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.

Description

[0001] Process

[0002] Technical field

[0003] 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.

[0004] Background art

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] Summary of the invention

[0013] In a first aspect, 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.

[0014] In a further aspect, the invention provides the use of an aluminium alkyl for the removal of one or more catalyst poisons in a process as herein defined.

[0015] Definitions

[0016] The term “first polymer product” is used to define the target polyolefin produced in the first reactor. The term “second polymer product” is used to define the target polypropylene produced in the gas phase reactor.

[0017] The term single site catalyst defines the combination of the metallocene complex and (internal) cocatalyst that is used to activate the complex.

[0018] The process of the invention occurs in a multistage polymerisation reactor system comprising a first reactor and at least one gas phase reactor. The single site catalysed process will involve therefore at least a first polymerisation reaction in the first reactor and a gas phase polymerisation reaction in the gas phase reactor.

[0019] These take place in the multistage polymerisation reactor system, i.e. in the first reactor and the gas phase reactor, respectively.

[0020] By free from an external carrier is meant that the catalyst does not contain an external support, such as an inorganic support, for example, silica or alumina, or an organic polymeric support material. The term C1-20 hydrocarbyl group includes C1-20 alkyl, C2-20 alkenyl, C2-20 alkynyl, C3-20 cycloalkyl, C3-20 cycloalkenyl, Ce-2o aryl groups, C7-20 alkylaryl groups or C 7-20 arylalkyl groups or of course mixtures of these groups such as cycloalkyl substituted by alkyl. Linear and branched hydrocarbyl groups cannot contain cyclic units. Aliphatic hydrocarbyl groups cannot contain aryl rings.

[0021] Unless otherwise stated, preferred C1-20 hydrocarbyl groups are C1-20 alkyl, C4- 20 cycloalkyl, C5-20 cycloalkyl-alkyl groups, C7-20 alkylaryl groups, C7-20 arylalkyl groups or C6-20 aryl groups, especially C1-10 alkyl groups, Ce- aryl groups, or C7-12 arylalkyl groups, e.g. C1-8 alkyl groups. Most especially preferred hydrocarbyl groups are methyl, ethyl, propyl, isopropyl, tertbutyl, isobutyl, Cs-6-cycloalkyl, cyclohexylmethyl, phenyl or benzyl.

[0022] The term halo includes fluoro, chloro, bromo and iodo groups, especially chloro groups, when relating to the complex definition.

[0023] The oxidation state of the metal ion is governed primarily by the nature of the metal ion in question and the stability of the individual oxidation states of each metal ion.

[0024] It will be appreciated that in the metal complexes described herein, the metal ion M is coordinated by ligands X so as to satisfy the valency of the metal ion and to fill its available coordination sites. The nature of these o-ligands can vary greatly.

[0025] Catalyst activity is defined in this application to be the amount of polymer produced / g catalyst / h. Catalyst metal activity is defined here to be the amount of polymer produced / g Metal / h. The term productivity is also sometimes used to indicate the catalyst activity although herein it designates the amount of polymer produced per unit weight of catalyst.

[0026] Detailed Description of Invention

[0027] This invention concerns the use of an aluminium alkyl as a feed to a gas phase reactor in a multistage polymerisation process, typically for the production of a polypropylene. A single site catalyst is used to catalyse the formation of the polyolefin in the polymerisation reactor system. Single Site Catalyst

[0028] A single site catalyst is fed to the first reactor to start the polymerisation process. At the end of the first polymerisation step, the single site catalyst is transferred to the gas phase reactor. The same single site catalyst is therefore used in both stages of the process.

[0029] The single site catalyst is preferably a metallocene or non-metallocene catalyst. Single site catalysts preferably comprise a transition metal complex which contains at least one cyclopentadienyl, indenyl or fluorenyl ligand. Preferably the single site complex contains two cyclopentadienyl, indenyl or fluorenyl ligands, especially two bridged cyclopentadienyl, indenyl or fluorenyl ligands. Further, the ligands may have substituents, such as alkyl groups, aryl groups, arylalkyl groups, alkylaryl groups, silyl groups, siloxy groups, alkoxy groups or other heteroatom groups. Examples of suitable metallocene compounds are given, among others, in EP 629631 , EP 629632, WO 00 / 26266, WO 02 / 002576, WO 02 / 002575, WO 99 / 12943, WO 98 / 40331, EP 776913, EP 1074557 and WO 99 / 42497, EP2402353, EP2729479, and EP2746289

[0030] The single site complex is ideally an organometallic compound (C) comprising a transition metal (M) of Group 3 to 10 of the Periodic Table (III PAG 2007) or of an actinide or lanthanide. The term "an organometallic compound (C)" in accordance with the present invention includes any metallocene or non-metallocene compound of a transition metal which bears at least one organic (coordination) ligand and exhibits the catalytic activity together with a cocatalyst. The transition metal compounds are well known in the art and the present invention covers compounds of metals from Group 3 to 10, e.g. Group 3 to 7, or 3 to 6, such as Group 4 to 6 of the Periodic Table, (IUPAC 2007), as well as lanthanides or actinides.

[0031] In one embodiment the organometallic compound (C) has the following formula (I):

[0032] (L)mRnMXq(I) wherein

[0033] “M” is a transition metal (M) transition metal (M) of Group 3 to 10 of the Periodic Table (IUPAC 2007), each “X” is independently a monoanionic ligand, such as a o-ligand, each “L” is independently an organic ligand which coordinates to the transition metal “M”,

[0034] “R” is a bridging group linking said organic ligands (L),

[0035] “m” is 1 , 2 or 3, preferably 2

[0036] “n” is 0, 1 or 2, preferably 1 ,

[0037] “q” is 1 , 2 or 3, preferably 2 and m+q is equal to the valency of the transition metal (M).

[0038] “M” is preferably selected from the group consisting of zirconium (Zr), hafnium (Hf), or titanium (Ti), more preferably selected from the group consisting of zirconium (Zr) and hafnium (Hf).

[0039] In a more preferred embodiment, each organic ligand (L) is independently:

[0040] (a) a substituted or unsubstituted cyclopentadienyl or a bi- or multicyclic derivative of a cyclopentadienyl which optionally bear further substituents and / or one or more hetero ring atoms from a Group 13 to 16 of the Periodic Table (IUPAC); or

[0041] (b) an acyclic q1- to q4- or q6-ligand composed of atoms from Groups 13 to 16 of the Periodic Table, and in which the open chain ligand may be fused with one or two, preferably two, aromatic or non-aromatic rings and / or bear further substituents; or

[0042] (c) a cyclic q1- to q4- or q6-, mono-, bi- or multidentate ligand composed of unsubstituted or substituted mono-, bi- or multicyclic ring systems selected from aromatic or non-aromatic or partially saturated ring systems, such ring systems containing optionally one or more heteroatoms selected from Groups 15 and 16 of the Periodic Table.

[0043] Organometallic compounds (C) preferably have at least one organic ligand (L) belonging to the group (a) above. Such organometallic compounds are called metallocenes.

[0044] More preferably at least one of the organic ligands (L), preferably both organic ligands (L), is (are) selected from the group consisting of cyclopentadienyl, indenyl, tetrahydroindenyl, fluorenyl, which can be independently substituted or unsubstituted. Further, in case the organic ligands (L) are substituted it is preferred that at least one organic ligand (L), preferably both organic ligands (L), comprise one or more substituents independently selected from Ci to C20 hydrocarbyl or silyl groups, which optionally contain one or more heteroatoms selected from groups 14 to 16 and / or are optionally substituted by halogen atom(s),

[0045] The term “Ci to C20 hydrocarbyl group”, whenever used in the present application, includes Ci to C20 alkyl, C2 to C20 alkenyl, C2 to C20 alkynyl, C3 to C20 cycloalkyl, C3 to C20 cycloalkenyl, Ce to C20 aryl, C7 to C20 alkylaryl or C7 to C20 arylalkyl groups or mixtures of these groups such as cycloalkyl substituted by alkyl.

[0046] Further, two substituents, which can be the same or different, attached to adjacent C-atoms of a ring of the ligands (L) can also be taken together to form a further mono or multicyclic ring fused to the ring.

[0047] Preferred hydrocarbyl groups are independently selected from linear or branched Ci to C10 alkyl groups, optionally interrupted by one or more heteroatoms of groups 14 to 16, like O, N or S, and substituted or unsubstituted Ce to C20 aryl groups.

[0048] Linear or branched Ci to C10 alkyl groups, optionally interrupted by one or more heteroatoms of groups 14 to 16, are more preferably selected from methyl, ethyl, propyl, isopropyl, tertbutyl, isobutyl, C5-6 cycloalkyl, OR, SR, where R is Ci to C10 alkyl group.

[0049] Ce to C20 aryl groups are more preferably phenyl groups, optionally substituted with 1 or 2 Ci to C10 alkyl groups as defined above.

[0050] By "o-ligand" is meant throughout the invention a group bonded to the transition metal (M) via a sigma bond.

[0051] Further, the ligands “X” are preferably independently selected from the group consisting of hydrogen, halogen, Ci to C20 alkyl, Ci to C20 alkoxy, C2 to C20 alkenyl, C2 to C20 alkynyl, C3 to C12 cycloalkyl, Ce to C20 aryl, Ce to C20 aryloxy, C7 to C20 arylalkyl, C7 to C20 arylalkenyl, -SR", -PR' s, -SiR' 3, -OSiR' 3 and -NR' 2, wherein each R" is independently hydrogen, Ci to C20 alkyl, C2 to C20 alkenyl, C2 to C20 alkynyl, C3 to C12 cycloalkyl or Ce to C20 aryl.

[0052] More preferably, the “X” ligands are selected from halogen, Ci to Ce alkyl, C5 to Ce cycloalkyl, Ci to Ce alkoxy, phenyl and benzyl groups. The bridging group “R” may be a divalent bridge, preferably selected from - R’2C-, -R’2C-CR’2-, — R’2Si-, -R’2Si-Si R’2-, -R’2Ge-, wherein each R’ is independently a hydrogen atom, Ci to C20 alkyl, C2 to C10 cycloalkyl, tri(Ci-C2o-alkyl)silyl, Ce- C20- aryl, C7- C20 arylalkyl and C7- C2o-alkylaryl .

[0053] More preferably the bridging group “R” is a divalent bridge selected from - R’2C-, — R’2Si-, wherein each R’ is independently a hydrogen atom, Ci to C20 alkyl, C2 to C10 cycloalkyl, Ce- C2o-aryl, C7- C20 arylalkyl and C7- C2o-alkylaryl.

[0054] Another subgroup of the organometallic compounds (C) of formula (I) is known as non-metallocenes wherein the transition metal (M), preferably a Group 4 to 6 transition metal, suitably Ti, Zr or Hf, has a coordination ligand other than a cyclopentadienyl ligand.

[0055] The term "non-metallocene" used herein means compounds, which bear no cyclopentadienyl ligands or fused derivatives thereof, but one or more non- cyclopentadienyl q-, or o-, mono-, bi- or multidentate ligand. Such ligands can be chosen e.g. from the groups (b) and (c) as defined above and described e.g. in WO 01 / 70395, WO 97 / 10248, WO 99 / 41290, and WO 99 / 10353), and further in V. C. Gibson et al., in Angew. Chem. Int. Ed., engl., vol 38, 1999, pp 428 447, the disclosures of which are incorporated herein by reference.

[0056] However, the organometallic compound (C) of the present invention is preferably a metallocene as defined above.

[0057] In one preferred embodiment, therefore, the invention relates to a process as hereinbefore defined, wherein the single site catalyst comprises a metallocene catalyst, preferably a supported metallocene catalyst.

[0058] Metallocenes are described in numerous patents. In the following just a few examples are listed; EP 260 130, WO 97 / 28170, WO 98 / 46616, WO 98 / 49208, WO 98 / 040331 , WO 99 / 12981 , WO 99 / 19335, WO 98 / 56831 , WO 00 / 34341 , WO00 / 148034, EP 423 101 , EP 537 130, W02002 / 02576, W02005 / 105863, WO 2006097497, W02007 / 116034, W02007 / 107448, W02009 / 027075, W02009 / 054832, WO 2012 / 001052, and EP 2532687, the disclosures of which are incorporated herein by reference. Further, metallocenes are described widely in academic and scientific articles.

[0059] In a preferred embodiment the organometallic compound (C) has the following formula (la): (L)2RnMX2(la) wherein

[0060] “M” is Zr or Hf; each “X” is a o-ligand; each “L” is an optionally substituted cyclopentadienyl, indenyl or tetrahydroindenyl;

[0061] “R” is SiMe2bridging group linking said organic ligands (L);

[0062] “n” is 0 or 1, preferably 1.

[0063] The metallocene catalyst complexes of the invention are preferably asymmetrical. Asymmetrical means simply that the two ligands forming the metallocene are different, that is, each ligand bears a set of substituents that are chemically different.

[0064] The metallocene catalyst complexes of the invention are typically chiral, racemic bridged bisindenyl Ci-symmetric metallocenes in their anti-configuration. Although such complexes are formally Ci-symmetric, the complexes ideally retain a pseudo-C2-symmetry since they maintain C2-symmetry in close proximity of the metal center although not at the ligand periphery. By nature of their chemistry both anti and syn enantiomer pairs (in case of Ci-symmetric complexes) are formed during the synthesis of the complexes. For the purpose of this invention, racemic-anti means that the two indenyl ligands are oriented in opposite directions with respect to the cyclopentadienyl-metal-cyclopentadienyl plane, while racemic-syn means that the two indenyl ligands are oriented in the same direction with respect to the cyclopentadienyl-metal-cyclopentadienyl plane, as shown in the scheme below.

[0065] Racemic Anti Racemic Syn Formula (I), and any sub formulae, are intended to cover both syn- and anticonfigurations. Preferred metallocene catalyst complexes are in the anti configuration.

[0066] The metallocene catalyst complexes of the invention are generally employed as the racemic-anti isomers. Ideally, therefore at least 95%mol, such as at least 98%mol, especially at least 99%mol of the metallocene catalyst complex is in the racemic-anti isomeric form.

[0067] Thus, viewed from one aspect the metallocene complex may be of formula (II) wherein

[0068] M is zirconium or hafnium; each X is a sigma ligand;

[0069] L is a divalent bridge selected from -R'2C-, -R'2C-CR'2-, -R'2Si-, -R'2Si-Si R'2-, - R'2Ge-, wherein each R' is independently a hydrogen atom, Ci-C2o-hydrocarbyl, tri(Ci-C2o-alkyl)silyl, Ce-C2o-aryl, C?-C2o-arylalkyl or C?-C2o-alkylaryl;

[0070] R2and R2' are each independently a C1-C20 hydrocarbyl radical optionally containing one or more heteroatoms from groups 14-16;

[0071] R5and R5' are each independently a C1-20 hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16 and optionally substituted by one or more halo atoms; R5may also be hydrogen;

[0072] R6and R6' are each independently hydrogen or a C1-20 hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16; R5and R6can be taken together to form a 5 membered saturated carbon ring which is optionally substituted by n groups R10, n being from 0 to 4;

[0073] R5’ ad R6’ can be taken together to form a 5 membered saturated carbon ring which is optionally substituted by n groups R10, n being from 0 to 4; each R10is the same or different and may be a Ci to C20 hydrocarbyl group, or a C1-C20 hydrocarbyl radical optionally containing one or more heteroatoms belonging to groups 14-16 of the periodic table of elements;

[0074] R7and R7' are each independently hydrogen or C1-20 hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16;

[0075] Ar is independently an aryl or heteroaryl group having up to 20 carbon atoms optionally substituted by one or more groups R1;

[0076] Ar' is independently an aryl or heteroaryl group having up to 20 carbon atoms optionally substituted by one or more groups R1; each R1is a C1-20 hydrocarbyl group or two R1groups on adjacent carbon atoms taken together can form a fused 5 or 6 membered non aromatic ring with the Ar group, said ring being itself optionally substituted with one or more groups R4; and each R4is a C1-20 hydrocarbyl group.

[0077] Viewed from another aspect the metallocene complex may be of formula (II) wherein M is zirconium or hafnium; each X is a sigma ligand;

[0078] L is a divalent bridge selected from -R'2C-, -R'2C-CR'2-, -R'2Si-, -R'2Si-Si R'2-, - R'2Ge-, wherein each R' is independently a hydrogen atom, Ci-C2o-hydrocarbyl, tri(Ci-C2o-alkyl)silyl, Ce-C2o-aryl, C?-C2o-arylalkyl or C?-C2o-alkylaryl;

[0079] R2and R2' are each independently a C1-C20 hydrocarbyl radical optionally containing one or more heteroatoms from groups 14-16;

[0080] R5and R5' are each independently a C1-20 hydrocarbyl group containing one or more heteroatoms from groups 14-16 optionally substituted by one or more halo atoms; R5may also be hydrogen;

[0081] R6and R6' are each independently hydrogen or a C1-20 hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16;

[0082] R5and R6can be taken together to form a 5 membered saturated carbon ring which is optionally substituted by n groups R10, n being from 0 to 4;

[0083] R5’ and R6’ can be taken together to form a 5 membered saturated carbon ring which is optionally substituted by n groups R10, n being from 0 to 4; each R10is the same or different and may be a Ci to C20 hydrocarbyl group, or a C1-C20 hydrocarbyl radical optionally containing one or more heteroatoms belonging to groups 14-16 of the periodic table of elements;

[0084] R7and R7' are each independently hydrogen or C1-20 hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16;

[0085] Ar is independently an aryl or heteroaryl group having up to 20 carbon atoms optionally substituted by one or more groups R1;

[0086] Ar' is independently an aryl or heteroaryl group having up to 20 carbon atoms optionally substituted by one or more groups R1; each R1is a C1-20 hydrocarbyl group or two R1groups on adjacent carbon atoms taken together can form a fused 5 or 6 membered non aromatic ring with the Ar group, said ring being itself optionally substituted with one or more groups R4; each R4is a C1-20 hydrocarbyl group;

[0087] In the catalyst complexes of the invention:

[0088] M is preferably Zr. Each X, which may be the same or different, is preferably a hydrogen atom, a halogen atom, a R, OR, OSO2CF3, OCOR, SR, NR2 or PR2 group wherein R is a linear or branched, cyclic or acyclic, C1-20 alkyl, C2-20 alkenyl, C2-20 alkynyl, C6-20 aryl, C7-20 alkylaryl or C7-20 arylalkyl radical; optionally containing heteroatoms belonging to groups 14-16. R is preferably a C1-6 alkyl, phenyl or benzyl group.

[0089] Most preferably each X is independently a hydrogen atom, a halogen atom, C1-6 alkoxy group or an R group, e.g. preferably a C1-6 alkyl, phenyl or benzyl group. Most preferably X is chlorine or a methyl radical. Preferably both X groups are the same.

[0090] L is preferably an alkylene linker or a bridge comprising a heteroatom, such as silicon or germanium, e.g. -SiR , wherein each R8is independently C1-20 alkyl, C3-10 cycloakyl, C6-20 aryl or tri(Ci-2o alkyl)silyl, such as trimethylsilyl. More preferably R8is C1-6 alkyl, especially methyl or C3-7 cycloalkyl, such as cyclohexyl. Most preferably, L is a dimethylsilyl or a methylcyclohexylsilyl bridge (i.e. Me-Si- cyclohexyl). It may also be an ethylene bridge.

[0091] R2and R2' can be different but they are preferably the same. R2and R2' are preferably a C1-10 hydrocarbyl group such as C1-6 hydrocarbyl group. More preferably it is a linear or branched C1-10 alkyl group. More preferably it is a linear or branched C1-6 alkyl group, especially linear C1-6 alkyl group such as methyl or ethyl.

[0092] The R2and R2' groups can be interrupted by one or more heteroatoms, such as 1 or 2 heteroatoms, e.g. one heteroatom, selected from groups 14 to 16 of the periodic table. Such a heteroatom is preferably O, N or S, especially O. More preferably however the R2and R2' groups are free from heteroatoms. Most especially R2and R2' are methyl, especially both methyl.

[0093] The two Ar groups Ar and Ar' can be the same or different. It is preferred however if the Ar groups are different. The Ar' group may be unsubstituted. The Ar' is preferably a phenyl based group optionally substituted by groups R1, especially an unsubstituted phenyl group.

[0094] The Ar group is preferably a C6-20 aryl group such as a phenyl group or naphthyl group. Whilst the Ar group can be a heteroaryl group, such as carbazolyl, it is preferable that Ar is not a heteroaryl group. The Ar group can be unsubstituted or substituted by one or more groups R1, more preferably by one or two R1groups, especially in position 4 of the aryl ring bound to the indenyl ligand or in the 3, 5- positions. In one embodiment both Ar and Ar' are unsubstituted. In another embodiment Ar' is unsubstituted and Ar is substituted by one or two groups R1.

[0095] R1is preferably a C1-20 hydrocarbyl group, such as a C1-20 alkyl group. R1groups can be the same or different, preferably the same. More preferably, R1is a C2-10 alkyl group such as C3-8 alkyl group. Highly preferred groups are tert butyl or isopropyl groups. It is preferred if the group R1is bulky, i.e. is branched. Branching might be alpha or beta to the ring. Branched C3-8 alkyl groups are also favoured therefore.

[0096] In a further embodiment, two R1groups on adjacent carbon atoms taken together can form a fused 5 or 6 membered non aromatic ring with the Ar group, said ring being itself optionally substituted with one or more groups R4. Such a ring might form a tetrahydroindenyl group with the Ar ring or a tetrahydronaphthyl group.

[0097] If an R4group is present, there is preferably only 1 such group. It is preferably a C1-10 alkyl group.

[0098] It is preferred if there is one or two R1groups present on the Ar group. Where there is one R1group present, the group is preferably para to the indenyl ring (4- position). Where two R1groups are present these are preferably at the 3 and 5 positions.

[0099] R5is preferably hydrogen or a C1-20 hydrocarbyl group containing one or more heteroatoms from groups 14-16 and optionally substituted by one or more halo atoms or R5is a C1-10 alkyl group, such as methyl but most preferably it is a group Z'R3.

[0100] R5' is preferably a C1-20 hydrocarbyl group containing one or more heteroatoms from groups 14-16 and optionally substituted by one or more halo atoms or R5' is a C1-10 alkyl group, such as methyl but most preferably it is a group Z'R3'.

[0101] R6and R6' may be the same or different. In one preferred embodiment one of R6and R6' is hydrogen, especially R6. It is preferred if R6and R6' are not both hydrogen. If not hydrogen, it is preferred if each R6and R6' is preferably a C1-20 hydrocarbyl group, such as a C1-20 alkyl group or Ce- aryl group. More preferably, R6and R6' are a C2-10 alkyl group such as C3-8 alkyl group. Highly preferred groups are tert-butyl groups. It is preferred if R6and R6' are bulky, i.e. are branched. Branching might be alpha or beta to the ring. Branched C3-8 alkyl groups are also favoured therefore. In another embodiment R5and R6can be taken together to form a 5 membered saturated carbon ring which is optionally substituted by n groups R10, n being from 0 to 4, preferably 0 or 2 and more preferably 0; whereby each R10can be the same or different and may be a Ci- C2o-hydrocarbyl group, or a C1-C20 hydrocarbyl radical optionally containing one or more heteroatoms belonging to groups 14-16 of the periodic table of elements; preferably a linear or branched Ci-Ce -alkyl group.

[0102] The R7and R7' groups can be the same or different. Each R7and R7' group is preferably hydrogen, a C1-6 alkyl group or is a group ZR3. It is preferred if R7' is hydrogen. It is preferred if R7is hydrogen, C1-6 alkyl or ZR3. The combination of both R7and R7' being hydrogen is most preferred.

[0103] Z and Z' are O or S, preferably O.

[0104] R3is preferably a C1-10 hydrocarbyl group, especially a C1-10 alkyl group, or aryl group optionally substituted by one or more halo groups. Most especially R3is a C1-6 alkyl group, such as a linear C1-6 alkyl group, e.g. methyl or ethyl

[0105] R3' is preferably a C1-10 hydrocarbyl group, especially a C1-10 alkyl group, or aryl group optionally substituted by one or more halo groups. Most especially R3' is a C1-6 alkyl group, such as a linear C1-6 alkyl group, e.g. methyl or ethyl or it is a phenyl based radical optionally substituted with one or more halo groups such as Ph or C6F5.

[0106] Thus, preferred metallocene complexes are of formula (III) wherein

[0107] M is zirconium or hafnium; each X is a sigma ligand, preferably each X is independently a hydrogen atom, a halogen atom, C1-6 alkoxy group, C1-6 alkyl, phenyl or benzyl group;

[0108] L is a divalent bridge selected from -R'2C-, -R'2C-CR'2-, -R'2Si-, -R'2Si-Si R'2-, - R'2Ge-, wherein each R' is independently a hydrogen atom, C1-20 alkyl, C3-10 cycloalkyl, tri(Ci-2o-alkyl)silyl, Ce-2o-aryl, C7-20 arylalkyl or C?-2o alkylaryl; each R2or R2' is a C1-10 alkyl group;

[0109] R5is hydrogen and R6is hydrogen or a C1-10 alkyl group; or R5and R6can be taken together to form a 5 membered saturated carbon ring;

[0110] R5' is a C1-10 alkyl group or Z'R3' group;

[0111] R6' is a C1-10 alkyl group or Ce- aryl group;

[0112] R7is hydrogen, a C1-6 alkyl group or ZR3group;

[0113] R7' is hydrogen or a C1-10 alkyl group;

[0114] Z and Z' are independently O or S;

[0115] R3' is a C1-10 alkyl group, or a Ce- aryl group optionally substituted by one or more halo groups;

[0116] R3is a Ci- -alkyl group; n is 0 to 4, e.g. 0, 1 or 2; and each R1is a C1-20 hydrocarbyl group, e.g. C1-10 alkyl group.

[0117] Viewed from another aspect the metallocene complex may be of formula (IV):

[0118]

[0119] M is zirconium or hafnium; each X is a sigma ligand, preferably each X is independently a hydrogen atom, a halogen atom, C1-6 alkoxy group, C1-6 alkyl, phenyl or benzyl group; L is a divalent bridge selected from -R'2C- or -R'2Si- wherein each R' is independently a hydrogen atom, C1-20 alkyl or C3-10 cycloalkyl;

[0120] R5is hydrogen and R6is hydrogen or a C1-10 alkyl group; or R5and R6can be taken together to form a 5 membered saturated carbon ring;

[0121] R6' is a C1-10 alkyl group or Ce- aryl group; R7is C1-6 alkyl or OC1-6 alkyl;

[0122] Z' is O or S;

[0123] R3' is a C1-10 alkyl group, or Ce- aryl group optionally substituted by one or more halo groups; n is 0 to 4, e.g. 0, 1 or 2; and each R1is a C1-10 alkyl group.

[0124] Viewed from a further preferred aspect the metallocene complex may be of formula (V)

[0125]

[0126] M is zirconium or hafnium; each X is a sigma ligand, preferably each X is independently a hydrogen atom, a halogen atom, Ci-6-alkoxy group, Ci-6-alkyl, phenyl or benzyl group; each R' is independently a hydrogen atom, C1-20 alkyl or C3-7 cycloalkyl;

[0127] R6is hydrogen or a C1-10 alkyl group;

[0128] R6' is a C1-10 alkyl group or Ce- aryl group;

[0129] R7is C1-6 alkyl or OC1-6 alkyl;

[0130] Z' is O or S; R3' is a C1-10 alkyl group, or Ce- aryl group optionally substituted by one or more halo groups; n is 0, 1 to 2; and each R1is a C3-8 alkyl group.

[0131] Most especially, the metallocene complex may be of formula (VI)

[0132] wherein each X is a sigma ligand, preferably each X is independently a hydrogen atom, a halogen atom, Ci-6-alkoxy group, Ci-6-alkyl, phenyl or benzyl group; R' is independently a C1-6 alkyl or C3-10 cycloalkyl;

[0133] R1is C3-8 alkyl;

[0134] R6is hydrogen or a C3-8 alkyl group;

[0135] R6' is a C3-8 alkyl group or Ce- aryl group;

[0136] R3' is a C1-6 alkyl group, or Ce- aryl group optionally substituted by one or more halo groups; and n is 0, 1 or 2.

[0137] Particular metallocene catalyst complexes suitable for use in the invention include:

[0138] Throughout the disclosure above, where a narrower definition of a substituent is presented, that narrower definition is deemed disclosed in conjunction with all broader and narrower definitions of other substituents in the application.

[0139] Synthesis

[0140] The ligands required to form the single site catalysts of the invention can be synthesised by any process and the skilled organic chemist would be able to devise various synthetic protocols for the manufacture of the necessary ligand materials.

[0141] WO20 13 / 007650, for example, discloses the necessary chemistry. Synthetic protocols can also generally be found in W02002 / 02576, WO2011 / 135004, WO20 12 / 084961 , WO2012 / 001052, WO2011 / 076780 and WO2015 / 158790.

[0142] To form an active single site catalytic species it is normally necessary to employ a cocatalyst as is well known in the art. According to the present invention a cocatalyst system comprising a boron containing cocatalyst and / or an aluminoxane cocatalyst is used in combination with the above defined metallocene catalyst complex.

[0143] The aluminoxane cocatalyst can be one of formula (X): where n is usually from 6 to 20 and R has the meaning below.

[0144] Aluminoxanes are formed on partial hydrolysis of organoaluminum compounds, for example those of the formula AIR3, AIR2Y and AI2R3Y3 where R can be, for example, C1-C10 alkyl, preferably C1-C5 alkyl, or C3-10 cycloalkyl, C7-C12 arylalkyl or alkylaryl and / or phenyl or naphthyl, and where Y can be hydrogen, halogen, preferably chlorine or bromine, or C1-C10 alkoxy, preferably methoxy or ethoxy. The resulting oxygen-containing aluminoxanes are not in general pure compounds but mixtures of oligomers of the formula (X).

[0145] The preferred aluminoxane is methylaluminoxane (MAO). Since the aluminoxanes used according to the invention as cocatalysts are not, owing to their mode of preparation, pure compounds, the molarity of aluminoxane solutions hereinafter is based on their aluminium content.

[0146] According to the present invention, also a boron containing cocatalyst can be used instead of the aluminoxane cocatalyst or the aluminoxane cocatalyst can be used in combination with a boron containing cocatalyst.

[0147] It will be appreciated by the skilled person that where boron based cocatalysts are employed, it is normal to pre-alkylate the complex by reaction thereof with an aluminium alkyl compound, such as TIBA. This procedure is well known and any suitable aluminium alkyl, e.g. AI(Ci-6-alkyl)3 can be used. Preferred aluminium alkyl compounds are triethylaluminium, tri-isobutylaluminium, tri-isohexylaluminium, tri-n-octylaluminium and tri-isooctylaluminium.

[0148] Alternatively, when a borate cocatalyst is used, the metallocene catalyst complex is in its alkylated version, that is for example a dimethyl or dibenzyl metallocene catalyst complex can be used.

[0149] Boron based cocatalysts of interest include those of formula (Z)

[0150] BY3(Z) wherein Y is the same or different and is a hydrogen atom, an alkyl group of from 1 to about 20 carbon atoms, an aryl group of from 6 to about 15 carbon atoms, alkylaryl, arylalkyl, haloalkyl or haloaryl each having from 1 to 10 carbon atoms in the alkyl radical and from 6-20 carbon atoms in the aryl radical or fluorine, chlorine, bromine or iodine. Preferred examples for Y are methyl, propyl, isopropyl, isobutyl or trifluoromethyl, unsaturated groups such as aryl or haloaryl like phenyl, tolyl, benzyl groups, p-fluorophenyl, 3,5- difluorophenyl, pentachlorophenyl, pentafluorophenyl, 3,4,5-trifluorophenyl and 3,5- di(trifluoromethyl)phenyl.

[0151] Preferred options are trifluoroborane, triphenylborane, tris(4- fluorophenyl)borane, tris(3,5-difluorophenyl)borane, tris(4-fluoromethylphenyl)borane, tris(2,4,6-trifluorophenyl)borane, tris(penta-fluorophenyl)borane, tris(tolyl)borane, tris(3,5-dimethyl-phenyl)borane, tris(3,5-difluorophenyl)borane and / or tris (3,4,5- trifluorophenyl)borane.

[0152] Particular preference is given to tris(pentafluorophenyl)borane.

[0153] However, it is preferred that borates are used, i.e. compounds containing a borate 3+ ion. Such ionic cocatalysts preferably contain a non-coordinating anion such as tetrakis(pentafluorophenyl)borate and tetraphenylborate. Suitable counterions are protonated amine or aniline derivatives such as methylammonium, anilinium, dimethylammonium, diethylammonium, N- methylanilinium, diphenylammonium, N,N-dimethylanilinium, trimethylammonium, triethylammonium, tri-n-butylammonium, methyldiphenylammonium, pyridinium, p-bromo-N,N- dimethylanilinium or p-nitro-N,N-dimethylanilinium.

[0154] Preferred ionic compounds which can be used according to the present invention include: triethylammoniumtetra(phenyl)borate, tributylammoniumtetra(phenyl)borate, trimethylammoniumtetra(tolyl)borate, tributylammoniumtetra(tolyl)borate, tributylammoniumtetra(pentafluorophenyl)borate, tripropylammoniumtetra(dimethylphenyl)borate, tributylammoniumtetra(trifluoromethylphenyl)borate, tributylammoniumtetra(4-fluorophenyl)borate,

[0155] N,N-dimethylcyclohexylammoniumtetrakis(pentafluorophenyl)borate,

[0156] N,N-dimethylbenzylammoniumtetrakis(pentafluorophenyl)borate,

[0157] N,N-dimethylaniliniumtetra(phenyl)borate,

[0158] N,N-diethylaniliniumtetra(phenyl)borate,

[0159] N,N-dimethylaniliniumtetrakis(pentafluorophenyl)borate,

[0160] N,N-di(propyl)ammoniumtetrakis(pentafluorophenyl)borate, di(cyclohexyl)ammoniumtetrakist(pentafluorophenyl)borate, triphenylphosphoniumtetrakis(phenyl)borate, triethylphosphoniumtetrakis(phenyl)borate, diphenylphosphoniumtetrakis(phenyl)borate, tri(methylphenyl)phosphoniumtetrakis(phenyl)borate, tri(dimethylphenyl)phosphoniumtetrakis(phenyl)borate, triphenylcarbeniumtetrakis(pentafluorophenyl)borate, or ferroceniumtetrakis(pentafluorophenyl)borate.

[0161] Preference is given to triphenylcarbeniumtetrakis(pentafluorophenyl) borate,

[0162] N,N- dimethylcyclohexylammoniumtetrakis(pentafluorophenyl)borate or

[0163] N,N- dimethylbenzylammoniumtetrakis(pentafluorophenyl)borate.

[0164] It has been surprisingly found that certain boron cocatalysts are especially preferred. Preferred borates of use in the invention therefore comprise the trityl ion. Thus the use of N,N-dimethylammonium-tetrakispentafluorophenylborate and Ph3CB(PhFs)4 and analogues therefore are especially favoured.

[0165] In a preferred embodiment of the invention, the metallocene catalyst is used in combination with a boron containing cocatalyst and / or an aluminoxane cocatalyst. According to the present invention, the preferred cocatalysts are alumoxanes, more preferably methylalumoxanes, combinations of alumoxanes with Al-alkyls, boron or borate cocatalysts and combination of alumoxanes with boron-based cocatalysts.

[0166] According to the most preferred embodiment of present invention, the preferred cocatalysts are alumoxanes, most preferably methylalumoxanes.

[0167] Suitable amounts of cocatalyst will be well known to the skilled person. The molar ratio of boron to the metal ion of the metallocene may be in the range 0.5:1 to 10:1 mol / mol, preferably 1:1 to 10:1 , especially 1 :1 to 5:1 mol / mol.

[0168] The molar ratio of Al in the aluminoxane to the metal ion of the metallocene may be in the range 1 :1 to 2000:1 mol / mol, preferably 10:1 to 1000:1 , and more preferably 50:1 to 500:1 mol / mol.

[0169] Catalyst Manufacture

[0170] The single site (preferably metallocene) catalyst complex can be used in supported or unsupported form. The particulate support material used is preferably an organic or inorganic material, such as silica, alumina or zirconia or a mixed oxide such as silica-alumina, in particular silica, alumina or silica-alumina. The use of a silica support is preferred. The skilled person is aware of the procedures required to support such a catalyst.

[0171] Especially preferably the support is a porous material so that the complex may be loaded into the pores of the support, e.g. using a process analogous to those described in WO94 / 14856, WO95 / 12622 and W02006 / 097497. The particle size is not critical but is preferably in the range 5 to 200 pm, more preferably 20 to 80 pm. The use of these supports is routine in the art.

[0172] In an alternative embodiment, no support is used at all. Such a catalyst can be prepared in solution, for example in an aromatic solvent like toluene, by contacting the metallocene (as a solid or as a solution) with the cocatalyst, for example methylaluminoxane or a borane or a borate salt previously dissolved in an aromatic solvent, or can be prepared by sequentially adding the dissolved catalyst components to the polymerisation medium. In one embodiment, no external carrier is used but the catalyst is still presented in solid particulate form. Thus, no external support material, such as inert organic or inorganic carrier, for example silica as described above is employed.

[0173] In order to provide the catalyst of the invention in solid form but without using an external carrier, it is preferred if a liquid / liquid emulsion system is used. The process involves forming dispersing catalyst components (i) (the complex) and (ii) (the cocatalyst) in a solvent, and solidifying said dispersed droplets to form solid particles.

[0174] In particular, the method involves preparing a solution of one or more catalyst components; dispersing said solution in a solvent to form an emulsion in which said one or more catalyst components are present in the droplets of the dispersed phase; immobilising the catalyst components in the dispersed droplets, in the absence of an external particulate porous support, to form solid particles comprising the said catalyst, and optionally recovering said particles.

[0175] This process enables the manufacture of active catalyst particles with improved morphology, e.g. with a predetermined spherical shape, surface properties and particle size and without using any added external porous support material, such as an inorganic oxide, e.g. silica. By the term "preparing a solution of one or more catalyst components" is meant that the catalyst forming compounds may be combined in one solution, which is dispersed to the immiscible solvent, or, alternatively, at least two separate catalyst solutions for each part of the catalyst forming compounds may be prepared, which are then dispersed successively to the solvent. Full disclosure of the necessary process can be found in W003 / 051934.

[0176] As noted above, the key to the invention is not the specific nature of the single site catalyst used and hence this may be chosen broadly however it is required that the second polymerisation process, i.e. the gas phase polymerisation, can be effected in the presence of the aluminium alkyl compound.

[0177] Polyolefin

[0178] The process of the invention produces a polyolefin polymer. The polyolefin polymer may be a polyolefin homopolymer or a polyolefin copolymer. The polyolefin may be a polyethylene or a polypropylene, preferably polypropylene. The polyethylene may be a polyethylene homopolymer or copolymer. More preferably, the polyolefin is a polypropylene and may be a polypropylene homopolymer or a polypropylene copolymer. If the polypropylene is a copolymer, it is preferred if the comonomer is ethylene.

[0179] Thus, in one embodiment, the invention relates to a process as hereinbefore defined wherein the polyolefin is a polypropylene and the olefin monomer is propylene.

[0180] Polyolefins made by the processes of the invention can be made with Mw (weight average molecular weight) values in the range of 40 to 2000 kg / mol, preferably in the range of 50 to 1 500 kg / mol depending on the use and amount of hydrogen used as Mw regulating agent.

[0181] Polypropylenes made by the processes of the invention can be made with an MFR2 of 2.0 to 15 g / 10min (measured at 230°C and 2.16 kg load ISO1133).

[0182] In a preferred embodiment the propylene homopolymer or copolymer formed by the process of the invention has a melting point of more than 120°C, such as more than 140.0 °C, preferably more than 143.0°C, especially more than 145.0°C. Preferably, the melting point is less than 160.0 °C, more preferably less than 155.0 °C, even more preferably less than 153.0 °C.

[0183] In one embodiment, the polypropylene is a copolymer of propylene. Polypropylene copolymers made by the processes of the invention are preferably copolymers of propylene with alpha-olefin comonomer(s), such as ethylene or C4 - C10 comonomers, especially with ethylene comonomers. Typically, the comonomer content is 0.1 to 15 wt%, such as 0.3 to 12 wt%, preferably 0.1 to 6.0 wt%, relative to the total weight of the copolymer as a whole.

[0184] In one preferred embodiment, the polypropylene is a polypropylene homopolymer or polypropylene copolymer with ethylene.

[0185] Aluminium Alkyl

[0186] The invention relies on the use of an aluminium alkyl scavenger in the at least one gas phase reactor. The aluminium alkyl is not introduced into the first reactor. As discussed below, the aluminium alkyl is fed only to the gas phase reactor(s) in the multistage polymerisation system. The aluminium alkyl may react with catalyst killers to produce compounds that may be easily purged or removed from the reactors. The aluminium alkyl of the invention may be of formula Al Rs-xCk where R is a C1-10 alkyl group and x is an integer 0 or 1. Mixtures of aluminium alkyls can be used in the process of the invention.

[0187] An aluminium alkyl of the invention is preferably of formula AI(C1 -10-alkyl)s such as AI(C1 -6-alkyl)3, especially AI(C1-4-alkyl)3. Each alkyl may be the same or different, preferably the same. It is also possible for the aluminium alkyl to be an aluminium-halo-alkyl, such as AIEt2CI. Alkyl groups can be linear or branched.

[0188] It is preferred if all alkyl groups are the same on the aluminium alkyl.

[0189] Preferred aluminium alkyls include triethylaluminum (TEAL), trimethylaluminum (TMA), tri-isobutylaluminum (TIBA), tri-n-butylaluminium (TNBA) and tri-n-hexylaluminum (TN HAL).

[0190] The use of triethyl-aluminium (TEAL), tri-isobutyl-aluminium (TIBA) or a mixture thereof is especially preferred.

[0191] The aluminium alkyl is typically fed directly to the fluidised bed of any gas phase reactor or fed to the circulation gas line. The aluminium alkyl is generally fed in pure form or in the form of a solution comprising a hydrocarbon diluent (e.g. propane, pentane or hexane). The aluminium alkyl is not fed to the first reactor, e.g. the prepolymerisation reactor (if present) and a slurry reactor.

[0192] The amount of aluminium alkyl feed is ideally 10 to 200 wt-ppm, preferably 10 to 100 wt-ppm, especially 25 to 75 wt-ppm, such as 25 to 50 wt-ppm based on the total polymer production in the gas phase reactor. Note that if a mixture of aluminium alkyl compounds is used then this figure refers to the total content of all aluminium alkyls used. The total polymer production in the gas phase reactor is the amount of polymer produced in the process as a whole as the polymer produced in the slurry is also present within the gas phase reactor.

[0193] The process of the invention is continuous and hence alternatively viewed, the amount of aluminium alkyl feed is ideally 10 to 200 wt-ppm, preferably 10 to 100 wt-ppm, especially 25 to 75 wt-ppm, such as 25 to 50 wt-ppm per hour based on the total polymer production in the gas phase reactor per hour. Note that if a mixture of aluminium alkyl compounds is used then this figure refers to the total content of all aluminium alkyls used. An optimum aluminium alkyl feed can also be calculated from the water content within the gas phase reactor. The mol ratio of aluminium alkyl to water present may range from 1 :1 to 5:1 , such as 2 mol aluminium alkyl against 1 mol water.

[0194] Process

[0195] The process according to the invention is a multistage polymerisation process, i.e. a process involving two or more stages (i.e. two or more reactors) which are connected "in series". A multistage process in the context of the invention is defined to be a polymerisation process in which a polymer comprising two or more fractions is produced by producing each or at least two polymer fraction(s) in a separate reaction stage, usually with different reaction conditions in each stage, in the presence of the reaction product of the previous stage which comprises a polymerisation catalyst. The polymerisation reactions used in each stage may involve conventional propylene homopolymerisation or copolymerisation reactions, e.g. gasphase, slurry phase, liquid phase polymerisations, using conventional reactors, e.g. loop reactors, gas phase reactors, batch reactors etc. (see for example WO97 / 44371 and WO96 / 18662).

[0196] The specific first and second polymerisation conditions depend on various factors such as the catalyst activity, type and amount of optional comonomer, type of polymer to be produced, and the production equipment. This is within the skills of the person skilled in the art.

[0197] As hereinbefore described, the process involves at least a first reactor and a gas phase reactor, these may be considered the first and second polymerisation stages, respectively. In one embodiment, more than one gas phase reactor is employed. In these cases, the second and any additional gas phase reactors are connected in series subsequent to the gas phase reactor of the second polymerisation stage. Preferably, in this case, the aluminium alkyl is fed to at least two, more preferably all, gas phase reactors.

[0198] Preferably, the multistage process is a two-stage polymerisation process, optionally and preferably preceded by a prepolymerisation step. If a prepolymerisation step is used, the prepolymerisation step comes before the first polymerisation stage. The first polymerisation stage typically produces a polyolefin such as propylene homopolymer or a propylene copolymer (the first polymer product), which is subsequently fed to the second polymerisation stage. The second polymerisation stage can produce a further propylene homopolymer, or a propylene copolymer (the second polymer product). In one embodiment, the first and second polymerisation stages both produce a propylene homopolymer. In an alternative embodiment, the first and second polymerisation stages produce a propylene copolymer.

[0199] The first polymerisation stage is preferably a slurry polymerisation step, thus the first reactor is preferably a slurry reactor, more preferably a slurry loop reactor.

[0200] The slurry polymerisation usually takes place in an inert diluent, typically a hydrocarbon diluent such as methane, ethane, propane, n-butane, isobutane, pentanes, hexanes, heptanes, octanes etc., or their mixtures. Preferably the diluent is a low-boiling hydrocarbon having from 1 to 4 carbon atoms or a mixture of such hydrocarbons. An especially preferred diluent is propane, possibly containing minor amounts of methane, ethane and / or butane.

[0201] The propylene content in the fluid phase of the slurry, if present, may be from 1 to 50 % by mole, preferably from 2 to 20 % by mole and in particular from 2 to 10 % by mole. The benefit of having a high propylene concentration is that the productivity of the catalyst is increased but the drawback is that more propylene then needs to be recycled than if the concentration was lower.

[0202] The temperature in the first polymerisation stage is typically from 50 to 110 °C (e.g. 60-100, or 70 to 110 °C), the reactor pressure will generally be in the range of 20 to 80 bar (e.g. 30-70 bar). An excessively high temperature should be avoided to prevent partial dissolution of the polymer into the diluent and the fouling of the reactor.

[0203] The slurry polymerisation may be conducted in any known reactor used for slurry polymerisation. Such reactors include a continuous stirred tank reactor and a loop reactor. It is especially preferred to conduct the slurry polymerisation in a loop reactor. In such reactors the slurry is circulated with a high velocity along a closed pipe by using a circulation pump. Loop reactors are generally known in the art and examples are given, for instance, in US-A-4582816, US-A-3405109, US-A-3324093, EP-A-479186 and US-A-5391654. It is thus preferred to conduct the first polymerisation stage as a slurry polymerisation in a loop reactor. In one embodiment, an antifouling agent can be used in the first polymerisation stage. Suitable antifouling agents are materials that prevent fouling of the inside of the reactor wall. In an embodiment, the antifouling agent is selected from cationic agents, anionic agents, nonionic agents, organometallic agents, polymeric agents or mixtures thereof - these are commercially available.

[0204] The slurry may be withdrawn from the reactor either continuously or intermittently. A preferred way of intermittent withdrawal is the use of settling legs where slurry is allowed to concentrate before withdrawing a batch of the concentrated slurry from the reactor. The use of settling legs is disclosed, among others, in US-A-3374211, US-A-3242150 and EP-A-1310295. Continuous withdrawal is disclosed, among others, in EP-A-891990, EP-A-1415999, EP-A-1591460 and WO-A-2007 / 025640. The continuous withdrawal is advantageously combined with a suitable concentration method, as disclosed in EP-A-1310295 and EP-A-1591460. It is preferred to withdraw the slurry from the first polymerisation stage continuously.

[0205] The average residence time in the first polymerisation stage will generally be in the range of 0.2 to 5.0 hours (e.g. 0.3 to 2 hours) in the slurry reactor. Preferably the residence time is in the range of 0.2 to 1.0 hour, more preferably in the range of 0.3 to 0.6 hours. As it is well known in the art the average residence time T can be calculated from Equation 1 below:

[0206] Equation 1: Residence time where VR is the volume of the reaction space (in case of a loop reactor, the volume of the reactor, in case of the fluidized bed reactor, the volume of the fluidized bed) and Qois the volumetric flow rate of the product stream (including the polymer product and the fluid reaction mixture).

[0207] The diluent used will generally be an aliphatic hydrocarbon having a boiling point in the range -70 to +100 °C. In such reactors, polymerisation may if desired be effected under supercritical conditions.

[0208] The production rate is suitably controlled with the catalyst feed rate. It is also possible to influence the production rate by suitable selection of the monomer concentration. It should be emphasised that the aluminium alkyl is not fed to the first reactor (or first polymerisation stage). If a prepolymerisation reactor is used the aluminium alkyl is not fed to the prepolymerisation reactor or the first reactor.

[0209] In the second polymerisation stage, olefin such as propylene is polymerised, optionally together with at least one other alpha-olefin comonomer, in the presence of the catalyst of the first polymerisation stage and the polymer produced in the first polymerisation stage. It will thus be appreciated that the second polymerisation stage generates a polyolefin polymer, which combines with the polyolefin polymer from the first polymerisation stage. Preferable comonomers are discussed hereinbefore.

[0210] The second polymerisation stage is a gas phase polymerisation step, i.e. carried out in a gas-phase reactor. Thus, the second reactor is a gas phase reactor. Any suitable gas phase reactor known in the art may be used, such as a fluidised bed gas phase reactor.

[0211] For gas phase reactors, the reaction temperature used will generally be in the range of 50 to 130 °C (e.g. 60 to 115 °C, or 60 to 100 °C), the reactor pressure will generally be in the range of 5 to 60 bar, preferably 10 to 40 bar and the residence time will generally be 1 to 8 hours. The gas used will commonly be a non-reactive gas such as nitrogen or low boiling point hydrocarbons such as propane together with monomer (e.g. propylene).

[0212] Hydrogen may be introduced into any reactor to control the molecular weight of the polymer as is well-known and routine in the art. In one embodiment, the mole ratio of hydrogen to total olefin monomer in the circulating gas stream is in a range of from 0.001 or 0.002 or 0.003 to 0.014 or 0.016 or 0.018 or 0.024, wherein a desirable range may comprise any combination of any upper mole ratio limit with any lower mole ratio limit described herein. Expressed another way, the amount of hydrogen in the reactor at any time may range from 1000 ppm to 20,000 ppm in one embodiment, and from 2000 to 10,000 in another embodiment, and from 3000 to 8,000 in yet another embodiment, and from 4000 to 7000 in yet another embodiment, wherein a desirable range may comprise any upper hydrogen limit with any lower hydrogen limit described herein.

[0213] The split between the first polymerisation stage and the second polymerisation stage (i.e. between the slurry polymerisation and the gas phase polymerisation) is typically 30:70 to 70:30, more preferably 35:65 to 65:35, most preferably 40:60 to 60:40. If a prepolymer is present, the prepolymer is counted as part of the first stage polymerisation product.

[0214] Thus, a preferred embodiment of the invention is wherein the first reactor is a slurry reactor, such as a loop reactor, and the second reactor is a gas phase reactor, such as a fluidised bed gas phase reactor. A preferred “loop-gas phase”-process, such as developed by Borealis A / S, Denmark (known as BORSTAR® technology) is described e.g. in patent literature, such as in EP 0887 379, in WO92 / 12182 or in WO 2005 / 002744.

[0215] In the fluidized bed reactor, the catalytic material in the fluidized bed reactor is typically supported by a porous plate known as a distributor. A fluid is then forced through the distributor and up through the catalytic material. As the fluid velocity is increased, the reactor will reach a stage where the force of the fluid on the solids is enough to balance the weight of the solid material. This stage is known as incipient fluidization and occurs at this minimum fluidization velocity. Once this minimum velocity is surpassed, the contents of the reactor bed begin to expand and swirl around much like an agitated tank.

[0216] It is conventional to provide the fluidized bed reactor with a circulation gas line to return the fluidizing gas to the base of the reactor.

[0217] In one embodiment, the process of the invention involves a prepolymerisation reactor, such as that described below. The polymerisation steps discussed above may be preferably preceded by a prepolymerisation step therefore. The purpose of the prepolymerisation is to polymerise a small amount of polymer onto the catalyst at a low temperature and / or a low monomer concentration. By prepolymerisation it is possible to improve the performance of the catalyst in slurry and / or modify the properties of the final polymer. The prepolymerisation step is preferably conducted in slurry.

[0218] Thus, the prepolymerisation step may be conducted in a loop reactor. The prepolymerisation is preferably conducted in an inert diluent, typically a hydrocarbon diluent such as methane, ethane, propane, n-butane, isobutane, pentanes, hexanes, heptanes, octanes etc., or their mixtures. Preferably the diluent is a low-boiling hydrocarbon having from 1 to 4 carbon atoms or a mixture of such hydrocarbons.

[0219] The temperature in the prepolymerisation step is typically from 0 to 90 °C, preferably from 20 to 80 °C and more preferably from 20 to 40 °C. The pressure is not critical and is typically from 1 to 150 bar, preferably from 40 to 80 bar.

[0220] The amount of monomer is typically such that from 0.1 to 1000 grams of monomer per one gram of solid catalyst component is polymerised in the prepolymerisation step. As the person skilled in the art knows, the catalyst particles recovered from a continuous prepolymerisation reactor do not all contain the same amount of prepolymer. Instead, each particle has its own characteristic amount which depends on the residence time of that particle in the prepolymerisation reactor. As some particles remain in the reactor for a relatively long time and some for a relatively short time, then also the amount of prepolymer on different particles is different and some individual particles may contain an amount of prepolymer which is outside the above limits. However, the average amount of prepolymer on the catalyst typically is within the limits specified above.

[0221] The molecular weight of the prepolymer may be controlled by hydrogen as it is known in the art. Further, antistatic additives may be used to prevent the particles from adhering to each other or the walls of the reactor, as disclosed in WO-A- 96 / 19503 and WO-A-96 / 32420. Furthermore, olefin and hydrogen and optionally the cocatalyst are added to the prepolymerisation reactor.

[0222] In the process of the invention, the single site catalysed polymerisation is preferably started as is known in the state of the art by introducing the single site catalyst, as described above, via a catalyst feed tank, preferably via an oil catalyst feed system or via a wax catalyst feed system to the first reactor, or if present, to the prepolymerisation reactor.

[0223] If the prepolymerisation reactor is used then the prepolymerized catalyst, additional olefin, hydrogen, optionally additional cocatalyst are introduced into the first reactor (typically a slurry reactor), afterwards recovering the polymerisation product from the slurry phase reactor and conducting it to the gas phase reactor, optionally feeding additional olefin and optional comonomer to the second reactor, optionally feeding additional hydrogen to the second reactor to control the hydrogen- to-olefin ratio to provide the desired molecular mass of the polymerisation product, recovering the polymerisation product from the second reactor.

[0224] The reaction conditions in the slurry phase and the gas phase reactor (like temperature, pressure, amount of propylene and optional comonomers, amount of hydrogen) are chosen according to the desired product parameters of the first product. In general, such a process is conventional.

[0225] The single site catalyst components are preferably all introduced to the prepolymerisation step when a prepolymerisation step is present. However, where the solid catalyst component and the cocatalyst can be fed separately it is possible that only a part of the cocatalyst is introduced into the prepolymerisation stage and the remaining part into subsequent polymerisation stages. Also in such cases it is necessary to introduce so much cocatalyst into the prepolymerisation stage that a sufficient polymerisation reaction is obtained therein.

[0226] The process of the invention will be understood to be a continuous process. The polymer produced in the first reactor is typically continuously fed to the second reactor throughout the process.

[0227] The precise control of the polymerisation conditions and reaction parameters is within the skill of the art. The pressure and temperature of the second reactor are typically kept essentially constant throughout the process.

[0228] Determination Methods

[0229] The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined.

[0230] Melt flow rate (MFR2) is measured according to ISO 1133. For propylene, conditions are 230 °C and 2.16 kg load. For polyethylene, conditions are 190 °C and 2.16 kg load.

[0231] Bulk Density: The bulk density of the polymer powder was determined according to ASTM D1895-96, method A.

[0232] Number average molecular weight (Mn), weight average molecular weight (Mw) and molecular weight distribution (MWD) are determined by Gel Permeation Chromatography (GPC) according to the following method:

[0233] The weight average molecular weight Mw and the molecular weight distribution (MWD = Mw / Mn wherein Mn is the number average molecular weight and Mw is the weight average molecular weight) is measured by a method based on ISO 16014- 1 :2003 and ISO 16014-4:2003. A Waters Alliance GPCV 2000 instrument, equipped with refractive index detector and online viscosimeter was used with 3 x TSK-gel columns (GMHXL-HT) from TosoHaas and 1,2,4-trichlorobenzene (TCB, stabilized with 200 mg / L 2,6-Di tert butyl-4-methyl-phenol) as solvent at 145 °C and at a constant flow rate of 1 mL / min. 216.5 pL of sample solution were injected per analysis. The column set was calibrated using relative calibration with 19 narrow MWD polystyrene (PS) standards in the range of 0.5 kg / mol to 11 500 kg / mol and a set of well characterised broad polypropylene standards. All samples were prepared by dissolving 5 - 10 mg of polymer in 10 mL (at 160 °C) of stabilized TCB (same as mobile phase) and keeping for 3 hours with continuous shaking prior sampling in into the GPC instrument.

[0234] Particle size (PS) and Average Particle Size (APS) were measured according to

[0235] ISO 13322-2 using Image analysis methods using a Camsizer P4 analyser.

[0236] Comonomer content was determined in a known manner based on Fourier transform infrared spectroscopy (FTIR) determination using Nicolet Magna 550 IR spectrometer together with Nicolet Omnic FTIR software calibrated with13C-NMR.

[0237] DSC analysis

[0238] Melting temperature Tm and crystallization temperature Ter was measured on approx. 5 mg samples with a Mettler-Toledo 822e differential scanning calorimeter (DSC), according to ISO11357-3 in a heat / cool / heat cycle with a scan rate of 10 °C / min in the temperature range of +23 to +225 °C under a nitrogen flow rate of 50 ml min-1. Melting temperature was taken as the endotherm peak, respectively in the second heating step. Calibration of the instrument was performed with H20, Lead, Tin, Indium, according to ISO 11357-1.

[0239] Xylene solubles

[0240] The xylene soluble fraction (XS) as defined and described in the present invention was determined as follows: 2.0 g of the polymer were dissolved in 250 mm p-xylene at 135 °C under agitation. After 30 minutes, the solution was allowed to cool for 15 minutes at ambient temperature and then allowed to settle for 30 minutes at 25 ± 0.5 °C. The solution was filtered with filter paper into two 100 mm flasks. The solution from the first 100 mm vessel was evaporated in nitrogen flow and the residue dried under vacuum at 90 °C until constant weight is reached. The xylene soluble fraction (percent) can then be determined as follows: XS% = (100 x mi X vo) / (mo x Vi), wherein mo designates the initial polymer amount (grams), r defines the weight of residue (grams), vo defines the initial volume (milliliter) and vi defines the volume of the analysed sample (milliliter).

[0241] Gel index

[0242] The optical gel index was measured with an OCS gel counting apparatus consisting of a measuring extruder, attached to this were a chill roll unit, a heating and cooling unit (Haake C40P with a temperature range of 15-90 °C), a line camera (FS-5 / 4096 pixel for dynamic digital processing of grey tone images) and a winding unit (with automatic drawing control up to 10 N). The details of film production is listed below session.

[0243] For each material, the average number of gel dots on a film surface of 5 m2 was detected by the line camera. The line camera was set to differentiate the gel dot size according to the following table:

[0244] The number of gel dots detected for each size was multiplied with its respective calculating factor. The sum of all those values gave one final value, which is called the optical gel index.

[0245] Examples

[0246] In the polymerisations exemplified below, the following catalyst was used. Catalyst

[0247] The single-site catalyst used in the polymerisation process for all examples was Ant / -dimethylsilylene[2-methyl-4-phenyl-5-methoxy-6-terf-butyl-indenyl)(2- methyl-4-phenyl-6-tert-butylindenyl) zirconium dichloride as disclosed in WO 2013 / 007650 A1 as metallocene E1. For examples IE1-IE2, Cat1 was used. For IE3, Cat2 was used.

[0248] Cat1: Catalyst with SiO2 / MAO support

[0249] Cat2: Catalyst with SiO2 / MAO / borate support

[0250] Polymerisations

[0251] Three inventive (IE1-IE3) and two reference polymerisation processes (CE1 and CE2) were carried out according to the conditions set out in Table 1 below.

[0252] In the homopolymer Examples in Table 1, TEAL feed to GPR increased productivity and production split in GPR. Two feed levels were used 25 wt-ppm and 50 wt-ppm in IE1 and IE2. The results demonstrate that the TEAL feed had no negative impact on MFR, Isotacticity, or morphology. Operability was good. TEAL feed did not affect gel level. Furthermore, the TEAL feed did not affect the thermal character of the product. This is reflected in DSC. The melting temperature (Tm) and the crystallisation temperature (Ter) was about the same for inventive and comparative examples.

[0253] IE3 demonstrates that the catalyst productivity and the reactor balance was good when 60 wt-ppm TEAL was fed to GPR as a scavenger. Productivity on the catalyst dropped in GPR when TEAL feed to GPR was stopped; this is shown in CE2. Table 1 : Reference (CE1) and Inventive Examples (IE1 & IE2), Polymerisation conditions

[0254]

Claims

Claims1 . 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. A process as claimed in claim 1 , wherein the polyolefin is a polypropylene and the olefin monomer is propylene.

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. The process as claimed in claim 12, wherein the metallocene catalyst comprises as a catalyst component an organometallic compound (C) of formula (la): (L)2RnMX2(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 SiMe2bridging group linking said organic ligands (L);“n” is 0 or 1 , preferably 1.

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. 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. 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.

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