An external circulation reactor and a method for removing heat from a polymerization reaction

Abstract

The present invention discloses an external circulation reactor and a heat removal method for polymerization reaction. The slurry external circulation heat removal method of the present invention includes making the hexane slurry containing ultra-high molecular weight polyethylene flowing out from the bottom of the polymerization kettle enter the inner tube of the annular tube condenser of the external circulation system, and then using circulating cooling water to perform heat exchange on the polymerization slurry in the inner tube. By interlocking the circulating cooling water flow rate with the temperature inside the polymerization kettle, the purpose of controlling the temperature of the polymerization kettle is achieved. Moreover, the cooled polymerization slurry can return to the polymerization kettle again from the upper side of the polymerization kettle to continue the polymerization reaction, so as to realize the circulating heat removal of the polymerization kettle. Compared with the traditional heat removal method, the heat of polymerization in the heat removal method of the present invention can be completely removed by the external circulation system, and at the same time, the single kettle output is increased. In addition, the internal coil in the polymerization kettle is cancelled, and the stirring intensity is increased, thus greatly preventing the occurrence of sticking to the kettle phenomenon. The ultra-high molecular weight polyethylene particles prepared thereby have more uniform particle sizes, and the product quality is improved.

Description

Technical Field

[0001] The present invention belongs to the fields of olefin polymerization reactors and polyolefin preparation processes, and particularly relates to an external circulation reactor and a heat removal method for polymerization reactions, and more particularly to a production process for preparing ultra-high molecular weight polyethylene by an intermittent slurry process and a heat dissipation method for the reactor during the polymerization process. Background Art

[0002] Ultra-high molecular weight polyethylene (UHMWPE) is a linear structure polyethylene with an extremely high relative molecular weight, and has been widely studied and applied because of its many excellent properties different from those of general polyethylene. Due to the above excellent comprehensive properties, UHMWPE has been widely used as an impact-resistant, shock-absorbing, bulletproof, anti-fatigue, wear-resistant, drag-reducing, and anti-sticking material in many fields such as daily use, industry, culture and sports, transportation, national defense, and machinery. For example, high-performance UHMWPE fibers prepared from UHMWPE raw materials by a gel spinning method have high strength and modulus and excellent mechanical properties, and have been widely used in the military, national defense and other fields.

[0003] The UHMWPE production process is similar to that of ordinary high-density polyethylene, and its main production processes include solution method, slurry method, and gas phase method. Among them, the slurry method is relatively mature and the product quality is good, so it has become the main production process of current UHMWPE production enterprises.

[0004] The patent document with the publication number CN108264599A discloses a production system and process for preparing ultra-high molecular weight polyethylene by an intermittent slurry process. This method uses a supercritical method with propane as a solvent, and the solvent is easily removed after the reaction, so the post-treatment step of drying can be omitted. However, this method has the following two problems: 1. Since the critical pressure of propane is 4.25 MPa, propane cannot be liquefied under the condition that the pressure in the kettle is 0.6 MPa; 2. The cost of the supercritical polymerization process is much higher than that of the ordinary slurry method process.

[0005] The patent document with publication number CN101113184A discloses a heat removal method in the polymerization process of ultra-high molecular weight polyethylene, i.e., a gas external circulation method. The gas external circulation method includes allowing the gas phase ethylene, hydrogen and hexane steam escaping from the polymerization kettle to enter the condenser, condensing the hexane steam, and then performing gas and liquid phase separation through a condensate tank, and then mixing the ethylene and hydrogen in the gas phase with the raw material ethylene and hydrogen and returning to the polymerization kettle, continuing the polymerization reaction, and the hexane in the liquid phase is returned to the polymerization kettle by the condensate pump to achieve the purpose of circulating heat removal. Although the above process solves the heat removal problem in the polymerization process, the method still has the problem that the ultra-high molecular weight polyethylene is easy to "stick to the kettle". In the polymerization process of the ultra-high molecular weight polyethylene of Sinopec, although the heat removal method of gas external circulation is also adopted, the external circulation heater used therein is mostly a shell and tube heat exchanger, because the viscosity of the ultra-high molecular weight polyethylene is extremely large, it is easy to cause the shell and tube heat exchanger to be blocked, which leads to low heat exchange efficiency, and the maintenance of the shell and tube heat exchanger is extremely troublesome. For example, the patent document with publication number CN1796420 discloses a polyethylene slurry external circulation production device, which is used to extract the slurry in the polymerization reactor from the bottom, pump it into the slurry cooler through the slurry cooling pump, and return it to the polymerization reactor after cooling. The slurry is circulated outside the polymerization reactor to cool and remove heat, which increases the heat exchange area and removes a part of the polymerization heat of the reaction process. However, the cooler used in the device is a common shell and tube heat exchanger, so its cooling and heat removal effect is not ideal in the actual production process, and it often gets blocked.

[0006] Ethylene polymerization is an exothermic reaction. As the polymerization continues, a large amount of heat will continue to be generated. Especially when producing ultra-high molecular weight polyethylene, whether the heat released during the reaction can be removed in time is the key to whether the ultra-high molecular weight polyethylene production process can be carried out continuously. If the reaction heat cannot be removed in time, it will not only reduce the polymerization rate, but even cause a "polymerization explosion" accident, making production impossible.

[0007] At present, the requirements for ultra-high molecular weight polyethylene are getting higher and higher, requiring not only small particle size, but also uniform particle size distribution. This requires good heat removal of the polymerization reaction and high stirring intensity. Obviously, the inner coil type polymerization kettle cannot meet the requirements. Therefore, how to remove the heat of reaction in the ultra-high molecular weight polyethylene production process in time, and prevent the ultra-high molecular weight polyethylene particles from sticking to the kettle, so as to produce a product with average particle size, so as to make the reaction proceed smoothly, and the heat removal device and heat removal method of the ultra-high molecular weight polyethylene industrial production method have become technical problems to be solved in this field. Summary of the invention

[0008] To address the above technical problems, the present invention provides a reactor, which comprises a reactor body and an external circulation system. An external circulation inlet and an external circulation outlet are respectively provided at the upper and lower parts of the reactor body, and the external circulation system is connected in series with the reactor body through the external circulation outlet and the external circulation inlet.

[0009] According to an embodiment of the present invention, a jacket is provided outside the reactor body.

[0010] According to an embodiment of the present invention, a discharge port is provided at the bottom of the reactor body, and a feed port is provided at the top.

[0011] According to an embodiment of the present invention, a stirrer is further provided inside the reactor body. Preferably, the stirrer comprises a stirring paddle, and the stirring paddle comprises at least two layers of stirring blades, exemplarily two layers, three layers, four layers or more layers.

[0012] Preferably, the stirring blades are propeller-type stirring blades, and the advancing directions of the stirring blades all face the bottom of the reaction kettle.

[0013] Preferably, the ratio of the radial length L of the propeller-type stirring blade to the diameter D of the reaction kettle is L / D = 0.1 - 0.4, preferably 0.2 - 0.4, exemplarily 0.1, 0.15, 0.2, 0.25, 0.3, 0.4.

[0014] According to an embodiment of the present invention, when the number of layers of the propeller-type stirring paddle is more than two, at least one layer of radial flat-pushing stirring paddle is further provided between the more than two layers of propeller-type stirring paddles, exemplarily one layer, two layers or more layers.

[0015] Preferably, the blades of the radial flat-pushing stirring paddle are rounded rectangular blades.

[0016] Preferably, the ratio of the radial length l of the blade of the radial flat-pushing stirring paddle to the diameter D of the reaction kettle is l / D = 0.15 - 0.4, preferably 0.2 - 0.3, exemplarily 0.15, 0.2, 0.25, 0.3, 0.4.

[0017] According to an embodiment of the present invention, the stirrer further comprises a driving part for adjusting the stirring speed of the stirrer. For example, the driving part is a motor, and the driving part is located at the top of the reactor body.

[0018] According to an embodiment of the present invention, no cooling coil is provided inside the reactor body.

[0019] According to an embodiment of the present invention, a plurality of baffle plates, for example, 2 - 4 baffle plates, may be provided inside the reactor body. Preferably, the plurality of baffle plates are installed on the inner wall of the reactor body. More preferably, the plurality of baffle plates are evenly spaced and installed on the inner wall of the reactor body corresponding to the stirring paddle.

[0020] Preferably, the baffle plate may be an arc-shaped flat plate or a square flat plate, preferably an arc-shaped flat plate.

[0021] For example, the arc-shaped flat plate may be a semi-circular flat plate; the square flat plate may be a rectangular flat plate or a square flat plate.

[0022] Further, when the baffle plate is a square flat plate, the long side of the baffle plate is fixed to the inner wall of the reactor body.

[0023] Preferably, the length of the baffle plate does not exceed the vertical height between the uppermost stirring paddle and the lowermost stirring paddle, and the width is (0.05 - 0.1)D, for example, 0.05D, 0.08D, 0.1D.

[0024] According to an embodiment of the present invention, the external circulation system includes an external circulation pipeline, an annular tube condenser, and a slurry pump. The external circulation outlet is sequentially connected in series with the slurry pump, the annular tube condenser, and the external circulation inlet through the external circulation pipeline.

[0025] Preferably, the annular tube condenser includes an inner tube and an outer tube sleeved outside the inner tube. Among them: the inner tube is used for the circulation of the reaction liquid, and the outer tube is used for the circulation of the cooling water.

[0026] Preferably, the length of the annular tube condenser is (5 - 50)D, preferably 20 - 30D.

[0027] Preferably, the diameter of the inner tube D 0 and the diameter of the outer tube D 1 The ratio is D 1 / D 0 = 1.1 - 1.5, preferably 1.2 - 1.4, for example, 1.1, 1.2, 1.3, 1.4, 1.5.

[0028] Preferably, the diameter of the inner tube D 0 is 100mm - 400mm, preferably 150 - 200mm, for example, 100mm, 150mm, 200mm, 300mm, 400mm.

[0029] Preferably, the position of the external circulation outlet is not higher than the lowermost stirring paddle (such as the bottom stirring paddle), preferably flush with the lowermost stirring paddle (such as the bottom stirring paddle).

[0030] Preferably, the outer circulation inlet is not higher than the uppermost stirring paddle (such as the top stirring paddle).

[0031] Preferably, both the outer circulation inlet and the outer circulation outlet are along the radial tangential direction of the reaction kettle. Preferably, the outer circulation inlet and the outer circulation outlet are symmetrically positioned relative to the centers of the uppermost stirring paddle and the lowermost stirring paddle.

[0032] According to an embodiment of the present invention, the reactor further includes a control system; preferably, the control system is a DCS control system.

[0033] Preferably, the control system is electrically connected or signal-connected to the reactor body, the outer circulation system, and the slurry pump to achieve the control of the ethylene feed flow rate and to achieve the interlocked temperature control of the cooling water flow rate in the outer pipe and the temperature inside the reactor body.

[0034] The present invention can control and adjust the temperature and flow rate of the cooling water through a DCS controller to meet the requirements for the temperature control of the reaction kettle during the polymerization reaction. Specifically, the control system is used to control the temperature inside the reactor body, the circulation flow rate of the reaction slurry in the inner pipe of the outer circulation system, and the circulation flow rate of the cooling water in the outer pipe. The temperature is controlled by the interlock between the cooling water flow rate in the outer pipe and the temperature inside the reactor body, so that the cooling water flow rate in the outer pipe can be adjusted according to the change of the temperature inside the reactor body.

[0035] For example, the slurry circulation amount (i.e., the circulation flow rate of the reaction slurry in the inner pipe) can be fixed, and the temperature control inside the reactor body can be achieved by adjusting the cooling water flow rate in the outer pipe. And when the heat generated by the reaction is the same, if it is necessary to make the temperature inside the reactor body higher, the cooling water flow rate can be reduced; on the contrary, if it is necessary to make the temperature inside the reactor body lower, the circulation cooling water flow rate can be increased.

[0036] The present invention also provides a method for producing ultra-high molecular weight polyethylene using the above reactor, and the method includes removing the reaction heat from the ultra-high molecular weight polyethylene slurry inside the reactor body through the outer circulation system.

[0037] According to an embodiment of the present invention, the polymerization reaction temperature inside the reactor body is 65 - 80 °C, and examples are 65 °C, 70 °C, 75 °C, 80 °C.

[0038] According to an embodiment of the present invention, the polymerization pressure inside the reactor body is 0.2 - 0.8 MPa, and examples are 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa.

[0039] According to an embodiment of the present invention, the method includes flowing the ultra-high molecular weight polyethylene slurry out from the external circulation outlet at the bottom of the reactor body, and transporting it into the loop condenser by a slurry pump, and then returning it to the inside of the reactor body through the external circulation inlet at the upper part of the reactor body to continue the reaction.

[0040] According to an embodiment of the present invention, the inlet temperature of the cooling water of the loop condenser can be 20 - 60 °C, preferably 25 - 55 °C, and exemplary values are 20 °C, 25 °C, 30 °C, 40 °C, 55 °C, 60 °C.

[0041] According to an embodiment of the present invention, the outlet temperature of the cooling water is 25 - 65 °C, preferably 30 - 60 °C, and exemplary values are 30 °C, 35 °C, 45 °C, 55 °C, 60 °C, 65 °C.

[0042] In the present invention, the flow rate of the cooling water is interlocked with the temperature inside the reactor body for temperature control. The flow direction of the cooling water is opposite to the flow direction of the slurry, that is, countercurrent flow. By interlocking the flow rate of the cooling water with the temperature inside the reactor body for temperature control, the temperature difference between the inlet and outlet of the cooling water is controlled at about 5 °C.

[0043] According to an embodiment of the present invention, the circulation volume of the polyethylene slurry of the slurry pump can be determined according to the volume of the reactor body, and it is preferably completed in 2 - 8 minutes for one in-kettle circulation, preferably 3 - 5 minutes, and exemplary values are 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 8 minutes.

[0044] In the present invention, "completing one in-kettle circulation" means the time required to completely flow out the slurry in the kettle when the slurry stops flowing in. Among them:

[0045] The time required to complete one in-kettle circulation = the volume of the reactor slurry / the flow rate of the polyethylene slurry.

[0046] According to an embodiment of the present invention, the heat transfer area of the loop condenser is calculated based on the reaction heat.

[0047] According to an embodiment of the present invention, the method for producing ultra-high molecular weight polyethylene in the reactor includes the following steps:

[0048] (1) Sequentially add the solvent hexane, Z-N catalyst and cocatalyst (triethylaluminum) into the reactor body (polymerization kettle), and start the stirrer and the slurry pump;

[0049] (2) Through the control system, perform temperature control on the reactor body (polymerization kettle) so that the temperature inside the reactor body (polymerization kettle) is not lower than 50 °C (such as 50 °C, 55 °C, 60 °C, 65 °C);

[0050] (3) After the temperature of the reactor body (polymerization kettle) rises to 50 °C, the feeding rate of ethylene is controlled by controlling the feeding flow rate of ethylene through the control system to introduce ethylene into the reactor body (polymerization kettle), and the circulating flow rate of the reaction slurry in the inner tube of the external circulation system and the temperature and circulating flow rate of the cooling water in the outer tube are regulated through the temperature interlock temperature control function of the control system to maintain the reaction temperature in the reactor body at 65-80 °C.

[0051] (3) Those skilled in the art can understand that the faster the ethylene feeding rate, the higher the ethylene concentration in the reactor, which will accelerate the polymerization reaction rate of ethylene, and the lower the molecular weight of polyethylene; conversely, the higher the molecular weight of polyethylene. And the higher the reaction pressure and the lower the reaction temperature, the higher the molecular weight; conversely, the lower the molecular weight. By regulating the feeding rate of ethylene, reaction pressure, and reaction temperature, the present invention can prepare polyethylenes with different molecular weights to meet different requirements.

[0052] Advantages of the present invention

[0053] (1) The external circulation condenser of the present invention adopts a ring-tube condenser. The diameter through which the fluid passes is large and will not cause blockage; and the heat transfer area of the ring-tube heat exchanger is easy to adjust, fully meeting the reaction heat removal, and the heat transfer area of the external circulation condenser can be designed according to the reaction heat. At the same time, the single-kettle output is increased.

[0054] (2) By optimizing and adjusting the positions of the external circulation condenser and the relative position of the stirring paddle, the present invention can maximize the mixing of the circulating feed with the liquid in the kettle within the shortest time, timely and fully complete the cooling of the slurry and achieve its uniform mixing, so that the particle size of the prepared ultra-high molecular weight polyethylene is more uniform. This overcomes the problems in the traditional ultra-high molecular weight polyethylene polymerization reaction process that the heat removal by relying on the jacket of the polymerization kettle and the cooling coil in the kettle has poor heat removal effect and uneven cooling, which is easy to form local overheating in the polymerization kettle, resulting in the phenomena of sticking to the kettle and the polymer particles becoming thick and uneven.

[0055] (3) The reactor of the present invention does not require an inner coil, so the stirring intensity can be significantly increased to prevent the phenomenon of sticking to the kettle, thereby avoiding the temperature unevenness in the reaction system caused by the cooling coil. The particle size of the ultra-high molecular weight polyethylene prepared thereby is more uniform, and the generation of coarse particles is reduced, improving the quality of the ultra-high molecular weight polyethylene product.

[0056] (4) The preparation process method of ultra-high molecular weight polyethylene of the present invention removes the reaction heat through the external circulation of the slurry, that is, the slurry flowing out from the bottom of the polymerization kettle returns to the polymerization kettle from the upper side part of the polymerization kettle after heat removal by the external circulation system. Therefore, the heat removal effect is better, the cooling is more uniform, and the temperature at each point in the polymerization kettle can be kept uniform to avoid local overheating that causes powder caking. Description of the drawings

[0057] Figure 1 It is a schematic structural diagram of the outer circulation reactor of the present invention.

[0058] Figure 2 It is a top view schematic diagram of the slurry outer circulation reactor of the present invention.

[0059] In the figure: 1. Reactor body; 2. Jacket; 3. Annular tube condenser; 4. Slurry pump; 5. Ethylene feed pipe; 6. Outer tube; 7. Outer circulation inlet; 8. Solvent feed port, 9. Driving part; 10. Catalyst feed port; 11. Discharge port; 12. Outer circulation outlet. Specific embodiments

[0060] The technical solution of the present invention will be further described in detail below in combination with specific embodiments. It should be understood that the following embodiments are only for illustrative explanation of the present invention and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0061] Unless otherwise specified, the raw materials and reagents used in the following embodiments are all commercially available products or can be prepared by known methods.

[0062] As Figure 1-2 shown, an outer circulation reactor, the reactor includes a reactor body 1 and an outer circulation system. An outer circulation inlet 7 and an outer circulation outlet 12 are respectively arranged at the upper and lower parts of the reactor body 1. The outer circulation system is connected in series with the reactor body 1 through the outer circulation outlet 12 and the outer circulation inlet 7.

[0063]

Reactor body

[0064] A jacket 2 is arranged outside the reactor body 1, a discharge port 11 is arranged at the bottom of the reactor body 1, and a feed port is arranged at the top.

[0065]

Stirrer

[0066] A stirrer is also arranged inside the reactor body 1. The stirrer includes a stirring paddle, and the stirring paddle includes two layers of stirring blades.

[0067] Preferably, the stirring blades are propeller-type stirring blades, and the propelling directions of the stirring blades all face the bottom of the reactor body 1.

[0068] Preferably, the ratio of the radial length L of the propeller-type stirring blade to the diameter D of the reaction kettle L / D = 0.1 - 0.4, preferably 0.2 - 0.4, and exemplary values are 0.1, 0.15, 0.2, 0.25, 0.3, 0.4.

[0069] There are also two layers of radial pusher agitators arranged between the two layers of pusher agitators, and the blades of the radial pusher agitators are rounded rectangular blades.

[0070] Preferably, the ratio of the radial length l of the blade of the radial pusher agitator to the diameter D of the reactor is l / D = 0.15 - 0.4, preferably 0.2 - 0.3, and exemplary values are 0.15, 0.2, 0.25, 0.3, 0.4.

[0071]

Drive unit

[0072] The agitator further includes a drive unit 9 for adjusting the stirring speed of the agitator. For example, the drive unit 9 is a motor, and the drive unit 9 is located at the top of the reactor body 1.

[0073] There is no cooling coil arranged inside the reactor body 1.

[0074]

Baffle plate

[0075] Multiple baffle plates can also be arranged inside the reactor body 1, for example, 2 - 4 pieces. Preferably, the multiple baffle plates are installed on the inner wall of the reactor body 1. More preferably, the multiple baffle plates are evenly spaced and installed on the inner wall of the reactor body 1 corresponding to the agitator.

[0076] Preferably, the baffle plate can be an arc-shaped flat plate or a square flat plate, preferably an arc-shaped flat plate.

[0077] For example, the arc-shaped flat plate can be a semi-circular flat plate; the square flat plate can be a rectangular flat plate or a square flat plate.

[0078] Further, when the baffle plate is a square flat plate, the long side of the baffle plate is fixed to the inner wall of the reactor body 1.

[0079] Preferably, the length of the baffle plate does not exceed the vertical height between the topmost agitator and the bottommost agitator, and the width is (0.05 - 0.1)D, and exemplary values are 0.05D, 0.08D, 0.1D.

[0080]

External circulation system

[0081] The external circulation system further includes an external circulation pipeline, an annular tube condenser 3, and a slurry pump 4. The external circulation outlet 12, the slurry pump 4, the annular tube condenser 3, and the external circulation inlet 7 are connected in series through the external circulation pipeline in sequence.

[0082] The annular tube condenser 3 includes an inner tube and an outer tube 6 sleeved outside the inner tube. Among them: the inner tube is used for the circulation of the reaction liquid, and the outer tube 6 is used for the circulation of the cooling water.

[0083] The length of the annular tube condenser 3 is (5 - 50)D, preferably 20 - 30D.

[0084] Inner tube diameter D0 The ratio with the outer tube 6 diameter D 1 is D 1 / D 0 = 1.1 - 1.5, preferably 1.2 - 1.4, and exemplary values are 1.1, 1.2, 1.3, 1.4, 1.5.

[0085] The inner tube diameter D 0 is 100 mm - 400 mm, preferably 150 - 200 mm, and exemplary values are 100 mm, 150 mm, 200 mm, 300 mm, 400 mm.

[0086] The position of the outer circulation outlet 12 is not higher than the bottommost stirring paddle (such as the bottom stirring paddle), and preferably is flush with the bottommost stirring paddle (such as the bottom stirring paddle).

[0087] Preferably, the outer circulation inlet 7 is not higher than the uppermost stirring paddle (such as the top stirring paddle).

[0088] Preferably, both the outer circulation inlet 7 and the outer circulation outlet 12 are along the tangential direction of the reactor radial direction. Preferably, the outer circulation inlet 7 and the outer circulation outlet 12 are symmetrically positioned with respect to the center of the uppermost stirring paddle and the bottommost stirring paddle.

[0089]

Control System

[0090] The reactor further includes a control system; preferably, the control system is a DCS control system. The control system is electrically connected or signal-connected to the reactor body 1, the outer circulation system, and the slurry pump 4 to achieve the control of the ethylene feed flow rate and to achieve the interlocked temperature control of the cooling water flow rate in the outer tube 6 and the temperature inside the reactor body 1.

[0091] The heat removal method of the present invention is an industrial production technology, which uses high-purity ethylene (volume content higher than 99.9%) as the main raw material, hexane as the solvent, and a highly active Z-N catalyst, and conducts low-pressure slurry polymerization to prepare ultra-high molecular weight polyethylene under the conditions of 60 - 85°C and 0.2 - 1.0 MPa. The molecular weight of the ultra-high molecular weight polyethylene product can be controlled by adjusting process parameters such as the polymerization pressure, the polymerization reaction temperature, and the catalyst concentration during the polymerization reaction process. The polyethylene slurry after the polymerization reaction further undergoes processes such as separation, drying, blending, and packaging to obtain ultra-high molecular weight polyethylene with excellent performance and an average molecular weight greater than 1.5 million.

[0092] A method for producing ultra-high molecular weight polyethylene, which includes processes such as catalyst preparation, polymerization, separation, drying, and packaging, and the specific method is as follows:

[0093] Ethylene, hydrogen, a co-catalyst prepared at a certain concentration, triethylaluminum, and a dilution of the Z-N catalyst (concentration 0.5 - 3.0 gcat / L) are respectively fed into the reactor body 1 (polymerization kettle) through metering pumps. Under the conditions of reaction pressure (0.2 - 0.8 MPa) and temperature (60 - 85 °C), slurry polymerization is carried out in the medium of hexane solvent. The polymerization heat released during the polymerization reaction (819 kcal / kg) is removed by increasing the external circulation system of the slurry, that is, the heat removal method of the external circulation of the slurry. After the polymerization reaction is completed, the entry of ethylene is stopped. Keep warm and depressurize until the pressure in the reactor body 1 (polymerization kettle) drops below 0.15 MPa. At this time, the ethylene consumption is more than 99.95%. When the temperature in the reactor body drops below 40 °C, discharging is carried out through the discharge port 11. The polyethylene slurry obtained after the polymerization reaction enters the filtration and drying kettle by its own pressure for separation operation.

[0094] The polymer slurry in the filtration and drying kettle is separated into wet cake and mother liquor through the filtration port. The wet content of the wet cake is 25 - 35%. The wet cake is vacuum dried into powder in the filtration and drying kettle, enters the vibrating screen through the rotary valve, and is sent to the silo through the powder conveying fan after screening, and then packaged into products. The gas coming out of the drying kettle enters the drying gas scrubbing tower, is washed with hexane, and then the hexane in the drying gas is recovered by cooling through a cooler. The washed drying gas is recycled. A part of the separated mother liquor is directly recycled to the polymerization kettle for use, and the other part is sent to the solvent recovery section for refining.

[0095] The slurry external circulation heat removal method for producing ultra-high molecular weight polyethylene resin of the present invention is realized through the following process, as Figure 1 shown:

[0096] 1. The hexane slurry containing ultra-high molecular weight polyethylene in the reactor body (polymerization kettle) 1 flows out from the bottom (pipe orifice 12) of the reactor body (polymerization kettle) 1, enters the annular tube condenser 3 through the external circulation inlet 7 under the push of the slurry pump 4, and returns to the reactor body (polymerization kettle) 1 from the external circulation inlet 7 of the reactor body (polymerization kettle) 1. The temperature of the slurry at the inlet of the annular tube condenser 3 is the same as the temperature inside the reactor body (polymerization kettle) 1 (65 - 80 °C), and the temperature of the slurry at the outlet of the annular tube condenser 3 is 55 - 70 °C.

[0097] 2. Circulating cooling water is passed through the inner tube of the annular tube condenser 3 for cooling. The circulating cooling water flows reversely along the annular tube condenser 3, opposite to the flow direction of the slurry. (The flow rate of the cooling water is interlocked with the temperature of the polymerization kettle.)

[0098] The polymerization reaction temperature is an important means to control the molecular weight of ultra-high molecular weight polyethylene products. When producing ultra-high molecular weight polyethylene of different grades, the polymerization reaction temperature is also different. In the present invention, the flow rate of the circulating cooling water is associated with the temperature in the reactor body (polymerization kettle) 1 through a DCS control system. Therefore, by controlling the circulation amount of the external circulation slurry and the flow rate of the cooling water, the heat removal amount of the reactor body (polymerization kettle) 1 can be adjusted, and then the polymerization reaction temperature can be controlled.

[0099] The inventors unexpectedly found that by controlling the slurry circulation amount within 2 - 8 min (preferably 3 - 5 min) to complete one slurry circulation in the polymerization kettle, the polymerization reaction temperature can be controlled within 65 - 80 °C.

[0100] The following will further illustrate the present invention with specific embodiments.

[0101] Example 1

[0102] Refer to Figure 1-2 , in this embodiment, the reactor adopted includes a reactor body 1 (polymerization kettle) and an external circulation system. The reactor body 1 is a 30 m 3 polymerization kettle with a diameter of 2.8 m. The upper and lower parts of the reactor body 1 are respectively provided with an external circulation inlet 7 and an external circulation outlet 12. The external circulation system is connected in series with the reactor body 1 through the external circulation outlet 12 and the external circulation inlet 7.

[0103] In this embodiment, the single-kettle output of the reactor body 1 (polymerization kettle) is 5000 kg, the slurry concentration is 300 g / L, the heat of ethylene polymerization is 819 kcal / kg, and the specific heat of hexane is calculated at 0.60 kcal / kg. The reaction heat is 682500 kcal / h, and the heat exchange area is 25 m 2 , and the heat exchange area of the loop tube condenser 3 is calculated as 1.5 times, which is 37.5 m 2 .

[0104] In this embodiment, a jacket 2 is provided outside the reactor body 1, a discharge port 11 is provided at the bottom of the reactor body 1, and a feed port (including a solvent hexane feed port 8 and a catalyst feed port 10) is provided at the top.

[0105] In this embodiment, a stirrer is further provided inside the reactor body 1. The stirrer is arranged in the center of the reactor body 1, and its drive shaft passes through an opening formed in the center of the top and is connected to a drive part 9 such as a motor for adjusting the stirring speed of the stirrer.

[0106] The stirrer includes four layers of stirring blades. The uppermost and lowermost stirring blades are propeller-type stirring blades that push downward, and the radial length of the blades is 0.84 m; in the middle, a radial flat-pushing stirring blade is adopted, and the radial length of the blade is 0.6 m.

[0107] The interior of the reactor body 1 is not provided with cooling coils.

[0108] In this embodiment, a semi-circular baffle plate can also be provided inside the reactor body 1. The length of the baffle plate does not exceed the vertical height between the uppermost stirring paddle and the lowermost stirring paddle, and the width is 0.08D.

[0109] In this embodiment, the external circulation system further includes an external circulation pipeline, an annular tube condenser 3, and a slurry pump 4. The external circulation outlet 12, the slurry pump 4, the annular tube condenser 3, and the external circulation inlet 7 are connected in series through the external circulation pipeline in sequence.

[0110] The annular tube condenser 3 includes an inner tube and an outer tube 6 sleeved outside the inner tube. Among them: the inner tube is used for the circulation of the reaction liquid. The inner tube selects a heat exchange tube with a diameter of DN200 and a tube length of 60 m, which can be divided into 3 groups, each group is 20 m, and adjacent groups are connected by 180° elbows. The maximum slurry flow rate is 600 m 3 / h; the outer tube 6 is a stainless steel tube with a diameter of DN300, and the outer tube 6 is used for the circulation of cooling water.

[0111] The diameter D of the inner tube 0 and the diameter D of the outer tube 6 1 The ratio is D 1 / D 0 = 1.2, and the diameter D of the inner tube 0 is 200 mm.

[0112] The position of the external circulation outlet 12 is flush with the bottom stirring paddle. Both the external circulation inlet 7 and the external circulation outlet 12 are along the radial tangential direction of the reaction kettle, and the external circulation inlet 7 and the external circulation outlet 12 are symmetrically positioned relative to the center of the uppermost stirring paddle and the lowermost stirring paddle.

[0113] In this embodiment, the reactor further includes a DCS control system. The control system is electrically connected or signal-connected to the reactor body 1, the external circulation system, and the slurry pump 4 to achieve the control of the ethylene feed flow rate and the interlocking temperature control of the cooling water flow rate in the outer tube 6 and the internal temperature of the reactor body 1.

[0114] A method for ultra-high molecular weight polyethylene polymerization reaction using the above reactor includes the following steps:

[0115] (1) Feed 21 m 3 of hexane, 2.7 L of alkyl aluminum (concentration 1.0 mol / L), and 80 L of prepared Z-N catalyst suspension (concentration 1 g / L) into the polymerization kettle through a metering pump;

[0116] (2) Start the agitator and the slurry pump 4, and heat up the reactor body (polymerization kettle 1) using the jacket 2. When the system temperature reaches 50 °C, ethylene is delivered to the polymerization kettle 1 through the ethylene flow controller 5 for polymerization reaction. The polymerization pressure is 0.5 - 0.6 MPa, and the polymerization temperature is 65 °C. The liquid level height of the polymerization kettle is 70 - 88% of the polymerization kettle, and the maximum concentration of the polymerization slurry is 300 g / L;

[0117] (3) Remove the heat of polymerization through the external circulation system (slurry external circulation method) and control the reaction temperature (wherein: the external circulation volume of the polymerization slurry is 600 m 3 / h. Calculated according to the hexane solvent amount of 21 m 3 , the time required for one internal circulation in the kettle is 2.1 min). After the polymerization slurry stays in the polymerization kettle for about 5 hours, stop the entry of ethylene. Keep warm and suck pressure. When the pressure inside the polymerization kettle drops to 0.2 MPa, turn on the jacket cooling water to cool the polymerization kettle to 40 °C. The slurry is pressed through the discharge port 11 to the filtration and drying kettle (under a pressure of 0.3 MPa), and the hexane is filtered and separated.

[0118] Nearly 80% of the hexane, i.e., the mother liquor, is separated here. The separated filter cake is vacuum dried (the vacuum drying temperature is about 65 °C) to obtain ultra-high molecular weight polyethylene dry powder with a moisture content of less than 0.05%. After removing the hexane in the polyethylene powder through vacuum drying, the polyethylene powder is transported to the mixing and packaging section by a nitrogen conveying fan.

[0119] The ultra-high molecular weight polyethylene prepared in this example has a molecular weight of 4.1 million, a bulk density of 0.48 g / cm 3 , a median particle size of 120 μm, and the ultra-high molecular weight polyethylene particles smaller than 40 mesh account for 1.5%.

[0120] Example 2

[0121] Carry out the polymerization production of ultra-high molecular weight polyethylene according to the method in Example 1, with 4 kettle polymerizations per day for 30 consecutive days. Through the sight glass of the polymerization kettle, there is no accumulated material in the kettle, and the kettle wall is clean. The ultra-high molecular weight polyethylene obtained has a molecular weight of 4.15 million, a bulk density of 0.48 g / cm 3 , a median particle size of 118 μm. The ultra-high molecular weight polyethylene particles smaller than 40 mesh account for 1.4%.

[0122] Comparative Example 1

[0123] The polymerization kettle is the same size as in Example 1, except that: a single-layer propeller agitator is used inside the polymerization kettle, the radius of the agitator is 0.6 m, a traditional jacket is used outside, and a ring pipe is set inside the kettle to introduce cooling water to remove heat, without using external circulation to remove heat. The other operating conditions are the same as in Example 1.

[0124] The molecular weight of the ultra-high molecular weight polyethylene prepared in this comparative example is 4.2 million, and the bulk density is 0.45 g / cm 3 , and the median particle size is 180 μm. The ultra-high molecular weight polyethylene particles smaller than 40 mesh account for 5.0%.

[0125] Comparative Example 2

[0126] The ultra-high molecular weight polyethylene polymerization production was carried out according to the method in Comparative Example 1. After continuous production for 10 days, through the sight glass observation, there was already accumulated material in the polymerization kettle, and there was also the phenomenon of sticking to the kettle wall.

[0127] The molecular weight of the ultra-high molecular weight polyethylene prepared is 4.5 million, and the bulk density is 0.43 g / cm 3 , and the median particle size is 220 μm. The ultra-high molecular weight polyethylene particles smaller than 40 mesh account for 8.0%.

[0128] Comparative Example 3

[0129] The ultra-high molecular weight polyethylene polymerization production was carried out according to the method in Comparative Example 1. After continuous production for 15 days, through the sight glass observation, there was a large amount of accumulated material in the polymerization kettle, and the sticking to the kettle wall was very serious. The kettle cleaning operation must be carried out.

[0130] The molecular weight of the ultra-high molecular weight polyethylene prepared is 4.4 million, and the bulk density is 0.41 g / cm 3 , and the median particle size is 260 μm. The ultra-high molecular weight polyethylene particles smaller than 40 mesh account for 30%.

[0131] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A reactor, characterized in that, the reactor comprises a reactor body and an external circulation system. An external circulation inlet and an external circulation outlet are respectively arranged at the upper and lower parts of the reactor body. The external circulation system is connected in series with the reactor body through the external circulation outlet and the external circulation inlet; a stirrer is further arranged inside the reactor body. The stirrer comprises a stirring paddle, and the stirring paddle comprises at least two layers of propeller stirring blades, and the advancing directions of the stirring blades all face the bottom of the reaction kettle; the number of layers of the propeller stirring paddle is more than two layers, and at least one layer of radial flat-pushing stirring paddle is further arranged between the two or more layers of propeller stirring paddles; the external circulation system further comprises an external circulation pipeline, an annular tube condenser and a slurry pump. The external circulation outlet, the slurry pump, the annular tube condenser and the external circulation inlet are connected in series through the external circulation pipeline in sequence; the annular tube condenser comprises an inner tube and an outer tube sleeved outside the inner tube; the position of the external circulation outlet is flush with the bottom stirring paddle, and the external circulation inlet is not higher than the top stirring paddle; the external circulation inlet and the external circulation outlet are symmetrically positioned with respect to the centers of the uppermost stirring paddle and the lowermost stirring paddle.

2. The reactor according to claim 1, characterized in that, a jacket is arranged outside the reactor body; and / or, a discharge port is arranged at the bottom of the reactor body, and a feed port is arranged at the top; and / or, the ratio L / D of the radial length L of the propeller stirring blade to the diameter D of the reaction kettle is 0.1 - 0.4; and / or, the paddle of the radial flat-pushing stirring paddle is a fillet rectangular paddle; and / or, the ratio l / D of the radial length l of the paddle of the radial flat-pushing stirring paddle to the diameter D of the reaction kettle is 0.15 - 0.

4.

3. The reactor according to claim 1, characterized in that, the stirrer further comprises a driving part for adjusting the stirring speed of the stirrer; the driving part is a motor, and the driving part is located at the top of the reactor body; and / or, no cooling coil is arranged inside the reactor body.

4. The reactor according to any one of claims 1 - 3, characterized in that, a plurality of baffle plates are further arranged inside the reactor body, and the plurality of baffle plates are evenly spaced and installed on the inner wall of the reactor body corresponding to the stirring paddle; and / or, the baffle plate is an arc-shaped flat plate or a square flat plate; and / or, the long side of the baffle plate is fixed to the inner wall of the reactor body; and / or, the length of the baffle plate does not exceed the vertical height between the uppermost stirring paddle and the lowermost stirring paddle, and the width is (0.05 - 0.1)D.

5. The reactor according to any one of claims 1 - 3, characterized in that, the length of the annular tube condenser is (5 - 50)D; and / or, the inner tube diameter D 0 and the outer tube diameter D 1 The ratio is D 1 / D 0 = 1.1 - 2.0; and / or, the inner tube diameter D 0 is 100 mm - 400 mm.

6. The reactor according to any one of claims 1 - 3, characterized in that, the reactor further comprises a control system, and the control system is a DCS control system; the control system is electrically connected or signal-connected to the reactor body, the external circulation system and the slurry pump.

7. A method for producing ultra-high molecular weight polyethylene by using the reactor according to any one of claims 1 - 6, characterized in that, The method includes removing the reaction heat by means of the external circulation system from the ultra-high molecular weight polyethylene slurry in the reactor body.

8. The method according to claim 7, wherein, the polymerization reaction temperature in the reactor body is 65 - 80 °C; and / or, the polymerization pressure in the reactor body is 0.2 - 0.8 MPa; and / or, the method includes flowing the ultra-high molecular weight polyethylene slurry out from the external circulation outlet at the bottom of the reactor body, transporting it into the shell-and-tube condenser by a slurry pump, and then returning it to the inside of the reactor body through the external circulation inlet at the upper part of the reactor body to continue the reaction.

9. The method according to claim 7, wherein, the inlet temperature of the cooling water in the shell-and-tube condenser is 20 - 60 °C; and / or, the outlet temperature of the cooling water is 25 - 65 °C; and / or, the circulation rate of the polyethylene slurry by the slurry pump completes one in-kettle circulation in 2 - 8 minutes.

10. The method according to claim 9, wherein, the inlet temperature of the cooling water in the shell-and-tube condenser is 25 - 55 °C; and / or, the outlet temperature of the cooling water is 30 - 60 °C; and / or, the circulation rate of the polyethylene slurry by the slurry pump completes one in-kettle circulation in 3 - 5 minutes.

11. The method according to any one of claims 7 - 9, wherein, the method for producing ultra-high molecular weight polyethylene in the reactor includes the following steps: (1) Sequentially adding the solvent hexane, Z-N catalyst, and cocatalyst into the reactor body, and starting the stirrer and the slurry pump; (2) Controlling the temperature rise of the reactor body through the control system to make the temperature in the reactor body reach at least 50 °C; (3) After the temperature of the reactor body rises to 50 °C, controlling the feeding rate of ethylene by controlling the feeding flow rate of ethylene through the control system to introduce ethylene into the reactor body, and regulating the circulation flow rate of the reaction slurry in the inner tube of the external circulation system and the temperature and circulation flow rate of the cooling water in the outer tube through the temperature interlock temperature control function of the control system to maintain the reaction temperature in the reactor body at 65 - 80 °C.

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