A method for preparing a MOFs mixed matrix membrane and its application in polyphenol purification

Abstract

The invention discloses a method for preparing a MOFs mixed matrix membrane and an application thereof in polyphenol purification, belonging to the technical field of membrane separation. The method for preparing the MOFs mixed matrix membrane comprises the following steps: (1) preparing MOFs particles: dissolving zinc acetate dihydrate in a solvent as solution 1, dissolving terephthalic acid and triethylamine in a solvent as solution 2, and dropping solution 1 into solution 2 to prepare MOFs particles; (2) preparing a casting solution: soaking the MOFs particles prepared in step 1) in a solvent in advance, adding polyethersulfone and polyethylene glycol-6000 to obtain a casting solution; (3) preparing a MOFs mixed matrix membrane: pouring the casting solution in step 2) onto a glass plate, scraping the film with a scraper, soaking, and forming a membrane sheet; the MOFs mixed matrix membrane of the invention has practical significance when applied to polyphenol purification. Compared with a commercial PES membrane, the invention improves the purification effect of polyphenols by membrane filtration, and can improve the purification effect of polyphenol feed solutions with different gradients by 10-20%.

Description

Technical Field

[0001] The invention relates to the technical field of membrane separation, and in particular to a method for preparing a MOFs mixed matrix membrane and application thereof in polyphenol purification. Background Art

[0002] Apple is a high-value fruit, and its planting areas are mainly distributed in Asia, America and Europe. China is the world's largest apple producing area. Apples are rich in nutrients, such as polyphenols (phenolic acids and flavonoids), triterpenes and phytosterols and other chemicals. In addition, they are rich in protein, vitamins, sugars and trace elements. With the development of processing technology, the output of apple by-products has gradually increased, and the amount of apple peel residue has also increased. Apple peel residue contains more nutrients than apples, such as carbohydrates, pectin, protein, fat, crude fiber, etc. In addition, it is rich in various amino acids, trace elements and polyphenols, but its current utilization rate is low, resulting in serious waste. Therefore, paying attention to the application of apple peel residue can not only recycle energy, but also increase the added value of apples.

[0003] The membrane filtration method for purifying polyphenols utilizes the selective permeability of the membrane to achieve the separation and purification of different components of the feed liquid. The membrane separation method requires the selection of a filter membrane with a suitable pore size according to the molecular weight of the substance to be separated. Mixed matrix membrane (MMM) is a new type of separation membrane that fills organic or inorganic fillers into polymers. It can successfully solve the problem that membrane flux and selectivity cannot be improved at the same time, and has been widely used in the field of filtration and purification. However, in the early attempts, some researchers found that after filling, gaps would form between the filling phase and the dispersed phase, which would reduce the separation performance of the membrane and could not meet the current higher purification requirements. Therefore, it is urgent to add high-performance filling materials to prepare high-performance filtration membranes, such as metal organic frameworks (MOFs).

[0004] MOFs is a new type of material composed of metal ions or metal clusters and organic ligands. This special structure allows the porosity of MOFs to be adjusted by the material composition and its proportion. The synthesis principle is to use the coordination reaction between metal ions and organic ligands to produce porous skeleton-type crystals with a microporous grid structure. Compared with general porous materials, MOFs has the following characteristics: 1. High porosity; 2. Large specific surface area; 3. Adjustable pore size.

[0005] At present, the membrane separation method is commonly used for polyphenol purification. According to the filter membrane material used, it is mainly divided into two categories: organic membrane and inorganic membrane. Organic polymer membranes (polyethersulfone membranes and polyvinylidene fluoride membranes) are usually short in service life, poor in thermal stability, and low in selectivity. These shortcomings limit their application in the field of membrane separation. And inorganic membranes (ceramic membranes and molecular sieve membranes) have difficult preparation methods and poor mechanical properties and stretchability. Both cannot overcome the bottleneck problem of improving membrane flux and selectivity at the same time. The present invention prepares a mixed matrix membrane with high purification performance by filling the prepared MOFs particles into PES, which is used for high-throughput and high-selectivity filtration separation, particularly applied to the efficient purification of polyphenols, and is conducive to promoting the further industrial application of membrane filtration technology. Summary of the invention

[0006] The object of the present invention is to provide a method for preparing a MOFs mixed matrix membrane and its application in polyphenol purification, so as to solve the problems raised in the above background technology.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing a MOFs mixed matrix membrane comprises the following steps:

[0009] (1) Preparation of MOFs particles: zinc acetate dihydrate is dissolved in a solvent and stirred evenly with a magnetic stirrer as solution 1; terephthalic acid and triethylamine are dissolved in a solvent and stirred evenly with a magnetic stirrer as solution 2; solution 1 is added dropwise to solution 2 and stirred with a magnetic stirrer until a uniformly dispersed solution is formed; a white precipitate is collected to prepare MOFs particles;

[0010] (2) preparing a casting solution: soaking the MOFs particles prepared in step 1) in a solvent in advance, adding polyethersulfone and polyethylene glycol-6000 thereto, heating and stirring until they are completely dissolved, to obtain a casting solution;

[0011] (3) Preparation of MOFs mixed matrix membrane: Pour the casting solution in step 2) onto a glass plate, adjust the scraper height to 200 μm, use the scraper to scrape the membrane, and then quickly immerse the glass plate in deionized water to form a membrane sheet after phase conversion. Take out the membrane sheet and store it in deionized water for subsequent use.

[0012] As a further technical solution of the present invention: the solvent is N,N-dimethylformamide.

[0013] As a further technical solution of the present invention: in step 1), the mass ratio between terephthalic acid and triethylamine in the solution 2 is 1.3:2.2.

[0014] As a further technical solution of the present invention: in step 2), the mass ratio of the added PES to polyethylene glycol-6000 is 2:1, and the configured MOFs particles account for 2.5-10% of the mass of the polymer.

[0015] As a further technical solution of the present invention: in step 2), after adding polyethersulfone and polyethylene glycol-6000, stir at 70°C at 600r / min for 6h until completely dissolved, and then let stand for 12h.

[0016] Another object of the present invention is to provide an application of a MOFs mixed matrix membrane in the purification of polyphenols, wherein the MOFs mixed matrix membrane is prepared by the above-mentioned method for preparing a MOFs mixed matrix membrane, and the application of the MOFs mixed matrix membrane in the purification of polyphenols comprises the following steps:

[0017] Preparation of apple peel powder: Dry fresh apple peel and grind it in a grinder;

[0018] Preparation of feed solution for membrane filtration: apple powder was dissolved in alcohol-water solution, cells were disrupted by ultrasound, and the supernatant was collected and diluted to a concentration;

[0019] Membrane filtration purification experiment: Use a membrane filtration device including a computer, an electronic balance, an ultrafiltration cup and an air compressor. Pour the feed liquid into the ultrafiltration cup, seal it, turn on the air compressor, adjust the output pressure of the air compressor, and turn on the computer to record the balance data. When there is no feed liquid left in the ultrafiltration cup, the membrane filtration purification process is over.

[0020] Analysis of membrane filtration purification effect: Collect the filtrate in the beaker to measure various physical and chemical parameters, compare them with the initial parameters of the feed liquid, and calculate the membrane filtration purification rate.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention prepares a mixed matrix membrane with high purification performance by filling the prepared MOFs particles into PES, which is used for high-throughput and high-selectivity filtration separation, especially for the efficient purification of polyphenols. The MOFs mixed matrix membrane prepared by the present invention has practical significance when actually applied to the purification of polyphenols. Compared with the commercial PES membrane, the present invention improves the purification effect of polyphenols by membrane filtration, and the purification effect of polyphenol feed solutions with different gradients can be improved by 10 to 20%. In addition, the preparation method of the MOFs mixed matrix membrane of the present invention is simple to operate, safe and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure of the membrane filtration device used in the embodiment of the present invention.

[0023] Notes on the accompanying drawings: 1-computer, 2-electronic balance, 3-ultrafiltration cup, 4-air compressor. DETAILED DESCRIPTION

[0024] The technical solution of this patent is further described in detail below in conjunction with specific implementation methods.

[0025] Example 1

[0026] A method for preparing a MOFs mixed matrix membrane comprises the following steps:

[0027] (1) Preparation of MOFs particles: 4.3 g zinc acetate dihydrate was dissolved in 125 mL N,N-dimethylformamide and stirred at 500 r / min for 5 min using a magnetic stirrer until completely dissolved, as solution 1. 1.3 g terephthalic acid and 2.2 g triethylamine were dissolved in 100 mL N,N-dimethylformamide and stirred at 500 r / min for 5 min using a magnetic stirrer until completely dissolved, as solution 2. Solution 1 was added dropwise to solution 2, and stirred at 500 r / min using a magnetic stirrer until a uniformly dispersed solution was formed, and further centrifuged at 3000 r / min for 10 min using a centrifuge, and the white precipitate was collected to prepare MOFs particles.

[0028] (2) Preparation of casting solution: 0.1 g of MOFs particles prepared in step (1) were soaked in 18.9 g of N,N-dimethylformamide for 12 h in advance, and stirred evenly at 500 r / min using a magnetic stirrer for 5 min, and then 4 g of PES and 2 g of polyethylene glycol-6000 were added thereto until completely dissolved, and the mass of MOFs particles was configured to account for 2.5-10% of the polymer, and heated and stirred for 6 h until completely dissolved to obtain a casting solution.

[0029] (3) Preparation of MOFs mixed matrix membrane: The casting solution was stirred at 70°C and 600 r / min for 6 h until completely dissolved. After standing for 12 h, it was poured onto a glass plate and the scraper height was adjusted to 200 μm. After scraping the film with the scraper, the glass plate was quickly immersed in deionized water. The casting solution underwent phase conversion in the water to form a membrane sheet. The membrane sheet was taken out and stored in deionized water for subsequent use.

[0030] The application of MOFs mixed matrix membrane in polyphenol purification includes the following steps:

[0031] (4) Preparation of apple peel powder: The collected fresh apple peels were placed in an oven and dried at 105°C until they were constant weight, and the moisture content was measured. The peels were ground into powder using a grinder for 1 minute.

[0032] (5) Preparation of membrane filtration feed solution: Apple powder and 25% alcohol aqueous solution were prepared into an apple peel polyphenol extraction solution at a ratio of 1:10, and then ultrasonicated at 450W for 30min to enhance the extraction of peel polyphenols. The obtained extract was centrifuged at 3000r / min for 10min. The supernatant was diluted with 25% alcohol aqueous solution according to the corresponding multiple.

[0033] (6) Membrane filtration purification experiment: A membrane filtration device including a computer 1, an electronic balance 2, an ultrafiltration cup 3 and an air compressor 4 was used. The feed liquid was poured into the ultrafiltration cup 3, which was sealed and then the air compressor 4 was turned on. The experimental pressure was adjusted to 2.6 bar. At the same time, the computer 1 was turned on to record the balance data. When there was no feed liquid left in the ultrafiltration cup 3, the membrane filtration purification process was completed. After the purification experiment was completed, the purified liquid in the beaker was collected for subsequent use.

[0034] (7) Analysis of membrane filtration purification effect: The polyphenol concentration and solid concentration of the purified liquid were measured and compared with the corresponding index parameters of the feed liquid. The polyphenol concentration was determined by comparing with the polyphenol standard curve; the solid concentration was determined by constant weight method.

[0035] Example 2

[0036] A method for preparing a MOFs mixed matrix membrane comprises the following steps:

[0037] (1) Preparation of MOFs particles: 4.3 g zinc acetate dihydrate was dissolved in 125 mL N,N-dimethylformamide and stirred at 500 r / min for 5 min using a magnetic stirrer until completely dissolved, as solution 1. 1.3 g terephthalic acid and 2.2 g triethylamine were dissolved in 100 mL N,N-dimethylformamide and stirred at 500 r / min for 5 min using a magnetic stirrer until completely dissolved, as solution 2. Solution 1 was added dropwise to solution 2, and stirred at 500 r / min using a magnetic stirrer until a uniformly dispersed solution was formed, and further centrifuged at 3000 r / min for 10 min using a centrifuge, and the white precipitate was collected to prepare MOFs particles.

[0038] (2) Preparation of casting solution: 0.2 g of MOFs particles prepared in step (1) were soaked in 18.8 g of N,N-dimethylformamide for 12 h in advance, and stirred evenly at 500 r / min using a magnetic stirrer for 5 min, and then 4 g of PES and 2 g of polyethylene glycol-6000 were added thereto until completely dissolved, and the mass of MOFs particles was configured to account for 2.5-10% of the polymer, and heated and stirred for 6 h until completely dissolved to obtain a casting solution.

[0039] (3) Preparation of MOFs mixed matrix membrane: The casting solution was stirred at 70°C and 600 r / min for 6 h until completely dissolved. After standing for 12 h, it was poured onto a glass plate and the scraper height was adjusted to 200 μm. After scraping the film with the scraper, the glass plate was quickly immersed in deionized water. The casting solution underwent phase conversion in the water to form a membrane sheet. The membrane sheet was taken out and stored in deionized water for subsequent use.

[0040] The application of MOFs mixed matrix membrane in polyphenol purification includes the following steps:

[0041] (4) Preparation of apple peel powder: The collected fresh apple peels were placed in an oven and dried at 105°C until they were constant weight, and the moisture content was measured. The peels were ground into powder using a grinder for 1 minute.

[0042] (5) Preparation of membrane filtration feed solution: Apple powder and 25% alcohol aqueous solution were prepared into an apple peel polyphenol extraction solution at a ratio of 1:10, and then ultrasonicated at 450W for 30min to enhance the extraction of peel polyphenols. The obtained extract was centrifuged at 3000r / min for 10min. The supernatant was diluted with 25% alcohol aqueous solution according to the corresponding multiple.

[0043] (6) Membrane filtration purification experiment: A membrane filtration device including a computer 1, an electronic balance 2, an ultrafiltration cup 3 and an air compressor 4 was used. The feed liquid was poured into the ultrafiltration cup 3, which was sealed and then the air compressor 4 was turned on. The experimental pressure was adjusted to 2.6 bar. At the same time, the computer 1 was turned on to record the balance data. When there was no feed liquid left in the ultrafiltration cup 3, the membrane filtration purification process was completed. After the purification experiment was completed, the purified liquid in the beaker was collected for subsequent use.

[0044] (7) Analysis of membrane filtration purification effect: The polyphenol concentration and solid concentration of the purified liquid were measured and compared with the corresponding index parameters of the feed liquid. The polyphenol concentration was determined by comparing with the polyphenol standard curve; the solid concentration was determined by constant weight method.

[0045] Example 3

[0046] A method for preparing a MOFs mixed matrix membrane comprises the following steps:

[0047] (1) Preparation of MOFs particles: 4.3 g zinc acetate dihydrate was dissolved in 125 mL N,N-dimethylformamide and stirred at 500 r / min for 5 min using a magnetic stirrer until completely dissolved, as solution 1. 1.3 g terephthalic acid and 2.2 g triethylamine were dissolved in 100 mL N,N-dimethylformamide and stirred at 500 r / min for 5 min using a magnetic stirrer until completely dissolved, as solution 2. Solution 1 was added dropwise to solution 2, and stirred at 500 r / min using a magnetic stirrer until a uniformly dispersed solution was formed, and further centrifuged at 3000 r / min for 10 min using a centrifuge, and the white precipitate was collected to prepare MOFs particles.

[0048] (2) Preparation of casting solution: 0.3 g of MOFs particles prepared in step (1) were soaked in 18.7 g of N,N-dimethylformamide for 12 h in advance, and stirred evenly at 500 r / min using a magnetic stirrer for 5 min, and then 4 g of PES and 2 g of polyethylene glycol-6000 were added thereto until completely dissolved, and the mass of MOFs particles was configured to account for 2.5-10% of the polymer, and heated and stirred for 6 h until completely dissolved to obtain a casting solution.

[0049] (3) Preparation of MOFs mixed matrix membrane: The casting solution was stirred at 70°C and 600 r / min for 6 h until completely dissolved. After standing for 12 h, it was poured onto a glass plate and the scraper height was adjusted to 200 μm. After scraping the film with the scraper, the glass plate was quickly immersed in deionized water. The casting solution underwent phase conversion in the water to form a membrane sheet. The membrane sheet was taken out and stored in deionized water for subsequent use.

[0050] The application of MOFs mixed matrix membrane in polyphenol purification includes the following steps:

[0051] (4) Preparation of apple peel powder: The collected fresh apple peels were placed in an oven and dried at 105°C until they were constant weight, and the moisture content was measured. The peels were ground into powder using a grinder for 1 minute.

[0052] (5) Preparation of membrane filtration feed solution: Apple powder and 25% alcohol aqueous solution were prepared into an apple peel polyphenol extraction solution at a ratio of 1:10, and then ultrasonicated at 450W for 30min to enhance the extraction of peel polyphenols. The obtained extract was centrifuged at 3000r / min for 10min. The supernatant was diluted with 25% alcohol aqueous solution according to the corresponding multiple.

[0053] (6) Membrane filtration purification experiment: A membrane filtration device including a computer 1, an electronic balance 2, an ultrafiltration cup 3 and an air compressor 4 was used. The feed liquid was poured into the ultrafiltration cup 3, which was sealed and then the air compressor 4 was turned on. The experimental pressure was adjusted to 2.6 bar. At the same time, the computer 1 was turned on to record the balance data. When there was no feed liquid left in the ultrafiltration cup 3, the membrane filtration purification process was completed. After the purification experiment was completed, the purified liquid in the beaker was collected for subsequent use.

[0054] (7) Analysis of membrane filtration purification effect: The polyphenol concentration and solid concentration of the purified liquid were measured and compared with the corresponding index parameters of the feed liquid. The polyphenol concentration was determined by comparing with the polyphenol standard curve; the solid concentration was determined by constant weight method.

[0055] Example 4

[0056] A method for preparing a MOFs mixed matrix membrane comprises the following steps:

[0057] (1) Preparation of MOFs particles: 4.3 g zinc acetate dihydrate was dissolved in 125 mL N,N-dimethylformamide and stirred at 500 r / min for 5 min using a magnetic stirrer until completely dissolved, as solution 1. 1.3 g terephthalic acid and 2.2 g triethylamine were dissolved in 100 mL N,N-dimethylformamide and stirred at 500 r / min for 5 min using a magnetic stirrer until completely dissolved, as solution 2. Solution 1 was added dropwise to solution 2, and stirred at 500 r / min using a magnetic stirrer until a uniformly dispersed solution was formed, and further centrifuged at 3000 r / min for 10 min using a centrifuge, and the white precipitate was collected to prepare MOFs particles.

[0058] (2) Preparation of casting solution: 0.4 g of MOFs particles prepared in step (1) were soaked in 18.6 g of N,N-dimethylformamide for 12 h in advance, and stirred evenly at 500 r / min for 5 min using a magnetic stirrer, and then 4 g of PES and 2 g of polyethylene glycol-6000 were added thereto until completely dissolved, and the mass of MOFs particles was configured to account for 2.5-10% of the polymer, and heated and stirred for 6 h until it was completely dissolved to obtain a casting solution.

[0059] (3) Preparation of MOFs mixed matrix membrane: The casting solution was stirred at 70°C and 600 r / min for 6 h until completely dissolved. After standing for 12 h, it was poured onto a glass plate and the scraper height was adjusted to 200 μm. After scraping the film with the scraper, the glass plate was quickly immersed in deionized water. The casting solution underwent phase conversion in the water to form a membrane sheet. The membrane sheet was taken out and stored in deionized water for subsequent use.

[0060] The application of MOFs mixed matrix membrane in polyphenol purification includes the following steps:

[0061] (4) Preparation of apple peel powder: The collected fresh apple peels were placed in an oven and dried at 105°C until they were constant weight, and the moisture content was measured. The peels were ground into powder using a grinder for 1 minute.

[0062] (5) Preparation of membrane filtration feed solution: Apple powder and 25% alcohol aqueous solution were prepared into an apple peel polyphenol extraction solution at a ratio of 1:10, and then ultrasonicated at 450W for 30min to enhance the extraction of peel polyphenols. The obtained extract was centrifuged at 3000r / min for 10min. The supernatant was diluted with 25% alcohol aqueous solution according to the corresponding multiple.

[0063] (6) Membrane filtration purification experiment: A membrane filtration device including a computer 1, an electronic balance 2, an ultrafiltration cup 3 and an air compressor 4 was used. The feed liquid was poured into the ultrafiltration cup 3, which was sealed and then the air compressor 4 was turned on. The experimental pressure was adjusted to 2.6 bar. At the same time, the computer 1 was turned on to record the balance data. When there was no feed liquid left in the ultrafiltration cup 3, the membrane filtration purification process was completed. After the purification experiment was completed, the purified liquid in the beaker was collected for subsequent use.

[0064] (7) Analysis of membrane filtration purification effect: The polyphenol concentration and solid concentration of the purified liquid were measured and compared with the corresponding index parameters of the feed liquid. The polyphenol concentration was determined by comparing with the polyphenol standard curve; the solid concentration was determined by constant weight method.

[0065] The MOFs mixed matrix membranes prepared in the above Examples 1-4 were used in the purification of polyphenols. The experimental data obtained are shown in Table 1 below.

[0066] Table 1

[0067] Example Polyphenol yield (%) Solids retention (%) 1 64.8 9.8 2 71.5 6.8 3 69.8 8.6 4 68.6 9.6

[0068] In summary: The present invention provides a method for preparing a MOFs mixed matrix membrane and its application in polyphenol purification. The MOFs mixed matrix membrane prepared by the present invention has practical significance when actually applied to polyphenol purification. Compared with the commercial PES membrane, the present invention improves the purification effect of polyphenols by membrane filtration, and the purification effect of polyphenol feed solutions with different gradients can be improved by 10-20%. The preparation method of the MOFs mixed matrix membrane of the present invention is simple to operate, safe and environmentally friendly. The present invention prepares a mixed matrix membrane with high purification performance by filling the prepared MOFs particles into PES, which is used for high-throughput and high-selectivity filtration separation, especially for efficient purification of polyphenols, and is conducive to promoting the further industrial application of membrane filtration technology.

[0069] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0070] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. Application of a MOFs mixed matrix membrane in polyphenol purification, characterized in that: The preparation method of the MOFs mixed matrix membrane comprises the following steps: Step 1: Preparation of MOFs particles: 4.3 g zinc acetate dihydrate was dissolved in 125 mL N, N-dimethylformamide, and stirred at 500 r / min for 5 min using a magnetic stirrer until completely dissolved, as solution 1; 1.3 g terephthalic acid and 2.2 g triethylamine were dissolved in 100 mL N, N-dimethylformamide, and stirred at 500 r / min for 5 min using a magnetic stirrer until completely dissolved, as solution 2; solution 1 was added dropwise to solution 2, and stirred at 500 r / min using a magnetic stirrer until a uniformly dispersed solution was formed, and further centrifuged at 3000 r / min for 10 min using a centrifuge, and the white precipitate was collected to prepare MOFs particles; Step 2: Prepare a casting solution: soak 0.4 g of the MOFs particles prepared in step 1 in 18.6 g of N,N-dimethylformamide for 12 h in advance, stir them evenly at 500 r / min for 5 min using a magnetic stirrer, then add 4 g of PES and 2 g of polyethylene glycol-6000 until they are completely dissolved, configure the MOFs particles to account for 2.5-10% of the mass of the polymer, heat and stir for 6 h until they are completely dissolved, and obtain a casting solution; Step 3: Preparation of MOFs mixed matrix membrane: Stir the casting solution at 70°C and 600r / min for 6h until it is completely dissolved, let it stand for 12h, pour it on a glass plate, adjust the scraper height to 200μm, scrape the film with the scraper, and then quickly soak the glass plate in deionized water. The casting solution undergoes phase conversion in water to form a membrane sheet. Take out the membrane sheet and store it in deionized water for subsequent use; The application of the MOFs mixed matrix membrane in polyphenol purification comprises the following steps: Step 4: Preparation of apple peel powder: The collected fresh apple peels were placed in an oven at 105°C and dried to a constant weight, the moisture content was measured, and the peels were ground into powder using a grinder for 1 minute; Step 5: Preparation of membrane filtration feed solution: apple powder and 25% alcohol aqueous solution are prepared into apple peel polyphenol extraction solution in a ratio of 1:10, and then 450W ultrasound is used for 30 minutes to enhance the extraction of peel polyphenols. The obtained extract is centrifuged at 3000r / min for 10 minutes, and the supernatant is diluted with 25% alcohol aqueous solution according to the corresponding multiple; Step 6: Membrane filtration purification experiment: using a membrane filtration device including a computer (1), an electronic balance (2), an ultrafiltration cup (3) and an air compressor (4), pouring the feed liquid into the ultrafiltration cup (3), sealing it and turning on the air compressor (4), adjusting the experimental pressure to 2.6 bar, and turning on the computer (1) to record the balance data. When there is no feed liquid left in the ultrafiltration cup (3), the membrane filtration purification process is completed. After the purification experiment is completed, collect the purified liquid in the beaker for subsequent use; Step 7: Analysis of membrane filtration purification effect: Determine the polyphenol concentration and solid concentration of the purified liquid, and compare them with the corresponding index parameters of the feed liquid. The polyphenol concentration is determined by comparing with the polyphenol standard curve; the solid concentration is determined by the constant weight method.

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