Purification process of polyvinylidene fluoride polymerization product

Abstract

The invention provides a process for purifying a polyvinylidene fluoride polymerization product, which comprises the following steps of: filtering the polymerization product polyvinylidene fluoride slurry to obtain a polyvinylidene fluoride filter cake; washing the polyvinylidene fluoride filter cake with pure water, dissolving polyvinylidene fluoride into an organic solvent, adding pure water to wash the organic phase, extracting impurities of polyvinylidene fluoride into a water phase, standing for layering to obtain an organic phase, and distilling to remove the organic solvent to obtain high-purity polyvinylidene fluoride; the organic solvent is insoluble in water but can dissolve the polyvinylidene fluoride. According to the purification process of the polyvinylidene fluoride polymerization product, the content of ions in the polyvinylidene fluoride polymerization product can be obviously reduced, and the prepared polyvinylidene fluoride product is high in purity, attractive in appearance, uniform in granularity, good in flowability and free of unpleasant odor; and the method is convenient to operate and reasonable in design, and has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of post-processing of fluorine-containing polymer products, and in particular relates to a purification process of polyvinylidene fluoride polymer products. Background Art

[0002] Polyvinylidene fluoride (PVDF) is a high molecular weight, semi-crystalline thermoplastic with excellent mechanical properties, high and low temperature resistance, weather resistance, radiation resistance and chemical corrosion resistance. It is widely used in the preparation of high value-added powder coatings, membrane materials and other high-performance composite materials.

[0003] The main methods for synthesizing polyvinylidene fluoride are suspension polymerization and emulsion polymerization. Suspension polymerization: The vinylidene fluoride monomer is suspended in an appropriate medium in the form of microparticles or particles. Typical suspension media include water, organic solvents and surfactants, etc., and then an appropriate initiator is added to generate free radicals to start the polymerization reaction. The initiator is usually persulfate or hydrogen peroxide. Emulsion polymerization: The vinylidene fluoride monomer is mixed with an emulsifier, a detackifier (paraffin) and water, and a uniform emulsion system is formed by stirring. The emulsifier is an anionic surfactant, such as sodium hexadecyl sulfonate; then an initiator is added to generate free radicals to start the polymerization reaction. The initiator is usually persulfate or hydrogen peroxide.

[0004] After the polymerization reaction, due to various reasons, for example, ionic impurities brought into the polymerization reaction system by raw materials such as initiators, surfactants and comonomers, or ionic impurities generated by corrosion of the reactor by initiators, etc., are adsorbed on the surface and inside of the polymer resin. In the prior art, the ionic impurities on the surface or inside of the polymer resin are removed by washing with water. For example, CN102336854A discloses a method for preparing highly heat-resistant polyvinylidene fluoride, which is to wash the polyvinylidene fluoride slurry with deionized water until the foam disappears. Repeated washing with water wastes water resources, and because water cannot enter the polyvinylidene fluoride, the cleaning effect is not good. Patent CN 105924554A discloses a method for preparing polyvinylidene fluoride resin, in which a strong oxidant of 0.01-0.1% relative to the weight of the PVDF wet material is added in the washing step, so that the residual organic dispersant in the resin can be thoroughly washed out, thereby obtaining a PVDF resin with excellent heat resistance, but it cannot remove ionic impurities. The existing technology cannot meet the increasing demand for high-purity polyvinylidene fluoride polymer resins, such as PVDF dielectric films, lithium battery separators and lithium battery binders, etc. Based on this, the present application was developed. Summary of the invention

[0005] In view of this, the purpose of the present invention is to overcome the defects of the prior art and provide a purification process for polyvinylidene fluoride polymerization products. The method can significantly reduce the ion content in the polyvinylidene fluoride polymerization products. The prepared polyvinylidene fluoride product has high purity, beautiful appearance, uniform particle size, good fluidity and no bad odor. The method is easy to operate and reasonably designed, and has broad application prospects.

[0006] To achieve the above object, the present invention adopts the following technical solution: A purification process for polyvinylidene fluoride polymerization products comprises filtering polyvinylidene fluoride slurry, a polymerization product, to obtain a polyvinylidene fluoride filter cake; washing the polyvinylidene fluoride filter cake with pure water, dissolving the polyvinylidene fluoride filter cake in an organic solvent, adding pure water to wash an organic phase, extracting impurities of the polyvinylidene fluoride into an aqueous phase, standing to separate layers, collecting the organic phase, distilling to remove the organic solvent, and drying to obtain high-purity polyvinylidene fluoride; the organic solvent is insoluble in water but can dissolve the polyvinylidene fluoride.

[0007] Specifically, the organic solvent includes but is not limited to one or two of dimethyl carbonate, cyclohexanone, etc. The amount of the organic solvent is 8 to 20 times that of the polyvinylidene fluoride filter cake, that is, 8 to 20 ml of organic solvent is added for every 1 g of polyvinylidene fluoride filter cake. Furthermore, the temperature at which the organic solvent dissolves the polyvinylidene fluoride is preferably 60-90°C.

[0008] Specifically, the polyvinylidene fluoride filter cake is washed with pure water for 3 to 5 times, and the amount of water used for each washing is 15-25 times that of the polyvinylidene fluoride filter cake. That is, 15 to 25 ml of pure water is added for every 1 g of polyvinylidene fluoride filter cake. Preferably, the washing starts from the second time, and the polyvinylidene fluoride filter cake is washed again with the filtered washing water. In the step of washing the polyvinylidene fluoride filter cake with pure water, the washing water of the first washing of the polyvinylidene fluoride filter cake is poured out, and the washing water of the second pure water washing can also be used to wash the polyvinylidene fluoride filter cake once more and then poured out; the washing water of the third pure water washing can also be used to wash the filter cake once more and then poured out. In this way, the overall water consumption can be saved by 10% to 20%, which is a considerable expense in industrial production.

[0009] Further preferably, the polyvinylidene fluoride filter cake prepared by the suspension method is generally washed three times; the polyvinylidene fluoride slurry prepared by the emulsion method needs to be washed five times because the slurry contains an emulsifier and a coagulant aluminum nitrate needs to be added to allow the slurry to coagulate to form a filter cake.

[0010] Furthermore, when the organic phase is washed with pure water, the temperature of the pure water for extracting impurities is kept consistent with the temperature of the organic phase, the volume of the pure water is 0.5-1 times that of the organic phase, and the organic phase is washed 2-4 times.

[0011] Furthermore, before filtering the polyvinylidene fluoride slurry, the polyvinylidene fluoride slurry is stirred and heated at 50-60° C. for 15-30 minutes. Before filtering, stirring and heating the polyvinylidene fluoride slurry can increase the filtration rate, thereby improving the filtration efficiency.

[0012] Specifically, the polymerization reaction is a suspension polymerization reaction or an emulsion polymerization reaction.

[0013] Further preferably, when the polyvinylidene fluoride slurry is prepared by emulsion polymerization, a coagulant is added after stirring the polyvinylidene fluoride slurry. Since the polyvinylidene fluoride slurry prepared by emulsion polymerization contains an emulsifier, aluminum nitrate is added as a coagulant to coagulate the polyvinylidene fluoride dispersed by the emulsifier for easy washing and filtration.

[0014] Furthermore, the filter used in the filtration may be a nano-grade nylon filter, which can well intercept polyvinylidene fluoride and filter out other impurities, and can be used repeatedly.

[0015] Preferably, the drying is performed by vacuum drying, the drying temperature is 70-80° C., and the vacuum degree is -0.1 to -0.6 Mpa.

[0016] The present invention filters the polyvinylidene fluoride slurry prepared by the suspension method or the emulsion method, and the polyvinylidene fluoride filter cake obtained by the first filtration has a large amount of impurities, and is first washed with pure water to remove other impurities, and then the filter cake is dissolved with an organic solvent to form an organic phase, and the organic phase is washed with pure water, and ionic impurities are extracted into the aqueous phase, and the organic phase is distilled and dried to obtain a high-purity polyvinylidene fluoride product. The organic solvent can dissolve the polymer product to form a homogeneous phase, so that when the organic phase is washed with pure water, ionic impurities with higher solubility in the aqueous phase are taken away, thereby improving the purity of the polyvinylidene fluoride in the organic phase, and after the organic phase is distilled, a high-purity polyvinylidene fluoride is obtained, and the organic solvent can be recycled.

[0017] Compared with the prior art, the beneficial effects of the process of the present invention are as follows: The purification process of the polyvinylidene fluoride polymer of the present invention adopts a two-phase extraction process, which gives full play to the solubility of the organic solvent in the resin and beneficially supplements the incompatibility between water and the resin. When water washes the organic phase, the ionic impurities adsorbed on the surface and inside of the resin can be cleaned out, thereby significantly reducing the ionic impurities in the polyvinylidene fluoride resin.

[0018] The purification process of the polyvinylidene fluoride polymer of the present invention only involves filtering, washing, stirring and heating, and has low requirements on equipment. The selected organic solvents are easy to obtain and inexpensive, and no additional production cost is required. In the process of washing with water, the washing water after the second time is reused, which reduces the amount of water used in the washing process and saves 10-20% of water overall.

[0019] The purification process of the polyvinylidene fluoride polymer of the present invention has been proved by experimental data to be able to effectively reduce metal ion impurities in the polyvinylidene fluoride polymerization product. The obtained polyvinylidene fluoride product has high purity, beautiful appearance, uniform particle size, good fluidity, and no bad odor. It can be widely used in high-end electronic fields such as lithium battery separators, capacitor films, and lithium battery binders. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described in combination with the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0021] The organic solvents and equipment materials of the embodiments of the present invention can be purchased from the market, including filtering equipment, such as vacuum pump filtration, ceramic Buchner funnel, and separatory funnel. The filter used is a 1000-mesh nano-grade nylon filter.

[0022] Filter cake refers to the aggregate of solid matter separated from the mixture by filtration during the separation of liquid and solid; these solid materials are usually gathered in the filter or filter cloth or filter screen in a cake-like form.

[0023] Example 1 A purification process for polyvinylidene fluoride polymerization products comprises the following specific steps: (1) Take 10 kg of polyvinylidene fluoride slurry prepared by the suspension method, stir it in a 20L kettle, set the speed to 120r / min, open the high-temperature closed circulation tank to heat the kettle to 55°C, maintain it for 20 minutes, put the polyvinylidene fluoride slurry into a stainless steel vacuum filter, start the vacuum pump to filter, and obtain a filter cake; (2) Take 100g of the filter cake, add it to a 2L beaker, add 2000ml of pure water, start mechanical stirring, set the speed to 500 r / min, maintain for 20 minutes, filter with a ceramic Büchner funnel to obtain a filter cake, and discard the washing water. Wash and filter twice with 20 times pure water, do not discard the washing water from the first filtration, directly wash the filter cake again, and discard it after filtering; the conductivity of the washing water after filtration is measured to be 8.7μS / cm; compared with Examples 2 and 3, the present embodiment uses the washing water from the second filtration to wash the filter cake again, and the conductivity of the washing water does not change significantly, indicating that this method is feasible and can save water.

[0024] (3) Using 1L of dimethyl carbonate heated to 80°C to dissolve the polyvinylidene fluoride filter cake, after complete dissolution, filter to remove insoluble particles, add 1L of 80°C ultrapure water to mix with the organic phase for washing, maintain the temperature and stir at 150r / min for 20min, let stand for 30min, collect the organic phase, and repeat the washing twice to obtain a dimethyl carbonate solution of polyvinylidene fluoride; (4) The organic phase (i.e., the dimethyl carbonate solution of polyvinylidene fluoride) is distilled under reduced pressure to remove the organic solvent, and the solid product is dried in an oven at a pressure of -0.1 MPa and a temperature of 80°C for 24 hours and then taken out to obtain polyvinylidene fluoride resin powder.

[0025] Example 2 A purification process for polyvinylidene fluoride polymerization products comprises the following specific steps: (1) Take 10 kg of polyvinylidene fluoride slurry prepared by the suspension method, stir it in a 20L kettle, set the speed to 120r / min, open the high-temperature closed circulation tank to heat the kettle to 50°C, maintain it for 30 minutes, put the polyvinylidene fluoride slurry into a stainless steel vacuum filter, start the vacuum pump to filter, and obtain a filter cake; (2) Take 100g of the above filter cake, add it to a 2L beaker, add 2000ml of pure water, start mechanical stirring, set the speed to 500 r / min, maintain for 20 minutes, filter with a ceramic Büchner funnel to obtain the filter cake. Repeat the washing and filtering twice with 20 times pure water (i.e., wash and filter once with 20 times pure water, pour out the washing water, and wash and filter once with 20 times pure water). The conductivity of the washed water after filtration is measured to be 6.3μS / cm; (3) Dissolve the polyvinylidene fluoride filter cake with 1 L of cyclohexanone heated to 70° C. After complete dissolution, filter to remove insoluble particles, add 0.8 L of 70° C. ultrapure water to mix with the organic phase for washing, maintain the temperature and stir at 150 r / min for 20 min, let stand for 30 min, collect the organic phase, and repeat washing twice to obtain a cyclohexanone solution of polyvinylidene fluoride; (4) The organic phase (i.e., the cyclohexanone solution of polyvinylidene fluoride) is distilled under reduced pressure to remove the organic solvent, and the solid product is dried in an oven at a pressure of -0.1 MPa and a temperature of 80°C for 24 hours and then taken out to obtain polyvinylidene fluoride resin powder.

[0026] Example 3 A purification process for polyvinylidene fluoride polymerization products comprises the following specific steps: (1) Take 10 kg of polyvinylidene fluoride slurry prepared by the emulsion method, stir it in a 20L kettle, set the speed to 120r / min, add 0.05% of the mass of the polyvinylidene fluoride slurry by aluminum nitrate, open the high-temperature closed circulation tank to heat the kettle to 50°C, maintain it for 30 minutes, put the polyvinylidene fluoride slurry into a stainless steel vacuum filter, start the vacuum pump to filter, and obtain a filter cake; (2) Take 100 g of the filter cake, add it to a 2L beaker, add 2000 ml of pure water, turn on the mechanical stirring, set the speed to 500 r / min, maintain for 20 min, filter with a ceramic Buchner funnel to obtain the filter cake, and then repeat the washing and filtration with 20 times pure water for 5 times. The conductivity of the washed water after filtration is measured to be 9.1 μS / cm; (3) Dissolve the polyvinylidene fluoride filter cake with 1 L of cyclohexanone heated to 70° C. After complete dissolution, filter to remove insoluble particles, add 0.8 L of 70° C. ultrapure water to mix with the organic phase for washing, maintain the temperature and stir at 150 r / min for 20 min, let stand for 30 min, collect the organic phase, and repeat washing twice to obtain a cyclohexanone solution of polyvinylidene fluoride; (4) The organic phase (i.e., the cyclohexanone solution of polyvinylidene fluoride) is distilled under reduced pressure to remove the organic solvent, and the solid product is dried in an oven at a pressure of -0.1 MPa and a temperature of 80°C for 24 hours and then taken out to obtain polyvinylidene fluoride resin powder.

[0027] Comparative Example 1 Comparative Example 1 Compared with Examples 1 to 3, the polyvinylidene fluoride filter cake was not subjected to the purification treatment of two-phase extraction.

[0028] A conventional post-treatment process for polyvinylidene fluoride polymerization products comprises the following specific steps: (1) Take 10 kg of polyvinylidene fluoride slurry prepared by the suspension method, stir it in a 20L kettle, set the speed to 120r / min, open the high-temperature closed circulation tank to heat the kettle to 55°C, maintain it for 20 minutes, put the polyvinylidene fluoride slurry into a stainless steel vacuum filter, start the vacuum pump to filter, and obtain a filter cake; (2) Take 100 g of the filter cake, add it to a 2L beaker, add 2000 ml of pure water, start mechanical stirring, set the speed to 500 r / min, maintain for 20 min, filter with a ceramic Buchner funnel to obtain the filter cake, then use 20 times pure water, repeat the washing and filtering 5 times, and measure the conductivity of the filtered washing water to be 7.3 μS / cm; (3) The filter cake was placed in a vacuum oven and dried for 24 hours at a pressure of -0.1 MPa and a temperature of 80°C to obtain polyvinylidene fluoride resin powder.

[0029] Comparison of metal ion content test results The ICP-MS method described in the invention title “A method for digesting polyvinylidene fluoride and measuring metal ions in polyvinylidene fluoride” with application number 202310683712.7 was used to detect the metal ion content of the polyvinylidene fluoride samples obtained in the above Examples 1-3 and Comparative Example 1, and the detection data were compared with the data of the comparative example samples. The results are shown in Table 1.

[0030] Table 1 Test results of different examples (Note: The unit of metal ion content in the table is mg / kg) It can be seen from the data in Table 1 that the metal ion content of the polyvinylidene fluoride resin in Examples 1-3 of the present invention is significantly lower than that in Comparative Example 1. The present invention can remove ionic impurities encapsulated inside and / or adsorbed on the surface of the polyvinylidene fluoride resin by using a two-phase extraction treatment method. Table 1 is a comparison of the metal ion content of polyvinylidene fluoride resin samples. Examples 1 to 3 all achieve a good metal ion removal effect. Compared with the data of the conventional treatment of Comparative Example 1, the metal ion removal effect is very significant.

[0031] The purification process of polyvinylidene fluoride polymerization products provided by the present invention can significantly reduce the ion content in the polyvinylidene fluoride polymerization products, and the prepared polyvinylidene fluoride product has high purity, beautiful appearance, uniform particle size, good fluidity, and no bad smell; and the method is easy to operate and reasonably designed, and has broad application prospects.

[0032] The embodiment of the present invention provides a washing scheme for polyvinylidene fluoride slurry prepared by suspension polymerization and emulsion polymerization. Because the suspension polymerization and emulsion polymerization contain more metal ions, they cannot meet the increasing demand; however, the washing method of the present invention is not limited to washing only the polymerization products of suspension polymerization and emulsion polymerization. When the polyvinylidene fluoride prepared by other polymerization methods contains more metal ions and needs to be cleaned, the present invention is also applicable.

[0033] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A purification process for polyvinylidene fluoride polymerization products, characterized in that: The polyvinylidene fluoride slurry produced by the polymerization reaction is filtered to obtain a polyvinylidene fluoride filter cake; the polyvinylidene fluoride filter cake is washed with pure water, and then the polyvinylidene fluoride filter cake is dissolved in an organic solvent, pure water is added to wash the organic phase, and impurities of the polyvinylidene fluoride are extracted into the aqueous phase, and the organic phase is allowed to stand for stratification, and the organic phase is collected, and the organic solvent is removed by distillation, and the mixture is dried to obtain the polyvinylidene fluoride filter cake; The organic solvent is insoluble in water but can dissolve the polyvinylidene fluoride.

2. The purification process of polyvinylidene fluoride polymerization product according to claim 1, characterized in that: The organic solvent includes one or both of dimethyl carbonate and cyclohexanone.

3. The purification process of polyvinylidene fluoride polymerization product according to claim 2, characterized in that: The amount of the organic solvent is 8 to 20 times that of the polyvinylidene fluoride filter cake.

4. The purification process of the polyvinylidene fluoride polymerization product according to any one of claims 1 to 3, characterized in that: The temperature of the organic solvent when dissolving polyvinylidene fluoride is 60-90°C.

5. The purification process of polyvinylidene fluoride polymerization product according to claim 1, characterized in that: The polyvinylidene fluoride filter cake is washed with pure water for 3 to 5 times, and the amount of water used for each washing is 15 to 25 times that of the polyvinylidene fluoride filter cake.

6. The purification process of polyvinylidene fluoride polymerization product according to claim 5, characterized in that: When the organic phase is washed with pure water, the temperature of the pure water for extracting impurities is kept consistent with the temperature of the organic phase, the volume of pure water is 0.5-1 times that of the organic phase, and the organic phase is washed 2-4 times.

7. The purification process of polyvinylidene fluoride polymerization product according to claim 1, characterized in that: Before filtering the polyvinylidene fluoride slurry, the polyvinylidene fluoride slurry is heated and stirred at 50-60° C. for 15-30 minutes.

8. The method for refining polyvinylidene fluoride polymerization products according to claim 1, characterized in that: The polymerization reaction is a suspension polymerization reaction or an emulsion polymerization reaction.

9. The purification process of polyvinylidene fluoride polymerization product according to claim 8, characterized in that: When the polyvinylidene fluoride slurry is prepared by emulsion polymerization, a coagulant is added after the polyvinylidene fluoride slurry is stirred.

10. The purification process of polyvinylidene fluoride polymerization product according to claim 1, characterized in that: The filter screen used in the filtration is a nano-grade nylon filter screen.

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