method

Abstract

The present invention provides a method for transitioning 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, comprising: 1. A process for transitioning 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, comprising: a) polymerizing propylene and optionally a comonomer in the presence of a Ziegler-Natta catalyst in a first reactor and thereafter in a second reactor; b) ceasing the supply of the Ziegler-Natta catalyst into the first reactor; c) ceasing the supply of external donor to the Ziegler-Natta catalyst and reducing the supply of Ziegler-Natta cocatalyst into 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 transition level in the range of 40 to 80% relative to the first operating level prior to step d); e) introducing the single-site catalyst into the first reactor, wherein step e) occurs at least 30 minutes, preferably 30 minutes to 2 hours, after step d); and f) increasing the solids content of said second reactor to a second operating level, preferably to the same level as before step d). The present invention relates to the above method, which comprises the steps of:

Description

[Technical Field]

[0001] The present invention relates to a method for catalyst transition in olefin polymerization, particularly in the operation of an olefin polymerization plant. More particularly, the present invention relates to transitioning between a Ziegler-Natta catalyst and a single-site catalyst in the production of polypropylene in a continuous multi-stage polymerization reaction. The transition is ideally carried out without the use of any catalyst deactivating agent. [Background technology]

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

[0003] One type of reactor suitable for producing propylene homopolymers and copolymers is a loop reactor. The polymer particles exiting the loop reactor can be introduced into one or more subsequent polymerization reactors, such as one or more gas-phase reactors, for further polymerization with other monomers, such as 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 adjusted by the selection of one or more catalyst systems.

[0004] During the production of olefin polymers, such as polypropylene homopolymer and polypropylene copolymer, in commercial reactors, it is often necessary to transition from one type of catalyst system producing a polymer with specific properties and characteristics to another catalyst system producing a polymer with different specifications. Transitions between similar or compatible catalysts are generally easy. However, when the catalysts are of different types and / or are incompatible, for example, it is well known that an active Ziegler-Natta catalyst can "poison" an active single-site catalyst, and the process is typically complicated. For example, changing from a Ziegler-Natta catalyst to a single-site catalyst or vice versa usually requires a long transition period. Moreover, during this transition period, the polyolefins produced undergo continuous changes in properties. If transitioning from one catalyst system to another requires significant changes in reactor conditions, there is a high risk of encountering production problems or producing polymers with extreme properties.

[0005] The transition from a polymerization reaction catalyzed by a first catalyst to a polymerization reaction catalyzed by a second catalyst is typically accomplished by shutting down the polymerization process, emptying and recharging the reactor, 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 during the transition.

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

[0007] European Patent No. EP0604993 discloses a method for restarting a temporarily stopped vapor phase olefin polymerization. The 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 is restarted by feeding an organoaluminum compound to the reaction system without discharging the preformed polymer particles and the subsequent solid catalyst components.

[0008] International Publication No. WO 92 / 14766 describes the use of volatile and non-volatile catalyst killers for metallocene catalysts in high-pressure polymerization processes, which are added downstream of the polymerization zone to suppress the polymerization of recycle monomer with the separated molten polymer. In metallocene / aluminoxane-based catalyst systems, methanol and n-butanol may also be used as catalyst killers.

[0009] US Patent No. 4,460,755 discloses a method for converting a continuous olefin polymerization reaction catalyzed by a Ziegler-type catalyst to a continuous olefin polymerization reaction catalyzed by a chromium-based catalyst without emptying and refilling the polymerization reactor. The procedure includes the steps of stopping the catalyst feed, introducing a hydroxyl-containing silica to react with the catalyst, and finally introducing the chromium-based catalyst, and maintaining polymerization conditions during the conversion.

[0010] International Publication 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 accomplished by a) stopping the supply of the first catalyst to the reactor, b) introducing a reversible catalyst killer, c) introducing an irreversible catalyst killer, and d) supplying a second catalyst to the reactor. The Ziegler-Natta catalyst contains titanium chloride-impregnated silica, magnesium chloride, tetrahydrofuran, and an organoaluminum compound. The metallocene catalyst contains silica mixed with methylaluminoxane and bis-n-butylcyclopentadienyl-zirconium dichloride, and triethylaluminum as a cocatalyst. Only the conversion from a Ziegler-Natta catalyst to a metallocene catalyst is exemplified. Carbon monoxide (CO) is used as the reversible catalyst killer, and water is used as the irreversible catalyst killer.

[0011] Generally, these prior art methods require that the first polymerization catalyst be "killed" or substantially deactivated. Although these techniques mitigate problems resulting from an undesired reaction between two incompatible catalysts, these techniques can introduce other problems, such as: (i) the need to carefully control the addition of deactivators (so as not to poison the fresh catalyst); and (ii) The need to allow downtime for the deactivation reaction (and typically the subsequent purging of the deactivating agent).

[0012] This second issue, or "downtime," can cause further problems, especially when polymer finishing operations (e.g., polymer degassing and pelletizing operations) need to be shut down and restarted. For example, seals and / or bearings, or mechanical pumps and compressors used in the polymer finishing operations, may be more likely to fail during a shutdown / startup cycle than during continuous operation.

[0013] It is well known that certain pairs of different polymerization catalysts are "incompatible"; for example, one catalyst may act as a "poison" for the other, or one catalyst may have a different reactivity ratio than the other, or one catalyst may have a different "hydrogen response" compared to the other. Further details regarding the problems caused by incompatible catalysts are described in U.S. Pat. No. 6,949,612.

[0014] Generally, transitioning between incompatible catalysts involves the production of large amounts of off-spec polymer and / or lost production time. Off-spec polymer material typically does not have the desired resin flow characteristics (e.g., melt index), isotacticity or xylene solubles content, or other properties of either the initial product or the desired target product. Because off-spec polymer material results in economic losses, it is desirable to minimize the period during which a reactor produces such material and the amount of material produced.

[0015] Ziegler-Natta catalysts are frequently used in olefin polymerization. However, recent catalyst developments have resulted in the use of single-site catalysts (SSCs), preferably metallocene catalysts containing transition metal compounds. These two types of catalysts are currently of great economic importance, and therefore, it is highly desirable to shorten the transition time from one catalyst to the other in the same polymerization plant. However, the catalysts are incompatible, and direct transition between them is usually difficult.

[0016] Therefore, it would be highly advantageous to find a way to transition between Ziegler-Natta and single-site catalysts without having to shut down the polymerization reactor, remove the original catalyst system, and restart the polymerization reaction with a different catalyst system and / or without the need for catalyst deactivators (catalyst killers). Additionally, it would be advantageous to reduce the amount of off-spec material produced during the transition process, reduce transition time, and increase the robustness and stability of the transition process.

[0017] Many methods have been described to reduce fugitive, off-spec polymeric material, including feeding a polymerization retarder or catalyst poison (e.g., CO, O) into the reactor, adjusting the reaction gas composition, temperature, and possibly pressure to new values, removing reaction gas from the reactor, reducing the catalyst feed rate, and / or adding a non-reactive gas, e.g., nitrogen, and / or other corrective measures.

[0018] WO 2010 / 086392 describes a method for transitioning between two catalysts during the production of propylene, in which the switch from the first catalyst to the second catalyst is carried out in a prepolymerization reactor, and the reaction conditions in all reactors are appropriately adapted. Summary of the Invention [Problem to be solved by the invention]

[0019] Despite existing approaches to limiting off-spec material, there continues to be a need and desire to provide more effective and efficient processes for reducing the amount of off-spec polymeric material produced during transition to new materials or as a result of variations during steady-state manufacturing. [Means for solving the problem]

[0020] The present invention relates to a method for the transition between Ziegler-Natta catalysts and single-site catalysts used in the polymerization of propylene.

[0021] In a first aspect, the present invention provides a method for transitioning between a Ziegler-Natta catalyst and a single-site catalyst during the production of a polypropylene homopolymer or copolymer in a sequential multi-stage polymerization reaction, comprising: a) polymerizing propylene and optionally a comonomer in the presence of a Ziegler-Natta catalyst in a first reactor and thereafter in a second reactor; b) discontinuing the supply of the Ziegler-Natta catalyst into the first reactor; c) stopping the supply of external donor to the Ziegler-Natta catalyst and reducing the supply of Ziegler-Natta cocatalyst into 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 transition level in the range of 40 to 80% relative to the first operating level prior to step d); e) introducing the single-site catalyst into the first reactor, wherein step e) occurs 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). The above method comprises the steps of:

[0022] Viewed from another aspect, the present invention provides a method for transitioning 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, comprising: a) polymerizing propylene and optionally a comonomer in the presence of a Ziegler-Natta catalyst in a first reactor and thereafter in a second reactor; b) discontinuing the supply of the Ziegler-Natta catalyst into the first reactor; c) stopping the supply of external donor to the Ziegler-Natta catalyst and reducing the supply of Ziegler-Natta cocatalyst into 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 transition level in the range of 40 to 80% relative to the first operating level prior to step d); e) introducing the single-site catalyst into the first reactor, wherein step e) occurs at least 30 minutes, preferably 30 minutes to 3.0 hours, preferably 30 minutes to 2 hours, after step b); and f) increasing the solids content of the second reactor to a second operating level, preferably to the same level as before step d). The above method comprises the steps of:

[0023] Viewed from another aspect, the present invention provides a method for transitioning 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, comprising: a) polymerizing propylene and optionally a comonomer in the presence of a Ziegler-Natta catalyst in a first reactor and thereafter in a second reactor; b) discontinuing the supply of the Ziegler-Natta catalyst into the first reactor; c) stopping the supply of external donor to the Ziegler-Natta catalyst and reducing the supply of Ziegler-Natta cocatalyst into 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 transition level in the range of 40 to 80% relative to the first operating level prior to step d); e) introducing the single-site catalyst into the first reactor, wherein step e) occurs at least 30 minutes, preferably 30 minutes to 3.0 hours, preferably 30 minutes to 2 hours, after step b); and f) increasing the solids content of the second reactor to a second operating level, preferably to the same level as before step d). The above method comprises the steps of: [Brief explanation of the drawings]

[0024] [Figure 1] Figure 1 shows the production rates of the loop reactor and the GPR as separate lines as a function of time on the x-axis. DETAILED DESCRIPTION OF THE INVENTION

[0025] Ziegler-Natta (ZN) catalyst

[0026] 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 containing compounds of Mg, Ti, and Cl and an internal donor component. In addition to the solid catalyst component, one or more cocatalysts and one or more external donors are typically used in the propylene polymerization process.

[0027] The catalyst component may be supported on a particulate support, for example on an inorganic oxide, such as silica or alumina, or magnesium halide may form the solid support. Solid catalyst components may also be prepared by emulsion-solidification methods or by precipitation methods.

[0028] The solid catalyst component for propylene polymerization usually contains an internal electron donor and an aluminum compound acting as a cocatalyst. Suitable internal electron donors are, inter alia, esters of carboxylic or dicarboxylic acids, such as phthalic acid esters, unsubstituted or substituted malonic acid esters, unsubstituted or substituted maleic acid esters, ethers and diethers, or oxygen- or nitrogen-containing silicon compounds, or combinations thereof.

[0029] Any aluminum compound used in combination with the catalyst preparation is typically selected from aluminum alkyl, aluminum alkyl halide, aluminum alkyl alkoxide or aluminum alkyl halide alkoxide compounds, wherein the alkyl group comprises 1 to 20 C atoms, preferably 1 to 10 C atoms, in particular 1 to 6 C atoms.

[0030] The cocatalyst typically comprises an aluminum trialkyl or aluminum alkyl halide compound, where the alkyl group typically comprises 1 to 20 carbon atoms, for example, 1 to 10 carbon atoms. The aluminum alkyl compound is preferably a trialkyl aluminum, such as trimethyl aluminum, triethyl aluminum (TEAL), triisobutyl aluminum, or tri-n-octylaluminum. Aluminum alkyl halides of interest include dialkyl aluminum halides, alkyl aluminum dihalides, or alkyl aluminum sesquihalides, such as diethyl aluminum chloride, dimethyl aluminum chloride, ethyl aluminum dichloride, or ethyl aluminum sesquichloride.

[0031] For catalyst activation, a cocatalyst is used together with the ZN catalyst. The cocatalyst is preferably an aluminum alkyl compound. The use of TEAL is particularly preferred.

[0032] It is also typical to use an external donor in the ZN polymerization process. Suitable external electron donors for use in propylene polymerization are well known in the art and include ethers, ketones, amines, alcohols, phenols, phosphines, esters, and silanes. Silane-type external donors are typically organosilane compounds containing a Si-OCOR bond, a Si-OR bond, or a Si-NR2 bond, with a silicon atom as the central atom, and R having 1 to 20 C atoms and being alkyl, alkenyl, aryl, arylalkyl, or cycloalkyl, as known in the art.

[0033] As used herein, the terms D-donor and external donor may be used interchangeably.

[0034] Preferred external donors are silane donors and include diisopropyldiethoxysilane (DIPDES), cyclohexylmethyldiethoxysilane (CHMDES), dicyclopentyldimethoxysilane (DCPDMS), cyclohexylmethyldimethoxysilane and dicyclopentadienyldiethoxysilane (DCPDES) and diethylaminotriethoxysilane.

[0035] Examples of suitable Ziegler-Natta catalysts are described, inter alia, 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 04 / 000757, WO 05 / 000759, WO 06 / 000759, WO 07 / 000759, WO 08 / 000759, WO 09 / 000759, WO 10 / 000759, WO 11 / 000759, WO 12 / 000759, WO 13 / 000759, WO 14 / 000759, WO 15 / 000759, WO 16 / 000759, WO 17 / 000759, WO 18 / 000759, WO 19 ... WO03 / 000757, International Publication No. WO03 / 000754, International Publication No. WO03 / 000755, International Publication No. WO2004 / 029112, European Patent No. EP2610271, International Publication No. WO2012 / 007430, International Publication No. WO92 / 19659, International Publication No. WO92 / 19653, International Publication No. WO92 / 19658, U.S. Patent No. US4382019, U.S. Patent Nos. 4,435,550, 4,465,782, 4,473,660, 4,560,671, 5,539,067, 5,539,067, 5,618,771, EP 45975, EP 45976, EP 45977, WO 95 / 32994, U.S. Pat. No. 4,107,414, 4,186,107, 4,226,963, 4,347,160, 4,472,524, 4,522,930, 4,530,912, 4,532,313, 4,657,882, 4,581,342, and 4,657,882.

[0036] The Ziegler-Natta catalyst used is most preferably a solid Ziegler-Natta catalyst selected from MgCl-supported titanium Ziegler-Natta catalyst and self-supported solid Ziegler-Natta catalyst.

[0037] Generally, the present invention relates to a method for transitioning from 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 that the ZN-catalyzed process includes the use of an alkylaluminum cocatalyst compound.

[0038] Single-site catalyst

[0039] 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 comprises two cyclopentadienyl, indenyl, or fluorenyl ligands, particularly two bridged cyclopentadienyl, indenyl, or fluorenyl ligands. Furthermore, the ligand may have a substituent, such as an alkyl group, an aryl group, an arylalkyl group, an alkylaryl group, a silyl group, a siloxy group, an alkoxy group, or another heteroatom group. Examples of suitable metallocene compounds are given, inter alia, 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, EP 2402353, EP 2729479 and EP 2746289.

[0040] The single-site catalyst is ideally an organometallic compound (C) containing a transition metal (M) from Groups 3 to 10 of the Periodic Table (IUPAC 2007) or an actinide or lanthanide transition metal (M). According to the present invention, the term "organometallic compound (C)" includes any metallocene or non-metallocene compound of a transition metal having at least one organic (coordinating) ligand and exhibiting catalytic activity alone or together with a cocatalyst. Such transition metal compounds are well known in the art, and the present invention covers compounds of metals from Groups 3 to 10 of the Periodic Table (IUPAC 2007), such as Groups 3 to 7, or Groups 3 to 6, such as Groups 4 to 6, as well as lanthanides or actinides.

[0041] In one embodiment, the organometallic compound (C) has the following formula (I): (L)m R n MX q (I) where: "M" is a transition metal (M) from groups 3 to 10 of the periodic table (IUPAC 2007); each "X" is independently a monoanionic ligand, e.g., a σ-ligand; each "L" is independently an organic ligand that coordinates to said transition metal "M"; "R" is a bridging group connecting the organic ligands (L); "m" is 1, 2 or 3, preferably 2; "n" is 0, 1 or 2, preferably 1; "q" is 1, 2 or 3, preferably 2; and m+q is equal to the valence of the transition metal (M).

[0042] "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).

[0043] In a more preferred definition, each organic ligand (L) independently represents: (a) substituted or unsubstituted cyclopentadienyl, or bicyclic or polycyclic derivatives of cyclopentadienyl, optionally bearing further substituents and / or one or more hetero ring atoms from groups 13 to 16 of the periodic table; or (b) Acyclic η atoms composed of atoms from groups 13 to 16 of the periodic table 1 - to η 4 - or η 6 -ligand, and the open-chain ligand may be fused to one or two, preferably two, aromatic or non-aromatic rings and / or may carry further substituents; or (c) a cyclic η group consisting of an unsubstituted or substituted monodentate, bidentate or polydentate ring system selected from aromatic, non-aromatic or partially saturated ring systems; 1 - to η 4 - or η6 - monodentate, bidentate or polydentate ligands, wherein such ring systems optionally contain one or more heteroatoms selected from groups 15 and 16 of the periodic table, is.

[0044] The organometallic compound (C) preferably has at least one organic ligand (L) belonging to the above group (a). Such organometallic compounds are called metallocenes.

[0045] More preferably, at least one organic ligand (L), preferably both organic ligands (L), are selected from the group consisting of cyclopentadienyl, indenyl, tetrahydroindenyl, fluorenyl, which can independently be substituted or unsubstituted.

[0046] Further, when the organic ligand (L) is substituted, at least one organic ligand (L), preferably both organic ligands (L), independently, are C1-C 20 It preferably contains one or more substituents selected from hydrocarbyl or silyl groups, which may optionally contain one or more heteroatoms selected from Groups 14 to 16 and / or may optionally be substituted by one or more halogen atoms.

[0047] Word “C1~C 20 Whenever used in this application, a "hydrocarbyl group" is a C1-C 20 Alkyl, C2-C 20 Alkenyl, C2-C 20 Alkynyl, C3-C 20 Cycloalkyl, C3-C 20 Cycloalkenyl, C6-C 20 Aryl, C7-C 20 Alkylaryl or C7-C 20 Arylalkyl groups, or combinations of these groups, such as cycloalkyl substituted by alkyl, are included.

[0048] Furthermore, two substituents, which may be identical or different, attached to adjacent C atoms of a ring of the ligand (L) can also together form a further monocyclic or polycyclic ring fused to said ring.

[0049] Preferred hydrocarbyl groups are independently straight or branched C1-C6 groups optionally interrupted by one or more heteroatoms of Groups 14-16, such as O, N, or S. 10 Alkyl groups and substituted or unsubstituted C6-C 20 aryl groups.

[0050] Straight or branched C1-C 10 The alkyl group may be optionally substituted with one or more heteroatoms of groups 14 to 16, and more preferably is methyl, ethyl, propyl, isopropyl, tertbutyl, isobutyl, C 5~6 Cycloalkyl, OR, SR, where R is C1-C 10 is an alkyl group.

[0051] C6~C 20 The aryl group is more preferably a phenyl group, optionally containing one or two C1-C6 alkyl groups, as defined above. 10 It may be substituted with an alkyl group.

[0052] By "σ-ligand" is meant throughout the present invention a group that is bonded to a transition metal (M) via a sigma bond.

[0053] Furthermore, the ligands "X" are preferably independently selected from hydrogen atoms, halogen atoms, C1-C 20 Alkyl, C1-C 20 Alkoxy, C2-C 20 Alkenyl, C2-C 20 Alkynyl, C3-C 12 Cycloalkyl, C6-C 20 Aryl, C6-C 20 Aryloxy, C7-C 20 Aryl alkyl, C7-C 20arylalkenyl, -SR", -Pr", -SiR", -OSiR", and -NR", where each R is independently a hydrogen atom, C1-C6 20 Alkyl, C2-C 20 Alkenyl, C2-C 20 Alkynyl, C3-C 12 Cycloalkyl or C6-C 20 It is aryl.

[0054] More preferably, the "X" ligand is selected from a halogen atom, a C1-C6 alkyl group, a C5-C6 cycloalkyl group, a C1-C6 alkoxy group, a phenyl group, and a benzyl group.

[0055] The bridging group "R" may be a divalent bridge, preferably a divalent bridge selected from -R'2C-, -R'2C-CR'2-, -R'2Si-, -R'2Si-SiR'2-, -R'2Ge-, where each R' is independently a hydrogen atom, a C1-C 20 Alkyl, C2-C 10 Cycloalkyl, tri(C1-C 20 Alkyl)silyl, C6-C 20 Aryl, C7-C 20 Aryl alkyl and C7-C 20 It is alkylaryl.

[0056] More preferably, the bridging group "R" is a divalent bridge selected from -R'2C-, -R'2Si-, where each R' is independently a hydrogen atom, a C1-C 20 Alkyl, C2-C 10 Cycloalkyl, C6-C 20 Aryl, C7-C 20 Aryl alkyl and C7-C 20 It is alkylaryl.

[0057] Another subgroup of organometallic compounds (C) of formula (I) is known as nonmetallocenes, in which the transition metal (M), preferably a transition metal of Groups 4 to 6, suitably Ti, Zr or Hf, has coordinating ligands other than cyclopentadienyl ligands.

[0058] As used herein, the term "nonmetallocene" refers to a compound that does not have a cyclopentadienyl ligand or a fused derivative thereof, but has one or more non-cyclopentadienyl η- or σ-, monodentate, bidentate, or polydentate ligands. Such ligands can be selected, for example, from groups (b) and (c) as defined above and described, for example, in WO 01 / 70395, WO 97 / 10248, WO 99 / 41290, and WO 99 / 10353, as well as in V.C. Gibson et al., Angew. Chem. Int. Ed., engl., vol. 38, 1999, pp. 428-447, the disclosures of which are incorporated herein by reference.

[0059] However, the organometallic compound (C) of the present invention is preferably a metallocene as defined above.

[0060] Metallocenes have been described in numerous patents, some of which are listed below: EP 260130, 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 423101, EP 537 130, WO 2002 / 02576, WO 2005 / 105863, WO 2006 / 097497, WO 2007 / 116034, WO 2007 / 107448, WO 2009 / 027075, WO 2009 / 054832, WO 2012 / 001052, and European Patent EP 2532687, the disclosures of which are incorporated herein by reference. Furthermore, metallocenes have been widely described in academic and scientific literature.

[0061] In a preferred embodiment, the organometallic compound (C) has the following formula (Ia): (L)2R n MX2(Ia) where: "M" is Zr or Hf; Each "X" is a σ-ligand; each "L" is an optionally substituted cyclopentadienyl, indenyl, or tetrahydroindenyl; "R" is a SiMe2 bridging group linking the organic ligands (L); "n" is 0 or 1, preferably 1.

[0062] The metallocene catalyst complexes of the present invention are preferably asymmetric, which simply means that the two ligands that form the metallocene are different, i.e., each ligand has a chemically different set of substituents.

[0063] The metallocene catalyst complexes of the present invention are typically chiral, racemic-bridged, bis-indenyl C1-symmetric metallocenes in their anti-configuration. Although such complexes are formally C1-symmetric, they ideally possess pseudo-C2-symmetry because they maintain C2-symmetry adjacent to the metal center, not around the ligands. Due to their chemical nature, both anti- and syn-enantiomeric pairs (in the case of C1-symmetric complexes) are formed during the synthesis of the complexes. For purposes of this invention, the racemic anti-form means that the two indenyl ligands are oriented in opposite directions relative to the cyclopentadienyl-metal-cyclopentadienyl plane, while the racemic syn-form means that the two indenyl ligands are oriented in the same direction relative to the cyclopentadienyl-metal-cyclopentadienyl plane, as shown in the diagram below. [ka]

[0064] Formula (I), and any subformulas, are intended to cover both the syn and anti configurations. Preferred metallocene catalyst complexes are in the anti configuration.

[0065] The metallocene catalyst complexes of the present invention are typically used as the rac-anti isomer, and therefore, ideally, at least 95 mole (mol) % of the metallocene catalyst complex is in the rac-anti isomer form, such as at least 98 mole %, particularly at least 99 mole %.

[0066] More preferably, the single-site catalyst is of formula (II): [ka] where: Mt is Hf or Zr; each X is a sigma ligand; Each R 1 may independently be the same or different, and CH-R 7 is a group, where R 7 is H or linear or branched C 1~6 Alkyl group, C 3~8 Cycloalkyl groups, C 6~10 is an aryl group; Each R 2 are independently a -CH= group, a -CY= group, a -CH2- group, a -CHY- group, or a -CY2- group, where Y is C 1~10 is a hydrocarbyl group, and n is 2 to 6; Each R 3 and R 4 may be independently the same or different and are each a hydrogen atom, a linear or branched C1 to C6 alkyl group, an OY group, or C 7~20 Aryl alkyl, C 7~20 Alkylaryl group or C 6~20 aryl groups, where at least one R per phenyl group 3 , and at least one R 4 is not a hydrogen atom, and two adjacent R3 or R 4 The groups may be part of a ring that includes the phenyl carbon to which they are attached; R 5 is a linear or branched C1-C6 alkyl group, C 7~20 Aryl alkyl, C 7~20 Alkylaryl group or C6-C 20 is an aryl group; R 6 is C(R 8 ) groups, where R 8 is a linear or branched C1-C6 alkyl group; and Each R is independently C1 to C 20 It is a hydrocarbyl.

[0067] Preferably, Mt is Zr.

[0068] Preferably, each X is independently a hydrogen atom, a halogen atom, C 1~6 an alkoxy group or an R' group, where R' is C 1~6 Preferably, X is an alkyl group, a phenyl group, or a benzyl group. Most preferably, X is a chlorine atom, a benzyl group, or a methyl group. Preferably, both X groups are the same. Most preferably, X is two chlorine atoms, two methyl groups, or two benzyl groups, especially two chlorine atoms.

[0069] Each R is independently C1 to C 20 Hydrocarbyl, for example, C-C 20 Aryl, C7-C 20 Aryl alkyl or C7-C 20 alkylaryl. Hence the word "C 1~20 The "hydrocarbyl group" is C 1~20 Alkyl, C 2~20 Alkenyl, C 2~20 Alkynyl, C 3~20 Cycloalkyl, C 3~20 Cycloalkenyl, C 6~20 Aryl group, C 7~20 Alkylaryl group or C 7~20arylalkyl groups, or of course combinations of these groups, such as cycloalkyl substituted by alkyl. Unless otherwise specified, preferred C 1~20 The hydrocarbyl group is C 1~20 Alkyl, C 4~20 Cycloalkyl, C 5~20 Cycloalkylalkyl groups, C 7~20 Alkylaryl group, C 7~20 Aryl alkyl group or C 6~20 It is an aryl group.

[0070] Preferably, both R groups are the same. 10 Hydrocarbyl group or C6-C 10 Aryl groups, such as methyl, ethyl, propyl, isopropyl, tertbutyl, isobutyl, C 5~6 -cycloalkyl, cyclohexylmethyl, phenyl or benzyl, more preferably both R are C1-C6 alkyl, C 3~8 Cycloalkyl or C6 aryl groups, such as C1-C4 alkyl, C 5~6 It is a cycloalkyl or C aryl group, most preferably both R are methyl, or one R is methyl and the other R is cyclohexyl. Most preferably, the bridge is -Si(CH)-.

[0071] Each R 1 may independently be the same or different, and CH-R 7 is a group, where R 7 is H or a linear or branched C 1~6 Alkyl groups, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl and tert.-butyl, or C 3~8 cycloalkyl groups (e.g., cyclohexyl), C 6~10 an aryl group (preferably phenyl).

[0072] Preferably, both R 1 is the same, CH2-R 7 is a group, where R7 is H or a linear or branched C1-C4 alkyl group, more preferably both R 1 is the same, CH2-R 7 is a group, where R 7 are H or a linear or branched C1-C3 alkyl group. Most preferably, both R 1 are both methyl.

[0073] Each R 2 are independently a -CH= group, a -CY= group, a -CH2- group, a -CHY- group, or a -CY2- group, where Y is C 1~10 Hydrocarbyl groups, preferably C 1~4 a hydrocarbyl group, and n is 2 to 6, preferably 3 to 4.

[0074] Each substituent R 3 and R 4 may be independently the same or different and are a hydrogen atom, a linear or branched C1 to C6 alkyl group, an OY group, or C 7~20 Aryl alkyl, C 7~20 Alkylaryl group or C 6~20 An aryl group, preferably a hydrogen atom, a linear or branched C1 to C6 alkyl group, or a C 6~20 an aryl group, and optionally two adjacent R 3 group or R 4 The groups may be part of a ring that includes the phenyl carbon to which they are attached. More preferably, R 3 and R 4 is a hydrogen atom, a linear or branched C1-C4 alkyl group, or an OY- group, where Y is C 1~4 Even more preferably, each R 3 and R 4 are independently a hydrogen atom, methyl, ethyl, isopropyl, tert-butyl or methoxy, in particular a hydrogen atom, methyl or tert-butyl, where at least one R 3 , and at least one R 4 is not a hydrogen atom.

[0075] Thus, preferably, there are one or two R per phenyl group. 3 is not hydrogen, and more preferably, for both phenyl groups, R 3 The groups are the same, such as 3',5'-di-methyl or 4'-tert-butyl.

[0076] In the case of an indenyl moiety, preferably one or two R on the phenyl group 4 is not a hydrogen atom, and more preferably, two R 4 are not hydrogen atoms, and most preferably, these two R 4 is the same as 3',5'-dimethyl or 3',5'-di-tert-butyl.

[0077] R 5 is a linear or branched C1-C6 alkyl group, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl and tert-butyl; 7~20 Aryl alkyl, C 7~20 Alkylaryl group or C6-C 20 It is an aryl group.

[0078] R 5 is preferably a linear or branched C1 to C6 alkyl group or a C6 to 20 It is preferably an aryl group, more preferably a linear C1-C4 alkyl group, even more preferably a C1-C2 alkyl group, and most preferably methyl.

[0079] R 6 is C(R 8 ) groups, where R 8 is a linear or branched C1 to C6 alkyl group. Preferably, each R 8 may be the same or different, where R 8 is a linear or branched C1-C4 alkyl group, and more preferably, 8 are the same and are C1-C2 alkyl groups. Most preferably, all R 8 The group is methyl.

[0080] In a further preferred embodiment, the organometallic compound (C) has the following formula (III): [ka] where: Mt is Zr or Hf, preferably Zr; Each R 3 and R 4 are independently the same or different and are a hydrogen atom or a linear or branched C1-C6 alkyl group, wherein at least one R 3 , and at least one R 4 is not a hydrogen atom.

[0081] Specific metallocene catalyst complexes of the present invention include rac-anti-dimethylsilanediyl[2-methyl-4,8-bis-(4´-tert-butylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3',5'-dimethyl-phenyl)-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride (MC-1); rac-anti-dimethylsilanediyl[2-methyl-4,8-bis-(3',5'-dimethylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3',5'-dimethylphenyl)-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride (MC-2); and rac-anti-dimethylsilanediyl[2-methyl-4,8-bis-(3',5'-dimethylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3',5'-ditert-butyl-phenyl)-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride (MC-3); or their corresponding zirconium dimethyl analogues Includes. [ka]

[0082] Throughout the above disclosure, wherever a narrow definition of a substituent is provided, that narrow definition is considered to be disclosed along with all broad and narrow definitions of other substituents in this application.

[0083] synthesis

[0084] The ligands required to form the single-site catalysts of the present invention can be synthesized by any method, and one skilled in the art will be able to devise various synthetic protocols for the preparation of the required ligand materials. For example, WO 2007 / 116034 discloses the necessary chemical reactions. Synthetic protocols can also generally be found in WO 2002 / 02576, WO 2011 / 135004, WO 2012 / 084961, WO 2012 / 001052, WO 2011 / 076780, and WO 2015 / 158790.

[0085] To form an active single-site catalyst species, it is usually necessary to use a cocatalyst, as is well known in the art. In accordance with the present invention, a cocatalyst system may be used that includes a boron-containing cocatalyst and / or an aluminoxane cocatalyst.

[0086] The aluminoxane cocatalyst can be one of the following formulas (X): [ka] Here, n is usually 6 to 20, and R has the following meaning.

[0087] Aluminoxanes are formed by the partial hydrolysis of organoaluminum compounds such as those of formula AlR3, AlR2Y and Al2R3Y3, where R is, for example, C1-C 10 Alkyl, preferably C1 to C5 alkyl or C3 to 10Cycloalkyl, C7-C 12 arylalkyl or alkylaryl and / or phenyl or naphthyl, and Y is a hydrogen atom, a halogen atom, preferably a chlorine atom or a bromine atom, or a C1-C 10 It can be alkoxy, preferably methoxy or ethoxy. The resulting oxygen-containing aluminoxanes are generally not pure compounds but mixtures of oligomers of formula (X).

[0088] A preferred aluminoxane is methylaluminoxane (MAO). Such aluminoxanes used according to the present invention as cocatalysts are not pure compounds due to their preparation method, but hereinafter the molar concentrations of the aluminoxane solutions are based on their aluminum content.

[0089] In accordance with the present invention, a boron-containing cocatalyst may also be used in place of an aluminoxane cocatalyst, or an aluminoxane cocatalyst may be used in combination with a boron-containing cocatalyst.

[0090] It will be appreciated by those skilled in the art that when a boron-based cocatalyst is used, it is common to pre-alkylate the complex by reaction with an aluminum alkyl compound, such as TIBA. This procedure is well known and can be carried out with any suitable aluminum alkyl, such as Al(C 1~6 Alkyl)3, can be used. Preferred aluminum alkyl compounds are triethylaluminum, triisobutylaluminum, triisohexylaluminum, tri-n-octylaluminum and triisooctylaluminum.

[0091] Alternatively, when a borate cocatalyst is used, the metallocene catalyst complex may be an alkylated version thereof, ie, for example, a dimethyl or dibenzyl metallocene catalyst complex.

[0092] Boron-based cocatalysts of interest include those of formula (Z): BY3(Z) wherein Y are the same or different and are 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, an arylalkyl, a haloalkyl, or a haloaryl (each having 1 to 10 carbon atoms in the alkyl radical and 6 to 20 carbon atoms in the aryl radical), or a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. Preferred examples of Y are methyl, propyl, isopropyl, isobutyl, or trifluoromethyl, unsaturated groups such as aryl or haloaryl, for example, phenyl, tolyl, benzyl, p-fluorophenyl, 3,5-difluorophenyl, pentachlorophenyl, pentafluorophenyl, 3,4,5-trifluorophenyl, and 3,5-di(trifluoromethyl)phenyl.

[0093] Preferred choices are trifluoroborane, triphenylborane, tris(4-fluorophenyl)borane, tris(3,5-difluorophenyl)borane, tris(4-fluoromethylphenyl)borane, tris(2,4,6-trifluorophenyl)borane, tris(pentafluorophenyl)borane, tris(tolyl)borane, tris(3,5-dimethyl-phenyl)borane, tris(3,5-difluorophenyl)borane and / or tris(3,4,5-trifluorophenyl)borane.

[0094] Tris(pentafluorophenyl)borane is particularly preferred.

[0095] However, it is preferred to use borates, i.e., compounds containing the borate 3+ ion. Such ionic cocatalysts preferably include non-coordinating anions, 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.

[0096] Preferred ionic compounds that can be used according to the present invention are: triethylammonium tetra(phenyl)borate, tributylammonium tetra(phenyl)borate, trimethylammonium tetra(tolyl)borate, tributylammonium tetra(tolyl)borate, tributylammonium tetra(pentafluorophenyl)borate, tripropylammonium tetra(dimethylphenyl)borate, tributylammonium tetra(trifluoromethylphenyl)borate, tributylammonium tetra(4-fluorophenyl)borate, N,N-dimethylcyclohexylammonium tetrakis(pentafluorophenyl)borate, N,N-dimethylbenzylammonium tetrakis(pentafluorophenyl)borate, N,N-dimethylanilinium tetra(phenyl)borate, N,N-diethylanilinium tetra(phenyl)borate, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, N,N-di(propyl)ammonium tetrakis(pentafluorophenyl)borate, di(cyclohexyl)ammonium tetrakis(pentafluorophenyl)borate, triphenylphosphonium tetrakis(phenyl)borate, triethylphosphonium tetrakis(phenyl)borate, diphenylphosphonium tetrakis(phenyl)borate, tri(methylphenyl)phosphonium tetrakis(phenyl)borate, tri(dimethylphenyl)phosphonium tetrakis(phenyl)borate, triphenylcarbenium tetrakis(pentafluorophenyl)borate, or Ferrocenium tetrakis(pentafluorophenyl)borate Includes.

[0097] triphenylcarbenium tetrakis(pentafluorophenyl)borate, N,N-dimethylcyclohexylammonium tetrakis(pentafluorophenyl)borate, or N,N-Dimethylbenzylammonium tetrakis(pentafluorophenyl)borate is preferably given.

[0098] It has surprisingly been found that certain boron cocatalysts are particularly preferred. Therefore, preferred borates for use in the present invention contain a trityl ion. Thus, the use of N,N-dimethylammonium-tetrakispentafluorophenylborate and PhCB(PhF) and their analogs is particularly preferred.

[0099] In accordance with the present invention, preferred cocatalysts are alumoxanes, more preferably methylalumoxanes, combinations of alumoxanes with Al alkyls, or boron or borate cocatalysts, and combinations of alumoxanes with boron-based cocatalysts.

[0100] In accordance with the most preferred embodiment of the present invention, the preferred cocatalyst is an alumoxane, most preferably methylalumoxane.

[0101] Suitable amounts of cocatalyst will be known to those skilled in the art. The molar ratio of boron to metal ion of the metallocene may range from 0.5:1 to 10:1 mol / mol, preferably from 1:1 to 10:1 mol / mol, in particular from 1:1 to 5:1 mol / mol.

[0102] The molar ratio of Al in the aluminoxane to the metal ion of the metallocene can range from 1:1 to 2000:1 mol / mol, preferably from 10:1 to 1000:1 mol / mol, more preferably from 50:1 to 500:1 mol / mol.

[0103] Catalyst production

[0104] 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. Those skilled in the art are aware of the procedures required to support such catalysts.

[0105] Particularly preferably, the support is a porous material such that the complex can be loaded onto the support using methods similar to those described in, for example, 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 20 to 80 μm. The use of these supports is routine in the art.

[0106] In an alternative embodiment, no support is used at all. Such catalysts can be prepared in solution, e.g., in an aromatic solvent such as toluene, by contacting the metallocene (as a solid or in solution) with a cocatalyst, e.g., methylaluminoxane, borane, or a borate salt previously dissolved in an aromatic solvent, or by sequentially adding the dissolved catalyst components to the polymerization medium.

[0107] In one embodiment, no external carrier is used, but the catalyst is still present in solid particulate form, and therefore no external support material, such as an inert organic or inorganic carrier, such as the silica described above, is used.

[0108] To provide the catalyst of the present invention in solid form without the use of an external carrier, a liquid / liquid emulsion system is preferably used, which method comprises dispersing catalyst components (i) and (ii) in a solvent and solidifying the dispersed droplets to form solid particles.

[0109] In particular, the method includes preparing a solution of one or more catalyst components; dispersing the solution in a solvent to form an emulsion in which the one or more catalyst components are present in dispersed phase droplets; solidifying 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.

[0110] This method allows for the production of active catalyst particles with improved morphology, e.g., predetermined spherical shape, surface properties, and particle size, without the use of additional external porous support materials, such as inorganic oxides, e.g., silica. The term "preparing a solution of one or more catalyst components" means that the catalyst-forming compounds may be combined in one solution, which may be dispersed in an immiscible solvent, or at least two separate catalyst solutions may be prepared, one for each portion of the catalyst-forming compounds, which may then be dispersed sequentially in the solvents. A complete disclosure of the necessary processes is described in International Publication No. WO 03 / 051934.

[0111] As mentioned above, the key to the present invention is not the specific nature of the single-site catalyst used, which can therefore be widely selected. However, the second prepolymerization process is required to be capable of being carried out in the presence of an aluminum alkyl compound. The key to the present invention is how the transition method is carried out.

[0112] polypropylene

[0113] The process of the present invention produces a polypropylene polymer, which is a polypropylene homopolymer or a polypropylene copolymer.

[0114] The propylene homopolymers produced by the process of the present invention can be produced with Mw (weight average molecular weight) values ​​in the range of 40 to 2000 kg / mol, preferably in the range of 50 to 1500 kg / mol, depending on the use and amount of hydrogen used as an Mw (weight average molecular weight) regulator. The catalyst of the present invention enables the formation of polypropylene homopolymers with high melting points. In a preferred embodiment, the propylene homopolymers formed by the process of the present invention have melting points above 149.0°C, preferably above 149.5°C, and especially above 150.0°C.

[0115] The polypropylene copolymers produced by the process of the present invention are generally copolymers of propylene and ethylene or C4-C6 10 Copolymers with comonomers, especially C6 comonomers.

[0116] In one preferred embodiment, the polypropylene is a polypropylene homopolymer.

[0117] method

[0118] The process according to the present invention is a "flying" transition in which the change from one type of produced polymer (herein referred to as the first polymer product) to another type of produced polymer (the second polymer product) is carried out continuously, i.e., without shutting down the reactor. When switching from the first catalyst to the second catalyst, the supply of the first catalyst is stopped. The second catalyst is then introduced. It will be understood that to produce the second polymer product, the reactor conditions must be adapted relative to the conditions used to produce the first polymer product. The change in conditions can be before or after introducing the second catalyst. Alternatively, some conditions can be changed before introducing the second catalyst, and other conditions can be changed after introducing the second catalyst.

[0119] The transfer method of the present invention is a multistage polymerization process, i.e., a process comprising two or more stages (reactors) connected "in series." In the context of the present invention, a multistage polymerization process 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 separate reaction stages in the presence of the reaction product of the previous stage, including a polymerization catalyst, usually using different reaction conditions in each stage. The polymerization reaction used in each stage may include conventional propylene homopolymerization or copolymerization reactions, such as gas phase polymerization, slurry phase polymerization, and liquid phase polymerization, using conventional reactors, such as loop reactors, gas phase reactors, batch reactors, etc. (see, for example, International Publication Nos. WO 97 / 44371 and WO 96 / 18662).

[0120] Changing from producing one grade of polymer to producing another grade of polymer typically requires a transition period to switch the polymerization reactor over to the new resin specification. Time is required to adjust the process conditions, such as reaction temperature, reactants and reactant concentration ratios, to allow for the formation of the targeted new polymer. It will be apparent that some "off-grade" polymer may be produced due to the transition process that occurs during the transition from a first multi-stage polymerization reaction intended to produce a first resin product meeting a first specification, to a second multi-stage polymerization reaction intended to produce a second target resin product meeting a second specification.

[0121] Unless the transition is performed properly, such off-grade product may become sticky under the conditions (including temperature) during the transition, resulting in clumping or sheeting (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 process of the present invention minimizes this risk.

[0122] It will also be apparent that the longer the transition, the more "off-grade" polymer may be produced, and there is a commercial incentive to make the conversion from the first polymer product to the second polymer product as clean and fast as possible.

[0123] The specific conditions for the first and second polymerizations depend on various factors, such as catalyst activity, the type and amount of optional comonomer, the type of polymer to be produced, and the production equipment. Consequently, the specific conditions for the transition between Ziegler-Natta and single-site catalysts must be determined for each specific product in each specific plant. This is within the skill of those skilled in the art.

[0124] As previously described herein, the process includes a first reactor and a second reactor, which can be considered a first polymerization stage and a second polymerization stage, respectively.

[0125] Preferably, the multi-stage polymerization process is a two-stage polymerization process, optionally, but preferably, preceded by a prepolymerization step.

[0126] The first polymerization stage produces a propylene homopolymer or copolymer (first polymer product), typically a propylene homopolymer, which is subsequently fed to a second polymerization stage, which can produce a further propylene homopolymer or copolymer (second polymer product), preferably a propylene homopolymer.

[0127] The first polymerization stage is preferably a slurry polymerization stage and therefore the first reactor is preferably a slurry reactor, more preferably a loop reactor.

[0128] The slurry polymerization is usually 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. A particularly preferred diluent is propane, optionally with minor amounts of methane, ethane, and / or butane.

[0129] The ethylene content in the fluid phase of the slurry is 1 to 50 mol%, preferably 2 to 20 mol%, particularly 2 to 10 mol%. The advantage of a high ethylene concentration is that the catalyst productivity is improved, but the disadvantage is that more ethylene needs to be recycled than when the concentration is low.

[0130] The temperature in the first polymerization stage is typically 50 to 110°C (e.g., 60 to 100°C, or 70 to 110°C), and the reactor pressure generally ranges from 20 to 80 bar (e.g., 30 to 70 bar). Excessively high temperatures should be avoided to prevent partial dissolution of the polymer in the diluent and fouling of the reactor.

[0131] The slurry polymerization can be carried out in a known reactor used for slurry polymerization. Such reactors include continuous stirred tank reactors and loop reactors. It is particularly preferred to carry out the slurry polymerization in a loop reactor. In such a reactor, the slurry is circulated at high speed along a closed pipe by using a circulation pump. Loop reactors are generally known in the art, and examples are given in, for example, U.S. Pat. Nos. 4,582,816, 3,405,109, 3,324,093, EP-A-479,186, and 5,391,654. Therefore, it is preferred to carry out the first polymerization stage as a slurry polymerization in a loop reactor.

[0132] The slurry may be withdrawn from the reactor either continuously or intermittently. A preferred method of intermittent withdrawal is the use of settling legs, which allow the slurry to thicken and then withdraw batches of concentrated slurry from the reactor. The use of settling legs is disclosed, inter alia, in U.S. Pat. Nos. 3,374,211, 3,242,150, and EP-A-1,310,295. Continuous withdrawal is disclosed, inter alia, in EP-A-899,990, EP-A-1,415,999, EP-A-1,591,460, and WO-A-2007 / 025640. Continuous withdrawal is advantageously combined with a suitable concentration method, as disclosed in EP-A-1 310 295 and EP-A-1 591 460. It is preferred to withdraw the slurry continuously from the first polymerization stage.

[0133] The average residence time in the first polymerization stage is generally 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 hours, more preferably in the range of 0.3 to 0.6 hours. As is well known in the art, the average residence time τ can be calculated from Equation 1 below:

number

[0134] where V R is the volume of the reaction space (reactor volume in the case of a loop reactor, or fluidized bed volume in the case of a fluidized bed reactor), and Q o is the volumetric flow rate of the product stream (including the polymer product and the flowing reaction mixture).

[0135] The diluents used are generally aliphatic hydrocarbons having a boiling point in the range of −70 to +100° C. In such reactors, polymerization can be carried out under supercritical conditions, if necessary.

[0136] The production rate is appropriately controlled by the catalyst feed rate. It is also possible to influence the production rate by appropriately selecting the monomer concentration. The desired monomer concentration can then be achieved by appropriately adjusting the ethylene feed rate.

[0137] In the second polymerization stage, propylene, optionally with at least one other alpha-olefin comonomer, is polymerized with the propylene polymer produced in the first polymerization stage in the presence of a catalyst. It will thus be understood that the second polymerization stage produces a propylene polymer that combines with the propylene polymer from the first polymerization stage. Preferred comonomers are described herein above.

[0138] The second polymerization stage is preferably a gas-phase polymerization process, i.e., carried out in a gas-phase reactor. Accordingly, the second reactor is preferably a gas-phase reactor. Any suitable gas-phase reactor known in the art may be used, such as a fluidized-bed gas-phase reactor.

[0139] In the case of a gas-phase reactor, the reaction temperature used is generally in the range of 50 to 130°C (e.g., 60 to 115°C, or 60 to 100°C), the reactor pressure is generally in the range of 5 to 60 bar, preferably 10 to 40 bar, and the residence time is generally 1 to 8 hours. The gas used is generally a non-reactive gas, such as nitrogen, or a low-boiling hydrocarbon, such as propane, together with the monomer (e.g., ethylene).

[0140] As is well known and routine in the art, hydrogen can be introduced into any reactor to control the molecular weight of the polymer. In one embodiment, the molar ratio of hydrogen to total olefin monomers in the cycle gas stream ranges from 0.001, 0.002, or 0.003 to 0.014, 0.016, 0.018, or 0.024, where desirable ranges can include any combination of any upper molar ratio limit and any lower molar ratio limit described herein. Expressed another way, the amount of hydrogen in the reactor at any time can range from 1,000 ppm to 20,000 ppm in one embodiment, from 2,000 to 10,000 ppm in another embodiment, from 3,000 to 8,000 ppm in yet another embodiment, and from 4,000 to 7,000 ppm in yet another embodiment, where desirable ranges can include any combination of any upper hydrogen limit and any lower hydrogen limit described herein.

[0141] The split between the first and second polymerization stages (i.e., between slurry and gas phase polymerization) is typically 30:70 to 70:30, more preferably 35:65 to 65:35, and most preferably 40:60 to 60:40.

[0142] Thus, a preferred embodiment of the present invention is where the first reactor is a slurry reactor, e.g., a loop reactor, and the second reactor is a gas-phase reactor, e.g., a fluidized bed gas-phase reactor. A preferred "loop-gas" process is the "loop-gas" process (BORSTAR) developed by Borealis A / S, Denmark. 登録商標 The technique, known as the "art", is described in the patent literature, for example in EP 0 887 379, WO 92 / 12182 or WO 2005 / 002744.

[0143] The polymerization step described above may preferably be preceded by a prepolymerization step. The purpose of prepolymerization is to polymerize a small amount of polymer on a catalyst at a low temperature and / or a low monomer concentration. Prepolymerization can improve the performance of the catalyst in the slurry and / or modify the properties of the final polymer. The prepolymerization step is carried out in the slurry.

[0144] Thus, the prepolymerization step can be carried out in a loop reactor. The prepolymerization is then 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.

[0145] The temperature in the prepolymerization stage is typically 0 to 90°C, preferably 20 to 80°C, more preferably 55 to 75°C.

[0146] The pressure is not critical and is typically between 1 and 150 bar, preferably between 40 and 80 bar.

[0147] The amount of monomer is typically such that 0.1 to 1000 grams of monomer are polymerized in the prepolymerization step per gram of solid catalyst component. As those skilled in the art know, 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 depending on the particle's residence time in the prepolymerization reactor. Because some particles remain in the reactor for a relatively long time and some particles remain in the reactor for a relatively short time, the amount of prepolymer on different particles also varies, and some individual particles may contain an amount of prepolymer exceeding the above-specified limit. However, the average amount of prepolymer on the catalyst is typically within the above-specified limit.

[0148] The molecular weight of the prepolymer can be controlled by hydrogen as known in the art. Additionally, antistatic additives can be used to prevent particles from adhering to each other or to the walls of the reactor, as disclosed in WO-A-96 / 19503 and WO-A-96 / 32420.

[0149] In the process of the present invention, the Ziegler-Natta catalyzed polymerization is preferably initiated as known in the art by introducing the above-described Ziegler-Natta catalyst into a prepolymerization reactor via a catalyst feed tank, preferably via an oil catalyst feed system or via a wax catalyst feed system, and then adding propylene and hydrogen, and optionally, a cocatalyst and an external donor (in whole or in part), to the prepolymerization reactor.

[0150] Next, prepolymerized catalyst, additional propylene, hydrogen, optional additional cocatalyst and external donors are introduced into the first reactor (typically a slurry reactor), after which a polymerization product is recovered from the slurry-phase reactor and conducted to a second reactor (typically a gas-phase reactor), additional propylene and optional comonomer are optionally fed to the second reactor, additional hydrogen is optionally fed to the second reactor, the hydrogen to propylene ratio is controlled to provide the desired molecular weight of the polymerization product, and the polymerization product is recovered from the gas-phase reactor.

[0151] The reaction conditions in the slurry and gas phase reactors (e.g., temperature, pressure, amount of propylene and optional comonomer, amount of hydrogen) are selected according to the desired product parameters of the first product. Generally, such processes are conventional.

[0152] The Ziegler-Natta catalyst component is preferably introduced entirely in the prepolymerization step, if a prepolymerization step is present. However, if the solid catalyst component and the cocatalyst can be fed separately, only a portion of the cocatalyst can be introduced in the prepolymerization step, and the remaining portion can be introduced in the subsequent polymerization step. In such a case, it is necessary to introduce an amount of cocatalyst in the prepolymerization step sufficient to obtain a sufficient polymerization reaction.

[0153] It will be appreciated that the method of the present invention is a continuous process.

[0154] A method for the "flying" transition from Ziegler-Natta catalyzed polymerization to single-site catalyst catalyzed polymerization according to the present invention is further described below.

[0155] During the Ziegler-Natta catalyzed polymerization, a single-site catalyst, such as the single-site catalysts described above, can be introduced into a catalyst feed tank connected to a prepolymerization reactor. Typically, the catalyst is prepared about 130 to 400 minutes before its desired introduction into the prepolymerization reactor.

[0156] Prior to introducing the single-site catalyst into the prepolymerization reactor, the reaction conditions in the prepolymerization reactor and the first reactor can be adapted to reflect the conditions required to produce the second polymer product. If a prepolymerization reactor is used, then it is considered part of the first reactor (thus, the prepolymerization reactor and the slurry reactor are the first reactor in this respect).

[0157] Therefore, the hydrogen concentration in the prepolymerization reactor and the first reactor may be adjusted. The temperature in the prepolymerization reactor and the first reactor may also be adjusted. Such adjustments in the prepolymerization reactor and the first reactor may be made about 15 to 100 minutes before the single-site catalyst is introduced into the first reactor. The hydrogen supply to the second reactor is preferably adjusted to reflect the hydrogen supply required to produce the second polymer product before the single-site catalyst is introduced.

[0158] Adjustments of other polymerization conditions (e.g., monomer content, temperature) necessary to target a second polymer product are preferably made after introduction of the single-site catalyst into the second reactor.

[0159] When adjustments in conditions are required in both the prepolymerization reactor and the first reactor, the order of adjustments does not matter: the prepolymerization conditions may be adjusted first, or the conditions in the first reactor may be adjusted first, or these adjustments may be made simultaneously.

[0160] Generally, 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 loop reactor, in liquid propylene (i.e., the liquid phase comprises primarily propylene with small amounts of other reactants and, optionally, inert components dissolved therein). The first polymerization is carried out in the presence of the Ziegler-Natta catalyst with an external donor and cocatalyst as defined herein. Conditions in the first reactor may be as defined herein for a slurry reactor.

[0161] At a defined time, the supply of Ziegler-Natta catalyst is stopped (step b).

[0162] After this step, after a period of at least 5 minutes, e.g., 5 to 60 minutes, preferably 10 to 55 minutes, more preferably 20 to 50 minutes, the supply of external donor to the Ziegler-Natta catalyst to the first reactor is stopped, and the supply of Ziegler-Natta cocatalyst to the first reactor is reduced (step c), typically to a level less than 25%, preferably less than 10%, of the supply before the Ziegler-Natta catalyst supply was stopped.

[0163] In one embodiment, the Ziegler-Natta cocatalyst feed is reduced to 1 to 5 wt-ppm calculated on the total weight of the propylene (C3) feed, i.e., 1 to 5 g of cocatalyst per 1000 kg of propylene.

[0164] In the next step (step d), the solids content in the second reactor is reduced from the first operating level to a transition level in the range of 40 to 80% of the first operating level. This step is performed at least 5 minutes, preferably 15 to 90 minutes, e.g., 20 to 60 minutes, after step c). Alternatively, this step is performed 45 minutes to 2.5 hours, e.g., 60 minutes to 2.0 hours, after the Ziegler-Natta feed is stopped. Typically, the solids content is adjusted 1.0 to 2.0 hours, e.g., 1.5 hours, after the ZN catalyst is stopped. The solids content of the second reactor is typically reduced by lowering the bed height (or bed level) of the polymer particles from the first operating level to the transition level. The bed height is typically reduced by increasing the product discharge rate from the reactor to downstream equipment, such as a purge bin. Other conventional techniques for reducing the bed height of the polymer particles are known in the art.

[0165] The initial solids content or level of the bed of polymer particles is considered to be the normal level measured during steady-state operation of a Ziegler-Natta polymerization, i.e., the first operating level. In a preferred embodiment, the solids content or level of the bed of polymer particles is reduced to a transition level that is 60-75% of the first operating level.

[0166] The single-site catalyst may be introduced into the first reactor at least 30 minutes, for example 30 minutes to 3.5 hours, preferably 45 minutes to 3.0 hours, after the Ziegler-Natta catalyst (step b) has been stopped. This step e) is carried out after step d) has been completed.

[0167] The single-site catalyst may also be introduced into the first reactor at least 30 minutes after step d), preferably between 30 minutes and 2 hours.

[0168] In one embodiment, the single-site catalyst is introduced into the first reactor at least 30 minutes, for example 30 minutes to 2 hours, preferably 45 minutes to 1.5 hours, after discontinuing the Ziegler-Natta catalyst.

[0169] Alternatively, the single-site catalyst is introduced into the first reactor after a period of at least 5 minutes, such as 5 to 45 minutes, following step d).

[0170] The second polymerization is a multi-stage process, so the single-site catalyst is finally transferred to the gas-phase reactor, which occurs 1.0 to 3.0 hours after the start of the single-site catalyst feed.

[0171] As a final step, the solids content of the second reactor is increased to the second operating level, i.e., the normal level measured during steady-state operation of single-site polymerization. The first and second operating levels are preferably the same. This step f) is preferably carried out at least 30 minutes after step e), preferably 1.0 to 6.0 hours, for example, 2.0 to 5.0 hours after the start of single-site catalyst feed. Gas-phase polymerization using the single-site catalyst is preferably initiated at this point. This step f) is preferably carried out 3.0 to 8.0 hours after step b).

[0172] For the avoidance of doubt, steps a) to f) are carried out sequentially.

[0173] Therefore, in one embodiment, the present invention provides a method for transitioning 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, comprising: a) polymerizing propylene and optionally a comonomer in the presence of a Ziegler-Natta catalyst in a first reactor and thereafter in a second reactor; b) discontinuing the supply of the Ziegler-Natta catalyst into the first reactor; c) stopping the supply of external donor to the Ziegler-Natta catalyst and reducing the supply of Ziegler-Natta cocatalyst into 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 transition level in the range of 40 to 80% relative to the first operating level before step d), wherein step d) is carried out at least 5 minutes, preferably 20 to 90 minutes, after step c); e) introducing the single-site catalyst into the first reactor, wherein step e) occurs at least 30 minutes, preferably 30 minutes to 2 hours, after step b); and 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) occurs at least 30 minutes, preferably 1.0 hour to 6.0 hours, after step e); The above method comprises the steps of:

[0174] It will be appreciated that the Ziegler-Natta catalyst and single-site catalyst components are both introduced into the first reactor, and once added to the first reactor, the single-site catalyst is fed to the second reactor where a second polymerization takes place.

[0175] The polymer produced in the first reactor is typically fed continuously to the second reactor throughout the process.

[0176] The precise control of polymerization conditions and reaction parameters is within the skill of one skilled in the art. The pressure and temperature of the second reactor are typically kept essentially constant throughout the process.

[0177] The process of the present invention is ideally carried out in the absence of any additional agents that deactivate or kill the Ziegler-Natta catalyst.

[0178] How to decide

[0179] The following definitions of terms and methods of determination apply to the above general description of the invention as well as the following examples, unless otherwise defined.

[0180] The melt flow rate MFR2 (230°C) is measured according to ISO 1133 (230°C, 2.16 kg load).

[0181] Bulk Density: The bulk density of the polymer powder was determined according to ASTM D1895-96, Method A.

[0182] Number average molecular weight (Mn ), weight average molecular weight (M w The molecular weight distribution (MWD) and the molecular weight distribution (MWD) are determined by gel permeation chromatography (GPC) according to the following method: Weight average molecular weight Mw and molecular weight distribution (MWD = M w / M n , where M n is the number average molecular weight and M w The weight-average molecular weight (MW) was measured according to 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. The analysis was performed at 145 °C and a constant flow rate of 1 mL / min using three TosoHaas TSK-gel columns (GMHXL-HT) and 1,2,4-trichlorobenzene (TCB, stabilized with 200 mg / L of 2,6-ditertbutyl-4-methylphenol) as the solvent. 216.5 μL of sample solution was injected per analysis. The column set was calibrated using 19 narrow-MWD polystyrene (PS) standards ranging from 0.5 kg / mol to 11,500 kg / mol and a relative calibration with a well-characterized broad-MWD polypropylene standard. All samples were prepared by dissolving 5-10 mg of polymer in 10 mL of stabilized TCB (same as the mobile phase) at 160 °C and holding for 3 h with continuous shaking before sampling into the GPC instrument.

[0183] Particle size (PS) and average particle size (APS) were measured using image analysis methods with a Camsizer P4 analyzer according to ISO 13322-2.

[0184] Comonomer content was determined based on Fourier transform infrared spectroscopy (FTIR) using a Nicolet Magna 550 IR spectrometer and 13 Determined by known methods using Nicolet Omnic FTIR software calibrated with C-NMR.

[0185] DSC analysis

[0186] The melting temperature Tm and crystallization temperature Tcr are -1 The measurements were performed on approximately 5 mg samples using a Mettler-Toledo 822e differential scanning calorimeter (DSC) in accordance with ISO 11357-3 in the temperature range +23 to +225 °C, at a scan rate of 10 °C / min, in a hot / cold / hot cycle. The melting temperatures were taken as the endothermic peaks in the second heating step, respectively. The instrument was calibrated with H2O, lead, tin, and indium according to ISO 11357-1.

[0187] Xylene solubles

[0188] The xylene soluble fraction (XS), as defined and described in this invention, was determined as follows: 2.0 g of polymer was dissolved in 250 mm of p-xylene at 135°C under stirring. After 30 minutes, the solution was cooled to ambient temperature for 15 minutes and then allowed to settle at 25±0.5°C for 30 minutes. The solution was filtered through filter paper and placed into two 100 mm flasks. The solution from the first 100 mm vessel was evaporated in a nitrogen stream, and the residue was dried under vacuum at 90°C until a constant weight was reached. The xylene soluble fraction (percent) can then be determined by the following formula:

number

[0189] Example

[0190] In the polymerizations exemplified below, two types of catalysts were used: metallocene and Ziegler-Natta catalysts.

[0191] catalyst

[0192] A) Single-site catalyst For all experiments, the single-site catalyst used in the polymerization process was anti-dimethylsilanediyl[2-methyl-4,8-di(3,5-dimethylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3,5-dimethylphenyl)-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride, disclosed as MC-2 in WO 2019 / 179959 A1. The supported metallocene catalyst was prepared similarly to IE2 in WO 2019 / 179959 A1.

[0193] B) Ziegler-Natta catalyst The Ziegler-Natta catalysts used in the examples were prepared as follows: raw materials TiCl4 (CAS 7550-45-90) was supplied by a commercial source. 20% solution of butylethylmagnesium (Mg(Bu)(Et)) in toluene, provided by Crompton 2-Ethylhexanol, provided by Merck Chemicals 3-Butoxy-2-propanol, provided by Sigma-Aldrich Bis(2-ethylhexyl) citraconate, provided by Contract Chemicals Viscoplex 登録商標 1-254, provided by Evonik Heptane, provided by Chevron

[0194] Preparation of Mg complexes 3.4 liters of 2-ethylhexanol and 810 ml of propylene glycol butyl monoether (molar ratio 4 / 1) were added to a 20-liter reactor. Next, 7.8 liters of a 20% solution of BEM (butylethylmagnesium) in toluene, provided by Crompton GmbH, was slowly added to the well-stirred alcohol mixture. During the addition, the temperature was maintained at 10°C. After the addition, the temperature of the reaction mixture was raised to 60°C, and stirring was continued at this temperature for 30 minutes. Finally, after cooling to room temperature, the resulting Mg-alkoxide was transferred to a storage container.

[0195] 21.2 g of the Mg alkoxide prepared above was mixed with 4.0 ml of bis(2-ethylhexyl)citraconate for 5 minutes, and the resulting Mg complex was immediately used in the preparation of the catalyst component.

[0196] Preparation of catalyst components 19.5 ml of titanium tetrachloride was placed in a 300 ml reactor equipped with a mechanical stirrer at 25°C. The stirring speed was adjusted to 170 rpm. 26.0 ml of the Mg complex prepared above was added within 30 minutes while 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 increased to 90°C within 30 minutes. The reaction mixture was further stirred at 90°C for 30 minutes. The stirring was then stopped, and the reaction mixture was allowed to settle at 90°C for 15 minutes. The solid was washed with 100 ml of toluene, 30 ml of TiCl4, 100 ml of toluene, and two 60 ml portions of heptane. One ml of donor (i.e., bis(2-ethylhexyl)citraconate) was added to the first two washes. The washes were performed at 80°C with stirring at 170 rpm for 30 minutes. After stirring was stopped, the reaction mixture was allowed to settle for 20-30 minutes and then siphoned.

[0197] The stirring was then stopped and the reaction mixture was allowed to settle for 10 minutes, cooled to 70°C, and subsequently siphoned, followed by 20 minutes of N2 sparging to obtain an air-sensitive powder. The catalyst had a surface area of ​​5 m2 measured by the BET method. 2 / g, i.e., below the detection limit.

[0198] Steps to migrate

[0199] The experimental example was performed at pilot scale, with the objective of simulating a Ziegler-Natta to metallocene catalyst fly transition at the GPR bed level, where the target GPR bed level at full scale is about 6 to about 12 m for the transition (60 to 120 cm in the pilot).

[0200] In IE1 and IE2, a transition from Ziegler-Natta (ZN) to metallocene was performed. The Ziegler-Natta polymerization process performed before the transition started was based on the conditions presented in Table 1 for the reference example.

[0201] The transfer procedure was as follows: At 0 hours, the ZN catalyst feed was stopped and the TEAL / donor (i.e., dicyclopentyldimethoxysilane (DCPDMS)) feed was continued. The TEAL was 150 g / tonne, i.e., 150 g / 1000 kg, and the D-donor (i.e., dicyclopentyldimethoxysilane (DCPDMS)) was 20 g / tonne, i.e., 20 g / 1000 kg. At this point, the Span 80 feed was started at 2 wt-ppm. (Step b) +45 min. The donor (i.e., dicyclopentyldimethoxysilane (DCPDMS)) feed was stopped, the TEAL feed was reduced to 2.5 g per ton of C3, and the loop reactor was controlled at T = 70 °C and GPR = 80 °C (step c). +45 min. The polymer slurry was still introduced into GPR1. The bed level was lowered from 160 cm to 120 cm (12 m at full scale) and fluidization, pressure and temperature were maintained at normal levels (i.e., 1.5 hours after the start of the subsequent step). One and a half hours after stopping the ZN catalyst feed, the loop reactor was empty and the target GPR bed level was reached (120 cm). (Step d) +15 min. The metallocene feed was started (1.75 hours after the start, i.e., the ZN catalyst feed was stopped). The loop was led to a dump tank during the ramp-up (step e). +1 hour 45 minutes after adding the single-site catalyst. Loop density is 470 kg / m 3 At this point, the polymer slurry was rotated to initiate mass transfer from the loop reactor to the GPR (+3.5 hours from the start of the subsequent reaction). After 2.5 hours of gas-phase mass transfer, the bed level of the GPR was raised to 160 cm (16 m at full scale). Samples were taken at the usual intervals. This was 6 hours after the start of the process and 4.25 hours after the single-site catalyst was started (step f). +3 hours. Lot recovery has begun, 9 hours after the start of the recovery.

[0202] The catalyst change was smooth and as planned. The polymerization conditions and resulting polymer properties for this example are also shown in Table 1 below. In Figure 1, the loop reactor and GPR production rates are plotted as separate lines as a function of time on the x-axis. The darker trend line is the loop reactor production rate, and the lighter trend line is the proportional production rate of the GPR.

[0203] The ZN catalyst feed was stopped at 12:00 and the metallocene catalyst was started at 13:45. The split before the change was 55 / 45% and the productivity was 36 kg PP / g catalyst with the ZN catalyst. After 12 hours with the metallocene catalyst, the split was 70 / 30% and the productivity was 13 kg PP / g catalyst.

[0204] A reference example was also performed, a Ziegler-Natta (ZN) to Ziegler-Natta transition. The same procedure as in IE1 and IE2 was followed, except that the ZN catalyst was reintroduced into the first reactor at +1.5 hours. The polymerization conditions and resulting polymer properties for this example are also shown in Table 1 below.

[0205] [Table 1] JPEG2025542270000009.jpg146170

[0206] The results in Table 1 reflect the polymerization results when transitioning from a ZN catalyst to a metallocene catalyst (i.e., a single-site catalyst) as outlined herein. The reference example is used as a comparison example where no single-site catalyst is introduced.

[0207] The transition from the ZN catalyst to the metallocene catalyst took approximately 13 hours. As can be seen from Figure 1, the ZN catalyst feed was stopped, and productivity dropped, first in the loop reactor and then in the gas-phase reactor. 1.5 hours after stopping the ZN catalyst feed, the bed level in the gas-phase reactor was adjusted, which temporarily increased productivity, but productivity continued to decline thereafter. After 1.75 hours, productivity in the loop reactor dropped to a very low level, and 1.75 hours after stopping the ZN catalyst, polymerization continued in the presence of the metallocene catalyst.

[0208] The productivity of the loop reactor increased immediately, but that of the gas-phase reactor continued to decline until 3.5 hours after the ZN catalyst was turned off, at which point metallocene formation in the gas-phase reactor began. The properties of the polymer fractions from each reactor were monitored in situ.

[0209] Gas phase reactor production continues for approximately 5.5 hours before samples are taken for analysis, at which point gas phase reactor productivity has essentially reached target levels.

[0210] The final polymer characteristics reflect the pelletized polymer isolated after 9 hours, thus completing the transition procedure. This is the polymer that was sequentially transferred from the prepolymerization reactor to the loop reactor and then finally to the gas-phase reactor. The final polypropylene (PP) polymer is the isolated end product of the multi-stage process and is therefore a combination of the prepolymer, the first polymer, and the second polymer. The "off-spec" polymer produced during the transition (not purged during solids content reduction step d) is small in quantity and can be ignored. During the transition, the catalyst is absent and the polymer is purged, thus limiting the amount of polymer produced.

Claims

1. 1. A process for transitioning 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, comprising: a) polymerizing propylene and optionally a comonomer in the presence of a Ziegler-Natta catalyst in a first reactor and thereafter in a second reactor; b) discontinuing the supply of the Ziegler-Natta catalyst into the first reactor; c) stopping the supply of external donor to the Ziegler-Natta catalyst and reducing the supply of Ziegler-Natta cocatalyst into 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 transition level in the range of 40 to 80% relative to the first operating level prior to step d); e) introducing the single-site catalyst into the first reactor, wherein step e) occurs at least 30 minutes, preferably 30 minutes to 2 hours, after step d); and f) increasing the solids content of said second reactor to a second operating level, preferably to the same level as before step d). The method comprises the steps of:

2. 10. The method of claim 1, wherein the transition is carried out in the absence of any additional agents that deactivate or kill the Ziegler-Natta catalyst.

3. 3. The process of claim 1 or 2, wherein the polypropylene homopolymer or copolymer is continuously fed 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 Ziegler-Natta catalyst is MgCl 2 6. The method of claim 1, wherein the catalyst is a solid Ziegler-Natta catalyst selected from titanium Ziegler-Natta catalysts supported on a support material and self-supported solid Ziegler-Natta catalysts.

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

8. 8. The process according to any one of claims 1 to 7, wherein the Ziegler-Natta cocatalyst is an aluminium trialkyl or aluminium alkyl halide compound, wherein the alkyl group preferably comprises 1 to 20 C atoms, more preferably 1 to 10 C atoms.

9. 9. The process of any one of claims 1 to 8, wherein in step c) the Ziegler-Natta cocatalyst feed is reduced to a level of less than 25%, preferably less than 10%, more preferably 1 to 5 wt-ppm calculated on the total weight of the propylene feed, of the feed before discontinuing the Ziegler-Natta catalyst 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 method according to claim 10, wherein the metallocene catalyst comprises, as a catalytic component, an organometallic compound (C) of the following formula (Ia): (L) 2 R n MX 2 (Ia) where: "M" is Zr or Hf; Each "X" is a σ-ligand; each "L" is an optionally substituted cyclopentadienyl, indenyl, or tetrahydroindenyl; "R" is a SiMe that connects the organic ligand (L). 2 is a bridging group; "n" is 0 or 1, preferably 1.

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

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

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

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

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

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