A method and device for preparing ethylene-polar monomer copolymer

Abstract

The present invention discloses a method for preparing an ethylene-polar monomer copolymer, comprising providing at least one kettle reactor and a tubular reaction system comprising at least one tubular reactor, wherein in the kettle reactor and the tubular reactor, under the conditions of a pressure of 100-400 MPa and a temperature of 120-350° C., ethylene, a polar monomer and an organic peroxide are contacted to undergo a polymerization reaction to prepare an ethylene-polar monomer copolymer. The present invention also discloses a device for copolymerizing ethylene-polar monomers. The copolymerization method and device proposed in the present invention can significantly improve the conversion rate of ethylene in the polymerization process of ethylene-polar monomers, and improve the utilization rate and applicability of the device.

Description

Technical Field

[0001] The invention belongs to the field of high-pressure free radical polymerization methods and devices, and in particular relates to a method and a device for preparing an ethylene-polar monomer copolymer. Background Art

[0002] Ethylene-polar monomer copolymers have good compatibility, flexibility, high melting point, high thermal stability, and good heat sealing performance. In particular, ethylene-polar monomer copolymers have the advantages of high polarity and thermal stability, making them widely used in the fields of construction, automobiles, house decoration, sports equipment, etc.

[0003] Commercial ethylene-polar monomer copolymers are usually produced by free radical polymerization of ethylene and polar monomers under high temperature and high pressure conditions, with a reaction pressure of up to 100-400MPa and a reaction temperature between 100-350°C. At present, kettle reactors and tubular reactors are commonly used reactors for preparing ethylene-polar monomer copolymers. Since the existing process usually uses a single kettle reactor or a single tubular reactor, the means of regulating the molecular chain structure of the product are limited. In addition, since high-pressure free radical polymerization has the characteristics of fast reaction rate and large heat release, compared with tubular reactors, it is very easy to form local hot spots in kettle reactors and decomposition accidents. Tubular reactors have the advantages of high monomer conversion rate and low energy consumption, but due to the problem of low degree of material backmixing in tubular reactors, for comonomers with high competitive polymerization rate, the comonomers in the molecular chain of ethylene-polar monomer copolymers produced by tubular reactors are unevenly distributed. It should be further pointed out that due to the limitation of the heat removal method of the autoclave reactor and the pressure drop limitation of the tubular reactor, at present, whether a separate tubular reactor or a separate autoclave reactor is used, or the solution of simply connecting the tubular reactor and the autoclave reactor in series, the monomer conversion rate (especially the ethylene monomer conversion rate) cannot be effectively improved while ensuring the stable operation of the reactor. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method and an apparatus for preparing an ethylene-polar monomer copolymer. In view of the problems that the molecular chain structure of the product in a high-pressure polymerization reactor is difficult to control (the control space is limited), the monomer conversion rate is low, and the production cost is high, the monomer conversion rate of the method of the present invention is higher than that of the existing high-pressure kettle process and tubular process.

[0005] One aspect of the present invention provides a method for preparing an ethylene-polar monomer copolymer, the method comprising at least the following steps:

[0006] Providing at least one tank reactor and a tubular reaction system comprising at least one tubular reactor;

[0007] In a kettle reactor and a tubular reactor, ethylene, polar monomers and organic peroxides are contacted to undergo polymerization reaction to prepare ethylene-polar monomer copolymers under the conditions of a pressure of 100-400 MPa and a temperature of 120-350° C. The materials at the outlet of the kettle reactor are introduced into the middle feed port of one or more tubular reactors or into the 10%-80% position of the total tube course of multiple tubular reactors connected in series with or without cooling, and the middle feed port of the tubular reactor is located at the 10%-80% position of the tube course of the tubular reactor.

[0008] In an optional embodiment of the present invention, the tubular reaction system comprises one tubular reactor, and the material at the outlet of the kettle reactor is introduced into the middle feed port of the tubular reactor with or without cooling. In an optional embodiment of the present invention, the tubular reaction system comprises a plurality of tubular reactors, and the tubular reactors can be connected in series, in parallel, or in a combination of series and parallel. The material at the outlet of the kettle reactor is introduced into the middle feed port of one or more tubular reactors with or without cooling.

[0009] In an optional embodiment of the present invention, the tubular reaction system comprises at least a plurality of tubular reactors connected in series, and the material at the outlet of the kettle reactor is introduced into the 10%-80% position of the total tube path of the plurality of tubular reactors connected in series with or without cooling. It should be noted that the 10%-80% position of the total tube path can be located on the tube wall of a tubular reactor, or on the connecting portion between two tubular reactors connected in series, and the connecting portion can be a pipeline, a tee or a cross.

[0010] It should be noted that the material at the outlet of the kettle reactor can also be divided into multiple streams and fed into the tubular reaction system, wherein each stream of material satisfies the aforementioned feed position requirements in the tubular reaction system. Correspondingly, there can be multiple feed positions on the tubular reaction system for receiving the material at the outlet of the kettle reactor.

[0011] The middle feed port of the present invention is different from the main feed port of the tubular reactor. In the art, the main feed port of the tubular reactor refers to the feed port located at the upstream end of the tubular reactor, while the middle feed port is located on the tube wall of the tubular reactor. In the present invention, it can be located at 10%-80% of the tube side of the tubular reactor. It is preferably located at 25%-60% of the tube side of the tubular reactor.

[0012] In a preferred embodiment of the present invention, the polar monomer is vinyl acetate, an acrylic ester monomer or a methacrylic ester monomer having a carbon number of 4 to 12. Preferably, the polar monomer is vinyl acetate, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, etc.

[0013] In a preferred embodiment of the present invention, the operating pressure of the autoclave reactor is 100-400MPa, preferably 120-350MPa, more preferably 150-270MPa; the operating temperature is 120-350°C, preferably 135-280°C, more preferably 145-250°C. The operating pressure of the autoclave reactor is the average pressure of the material in the autoclave reactor, which can be measured according to the pressure instrument installed in the autoclave reactor, the pressure instrument installed in the organic peroxide feed pump upstream of the autoclave reactor, and the pressure instrument installed on the feed pipeline of the autoclave reactor. If there are multiple pressure instruments, select the measured value of a representative pressure instrument, and calculate the arithmetic mean of the measured value as the operating pressure of the autoclave reactor. The operating temperature of the autoclave reactor is the average temperature of the material in the autoclave reactor, which can be measured according to the temperature instrument installed on the autoclave reactor. If there are multiple temperature instruments, select the representative temperature instrument measured value, and calculate the arithmetic mean of the measured value as the operating temperature of the autoclave reactor.

[0014] In a preferred embodiment of the present invention, the operating pressure of the tubular reactor is 100-400MPa, preferably 120-350MPa, more preferably 150-270MPa; the operating temperature is 120-350°C, preferably 135-280°C, more preferably 145-250°C. The operating pressure of the tubular reactor is the average pressure of the material in the tubular reactor, which can be measured according to the pressure instrument installed in the tubular reactor, the pressure instrument installed in the organic peroxide feed pump upstream of the tubular reactor, and the pressure instrument installed on the feed pipeline of the tubular reactor. If there are multiple pressure instruments, select the measured value of the representative pressure instrument, and calculate the arithmetic mean of the measured value as the operating pressure of the tubular reactor. The operating temperature of the tubular reactor is the average temperature of the material in the tubular reactor, which can be measured according to the temperature instrument installed on the tubular reactor. If there are multiple temperature instruments, select the representative temperature instrument measured value, and calculate the arithmetic mean of the measured value as the operating temperature of the tubular reactor.

[0015] In a preferred embodiment of the present invention, a tubular reaction system with only one tubular reactor is used, and the absolute value of the difference between the inlet pressure of the kettle reactor and the inlet pressure of the tubular reactor is less than or equal to 40MPa, and preferably the absolute value of the difference between the inlet pressure of the kettle reactor and the inlet pressure of the tubular reactor is less than or equal to 20MPa. A tubular reaction system with multiple tubular reactors is used, and the absolute value of the difference between the inlet pressure of the kettle reactor and the inlet pressure of the tubular reaction system is less than or equal to 40MPa, and preferably the absolute value of the difference between the inlet pressure of the kettle reactor and the inlet pressure of the tubular reaction system is less than or equal to 20MPa. By controlling the difference in reaction pressure between the kettle reactor and the tubular reactor, the flow in the kettle reactor and the tubular reactor can be controlled more smoothly, reducing the potential risks of factors such as material flow fluctuation and temperature fluctuation in the reactor to the safe and stable operation of the polymerization device.

[0016] In a preferred embodiment of the present invention, a tubular reaction system with only one tubular reactor is used, and the outlet pressure of the kettle reactor is greater than or equal to 5MPa, and preferably the outlet pressure of the kettle reactor is greater than or equal to 10MPa. A tubular reaction system with multiple tubular reactors is used, and the outlet pressure of the kettle reactor is greater than or equal to 5MPa, and preferably the outlet pressure of the kettle reactor is greater than or equal to 10MPa. By controlling the outlet pressure of the kettle reactor to be at least 5MPa higher than the outlet pressure of the tubular reactor, the materials at the outlet of the kettle reactor and the materials in the tubular reactor, especially the polymer, can be better mixed, thereby ensuring the stability of the product quality. In addition, after the materials in the kettle reactor and the tubular reactor are mixed, the reaction can be further initiated, so that the adjustable range of the molecular structure of the product (such as short chain branch content, monomer sequence distribution, etc.) is wider.

[0017] In a preferred embodiment of the present invention, the average flow rate of the material in the tubular reactor is 10-25 m / s, preferably 12-20 m / s, and more preferably 13-18 m / s. The average flow rate of the material in the tubular reactor is the arithmetic mean of the material flow rate at the inlet of the tubular reactor and the material flow rate at the outlet of the tubular reactor. The material flow rate in the tubular reactor can be calculated by the density and flow calculated by the PC-SAFT equation, or can be measured by a non-invasive flow measurement device, such as an ultrasonic flowmeter.

[0018] In a preferred embodiment of the present invention, the concentration of the ethylene-polar monomer copolymer in the material at the outlet of the tubular reaction system is higher than the concentration of the ethylene-polar monomer copolymer at the outlet of the autoclave reactor. Preferably, the concentration of the ethylene-polar monomer copolymer in the material at the outlet of the tubular reaction system is more than 1.2 times the concentration of the ethylene-polar monomer copolymer at the outlet of the autoclave reactor.

[0019] In a preferred embodiment of the present invention, the mass fraction of the polar monomer in the ethylene-polar monomer copolymer is 3-45wt%, preferably 10-35wt%. The mass fraction of the polar monomer in the ethylene-polar monomer copolymer can be calculated by Fourier infrared, ATR infrared, nuclear magnetic resonance spectroscopy, elemental analysis and other methods.

[0020] In a preferred embodiment of the present invention, the method may or may not add a molecular weight regulator. The molecular weight of the ethylene-polar monomer copolymer can be regulated by the above operation. When producing certain ethylene-polar monomer copolymer products, one or more of hydrogen, C1-C6 alkanes, C1-C6 olefins, aldehydes, ketones, and alcohols may be optionally added, preferably one or more of propylene, butene, hexene, propionaldehyde, butyraldehyde, and acetone, more preferably propylene and propionaldehyde.

[0021] In a preferred embodiment of the present invention, the present invention also provides a device for preparing an ethylene-polar monomer copolymer, comprising:

[0022] a. a tubular reaction system comprising at least one tubular reactor and at least one tank reactor,

[0023] b. at least one heat exchanger connected to the inlet of the tank reactor,

[0024] c. at least one heat exchanger connected to the inlet of the tubular reactor,

[0025] d. at least one pressure reducing valve located upstream or downstream of the autoclave reactor,

[0026] f. at least one pressure reducing valve located upstream or downstream of the autoclave reactor,

[0027] The material at the outlet of the kettle reactor is introduced into the middle feed port of one or more tubular reactors with or without cooling, or introduced into 10%-80% of the total tube length of multiple tubular reactors connected in series, and the middle feed port of the tubular reactor is located at 10%-80% of the tube length of the tubular reactor.

[0028] In a preferred embodiment, the operating pressure of the tank reactor is controlled by at least one pressure reducing valve located upstream of the tank reactor, and the flow rate of the material in the tubular reactor is controlled by at least one pressure reducing valve located upstream of the tubular reactor.

[0029] In a preferred embodiment, the tank reactor and a part of the tubular reactor are connected in parallel, and then the materials entering the remaining part of the tubular reactor, i.e., the outlet of the tank reactor, are introduced into the middle feed port of the tubular reactor. The middle feed port of the tubular reactor is located at 10%-80% of the tube side of the tubular reactor, preferably at 25%-60% of the tube side of the tubular reactor.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) Compared with the prior art, the present invention significantly reduces the pressure drop of the device by combining a tubular reactor and a kettle reactor, selecting the feed position of the kettle reactor outlet material to introduce the tubular reaction system, and selecting the operating temperature and pressure of the tubular reactor and the kettle reactor, and can improve the conversion rate of ethylene and polar monomers and reduce energy consumption.

[0032] (2) Through the combination of tubular reactors and kettle reactors, the molecular chain structure of the product can be improved to produce special grades of ethylene-polar monomer copolymers. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The present invention is a schematic diagram of a process for preparing ethylene-polar monomer copolymer.

[0034] In the figure, 1. the first compressor; 2. the second compressor; 3. the third compressor; 4 / 5. the heat exchanger; 6. the kettle reactor; 7-1 the first part of the tubular reactor; 7-2 the second part of the tubular reactor; 8. the pressure reducing valve; 9. the product cooler; 10. the high-pressure separator; 11. the high-pressure circulating heat exchange system; 12. the low-pressure separator; 13. the low-pressure circulating heat exchange system. Specific implementation methods

[0035] The present invention is further described and illustrated below in conjunction with specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0036] Figure 1 A process for preparing ethylene-polar monomer copolymers. Figure 1As described above, fresh ethylene, polar monomers and molecular weight regulators enter the autoclave reactor 6 and the first part 7-1 of the tubular reactor after being pressurized, and then contact with the initiator (organic peroxide) to initiate ethylene-polar monomer copolymerization to prepare ethylene-polar monomer copolymer.

[0037] In a preferred embodiment of the present invention, the first compressor 1 pressurizes the material from the low-pressure circulation heat exchange system 13, mixes it with fresh ethylene material, and then introduces it into the inlet of the second compressor 2. The second compressor 2 pressurizes the material from the first compressor 1, introduces the molecular weight regulator and polar monomer, and then sends it to the inlet of the third compressor 3. The outlet pressure of the first compressor 1 is 1-5MPa, the outlet pressure of the second compressor 2 is 10-40MPa, and the outlet pressure of the third compressor 3 is 100-400MPa.

[0038] In a preferred embodiment of the present invention, Figure 1 As shown, the material at the outlet of the third compressor 3 passes through the heat exchangers 4 and 5 and then enters the autoclave reactor 6 and the first part 7-1 of the tubular reactor respectively. The material at the outlet of the autoclave reactor 6 is mixed with the material at the outlet of the first part 7-1 of the tubular reactor and then enters the second part 7-2 of the tubular reactor. The material at the outlet of the second part 7-2 of the tubular reactor passes through the pressure reducing valve 8 and then enters the product cooler 9 for cooling. The cooled material is then sequentially separated through the high-pressure separator 10 and the low-pressure separator 12 to obtain high-pressure circulating material, low-pressure circulating material and ethylene-polar monomer copolymer. It should be noted that Figure 1 The two parts of the tubular reactor given in the figure are only schematic, and they may be two separate tubular reactors, or two reaction sections or two parts of a total tubular reactor. When they are two reaction parts of a tubular reactor, Figure 1 The outlet material of the middle tank reactor is introduced into the tubular reactor from the middle feed port of the total tubular reactor, and the middle feed port is located on the tube wall at 10%-80% of the tube path of the tubular reactor. When they are two separate tubular reactors, the introduction position of the outlet material of the tank reactor should be located at 10%-80% of the total tube path of the two tubular reactors.

[0039] In a preferred embodiment of the present invention, the unreacted ethylene and polar monomer separated in the high-pressure separator 10 are introduced into the inlet of the third compressor 3 after being cooled by the high-pressure circulation heat exchange system 11. The high-pressure circulation heat exchange system includes at least two heat exchangers and at least one separator, and the heat exchanger can be a combination of at least one or more of a shell-and-tube heat exchanger, a shell-and-tube heat exchanger, a waste heat boiler, etc.

[0040] In a preferred embodiment of the present invention, the unreacted ethylene and polar monomer separated in the low-pressure separator 12 are returned to the inlet of the first compressor 1 through the low-pressure circulation system 13. The low-pressure circulation system 13 includes at least one heat exchanger and one separator.

[0041] Example 1

[0042] exist Figure 1 The high-pressure free radical polymerization device shown prepares ethylene-polar monomer copolymer, wherein the polar comonomer is vinyl acetate. A portion of the material pressurized to 250MPa by the third compressor 3 is reduced to 240MPa after passing through the pressure reducing valve, and then cooled to 50°C by the heat exchanger 4, and then enters the autoclave reactor 6 for reaction, and the operating temperature of the autoclave reactor is 210°C. The remaining material pressurized to 250MPa by the third compressor 3 is first preheated to 145°C by the heat exchanger, and then enters the first part 7-1 of the tubular reactor for reaction. Among them, the material flow rate entering the autoclave reactor 6 is 45 tons per hour, and the material flow rate entering the first part 7-1 of the tubular reactor is 45 tons per hour. The mass fraction of ethylene-vinyl acetate copolymer in the outlet material of the autoclave reactor is 15%. The outlet material of the autoclave reactor 6 enters the second part 7-2 of the tubular reactor from a position 540m away from the inlet of the tubular reactor (middle feed port), and at this time, the middle feed port of the tubular reactor is located at 36% of the total tube length of the tubular reactor. The mass fraction of ethylene-vinyl acetate copolymer in the outlet material of the tubular reactor is 24%. The inlet pressure of the tubular reactor is 245 MPa, and the outlet pressure is 210 MPa. The average flow rate of the material in the tubular reactor is 14.5 m / s, and the operating temperature is 220°C.

[0043] The absolute value of the difference between the inlet pressure of the tank reactor 6 and the inlet pressure of the tubular reactor is 5 MPa, and the difference between the outlet pressure of the tank reactor 6 and the outlet pressure of the tubular reactor is 30 MPa.

[0044] Organic peroxide is used to initiate the reaction in the autoclave reactor 6. The organic peroxide is di(2-ethylhexyl) peroxydicarbonate and tert-butyl peroxyvalerate, and the mass ratio is 1:1.

[0045] Organic peroxides are used to initiate the reaction in the tubular reactor. The types of organic peroxides are di(2-ethylhexyl) peroxydicarbonate, tert-butyl peroxyvalerate, tert-butyl peroxy-2-ethylhexanoate, and tert-butyl peroxybenzoate, with a mass ratio of 1:1:1:1. The organic peroxides enter the tubular reactor from 0m, 540m, and 1020m of the total tube of the tubular reactor, respectively.

[0046] The content of vinyl acetate in the ethylene-vinyl acetate copolymer was 27 wt %. The conversion rate of ethylene monomer was 24%. The pressure drop of the tubular reactor was 35 MPa.

[0047] Compared with Comparative Example 1, the ethylene monomer conversion rate of Example 1 increases by 9%. After using the tank reactor, a relatively high concentration of ethylene-vinyl acetate copolymer can be obtained under reduced pressure drop loss. Therefore, compared with Comparative Example 2, the ethylene monomer conversion rate of Example 1 increases by 41%, and compared with Comparative Example 3, the ethylene monomer conversion rate of Example 1 increases by 20%.

[0048] Example 2

[0049] exist Figure 1 The high-pressure free radical polymerization device shown prepares ethylene-polar monomer copolymer, wherein the polar comonomer is vinyl acetate. A portion of the material pressurized to 230MPa by the third compressor 3 is reduced to 220MPa after passing through the pressure reducing valve, and then cooled to 50°C by the heat exchanger 4, and then enters the kettle reactor 6 for reaction, and the operating temperature of the kettle reactor is 220°C. The remaining material pressurized to 230MPa by the third compressor 3 is first preheated to 140°C by the heat exchanger 5, and then enters the first part 7-1 of the tubular reactor for reaction. Among them, the material flow rate entering the kettle reactor 6 is 60 tons per hour, and the material flow rate entering the first part 7-1 of the tubular reactor is 60 tons per hour. The mass fraction of ethylene-vinyl acetate copolymer in the material at the outlet of the kettle reactor is 16%. The outlet material of the kettle reactor 6 is cooled to 190°C and then enters the second part 7-2 of the tubular reactor from a position 600m away from the inlet of the tubular reactor (middle feed port). At this time, the middle feed port of the tubular reactor is located at 40% of the total tube length of the tubular reactor. The mass fraction of ethylene-vinyl acetate copolymer in the outlet material of the tubular reactor is 26%. The inlet pressure of the tubular reactor is 225MPa, and the outlet pressure is 185MPa. The average flow rate of the material in the tubular reactor is 14m / s, and the operating temperature is 215°C.

[0050] The absolute value of the difference between the inlet pressure of the kettle reactor and the inlet pressure of the tubular reactor is 10 MPa, and the difference between the outlet pressure of the kettle reactor and the outlet pressure of the tubular reactor is 35 MPa.

[0051] An organic peroxide is used to initiate the reaction in the autoclave reactor 6. The types of the organic peroxide are di(2-ethylhexyl) peroxydicarbonate and tert-butyl peroxyvalerate, with a mass ratio of 1:1.

[0052] The reaction was initiated by organic peroxides in the tubular reactor, which were di(2-ethylhexyl) peroxydicarbonate, tert-butyl peroxyvalerate, tert-butyl peroxy-2-ethylhexanoate, and tert-butyl peroxybenzoate, with a mass ratio of 1:1:1:1. The organic peroxides entered the tubular reactor from 0m, 600m, and 1080m of the total tube of the tubular reactor, respectively.

[0053] The content of vinyl acetate in the ethylene-vinyl acetate copolymer was 27 wt %. The conversion rate of ethylene monomer was 26%. The pressure drop of the tubular reactor was 40 MPa.

[0054] Compared with Comparative Example 1, the ethylene monomer conversion rate of Example 2 increased by 18%, compared with Comparative Example 2, the ethylene monomer conversion rate of Example 2 increased by 53%, and compared with Comparative Example 3, the ethylene monomer conversion rate of Example 2 increased by 30%.

[0055] Example 3

[0056] exist Figure 1 The high pressure free radical polymerization apparatus shown in the figure prepares ethylene-polar monomer copolymers, and the different conditions compared with Example 2 are as follows:

[0057] The material at the outlet of the tank reactor 6 is cooled to 190°C and then enters the tubular reactor from a position 600m away from the inlet of the tubular reactor (middle feed port). At this time, the middle feed port of the tubular reactor is located at 66.7% of the total tube length of the tubular reactor. The mass fraction of ethylene-vinyl acetate copolymer in the material at the outlet of the tank reactor 6 is 15%.

[0058] The organic peroxide enters the tubular reactor from 0m and 600m of the total tube length of the tubular reactor respectively.

[0059] The content of vinyl acetate in the ethylene-vinyl acetate copolymer was 27 wt %. The conversion rate of ethylene monomer was 20%. The pressure drop of the tubular reactor was 18 MPa.

[0060] Compared with Comparative Example 1, the pressure drop of Example 3 is significantly reduced. Compared with Comparative Example 2, the ethylene monomer conversion rate of Example 3 is increased by 18%. Compared with Comparative Example 3, under the same ethylene monomer conversion rate conditions, the reactor pressure drop of Example 3 is lower.

[0061] Comparative Example 1

[0062] The tubular reactor is used to produce ethylene-polar monomer copolymer by tubular process, and the polar monomer is vinyl acetate. Different from Example 1, the total tube length of the tubular reactor of Comparative Example 1 is further extended by 400m compared with that of Example 1, and an organic peroxide injection point is added, thereby further improving the ethylene monomer conversion rate at the outlet of the tubular reactor. The organic peroxide enters the tubular reactor from 0m, 540m, 1020m and 1450m of the tubular reactor respectively. The content of vinyl acetate in the ethylene-vinyl acetate copolymer is 27wt%. The ethylene monomer conversion rate is 22%. The pressure drop of the tubular reactor is 45MPa.

[0063] Although the extension of the tubular reactor in Comparative Example 1 is beneficial to improving the ethylene monomer conversion rate, and the ethylene monomer conversion rate in Comparative Example 1 is increased to 22%, the ethylene monomer conversion rate is still significantly lower than that in Example 1, and the pressure drop of the tubular reactor is significantly increased.

[0064] Comparative Example 2

[0065] The autoclave reactor in Example 1 was used to produce an ethylene-polar monomer copolymer by an autoclave process, wherein the polar monomer was vinyl acetate. Different from Example 1, in order to improve the monomer conversion rate, the feed temperature of the autoclave reactor was 30° C., the operating pressure of the autoclave reactor was 220 MPa, the operating temperature was 210° C., and the flow rate was 90 tons per hour. The content of vinyl acetate in the ethylene-vinyl acetate copolymer was 27wt%. The ethylene monomer conversion rate was 17%.

[0066] Comparative Example 3

[0067] The ethylene-polar monomer copolymer is produced by combining a kettle reactor and a tubular reactor, and the polar monomer is vinyl acetate. Unlike Example 1, Comparative Example 3 first uses a kettle reactor to produce the first fraction of the ethylene-polar monomer copolymer, and then directly introduces all the materials at the outlet of the kettle reactor into the inlet (main feed port) of the tubular reactor in Example 1 to produce an ethylene-polar monomer copolymer product. The polar monomer is vinyl acetate. Since the tubular reactor is located downstream of the kettle reactor, the operating pressure of the tubular reactor is 240MPa. In order to avoid excessive pressure drop, the total tube length of the tubular reactor in Comparative Example 3 is shortened by 430m compared with Example 1, and one organic peroxide injection point is reduced. The organic peroxide enters the tubular reactor from 0m and 540m of the total tube length of the tubular reactor respectively. The content of vinyl acetate in ethylene-vinyl acetate is 27wt%. The ethylene monomer conversion rate is 20%. The pressure drop of the tubular reactor is 22MPa.

[0068] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. For ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for preparing an ethylene-polar monomer copolymer, characterized in that include: Providing at least one autoclave reactor and a tubular reaction system comprising at least one tubular reactor, in which ethylene, a polar monomer and an organic peroxide are contacted and polymerized to prepare an ethylene-polar monomer copolymer under a pressure of 100-400 MPa and a temperature of 120-350° C. in the autoclave reactor and the tubular reactor; The material at the outlet of the kettle reactor is introduced into the middle feed port of one or more tubular reactors or into the 10%-80% position of the total tube course of multiple tubular reactors connected in series after cooling or without cooling, and the middle feed port of the tubular reactor is located at the 10%-80% position of the tube course of the tubular reactor; The absolute value of the difference between the inlet pressure of the autoclave reactor and the inlet pressure of the tubular reaction system is less than or equal to 40 MPa, and the difference between the outlet pressure of the autoclave reactor and the outlet pressure of the tubular reaction system is greater than or equal to 5 MPa.

2. The method according to claim 1, characterized in that The polar monomer is vinyl acetate, an acrylic acid ester monomer or a methacrylic acid ester monomer having 4 to 12 carbon atoms.

3. The method according to claim 1, characterized in that The operating pressure of the kettle reactor is 120-350 MPa; the operating temperature is 135-280°C.

4. The method according to claim 3, characterized in that The operating pressure of the kettle reactor is 150-270Mpa; the operating temperature is 145-250°C.

5. The method according to claim 1, characterized in that The operating pressure of the tubular reactor is 120-350 MPa; the operating temperature is 135-280°C.

6. The method according to claim 5, characterized in that The operating pressure of the tubular reactor is 150-270 MPa; the operating temperature is 145-250°C.

7. The method according to claim 1, characterized in that The average flow rate of the material in the tubular reactor is 10-25 m / s.

8. The method according to claim 7, characterized in that The average flow rate of the material in the tubular reactor is 12-20 m / s.

9. The method according to claim 1, characterized in that: The concentration of the ethylene-polar monomer copolymer in the material at the outlet of the tubular reaction system is higher than the concentration of the ethylene-polar monomer copolymer at the outlet of the autoclave reactor.

10. The method according to claim 9, characterized in that The concentration of the ethylene-polar monomer copolymer in the material at the outlet of the tubular reaction system is more than 1.2 times the concentration of the ethylene-polar monomer copolymer at the outlet of the autoclave reactor.

11. The method according to any one of claims 1 to 10, characterized in that: The mass fraction of the polar monomer in the ethylene-polar monomer copolymer finally prepared by the method is 3-45wt%.

12. The method according to any one of claims 1 to 10, characterized in that: The mass fraction of the polar monomer in the ethylene-polar monomer copolymer finally prepared by the method is 10-35wt%.

13. The method according to claim 1, characterized in that In the polymerization reaction, a molecular weight regulator is also added to the autoclave reactor and / or tubular reaction system, and the molecular weight regulator is selected from hydrogen, C1-C6 alkanes, C1-C6 olefins, aldehydes, ketones or alcohol compounds.

14. The method according to claim 13, characterized in that The molecular weight regulator is selected from propylene, butene, hexene, propionaldehyde, butyraldehyde or acetone.

15. The method according to claim 1, characterized in that The middle feed inlet of the tubular reactor is preferably located at 25%-60% of the tube length of the tubular reactor.

16. A device for preparing ethylene-polar monomer copolymer, characterized in that: include A tubular reaction system comprising at least one tubular reactor and at least one tank reactor; at least one heat exchanger connected to the inlet of the tank reactor; at least one heat exchanger connected to the inlet of the tubular reactor; at least one pressure reducing valve located upstream or downstream of the autoclave reactor; at least one pressure reducing valve connected to the outlet of the tubular reactor; In the kettle reactor and the tubular reactor, ethylene, polar monomers and organic peroxides are contacted to undergo polymerization reaction to prepare ethylene-polar monomer copolymers under the conditions of a pressure of 100-400 MPa and a temperature of 120-350° C.; the material at the outlet of the kettle reactor is introduced into the middle feed port of one or more tubular reactors or into 10%-80% of the total tube course of multiple tubular reactors connected in series with or without cooling, and the middle feed port of the tubular reactor is located at 10%-80% of the tube course of the tubular reactor.

Images