Gas Phase Polymerization Equipment

Abstract

An olefin gas-phase polymerization apparatus is provided, comprising a reactor including at least one polymerization zone, a recycle line for withdrawing a reaction gas from the reactor and returning it to the reactor, a compressor for transporting the reaction gas along the recycle line, and a heat exchanger for cooling the reaction gas, wherein at least a portion of an inner surface of the recycle line in contact with the reaction gas has a surface roughness Ra of less than 5 m.

Description

[Technical field]

[0001] The present disclosure provides an olefin gas phase polymerization apparatus. The present disclosure particularly provides an olefin gas phase polymerization apparatus, comprising a recirculation line having an inner surface in contact with a reaction gas having a surface roughness Ra of less than 5 m. The present disclosure also provides a process for producing an olefin polymer carried out in the apparatus. [Background technology]

[0002] Polyolefins are a class of polymers derived primarily from simple olefins such as ethylene and propylene. Despite more than 80 years of development, there is a high need for efficient, resource-saving processes to produce polyolefins.

[0003] Gas phase polymerization processes are economical processes for producing polyolefins. Suitable reactors for carrying out such gas phase polymerizations are, for example, fluidized bed reactors, stirred gas phase reactors, or multi-zone circulation reactors with two different gas phase polymerization zones connected to each other. These processes are usually carried out in a gas phase containing monomer and comonomer, and often also other gaseous components such as polymerization diluents, e.g. nitrogen or alkanes, or hydrogen as molecular weight regulators or low molecular weight reaction products. The resulting products are usually solid polyolefin particles formed by a polymerization catalyst system containing a particulate catalytic solid.

[0004] The olefin gas phase polymerization process is characterized in that a large volume of gas is removed from the reaction zone, passed through a heat exchanger to remove the heat of polymerization, and then returned to the polymerization zone. In a fluidized bed reactor, the returned reaction gas also serves to keep the polyolefin particles in a fluidized state. In a multi-zone circulating reactor, the circulation between the reactor zones is influenced by the returned reaction gas. To drive all these processes, the reaction gas recycle line is usually equipped with a centrifugal compressor.

[0005] One way to increase the efficiency of a production process is to improve the equipment used in production.

[0006] WO 2018 / 210780 A1 discloses a fluidized bed reactor for the gas phase polymerization of olefins, comprising a gas distribution grid installed at the bottom of the fluidized bed reactor, and a gas recirculation line including a compressor and a heat exchanger and connected at its upper end to the top of the fluidized bed reactor, the gas recirculation line being divided at its lower end into at least two substantially horizontal branches, the two branches being tangentially connected to the fluidized bed reactor at the bottom of the gas distribution grid. According to the teachings of WO 2018 / 210780 A1, the grid allows the polymer fines that may be carried by the recirculation gas to be easily returned to the fluidized bed of polymer fines.

[0007] WO 2008 / 074632 A1 relates to a gas distribution grid adapted to distribute an upward gas flow into a vessel containing a polymer under flow conditions. The gas distribution disclosed comprises a plurality of trays arranged to form the sidewall of an inverted cone, said plurality of trays being attached to one another to form slots in the overlapping areas of adjacent trays.

[0008] WO 2007 / 071527 A1 describes a gas-phase process for polymerizing one or more (-olefins) in a fluidized bed reactor in the presence of a polymerization catalyst. The fluidized bed reactor comprises a fluidization grid arranged at its bottom and an external device for recirculating and cooling unreacted gas from the top of the reactor to the fluidization grid, the process being characterized in that (i) the fluidization grid is connected to a circulation loop in the upper region of the fluidized bed reactor, thereby providing a continuous pneumatic recirculation of the polymer, and (ii) the polymer is continuously discharged from the region of the circulation loop where the polymer concentration is higher than the polymer concentration in the fluidized bed.

[0009] WO 2019 / 154756 A1 relates to a gas-phase polymerization reactor for the gas-phase polymerization of olefins comprising at least one polymerization zone including a recycle line for withdrawing reaction gas from the reactor, directing the reaction gas through a heat exchanger for cooling and returning it to the reactor, the recycle line comprising a heat exchanger, a centrifugal compressor comprising a variable guide vane and a butterfly valve, the variable guide vane being arranged upstream of the centrifugal compressor and the butterfly valve being arranged downstream of the centrifugal compressor.

[0010] US Patent Application 10,781,273 B2 discloses an apparatus and process for producing multimodal polyolefins, particularly polyethylene resins. Production is accomplished using two reactors connected in series, one reactor being a multi-zone circulation reactor capable of circulating polyolefin particles through two polymerization zones, one reactor configured to produce a first polyolefin and a second reactor configured to produce a second polyolefin, the second reactor configured to receive the first polyolefin from the first reactor, or the first reactor configured to receive the second polyolefin from the second reactor, the second reactor having an inner surface polished to a root mean square of less than about 150 microinches.

[0011] US 2015 / 0367319 A1 relates to a process for polymerizing olefin monomers in a loop reactor in the presence of a catalyst and a diluent to produce a slurry comprising a solid particulate olefin polymer and the diluent. During the polymerization process, the Biot number in the loop reactor is maintained at or below about 3.0. The slurry in the loop reactor forms a slurry film having a film coefficient along the inner surface of the reactor wall.

[0012] EP 2,602,269 A1 discloses a multi-stage process for olefin polymerization. Polyolefin particles are transferred from a first gas-phase polymerization reactor to a second gas-phase polymerization reactor. The first gas-phase reactor is a fluidized bed reactor comprising a gas distribution grid and a settling tube with an upper opening integrated into the distribution grid, containing a bed of polyolefin particles moving from the top to the bottom of the settling tube.

[0013] WO 2012 / 031986 A1 describes a gas-phase polymerization reactor having interconnected polymerization zones, including a riser through which polymer particles flow upward under fast fluidization or transport conditions. The reactor further includes a downcomer through which the polymer particles flow downward in dense form under the action of gravity, the bottom of the downcomer being connected to the lower region of the riser by a transport section. The transport section is designed to curve downward from the downcomer towards the riser.

[0014] A polymer stream transport process is disclosed in EP 2,110,173 A1. The disclosed process comprises heating a stream containing the polymer from a polymerization reactor to a separation zone or device. The stream passes through a heater comprising at least one transport line for the stream and a means for heating the transport line, and the average particle size of the solid polymer is less than 3 mm.

[0015] WO 2006 / 050919 A1 relates to an apparatus for the gas phase polymerization of olefins. The apparatus comprises a gas phase fluidized bed reactor and a recycle gas stream connected to the reactor for discharging and recycling the recycle gas. The apparatus also comprises a cyclone arranged in the recycle gas line for reducing and precipitating solid particles entrained in the recycle gas from the reactor. Summary of the Invention [Problem to be solved by the invention]

[0016] One of the problems in the gas phase polymerization of polyolefins is the presence of polymer particles in the circulating reaction gas, which may cause the accumulation of polymer particles to contaminate the equipment, and in extreme cases, may cause clogging of the equipment, especially the recirculation line. Therefore, it is necessary to provide a polyolefin production equipment that can circulate the reaction gas in the recirculation line without causing fouling even if polymer particles are present in the circulating reaction gas, and can minimize the effect of powder entrained in the circulating gas and reduce the risk of the powder adhering to the inner surface of the equipment.

[0017] The present disclosure provides an olefin gas phase polymerization apparatus, comprising: a reactor comprising at least one polymerization zone; a recycle line for withdrawing reaction gas from the reactor and for returning reaction gas to the reactor; a compressor for transporting the reaction gas along the recycle line; a heat exchanger for cooling the reaction gas, At least a portion of the inner surface of the recirculation line that comes into contact with the reaction gas has a surface roughness R determined in accordance with ASME B46.1. a is less than 5 m, preferably less than 3 m.

[0018] In some embodiments, at least a portion of the inner surface of the recirculation line has a surface roughness R determined in accordance with ASME B46.1. a but is made of stainless steel, less than 2.5m long, preferably less than 2m long.

[0019] In some embodiments, at least a portion of the inner surface of the recirculation line has a surface roughness R determined in accordance with ASME B46.1. a It is manufactured from low temperature carbon steel (LTCS) with a length of less than 3m.

[0020] In some embodiments, the device has no protrusions greater than 1.5 mm in height on the surfaces in contact with the reactant gas.

[0021] In some embodiments, any bend in the recirculation line satisfies the condition that the radius of the bend, r, is greater than 5 times the diameter of the recirculation line.

[0022] In some embodiments, the compressor is located upstream of the heat exchanger.

[0023] In some embodiments, the compressor has a surface roughness R determined in accordance with ASME B46.1. a It is an open type centrifugal compressor including an impeller that increases the pressure of the reaction gas below 3 m.

[0024] In some embodiments, the apparatus includes a variable guide vane disposed upstream of the compressor, the variable guide vane having a surface in contact with the reactant gas that has a surface roughness R determined in accordance with ASME B46.1. a is less than 3m.

[0025] In some embodiments, the apparatus further includes a butterfly valve disposed downstream of the heat exchanger, the butterfly valve having a surface in contact with the reactant gas having a surface roughness R determined in accordance with ASME B46.1. a > is less than 3m.

[0026] In some embodiments, the butterfly valve includes a rotating disk having an area smaller than the cross-section of the recirculation line at the location of the butterfly valve.

[0027] In some embodiments, the heat exchanger is a shell-and-tube heat exchanger including an inlet chamber, a tube bundle enclosed within a shell structure, and an outlet chamber, each tube including an inlet, a middle longitudinal section, and an outlet, and a diameter d1 of the inlet of each tube being greater than a diameter d2 of the corresponding middle longitudinal section of the tube.

[0028] In some embodiments, the reactor is a fluidized bed reactor comprising a fluidized bed of polyolefin particles and a fluidization grid disposed at the bottom of the reactor.

[0029] In some embodiments, the fluidization grid comprises a plurality of trays arranged to form the sidewall of an inverted cone, the plurality of trays arranged to form grooves in overlapping areas of adjacent trays, the trays having a surface roughness Ra of less than 3 m as determined in accordance with ASME B46.1.

[0030] In some embodiments, the overlapping area of ​​the first tray forms the top of the slot and the successive tray forms the bottom of the slot.

[0031] In some embodiments, the apparatus is a multi-zone circulation reactor, in which in the first polymerization zone, the grown polyolefin particles flow upward under fast fluidization or transport conditions, and in the second polymerization zone, the grown polyolefin particles flow downward in a compact form, the first polymerization zone and the second polymerization zone are connected to each other, the polyolefin particles leaving the first polymerization zone enter the second polymerization zone and the polyolefin particles leaving the second polymerization zone enter the first polymerization zone, and a circulation of the polyolefin particles through the first polymerization zone and the second polymerization zone is established.

[0032] In some embodiments, the device is part of a series of devices.

[0033] In another aspect, the present disclosure provides a process for producing an olefin polymer, comprising homopolymerizing an olefin or copolymerizing an olefin with one or more other olefins in the presence of a polymerization catalyst at a temperature of 20-200° C. and a pressure of 0.5-10 MPa, the process being carried out in an apparatus according to the present disclosure.

[0034] In some embodiments, the polymerization is a homopolymerization of ethylene or a copolymerization of ethylene with one or more other olefins selected from the group consisting of 1-butene, 1-hexene, and 1-octene; alternatively, the polymerization is a homopolymerization of propylene or a copolymerization of propylene with one or more other olefins selected from the group consisting of ethylene, 1-butene, and 1-hexene.

[0035] In some embodiments, the process is carried out with a reactant gas flow velocity between 5 m / s and 25 m / s, preferably between 15 m / s and 20 m / s.

[0036] In some embodiments, the flow velocity in the reactor is 0.3-1.5 m / s, preferably 0.5-1.2 m / s. [Brief description of the drawings]

[0037] [Figure 1] FIG. 1 shows a schematic diagram of an apparatus according to the present disclosure including a fluidized bed reactor for carrying out the process of the present disclosure. [Diagram 2] FIG. 2 shows a schematic of an apparatus according to the present disclosure including a multi-zone circulating reactor for carrying out the process of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] The present disclosure provides an olefin gas-phase polymerization apparatus comprising a reactor containing at least one polymerization zone, a recycle line for withdrawing reaction gas from the reactor and returning the reaction gas to the reactor, a compressor for transporting the reaction gas along the recycle line, and a heat exchanger for cooling the reaction gas. Such a reactor may be a fluidized bed reactor, a stirred gas-phase reactor, or a multi-zone circulation reactor having two different gas-phase polymerization zones connected to each other. These types of reactors are known to those skilled in the art. Agitated gas-phase reactors can be, for example, horizontally or vertically stirred. Preferred gas-phase polymerization reactors according to the present disclosure are fluidized bed reactors and multi-zone circulation reactors.

[0039] Olefins that can be polymerized in the device according to the present disclosure are particularly, but not limited to, 1-olefins, i.e., hydrocarbons with terminal double bonds. Non-polar olefinic compounds are preferred. Particularly preferred 1-olefins are linear or branched C 2 ~C 12-1-Alkenes, in particular linear or branched C such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, and 1-decene 2 ~C 10 -1-alkene or 4-methyl-pentene, etc. 2 -C 10 -1-alkenes; conjugated and non-conjugated dienes such as 1,3-butadiene, 1,4-hexene, 1,7-octene. Mixtures of different 1-olefins can also be polymerized. Suitable olefins also include olefins in which the double bond is part of a ring structure that 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. It is also possible to polymerize mixtures of two or more olefins.

[0040] This apparatus is particularly useful for the homopolymerization or copolymerization of ethylene or propylene, and is particularly suitable for the homopolymerization or copolymerization of ethylene. The preferred comonomers in propylene polymerization are up to 40% by weight of ethylene, 1-butene and / or 1-hexene, preferably 0.5% to 35% by weight of ethylene, 1-butene and / or 1-hexene. The comonomers in ethylene polymerization are C 3 ~C 8 20% by weight or less of 1-alkene, particularly 1-butene, 1-pentene, 1-hexene and / or 1-octene, more preferably 0.01% to 15% by weight, particularly 0.05% to 12% by weight, is used. Particularly preferred is copolymerization of ethylene with 0.1% to 12% by weight of 1-hexene and / or 1-butene.

[0041] The apparatus according to the present disclosure has a surface roughness R determined in accordance with ASME B46.1 on at least a portion, preferably the entire inner surface of the recirculation line that is in contact with the reaction gas. aThe length of the reaction gas is less than 5 m, preferably less than 3 m. In the apparatus according to the present disclosure, the compressor transports the reaction gas along the recycle line, so that the reaction gas is extracted from the reactor, passes through the heat exchanger, and is returned to the reactor, ensuring the circulation of the reaction gas. In such a configuration, it is not possible to completely avoid the entrainment of polymer particles in the circulating reaction gas. Surface roughness R a By designing the recirculation line with an inner surface of less than 5 m, it is possible to minimize the accumulation of polymer particles present in the recirculation line, reducing the risk of clogging the recirculation line and interrupting the production process.

[0042] If the surface roughness is less than 5 mm, it is possible to operate with continuous circulation of fine particles. Therefore, reliable gas-phase polymerization of olefins can be operated without the installation of a gas-solid separation device such as a cyclone. A gas / solid separation device may cause material loss because solid particles such as catalyst are removed from the device. Furthermore, such devices including a gas / solid separation device are not suitable for polymerization because small sized polymer particles may be carried out of the reactor and removed from the device by the gas / solid separation device. Thus, it is possible to install a recirculation line with a surface roughness of R a Providing an inner surface with a diameter of less than 5 m allows greater flexibility in the operation of the device. The head of the reactor generally has a wider inner diameter than the bottom to reduce the air velocity and to avoid introducing small particles into the recirculation line. Such reactors can still be applied to the device according to the present disclosure, but the reactor with the widened head is no longer required. The recirculation line of the above device has a low surface roughness, so that small particles flow through the recirculation line back into the reactor without adhering to the inner surface of the recirculation line. Thus, circulation of small particles through the recirculation line is possible, and the requirement to mitigate small particle entrainment in the recirculation line is reduced. In some embodiments, the recirculation line does not include a cyclone. In particular, the recirculation line may not include a cyclone upstream of the compressor and / or heat exchanger.

[0043] Surface roughness R as defined in this disclosureA can be accomplished, for example, by polishing, such as, for example, mechanical polishing or electrolytic polishing.

[0044] Preferably, the different components of the olefin gas phase polymerization apparatus, especially the recirculation line, are made of durable materials that do not interfere with the polymerization reaction and can withstand the high temperature and pressure reaction conditions. In a preferred embodiment, at least a part of the recirculation line and the equipment installed in the recirculation line, preferably the entire recirculation line and the equipment installed in the recirculation line, are made of steel, preferably stainless steel or low temperature carbon steel. In the case of stainless steel, the surface roughness R of the inner surface in contact with the reaction gas, determined according to ASME B46.1, is a In another preferred embodiment, the recirculation line and at least a part of the equipment installed in the recirculation line are manufactured from low temperature carbon steel (LTCS), and the inner surface of the low temperature carbon steel in contact with the reaction gas has a surface roughness R determined in accordance with ASME B46.1. a is less than 3m.

[0045] In addition to employing an inner surface of the recirculation line with a particularly low surface roughness, a further improvement in the flow is observed in the case of the present disclosure by keeping as small as possible the protrusions on any surfaces in contact with the reaction gas, such as protrusions on which elements from the polymerization apparatus are welded. Thus, in a preferred embodiment, the apparatus according to the present disclosure is characterized in that the surfaces in contact with the reaction gas have no protrusions with a height of more than 1.5 mm.

[0046] In particular, the recirculation line of the device according to the present disclosure is designed with the aim of preventing polymer fines from adhering to the inner surface and generating sheets or plugs that may initiate undesired polymerization and block the fluidization process over time. In this regard, it has also been found to be advantageous to avoid sharp bends and angles in the recirculation line. Therefore, the bends in the recirculation line should have a large diameter to reduce the wear of the recirculated polymer powder and limit the centrifugal forces on the walls. Surprisingly, it has been found that this aim can be achieved if the radius r of the bend in the recirculation line is larger than its diameter. In a preferred embodiment, any bend in the recirculation line satisfies the condition that the radius r of the bend is greater than 5 times the diameter d of the recirculation line. This ratio can therefore be expressed as r>5d.

[0047] The apparatus according to the present disclosure also includes a compressor, preferably a centrifugal compressor, for transporting the reactant gas along the recycle line. To achieve maximum efficiency of the reactant gas flow, the compressor is preferably located upstream of the heat exchanger. In a preferred embodiment of the present disclosure, the compressor is configured such that any portion of the surface within the compressor that comes into contact with the reactant gas has a surface roughness R determined in accordance with ASME B46.1. a The compressor used in the apparatus according to the present disclosure preferably includes an impeller. In a further preferred embodiment of the apparatus according to the present disclosure, the compressor is an open centrifugal compressor including an impeller. Preferably, the compressor has a surface roughness R determined in accordance with ASME B46.1. A By ensuring that the surface roughness of the impeller is within the claimed range, the circulation rate of the reaction gas can be optimized and interference with the flow of the polymer particles can be reduced.

[0048] In a preferred embodiment, the apparatus further includes a variable guide vane disposed upstream of the compressor. The surface of the variable guide vane in contact with the reaction gas has a surface roughness R determined in accordance with ASME B46.1. A It is preferable that the distance is less than 3 m.

[0049] The apparatus according to the present disclosure further includes a heat exchanger for cooling the reactant gas. In a preferred embodiment of the present disclosure, the heat exchanger is configured such that any portion of the surface within the heat exchanger that contacts the reactant gas has a surface roughness R determined in accordance with ASME B46.1. a In particularly preferred embodiments, the heat exchanger is a shell-and-tube heat exchanger. In these embodiments, the inner surfaces of the inlet chamber, the tubes and the outlet chamber of the shell-and-tube heat exchanger are designed to have a surface roughness R determined in accordance with ASME B46.1. A is less than 7 m, more preferably less than 3 m, especially less than 2 m.

[0050] In a particularly preferred embodiment, the heat exchanger is a multi-tube heat exchanger comprising an inlet chamber, a tube bundle enclosed in a shell structure, and an outlet chamber, each tube comprising an inlet, a longitudinal middle section, and an outlet, the diameter d1 of the inlet of each tube being greater than the diameter d2 of the corresponding longitudinal middle section of the tube. Due to the special design of the tubes, the polymer particles present in the air stream are smoothly guided through the tubes of the heat exchanger, the risk of accumulation and fouling is significantly reduced. In these embodiments, the ratio of the diameter d1 to the diameter d2 is preferably 1.75:1 to 1.5:1, more preferably 1.4:1 to 1.3:1. The inlet of each tube is preferably conical in shape, the angle between the conical region and the central axis of the tube being preferably in the range of 20° to 60°, more preferably in the range of 30° to 50°, in particular 45°. The diameter d1 of the inlet of each tube is preferably 25 mm to 45 mm, more preferably 30 mm to 40 mm. Diameters in the scope of this disclosure are inner diameters, and for the inlet of a tube, are defined as any straight line segment that passes through the center of a circle defined by the circumference of the inlet of the tube and terminates within that circle. The diameter d2 of the longitudinal middle portion of each tube, i.e., the inner diameter of the longitudinal middle portion of each tube, is preferably 10 mm to 30 mm, more preferably 15 mm to 25 mm. It is preferable that the longitudinal middle portion of the tube has a constant diameter.

[0051] In a further preferred embodiment, the apparatus according to the present disclosure further comprises a butterfly valve disposed downstream of the heat exchanger. By using the butterfly valve as an instrument to control the flow rate of the reactant gas in the recirculation line, a variable pressure drop can be achieved in the recirculation line with a low risk of fouling. Preferably, the butterfly valve is constructed to avoid sharp edges and corners in the butterfly valve to minimize the risk of small particles entrained in the reactant gas depositing on the butterfly valve components. To further minimize this risk, the butterfly valve surface in contact with the reactant gas has a surface roughness R determined in accordance with ASME B46.1. a Preferably, the distance between the recirculation line and the butterfly valve is less than 3 m. Preferably, the butterfly valve comprises a rotating disc having an area smaller than the cross section of the recirculation line at the butterfly valve. This means that the air flow is not completely blocked when the butterfly valve is in the fully closed position, i.e. when the rotary valve flaps are arranged perpendicular to the air flow. Preferably, the area of ​​the rotating disc is 90-99% of the cross section of the recirculation line at the butterfly valve, more preferably, the area of ​​the rotating disc is 94-98% of the cross section of the recirculation line at the butterfly valve. In a preferred embodiment, the rotating disc is circular, and the unblocked area of ​​the recirculation line at the butterfly valve closed position forms an annular gap around the rotating disc. In a preferred embodiment, the rotating disc centre is fixed and rotates around an axis passing through the rotating disc centre. Surface roughness R determined according to ASME B46.1 A It is preferable that the distance is less than 3 m.

[0052] In a preferred embodiment, the apparatus according to the present disclosure comprises a reactor, which is a fluidized bed reactor, comprising a fluidized bed of polyolefin particles, a fluidization grid at the bottom of the reactor, and an optional velocity reduction zone at the top of the reactor. Such a reactor design allows for a constant flow of reaction gas and a stable fluidized bed of polyolefin particles.

[0053] A fluidized bed reactor is a reactor in which polymerization occurs in a polyolefin particle layer, and the reaction gas mixture is fed into the reactor at the lower end of the reactor under a gas distribution grid, usually with a distribution gas flow function, and the polyolefin particle layer is maintained in a fluidized bed state by withdrawing the gas again at the top of the fluidized bed reactor. The reaction gas mixture is then returned to the lower end of the reactor through a recycle line containing a compressor and a heat exchanger to remove the heat of polymerization. The flow rate of the reaction gas mixture must be high enough, firstly, to fluidize the fine polymer particle layer present in the polymerization zone, and secondly, to effectively remove the heat of polymerization.

[0054] Preferably, the trays are arranged to form the sidewall of an inverted cone, with adjacent trays arranged to form slots in the overlapping areas, said trays having a surface roughness R determined in accordance with ASME B46.1. a The grid is preferably less than 3 m. In a preferred embodiment, the overlapping area of ​​the first tray forms the top of the slot and the successive tray forms the bottom of the slot. Such a grid is particularly suitable for uniformly distributing an upward gas flow in a vessel containing a polymer in a fluidized state. Suitable arrangements of trays are described, for example, in WO 2008 / 074632 A1.

[0055] In a further preferred embodiment, the fluidized bed reactor comprises a settling tube, which preferably has an upper opening and a gas distribution grid integrated therein. Preferably, the gas distribution grid and the settling tube are arranged such that the gas distribution grid is tapered downwards towards the settling tube, facilitating the entry of the polyolefin particles into the settling tube by gravity.

[0056] In a preferred embodiment, the fluid velocity in the fluidized bed reactor is 0.3-1.5 m / s, more preferably 0.5-1.2 m / s, to provide a uniform and stable fluidized polymer particle bed.

[0057] FIG. 1 shows a schematic of an apparatus of the present disclosure including a fluidized bed reactor.

[0058] The fluidized bed reactor (1) comprises a fluidized bed (11) of polyolefin particles, a gas distribution grid (12), and a velocity reduction zone (13) having a diameter larger than that of the fluidized bed portion of the reactor. The polyolefin bed is maintained in a fluidized state by gas flowing upwards through the gas distribution grid (12) located at the bottom of the reactor (1). The gas stream of reaction gas leaving the top of the velocity reduction zone (13) through the recycle line (3) is compressed by a compressor (4) containing variable guide vanes (5), transferred to a heat exchanger (6), cooled in the heat exchanger, and then recycles to the bottom of the fluidized bed reactor (1) at a point below the gas distribution grid (12). The recycle line (3) further comprises a butterfly valve (7) located downstream of the heat exchanger (6). Supplemental monomers, molecular weight regulators, and optionally inert gases and / or process additives may be fed to the reactor (1) at different points through a line (8) upstream of the compressor (4).

[0059] The fluidized bed reactor (1) is provided with continuous air circulation of the polyolefin particles by a circulation loop (14) connecting the gas distribution grid (12) to the upper region of the fluidized bed reactor (1). The circulation loop (14) includes a settling tube (15) and an air transport tube (16). The settling tube (15) is integrated with its upper opening into the gas distribution grid (12) and is preferably arranged substantially vertically. The gas distribution grid (12) is tapered so as to slope downwards towards the settling tube (15) and thereby facilitate the entry of the polyolefin particles into the settling tube (15) by gravity. The upper opening of the settling tube (15) is preferably centrally located with respect to the gas distribution grid (12). A carrier gas, supplied via a line (17) for transporting the polyolefin particles through the pneumatic transport vessel (16), is taken from the gas recirculation line at a point downstream of the compressor (4) and upstream of the heat exchanger (6). The polyolefin particles are discharged from the fluidized bed reactor (1) through a discharge conduit (9) and out of a settling tube (15).

[0060] In another preferred embodiment, the apparatus according to the present disclosure comprises a reactor that is a multi-zone circulation reactor, in which in the first polymerization zone, the grown polyolefin particles flow upward under fast fluidization or transport conditions, in the second polymerization zone, the grown polyolefin particles flow downward under densification conditions, the first polymerization zone and the second polymerization zone are connected to each other, the polyolefin particles leaving the first polymerization zone enter the second polymerization zone, and the polyolefin particles leaving the second polymerization zone enter the first polymerization zone, and a circulation of the polyolefin particles through the first polymerization zone and the second polymerization zone is established. It has been found that by carrying out the polymerization in this reactor, the polymer properties, in particular the molecular weight distribution, can be well controlled.

[0061] Multi-zone circulation reactors are described, for example, in WO 97 / 04015A1 and WO 00 / 02929A1, and have two mutually connected polymerization zones, a riser through which the grown polyolefin particles flow upward under fast fluidization or transport conditions, and a downcomer through which the grown polyolefin particles flow downward in a dense form by gravity. The polyolefin particles leaving the riser enter the downcomer, and the polyolefin particles leaving the downcomer are reintroduced into the riser, thus establishing a circulation of the polymer between the two polymerization zones, and the polymer passes through these two zones alternately multiple times. The polymerization reactor of the present disclosure has a solid-gas separator disposed above the downcomer, which separates the polyolefin from the riser and the reaction gas mixture. The grown polyolefin particles enter the downcomer, and the reaction gas mixture separated in the riser is continuously circulated to one or more points where it is reintroduced into the polymerization reactor via a gas recirculation line. Preferably, the main part of the circulation gas is circulated to the bottom of the riser. The recycle line includes a centrifugal compressor and a heat exchanger for removing the heat of polymerization. Preferably, the line feeding the catalyst or the line feeding the polyolefin particles from the upstream reactor is located in the riser and the polymer discharge system is located at the bottom of the downcomer. The introduction of make-up monomer, comonomer, hydrogen and / or inert components may be carried out at different points along the riser and the downcomer.

[0062] FIG. 2 shows a schematic of an apparatus according to the present disclosure, including a multi-zone circulating reactor.

[0063] The multi-zone circulation reactor (2) includes a riser (21) as a first reaction zone and a downcomer (22) as a second reaction zone. The polyolefin particles repeatedly pass through the riser (21) and the downcomer (22). In the riser (21), the polyolefin particles flow upward in a fast fluidized state, and in the downcomer (22), the polyolefin particles flow downward by gravity. The riser (21) and the downcomer (22) are appropriately interconnected via interconnecting bends (23), (24).

[0064] The polyolefin particles and the reaction gas mixture flow through the riser (21) and then exit the riser (21) into a solid-gas separation zone (25). Such solid-gas separation can be accomplished using conventional separation equipment, such as a centrifugal separator, such as a cyclone. The polyolefin particles descend from the separation zone (25) into the downcomer (22). A blocking fluid can be fed to the top of the downcomer (22) via line (26) to prevent the reaction gas mixture in the riser (21) from entering the downcomer (22).

[0065] The reaction gas mixture leaving the separation zone (25) is recycled to the bottom of the riser (21) via a recycle line (3) that includes a compressor (4) that includes variable guide vanes (5) to establish rapid fluidization conditions in the riser (21). The recycle line (3) further includes a heat exchanger (6) and a butterfly valve (7) downstream of the heat exchanger (6). Supplemental monomers, supplemental comonomers, and optionally inert gases and / or process additives can be fed to the reactor (2) at different points so as to enter the recycle line (3) via line (8). Between the compressor (4) and the heat exchanger (6), a line (27) branches off to send a portion of the recycle gas to an interconnecting bend (24) for sending polyolefin particles from the downcomer (22) to the riser (21).

[0066] The bottom of the downcomer (22) is fitted with a butterfly valve (28) having an adjustable opening for adjusting the flow of polyolefin particles from the downcomer (22) through the interconnecting bend (24) to the riser (21). Above the butterfly valve (28), a metered amount of the recycle gas mixture coming from the recycle line (3) through lines (26) and (29) is introduced into the downcomer (22) to facilitate the flow of polyolefin particles through the butterfly valve (28). The polyolefin particles are discharged from the downcomer (22) through the discharge conduit (9) from the multi-zone circulating reactor (2).

[0067] In a further preferred embodiment of the present disclosure, the apparatus is part of a series of apparatus. Preferably, the series comprises a first gas phase apparatus followed by a second gas phase apparatus.

[0068] Another object of the present disclosure is a process for the production of olefin polymers comprising homopolymerizing an olefin or copolymerizing an olefin with one or more other olefins in the presence of a polymerization catalyst at a temperature between 20 and 200° C. and a pressure between 0.5 and 10 MPa, the process being carried out in an apparatus according to the present disclosure.

[0069] Preferably, the polymerization is a homopolymerization of ethylene or a copolymerization of ethylene with one or more other olefins selected from 1-butene, 1-hexene, 1-octene, or a homopolymerization of propylene or a copolymerization of propylene with one or more other olefins selected from ethylene, 1-butene, 1-hexene. Preferably, the resulting polyolefin has a density of 0.945 to 965 g / cm, measured at 23° C. according to ISO 1183. 3 It is high density polyethylene.

[0070] The process of the present disclosure can be carried out at pressures of 0.5 MPa to 10 MPa, preferably 1.0 MPa to 8 MPa, in particular 1.5 MPa to 4 MPa, where these pressures, as all pressures given in this disclosure, must be understood as absolute pressures, i.e. pressures with dimensions MPa (abs). The polymerization is preferably carried out at temperatures of 30°C to 160°C, particularly preferably 65°C to 125°C, with temperatures in the upper part of this range being preferred for producing ethylene copolymers of relatively high density and relatively high temperature. The lower end of this range is preferred for producing ethylene copolymers of lower density.

[0071] The process can also be carried out in a condensed or super-condensed mode where a portion of the circulating reaction gas mixture is cooled below the dew point and returned to the reactor as liquid and vapor phases separately, or returned together as a two-phase mixture to utilize additional enthalpy of vaporization to cool the reaction gas. When operated in a condensed or super-condensed mode, the process of the present disclosure is preferably carried out in a fluidized bed reactor.

[0072] In a preferred 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, n-hexane, or a mixture thereof. As the inert gas, nitrogen gas or propane is preferably used, preferably in combination with other alkanes if appropriate. In a particularly preferred embodiment of the present disclosure, the polymerization is carried out in the presence of C 2 O 4 as the polymerization diluent. 3 ~C 5It is carried out in the presence of an alkane, and most preferably in the presence of propane, especially in the case of homopolymerization or copolymerization of ethylene. The reaction gas mixture in the reactor then further comprises the olefin to be polymerized, i.e. the main monomer and one or more optional comonomers. In a preferred embodiment of the present disclosure, the reaction gas mixture has a content of inert components of 30-99% by volume, more preferably 40-95% by volume, especially 45-85% by volume. In another preferred embodiment of the present disclosure, especially when the main monomer is propylene, no inert diluent is added at all or only in small amounts. The reaction gas mixture may further comprise additional components such as antistatic agents or molecular weight regulators such as hydrogen gas. The components of the reaction gas mixture may be fed in gaseous or liquid form to the gas phase polymerization reactor or recycle line and then evaporated in the reactor or recycle line.

[0073] The polymerization of olefins can be carried out using any commonly used olefin polymerization catalyst. That is, the polymerization can be carried out using a Phillips catalyst based on chromium oxide, a Ziegler or Ziegler-Natta catalyst, or a single-site catalyst. For the purposes of this disclosure, a single-site catalyst is a catalyst based on a chemically uniform transition metal coordination compound. Furthermore, a mixture of two or more of these catalysts can be used to polymerize olefins. Such mixed catalysts are generally called hybrid catalysts. The preparation and use of these catalysts for olefin polymerization are generally known.

[0074] Preferred catalysts are of the Ziegler type, preferably comprising a compound of titanium or vanadium, a compound of magnesium and, optionally, an electron donor compound and / or a particulate inorganic oxide as support material.

[0075] Ziegler-type catalysts are usually polymerized in the presence of a cocatalyst. Preferred cocatalysts are organometallic compounds of metals of Groups 1, 2, 12, 13 or 14 of the Periodic Table of Elements, especially organometallic compounds of metals of Group 13, especially organoaluminum compounds. Preferred cocatalysts are, for example, organometallic alkyls, organometallic alkoxides, organometallic halides.

[0076] Preferred organometallic compounds include lithium alkyls, magnesium or zinc alkyls, magnesium alkyl halides, aluminum alkyls, silicon alkyls, silicon alkoxides and silicon alkyl halides. More preferably, the organometallic compounds include alkylaluminums and alkylmagnesiums. Even more preferably, the organometallic compounds include alkylaluminums, most preferably trialkylaluminum compounds, or compounds of this type in which the alkyl groups are replaced by halogen atoms, such as chlorine or bromine. Examples of such aluminum alkyls are trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum or diethylaluminum chloride, or mixtures thereof.

[0077] Also preferably, it is a Phillips type chromium catalyst, which is produced by applying a chromium compound to an inorganic support, and then activating the catalyst precursor at a temperature in the range of 350 to 1000 ° C, thereby converting chromium less than 6-valent to 6-valent state. In addition to chromium, other elements such as magnesium, calcium, boron, aluminum, phosphorus, titanium, vanadium, zirconium, zinc, etc. can be used. In particular, it is preferable to use titanium, zirconium or zinc. Combinations of the above elements are also possible. The catalyst precursor can be doped with fluoride before or during activation. Supports for Phillips type catalysts, which are also known to those skilled in the art, include alumina, silica (silica gel), titania, zirconia or mixed oxides or gels thereof, and aluminum phosphate. More suitable support materials can be obtained by modifying the pore surface area, for example, by compounds of the elements boron, aluminum, silicon or phosphorus. It is preferable to use silica gel. It is preferable to use spherical or granular silica gel, the former of which can also be spray-dried. The activated chromium catalyst can be subsequently prepolymerized or prereduced. The pre-reduction is usually carried out in an activator at 250° C. to 500° C., preferably 300° C. to 400° C., using cobalt or using hydrogen.

[0078] In another preferred embodiment of the present disclosure, the polymerization is a polymerization in a gas-phase reactor that is part of a polymerization reactor cascade, and one or more polymerizations in other gas-phase reactors of the polymerization reactor cascade can also be polymerizations according to the present disclosure.Suitable combinations of polymerization reactors include a fluidized bed reactor followed by a multi-zone circulation reactor, a multi-zone circulation reactor followed by a fluidized bed reactor, a cascade of two or three fluidized bed reactors, and one or two loop reactors followed by one or two fluidized bed reactors.

[0079] The apparatus according to the present disclosure is designed so that the reaction gas circulates rapidly through the recirculation line. Thus, in a preferred embodiment, the process of the present disclosure is carried out in the recirculation line with a reaction gas flow velocity of 5 m / s to 25 m / s, more preferably 15 m / s to 20 m / s. A reaction gas flow velocity of said magnitude ensures good exchange and transport of fine polymer and also helps to avoid deposition or accumulation of polymer particles.

[0080] The apparatus according to the present disclosure allows the gas-phase polymerization of olefins to be carried out without fouling in the recycle line or in the equipment installed in the recycle line, and without the accumulation of polymer powder on the inner surface of the apparatus, even if polymer particles are present in the circulating reaction gas. The gas-phase polymerization of olefins can be operated reliably without the installation of gas-solid separation devices such as cyclones. Thus, in a preferred embodiment of the present disclosure, the recycle line is not equipped with cyclones, for example upstream of the compressor and the heat exchanger. The apparatus allows the gas-phase polymerization of olefins to be carried out with polymer particles having a small size, thus expanding the flexibility of the operation of the apparatus. In this way, the apparatus also allows the start of the polymerization to be carried out with an empty reactor, i.e., no seed bed is required for the introduction of polymer particles before the start of the polymerization. The low sensitivity of the apparatus to circulating polymer particles further increases the reliability of the entire polymerization system.

Claims

1. An olefin gas phase polymerization apparatus, comprising: a reactor (1, 2) comprising at least one polymerization zone, a recycle line (3) for withdrawing the reaction gas from said reactors (1, 2) and for returning said reaction gas to said reactors (1, 2); a compressor (4) for transporting said reaction gas along said recycle line (3); a heat exchanger (6) for cooling the reaction gas, At least a portion of the inner surface of the recirculation line (3) that comes into contact with the reaction gas has a surface roughness R determined in accordance with ASME B46.

1. ａ is less than 3 μm, Any bend in the recirculation line (3) satisfies the condition that the radius of the bend r is greater than five times the diameter of the recirculation line (3). Olefin gas phase polymerization equipment.

2. At least a portion of the inner surface of the recirculation line (3) has a surface roughness R determined in accordance with ASME B46.

1. ａ or at least a portion of the inner surface of the recirculation line (3) has a surface roughness R determined in accordance with ASME B46.1 ａ 10. The apparatus of claim 1, wherein the apparatus is fabricated from low temperature carbon steel (LTCS) having a thickness of less than 3 μm.

3. 3. The device according to claim 1, wherein the inner surface of the recirculation line (3) in contact with the reaction gas has no protrusions exceeding 1.5 mm in height.

4. The compressor (4) has a surface roughness R determined in accordance with ASME B46.

1. ａ The apparatus is an open centrifugal compressor including an impeller having a surface roughness R of less than 3 μm, the apparatus optionally including a variable guide vane (5) arranged upstream of the compressor (4), the surface of the variable guide vane (5) in contact with the reaction gas having a surface roughness R determined in accordance with ASME B46.

1. ａ 3. The device of claim 1, wherein the thickness is less than 3 μm.

5. The method further includes a butterfly valve (7) disposed downstream of the heat exchanger (6), and the surface of the butterfly valve (7) that comes into contact with the reaction gas has a surface roughness R determined in accordance with ASME B46.

1. ａ 3. The device of claim 1, wherein the thickness is less than 3 μm.

6. 3. The apparatus according to claim 1, wherein the heat exchanger (6) is a shell-and-tube heat exchanger including an inlet chamber, a tube bundle enclosed in a shell structure, and an outlet chamber, each tube including an inlet, a longitudinal intermediate portion, and an outlet, and wherein the diameter d1 of the inlet of each tube is larger than the diameter d2 of the corresponding longitudinal intermediate portion of the tube.

7. 3. The apparatus according to claim 1, wherein the reactor (1) is a fluidized bed reactor comprising a fluidized bed (11) of polyolefin particles and a fluidization grid (12) arranged at the bottom of the reactor (1), and wherein the reactor is a multi-zone circulation reactor (2), in which in a first polymerization zone (21) the grown polyolefin particles flow upward under fast fluidization or transport conditions, and in a second polymerization zone (22) the grown polyolefin particles flow downward at a higher density than the polyolefin particles in the first polymerization zone (21), the first polymerization zone (21) and the second polymerization zone (22) are connected to each other, the polyolefin particles leaving the first polymerization zone (21) enter the second polymerization zone (22) and the polyolefin particles leaving the second polymerization zone (22) enter the first polymerization zone (22), and a circulation of polyolefin particles through the first and second polymerization zones (21, 22) is established.

8. A process for producing an olefin polymer, which comprises homopolymerizing an olefin or copolymerizing an olefin with one or more other olefins in the presence of a polymerization catalyst at a temperature of 20 to 200°C and a pressure of 0.5 to 10 MPa, wherein the process is carried out in the apparatus according to claim 1 or 2.

9. 9. The process of claim 8, carried out at a reactant gas flow velocity of from 5 m / s to 25 m / s.

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