Crosslinkable cable insulation base and process for its preparation

Abstract

The present application relates to the technical field of insulating base preparation, in particular to an easy crosslinking cable insulating base and a preparation method thereof.The preparation method of the easy crosslinking cable insulating base comprises the following steps: pressurizing ethylene and feeding it into a first-stage tubular reactor, adding end olefins, di-olefins and initiators in front of each stage of the tubular reactor respectively to initiate a reaction, and obtaining a high-pressure polyethylene base, which is the easy crosslinking cable insulating base.The present application increases the content of double bonds and branched chains by adding di-olefins and end olefins, preferably adding di-olefins and end olefins at a certain position, increasing the reaction temperature, reducing the reaction pressure, using a high-temperature initiator instead of a low-temperature initiator and other methods, enhances the chain transfer reaction and copolymerization reaction, increases the content of double bonds and branched chains, and prepares the easy crosslinking cable insulating base.Using the easy crosslinking cable insulating base to produce high-voltage cable insulating material can reduce the amount of crosslinking agents, antioxidants and other additives, and better meet the use requirements of high-voltage cables.

Description

Technical Field

[0001] This invention relates to the field of insulating material preparation technology, specifically to easily cross-linked cable insulating materials and their preparation methods. Background Technology

[0002] High-density polyethylene (HDPE) has a low processing temperature and good electrical properties, making it suitable as a base material for cable insulation. It can be melt-extruded and granulated with crosslinking agents, antioxidants, and other additives, and then mixed for the production of crosslinked polyethylene insulation materials for high-voltage cables. For high-voltage cable insulation materials, the lower the amount of antioxidants, crosslinking agents, and other additives added, the fewer byproducts are generated after cable extrusion crosslinking, the better the electrical properties, and the shorter the degassing time. This requires HDPE base materials to have better crosslinking properties.

[0003] High-density polyethylene (HDPE) production utilizes a jacketed tubular reactor. The entire reactor is typically divided into 3-5 sections. An initiator is added at the inlet of each section to initiate the reaction. Figure 1 As shown.

[0004] The peak reaction temperature is controlled below the ethylene decomposition temperature (around 350℃), typically around 300℃. Cooling is achieved using a jacketed cooling water system. The heat dissipation at each stage can be controlled by adjusting the temperature and flow rate of the cooling water. Appropriate adjustments are made to the valley temperature at the end of each reactor stage, which serves as the initiation temperature for the next reactor stage (temperature distribution within the reactor is shown in the figure). Figure 2 (As shown).

[0005] The chemical cross-linking of high-voltage cable insulation follows the principle of free radical reaction, and the double bonds in the base material are a crucial factor affecting cross-linking. This is because double bonds have high reactivity and easily capture free radicals to react and cross-link polyethylene molecules, forming a network structure. Simultaneously, the branching of the base material is another important factor influencing cross-linking; the higher the branching content, the more susceptible it is to free radical attack and reaction to form a cross-linked structure.

[0006] Therefore, the higher the content of double bonds and branches in high-pressure polyethylene base material, the faster and more complete the cross-linking reaction is initiated, the shorter the time required to reach the same degree of cross-linking, and the less cross-linking agent and reaction by-products are required, which is more beneficial to improving the performance of cross-linked polyethylene. Summary of the Invention

[0007] To address the problem of cable insulation base materials being difficult to crosslink, this invention provides an easily crosslinkable cable insulation base material.

[0008] This invention also provides a preparation method that is scientific, reasonable, simple, and easy to implement, making it suitable for large-scale production.

[0009] To solve the above problems, the technical solution of the present invention is:

[0010] The preparation method of the easily cross-linked cable insulation base material of the present invention comprises the following steps: Ethylene is pressurized and introduced into the starting end of a tubular reactor; terminal olefins, dienes, and initiators are added to each section of the tubular reactor to initiate the reaction, thereby obtaining high-pressure polyethylene base material, which is the easily cross-linked cable insulation base material. A schematic diagram of the reaction process of the present invention is shown below. Figure 3 As shown.

[0011] The tubular reactor comprises four sections, namely reactor R1, reactor R2, reactor R3, and reactor R4.

[0012] The initiation temperatures of reactors R1, R2, R3, and R4 are, respectively, 160-220℃, 170-230℃, 180-240℃, and 180-240℃.

[0013] The reaction pressures of reactors R1, R2, R3, and R4 are controlled sequentially at: 240-260 MPa, 225-245 MPa, 210-230 MPa, and 190-210 MPa.

[0014] The initiator is di-tert-butyl peroxide.

[0015] The amount of ethylene added is 40,000-130,000 kg / h, the amount of terminal olefins added before each section of the tubular reactor is 0.001-0.005 times the amount of ethylene added, and the amount of diene added before each section of the tubular reactor is 0.001-0.005 times the amount of ethylene added.

[0016] Preferably, the terminal olefin includes one or more of propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene.

[0017] The diene includes one or more of 1,4-pentadiene, 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, 1,8-nonadiene, and 1,9-decadiene.

[0018] The mass ratio of the terminal olefin to the diene is (52-60):(38-53).

[0019] To increase the double bond and branched chain content of high-pressure polyethylene, this invention introduces diene monomers (CH2=CH-R-CH=CH2) and terminal olefin monomers (CH2=CH-R).

[0020] Diene monomers copolymerize with ethylene monomers via the following chemical reaction pathway to generate branched chains with double bonds, which can increase the double bond content of polyethylene:

[0021]

[0022] Moreover, the more CH2 groups R in the diene monomer CH2=CH-R-CH=CH2, the longer the generated -R-CH=CH2 branch chain, the smaller the steric hindrance of the double bond, and the easier it is to participate in the cross-linking reaction of cable insulation.

[0023] The terminal olefin monomers added to the system can participate in chain transfer reactions to form double bonds, or they can participate in copolymerization reactions to form branched chains.

[0024] (1) Terminal olefin monomers participate in chain transfer reactions

[0025] Terminal olefins undergo chain transfer reactions with free radicals via the following chemical reaction pathway to generate polyethylene with double bonds.

[0026]

[0027] Moreover, the fewer CH2 groups in the terminal olefin monomer CH2=CH-R, the smaller the steric hindrance of the generated double bond, and the easier it is to participate in the cross-linking reaction of cable insulation.

[0028] (2) Terminal olefin monomers participate in copolymerization reaction

[0029] Terminal olefins copolymerize with ethylene monomers via the following chemical reaction pathway to produce branched polyethylene.

[0030]

[0031] This invention increases the content of double bonds and branches by adding dienes and terminal olefin monomers, and by modifying some reaction conditions, it is even more conducive to increasing the content of double bonds and branches.

[0032] 1. By adding terminal olefins and dienes from the inlet of each reactor section, the concentration of terminal olefins and dienes in reactors R2, R3 and R4 can be increased, which is more conducive to the participation of terminal olefins and dienes in chain transfer reactions and copolymerization reactions to generate double bonds and branches.

[0033] 2. Increasing the initiation temperature of each reaction stage raises the average temperature of each stage, thus increasing the overall rate of chain transfer. Free radicals transfer to terminal olefin monomers to form double bonds and to the polymer to form branched chains. Since high-pressure polyethylene polymerization is a free radical reaction, the process includes four stages: chain initiation, chain propagation, chain termination, and chain transfer. The chain transfer reaction is primarily influenced by reaction temperature and pressure; higher temperatures and lower pressures favor the chain transfer reaction.

[0034] ① Intermolecular chain transfer: Active growing chains transfer between polymer molecules, generating new free radicals. Ethylene molecules continue to combine with these new free radicals to produce branched chains.

[0035] R-CH2·+R′-CH2-R″→R-CH3+R′-·CH-R″;

[0036] ② Intramolecular chain transfer: Hydrogen atoms in the active growth chain are captured by the same chain, and the active center is transferred intramolecularly. The ethylene molecule continues to react with it to form branched chains.

[0037] R-CH2-CH2-CH2-CH2-CH2·→R-·CH-CH2-CH2-CH2-CH3.

[0038] 3. At the same time, reducing the compressor outlet pressure will reduce the pressure in each section of the reactor accordingly, which is more conducive to the chain transfer reaction and thus more conducive to the formation of double bonds and branches.

[0039] 4. The initiator with a higher initiation temperature, di-tert-butyl peroxide (D), was used to replace the initiators with lower initiation temperatures (A) tert-butyl peroxypentanoate, B tert-butyl peroxy-2-ethylhexanoate, and C tert-butyl peroxide-3,5,5-trimethylhexanoate (D) in stages R1, R2, and R3. Initiator D has a higher half-life temperature, a slower reaction rate, fewer free radical active sites, and a larger average molecular weight of the resulting polyethylene, which is more conducive to the formation of a network structure for insulation cross-linking. Table 1 below shows the molecular formulas and corresponding half-life temperatures of initiators A, B, C, and the improved initiator D before and after the improvement.

[0040] Table 1. Molecular formulas and corresponding half-life temperatures of initiators A, B, C before and after improvement, and initiator D after improvement.

[0041]

[0042] The beneficial effects of this invention are as follows:

[0043] 1) This invention increases the content of double bonds and branches by adding dienes and terminal olefin monomers, and by changing some reaction conditions, it is even more conducive to increasing the content of double bonds and branches.

[0044] 2) This invention enhances chain transfer and copolymerization reactions and increases the content of double bonds and branches by adding diene and terminal olefin monomers at preferred positions, increasing reaction temperature, reducing reaction pressure, and using high-temperature initiators instead of low-temperature initiators, thereby preparing easily cross-linked cable insulation base materials.

[0045] 3) Using the easily cross-linked cable insulation base material described in this invention to produce high-voltage cable insulation material can reduce the amount of cross-linking agents, antioxidants and other additives used, and better meet the requirements of high-voltage cable use. Attached Figure Description

[0046] In the attached diagram:

[0047] Figure 1To improve the schematic diagram of the reaction process before;

[0048] Figure 2 This is a temperature distribution diagram inside the reactor;

[0049] Figure 3 This is a schematic diagram of the reaction process of the improved present invention;

[0050] Figure 4 This is a schematic diagram of the reaction process for Comparative Example 2. Detailed Implementation

[0051] The present invention will now be described in conjunction with embodiments to provide an understanding of its implications.

[0052] Unless otherwise specified, all raw materials used in the examples were commercially available.

[0053] Example 1

[0054] The preparation method of the easily cross-linkable cable insulation base material includes the following steps: Ethylene is pressurized and fed into the first tubular reactor at a rate of 60,000 kg / h. Terminal olefins (1-butene 53 kg / h), dienes (1,9-decadiene 60 kg / h), and initiator D (di-tert-butyl peroxide 30 kg / h) are added before reactors R1, R2, R3, and R4 to initiate the reaction. The initiation temperatures of reactors R1, R2, R3, and R4 are 220℃, 230℃, 240℃, and 240℃, respectively. The reaction pressures of reactors R1, R2, R3, and R4 are controlled at 260 MPa, 245 MPa, 230 MPa, and 210 MPa, respectively. High-pressure polyethylene base material is obtained, which is the easily cross-linkable cable insulation base material. A schematic diagram of the reaction process is shown below. Figure 3 As shown.

[0055] Example 2

[0056] The preparation method of the easily cross-linkable cable insulation base material includes the following steps: Ethylene is pressurized and fed into the first tubular reactor at a rate of 80,000 kg / h. Terminal olefin (1-butene) 53 kg / h, diene (1,9-decadiene) 60 kg / h, and initiator D (di-tert-butyl peroxide) 40 kg / h are added before reactors R1, R2, R3, and R4 to initiate the reaction. The initiation temperatures of reactors R1, R2, R3, and R4 are 200℃, 220℃, 230℃, and 230℃, respectively. The reaction pressures of reactors R1, R2, R3, and R4 are controlled at 250 MPa, 235 MPa, 220 MPa, and 200 MPa, respectively. High-pressure polyethylene base material is obtained, which is the easily cross-linkable cable insulation base material. A schematic diagram of the reaction process is shown below. Figure 3 As shown.

[0057] Example 3

[0058] The preparation method of the easily cross-linkable cable insulation base material includes the following steps: Ethylene is pressurized and fed into the first tubular reactor at a rate of 100,000 kg / h. Terminal olefins (1-butene 53 kg / h), dienes (1,9-decadiene 60 kg / h), and initiator D (di-tert-butyl peroxide 50 kg / h) are added before reactors R1, R2, R3, and R4 to initiate the reaction. The initiation temperatures of reactors R1, R2, R3, and R4 are 190℃, 210℃, 220℃, and 220℃, respectively. The reaction pressures of reactors R1, R2, R3, and R4 are controlled at 240 MPa, 225 MPa, 210 MPa, and 190 MPa, respectively. High-pressure polyethylene base material is obtained, which is the easily cross-linkable cable insulation base material. A schematic diagram of the reaction process is shown below. Figure 3 As shown.

[0059] Example 4

[0060] The preparation method of the easily cross-linkable cable insulation base material includes the following steps: Ethylene is pressurized and fed into the first tubular reactor at a rate of 130,000 kg / h. Terminal olefins (1-butene) at 38 kg / h, dienes (1,9-decadiene) at 52 kg / h, and initiator D (di-tert-butyl peroxide) at 60 kg / h are added before reactors R1, R2, R3, and R4, respectively, to initiate the reaction. The initiation temperatures of reactors R1, R2, R3, and R4 are 180℃, 200℃, 225℃, and 240℃, respectively. The reaction pressures of reactors R1, R2, R3, and R4 are controlled at 270 MPa, 255 MPa, 240 MPa, and 220 MPa, respectively. High-pressure polyethylene base material is obtained, which is the easily cross-linkable cable insulation base material. A schematic diagram of the reaction process is shown below. Figure 3 As shown.

[0061] Comparative Example 1

[0062] The preparation method of the easily cross-linkable cable insulation base material comprises the following steps: Ethylene is pressurized and introduced into the first tubular reactor at a rate of 140,000 kg / h. Initiators A (10 kg / h of tert-butyl peroxypentanoate), B (20 kg / h of tert-butyl peroxy-2-ethylhexanoate), and C (40 kg / h of tert-butyl peroxy-3,5,5-trimethylhexanoate) are added sequentially before reactors R1, R2, R3, and R4 to initiate the reaction. The initiation temperatures of reactors R1, R2, R3, and R4 are 180℃, 200℃, 225℃, and 240℃, respectively. The reaction pressures of reactors R1, R2, R3, and R4 are controlled sequentially at 270 MPa, 255 MPa, 240 MPa, and 220 MPa, respectively. High-pressure polyethylene base material is obtained, which is the easily cross-linkable cable insulation base material. A schematic diagram of the reaction process is shown below. Figure 1 As shown.

[0063] Comparative Example 2

[0064] The preparation method of the easily cross-linkable cable insulation base material comprises the following steps: Ethylene, 1-butene, and 1,9-decadiene are pressurized and fed into a first-stage tubular reactor. The addition rate of ethylene is 60,000 kg / h, 1-butene is 212 kg / h, and 1,9-decadiene is 240 kg / h. Initiator D (di-tert-butyl peroxide) at a rate of 30 kg / h is added sequentially before reactors R1, R2, R3, and R4 of the tubular reactor to initiate the reaction. The initiation temperatures of reactors R1, R2, R3, and R4 are 220℃, 230℃, 240℃, and 240℃, respectively. The reaction pressures of reactors R1, R2, R3, and R4 are controlled sequentially at 240 MPa, 225 MPa, 210 MPa, and 190 MPa, respectively. High-pressure polyethylene base material is obtained, which is the easily cross-linkable cable insulation base material. A schematic diagram of the reaction process is shown below. Figure 4 As shown in Table 2 below, the test results of the high-pressure polyethylene base materials prepared in the examples and comparative examples are as follows:

[0065] Table 2. Test Results of Examples and Comparative Examples

[0066]

[0067] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0068] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for preparing an easily cross-linked cable insulation base material, characterized in that, The steps are as follows: After pressurizing ethylene, it is introduced into the starting end of a tubular reactor. Terminal olefins, dienes, and initiators are added to each section of the tubular reactor to initiate the reaction, thereby obtaining high-pressure polyethylene base material, which is the easily cross-linked cable insulation base material.

2. The method for preparing the easily cross-linked cable insulation base material according to claim 1, characterized in that, The tubular reactor comprises four sections, namely reactor R1, reactor R2, reactor R3, and reactor R4.

3. The method for preparing the easily cross-linked cable insulation base material according to claim 2, characterized in that, The initiation temperatures of reactors R1, R2, R3, and R4 are, respectively, 160-220℃, 170-230℃, 180-240℃, and 180-240℃.

4. The method for preparing the easily cross-linked cable insulation base material according to claim 2, characterized in that, The reaction pressures of reactors R1, R2, R3, and R4 are controlled sequentially at: 240-260 MPa, 225-245 MPa, 210-230 MPa, and 190-210 MPa.

5. The method for preparing the easily cross-linked cable insulation base material according to claim 1, characterized in that, The initiator is di-tert-butyl peroxide.

6. The method for preparing the easily cross-linked cable insulation base material according to claim 1, characterized in that, The amount of ethylene added is 40,000-130,000 kg / h, the amount of terminal olefins added before each section of the tubular reactor is 0.001-0.005 times the amount of ethylene added, and the amount of diene added before each section of the tubular reactor is 0.001-0.005 times the amount of ethylene added.

7. The method for preparing the easily cross-linked cable insulation base material according to claim 1, characterized in that, The terminal olefins include one or more of propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene.

8. The method for preparing the easily cross-linked cable insulation base material according to claim 1, characterized in that, The diene includes one or more of 1,4-pentadiene, 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, 1,8-nonadiene, and 1,9-decadiene.

9. The method for preparing the easily cross-linked cable insulation base material according to claim 1, characterized in that, The mass ratio of the terminal olefin to the diene is (52-60):(38-53).

10. A cross-linkable cable insulation base material, characterized in that, It is prepared by any one of the preparation methods described in claims 1-9.

Images