Shunt loop propylene polymerization device and shunt loop propylene polymerization method

Abstract

The invention relates to a ring pipe-ring pipe-gas phase reactor polypropylene device and a method for preparing polypropylene and a polypropylene copolymer.

Description

Technical Field

[0001] The present invention relates to a polymerization device suitable for ultra-large-scale propylene polymerization and a method for polymerizing propylene using the device. Background Art

[0002] Coupling of loop reactor and gas phase reactor The trademark has been well known for more than two decades and is described in almost all textbooks in the field of polyolefins. For example, in WO9858975A1, which relates to the preparation of propylene homopolymers and copolymers, a basic process layout is described, which comprises polymerizing propylene optionally with comonomers in at least one slurry reactor and at least one gas phase reactor in the presence of a catalyst under conditions of high temperature and pressure, the polymerization product of at least one slurry reactor containing unreacted monomers being introduced directly into the first gas phase reactor, substantially without recycling the unreacted monomers to the slurry reactor.

[0003] Unfortunately, the operating costs and fixed costs per ton of product produced are much higher for medium-sized PP production units compared to very large PP units. However, as the production scale increases, quality issues and operational problems also increase. The capacity of the loop reactor can be increased by adding more legs to the reactor. In industry, loop reactors have been expanded from two legs to six legs, and even eight-leg loop reactors are not uncommon. Unfortunately, this modification leads to some disadvantages, such as the possibility of significant reactant concentration gradients. For example, in the homopolymerization of polypropylene, the ratio of hydrogen to propylene varies with the length of the loop reactor. In addition to this, in the copolymerization of propylene, the ratio of comonomer to propylene leads to significant gradients in the loop reactor. It goes without saying that when the monomer / C3 ratio decreases with the length of the loop reactor, characteristics such as randomness will be affected. In addition, the distribution of olefin comonomers (i.e. ethylene) between and within macromolecules is not uniform, resulting in a higher organoleptic content. Organoleptic factors refer to the phenomenon that organic compounds may migrate from polymer packaging into food, thereby changing the taste and / or smell of the food. This problem is particularly acute when using single-site catalysts, which are more sensitive in terms of hydrogen response and comonomer incorporation.

[0004] Therefore, there remains a need for a process and apparatus for scaling up production to ultra-large scale to at least partially avoid the above-mentioned and related problems.

[0005] WO2021 / 045889 discloses a process in which an α-olefin monomer is polymerized with a catalyst and hydrogen in a slurry to produce a low molecular weight polyolefin in a first step, and in a second step, the hydrogen is discharged from the low molecular weight polyolefin, and the obtained intermediate is further polymerized in a gas phase reactor.

[0006] US 6,455,643 relates to a process for preparing homopolymers and copolymers in the presence of a catalyst in a slurry reactor and a gas phase reactor. RU 2440842 C2 relates to the circulation of a slurry through a continuous circulation reaction system.

[0007] WO2017 / 032682 relates to a process and system for the continuous polymerization of more than one α-olefin monomer, comprising the following steps: a) introducing a catalyst and / or a polymer from at least one loop reactor into at least one second reactor; b) extracting a fluid from the at least one second reactor; c) cooling a fluid comprising the extracted fluid using a cooling unit; d) introducing the cooled fluid into a separator to separate at least part of the liquid from these fluids to form a liquid phase and a gas / liquid phase; e) introducing the gas / liquid phase downwardly into the reactor below the distribution plate; f) introducing the liquid phase into a settling tank to separate the liquid from fine particles settled in the settling tank; g) introducing liquid from a settling tank upstream of the cooling unit; h) introducing a slurry comprising solid polymer particles from the settling tank into at least one loop reactor. Summary of the invention

[0008] The present invention provides a device for preparing a propylene homopolymer or a propylene copolymer, comprising:

[0009] (i) a feed tank for the single-site catalyst (1) and optionally a feed tank for the co-catalyst (2), an optional activator and an optional external donor (3);

[0010] (ii) an optional pre-contact unit (4) for catalyst mixing, which is connected to the feed tank via a feed line (5, 5', 5");

[0011] (iii) a propylene feed tank (7);

[0012] (iv) a prepolymerization reactor (6) connected to the feed tanks (1, 2, 3) or the precontact unit (4) and a propylene feed tank (7);

[0013] (v) a first loop reactor (8) connected to the prepolymerization reactor;

[0014] (vi) a second loop reactor (9) connected to the first loop reactor via a loop reactor connecting line (10);

[0015] wherein the volume of the first loop reactor is at most 40 vol.-% relative to the total volume of the first loop reactor and the second loop reactor; the volume of the second loop reactor is at least 60 vol.-% relative to the total volume of the first loop reactor and the second loop reactor; and the total volume of the first loop reactor and the second loop reactor is between 50 and 150 m 3and the propylene feed tank is connected to the first loop reactor and the second loop reactor;

[0016] (vii) a single feed point (11) for introducing propylene monomer, optionally comonomers, into the first loop reactor (8), a single feed point (12) for introducing hydrogen into the first loop reactor (8), and a single feed point (11) for introducing propylene monomer, optionally comonomers, into the second loop reactor (9), a single feed point (12) for introducing hydrogen into the second loop reactor (9);

[0017] (viii) a gas phase reactor (13) equipped with a gas recycle line (14), a recycle gas compressor (15) and a recycle gas cooler (16), which is connected to the second loop reactor via a direct feed line (17);

[0018] (ix) a device (44) for introducing propylene monomer into the gas phase reactor (13) and / or a device (18) for introducing comonomer into the gas phase reactor (13) and / or a device (19) for introducing hydrogen into the gas phase reactor (13); preferably, the device for introducing monomer and / or the device for introducing comonomer is suitable for introducing monomer and / or comonomer in condensed form;

[0019] (x) an optional product discharge vessel (20) connected to the gas phase reactor;

[0020] (xi) an optional product outlet heater (21);

[0021] (xii) a product receiving tank (22) connected to an optional product discharge vessel (20) or a gas phase reactor (13);

[0022] (xiii) an apparatus (25) for recovering propylene homopolymer or propylene copolymer; the apparatus optionally comprises apparatus for homogenization, addition of additives and pelletization.

[0023] The present invention further provides a method for preparing propylene homopolymer and propylene copolymer, comprising:

[0024] a) adding a single-site catalyst, an optional co-catalyst, and an optional activator into a feed tank (1, 2, 3);

[0025] b) introducing the single-site catalyst, the optional co-catalyst, and the optional activator into a pre-contact unit (4) to provide a mixed catalyst system; introducing the mixed catalyst system into the prepolymerization reactor,

[0026] or,

[0027] introducing the single site catalyst, the optional cocatalyst, and the optional activator into a prepolymerization reactor (6);

[0028] c) initiating prepolymerization by introducing propylene monomer and optionally comonomer to provide a prepolymer;

[0029] d) introducing the prepolymer into a first loop reactor (8) and polymerizing propylene and optionally a comonomer to produce a first intermediate;

[0030] e) introducing the first intermediate into a second loop reactor (9) via a loop reactor connecting line (10) and further polymerizing propylene, optionally with a comonomer, to produce a second intermediate;

[0031] f) wherein the volume of the first loop reactor is at most 40 vol.-% relative to the total volume of the first loop reactor and the second loop reactor; the volume of the second loop reactor is at least 60 vol.-% relative to the total volume of the first loop reactor and the second loop reactor; the total volume of the first loop reactor and the second loop reactor is between 50 and 150 m 3 and further comprising a single feed point (11) for introducing monomers and comonomers into the first loop reactor (8), a single feed point (12) for introducing hydrogen into the first loop reactor (8), and a single feed point (11) for introducing monomers and comonomers into the second loop reactor (9), a single feed point (12) for introducing hydrogen into the second loop reactor (9); the second intermediate containing unreacted monomers is directly introduced into the gas phase reactor (13) via a direct feed line (17);

[0032] g) further polymerizing propylene and optionally comonomers in the gas phase reactor (13) by introducing propylene and / or comonomers and / or hydrogen and circulating the gas in upward direction via the gas circulation line (14);

[0033] h) optionally discharging the gas phase reactor product to an optional product discharge vessel (20) and then to a product receiving tank (22) via a connecting line (34) to provide a feed mixture or

[0034] The gas phase reactor product is discharged directly into a product receiving tank (22) to provide a feed mixture.

[0035] In a further aspect the present invention relates to the use of the above described apparatus for the preparation of a propylene homopolymer or preferably a propylene copolymer.

[0036] In a further aspect, the present invention relates to the use of the above-mentioned device for reducing comonomer / propylene molar ratio drift and / or hydrogen / propylene molar ratio drift over the length of at least one of said loop reactors.

[0037] Compared with conventional devices of this type, the device of the present invention comprises two total volumes of 50 to 150 m 3 A loop reactor, wherein the volume of the first loop reactor is at most 40 vol.-% relative to the total volume of the first loop reactor and the second loop reactor. The present invention further applies a catalyst selected from single-site catalysts, which is a class of catalysts that are sensitive to gradients of monomers, comonomers and / or hydrogen.

[0038] Surprisingly, it turned out that segregation phenomena in gas phase reactors can be controlled more easily, solid flowability can be improved and the formation of agglomerates is reduced.

[0039] The device according to the present invention preferably comprises one or more of the following:

[0040] (xiv) at least one purge tank (23), which is preferably connected to the product receiving tank (22) via a purge tank feed line (48);

[0041] (xv) at least one propylene nitrogen recovery unit (24), which is preferably connected to at least one purge tank (23) via a feed line (51);

[0042] (xvi) a column supply line (241) for introducing a hydrocarbon stream into the column (28);

[0043] (xvii) a nitrogen refeed line (243) for reintroducing a nitrogen-rich stream into the purge chamber (23);

[0044] (xviii) an optional thermal oxidizer unit (43);

[0045] (xix) a vent line (242) for discharging an exhaust gas stream, optionally to an optional thermal oxidizer (43), the exhaust gas stream optionally coming from at least one propylene nitrogen recovery unit (24);

[0046] (xx) a recovery gas treatment unit (26) comprising at least one compressor (27), a column (28) and a reflux feed container (28a), the reflux feed container (28a) being connected to the gas circulation line (14) of the gas phase reactor (13) via a recovery line (29);

[0047] (xxi) a cooling circuit (30) for a circulation gas cooler (16);

[0048] (xxii) a discharge unit (31) comprising a high-pressure discharge vessel (32) and a low-pressure discharge vessel (33), wherein the discharge unit (31) is preferably connected to the product receiving tank (22) via a connecting line (34); and

[0049] (xxiii) A recovery feed pipeline (35) connecting the recovery gas processing unit (26) and the propylene feed tank (7).

[0050] The device according to the present invention preferably further comprises one or more of the following:

[0051] (xxiv) knock out drum (38);

[0052] (xxv) a gas phase reactor zone decompression cyclone (39);

[0053] (xxvi) Gas phase reactor flare gas-liquid separation tank (40).

[0054] Such a unit increases the safety of the device according to the invention.

[0055] Preferably, in the device according to the invention, the loop reactor connecting line (10) comprises a concentrator, more preferably a hydrocyclone. Such concentrators, in particular hydrocyclones, and their configurations have been described in WO2017 / 097577, which is incorporated herein by reference. In particular, all configurations disclosed in WO2017 / 097577, which are compatible with a single feed to each of the two loop reactors, are incorporated herein by reference.

[0056] The above method preferably further comprises a concentrator, more preferably a hydrocyclone.

[0057] All aspects described herein in relation to the apparatus shall also be applicable and disclosed to the method. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Hereinafter, the present invention will be described with reference to the accompanying drawings.

[0059] Figure 1 and Figure 2 Reference numerals:

[0060] 1 Feed tank for catalyst

[0061] 2 Optional feed tank for co-catalyst

[0062] 3 Optional feed tank for activator and / or optional external donor

[0063] 4 Optional pre-contact unit for catalyst mixing

[0064] 5,5',5" Feed line connecting feed tank and catalyst feed vessel or prepolymerization reactor

[0065] 6 Prepolymerization Reactor

[0066] 7 Propylene feed tank

[0067] 8. First loop reactor

[0068] 9 Second loop reactor

[0069] 10 Loop reactor connecting pipeline

[0070] 101 Hydrocyclone (only in Figure 2 (shown in

[0071] 11 Equipment for introducing monomers and optional comonomers

[0072] 12 Equipment for introducing hydrogen

[0073] 13 Gas Phase Reactor

[0074] 14 Gas circulation pipeline

[0075] 15. Circulating gas compressor

[0076] 16 Circulating gas cooler

[0077] 17 Direct feed line

[0078] 18 Equipment for introducing comonomer

[0079] 19 Equipment for introducing hydrogen

[0080] 20 Optional product discharge container

[0081] 21 Product outlet heater

[0082] 22 Product receiving tank

[0083] 23 Purge Chamber

[0084] 24 Propylene Nitrogen Recovery Unit

[0085] 25 Export line (polymer powder) with propylene homopolymer or propylene copolymer recovery equipment (optionally including equipment for homogenization, addition of additives and pelletization)

[0086] 26 Recovery gas processing unit

[0087] 27 Gas Recovery Compressor

[0088] 28 Tower

[0089] 28a Reflux recovery feed container

[0090] 29,29' Recovery Feed Line

[0091] 30 Cooling circuit of circulating gas cooler

[0092] 31 Emission Unit

[0093] 32 High pressure discharge chamber

[0094] 33 Low pressure discharge chamber

[0095] 34 Connecting pipeline

[0096] 35 Recovery feed line

[0097] 36 Optionally include additional feed lines to the dryer

[0098] 38 Gas-liquid separation tank

[0099] 39 Gas phase reactor zone pressure reducing cyclone

[0100] 40 Gas phase reactor flare gas-liquid separation tank

[0101] 41,41',41" Propylene Feed Line

[0102] 42 Catalyst deactivation equipment (e.g. equipment for introducing low-pressure steam)

[0103] 43 Thermal Oxidation Unit

[0104] 44 Apparatus for introducing liquid propylene monomer

[0105] 48 Purge bin feed line

[0106] 49 Pipeline connecting the product receiving tank (22) and the gas recovery compressor (27)

[0107] 51 Feed line from purge bin (23) to propylene nitrogen recovery device (24)

[0108] 241 Tower Supply Line

[0109] 242 Exhaust line

[0110] 243 Nitrogen refeed line

[0111] 244 External nitrogen feed line

[0112] 245 Feed line for catalyst deactivator (usually low pressure steam)

[0113] 246 Other nitrogen feed lines

[0114] 247 Nitrogen delivery pipeline

[0115] 249 Oligomer export pipeline

[0116] Figure 1 An apparatus for carrying out the method of the invention is shown.

[0117] Figure 2 A preferred connection of a loop reactor is shown. DETAILED DESCRIPTION

[0118] Will refer to Figure 1 and Figure 2 The device according to the invention is further described.

[0119] The apparatus for preparing propylene homopolymers and propylene copolymers according to the present invention comprises a feed tank (1) for a single-site catalyst, an optional feed tank (2) for a co-catalyst, and an optional feed tank for an activator. Optionally, a pre-contact unit (4) for single-site catalyst mixing is also included, which is connected to the feed tank via a feed line (5, 5', 5"). In different embodiments, a pre-contact tank is not necessary for different single-site catalyst systems.

[0120] The apparatus according to the invention further comprises a prepolymerization reactor (6) connected to the feed tank (1, 2, 3) or the precontact unit (4). Such prepolymerization is well known in the art. The apparatus further comprises a propylene feed tank (7), a first loop reactor (8) connected to the prepolymerization reactor and a second loop reactor (9) connected to the first loop reactor via a loop reactor connecting line (10), as well as one or more devices (11) for introducing comonomer into the first loop reactor (8), the second loop reactor (9) and / or the loop reactor connecting line (10) between the loop reactors, and one or more devices (12) for introducing hydrogen into the first loop reactor (8), the second loop reactor (9) and / or the loop reactor connecting line (10) between the loop reactors.

[0121] As described in the Summary of the Invention, the total volume of the first loop reactor and the second loop reactor is 50 to 150 m 3 Plants with such huge loop reactors are often referred to as "large-scale plants". Furthermore, as mentioned above, the volume of the first loop reactor is at most 40 vol.-% relative to the total volume of the first loop reactor and the second loop reactor; the volume of the second loop reactor is at least 60 vol.-% relative to the total volume of the first loop reactor and the second loop reactor. These features ensure a preferential particle size distribution.

[0122] In addition to the loop reactor, the device according to the invention also includes a gas phase reactor (13) equipped with a gas circulation line (14), a circulation gas compressor (15) and a circulation gas cooler (16), which is connected to at least a second loop reactor via a direct feed line (17). An apparatus (44) for feeding monomers to the gas phase reactor (13) and / or an apparatus (18) for feeding optional comonomers to the gas phase reactor (13) and / or an apparatus (19) for feeding hydrogen to the gas phase reactor (13). In addition, the device optionally includes a product discharge container (20) connected to the gas phase reactor. Such a product discharge container contributes to operational stability. Optionally, a product outlet heater (21) is also included. Typically, the product outlet heater has several units.

[0123] The apparatus according to the invention preferably also comprises a product receiving tank (22) connected to an optional product discharge vessel (20) or to the gas phase reactor (13), and at least one purge chamber (23).

[0124] In addition, the apparatus comprises at least one propylene nitrogen recovery unit (24) having a tower supply line (241) for introducing a hydrocarbon stream into the tower (28), a nitrogen re-feed line (243) for reintroducing a nitrogen-rich stream into the purge bin (23), an optional thermal oxidizer unit (43) and an exhaust line (242) for optionally discharging an exhaust gas stream to the optional thermal oxidizer (43). Optionally, there may be additional feed lines, such as a nitrogen re-feed line (243), an external nitrogen feed line (245), a feed line for a catalyst deactivator (usually low-pressure steam). Preferably, an outlet (249) for oligomers is also included.

[0125] The apparatus according to the invention further comprises a device (25) for recovering propylene homopolymer or propylene copolymer, the device (25) optionally comprising devices for homogenization, addition of additives and pelletization, and also comprises a recovery gas treatment unit (26) having at least one compressor (27), a tower (28) and a reflux feed container (28a), the reflux feed container (28a) being connected to the gas circulation line (14) of the gas phase reactor (13) via a recovery line (29).

[0126] In addition, a cooling circuit (30) for a circulating gas cooler (16) is included. Such a circulating gas cooler helps to expand the operating window.

[0127] In addition, there is a discharge unit (31) comprising a high-pressure discharge tank (32) and a low-pressure discharge tank (33), and the discharge unit (31) is preferably connected to the product receiving tank (22) via a connecting pipeline (34).

[0128] The device according to the present invention further comprises a recovery feed line (35) connecting the recovery gas processing unit (26) and the propylene feed tank (7). This important recovery feed line (35) can also reintroduce propylene into the loop reactor, i.e., form an integrated recovery system.

[0129] Experimental Section

[0130] The apparatus and method according to the present invention are illustrated in the following examples. These examples are for illustrative purposes only and are not intended to limit the present invention.

[0131] Reference Example 1 (RE1)

[0132] At T = 30 ° C, P = 57 barg, a conventional Ziegler Natta catalyst was first introduced into a prepolymerization reactor together with propylene. After 30 minutes of polymerization, a propylene homopolymer was obtained. The product was transferred to a single loop reactor with a length of 250 m and a diameter of 0.57 m, which was provided with a single feed point for propylene monomer, comonomer and hydrogen. 30 t / h of propylene, 0.45 t / h of ethylene and 10 kg / h of hydrogen were injected into the loop reactor through a single feed point. The polymerization reaction was carried out under the conditions of T = 70 ° C, P = 55 barg, and the average residence time was 1.5 h. The crystallinity of the propylene-ethylene copolymer obtained was 50%, the average particle size was 950 μm, and the solid concentration in the reactor was 35% wt. Table 1 shows the C2 / C3 ratio and H2 / C3 ratio in the liquid phase at different reactor lengths.

[0133] Table 1. C2 / C3 molar ratio and H2 / C3 molar ratio at different positions in the loop reactor (single loop reactor configuration; single feed point)

[0134] Composition (mol / Kmol) L=0m L=75m L=150m L=250m C2 / C3(Liquid) 20 18.6 14.4 11.8 H2 / C3(liquid) 4 3.88 3.38 3.14

[0135] It can be seen that along the reactor pipe, the C2 / C3 molar ratio drifts by 40% and the H2 / C3 molar ratio drifts by 21.5%.

[0136] Reference Example 2 (RE2)

[0137] The procedure of Comparative Example 1 was repeated, except that two loop reactors were used. The first loop reactor had a length of 87 m and a diameter of 0.57 m, and the second loop reactor had a length of 163 m and a diameter of 0.57 m. In the first loop reactor, 10 t / h of propylene, 0.15 t / h of ethylene and 3.5 Kg / h of hydrogen were injected (also through a single feed point), and in the second loop reactor of the series, 20 t / h of propylene, 0.30 t / h of ethylene and 6.5 Kg / h of hydrogen were injected (also through a single feed point). The polymerization conditions in the first loop were T=70°C, P=55 barg, and the average residence time was 45 min. The polymerization conditions in the second loop were T=70°C, P=53 barg, and the average residence time was 45 min. Table 2 shows the C2 / C3 ratio and the H2 / C3 ratio in the liquid phase at different reactor lengths in the two loop reactors.

[0138] Table 2. C2 / C3 molar ratio and H2 / C3 molar ratio at different positions in the loop reactor (split loop reactor configuration)

[0139] Composition (mol / Kmol) (first ring) L=0m L=43m L=87m C2 / C3(Liquid) 20 19.4 18.1 H2 / C3(liquid) 4 3.90 3.79 Composition (mol / Kmol) (Second ring) L=0m L=82m L=163m C2 / C3(Liquid) 20 18.1 15.9 H2 / C3(liquid) 4 3.83 3.55

[0140] It can be seen that in the first loop reactor, along the reactor pipe, the C2 / C3 molar ratio drift is 9.5%, the H2 / C3 molar ratio drift is 5.25%, and from the inlet of the first loop reactor to the outlet of the second loop reactor, the C2 / C3 molar ratio drift is 20.5% and the total H2 / C3 molar ratio drift is 11.2%.

[0141] Reference Example 1 shows the advantages of two loop reactors.

[0142] Comparative Example 1 (CE1)

[0143] The procedure of Reference Example 1 was repeated, except that a commercially available single-site catalyst was used and the loop reactor was connected to a gas phase reactor (GPR). More specifically, polymer particles with d10=150 μm, d50=820 μm and d90=1750 μm (span=1.95, span=(d90-d10) / d50)) were transferred to the GPR and polymerized for 2.5 hours at operating conditions of T=85°C and P=21 barg, with a selected superficial gas velocity (SGV) of 0.55 m / s. In this reactor (GPR), ethylene was added as a comonomer in a molar ratio of C2 / C3=500 mol / kmol to produce 35% wt of the rubber component. During the test run, the segregation phenomenon in the gas phase reactor was monitored. More specifically, the corresponding local fluidized bulk density values ​​were measured based on the pressure difference measurement of the gas-solid fluidized bed reactor. Therefore, the fluidized bulk density is 280 kg / m3 (near the bottom of GPR) to 230kg / m 3 (GPR middle area) and 195kg / m 3 In addition, agglomerates were detected and the fluidization quality was poor (i.e., temperature deviations up to 5.0°C and GPR operating pressure fluctuations up to 25% of the set value). The bulk density of the PP powder was 340 kg / m 3 , reflecting severe morphology problems (agglomeration resulting in poor external morphology of the polymer particles) and segregation problems at the height of the fluidized bed. The GPR run was interrupted after 7 days due to operability problems related to segregation and agglomeration.

[0144] Comparative Example 2 (CE2)

[0145] The procedure of Reference Example 2 (RE2) was repeated, except that a commercially available single-site catalyst was used and the loop reactor was connected to a gas phase reactor (GPR). The volume of loop reactor 1 was about 35 vol.-%, and the volume of loop reactor 2 was about 65 vol.-%, relative to the total volume.

[0146] More specifically, polymer particles with d10=380 μm, d50=960 μm and d90=1600 μm (span=1.27) were transferred to a GPR and polymerized for 2.5 hours at operating conditions of T=85°C and P=21 barg, with a selected superficial gas velocity (SGV) of 0.55 m / s. In this reactor (GPR), ethylene was added as a comonomer in a molar ratio of C2 / C3=500 mol / kmol to produce a 35% wt rubber component. During the test run, the segregation phenomenon in the gas phase reactor was monitored. More specifically, based on the pressure difference measurement of the gas-solid fluidized bed reactor, the corresponding local fluidized bulk density values ​​were measured. Therefore, the fluidized bulk density is 284 kg / m 3 (near the bottom of GPR) to 278kg / m 3 (GPR middle area) and 274kg / m 3 (GPR top area). In addition, no agglomerates were detected and the fluidization quality was very high (i.e., temperature deviations were at most 1.0°C and GPR operating pressure fluctuations were up to 8% of the set value). The bulk density of the PP powder was 460 kg / m 3 , reflecting the very good morphology of the polymer particles produced. The GPR operation lasted for 15 days without any operational problems.

[0147] Based on Comparative Examples 1 and 2, it can be concluded that the use of a split loop reactor configuration in the bulk stage of the process results in i) polymer particles with a narrower particle size distribution (lower span value) in the bulk polymerization stage, and ii) significantly reduced segregation and agglomeration in the subsequent gas phase polymerization reactor. The use of a split loop reactor configuration in the bulk stage of a multistage process helps to smooth the concentration drift of the reactants over the length of the bulk loop reactor, thereby producing polymer particles with higher internal uniformity (i.e., the comonomer is more evenly distributed in the polymer particles). This in turn results in polymer particles with uniformly distributed molecular properties (i.e., molecular weight, crystallinity, XS, amorphous fraction, etc.). All of this helps to produce polymer particles with uniform local growth rate and uniform molecular properties at the particle level, thereby achieving a narrow particle size distribution and a lower tendency to stickiness in the subsequent polymerization stage.

[0148] The results are shown in the following table:

[0149]

[0150]

Claims

1. A device for preparing a propylene homopolymer or a propylene copolymer, comprising: (i) a feed tank for the single-site catalyst (1) and optionally a feed tank for the co-catalyst (2), an optional activator and an optional external donor (3); (ii) an optional pre-contact unit (4) for catalyst mixing, which is connected to the feed tank via a feed line (5, 5', 5"); (iii) a propylene feed tank (7); (iv) a prepolymerization reactor (6) connected to the feed tank (1, 2, 3) or the precontact unit (4) and the propylene feed tank (7); (v) a first loop reactor (8) connected to the prepolymerization reactor; (vi) a second loop reactor (9) connected to the first loop reactor via a loop reactor connecting line (10); wherein the volume of the first loop reactor is at most 40 vol.-% relative to the total volume of the first loop reactor and the second loop reactor; the volume of the second loop reactor is at least 60 vol.-% relative to the total volume of the first loop reactor and the second loop reactor; the total volume of the first loop reactor and the second loop reactor is between 50 and 150 m 3 within the range of; and the propylene feed tank is connected to the first loop reactor and the second loop reactor; (vii) a single feed point (11) for introducing propylene monomer, optionally comonomers, into the first loop reactor (8), a single feed point (12) for introducing hydrogen into the first loop reactor (8), and a single feed point (11) for introducing propylene monomer, optionally comonomers, into the second loop reactor (9), a single feed point (12) for introducing hydrogen into the second loop reactor (9); (viii) a gas phase reactor (13) equipped with a gas recycle line (14), a recycle gas compressor (15) and a recycle gas cooler (16), said gas phase reactor being connected to said second loop reactor via a direct feed line (17); (ix) a device (44) for introducing propylene monomer into the gas phase reactor (13) and / or a device (18) for introducing comonomer into the gas phase reactor (13) and / or a device (19) for introducing hydrogen into the gas phase reactor (13); preferably, the device for introducing monomer and / or the device for introducing comonomer are suitable for introducing monomer and / or comonomer in condensed form; (x) an optional product discharge vessel (20) connected to the gas phase reactor; (xi) an optional product outlet heater (21); (xii) a product receiving tank (22) connected to the optional product discharge vessel (20) or the gas phase reactor (13); (xiii) a device (25) for recovering propylene homopolymer or propylene copolymer; said device (25) optionally comprising devices for homogenization, addition of additives and pelletization.

2. The device according to claim 1, wherein: The device also includes: (xiv) at least one purge tank (23), which is preferably connected to the product receiving tank (22) via a purge tank feed line (48); (xv) at least one propylene nitrogen recovery unit (24), which is preferably connected to at least one of the purge bins (23) via a feed line (51); (xvi) a column supply line (241) for introducing a hydrocarbon stream into the column (28); (xvii) a nitrogen re-feed line (243) for reintroducing a nitrogen-rich stream into the purge bin (23); (xviii) an optional thermal oxidizer unit (43); (xix) a vent line (242) for discharging a waste gas stream, optionally to said optional thermal oxidizer (43), said waste gas stream optionally coming from at least one of said propylene nitrogen recovery units (24); (xx) a recovery gas treatment unit (26) comprising at least one compressor (27), the column (28) and a reflux feed vessel (28a), the reflux feed vessel (28a) being connected to the gas circulation line (14) of the gas phase reactor (13) via a recovery line (29); (xxi) a cooling circuit (30) for a circulation gas cooler (16); (xxii) a discharge unit (31) comprising a high-pressure discharge tank (32) and a low-pressure discharge tank (33), wherein the discharge unit (31) is preferably connected to the product receiving tank (22) via a connecting line (34); and (xxiii) A recovery feed pipeline (35) connecting the recovery gas processing unit (26) and the propylene feed tank (7).

3. The device according to claim 1 or 2, wherein: The device also includes one or more of the following: (xxiv) a gas-liquid separation tank (38); (xxv) a gas phase reactor zone pressure reducing cyclone (39); (xxvi) Gas phase reactor flare gas-liquid separation tank (40).

4. A device according to any one of the preceding claims, wherein: The loop reactor connecting pipeline (10) comprises a concentrator (101).

5. The device according to claim 4, wherein: The concentrator (101) is a hydrocyclone.

6. A method for preparing a propylene homopolymer or a propylene copolymer, comprising: a) adding a single-site catalyst, an optional co-catalyst, and an optional activator into a feed tank (1, 2, 3); b) introducing the single-site catalyst, the optional co-catalyst, and the optional activator into a pre-contact unit (4) to provide a mixed catalyst system; introducing the mixed catalyst system into the prepolymerization reactor, or, introducing the single site catalyst, the optional cocatalyst, and the optional activator into a prepolymerization reactor (6); c) initiating prepolymerization by introducing propylene monomer and optionally comonomer to provide a prepolymer; d) introducing the prepolymer into a first loop reactor (8) and polymerizing propylene and optionally a comonomer to produce a first intermediate; e) introducing the first intermediate into a second loop reactor (9) via a loop reactor connecting line (10) and further polymerizing propylene, optionally with a comonomer, to produce a second intermediate; f) wherein the volume of the first loop reactor is at most 40 vol.-% relative to the total volume of the first loop reactor and the second loop reactor; the volume of the second loop reactor is at least 60 vol.-% relative to the total volume of the first loop reactor and the second loop reactor; the total volume of the first loop reactor and the second loop reactor is between 50 and 150 m 3 and further comprising a single feed point (11) for introducing monomers, optionally comonomers, into the first loop reactor (8), a single feed point (12) for introducing hydrogen into the first loop reactor (8), and a single feed point (11) for introducing monomers, optionally comonomers into the second loop reactor (9), a single feed point (12) for introducing hydrogen into the second loop reactor (9); the second intermediate comprising unreacted monomers is introduced directly into the gas phase reactor (13) via a direct feed line (17); g) further polymerizing propylene and optionally comonomers in the gas phase reactor (13) by introducing propylene and / or comonomers and / or hydrogen and circulating the gas in upward direction via the gas circulation line (14); h) optionally discharging the gas phase reactor product to an optional product discharge vessel (20) and subsequently to a product receiving tank (22) via a connecting line (34) to provide a feed mixture or The gas phase reactor product is discharged directly into a product receiving tank (22) to provide a feed mixture.

7. The method according to claim 6, wherein: The first intermediate passes through a concentrator, preferably a hydrocyclone.

8. Use of the device according to claim 1 for the preparation of propylene homopolymers or preferably propylene copolymers.

9. Use of the device according to claim 1 for reducing a comonomer / propylene molar ratio drift and / or a hydrogen / propylene molar ratio drift over the length of at least one of the loop reactors.

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