wherein the metallocene-type catalyst system comprises a metallocene complex supported on a porous silica support having an average particle size of from 10 to 120 μm, a pore volume of ≥0.5 and ≤3.0 cm.sup.3/g], and a surface area of ≥50 and ≤500 m.sup.2/g, as determined in accordance with ISO 9276-2 (2014).

8. Process according to claim 1, wherein the antistatic agent is present as a catalyst component in a quantity such that the molar ratio of the antistatic agent to active species of the catalyst system is ≥0.001 and ≤10.0.

9. Process according to claim 1, wherein each of R1, R2 and R3 in formula I is independently a moiety according to formula II.

10. Process according to claim 1, wherein each of R4, R5 and R6 in formula II is independently a linear or branched hydrocarbon moiety comprising 1-5 carbon atoms.

11. Process according to claim 1, wherein the antistatic agent is a compound selected from tris(trimethylsilyl)amine, tris(triethylsilyl)amine, tris(triisopropylsilyl)amine, tris(triisobutylsilylamine), N,N-bis(trimethylsilyl)methylamine, N,N-bis(trimethylsilyl)dodecylamine, and N,N-bis(trimethylsilyl)octadecylamine.

12. Process according to claim 1, wherein the process is performed in a fluidised bed reactor.

13. Process according to claim 3, wherein the process is continuously operated by providing to a reactor a continuous supply of a reactant feed comprising ethylene, a continuous supply of the metallocene-type catalyst system, and a continuous supply of the antistatic agent, such that the molar ratio of the metallocene complex in the metallocene-type catalyst system to the antistatic agent is maintained in the range of ≥0.01 and ≤100, and wherein a product stream comprising the polyethylene produced in the polymerisation reactor is withdrawn continuously from the reactor.

14. Process according to claim 13, wherein the feed further comprises one or more α-olefins comprising 3 to 10 carbon atoms.

15. (canceled)

16. Process of claim 9, wherein R1, R2 and R3 in formula I are the same.

17. Process according to any one of claim 10, wherein R4, R5 and R6 in formula II are the same.

18. Process according to claim 13, wherein the α-olefin comprising 3 to 10 carbon atoms is 1-butene, 4-methyl-1-pentene, 1-hexene or 1-octene.

19. Process according to claim 13, wherein the feed comprises ≥5.0 and ≤20.0 wt % of the α-olefin comprising 3 to 10 carbon atoms with regard to the total weight of ethylene and the α-olefin comprising 3 to 10 carbon atoms.

Description

[0069] The invention will now be illustrated by the following non-limiting examples.

Materials

[0070]

TABLE-US-00001 Metallocene [2,2′-bis(2-indenyl)biphenyl]zirconium dichloride, CAS reg. nr. 312968-31-3, obtainable from Innovasynth Technologies Support Silica 955, obtainable from W. R. Grace & Co Cocatalyst Methyl aluminoxane (MAO), CAS reg. nr. 29429-58-1, obtainable from W. R. Grace & Co Cocatalyst Triisobutyl aluminium (TIBAL), CAS reg. nr. 100-99-2, aid obtainable from Sigma-Aldrich Antistatic agents AA1 Tris(trimethylsilyl)amine, CAS reg. nr. 1586-73-8, obtainable from Acros Chemicals AA2 N,N-Diisopropylethylamine, CAS reg. nr. 7087-68-5 AA3 Atmer 163, a fatty alkyl dihydroxyethyl amine, CAS reg. nr. 107043-84-5, obtainable from Croda AA4 Hostastat FE 2, a fatty acid ester, CAS reg. nr. 183563- 20-4, obtainable from Clariant AA5 Octastat 5000, obtainable from Octel Corporation

Preparation of Supported Metallocene Complex

[0071] The support was pre-dehydrated at 600° C. for 4 hours. 3 g of the pre-dehydrated support was charged into a 100 ml two-neck Schlenk flask in a glovebox under nitrogen atmosphere, followed by addition of 15 ml of toluene. After shaking, a suspension was obtained. 0.052 g of the metallocene was activated by mixing it with 6.3 ml of a 10 wt % solution of the cocatalyst in toluene in a 25 ml vial at room temperature for 10 min in the glovebox, also under nitrogen atmosphere. The activated metallocene was transferred into the suspension. The mixture was heated to 70° C. and maintained at that temperature for 1 hour. Subsequently, the product was dried at 70° C. under vacuum to obtain the supported catalyst, which was isolated as free-flowing powder. The supported catalyst contained 0.24 wt % of Zr and 7.2 wt % of Al, which translates to a molar ratio of Al to Zr of ca. 100.

A. Preparation of mixtures of cocatalyst aid and antistatic agents

[0072] Mixtures of cocatalyst aid and antistatic agents were prepared according to the below method, using the materials and quantities of such materials as presented in the below table.

[0073] To a 50 ml vial, 15 ml of hexane was charged in a glovebox under nitrogen atmosphere. 5 ml of the cocatalyst aid was added to the vial, followed by a given quantity and type of antistatic agent. The obtained solution contained 1M of the cocatalyst aid.

TABLE-US-00002 Molar ratio of Appearance Antistatic cocatalyst aid to of obtained Experiment agent Quantity antistatic agent solution A1 AA1 0.5 g 10:1  Colourless A2 AA1 1.6 g 3:1 Colourless A3 AA1 2.3 g 2:1 Colourless A4 AA1 4.7 g 1:1 Colourless A5 AA1 9.4 g 1:2 Light yellow A6 AA2 0.9 g 3:1 Colourless A7 AA2 2.6 g 1:1 Colourless A8 AA3 2.0 g 3:1 Light yellow A9 AA3 6.0 g 1:1 Light yellow A10 AA4 2.4 g 3:1 Light yellow A11 AA5 3.1 g 3:1 Light yellow A12 —* — — *A12 represents a cocatalyst solution without any antistatic agent, and was used for comparative purposes to demonstrate the productivity of the catalyst without any effect of an antistatic agent.
B. Polymerisation experiments

[0074] The effect of the antistatic agents prepared according to the table above was investigated by conducting a multitude of polymerisation experiments in gas phase. A 1.6 I stainless steel reactor vessel equipped with a helical stirrer and a heating/cooling control unit was heated to 110° C. at a nitrogen flow rate of 100 g/h for 2 hours. After that, the reactor was pressure purged with nitrogen, followed by a purge with ethylene. This purging cycle was repeated three times.

[0075] The reactor was then cooled to 88° C. under ethylene pressurised to 10 bar. After venting, a quantity of the cocatalyst aid/antistatic agent mixture as produced according to the above presented experiment was provided to the reactor via a cocatalyst injection pump. Ethylene was then introduced to the reactor under control of mass flow parameters to maintain an ethylene pressure in the reactor of 10 bar. Nitrogen was introduced to maintain a nitrogen pressure of 8 bar. Upon reaching a stable level of temperature and pressure, 30 mg of catalyst was injected via a catalyst injection pump and the reaction started. After 1 hour, the ethylene supply was discontinued and the reactor was cooled to 40° C. The reactor was opened after venting. The polyethylene product was collected to a sample tray and dried at ambient temperature under atmospheric pressure.

[0076] The results of the polymerisation experiments are presented in the table below.

TABLE-US-00003 Cocatalyst/ Quantity PE Experi- antistatic antistatic yield Productivity ment agent mixture agent (g) (g) (g PE/g cat) Sheeting B1 A1 0.075 28.9 960 No B2 A2 0.240 30 987 No B3 A3 0.350 27 877 No B4 A4 0.700 25.6 839 No B5 A5 1.400 24.9 833 No B6 A6 0.140 1.1 37 No B7 A7 0.390 0.9 30 No B8 A8 0.300 12.4 407 No B9 A9 0.900 0 0 No B10 A10 0.360 3.8 128 No B11 A11 0.470 2.9 98 No B12 A12 — 29 939 Yes

[0077] Herein, B12 presents a control experiment to show the yield and productivity of the catalyst in the absence of any antistatic agent. Experiments B1 through B11 show that each of the employed antistatic agents indeed ensures the reduction of the static build-up such that sheeting does not occur during the conduct of the experiments. However it can be noted that the antistatic agents used in the examples B6 through B11 significantly affect the product yield and the catalyst productivity, whereas in experiments B1 through B5, representing the present invention, the provision of the antistatic effect goes together with a high yield and catalyst productivity. Even more, in example B2, the productivity and yield exceed that of the control experiment B12. This demonstrates the process of the present invention to provide an excellent balance of yield, productivity and static charge reduction.