A high pressure radical polymerization apparatus and process for producing ethylene homopolymers or copolymers

Abstract

The application discloses a high-pressure radical polymerization device and method for producing ethylene homopolymer or copolymer, which comprises at least four reaction sub-zones in series, each reaction sub-zone is composed of a straight turbine blade at the top of the sub-zone and a reaction space below the blade; the first, second and fourth sub-zones are respectively provided with one feed in the upper half and the lower half of the reaction space, the mixture of polymerization monomer and initiator is injected into the upper half, and the polymerization monomer without initiator is injected into the lower half; the third sub-zone is provided with only one feed, and the injected material can be the polymerization monomer or the mixture of the polymerization monomer and the initiator; the flow of each feed of the fourth sub-zone is controlled by the measured temperature of multiple temperature measuring points in the sub-zone. The application is not only beneficial to controlling the temperature distribution in the reactor, but also can realize the cooling in the reactor and improve the cooling efficiency of the discharge through operation optimization.

Description

Technical Field

[0001] This invention generally relates to a high-pressure free radical polymerization apparatus and method for producing ethylene homopolymers or copolymers, belonging to the field of high-pressure free radical polymerization equipment and production processes, and particularly to a high-pressure free radical polymerization apparatus and method for producing ethylene-vinyl acetate copolymers. Background Technology

[0002] The reactor is one of the key pieces of equipment in the production of high-density polyethylene (HDPE). Depending on the type of polymerization reactor, HDPE production processes can be divided into tubular and batch processes. The polymers produced by these two methods differ significantly in molecular structure and product performance. Compared to the tubular process, the polymer produced by the batch process has a wider molecular weight distribution and a higher degree of long-chain / short-chain branching in its molecular structure, especially in the long-chain branching, giving it an unparalleled advantage in the production of coatings compared to products from the tubular process.

[0003] Reactor partitioning and multi-point feeding are key features of high-pressure autoclave reactors. On the one hand, due to the short residence time of materials in the reactor and the thick reactor wall, heat transfer through the reactor wall is limited, necessitating the injection of cold ethylene at multiple points to balance the heat of reaction. On the other hand, by installing multiple partition baffles on the reactor's stirring shaft, forming multiple partitions connected in series at the same pressure but different temperatures, backmixing between partitions can be reduced, providing more possibilities for the development of new grades.

[0004] To achieve the aforementioned objectives, existing technology patent holders (Basel, Sumitomo, Eni, and ExxonMobil) have designed unique partitioning and partitioned feeding schemes in their respective technologies. However, under these existing partitioned feeding schemes, heat is still not well controlled, and thermal decomposition accidents still occur frequently during start-up and operation. This technology aims to address these objectives by providing an optimized partitioning and partitioned feeding scheme, reducing the occurrence of thermal decomposition accidents and improving the safety of plant operation.

[0005] Furthermore, in conventional high-pressure polyethylene production processes, polyethylene products need to be cooled after flowing out of the reactor before entering the separation section. External cooling is widely used in existing processes. Patents ZL202110380252.1 and ZL201680051849.9 disclose a method and implementation details for cooling products outside the reactor using a tubular cooler. By placing the cooler before the high-pressure discharge valve, both discharge cooling and prevention of initiator residue in the reactor are achieved. However, this method still has very noticeable drawbacks. For jacketed tubular heat exchangers, radial temperature distribution is very likely to occur inside the tubes, and low wall temperatures may lead to wall adhesion. In fact, wall adhesion has always been a major problem affecting the stable operation of tubular reactors using jacketed heat exchangers.

[0006] For batch reactors, the temperature inside the reactor is extremely uniform due to high-speed stirring, making it an ideal environment for quench heat exchange. Therefore, another objective and advantage of this patent is to achieve in-reactor cooling by setting a suitable cold ethylene quenching feed at the bottom of the batch reactor. This effectively utilizes the reaction volume, reduces downstream equipment investment, and greatly improves cooling efficiency. This method is particularly suitable for the production of high MI (up to 1000) and high VA products. Summary of the Invention

[0007] The problem this invention aims to solve is that the temperature inside the reactor is difficult to control and the material cooling efficiency is low during the discharge process in existing batch high-pressure free radical polymerization processes.

[0008] To solve the above-mentioned technical problems, the present invention proposes a high-pressure free radical polymerization apparatus for producing ethylene homopolymers or copolymers. The polymerization apparatus includes at least four reaction zones connected in series, each reaction zone consisting of a straight-bladed turbine propeller at the top of the zone and a reaction space below the propeller.

[0009] Both the first and second sections are equipped with two feed streams. The first feed stream is located no more than half the height of the section from the top and is used to inject a mixture of monomers and initiators. The second feed stream is located no more than one-third the height of the section from the bottom and is used to inject monomers without initiators.

[0010] Only one feed stream is provided in the third section for injecting the monomer, or a mixture of monomer and initiator;

[0011] The fourth section is equipped with two feed streams. The first feed stream is located at a distance of no more than 1 / 4 of the section height from the top of the section and is used to inject polymer monomers or a mixture of polymer monomers and initiators. The second feed stream is located at a distance of no less than 1 / 2 and no more than 3 / 4 of the section height from the top of the section and is used to inject polymer monomers.

[0012] The top of the third section is equipped with a circular physical partition, located above the straight-bladed turbine propeller of the third section;

[0013] The fourth section has no fewer than five temperature measuring points along the axial direction. The first temperature measuring point is at the same height as the feed inlet of the first feed inlet in the fourth section, the fourth temperature measuring point is at the same height as the feed inlet of the second feed inlet in the fourth section, and the second and third temperature measuring points are equidistantly distributed between the first and fourth temperature measuring points.

[0014] Furthermore, when the number of temperature measuring points in the fourth zone is more than five, the additional temperature measuring points are arranged at equal intervals between the fourth temperature measuring point and the outlet.

[0015] Furthermore, the distance between the physical partition and the inner wall of the reactor is between 3-20 mm, preferably 5-10 mm.

[0016] The present invention also provides a method for producing ethylene homopolymers or copolymers based on the high-pressure free radical polymerization apparatus: during the polymerization reaction, stirring is turned on in each reaction zone; by controlling the injection of materials into different feed ports of each reaction zone, ethylene homopolymers or copolymers are produced.

[0017] Specifically, a mixture of monomers and initiator is injected into the first feed inlet of the first and second zones; monomers without initiator are injected into the second feed inlet of the first and second zones during the polymerization process.

[0018] Injecting the polymer monomer or a mixture of polymer monomer and initiator into the third zone;

[0019] Inject the monomer or a mixture of monomer and initiator into the first feed inlet of section 4; control the injection and control of the second feed inlet of section 4 according to the following rules:

[0020] (1) The second feed is turned on only when the first feed in the fourth zone is a mixture of polymer monomer and initiator, and the temperature difference measured at the third and fourth temperature measuring points in the fourth zone is not greater than 2°C.

[0021] (2) When the difference between the outlet temperature of the fourth zone and the polymer cloud point temperature under the outlet pressure condition is less than 10°C, the feed will be automatically shut off.

[0022] According to a preferred embodiment of the present invention, when the first feed point of the fourth zone is only polymer monomer, the injection flow rate of polymer monomer and the reactor outlet temperature form a safety interlock control. When the difference between the outlet temperature and the cloud point temperature of the polymer under the outlet conditions is less than 10°C, the feed is automatically shut off.

[0023] According to a preferred embodiment of the present invention, the feed temperature at each feed inlet is between 20-100°C.

[0024] According to a preferred embodiment of the present invention, the polymerizing monomer is ethylene, or a mixture of ethylene and unsaturated carboxylic acid comonomers; the initiator is a certain organic peroxide initiator or a mixture of several organic peroxide initiators.

[0025] According to a preferred embodiment of the present invention, the amount of polymeric monomers fed with the initiator in any partition is not less than 15% of the total feed amount of that partition.

[0026] According to a preferred embodiment of the present invention, the stirring speed is 500-1500 rpm, the reaction temperature is 150-350℃, and the reaction pressure is 100-300 MPa.

[0027] The present invention has the following advantages:

[0028] (1) For the first and second zones, the cold ethylene required for the zone is divided into two streams for separate feeding. This can control the temperature rise near the initiator injection point to a certain extent, and avoid the problems of low injection point temperature, easy accumulation of initiator, and risk of ethylene decomposition caused by excessive cold ethylene flow rate when one stream is injected.

[0029] (2) For the fourth section, the cold ethylene feed set in the lower half of the section can flexibly achieve in-vessel cooling and improve cooling efficiency, which is particularly suitable for the production of high MI (up to 1000) and high VA products. Attached Figure Description

[0030] Figure 1 A schematic diagram of a high-pressure free radical polymerization apparatus for producing ethylene homopolymers or copolymers. Detailed Implementation

[0031] The present invention will now be described in detail with reference to embodiments and accompanying drawings. However, it should be understood that the embodiments and drawings are for illustrative purposes only and do not constitute any limitation on the scope of protection of the present invention. All reasonable modifications and combinations included within the inventive spirit of the present invention fall within the scope of protection of the present invention.

[0032] like Figure 1 As shown, the polymerization apparatus provided in this embodiment includes at least four reaction zones connected in series, each reaction zone consisting of a straight-bladed turbine propeller at the top of the zone and a reaction space below the blades;

[0033] Both the first and second sections are equipped with two feed streams. The first feed stream is located no more than half the height of the section from the top and is used to inject a mixture of monomers and initiators. The second feed stream is located no more than one-third the height of the section from the bottom and is used to inject monomers without initiators.

[0034] Only one feed stream is provided in the third section for injecting the monomer, or a mixture of monomer and initiator;

[0035] The fourth section is equipped with two feed streams. The first feed stream is located at a distance of no more than 1 / 4 of the section height from the top of the section and is used to inject polymer monomers or a mixture of polymer monomers and initiators. The second feed stream is located at a distance of no less than 1 / 2 and no more than 3 / 4 of the section height from the top of the section and is used to inject polymer monomers.

[0036] The top of the third section is equipped with a circular physical partition, located above the straight-bladed turbine propeller of the third section;

[0037] The fourth section has no fewer than five temperature measuring points along the axial direction. The first temperature measuring point is at the same height as the feed inlet of the first feed inlet in the fourth section, the fourth temperature measuring point is at the same height as the feed inlet of the second feed inlet in the fourth section, and the second and third temperature measuring points are equidistantly distributed between the first and fourth temperature measuring points.

[0038] The high-pressure free radical polymerization of the present invention can be used to produce ethylene homopolymers or copolymers, for example, for the production of ethylene-vinyl acetate copolymers.

[0039] This invention provides a method for producing ethylene homopolymers or copolymers based on the aforementioned high-pressure free radical polymerization apparatus: during the polymerization reaction, stirring is activated in each reaction zone; by controlling the injection of materials into different feed ports of each reaction zone, ethylene homopolymers or copolymers are produced.

[0040] Specifically, a mixture of monomers and initiator is injected into the first feed inlet of the first and second zones; monomers without initiator are injected into the second feed inlet of the first and second zones during the polymerization process.

[0041] Injecting the polymer monomer or a mixture of polymer monomer and initiator into the third zone;

[0042] Inject the monomer or a mixture of monomer and initiator into the first feed inlet of section 4; control the injection and control of the second feed inlet of section 4 according to the following rules:

[0043] (1) The second feed is turned on only when the first feed in the fourth zone is a mixture of polymer monomer and initiator, and the temperature difference measured at the third and fourth temperature measuring points in the fourth zone is not greater than 2°C.

[0044] (2) When the difference between the outlet temperature of the fourth zone and the polymer cloud point temperature under the outlet pressure condition is less than 10°C, the feed will be automatically shut off.

[0045] In a preferred embodiment of this aspect, the monomer is a mixture of 28% vinyl acetate and 72% ethylene by mass, with a total feed flow rate of 40 tons / hour, and the monomer is distributed in a ratio of 5 / 5 / 5 / 5 / 10 / 5 / 5 tons / hour respectively through... Figure 1 The feed is injected into the reactor through seven feed points from top to bottom.

[0046] The initiator for the first three sections from top to bottom is tert-butyl peroxide-2-ethylhexyl ester, with a feed flow rate of 2 kg / h. The initiator for the last section is tert-butyl peroxide neopentyl ester, with a feed flow rate of 1 kg / h.

[0047] At the beginning of the reaction, ethylene and comonomers from the refining area are pressurized to the required reaction pressure by an ultra-high pressure compressor. The reactor is preheated to 150°C before the raw materials are injected. The initiator is added point by point to establish the reaction. After the reactor temperature rises to the required conditions with the addition of the initiator, the amount of initiator injected is automatically adjusted to maintain the reaction temperature at the required reaction conditions. After the temperature stabilizes, the next section begins to inject the initiator until the reaction is fully established.

[0048] Example 1 Operating Conditions

[0049]

[0050] Example 2 Operating Conditions

[0051]

[0052] Operating conditions of Comparative Example 1

[0053]

[0054] Compared with the comparative example, by using the operation method described in Example 1, the temperature at feed sites 1 and 3 can be increased from 206°C to 211°C, which increases the reaction temperature near the initiator injection point, improves the initiator efficiency, and reduces the decomposition accidents caused by initiator accumulation from 4 times a year to 2 times a year.

[0055] Compared with the comparative example, by using the operation method described in Example 2, 2 t / h of pure ethylene was injected at the feed point 7 as the in-reactor cold quench stream. Without affecting the product properties, the reactor outlet temperature was reduced from 209°C to 195°C, thus achieving in-reactor cooling.

[0056] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A high-pressure free radical polymerization apparatus for producing ethylene homopolymers or copolymers, characterized in that: The polymerization device includes at least four reaction zones connected in series, each reaction zone consisting of a straight-bladed turbine at the top of the zone and a reaction space below the blades; Both the first and second sections are equipped with two feed streams. The first feed stream is located no more than half the height of the section from the top and is used to inject a mixture of monomers and initiators. The second feed stream is located no more than one-third the height of the section from the bottom and is used to inject monomers without initiators. Only one feed stream is provided in the third section for injecting the monomer, or a mixture of monomer and initiator; The fourth section is equipped with two feed streams. The first feed stream is located at a distance of no more than 1 / 4 of the section height from the top of the section and is used to inject polymer monomers or a mixture of polymer monomers and initiators. The second feed stream is located at a distance of no less than 1 / 2 and no more than 3 / 4 of the section height from the top of the section and is used to inject polymer monomers. The top of the third section is equipped with a circular physical partition, located above the straight-bladed turbine propeller of the third section; The fourth section has no fewer than five temperature measuring points along the axial direction. The first temperature measuring point is at the same height as the feed inlet of the first feed inlet in the fourth section, the fourth temperature measuring point is at the same height as the feed inlet of the second feed inlet in the fourth section, and the second and third temperature measuring points are equidistantly distributed between the first and fourth temperature measuring points.

2. The high-pressure free radical polymerization apparatus according to claim 1, characterized in that, When there are more than 5 temperature measuring points in the 4th zone, the extra temperature measuring points are arranged at equal intervals between the 4th temperature measuring point and the outlet.

3. The high-pressure free radical polymerization apparatus according to claim 1, characterized in that, The distance between the physical partition and the inner wall of the reactor is between 3 and 20 mm.

4. A method for producing ethylene homopolymers or copolymers based on the high-pressure free radical polymerization apparatus of claim 1, characterized in that: during the polymerization reaction, stirring is activated in each reaction zone; and ethylene homopolymers or copolymers are produced by controlling the injection of materials into different feed ports of each reaction zone. in, A mixture of monomers and initiator is injected into the first feed inlet of Zone 1 and Zone 2; monomers without initiator are injected into the second feed inlet of Zone 1 and Zone 2 during the polymerization process. Injecting the polymer monomer or a mixture of polymer monomer and initiator into the third zone; Inject the monomer or a mixture of monomer and initiator into the first feed inlet of section 4; control the injection and control of the second feed inlet of section 4 according to the following rules: (1) The second feed is turned on only when the first feed in the fourth zone is a mixture of polymer monomer and initiator, and the temperature difference measured at the third and fourth temperature measuring points in the fourth zone is not greater than 2°C. (2) When the difference between the outlet temperature of the fourth zone and the polymer cloud point temperature under the outlet pressure condition is less than 10°C, the feed will be automatically shut off.

5. The method according to claim 4, characterized in that, When the first feed point of the fourth section is only polymer monomer, the injection flow rate of polymer monomer and the reactor outlet temperature form a safety interlock control. When the difference between the outlet temperature and the cloud point temperature of the polymer under the outlet conditions is less than 10°C, the feed is automatically shut off.

6. The method according to claim 4, characterized in that, The feed temperature at each inlet is between 20-100℃.

7. The method according to claim 4, characterized in that, The polymerizing monomer is ethylene, or a mixture of ethylene and unsaturated carboxylic acid comonomers; the initiator is a certain organic peroxide initiator or a mixture of several organic peroxide initiators.

8. The method according to claim 4, characterized in that The amount of monomers fed with the initiator in any zone shall not be less than 15% of the total feed amount in that zone.

9. The method according to claim 4, characterized in that, The stirring speed is 500-1500 rpm, the reaction temperature is 150-350℃, and the reaction pressure is 100-300 MPa.

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