Feed regulation in high pressure ethylene polymerization

Abstract

The invention relates to feed regulation in high pressure ethylene polymerization. The present application discloses a process for performing ethylene polymerization, comprising: compressing an ethylene monomer in a compressor to obtain a compressed ethylene monomer; the compressed ethylene monomer is introduced into a reactor, where the reactor comprises N reaction zones, N is an integer > = 5, the compressed ethylene monomer is introduced into the reactor at the front end of the reactor in a front stream, and the compressed ethylene monomer is introduced into the reactor at the back end of the reactor. Introducing compressed ethylene monomers into the reactor from the tail ends of the first reaction zone to the (N-2)-th reaction zone on the side surface of the reactor in the (N-2)-th side flow; wherein the amount of ethylene monomer supplied through the side stream introduced at the tail end of the (N-3)-th reaction zone is greater than the amount of ethylene monomer supplied through each of the other side streams other than the side stream introduced at the tail end of the (N-3)-th reaction zone. The ethylene high-pressure polymerization method can improve the conversion rate of ethylene, reduce the scaling of the reactor and reduce the energy consumption.

Description

Technical Field

[0001] The present application relates to feed regulation in high pressure ethylene polymerization, and in particular, to a method for ethylene polymerization by specific feed regulation and an ethylene polymerization reactor system for carrying out the method. Background Art

[0002] High pressure reactor polymerization equipment converts relatively low cost olefin monomers (e.g. ethylene), optionally in combination with one or more comonomers, into valuable polyolefin products. Such methods using oxygen or organic free radical initiators (particularly peroxide initiators) are known in the art and have been used in industry for a long time. The polymerization is carried out at relatively high temperature and pressure and is highly exothermic. The polymer formed is a low density polyethylene (LDPE), optionally containing a comonomer.

[0003] High pressure polymerization processes are usually carried out in autoclave reactors or tubular reactors. In principle, autoclave and tubular polymerization processes are very similar, except for the design of the reactor itself. The apparatus usually uses two main compressors arranged in series, each with multiple stages, to compress the monomer feed. The primary compressor provides the initial compression for the monomer feed, and the secondary compressor increases the pressure generated by the primary compressor to a level at which polymerization occurs in the reactor. Typically, the pressure is about 210-about 320 MPa for tubular reactors and about 120-about 200 MPa for autoclave reactors.

[0004] The high pressure polymerization of ethylene is an extremely exothermic process. In order for the reaction to continue to occur under favorable conditions, heat must be continuously removed from the polymerization zone. During polymerization, the polymer will adhere to the inner wall of the reactor and significantly reduce the heat removal capacity. These deposits may separate from the inner wall and migrate into the reactor. The deposits can cause blockages, resulting in severe and rapid pressure increases in the reactor, which in turn leads to monomer decomposition or thermal runaway in the reaction mixture. Therefore, the maximum productivity of the reactor is limited by cooling. Heat in tubular reactors is usually removed by heat transfer from the tube wall to a pressurized closed circulation jacket water system. However, the performance of the jacket water system is limited because it cannot fully carry away the heat.

[0005] Therefore, the object of the present invention is to provide a new method for ethylene polymerization, especially ethylene high-pressure polymerization, which can overcome the shortcomings of the prior art methods, make up for the shortcomings of using a jacket water system for cooling alone, and improve the cooling efficiency of the ethylene polymerization system, thereby improving the ethylene conversion rate, reducing reactor fouling and reducing energy consumption. Summary of the invention

[0006] In a first aspect, the present disclosure provides a method for polymerizing ethylene, comprising:

[0007] compressing the ethylene monomer in a compressor to obtain compressed ethylene monomer;

[0008] The compressed ethylene monomer is introduced into the reactor,

[0009] Wherein, the reactor comprises N reaction zones, N being an integer ≥5,

[0010] In the front flow, the compressed ethylene monomer is introduced into the reactor at the front end of the reactor,

[0011] In N-2 side streams, compressed ethylene monomer is introduced into the reactor at the end of the first to N-2 reaction zones on the side of the reactor, respectively.

[0012] The amount of ethylene monomer supplied through the side stream introduced at the tail end of the N-3 reaction zone is greater than the amount of ethylene monomer supplied through each other side stream except the side stream introduced at the tail end of the N-3 reaction zone.

[0013] In a second aspect, the present disclosure provides a method for polymerizing ethylene, the method comprising:

[0014] compressing ethylene monomer in a compressor to obtain compressed ethylene monomer;

[0015] The compressed ethylene monomer is introduced into the reactor,

[0016] Wherein, the reactor comprises 6 reaction zones,

[0017] In the front flow, the compressed ethylene monomer is introduced into the reactor at the front end of the reactor,

[0018] The compressed ethylene monomer is introduced into the reactor at the end of the first to fourth reaction zones at the side of the reactor in four side streams.

[0019] No side stream ethylene monomer is introduced into the reactor in the fifth and sixth reaction zones;

[0020] wherein the amount of ethylene monomer supplied via the side stream introduced at the tail end of the third reaction zone is greater than the amount of ethylene monomer supplied via each of the other side streams,

[0021] the amount of ethylene monomer supplied via the side stream introduced at the tail end of the first reaction zone is smaller than the amount of ethylene monomer supplied via each other side stream except the side stream introduced at the tail end of the first reaction zone,

[0022] The amount of ethylene monomer supplied through the front stream is 15-25 wt %, based on the total weight of ethylene monomer supplied through the front stream and all side streams.

[0023] The amount of ethylene monomer supplied through the side stream introduced at the tail end of the third reaction zone is 33-43% by weight, based on the total weight of ethylene monomer supplied through the front stream and all side streams.

[0024] The amount of ethylene monomer supplied through the side stream introduced at the tail end of the first reaction zone is 8-18% by weight, based on the total weight of ethylene monomer supplied through the front stream and all side streams.

[0025] The amounts of ethylene monomer supplied through the side stream introduced at the tail end of the second reaction zone and through the side stream introduced at the tail end of the fourth reaction zone are each independently 11-21 wt % based on the total weight of ethylene monomer supplied through the front stream and all side streams.

[0026] In a third aspect, the present disclosure provides an ethylene polymerization reactor system for carrying out the method as described above and below, comprising:

[0027] first and second compressors for compressing the monomer;

[0028] A reactor, wherein the reactor comprises N reaction zones, where N is an integer ≥ 5;

[0029] The front flow is used to introduce the compressed ethylene monomer into the reactor at the front end of the reactor.

[0030] N-2 side streams are used to introduce compressed ethylene monomer into the reactor at the tail ends of the 1st to N-2nd reaction zones on the side of the reactor.

[0031] Surprisingly, it was found that the technical solution of the present application can improve the ethylene conversion rate, reduce reactor fouling and reduce energy consumption by carrying out high-pressure ethylene polymerization through specific feed regulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 An ethylene polymerization system according to one embodiment of the present invention is schematically shown.

[0033] Figure 2 A portion of the tubular reactor system used in the examples is schematically shown.

[0034] Figure 3 The reactor temperature profile for the production of LDPE according to Example 1 is shown.

[0035] Details

[0036] In the method of the present invention, ethylene monomer is first compressed in a compressor to obtain compressed ethylene monomer. The compressor generally includes two compressors arranged in series to compress the monomer feed to a certain pressure, and each compressor may have multiple stages. The primary compressor provides initial compression of the monomer feed, and the secondary compressor provides further compression of the monomer feed to increase the pressure to a level at which polymerization occurs in the reactor. For tubular reactors, the pressure reached by the compressed monomer feed is generally about 210 to about 310 MPa; for autoclave reactors, the pressure reached by the compressed monomer feed is generally about 120 to about 320 MPa.

[0037] After the ethylene monomer is compressed to a sufficient pressure, the compressed ethylene monomer is introduced into the reactor. The reactor usually includes several reaction zones. Before the compressed ethylene monomer is introduced into the reactor, the ethylene monomer needs to be preheated (usually by using high-pressure steam) to the "initiation temperature" (i.e., the lowest temperature at which the initiator begins to work) of the first reaction zone of the reactor. In conventional ethylene polymerization, the ethylene monomer is usually introduced into the reactor at the front end of the reactor. In this case, all the ethylene monomers need to be preheated to the initiation temperature, which consumes a lot of high-pressure steam and therefore very high energy. In addition, too much premature introduction of ethylene monomers can cause the polymerization reaction in the front part of the reactor to polyaddition, thereby rapidly releasing heat and causing the temperature to rise, requiring more cold to take away the polymerization reaction heat, which also consumes more energy. In addition, the generated polymer envelops the unreacted ethylene monomer and moves forward into the subsequent reaction zone, which may cause local loss of control and lead to decomposition reactions, causing safety risks.

[0038] In the method of the present invention, by means of specific feed regulation, the cooling capacity of the ethylene monomer itself is fully utilized to control the temperature of the reactor system, thereby achieving comprehensive improvements in conversion rate, fouling and energy consumption.

[0039] In the method of the present invention, the reactor may include N reaction zones, wherein N is an integer ≥5, preferably N≤10, for example, N may be 5, 6, 7, 8, 9, or 10.

[0040] In the method of the present invention, the compressed ethylene monomer can be introduced into the reactor at the front end of the reactor in the front flow, and the compressed ethylene monomer can be introduced into the reactor at the tail end of the 1st to the N-2th reaction zones on the side of the reactor in the N-2 side streams, wherein the amount of ethylene monomer supplied through the side stream introduced at the tail end of the N-3th reaction zone is greater than the amount of ethylene monomer supplied through each other side stream except the side stream introduced at the tail end of the N-3th reaction zone. For example, when N is 6, the compressed ethylene monomer can be introduced into the reactor at the front end of the reactor in the front flow, and the compressed ethylene monomer can be introduced into the reactor at the tail end of the 1st to the 4th reaction zones on the side of the reactor in the 4 side streams, wherein the amount of ethylene monomer supplied through the side stream introduced at the tail end of the 3rd reaction zone is greater than the amount of ethylene monomer supplied through each other side stream except the side stream introduced at the tail end of the 3rd reaction zone.

[0041] In one embodiment, the amount of ethylene monomer supplied through each side stream is independently 5-45 wt %, based on the total weight of ethylene monomer supplied through the front stream and all side streams, for example, in the range of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 , 32, 33, 34 or 35 weight % to an upper limit of 45, 44, 43, 42, 41, 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16 or 15 weight %, as long as the lower limit is less than the upper limit, for example 8-43 weight %.

[0042] In one embodiment, the amount of ethylene monomer supplied through the front stream is 10-30 wt%, based on the total weight of ethylene monomer supplied through the front stream and all side streams, for example, in the range of from a lower limit of 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or 25 wt% to an upper limit of 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16 or 15 wt%, as long as the lower limit is less than the upper limit, for example, 15-25 wt%.

[0043] In one embodiment, the amount of ethylene monomer supplied through the side stream introduced at the tail end of the N-3 reaction zone is 10-45% by weight, based on the total weight of ethylene monomer supplied through the front stream and all side streams, for example, in the range of from a lower limit of 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34 or 35% by weight to an upper limit of 45, 44, 43, 42, 41, 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21 or 20% by weight, as long as the lower limit is less than the upper limit, for example, 33-43% by weight.

[0044] In one embodiment, based on the total weight of ethylene monomers supplied through the front stream and all side streams, the amount of ethylene monomer supplied through each other side stream except the side stream introduced at the tail end of the N-3 reaction zone is independently 5-30 weight %, for example, in the range of from a lower limit of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or 25 weight % to an upper limit of 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6 or 5 weight %, as long as the lower limit is less than the upper limit, for example, 8-25 weight %.

[0045] In one embodiment, the amount of ethylene monomer supplied through the side stream introduced at the tail end of the first reaction zone is less than the amount of ethylene monomer supplied through each other side stream except the side stream introduced at the tail end of the first reaction zone. In this embodiment, the amount of ethylene monomer supplied through the side stream introduced at the tail end of the first reaction zone is 5-20% by weight, for example, in the range from a lower limit of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 or 18% by weight to an upper limit of 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8 or 7% by weight, as long as the lower limit is less than the upper limit, for example, 8-18% by weight.

[0046] In one embodiment, based on the total weight of ethylene monomers supplied through the front stream and all side streams, the amount of ethylene monomers supplied through each other side stream except the side stream introduced at the tail end of the N-3 reaction zone and the side stream introduced at the tail end of the 1st reaction zone differs from each other by ≤7 weight%, for example, ≤6 weight%, ≤5 weight%, ≤4 weight%, ≤3 weight%, ≤2 weight%, ≤1 weight%, and are preferably the same as each other. %, based on the total weight of ethylene monomers supplied through the front stream and all side streams, the amount of ethylene monomers supplied through each other side stream except the side stream introduced at the tail end of the N-3 reaction zone and the side stream introduced at the tail end of the 1st reaction zone is 8-30% by weight, for example, in the range of from a lower limit of 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20% by weight to an upper limit of 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, or 13% by weight, at least the lower limit is less than the upper limit, for example 11-21% by weight.

[0047] In a preferred embodiment, the amount of ethylene monomer supplied through the side stream introduced at the tail end of the N-3 reaction zone is greater than the amount of ethylene monomer supplied through each other side stream except the side stream introduced at the tail end of the N-3 reaction zone and the side stream introduced at the tail end of the 1st reaction zone, and the amount of ethylene monomer supplied through each other side stream except the side stream introduced at the tail end of the N-3 reaction zone and the side stream introduced at the tail end of the 1st reaction zone is greater than the amount of ethylene monomer supplied through the side stream introduced at the tail end of the 1st reaction zone. Preferably, no side stream ethylene monomer is introduced into the reactor at the N-1st and Nth reaction zones. For example, when N is 6, the compressed ethylene monomer is introduced into the reactor at the front end of the reactor in the front flow, and the compressed ethylene monomer is introduced into the reactor at the tail end of the first to fourth reaction zones on the side of the reactor in the four side streams, respectively, wherein the amount of ethylene monomer supplied by the side stream introduced at the tail end of the third reaction zone is > (greater than) the amount of ethylene monomer supplied by the side stream introduced at the tail end of the second reaction zone is ≈ (approximately equal to) the amount of ethylene monomer supplied by the side stream introduced at the tail end of the fourth reaction zone is > (greater than) the amount of ethylene monomer supplied by the side stream introduced at the tail end of the first reaction zone. Preferably, no side stream ethylene monomer is introduced into the reactor in the fifth and sixth reaction zones.

[0048] In one embodiment, the amount of ethylene monomer supplied by the side stream introduced at the tail end of the N-3 reaction zone is greater than the amount of ethylene monomer supplied by the front stream. In one embodiment, the amount of ethylene monomer supplied by the side stream introduced at the tail end of the 1st reaction zone is less than the amount of ethylene monomer supplied by the front stream.

[0049] In this article, the tail end of the reaction zone refers to the last third of the reaction zone along the flow direction of the stream in the reactor. When ethylene monomer is introduced into the reactor at the tail end of a reaction zone, the ethylene monomer quickly flows to the next reaction zone, and the introduced ethylene monomer provides fresh ethylene for the next reaction zone and provides cooling for the reaction zone.

[0050] Compared with a feeding method in which all ethylene is introduced into the reactor via a front stream, and compared with other feeding methods (for example, a feeding method in which the amount of ethylene introduced via a front stream and a side stream is substantially equal), the technical solution of the present application can improve the ethylene conversion rate, reduce reactor fouling and reduce energy consumption through specific feed regulation.

[0051] In one embodiment, the initiator is introduced into the reactor in N streams, respectively, at the beginning of each reaction zone. In other words, the beginning of the reaction zone is defined by the initiator inlet.

[0052] In one embodiment, before the compressed ethylene monomer is introduced into the reactor, the ethylene monomer supplied via the front stream is preheated by a preheater in order to bring the temperature of the ethylene monomer to the initiation temperature of the first reaction zone.

[0053] In one embodiment, before the compressed ethylene monomer is introduced into the reactor, the ethylene monomer supplied through each side stream is cooled separately by N-2 coolers in order to cool down the overheated system and return to the initiation temperature of each reaction zone.

[0054] In one embodiment, the pressure gradually decreases from the 1st reaction zone to the Nth reaction zone. In one embodiment, the pressure difference between two adjacent reaction zones is 5-20 MPa, for example, in the range from a lower limit of 5, 6, 8, 10, 12, 14 or 15 MPa to an upper limit of 20, 18, 16, 15, 14, 12 or 10 MPa, as long as the lower limit is less than the upper limit.

[0055] In one embodiment, the temperature difference between any two reaction zones is 0-40°C, for example, in the range of from a lower limit of 0, 5, 10, 15, 20, 25 or 30°C to an upper limit of 40, 35, 30, 25, 20, 15 or 10°C, at least the lower limit is less than the upper limit.

[0056] In one embodiment, the reactor is a tubular reactor or an autoclave reactor, preferably a tubular reactor.

[0057] In one embodiment, the method further comprises recovering an ethylene polymer from the reactor, wherein the ethylene polymer has a density of 0.918 to 0.934 g / cm 3(measured by ASTM D1505), and / or the ethylene polymer has a melt index of 0.2-50 g / 10 min (measured by ASTM D1238 at 190°C / 2.16 kg).

[0058] Process for producing ethylene polymers

[0059] Figure 1 1 is a diagram of a polymerization device 1, which includes an ethylene feed line 2, which supplies fresh ethylene to a primary compressor 3. The role of the primary compressor 3 is to pressurize fresh ethylene (make-up ethylene) to the pressure of the ethylene recycling system to feed the secondary compressor. The primary compressor can be a single compressor that compresses the ethylene alone, or it can be two or more compressors connected in series or in parallel that are combined to compress ethylene to the pressure of the ethylene recycling system. In some existing ethylene reactor devices, the ethylene discharged from the primary compressor is divided into two streams (not shown), one stream is combined with recycled ethylene and supplied to the suction of the secondary compressor, and the other stream is injected into the ethylene / polymer mixture downstream of the high-pressure blowdown valve, thereby providing rapid cooling of the ethylene / polymer mixture before entering the product separation unit.

[0060] Ethylene discharged from the primary compressor 3 flows to the pipeline 6a and then to the secondary compressor 5 via the pipeline 4 with the valve 4a. Recycled ethylene is also supplied to the secondary compressor 5 from the high pressure recycle system 16 via the pipeline 6b. The secondary compressor compresses the ethylene to a pressure of at least 100 MPa to supply it to the reactor 9. The secondary compressor 5 is usually a single motor driven unit, but can alternatively include two or more compressors connected in series or in parallel driven by separate motors (not shown). Any configuration of the compressor is intended to be within the scope of the present disclosure, as long as the configuration is suitable for compressing the ethylene from the ethylene pressure when it leaves the primary compressor 3 to the desired reactor pressure of 100 MPa-350 MPa.

[0061] Secondary compressor 5 discharges compressed ethylene in five streams 8a, 8b, 8c, 8d and 8e. Stream 8a enters the reactor at the front end of the reactor, also referred to as front stream 8a. Streams 8b, 8c, 8d and 8e each enter the reactor as a side stream at the tail end of the 1st, 2nd, 3rd and 4th reaction zones, also referred to as side streams 8b, 8c, 8d and 8e. Stream 8a can account for about 15-25% by weight of the total ethylene flow, such as 18-22% by weight. The ethylene flow in side stream 8d is greater than the ethylene flow in each side stream 8b, 8c and 8e. The ethylene flow in side stream 8d can account for about 33-43% by weight of the total ethylene flow, such as 37-43% by weight. The ethylene flow in side stream 8b is less than the ethylene flow in each side stream 8c, 8d and 8e. The ethylene flow in side stream 8b can account for about 8-18% by weight of the total ethylene flow, such as 8-12% by weight. The ethylene flow rate in the side streams 8c and 8e can be 11-21% by weight, for example 17-21% by weight, respectively. The front stream 8a can be heated by a preheater (such as a steam heat exchanger) before entering the front end of the reactor 9. The side streams 8b, 8c, 8d and 8e can be cooled by a cooler (such as a shell and tube heat exchanger) before entering the reactor. In the present invention, part of the ethylene is injected from the side stream, so that the amount of ethylene injected at the front end that needs to be heated by the preheater is reduced, thereby reducing the need for heat exchanger steam and reducing energy consumption.

[0062] Reactor 9 has an initiator pumping station 11 for injecting initiator into the reactor via initiator streams 11a, 11b, 11c, 11d, 11e and 11f. Figure 1 In the reactor with multiple reaction zones shown, each initiator inlet defines the beginning of a reaction zone. Therefore, initiator stream 11a defines the beginning of the first reaction zone. As the initiator is consumed in the reaction zone, the polymerization rate decreases. Additional initiator inlets are added downstream to form additional reaction zones. The injection of initiator causes an exothermic temperature rise downstream of the inlet, which can be removed by cooling. The cooling can be through the reactor wall, via a cooling jacket (not shown) mounted on the reactor 9 with the aid of a cooling liquid. In the present invention, the introduction of side stream monomers can provide additional cooling.

[0063] Alternatively, the modifier may be supplied to the reactor system from the modifier pump 6 via the conduit 6 c to the discharge or intake of the second stage of the secondary compressor 5 .

[0064] After the initiator is injected, the polymerization reaction begins to occur vigorously. The polymerization reaction generates a large amount of heat, which causes the temperature in the reactor to rise. As the initiator is consumed, initiation and polymerization slow down. When the heat generated by the polymerization reaction is equal to the heat withdrawn from the reaction mixture, the temperature reaches a peak and then begins to decline.

[0065] The tubular reactor ends at a high pressure blowdown valve 12. The high pressure blowdown valve 12 controls the pressure in the tubular reactor 9. Immediately downstream of the high pressure blowdown valve 12 is a product cooler 13. After entering the product cooler 13, the reaction mixture phase separates. It leaves into a high pressure separator 14. The overhead gas of the high pressure separator 14 flows into a high pressure recycle system 16 where unreacted ethylene is cooled and returned to the secondary compressor 5.

[0066] The polymer product flows from the bottom of the high pressure separator 14 to the low pressure separator 15, which separates almost all of the remaining ethylene from the polymer. The ethylene is transferred to a flare (not shown) or a purification unit (not shown), or it is recycled to the primary compressor 3. The molten polymer flows from the bottom of the low pressure separator 15 to downstream processing, which can be, for example, an extruder (not shown) for extrusion, cooling and pelletizing.

[0067] The proportion of the total ethylene entering the reactor 9 (whether in the front stream 8a or as a side stream 8b, 8c, 8d or 8e) that is converted into polymer before leaving the reactor 9 is called the conversion rate. In the present invention, the injection of the side stream can quickly cool down, thereby increasing the temperature difference between the peak and the initiation temperature, thereby improving the conversion rate. In addition, the turbulence formed when the side stream is injected can reduce the occurrence of polymer wall adhesion (fouling), thereby improving the heat exchange efficiency of the tube wall, which is also conducive to improving the conversion rate. In one embodiment of the present invention, the conversion rate can be 27-39%, or 35-39%. A conversion rate higher than 40% is feasible, but not preferred, partly because the viscosity of the reaction mixture increases with the polymer content therein, which in turn leads to an increase in the pressure drop required to maintain the necessary flow rate.

[0068] The ethylene polymer product produced according to the present invention may have a density of 0.918-0.934 g / cm 3 (measured by ASTM D1505) and a melt index of 0.2-50 g / 10 min (measured by ASTM D1238 at 190°C / 2.16 kg). For example, the ethylene polymer obtained by the process according to the present invention may have a density of 0.920-0.935 g / cm 3 and a melt index of 0.33-20.5 g / 10 min.

[0069] The method herein can be used to make ethylene homopolymers and copolymers, such as ethylene-vinyl acetate copolymers. Typically, the comonomer(s) are pressurized and injected into the secondary compressor at one or more points. Other possible comonomers include propylene, 1-butene, isobutylene, 1-hexene, 1-octene, other lower alpha-olefins, methacrylic acid, methyl acrylate, acrylic acid, ethyl acrylate and n-butyl acrylate. Reference to "ethylene" herein should be understood to include ethylene and comonomer mixtures, except where the context implies otherwise.

[0070] Initiator

[0071] As used herein, the term "initiator" refers to a compound that initiates a free radical ethylene polymerization process. Suitable initiators for the present invention include, but are not limited to, organic peroxide initiators. Peroxides are, for example, pure peroxides. Other examples of suitable initiators include peresters, including, but are not limited to, bis(2-ethylhexyl) peroxydicarbonate, per(2-ethyl) tert-butyl hexanoate, pert-butyl pivalate, pert-butyl neodecanoate, pert-butyl isobutyrate, per-3,5,5-trimethyl tert-butyl hexanoate, pert-butyl benzoate, and dialkyl peroxides, including, but not limited to, di-tert-butyl peroxide, and mixtures thereof.

[0072] The pure peroxide is typically mixed in a hydrocarbon solvent and then injected into the reactor at the injection point described herein.Any suitable pump may be used, such as a hydraulically driven piston pump.

[0073] Modifier

[0074] As used herein, the term "modifier" refers to a compound added to the process to control the molecular weight and / or melt index of the polymer produced. As used herein, the term "chain transfer agent" is interchangeable with the term "modifier". The modifier can be at least one of the following: tetramethylsilane, cyclopropane, sulfur hexafluoride, methane, tert-butyl alcohol, perfluoropropane, deuterated benzene, ethane, ethylene oxide, 2,2-dimethylpropane, benzene, dimethyl sulfoxide, vinyl methyl ether, methanol, propane, 2-methyl-3-butene-2-ol, methyl acetate, tert-butyl acetate, methyl formate, ethyl acetate, butane, triphenylphosphine, methylamine, methyl benzoate, ethyl benzoate, N,N-diisopropylacetamide, 2,2,4-trimethylpentane, n-hexane, isobutane, dimethoxymethane, Ethanol, n-heptane, n-butyl acetate, cyclohexane, methylcyclohexane, 1,2-dichloroethane, acetonitrile, N-ethylacetamide, propylene, n-decane, N,N-diethylacetamide, cyclopentane, acetic anhydride, n-tridecane, n-butyl benzoate, isopropanol, toluene, hydrogen, acetone, 4,4-dimethylpentene-1, trimethylamine, N,N-dimethylacetamide, isobutylene, n-butyl isocyanate, methyl butyrate, n-butylamine, N,N-dimethylformamide, diethyl sulfide, diisobutylene, tetrahydrofuran, 4-methylpentene-1, p-xylene, p-dimethylbenzene Alkane, trimethylamine, butene-2, 1-bromo-2-chloroethane, octene-1, 2-methylbutene-2, cumene, butene-1, methyl vinyl sulfide, n-butyronitrile, 2-methylbutene-1, ethylbenzene, n-hexadecene, 2-butanone, n-butyl isothiocyanate, methyl 3-cyanopropionate, tri-n-butylamine, 3-methyl-2-butanone, isobutyronitrile, di-n-butylamine, methyl chloroacetate, 3-methylbutene-1, 1,2-dibromoethane, dimethylamine, benzaldehyde, chloroform, 2-ethylhexene-1, propionaldehyde, 1,4-dichlorobutene-2, tri-n-butylphosphine, dimethylphosphine, methyl cyanoacetate, carbon tetrachloride, bromotrichloromethane, di-n-butylphosphine, acetaldehyde, phosphine and mixtures thereof. Often the modifier is an aldehyde including acetaldehyde, propionaldehyde, butyraldehyde and mixtures thereof.

[0075] For additional details on modifiers, see Advances in Polymer Science, Vol. 7, pp. 386-448, (1970). Table 7 therein ranks several chain transfer agents in the order of chain transfer constants measured under set conditions. Aldehydes (including propionaldehyde and acetaldehyde) are known to have higher chain transfer constants than other chain transfer agents (e.g., propane, butane, isobutane, propylene, isobutylene, and 1-butene).

[0076] The modifier may contain C2-C 20 or C2-C 12 The modifier may also contain C2-C 20 or C2-C 12In addition, the modifier may contain C2-C 20 or C2-C 12 Unsaturated modifier.

[0077] The present application also relates to the following embodiments.

[0078] 1. A method for polymerizing ethylene, comprising:

[0079] compressing ethylene monomer in a compressor to obtain compressed ethylene monomer;

[0080] The compressed ethylene monomer is introduced into the reactor,

[0081] Wherein, the reactor comprises N reaction zones, N being an integer ≥5,

[0082] In the front flow, the compressed ethylene monomer is introduced into the reactor at the front end of the reactor,

[0083] In N-2 side streams, compressed ethylene monomer is introduced into the reactor at the end of the first to N-2 reaction zones on the side of the reactor, respectively.

[0084] The amount of ethylene monomer supplied through the side stream introduced at the tail end of the N-3 reaction zone is greater than the amount of ethylene monomer supplied through each other side stream except the side stream introduced at the tail end of the N-3 reaction zone.

[0085] 2. The method according to embodiment 1, wherein:

[0086] The amount of ethylene monomer supplied through each side stream is independently 5-45 wt% based on the total weight of ethylene monomer supplied through the front stream and all side streams; and / or

[0087] The amount of ethylene monomer supplied through the front stream is 10 to 30 wt % based on the total weight of ethylene monomers supplied through the front stream and all side streams.

[0088] 3. The method according to embodiment 1 or 2, wherein:

[0089] The amount of ethylene monomer supplied via the side stream introduced at the tail end of the N-3 reaction zone is 10-45 wt% based on the total weight of ethylene monomer supplied via the front stream and all side streams; and / or

[0090] The amount of ethylene monomer supplied through each other side stream except the side stream introduced at the tail end of the N-3th reaction zone is independently 5-30 wt% based on the total weight of ethylene monomer supplied through the front stream and all side streams.

[0091] 4. The method according to embodiment 1 or 2, wherein:

[0092] The amount of ethylene monomer supplied through the side stream introduced at the tail end of the first reaction zone is smaller than the amount of ethylene monomer supplied through each of the other side streams except the side stream introduced at the tail end of the first reaction zone.

[0093] 5. The method according to embodiment 4, wherein:

[0094] The amount of ethylene monomer supplied via the side stream introduced at the tail end of the first reaction zone is 5-20 wt% based on the total weight of ethylene monomer supplied via the front stream and all side streams; and / or

[0095] Based on the total weight of ethylene monomer supplied through the front stream and all side streams, the amount of ethylene monomer supplied through each other side stream except the side stream introduced at the tail end of the N-3 reaction zone and the side stream introduced at the tail end of the 1st reaction zone differs from each other by ≤7 weight %; and / or

[0096] The amount of ethylene monomer supplied through each other side stream except the side stream introduced at the tail end of the N-3 reaction zone and the side stream introduced at the tail end of the 1st reaction zone is 8-30 wt% based on the total weight of ethylene monomer supplied through the front stream and all side streams.

[0097] 6. The method according to embodiment 1 or 2, wherein:

[0098] No side stream ethylene monomer is introduced into the reactor in the N-1th and Nth reaction zones.

[0099] 7. The method according to embodiment 1 or 2, wherein:

[0100] The initiator is introduced into the reactor in N streams, respectively, at the beginning of each reaction zone.

[0101] 8. The method according to embodiment 1 or 2, wherein:

[0102] preheating the ethylene monomer supplied via a front stream by a preheater before introducing the compressed ethylene monomer into the reactor; and / or

[0103] Before the compressed ethylene monomer is introduced into the reactor, the ethylene monomer supplied through each side stream is cooled respectively by N-2 coolers.

[0104] 9. The method according to embodiment 1 or 2, wherein:

[0105] The pressure gradually decreases from the 1st reaction zone to the Nth reaction zone; and / or

[0106] The pressure difference between two adjacent reaction zones is 5-20 MPa.

[0107] 10. The method according to embodiment 1 or 2, wherein:

[0108] The temperature difference between any two reaction zones is 0-40°C.

[0109] 11. The method according to embodiment 1 or 2, wherein:

[0110] The reactor is a tubular reactor or an autoclave reactor.

[0111] 12. The method according to embodiment 1 or 2, wherein:

[0112] The ethylene polymer is recovered from the reactor, and the density of the ethylene polymer is 0.918-0.934 g / cm 3 and / or a melt index of 0.2 to 50 g / 10 min at 190°C and 2.16 kg.

[0113] 13. A method for polymerizing ethylene, the method comprising:

[0114] compressing ethylene monomer in a compressor to obtain compressed ethylene monomer;

[0115] The compressed ethylene monomer is introduced into the reactor,

[0116] Wherein, the reactor comprises 6 reaction zones,

[0117] In the front flow, the compressed ethylene monomer is introduced into the reactor at the front end of the reactor,

[0118] The compressed ethylene monomer is introduced into the reactor at the end of the first to fourth reaction zones at the side of the reactor in four side streams.

[0119] No side stream ethylene monomer is introduced into the reactor in the fifth and sixth reaction zones;

[0120] wherein the amount of ethylene monomer supplied via the side stream introduced at the tail end of the third reaction zone is greater than the amount of ethylene monomer supplied via each of the other side streams,

[0121] the amount of ethylene monomer supplied via the side stream introduced at the tail end of the first reaction zone is smaller than the amount of ethylene monomer supplied via each other side stream except the side stream introduced at the tail end of the first reaction zone,

[0122] The amount of ethylene monomer supplied through the front stream is 15-25 wt %, based on the total weight of ethylene monomer supplied through the front stream and all side streams.

[0123] The amount of ethylene monomer supplied through the side stream introduced at the tail end of the third reaction zone is 33-43% by weight, based on the total weight of ethylene monomer supplied through the front stream and all side streams.

[0124] The amount of ethylene monomer supplied through the side stream introduced at the tail end of the first reaction zone is 8-18% by weight, based on the total weight of ethylene monomer supplied through the front stream and all side streams.

[0125] The amounts of ethylene monomer supplied through the side stream introduced at the tail end of the second reaction zone and through the side stream introduced at the tail end of the fourth reaction zone are each independently 11-21 wt % based on the total weight of ethylene monomer supplied through the front stream and all side streams.

[0126] 14. An ethylene polymerization reactor system for carrying out the method according to any one of embodiments 1-13, comprising:

[0127] first and second compressors for compressing the monomer;

[0128] A reactor, wherein the reactor comprises N reaction zones, where N is an integer ≥ 5;

[0129] The front flow is used to introduce the compressed ethylene monomer into the reactor at the front end of the reactor.

[0130] N-2 side streams are used to introduce compressed ethylene monomer into the reactor at the tail ends of the 1st to N-2nd reaction zones on the side of the reactor. DETAILED DESCRIPTION

[0131] In order to facilitate a better understanding of the embodiments of the present invention, the following examples of preferred or representative embodiments are given. The following examples should in no way be construed as limiting or defining the scope of the present invention.

[0132] Example

[0133] Figure 2 A portion of the tubular reactor system used in the embodiment is schematically shown. In this reactor system, compressed ethylene enters the reactor from the secondary compressor. The reactor includes 6 reaction zones, and an initiator (shown by a red arrow) is injected at the beginning of each reaction zone.

[0134] In comparative example 1, all ethylene enters the reactor at the front end of the reactor via the forestream. The forestream is preheated by a preheater before entering the reactor. The pressure of the reactor is 270-310 MPa (gauge pressure) and the temperature is 260-310°C.

[0135] In Example 1, ethylene enters the reactor at the front end of the reactor via a front stream a and enters the reactor at the tail end of the first to fourth reaction zones via four side streams b, c, d, and e on the side of the reactor. The front stream is preheated by a preheater before entering the reactor, and the four side streams are cooled by a cooler before entering the reactor. The pressure of the reactor is 270-310 MPa (gauge pressure) and the temperature is 260-310° C. Table 1 below provides the weight proportion of each ethylene stream in the total ethylene flow in Example 1.

[0136] Table 1

[0137] Material flow Front Flow Side Flow Side Flow Side Flow Lateral flowe Ethylene ratio 15-25％ 8-18％ 11-21％ 33-43％ 11-21％

[0138] The results show that the conversion rate of Example 1 is 37-39%. In contrast, the conversion rate of Comparative Example 1 is only 24-35%. In addition, compared with Comparative Example 1, the overall energy consumption of Example 1 is reduced by about 80%, and the fouling in the reactor is significantly reduced.

[0139] Figure 3 The reactor temperature profile for producing LDPE according to Example 1 is shown. Figure 3 As can be seen in Figure 5, the injection of the side stream makes the temperature drop trend steeper and increases the temperature difference between the peak temperature and the initiation temperature. It is believed that this increased temperature difference, together with the reduced fouling caused by the side stream, leads to an increase in conversion.

[0140] In summary, in the present invention, the injection of the side stream can quickly reduce the temperature, thereby increasing the temperature difference between the peak and the triggering temperature, thereby improving the conversion rate. In addition, the turbulence formed during the injection of the side stream can reduce the occurrence of polymer wall adhesion (scaling), thereby improving the heat exchange efficiency of the tube wall, which is also conducive to improving the conversion rate. In addition, part of the ethylene is injected from the side stream, so that the amount of ethylene injected at the front end that needs to be heated by the preheater is reduced, thereby reducing the need for heat exchanger steam and reducing energy consumption.

[0141] Certain embodiments and features have been described using a set of numerical upper limits and a set of numerical lower limits. It should be understood that combinations from any lower limit to any upper limit are contemplated unless otherwise indicated. Certain lower limits, upper limits, and ranges appear in one or more claims below. All numerical values ​​are "about" or "approximately" the values ​​shown, and experimental errors and deviations that would be expected by a person skilled in the art are contemplated.

[0142] To the extent a term used in a claim is not defined above, it should be given the broadest definition persons skilled in the relevant art have given that term as reflected in at least one printed publication or issued patent. In addition, all patents, test procedures, and other documents cited in this application are incorporated herein by reference in their entirety, to the extent such disclosure is not inconsistent with this application, for all jurisdictions in which such incorporation is permitted.

[0143] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope of the invention, which is defined by the claims that follow.

Claims

1. A method for polymerizing ethylene, comprising: compressing the ethylene monomer in a compressor to obtain compressed ethylene monomer; The compressed ethylene monomer is introduced into the reactor, Wherein, the reactor comprises N reaction zones, N being an integer ≥5, In the front flow, the compressed ethylene monomer is introduced into the reactor at the front end of the reactor, In N-2 side streams, compressed ethylene monomer is introduced into the reactor at the end of the first to N-2 reaction zones on the side of the reactor, respectively. The amount of ethylene monomer supplied through the side stream introduced at the tail end of the N-3 reaction zone is greater than the amount of ethylene monomer supplied through each other side stream except the side stream introduced at the tail end of the N-3 reaction zone.

2. The method according to claim 1, wherein: The amount of ethylene monomer supplied through each side stream is independently 5-45 wt% based on the total weight of ethylene monomer supplied through the front stream and all side streams; and / or The amount of ethylene monomer supplied through the front stream is 10 to 30 wt % based on the total weight of ethylene monomers supplied through the front stream and all side streams.

3. The method according to claim 1 or 2, wherein: The amount of ethylene monomer supplied via the side stream introduced at the tail end of the N-3 reaction zone is 10-45 wt% based on the total weight of ethylene monomer supplied via the front stream and all side streams; and / or The amount of ethylene monomer supplied through each other side stream except the side stream introduced at the tail end of the N-3th reaction zone is independently 5-30 wt% based on the total weight of ethylene monomer supplied through the front stream and all side streams.

4. The method according to claim 1 or 2, wherein: The amount of ethylene monomer supplied through the side stream introduced at the tail end of the first reaction zone is smaller than the amount of ethylene monomer supplied through each of the other side streams except the side stream introduced at the tail end of the first reaction zone.

5. The method according to claim 4, wherein: The amount of ethylene monomer supplied via the side stream introduced at the tail end of the first reaction zone is 5-20 wt% based on the total weight of ethylene monomer supplied via the front stream and all side streams; and / or Based on the total weight of ethylene monomer supplied through the front stream and all side streams, the amount of ethylene monomer supplied through each other side stream except the side stream introduced at the tail end of the N-3 reaction zone and the side stream introduced at the tail end of the 1st reaction zone differs from each other by ≤7 weight %; and / or The amount of ethylene monomer supplied through each other side stream except the side stream introduced at the tail end of the N-3 reaction zone and the side stream introduced at the tail end of the 1st reaction zone is 8-30 wt% based on the total weight of ethylene monomer supplied through the front stream and all side streams.

6. The method according to claim 1 or 2, wherein: No side stream ethylene monomer is introduced into the reactor in the N-1th and Nth reaction zones.

7. The method according to claim 1 or 2, wherein: The initiator is introduced into the reactor in N streams, respectively, at the beginning of each reaction zone.

8. The method according to claim 1 or 2, wherein: preheating the ethylene monomer supplied via a front stream by a preheater before introducing the compressed ethylene monomer into the reactor; and / or Before the compressed ethylene monomer is introduced into the reactor, the ethylene monomer supplied through each side stream is cooled respectively by N-2 coolers.

9. The method according to claim 1 or 2, wherein: The pressure gradually decreases from the 1st reaction zone to the Nth reaction zone; and / or The pressure difference between two adjacent reaction zones is 5-20 MPa.

10. The method according to claim 1 or 2, wherein: The temperature difference between any two reaction zones is 0-40°C.

11. The method according to claim 1 or 2, wherein: The reactor is a tubular reactor or an autoclave reactor.

12. The method according to claim 1 or 2, wherein: The ethylene polymer is recovered from the reactor, and the density of the ethylene polymer is 0.918-0.934 g / cm 3 and / or a melt index of 0.2 to 50 g / 10 min at 190°C and 2.16 kg.

13. A method for polymerizing ethylene, the method comprising: compressing the ethylene monomer in a compressor to obtain compressed ethylene monomer; The compressed ethylene monomer is introduced into the reactor, Wherein, the reactor comprises 6 reaction zones, In the front flow, the compressed ethylene monomer is introduced into the reactor at the front end of the reactor, The compressed ethylene monomer is introduced into the reactor at the end of the first to fourth reaction zones at the side of the reactor in four side streams. No side stream ethylene monomer is introduced into the reactor in the fifth and sixth reaction zones; wherein the amount of ethylene monomer supplied via the side stream introduced at the tail end of the third reaction zone is greater than the amount of ethylene monomer supplied via each of the other side streams, the amount of ethylene monomer supplied via the side stream introduced at the tail end of the first reaction zone is less than the amount of ethylene monomer supplied via each other side stream except the side stream introduced at the tail end of the first reaction zone, The amount of ethylene monomer supplied through the front stream is 15-25 wt %, based on the total weight of ethylene monomer supplied through the front stream and all side streams. The amount of ethylene monomer supplied through the side stream introduced at the tail end of the third reaction zone is 33-43% by weight, based on the total weight of ethylene monomer supplied through the front stream and all side streams. The amount of ethylene monomer supplied through the side stream introduced at the tail end of the first reaction zone is 8-18% by weight, based on the total weight of ethylene monomer supplied through the front stream and all side streams. The amounts of ethylene monomer supplied through the side stream introduced at the tail end of the second reaction zone and through the side stream introduced at the tail end of the fourth reaction zone are each independently 11-21 wt % based on the total weight of ethylene monomer supplied through the front stream and all side streams.

14. An ethylene polymerization reactor system for carrying out the process according to any one of claims 1 to 13, comprising: first and second compressors for compressing the monomer; A reactor, wherein the reactor comprises N reaction zones, where N is an integer ≥ 5; The front flow is used to introduce the compressed ethylene monomer into the reactor at the front end of the reactor. N-2 side streams are used to introduce compressed ethylene monomer into the reactor at the tail ends of the 1st to N-2nd reaction zones on the side of the reactor.

Images