High-whiteness cross-linked povidone, preparation method therefor and use thereof

Abstract

A high-whiteness cross-linked povidone, a preparation method therefor and a use thereof. The preparation method comprises the following steps: mixing cross-linked povidone, water, a Lewis acid and an oxidizing agent, and reacting to obtain the high-whiteness cross-linked povidone. By means of an aqueous solution system, the Lewis acid is used to enhance the oxidation effect of the oxidizing agent, so as to implement thorough oxidative decomposition of impurities such as N-vinyl pyrrolidone, acetaldehyde and aldehyde condensates adsorbed in the cross-linked povidone, so that the problem of yellowing of a cross-linked povidone product is fundamentally solved; in addition, the cross-linked povidone is further subjected to strong oxidation bleaching, so that the whiteness of the cross-linked povidone product is remarkably improved, and the whiteness value can reach 90%; and according to the preparation method, the quality of the product will not be affected due to additional introduction of impurities, the product can meet the requirements of pharmacopoeia, the process is simple, the process energy consumption is low, the cost is low, less pollution is produced, and the method is environmentally-friendly.

Description

A high-whiteness cross-linked polyvinylpyrrolidone and its preparation method and application Technical Field

[0001] The embodiments of the present application relate to the field of polymer polymerization technology, for example, a high-whiteness cross-linked polyvinylpyrrolidone and its preparation method and application. Background Art

[0002] Cross-linked polyvinyl pyrrolidone (PVPP) is a highly absorbent resin with strong water absorption and retention capabilities. Its water absorption capacity can reach several times, or even dozens of times, its own weight. Hydrogen bonds are formed between the matrix and the adsorbed water, preventing the adsorbed water from escaping even under certain pressures, making it recyclable and reusable. PVPP's excellent physiological safety, water absorption, water insolubility, and complexing properties hold broad application prospects in the pharmaceutical and food industries.

[0003] Cross-linked polyvinylpyrrolidone (PVPP) is a porous, granular, nonionic product with strong interfacial activity, produced through a unique popcorn polymerization process. Popcorn polymerization is a unique polymerization method whose reaction mechanism is still unclear. The resulting polymer is highly cross-linked, but the crosslinks are primarily formed by the entanglement of long molecular chains. Currently, cross-linked polyvinylpyrrolidone (NVP) is generally produced through popcorn polymerization using an alkali metal hydroxide, purified water, and N-vinylpyrrolidone (NVP). However, the PVPP produced by this method may absorb small amounts of impurities such as residual mono-NVP, acetaldehyde, and aldehyde condensates. The semi-finished PVPP produced by this process is alkaline. When heated with alkali, these impurities, such as residual mono-NVP, acetaldehyde, and aldehyde condensates, undergo condensation and dehydration reactions to form crotonaldehyde. Crotonaldehyde, upon exposure to air, undergoes oxidation to form crotonic acid, causing the PVPP product to yellow. Furthermore, the resulting crotonaldehyde can further condense with acetaldehyde to form a semi-solid resin, which also contributes to the yellowing of the PVPP. The whiteness of cross-linked polyvinylpyrrolidone (PVPP) has decreased, affecting product sales.

[0004] CN106800616A discloses a method for preparing high-bulk-density cross-linked polyvinylpyrrolidone. The method optimizes the preparation of conventional cross-linked polyvinylpyrrolidone to obtain high-bulk-density cross-linked polyvinylpyrrolidone, and the bulk density can reach 0.35 g / mL-0.4 g / mL. The optimization method includes: polymerization reaction and drying. The technical effect is that under the traditional preparation method of cross-linked polyvinylpyrrolidone, a simple optimized preparation method can be used to produce high-bulk-density cross-linked polyvinylpyrrolidone, and the bulk density can reach 0.35 g / mL-0.4 g / mL. Not only is the bulk density increased, but the fluidity is also greatly improved. However, the cross-linked polyvinylpyrrolidone is prone to yellowing and has poor whiteness, which affects its use.

[0005] CN106883333A discloses a method for preparing large-particle cross-linked polyvinylpyrrolidone. The method comprises the following steps: adding 3.0% alkali metal hydroxide to a mixture of monomer NVP and water at a mass ratio of 9:1, introducing nitrogen protection, heating to 55°C to initiate popcorn polymerization, and stirring at 60 rpm. When the temperature rises to 70°C, adding 0.5%-5.0% of a forming agent, and reducing the stirring speed to 20 rpm. After the particles are formed, they are washed and dried to obtain cross-linked polyvinylpyrrolidone with a particle size between 140 and 200 μm. The forming agent is generally at least one of tert-butyl hydroperoxide, benzoyl peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, and tert-butyl perbenzoate. By adding the forming agent during the polymerization process, the surface tension of the particles during formation is changed, so that the particles are suspended in the aqueous phase in the form of larger particles, and the product particle size between 140 and 200 μm accounts for more than 80%. Residual NVP in the synthesis process increases the possibility of yellowing of the product.

[0006] Since the related art cross-linked polyvinylpyrrolidone has problems such as yellowing and poor whiteness, it is an urgent problem to be solved in the field to develop a cross-linked polyvinylpyrrolidone with high whiteness that is not prone to yellowing and has a simple preparation process to meet the application needs of cross-linked polyvinylpyrrolidone.

[0007] Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] The present application provides a high-whiteness cross-linked polyvinylpyrrolidone and its preparation method and application. The preparation method uses an aqueous solution system and a Lewis acid to enhance the oxidizing action of an oxidant, thereby completely oxidizing and decomposing impurities such as NVP, acetaldehyde, and aldehyde condensates adsorbed in PVPP, and further strongly oxidatively bleaching the PVPP, thereby significantly improving the whiteness of the PVPP.

[0010] In a first aspect, an embodiment of the present application provides a method for preparing high-whiteness cross-linked polyvinylpyrrolidone, the method comprising the following steps: mixing cross-linked polyvinylpyrrolidone, water, a Lewis acid, and an oxidant, and reacting to obtain the high-whiteness cross-linked polyvinylpyrrolidone.

[0011] Preferably, the Lewis acid comprises any one or a combination of at least two of aluminum chloride, ferric chloride, zinc chloride, boron trifluoride, sulfur trioxide, ferric bromide or magnesium bromide.

[0012] Preferably, the oxidant comprises any one of peroxide, tert-butyl peroxide or persulfate, or a combination of at least two thereof.

[0013] Preferably, the oxidant comprises any one of peracetic acid, tert-butyl hydroperoxide, di-tert-butyl hydroperoxide, sodium persulfate, ammonium persulfate or potassium persulfate, or a combination of at least two thereof.

[0014] The cross-linked polyvinylpyrrolidone includes any one of PVPP XL finished product, PVPP XL-10 finished product or cross-linked polyvinylpyrrolidone polymer intermediate.

[0015] Preferably, the mass ratio of the cross-linked polyvinylpyrrolidone to water is 100:(500-900), for example, it can be 100:500, 100:600, 100:700, 100:800, 100:900, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0016] Preferably, the mass ratio of the cross-linked polyvinylpyrrolidone to the Lewis acid is 100:(0.001-0.01), for example, it can be 100:0.001, 100:0.002, 100:0.003, 100:0.004, 100:0.005, 100:0.006, 100:0.007, 100:0.008, 100:0.009, 100:0.01, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0017] Preferably, the mass ratio of the cross-linked polyvinylpyrrolidone to the oxidant is 100:(0.1-1), for example, it can be 100:0.1, 100:0.2, 100:0.3, 100:0.4, 100:0.5, 100:0.6, 100:0.7, 100:0.8, 100:0.9, 100:1, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0018] Preferably, the reaction temperature is 70-90°C, for example, it can be 70°C, 75°C, 80°C, 85°C, 90°C, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0019] Preferably, the reaction time is 30-60 min, for example, 30 min, 40 min, 50 min, 60 min, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0020] Preferably, after the reaction is completed, the process further comprises washing with water, alkalization, centrifugal dehydration, and drying to obtain the high-whiteness cross-linked polyvinylpyrrolidone.

[0021] Preferably, the water washing comprises adding hot water and stirring.

[0022] Preferably, the temperature of the hot water is 60-80°C, for example, it can be 60°C, 65°C, 70°C, 75°C, 80°C, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0023] Preferably, the mass ratio of the cross-linked polyvinylpyrrolidone to hot water is 1:(5-9), for example, it can be 1:5, 1:6, 1:7, 1:8, 1:9, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0024] In the present application, water washing is performed at least once, and the water washing includes heating water, dehydrating, adding hot water, stirring evenly, and then alkalizing after the soluble matter in the water sampled and tested is less than 1%. After alkalization, it can be directly transferred to a centrifuge for centrifugal dehydration, and then a drying step is performed.

[0025] Preferably, the stirring rate is 500-1000r / min, for example, it can be 500r / min, 600r / min, 700r / min, 800r / min, 900r / min, 1000r / min, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0026] Preferably, the stirring time is 30-60 min, for example, it can be 30 min, 40 min, 50 min, 60 min, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0027] Preferably, the alkalization comprises using an alkaline solution to adjust the pH value to 7.0-9.0, for example, 7.0, 7.5, 8.0, 8.5, 9.0, and specific values ​​between the above points. Due to space limitations and for the sake of brevity, this application no longer exhaustively lists the specific points included in the range.

[0028] Preferably, the alkaline solution comprises concentrated ammonia water and / or sodium hydroxide solution.

[0029] Preferably, the drying method comprises air flow drying.

[0030] Preferably, the air inlet temperature of the air flow drying is 150-180°C, for example, it can be 150°C, 160°C, 170°C, 180°C, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0031] Preferably, the outlet temperature of the air flow drying is 70-90°C, for example, it can be 70°C, 75°C, 80°C, 85°C, 90°C, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0032] Preferably, the preparation method specifically comprises the following steps:

[0033] Mixing cross-linked polyvinylpyrrolidone, water, Lewis acid and oxidant, reacting at 70-90° C. for 30-60 minutes, washing with water, alkalizing to adjust the pH to 7.0-9.0, centrifuging and dehydrating, and air drying to obtain the high-whiteness cross-linked polyvinylpyrrolidone;

[0034] The Lewis acid includes any one of aluminum chloride, ferric chloride, zinc chloride, boron trifluoride, sulfur trioxide, ferric bromide or magnesium bromide, or a combination of at least two of them; the oxidant includes any one of peracetic acid, tert-butyl hydroperoxide, di-tert-butyl hydroperoxide, sodium persulfate, ammonium persulfate or potassium persulfate, or a combination of at least two of them.

[0035] The "high whiteness" in the high-whiteness cross-linked polyvinylpyrrolidone described in this application refers to a whiteness of more than 80%, for example, it can be 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99%, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0036] In a second aspect, an embodiment of the present application provides a high-whiteness cross-linked polyvinylpyrrolidone, which is prepared using the preparation method described in the first aspect.

[0037] In a third aspect, an embodiment of the present application provides an application of the high-whiteness cross-linked polyvinylpyrrolidone as described in the first aspect in the preparation of medicines and foods.

[0038] Compared with the related art, the embodiments of the present application have the following beneficial effects:

[0039] The high-whiteness cross-linked polyvinylpyrrolidone provided in the embodiments of the present application uses an aqueous solution system and a Lewis acid to enhance the oxidizing action of the oxidant, thereby completely oxidizing and decomposing impurities such as NVP, acetaldehyde, and aldehyde condensates adsorbed in PVPP, thereby fundamentally solving the problem of yellowing of PVPP products. At the same time, PVPP is further subjected to strong oxidative bleaching, so that the whiteness of the PVPP product is significantly improved, and the whiteness value can reach 90%. The preparation method does not introduce additional impurities that affect the quality of the product. The product can meet the requirements of the pharmacopoeia, and the process is simple, low in process energy consumption, low in cost, low in pollution, and green and environmentally friendly.

[0040] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0041] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0042] The experimental materials used in the examples and comparative examples of this application are as follows:

[0043] Cross-linked polyvinylpyrrolidone, brand name PVPP XL, manufacturer Yuang Technology Co., Ltd.; brand name PVPP XL, manufacturer Yanhong Sifang; brand name Kollidon CL, manufacturer BASF.

[0044] Example 1

[0045] This embodiment provides a method for preparing high-whiteness cross-linked polyvinylpyrrolidone, the method comprising the following steps:

[0046] (1) Add 100 kg PVPP and 500 kg purified water into the reactor, heat to 70 °C, start stirring, and set the speed to 500 rpm;

[0047] (2) Add 0.001 kg of aluminum chloride and 0.1 kg of peracetic acid to the reactor, continue stirring for 30 minutes, and then stop stirring;

[0048] (3) Transfer the reaction mixture to a clean filter equipped with a 1000-mesh filter cloth, start stirring, and vacuum dehydrate;

[0049] (4) Add 500 kg of hot water at 60°C to the cleaning filter, control the speed to 500 rpm, stir and react for 30 minutes, and then take a sample to test the soluble matter in the water, which is 0.9%;

[0050] (5) After adding concentrated ammonia water to adjust the pH of the material to 7.0, the material in the cleaning filter is transferred to a centrifuge for centrifugal dehydration;

[0051] (6) Control the air inlet temperature at 150-180°C and the air outlet temperature at 70-90°C, and obtain a high-whiteness cross-linked polyvinylpyrrolidone product by air drying.

[0052] Example 2

[0053] This embodiment provides a method for preparing high-whiteness cross-linked polyvinylpyrrolidone, the method comprising the following steps:

[0054] (1) Add 100 kg PVPP and 600 kg purified water into the reactor, heat to 75 °C, start stirring, and set the speed to 600 rpm;

[0055] (2) Add 0.001 kg of aluminum chloride, 0.001 kg of ferric chloride, 0.001 kg of zinc chloride, and 0.3 kg of tert-butyl hydroperoxide to the reactor, continue stirring for 40 minutes, and then stop stirring;

[0056] (3) Transfer the reaction mixture to a clean filter equipped with a 1000-mesh filter cloth, start stirring, and vacuum dehydrate;

[0057] (4) Add 600 kg of hot water at 65°C to the cleaning filter, control the speed to 600 rpm, stir and react for 40 minutes, and then take a sample to test the soluble matter in the water, which is 0.8%;

[0058] (5) After adding concentrated ammonia water to adjust the pH of the material to 7.5, the material in the cleaning filter is transferred to a centrifuge for centrifugal dehydration;

[0059] (6) Control the air inlet temperature at 150-180°C and the air outlet temperature at 70-90°C, and obtain a high-whiteness cross-linked polyvinylpyrrolidone product by air drying.

[0060] Example 3

[0061] This embodiment provides a method for preparing high-whiteness cross-linked polyvinylpyrrolidone, the method comprising the following steps:

[0062] (1) Add 100 kg PVPP and 700 kg purified water into the reactor, heat to 80 °C, start stirring, and set the speed to 700 rpm;

[0063] (2) Add 0.001 kg of ferric chloride, 0.002 kg of zinc chloride, 0.002 kg of ferric bromide, 0.25 kg of tert-butyl hydroperoxide, and 0.3 kg of di-tert-butyl hydroperoxide to the reactor, continue stirring for 45 minutes, and then stop stirring;

[0064] (3) Transfer the reaction mixture to a clean filter equipped with a 1000-mesh filter cloth, start stirring, and vacuum dehydrate;

[0065] (4) Add 700 kg of hot water at 70°C to the cleaned filter, control the speed to 700 rpm, stir and react for 45 minutes, and then vacuum dehydrate;

[0066] (5) Repeat step (4) once more and take a sample to detect 0.6% of soluble matter in water;

[0067] (6) After adding concentrated ammonia water to adjust the pH of the material to 8.0, the material in the cleaning filter is transferred to a centrifuge for centrifugal dehydration;

[0068] (7) Control the air inlet temperature at 150-180°C and the air outlet temperature at 70-90°C, and obtain a high-whiteness cross-linked polyvinylpyrrolidone product by air drying.

[0069] Example 4

[0070] This embodiment provides a method for preparing high-whiteness cross-linked polyvinylpyrrolidone, the method comprising the following steps:

[0071] (1) Add 100 kg PVPP and 800 kg purified water into the reactor, heat to 80 °C, start stirring, and set the speed to 800 rpm;

[0072] (2) Add 0.004 kg of sulfur trioxide, 0.004 kg of boron trifluoride, 0.2 kg of sodium persulfate, 0.3 kg of ammonium persulfate, and 0.3 kg of potassium persulfate to the reactor, continue stirring for 45 minutes, and then stop stirring;

[0073] (3) Transfer the reaction mixture to a clean filter equipped with a 1000-mesh filter cloth, start stirring, and vacuum dehydrate;

[0074] (4) Add 700 kg of hot water at 70°C to the cleaned filter, control the speed to 800 rpm, stir and react for 45 minutes, and then vacuum dehydrate;

[0075] (5) Repeat step (4) once more and take a sample to detect 0.8% of soluble matter in water;

[0076] (6) After adding sodium hydroxide solution to adjust the pH of the material to 8.5, the material in the cleaning filter is transferred to a centrifuge for centrifugal dehydration;

[0077] (7) Control the air inlet temperature at 150-180°C and the air outlet temperature at 70-90°C, and obtain a high-whiteness cross-linked polyvinylpyrrolidone product by air drying.

[0078] Example 5

[0079] This embodiment provides a method for preparing high-whiteness cross-linked polyvinylpyrrolidone, the method comprising the following steps:

[0080] (1) Add 100 kg PVPP and 900 kg purified water into the reactor, heat to 85 °C, start stirring, and set the speed to 900 rpm;

[0081] (2) Add 0.008 kg of sulfur trioxide, 0.002 kg of magnesium bromide, 0.5 kg of peracetic acid, and 0.5 kg of sodium persulfate to the reactor, continue stirring for 50 minutes, and then stop stirring;

[0082] (3) Transfer the reaction mixture to a clean filter equipped with a 1000-mesh filter cloth, start stirring, and vacuum dehydrate;

[0083] (4) Add 900 kg of hot water at 75°C to the cleaning filter, control the speed to 900 rpm, stir and react for 50 minutes, and then vacuum dehydrate;

[0084] (5) Repeat step (4) twice and take samples to test the soluble matter in water at 0.6%;

[0085] (6) After adding sodium hydroxide solution to adjust the pH of the material to 9.0, the material in the cleaning filter is transferred to a centrifuge for centrifugal dehydration;

[0086] (7) Control the air inlet temperature at 150-180°C and the air outlet temperature at 70-90°C, and obtain a high-whiteness cross-linked polyvinylpyrrolidone product by air drying.

[0087] Example 6

[0088] This embodiment provides a method for preparing high-whiteness cross-linked polyvinylpyrrolidone, the method comprising the following steps:

[0089] (1) Add 100 kg PVPP and 900 kg purified water into the reactor, heat to 90 °C, start stirring, and set the speed to 1000 rpm;

[0090] (2) Add 0.004 kg of sulfur trioxide, 0.05 kg of peracetic acid, and 0.05 kg of di-tert-butyl hydroperoxide to the reactor, continue stirring for 60 minutes, and then stop stirring;

[0091] (3) Transfer the reaction mixture to a clean filter equipped with a 1000-mesh filter cloth, start stirring, and vacuum dehydrate;

[0092] (4) Add 900 kg of hot water at 80°C to the cleaning filter, control the speed to 1000 rpm, stir and react for 60 minutes, and then vacuum dehydrate;

[0093] (5) Repeat step (4) twice and take samples to test the soluble matter in water at 0.4%;

[0094] (6) After adding sodium hydroxide solution to adjust the pH of the material to 8.0, the material in the cleaning filter is transferred to a centrifuge for centrifugal dehydration;

[0095] (7) Control the air inlet temperature at 150-180°C and the air outlet temperature at 70-90°C, and obtain a high-whiteness cross-linked polyvinylpyrrolidone product by air drying.

[0096] Comparative Example 1

[0097] A cross-linked polyvinylpyrrolidone, which differs from Example 6 only in that no Lewis acid is added; the types, amounts and preparation methods of other components are the same as those in Example 6.

[0098] Comparative Example 2

[0099] A cross-linked polyvinylpyrrolidone, which differs from Example 6 only in that no oxidant is added; the types, amounts and preparation methods of other components are the same as those in Example 6.

[0100] Comparative Example 3

[0101] A cross-linked polyvinylpyrrolidone, which differs from Example 6 only in that no Lewis acid and oxidant are added; the types, amounts and preparation methods of other components are the same as those in Example 6.

[0102] Comparative Example 4

[0103] A cross-linked polyvinylpyrrolidone, the original PVPP XL powder without any treatment.

[0104] Comparative Example 5

[0105] This comparative example provides a commercially available product A, cross-linked polyvinylpyrrolidone PVPP XL purchased from Zhongyan Hongsifang.

[0106] Comparative Example 6

[0107] This comparative example provides a commercially available product B, cross-linked polyvinylpyrrolidone PVPP XL purchased from BASF.

[0108] The performance test of the high-whiteness cross-linked polyvinylpyrrolidone provided in Examples 1-6 and Comparative Examples 1-6 was carried out as follows:

[0109] (1) Whiteness

[0110] Test method: Use WSD-3C automatic whiteness meter to test the whiteness of the product according to the method specified in the national standard GB / T 15595-2008.

[0111] The various properties of the high-whiteness cross-linked polyvinylpyrrolidone obtained in Examples 1-6 and the cross-linked polyvinylpyrrolidone obtained in Comparative Examples 1-6 were tested according to the above-mentioned performance testing method. The test results are shown in Table 1.

[0112] (2) The tests for pH, soluble matter in water and residue on ignition shall be carried out in accordance with the relevant provisions of "Cross-linked Polyvinylpyrrolidone" in the "Chinese Pharmacopoeia" (2020 edition).

[0113] Table 1

[0114] As can be seen from the data in Table 1, the high-whiteness cross-linked polyvinylpyrrolidone prepared according to the technology of the present application has a whiteness between 83% and 90%, which is significantly higher than the cross-linked polyvinylpyrrolidone products of Comparative Examples 1 to 6; the pH, water-soluble matter and ignition residue meet the requirements of the pharmacopoeia, indicating that the preparation method does not introduce additional impurities that affect the quality of the product.

[0115] The applicant declares that this application uses the above-mentioned embodiments to illustrate a high-whiteness cross-linked polyvinylpyrrolidone, its preparation method, and application. However, this application is not limited to the above-mentioned embodiments, that is, it does not mean that this application must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvements to this application, equivalent replacements for the raw materials of the product of this application, the addition of auxiliary ingredients, the selection of specific methods, etc., all fall within the scope of protection and disclosure of this application.

Claims

1. A method for preparing high-whiteness cross-linked polyvinylpyrrolidone, comprising the following steps: The cross-linked polyvinylpyrrolidone, water, Lewis acid and an oxidant are mixed and reacted to obtain the high-whiteness cross-linked polyvinylpyrrolidone.

2. The preparation method according to claim 1, in, The Lewis acid includes any one of aluminum chloride, ferric chloride, zinc chloride, boron trifluoride, sulfur trioxide, ferric bromide or magnesium bromide, or a combination of at least two thereof.

3. The preparation method according to claim 1 or 2, in, The oxidant includes any one of peroxide, tert-butyl peroxide or persulfate, or a combination of at least two thereof.

4. The preparation method according to any one of claims 1 to 3, in, The oxidant includes any one of peracetic acid, tert-butyl hydroperoxide, di-tert-butyl hydroperoxide, sodium persulfate, ammonium persulfate or potassium persulfate, or a combination of at least two thereof.

5. The preparation method according to any one of claims 1 to 4, in, The mass ratio of the cross-linked polyvinylpyrrolidone to water is 1:(5-9); Preferably, the mass ratio of the cross-linked polyvinylpyrrolidone to the Lewis acid is 100:(0.001-0.01); Preferably, the mass ratio of the cross-linked polyvinylpyrrolidone to the oxidant is 100:(0.1-1).

6. The preparation method according to any one of claims 1 to 5, in, The reaction temperature is 70-90°C.

7. The preparation method according to any one of claims 1 to 6, in, The reaction time is 30-60 min.

8. The preparation method according to any one of claims 1 to 7, in, After the reaction is completed, the steps include washing, alkalization, centrifugal dehydration and drying to obtain the high-whiteness cross-linked polyvinylpyrrolidone.

9. The preparation method according to claim 8, It is characterized in that The water washing includes adding hot water and stirring; Preferably, the temperature of the hot water is 60-80°C; Preferably, the stirring rate is 500-1000r / min; Preferably, the stirring time is 30-60 min; Preferably, the alkalization comprises adjusting the pH value to 7.0-9.0 using an alkaline solution; Preferably, the alkaline solution comprises concentrated ammonia water and / or sodium hydroxide solution; Preferably, the drying method comprises air flow drying; Preferably, the air inlet temperature of the airflow drying is 150-180°C; Preferably, the air outlet temperature of the airflow drying is 70-100°C.

10. The preparation method according to any one of claims 1 to 9, in, The preparation method specifically comprises the following steps: The cross-linked polyvinylpyrrolidone, water, Lewis acid and oxidant are mixed, reacted at 70-90° C. for 30-60 min, washed with water, alkalized to adjust the pH to 7.0-9.0, centrifuged for dehydration, and air-dried at an inlet air temperature of 150-180° C. and an outlet air temperature of 70-100° C. to obtain the high-whiteness cross-linked polyvinylpyrrolidone; The Lewis acid includes any one of aluminum chloride, ferric chloride, zinc chloride, boron trifluoride, sulfur trioxide, ferric bromide or magnesium bromide, or a combination of at least two of them; the oxidant includes any one of peracetic acid, tert-butyl hydroperoxide, di-tert-butyl hydroperoxide, sodium persulfate, ammonium persulfate or potassium persulfate, or a combination of at least two of them.

11. A high whiteness cross-linked polyvinylpyrrolidone, in, The high-whiteness cross-linked polyvinylpyrrolidone is prepared by the preparation method according to any one of claims 1 to 10.

12. Use of the high-whiteness cross-linked polyvinylpyrrolidone as claimed in claim 11 in the preparation of medicines and foods.

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