Hexane refining system and method for high-density polyethylene production

Abstract

The invention discloses a hexane refining system and method for high density polyethylene production, the middle lower part of a separator is connected with the upper part of an evaporator, the lower end feed port of the evaporator is connected with the bottom discharge port of the separator, and the bottom feed port of the separator is connected with a mother liquor preheater through a feed pipeline; the feeding pipeline is horizontally arranged, a diameter expanding pipeline is arranged on the feeding pipeline, a gas distribution element is arranged in the diameter expanding pipeline, the gas distribution element comprises a gas distribution supporting piece, an anti-settling gas distribution piece and a plurality of gas distribution disc bodies distributed between the gas distribution supporting piece and the anti-settling gas distribution piece, and the gas distribution supporting piece, the anti-settling gas distribution piece and the gas distribution disc bodies are all of hollow structures; the three parts are communicated with one another; the anti-settling gas distribution piece is arranged at the bottom of the expanding pipeline, and a plurality of gas distribution holes are distributed in the inner side of the anti-settling gas distribution piece; the gas distribution disc body covers the cross section of the expanding pipeline, a plurality of cylindrical runners are arranged on the gas distribution disc body in the axial direction of the gas distribution disc body, and a plurality of gas distribution holes are formed in the side walls of the cylindrical runners.

Description

Technical Field

[0001] The invention belongs to the technical field of hexane refining, and in particular relates to a hexane refining system and a refining method for high-density polyethylene production. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] LyondellBasell's Hostalen ACP low-pressure slurry polymerization process occupies a pivotal position in the world. This process uses ethylene, butene-1, and hydrogen as raw materials and hexane as a dispersant. Under the action of ZN catalyst, it produces unimodal, bimodal and multimodal high-density polyethylene HDPE products. In this process, the hexane refining system evaporates, distills and refines the mother liquor separated from the polymerization reaction system to obtain refined hexane, which can be recycled.

[0004] While producing high-density polyethylene (HDPE) products, the above process will also produce some difficult-to-separate low-molecular-weight polymers dispersed in the mother liquor. As the temperature of the mother liquor in the hexane refining system increases and under the action of residual catalysts, the low-molecular-weight polymers may further undergo polymerization reactions. The products are likely to cause blockage of the heat exchanger and the hexane evaporator, affecting the production stability of the hexane refining system.

[0005] The existing hexane refining method is: add a deactivator to the mother liquor to inactivate the substances in the mother liquor; after being evaporated and concentrated in an evaporator, most of the reaction products and excess deactivator are discharged from the bottom of the evaporator together with polyethylene wax, and the residual deactivator and the inorganic solution generated by the reaction enter the distillation tower and adsorption tower and are removed, and finally qualified refined hexane is obtained. The inventor found that when using this process, in order to prevent the possible residual catalyst powder particles from inducing side reactions and causing by-products to adhere and block the preheater, water vapor is introduced into the mother liquor entering the preheater to deactivate the catalyst powder, thereby achieving the purpose of preventing the occurrence of side reactions and avoiding the blockage of the preheater. However, when water vapor is directly introduced, it is difficult for water vapor to be evenly distributed in the mother liquor. Therefore, when a small amount of water vapor is introduced, it cannot be guaranteed that the catalyst in the mother liquor is fully contacted to deactivate it. In order to fully deactivate the catalyst, too much water vapor must be introduced, resulting in an increase in the load of the subsequent hexane distillation tower, which may cause the water content in the hexane at the bottom of the hexane distillation tower to exceed the standard. When the hexane is recovered for the preparation of high-density polyethylene, the catalyst will be deactivated when it comes into contact with water, thereby affecting the activity of the catalyst. Summary of the invention

[0006] In view of the shortcomings of the prior art, the object of the present invention is to provide a hexane refining system and a refining method for high-density polyethylene production.

[0007] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0008] In a first aspect, the present invention provides a hexane refining system for high-density polyethylene production, comprising a separator and an evaporator; wherein:

[0009] The middle and lower part of the separator is connected to the upper part of the evaporator, the lower end feed port of the evaporator is connected to the bottom discharge port of the separator, and the bottom feed port of the separator is connected to the mother liquor preheater through a feed pipeline;

[0010] The feed pipeline is arranged horizontally, and an expansion pipe is arranged on the feed pipeline, and an air distribution element is arranged inside the expansion pipe, and the air distribution element includes an air distribution support, an anti-settling air distribution member, and a plurality of air distribution discs distributed therebetween, and the air distribution support, the anti-settling air distribution member, and the air distribution discs are all hollow structures, and the three are interconnected;

[0011] The anti-settling gas distribution part is arranged at the bottom of the expanded diameter pipeline, and a plurality of gas distribution holes are arranged on the inner side thereof;

[0012] The gas distribution support is arranged on the top of the expanded diameter pipeline and is connected to the water vapor delivery pipeline;

[0013] The air distribution disc covers the cross section of the expanded pipe, and a plurality of air distribution discs are arranged at intervals. A plurality of columnar flow channels are arranged on the air distribution disc along the axial direction, and a plurality of air distribution holes are opened on the side walls of the columnar flow channels.

[0014] The catalyst in the mother liquor is deactivated by introducing water vapor into the mother liquor, thereby preventing the occurrence of side reactions and avoiding blockage of the preheater. When water vapor is introduced directly into the mother liquor, the water vapor enters the mother liquor in the form of bubbles, and then diffuses and contacts the catalyst in the mother liquor to deactivate the catalyst. Since it is difficult to ensure that the water vapor is evenly distributed in the mother liquor, it is necessary to introduce too much water vapor, which increases the load of the subsequent hexane distillation tower, not only increasing the distillation energy consumption, but also causing the water content of the bottom liquid of the distillation tower to exceed the standard, affecting the quality of the hexane product.

[0015] Since the mother liquor refining process requires steps such as preheating, heating evaporation, condensation separation, dehydration, and distillation purification, the low molecular weight polymers that are difficult to separate as by-products in the mother liquor will polymerize again at higher temperatures, so the catalyst in the mother liquor needs to be deactivated when the mother liquor temperature is low.

[0016] To solve the above problems, the inventors tried to set an expansion pipe on the connecting pipeline between the mother liquor preheater and the evaporation separator. The temperature of the preheated mother liquor is not high, and the repolymerization of the by-product low molecular weight polymer will not occur at this time. When the mother liquor flows through the expansion pipe, the flow rate slows down. At this time, water vapor is introduced into the mother liquor in the expansion pipe, which can help the uniform mixing of water vapor and mother liquor and reduce the introduction of water vapor to a certain extent.

[0017] However, the inventors found that the effect of this method is relatively limited, and it is necessary to introduce excessive water vapor to ensure that the catalyst in the mother liquor is fully deactivated. Therefore, the inventors tried to introduce a gas distribution element into the expansion pipe. The main gas distribution element is a gas distribution disc, which is installed on the cross-section of the expansion pipe, that is, to allow all mother liquor to flow through the gas distribution disc. On the gas distribution disc, a number of columnar flow channels are arranged along its axial direction, and a number of gas distribution holes are arranged on the side walls of the columnar flow channels. With this arrangement, the mother liquor is divided into a number of small fluids by a number of columnar flow channels, and when gas is distributed to the small fluids respectively, it is beneficial to increase the distribution density of water vapor bubbles in the mother liquor, and then to improve the uniformity of water vapor dispersion in the mother liquor, so as to help improve the deactivation efficiency of the catalyst in the mother liquor, thereby effectively reducing the amount of water vapor introduced.

[0018] In addition, the inventors also found that since the catalyst is dispersed in the mother liquor in the form of solid particles and has a greater density than the mother liquor, it is inevitable that the solid particles of the catalyst will settle in the mother liquor. When the mother liquor flows through the expansion pipe, the flow rate slows down, making it easier for the catalyst to settle. At this time, along the depth direction of the mother liquor, the catalyst concentration at the bottom of the mother liquor is greater than the catalyst concentration above the mother liquor. When the mother liquor with this catalyst distribution flows through several columnar flow channels of the gas distribution disk, the catalyst concentration in the mother liquor entering different columnar flow channels is different. However, the amount of water vapor introduced into different columnar flow channels is difficult to accurately control in real time, and it is easy for some columnar flow channels to have too much water vapor introduced. In the columnar flow channels near the bottom, the amount of water vapor introduced is small and the amount of catalyst is large, making it difficult for some catalysts to be fully deactivated.

[0019] In order to solve the above problems, the inventors set an anti-sedimentation gas distribution part at the bottom of the expanded diameter pipe, and set gas distribution holes on the inner side thereof. Water vapor can be sprayed into the mother liquor through the gas distribution holes, which plays a role in overall disturbance of the mother liquor and preventing the catalyst from settling. In addition, the catalyst can also be deactivated to a certain extent. When the mother liquor with uniform catalyst distribution flows through the gas distribution disk, it is more conducive to ensuring the full deactivation of the catalyst while minimizing the amount of water vapor added.

[0020] Since the anti-settling gas distribution parts spray water vapor into the mother liquor, it is difficult to ensure that the water vapor and the mother liquor are evenly mixed. Therefore, a number of gas distribution disks are arranged, and the several gas distribution disks are arranged at intervals. When the mother liquor flows through the columnar flow channel of the gas distribution disk, the overall cross-sectional area of ​​the columnar flow channel is reduced, and the flow rate of the mother liquor is increased. In the process of flowing out of the columnar flow channel at a high flow rate, a better turbulence effect is generated, which promotes the even mixing of water vapor and mother liquor.

[0021] In summary, the above-mentioned configuration can ensure that the introduced water vapor and the mother liquor are evenly mixed to a large extent, thereby ensuring that the catalyst in the mother liquor is fully deactivated by using a smaller amount of water vapor introduced.

[0022] In some embodiments, the anti-settling gas distribution member is arc-shaped and is arranged to fit the inner wall of the expanded diameter pipe.

[0023] Preferably, the central angle corresponding to the anti-settling air distribution component is 60°-180°.

[0024] The anti-settling gas distribution piece is set to be arc-shaped with a larger central angle, so that gas can be distributed in a larger range to ensure the purpose of preventing catalyst sedimentation.

[0025] Preferably, the ratio of the length of the anti-settling gas distribution component to the length of the expanded diameter pipe is 1:1-1.5.

[0026] Further preferably, the anti-settling air distribution member is arranged close to the inlet end of the expanded diameter pipeline.

[0027] In some embodiments, the diameter of the columnar flow channel is 0.5-3 cm. Since the mother liquid contains catalyst solid particles and low molecular weight polymers, it has a certain viscosity. Therefore, the diameter of the columnar flow channel cannot be too small to prevent clogging.

[0028] In some embodiments, a plurality of gas distribution trays are evenly arranged along the axis of the anti-settling gas distribution member.

[0029] Preferably, the ratio of the distance between adjacent gas distribution trays to the diameter of the gas distribution trays is 0.5-1.5:2.

[0030] In some embodiments, a condenser, a feed tank, a coalescing separator and a distillation tower are also included, and the top outlet of the separator is connected to the condenser, the feed tank, the coalescing separator and the distillation tower in sequence.

[0031] In a second aspect, the present invention provides a method for refining hexane for high-density polyethylene production, comprising the following steps:

[0032] After the mother liquid for high-density polyethylene production is preheated, it flows through the expansion pipe. Inside the expansion pipe, the mother liquid is divided into several small streams by the gas distribution disc. At the same time, water vapor is distributed into the small streams to deactivate the catalyst.

[0033] When the mother liquid flows between two adjacent gas distribution discs, water vapor is distributed into the mother liquid using an anti-settling gas distribution piece to disturb the mother liquid, prevent the catalyst from settling, and deactivate the catalyst;

[0034] The mother liquor flowing through the expanded diameter pipe enters the evaporation separation process.

[0035] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0036] Water vapor is introduced into the expanded pipe to fully deactivate the catalyst powder while minimizing the amount of water vapor introduced, and moisture is removed in the subsequent agglomerator to improve the production stability of the hexane refining system. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0038] Figure 1 is a schematic diagram of the overall structure of an embodiment of the present invention;

[0039] Figure 2 is a schematic diagram of the internal structure of the expanded diameter pipeline according to an embodiment of the present invention;

[0040] Figure 3 Schematic diagram of the structure of the air distribution element according to the embodiment of the present invention.

[0041] Among them, 1. Evaporator; 2. Separator; 3. Condenser; 4. Feed tank; 5. Coalescing separator; 6. Expansion pipe; 7. Water vapor delivery pipe; 8. Gas distribution support; 9. Gas distribution plate; 10. Anti-settling gas distribution parts; 11. Columnar flow channel. DETAILED DESCRIPTION

[0042] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0043] The present invention will be further described below in conjunction with the embodiments.

[0044] like Figure 1 As shown, a hexane refining system for high-density polyethylene production includes a separator 2, an evaporator 1, a condenser 3, a feed tank 4, a coalescing separator 5 and a distillation tower; wherein,

[0045] The middle and lower part of the separator 2 is connected to the upper part of the evaporator 1, the lower end feed port of the evaporator 1 is connected to the bottom discharge port of the separator 2, the bottom feed port of the separator 2 is connected to the mother liquid preheater through a feed pipeline, and the top outlet of the separator 2 is connected to the condenser 3, the feed tank 4, the coalescing separator 5 and the distillation tower in sequence;

[0046] The feed pipeline is arranged horizontally, and an expansion pipe 6 is arranged on the feed pipeline. Figure 2 As shown, the expanded pipe 6 is provided with an air distribution element, which includes an air distribution support 8, an anti-settling air distribution member 10 and a plurality of air distribution discs 9 distributed therebetween. The air distribution support 8, the anti-settling air distribution member 10 and the air distribution discs 9 are all hollow structures, and the three are interconnected.

[0047] The anti-settling gas distribution member 10 is arranged at the bottom of the enlarged diameter pipe 6, and a plurality of gas distribution holes are distributed inside the anti-settling gas distribution member 10;

[0048] The air distribution support 8 is arranged on the top of the diameter expansion pipe 6 and is connected to the water vapor delivery pipe;

[0049] like Figure 3 As shown, the gas distribution disc 9 covers the cross section of the expanded pipe, and a plurality of gas distribution discs 9 are arranged at intervals and evenly arranged along the axis of the anti-settling gas distribution member 10. The ratio of the spacing between adjacent gas distribution discs 9 to the diameter of the gas distribution disc 9 is 0.5-1.5:2. The thickness of the gas distribution disc 9 can be selected according to the specific working conditions, such as 1-10 cm.

[0050] A plurality of columnar flow channels 11 are arranged on the gas distribution disc body 9 along its axial direction. The diameter of the columnar flow channels 11 is 0.5-3 cm. A plurality of gas distribution holes are opened on the side wall of the columnar flow channels 11 .

[0051] The anti-settling gas distribution piece 10 is arc-shaped and is arranged to fit the inner wall of the diameter-expanding pipe 6. The central angle of the anti-settling gas distribution piece 10 is 60°-180°. The ratio of the length of the anti-settling gas distribution piece 10 to the length of the diameter-expanding pipe 6 is 1:1-1.5. The anti-settling gas distribution piece 10 is arranged close to the inlet end of the diameter-expanding pipe 6.

[0052] A plurality of columnar flow channels 11 are arranged along the axial direction of the gas distribution disc 9, and a plurality of gas distribution holes are arranged on the side wall of the columnar flow channels 11. With this arrangement, the mother liquid is divided into a plurality of small streams by the columnar flow channels 11, and when gas is distributed to the small streams respectively, it is beneficial to increase the distribution density of water vapor bubbles in the mother liquid, and further to improve the uniformity of water vapor dispersion in the mother liquid, so as to help improve the deactivation efficiency of the catalyst in the mother liquid, and further effectively reduce the amount of water vapor introduced.

[0053] An anti-sedimentation gas distribution member 10 is arranged at the bottom of the expanded diameter pipe 6, and gas distribution holes are arranged on the inner side thereof. Water vapor can be sprayed into the mother liquor through the gas distribution holes, which plays a role in overall disturbance of the mother liquor and preventing the catalyst from settling. In addition, the catalyst can also be deactivated to a certain extent. When the mother liquor with uniform catalyst distribution flows through the gas distribution disk 9 again, it is more conducive to ensuring the full deactivation of the catalyst while minimizing the amount of water vapor added.

[0054] Since the anti-settling gas distribution parts 10 spray water vapor into the mother liquor, but it is difficult to ensure that the water vapor and the mother liquor are evenly mixed, a plurality of gas distribution disks 9 are arranged, and the plurality of gas distribution disks 9 are arranged at intervals. When the mother liquor flows through the columnar flow channel 11 of the gas distribution disks 9, the overall cross-sectional area of ​​the columnar flow channel 11 is reduced, and the flow rate of the mother liquor is increased. In the process of flowing out of the columnar flow channel 11 at a high flow rate, a better turbulent effect is generated, which promotes the uniform mixing of water vapor and the mother liquor.

[0055] The feed from the mother liquor preheater is fed with an appropriate amount of water vapor through a section of expanded diameter pipeline to deactivate the catalyst powder and aluminum compounds that may be contained in the feed, and to fully deactivate the catalyst remaining in the mother liquor, thereby preventing the unseparated low-weight polymers, ethylene, and butene-1 raw materials in the mother liquor from continuing to polymerize under the action of the catalyst to produce solid matter attached to the tube bundle of the evaporator, thereby ensuring the workload and working time of the evaporator and reducing the start-up and shutdown losses caused by evaporator blockage.

[0056] Then the mother liquor enters the separator 2, and enters the evaporator 1 through the separator 2. In the evaporator 1, the heavy components such as wax, powder and aluminum compounds in the mother liquor are concentrated and transported to the wax treatment tank. During the transportation process, the concentrated heavy compound mixture is further processed in the wax evaporator, and the residual hexane is evaporated. In the evaporation step of the mother liquor, the evaporator 1 uses medium-pressure steam as a heating medium to evaporate the mother liquor. The obtained hexane vapor first enters the separator 2, and then enters the condenser to condense. The components that cannot be condensed (including butene, ethylene, hydrogen, nitrogen, etc.) enter the butene recovery unit through the adsorption tower for further processing. Various condensates are collected in the hexane feed tank 4, and then enter the coalescing separator 5 to remove moisture, and then separate in the subsequent hexane distillation tower. Add a coalescing separator 5 after the hexane feed tank 4 to remove moisture from the hexane distillation tower feed, and improve the overall stable production and operation capacity of the distillation tower.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A hexane refining system for high-density polyethylene production, characterized in that: It includes a separator and an evaporator; wherein, The middle and lower part of the separator is connected to the upper part of the evaporator, the lower end feed port of the evaporator is connected to the bottom discharge port of the separator, and the bottom feed port of the separator is connected to the mother liquor preheater through a feed pipeline; The feed pipeline is arranged horizontally, and an expansion pipe is arranged on the feed pipeline, and an air distribution element is arranged inside the expansion pipe, and the air distribution element includes an air distribution support, an anti-settling air distribution member, and a plurality of air distribution discs distributed therebetween, and the air distribution support, the anti-settling air distribution member, and the air distribution discs are all hollow structures, and the three are interconnected; The anti-settling gas distribution part is arranged at the bottom of the expanded diameter pipeline, and a plurality of gas distribution holes are arranged on the inner side thereof; The gas distribution support is arranged on the top of the expanded diameter pipeline and is connected to the water vapor delivery pipeline; The air distribution disc covers the cross section of the expanded pipe, and a plurality of air distribution discs are arranged at intervals. A plurality of columnar flow channels are arranged on the air distribution disc along the axial direction, and a plurality of air distribution holes are opened on the side walls of the columnar flow channels.

2. The hexane refining system for high-density polyethylene production according to claim 1, characterized in that: The anti-settling gas distribution member is arc-shaped and is arranged to fit the inner wall of the expanded diameter pipeline.

3. The hexane refining system for high-density polyethylene production according to claim 2, characterized in that: The central angle corresponding to the anti-settling air distribution component is 60°-180°.

4. The hexane refining system for high-density polyethylene production according to claim 3, characterized in that: The ratio of the length of the anti-settling gas distribution component to the length of the expanded diameter pipeline is 1:1-1.

5.

5. The hexane refining system for high-density polyethylene production according to claim 2, characterized in that: The anti-settling gas distribution member is arranged close to the inlet end of the expanded diameter pipeline.

6. The hexane refining system for high-density polyethylene production according to claim 1, characterized in that: The diameter of the cylindrical flow channel is 0.5-3 cm.

7. The hexane refining system for high-density polyethylene production according to claim 1, characterized in that: A plurality of air distribution discs are evenly arranged along the axis of the anti-settling air distribution member.

8. The hexane refining system for high-density polyethylene production according to claim 7, characterized in that: The ratio of the distance between adjacent gas distribution discs to the diameter of the gas distribution discs is 0.5-1.5:

2.

9. The hexane refining system for high-density polyethylene production according to claim 1, characterized in that: It also includes a condenser, a feed tank, a coalescing separator and a distillation tower. The top outlet of the separator is connected with the condenser, the feed tank, the coalescing separator and the distillation tower in sequence.

10. A method for refining hexane for high-density polyethylene production, characterized in that: The refining system according to any one of claims 1 to 9 is used for refining, comprising the following steps: After the mother liquid for high-density polyethylene production is preheated, it flows through the expansion pipe. Inside the expansion pipe, the mother liquid is divided into several small streams by the gas distribution disc. At the same time, water vapor is distributed into the small streams to deactivate the catalyst. When the mother liquid flows between two adjacent gas distribution discs, water vapor is distributed into the mother liquid using an anti-settling gas distribution piece to disturb the mother liquid, prevent the catalyst from settling, and deactivate the catalyst; The mother liquor flowing through the expanded diameter pipe enters the evaporation separation process.

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