Fluidized bed reactor for olefin gas phase polymerization

Abstract

A fluidized bed reactor for gas phase polymerization of olefins; the fluidized bed reactor (1) has an inner chamber (2) which in turn has at least one lower part (3) and at least one upper part (4); the fluidized bed reactor (1) comprises: a gas distribution grid (7) located within the inner chamber (2) and at least partially separated from the lower part (3) from the upper part (4); and a recirculation line (8) configured to feed fluidizing gas to the lower portion (3) and having a first end (9) connected to the inner chamber (2) at the upper portion (4); the gas distribution grid (7) comprises a plurality of openings configured to allow passage of the fluidizing gas and comprising a plurality of openings (11 ') located less than 30 mm from the inner surface (6) of the side wall (5).

Description

Technical Field

[0001] The present invention relates to a fluidized bed reactor for olefin gas phase polymerization and a method for preparing olefin polymer. Background Art

[0002] Gas phase polymerization is an economical method for preparing polyolefins (such as homopolymers of ethylene or propylene or copolymers of ethylene or propylene with other olefins). Fluidized bed reactors for implementing this method have been around for a long time. These reactors include a bed of polymer particles, which is kept fluidized by an upwardly flowing fluidizing gas. Conventional reactors mainly include a reactor space in the form of an inner chamber of a vertical cylinder. These reactors have a recycle gas line, in which a cooler for removing the heat of polymerization, a recycle gas compressor, and, if necessary, other elements such as a cyclone separator for removing fine polymer dust can also be installed. The monomers consumed by the polymerization reaction are usually replaced by adding supplementary gas to the recycle gas stream.

[0003] In order to achieve uniform distribution of the fluidizing gas in the growing bed of polymer particles, some reactors are equipped with a gas distribution grid, sometimes also called a gas fluidizing grid or a distributor plate. Such a gas distribution grid is a device provided with openings that distribute the gas flow introduced below the grid itself into the bed. The grid can also serve as a support for the bed when the gas supply is cut off.

[0004] The gas distribution grid can be configured as a perforated plate or a porous plate, sometimes in combination with an upstream flow divider. For example, as disclosed in EP 0 697 421 A1, a roof-shaped guide plate can be arranged above the opening of the distributor plate, or the opening can be covered with a top cover as described in EP 0 600 414 A1. The geometry of the gas distribution grid can also deviate from the plate. EP0 088 638 A2 discloses a gas distributor with a double cone for a fluidized bed reactor. WO 2008 / 074632A1 describes a gas distribution grid with an inverted cone form. Due to the large amount of recycled fluidizing gas, the size of the gas inlet nozzle also becomes larger, so a relatively large volume is required below the gas distribution grid.

[0005] Over time, fines present in the fluidizing gas accumulate in the space below the reactor grid. These reactive fines, under stagnant conditions, form polymer agglomerates that eventually block the grid openings, compromising the operability and reliability of the reactor system.

[0006] It would therefore be desirable to provide a fluidized bed reactor which allows fine polymer particles carried by the fluidizing gas to be easily transported back into the fluidized bed of polymer particles.

[0007] The object of the present invention is to provide a fluidized bed reactor and a process for preparing olefin polymers which can at least partially overcome the disadvantages of the prior art and which at the same time are simple and inexpensive to implement. Summary of the invention

[0008] According to the present invention, according to the attached independent claim and preferably according to any claim directly or indirectly dependent on the independent claim, there is provided a fluidized bed reactor and a process for preparing olefin polymers.

[0009] BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The invention will be described hereinafter with reference to the accompanying drawings, which show non-limiting embodiments of the invention, in which:

[0011] - Figure 1 is a schematic side view of a fluidized bed reactor according to the present invention;

[0012] - Figure 2 yes Figure 1 A partial plan view of the site with some details removed for clarity;

[0013] - Figure 3 yes Figure 1 A partial side cross-sectional view of a fluidized bed reactor;

[0014] - Figure 4 yes Figure 3 A front cross-sectional view of a detail;

[0015] - Figure 5 yes Figure 4 A side cross-sectional view of a detail. DETAILED DESCRIPTION

[0016] exist Figure 1 , numeral 1 as a whole denotes a fluidized bed reactor for gas phase polymerization of olefins. The fluidized bed reactor 1 has an inner chamber 2, which in turn has at least one lower portion 3 and at least one upper portion 4. The fluidized bed reactor 1 comprises: at least one side wall 5 having an inner surface 6, which laterally (at least partially) delimits the inner chamber 2; a gas distribution grid 7, which is located in the inner chamber 2 and (at least partially) separates the lower portion 3 from the upper portion 4; and a gas recirculation line 8, which has a first end 9 connected to the inner chamber 2 at the upper portion 4 and a second end 10 connected to the inner chamber 2 at the lower portion 3.

[0017] In particular, the olefins that can be polymerized in the fluidized bed reactor of the present disclosure are especially 1-olefins, i.e. hydrocarbons with terminal double bonds, but are not limited thereto. Non-polar olefin compounds are preferred. Particularly preferred 1-olefins are linear or branched C2 to C 12-1-olefins, especially linear C2 to C 10 -1-olefins, such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, or branched C2 to C 10 -1-olefins, such as 4-methyl-1-pentene, conjugated and non-conjugated dienes, such as 1,3-butadiene, 1,4-hexadiene or 1,7-octadiene. It is also possible to polymerize a mixture of various 1-olefins. Suitable olefins also include olefins in which the double bond is part of a cyclic structure that may have one or more ring systems. Examples are cyclopentene, norbornene, tetracyclododecene or methyl norbornene or dienes, such as 5-ethylidene-2-norbornene, norbornadiene or ethylnorbornadiene. It is also possible to polymerize a mixture of two or more olefins.

[0018] In this article, “C x -C y ” refers to groups and / or compounds having x to y carbon atoms.

[0019] The fluidized bed reactor 1 is particularly suitable for homopolymerization or copolymerization of ethylene or propylene, and is particularly preferably used for homopolymerization or copolymerization of ethylene. Preferred comonomers in propylene polymerization are ethylene, 1-butene and / or 1-hexene at most 40 wt %, preferably ethylene, 1-butene and / or 1-hexene from 0.5 wt % to 35 wt %. As comonomers in ethylene polymerization, preferably use C3 to C8-1-olefins at most 20 wt %, more preferably from 0.01 wt % to 15 wt %, and especially from 0.05 wt % to 12 wt %, particularly 1-butene, 1-pentene, 1-hexene and / or 1-octene. Particularly preferably is the polymerization of ethylene copolymerized with 1-hexene and / or 1-butene from 0.1 wt % to 12 wt %.

[0020] In an advantageous but non-limiting embodiment of the present disclosure, polymerization is carried out in the presence of an inert gas such as nitrogen or an alkane (such as methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane or n-hexane or a mixture thereof) having from 1 to 10 carbon atoms. It is advantageous to use nitrogen or propane as an inert gas, if appropriate, in combination with another alkane. In an especially advantageous embodiment of the present disclosure, polymerization is carried out in the presence of C3 to C5 alkanes as a polymerization diluent and most preferably in the presence of propane, particularly in the case of homopolymerization or copolymerization of ethylene. The reaction gas mixture in the reactor additionally includes olefins to be polymerized, i.e., main monomers and one or more optional comonomers. In an advantageous embodiment of the present disclosure, the reaction gas mixture has an inert component content of from 30% by volume to 99% by volume, particularly from 40% by volume to 95% by volume, and especially from 45% by volume to 85% by volume. In another advantageous embodiment of the present disclosure, particularly if the main monomer is propylene, no or only a small amount of inert diluent is added. The reaction gas mixture may also comprise additional components, such as antistatic agents or molecular weight regulators, such as hydrogen. The components of the reaction gas mixture may be fed into the gas phase polymerization reactor or the recycle gas line in gaseous form or as liquids and then evaporated within the reactor or the recycle gas line.

[0021] According to some non-limiting embodiments, all conventional olefin polymerization catalysts are used to carry out the polymerization of olefins. This means, for example, that a Phillips catalyst based on chromium oxide can be used, a Ziegler catalyst or a Ziegler-Natta catalyst can be used, or a single-site catalyst can be used to carry out polymerization. For the purposes of this disclosure, a single-site catalyst is a catalyst based on a chemically uniform transition metal coordination compound. In addition, a mixture of two or more of these catalysts can also be used for the polymerization of olefins. This mixed catalyst is generally referred to as a composite catalyst. The preparation and use of these catalysts for olefin polymerization are generally known.

[0022] Advantageous examples of Ziegler-type catalysts comprise a titanium or vanadium compound, a magnesium compound and optionally an electron donor compound and / or a particulate inorganic oxide as support material.

[0023] Ziegler-type catalysts are usually used in the presence of a cocatalyst. Examples of cocatalysts are organometallic compounds of metals of Groups 1, 2, 12, 13 or 14 of the Periodic Table, in particular organometallic compounds of metals of Group 13, and especially organoaluminium compounds. Preferred cocatalysts are, for example, organometallic alkyls, organometallic alkoxides or organometallic halides.

[0024] Advantageous examples of organometallic compounds include alkyl lithium, alkyl magnesium or alkyl zinc, alkyl magnesium halides, alkyl aluminum, alkyl silicon, silicon alkoxides and alkyl silicon halides. More advantageously, the organometallic compound includes alkyl aluminum and alkyl magnesium. Even more advantageously, the organometallic compound includes alkyl aluminum, most advantageously trialkyl aluminum compounds or compounds of this type in which the alkyl group is replaced by a halogen atom such as chlorine or bromine. Examples of such alkyl aluminums are trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, tri-n-hexyl aluminum or diethyl aluminum chloride or mixtures thereof.

[0025] According to some non-limiting embodiments, the fluidized bed reactor of the present disclosure is operated at a pressure of 0.5 MPa to 10 MPa, advantageously from 1.0 MPa to 8 MPa, and particularly at a pressure of 1.5 MPa to 4 MPa. The polymerization is advantageously, but not necessarily, carried out at a temperature of 30° C. to 60° C., particularly advantageously at a temperature of 65° C. to 125° C., and temperatures in the upper half of this range are preferably used to prepare ethylene copolymers with relatively high density, and temperatures in the lower half of this range are preferably used to prepare ethylene copolymers with lower density.

[0026] According to some non-limiting embodiments, the polymerization in the fluidized bed reactor can also be carried out in a condensing or supercondensing mode, wherein a portion of the recycled reaction gas mixture is cooled below the dew point and returned to the reactor as a liquid phase and a gas phase, respectively, or together as a two-phase mixture, in order to additionally utilize the evaporation enthalpy for cooling the reaction gas.

[0027] See Figure 1 , a gas recycle line 8 is configured to feed a fluidizing gas to the lower portion 3 of the inner chamber 2, the fluidizing gas comprising a recycle portion (taken from the inner chamber 2) and fresh olefin monomer (added along the gas recycle line 8).

[0028] Specific reference Figure 2 The gas distribution grid 7 includes a plurality of openings configured to allow fluidizing gas to pass from the lower portion 3 of the inner chamber 2 to the upper portion 4, and includes a plurality of first openings 11 located at a distance greater than 30 mm (particularly greater than 40 mm; more particularly greater than 80 mm) from the inner surface 6 of the side wall 5 and a plurality of second openings 11' located at a distance less than 30 mm (particularly less than 20 mm; more particularly less than 5 mm) from the inner surface 6 of the side wall 5.

[0029] By this means, it was experimentally found that the formation of polymer agglomerates inside the lower portion 3, in particular in the area between the peripheral edge of the grid 7 and the side wall 5, is reduced.

[0030] Advantageously, but not necessarily, the fluidized bed reactor 1 comprises lateral supports 12 extending along the inner surface 6 (in the form of an annular ring) and in contact with the inner surface 6 (and at least partially supporting the gas distribution grid 7). The gas distribution grid 7 has a peripheral edge 13, which is (at least) partially arranged on (in particular resting on) the lateral supports 12 and in contact with the lateral supports. The lateral supports 12 have holes 14, each hole is located below the corresponding second opening 11' and is configured to allow the fluidizing gas to pass from the lower part 3 to the upper part 4 of the inner chamber 2 through the corresponding second opening 11'. This ensures that the grid 7 has sufficient mechanical stability while not hindering the passage through the openings.

[0031] According to some non-limiting embodiments, the width of the lateral support 12 (measured from the inner surface 6 to the center of the inner chamber 2) is at least 2 cm (especially at least 3 cm). More precisely, but not necessarily, such a width (measured from the inner surface 6 to the center of the inner chamber 2) does not exceed 6 cm (especially, does not exceed 4 cm).

[0032] Please note that Figure 2 In FIG. 1 , only a portion (approximately half) of the grille 7 is depicted in order to better show the structure of the lateral support 12 .

[0033] According to some non-limiting embodiments, the hole 14 is at least as large as the opening. In particular, the length of the hole 14 is at least 40 mm (particularly at least 50 mm; more particularly at least 70 mm; particularly no more than 200 mm; more particularly no more than 150 mm; more particularly no more than 100 mm).

[0034] Advantageously, but not necessarily, the hole 14 is a complete interruption (gap) of the lateral support 12. In other words, the hole 14 opens towards the centre (not defined) of the internal chamber 2. More precisely, but not necessarily, the lateral support 12 is not present at all at the hole 14, nor even partially at the hole (a first section of the lateral support 12 ends just upstream / before the hole 14 and a second section of the lateral support begins just downstream / after this hole 14).

[0035] According to some non-limiting embodiments, the openings are formed such that the flow of the fluidizing gas after passing through the openings is substantially parallel to the plane of the gas distribution grid 7 (particularly tangential to the gas distribution grid 7; more particularly substantially horizontal).

[0036] Advantageously, but not necessarily, the opening is a slot. According to some non-limiting embodiments, the width of the slot (opening) is greater than its height (particularly greater than twice its height).

[0037] In particular, the width of the opening is at least 3 mm (in particular, the width is in a direction from the inner surface 6 towards the center of the inner chamber 2). Additionally or alternatively, the width of the opening is at most 10 cm (in particular, the width is at most 5 cm).

[0038] More precisely, but without limitation, the opening is made in the manner disclosed in patent application WO2008074632 of the same applicant.

[0039] Advantageously, but not necessarily, the number of the openings is at least 10 (particularly, at least 100).

[0040] In some non-limiting cases, the openings include a group of openings aligned with each other (particularly radially aligned with respect to the axis of the inner chamber 2). In other words, a group of openings are aligned with each other (radially aligned with respect to the axis of the inner chamber 2).

[0041] In some non-limiting embodiments, the fluidized bed reactor 1 includes: an upper wall 15 that defines the top of the inner chamber 2 and is connected to the side wall 5; and a lower wall 16 that defines the bottom of the inner chamber 2 and is connected to the side wall 5.

[0042] According to some non-limiting (and not shown) embodiments, the gas recirculation line 8 is configured to convey a recirculated portion of the fluidizing gas from the upper portion 4 of the inner chamber 2 through the upper wall 15 and to convey the fluidizing gas through the side walls 5 to the lower portion 4 .

[0043] According to some non-limiting embodiments, the fluidized bed reactor 1 further includes a polymer discharge pipe 17 including an upper opening 18 integrated into the gas distribution grid 7. In particular, the upper opening 18 of the polymer discharge pipe 17 is arranged at the center of the gas distribution grid 7. More particularly, the polymer discharge pipe 17 is configured to discharge the polymer produced inside the upper part 4.

[0044] According to some non-limiting embodiments, the discharge pipe 17 includes a regulating device 21, such as a discharge valve, which is configured to adjust the mass flow rate of the polymer discharged from the reactor 1. The opening of the regulating device 21 can be continuously adjusted to maintain a constant height of the fluidized polymer bed in the reactor.

[0045] The discharge pipe 17 may be made with a uniform diameter, but preferably comprises more sections with decreasing diameter in the downward direction. Figure 1 As shown, the adjustment device 21 is preferably placed in the restricted area between the larger diameter portion and the smaller diameter portion.

[0046] As an alternative, an exhaust system is disclosed in patent application Wo2007071527A1 of the same applicant.

[0047] In a specific and non-limiting case, the gas recirculation line 8 is provided with (a compressor 19 and) a heat exchanger 20 configured to reduce the heat of the recirculation portion.

[0048] Advantageously but not necessarily, the recycle line 8 is provided with a supplementary line 22 for feeding (particularly to the main pipe 23 of the recycle line 8) fresh olefin monomer, molecular weight regulator and optional inert gas (as well as antistatic agent, mileage improver, etc.). More precisely but not necessarily, the supplementary line 22 is configured to feed fresh olefin monomer, molecular weight regulator and optional inert gas (as well as antistatic agent, mileage improver, etc.) from the upstream of the heat exchanger 20 (particularly between the upper part 4 and the compressor 19; more particularly upstream of the compressor 19).

[0049] According to some non-limiting embodiments, the gas distribution grid 7 has a side surface substantially in the form of a truncated cone (and an inverted cone).

[0050] Patent application Wo2008074632 of the same applicant provides more detailed information about the fluidized bed reactor 1 and its operating principle.

[0051] According to another aspect of the present invention, there is also provided a method for preparing olefin polymers, which comprises homopolymerizing olefins or copolymerizing olefins with one or more other olefins in the presence of a polymerization catalyst (in particular, at a temperature of 20°C to 200°C; in particular, at a pressure of 0.5MPa to 10MPa), wherein the polymerization is carried out in a fluidized bed reactor 1 as described above.

[0052] According to some non-limiting embodiments, the fluidized bed reactor 1 includes a polymer discharge pipe 17 through which the polymer is continuously discharged.

[0053] According to some non-limiting embodiments, polymerization conditions are the conditions conventionally adopted in the gas phase reactor for olefin polymerization, i.e., temperature is in the range of 60°C to 120°C, and pressure is in the range of 5 bar to 40 bar. Gas phase polymerization process can be combined with conventional techniques operated in slurry, bulk or gas phase to carry out continuous multi-stage polymerization process. Therefore, upstream or downstream of the polymerization reactor of the present disclosure, one or more polymerization stages operated in a loop reactor, or a conventional fluidized bed reactor, or a stirred bed reactor can be provided. In particular, the gas phase polymerization reactor with interconnected polymerization zones as described in EP 782 587 and EP 1012195 can be advantageously arranged upstream or downstream of the equipment of the present invention.

[0054] The gas phase polymerization process allows the preparation of large quantities of olefin powders with an optimal particle size distribution and a low fines content. The [α]-olefins which are advantageously polymerized by the process of the invention have the formula CH2=CHR, wherein R is hydrogen or a hydrocarbon radical having 1 to 12 carbon atoms. Examples of polymers which can be obtained are:

[0055] High-density polyethylene (HDPE with a relative density above 0.940), including homopolymers and copolymers of ethylene with [α]-olefins having 3 to 12 carbon atoms;

[0056] Low density linear polyethylene (LLDPE with a relative density below 0.940) and very low density and ultra low density linear polyethylene (VLDPE and ULDPE with a relative density below 0.920 to 0.880) consisting of copolymers of ethylene with one or more [alpha]-olefins having 3 to 12 carbon atoms; elastomeric terpolymers of ethylene and propylene with small amounts of dienes, or elastomeric copolymers of ethylene and propylene in which the content of ethylene-derived units is from about 30% to 70% by weight;

[0057] Isotactic polypropylene and crystalline copolymers of propylene with ethylene and / or other [α]-olefins, wherein the content of propylene-derived units exceeds 85% by weight;

[0058] Isotactic copolymers of propylene and [α]-olefins (e.g. 1-butene), wherein the [α]-olefin content does not exceed 30% (by weight); impact propylene polymers prepared by the sequential polymerization of propylene and a mixture of propylene and ethylene (wherein the ethylene content does not exceed 30% (by weight));

[0059] Random polypropylene and amorphous copolymers of propylene with ethylene and / or other [α]-olefins, wherein the content of propylene-derived units exceeds 70% by weight.

[0060] The gas phase polymerization process described herein is not limited to the use of any particular series of polymerization catalysts. The process can be implemented in any exothermic polymerization reaction using any catalyst, whether it is supported or unsupported, and whether it is in prepolymerized form or not.

[0061] The polymerization reaction can be carried out in the presence of a highly active catalytic system (eg Ziegler-Natta catalyst, single-site catalyst, chromium-based catalyst, vanadium-based catalyst).

[0062] Unless otherwise expressly stated, the contents of the references (articles, books, patent applications, etc.) cited herein are all cited in their entirety herein. In particular, the above references are incorporated herein by reference.

Claims

1. A fluidized bed reactor for gas phase polymerization of olefins; the fluidized bed reactor (1) having an inner chamber (2), the inner chamber having at least one lower part (3) and at least one upper part (4); The fluidized bed reactor (1) comprises: at least one side wall (5) having an inner surface (6) which at least partially laterally delimits the inner chamber (2); a gas distribution grid (7) located in the inner chamber (2) and at least partially separating the lower part (3) from the upper part (4); and a recirculation line (8) having a first end (9) connected to the inner chamber (2) at the upper part (4) of the inner chamber (2) and a second end (10) connected to the inner chamber (2) at the lower part (3) of the inner chamber (2); the recycle line (8) being configured to feed a fluidizing gas into the lower portion (3) of the inner chamber (2), the fluidizing gas comprising recycled unreacted and / or partially reacted olefin monomer and fresh olefin monomer; The gas distribution grid (7) comprises a plurality of openings configured to allow the fluidizing gas to pass from the lower portion (3) to the upper portion (4) of the inner chamber (2); The openings include a plurality of first openings (11) located more than 30 mm from the inner surface (6) of the side wall (5), and a plurality of second openings (11') located less than 30 mm from the inner surface (6) of the side wall (5).

2. The fluidized bed reactor according to claim 1, wherein the second opening (11') is less than 20 mm from the side wall (5).

3. The fluidized bed reactor according to claim 1, wherein the second opening (11') is less than 5 mm from the side wall (5).

4. A fluidized bed reactor according to any one of the preceding claims, comprising lateral supports (12) extending along and in contact with the inner surface (6); The gas distribution grid (7) has a peripheral edge (13) which is at least partially in contact with the lateral support (12); the lateral support (12) has holes (14), each hole is located at a corresponding second opening (11') and is configured to allow the fluidizing gas to pass from the lower part (3) to the upper part (4) of the inner chamber (2) through the corresponding second opening (11').

5. Fluidized bed reactor according to claim 4, wherein the hole (14) is a complete interruption of the lateral support (12) and in particular has a length of at least 40 mm.

6. A fluidized bed reactor according to any one of the preceding claims, wherein the openings are formed so that the flow of the fluidizing gas after passing through the openings is substantially parallel to the plane of the gas distribution grid (7).

7. A fluidized bed reactor according to any one of the preceding claims, wherein the openings are slots and have a width of at least 3 mm.

8. The fluidized bed reactor according to any one of the preceding claims, wherein the width of the opening is at most 10 cm and the number of the openings is at least 10 (in particular, at least 100).

9. A fluidized bed reactor according to any one of the preceding claims, comprising an upper wall (15), which defines the top of the inner chamber (2) and is connected to the side wall (5); and a lower wall (16), which defines the bottom of the inner chamber (2) and is connected to the side wall (5); the recirculation line (8) is configured to transport the recirculated portion of the fluidizing gas from the upper part (4) of the inner chamber (2) through the upper wall (15) to the lower part (3), and to transport the fluidizing gas to the lower part.

10. A fluidized bed reactor according to any one of the preceding claims, further comprising a polymer discharge pipe (17) comprising an upper opening (18) integrated into the gas distribution grid (7).

11. Fluidized bed reactor according to any of the preceding claims, wherein the recirculation line (8) is provided with a heat exchanger (20) which is configured to reduce the heat of the recirculation portion.

12. A fluidized bed reactor according to any one of the preceding claims, wherein the gas distribution grid (7) is substantially in the shape of a truncated cone side surface.

13. A process for preparing olefin polymers, the process comprising homopolymerizing olefins or copolymerizing olefins with one or more other olefins in the presence of a polymerization catalyst, wherein the polymerization is carried out in a fluidized bed reactor (1) according to any one of claims 1 to 12.

14. The method according to claim 13, wherein the fluidized bed reactor (1) comprises a polymer discharge pipe (17) through which the polymer is continuously discharged.

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