Heat exchanger for gas-phase polymerization

Abstract

A shell-and-tube heat exchanger for cooling a gas stream includes an inlet chamber, a bundle of tubes enclosed in a shell structure, and an outlet chamber, each tube including an inlet, a longitudinal center, and an outlet, each tube having a diameter d1 at the inlet that is greater than a diameter d2 at the longitudinal center of the tube.

Description

Technical Field

[0001] The present disclosure provides a heat exchanger useful for the gas-phase polymerization of olefins. In particular, the present disclosure provides a heat exchanger comprising a tube bundle with an enlarged diameter at the inlet of the tubes. The present disclosure also provides an apparatus for the gas-phase polymerization of olefins comprising a heat exchanger, and a process for producing an olefin polymer carried out within the apparatus.

Background Art

[0002] A heat exchanger is a system widely used for transferring heat between two gases or fluids and can be used in both cooling and heating processes. A common design is the shell-and-tube type heat exchanger mainly used in oil refineries and other large-scale chemical processes operating under high pressure. This type of heat exchanger usually consists of a shell, which is a large pressure vessel containing a tube bundle. These tubes contain a first fluid that needs to be cooled or heated. A second fluid flows over the heated or cooled tubes and can provide or absorb heat as needed.

[0003] One of the application fields where heat exchangers can be employed is the gas-phase polymerization of olefins. The gas-phase polymerization process is an economical process for producing polyolefins. Reactors suitable for carrying out such gas-phase polymerization are, for example, fluidized bed reactors, stirred gas-phase reactors, or multi-zone circulation reactors having two different interconnected gas-phase polymerization zones. These processes are usually carried out in the gas phase containing monomers and comonomers, and often further include a polymerization diluent such as nitrogen or alkane, or other gas components such as hydrogen as a molecular weight regulator or low molecular weight reaction product. The resulting product is usually solid polyolefin particles formed by a polymerization catalyst system containing particulate catalyst solids.

[0004] The olefin gas-phase polymerization process is characterized by withdrawing a large amount of gas from the reaction zone, passing it through a heat exchanger for removing the heat of polymerization, and then returning it to the polymerization zone. In a fluidized-bed reactor, the returned reaction gas further serves to maintain the polyolefin particles in a fluidized state. In a multi-zone circulation reactor, circulation between the reactor zones is effected by the returned reaction gas. To drive all these processes, the recycle line of the reaction gas is usually equipped with a centrifugal compressor. However, because polymer particles and other solids are present in the reaction gas, the equipment used for carrying out gas-phase polymerization, particularly heat exchangers, are prone to fouling.

[0005] When solid particles (such as polymer particles or other impurities) accumulate on the surface of the heat exchanger, fouling occurs, which results in a decrease in thermal efficiency, a decrease in heat flux, an increase in temperature on the high-temperature side, and a decrease in temperature on the low-temperature side. Such accumulation of solids may also cause corrosion under the deposits, which can reduce not only the efficiency of the process but also the lifespan of the equipment used.

[0006] For a long time, many efforts have been made to address the problem of fouling.

[0007] A continuous gas-fluidized bed process for producing a polymer, in which a gas stream containing a monomer is passed through the fluidized bed of a reactor zone, polymer particles are withdrawn from the reactor zone, the gas stream containing unreacted monomer and solid particles is cooled to condense a portion thereof, and a liquid-containing mixture having a weight ratio of liquid to solid particles of 2:1 or more is formed, is disclosed in U.S. Patent No. 4,588,790. The mixture is reintroduced into the reaction zone, where the liquid in the mixture evaporates. This avoids the formation of wet agglomerated solid particles that accumulate in the low-velocity zone.

[0008] WO 00 / 61278 A1 provides a polymerization process and a polymerization apparatus with means for limiting or preventing the deposition, accumulation or build-up of particles in a heat exchanger. In this regard, a fluidized bed reactor to which olefins and a catalyst are supplied, at least one first tube for transporting a recycle gas stream withdrawn from the upper part of the reactor, at least one heat exchanger for cooling the recycle gas stream, at least one compressor for moving the recycle gas stream, and a recycle circuit including at least one second tube for transporting the recycle gas stream and introducing it into the lower part of the reactor. The heat exchanger is a multi-tube heat exchanger, which sequentially and combinatorially includes an inlet chamber, a tube bundle enclosed in a horizontal cylindrical shell having a horizontal longitudinal axis, and an outlet chamber. The outlet chamber is provided with a discharge hole and has a wall extending in a frustoconical shape along an inclined direction. The large base of the frustum is connected to the shell, and the small base corresponds to the discharge hole connected to the second tube. The lower generatrix of the inclined frustum is horizontal or inclined downward.

[0009] KR 200406359 Y1 is a high-temperature heat exchanger for recovering the high heat of exhaust gas discharged from power plants, steel mills, etc. A plurality of tubes are densely installed inside, and the lower ends are fixed in soft sockets.

[0010] EP2 662459 A2 relates to an exhaust gas cooler for cooling raw high-temperature exhaust gas from an electric furnace in a steel production plant. Each combustion exhaust gas cooler has a gas inlet chamber, a gas outlet chamber, and a matrix of gas cooling tubes extending between and within the inlet chamber and the outlet chamber. Each gas cooling tube has a bell-shaped inlet end including an aerodynamically curved gas acceleration profile effective for promoting a streamlined flow of flue gas into the gas cooling tube.

[0011] WO 2007 / 082515 A1 is a tube bundle heat exchanger in which tubes are held on both sides of a tube sheet and are joined to the tube sheet by welding in each case. The connection part of the inlet side tube sheet is formed by a conical and / or trumpet-shaped transition part in each case, and its cross section decreases in the gas flow direction.

[0012] US 2014 / 0000850 A1 relates to a heat exchanger having an outer tube part provided with a plurality of inner tube parts having channels for a fluid to be cooled. The outer tube part is provided with at least one cooling fluid channel. At least one cooling fluid channel and at least one channel of the fluid to be cooled are in thermal contact with each other and are fluidly separated from each other. The plurality of inner tube parts having openings at both ends form a form of a tube bundle in which the ends are firmly fixed to corresponding conduction holes of the upstream end body and the other ends are firmly fixed to corresponding conduction holes of the downstream end body.

[0013] CH 276825 A is a heat exchanger including a finned tube bundle extending between tube sheets fixed to a tube sheet for a heat exchange medium to pass through the tubes, and relates to a heat exchanger including a finned tube bundle.

[0014] DE 10333577 A1 describes an evaporation device for treating a viscous medium and a method for evaporating volatile components from a polymer solution or melt. The evaporation device includes at least one delivery chamber having a perforated bottom, a shell and tube heat exchanger surrounding a vertical tube connected thereto, and a degassing chamber arranged adjacent thereto. Summary of the Invention Problems to be Solved by the Invention

[0015] Efforts have been made to reduce fouling in the gas-phase polymerization reactor, but in particular, when an additional heat exchanger is installed to increase the heat exchange capacity and thus increase the polymer production in the reactor, the problem becomes severe. Therefore, it is necessary to provide a heat exchanger for a gas-phase polymerization process that minimizes the risk of fouling due to the accumulation of undesired polymer particles.

[0016] Provided is a shell-and-tube heat exchanger for cooling a gas stream, which includes an inlet chamber, a tube bundle enclosed within a shell structure, and an outlet chamber. Each tube includes an inlet, a longitudinal central portion, and an outlet, and the diameter d1 of the inlet of each tube is larger than the diameter d2 of the corresponding longitudinal central portion of the tube. The inlet of the tube of the heat exchanger of the present disclosure is integrated with a tube sheet that separates the inlet chamber from the volume within the shell structure, and the upper surface of the tube sheet between two adjacent tubes is three-dimensionally formed so as to form a vertex in the middle between the two tubes.

[0017] In some embodiments, the ratio of the diameter d1 to the diameter d2 is from 1.75:1 to 1.5:1, more preferably from 1.4:1 to 1.3:1.

[0018] In some embodiments, the inlet of each tube has a conical shape.

[0019] In some embodiments, the diameter d1 of the inlet of each tube is from 25 to 45 mm, preferably from 30 to 40 mm.

[0020] In some embodiments, the diameter d2 of the longitudinal central portion of the tube is from 10 to 30 mm, preferably from 15 to 25 mm.

[0021] In some embodiments, the tubes are arranged in a triangular packing pattern within the shell structure.

[0022] In some embodiments, the tubes are arranged in a square packing pattern within the shell structure.

[0023] In some embodiments, the tube bundle includes at least 500 tubes, preferably 500 to 6000 tubes.

[0024] In some embodiments, the distance between the centers of adjacent tubes, measured from tube axis to tube axis, is 25 to 45 mm, preferably 30 to 35 mm.

[0025] In some embodiments, the angle between the conical region and the central axis of the tube is preferably in the range of 20° to 60°, more preferably in the range of 30° to 50°, and particularly 45°.

[0026] In some embodiments, the tube sheet includes holes for each tube, and the tube portion may be received within the corresponding holes. The holes taper towards the upper surface, forming the inlet of the tube and may form a sharp top between adjacent tubes.

[0027] In some embodiments, at least a portion of the upper surface of the tube sheet does not include flat portions between the holes that extend on a plane perpendicular to the axial direction of the tubes.

[0028] In some embodiments, at least a portion of the upper surface of the tube sheet has axially protruding ribs that extend between the holes and may be ribbed by ribs that gradually taper towards their free ends to form vertices.

[0029] In some embodiments, the vertices may limit the angle to 40° to 120°, more preferably 60° to 100°, and particularly 90°.

[0030] In some embodiments, the vertices may be symmetric and slopes of each side extending to adjacent holes may be formed.

[0031] In some embodiments, the tubes may be welded to the tube sheet inside each hole, and in this case, a fillet weld is formed between the front surface of the tube and the inner surface of the hole.

[0032] In some embodiments, when the inner surface of the tube and / or the surfaces of the inlet chamber and the outlet chamber are determined in accordance with ASME B46.1, they have a surface roughness R of less than 7 m, preferably less than 3 m, and particularly less than 2 m. a having.

[0033] In some embodiments, the inner surface of the tube and / or the surfaces of the inlet chamber and the outlet chamber are made of stainless steel.

[0034] Another embodiment of the present disclosure provides an apparatus for the gas-phase polymerization of olefins, - a reactor including at least one polymerization zone, - a recycle line for withdrawing the reaction gas from the reactor and returning it to the reactor, - a compressor for transporting the reaction gas along the recycle line, - a heat exchanger for cooling the reaction gas, and the heat exchanger employed in the apparatus is the heat exchanger of the present disclosure.

[0035] In some embodiments, the heat exchanger is arranged horizontally or vertically.

[0036] In some embodiments, the reactor further includes a butterfly valve arranged downstream of the heat exchanger.

[0037] In some embodiments, the reactor is a fluidized bed reactor.

[0038] In some embodiments, the reactor is a multi-zone circulation reactor. 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 in a dense form. The first polymerization zone and the second polymerization zone are interconnected. 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, forming a circulation of polyolefin particles passing through the first polymerization zone and the second polymerization zone.

[0039] In some embodiments, the reactor is part of a series of reactors.

[0040] Further embodiments provide a process for producing an olefin polymer, which comprises homopolymerizing an olefin or copolymerizing an olefin with one or more other olefins at a temperature of 20 to 200 °C and a pressure of 0.5 to 10 MPa in the presence of a polymerization catalyst, and which is carried out in the apparatus of the present disclosure.

[0041] In some embodiments, this process is carried out at a reaction gas flow rate of 5 m / s to 25 m / s, preferably 15 m / s to 20 m / s.

Brief Description of the Drawings

[0042]

Fig. 1a

Fig. 1b

Fig. 1c

Fig. 2

Fig. 3

Modes for Carrying Out the Invention

[0043] The present disclosure provides a heat exchanger for cooling a gas stream, the heat exchanger including an inlet chamber, a tube bundle enclosed within a shell structure, and an outlet chamber. Each tube includes an inlet, a longitudinal central portion, and an outlet. Thus, the heat exchanger of the present disclosure is a one-pass straight-tube heat exchanger. The general concept of such a heat exchanger is well known to those skilled in the art. The tubes through which the gas to be cooled passes are completely surrounded by a circulating cooling medium. To provide mechanical stability, the tubes of the heat exchanger of the present disclosure are preferably fixedly connected to a tube sheet that separates the inlet chamber and the outlet chamber from the volume within the shell structure filled with the circulating cooling medium. Preferably, the ends of the tubes pass through holes in the tube sheet before being fixedly connected to the tube sheet.

[0044] Particularly in gas phase polymerization processes, small polymer particles and other solids can be entrained in the gas stream to be cooled passing through the tubes of the heat exchanger. These solid particles can accumulate within the heat exchanger and foul the equipment. Thus, the heat exchanger of the present disclosure is designed to avoid dead zones where solid particles can accumulate, polymerize, grow, and ultimately clog the heat exchanger.

[0045] To avoid the dead zone, the diameter d1 of the inlet of each tube is larger than the diameter d2 at the longitudinal center of each tube. In this way, the solid particles mixed in the gas flow are easily swept out of the tube and returned to the reactor for further polymerization and growth. In a preferred embodiment of the present disclosure, the ratio of the diameter d1 to the diameter d2 is from 1.75:1 to 1.5:1, more preferably from 1.4:1 to 1.3:1. In a further preferred embodiment, the inlet of each tube has a conical shape, and the angle between the conical zone and the central axis of the tube is preferably within the range of 20° to 60°, more preferably within the range of 30° to 50°, and particularly 45°. The conical shape of the inlet of the tube can be manufactured using a grinding tool, preferably a rotary grinding tool having a conical shape. To manufacture a tube having a preferred conical inlet, the conical angle of the rotary grinding wheel is preferably within the range of 40° to 120°, more preferably within the range of 60° to 100°, and particularly 90°. The slope of the inlet of the tube is specifically designed so that solid particles cannot stop on its surface and are flushed into the tube.

[0046] In a more preferred embodiment, the diameter d1 of the inlet of each tube is 25 mm to 45 mm, more preferably 30 mm to 40 mm. The diameter within the scope of the present disclosure is the inner diameter. For the inlet of the tube, it is defined as any straight line segment passing through the center of the circle defined by the circumference of the inlet of the tube and having its end located within that circle. Preferably, the diameter d2 at the longitudinal center of each tube, i.e., the inner diameter at the longitudinal center of each tube, is 10 mm to 30 mm, more preferably 15 mm to 25 mm as described above, and is defined in the widest range at the central part of the tube. Preferably, the longitudinal center of the tube has a constant diameter.

[0047] The tubes of the heat exchanger of the present disclosure are arranged in the form of a bundle enclosed within a shell structure. The tubes can be arranged within the tube bundle in a manner that can efficiently utilize the space while providing sufficient space for the cooling medium to pass around the tubes. In a preferred embodiment, the tubes are arranged regularly, more preferably in a square packing pattern or a triangular packing pattern. In a particularly preferred embodiment, the tubes are arranged in a triangular packing pattern within the shell structure. This enables optimal utilization of the available space within the heat exchanger shell while achieving an efficient cooling effect. In a preferred embodiment of the present disclosure, the tube bundle enclosed within the shell structure includes at least 500 tubes, more preferably 500 to 6000 tubes.

[0048] To enable efficient heat transfer between the gas flow to be cooled and the cooling medium, it is necessary for the cooling medium to flow around the tubes through which the gas flow can easily pass, without significantly increasing the overall size of the heat exchanger and while reducing the construction cost. In the process of the present disclosure, it has been found that efficient heat transfer is possible if the distance between the outer sides of the tubes that define the space occupied by the cooling medium is 5 mm or more. Accordingly, the distance between the centers of adjacent tubes, measured from tube axis to tube axis, is 25 to 45 mm, preferably 30 to 35 mm, and the axis passes through the center of the tube along the longitudinal direction of the tube.

[0049] The inlet of the tube of the heat exchanger of the present disclosure is integrated within a tube sheet that separates an inlet chamber from the volume within the shell structure. Preferably, the inlet of the tube is conical, formed by partially removing the tube sheet material, and the upper surface of the tube sheet between the two tubes is three-dimensionally formed. The tube sheet forms a vertex in the middle between two adjacent tubes. The correspondingly formed tube sheet enables any solids present in the gas flow to be guided into the tube and avoids the accumulation of polymer particles on the tube sheet.

[0050] Within the scope of the present disclosure, the "upper surface" of the tube sheet represents the surface of the tube sheet facing upstream. As a result, the upper surface of the tube sheet faces away from the volume within the shell structure and is exposed to the gas flow, particularly to solids in the gas flow.

[0051] The tube sheet is provided with holes for each tube, and the tubes are partially accommodated in their respective holes. The holes taper towards the upper surface, forming the inlet of the tube and forming a sharp vertex between adjacent tubes. The vertex may be symmetric, and the angle may be defined to be in the range of 40° to 120°, more preferably 60° to 100°, particularly 90°. Thereby, each side of the vertex may extend into the hole and form a slope leading to the corresponding tube accommodated in the hole. Thereby, the inlet may be formed by the slope of the hole.

[0052] This hole may taper towards the upper surface from a height exceeding the tip of the tube accommodated in this hole.

[0053] The tubes may be partially accommodated in their respective holes, and the tubes do not extend through the entire hole. A gap is provided between the upper surface of the tube sheet and the tip of the tube. To fix the tube in the hole, the tube may be welded to the tube sheet. In one embodiment, a fillet weld seam may be formed between the front end of the tube and the inner surface of the hole. The fillet weld may form an inclined surface for particles to slide into the tube. In one embodiment, the fillet weld may form a continuation of the slope to the vertex formed on the tube sheet.

[0054] Optionally, at least a part of the upper surface of the tube sheet in contact with the gas flow does not include a flat portion extending in a plane perpendicular to the axial direction of the tube.

[0055] Since vertices are formed on the upper surface between two adjacent tubes, solid particles slide from the slopes forming the vertices and are guided into the tubes of the heat exchanger. Thereby, accumulation of solid particles on the upper surface can be prevented. Thereby, a heat exchanger can be arranged in a highly reliable gas-phase polymerization apparatus without installing a gas-solid separator such as a cyclone. A gas / solid separator may cause material loss because solid particles such as a catalyst are removed from the apparatus. Further, such an apparatus including a gas / solid separator is not suitable for polymerizing small-sized polymer particles because it may be contaminated by the gas / solid separator from the reactor and removed from the apparatus. Therefore, by providing the heat exchanger of the present disclosure, the degree of freedom in operating the apparatus is increased. Thereby, the requirement of reducing the contamination of small particles into the recycle line by the circulation of small particles through the recycle line is reduced. In some embodiments, the recycle line does not include a cyclone. In particular, the recycle line may not include a cyclone upstream of the compressor and / or the heat exchanger.

[0056] In the process of the present disclosure, it was also found that the gas flow can be further improved by applying a certain finish to the portion of the tube in contact with the gas flow. In a preferred embodiment, when the inner surface of the tube and / or the surface of the connecting means are determined according to ASME B46.1, the surface roughness R is less than 7 m, preferably less than 3 m, particularly less than 2 m. a By this, accumulation of solid particles present on the inner surface of the tube or on the connecting means into the gas flow can be reduced, whereby a constant and uniform gas flow can pass through the heat exchanger. A material suitable for achieving a specific surface roughness is stainless steel, and it has been found that an inert material that can withstand the reaction conditions of gas-phase polymerization is further provided. Therefore, in a preferred embodiment, the inner surface of the tube and / or the surface of the connecting means is stainless steel. A particularly preferred material in this regard is AISI 304 stainless steel.

[0057] In a preferred embodiment of the present disclosure, the heat exchanger does not have protrusions on the surface in contact with the reaction gas, such as protrusions caused by welding elements of the heat exchanger, and its height exceeds 1.5 mm.

[0058] The heat exchanger of the present disclosure can be used in many applications, but is particularly designed for use in an olefin gas-phase polymerization process. Accordingly, in other embodiments, the present disclosure provides an apparatus for performing gas-phase polymerization of olefins using the heat exchanger of the present disclosure. This apparatus preferably includes a reactor including at least one polymerization zone, a recycle line for withdrawing the 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.

[0059] The heat exchanger may be disposed at various positions in the recycle line. The heat exchanger may be disposed horizontally or vertically. In a preferred embodiment, the heat exchanger is disposed vertically.

[0060] In a preferred embodiment, the reactor of the present disclosure further includes a butterfly valve disposed downstream of the heat exchanger. The butterfly valve can be used as an additional device for controlling the flow rate of the gas stream, thereby establishing a variable pressure drop in the recycle line, while the apparatus itself has a low risk of fouling in accordance with the spirit of the present disclosure.

[0061] To minimize the presence of solid particles in the reaction gas stream, the recycle circuit also includes a cyclone upstream of the compressor and the heat exchanger, which can minimize the transport of solid particles.

[0062] In a preferred embodiment, the reactor of the present disclosure is a fluidized bed reactor. A fluidized bed reactor is a reactor in which polymerization occurs within a polyolefin particle layer. A reaction gas mixture is supplied into the reactor at the lower end of the reactor usually under a gas distribution grid having a distributed gas flow function, and the gas is withdrawn again at the top of the fluidized bed reactor, whereby the polyolefin particle layer maintains a fluidized bed state. Then, the reaction gas mixture is returned to the lower end of the reactor via a circulation line equipped with 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 region and, secondly, to effectively remove the heat of polymerization. Suitable reactors are described, for example, in WO 2007 / 071527 A1.

[0063] In a more preferred embodiment, the reactor of the present disclosure is a multi-zone circulation reactor. 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 dense form. The first polymerization zone and the second polymerization zone are interconnected, 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, forming a circulation of polyolefin particles passing through the first polymerization zone and the second polymerization zone. It has been found that by performing polymerization in this reactor, polymer properties, particularly the molecular weight distribution, can be well controlled.

[0064] Multi-zone circulation reactors are described, for example, in WO 97 / 04015 A1 and WO 00 / 02929 A1, and have two interconnected polymerization zones, a riser in which the grown polyolefin particles flow upward under fast fluidization or transport conditions, and a downcomer in which the grown polyolefin particles flow downward in a dense form under gravity. The polyolefin particles exiting the riser enter the riser, and by being reintroduced into the riser, a polymer circulation is established between two polymerization zones through which the polymer passes alternately multiple times. The polymerization reactor has a solid / gas separator disposed above the downcomer to separate the polyolefin from the reaction gas mixture coming from the riser. 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 circulation line. Preferably, the main part of the recycled gas is circulated to the bottom of the riser tube. A centrifugal compressor and a heat exchanger for removing the polymerization heat are installed in the recycle line. Preferably, a line for supplying a catalyst or a line for supplying polyolefin particles coming from an upstream reactor is disposed in the riser, and a polymer discharge system is disposed at the bottom of the downcomer. The introduction of make-up monomers, comonomers, hydrogen and / or inert components can occur at different points along the riser and the downcomer.

[0065] In a particularly preferred embodiment, the reactor of the present disclosure is part of a series of reactors. Preferably, this series includes a first gas-phase device followed by a second gas-phase device.

[0066] Another embodiment of the present disclosure provides a process for producing an olefin polymer, which comprises homopolymerizing an olefin or copolymerizing an olefin with one or more other olefins at a temperature of 20 to 200 °C and a pressure of 0.5 to 10 MPa in the presence of a polymerization catalyst, and the process is carried out in the apparatus of the present disclosure.

[0067] The process of the present disclosure is particularly suitable for the polymerization of olefins, especially 1-olefins, i.e., hydrocarbons having a terminal double bond. 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, 1-decene, etc. 10 -1-alkenes or linear or branched C2~C such as 4-methyl-1-pentene 10 -1-alkenes; conjugated and non-conjugated dienes such as 1,3-butadiene, 1,4-hexene, 1,7-octene. Mixtures of various 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. Examples are cyclopentene, norbornene, tetracyclododecene or methylnorbornene, or dienes such as 5-ethylidene-2-norbornene, norbornadiene or ethylnorbornadiene.

[0068] This apparatus is particularly suitable for the homopolymerization or copolymerization of ethylene or propylene, and is particularly preferred for the homopolymerization or copolymerization of ethylene. 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. As comonomers in ethylene polymerization, C3~C8-1-alkenes, especially 1-butene, 1-pentene, 1-hexene and / or 1-octene, are preferably used in an amount of at most 20% by weight, more preferably 0.01% to 15% by weight, especially 0.05% to 12% by weight. Polymerization of copolymerizing ethylene with 0.1% to 12% by weight of 1-hexene and / or 1-butene is particularly preferred.

[0069] The process of the present disclosure can be carried out at a pressure of 0.5 MPa to 10 MPa, preferably 1.0 MPa to 8 MPa, particularly 1.5 MPa to 4 MPa. These pressures, like all pressures given in the present disclosure, should be understood as absolute pressures, i.e., pressures having the dimension of MPa (abs). The polymerization is preferably carried out at a temperature of 30 °C to 160 °C, particularly preferably 65 °C to 125 °C. The upper temperature in this range is preferred for producing ethylene copolymers with relatively high density and relatively high temperature. The lower limit of this range is preferred for producing ethylene copolymers with lower density.

[0070] This process can also be carried out in a condensation mode or a supercondensation mode in which a part of the circulating reaction gas mixture is cooled below the dew point and returned to the reactor separately as a liquid phase and a gas phase, or returned together as a two-phase mixture to additionally utilize the evaporation enthalpy for cooling the reaction gas. When the process of the present disclosure is operated in the condensation mode or the supercondensation mode, it is preferably carried out in a fluidized bed reactor.

[0071] 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, it is preferable to use nitrogen gas or propane, and it is preferably used in combination with other alkanes if appropriate. In a particularly preferred embodiment of the present invention, the polymerization is carried out in the presence of a C3-C5 alkane as a polymerization diluent, and in the case of homopolymerization or copolymerization of ethylene in particular, it is most preferably carried out in the presence of propane. Next, the reaction gas mixture in the reactor further contains 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 an inert component content of 30 to 99% by volume, more preferably 40 to 95% by volume, particularly 45 to 85% by volume. In another preferred 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 contain additional components such as an antistatic agent or a molecular weight regulator such as hydrogen. The components of the reaction gas mixture are supplied to the gas-phase polymerization reactor or the recycle line in gaseous or liquid form and can then evaporate in the reactor or the recycle line.

[0072] The polymerization of olefins can be carried out using any generally used olefin polymerization catalyst. This means that the polymerization can be carried out using a Ziegler catalyst or a Ziegler-Natta catalyst, a Phillips catalyst based on chromium oxide, or a single-site catalyst. For the purposes of the present disclosure, a single-site catalyst is a catalyst based on a chemically homogeneous transition metal coordination compound. Furthermore, olefins can also be polymerized using a mixture of two or more of these catalysts. Such a mixed catalyst is generally called a hybrid catalyst. The production and use of these olefin polymerization catalysts are well known.

[0073] Preferred catalysts are preferably Ziegler-type catalysts containing a compound of titanium or vanadium, a compound of magnesium, and optionally an electron donor compound and / or a particulate inorganic oxide as a support material.

[0074] 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 the Elements, especially organometallic compounds of metals of Group 13, especially organoaluminum compounds. Preferred cocatalysts are, for example, organometallic alkyls, organometallic alkoxides, organometallic halides.

[0075] 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 group is substituted by a halogen atom, for example chlorine or bromine. Examples of such aluminum alkyls are trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum or diethylaluminum chloride, or mixtures thereof.

[0076] Also preferably, after applying a chromium compound to an inorganic carrier, the catalyst precursor is activated at a temperature in the range of 350 to 1000 °C to convert chromium less than hexavalent to the hexavalent state, thereby producing a Phillips-type chromium catalyst. In addition to chromium, other elements such as magnesium, calcium, boron, aluminum, phosphorus, titanium, vanadium, zirconium, and zinc 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 a fluoride before or during activation. As the carrier of the Phillips-type catalyst, although this is also known to those skilled in the art, examples include aluminum oxide, silicon dioxide (silica gel), titanium dioxide, zirconium dioxide, or their mixed oxides or cogels, or aluminum phosphate. Further suitable carrier materials can be obtained, for example, by modifying the pore surface area using compounds of boron, aluminum, silicon, or phosphorus elements. It is preferable to use silica gel. Preferably, it is spherical or granular silica gel, and the former can also be spray-dried. The activated chromium catalyst can subsequently be prepolymerized or pre-reduced. The pre-reduction is usually carried out with cobalt or hydrogen in an activator at 250 to 500 °C, preferably 300 to 400 °C.

[0077] In another preferred embodiment of the present disclosure, the polymerization is 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 connecting a multi-zone circulation reactor after a fluidized-bed reactor, connecting a fluidized-bed reactor after a multi-zone circulation reactor, connecting a cascade of two or three fluidized-bed reactors, and connecting one or two fluidized-bed reactors after one or two circulation reactors.

[0078] In order to further minimize the accumulation of solid particles in the reactor and at the same time achieve a high reaction turnover rate, the velocity of the reaction gas flow in the process of the present disclosure can be adjusted. In a preferred embodiment, this process is carried out at a reaction gas flow velocity of 5 m / s to 25 m / s, more preferably 15 m / s to 20 m / s.

[0079] In a more preferred embodiment, the flow velocity in the polymerization zone is 0.3 to 1.5 m / s, preferably 0.5 to 1.2 m / s.

[0080] Figure 1a schematically shows the heat exchanger of the present disclosure.

[0081] The heat exchanger (6) shown in Figure 1a has an inlet chamber (61), a tube bundle (62) enclosed in a shell structure, and an outlet chamber (63). The inlet chamber (61) and the outlet chamber (63) are separated from the shell structure filled with a cooling medium by tube sheets (64), (65).

[0082] Figures 1b and 1c schematically show the details of the heat exchanger of the present disclosure.

[0083] Figure 1b schematically shows a cross-section of the inlets of three tubes (62) passing through a heat exchanger (6). The conical inlet (621) of the tube (62) and the upper area of the longitudinal central part (622) of the tube (62) are shown. The tube (62) is fixed within the heat exchanger (6) by being fixedly connected to a tube sheet (64) at the upper end of the tube (62). The conical inlet (621) of the tube (62) is formed by partially removing the tube sheet material such that the upper surface of the tube sheet (64) between two tubes (62) is three-dimensionally formed and a vertex (641) is formed in the middle between two adjacent tubes (62). As shown in Figure 1b, the ends of the tubes (62) can be welded to the tubes (62) to form a fillet weld seam (642). In particular, the fillet weld may extend from the tip of the tube (62) to the inner surface of each hole formed in the tube sheet. The fillet weld seam (642) may form a continuous portion of the slope towards the vertex (641). Thereby, it is possible to prevent the accumulation of solid particles at the tip of the tube.

[0084] Figure 1c schematically shows a cross-section of the outlets of three tubes (62) passing through a heat exchanger (6). The uniform outlet (623) of the tube (62) and the lower area of the longitudinal central part (622) of the tube (62) are shown. The tube (62) is fixed within the heat exchanger (6) by being fixedly connected to a tube sheet (65) at the lower end of the tube (62). The outlet (623) of the tube (62) is arranged slightly below the lower surface of the tube sheet (65).

[0085] Figure 2 schematically shows an apparatus including a fluidized bed reactor and a heat exchanger of the present disclosure for implementing a process for manufacturing an olefin polymer.

[0086] The fluidized bed reactor (1) includes a fluidized bed (11) of polyolefin particles, a gas distribution grid (12), and a deceleration zone (13) having a diameter larger than the diameter of the fluidized bed portion of the reactor. The polyolefin bed is kept in a fluidized state by an upward flow of gas supplied through the gas distribution grid (12) installed at the bottom of the reactor (1). The gas flow of the reaction gas exiting from the upper part of the deceleration zone (13) via the recycle line (3) is compressed by a compressor (4) equipped with variable guide vanes (5), transferred to a heat exchanger (6), cooled therein, and then recycled to the bottom of the fluidized bed reactor (1) at a point below the gas distribution grid (12). The recycle line (3) further includes a butterfly valve (7) located downstream of the heat exchanger (6). The feed monomer, molecular weight regulator, and any inert gas and / or process additive can be supplied to the reactor (1) at various positions, for example, via a line (8) upstream of the compressor (4).

[0087] The fluidized bed reactor (1) has a continuous air circulation of polyolefin particles via a circulation circuit (14) connecting the gas distribution grid (12) to the upper zone of the fluidized bed reactor (1). The circulation circuit (14) includes a sedimentation tube (15) and an air transport tube (16). The sedimentation tube (15) has its upper opening incorporated into the gas distribution grid (12) and is preferably arranged substantially vertically. The gas distribution grill (12) is tapered so as to promote the entry of polyolefin particles into the sedimentation tube (15) by gravity by inclining downward toward the sedimentation tube (15). The upper opening of the sedimentation tube (15) is preferably centered with respect to the gas distribution grid (12). At a point downstream of the compressor (4) and upstream of the heat exchanger (6), a carrier gas supplied via a line (17) for transporting polyolefin particles through the air transport tube (16) is taken out from the gas recycle line. The polyolefin particles are discharged from the sedimentation tube (15) through a discharge conduit (9) from the fluidized bed reactor (1).

[0088] Figure 3 schematically shows an apparatus including the multi-zone circulation reactor and heat exchanger of the present disclosure for carrying out a process for producing an olefin polymer.

[0089] The multi-zone circulation reactor (2) includes a riser (21) as the first reaction zone and a downcomer (22) as the 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 rapid flow state, and in the downcomer (22), the polyolefin particles flow downward due to gravity. The riser (21) and the downcomer (22) are appropriately interconnected by interconnecting bends (23) and (24).

[0090] After flowing through the riser (21), the polyolefin particles and the reaction gas mixture exit the riser (21) and are carried to the solid / gas separation zone (25). This solid / gas separation can be performed using a conventional separator such as a centrifuge, for example, a cyclone. The polyolefin particles move from the separation zone (25) to the downcomer (22). A blocking fluid for preventing the reaction gas mixture in the riser (21) from entering the downcomer (22) can be supplied to the top of the downcomer (22) via line (26).

[0091] The reaction gas mixture exiting the separation zone (25) is recycled to the bottom of the riser (21) via a recycle line (3) equipped with a compressor (4) including variable guide vanes (5) to establish the rapid flow state 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). A supplementary monomer, a supplementary comonomer, and optionally an inert gas and / or a process additive can be supplied to the recycle line (3) at various positions of the reactor (2), for example, via line (8). A line (27) branches between the compressor (4) and the heat exchanger (6), and a part of the recycle gas is sent to the interconnecting bend (24) for sending polyolefin particles from the downcomer (22) to the riser (21).

[0092] At the bottom of the downcomer (22), there is a butterfly valve (28) having an adjustable opening for adjusting the flow of polyolefin particles entering the riser (21) from the downcomer (22) through the interconnecting bend (24). Above the butterfly valve (28), an amount of recycled gas mixture supplied from the recycle line (3) through lines (26), (29) is introduced into the downcomer (22) as a metering gas that promotes the flow of polyolefin particles through the butterfly valve (28). The polyolefin particles are discharged from the downcomer (22) via the discharge conduit (9) from the multi-zone circulation reactor (2).

Claims

1. - An inlet chamber (61); - A tube bundle (62) enclosed within a shell structure; - An outlet chamber (63), and each of said tubes (62) includes - An inlet (621); - A longitudinal center portion (622); - An outlet (623), and the diameter d1 of the inlet (621) of each of said tubes (62) is larger than the diameter d2 of the corresponding longitudinal center portion (622) of the tube, the inlet (621) of the tube (62) of the heat exchanger is integrated within a tube sheet (64) to separate the inlet chamber (61) from the volume within the shell structure, a multi-tube heat exchanger (6) for cooling a gas flow, wherein the upper surface of the tube sheet (64) between two of said tubes is three-dimensionally formed such that the tube sheet (64) forms a vertex (641) in the middle between the two adjacent tubes, and the ratio of the diameter d1 to the diameter d2 is from 1.75:1 to 1.5:1, and / or the diameter d1 of the inlet (621) of each of said tubes (62) is from 25 to 45 mm, preferably from 30 to 40 mm. A multi-tube heat exchanger (6) characterized by this.

2. The heat exchanger (6) according to claim 1, wherein the inlet (621) of each of said tubes (62) has a conical shape.

3. The distance between the central portions (622) of the adjacent tubes (62) is measured from tube axis to tube axis and is from 25 to 45 mm, preferably from 30 to 35 mm, and / or the angle between the conical region and the central axis of the tube is preferably within the range of 20° to 60°, more preferably within the range of 30° to 50°, and particularly 45°. The heat exchanger (6) according to claim 1 or 2.

4. The tube sheet (64) includes holes for the respective tubes (62), the tubes (62) are partially received within the corresponding holes, the holes are tapered at least partially towards the upper surface, form the inlet (621) of the tubes (62), and form sharp vertices (641) between the adjacent tubes (62), the heat exchanger (6) according to claim 1 or 2.

5. If the inner surface of the tubes (62) and / or the surfaces of the inlet chamber (61) and the outlet chamber (63) are determined based on ASME B46.1, the heat exchanger (6) according to claim 1 or 2 having a surface roughness R of less than 7 m, preferably less than 3 m, particularly less than 2 m. ａ

6. An apparatus for the gas-phase polymerization of olefins, - a reactor (1, 2) including at least one polymerization zone, - a recycle line (3) for withdrawing the reaction gas from the reactor (1, 2) and returning the reaction gas to the reactor (1, 2), - a compressor (4) for transporting the reaction gas along the recycle line (3), - a heat exchanger (6) for cooling the reaction gas, and the heat exchanger (6) - an inlet chamber (61), - a tube bundle (62) enclosed within a shell structure, - an outlet chamber (63), each of the tubes (62) - an inlet (621), - a longitudinal central portion (622), - an outlet (623), The diameter d1 of the inlet (621) of each of the tubes (62) is larger than the diameter d2 of the corresponding longitudinal central portion (622) of the tube. The inlet (621) of the tube (62) of the heat exchanger is integrated within a tube sheet (64) to separate the inlet chamber (61) from the volume within the shell structure. A multi-tube heat exchanger (6) for cooling a gas stream, wherein the upper surface of the tube sheet (64) between two of the tubes is three-dimensionally formed such that the tube sheet (64) forms a vertex (641) in the middle between the two adjacent tubes. A multi-tube heat exchanger (6), characterized in that. Device.

7. The apparatus according to claim 6, wherein the reactor is a fluidized bed reactor.

8. The reactor is a multi-zone circulation reactor. In the first polymerization zone (21), the grown polyolefin particles flow upward under fast fluidization or transport conditions. In the second polymerization zone (22), the grown polyolefin particles flow downward in a dense form. The first polymerization zone (21) and the second polymerization zone (22) are interconnected. Polyolefin particles leaving the first polymerization zone (21) enter the second polymerization zone (22), and polyolefin particles leaving the second polymerization zone (22) enter the first polymerization zone (21), forming a circulation of polyolefin particles passing through the first polymerization zone (21) and the second polymerization zone (21). The apparatus according to claim 6.

9. A process for producing an olefin polymer, comprising homopolymerizing an olefin or copolymerizing an olefin with one or more other olefins at a temperature of 20 to 200 °C and a pressure of 0.5 to 10 MPa in the presence of a polymerization catalyst, wherein the method is carried out using the apparatus according to any one of claims 6 to 8.

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