Modified PVDF (polyvinylidene fluoride) membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of polyether refining, and particularly relates to a modified PVDF (polyvinylidene fluoride) membrane and a preparation method and application thereof, and the modified PVDF membrane is prepared from the following raw materials in parts by mass: 13-15 parts of polyvinylidene fluoride; 85 to 87 parts of N, N-dimethyl formamide; 0.3 to 0.5 part of an adsorbent; and 1 to 1.2 parts of a pore-foaming agent. The modified PVDF membrane disclosed by the invention is applied to polyether post-treatment of a KOH process, and compared with conventional physical adsorption, the modified PVDF membrane has stronger adsorption capacity on K < + >, and the production efficiency is improved. The invention also provides a preparation method thereof.

Description

Technical Field

[0001] The invention belongs to the technical field of polyether refining, and specifically relates to a modified PVDF membrane and a preparation method and application thereof. Background Art

[0002] The development of polyether polyols began in the 1930s, and was initially used in the field of non-ionic surfactants. In 1953, DuPont first applied polyether polyols to polyurethane soft foams; then Wyandot Chemical Company of the United States industrialized polyether polyurethane foams in 1957. Over the past few decades, polyether polyols have developed rapidly, and their output has increased year by year.

[0003] At present, the processes used by various manufacturers to produce polyether polyols are different, but in summary, they can be generally divided into three categories according to the different catalytic systems used in the polymerization reaction: (1) amine process; (2) KOH process; (3) bimetallic DMC process. Among them, the polymerization reaction mechanism of the KOH process belongs to anionic polymerization. The reaction process involves chain initiation, chain growth and proton transfer. Once the reaction is initiated, the rate of chain growth reaction is very fast in the initial growth stage. As the reaction continues, the transfer to small molecules intensifies, inhibiting the formation of high molecular weight polyether polyols. Therefore, the synthesized polyether polyols have the characteristics of low molecular weight and wide molecular weight distribution. After neutralization in the KOH post-treatment process, K3PO4 is obtained, which is usually adsorbed and precipitated by aluminum silicate or magnesium aluminum silicate and then filtered to obtain refined polyether. If the by-product K of the KOH process exists in the polyether + , which will affect the foaming speed of polyether, thus affecting the quality and performance of its downstream product polyurethane. Therefore, how to efficiently remove potassium is one of the key points of KOH process polyether post-treatment. At present, the conventional post-treatment is to add physical adsorbents, such as activated alumina and magnesium aluminum silicate, into polyether to remove K by adsorption, sedimentation and filtration. + This increases the complexity of the process, lengthens the post-processing cycle, and affects production efficiency. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a modified PVDF membrane, which is applied to the post-treatment of polyether in the KOH process. Compared with conventional physical adsorption, the modified PVDF membrane has a better effect on KOH. + The adsorption capacity of the polyol is stronger and the production efficiency is improved. The invention also provides a preparation method thereof.

[0005] The modified PVDF membrane of the present invention is prepared from the following raw materials in parts by weight: Polyvinylidene fluoride (PVDF), 13-15 parts; N,N-dimethylformamide (DMF), 85-87 parts; Adsorbent, 0.3-0.5 parts; Porogen, 1-1.2 parts.

[0006] Preferably, the adsorbent is magnesium silicate, and the magnesium silicate is further preferably magnesium aluminum silicate.

[0007] Preferably, the porogen is lithium chloride (LiCl).

[0008] The method for preparing the modified PVDF membrane of the present invention comprises the following steps: (1) placing the adsorbent and the porogen in N,N-dimethylformamide and ultrasonically dispersing them to obtain a mixed solution; (2) drying the polyvinylidene fluoride powder and placing it in a mixed solution for blending to obtain a casting solution; (3) Apply the casting solution to a glass plate, scrape the film with a scraper, and place it in an ethanol-water solution for phase conversion. After drying, a 0.2-0.3 μm PVDF membrane is obtained.

[0009] The modified PVDF membrane of the present invention is used in the post-treatment of polyether refined by KOH process.

[0010] Preferably, the post-treatment is desalination.

[0011] Preferably, the modified PVDF membrane is used as a filter membrane to filter the polyether during desalination.

[0012] Compared with the prior art, the present invention has the following beneficial effects: Different from conventional adsorbent physical adsorption sedimentation filtration, the present invention applies modified PVDF membrane to the KOH process for polyether desalination, thereby improving the K removal efficiency. + The polyether to be desalted is directly filtered using the modified PVDF membrane, which simplifies the post-treatment desalination process, shortens the post-treatment cycle, and improves production efficiency. DETAILED DESCRIPTION

[0013] The technical solution of the present invention will be clearly and completely described below in conjunction with embodiments.

[0014] Unless otherwise specified, all raw materials used in the examples are commercially available.

[0015] Example 1 The method for preparing the modified PVDF membrane comprises the following steps (the following are all weight parts): (1) 0.3 parts of magnesium aluminum silicate and 1.2 parts of porogen LiCl were placed in 85 parts of DMF and ultrasonically dispersed for 30 minutes to obtain a mixed solution; (2) 15 parts of PVDF powder (number average molecular weight 10 6) After being fully dried, the mixture is placed in a mixed solution and mixed, magnetically stirred at 65°C for 12 hours, and degassed in a forced air drying oven at 50°C for 12 hours to obtain a casting solution; (3) The casting solution was applied to a glass plate, and the film was scraped with a scraper and then placed in an ethanol aqueous solution (the mass ratio of water to ethanol was 1:2) for phase conversion for 24 hours. After drying, the modified PVDF membrane with a thickness of 0.2 μm was obtained. Example 2 The method for preparing the modified PVDF membrane comprises the following steps (the following are all weight parts): (1) 0.4 parts of magnesium aluminum silicate and 1.1 parts of porogen LiCl were placed in 86 parts of DMF and ultrasonically dispersed for 30 minutes to obtain a mixed solution; (2) 14 parts of PVDF powder (number average molecular weight 10 6 ) After being fully dried, the mixture is placed in a mixed solution and mixed, magnetically stirred at 65°C for 12 hours, and degassed in a forced air drying oven at 50°C for 12 hours to obtain a casting solution; (3) The casting solution was applied to a glass plate, and the film was scraped with a scraper and then placed in an ethanol aqueous solution (the mass ratio of water to ethanol was 1:2) for phase conversion for 24 hours. After drying, the modified PVDF membrane with a thickness of 0.2 μm was obtained.

[0016] Example 3 The method for preparing the modified PVDF membrane comprises the following steps (the following are all weight parts): (1) 0.5 parts of magnesium aluminum silicate and 1.0 parts of porogen LiCl were placed in 87 parts of DMF and ultrasonically dispersed for 30 minutes to obtain a mixed solution; (2) 13 parts of PVDF powder (number average molecular weight 10 6 ) After being fully dried, the mixture is placed in a mixed solution and mixed, magnetically stirred at 65°C for 12 hours, and degassed in a forced air drying oven at 50°C for 12 hours to obtain a casting solution; (3) The casting solution was applied to a glass plate, and the film was scraped with a scraper and then placed in an ethanol aqueous solution (the mass ratio of water to ethanol was 1:2) for phase conversion for 24 hours. After drying, the modified PVDF membrane with a thickness of 0.2 μm was obtained.

[0017] Example 4 The method for preparing the modified PVDF membrane comprises the following steps (the following are all weight parts): (1) 0.5 parts of magnesium aluminum silicate and 1.0 parts of porogen LiCl were placed in 87 parts of DMF and ultrasonically dispersed for 30 minutes to obtain a mixed solution; (2) 13 parts of PVDF powder (number average molecular weight 10 6 ) After being fully dried, the mixture is placed in a mixed solution and mixed, magnetically stirred at 65°C for 12 hours, and degassed in a forced air drying oven at 50°C for 12 hours to obtain a casting solution; (3) The casting solution was applied to a glass plate, and the film was scraped with a scraper and then placed in an ethanol aqueous solution (the mass ratio of water to ethanol was 1:2) for phase conversion for 24 hours. After drying, the modified PVDF membrane with a thickness of 0.3 μm was obtained.

[0018] Comparative Example 1 In this comparative example 1, magnesium aluminum silicate adsorbent, which is a common adsorbent in the production of polyether by KOH process, is used as the adsorbent for post-treatment of refined polyether.

[0019] Performance Testing In the laboratory, 200g glycerol was used as the initiator, 6g KOH catalyst was added, and 600g propylene oxide was polymerized in the reactor to obtain a KOH process crude polyether with a hydroxyl value of 450mg KOH / g and a viscosity of 300-500mPa·s (25°C). After neutralization with phosphoric acid, K-containing + Polyether, neutralized with phosphoric acid to obtain K-containing + Polyether.

[0020] The modified PVDF membranes obtained in Examples 1-3 were cut into pieces and placed on three ceramic funnels of the same suction flasks, respectively. + The modified PVDF membrane was completely fitted into the funnel by wetting with polyether; three portions of 500 g of K-containing + The polyether was filtered, and the timing was started from the first drop of polyether liquid dripping, and the timing was stopped until no liquid dripped, and the filtration time was recorded; The magnesium aluminum silicate adsorbent of Comparative Example 1 was added with 500 g of K-containing + polyether (the amount added is the conventional amount used in production, i.e. 0.3% of the mass of the polyether to be post-treated), stirred for 30 minutes, and then filtered with the same type of filtration equipment as in Example 1-3 (using qualitative filter paper), with the first drop of polyether liquid dripping as the starting point of timing, until no liquid drips and stop timing, record the filtration time; The K content of the polyethers obtained after filtration in Examples 1-4 and Comparative Example 1 was determined by flame photometry. + The results are shown in Table 1.

[0021] Table 1 Performance test table of Examples 1-4 and Comparative Example 1

[0022] From Table 1, by comparing Examples 1-3, the present invention shows that as the amount of magnesium aluminum silicate added as the modifier increases, the residual K in the polyether + The content of K in Example 3 is gradually reduced, but the K in Example 2 is +The content of magnesium aluminum silicate has no obvious advantage, and the filtration time is relatively longer. This may be because as the content of magnesium aluminum silicate increases, the adsorption capacity of the modified PVDF membrane is enhanced, which has a blocking effect on the membrane pores, resulting in a longer filtration time. + By comparing Examples 1-4 with Comparative Example 1, compared with the prior art physical adsorption filtration, which still requires stirring and filtration after the adsorbent is added, the PVDF membrane of the present invention has a great advantage in that it simplifies the post-treatment desalination process, shortens the post-treatment cycle, improves production efficiency, and has a stronger potassium removal capacity.

Claims

1. A modified PVDF membrane, characterized in that: Prepared from the following raw materials in parts by weight: Polyvinylidene fluoride, 13-15 parts; N,N-dimethylformamide, 85-87 parts; Adsorbent, 0.3-0.5 parts; Porogen, 1-1.2 parts.

2. The modified PVDF membrane according to claim 1, characterized in that The adsorbent is magnesium silicate.

3. The modified PVDF membrane according to claim 1, characterized in that The porogen is lithium chloride.

4. A method for preparing a modified PVDF membrane according to any one of claims 1 to 3, characterized in that: The steps include: (1) placing the adsorbent and the porogen in N,N-dimethylformamide and ultrasonically dispersing them to obtain a mixed solution; (2) drying the polyvinylidene fluoride powder and placing it in a mixed solution for blending to obtain a casting solution; (3) Apply the casting solution to a glass plate, scrape the film with a scraper, and place it in an ethanol-water solution for phase conversion. After drying, a 0.2-0.3 μm PVDF membrane is obtained.

5. Use of the modified PVDF membrane according to any one of claims 1 to 3 in the post-treatment of polyether refined by KOH process.

6. The use according to claim 5, characterized in that: The post-treatment is desalination.

7. The use according to claim 6, characterized in that: The modified PVDF membrane is used as a filter membrane to filter polyether during desalination.

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