Method for producing ethylene polymer by slurry polymerization

Abstract

A process for polymerizing or copolymerizing ethylene by slurry polymerization in a reactor system including a polymerization reactor, one or more first heat exchangers arranged outside the polymerization reactor, and a closed loop of a temperature control medium for cooling or heating the first heat exchanger, the closed loop being equipped with a second heat exchanger for cooling the temperature control medium and a third heat exchanger for heating the temperature control medium, during polymerization, the slurry is cooled in the first heat exchanger, the temperature of the temperature control medium cooling the first heat exchanger is in the range of 20°C to 50°C, and the temperature control medium is cooled in the second heat exchanger by a coolant having a temperature of -20°C to 45°C.

Description

[Technical field]

[0001] The present disclosure relates to a method for polymerizing ethylene by slurry polymerization or a method for polymerizing ethylene and one or more C3-C 12 The present disclosure provides a process for copolymerizing ethylene and one or more C3-C alkene in a slurry polymerization carried out in a reactor system including a polymerization reactor and one or more heat exchangers disposed outside the polymerization reactor, or for copolymerizing ethylene and one or more C3-C alkene in a slurry polymerization carried out in a reactor system including a polymerization reactor and one or more heat exchangers disposed outside the polymerization reactor. 12 The present disclosure further provides a process for copolymerizing ethylene with one or more C3-C alkene in a slurry polymerization including a washing step, or a process for copolymerizing ethylene with one or more C3-C alkene in a slurry polymerization including a washing step. 12 The present invention provides a process for copolymerizing .alpha.-1 alkenes. [Background technology]

[0002] Slurry polymerization processes for producing ethylene polymers are well-established methods for producing ethylene polymers and are disclosed, for example, in EP 0905152 A1 or WO 2012 / 028591 A1. Such processes are often carried out in a series of reactors, so that different reaction conditions can be set in the polymerization reactors, thereby producing different polymer compositions in the individual polymerization reactors. Multimodal ethylene copolymers produced in this way are characterized, for example, by a good combination of product properties and processability. In slurry processes for producing ethylene polymers, a hydrocarbon or a mixture of hydrocarbons is usually used as diluent. Thus, the slurry is a suspension of ethylene polymer particles in a liquid medium which, besides the main hydrocarbon diluent, also contains further components such as dissolved ethylene, comonomers, aluminum alkyls, hydrogen, and dissolved reaction products such as oligomers and waxes. The principle of producing multimodal ethylene copolymers in a series of reactors by slurry polymerization is disclosed, for example, in F. Alt et al., Macromol. Symp.2001, 163, 135-143.

[0003] Slurry polymerization systems producing ethylene polymers can use an external heat exchanger in the reactor recirculation loop to remove heat generated in the ethylene polymerization reaction. Due to reduced solubility at low temperatures, low molecular weight waxes produced as by-products in the reactor can solidify when the slurry flows through the cooler and comes into contact with the cold wall of the heat exchanger. This can lead to fouling of the heat exchanger. That is, oligomer or polymer layers can accumulate on the cold wall of the heat exchanger, reducing heat transfer within the heat exchanger and reducing heat removal efficiency. Such unwanted wall layer accumulation can also occur on the walls of polymerization reactors. Various methods have been disclosed to reduce fouling of heat exchangers and reactor walls. For example, WO 2015 / 197561 A1 discloses a polyethylene production process in which an external heat exchanger is cooled with a coolant at a temperature of 29°C or higher. However, wall layer accumulation cannot be completely avoided and cleaning of the polymerization system may be necessary from time to time.

[0004] Methods for cleaning polymerization systems for producing ethylene polymers include cleaning the polymerization system with a hydrocarbon at room temperature. However, such cleaning only removes loose particles on the surface of the inner walls. Another option is mechanical cleaning, for example with a hydrojet device. However, the inner surface of the polymerization system can be adversely affected, for example by the formation of rust. Moreover, mechanical cleaning requires a lot of effort. It is necessary to carefully prepare the reactor system in order to open it and enter the reactor system and then remove all traces of water and moisture from the reactor system.

[0005] A preferred method for cleaning a polymerization system for producing ethylene polymers is to wash the reactor system with a hot hydrocarbon. For example, WO 2015 / 197561 A1 discloses that in order to clean a heat exchanger of a reactor system including a polymerization reactor and one or more heat exchangers arranged outside the polymerization reactor, the heat exchanger is usually isolated and a hot hydrocarbon such as hexane, usually at about 155° C., is circulated through the heat exchanger to redissolve deposits.

[0006] US Patent No. 10370,307 B2 discloses a process for oligomerizing ethylene to alpha-olefins, which includes the steps of ethylene oligomerization, catalyst deactivation, and product separation. The reactor is equipped with a cooling loop, which passes at least a portion of the reaction effluent through at least two switchable heat exchangers, which are alternately washed by an integrated washing device.

[0007] Cleaning of reactor systems with hot hydrocarbons has high cleaning efficiency, does not require opening the reactor system, does not affect the inner surface of the polymerization system, and can be performed in a relatively short time with limited personnel. Cleaning of reactor systems with hot hydrocarbons requires replacing the slurry in the reactor system with a hydrocarbon or a mixture of hydrocarbons and heating the hydrocarbon to the appropriate temperature. This can be done using an external heat exchanger and / or reactor cooling jacket as a heater, and instead of cooling these temperature adjustment devices with a coolant, low or medium pressure steam is usually used to heat the device. However, when steam is used as a heating medium, the temperature of the reactor system cannot be smoothly and easily controlled, and steam hammer due to cavitation cannot be avoided. In addition, repeated changes of the temperature adjustment medium from a coolant (usually water) to steam or vice versa can cause corrosion of the external heat exchanger and the polymerization reactor cooling jacket. Corrosion of the heat exchanger, on the one hand, reduces heat transfer due to increased wall roughness, and on the other hand, if the corrosion is severe, it may cause leakage of the temperature adjustment medium, which may require regular replacement of the heat exchanger or parts of the heat exchanger.

[0008] Therefore, ethylene is polymerized in a reactor system by slurry polymerization or by polymerization of ethylene and one or more C3-C 12

[0005] There is a need to provide a process for copolymerizing ethylene with -1 alkenes that can easily and quickly clean the reactor system with hot hydrocarbons in a controlled manner, without the need to replace failed external heat exchangers or polymerization reactor cooling jackets, and that can produce ethylene polymers having a targeted combination of polymer properties in a process that is free of operational problems. Summary of the Invention

[0009] The present disclosure relates to a method for polymerizing ethylene by slurry polymerization at a temperature of 40 to 150°C and a pressure of 0.1 to 5 MPa in the presence of a polymerization catalyst, or a method for polymerizing ethylene and one or more C3 to C6 olefins by slurry polymerization. 12 1. A process for copolymerizing .alpha.-1 alkenes, comprising the steps of: The process is carried out in a reactor system, the reactor system comprising: a polymerization reactor configured to have a liquid content; - an agitator for agitating the reactor contents; - one or more first heat exchangers arranged outside the polymerization reactor for cooling or heating the reactor contents; - one or more circulation pumps for removing the reactor contents from the polymerization reactor and circulating the reactor contents through the one or more first heat exchangers; a closed loop of a temperature adjustment medium for cooling or heating one or more of the first heat exchangers, the closed loop being equipped with a second heat exchanger for cooling the temperature adjustment medium and a third heat exchanger for heating the temperature adjustment medium; During the polymerization of ethylene, or during the polymerization of ethylene and one or more C3 to C 12 During copolymerization with -1 alkenes, - said polymerization reactor is filled with a slurry of ethylene polymer particles in a liquid medium comprising a hydrocarbon diluent; - the slurry is cooled by removing the slurry from the polymerization reactor, cooling the slurry in one or more of the first heat exchangers, and returning the cooled slurry to the polymerization reactor; The temperature of the temperature control medium cooling the one or more first heat exchangers is in the range of 20°C to 50°C; The temperature control medium is cooled in a second heat exchanger by a coolant having a temperature between -20°C and 45°C.

[0010] In some embodiments, the reactor system is part of a two, three, or more reactor system, each of which includes the polymerization reactor and one or more first heat exchangers disposed outside the polymerization reactor for cooling or heating the reactor contents.

[0011] In some embodiments, the first heat exchanger is a double-tube heat exchanger, preferably having a surface roughness R measured according to ASME B46.1 a is less than 5 μm.

[0012] In some embodiments, the polymerization reactor is further equipped with a temperature regulating jacket outside the reactor.

[0013] In some embodiments, the temperature regulating jacket consists of a series of half pipes attached to the outside of the polymerization reactor.

[0014] In some embodiments, a temperature regulation medium for cooling or heating the temperature regulation jacket is a temperature regulation medium for cooling or heating the first heat exchanger or heat exchangers.

[0015] In some embodiments, the process comprises cleaning the polymerization reactor, cleaning one or more of the first heat exchangers, or cleaning the polymerization reactor and one or more of the first heat exchangers, the cleaning step comprising: The polymerization of ethylene or ethylene and one or more C3-C 12terminating the copolymerization with the -1-alkene and discharging the slurry of ethylene polymer particles from the reactor system until the reactor system is empty; introducing a hydrocarbon solvent into the emptied reactor system, thereby forming a wash charge within the reactor system; heating the wash charge in the reactor system to a temperature of 100 to 180° C. -activating an agitator in the polymerization reactor; - heating the wash packing by removing a portion of the wash packing from the polymerization reactor, heating the portion of the wash packing in one or more of the first heat exchangers, and returning the heated portion of the wash packing to the polymerization reactor; - heating a temperature control medium in the third heat exchanger by supplying a heating medium having a temperature between 150 ° C. and 250 ° C. to the third heat exchanger; maintaining the wash packing in the reactor system at a temperature between 100° C. and 180° C. for a period of between 4 and 120 hours while continuously circulating the wash packing through the first heat exchanger or heat exchangers and continuously operating the agitator; draining a wash charge from the reactor system until the reactor system is empty; Polymerization of ethylene or ethylene and one or more C3-C 12 and reinitiating the copolymerization with the -1 alkene.

[0016] In some embodiments, after the slurry of ethylene polymer particles is discharged from the reactor system, a substep is performed of flushing the reactor system with the hydrocarbon diluent prior to introducing the wash charge into the reactor system.

[0017] In some embodiments, the hydrocarbon solvent is introduced into the empty reactor system until the level of the wash charge in the polymerization reactor is at least as high as the level of the slurry in the polymerization reactor during polymerization.

[0018] In some embodiments, after the introduction of the hydrocarbon solvent into the reactor system is terminated after the wash charge has been formed in the reactor system, the wash charge in the reactor system is maintained at a temperature between 100° C. and 180° C., and the wash charge is discharged from the reactor system, without the need for additional introduction of the hydrocarbon solvent.

[0019] In some embodiments, the hydrocarbon solvent is continuously introduced into the reactor system and the wash charge is continuously discharged from the reactor system while maintaining the wash charge in the reactor system at a temperature between 100° C. and 180° C.

[0020] In some embodiments, after terminating circulation of the wash charge from the polymerization reactor through the first heat exchanger or exchangers, the contents of the first heat exchanger or exchangers and the polymerization reactor are discharged to empty the reactor system before resuming polymerization.

[0021] In some embodiments, the wash charge discharged from the reactor system is transferred to the agitated evaporation vessel configured to remove the hydrocarbon solvent from the liquid medium comprising the hydrocarbon solvent by evaporation.

[0022] In some embodiments, the discharge of the wash packing from the reactor system into the stirred distillation vessel occurs by a pressure differential between the wash packing in the reactor system and the stirred distillation vessel.

[0023] In some embodiments, the resulting ethylene polymer is a bimodal or multimodal ethylene polymer. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 shows a schematic of a setup for producing multimodal ethylene polymers in three polymerization reactors by a slurry polymerization process. [Diagram 2] FIG. 2 shows a schematic configuration of a reactor system for carrying out the process for copolymerizing ethylene or ethylene with one or more C3-C12-1 alkenes of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The present invention relates to a method for polymerizing ethylene by slurry polymerization at a temperature of 40 to 150°C and a pressure of 0.1 to 20 MPa in the presence of a polymerization catalyst, or a method for polymerizing ethylene and one or more C3 to C6 olefins by slurry polymerization. 12 A process for copolymerizing C3-C1 alkenes is provided. 12 The C-1 alkene may be linear or branched. 12 -1 alkenes are linear C3-C olefins such as propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, and 1-decene. 10 -1 alkene or branched C2-C such as 4-methyl-1-pentene 10 -1 alkene. Ethylene and two or more C3-C 12 A mixture of ethylene and 1-1-alkene may be copolymerized. Preferred comonomers are C3-C8-1 alkenes, particularly 1-butene, 1-pentene, 1-hexene, 1-heptene and / or 1-octene. In the produced ethylene copolymer, the amount of units incorporating the comonomer is preferably 0.01-25% by weight, more preferably 0.05-15% by weight, and particularly preferably 0.1-12% by weight. Particularly preferred is a process in which ethylene is copolymerized with 0.1% by weight to 12% by weight of 1-hexene and / or 1-butene, particularly 0.1% by weight to 12% by weight of 1-butene.

[0026] The polymerization can be carried out using all of the usual olefin polymerization catalysts; that is, the polymerization can be carried out using, for example, Phillips catalysts based on chromium oxide, Ziegler or Ziegler-Natta catalysts based on titanium, single-site catalysts, or mixtures of such catalysts. For the purposes of this disclosure, single-site catalysts are catalysts based on chemically uniform transition metal coordination compounds. Furthermore, it is also possible to use mixtures of two or more of these catalysts for the polymerization of olefins. Such mixed catalysts are often called hybrid catalysts. The preparation and use of these catalysts for the polymerization of olefins is generally known.

[0027] Preferred catalysts are of the Ziegler type and preferably comprise 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.

[0028] 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, or organometallic halides.

[0029] 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 aluminum alkyls and magnesium alkyls. Even more preferably, the organometallic compounds include aluminum alkyls, most preferably trialkylaluminum compounds or compounds of this type in which the alkyl group is replaced by a halogen atom, such as chlorine or bromine. Examples of such aluminum alkyls include trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, diethylaluminum chloride, or mixtures thereof.

[0030] The process of the present disclosure is a polymerization process carried out as a slurry polymerization. Such a slurry polymerization, also called suspension polymerization, is carried out in a liquid medium containing a hydrocarbon diluent, in which the ethylene polymer produced is insoluble and forms solid particles. Depending on the conditions in the respective polymerization reactor, the remaining liquid medium of the slurry may also be in a supercritical state under the conditions in the polymerization reactor. The solids content of the slurry is generally in the range of 10-80% by weight, preferably in the range of 20-40% by weight.

[0031] In a preferred embodiment, the liquid medium contains, besides the hydrocarbon diluent as the main component, further components such as dissolved monomers or comonomers, dissolved cocatalysts or scavengers (such as aluminum alkyls), dissolved reaction aids (such as hydrogen) or dissolved polymerization reaction products (such as oligomers or waxes). Suitable hydrocarbon diluents should be inert, i.e. they should not decompose under the reaction conditions. Such hydrocarbon diluents are, for example, hydrocarbons having 3 to 12 carbon atoms, in particular saturated hydrocarbons such as isobutane, butane, propane, isopentane, pentane, hexane or octane, or mixtures thereof. In a preferred embodiment, the hydrocarbon diluent is a hydrocarbon mixture. To produce a hydrocarbon mixture from a raw material, less components of the raw material need to be separated than in the case of producing a specific hydrocarbon, and thus the hydrocarbon mixture is economically more attractive as a diluent, but exhibits the same diluent performance as a specific hydrocarbon. However, the hydrocarbon mixture may have a boiling point range.

[0032] The hydrocarbon diluent preferably has a boiling point significantly different from that of the monomers and comonomers used, so as to enable these starting materials to be recovered from the mixture by distillation. Such hydrocarbon diluents are, for example, hydrocarbons with a boiling point above 40° C. or above 60° C., or mixtures containing a high proportion of these hydrocarbons. Thus, in a preferred embodiment of the present disclosure, the polymerization is carried out in a liquid medium containing at least 50% by weight of saturated hydrocarbons having a boiling point above 60° C. at 0.1 MPa, or at least 80% by weight of saturated hydrocarbons having a boiling point above 60° C. at 0.1 MPa.

[0033] The process of the present disclosure is carried out at temperatures in the range of 40-150°C, preferably 50-130°C, particularly preferably 60-90°C, and at pressures of 0.1-5 MPa, preferably 0.15-3 MPa, particularly preferably 0.2-2 MPa, which pressures, like all pressures indicated in the present invention, must be understood as absolute pressures, i.e. pressures having the dimension MPa (abs).

[0034] In a preferred embodiment of the present disclosure, the polymerization is carried out in a series of at least two polymerization reactors connected in series. There is no limit to the number of such reactors in series, but preferably the series consists of two, three or four reactors, most preferably two or three reactors. When a series of polymerization reactors is used in the process of the present disclosure, the polymerization conditions in the polymerization reactors can be different, for example, depending on the nature and / or amount of comonomers, or due to different concentrations of polymerization coagents such as hydrogen.

[0035] Ethylene polymers are usually obtained as powders, i.e. in the form of small particles. The particles usually have a more or less regular shape and size, depending on the shape and size of the catalyst and the polymerization conditions. Depending on the catalyst used, the particles of the polyolefin powder usually have an average diameter of several hundred to several thousand micrometers. In the case of chromium catalysts, the average particle diameter is usually about 300 to about 1600 μm, and in the case of Ziegler-type catalysts, the average particle diameter is usually about 50 to about 3000 μm. Preferred polyolefin powders have an average particle diameter of 100 to 250 μm. The particle size distribution can be advantageously determined, for example, by sieving. Suitable techniques are, for example, vibrating sieve analysis or sieve analysis under an air jet.

[0036] The preferred ethylene polymer obtained by the process of the present disclosure has a density of 0.90 g / cm 3 ~0.97g / cm 3 Preferably, the density is 0.920 to 0.968 g / cm 3 In particular, the range is 0.945 to 0.965 g / cm 3 Density is understood to be the density determined according to DIN EN ISO 1183-1:2004, method A (immersion) on a compression-molded plate of thickness 2 mm, pressed at 180° C. and 20 MPa for 8 min and subsequently crystallized in boiling water for 30 min.

[0037] In a preferred embodiment, the ethylene polymers produced by the process of the present disclosure have a MFR measured according to DIN EN ISO 1133:2005, condition G, at a temperature of 190° C. and a load of 21.6 kg. 21.6 The flow rate is preferably 0.5 to 300 g / 10 min, more preferably 1 to 100 g / 10 min, further preferably 1.2 to 100 g / 10 min, and particularly preferably 1.5 to 50 g / 10 min.

[0038] The ethylene polymer obtained by the process of the present disclosure may be a monomodal, bimodal or multimodal ethylene polymer. Preferably, the ethylene polymer is a bimodal or multimodal ethylene polymer. The term "multimodal" here refers to the mode of the obtained ethylene copolymer, indicating that the ethylene copolymer comprises at least two polymer fractions obtained under different reaction conditions, whether or not this mode is recognizable as a separated maximum in a gel permeation chromatography (GPC) curve. Different polymerization conditions can be achieved, for example, by using different hydrogen concentrations and / or by using different comonomer concentrations in different polymerization reactors. Such polymers can be obtained by polymerizing olefins in a series of two or more polymerization reactors under different reaction conditions. However, it is also possible to obtain such bimodal or multimodal polyolefins by using mixed catalysts. In addition to the molecular weight distribution, the polyolefins can also have a comonomer distribution, preferably the average comonomer content of the polymer chains with higher molecular weight is higher than the average comonomer content of the polymer chains with lower molecular weight. The term "multimodal" as used herein is also intended to include "bimodal".

[0039] In a preferred embodiment of the disclosed process, the polymerization is carried out in a series of polymerization reactors, with an ethylene homopolymer, preferably a low molecular weight ethylene homopolymer, being produced in the first polymerization reactor and an ethylene copolymer, preferably a high molecular weight ethylene copolymer, being produced in the next polymerization reactor. To enable the production of ethylene homopolymer in the first polymerization reactor, no comonomer is fed to the first polymerization reactor, either directly or as a component of a feed or recycle stream introduced into the first polymerization reactor of the series. The multimodal ethylene copolymer thus obtained preferably comprises 35-65% by weight of the ethylene homopolymer produced in the first polymerization reactor and 35-65% by weight of the ethylene copolymer produced in the subsequent polymerization reactor. If the series of polymerization reactors comprises one or more prepolymerization reactors, the prepolymerization is preferably carried out without the addition of comonomer.

[0040] In another preferred embodiment of the present disclosure, ethylene polymer is produced in a series of three polymerization reactors, i.e., a first polymerization reactor and two subsequent polymerization reactors, the ethylene polymer produced in the first polymerization reactor is an ethylene homopolymer, preferably a low molecular weight ethylene homopolymer, the ethylene polymer produced in one of the subsequent polymerization reactors is an ethylene copolymer, preferably a high molecular weight copolymer, and the ethylene polymer produced in the other subsequent polymerization reactor is an ethylene copolymer of higher molecular weight, preferably an ultra-high molecular weight copolymer. The multimodal ethylene copolymer thus obtained preferably comprises 30-60%, more preferably 45-55%, by weight of the ethylene homopolymer produced in the first polymerization reactor, 30-65%, more preferably 20-40%, by weight of the ethylene copolymer produced in one subsequent polymerization reactor, and 1-30%, more preferably 15-30%, by weight of the higher molecular weight ethylene copolymer produced in the other subsequent polymerization reactor.

[0041] FIG. 1 shows a schematic of a setup for producing multimodal ethylene polymers in a series of three polymerization reactors by a slurry polymerization process.

[0042] Polymerization of ethylene or polymerization of ethylene and one or more C3-C olefins in the slurry in the first polymerization reactor (1) 12 A diluent for copolymerization with the -1-alkene is fed to the reactor via a feed line (2), while other components of the reaction mixture, such as catalyst, ethylene, possible comonomers and polymerization aids, are fed to the reactor via one or more feed lines (3). As a result of the polymerization in the reactor (1), a slurry of solid polyolefin particles in a liquid medium is formed. This slurry is fed via line (4) to a second polymerization reactor (5), where further polymerization takes place. Fresh comonomer or further components of the reaction mixture can be fed to the reactor (5) via one or more feed lines (6). The slurry from the reactor (5) is then fed via line (7) to a third polymerization reactor (8), where further polymerization takes place. One or more feed lines (9) allow supplemental feeding of comonomer or other components of the reaction mixture to the reactor (8).

[0043] The slurry of solid polyolefin particles in liquid medium produced in the reactor (8) is continuously transferred via line (10) to a collection vessel (15). The slurry is then sent via line (20) to a centrifuge (21) where the solid polyolefin particles are separated from the liquid medium. The separated polyolefin particles, which after removal of the liquid medium still have residual moisture, i.e., 10-30 wt. % residual liquid medium, are transferred via line (22) to a dryer (not shown) and then to a pelletizing unit (not shown).

[0044] The separated liquid medium is transferred via line (23) to a separate collection vessel (24) and from there by pump (25) via line (26) to the polymerization reactors (1), (5) and / or (8). To control and regulate the transfer of the liquid medium to the reactors (1), (5) and / or (8), line (26) and its branches are equipped with valves (27), (28) and (29).

[0045] The process of the present disclosure is carried out in a reactor system including a polymerization reactor configured such that the contents are in liquid form, i.e., the contents may be, for example, a slurry of polymer particles in a liquid medium or a solution of a polymer in a solvent. The reactor system further includes an agitator for agitating the reactor contents. The reactor of such a reactor system is commonly referred to as a stirred tank reactor.

[0046] A preferred polymerization reactor is a cylindrical polymerization reactor comprising a cylindrical reactor wall, a bottom reactor head connected to the cylindrical reactor wall by a bottom tangent, and a top reactor head connected to the cylindrical reactor wall by a top tangent. The cylindrical polymerization reactor preferably has an inner diameter D corresponding to the inner diameter of the cylindrical reactor wall, and a height H which is the distance from the bottom tangent to the top tangent measured along the central axis of the cylindrical polymerization reactor. Such a cylindrical polymerization reactor preferably has a height / diameter ratio (H / D) of 1.5-4, more preferably a height / diameter ratio (H / D) of 2.5-3.5. In a preferred embodiment, the polymerization reactor has an inner surface in contact with the slurry, the surface roughness R a is less than 5 μm, preferably less than 3 μm, in particular less than 1.5 μm, measured in accordance with ASME B46.1.

[0047] The agitator of the reactor system of the present disclosure can induce the flow of the reactor contents and mix the reactor contents. In a preferred embodiment, the agitator is located at the center of the reactor, preferably including a motor located at the upper reactor head, a rotating shaft extending along the central axis of the reactor, and one or more stages of agitator blades. Preferably, the agitator blades attached to the rotating shaft are 2 to 6 stages. More preferably, the agitator blades are 4 or 5 stages. One stage of agitator blades is usually composed of multiple agitator blades. A preferred stage of agitator blades is composed of 2 to 4 blades.

[0048] In a preferred embodiment, a motor rotates the agitator shaft and attached agitator blades. The rotation of the blades induces a vertical flow of the reactor contents, mainly in a circular cross section around the agitator shaft. This vertical flow of the reactor contents is preferably a downward flow. At the bottom head, this flow changes direction and flows initially outward towards the reactor wall, then back upward to the top, where it changes direction again and returns to the center of the polymerization reactor. The rotation of the agitator also creates a secondary flow pattern within the reactor of the reactor contents. This secondary flow is a circular flow in the direction of the agitator rotation. To control this circular flow, the polymerization reactor is preferably equipped with one or more baffles.

[0049] The reactor system of the disclosed process supports slurry polymerization of ethylene and, optionally, one or more comonomers and includes a polymerization reactor and one or more first heat exchangers disposed outside the polymerization reactor.

[0050] The reactor system for carrying out the process of the present disclosure includes one or more first heat exchangers disposed outside the polymerization reactor to cool or heat the reactor contents. During polymerization, polymerization heat is removed from the polymerization reactor by removing the slurry from the polymerization reactor, cooling the slurry in one or more first heat exchangers, and returning the cooled slurry to the polymerization reactor. The one or more first heat exchangers can be any of those typically used at the temperatures and pressures associated with the fluids described herein, for example, the heat exchanger may be selected from double tube, shell & tube, plate, plate & shell, and spiral heat exchangers.

[0051] Preferably, the first heat exchanger is a double-tube heat exchanger. It is essentially a long jacketed pipe, usually with a length of about 100 m to 600 m. The internal diameter of the pipe usually ranges from about 150 mm to 400 mm. Preferably, the double-tube heat exchanger is composed of individual jacketed segments. These segments are joined, preferably with flanges, either directly or separated by a bend. The preferred bend is a 180° bend. Preferably, the length of the straight individual segments is 6 m to 12 m. Each double-tube heat exchanger is preferably composed of 4 to 50, more preferably 5 to 40, in particular 10 to 35 individual jacketed segments. The flow of reactor contents and temperature control medium through the jacket of the double-tube heat exchanger may be parallel, countercurrent or a combination of parallel / countercurrent. Preferably, the flow in the first heat exchanger is a combination of parallel / countercurrent.

[0052] In a preferred embodiment of the present disclosure, the first heat exchanger has a surface roughness R measured in accordance with ASME B46.1. a The double-pipe heat exchanger has an inner surface in contact with the slurry, the inner surface having a surface roughness R of less than 5 μm, preferably less than 3 μm, and particularly less than 1.5 μm. a The surface roughness R defined in this disclosure is determined by the surface roughness of the inner surface of the wall layer. a can be achieved, for example, by polishing, such as mechanical polishing or electrolytic polishing.

[0053] The reactor system may comprise one first heat exchanger outside the polymerization reactor. However, the reactor system may also comprise two, three, four or more first heat exchangers outside the polymerization reactor. Preferably, the reactor system comprises two or three first heat exchangers <264 / >.

[0054] The reactor system for carrying out the process of the present disclosure further comprises one or more circulation pumps for removing the reactor contents from the polymerization reactor and circulating the reactor contents through the one or more first heat exchangers. The temperature control medium is preferably circulated by the circulation pump, which provides a substantially constant flow rate of the temperature control medium at the outlet of the circulation pump. The one or more circulation pumps are preferably located upstream of the one or more first heat exchangers, i.e. between the outlet of the polymerization reactor, where the removed reactor contents leave the polymerization reactor, and the one or more first heat exchangers. A preferred circulation pump is a centrifugal pump with a semi-open impeller made of electropolished stainless steel.

[0055] In the disclosed process, the temperature adjustment medium for cooling or heating the first heat exchanger or heat exchangers is circulated in a closed loop. If the reactor system comprises one or more first heat exchangers, preferably all first heat exchangers of the reactor system are operated in parallel in one closed loop of circulating temperature adjustment medium. The first heat exchanger or heat exchangers arranged outside the polymerization reactor serve to cool the polymerization reactor contents as well as to heat the polymerization reactor contents. Depending on the function, the first heat exchanger must be equipped with a cooling medium when cooling the polymerization reactor contents and with a heating medium when heating the polymerization reactor contents. In the disclosed process, both tasks are performed by the temperature adjustment medium, which serves to cool the first heat exchanger or heat exchangers and to heat the first heat exchanger or heat exchangers. The closed loop of the temperature adjustment medium is equipped with two further heat exchangers: a second heat exchanger for cooling the temperature adjustment medium and a third heat exchanger for heating the temperature adjustment medium.

[0056] Cooling of the temperature control medium, i.e. using the temperature control medium as a coolant, is carried out during the polymerization of ethylene in a polymerization reactor or during the polymerization of ethylene and one or more CC3-C 12During copolymerization with -1-alkene, the heat of polymerization is removed. The second heat exchanger for cooling the temperature adjustment medium is cooled by a coolant (preferably water). The coolant is fed through a coolant feed line, passes through the second heat exchanger and then discharged through a coolant outlet line. Preferably, the second heat exchanger for cooling the temperature adjustment medium is a plate heat exchanger. In a preferred embodiment of the present disclosure, the second heat exchanger is divided into a number of plate heat exchangers operating in parallel, for example a battery of 2, 3, 4, 5, 6, 7, 8, 9, or 10 plate heat exchangers operating in parallel. In another preferred embodiment, the second heat exchanger for cooling the temperature adjustment medium is a cooling tower, for example an atmospheric cooling tower.

[0057] During polymerization, the temperature of the circulating temperature control medium can be maintained by adjusting the flow rate of the coolant through the second heat exchanger by a control valve arranged in the coolant supply line or preferably in the coolant outlet line. In a preferred embodiment, the control of the temperature of the circulating temperature control medium is performed by splitting the flow of the temperature control medium conveyed to the second heat exchanger into two parts. One part passes through the second heat exchanger and is cooled by the coolant, while the second part bypasses the second heat exchanger and returns directly to the inlet side of the circulation pump circulating the temperature control medium. The flow rate of the temperature control medium through the bypass is preferably adjusted by a control valve arranged in the bypass line. Changing the opening of the control valve changes the ratio of the part of the temperature control medium passing through the second heat exchanger to the part bypassing the second heat exchanger and therefore the temperature of the combined temperature control medium after bringing these two parts together again.

[0058] Heating of the temperature control medium, i.e. use of the temperature control medium as a heating medium for the polymerization reactor contents, is carried out, for example, at the start of the polymerization or during cleaning of the reactor system. The third heat exchanger for heating the temperature control medium is heated by a heating medium, which is preferably steam. The heating medium is then fed via the heating medium feed line, passes through the third heat exchanger and is then removed via the heating medium outlet line. The third heat exchanger for heating the temperature control medium is preferably a shell-and-tube heat exchanger.

[0059] When carrying out the process to produce ethylene polymers as a multi-reactor polymerization in a combination of two, three or more reactor systems, it is particularly preferred that all first heat exchangers are cooled or heated by a temperature control medium circulated in one closed loop system, and that all first heat exchangers are operated in parallel in a closed loop of circulating temperature control medium cooled by one second heat exchanger.

[0060] According to a preferred embodiment of the present disclosure, the slurry in the polymerization reactor is not only cooled or heated by one or more first heat exchangers located outside the polymerization reactor, but also cooled or heated by a temperature control jacket outside the polymerization reactor. Preferably, the temperature control jacket is also temperature controlled by a temperature control medium that cools or heats one or more first heat exchangers used to cool or heat the reactor contents. The temperature control jacket preferably consists of a series of half pipes attached to the outside of the polymerization reactor. Furthermore, it is preferred that the first heat exchanger and the temperature control jacket outside the polymerization reactor are operated in parallel in a closed loop of a circulating temperature control medium. When carrying out the process of producing ethylene polymers as a multi-reactor polymerization in a combination of two, three or more reactor systems, preferably each reactor reactor is equipped with a temperature control jacket outside the reactor. Particularly preferably, all first heat exchangers and all cooling jackets are operated in parallel in a closed loop of a circulating temperature control medium.

[0061] During polymerization of ethylene or ethylene and one or more C3-C 12 During copolymerization with the -1-alkene, the polymerization reactor is filled with a slurry of ethylene polymer particles in a liquid medium comprising a hydrocarbon diluent, and the slurry is cooled by withdrawing the slurry from the polymerization reactor, cooling the slurry in one or more first heat exchangers, and returning the cooled slurry to the polymerization reactor.

[0062] According to the process of the present invention, during the polymerization of ethylene or ethylene and one or more C3-C 12 During copolymerization with -1-alkene, the temperature of the temperature control medium cooling the one or more first heat exchangers is in the range of 20°C to 50°C, preferably 25°C to 45°C, more preferably 29°C to 40°C, and the temperature control medium is cooled in the second heat exchanger by a coolant having a temperature of -20°C to 45°C, preferably 15°C to 40°C, more preferably 20°C to 36°C.

[0063] In a preferred embodiment of the process of the present disclosure, the process is for polymerizing ethylene or ethylene and one or more C3-C 12 The process for copolymerizing ethylene with one or more C3-C olefins includes the steps of washing the polymerization reactor, washing the one or more first heat exchangers, or washing the polymerization reactor and the one or more first heat exchangers. The washing step preferably includes the steps of terminating the polymerization, introducing a hydrocarbon solvent into the reactor system to form a wash packing, heating the wash packing and circulating the wash packing in the reactor system while operating an agitator in the polymerization reactor, discharging the wash packing from the reactor system, and copolymerizing ethylene with one or more C3-C olefins in the reactor system. 12 and reinitiating the copolymerization with the -1 alkene.

[0064] Polymerization of ethylene or ethylene and one or more C3-C 12Termination of the copolymerization with -1-alkene is preferably carried out by stopping all feed flows to the reactor system or combination of double-tube reactor systems, while preferably continuing operation of the circulation pump or circulation pumps. Termination of the feed flows means that ethylene, comonomer, catalyst, hydrogen and hydrocarbon diluent are no longer fed to the reactor system. The slurry of ethylene polymer particles in a liquid medium is then discharged from the reactor system until the reactor system is empty. A preferred method for discharging the slurry of ethylene polymer particles in a liquid medium from a multi-reactor slurry polymerization system is disclosed, for example, in International Publication No. 2018 / 127472 A1.

[0065] After emptying the reactor system from the slurry, it is preferred to flush the reactor system with a hydrocarbon in order to remove any ethylene polymer particles that may remain in the reactor system after the slurry has been discharged. The hydrocarbon for flushing the reactor system is preferably the hydrocarbon used as a diluent in the polymerization. In a preferred embodiment, the hydrocarbon for removing the residual ethylene polymer particles is introduced into the reactor system and then circulated by one or more circulation pumps through one or more first heat exchangers for, for example, 10 minutes to 3 hours. The agitator of the polymerization reactor is then preferably stopped and the circulation pump is operated for 1 hour to 12 hours, more preferably 1.5 hours to 8 hours, in particular 2 hours to 4 hours. The circulation pump is then preferably stopped and the reactor contents are preferably discharged from the bottom outlet of the polymerization reactor. In a preferred embodiment, the agitator of the polymerization reactor is restarted while a portion of the hydrocarbon used for scrubbing the reactor system still remains in the polymerization reactor. Preferably, at least the bottom of the polymerization reactor is washed a second time with a hydrocarbon in order to remove any ethylene polymer particles still remaining.

[0066] To wash the reactor system, a hydrocarbon solvent is introduced into the emptied reactor system, thereby forming a wash charge in the reactor system. The hydrocarbon solvent for washing the reactor system is preferably the hydrocarbon diluent used in the polymerization. The hydrocarbon solvent is preferably introduced into the empty reactor system until the liquid level of the wash charge in the polymerization reactor reaches at least the same height as the liquid level of the slurry in the polymerization reactor during polymerization. In a preferred embodiment, the reactor system is completely filled with the hydrocarbon solvent.

[0067] The wash packing in the reactor system is then preferably heated to a temperature of 100°C to 180°C, preferably 110°C to 170°C, more preferably 120°C to 160°C, while the agitator in the polymerization reactor is operating. Heating is preferably performed by removing a portion of the wash packing from the polymerization reactor, heating the removed wash packing in one or more first heat exchangers, and returning the heated wash packing to the polymerization reactor. The temperature control medium is preferably heated in the third heat exchanger by supplying the third heat exchanger with a heating medium having a temperature of 150°C to 250°C, preferably 170°C to 230°C, more preferably 180°C to 210°C. The heating medium for heating the third heat exchanger is preferably steam having a pressure of 0.6MPa to 1.5MPa, more preferably having a pressure of 0.7MPa to 1.1MPa. In a preferred embodiment, the wash packing is heated not only by passing a portion of the wash packing through a heated first heat exchanger or exchangers, but also by heating a temperature regulating jacket on the outside of the polymerization reactor.

[0068] The heated wash packing is preferably maintained at a temperature of from 100°C to 180°C, preferably from 110°C to 170°C, more preferably from 120°C to 160°C, for a period of from 4 hours to 120 hours, preferably from 10 hours to 80 hours, more preferably from 15 hours to 50 hours, in the reactor system with the wash packing being continuously circulated through the first heat exchanger or exchangers and the agitator being continuously operated.

[0069] Preferably, the wash charge is then discharged from the reactor system until the reactor system is empty. Thereafter, polymerization of ethylene or polymerization of ethylene and one or more C3-C 12 Copolymerization with the -1 alkene is resumed in the reactor system.

[0070] The polymerization reactor contents and the contents of the first heat exchanger(s) may be discharged together from one outlet of the reactor system. Preferably, the polymerization reactor contents and the contents of the first heat exchanger(s) are discharged separately from two or more outlets of the reactor system. In a preferred embodiment, the circulation of the wash charge from the polymerization reactor through the first heat exchanger(s) is terminated, and the first heat exchanger(s) and the polymerization reactor contents are then discharged from two or more outlets of the reactor system.

[0071] In a preferred embodiment of the process of the present disclosure, the introduction of the hydrocarbon solvent into the reactor system is terminated after the wash charge is formed in the reactor system, and thereafter, the wash charge in the reactor system is maintained at a temperature between 100° C. and 180° C., and the wash charge is discharged from the reactor system without the introduction of additional hydrocarbon solvent.

[0072] In another preferred embodiment of the process of the present disclosure, the introduction of the hydrocarbon solvent into the reactor system is not terminated after the formation of the wash charge in the reactor system, and the liquid level of the wash charge in the polymerization reactor is maintained by draining the wash charge from the reactor system. By continuously introducing the hydrocarbon solvent and continuously removing the wash charge from the reactor system, the increase in viscosity of the wash charge in the reactor system due to dissolution of the oligomer or polymer wall layer becomes less significant, and saturation of the wash charge by the dissolved wall layer does not occur or is at least reached later.

[0073] In a preferred embodiment of the present disclosure, the wash charge discharged from the reactor system is transferred to an agitated evaporation vessel configured to allow the extraction of the hydrocarbon solvent from the liquid medium comprising the hydrocarbon solvent by evaporation. The discharge of the wash charge from the reactor system to the agitated distillation vessel is preferably performed by a pressure difference between the wash charge in the reactor system and the agitated distillation vessel. In a preferred embodiment of the present disclosure, the hot wash charge is depressurized during its entry into the evaporation vessel, resulting in a significant temperature drop as well as the evaporation of a significant amount of the hydrocarbons.

[0074] Preferably, the evaporation vessel is first filled with the wash charge discharged from the reactor system, after which evaporation of the hydrocarbon solvent is started. Preferably, evaporation is continued until a concentrated mixture of the previously dissolved oligomeric and polymeric material and the remaining hydrocarbon solvent is formed. Usually, at least a portion of the previously dissolved oligomeric and polymeric material has precipitated. After discharging the remaining concentrated mixture, the evaporation vessel can be filled again with the wash charge discharged from the reactor system. In a preferred embodiment, the wash charge discharged from the reactor system is fed to a second stirred evaporation vessel, rather than ceasing discharge until the stirred evaporation vessel is empty again, when it is no longer possible to feed the stirred evaporation vessel because the evaporation vessel is completely full.

[0075] FIG. 2 shows a process for polymerizing ethylene or ethylene and one or more CC3-C 12 1 shows a schematic of a reactor system setup for carrying out the process of the present disclosure for copolymerizing -1-alkene.

[0076] The polymerization reactor (100) includes an agitator (101) for agitating the reactor contents. The agitator (101) includes a motor (102), a rotating shaft (103) installed substantially vertically in the center of the reactor (100), and at least one impeller (104). The polymerization reactor (100) is equipped with a temperature control jacket (105) on the outer surface of the reactor (100), through which a temperature control medium flows. The reactor contents are taken out of the polymerization reactor (100) via line (106) to a circulation pump (107), which pumps the reactor contents through line (108) to a first heat exchanger (109). The conditioned reactor contents that have passed through the first heat exchanger (109) are returned to the polymerization reactor (100) via line (110). The conditioning medium for conditioning the first heat exchanger (109) comes through line (111).

[0077] The components of the reaction mixture, such as catalyst components, ethylene, possible comonomers, hydrogen, and a hydrocarbon diluent, are fed to the reactor through one or more feed lines (112). The polymerization of ethylene or the polymerization of ethylene and one or more C3-C olefins in the polymerization reactor (100) is carried out. 12 During copolymerization with -1-alkene, the slurry is removed from the polymerization reactor (100) and the first heat exchanger (109) acts as a cooler. The slurry is then sent through line (113) to a downstream reactor or to product recovery.

[0078] During polymerization, valves (163), (165), (180) and (181) are closed. The cooled temperature control medium for cooling the first heat exchanger (109) comes from the second heat exchanger (120). The cooled temperature control medium leaving the second heat exchanger (120) through line (130) is circulated by the second circulation pump (121) through lines (122) and (123), valve (124) and line (111) to the first heat exchanger (109) and then through valves (125) and (126), control valve (127) and lines (128) and (129) back to the second heat exchanger (120).

[0079] During the polymerization, the temperature control jacket (105) of the polymerization reactor (100) is preferably also cooled by the temperature control medium. To cool the temperature control jacket (105), the second circulation pump (121) circulates the cooled temperature control medium from the second heat exchanger (120) through the temperature control jacket (105) via line (130), lines (122) and (131), valve (132), line (133) and then back to the second heat exchanger (120) via line (134), valve (135), control valve (136) and line (129).

[0080] To control the temperature of the polymerization reactor (100), a temperature transducer (140) generates a temperature signal (141) representative of the temperature of the polymerization reactor (100). A temperature controller (142) receives the temperature signal (141) along with a set point (SP) representative of the desired temperature of the polymerization reactor (100). In response to the temperature signal (141), the temperature controller (142) provides output signals (143) and (144) responsive to the difference between the temperature signal (141) and the set point of the reactor temperature. Control valves (127) and (136), which control the flow of temperature regulating medium from the first heat exchanger (109) and the temperature regulating jacket (105) to the second heat exchanger (120), are operated in response to the signals (143) and (144).

[0081] The temperature control medium is cooled in the second heat exchanger (120) using coolant that enters the second heat exchanger (120) via line (150) and exits the second heat exchanger (120) via line (151). To control the temperature of the temperature control medium cooling the first heat exchanger (109), a portion of the temperature control medium conveyed through line (129) does not pass through the second heat exchanger (120) but bypasses the second heat exchanger (120) via line (152). The flow rate of the temperature control medium bypassing the second heat exchanger (120) is regulated by a control valve (153). A temperature transducer (154) generates a temperature signal (155) representative of the temperature of the combined temperature control medium after combining the portion of the temperature control medium passing through the second heat exchanger (120) with the portion of the temperature control medium bypassing the second heat exchanger (120) via line (152). The temperature controller (156) receives a temperature signal (155) together with a set point (SP) representative of the desired temperature of the temperature control medium entering the second circulating pump (121). In response to the temperature signal (155), the temperature controller (156) provides an output signal (157) which is dependent on the difference between the temperature signal (155) and the set point temperature of the temperature control medium flowing in line (130). The control valve (153) is operated in response to the signal (157).

[0082] The first heat exchanger (109) acts as a heater to heat a portion of the reactor contents that is removed from the polymerization reactor (100) and circulated through the first heat exchanger (109) for cleaning the polymerization reactor, for cleaning the first heat exchanger(s), or for cleaning the polymerization reactor and the first heat exchanger(s).

[0083] To heat the contents of the polymerization reactor (100), valves (124), (126), (132), and (135) are closed and a temperature control medium for heating the first heat exchanger (109) is provided from the third heat exchanger (160). The temperature control medium is circulated by the third circulation pump (161) through the third heat exchanger (160), line (162), valve (163), line (111) to the first heat exchanger (109) and then returns to the third circulation pump (161) through valve (125), line (164), valve (165), line (166).

[0084] The temperature control medium is heated in the third heat exchanger (160), preferably using medium pressure steam entering the third heat exchanger (160) through line (170). The medium pressure steam flows through line (171) to a control valve (172) which regulates the flow of the medium pressure steam. The medium pressure steam then flows through line (170) into the third heat exchanger (160), passes through the third heat exchanger (160), and exits the third heat exchanger (160) through line (173). To control the temperature of the temperature control medium heating the first heat exchanger (109), a temperature transducer (174) generates a temperature signal (175) representative of the temperature of the temperature control medium exiting the third heat exchanger (160) through line (162). A temperature controller (176) receives the temperature signal (175) along with a set point (SP) representative of the desired temperature of the temperature control medium flowing through line (162). In response to temperature signal (175), temperature controller (176) provides an output signal (177) responsive to the difference between temperature signal (175) and a setpoint temperature of the temperature regulating medium flowing in line (162). Control valve (172) is operated in response to signal (177).

[0085] Additionally, the temperature control medium can also be used to heat the temperature control jacket (105). The temperature control medium is then circulated by the third circulation pump (161) through the third heat exchanger (160), line (162), valve (180) and line (133) to the temperature control jacket (105) and then back to the third circulation pump (161) through line (133), valve (181), line (164), valve (165) and line (166).

[0086] After the reactor system has been cleaned, the circulation pumps (107) and (161) are stopped from operating, valves (190) and (191) are opened and the contents of the first heat exchanger (109) are discharged via line (108), circulation pump (107), valve (190), lines (192) and (193) and valve (191) into the evaporation vessel (194). Once the first heat exchanger (109) is empty, valve (190) is closed, valve (195) is opened and the contents of the polymerization reactor (100) are discharged via valve (195), lines (196) and (193) and valve (191) into the evaporation vessel (194).

[0087] The evaporation vessel (194) includes an agitator (197) for agitating the reactor contents. The agitator (197) includes a motor (198), a rotating shaft (199) mounted substantially vertically in the center of the evaporation vessel (194), and at least one impeller (200). During evaporation, the evaporated hydrocarbon solvent is withdrawn through line (201) to an off-gas system (not shown). After evaporation, a concentrated mixture of previously dissolved oligomeric and polymeric materials and remaining hydrocarbon solvent is withdrawn through line (202) and disposed of.

[0088] The disclosed process allows for a fast and economical cleaning of the reactor system with hot hydrocarbons, and in particular allows for a fast transition from cooling the first heat exchanger and temperature regulating jacket to heating the first heat exchanger and temperature regulating jacket, and vice versa. The process is easy to control and does not require the time-to-time replacement of defective external heat exchangers or polymerization reactor temperature regulating jackets. Nevertheless, the process allows for the preparation of ethylene polymers with a targeted combination of polymer properties without operational problems. EXAMPLES

[0089] Comparative example A Ethylene polymers were produced continuously in a commercially operated series of three reactor systems, each containing a polymerization reactor, as shown in Figure 1. Each polymerization reactor was part of a reactor system further including two parallel first heat exchangers located outside the polymerization reactor to remove the heat of polymerization. All first heat exchangers consisted of straight jacketed segments, each 12 m long, which were flanged together. The polymerization reactors were further equipped with temperature-regulating jackets. All first heat exchangers and temperature-regulating jackets of the polymerization reactors were cooled by a coolant circulating in a closed loop, which in turn was cooled by a second heat exchanger. For over five years, ethylene and 1-butene have been copolymerized in a slurry in the presence of a Ziegler-type catalyst to produce various grades of polyethylene at reactor temperatures between 65 °C and 85 °C and reactor pressures between 0.2 MPa and 1.3 MPa. Depending on the grade, the production rate varied in the range of 30 to 41 t / h.

[0090] During this period, a decrease in heat transfer in the first heat exchanger was periodically observed due to the accumulation of a wall layer in the first heat exchanger. To remove the wall layer in the first heat exchanger, the reactor system was washed with hot hydrocarbons on average twice a year. To heat the reactor contents during the washing, the first heat exchanger and the temperature control jacket were disconnected from the closed loop of circulating coolant and connected to a supply of saturated steam at a pressure of 0.8 MPa. Each washing of the first heat exchanger and the temperature control jacket of the polymerization reactor took 5 days from the end of the polymerization to the resumption of polymerization after the washing of the reactor system.

[0091] At the end of the year period, an inspection of the first heat exchanger was carried out and it was found that approximately 20% of the straight segments of the first heat exchanger were so corroded that a coolant leak in the next future could not be ruled out, and so the segments had to be replaced. Example 1

[0092] Ethylene polymers were produced continuously in a commercially operated series of three reactor systems, each containing a polymerization reactor, as shown in Figure 1. Each polymerization reactor was part of a reactor system, as shown in Figure 2, but consisted of two parallel first heat exchangers placed outside the polymerization reactor, instead of one as shown in Figure 2, to remove the heat of polymerization. All first heat exchangers consisted of straight jacket segments, each 12 m long, and the segments were flanged together. The polymerization reactors were further equipped with temperature-control jackets. The first heat exchangers and the temperature-control jackets of the polymerization reactors were all cooled by a temperature-control medium circulating in a closed loop. During polymerization, the temperature-control medium was cooled by the second heat exchanger. Over a period of more than five years, ethylene and 1-butene were polymerized in a slurry in the presence of a Ziegler-type catalyst at reactor temperatures of 65 °C to 85 °C and reactor pressures of 0.2 MPa to 1.3 MPa to produce various grades of polyethylene. Depending on the grade, the production rate varied in the range of 30 to 41 t / h.

[0093] During this period, a decrease in heat transfer in the heat exchangers was periodically observed due to the accumulation of a wall layer in the first heat exchanger. To remove the wall layer in the first heat exchanger, the reactor system was washed with hot hydrocarbons on average twice a year. To heat the reactor contents, the closed loop of the circulating temperature control medium was equipped with a third heat exchanger connected to a saturated steam source with a pressure of 0.9 MPa. Cleaning of the first heat exchanger and the temperature control jacket of the polymerization reactor took 3 days from the end of the polymerization to the resumption of polymerization after cleaning of the reactor system.

[0094] At the end of the five year period, the first heat exchanger was inspected. None of the straight segments of the first heat exchanger were severely corroded enough to require replacement of the segments.

Claims

1. Polymerizing ethylene by slurry polymerization at a temperature of 40 to 150° C. and a pressure of 0.1 to 5 MPa in the presence of a polymerization catalyst, or polymerizing ethylene and one or more C ３ ~C １２ 1. A process for copolymerizing 1-1 alkenes comprising the steps of: The process is carried out in a reactor system, the reactor system comprising: a polymerization reactor configured so that the contents are in liquid form; - a stirrer for stirring the contents of the reactor; one or more first heat exchangers arranged outside the polymerization reactor for cooling or heating the contents of the reactor; - one or more circulation pumps for removing the reactor contents from the polymerization reactor and circulating the reactor contents through the first heat exchanger or heat exchangers; a closed loop of a temperature adjustment medium for cooling or heating one or more of the first heat exchangers, the closed loop being capable of forming a cooling closed loop comprising a second heat exchanger for cooling the temperature adjustment medium but not a third heat exchanger for heating the temperature adjustment medium, and a heating closed loop comprising a third heat exchanger for heating the temperature adjustment medium but not a second heat exchanger for cooling the temperature adjustment medium, During the polymerization of ethylene or ethylene and one or more C ３ ~C １２ During copolymerization with -1 alkenes, - said polymerization reactor is filled with a slurry of ethylene (co)polymer particles in a liquid medium comprising a hydrocarbon diluent; - the slurry is cooled by removing the slurry from the polymerization reactor, cooling the slurry in one or more of the first heat exchangers, and returning the cooled slurry to the polymerization reactor; the temperature of the temperature control medium in the closed cooling loop cooling the first heat exchanger or exchangers is in the range of 20°C to 50°C; The temperature control medium in the closed cooling loop is cooled in a second heat exchanger by a coolant having a temperature between -20°C and 45°C.

2. 10. The process of claim 1, wherein the reactor system is part of a two, three or more reactor system each including the polymerization reactor and one or more first heat exchangers disposed outside the polymerization reactor for cooling or heating the reactor contents.

3. 3. The process according to claim 1 or 2, wherein the polymerization reactor is further equipped with a temperature control jacket on the outside of the reactor.

4. 4. The process according to claim 3, wherein the temperature control jacket is composed of a series of half pipes attached to the outside of the polymerization reactor and / or the temperature control medium for cooling or heating the temperature control jacket is the temperature control medium for cooling or heating the first heat exchanger or heat exchangers.

5. 5. The process according to any one of claims 1 to 4, comprising the steps of cleaning the polymerization reactor, cleaning one or more of the first heat exchangers, or cleaning the polymerization reactor and one or more of the first heat exchangers, wherein the cleaning step comprises: The polymerization of ethylene or ethylene and one or more C ３ ~C １２ -terminating the copolymerization with the 1-alkene and discharging the slurry of ethylene (co)polymer particles from the reactor system until the reactor system is empty; introducing a hydrocarbon solvent into the emptied reactor system, thereby forming a wash charge within the reactor system; heating the wash charge in the reactor system to a temperature of from 100° C. to 180° C. - activating the agitator in the polymerization reactor, - heating the wash packing by removing a portion of the wash packing from the polymerization reactor, heating the portion of the wash packing in one or more of the first heat exchangers, and returning the heated portion of the wash packing to the polymerization reactor; - heating a temperature control medium in the closed heating loop in the third heat exchanger by supplying the third heat exchanger with a heating medium having a temperature between 150°C and 250°C; maintaining said washing charge in said reactor system at a temperature of from 100° C. to 180° C. for a period of from 4 to 120 hours while continuously circulating said washing charge through said first heat exchanger or heat exchangers and continuously operating said agitator; draining a wash charge from the reactor system until the reactor system is empty; Polymerization of ethylene or ethylene and one or more C ３ ~C １２ and reinitiating copolymerization with the -1 alkene.

6. 6. The process according to claim 5, wherein after the slurry of ethylene (co)polymer particles is discharged from the reactor system and before the wash charge is introduced into the reactor system, a substep of flushing the reactor system with the hydrocarbon solvent is carried out and / or the hydrocarbon solvent is introduced into the empty reactor system until the liquid level of the wash charge in the polymerization reactor is at least as high as the liquid level of the slurry in the polymerization reactor during polymerization.

7. 7. The process of any one of claims 5 or 6, wherein the hydrocarbon solvent is continuously introduced into the reactor system and the wash charge is continuously discharged from the reactor system while the wash charge in the reactor system is maintained at a temperature of from 100°C to 180°C and the wash charge is continuously discharged from the reactor system; and / or wherein the wash charge in the reactor system is maintained at a temperature of from 100°C to 180°C and the wash charge is discharged from the reactor system after introduction of the hydrocarbon solvent into the reactor system is terminated after the wash charge has been formed in the reactor system, but no additional introduction of the hydrocarbon solvent is required.

8. 7. The process of claim 5, wherein the contents of the first heat exchanger(s) and the polymerization reactor are discharged after terminating the circulation of the wash charge from the polymerization reactor through the first heat exchanger(s) to empty the reactor system before resuming polymerization.

9. 7. The process of claim 5 or 6, wherein the wash charge discharged from the reactor system is transferred to an agitated evaporation vessel configured to enable removal of the hydrocarbon solvent from the liquid medium comprising the hydrocarbon solvent by evaporation.

10. 10. The process of claim 9, wherein the discharge of the washing charge from the reactor system to the agitated evaporation vessel occurs by a pressure differential between the washing charge in the reactor system and the agitated evaporation vessel.

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