Process

Abstract

The present invention provides a process for converting between a Ziegler-Natta catalyst and a single site catalyst during the production of a polypropylene homopolymer or copolymer in a continuous multi-stage polymerization reaction, the process comprising the successive steps of: a) in the presence of a Ziegler-Natta catalyst, reacting the Ziegler-Natta catalyst with a single site catalyst, polymerizing propylene and optionally comonomers in a first reactor, and then polymerizing propylene and optionally comonomers in a second reactor; b) stopping feeding the Ziegler-Natta catalyst to the first reactor; c) stopping the feeding of the external donor to the Ziegler-Natta catalyst in the first reactor and reducing the feeding of the Ziegler-Natta co-catalyst in the first reactor wherein step c) is carried out at least 5 minutes, preferably after 5 to 60 minutes, after step b); d) reducing the solids content of the second reactor from the first operating level to a conversion level in the range of 40% to 80% relative to the level prior to step d); e) introducing a single site catalyst into the first reactor, wherein step e) proceeds at least 30 minutes, preferably 30 minutes to 2 hours, after step d); and f) increasing the solids content of the second reactor to a second operating level, preferably to the same level as before step d).

Description

Technical Field

[0001] The present invention relates to a method for catalyst conversion in olefin polymerization, and more particularly to the operation of an olefin polymerization unit. More specifically, the invention relates to converting between Ziegler-Natta catalysts and single-site catalysts in the production of polypropylene in a continuous multi-stage polymerization reaction. Ideally, the conversion can be accomplished without the use of any catalyst deactivators. Background Art

[0002] Polypropylene homopolymers and polypropylene copolymers can be formed in a polymerization reactor in the presence of a suitable catalyst and can be used to prepare a variety of end products such as films, pipes and molded articles.

[0003] One form of reactor suitable for the production of propylene homopolymers and copolymers is a loop reactor. The polymer particles leaving the loop reactor can be introduced into one or more subsequent polymerization reactors, for example one or more gas phase reactors, for further polymerization with other monomers, for example ethylene, to modify the physical and chemical properties of the propylene polymer resin. In addition, the physical and chemical properties of the propylene resin can be customized by selecting one or more catalyst systems.

[0004] During the production of olefin polymers, such as polypropylene homopolymers and polypropylene copolymers, in commercial reactors, it is often necessary to switch from a catalyst system that produces polymers with certain properties and characteristics to another catalyst system that produces polymers with different specifications. Switching between similar or compatible catalysts is usually easy to do. However, when the catalyst types are different and / or incompatible, for example, the well-known active Ziegler-Natta catalyst may "poison" the active single-site catalyst, this method can usually be complicated. For example, switching from a Ziegler-Natta catalyst to a single-site catalyst, or vice versa, usually requires a long transition period. In addition, the properties of the polyolefins produced during this transition period will continue to change. If switching from one catalyst system to another catalyst system requires a significant change in reactor conditions, then there may be a risk of production problems and producing polymers with extreme properties.

[0005] The switch from a polymerization reaction catalyzed by a first catalyst to a polymerization reaction catalyzed by a second catalyst is typically performed by stopping the polymerization process, emptying the reactor, recharging, and then introducing the second catalyst into the reactor. Such catalyst changes are time-consuming and costly due to the need to shut down the reactor for an extended period of time during the switch.

[0006] However, the polymerization reaction can be inhibited or stopped temporarily or permanently in a variety of ways without emptying the reactor.

[0007] EP 0604993 discloses a method for restarting a temporarily stopped gas-phase olefin polymerization. Olefin polymerization using a Ziegler-Natta catalyst is stopped by introducing a deactivator, such as oxygen, water, carbon dioxide, carbon monoxide, an alcohol, or a ketone. The reaction system is restarted by adding an organoaluminum compound to the reaction system without discharging the previously formed polymer particles and then the solid catalyst component.

[0008] WO 92 / 14766 describes the use of a volatile and a non-volatile catalyst scavenger for a metallocene catalyst in a high pressure polymerization process, the scavenger being added downstream of the polymerization zone to inhibit the polymerization of recycled monomer and separated molten polymer. Methanol and n-butanol can also be used as catalyst scavengers for metallocene / aluminoxane-based catalyst systems.

[0009] US Pat. No. 4,460,755 discloses a method for converting a continuous olefin polymerization reaction catalyzed by a Ziegler-type catalyst to one catalyzed by a chromium-based catalyst without the need to empty and recharge the polymerization reactor. The process comprises the following steps: stopping the catalyst feed, introducing hydroxyl-containing silica that reacts with the catalyst, and finally introducing the chromium-based catalyst, while maintaining polymerization conditions during the conversion.

[0010] WO 95 / 26370 discloses a method for converting a polymerization reaction catalyzed by a Ziegler-Natta catalyst to a polymerization reaction catalyzed by a metallocene catalyst. This is achieved by a) stopping the first catalyst feed to the reactor, b) introducing a reversible catalyst scavenger, c) introducing an irreversible catalyst scavenger, and d) feeding the reactor with a second catalyst. The Ziegler-Natta catalyst consists of silica impregnated with titanium chloride, magnesium chloride, and tetrahydrofuran, and an organoaluminum compound. The metallocene catalyst comprises silica mixed with methylaluminoxane and bis-n-butylcyclopentadienyl zirconium dichloride, and triethylaluminum as a cocatalyst. The conversion from a Ziegler-Natta catalyst to a metallocene catalyst is illustrated by way of example only. Carbon monoxide (CO) is used as a reversible catalyst scavenger, and water is used as an irreversible catalyst scavenger.

[0011] Generally speaking, these prior art methods require that the first polymerization catalyst be "purged" or substantially deactivated. While these techniques do mitigate the problems caused by the undesirable reaction between the two incompatible catalysts, they can introduce other problems, such as:

[0012] (i) The addition of the deactivator needs to be carefully controlled (so that it does not poison the new catalyst);

[0013] (ii) Downtime is required to carry out the deactivation reaction (usually including subsequent deactivation agent cleaning).

[0014] The second issue – “downtime” – can lead to further problems, especially if it requires stopping and restarting polymer finishing operations (such as polymer degassing and pelletizing operations). For example, seals and / or bearings or mechanical pumps and compressors used in polymer finishing operations are more likely to fail during stop / start cycles than during continuous operation.

[0015] It is well known that certain pairs of polymerization catalysts are "incompatible," for example, one catalyst may act as a "poison" to the other; one catalyst may have a different reactivity ratio than the other; or one catalyst may have a different "hydrogen response" than the other. Further details on the problems caused by incompatible catalysts are set forth in US Pat. No. 6,949,612.

[0016] Typically, switching between incompatible catalysts results in the production of significant amounts of substandard polymer and / or lost production time. Substandard polymer material typically does not possess the desired resin flow properties (e.g., melt index), isotacticity, or xylene solubles content, or other properties of the initial or desired target product. Because substandard polymer material can result in economic losses, it is desirable to minimize the length of time a reactor is operating to produce such material and the amount of material produced.

[0017] In olefin polymerization, Ziegler-Natta catalysts are often used. However, recent catalyst developments have led to the use of single-site catalysts (SSCs), preferably metallocene catalysts, which contain metallocene compounds of transition metals. Currently, these two types of catalysts have important economic significance, so the time-saving conversion from one catalyst to another in the same polymerization unit is very desirable. However, the catalysts are incompatible and the direct conversion between them is usually challenging.

[0018] Therefore, it would be highly advantageous to find a method for switching between Ziegler-Natta catalysts and single-site catalysts that does not require shutting down the polymerization reactor to remove the original catalyst system, restarting the polymerization reaction with another catalyst system, and / or does not require any catalyst deactivators (catalyst scavengers). Additionally, it would be advantageous if the method for switching could reduce the amount of off-specification material generated during the switching process, reduce the switching time, and increase the robustness and stability of the switching process.

[0019] Various methods have been described to reduce transient off-spec polymer material. These methods include feeding polymerization retardants or catalyst poisons (e.g., CO2, O2) to the reactor, adjusting the reaction gas composition, temperature, and possibly pressure to new values, removing the reaction gas from the reactor, reducing the catalyst feed rate, and / or adding non-reactive gases, such as nitrogen, among other remedial measures.

[0020] WO 2010 / 086392 describes a process for switching between two catalysts in a propylene production process, wherein the switch from the first catalyst to the second catalyst is performed in a prepolymerization reactor and the reaction conditions in all reactors are appropriately adjusted.

[0021] While methods exist for limiting off-spec material, there remains a need and desire to provide more effective and efficient methods for reducing the amount of off-spec polymer material generated during changeovers to new products or due to fluctuations during steady state manufacturing.

[0022] The invention relates to a method for converting a Ziegler-Natta catalyst and a single-site catalyst used for propylene polymerization. Summary of the Invention

[0023] In a first aspect, the present invention provides a method for switching between a Ziegler-Natta catalyst and a single-site catalyst in a continuous multi-stage polymerization process for producing a polypropylene homopolymer or copolymer, the method comprising the following steps in sequence:

[0024] a) polymerizing propylene and optionally a comonomer in a first reactor and then polymerizing propylene and optionally a comonomer in a second reactor in the presence of a Ziegler-Natta catalyst;

[0025] b) stopping feeding the Ziegler-Natta catalyst to the first reactor;

[0026] c) stopping the feed of the external supplier of Ziegler-Natta catalyst to the first reactor and reducing the feed of the Ziegler-Natta cocatalyst to the first reactor, wherein step c) is carried out at least 5 minutes, preferably 5 to 60 minutes after step b);

[0027] d) reducing the solids content of the second reactor from the first operating level to a conversion level in the range of 40% to 80% relative to the first operating level prior to step d);

[0028] e) introducing a single site catalyst into a first reactor, wherein step e) is performed at least 30 minutes, preferably 30 minutes to 2 hours, after step d); and

[0029] f) increasing the solids content of the second reactor to a second operating level, preferably to the same level as before step d).

[0030] Viewed from another aspect, the present invention provides a method for switching between a Ziegler-Natta catalyst and a single-site catalyst in a continuous multi-stage polymerization process for producing a polypropylene homopolymer or copolymer, the method comprising the following steps in sequence:

[0031] a) polymerizing propylene and optionally a comonomer in a first reactor and then polymerizing propylene and optionally a comonomer in a second reactor in the presence of a Ziegler-Natta catalyst;

[0032] b) stopping feeding the Ziegler-Natta catalyst to the first reactor;

[0033] c) stopping the feed of the external supplier of Ziegler-Natta catalyst to the first reactor and reducing the feed of the Ziegler-Natta cocatalyst to the first reactor, wherein step c) is carried out at least 5 minutes, preferably 5 to 60 minutes after step b);

[0034] d) reducing the solids content of the second reactor from the first operating level to a conversion level in the range of 40% to 80% relative to the first operating level prior to step d);

[0035] e) introducing a single site catalyst into a first reactor, wherein step e) is performed at least 30 minutes, preferably 30 minutes to 3.0 hours, preferably 30 minutes to 2 hours after step b); and

[0036] f) increasing the solids content of the second reactor to a second operating level, preferably to the same level as before step d).

[0037] Viewed from another aspect, the present invention provides a method for switching between a Ziegler-Natta catalyst and a single-site catalyst in a continuous multi-stage polymerization process for producing a polypropylene homopolymer or copolymer, the method comprising the following steps in sequence:

[0038] a) polymerizing propylene and optionally a comonomer in a first reactor and then polymerizing propylene and optionally a comonomer in a second reactor in the presence of a Ziegler-Natta catalyst;

[0039] b) stopping feeding the Ziegler-Natta catalyst to the first reactor;

[0040] c) stopping the feed of the external supplier of Ziegler-Natta catalyst to the first reactor and reducing the feed of the Ziegler-Natta cocatalyst to the first reactor, wherein step c) is carried out at least 5 minutes, preferably 5 to 60 minutes after step b);

[0041] d) reducing the solids content of the second reactor from the first operating level to a conversion level in the range of 40% to 80% relative to the first operating level prior to step d);

[0042] e) introducing a single site catalyst into a first reactor, wherein step e) is performed at least 30 minutes, preferably 30 minutes to 3.0 hours, preferably 30 minutes to 2 hours after step b); and

[0043] f) increasing the solids content of the second reactor to a second operating level, preferably to the same level as before step d). Detailed Description of the Invention

[0045] Ziegler-Natta (ZN) catalyst

[0046] The Ziegler-Natta catalyst can be any Ziegler-Natta catalyst known in the art. The Ziegler-Natta catalyst typically used in the present invention for propylene polymerization is a stereospecific, solid, high-yield Ziegler-Natta catalyst component comprising a compound of Mg, Ti, and Cl and an internal donor component. In addition to the solid catalyst component, a cocatalyst and an external donor are typically used in propylene polymerization processes.

[0047] The catalyst component can be supported on a particulate support, for example an inorganic oxide such as silica or alumina, or a magnesium halide can form a solid support. The solid catalyst component can be prepared by emulsion solidification or precipitation.

[0048] The solid catalyst component for propylene polymerization generally consists of an internal electron donor and an aluminum compound as a cocatalyst. Suitable internal electron donors include esters of carboxylic acids or dicarboxylic acids, such as phthalates, unsubstituted or substituted malonates, unsubstituted or substituted maleates, ethers and diethers or oxygen- or nitrogen-containing silicon compounds, or mixtures thereof.

[0049] The optional aluminum compound used in conjunction with the catalyst preparation is generally selected from aluminum alkyl, aluminum alkyl halide, aluminum alkyl alkoxide or aluminum alkyl halide alkoxide compounds wherein the alkyl group contains 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, especially 1 to 6 carbon atoms.

[0050] The cocatalyst typically comprises a trialkylaluminum or alkylaluminum halide compound, wherein the alkyl group typically contains 1 to 20 carbon atoms, for example 1 to 10 carbon atoms. The alkylaluminum compound is preferably a trialkylaluminum, such as trimethylaluminum, triethylaluminum (TEAL), triisobutylaluminum or tri-n-octylaluminum. Alkylaluminum halides of interest include dialkylaluminum halides, alkylaluminum dihalides or alkylaluminum sesquihalides, such as diethylaluminum chloride, dimethylaluminum chloride, ethylaluminum dichloride or ethylaluminum sesquichloride.

[0051] To activate the catalyst, a cocatalyst is used in combination with the ZN catalyst. Preferably, the cocatalyst is an alkyl aluminum compound. TEAL is particularly preferred.

[0052] External donors are also commonly used in ZN polymerization processes. Suitable external electron donors for propylene polymerization are well known in the art and include ethers, ketones, amines, alcohols, phenols, phosphines, esters, and silanes. Silane-based external donors are typically organosilane compounds containing Si-OCOR, Si-OR, or Si-NR2 bonds, with silicon as the central atom and R being an alkyl, alkenyl, aryl, arylalkyl, or cycloalkyl group having 1 to 20 carbon atoms, as known in the art.

[0053] As used herein, the terms D-donor and external donor are used interchangeably.

[0054] Preferred external donors are silane donors including diisopropyldiethoxysilane (DIPDES), cyclohexylmethyldiethoxysilane (CHMDES), dicyclopentyldimethoxysilane, cyclohexylmethyldimethoxysilane and dicyclopentadienyldiethoxysilane (DCPDES) and diethylaminotriethoxysilane.

[0055] Examples of suitable Ziegler-Natta catalysts are described in WO 87 / 07620, WO 92 / 21705, WO 93 / 11165, WO 93 / 11166, WO 93 / 19100, WO 97 / 36939, WO 98 / 12234, WO 99 / 33842, WO 03 / 000756, WO 03 / 000757, WO 03 / 000754, WO 03 / 000755, WO 2004 / 029112, EP 2610271, WO 2012 / 007430, WO 92 / 19659, WO 92 / 19653, WO 92 / 19658, US 4382019, US 4435550, US4465782, US 4473660, US 4560671, US 5539067, US5618771, EP45975, EP45976, EP45977, WO95 / 32994, US 4107414, US 4186107, US 4226963, US 4347160, US 4472524, US 4522930, US 4530912, US 4532313, US 4657882, US 4581342 and US 4657882.

[0056] The Ziegler-Natta catalyst used is most preferably a solid Ziegler-Natta catalyst selected from the group consisting of a MgCl2-supported titanium Ziegler-Natta catalyst and a self-supported solid Ziegler-Natta catalyst.

[0057] In general, the present invention relates to a method for converting a process catalyzed by a conventional ZN catalyst to a process catalyzed by a conventional single-site catalyst. The specific nature of the ZN catalyst is not critical, but it is preferred if the ZN catalyzed process involves the use of an alkylaluminum cocatalyst compound.

[0058] Single-site catalyst

[0059] The single-site catalyst is preferably a metallocene catalyst or a non-metallocene catalyst. The single-site catalyst preferably comprises a transition metal compound containing at least one cyclopentadienyl, indenyl or fluorenyl ligand. Preferably, the single-site catalyst contains two cyclopentadienyl, indenyl or fluorenyl ligands, in particular two bridged cyclopentadienyl, indenyl or fluorenyl ligands. In addition, the ligand may have a substituent, for example, an alkyl, aryl, arylalkyl, alkylaryl, silyl, siloxy, alkoxy or other heteroatom groups. Examples of suitable metallocene compounds are shown in EP 629631, EP 629632, WO 00 / 26266, WO 02 / 002576, WO 02 / 002575, WO 99 / 12943, WO 98 / 40331, EP 776913, EP 1074557, WO 99 / 42497, EP 2402353, EP 2729479 and EP 2746289.

[0060] The single-site catalyst is ideally an organometallic compound (C) comprising a transition metal (M) from Groups 3 to 10 of the Periodic Table of the Elements (IUPAC 2007) or from the actinides or lanthanides. According to the present invention, the term "organometallic compound (C)" comprises any metallocene or non-metallocene compound of a transition metal which carries at least one organic (coordinating) ligand and which exhibits catalytic activity alone or in combination with a cocatalyst. Transition metal compounds are well known in the art, and the present invention encompasses compounds of metals from Groups 3 to 10, e.g., Groups 3 to 7 or Groups 3 to 6, e.g., Groups 4 to 6, of the Periodic Table of the Elements (IUPAC 2007), as well as compounds of lanthanides or actinides.

[0061] In one embodiment, the organometallic compound (C) has the following formula (I):

[0062] (L) m R n MX q (I)

[0063] in

[0064] "M" is a transition metal (M) from Groups 3 to 10 of the Periodic Table of the Elements (IUPAC 2007),

[0065] Each "X" is independently a monoanionic ligand, such as a sigma-ligand,

[0066] Each "L" is independently an organic ligand coordinated to the transition metal "M",

[0067] "R" is a bridging group connecting the organic ligand (L),

[0068] "m" is 1, 2 or 3, preferably 2

[0069] "n" is 0, 1 or 2, preferably 1

[0070] "q" is 1, 2 or 3, preferably 2, and

[0071] m+q equals the valence of the transition metal (M).

[0072] “M” is preferably selected from the group consisting of zirconium (Zr), hafnium (Hf), or titanium (Ti), and more preferably selected from the group consisting of zirconium (Zr) and hafnium (Hf).

[0073] In a more preferred definition, each organic ligand (L) is independently:

[0074] (a) substituted or unsubstituted cyclopentadienyl or a bicyclic or polycyclic derivative of cyclopentadienyl, which optionally carries further substituents and / or one or more heteroatoms from Groups 13 to 16 of the Periodic Table of the Elements (IUPAC); or

[0075] (b) acyclic η composed of atoms from Groups 13 to 16 of the Periodic Table of Elements 1 - to η 4 - or η 6 - ligands, wherein the open-chain ligands may be fused to one or two, preferably two, aromatic or non-aromatic rings and / or carry further substituents; or

[0076] (c) cyclic η1- to η4- or η6-monodentate, bidentate or polydentate ligands consisting of unsubstituted or substituted monocyclic, bicyclic or polycyclic ring systems selected from aromatic or non-aromatic or partially saturated ring systems, such ring systems optionally containing one or more heteroatoms selected from Groups 15 and 16 of the Periodic Table of the Elements.

[0077] Preferably, the organometallic compound (C) has at least one organic ligand (L) belonging to the above-mentioned group (a). Such organometallic compounds are known as metallocenes.

[0078] More preferably, at least one organic ligand (L), preferably two organic ligands (L), are selected from the group consisting of cyclopentadienyl, indenyl, tetrahydroindenyl, fluorenyl, which may independently be substituted or unsubstituted.

[0079] Furthermore, in the case where the organic ligand (L) is substituted, it is preferred that at least one organic ligand (L), preferably two organic ligands (L), comprise one or more organic ligands independently selected from C1 to C 20 a substituent of a hydrocarbyl or silyl group, which optionally contains one or more heteroatoms selected from Groups 14 to 16 and / or is optionally substituted by a halogen atom,

[0080] Whenever used in this application, the term "C1 to C 20 "Hydrocarbon" includes C1 to C 20 Alkyl, C2 to C 20 Alkenyl, C2 to C 20 Alkynyl, C3 to C 20 Cycloalkyl, C3 to C 20 Cycloalkenyl, C6 to C 20 Aryl, C7 to C 20 Alkyl aryl or C7 to C 20 Arylalkyl or mixtures of these groups, for example cycloalkyl substituted by alkyl.

[0081] Furthermore, two substituents attached to adjacent C atoms of a ring of the ligand (L), which may be identical or different, may also together form a further monocyclic or polycyclic ring fused to this ring.

[0082] Preferred hydrocarbyl groups are independently selected from linear or branched C1 to C10 alkyl groups, optionally interrupted by one or more Group 14 to 16 heteroatoms, such as O, N or S, and substituted or unsubstituted C6 to C 20 Aryl.

[0083] Straight or branched C1 to C 10 Alkyl, optionally interrupted by one or more heteroatoms from Groups 14 to 16, more preferably selected from methyl, ethyl, propyl, isopropyl, tert-butyl, isobutyl, C 5-6 Cycloalkyl, OR, SR, where R is C1 to C 10 alkyl.

[0084] C6 to C 20 Aryl is more preferably phenyl, which is optionally substituted by 1 or 2 C1 to C10 alkyl groups as defined above.

[0085] In the present invention, "σ-ligand" refers to a group that bonds to the transition metal (M) through a σ bond.

[0086] Furthermore, the ligand "X" is preferably independently selected from hydrogen, halogen, C1 to C 20 Alkyl, C1 to C 20 Alkoxy, C2 to C 20 Alkenyl, C2 to C 20 Alkynyl, C3 to C 12Cycloalkyl, C6 to C 20 Aryl, C6 to C 20 Aryloxy, C7 to C 20 Arylalkyl, C7 to C 20 The group consisting of aralkenyl, -SR", -PR"3, -SiR"3, -OSiR"3 and -NR"2, wherein each R" is independently hydrogen, C1 to C 20 Alkyl, C2 to C 20 Alkenyl, C2 to C 20 Alkynyl, C3 to C 12 Cycloalkyl or C6 to C 20 Aryl.

[0087] More preferably, the "X" ligand is selected from halogen, C1 to C6 alkyl, C5 to C6 cycloalkyl, C1 to C6 alkoxy, phenyl and benzyl.

[0088] The bridging group "R" can be a divalent bridge, preferably selected from -R'2C-, -R'2C-CR'2-, -R'2Si-, -R'2Si-SiR'2- and -R'2Ge-, wherein each R' is independently a hydrogen atom, a C1 to C 20 Alkyl, C2 to C 10 Cycloalkyl, tri(C1-C 20 Alkyl)silyl, C6-C 20 Aryl, C7-C 20 Arylalkyl and C7-C 20 Alkylaryl.

[0089] More preferably, the bridging group "R" is a divalent bridge selected from -R'2C-, -R'2Si-, wherein each R' is independently a hydrogen atom, a C1 to C 20 Alkyl, C2 to C 10 Cycloalkyl, C6-C 20 Aryl, C7-C 20 Arylalkyl and C7-C 20 Alkylaryl.

[0090] Another subgroup of organometallic compounds (C) of formula (I) are known as non-metallocenes, wherein the transition metal (M), preferably a Group 4 to 6 transition metal, suitably Ti, Zr or Hf, has coordinating ligands other than cyclopentadienyl ligands.

[0091] As used herein, the term "non-metallocene" refers to a compound that does not carry a cyclopentadienyl ligand or a fused derivative thereof, but carries one or more non-cyclopentadienyl η- or σ-monodentate, bidentate or multidentate ligands. Such ligands can, for example, be selected from groups (b) and (c) as defined above, and are described, for example, in WO 01 / 70395, WO 97 / 10248, WO 99 / 41290 and WO 99 / 10353 and VC Gibson et al. in Angew. Chem. Int. Ed., Engl., vol 38, 1999, pp 428-447, the disclosures of which are incorporated herein by reference.

[0092] However, the organometallic compound (C) according to the present invention is preferably a metallocene as defined above.

[0093] Many patents describe metallocenes. Here are just a few examples: 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 WO 00 / 148034, EP 423 101, EP 537 130, WO 2002 / 02576, WO 2005 / 105863, WO 2006097497, WO 2007 / 116034, WO 2007 / 107448, WO 2009 / 027075, WO 2009 / 054832, WO 2012 / 001052 and EP 2532687, the disclosure of which is incorporated herein by reference. In addition, metallocenes are extensively described in academic and scientific articles.

[0094] In a preferred embodiment, the organometallic compound (C) has the following formula (Ia):

[0095] (L)2R n MX2(Ia)

[0096] in

[0097] "M" is Zr or Hf;

[0098] Each "X" is a sigma ligand;

[0099] each "L" is optionally substituted cyclopentadienyl, indenyl, or tetrahydroindenyl;

[0100] "R" is a SiMe2 bridging group connecting the organic ligand (L);

[0101] "n" is 0 or 1, preferably 1;

[0102] The metallocene catalyst complexes of the present invention are preferably asymmetric. Asymmetric simply means that the two ligands forming the metallocene are different, that is, each ligand carries a chemically different set of substituents.

[0103] Metallocene catalyst complex of the present invention is normally the chirality of anti-configuration, the bridging bis-indenyl C1-symmetric metallocene of racemization.Although this complex is C1-symmetric formally, because they keep C2-symmetry near metal center, rather than in the ligand periphery, so complex ideally keeps false C2-symmetry.According to its chemical property, can form trans and cis enantiomer pair (in the case of C1-symmetrical complex) in complex building-up process.For the present invention, racemization-trans refers to that two indenyl ligands are towards opposite directions with respect to cyclopentadienyl-metal-cyclopentadienyl plane, and racemization-cis refers to that two indenyl ligands are towards same direction with respect to cyclopentadienyl-metal-cyclopentadienyl plane, as shown below.

[0104]

[0105] Formula (I) and any subformulae are intended to encompass both cis and trans configurations.Preferred metallocene catalyst complexes are in the trans configuration.

[0106] The metallocene catalyst complex of the present invention is usually used in the form of racemic-trans isomers. Therefore, ideally, at least 95% mol, for example at least 98% mol, particularly at least 99% mol of the metallocene catalyst complex is in the form of racemic-trans isomers.

[0107] More preferably, the single site catalyst has formula (II):

[0108]

[0109] Mt is Hf or Zr;

[0110] Each X is a σ ligand;

[0111] Each R 1 are independently the same or may be different and are CH2-R 7 Group, where R 7 H or linear or branched C 1-6 Alkyl, C 3-8 Cycloalkyl, C 6-10 Aryl,

[0112] Each R 2 are independently -CH=--CY=, -CH2-, -CHY- or -CY2- groups, wherein Y is C 1-10 hydrocarbon group, and n is 2-6,

[0113] Each R 3 and R 4 are independently the same or may be different and are hydrogen, a linear or branched C1-C6 alkyl group, an OY group or a C 7-20 Arylalkyl, C 7-20 Alkyl aryl or C 6-20 Aryl, wherein each phenyl group has at least one R 3 and at least one R 4 is not hydrogen, and optionally two adjacent R 3 or R 4 The groups may be part of a ring including the phenyl carbon atom to which they are bonded,

[0114] R 5 is a straight or branched C1-C6 alkyl group, C 7-20 Arylalkyl, C 7-20 Alkyl aryl or C6-C 20 Aryl,

[0115] R 6 C(R 8 )3 groups, wherein R 8 is a linear or branched C1-C6 alkyl group, and

[0116] Each R is independently C1-C 20 Hydrocarbon group.

[0117] It is preferred if Mt is Zr.

[0118] Preferably, each X is independently a hydrogen atom, a halogen atom, a C 1-6 Alkoxy or R' group, where R' is C 1-6 alkyl, phenyl or benzyl. Most preferably, X is chlorine, benzyl or methyl. Preferably, the two X groups are the same. The most preferred selections are two chlorides, two methyls or two benzyls, especially two chlorides.

[0119] Each R is independently C1-C 20 Hydrocarbon, C6-C 20 Aryl, C7-C 20 Arylalkyl or C7-C 20 Alkylaryl. Term C 1-20 Hydrocarbyl groups thus include C 1-20 Alkyl, C 2-20 Alkenyl, C 2-20 Alkynyl, C 3-20 Cycloalkyl, C 3-20 Cycloalkenyl, C 6-20 Aryl, C 7-20 Alkyl aryl or C 7-20Unless otherwise specified, preferred C 1-20 The hydrocarbon group is C 1-20 Alkyl, C 4-20 Cycloalkyl, C 5-20 Cycloalkyl-alkyl, C 7-20 Alkyl aryl, C 7-20 Arylalkyl or C 6-20 Aryl.

[0120] Preferably, the two R groups are the same. Preferably, R is C1-C 10 Hydrocarbon or C6-C 10 Aryl, such as methyl, ethyl, propyl, isopropyl, tert-butyl, isobutyl, C 5-6 cycloalkyl, cyclohexylmethyl, phenyl or benzyl, more preferably, both R are C1-C6 alkyl, C 3-8 Cycloalkyl or C6 aryl, such as C1-C4 alkyl, C 5-6 Cycloalkyl or C6 aryl, most preferably, both R are methyl, or one is methyl and the other is cyclohexyl. Most preferably, the bridge is -Si(CH3)2-.

[0121] Each R 1 are independently the same or may be different and are CH2-R 7 Group, where R 7 H or linear or branched C 1-6 Alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl, or C 3-8 Cycloalkyl (e.g. cyclohexyl), C 6-10 Aryl (preferably phenyl)

[0122] Preferably, the two R 1 Same, and CH2-R 7 Group, where R 7 is H or a linear or branched C1-C4 alkyl group, more preferably, two R 1 Same, and CH2-R 7 Group, where R 7 is H or a linear or branched C1-C3 alkyl group. Most preferably, the two R 1 All are methyl.

[0123] Each R 2 are independently -CH=--CY=, -CH2-, -CHY- or -CY2- groups, wherein Y is C 1-10 Hydrocarbyl, preferably C 1-4 A hydrocarbon group, and n is 2-6, preferably 3-4.

[0124] Each substituent R3 and R4 are independently the same or may be different and are hydrogen, linear or branched C1-C6 alkyl, OY group or C7-20 arylalkyl, C7-20 alkylaryl or C6-20 aryl, preferably hydrogen, linear or branched C1-C6 alkyl, or C6-20 aryl, and optionally two adjacent R 3 or R 4 The groups may be part of a ring including the phenyl carbon atom to which they are bonded. More preferably, R 3 and R 4 is hydrogen or a linear or branched C1-C4 alkyl group or an OY-group, wherein Y is C 1-4 Even more preferably, each R 3 and R 4 are independently hydrogen, methyl, ethyl, isopropyl, tert-butyl or methoxy, especially hydrogen, methyl or tert-butyl, wherein each phenyl group has at least one R 3 and at least one R 4 Not hydrogen.

[0125] Therefore, it is preferred that there be one or two R 3 is not hydrogen, more preferably R on the two phenyl groups 3 The same, such as two phenyl groups are 3',5'-dimethyl or 4'-tert-butyl.

[0126] For the indenyl moiety, one or two R 4 Not hydrogen, more preferably two R 4 Not hydrogen, most preferably these two R 4 The same, such as 3',5'-dimethyl or 3',5'-di-tert-butyl.

[0127] R 5 is a linear or branched C1-C6 alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl, C 7-20 Arylalkyl, C 7-20 Alkyl aryl or C6-C 20 Aryl.

[0128] R 5 Preferably a linear or branched C1-C6 alkyl group or a C 6-20 Aryl, more preferably linear C1-C4 alkyl, even more preferably C1-C2 alkyl, most preferably methyl.

[0129] R 6 C(R 8 )3 groups, wherein R 8 is a straight or branched C1-C6 alkyl group. 8 Same or different, and R 8is a linear or branched alkyl group, more preferably, R 8 are the same and are C1-C2 alkyl. Most preferably, all R 8 All are methyl.

[0130] In another preferred embodiment, the organometallic compound (C) has the following formula (III):

[0131]

[0132] in

[0133] Mt is Zr or Hf, preferably Zr;

[0134] Each R 3 and R 4 are independently the same or may be different and are hydrogen or a linear or branched C1-C6 alkyl group, wherein at least one R 3 and at least one R 4 Not hydrogen.

[0135] Specific metallocene catalyst complexes include:

[0136] rac-trans-dimethylsilanediyl[2-methyl-4,8-bis-(4'-tert-butylphenyl)-1,5,6,7-tetrahydro-s-inden-yl][2-methyl-4-(3',5'-dimethylphenyl)-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride (MC-1);

[0137] rac-trans-dimethylsilanediyl[2-methyl-4,8-bis-(3',5'-dimethylphenyl)-1,5,6,7-tetrahydro-s-indan-1-yl][2-methyl-4-(3',5'-dimethylphenyl)-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride (MC-2); and

[0138] Racemic-trans-dimethylsilanediyl[2-methyl-4,8-bis-(3',5'-dimethylphenyl)-1,5,6,7-tetrahydro-s-indan-1-yl][2-methyl-4-(3',5'-di-tert-butylphenyl)-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride (MC-3); or its corresponding dimethyl zirconium analog.

[0139]

[0140] Throughout the above disclosure, where a narrower definition of a substituent is set forth, that narrower definition is deemed disclosed along with all other broader and narrower definitions of substituents in this application.

[0141] synthesis

[0142] The ligands required to form the single-site catalysts of the present invention can be synthesized by any method, and a skilled organic chemist can devise various synthetic schemes to produce the necessary ligand materials. For example, WO2007 / 116034 discloses the necessary chemical processes. Synthetic schemes can also generally be found in WO2002 / 02576, WO2011 / 135004, WO2012 / 084961, WO2012 / 001052, WO2011 / 076780, and WO2015 / 158790.

[0143] In order to form an active single-site catalytic species, it is generally necessary to use a cocatalyst 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 metallocene catalyst complex defined above.

[0144] The aluminoxane cocatalyst may be one of formula (X):

[0145]

[0146] wherein n is generally 6 to 20, and R has the following meanings.

[0147] Aluminoxanes are formed by partial hydrolysis of organoaluminum compounds, such as those of the formula AlR3, AlR2Y, and Al2R3Y3, where R can be, for example, C1-C 10 Alkyl, preferably C1-C5 alkyl, or C 3-10 Cycloalkyl, C7-C 12 Arylalkyl or alkylaryl and / or phenyl or naphthyl, wherein Y can be hydrogen, halogen, preferably chlorine or bromine, or C1-C10 alkoxy, preferably methoxy or ethoxy. The resulting oxygen-containing aluminoxane is usually not a pure compound, but a mixture of oligomers of formula (X).

[0148] The preferred aluminoxane is methylaluminoxane (MAO).Since the aluminoxanes used as cocatalysts according to the invention are not pure compounds due to the way they are prepared, the molar concentrations of the aluminoxane solutions hereinafter are based on their aluminum content.

[0149] According to the present invention, a boron-containing cocatalyst may also be used instead of the aluminoxane cocatalyst, or the aluminoxane cocatalyst may be used in combination with the boron-containing cocatalyst.

[0150] It will be appreciated by those skilled in the art that when a boron cocatalyst is used, the complex is typically pre-alkylated by reaction with an alkyl aluminum compound, such as TIBA. This process is well known and any suitable aluminum alkyl may be used, such as Al(C 1-6-alkyl) 3. Preferred alkylaluminum compounds are triethylaluminum, triisobutylaluminum, triisohexylaluminum, tri-n-octylaluminum and triisooctylaluminum.

[0151] Alternatively, when a borate cocatalyst is used, the metallocene catalyst complex is in its alkylated form, ie, for example, a dimethyl or dibenzyl metallocene catalyst complex may be used.

[0152] Boron-based cocatalysts of interest include those of formula (Z)

[0153] BY3(Z)

[0154] wherein Y is the same or different and is a hydrogen atom, an alkyl group having 1 to about 20 carbon atoms, an aryl group having 6 to about 15 carbon atoms, an alkylaryl group, an arylalkyl group, a haloalkyl group, or a haloaryl group, each having 1 to 10 carbon atoms in the alkyl group and 6 to 20 carbon atoms in the aryl group, or fluorine, chlorine, bromine, or iodine. Preferred examples of Y are methyl, propyl, isopropyl, isobutyl, or trifluoromethyl, unsaturated groups such as aryl or haloaryl groups such as phenyl, tolyl, benzyl, p-fluorophenyl, 3,5-difluorophenyl, pentachlorophenyl, pentafluorophenyl, 3,4,5-trifluorophenyl, and 3,5-bis(trifluoromethyl)phenyl.

[0155] Preferred options are trifluoroborane, triphenylborane, tri(4-fluorophenyl)borane, tri(3,5-difluorophenyl)borane, tri(4-fluoromethylphenyl)borane, tri(2,4,6-trifluorophenyl)borane, tri(pentafluorophenyl)borane, tri(tolyl)borane, tri(3,5-dimethylphenyl)borane, tri(3,5-difluorophenyl)borane and / or tri(3,4,5-trifluorophenyl)borane.

[0156] Tris(pentafluorophenyl)borane is particularly preferred.

[0157] However, preference is given to using borates, i.e. compounds containing borate ions. Such ionic promoters preferably contain non-coordinating anions, such as tetrakis(pentafluorophenyl)borate and tetraphenylborate. Suitable counterions are protonated amines or aniline derivatives, such as methylammonium, aniline, dimethylammonium, diethylammonium, N-methylaniline, diphenylammonium, N,N-dimethylaniline, trimethylammonium, triethylammonium, tri-n-butylammonium, methyldiphenylammonium, pyridine, p-bromo-N,N-dimethylaniline or p-nitro-N,N-dimethylaniline.

[0158] Preferred ionic compounds that can be used according to the present invention include: triethylammonium tetra(phenyl)borate,

[0159] Tributylammonium tetra(phenyl)borate,

[0160] trimethylammonium tetra(tolyl)borate,

[0161] Tributylammonium tetra(tolyl)borate,

[0162] tributylammonium tetrakis(pentafluorophenyl)borate, tripropylammonium tetrakis(dimethylphenyl)borate, tributylammonium tetrakis(trifluoromethylphenyl)borate,

[0163] Tributylammonium tetrakis(4-fluorophenyl)borate,

[0164] N,N-dimethylcyclohexyltetrakis(pentafluorophenyl)ammonium borate,

[0165] N,N-dimethylbenzyltetrakis(pentafluorophenyl)ammonium borate,

[0166] N,N-dimethylphenyltetra(phenyl)ammonium borate,

[0167] N,N-diethylphenyltetra(phenyl)ammonium borate,

[0168] N,N-dimethylphenyltetrakis(pentafluorophenyl)ammonium borate,

[0169] N,N-di(propyl)tetrakis(pentafluorophenyl)ammonium borate, di(cyclohexyl)tetrakis(pentafluorophenyl)ammonium borate, triphenylphosphonium tetrakis(phenyl)borate,

[0170] triethylphosphonium tetra(phenyl)borate,

[0171] Diphenylphosphonium tetrakis(phenyl)borate, tri(methylphenyl)phosphonium tetrakis(phenyl)borate, tri(dimethylphenyl)phosphonium tetrakis(phenyl)borate, triphenylcarbonium tetrakis(pentafluorophenyl)borate,

[0172] Or tetrakis(pentafluorophenyl)ferric borate.

[0173] Preferably triphenylcarbonium tetrakis(pentafluorophenyl)borate,

[0174] N,N-dimethylcyclohexyltetrakis(pentafluorophenyl)ammonium borate, or

[0175] N,N-dimethylbenzyltetrakis(pentafluorophenyl)ammonium borate.

[0176] Surprisingly, it has been found that certain boron cocatalysts are particularly preferred. Thus, preferred borates for use in the present invention include trityl ions. Thus, N,N-dimethyltetrapentafluorophenylammonium borate and Ph3CB(PhF5)4 and their analogs are particularly preferred.

[0177] According to the present invention, preferred cocatalysts are alumoxanes, more preferably methylalumoxane, combinations of alumoxanes with alkylaluminum, boron or borate cocatalysts and combinations of alumoxanes with boron-based cocatalysts.

[0178] According to the most preferred embodiment of the present invention, the preferred cocatalyst is an aluminoxane, most preferably methylaluminoxane.

[0179] Suitable amounts of cocatalyst are known to those skilled in the art.The molar ratio of boron to metal ion of the metallocene may be from 0.5:1 to 10:1 mol / mol, preferably from 1:1 to 10:1, in particular from 1:1 to 5:1 mol / mol.

[0180] The molar ratio of Al in the aluminoxane to the metal ion of the metallocene may be 1:1 to 2000:1 mol / mol, preferably 10:1 to 1000:1, and especially 50:1 to 500:1 mol / mol.

[0181] Catalyst manufacturing

[0182] 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 zirconium oxide or a mixed oxide, such as silica-alumina, in particular silica, alumina or silica-alumina. Silica supports are preferably used. Those skilled in the art are aware of the procedures required for supporting such catalysts.

[0183] Particularly preferably, the support is a porous material so that the complex can be loaded into the pores of the support, for example using methods similar to those described in WO 94 / 14856, WO 95 / 12622, and WO 2006 / 097497. The particle size is not critical but is preferably in the range of 5 to 200 μm, more preferably in the range of 20 to 80 μm. The use of such supports is conventional in the art.

[0184] In an alternative embodiment, no support is used at all. Such catalysts can be prepared in solution, for example in an aromatic solvent such as toluene, by contacting the metallocene (as a solid or in solution) with a cocatalyst such as methylaluminoxane or borane or a borate predissolved in an aromatic solvent, or by sequentially adding the dissolved catalyst components to the polymerization medium.

[0185] In one embodiment, no external support is used, but the catalyst is still present in solid particulate form. Thus, there is no need to employ an external support material, such as an inert organic or inorganic support, such as the silica described above.

[0186] In order to provide the catalyst of the present invention in solid form without the use of an external support, a liquid / liquid emulsion system is preferably used. The method comprises forming a dispersion of catalyst components (i) and (ii) in a solvent and solidifying the dispersed droplets to form solid particles.

[0187] Specifically, the method includes preparing a solution of one or more catalyst components; dispersing the solution in a solvent to form an emulsion, wherein the one or more catalyst components are present in droplets of a dispersed phase; immobilizing the catalyst components in the dispersed droplets in the absence of an external particulate porous support to form solid particles comprising the catalyst, and optionally recovering the particles.

[0188] This method can produce active catalyst particles with improved morphology, such as a predetermined spherical shape, surface properties, and particle size, without the use of any added external porous support material, such as an inorganic oxide, such as silica. The term "preparing a solution of one or more catalyst components" means that the catalyst-forming compounds can be mixed in one solution and then dispersed into an immiscible solvent, or at least two separate catalyst solutions can be prepared for each portion of the catalyst-forming compounds and then dispersed sequentially into the solvent. A complete disclosure of the necessary procedures can be found in WO 03 / 051934.

[0189] As mentioned above, the key to the present invention is not the specific nature of the single-site catalyst used, so a wide range of choices can be made, however, it is required that the second prepolymerization process can be carried out in the presence of an alkyl aluminum compound. The key to the present invention is how to carry out the conversion process.

[0190] Polypropylene

[0191] The process of the present invention produces a polypropylene polymer. The polypropylene polymer may be a polypropylene homopolymer or a polypropylene copolymer.

[0192] Depending on the use and amount of hydrogen as an Mw regulator, the Mw (weight average molecular weight) values ​​of the propylene homopolymers produced by the process of the present invention can be in the range of 40 kg / mol to 2000 kg / mol, preferably in the range of 50 kg / mol to 1500 kg / mol. The catalyst of the present invention is capable of forming polypropylene homopolymers with a high melting point. In a preferred embodiment, the propylene homopolymers formed by the process of the present invention have a melting point greater than 149.0°C, preferably greater than 149.5°C, and in particular greater than 150.0°C.

[0193] The polypropylene copolymer prepared by the method of the present invention is generally a copolymer of propylene with ethylene or with a C4-C10 comonomer, especially with a C6 comonomer.

[0194] In a preferred embodiment, the polypropylene is a polypropylene homopolymer.

[0195] method

[0196] The method according to the present invention is a kind of " flying " conversion, and wherein the change from one type of production polymer (the first polymer product herein) to another kind (the second polymer product) is continuous, that is to say without shutting down the reactor.When converting from the first catalyst to the second catalyst, the feeding of the first catalyst stops.The second catalyst is subsequently introduced.In order to produce the second polymer product, it should be understood that the reactor conditions must be adjusted relative to the conditions used for producing the first polymer product.The change of conditions can be carried out before or after introducing the second catalyst.Or, some conditions may change before introducing the second catalyst, and other conditions may change after introducing the second catalyst.

[0197] The conversion process of the present invention is a multi-stage polymerization process, i.e., a process involving two or more stages (reactors) connected in series. A multi-stage process in the context of the present invention is defined as a polymerization process in which a polymer comprising two or more fractions is produced by producing each or at least two polymer fractions in a separate reaction stage, typically employing different reaction conditions in each stage, including the presence of a polymerization catalyst from the reaction product of the previous stage. The polymerization reaction employed in each stage may comprise a conventional propylene homopolymerization or copolymerization reaction, such as gas phase, slurry phase, or liquid phase polymerization, using conventional reactors, such as loop reactors, gas phase reactors, batch reactors, etc. (see, for example, WO 97 / 44371 and WO 96 / 18662).

[0198] Switching from producing one polymer grade to another typically requires a transition period, allowing the polymerization reactor to switch to the new resin specification. This requires time to adjust process conditions, such as reaction temperature, reactants, and reactant concentration ratios, to form the desired new polymer. During the transition from a first polymerization reaction designed to produce a first resin product meeting a first specification to a second polymerization reaction designed to produce a second target resin product meeting a second specification, some "off-spec" polymer may be produced while the transition occurs.

[0199] Unless the changeover is properly implemented, this off-spec product may become viscous under the conditions (including temperature) during the changeover and may cause lumps or sheets (on the reactor walls or dome) and product discharge problems. The formation of sticky polymer may force the reactor to be shut down for cleaning. The method of the present invention minimizes this risk.

[0200] Obviously, the longer the changeover time, the more "off-spec" polymer is likely to be produced, and there is a commercial incentive to make the changeover from the first polymer product to the second polymer product as cleanly and quickly as possible.

[0201] The specific first and second polymerization conditions depend on various factors, such as catalyst activity, the type and amount of optional comonomers, the type of polymer to be produced, and the production equipment. Therefore, the specific conditions during the transition between Ziegler-Natta and single-site catalysts must be determined for each specific product in a specific equipment. This is within the capabilities of those skilled in the art.

[0202] As previously mentioned, the process involves a first reactor and a second reactor, which may be considered as a first and a second polymerisation stage, respectively.

[0203] Preferably, the multi-stage process is a two-stage polymerisation process, optionally and preferably preceded by a prepolymerisation step.

[0204] The first polymerization stage produces a propylene homopolymer or propylene copolymer (first polymer product), typically a propylene homopolymer, which is subsequently fed to the second polymerization stage. The second polymerization stage may produce a further propylene homopolymer or propylene copolymer (second polymer product), preferably a propylene homopolymer.

[0205] The first polymerisation stage is preferably a slurry polymerisation step, and thus the first reactor is preferably a slurry reactor, more preferably a loop reactor.

[0206] Slurry polymerization is typically carried out in an inert diluent, typically a hydrocarbon diluent such as methane, ethane, propane, n-butane, isobutane, pentane, hexane, heptane, octane, or a mixture thereof. Preferably, the diluent is a low-boiling hydrocarbon having 1 to 4 carbon atoms or a mixture of such hydrocarbons. A particularly preferred diluent is propane, which may contain small amounts of methane, ethane, and / or butane.

[0207] The ethylene content in the fluid phase of the slurry can be 1 to 50 mol%, preferably 2 to 20 mol%, and particularly 2 to 10 mol%. The benefit of a high ethylene concentration is that the productivity of the catalyst is increased, but the disadvantage is that more ethylene needs to be recycled compared to a lower concentration.

[0208] The temperature of the first polymerization stage is generally in the range of 50° C. to 110° C. (e.g., 60° C. to 100° C. or 70° C. to 110° C.), and the reactor pressure is generally in the range of 20 bar to 80 bar (e.g., 30 bar to 70 bar). Excessive temperatures should be avoided to prevent partial dissolution of the polymer into the diluent and resulting in reactor fouling.

[0209] Slurry polymerization can be carried out in any known reactor for slurry polymerization. Such reactors include continuous stirred tank reactors and loop reactors. It is particularly preferred to carry out slurry polymerization in a loop reactor. In such a reactor, the slurry is circulated at high speed along a closed pipeline by a circulation pump. Loop reactors are well known in the art, and examples are given, for example, in US-A-4582816, US-A-3405109, US-A-3324093, EP-A-479186 and US-A-5391654. Therefore, it is preferred to carry out the first polymerization stage as slurry polymerization in a loop reactor.

[0210] The slurry can be removed from the reactor continuously or intermittently. A preferred method for intermittent removal is to use settling legs, which allow the slurry to concentrate and then extract a batch of concentrated slurry from the reactor. US-A-3374211, US-A-3242150, and EP-A-1310295 disclose the use of settling legs. EP-A-891990, EP-A-1415999, EP-A-1591460, and WO-A-2007 / 025640 disclose continuous extraction. As disclosed in EP-A-1310295 and EP-A-1591460, continuous extraction is preferably combined with a suitable concentration method. Preferably, the slurry is removed continuously from the first polymerization stage.

[0211] In a slurry reactor, the average residence time of the first polymerization stage is generally in the range of 0.2 hours to 5.0 hours (e.g., 0.3 hours to 2 hours). Preferably, the residence time is 0.2 hours to 1.0 hours, more preferably 0.3 hours to 0.6 hours. As is well known in the art, the average residence time τ can be calculated by the following formula 1:

[0212] Formula 1: Residence time

[0213]

[0214] Where V R is the volume of the reaction space (in a loop reactor, the volume of the reactor, in a fluidized bed reactor, the volume of the fluidized bed), and Q o is the volumetric flow rate of the product stream (comprising polymer product and fluid reaction mixture).

[0215] The diluents used are generally aliphatic hydrocarbons having a boiling point in the range from -70° C. to +100° C. In such reactors, the polymerization can, if desired, be carried out under supercritical conditions.

[0216] The production rate is appropriately controlled by the catalyst feed rate. The production rate can also be influenced by appropriately selecting the monomer concentration. The desired monomer concentration can then be achieved by appropriately adjusting the ethylene feed rate.

[0217] In the second polymerization stage, propylene is optionally polymerized with at least one other α-olefin comonomer in the presence of a catalyst and the propylene polymer produced in the first polymerization stage. It will therefore be understood that the second polymerization stage produces a propylene polymer that is combined with the propylene polymer from the first polymerization stage. Preferred comonomers have been discussed above.

[0218] The second polymerization stage is preferably a gas phase polymerization step, i.e. carried out in a gas phase reactor. Therefore, the second reactor is preferably a gas phase reactor. Any suitable gas phase reactor known in the art can be used, such as a fluidized bed gas phase reactor.

[0219] For gas phase reactors, the reaction temperature used is generally 50° C. to 130° C. (e.g., 60° C. to 115° C., or 60° C. to 100° C.), the reactor pressure is generally 5 bar to 60 bar, preferably 10 bar to 40 bar, and the residence time is generally 1 hour to 8 hours. The gas used is generally a non-reactive gas, such as nitrogen or a low boiling hydrocarbon, such as propane and a monomer (e.g., ethylene).

[0220] Hydrogen can be introduced into any reactor to control the molecular weight of the polymer, as is well known and conventional in the art. In one embodiment, the molar ratio of hydrogen to total olefin monomer in the recycle gas stream is in the range of 0.001 or 0.002 or 0.003 to 0.014 or 0.016 or 0.018 or 0.024, where the desired range may include any combination of any molar ratio upper limit and any molar ratio lower limit described herein. In other words, the amount of hydrogen in the reactor at any time may be in the range of 1000 ppm to 20,000 ppm in one embodiment; in another embodiment, in the range of 2000 ppm to 10,000 ppm; in yet another embodiment, in the range of 3000 ppm to 8,000 ppm; and in yet another embodiment, in the range of from 4000 ppm to 7000 ppm, where the desired range may include any hydrogen upper limit and any hydrogen lower limit described herein.

[0221] The share between the first and second polymerization stages (ie the share between slurry polymerization and gas phase polymerization) is generally from 30:70 to 70:30, more preferably from 35:65 to 65:35, most preferably from 40:60 to 60:40.

[0222] Therefore, a preferred embodiment of the present invention is one in which the first reactor is a slurry reactor, such as a loop reactor, and the second reactor is a gas phase reactor, such as a fluidized bed gas phase reactor. A preferred "loop gas phase" process is, for example, the one developed by Borealis A / S, Denmark (called Technology) is described in the patent literature, for example EP 0887 379, WO 92 / 12182 or WO 2005 / 002744.

[0223] The polymerization steps described above are preferably preceded by a prepolymerization step. The purpose of prepolymerization is to polymerize a small amount of polymer onto the catalyst at low temperatures and / or low monomer concentrations. Prepolymerization can improve the performance of the catalyst in the slurry and / or alter the properties of the final polymer. The prepolymerization step is performed in the slurry.

[0224] Therefore, the prepolymerization step can be carried out in a loop reactor. The prepolymerization is preferably carried out in an inert diluent, typically a hydrocarbon diluent such as methane, ethane, propane, n-butane, isobutane, pentane, hexane, heptane, octane, etc., or a mixture thereof. Preferably, the diluent is a low-boiling hydrocarbon having 1 to 4 carbon atoms or a mixture of such hydrocarbons.

[0225] The temperature in the prepolymerization step is generally from 0 to 90°C, preferably from 20 to 80°C, more preferably from 55 to 75°C.

[0226] The pressure is not critical and is generally from 1 to 150 bar, preferably from 40 to 80 bar.

[0227] The amount of monomer is typically 0.1 to 1000 grams of monomer per gram of solid catalyst component polymerized in the prepolymerization step. Those skilled in the art will appreciate that the catalyst particles recovered from a continuous prepolymerization 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 the particle in the prepolymerization reactor. Because some particles spend a relatively long time in the reactor, while some stay a relatively short time, the amount of prepolymer on different particles is also different, and some individual particles may contain an amount of prepolymer that exceeds the above-mentioned limits. However, the average amount of prepolymer on the catalyst is typically within the limits specified above.

[0228] As is well known in the art, the molecular weight of the prepolymer can be controlled by hydrogen. In addition, antistatic additives can be used to prevent the particles from adhering to each other or to the reactor walls, as disclosed in WO-A-96 / 19503 and WO-A-96 / 32420.

[0229] In the process of the present invention, the Ziegler-Natta catalyzed polymerization is preferably started in a manner known in the art by introducing the above-mentioned Ziegler-Natta catalyst into the prepolymerization reactor via a catalyst feed tank, preferably via an oil catalyst feed system or via a wax catalyst feed system. In addition, propylene and hydrogen, as well as optional cocatalysts and external donors (all or part) are added to the prepolymerization reactor.

[0230] The prepolymerized catalyst, additional propylene, hydrogen, optionally additional cocatalyst, and external donor are then introduced into a first reactor (typically a slurry phase reactor), after which the polymer product is recovered from the slurry phase reactor and introduced into a second reactor (typically a gas phase reactor), optionally additional propylene and optional comonomer are fed into the second reactor, optionally additional hydrogen is fed into the second reactor to control the hydrogen to propylene ratio to provide the desired polymer product molecular weight, and the polymer product is recovered from the second reactor.

[0231] The reaction conditions in the slurry phase and gas phase reactors (such as temperature, pressure, amount of propylene and optional comonomers, amount of hydrogen) are selected according to the desired product parameters of the first product. Generally speaking, such processes are conventional.

[0232] When a prepolymerization step is present, it is preferred that the entirety of the Ziegler-Natta catalyst component be introduced into the prepolymerization step. However, when the solid catalyst component and the cocatalyst can be fed separately, only a portion of the cocatalyst may be introduced into the prepolymerization stage, while the remainder is introduced into the subsequent polymerization stage. In this case as well, it is necessary to introduce sufficient separate cocatalyst into the prepolymerization stage in order to obtain a sufficient polymerization reaction therein.

[0233] The process of the present invention is to be understood as a continuous process.

[0234] The "on the fly" conversion process from Ziegler-Natta catalyzed polymerization to single-site catalyzed polymerization according to the present invention is further described below.

[0235] In the Ziegler-Natta catalytic polymerization process, a single-site catalyst such as that described above can be introduced into a catalyst feed tank connected to the prepolymerization reactor. Typically, the catalyst is prepared within about 130 to 400 minutes before the catalyst is introduced into the prepolymerization reactor.

[0236] The reaction conditions in the prepolymerization reactor and the first reactor can be adjusted to reflect the reaction conditions required to produce the second polymer product before the single site catalyst is introduced into the prepolymerization reactor. If a prepolymerization reactor is used, it is considered to be part of the first reactor (thus, for this purpose, the prepolymerization reactor and the slurry reactor are the first reactor).

[0237] Thus, the hydrogen concentration in the prepolymerization and first reactor can be adjusted. The temperature in the prepolymerization and first reactor can be adjusted, among other things. Such adjustments in the prepolymerization and first reactor can occur from about 15 minutes to 100 minutes before the single-site catalyst is introduced into the first reactor. Preferably, the hydrogen feed to the second reactor is adjusted to reflect the amount of hydrogen required to produce the second polymer product prior to the introduction of the single-site catalyst.

[0238] Preferably, any other polymerization conditions (eg, monomer content, temperature) required to achieve a second polymer product are adjusted after the single-site catalyst is introduced into the second reactor.

[0239] When both the prepolymerization reactor and the first reactor need to adjust the conditions, the order of adjustment is not important. The prepolymerization conditions can be adjusted first, the first reactor conditions can be adjusted first, or both can be adjusted simultaneously.

[0240] Typically, the first polymerization is carried out in a first reactor, preferably as a bulk slurry polymerization, for example in a continuous stirred tank reactor (CSTR) or a loop reactor, in liquid propylene, i.e. the liquid phase comprises mainly propylene with small amounts of other reactants and optionally inert components dissolved therein. The first polymerization is carried out in the presence of a Ziegler-Natta catalyst and an external donor and cocatalyst as defined above. The conditions in the first reactor may be as defined above for a slurry reactor.

[0241] At the specified time point, the addition of the Ziegler-Natta catalyst was stopped (step b).

[0242] After this step, and after a period of at least 5 minutes, for example 5 to 60 minutes, preferably 10 to 55 minutes, more preferably 20 to 50 minutes, the feed of the external supplier of Ziegler-Natta catalyst to the first reactor is stopped and the feed of Ziegler-Natta cocatalyst to the first reactor is reduced (step c). Before stopping the feed of Ziegler-Natta catalyst, the feed of cocatalyst is typically reduced to a level of less than 25%, preferably less than 10%, of the feed.

[0243] In one embodiment, the feed of Ziegler-Natta cocatalyst is reduced to 1 to 5 wt-ppm, calculated on the total weight of propylene (C3) feed, ie 1 to 5 g cocatalyst per 1000 kg propylene.

[0244] As a next step (step d) the solids content of the second reactor is reduced from the first operating level to a conversion level in the range of 40% to 80% relative to the first operating level; this step is carried out at least 5 minutes, preferably 15 minutes to 90 minutes, for example 20 to 60 minutes after step c). Alternatively, this step occurs 45 minutes to 2.5 hours, for example 60 minutes to 2.0 hours after stopping the Ziegler-Natta feed. Typically, the solids content is adjusted 1.0 to 2.0 hours after stopping the use of the ZN catalyst, for example 1.5 hours. The solids content of the second reactor is typically reduced by reducing the height of the polymer particle bed (or the level of the polymer particle bed) from the first operating level to the conversion level. Traditionally, the bed height is reduced by increasing the product discharge rate from the reactor to downstream equipment, such as a wash tank. Other conventional techniques for reducing the polymer particle bed height are known in the art.

[0245] The initial solids content or polymer particle bed level is considered to be the normal level measured during steady state operation of the Ziegler-Natta polymerization, i.e., the first operating level. In a preferred embodiment, the solids content or polymer particle bed level is reduced to a conversion level that is 60% to 75% of the first operating level.

[0246] The single site catalyst may be introduced into the first reactor at least 30 minutes, such as 30 minutes to 3.5 hours, preferably 45 minutes to 3.0 hours after stopping the use of the Ziegler Natta catalyst (step b).Step e) occurs after step d) is completed.

[0247] It is also possible to introduce the single site catalyst into the first reactor at least 30 minutes, preferably 30 minutes to 2 hours after step d).

[0248] In one embodiment, the single site catalyst may be introduced into the first reactor at least 30 minutes, such as 30 minutes to 2 hours, preferably 45 minutes to 1.5 hours after stopping the use of the Ziegler Natta catalyst (step b).

[0249] In other words, the single site catalyst may be introduced into the first reactor at least 5 minutes after step d), such as after 5 minutes to preferably 45 minutes to 1.5 hours.

[0250] The second polymerization is a multi-stage process, so the single-site catalyst is eventually transferred to the gas phase reactor. This can occur between 1.0 and 3.0 hours after the start of the single-site catalyst feed.

[0251] As a final step, the solids content of the second reactor is increased to a second operating level, i.e., the normal level measured during steady-state operation of the single-site polymerization. The first and second operating levels are preferably the same. This step f) is preferably performed at least 30 minutes after step e), preferably 1.0 to 6.0 hours after, for example, increasing the bed level 2.0 to 5.0 hours after the start of single-site catalyst feed. Gas-phase polymerization using the single-site catalyst has preferably already begun at this point. This step f) is preferably performed 3.0 to 8.0 hours after step b).

[0252] For the avoidance of doubt, steps a) to f) are performed sequentially.

[0253] Thus, in one embodiment, the present invention provides a method for switching between a Ziegler-Natta catalyst and a single-site catalyst in the production of polypropylene homopolymer or copolymer in a continuous multistage polymerization reaction, the method comprising the following steps in sequence:

[0254] a) polymerizing propylene and optionally a comonomer in a first reactor and then polymerizing propylene and optionally a comonomer in a second reactor in the presence of a Ziegler-Natta catalyst;

[0255] b) stopping feeding the Ziegler-Natta catalyst to the first reactor;

[0256] c) stopping the feed of the external supplier of Ziegler-Natta catalyst to the first reactor and reducing the feed of the Ziegler-Natta cocatalyst to the first reactor, wherein step c) is carried out at least 5 minutes, preferably 5 to 60 minutes after step b);

[0257] d) reducing the solids content of the second reactor from the first operating level to a conversion level in the range of 40% to 80% relative to the first operating level before step d), wherein step d) is performed at least 5 minutes, preferably 20 minutes to 90 minutes, after step c);

[0258] e) introducing a single site catalyst into a first reactor, wherein step e) is performed at least 30 minutes, preferably 30 minutes to 3.0 hours, preferably 30 minutes to 2 hours after step b); and

[0259] f) increasing the solids content of the second reactor to a second operating level, preferably to the same level as before step d), wherein step f) is performed at least 30 minutes, preferably 1.0 hour to 6.0 hours after step e).

[0260] Both the Ziegler-Natta catalyst and the single site catalyst component are introduced into the first reactor. It is understood that once added to the first reactor, the single site catalyst will be fed to the second reactor to carry out a second polymerization in that reactor.

[0261] Throughout the process, the polymer produced in the first reactor is usually continuously fed to the second reactor.

[0262] The precise control of the prepolymerization conditions and reaction parameters is within the capabilities of the skilled artisan.The pressure and temperature of the second reactor are typically maintained substantially constant throughout the process.

[0263] Ideally, the process of the present invention is carried out in the absence of any additives that would deactivate or eliminate the Ziegler-Natta catalyst.

[0264] Determination method

[0265] Unless otherwise defined, the following definitions of terms and assay methods apply to the above general description of the invention as well as to the following examples.

[0266] Melt flow rate (MFR2) (230°C) is measured according to ISO 1133 (230°C, 2.16 kg load).

[0267] Bulk density: The bulk density of the polymer powder was determined according to ASTM D1895-96 Method A.

[0268] Number average molecular weight (M n ), weight average molecular weight (M w ) and molecular weight distribution (MWD) were determined by gel permeation chromatography (GPC) according to the following method:

[0269] Weight-average molecular weight (Mw) and molecular weight distribution (MWD = Mw / Mn, where Mn is the number-average molecular weight and Mw is the weight-average molecular weight) were determined using methods based on ISO 16014-1:2003 and ISO 16014-4:2003. A Waters Alliance GPCV 2000 instrument equipped with a refractive index detector and an online viscometer was used, along with a TosoHaas 3x TSK gel column (GMHXL-HT) and 1,2,4-trichlorobenzene (TCB, stabilized with 200 mg / L 2,6-di-tert-butyl-4-methylphenol) as the solvent at 145°C and a constant flow rate of 1 mL / min. 216.5 μL of sample solution was injected for each analysis. The column set was calibrated using relative calibration using 19 narrow MWD polystyrene (PS) standards ranging from 0.5 kg / mol to 11,500 kg / mol and a set of well-characterized broad polypropylene standards. All samples were prepared by dissolving 5 mg to 10 mg of polymer in 10 mL (160° C.) of stabilized TCB (same as mobile phase) and keeping under continuous shaking for 3 h before sampling in the GPC instrument.

[0270] Particle size (PS) and average particle size (APS) were measured according to ISO 13322-2 using the image analysis method using a Camsizer P4 analyzer.

[0271] The comonomer content is determined in a known manner based on Fourier transform infrared spectroscopy (FTIR) measurements using a Nicolet Magna 550 IR spectrometer and Nicolet Omnic FTIR software calibrated with 13 C-NMR.

[0272] DSC analysis

[0273] Melting temperature (Tm) and crystallization temperature (Tcr) were measured on approximately 5 mg of sample using a Mettler-Toledo 822e differential scanning calorimeter (DSC) in accordance with ISO 11357-3, using a heating / cooling / heating cycle at a scan rate of 10°C / min over the temperature range of +23 to +225°C, under a nitrogen flow rate of 50 ml min⁻¹. The melting temperature during the second heating step was taken as the endothermic peak. The instrument was calibrated using H₂O, lead, tin, and indium according to ISO 11357-1.

[0274] Xylene solubles

[0275] The xylene soluble fraction (XS), as defined and described herein, is determined as follows: 2.0 g of polymer is dissolved in 250 mm p-xylene at 135° C. with stirring. After 30 minutes, the solution is allowed to cool at ambient temperature for 15 minutes and then allowed to stand at 25±0.5° C. for 30 minutes. The solution is filtered with filter paper into two 100 mm flasks. The solution in the first 100 mm container is evaporated in a stream of nitrogen, and the residue is dried under vacuum at 90° C. until a constant weight is reached. The xylene soluble fraction (percentage) can then be determined as follows:

[0276] XS%=(100x m1 X v0) / (m0 x v1),

[0277] where m0 represents the initial polymer amount (g), m1 defines the weight of the residue (g), v0 defines the initial volume (ml), and v1 defines the volume of the analyzed sample (ml). Example

[0278] Two types of catalysts are used in the polymerization reactions illustrated below: metallocene catalysts and Ziegler-Natta catalysts.

[0279] catalyst

[0280] A) Single-site catalyst

[0281] The single-site catalyst used in the polymerization process of all examples is trans-dimethylsilylene [2-methyl-4,8-bis (3,5-dimethylphenyl) -1,5,6,7-tetrahydro-s-indacene-1-yl] [2-methyl-4- (3,5-dimethylphenyl) -5-methoxy-6-tert-butylinden-1-yl] zirconium dichloride, such as MC-2 disclosed in WO2019 / 179959A1. The production method of the supported metallocene catalyst is similar to IE2 in WO2019 / 179959A1.

[0282] B) Ziegler-Natta catalyst

[0283] The production process of the Ziegler-Natta catalyst used in the embodiment is as follows:

[0284] raw material

[0285] TiCl4 (CAS 7550-45-90) was provided by a commercial source.

[0286] 20% toluene solution of butylethylmagnesium (Mg(Bu)(Et)) supplied by Crompton

[0287] 2-Ethylhexanol, supplied by Merck Chemicals

[0288] 3-Butoxy-2-propanol, provided by Sigma-Aldrich

[0289] Bis(2-ethylhexyl)citraconate, supplied by Contract Chemicals

[0290] 1-254, provided by Evonik

[0291] Heptane, provided by Chevron

[0292] Preparation of magnesium complexes

[0293] 3.4 liters of 2-ethylhexanol and 810 milliliters of propylene glycol butyl monoether (4 / 1 molar ratio) were added to a 20-liter reactor. 7.8 liters of a 20% BEM (butylethylmagnesium) toluene solution (supplied by Crompton GmbH) were then slowly added to the well-stirred alcohol mixture. The temperature was maintained at 10°C during the addition. After the addition was complete, the reaction mixture was heated to 60°C and stirred at this temperature for 30 minutes. Finally, after cooling to room temperature, the resulting magnesium alkoxide was transferred to a storage container.

[0294] 21.2 g of the magnesium alkoxide prepared above was mixed with 4.0 ml of bis(2-ethylhexyl)citraconate for 5 minutes. After mixing, the resulting magnesium complex was immediately used to prepare the catalyst component.

[0295] Preparation of catalyst components

[0296] 19.5 ml of titanium tetrachloride was added to a 300 ml reactor equipped with a mechanical stirrer at 25°C and 170 rpm. Over 30 minutes, 26.0 g of the magnesium complex prepared above was added, maintaining the temperature at 25°C. 3.0 ml of Viscoplex 1-254 and 24.0 ml of heptane were added to form an emulsion. Mixing was continued at 25°C for 30 minutes. The reactor temperature was then raised to 90°C over 30 minutes. The reaction mixture was stirred at 90°C for another 30 minutes. Stirring was then stopped, and the reaction mixture was allowed to stand at 90°C for 15 minutes. The solid material was washed sequentially with 100 ml of toluene, 30 ml of TiCl₄, 100 ml of toluene, and twice with 60 ml of heptane. 1 ml of donor (i.e., bis(2-ethylhexyl)citraconate) was added to the first two washes. Washes were performed by stirring at 80°C at 170 rpm for 30 minutes. After stirring was stopped, the reaction mixture was allowed to stand for 20 to 30 minutes before being siphoned.

[0297] Then, the stirring was stopped and the reaction mixture was allowed to stand for 10 minutes. The temperature was lowered to 70°C and then siphoned and purged with N2 for 20 minutes to obtain an air-sensitive powder. The surface area of ​​the catalyst was measured by the BET method and was less than 5 m 2 / g, which is below the detection limit.

[0298] Conversion Program

[0299] These examples were conducted at pilot scale to simulate the catalyst transition from a Ziegler-Natta catalyst to a metallocene catalyst in a GPR bed, with a target GPR bed height of approximately 6 to 12 meters at full scale (60 to 120 cm for pilot scale).

[0300] In IE1 and IE2, a switch from Ziegler-Natta (ZN) to metallocene was performed. The Ziegler-Natta polymerization process performed before the start of the switch was based on the conditions of the reference example shown in Table 1.

[0301] The conversion method is as follows:

[0302] At 0 h, the ZN catalyst feed was stopped, and the TEAL / donor (i.e., dicyclopentyldimethoxysilane (DCPDMS)) feed was maintained. TEAL 150 g / t, i.e., 150 g / 1000 kg, and D-donor (i.e., dicyclopentyldimethoxysilane (DCPDMS)) 20 g / t, i.e., 20 g / 1000 kg. At this time, the addition of 2 wt-ppm of Span 80 was started. (Step b)

[0303] +45 minutes: Stop the donor (i.e., dicyclopentyldimethoxysilane (DCPDMS)) feed, reduce the TEAL feed to 2.5 g / t C3, and control the loop to T of 70°C and GPR of 80°C. (Step c)

[0304] +45 minutes Polymer slurry is still introduced into GPR1. The bed height is reduced from 160 cm to 120 cm (full size 12 m), fluidization, pressure and temperature are kept normal (i.e. 1.5 hours from the start of the switch). 1.5 hours after stopping the ZN catalyst feed, the loop reactor is empty and the target GPR bed level (120 cm) is reached (step d)

[0305] +15 minutes from the start of the metallocene feed (1.75 hours from the start of the switch, the ZN catalyst feed is stopped). During the production rate ramp-up period, the loop is directed to the discharge tank. (Step e)

[0306] · After the addition of the single-site catalyst + 1 hour 45 minutes. When the loop density is 470 kg / m3, the polymer slurry starts to transfer from the loop to the GPR (after the start of the transition + 3.5 hours).

[0307] +2.5 hours after gas phase mass transfer. GPR bed height increased to 160 cm (full size 16 m). Samples were collected at normal frequency. This was 6 hours after the start of the conversion and 4.25 hours after the start of the single-site catalyst. (Step f)

[0308] +3h Batch collection has started. This is 9 hours after the start of the conversion.

[0309] The catalyst change went smoothly and as planned. The polymerization conditions for this example and the properties of the resulting polymer are also shown in Table 1. Figure 1 Displays the annular and GPR production rates as separate lines on the x-axis over time. The darker trend line is the annular production rate, and the lighter trend line is the proportional GPR production rate.

[0310] The ZN catalyst feed was stopped at 12:00 PM, and the metallocene catalyst feed was restarted at 1:45 PM. Before the change, the split was 55 / 45%, and the yield using the ZN catalyst was 36 kg PP / g cat. Twelve hours after the change, the split was 70 / 30%, and the yield using the metallocene catalyst was 13 kg PP / g cat.

[0311] A comparative example of the transition from Ziegler-Natta (ZN) to Ziegler-Natta was also performed. The same procedure as for IE1 and IE2 was followed except that at +1 1 The polymerization conditions of this example and the properties of the resulting polymer are also shown in Table 1.

[0312] Table 1: Comparative Examples and Inventive Examples, Polymerization Conditions

[0313]

[0314]

[0315] The results in Table 1 reflect the polymerization results of the transition from ZN catalyst to metallocene catalyst (ie, single-site catalyst) as described herein. Comparative Examples were used as a comparison, in which no single-site catalyst was introduced.

[0316] The transition from the ZN catalyst to the metallocene catalyst occurred over a period of approximately 13 hours. Figure 1 As can be clearly seen in the figure, after the ZN catalyst feed is stopped, productivity first decreases in the loop reactor and then in the gas phase reactor. Adjusting the bed level in the gas phase reactor 1.5 hours after the ZN catalyst is stopped results in a brief increase in productivity, but productivity then continues to decrease. After 1.75 hours, the loop productivity drops to very low levels, and polymerization continues in the presence of the metallocene catalyst 1.75 hours after the ZN catalyst is stopped.

[0317] The loop productivity increased immediately, but the gas phase productivity continued to decline until 3.5 hours after the ZN catalyst was stopped, as metallocene formation began in the gas phase.The properties of the polymer fraction from each reactor were monitored in situ.

[0318] Gas production continued for approximately 5.5 hours before samples were collected for analysis. By this time, the gas production rate had essentially reached the target level.

[0319] The final polymer characteristics reflect the isolated granular polymer after 9 hours, when the conversion process is complete. This is the polymer that is sequentially transferred from the prepolymerization reactor to the loop reactor and finally to the gas phase reactor. The final polypropylene (PP) polymer is the final isolated product of the multi-stage process and is therefore a combination of the prepolymer, the first polymer, and the second polymer. Any "off-spec" polymer produced during the conversion (not removed in the solids reduction step (d)) is minimal and can be ignored. In the absence of catalyst during the conversion process, polymer is removed, resulting in a limited amount of polymer produced.

Claims

1. A method for switching between a Ziegler-Natta catalyst and a single-site catalyst in the production of a polypropylene homopolymer or copolymer in a continuous multistage polymerization reaction, the method comprising the following steps in sequence: a) polymerizing propylene and optionally a comonomer in a first reactor and then polymerizing propylene and optionally a comonomer in a second reactor in the presence of a Ziegler-Natta catalyst; b) stopping feeding the Ziegler-Natta catalyst to the first reactor; c) stopping the feed of the external supplier of Ziegler-Natta catalyst to the first reactor and reducing the feed of the Ziegler-Natta cocatalyst to the first reactor, wherein step c) is carried out at least 5 minutes, preferably 5 to 60 minutes after step b); d) reducing the solids content of the second reactor from the first operating level to a conversion level in the range of 40% to 80% relative to the first operating level prior to step d); e) introducing a single site catalyst into a first reactor, wherein step e) is performed at least 30 minutes, preferably 30 minutes to 2 hours, after step d); and f) increasing the solids content of the second reactor to a second operating level, preferably to the same level as before step d).

2. The process of claim 1, wherein the conversion is carried out in the absence of any additives that would deactivate or eliminate the Ziegler-Natta catalyst.

3. The process according to claim 1 or 2, wherein the polypropylene homopolymer or copolymer is fed continuously from the first reactor to the second reactor.

4. The process according to any one of claims 1 to 3, wherein the first reactor is a slurry reactor, preferably a slurry loop reactor.

5. The process according to any one of claims 1 to 4, wherein the second reactor is a gas phase reactor, preferably a fluidized bed gas phase reactor.

6. The process according to any one of claims 1 to 5, wherein the Ziegler-Natta catalyst is a solid Ziegler-Natta catalyst selected from the group consisting of MgCl2-supported titanium Ziegler-Natta catalysts and self-supported solid Ziegler-Natta catalysts.

7. The process according to any one of claims 1 to 6, wherein the external donor of the Ziegler-Natta catalyst is selected from ethers, ketones, amines, alcohols, phenols, phosphines, esters and silanes.

8. The process according to any one of claims 1 to 7, wherein the Ziegler-Natta cocatalyst is a trialkylaluminum or alkylaluminum halide compound, wherein the alkyl group preferably contains 1 to 20 carbon atoms, more preferably 1 to 10 carbon atoms.

9. The process according to any one of claims 1 to 8, wherein in step c) the feed of Ziegler-Natta cocatalyst is reduced to less than 25%, preferably less than 10%, of the feed level before stopping the feed of Ziegler-Natta catalyst, more preferably to 1 to 5 wt-ppm, calculated on the total weight of the propylene feed.

10. The process according to any one of claims 1 to 9, wherein the single-site catalyst is a metallocene catalyst, preferably a supported metallocene catalyst.

11. The process according to claim 10, wherein the metallocene catalyst comprises an organometallic compound of formula (Ia) as a catalyst component: (L)2R n MX2(Ia) in "M" is Zr or Hf; Each "X" is a sigma ligand; each "L" is optionally substituted cyclopentadienyl, indenyl, or tetrahydroindenyl; "R" is a SiMe2 bridging group connecting the organic ligand (L); "n" is 0 or 1, preferably 1.

12. The process according to claim 10 or 11, wherein the metallocene catalyst is used in combination with a boron-containing cocatalyst and / or an aluminoxane cocatalyst.

13. The process according to any one of claims 1 to 12, wherein the pressure and temperature of the second reactor are kept substantially constant during the process.

14. The process according to any one of claims 1 to 13, wherein the residence time in the first reactor is from 0.2 h to 5.0 h.

15. The process according to any one of claims 1 to 14, wherein the polypropylene is a propylene homopolymer.

16. The process according to any one of claims 1 to 15, wherein step d) is performed at least 5 minutes, preferably 20 to 90 minutes after step c).

17. The process according to any one of claims 1 to 16, wherein step f) is performed at least 30 minutes, preferably 1.0 hour to 6.0 hours after step e).

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