Polyethylene resin for lithium battery diaphragm, preparation method of polyethylene resin and lithium battery diaphragm

Abstract

The invention relates to a preparation method of polyethylene resin for a lithium battery diaphragm. The preparation method comprises the following steps: carrying out desulfurization treatment on raffinate oil, and then feeding the desulfurized raffinate oil into a refining tower for refining to obtain a mixed straight-chain alkane diluent; the method comprises the following steps: continuously introducing a diluent, a main catalyst, a cocatalyst, ethylene and hydrogen into a polymerization kettle, adjusting the reaction temperature and pressure for polymerization, enabling slurry in the kettle to flow out from the lower 1 / 3 part of a straight section of the polymerization kettle under the driving of an external circulating pump, entering an external circulating system, and returning to the polymerization kettle from the upper 1 / 3 part of the straight section of the polymerization kettle after heat removal; and putting slurry overflowing from the polymerization kettle into a centrifugal machine for solid-liquid separation, enabling a solid phase obtained by separation to enter a water washing purification system and dehydration equipment, drying by a fluidized bed, and feeding into a powder bin, so as to obtain a powder product of the polyethylene resin for the lithium battery diaphragm. According to the polymerization system, a single-kettle and external circulation combined mode is adopted, so that the production capacity of the polymerization kettle is improved; the water washing purification unit is added, so that the ash content of the product is effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the field of polyolefin polymerization, and more specifically, relates to a polyethylene resin for lithium battery separators and a preparation method thereof, as well as a lithium battery separator. Background Art

[0002] Currently, the production process of polyethylene resin for lithium battery separators is mainly the slurry method. The diluent is hexane, and propylene or butene is used as the comonomer. Two or three reactors are connected in series, and there is no subsequent water washing and purification unit. In recent years, the loop slurry continuous production process and the batch slurry process using pentane as the solvent have been developed, but the technical maturity needs to be verified. In the Chinese market, 70% of the polyethylene resin for lithium battery separators depends on imports. Therefore, it is crucial to develop a new polymerization process to produce polyethylene resin for lithium battery separators. Summary of the Invention

[0003] The object of the present invention is to develop a batch slurry process for producing polyethylene resin for lithium battery separators. This process can use mixed linear alkanes as the diluent and 1-hexene as the comonomer. This process uses a combination of a single polymerization reactor and an external circulation to increase the device load, reduce the operation difficulty, and improve the product quality stability. This process adds a water washing and purification unit to reduce the product ash content and improve the product quality.

[0004] To solve the above technical problems or achieve the above object, the present invention adopts the following specific technical solutions:

[0005] According to one aspect of the present invention, there is provided a method for preparing a polyethylene resin for lithium battery separators, comprising the following steps:

[0006] 1) After the raffinate oil is desulfurized, it is sent to a refining tower for two-stage hydrorefining to obtain mixed linear alkanes, and the mixed linear alkanes are used as the diluent;

[0007] 2) Continuously introduce the diluent, main catalyst, cocatalyst, ethylene, and hydrogen into the polymerization reactor, adjust the polymerization reaction temperature and pressure, carry out polymerization, and under the drive of an external circulation pump, the slurry in the polymerization reactor flows out from the lower 1 / 3 of the straight section of the polymerization reactor, enters the external circulation system, and then returns to the polymerization reactor from the upper 1 / 3 of the straight section of the polymerization reactor after heat removal;

[0008] 3) Place the slurry overflowing from the polymerization reactor in a centrifuge for solid-liquid separation, and make the separated solid phase enter the water washing and purification system and the dehydration equipment, and then through fluidized bed drying, it is sent to a powder silo to obtain the powder product of the polyethylene resin for lithium battery separators.

[0009] In an embodiment of the present invention, the preparation method further includes the step:

[0010] 4) After adding some additives to the obtained powder product, it is homogenized, directly packaged without granulation, and sent to downstream manufacturers for diaphragm processing.

[0011] In one embodiment of the present invention, in step 1), the refining conditions are as follows: the hydrogen-oil ratio is 50 - 150, and the liquid hourly space velocity is 1.5 h -1 .

[0012] In one embodiment of the present invention, in step 1), the prepared paraffin has a boiling range of 125 - 175 °C, an aromatic content of less than 100 mg / kg, a sulfur content of ≤ 3 mg / kg, and a water value of ≤ 5 ppm.

[0013] In one embodiment of the present invention, in step 2), the main catalyst is a titanium-containing catalyst.

[0014] In one embodiment of the present invention, in step 2), the cocatalyst is at least one of triethylaluminum, tripropylaluminum, tri-n-butylaluminum, trihexylaluminum, trimethylaluminum, and triisobutylaluminum.

[0015] In one embodiment of the present invention, in step 2), a comonomer is continuously introduced into the polymerization kettle.

[0016] In one embodiment of the present invention, the comonomer includes 1-hexene.

[0017] In one embodiment of the present invention, in step 2), the polymerization reaction temperature is 60 - 85 °C, and the polymerization pressure is 0.7 - 1.0 MPa.

[0018] In one embodiment of the present invention, in step 3), the separated liquid phase is refluxed to the polymerization system composed of the polymerization kettle and the external circulation system or refluxed to the recovery system.

[0019] In one embodiment of the present invention, in step 3), the powder feed rate in the water washing and purification system is 2 - 4.5 t / h, and the steam feed rate is 1 - 3 t / h.

[0020] In one embodiment of the present invention, in step 3), the ash removal rate of the powder product is above 60%, and the total ash content of the powder product is reduced to below 35 ppm.

[0021] According to another aspect of the present invention, there is provided a polyethylene resin for a lithium battery diaphragm, which is prepared by using the preparation method of the polyethylene resin for a lithium battery diaphragm as described above.

[0022] According to still another aspect of the present invention, there is provided a lithium battery diaphragm, which includes the polyethylene resin for a lithium battery diaphragm as described above.

[0023] By adopting the above technical solutions, the present invention has the following advantages compared with the prior art:

[0024] After the diluent of the present invention is changed from hexane to paraffin, the boiling point difference from 1-hexene becomes larger, which is convenient for separation. Moreover, 1-hexene is newly added as a comonomer in the present invention; the density of the diluent of the present invention increases, and the polymer suspension and dispersion effect is better; the present invention can use 1-hexene as a comonomer, and compared with propylene or butene, the addition amount is less, and the mechanical properties of the product are better.

[0025] The polymerization system of the present invention is changed from a two-reactor series or a three-reactor series to a single reactor plus an external circulation combination mode, which improves the production capacity of the polymerization reactor, and the single-reactor load is increased by 75%-100%; moreover, compared with the two-reactor or three-reactor series, the operation difficulty of the single-reactor polymerization decreases.

[0026] The water washing and purification unit added in the present invention can effectively reduce the ash content of the product, and the ash removal rate is as high as 60%, and the total ash content of the powder product is reduced to less than 35 ppm.

[0027] The powder product obtained in the present invention is processed by a diaphragm manufacturer, and the diaphragm film surface, defect rate, comprehensive film properties, lithium-ion battery breakdown voltage test, film-forming property, thickness uniformity, porosity, film grammage, puncture strength, etc. can all meet the user's requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other embodiments can be obtained based on these drawings without creative efforts.

[0029] Figure 1 The flow diagram showing a method for preparing a polyethylene resin for a lithium battery separator provided by the present invention is shown. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] It should be understood that the embodiments of the present invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments of the present invention are described in detail, those skilled in the art can easily understand that various modifications are feasible without substantially departing from the teachings of the subject matter of the present invention. Accordingly, all such modifications should be included within the scope of the present invention. Without departing from the gist of the present invention, other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, parameters, etc. of the following exemplary embodiments.

[0031] As Figure 1 shown, a method for preparing a polyethylene resin for a lithium battery separator provided by the present invention includes the following steps:

[0032] S101: Feed the raffinate oil into a refining column after desulfurization treatment, and obtain mixed linear alkanes through two-stage hydrorefining. Then use the mixed linear alkanes as diluents.

[0033] S102: Continuously feed diluents, main catalyst, cocatalyst, ethylene and hydrogen into a polymerization kettle. Adjust the polymerization reaction temperature and pressure to carry out polymerization. Driven by an external circulation pump, let the slurry in the polymerization kettle flow out from the lower 1 / 3 of the straight section of the polymerization kettle, enter the external circulation system, and then return to the polymerization kettle from the upper 1 / 3 of the straight section of the polymerization kettle after heat removal.

[0034] S103: Place the slurry overflowed from the polymerization kettle in a centrifuge for solid-liquid separation. Let the separated solid phase enter a water washing and purification system and a dehydration device, and then enter a fluidized bed dryer and be sent to a powder silo to obtain the powder product of the polyethylene resin for lithium battery separators.

[0035] Through the above technical solutions of the present invention, the polymerization system of the present invention is changed from a double-kettle series connection or a triple-kettle series connection to a single-kettle plus external circulation combination mode, which improves the production capacity of the polymerization kettle. The single-kettle load is increased by 75%-100%. And the operation difficulty of single-kettle polymerization is lower than that of double-kettle or triple-kettle series connection. The added water washing and purification unit in the present invention can effectively reduce the ash content of the product. The ash removal rate is as high as 60%, and the total ash content of the powder product is reduced to less than 35 ppm.

[0036] In the above preparation method, the preparation method further includes the step of adding some additives to the obtained powder product, homogenizing it, directly packaging it without granulation, and sending it to downstream manufacturers for separator processing.

[0037] The powder product obtained by the present invention is processed by a separator manufacturer. The separator film surface, defect rate, comprehensive film performance, lithium-ion battery breakdown voltage test, film-forming property, thickness uniformity, porosity, film grammage, puncture strength, etc. can all meet the user's requirements.

[0038] In the above preparation method, in S101, the refining conditions are: the hydrogen-oil ratio is 50-150, and the liquid hourly space velocity is 1.5 h -1 .

[0039] In the above preparation method, in S101, the boiling range of the prepared alkanes is 125-175 °C, the aromatic hydrocarbon content is less than 100 mg / kg, the sulfur content is ≤ 3 mg / kg, and the water value is ≤ 5 ppm.

[0040] In the above preparation method, in S102, the main catalyst is a titanium-containing catalyst; the cocatalyst is at least one of triethylaluminum, tripropylaluminum, tri-n-butylaluminum, trihexylaluminum, trimethylaluminum and triisobutylaluminum. Preferably, it is triethylaluminum.

[0041] In the above preparation method, in S102, a comonomer is continuously introduced into the polymerization kettle. The comonomer preferably includes 1-hexene. In the present invention, 1-hexene is used as the comonomer. Compared with propylene or butene, the addition amount is less, and the mechanical properties of the product are better.

[0042] In the above preparation method, in S102, the polymerization reaction temperature is 60-85 °C, and the polymerization pressure is 0.7-1.0 MPa.

[0043] In the above preparation method, in S103, the separated liquid phase is refluxed to the polymerization system composed of the polymerization kettle and the external circulation system or refluxed to the recovery system.

[0044] In the above preparation method, in S103, the powder feed amount in the water washing and purification system is 2-4.5 t / h, and the steam feed amount is 1-3 t / h.

[0045] In the above preparation method, in S103, the ash removal rate of the powder product is above 60%, and the total ash content of the powder product is reduced to below 35 ppm.

[0046] In addition, the present invention also provides a polyethylene resin for lithium battery separators, which is prepared by using the preparation method of the polyethylene resin for lithium battery separators as described above.

[0047] Furthermore, the present invention also provides a lithium battery separator, which includes the polyethylene resin for lithium battery separators as described above.

[0048] The above technical solutions of the present invention will be described in detail below through specific examples.

[0049] A preparation method of a polyethylene resin for lithium battery separators provided in an embodiment of the present invention is specifically as follows:

[0050] (1) Diluent preparation: After the raffinate is desulfurized, under the action of a catalyst, it is subjected to two-stage hydrofining to obtain a mixed straight-chain alkane, and the mixed straight-chain alkane is used as the diluent. The refining conditions are a hydrogen-oil ratio of 50-150 and a liquid hourly space velocity of 1.5 h -1 . The prepared alkane has a distillation range of 125-175 °C, an aromatic content of less than 100 mg / kg, a sulfur content of ≤3 mg / kg, and a water value of ≤5 ppm.

[0051] (2) In the polymerization kettle, a mixed straight-chain alkane diluent, a main catalyst, a cocatalyst (preferably triethylaluminum), ethylene, hydrogen, and a comonomer (as required) are continuously introduced, and polymerization is carried out at a reaction temperature of 60-85 °C and a polymerization pressure of 0.7-1.0 MPa. Under the drive of an external circulation pump, the slurry in the polymerization kettle flows out from the lower 1 / 3 of the straight section of the polymerization kettle, enters the external circulation system, and then returns to the polymerization kettle from the upper 1 / 3 of the straight section of the polymerization kettle after heat removal.

[0052] (3) The slurry overflowing from the polymerization kettle enters a centrifuge for solid-liquid separation. The liquid phase (mother liquor) is recycled to the polymerization system or the recovery system, and the solid phase (wet powder cake) enters the water washing and purification system and the dehydration equipment, and then is dried in a fluidized bed and sent to the powder silo.

[0053] (4) After adding some additives, the powder is homogenized, directly packaged without granulation, and sent to downstream manufacturers for diaphragm processing.

[0054] More specifically, the relevant technical solutions of the present invention will be compared and described through Examples 1-4 and Comparative Examples 1-2.

[0055] It should be noted that the properties of the polyethylene resin in the examples of the present invention are measured according to the following methods:

[0056] The ash content of the polyethylene product is determined by "GB / T 9345.1-2008 General Method for the Determination of Ash in Plastics". In the experiment, the direct calcination method is selected, and the sample is calcined in a muffle furnace at 600±25°C for 1 h, and the ash content of the sample is weighed after cooling to constant weight.

[0057] Example 1

[0058] The raffinate oil is sent to a refining tower for treatment after desulfurization. The refining conditions are a hydrogen-oil ratio of 50-150 and a liquid hourly space velocity of 1.5 h -1 , and the hydrogen-oil ratio is preferably 90-105; the prepared paraffin has a boiling range of 125-175°C, an aromatic content of less than 100 mg / kg, a sulfur content of ≤3 mg / kg, a water value of ≤5 ppm, and the aromatic content is preferably less than 50 ppm. The refined mixed straight-chain paraffin product is used as a diluent for the polymerization system; the polymerization system is a single polymerization kettle with an external circulation system. Diluent, titanium-containing catalyst, triethylaluminum, ethylene and hydrogen are continuously introduced into the polymerization kettle. Polymerization is carried out at a polymerization reaction temperature of 60-85°C, preferably 65-80°C, and a polymerization pressure of 0.7-1.0 MPa, preferably 0.8 MPa. Driven by an external circulation pump, the slurry in the polymerization kettle flows out from the lower 1 / 3 of the straight section of the polymerization kettle and enters the external circulation system. After heat removal, it returns to the polymerization kettle from the upper 1 / 3 of the straight section of the polymerization kettle; the slurry overflowing from the polymerization kettle enters a centrifuge for solid-liquid separation. The liquid phase (mother liquor) is recycled to the polymerization system or the recovery system, and the solid phase (wet powder cake) enters the water washing and purification system and the dehydration equipment. The powder feed rate of the water washing and purification system is 2-4.5 t / h, and the steam feed rate is 1-3 t / h. After drying in a fluidized bed, it is sent to the powder silo. Recorded as VHMWPE-1.

[0059] Example 2

[0060] The polyethylene resin was prepared according to the preparation method of Example 1. The difference between Example 2 and Example 1 is that: in Example 2, no external circulation system was designed, and the polymerization system only had a single polymerization kettle. It is denoted as VHMWPE-2.

[0061] Example 3

[0062] The polyethylene resin was prepared according to the preparation method of Example 1. The difference between Example 3 and Example 1 is that: in Example 3, no water washing and purification system was designed, and the wet powder directly entered the drying process after solid-liquid separation. It is denoted as VHMWPE-3.

[0063] Example 4

[0064] The polyethylene resin was prepared according to the preparation method of Example 1. The difference between Example 4 and Example 1 is that: in Example 4, the comonomer 1-hexene was added for the polymerization reaction. It is denoted as VHMWPE-4.

[0065] Comparative Example 1

[0066] The special polyethylene resin 4016 for lithium battery separators produced by Celanese was tested for ash content with reference to the determination method of the examples. 4016 and the special polyethylene resins for lithium battery separators prepared in Examples 1 and 4 of the present invention were tested by downstream separator manufacturers under the same separator processing conditions and separator testing conditions.

[0067] Comparative Example 2

[0068] The special polyethylene resin T0604 for lithium battery separators produced by a certain petrochemical company was tested for ash content with reference to the determination method of the examples. T0604 and the special polyethylene resins for lithium battery separators prepared in Examples 1 and 4 of the present invention were tested by downstream separator manufacturers under the same separator processing conditions and separator testing conditions.

[0069] The relevant test data and results are shown in Tables 1-3 below.

[0070] Table 1 Influence of the external circulation system on the device load

[0071]

[0072] As can be seen from Table 1, when the polymerization system of the present invention adopts the combined mode of a single polymerization kettle plus an external circulation, in the case of an external circulation system, the present invention can significantly increase the load of the polymerization kettle and improve the production capacity of the polymerization kettle.

[0073] Table 2 Influence of the water washing and purification system on the ash content of the product

[0074]

[0075] As can be seen from Table 2, when the water washing and purification system is adopted in the process of the present invention, the ash content of the product can be effectively reduced. For example, compared with VHMWPE-3 without the water washing and purification system, the ash contents in VHMWPE-1 and VHMWPE-2 with the water washing and purification system are only 22 ppm and 25 ppm respectively, which are significantly lower than the ash content of 105 ppm in VHMWPE-3. Therefore, the added water washing and purification unit in the present invention can effectively reduce the ash content of the product, and the total ash content of the product is reduced to less than 35 ppm.

[0076] Table 3 Performance Comparison of 12-μm Lithium Battery Separators

[0077]

[0078] As can be seen from Table 3, compared with the polyethylene for lithium battery separators prepared by other existing units or companies, the polyethylene resin prepared in the embodiments of the present invention has a low ash content, and the puncture resistance, tensile strength MD and TD of the separator are all relatively high.

[0079] Thus, it can be seen that the polymerization system of the present invention adopts a single reactor plus external circulation combination mode, which improves the production capacity of the polymerization reactor. The present invention adds a water washing and purification unit, which can effectively reduce the ash content of the product. The powder product obtained by the present invention is processed by a separator manufacturer, and has very good puncture resistance and tensile strength, meeting the user requirements.

[0080] The above are only the preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention; any modifications or equivalent replacements made to the present invention without departing from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A preparation method of polyethylene resin for lithium battery separator, characterized in that, It includes the following steps: 1) After subjecting raffinate oil to desulfurization treatment, it is sent into a refining tower for two-stage hydrorefining to obtain mixed straight-chain alkanes, and the mixed straight-chain alkanes are used as diluents; 2) Diluent, main catalyst, cocatalyst, ethylene and hydrogen are continuously introduced into a polymerization kettle. The polymerization reaction temperature and polymerization pressure are adjusted for polymerization. Driven by an external circulation pump, the slurry in the polymerization kettle flows out from the lower 1 / 3 of the straight section of the polymerization kettle, enters the external circulation system, and then returns to the polymerization kettle from the upper 1 / 3 of the straight section of the polymerization kettle after heat removal; 3) The slurry overflowing from the polymerization kettle is placed in a centrifuge for solid-liquid separation, and the separated solid phase enters a water washing and purification system and a dehydration device, and then is dried in a fluidized bed and sent into a powder silo to obtain the powder product of the polyethylene resin for lithium battery separator; 2. The preparation method of polyethylene resin for lithium battery separator according to claim 1, characterized in that, It also includes the step: 4) After adding some additives to the obtained powder product, it is homogenized, directly packaged without granulation, and sent to downstream manufacturers for separator processing.

3. The preparation method of polyethylene resin for lithium battery separator according to claim 1, characterized in that, In step 1), the refining conditions are as follows: the hydrogen-oil ratio is 50 - 150, and the liquid hourly space velocity is 1.5 h -1 .

4. The preparation method of polyethylene resin for lithium battery separator according to claim 3, characterized in that, In step 1), the prepared alkane has a distillation range of 125 - 175 °C, an aromatic content of less than 100 mg / kg, a sulfur content of ≤ 3 mg / kg, and a water value of ≤ 5 ppm.

5. The preparation method of polyethylene resin for lithium battery separator according to claim 1, characterized in that, In step 2), the main catalyst is a titanium-containing catalyst.

6. The preparation method of polyethylene resin for lithium battery separator according to claim 5, characterized in that, In step 2), the cocatalyst is at least one of triethylaluminum, tripropylaluminum, tri-n-butylaluminum, trihexylaluminum, trimethylaluminum and triisobutylaluminum.

7. The preparation method of polyethylene resin for lithium battery separator according to claim 6, characterized in that, In step 2), a comonomer is also continuously introduced into the polymerization kettle.

8. The preparation method of polyethylene resin for lithium battery separator according to claim 7, characterized in that, The comonomer includes 1-hexene.

9. The preparation method of polyethylene resin for lithium battery separator according to claim 8, characterized in that, In step 2), the polymerization reaction temperature is 60 - 85 °C, and the polymerization pressure is 0.7 - 1.0 MPa.

10. The preparation method of polyethylene resin for lithium battery separator according to claim 1, characterized in that, In step 3), the separated liquid phase is refluxed to the polymerization system composed of the polymerization kettle and the external circulation system or refluxed to the recovery system.

11. The preparation method of polyethylene resin for lithium battery separator according to claim 10, characterized in that, In step 3), the powder feed rate in the water washing and purification system is 2 - 4.5 t / h, and the steam feed rate is 1 - 3 t / h.

12. The preparation method of polyethylene resin for lithium battery separator according to claim 11, characterized in that, In step 3), the ash removal rate of the powder product is above 60%, and the total ash content of the powder product is reduced to below 35 ppm.

13. A polyethylene resin for lithium battery separator, characterized in that, It is prepared by using the preparation method of the polyethylene resin for lithium battery separator according to any one of claims 1 to 12.

14. A lithium battery separator, characterized in that, It includes the polyethylene resin for lithium battery separator according to claim 13.

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