Preparation method of polyethylene with high melt index

Abstract

The invention discloses a preparation method of high melt index polyethylene, and belongs to the technical field of polyolefin production. According to the preparation method of the high melt index polyethylene, the slurry catalyst is used in the polyethylene reactor, and parameters such as the temperature, the pressure, the ratio of the cocatalyst to the reducing agent, the ratio of hydrogen to the ethylene monomer, the ratio of butene-1 to the ethylene monomer and the like in the polymerization reaction process are optimized, so that the high melt index polyethylene with the melt index of more than or equal to 50g / 10min and the high melt index can be prepared. The polyethylene product is good in various properties; the method provided by the invention overcomes the technical problems that the fluidity of the powder becomes poor due to the increase of the polyethylene melt index in the current high melt index polyethylene production process, and a condensing agent cannot be added into the reactor to remove heat, so that only low-load production can be realized, and the production efficiency is influenced.

Description

Technical Field

[0001] The invention relates to the technical field of polyolefin production, and in particular to a method for preparing high melt index polyethylene. Background Art

[0002] Polyethylene is one of the most widely used plastics. With the continuous development of polyethylene applications in various fields, the development of high-performance catalysts and the production of high-value-added polyethylene have become the focus of current scientific research. In the industrial production of polyethylene, the melt index (melt mass flow rate) is an important product indicator. It is often used in industry to control product quality and classify polyethylene products of different grades. It reflects the melt flow characteristics and molecular weight. It is a key indicator in the field of product processing and application. It can make the selected raw materials better adapt to the requirements of the processing technology and improve the reliability and quality of the products in molding. High melt index polyethylene has the advantages of making injection molded products easy to mold and reduce injection defects and scrap rates; in the process of product processing and production, it can reduce processing temperature, injection pressure and clamping force, thereby reducing energy consumption, shortening the molding cycle of products, and increasing product output; it can be used to injection mold thin-walled products with complex structures and produce parts with complex design parameters or long flow lengths, simplifying the injection molding process and reducing the cost of raw materials. Therefore, the production of high melt index polyethylene injection molding materials is one of the important directions of polyethylene development, with good comprehensive performance and broad market prospects.

[0003] At present, the method of increasing the melt index of polyethylene products by increasing the amount of hydrogen added to the reactor is usually adopted. For gas phase reactors, the reactor pressure increases with the increase of hydrogen addition, and with the increase of polyethylene melt index, the ability of powder to adsorb heavy components becomes stronger, and the powder tends to become sticky, resulting in poor powder fluidity. It is impossible to add condensing agent to the reactor to remove heat, so it can only be produced at low load, which greatly affects the production efficiency. In addition, the polyethylene product powder obtained by the dry powder catalyst currently used is relatively fine, and the fine powder is easily entrained by the circulating gas to the circulating gas pipeline, which brings great difficulty to production adjustment.

[0004] In view of the defects in the above-mentioned methods for improving the melt index of polyethylene products and the growing demand for high melt index polyolefin products on the market, developing a method that can improve the melt index of polyethylene without affecting the production efficiency of polyethylene is currently the focus of research in the field of polyolefin production technology. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a method for preparing high melt index polyethylene, which can improve the melt index of the produced polyethylene without affecting the production efficiency of the polyethylene.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] In a first aspect, the present invention provides a method for preparing high melt index polyethylene, the method comprising the following steps:

[0008] S1, adding the catalyst active component A and the reducing agent B into a polyethylene reactor for premixing, and then adding the co-catalyst C to blend to obtain a mixed catalyst;

[0009] S2, subjecting the mixed catalyst described in step S1 to polymerization reaction with ethylene, hydrogen and butene-1 under condensation conditions to obtain the polyethylene with a high melt index;

[0010] The mass ratio of the promoter C to the reducing agent B is promoter C: reducing agent B = 30-45: 18-22;

[0011] The conditions of the polymerization reaction are as follows:

[0012] The reaction temperature is 84.5-88°C, the reaction pressure is 2.2-2.5MPa, the molar ratio of hydrogen to ethylene is 0.400-0.800, and the molar ratio of butene-1 to ethylene is 0.200-0.600.

[0013] The present invention adopts the above method, in the presence of hydrogen, a multi-catalyst system and ethylene monomer are polymerized under high load under condensation conditions, and the molecular weight of polyethylene is adjusted by hydrogen, and the density of polyethylene is adjusted by butene-1, so that a high melt index polyethylene product with a melt index greater than 50g / 10min can be prepared; the technical difficulties that the fluidity of powder is deteriorated due to the increase of the melt index of polyethylene in the current production process of high melt index polyethylene, and a condensing agent cannot be added in the reactor to remove heat, so that low-load production can only be carried out, which affects the production efficiency, are overcome.

[0014] The inventors have found through a large number of experiments that the mass ratio of the co-catalyst C to the reducing agent B has a significant impact on the melt index value of the final polyethylene. When the mass ratio of the co-catalyst C to the reducing agent B is within the above range, the particle size of the polymer in the polymerization reaction can be improved, and the problems of poor powder fluidity, a large amount of fine powder, and easy stickiness can be solved. The melt index of the produced polyethylene can be made greater than 50g / 10min. If the mass ratio of the co-catalyst C to the reducing agent B exceeds the range provided by the present invention, the melt index of the final polyethylene cannot reach the required value.

[0015] The inventors also found that a specific reaction temperature and reaction time during the polymerization reaction can enable the final polyethylene melt index to meet the requirements without affecting the production efficiency of the polyethylene; at the same time, the material level of the polyethylene reactor needs to be monitored during the polymerization process, and the above parameters need to be adjusted in time according to changes in the bed bulk density and bed weight to prevent excessive fine powder, and the powder resin screening should be analyzed regularly to monitor the changes in fine powder in real time.

[0016] The inventors also found that the molar ratio of hydrogen to ethylene and the molar ratio of butene-1 to ethylene affect the polymerization performance in the ethylene polymerization process. By adjusting the molar ratio of hydrogen to ethylene and the molar ratio of butene-1 to ethylene within the above-mentioned range, the polymerization performance in the ethylene polymerization process can be effectively controlled so that the final polyethylene melt index meets the requirements.

[0017] In the preparation process of the high melt index polyethylene of the present invention, the limitation of the above parameters is very important, and each link is closely linked and directly affects the final polyethylene melt index.

[0018] As a preferred embodiment of the method for preparing high melt index polyethylene of the present invention, in step S1, the catalyst active component A is a dry powder or slurry Ziegler-Natta catalyst.

[0019] As a more preferred embodiment of the method for preparing high melt index polyethylene of the present invention, the catalyst active component A is a slurry-type Ziegler-Natta catalyst; the inventors have found through a large number of experiments that the polyethylene product powder obtained by the dry powder catalyst is relatively fine, and the fine powder is easily entrained by the circulating gas in the polyethylene reactor to the circulating gas pipeline, which brings great difficulty to production adjustment.

[0020] As the most preferred embodiment of the preparation method of high melt index polyethylene of the present invention, the slurry Ziegler-Natta catalyst contains MgCl2, a titanium-containing compound and SiO2; the mass percentage of the Ti element is 2.2%-7.8%, and the mass percentage of the Mg element is 5%-18%.

[0021] Preferably, the molar ratio of the titanium element in the slurry Ziegler-Natta catalyst to the aluminum in the reducing agent B and the co-catalyst C is Ti:Al=5-500:1.

[0022] More preferably, the molar ratio of the titanium element in the slurry Ziegler-Natta catalyst to the aluminum in the reducing agent B and the co-catalyst C is Ti:Al=20-200:1.

[0023] As a preferred embodiment of the method for preparing high melt index polyethylene of the present invention, in step S1, the reducing agent B is an alkyl aluminum or a halogenated alkyl aluminum compound.

[0024] As a more preferred embodiment of the method for preparing high melt index polyethylene of the present invention, the reducing agent B is tri-n-hexylaluminum (T3) reducing agent.

[0025] As a preferred embodiment of the method for preparing high melt index polyethylene of the present invention, in step S1, the co-catalyst C is an electron donor compound.

[0026] As a more preferred embodiment of the method for preparing high melt index polyethylene of the present invention, the cocatalyst C is a diurethane (DC) catalyst. The DC catalyst in the present invention is mainly used to improve the responsiveness to the comonomer ethylene monomer during the polymerization reaction.

[0027] As a preferred embodiment of the method for preparing high melt index polyethylene of the present invention, in step S1, the polyethylene reactor is a gas phase reactor.

[0028] As a preferred embodiment of the method for preparing high melt index polyethylene of the present invention, in step S2, condensation conditions are created by adding a condensing agent.

[0029] As a more preferred embodiment of the method for preparing high melt index polyethylene of the present invention, the condensing agent is isopentane.

[0030] As the most preferred embodiment of the method for preparing high melt index polyethylene of the present invention, in step S2, the concentration of the condensing agent is 0.8%-9%; the inventors have found through a large number of creative experiments that only when the concentration of the condensing agent is within the above range, the melt index of the final polyethylene product can meet the requirements, and the polyethylene product will not have problems such as poor feeding in the polyethylene reactor; when the concentration of the condensing agent is greater than 9%, the melt index of the polyethylene cannot continue to rise after reaching 20g / 10min, and the product in the polyethylene reactor becomes sticky, has poor feeding, and is difficult to granulate, which can easily lead to the inability to continue production; when the concentration of the condensing agent is less than 0.8%, heat is dissipated in the reactor, and the melt index of the polyethylene cannot continue to rise after reaching 20g / 10min.

[0031] As a more preferred embodiment of the method for preparing high melt index polyethylene of the present invention, in step S2, the load of the polymerization reaction is 10-20 t / h.

[0032] In a second aspect, the present invention provides a high melt index polyethylene, which is prepared by the preparation method of high melt index polyethylene as described in the first aspect.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention establishes a method for preparing high melt index polyethylene, and by using a slurry catalyst in a polyethylene reactor and optimizing parameters such as temperature, pressure, the ratio of a co-catalyst to a reducing agent, the ratio of hydrogen to ethylene monomer, and the ratio of butene-1 to ethylene monomer during the polymerization reaction, a polyethylene product with a melt index of ≥50 g / 10 min can be prepared; the method of the present invention overcomes the technical difficulties that the fluidity of the powder is deteriorated due to the increase in the melt index of the polyethylene in the current production process of high melt index polyethylene, and a condensing agent cannot be added in the reactor to remove heat, so that low-load production can only be carried out, which affects the production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a diagram of high melt index polyethylene powder prepared according to one embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to better reflect the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments and comparative examples, its purpose is to explain the content of the present invention in detail, rather than to limit the present invention. All other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the protection scope of the present invention. The experimental reagents and equipment designed for the implementation of the present invention are all commonly used common reagents and equipment unless otherwise specified.

[0036] Example 1

[0037] This embodiment provides a method for preparing ultra-high melt index polyethylene PE-L M2750, the preparation method comprising the following steps:

[0038] S1, adding the catalyst active component A and the T3 reducing agent into the polyethylene reactor for premixing, then adding the co-catalyst DC for blending, and obtaining the mixed catalyst after 3 hours;

[0039] S2, polymerizing the mixed catalyst described in step S1 with ethylene, hydrogen, and butene-1 under condensation conditions where the concentration of the condensing agent isopentane is 0.8%, thereby obtaining the polyethylene with a high melt index;

[0040] The mass ratio of the co-catalyst DC to the reducing agent T3 is co-catalyst DC: reducing agent T3 = 40:20;

[0041] The conditions of the polymerization reaction are as follows:

[0042] The reaction temperature is 85°C, the reaction pressure is 2.406MPa, and the reaction polymerization load is 11t / h; the molar ratio of hydrogen to ethylene is: hydrogen:ethylene = 0.789:1, and the molar ratio of butene-1 to ethylene is: butene-1:ethylene = 0.323:1.

[0043] In this embodiment, the melt index of the polyethylene powder is 50g / 10min and the density is 0.9260g / cm 3 .

[0044] Example 2

[0045] The difference between this embodiment and embodiment 1 is only that:

[0046] The conditions of the polymerization reaction are as follows:

[0047] The concentration of isopentane is 1.3%, the reaction temperature is 86°C, the reaction pressure is 2.402 MPa, and the reaction polymerization load is 12 t / h; the molar ratio of hydrogen to ethylene is: hydrogen:ethylene = 0.6948:1, and the mass ratio of butene-1 to ethylene is: butene-1:ethylene = 0.4014:1; the remaining steps are consistent with Example 1.

[0048] In this embodiment, the melt index of the polyethylene powder is 50g / 10min and the density is 0.9260g / cm 3 .

[0049] Example 3

[0050] The difference between this embodiment and embodiment 1 is only that:

[0051] The mass ratio of the co-catalyst DC to the reducing agent T3 is co-catalyst DC: reducing agent T3 = 38:18;

[0052] The conditions of the polymerization reaction are as follows:

[0053] The concentration of isopentane is 7.22%, the reaction temperature is 84.91°C, the reaction pressure is 2.394MPa, and the reaction polymerization load is 18t / h; the molar ratio of hydrogen to ethylene is: hydrogen:ethylene = 0.6738:1, and the mass ratio of butene-1 to ethylene is: butene-1:ethylene = 0.2822:1; the remaining steps are consistent with Example 1.

[0054] In this embodiment, the melt index of the polyethylene powder is 50g / 10min and the density is 0.9260g / cm 3 .

[0055] Example 4

[0056] The difference between this embodiment and embodiment 1 is only that:

[0057] The mass ratio of the co-catalyst DC to the reducing agent T3 is co-catalyst DC: reducing agent T3 = 38:18;

[0058] The conditions of the polymerization reaction are as follows:

[0059] The concentration of isopentane is 6.9%, the reaction temperature is 85.5°C, the reaction pressure is 2.426MPa, and the reaction polymerization load is 18.83t / h; the molar ratio of hydrogen to ethylene is: hydrogen:ethylene = 0.6892:1, and the mass ratio of butene-1 to ethylene is: butene-1:ethylene = 0.2753:1; the remaining steps are consistent with Example 1.

[0060] In this embodiment, the melt index of the polyethylene powder is 50g / 10min and the density is 0.9260g / cm 3 .

[0061] Example 5

[0062] The difference between this embodiment and embodiment 1 is only that:

[0063] The mass ratio of the co-catalyst DC to the reducing agent T3 is co-catalyst DC: reducing agent T3 = 30:18;

[0064] The conditions of the polymerization reaction are as follows:

[0065] The concentration of isopentane is 0.8%, the reaction temperature is 88°C, the reaction pressure is 2.2 MPa, and the reaction polymerization load is 12 t / h; the molar ratio of hydrogen to ethylene is: hydrogen:ethylene = 0.4:1, and the mass ratio of butene-1 to ethylene is: butene-1:ethylene = 0.2:1; the remaining steps are consistent with Example 1.

[0066] In this embodiment, the melt index of the polyethylene powder is 50g / 10min and the density is 0.9260g / cm 3 .

[0067] Example 6

[0068] The difference between this embodiment and embodiment 1 is only that:

[0069] The mass ratio of the promoter DC to the reducing agent T3 is promoter DC: reducing agent T3 = 45:22;

[0070] The conditions of the polymerization reaction are as follows:

[0071] The concentration of isopentane is 9%, the reaction temperature is 84.5°C, the reaction pressure is 2.5 MPa, and the reaction polymerization load is 12 t / h; the molar ratio of hydrogen to ethylene is hydrogen:ethylene = 0.8:1, and the mass ratio of butene-1 to ethylene is butene-1:ethylene = 0.6:1; the remaining steps are consistent with Example 1.

[0072] In this embodiment, the melt index of the polyethylene powder is 50g / 10min and the density is 0.9260g / cm 3 .

[0073] Comparative Example 1

[0074] The difference between this comparative example and Example 1 is that in step S2, the concentration of the condensing agent isopentane is greater than 9%; the remaining steps are consistent with Example 1.

[0075] Comparative Example 2

[0076] The difference between this comparative example and Example 1 is that in step S2, the concentration of the condensing agent isopentane is less than 0.8%; the remaining steps are consistent with Example 1.

[0077] Comparative Example 3

[0078] The difference between this comparative example and Example 1 is that the mass ratio of the co-catalyst DC to the reducing agent T3 is co-catalyst DC: reducing agent T3=20:18; the other steps are consistent with Example 1.

[0079] Comparative Example 4

[0080] The difference between this comparative example and Example 1 is that the mass ratio of the co-catalyst DC to the reducing agent T3 is co-catalyst DC: reducing agent T3 = 45:30; the other steps are consistent with Example 1.

[0081] Comparative Example 5

[0082] The only difference between this comparative example and Example 1 is that the molar ratio of hydrogen to ethylene is hydrogen:ethylene=0.234:1, and the remaining steps are consistent with Example 1.

[0083] Comparative Example 6

[0084] The only difference between this comparative example and Example 1 is that the molar ratio of hydrogen to ethylene is hydrogen:ethylene=1.5:1, and the remaining steps are consistent with Example 1.

[0085] Comparative Example 7

[0086] The difference between this comparative example and Example 1 is that the mass ratio of butene-1 to ethylene is butene-1:ethylene=0.1:1; the remaining steps are consistent with Example 1.

[0087] Comparative Example 8

[0088] The difference between this comparative example and Example 1 is that the mass ratio of butene-1 to ethylene is butene-1:ethylene=1:1; the remaining steps are consistent with Example 1.

[0089] Comparative Example 9

[0090] The only difference between this comparative example and Example 1 is that the polymerization reaction temperature is 70° C. and the reaction pressure is 1.5 MPa; the remaining steps are consistent with Example 1.

[0091] Comparative Example 10

[0092] The only difference between this comparative example and Example 1 is that the polymerization reaction temperature is 90° C. and the reaction pressure is 2.7 MPa; the remaining steps are consistent with Example 1.

[0093] Effect example

[0094] Various performance tests were performed on the polyethylene powders prepared by the methods described in Examples 1-6 and Comparative Examples 1-10. To increase the test accuracy of the present invention, three samples were measured in each example in Examples 1-6 to reduce the test error of the present invention. In Tables 1-6, 1-1, 1-2, 1-3, etc. represent each group of samples in Examples 1-6; Tables 7 and 8 are the test results of Comparative Examples 1-10.

[0095] Table 1

[0096]

[0097]

[0098] Table 2

[0099]

[0100]

[0101] Table 3

[0102]

[0103] Table 4

[0104]

[0105]

[0106] Table 5

[0107]

[0108]

[0109] Table 6

[0110]

[0111]

[0112] Table 7

[0113]

[0114] Table 8

[0115]

[0116]

[0117] It can be seen from Table 1-8 that, by adjusting the preparation parameters, the polyethylene products of Examples 1-6 of the present invention have a melt index of 50 g / 10 min, and all properties of the polyethylene products meet the standards of premium products. However, after the melt index of the polyethylene product of Comparative Example 1-10 reaches 20 g / 10 min, the melt index of the product cannot be further increased, the powdered resin product in the reactor becomes sticky, the material discharge is not smooth, granulation is difficult, and production cannot be continued. In addition, all properties of the final product are inferior to those of Examples 1-6.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing high melt index polyethylene, characterized in that: The method comprises the following steps: S1, adding the catalyst active component A and the reducing agent B into a polyethylene reactor for premixing, and then adding the co-catalyst C for blending to obtain a mixed catalyst; S2, subjecting the mixed catalyst described in step S1 to polymerization reaction with ethylene, hydrogen and butene-1 under condensation conditions to obtain the polyethylene with a high melt index; The mass ratio of the promoter C to the reducing agent B is promoter C: reducing agent B = 30-45: 18-22; The conditions of the polymerization reaction are as follows: The reaction temperature is 84.5-88°C, the reaction pressure is 2.2-2.5MPa, the molar ratio of hydrogen to ethylene is 0.400-0.800, and the molar ratio of butene-1 to ethylene is 0.200-0.

600.

2. The method for preparing high melt index polyethylene according to claim 1, characterized in that: In the step S1, the catalyst active component A is a dry powder or slurry Ziegler-Natta catalyst.

3. The method for preparing high melt index polyethylene according to claim 2, characterized in that: The catalyst active component A is a slurry Ziegler-Natta catalyst; Preferably, the catalyst active component A comprises MgCl2, a titanium-containing compound and SiO2.

4. The method for preparing high melt index polyethylene according to claim 1, characterized in that: In the step S1, the reducing agent B is an alkyl aluminum or a halogenated alkyl aluminum compound.

5. The method for preparing high melt index polyethylene according to claim 4, characterized in that: The reducing agent B is tri-n-hexylaluminum reducing agent.

6. The method for preparing high melt index polyethylene according to claim 1, characterized in that: In the step S1, the co-catalyst C is an electron donor compound.

7. The method for preparing high melt index polyethylene according to claim 1, characterized in that: In the step S1, the co-catalyst C is a diurethane catalyst.

8. The method for preparing high melt index polyethylene according to claim 1, characterized in that: In step S2, condensation conditions are created by adding a condensing agent; Preferably, the condensing agent is isopentane.

9. The method for preparing high melt index polyethylene according to claim 8, characterized in that: The concentration of isopentane is 0.8%-9%.

10. A high melt index polyethylene material, characterized in that: The high melt index polyethylene material is prepared by the preparation method of high melt index polyethylene according to any one of claims 1 to 9.

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