Fluidized bed reactor for gas phase polymerization of olefins

Abstract

A fluidized bed reactor for the gas-phase polymerization of olefins, comprising: a fluidized bed reactor (1) having an inner chamber (2) having, in order, at least one lower section (3) and at least one upper section (4); a gas distribution grid (7) located in the inner chamber (2) and at least partially separating the lower section (3) from the upper section (4); and a recycle line (8) configured to supply fluidizing gas to the lower section (3) and having a first end (9) connected to the inner chamber (2) at the upper section (4); The gas distribution grid (7) comprises a plurality of openings (11') configured to allow the passage of fluidizing gas, the plurality of openings (11') being located less than 30 mm from the inner surface (6) of the lateral wall (5).

Description

[Technical Field]

[0001] The present invention relates to a fluidized bed reactor for the gas phase polymerization of olefins and to a process for the preparation of olefin polymers. [Background technology]

[0002] Gas-phase polymerization processes are economical processes for preparing polyolefins, such as ethylene or propylene homopolymers or copolymers of ethylene or propylene with other olefins. Fluidized-bed reactors for carrying out such processes have long been known. These reactors contain a bed of polymer particles maintained in a fluidized state by the upward flow of a fluidizing gas. Typical reactors include a reactor space in the form of a vertical cylindrical interior. These reactors have a cooler to remove the heat of polymerization, a recycle gas compressor, and, if desired, a recycle gas line equipped with components such as a cyclone to remove fine polymer dust. Monomer consumed by the polymerization reaction is usually replaced by adding make-up gas to the recycle gas stream.

[0003] To ensure a homogeneous distribution of the fluidizing gas in the bed of growing polymer particles, the reactor is fitted with a gas distribution grid, sometimes called a gas fluidization grid or distribution plate. Such a gas distribution grid is a device with openings that distribute the gas flow introduced below the grid to the bed. The grid also serves as a support for the bed when the gas supply is stopped.

[0004] The gas distribution grid can be configured as a perforated or porous plate and may be combined with an upstream flow divider. For example, a roof-like defractor plate can be placed over the openings in the distributor plate, as disclosed in EP 0 697 421 A1, or the openings can be covered with caps, as described in EP 0 600 414 A1. The shape of the gas distribution grid can also differ from that of the plate. EP 0 088 638 A2 discloses a gas distributor for a fluidized bed reactor having a double cone. WO 2008 / 074632 A1 describes a gas distribution grid having an inverted cone shape. Due to the large amount of circulating fluidizing gas and the resulting large size of the gas inlet nozzle, a relatively large volume is required below the gas distribution grid.

[0005] Over time, fines present in the fluidizing gas can accumulate in the space below the reactor grid. These reactive fines can form polymer agglomerates in a stagnant state and eventually block the grid openings, thereby jeopardizing the operability and reliability of the reactor system.

[0006] Therefore, there is a need to provide a fluidized bed reactor in which the fine polymer particles carried by the fluidizing gas can be easily returned to the fluidized bed of polymer particles.

[0007] The object of the present invention is to provide a fluidized bed reactor and a process for the preparation of olefin polymers which is able to at least partially overcome the drawbacks of the known art and which is at the same time simple and inexpensive to implement. Summary of the Invention

[0008] According to the present invention there is provided a fluidized bed reactor and a process for the preparation of olefin polymers according to the accompanying independent claims, preferably according to any claim that depends directly or indirectly on the independent claims. [Brief explanation of the drawings]

[0009] The invention will now be described with reference to the accompanying drawings, which show non-limiting embodiments thereof.

[0010] [Figure 1] FIG. 1 is a schematic diagram and side view of a fluidized bed reactor according to the present invention. [Figure 2] FIG. 2 is a plan view of a portion of FIG. 1 with some of the details removed for clarity. [Figure 3] FIG. 3 is a cross-sectional view of a portion of the fluidized bed reactor of FIG. [Figure 4] FIG. 4 is a cross-sectional front view of a detail of FIG. [Figure 5] FIG. 5 is a cross-sectional view of a detail of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] In Figure 1, the numeral 1 generally designates a fluidized-bed reactor for the gas-phase polymerization of olefins. The fluidized-bed reactor 1 has an inner chamber 2, which has at least one lower section 3 and at least one upper section 4. The fluidized-bed reactor 1 comprises at least one lateral wall 5 having an inner surface 6 that laterally defines (at least partially) the inner chamber 2, a gas distribution grid 7 located within the inner chamber 2 and separating (at least partially) the lower section 3 from the upper section 4, and a gas recycle line 8 having a first end 9 connected to the inner chamber 2 at the upper section 4 and a second end 10 connected to the inner chamber 2 at the lower section 3.

[0012] In particular, the olefins that can be polymerized in the fluidized bed reactor of the present disclosure are specifically, but not limited to, 1-olefins, i.e., hydrocarbons with terminal double bonds. Non-polar olefin compounds are preferred. Particularly preferred 1-olefins are linear or branched C2-C 12 -1-Alkenes, especially linear or branched C2-C, such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, and 1-decene 10 -Linear or branched C2-C, such as 1-alkene or 4-methylpentene 101-alkenes; conjugated and non-conjugated dienes such as 1,3-butadiene, 1,4-hexene, and 1,7-octene. Mixtures of various 1-olefins can also be polymerized. Suitable olefins also include those in which the double bond is part of a cyclic structure, which may have one or more ring systems. For example, cyclopentene, norbornene, tetracyclododecene, or methylnorbornene, or dienes such as 5-ethylidene-2-norbornene, norbornadiene, or ethylnorbornadiene. Mixtures of two or more olefins can also be polymerized.

[0013] In this document, "C x -C y " means groups and / or compounds having x to y carbon atoms.

[0014] This fluidized-bed reactor 1 is particularly suitable for the homopolymerization or copolymerization of ethylene or propylene, and is particularly suitable for the homopolymerization or copolymerization of ethylene. Preferred comonomers for propylene polymerization are 40% by weight or less of ethylene, 1-butene, and / or 1-hexene, and preferably 0.5 to 35% by weight of ethylene, 1-butene, and / or 1-hexene. As comonomers for ethylene polymerization, it is preferred to use C3-C8-1-alkene, particularly 1-butene, 1-pentene, 1-hexene, and / or 1-octene, in an amount of 20% by weight or less, more preferably 0.01 to 15% by weight, and particularly 0.05 to 12% by weight. Particularly preferred is copolymerization of ethylene with 0.1 to 12% by weight of 1-hexene and / or 1-butene.

[0015] In an advantageous, non-limiting embodiment of the present disclosure, the polymerization is carried out in the presence of an inert gas such as nitrogen, or an alkane having 1 to 10 carbon atoms, such as methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, or n-hexane, or a mixture thereof. Nitrogen gas or propane is preferably used as the inert gas, and an alkane can be advantageously used in combination. In a particularly preferred embodiment of the present disclosure, the polymerization is carried out in the presence of a C3-C5 alkane as a polymerization diluent, and most advantageously in the case of ethylene homopolymerization or copolymerization, propane is most advantageous. The reaction gas mixture in the reactor further comprises the olefin to be polymerized, i.e., the main monomer, and one or more optional comonomers. In an advantageous embodiment of the present disclosure, the reaction gas mixture has an inert component content of 30 to 99% by volume, particularly 40 to 95% by volume, and particularly 45 to 85% by volume. In another advantageous embodiment of the present disclosure, particularly when the main monomer is propylene, no inert diluent is added, or only a small amount is added. The reaction gas mixture may further include additional components such as antistatic agents or molecular weight regulators, such as hydrogen gas. The components of the reaction gas mixture may be fed to the gas-phase polymerization reactor or recycle gas line in gaseous or liquid form and then vaporized within the reactor or recycle gas line.

[0016] According to some non-limiting examples, olefin polymerization can be carried out using any commonly used olefin polymerization catalyst. That is, for example, chromium oxide-based Phillips catalysts, Ziegler or Ziegler-Natta catalysts, or single-site catalysts can be used. For purposes of this disclosure, a single-site catalyst is a catalyst based on a chemically uniform transition metal coordination compound. Furthermore, it is also possible to use a mixture of two or more of these catalysts in the polymerization of olefins. Such mixed catalysts are often referred to as hybrid catalysts. The preparation and use of these olefin polymerization catalysts is generally known.

[0017] Advantageous examples of Ziegler-type catalysts preferably contain a titanium or vanadium compound, a magnesium compound, and optionally an electron donor compound and / or a particulate inorganic oxide as support material.

[0018] Ziegler-type catalysts are usually used in the presence of a cocatalyst. Examples of the cocatalyst include organometallic compounds of metals in Groups 1, 2, 12, 13, or 14 of the Periodic Table, especially organometallic compounds of metals in Group 13, especially organoaluminum compounds. Preferred cocatalysts are, for example, organometallic alkyls, organometallic alkoxides, or organometallic halides.

[0019] Advantageous examples of organometallic compounds include lithium alkyls, magnesium or zinc alkyls, magnesium alkyl halides, aluminum alkyls, silicon alkyls, silicon alkoxides, and silicon alkyl halides. More advantageously, the organometallic compounds include aluminum alkyls and magnesium alkyls. Even more advantageously, the organometallic compounds include aluminum alkyls, most advantageously trialkylaluminum compounds, or compounds of this type in which the alkyl group is replaced with a halogen atom, such as chlorine or bromine. Examples of such aluminum alkyls include trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, diethylaluminum chloride, or mixtures thereof.

[0020] 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 1.0 MPa to 8 MPa, and particularly 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 65° C. to 125° C., with temperatures in the upper part of this range being preferred for preparing ethylene copolymers with relatively high density and temperatures in the lower part of this range being preferred for preparing ethylene copolymers with low density.

[0021] According to some non-limiting embodiments, polymerization in a fluidized bed reactor is carried out in a condensed or hypercondensed mode, in which a portion of the circulating reaction gas mixture is cooled below the dew point and returned to the reactor as liquid and gas phases, respectively, or together as a two-phase mixture, further utilizing the enthalpy of vaporization to cool the reaction gas.

[0022] With particular reference to FIG. 1 , gas recycle line 8 is configured to supply fluidizing gas comprising a recycle portion (removed from inner chamber 2) and fresh olefin monomer (added along gas recycle line 8) to lower portion 3 of inner chamber 2.

[0023] With particular reference to Figure 2, the gas distribution grid 7 has a plurality of openings configured to allow the passage of fluidizing gas from the lower portion 3 to the upper portion 4 of the inner chamber 2, and includes a plurality of first openings 11 located more than 30 mm (particularly more than 40 mm, more particularly more than 80 mm) from the inner surface 6 of the lateral wall 5, and second openings 11' located less than 30 mm (particularly less than 20 mm, more particularly less than 5 mm) from the inner surface 6 of the lateral wall 5.

[0024] In this way, it has been surprisingly confirmed by experiments that the growth of polymer agglomerates inside the lower part 3 (in particular in the region between the peripheral edge of the grid 7 and the lateral wall 5) is reduced.

[0025] Advantageously, but not necessarily, the fluidized bed reactor 1 comprises lateral supports 12 extending (loop-shaped) along and in contact with the inner surface 6 (and at least partially supporting the gas distribution grid 7). The gas distribution grid 7 is (at least) partially arranged on (in particular rests on) the lateral supports 12 and has a peripheral edge 13 in contact with the lateral supports 12. The lateral supports 12 have apertures 14, each of which is located below a corresponding second opening 11' and is configured to allow passage of the fluidizing gas from the lower part 3 to the upper part 4 of the inner chamber 2 through the corresponding second opening 11'. This ensures sufficient mechanical stability of the grid 7 without at the same time hindering passage through the openings.

[0026] According to some non-limiting embodiments, the lateral support 12 has a width (measured from the inner surface 6 towards the centre of the chamber 2) of at least 2 cm (in particular at least 3 cm). More precisely, but not necessarily, such width (measured from the inner surface 6 towards the centre of the chamber 2) is at most 6 cm (in particular at most 4 cm).

[0027] It should be noted that in FIG. 2 only a portion (approximately half) of the grid 7 is depicted in order to better show the structure of the lateral supports 12 .

[0028] According to some non-limiting embodiments, aperture 14 is at least as large as the opening. In particular, aperture 14 has a length of at least 40 mm (in particular at least 50 mm, more particularly at least 70 mm, particularly at most 200 mm, more particularly at most 150 mm, and even more particularly at most 100 mm).

[0029] Advantageously, but not necessarily, the aperture 14 is a complete separation (gap) of the transverse supports 12. In other words, the aperture 14 is open towards the centre of the inner chamber 2, i.e. it is not delimited. More precisely, but not necessarily, the transverse supports 12 are not entirely or even partially absent from the aperture 14 (a first extension of the transverse supports 12 ends just upstream (before) the aperture 14, and a second extension of the transverse supports 12 starts just downstream (after) such aperture 14).

[0030] According to some non-limiting embodiments, the openings are formed so that the flow of 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).

[0031] 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 (in particular, greater than twice its height).

[0032] In particular, the width of the opening is at least 3 mm (in particular, the width is in the 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, at most 5 cm).

[0033] More precisely, but without any limitation, the openings are made as disclosed in the applicant's patent application WO2008074632.

[0034] Advantageously, although not necessarily, there are at least 10 (in particular at least 100) openings.

[0035] In some non-limiting cases, the openings include a group of openings that are aligned one-to-one with respect to other openings (particularly radially with respect to the axis of the inner chamber 2). In other words, one group of openings is aligned one-to-one with respect to other groups of openings (radially with respect to the axis of the inner chamber 2).

[0036] 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 lateral wall 5, and a lower wall 16 that defines the bottom of the inner chamber 2 and is connected to the lateral wall 5.

[0037] According to some non-limiting (and not shown) embodiments, the gas recycle line 8 is configured to transport the recycled portion of the fluidizing gas from the upper portion 4 of the inner chamber 2 through the upper wall 15 and the fluidizing gas through the lateral wall 5 to the lower portion 4.

[0038] According to some non-limiting embodiments, the fluidized bed reactor 1 further comprises a polymer discharge pipe 17 having an upper opening 18 integrated with the gas distribution grid 7. In particular, the upper opening 18 of the polymer discharge pipe 17 is located at the center of the gas distribution grid 7. More specifically, the polymer discharge pipe 17 is configured to discharge the polymer produced in the upper portion 4.

[0039] According to some non-limiting embodiments, the discharge pipe 17 is equipped with a regulating means 21, such as a discharge valve, configured to regulate the mass flow rate of polymer discharged from the reactor 1. The opening of the regulating means 21 is continuously adjusted to maintain a constant height of the fluidized polymer bed in the reactor.

[0040] The discharge pipe 17 may be of uniform diameter, but preferably comprises a portion with a decreasing diameter in the downward direction. The adjusting means 21 is preferably located in the region of the restriction (at the restriction) between the larger and smaller diameter portions, as shown in Figure 1.

[0041] An alternative is a discharge system such as that disclosed in the applicant's patent application WO2007071527A1.

[0042] In a specific, non-limiting case, the gas recycle line 8 is provided with (a compressor 19 and) a heat exchanger 20 configured to reduce the heat of the recycle portion.

[0043] Advantageously, but not necessarily, the recycle line 8 is provided with a make-up line 22 for feeding fresh olefin monomer, molecular weight regulator and optionally inert gas (and antistatic agents, mobility improvers, etc.) to (in particular to the main pipe 23 of the recycle line 8). More precisely, but not necessarily, the make-up line 22 is configured to feed fresh olefin monomer, molecular weight regulator and optionally inert gas (and antistatic agents, mobility improvers, etc.) upstream of the heat exchanger 20 (in particular between the upper part 4 and the compressor 19, more particularly upstream of the compressor 19).

[0044] According to some non-limiting embodiments, the gas distribution grid 7 has substantially the form of the horizontal surface of a truncated (and inverted) cone.

[0045] Further details about the fluidized bed reactor 1 and its functioning method are given in the applicant's patent application WO2008074632.

[0046] According to a further aspect of the present invention, there is also provided herein a process for preparing an olefin polymer, comprising homopolymerizing an olefin or copolymerizing an olefin with one or more other olefins in the presence of a polymerization catalyst (particularly at a temperature of 20 to 200°C, particularly at a pressure of 0.5 to 10 MPa), wherein the polymerization is carried out in a fluidized bed reactor 1 as disclosed above.

[0047] According to some non-limiting embodiments, the fluidized bed reactor 1 is equipped with a polymer discharge pipe 17 through which the polymer is continuously discharged.

[0048] According to some non-limiting embodiments, polymerization conditions are those conventionally employed in gas-phase reactors for olefin polymerization, i.e., temperatures ranging from 60 to 120°C and pressures ranging from 5 to 40 bar. Gas-phase polymerization processes can be combined with conventional techniques operating in slurry, bulk, or gas phase to carry out continuous multistage polymerization processes. Thus, one or more polymerization stages operating in loop reactors, conventional fluidized-bed reactors, or stirred-bed reactors can be provided upstream or downstream of the polymerization reactor of the present disclosure. Specifically, gas-phase polymerization reactors with interconnected polymerization zones, such as those described in EP 782 587 and EP 1 012 195, can be advantageously located upstream or downstream of the apparatus of the present invention.

[0049] The gas phase polymerization process allows the preparation of a large number of olefin powders with optimal particle size distributions, including a small amount of fines. The α-olefins advantageously polymerized by the process of the present invention have the formula CH═CHR, where R is hydrogen or a hydrocarbon radical having 1 to 12 carbon atoms. Examples of the resulting polymers are as follows: High density polyethylene (HDPE having a relative density greater than 0.940) including ethylene homopolymers and ethylene copolymers with α-olefins having 3 to 12 carbon atoms; Low density (LLDPEs with a relative density of less than 0.940) and very low and ultra low density (VLDPEs and ULDPEs with a relative density of 0.880 to less than 0.920) linear polyethylenes composed of ethylene copolymers with one or more α-olefins having 3 to 12 carbon atoms; elastomeric terpolymers of ethylene and propylene with small proportions of dienes or elastomeric copolymers of ethylene and propylene with a content of units derived from ethylene of about 30 to 70% by weight; Isotactic polypropylene, a crystalline copolymer of propylene with ethylene and / or other α-olefins, having a content of units derived from propylene of more than 85% by weight; Isotactic copolymers of propylene and α-olefins, such as 1-butene, having an α-olefin content of up to 30% by weight; impact propylene polymers obtained by sequential polymerization of propylene and mixtures of propylene and ethylene containing up to 30% by weight of ethylene; Atactic polypropylene, an amorphous copolymer of propylene and other α-olefins containing more than 70% by weight of units derived from ethylene and / or propylene.

[0050] The gas phase polymerization process described herein is not limited to the use of any particular polymerization catalyst family, and can be carried out in any exothermic polymerization reaction using any catalyst, whether supported or unsupported, and whether in prepolymerized form or not.

[0051] The polymerization reaction can be carried out in the presence of a highly active catalyst system such as a Ziegler-Natta catalyst, a single-site catalyst, a chromium-based catalyst, or a vanadium-based catalyst.

[0052] Unless expressly stated otherwise, the contents of the references (articles, books, patent applications, etc.) cited in this document are incorporated herein in their entirety. In particular, the above-mentioned references are incorporated herein by reference.

Claims

1. A fluidized bed reactor for the gas-phase polymerization of olefins, comprising: an internal chamber (2) having, in order, at least one lower section (3) and at least one upper section (4); at least one transverse wall (5) having an inner surface (6) that at least partially defines the internal chamber (2) laterally; a gas distribution grid (7) located in the internal chamber (2) and at least partially separating the lower section (3) from the upper section (4); and a recycle line (8) having a first end (9) connected to the internal chamber (2) at the upper section (4) of the internal chamber (2) and a second end (10) connected to the internal chamber (2) at the lower section (3) of the internal chamber (2), the recycle line (8) is configured to supply a fluidizing gas containing recycled unreacted and / or partially reacted olefin monomer and fresh olefin monomer to the lower part (3) of the inner chamber (2); the gas distribution grid (7) comprises a plurality of openings configured to allow passage of the fluidizing gas from the lower part (3) to the upper part (4) of the inner chamber (2); The fluidized bed reactor, wherein the openings include a plurality of first openings (11) located more than 30 mm from the inner surface (6) of the lateral wall (5) and a plurality of second openings (11') located less than 30 mm from the inner surface (6) of the lateral wall (5).

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

3. 2. The fluidized bed reactor of claim 1, wherein the second opening (11') is located less than 5 mm from the lateral wall (5).

4. a lateral support (12) extending along and in contact with said inner surface (6); 10. The fluidized bed reactor according to claim 9, wherein the gas distribution grid (7) has a peripheral edge (13) arranged in at least partial contact with the lateral supports (12), the lateral supports (12) having apertures (14), each of the apertures (14) being arranged in a corresponding second opening (11') and configured to allow the fluidizing gas to pass through the corresponding second opening (11') from the lower part (3) to the upper part (4) of the inner chamber (2).

5. 5. A fluidized bed reactor according to claim 4, wherein the aperture (14) is a complete separator of the lateral supports (12) and in particular has a length of at least 40 mm.

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

7. 10. 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. 10. A fluidized bed reactor according to any one of the preceding claims, wherein the openings are at most 10 cm wide and there are at least 10 of them (in particular at least 100 of them).

9. 10. The fluidized bed reactor according to claim 9, further comprising an upper wall (15) defining the top of the inner chamber (2) and connected to the lateral wall (5), and a lower wall (16) defining the lower part of the inner chamber (2) and connected to the lateral wall (5), wherein the recycle line (8) is configured to convey the recycle portion of the fluidizing gas from the upper part (4) of the inner chamber (2) through the upper wall (15) and the fluidizing gas to the lower part (3).

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

11. 10. A fluidized bed reactor according to any one of the preceding claims, wherein the recycle line (8) is provided with a heat exchanger (20) configured to reduce the heat of the recycle section.

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

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

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

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