Olefin polymerization method

Abstract

The present invention relates to the field of slurry polymerization, and discloses an olefin polymerization method, which comprises that at least one olefin contacts with an olefin polymerization catalyst and pentane as a diluent in a polymerization reactor under a slurry polymerization condition to obtain a slurry polymerization product, the method further comprises the steps that part of the slurry polymerization product is led out of the polymerization reactor to serve as a first slurry product, heat exchange is conducted on the first slurry product and a cooling medium, the first slurry product obtained after heat exchange is conducted is obtained, the temperature of the first slurry product obtained after heat exchange is lower than that of the first slurry product, and the second slurry product obtained after heat exchange is conducted is obtained. And introducing the first slurry product after heat exchange back into the polymerization reactor, wherein the temperature of the cooling medium is higher than 40 DEG C. According to the process method provided by the invention, wax in the polymer slurry is not easy to separate out and accumulate on the wall of the heat exchanger.

Description

Technical Field

[0001] The present invention relates to the technical field of slurry polymerization, and particularly relates to a method for olefin polymerization. Background Art

[0002] Polyethylene is a product with a relatively high output among polymer materials. Different polyethylene varieties usually adopt different production processes. HDPE and LLDPE are both produced by the low-pressure polyethylene process, and the polymerization pressure is usually lower than 6 MPa; while LDPE is produced by the high-pressure polyethylene process, and the polymerization pressure is usually higher than 200 MPa. The polyethylene produced by the slurry process is in a slurry state because it is insoluble in the solvent.

[0003] In order to control the production temperature in the polyethylene production process, it is necessary to timely remove the heat generated in this process. The existing methods usually add a slurry heat exchanger or a gas-phase heat exchanger outside the reactor. When using a slurry heat exchanger, the reaction material returns to the polymerization reactor after being cooled by the slurry heat exchanger, and the heat exchanger is filled with a circulating coolant. In order to achieve high heat exchange efficiency, a coolant with as low a temperature as possible is usually used for heat exchange in the heat exchanger, and the flow rate of the coolant is increased to keep the temperature difference between the inlet and outlet of the heat exchanger coolant at a relatively low level. When using a gas-phase heat exchanger, the gas phase in the reaction kettle is condensed by the gas-phase heat exchanger, the condensate is pumped back to the reactor through a pump, and the non-condensable gas is sent back to the reactor through a compressor.

[0004] However, the oligomer impurities in the polyethylene process are prone to precipitate into wax in a low-temperature environment, resulting in the blockage of the heat exchanger within a short time and requiring shutdown for treatment.

[0005] The problems of higher heat exchange efficiency and precipitation blockage caused by low coolant temperature have prompted researchers to conduct more in-depth research on the polyethylene production process.

[0006] For example, CN103539875A discloses a device for improving the production of high-density polyethylene by the slurry method, which requires that when the temperature of the cooling water is higher than 60 °C, the supplementary cooling water regulating valve is automatically opened to keep the cooling water between 58 and 62 °C, and the temperature difference between the reaction material at the inlet and outlet of the heat exchanger is not higher than 5 ± 1 °C. In this prior art, by controlling the circulating cooling water temperature at 60 °C, it is ensured that the polymer slurry in the cooler tubes will not have the phenomenon of oligomer precipitation and wall sticking; by controlling the temperature difference between the inlet and outlet of the slurry in the cooler within 5 ± 1 °C, the quality of the polymer product can be stably controlled. However, in this prior art, the cooling water temperature must be controlled between 58 and 62 °C, and the operating flexibility of the reaction kettle is small. On the premise of the existing heat removal equipment, controlling the water temperature within this range cannot further improve the heat removal capacity.

[0007] For another example, CN106471011A discloses a method for preparing polyethylene by polymerizing ethylene and optionally one or more C3-C10 α-olefins in a slurry in a reactor system, wherein it is proposed that in order to ensure the heat removal efficiency of the polymerization system, there are two main means, one is to reduce the temperature of the coolant in the heat exchanger as much as possible, and the other is to change the flow rate of the coolant in the heat exchanger. However, excessive reduction in the temperature of the coolant will cause low molecular impurities in the polymerization system to accumulate on the inner wall of the heat exchanger due to cooling, causing blockage of the heat exchanger and affecting the heat removal efficiency. Therefore, the prior art proposes that the temperature of the coolant in the heat exchanger is 29°C or higher (up to 40°C), and requires that the maximum fluctuation of the temperature of the coolant in the heat exchanger is within 2°C. Therefore, the design concept of the prior art is to "maintain the temperature of the first coolant that cools the first heat exchanger at a very narrow interval to minimize the accumulation of the wax layer on the wall of the heat exchanger". However, due to the relatively low temperature, the wax wall layer in the heat exchanger will still be produced, and once the wax is solidified, unless the temperature of the first coolant is increased to the point where the wax begins to melt (however, to achieve this effect, the reaction temperature will be higher than the polymerization temperature), otherwise, the solidified wax wall layer is not easy to dissolve, which puts higher requirements on the structure of the heat exchanger; thereby limiting the widespread application of the process.

[0008] Furthermore, the method disclosed in CN106471011A has relatively poor product selectivity. In other words, the polyolefin products produced by the prior art have relatively poor processability. If this method is applied to produce polyolefin products with better processability, obvious blockage will occur in a short period of time, resulting in the need to stop production and clean the device. Summary of the invention

[0009] The purpose of the present invention is to overcome the defect that the wax in the polymer slurry is easily precipitated and accumulated on the wall of the heat exchanger in a short time when producing a polyolefin product with good processability in the prior art, resulting in the inability of the device to operate for a long period of time.

[0010] In order to achieve the above-mentioned purpose, the present invention provides an olefin polymerization method, which comprises contacting at least one olefin with an olefin polymerization catalyst and pentane as a diluent in a polymerization reactor under slurry polymerization conditions to obtain a slurry polymerization product, characterized in that the method also comprises withdrawing a portion of the slurry polymerization product from the polymerization reactor as a first slurry product, exchanging heat between the first slurry product and a cooling medium to obtain a first slurry product after heat exchange, the temperature of the first slurry product after heat exchange being lower than the temperature of the first slurry product, and introducing the first slurry product after heat exchange back into the polymerization reactor, and the temperature of the cooling medium is higher than 40°C.

[0011] The inventors found that in the slurry process for polyethylene production, when using conventional hexane or butane solvents as diluents, since the boiling points of hexene and hexane are close and difficult to separate, hexene cannot be used as a comonomer; if using butane solvent, due to its very low boiling point and high volatility, the reaction conditions are demanding. Therefore, through research, the inventors found that in the slurry polymerization process of polyethylene, when using pentane as a diluent, the reaction conditions are mild, and solvent recovery can be carried out with significantly lower energy consumption, making the solution of the present invention suitable for large-scale industrial production.

[0012] The method provided by the present invention has more advantages in copolymerization and hydrogen regulation performance under n-pentane solvent. Even at a high hydrogen-to-ethylene ratio, it can still maintain high activity, shorten the polymerization time for producing low molecular weight fractions, which is beneficial for tandem and / or parallel production of bimodal / broad distribution high-performance pipe materials and film materials. In the third reaction kettle of a three-kettle process, it is easier to obtain high molecular weight fractions, and thus excellent performance PERT pipe materials can be obtained.

[0013] Meanwhile, the n-pentane solvent used in the method of the present invention has low solubility for oligomers, which is beneficial for establishing a new balance between the mechanical properties and processing properties of HDPE.

[0014] In the process method provided by the present invention, even when producing polyolefin products with good processability, by optimizing the structure of the heat exchanger, wax in the polymer slurry is not likely to precipitate and accumulate on the wall of the heat exchanger, enabling the polyolefin production device to operate continuously for a long time.

[0015] The method of the present invention can continuously produce polyethylene products with a melt index (2.16 kg) of more than 10 (especially 12 - 17) and a density of 0.950 - 0.965 g / cm 3 ³.

[0016] The temperature range controlled by the method provided by the present invention can greatly improve the operating flexibility of the reaction kettle (exemplarily, the operating flexibility of the reaction kettle can be increased by 60% - 300%).

[0017] In the method provided by the present invention, the oligomer wax generated enters the subsequent process together with the product, and the high-density polyethylene products obtained by this technology are easy to process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic structural diagram of the first end of the heat exchanger according to the preferred embodiment of the present solution;

[0019] Figure 2 is a schematic structural diagram of the first end plate according to the preferred embodiment of the present solution;

[0020] Figure 3It is a cross-sectional view of the first end plate described in the preferred embodiment of this solution;

[0021] Figure 4 It is a schematic structural diagram of the second end of the heat exchanger described in the preferred embodiment of this solution;

[0022] Figure 5 It is a schematic structural diagram of the second end plate described in the embodiment of this solution;

[0023] Figure 6 It is a cross-sectional view of the second end plate described in the preferred embodiment of this solution;

[0024] Figure 7 It is a schematic structural diagram of a reactor containing a heat exchanger described in the preferred embodiment of this solution;

[0025] Figure 8 It is a schematic diagram of the sampling assembly described in the embodiment of this solution.

[0026] Explanation of reference numerals

[0027] 100 - Heat exchanger, 110 - Shell-side cylinder, 111 - First pipe joint, 112 - Second pipe joint, 113 - Baffle plate, 120 - First tube sheet, 121 - First drain pipe, 130 - Second tube sheet, 131 - Second drain pipe, 140 - First end plate, 141 - Input through-hole, 142 - Output through-hole, 143 - Partition member, 144 - First recess, 145 - Input pipe, 146 - Output pipe, 147 - Input cavity, 148 - Output cavity, 150 - Second end plate, 151 - Return cavity, 152 - Second recess, 153 - Exhaust pipe, 154 - Plugging block, 160 - Heat exchange tube, 200 - Main housing, 201 - Circulation pipeline, 202 - Discharge pipeline, 300 - Sampling assembly, 301 - Filter container, 302 - Collection container, 303 - Sampling pipeline, 304 - Test pipeline, 305 - Pre-cleaning pipeline, 306 - Liquid supply pipeline, 307 - Heating pipeline, 308 - Condensate pipeline, 309 - Exhaust pipeline, 310 - Drain pipeline, 1431 - First slope, 1432 - Second slope, 1441 - Third slope, 1442 - Fourth slope. Detailed implementation manners

[0028] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0029] As described above, the present invention provides a method for olefin polymerization, which includes contacting at least one olefin with an olefin polymerization catalyst and pentane as a diluent in a polymerization reactor under slurry polymerization conditions to obtain a slurry polymerization product. It is characterized in that the method further includes withdrawing a part of the slurry polymerization product from the polymerization reactor as a first slurry product, exchanging heat between the first slurry product and a cooling medium to obtain a first slurry product after heat exchange, the temperature of the first slurry product after heat exchange being lower than that of the first slurry product, and introducing the first slurry product after heat exchange back into the polymerization reactor, the temperature of the cooling medium being higher than 40°C.

[0030] Preferably, the temperature of the cooling medium is higher than 40°C and not higher than 65°C.

[0031] Preferably, the heat exchange is carried out in at least one heat exchanger, and the temperature of the cooling medium at the inlet of the heat exchanger is higher than 40°C and not higher than 55°C. Particularly preferably, the heat exchange is carried out in at least one heat exchanger, and the temperature of the cooling medium at the inlet of the heat exchanger is 41°C - 55°C.

[0032] According to a preferred specific embodiment, the residence time of the first slurry product in the heat exchanger is 1 - 30 s.

[0033] Preferably, the temperature of the first slurry product after heat exchange is 72 - 85°C.

[0034] In order to reduce the residence time of the first slurry product in the heat exchanger to avoid dead zones, and to prevent the medium from staying, accumulating, and adhering to the tube sheet in the shell side, and improve the heat exchange efficiency, the present invention provides a preferred heat exchanger structure. The heat exchanger includes a shell side cylinder, heat exchange tubes arranged in the shell side cylinder, a first tube sheet arranged at the first end of the shell side cylinder, and a first end plate connected to the outer side of the first tube sheet. The first end plate is provided with an input through hole and an output through hole. A partition is arranged on the surface of the first end plate facing the first tube sheet between the input through hole and the output through hole. The partition divides and forms an input cavity and an output cavity communicating with the heat exchange tubes between the first tube sheet and the first end plate.

[0035] In order to further reduce the residence time of the first slurry product in the heat exchanger, and thus further improve the heat exchange efficiency, in some preferred embodiments, the partition is in the shape of a dam and is preferably arranged at the middle position of the first end plate. In the direction from the first end plate to the first tube sheet, the thickness of the partition gradually decreases.

[0036] Preferably, a first slope surface extending to the edge of the input through hole and a second slope surface extending to the edge of the output through hole are respectively formed on both sides of the partition, and the first slope surface and the second slope surface extend to the first tube sheet.

[0037] Preferably, a first recessed portion is provided on a surface of the first end plate facing the first tube plate, the separator is provided in the first recessed portion, and the first recessed portion is formed with a third slope extending to the edge of the input through hole and a fourth slope extending to the edge of the output through hole.

[0038] Preferably, the first slope surface and the third slope surface transition smoothly to form a smooth gradually expanding wall surface defining the input cavity; the second slope surface and the fourth slope surface transition smoothly to form a smooth gradually contracting wall surface defining the output cavity.

[0039] Preferably, the flow area of the input through hole is larger than the flow area of the output through hole.

[0040] In some preferred embodiments, an input pipe connected to the input through hole and an output pipe connected to the output through hole are provided on a side of the first end plate facing away from the first tube plate.

[0041] In some preferred embodiments, a first drain pipe connected to the shell-side cylinder is provided on the first tube sheet.

[0042] In some preferred embodiments, the heat exchanger includes a second tube sheet connected to the second end of the shell-side cylinder and a second end plate connected to the outside of the second tube sheet, and a return cavity connected to the heat exchange tube is formed between the second end plate and the second tube sheet, and the volume of the return cavity gradually decreases from the center to the edge.

[0043] In some preferred embodiments, a conical second recessed portion is provided on a surface of the second end plate facing the second tube plate, and a cross-sectional area of the second recessed portion gradually decreases in a direction away from the second tube plate.

[0044] In some preferred embodiments, an exhaust pipe communicating with the return cavity is provided on a side of the second end plate facing away from the second tube plate.

[0045] In some preferred embodiments, a second drain pipe connected to the shell-side cylinder is provided on the second tube sheet.

[0046] In some preferred embodiments, a first connecting pipe and a second connecting pipe are provided on the side walls of both ends of the shell-side cylinder.

[0047] On the other hand, the method provided by the present invention is preferably carried out in a polymerization reactor containing the aforementioned heat exchanger. The polymerization reactor includes a main shell and the heat exchanger described above. The main shell is provided with a first opening at the upper part and a second opening at the lower part. A circulation pipeline is arranged between the first opening and the second opening, and the heat exchanger is arranged on the circulation pipeline.

[0048] In some preferred embodiments, a plurality of baffles are arranged inside the shell-side cylinder.

[0049] The following will Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 describe the preferred heat exchanger of the present invention and the polymerization reactor containing the heat exchanger.

[0050] The method of the present invention relates to a preferred heat exchanger. Among them, the heat exchanger 100 includes a shell-side cylinder 110, heat exchange tubes 160 arranged in the shell-side cylinder 110, a first tube sheet 120 arranged at the first end of the shell-side cylinder 110, and a first end plate 140 connected to the outer side of the first tube sheet 120. The first end plate 140 is provided with an input through hole 141 and an output through hole 142. A partition 143 is arranged on the surface of the first end plate 140 facing the first tube sheet 120 between the input through hole 141 and the output through hole 142. The partition 143 divides and forms an input cavity 147 and an output cavity 148 communicating with the heat exchange tubes 160 between the first tube sheet 120 and the first end plate 140.

[0051] Preferably, the partition 143 is in the shape of a dam and is preferably arranged at the middle position of the first end plate 140. In the direction of the first end plate 140 pointing to the first tube sheet 120, the thickness of the partition 143 gradually decreases.

[0052] Preferably, two sides of the partition 143 respectively form a first slope surface 1431 extending to the edge of the input through hole 141 and a second slope surface 1432 extending to the edge of the output through hole 142. The first slope surface 1431 and the second slope surface 1432 extend to the first tube sheet 120.

[0053] Preferably, the heat exchanger is a shell-and-tube heat exchanger. Among them, the shell-side cylinder 110 is the main structure, and its cross-section can be circular, square, etc. Heat exchange tubes 160 are arranged therein. The space between the heat exchange tubes 160 and the shell-side cylinder 110 is the shell side, and the internal space of the heat exchange tubes 160 is the tube side.

[0054] Preferably, at the first end of the heat exchanger, a first tube sheet 120 and a first end plate 140 are provided on the shell-side cylinder 110. The first tube sheet 120 is provided with holes for accommodating the heat exchange tubes 160 to be inserted or docked with the heat exchange tubes 160 to support the heat exchange tubes 160. The edge portions of the mutually facing surfaces of the first end plate 140 and the first tube sheet 120 are fitted together to form a seal.

[0055] Preferably, at least one of the mutually facing surfaces of the first end plate 140 and the first tube sheet 120 forms a recess, so as to form a cavity for accommodating fluid between the first tube sheet 120 and the first end plate 140. The partition member 143 divides this cavity into two cavities, namely an input cavity 147 and an output cavity 148. The input cavity 147 communicates with the input through-hole 141 and a part of the heat exchange tubes 160, and the output cavity 148 communicates with the output through-hole 142 and the other part of the heat exchange tubes 160. The fluid sequentially passes through the input through-hole 141, the input cavity 147, the heat exchange tubes 160, reaches the other end of the heat exchanger, and then returns (for example, through the return cavity described below) to the heat exchange tubes 160, and sequentially passes through the output cavity 148 and the output through-hole 142 and is discharged. The partition member 143 is used to divide and form the input cavity 147 and the output cavity 148. It can be a part of the first end plate 140, or a part of the first tube sheet 120. Of course, it can also be independent of the first end plate 140 and the tube sheet 120 and is only located between the two.

[0056] It can be seen that the first end plate 140 replaces the head with a flat partition plate in the prior art.

[0057] Regarding the return cavity at the other end of the shell-side cylinder 110, it can be formed by a spherical head in the prior art, or can be formed by the structure described below in this solution.

[0058] The input cavity and the output cavity are separated by a partition member between the first end plate and the first tube sheet. Slopes are formed on both sides of the partition member, eliminating the medium static area and the turbulent flow area, and can guide the fluid to flow quickly along the slopes. When used for slurry heat exchange, it can make the medium flow more smoothly, so that the fluid medium can flow through the tube box (i.e., the input cavity and the output cavity) more quickly, avoid wax aggregation or even blockage in the tube box, effectively ensure the heat exchange effect, and extend the continuous operation period of the equipment.

[0059] In the shell-and-tube heat exchanger in the prior art, wax aggregation or even blockage easily occurs in the tube box part. Therefore, its operation period is short and it needs to be shut down for maintenance and cleaning. By optimizing the end plate structure and the structures of the input cavity 147 and the output cavity 148 in this solution, the fluid can pass through quickly, shortening the flow time, and avoiding or reducing wax aggregation or even blockage.

[0060] Preferably, the first end plate 140 is made of stainless steel, and its thickness can be set to be relatively small. A pressing plate made of carbon steel is arranged on its outer side, and the pressing plate and the first end plate 140 are connected to the first tube sheet 120 by bolts or other connection means, which can improve the overall strength and reduce the material cost.

[0061] Preferably, referring to Figure 2 As shown, the partition 143 is roughly formed on the first end plate 140 and can be located at one of the diameters of the first end plate 140. As Figure 3 shown, the thickness of the partition 143 gradually decreases, so as to form a first slope surface 1431 extending to the edge of the input through hole 141 and a second slope surface 1432 extending to the edge of the output through hole 142 on both sides. This makes the axial dimension of the input cavity 147 or the output cavity 148 aligned with the heat exchange tubes 160 in the middle part of the first tube sheet 120 relatively smaller. Compared with a plate structure with a uniform thickness (the thickness corresponding to the minimum thickness of the partition 143), the volumes of the input cavity 147 and the output cavity 148 are reduced. In addition, the first slope surface 1431 forms a guiding surface between the first tube sheet 120 and the input through hole 141, so that the fluid flows directly from the input through hole 141 to the first tube sheet 120 along the first slope surface 1431 to enter the heat exchange tubes 160. The second slope surface 1432 forms a guiding surface between the first tube sheet 120 and the output through hole 142, so that the fluid flows from the first tube sheet 120 to the output through hole 142 along the second slope surface 1432. The two guiding surfaces can further eliminate the medium static area and the turbulent flow area, guide the flow of the medium fluid, make the medium flow more smoothly, be beneficial to reducing the pressure drop, reducing the material aggregation and blockage, ensuring that the fluid passes through the input cavity, the output cavity and the heat exchange tubes 160 more smoothly, and avoiding or reducing the occurrence of wax aggregation and even blockage.

[0062] Preferably, referring to Figure 2 As shown, a first recess 144 is provided on the surface of the first end plate 140 facing the first tube sheet 120, and the partition 143 is arranged in the first recess 144. The first recess 144 is formed with a third slope surface 1441 extending to the edge of the input through hole 141 and a fourth slope surface 1442 extending to the edge of the output through hole 142. In other embodiments, a recess can also be provided on the tube sheet. In this solution, the first tube sheet 120 adopts a traditional tube sheet structure, and the first end plate 140 replacing the traditional spherical head is generally a flat plate as a whole. A first recess 144 is provided thereon and divided into two recesses by the partition 143, so as to cooperate with the first tube sheet 120 to form an input cavity 147 and an output cavity 148. Among them, the thickness of the first end plate 140 is 160 - 170 mm, and the depth of the first recess 144 is approximately 70 - 80 mm. Figure 2In it, the first recessed portion 144 is provided with two third slopes 1441 on both sides of the first slope 1431 around the input through hole 141. The two third slopes 1441 form a guiding surface between the input through hole 141 and the first tube sheet 120. Similar to the first slope 1431, the third slopes 1441 can guide the fluid flow and reduce the flow dead angle. The second recessed portion 144 is provided with two fourth slopes 1442 on both sides of the second slope 1432 around the output through hole 142. The two fourth slopes 1442 form a guiding surface between the output through hole 142 and the first tube sheet 120. Similar to the second slope 1432, the fourth slopes 1442 can guide the fluid flow and reduce the flow dead angle.

[0063] Preferably, the first slope 1431 and the third slope 1441 are smoothly transitioned to form a smoothly expanding wall surface defining the input cavity 147; the second slope 1432 and the fourth slope 1442 are smoothly transitioned to form a smoothly contracting wall surface defining the output cavity 148. Refer to Figure 2 , one end of the first recessed portion 144 facing the first tube sheet 120 is a circular interface, and the separator 143 divides it into two semi-circular interfaces. One end of the input cavity 147 and the output cavity 148 facing the first tube sheet 120 is a semi-circular interface. Among them, the first slope 1431 and the third slope 1441 are smoothly transitioned, so that a smooth transition is formed between the input through hole 141 and the semi-circular interface, guiding the fluid to flow to the first tube sheet 120 more quickly from the input channel 141; the second slope 1432 and the fourth slope 1442 are smoothly transitioned, so that a smooth transition is formed between the output through hole 142 and the semi-circular interface, guiding the fluid to flow to the output through hole 142 more quickly from the first tube sheet 120. Both the input cavity 147 and the output cavity 148 are cavities with a semi-circular interface at one end and a circular interface with a smaller size at the other end. The semi-circular interface and the circular interface are transitioned through a special-shaped smooth transition surface to form a tapered structure, which can reduce the flow dead angle, reduce the cavity volume, enable the fluid to pass through more quickly, and improve the flow velocity. Or rather, the input cavity 147 and the output cavity 148 are formed into a special-shaped funnel shape or flared shape. It should be noted that there is a certain processing difficulty for the special-shaped smooth transition surface in the input cavity 147 and the output cavity 148. Therefore, a square flat bottom surface can be provided at the bottom of the cavity, the input through hole 141 or the output through hole 142 can be provided on the flat bottom surface, and the corresponding slopes described above can be provided around the flat bottom surface, and a smooth transition may not be formed between adjacent slopes.

[0064] Preferably, when the input cavity 147 is formed as a gradually expanding type, the axial dimension of the edge portion is smaller, so the volume of the edge portion of the input cavity 147 is smaller. In addition, the distribution density of the heat exchange tubes 160 provided in the edge portion of the shell-side cylinder 110 is relatively small, and the flow rate of the fluid medium is relatively small. A part of the edge of the input cavity 147 corresponds to the edge portion of the shell-side cylinder 110. Therefore, the edge portion of the input cavity 147 with a smaller volume adapts to the characteristic that the flow rate of the heat exchange tubes 160 in the edge portion of the shell-side cylinder 110 is smaller. By reducing the volume of the edge portion of the input cavity 147, the flow rate of the fluid medium in its edge portion is ensured, so that the medium fluid can flow rapidly in the corresponding heat exchange tubes 160, ensuring the overall flow rate of the medium fluid and avoiding wax accumulation or even blockage. The output cavity 148 has a similar mechanism and will not be described in detail here.

[0065] Preferably, on the side of the first end plate 140 facing away from the first tube sheet 120, an input pipe 145 communicating with the input through-hole 141 and an output pipe 146 communicating with the output through-hole 142 are provided. Flanges can be provided at the free ends of the input pipe 145 and the output pipe 146 to facilitate connection with other pipe fittings.

[0066] Preferably, referring to Figure 2 and Figure 3 As shown, the flow area of the input through-hole 141 is larger than that of the output through-hole 142, which allows the flow rate of the input fluid to be greater than that of the output through-hole 142, and is applicable to the case where the volume decreases after the fluid temperature drops, such as partial gas liquefaction. Among them, the ratio of the flow area of the input through-hole 141 to that of the output through-hole 142 is 18:10 - 15. In addition, since the flow area of the output channel 142 is smaller, it is more conducive to the rapid flow of the medium fluid through the output pipe 146, avoiding wax accumulation or even blockage in the output pipe 146. Correspondingly, the slopes of the two sides of the partition plate 143 are also different. The slope of the first slope surface 1431 is greater than that of the second slope surface 1432, and the slope of the third slope surface 1441 is also greater than that of the fourth slope surface 1442.

[0067] Preferably, referring to Figure 3 As shown, the free end of the partition member 143 (i.e., the end facing the first tube sheet 120) includes a portion with a constant thickness, and this portion can be inserted into the first tube sheet 120 to form a good seal.

[0068] Preferably, a first drain pipe 121 communicating with the shell-side cylinder 110 is provided on the first tube sheet 120. The first drain pipe 121 communicates with the shell-side and can be used to drain the fluid therein. During normal use, it is in a disconnected state.

[0069] Preferably, the heat exchanger includes a second tube sheet 130 connected to the second end of the shell-side cylinder 110 and a second end plate 150 connected to the outer side of the second tube sheet 130. A return cavity 151 communicating with the heat exchange tubes 160 is formed between the second end plate 150 and the second tube sheet 130. At least one of the surfaces of the second tube sheet 130 and the second end plate 150 facing each other forms a recessed portion to form the return cavity 151 therebetween. The first part of the heat exchange tubes 160 communicating with the input cavity 147 inputs fluid into the return cavity 151 and then into the second part of the heat exchange tubes 160 to return to the output cavity 148.

[0070] Preferably, as Figure 5 shown, a second recessed portion 152 is provided on the surface of the second end plate 150 facing the second tube sheet 130, and the cross-sectional area of the second recessed portion 152 gradually decreases in the direction away from the second tube sheet 130. The number of heat exchange tubes 160 provided at the central position of the second tube sheet 130 is larger, and the number of heat exchange tubes 160 at the edge portion is smaller. Therefore, the axial dimension of the edge portion of the second recessed portion 152 is smaller than that of the central portion, and the space is relatively smaller, that is, the space in the central portion of the return cavity 151 is larger, and the space in the edge portion is smaller, to adapt to the flow rate distribution of the fluid at different positions, and to minimize the volume of the second recessed portion 152 as much as possible, so that the fluid can quickly pass through the second recessed portion 152. Among them, the maximum depth of the second recessed portion 152 is 12 mm - 15 mm. Among them, the second recessed portion 152 is in a conical or frustum shape.

[0071] Preferably, the second recessed portion 152 is conical. First connecting pipes 111 and second connecting pipe heads 112 are provided on the outer peripheries of both ends of the shell-side cylinder 110. Avoidance areas are provided in the shell-side cylinder 110 adjacent to the first connecting pipes 111 and the second connecting pipes 112 respectively, and no heat exchange tubes 160 are provided in the avoidance areas. A blocking block 154 axially aligned with the avoidance areas is provided in the second recessed portion 152. For the convenience of description, the second recessed portion 152 is set as conical. Actually, after the blocking block 154 is provided, the second recessed portion 152 is only approximately conical, equivalent to cutting off two parts at the edge of the cone. The cross-section of the blocking block 154 in the direction perpendicular to the axial direction of the shell-side cylinder 110 is in a bow shape, as Figure 5 shown.

[0072] Preferably, both the first connecting pipe 111 and the second connecting pipe 112 communicate with the inside of the shell-side cylinder 110, that is, communicate with the shell side, and can be used to input and output the heat exchange fluid. Flanges can be provided at their free ends to facilitate connection with other pipe fittings. Among them, near the connection of the first connecting pipe 111 and the second connecting pipe 112, no heat exchange tubes 160 are provided on the tube sheet to form an avoidance area, that is, no heat exchange tubes 160 are provided to avoid the fluid flowing into or out of the first connecting pipe 111 and the second connecting pipe 112, so as to ensure the medium flow space at the shell-side inlet and outlet positions. The area of the second tube sheet 130 where no heat exchange tubes 160 are provided is arcuate. Therefore, the plugging block 154 provided in the second recess 152 is aligned with the arcuate area of the second tube sheet 130 where no heat exchange tubes 160 are provided to occupy the area of the second tube sheet 130 where no heat exchange tubes are provided, and to avoid forming a medium static area and a turbulent flow area here.

[0073] Preferably, the plugging block 154 is integrally formed on the second end plate 150; and / or, two plugging blocks 154 symmetrically arranged about the central axis of the shell-side cylinder 110 are provided in the second recess 152. Since the second recess 152 does not extend to the arcuate area occupied by the plugging block 154, it forms an approximate conical shape, that is, a conical shape with the arcuate part cut off. That is to say, a recessed area in the shape of a cone with the arcuate part cut off is machined in the second end plate 150 to form the second recess 152. The introduction of the plugging block 154 structure is to more clearly describe the irregular shape of the second recess 152, as Figure 5 shown. In addition, the first connecting pipe 111 and the second connecting pipe 112 are located at both ends of the shell-side cylinder 110, and the circumferential angle between their positions is 180 degrees. For example, they are respectively located on the upper side and the lower side of the horizontally extending shell-side cylinder 110. Correspondingly, the circumferential angle between the two plugging blocks 154 is also 180 degrees, that is, symmetric about the central axis, to ensure the symmetry of the second recess 152 so that the distribution of the fluid is also symmetric; of course, the first connecting pipe 111 and the second connecting pipe 112 can also be arranged axially aligned, and the circumferential angle between the two plugging blocks 154 is still 180 degrees, which is also to ensure the symmetry of the second recess 152 so that the distribution of the fluid is symmetric.

[0074] Preferably, an exhaust pipe 153 communicating with the return cavity 151 is provided on the side of the second end plate 150 facing away from the second tube sheet 130. The exhaust pipe 153 can discharge the gas or liquid in the return cavity, and it remains disconnected during normal use and can be opened during maintenance.

[0075] Preferably, a second drain pipe 131 communicating with the shell-side cylinder 110 is provided on the second tube sheet 130. The function of the second drain pipe 131 is similar to that of the first drain pipe 121, and will not be repeated here.

[0076] Preferably, the arrangement density of the heat exchange tubes 160 is arranged from dense to sparse in the direction from the center of the shell-side cylinder 110 towards the edge. For example, the shell-side cylinder 110 can be a circular cylinder, and the density of the heat exchange tubes 160 at the central position is greater, while the density at the edge part is smaller, so as to adapt to the space limitation at the edge part.

[0077] Preferably, a plurality of baffles 113 are arranged inside the shell-side cylinder 110. Refer to Figure 1 and Figure 4 As shown, the baffles 113 are alternately arranged on both sides of the shell-side cylinder 110 to form a tortuous channel, so that the fluid forms a cross flow therein, extending the flow path of the fluid to exchange heat with the heat exchange tubes 160 more fully.

[0078] Preferably, as shown in Figure 7 the present solution provides a reactor, wherein the reactor includes a main shell 200 and the heat exchanger 100 described in the above solution. The main shell 200 is provided with a first opening at the upper part and a second opening at the lower part, and a ring pipeline 201 is arranged between the first opening and the second opening. The heat exchanger 100 is arranged on the circulation pipeline 201.

[0079] Preferably, the main shell 200 can be used as a carrier for the reaction. The circulation pipeline 201 can lead out the materials therein, and carry out heat removal treatment through the heat exchanger 100, and then introduce the cooled materials into the main shell 200 to realize heat removal treatment of the internal environment.

[0080] Preferably, as shown in Figure 7 and Figure 8 the reactor includes a discharge pipeline 202 connected to the bottom of the main shell 200 and a sampling assembly 300 bypassed to the discharge pipeline 202. The sampling assembly 300 includes a sampling pipeline 303, a liquid delivery pipeline 306, a filtration container 301, and a collection container 302. Both ends of the sampling pipeline 303 are respectively connected to the top inlet of the discharge pipeline 202 and the filtration container 301, and both ends of the liquid delivery pipeline 306 are respectively connected to the bottom outlet of the filtration container 301 and the top inlet of the collection container 302. The discharge pipeline 202 can discharge the reaction products in the main shell 200; the sampling assembly 300 is used to take out part of the materials in the discharge pipeline 202 for sampling operation to facilitate detection of the reaction products.

[0081] Preferably, the sampling pipeline 303 is connected in parallel to the discharge pipeline 202 to extract a part of the reaction product and convey it to the filtration container 301. The filtration container 301 can filter the reaction product to achieve solid-liquid separation; the collection container 302 is connected to the filtration container 301 and can collect the separated solution.

[0082] Preferably, a control valve is provided on the discharge pipeline 202, and the sampling pipeline 303 is connected to the control valve. The control valve, such as a plunger valve, is provided on the discharge pipeline 202 to control the connection and disconnection of the sampling pipeline 303. When disconnected, the reaction product in the discharge pipeline 202 will not enter the sampling pipeline 303, preventing the reaction product from remaining in the sampling pipeline 303. In other embodiments, a three-way valve can also be provided on the discharge pipeline 202, and its main purpose is also to prevent the material from entering the sampling pipeline 303 when sampling is not being performed.

[0083] Preferably, referring to Figure 8 As shown, the sampling assembly 300 includes a test pipeline 304. One end of the test pipeline 304 is connected to a compressed gas source, and the other end is connected in parallel to the sampling pipeline 303. Before sampling, when the sampling pipeline 303 is disconnected from the discharge pipeline 202, compressed gas (such as nitrogen, etc.) can be introduced into each pipeline, the filtration container 301, and the collection container 302 through the test pipeline 304 to check the airtightness of the pipeline.

[0084] Preferably, the sampling assembly 300 includes a pre-cleaning pipeline 305. One end of the pre-cleaning pipeline 305 is connected to a cleaning solvent container, and the other end is connected in parallel to the sampling pipeline 303. The cleaning solvent can be introduced into the sampling pipeline 303 through the pre-cleaning pipeline 305 to clean the residual reaction product and avoid affecting the sampling detection. The pre-cleaning operation can be performed before the sampling operation to ensure the accuracy of the sampling detection.

[0085] Preferably, the sampling assembly 300 includes a jacket provided outside the filtration container 301, a heating pipeline 307, and a condensate pipeline 308. A filter bag is provided in the filtration container 301. One end of the heating pipeline 307 communicates with the steam network and the other end communicates with the upper part of the jacket. One end of the condensate pipeline 308 communicates with the lower part of the jacket and the other end communicates with the steam condensate network. The filter bag is used to filter the reaction product to achieve solid-liquid separation; steam can be introduced into the jacket through the heating pipeline 307 to heat the filtration container 301, causing the liquid remaining on the filtration container 301 after filtration to evaporate, discharging the hydrocarbons in the sampling system, and safely opening the filter; the steam in the jacket condenses to form condensate, and the condensate returns to the steam condensate network through the condensate pipeline 308. In other embodiments, an electric heater can also be used to heat the filtration container 301.

[0086] Preferably, with reference to Figure 8 As shown, the sampling assembly 300 includes an exhaust gas pipeline 309 connected to the top outlet of the collection container 302 and a liquid discharge pipeline 310 connected to the bottom outlet of the collection container 302. The exhaust gas pipeline 309 can discharge the gas during nitrogen replacement (such as introduced during the test by the test pipeline 304), avoiding the residual hydrocarbon gas inside. When there is a large amount of solution stored in the collection container 302, the liquid discharge pipeline 310 at the bottom can be opened to discharge the solution.

[0087] Preferably, at least part of the wall of the polymerization reactor is provided with a jacket, and the method further includes introducing a second cooling medium into the jacket to exchange heat with the inside of the polymerization reactor.

[0088] Preferably, the polymerization reactor is a kettle - type polymerization reactor.

[0089] Preferably, the method further includes drawing out at least part of the vapor phase from the polymerization reactor, cooling the vapor phase, separating the cooled vapor phase into a liquid phase and a gas phase, and introducing at least part of the gas phase back into the polymerization reactor. The inventors found that in this preferred case, the method of the present invention rarely or does not reduce the production capacity due to the formation of a film on the polymerization reactor wall; and, ordinary cooling water involved in the aforementioned heat exchanger of the present invention can be used in this method instead of chilled water; and in this preferred case, the heat removal efficiency per unit volume of the polymerization reactor is high, and even all the heat of the polymerization reactor can be removed.

[0090] Preferably, through the above - mentioned technical solution, an input cavity and an output cavity are separated by a separator between the first end plate and the first tube sheet. The two sides of the separator form slopes to direct the flow of the medium, reasonably allocate the flow space, reduce the residence time of the medium in the tube box, thereby effectively suppressing the wax aggregation phenomenon in the heat exchanger; the input cavity and the output cavity are of a gradually changing structure, which can adapt to the characteristic that the distribution density of the heat exchange tubes in the edge part is small, ensure the fluid velocity in the heat exchange tubes corresponding to the edge part, ensure the overall flow velocity stability, and further avoid or reduce the occurrence of the wax aggregation phenomenon.

[0091] According to a preferred embodiment, in the method of the present invention, the reaction heat is removed by the aforementioned method of drawing out the vapor.

[0092] According to another preferred embodiment, the reaction heat is removed by the aforementioned method of using a heat exchanger.

[0093] According to still another preferred embodiment, the reaction heat is removed by the aforementioned method of setting a jacket.

[0094] Preferably, the olefin is ethylene, or a combination of ethylene and at least one monomer selected from 1-hexene, 1-butene, and 1-octene.

[0095] According to a preferred specific embodiment, the olefin is ethylene.

[0096] According to another preferred specific embodiment, the olefin is a combination of ethylene and at least one monomer selected from 1-hexene and 1-butene.

[0097] Preferably, the olefin polymerization catalyst is one or more selected from Ziegler-Natta catalysts (Z-N), metallocene catalysts, and non-metal catalysts.

[0098] The present invention has no particular requirement for the introduction form of the olefin polymerization catalyst, and it can be supplied in the form of slurry or dry powder. For example, it can be diluted with pentane to a certain concentration and then added to the polymerization reactor with a metering pump.

[0099] Preferably, the conditions in the polymerization reactor include: the polymerization temperature is 60 - 90 °C, and the polymerization pressure is 0.4 - 2.8 MPa.

[0100] Preferably, in the polymerization reactor of the present invention, the weight ratio of the amount of the olefin to the amount of hydrogen is 800 - 1500:1.

[0101] Preferably, in the polymerization reactor of the present invention, relative to every 1 kg of the olefin, the amount of the catalyst used is 0.01 g - 0.1 g.

[0102] Preferably, the amount of pentane used is such that the concentration of the bottom slurry in the polymerization reactor is 35 - 42 wt%, preferably 37 - 40 wt%.

[0103] The method of the present invention has no particular requirement for the heat transfer area of the heat exchanger and the flow rate of the slurry in the heat exchanger. Those skilled in the art can determine a reasonable heat transfer area of the heat exchanger and the flow rate of the slurry in the heat exchanger according to the designed temperature difference requirements in combination with the temperature of the cooling medium. Specific data values are exemplarily provided in the examples in the following text of the present invention, and those skilled in the art should not understand it as a limitation to the present invention.

[0104] The method of the present invention has no special requirements for the post-treatment operation of the slurry polymerization product, and can be carried out by using the operation methods known in the art. Taking the polymerization process of ethylene as an example, the slurry polymerization product obtained in the method of the present invention can be partially taken out by a slurry external circulation pump, and then the unreacted ethylene monomer and hydrogen are separated by flash evaporation. The separated slurry can enter the next polymerization kettle system according to the grade or be combined with the slurry of another polymerization kettle system and enter the centrifugal separation system. The flash gas is recovered by condensation and compression. The slurry is continuously added to a horizontally rotating centrifuge at a high speed by a slurry transfer pump, and separated into a polymer wet cake and mother liquor. Part of the mother liquor is recycled, part enters the solvent recovery unit for recovery, the wet cake enters the dryer for drying and then enters the degassing bin for further drying, and then is sent to the blending system for blending through the pneumatic conveying system, and then sent to the packaging system.

[0105] The method of the present invention has no special requirements for the ratio of raw materials (such as olefins, olefin polymerization catalysts, diluents, hydrogen, etc.) participating in the polymerization reaction, and can be carried out by using the parameter conditions known in the art. Several dosage relationships are exemplarily provided as examples in the following text of the present invention, and those skilled in the art should not understand it as a limitation to the present invention.

[0106] The polymerization reactor of the present invention is preferably at least 3 reactors arranged in parallel.

[0107] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, the raw materials used are all ordinary commercially available products.

[0108] Unless otherwise specified, the following examples and comparative examples all use the pentane slurry process for polyethylene production, and this process involves 3 reactors connected in parallel (each reactor is provided with a heat exchanger, and the connection mode between the reactor and the heat exchanger is as Figure 7 shown); the specific process includes:

[0109] Ethylene (the introduced flow rate of ethylene in each reactor is 60.63 kg / h) and hydrogen (the introduced flow rate of hydrogen in each reactor is 0.048 g / h) are introduced into the polymerization reactor and dispersed in pentane, and at the same time, a catalyst (3.7 g / h of BCE catalyst (purchased from Beijing Aoda Branch of Sinopec Catalyst Co., Ltd.) is introduced into each reactor) is introduced. The concentration of the bottom slurry of the polymerization reactor is 38.8 wt%, and the temperature of the polymerization reactor is controlled within the range of 75 - 78 °C.

[0110] Example 1

[0111] This example is carried out by using the heat exchanger shown in the present invention Figures 1 to 6 which is provided with a partition, as Figure 3As shown, in the direction from the first end plate towards the first tube sheet, the thickness of the separator gradually decreases. On both sides of the separator, a first slope extending to the edge of the input through-hole and a second slope extending to the edge of the output through-hole are formed. The first end plate is provided with a first recess, and the separator is arranged in the first recess to separate and form an input cavity and an output cavity. The first recess is formed with a third slope extending to the edge of the input through-hole and a fourth slope extending to the edge of the output through-hole. Among them, the ratio of the flow-through area of the input through-hole to the flow-through area of the output through-hole is 18:10, and the arrangement density of the heat exchange tubes is arranged from dense to sparse in the direction from the center of the shell-side cylinder towards the edge; the return cavity formed in the second end plate is conical and provided with a blocking block (as Figure 6 shown).

[0112] In this embodiment, the situations of the three polymerization reactors are the same. The situation of one polymerization reactor is listed as follows: The temperature of the cooling medium in the heat exchanger at the inlet of the heat exchanger is 47 °C, and the temperature at the outlet is 57.1 °C. The heat exchange area of the heat exchanger is 0.94 m 2 , and the flow velocity of the slurry in the heat exchange tubes is 5.07 m / s; the temperature of the slurry entering the heat exchanger is 85 °C, and the temperature of the slurry at the outlet of the heat exchanger is 83 °C. The average residence time of the slurry in the heat exchanger is 1.2 s.

[0113] The performance index distribution of the polyethylene product obtained in this embodiment is within the following range: The melt index (2.16 kg, 190 °C) is 12 - 17 (determined according to GB / T3682.1 - 2018, the same below), and the density is 0.960 - 0.964 g / cm 3 (determined according to GB 1033 - 86, the same below). It can be seen that the product obtained by the method of the present invention has excellent processability.

[0114] The scale of the device in this embodiment is a test device of 0.144×10⁴ t / year, and no wax accumulation phenomenon occurred during the continuous operation of the device for 48 months.

[0115] Example 2

[0116] The heat exchanger applied in this embodiment is slightly different in structure from the heat exchanger in Example 1. The difference is that: the heat exchanger in this embodiment does not have a special-shaped separator. The separator in this heat exchanger is a separator with a uniform thickness, and the thickness of this separator is the smallest thickness among the separators in the heat exchanger in Example 1.

[0117] In this embodiment, the situations of the three polymerization reactors are the same. The situation of one polymerization reactor is listed as follows: The temperature of the cooling medium in the heat exchanger in this embodiment at the inlet of the heat exchanger is 48 °C, and the temperature at the outlet is 60 °C. The heat exchange area of the heat exchanger is 0.94 m 2, the flow velocity of the slurry in the heat exchange tube is 5.07 m / s; the temperature of the slurry entering the heat exchanger is 85 °C, the temperature of the slurry at the outlet of the heat exchanger is 83 °C, and the average residence time of the slurry in the heat exchanger is 1.2 s.

[0118] The performance index of the polyethylene product obtained in this example is distributed within the following ranges: the melt index (2.16 kg, 190 °C) is 10 - 15, and the density is 0.956 - 0.961 g / cm 3 . It can be seen from this that the product obtained by the method of the present invention has good processability.

[0119] Result: The test device of this example has a device scale of 0.144×10⁴ t / year. Wax accumulation occurred after the device had been continuously operating for 21 months.

[0120] Moreover, compared with Example 1, material deposition is likely to occur at the head tube sheet of the heat exchanger in this example.

[0121] Example 3

[0122] This example is carried out using the same heat exchanger as in Example 2.

[0123] The conditions of the three polymerization reactors in this example are the same. The conditions of one of the polymerization reactors are listed as follows: the temperature of the cooling medium in the heat exchanger in this example at the inlet of the heat exchanger is 41 °C, and the temperature at the outlet is 51 °C. The heat transfer area of the heat exchanger is 0.94 m 2 , the flow velocity of the slurry in the heat exchange tube is 5.07 m / s; the temperature of the slurry entering the heat exchanger is 85 °C, the temperature of the slurry at the outlet of the heat exchanger is 83 °C, and the average residence time of the slurry in the heat exchanger is 1.2 s.

[0124] The performance index of the polyethylene product obtained in this example is distributed within the following ranges: the melt index (2.16 kg, 190 °C) is 10 - 15, and the density is 0.954 - 0.958 g / cm 3 . It can be seen from this that the product obtained by the method of the present invention has good processability.

[0125] Result: The test device of this example has a device scale of 0.144×10⁴ t / year. Wax accumulation occurred after the device had been continuously operating for 17 months.

[0126] Moreover, compared with Example 1, material deposition is likely to occur at the head tube sheet of the heat exchanger in this example.

[0127] Example 4

[0128] This example is carried out with reference to the method and equipment of Example 1.

[0129] The difference between this example and Example 1 is that:

[0130] A cylindrical cavity (with the same maximum inner diameter as the first recess) is formed between the first end plate and the first tube sheet. The cylindrical cavity is divided into an input cavity and an output cavity by using the same partition as in Embodiment 1. On both sides of the partition, a first slope extending to the edge of the input through-hole and a second slope extending to the edge of the output through-hole are formed.

[0131] The performance indexes of the polyethylene product obtained in this embodiment are distributed within the following ranges: the melt index (2.16 kg, 190 °C) is 12 - 17, and the density is 0.960 - 0.964 g / cm 3 . It can be seen from this that the processability of the product obtained by the method of the present invention is excellent.

[0132] The scale of the device in this embodiment is a test device of 0.144×10⁴ t / year, and no wax accumulation phenomenon occurred during the continuous operation of the device for 27 months.

[0133] Embodiment 5

[0134] This embodiment is carried out with reference to the method and equipment of Embodiment 1.

[0135] The difference between this embodiment and Embodiment 1 is that: the return cavity is cylindrical and no plugging block is provided, and the inner diameter of this return cavity is the same as the maximum inner diameter of the conical return cavity in Embodiment 1.

[0136] The performance indexes of the polyethylene product obtained in this embodiment are distributed within the following ranges: the melt index (2.16 kg, 190 °C) is 12 - 17, and the density is 0.960 - 0.964 g / cm 3 . It can be seen from this that the processability of the product obtained by the method of the present invention is excellent.

[0137] The scale of the device in this embodiment is a test device of 0.144×10⁴ t / year, and no wax accumulation phenomenon occurred during the continuous operation of the device for 30 months.

[0138] Embodiment 6

[0139] This embodiment is carried out with reference to the method and equipment of Embodiment 1.

[0140] The difference between this embodiment and Embodiment 1 is that:

[0141] (1) A cylindrical cavity (with the same maximum inner diameter as the first recess) is formed between the first end plate and the first tube sheet. The cylindrical cavity is divided into an input cavity and an output cavity by using the same partition as in Embodiment 1. On both sides of the partition, a first slope extending to the edge of the input through-hole and a second slope extending to the edge of the output through-hole are formed,

[0142] (2) The return cavity is cylindrical and no plugging block is provided. The inner diameter of the return cavity is the same as the maximum inner diameter of the conical return cavity in Embodiment 1.

[0143] (3) The flow-through area of the input through-hole is the same as that of the output through-hole.

[0144] (4) The arrangement density of the heat exchange tubes is the same in the direction from the center to the edge of the shell-side cylinder.

[0145] The performance index distribution of the polyethylene product obtained in this embodiment is within the following range: the melt index (2.16 kg, 190 °C) is 12 - 17, and the density is 0.960 - 0.964 g / cm 3 . It can be seen that the product obtained by the method of the present invention has excellent processability.

[0146] The scale of the device in this embodiment is a test device of 0.144×10⁴ t / year, and no wax accumulation phenomenon occurred during the continuous operation of the device for 23 months.

[0147] Embodiment 7

[0148] This embodiment is carried out with reference to the method and equipment of Embodiment 6.

[0149] The difference between this embodiment and Embodiment 6 is that the temperature of the cooling medium in the heat exchanger is different at the inlet and outlet of the heat exchanger. Among them, in this Embodiment 7, the temperature of the cooling medium at the inlet of the heat exchanger is 41 °C, and the temperature at the outlet is 51 °C.

[0150] The performance index distribution of the polyethylene product obtained in this embodiment is within the following range: the melt index (2.16 kg, 190 °C) is 12 - 17, and the density is 0.960 - 0.964 g / cm 3 . It can be seen that the product obtained by the method of the present invention has excellent processability.

[0151] The scale of the device in this embodiment is a test device of 0.144×10⁴ t / year, and no wax accumulation phenomenon occurred during the continuous operation of the device for 20 months.

[0152] From the above results, it can be seen that by using the method of the present invention, on the premise of obtaining a product with good processability, the continuous operation period of the device is long. By optimizing the structure of the heat exchanger, the medium fluid can be quickly discharged from the output through-hole and the output pipe, ensuring that the medium fluid in the heat exchanger has sufficient flow velocity, especially ensuring that the fluid in the heat exchange tubes corresponding to the peripheral edge part has a sufficiently high flow velocity, avoiding or reducing the wax accumulation phenomenon in the heat exchanger, effectively extending the stability time of the heat exchanger. The method of the present invention does not produce wax accumulation phenomenon and is not prone to material deposition phenomenon.

[0153] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A process for olefin polymerization, which process comprises contacting at least one olefin with an olefin polymerization catalyst and pentane as a diluent in a polymerization reactor under slurry polymerization conditions to obtain a slurry polymerization product, characterized in that, The method further includes withdrawing a part of the slurry polymerization product from the polymerization reactor as a first slurry product, exchanging heat between the first slurry product and a cooling medium to obtain a first slurry product after heat exchange, the temperature of the first slurry product after heat exchange being lower than the temperature of the first slurry product, and introducing the first slurry product after heat exchange back into the polymerization reactor, the temperature of the cooling medium being higher than 40°C.

2. The method according to claim 1, wherein, The temperature of the cooling medium is higher than 40°C and not higher than 65°C.

3. The method according to claim 1 or 2, wherein The heat exchange is carried out in at least one heat exchanger, and the temperature of the cooling medium at the inlet of the heat exchanger is higher than 40°C and not higher than 55°C.

4. The method according to any one of claims 1 to 3, wherein, The residence time of the first slurry product in the heat exchanger is 1 - 30 s.

5. The method according to any one of claims 1 to 4, wherein The temperature of the first slurry product after heat exchange is 72 - 85°C.

6. The method according to any one of claims 1-5, wherein The heat exchanger includes a shell-side cylinder, heat exchange tubes arranged in the shell-side cylinder, a first tube sheet arranged at the first end of the shell-side cylinder, and a first end plate connected to the outer side of the first tube sheet. The first end plate is provided with an input through-hole and an output through-hole. A partition is arranged on the surface of the first end plate facing the first tube sheet between the input through-hole and the output through-hole. The partition divides and forms an input cavity and an output cavity communicating with the heat exchange tubes between the first tube sheet and the first end plate.

7. The method according to claim 6, wherein, In the heat exchanger, the partition is in the shape of a dam and is preferably arranged at the middle position of the first end plate. In the direction from the first end plate to the first tube sheet, the thickness of the partition gradually decreases; Preferably, a first slope surface extending to the edge of the input through-hole and a second slope surface extending to the edge of the output through-hole are respectively formed on both sides of the partition, and the first slope surface and the second slope surface extend to the first tube sheet; Preferably, a first recess is arranged on the surface of the first end plate facing the first tube sheet, the partition is arranged in the first recess, and the first recess is formed with a third slope surface extending to the edge of the input through-hole and a fourth slope surface extending to the edge of the output through-hole.

8. The method according to claim 7, wherein The first slope surface and the third slope surface are smoothly transitioned to form a smooth gradually expanding wall surface defining the input cavity; the second slope surface and the fourth slope surface are smoothly transitioned to form a smooth gradually shrinking wall surface defining the output cavity; Preferably, the flow-through area of the input through-hole is larger than the flow-through area of the output through-hole; Preferably, a jacket is arranged on at least part of the wall of the polymerization reactor, and the method further includes introducing a second cooling medium into the jacket to exchange heat with the inside of the polymerization reactor; Preferably, the polymerization reactor is a kettle-type polymerization reactor.

9. The method according to any one of claims 1-8, wherein, The method further includes withdrawing at least part of the vapor phase from the polymerization reactor, cooling the vapor phase, performing gas-liquid separation on the cooled vapor phase to obtain a liquid phase and a gas phase, and introducing at least part of the gas phase back into the polymerization reactor.

10. The method according to any one of claims 1-9, wherein, The olefin polymerization catalyst is one or more selected from Ziegler-Natta catalysts, metallocene catalysts, and non-metal catalysts.

11. According to the method described in any one of claims 1-10, wherein, The conditions in the polymerization reactor include: a polymerization temperature of 60 - 90°C and a polymerization pressure of 0.4 - 2.8 MPa.

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