EP-4735486-A1 - PROCESS

Abstract

The invention provides a process for the production of a polyolefin homo- or copolymer in a continuous multistage polymerisation reaction in the presence of a single site catalyst, wherein the process comprises polymerising an olefin monomer and optionally comonomer(s) in a multi stage polymerisation reactor system comprising a first reactor and thereafter one or more gas phase reactor(s), wherein an aluminium alkyl is introduced into the gas phase reactor(s) and wherein the aluminium alkyl is not introduced to the first reactor.

Inventors

• LESKINEN, PAULI
• WANG, JINGBO
• GAHLEITNER, MARKUS
• BERNREITNER, KLAUS

Assignees

• Borealis GmbH

Dates

Publication Date

20260506

Application Date

20240628

Claims (16)

1. 1 . A process for the production of a polyolefin homo- or copolymer in a continuous multistage polymerisation reaction in the presence of a single site catalyst, wherein the process comprises polymerising an olefin monomer and optionally comonomer(s) in a multi stage polymerisation reactor system comprising a first reactor and thereafter one or more gas phase reactor(s), wherein an aluminium alkyl is introduced into the gas phase reactor(s), and wherein the aluminium alkyl is not introduced to the first reactor.
2. 2. A process as claimed in claim 1 , wherein the polyolefin is a polypropylene and the olefin monomer is propylene.
3. 3. The process as claimed in claim 1 or 2, wherein the optional comonomer(s) are alpha-olefin comonomer(s), preferably selected from the group consisting of ethylene and C4 to C10 alpha-olefins.
4. 4. The process as claimed in any of claims 1 to 3, wherein the first reactor is a slurry reactor, preferably a slurry loop reactor.
5. 5. The process as claimed in any of claims 1 to 4, wherein the gas phase reactor is a fluidised bed gas phase reactor comprising a fluidised bed and a circulation gas line.
6. 6. The process as claimed in any of claims 1 to 5, wherein the polymerisation reactor system comprises two gas phase reactors connected in series and the aluminium alkyl is introduced into both gas phase reactors.
7. 7. The process as claimed in any of claims 1 to 6, wherein the aluminium alkyl has the formula AIRa-xClx, wherein R is a C1-10 alkyl group and x is 0 or 1 , preferably wherein the aluminium alkyl has the formula AI(C1-10-alkyl)s.
8. 8. The process as claimed in claim 7, wherein each alkyl group is the same or different, preferably wherein each alkyl group is the same.
9. 9. The process as claimed in any of claims 1 to 8, wherein the aluminum alkyl is triethyl-aluminium (TEAL), tri-isobutyl-aluminium (TIBA) or a mixture thereof.
10. 10. The process as claimed in any of claims 5 to 9, wherein the aluminium alkyl is introduced directly to the fluidised bed of the gas phase reactor and/or to the circulation gas line of the gas phase reactor.
11. 11. The process as claimed in any of claims 1 to 10, wherein the amount of aluminium alkyl introduced is 10 to 200 wt-ppm, preferably 25 to 100 wt-ppm, especially 25 to 50 wt-ppm based on the total weight of polyolefin produced in the gas phase reactor.
12. 12. The process as claimed in any of claims 1 to 11 , wherein the single site catalyst is a metallocene catalyst, preferably a supported metallocene catalyst.
13. 13. The process as claimed in claim 12, wherein the metallocene catalyst comprises as a catalyst component an organometallic compound (C) of formula (la): (L) 2 RnMX 2 (la) wherein “M” is Zr or Hf; each “X” is a o-ligand; each “L” is an optionally substituted cyclopentadienyl, indenyl or tetrahydroindenyl; “R” is SiMe 2 bridging group linking said organic ligands (L); “n” is 0 or 1 , preferably 1.
14. 14. The process as claimed in claim 12 or 13, wherein the metallocene catalyst is used in combination with a boron containing cocatalyst and/or an aluminoxane cocatalyst.
15. 15. The process as claimed in any of claims 1 to 14, wherein the aluminium alkyl is introduced in pure form or in the form of a solution comprising a hydrocarbon diluent.
16. 16. Use of an aluminium alkyl for the removal of one or more catalyst poisons in a process as defined in any of claims 1 to 15.

Description

Process Technical field The present invention relates to a process for the production of a polyolefin homo- or copolymer in a continuous multistage polymerisation reaction. More particularly, the present invention relates to such a process carried out in the presence of a single site catalyst wherein an aluminium alkyl is introduced only into a gas phase reactor during the process and wherein the aluminium alkyl is not introduced to the first reactor. Background art Polyolefin homopolymers and copolymers may be formed in a polymerisation reactor in the presence of an appropriate catalyst and can be used for the preparation of numerous end products, like films, pipes and moulded articles. During the production of olefin polymers, like polypropylene homopolymers and polypropylene copolymers, in a commercial reactor a catalyst is used. In olefin polymerisations, Ziegler-Natta catalysts are frequently used. However, catalyst developments have resulted in use of single site catalysts (SSC), preferably metallocene catalysts, which comprise metallocene complexes of transition metals in combination with a cocatalyst. One significant problem which is associated with the use of single site catalysts is, however, their sensitivity to poisons. Typically, in Ziegler Natta polymerisation processes, an external co-catalyst is employed to remove catalyst poisons. The external cocatalyst partly works as a scavenger therefore. The use of aluminium alkyls in propylene polymerisation processes in general and gas-phase polymerisation processes in particular has been known since the introduction of heterogeneous Ziegler-Natta type catalysts. Patents as early as US 3652527 describe the use of triethyl aluminium (TEAL) as an external co-catalyst. However external co-catalysts are not generally used together with SSC (only the internal cocatalyst is used, typically an aluminoxane or boron compound). One reason for this is that in the liquid or slurry phase (often comprising an alkane like propane as a diluent) or bulk polymerisation (often comprising a monomer e.g. propene as a diluent), the single site catalyst may dissolve in the diluent which allows the external co-catalyst to extract the complex away from the cocatalyst. This has the effect of causing fouling or damage to the reactor. TEAL is chemically similar to common internal donor MAO and the TEAL can therefore coordinate with the single site complex and extract it from the catalyst. Another problem and challenge when using aluminium alkyls with SSC is the use of an antistatic agent or antifouling feed to the reactor. It has been found that on an industrial scale polymer product may deposit on the walls of the polymerization reactor. This so-called “fouling” is often caused in part by fines and build-up of electrostatic charge on the walls on the reactor. Antifouling agents are added to the polymerization medium and well-dispersed therein to avoid such fouling during slurry polymerization. If an external co-catalyst is used however, it eliminates the effect of the antifouling agent so both cannot be used together. There remains a need to develop new approaches to tackling the problem of poisoning of single site catalysts, ideally without leading to fouling. This in turn may offer the possibility to improve catalyst lifetime and production efficiency in multistage polymerisation processes. The present inventors have surprisingly found that, in a continuous multistage polymerisation reactor system, feeding an aluminium alkyl specifically to the gas phase reactor(s) offers an attractive solution. The invention is to feed aluminium alkyl directly to the gas phase reactor as a scavenger to remove catalyst poisons like water, oxygen, alcohols etc present in the gas phase reactor. Without wishing to be bound by theory it is considered that, in gas phase, the catalyst is in a much more stable form and thus the external aluminium alkyl co-catalyst can’t extract complex from the catalyst. Moreover, by the time the catalyst has reached the gas phase reactor, it has been involved in polymerisation within the first reactor (and prepolymerisation reactor if present). These processes give rise to a more robust and stable catalyst particle that better resists reaction with the aluminium alkyl. Moreover, as the aluminium alkyl isn’t added into the first reactor, an antifouling agent can be used without the risk of this being deactivated by the aluminium alkyl. Finally, we observe that it isn’t necessary to add the aluminium alkyl to the first reactor in order to realise the benefits we observe in terms of improved catalyst productivity and higher gas phase split. This differentiated feed of an aluminium alkyl co-catalyst in only the gas phase reactor in a single site catalysed multistage polymerisation process therefore presents a new and promising route for addressing the problem of single site catalyst poisoning. Summary of the invention In a first aspect, the invention provides a p