Preparation process of polyvinylpyrrolidone

Abstract

The invention belongs to the field of PVP (Polyvinyl Pyrrolidone) production, and relates to a preparation process of polyvinylpyrrolidone, which specifically comprises the following steps: S1, dissolving NVP in deionized water to obtain an NVP solution; s2, adding a composite catalyst composed of soluble cobalt salt and cerium salt and a composite initiator composed of a redox initiator and an azo initiator into the NVP solution, and carrying out a first polymerization reaction; the redox initiator comprises persulfate and sulfite. And S3, carrying out a second polymerization reaction to obtain a polyvinylpyrrolidone liquid. And S4, performing post-treatment to obtain polyvinylpyrrolidone powder. Under the combined action of the composite catalyst and the composite initiator, the polymerization reaction rate of the NVP monomer can be remarkably increased, the temperature and time of the polymerization reaction are reduced, monomer residues and side reactions are reduced, and white polyvinylpyrrolidone is prepared.

Description

Technical Field

[0001] The invention relates to the technical field of PVP homopolymer production, and in particular to a preparation process of polyvinyl pyrrolidone. Background Art

[0002] Polyvinyl pyrrolidone (PVP), molecular formula (C6H9NO) n It has excellent solubility, biocompatibility, physiological inertness, film-forming properties, and the ability to form complexes with a variety of organic and inorganic compounds. Polyvinyl pyrrolidone is easily soluble in water and relatively stable to acid, salt and heat. It is widely used in cosmetics, medicine, ink, printing ink, paper, coatings, printing and dyeing industries, and other fields.

[0003] In the field of cosmetics, polyvinyl pyrrolidone can be used as a surfactant in toiletries to provide foam stability, and can also be added to skin care products as a moisturizer and film former. In the field of medicine, polyvinyl pyrrolidone can be used as an adhesive for tablets and granules, a flow aid for capsules, a cosolvent for injections, a dispersant for liquid preparations, a stabilizer for enzymes and thermosensitive drugs, etc. In the field of inks, inks and paper, polyvinyl pyrrolidone can be used as an adhesive to firmly adhere the handwriting to the paper to prevent fading, and improve the strength of the paper, solubilize the dye, and improve the gloss and printability of the paper. In the field of coatings, polyvinyl pyrrolidone has important uses in transparent coatings, conductive coatings and anti-leakage coatings. In the field of printing and dyeing industry, polyvinyl pyrrolidone can improve the dyeability of certain fibers, improve the coloring power and dyeing depth, and improve the hygroscopicity and sun protection of synthetic fibers. Polyvinyl pyrrolidone can also be used in membrane separation technology, such as blending with brominated polyphenylene ether membranes to increase polarity, and can also be used as a film-forming pore-forming agent in sewage treatment and water purification processes.

[0004] The K value of polyvinyl pyrrolidone is an important parameter to measure its molecular weight. It is closely related to the viscosity of polyvinyl pyrrolidone. The higher the K value, the larger the molecular weight of polyvinyl pyrrolidone. Polyvinyl pyrrolidone with different K values ​​has different physical and chemical properties and is suitable for different fields. For example, PVP-K15 is suitable for applications that require low viscosity and high fluidity, and can be used in cosmetics, coatings, inks, adhesives and other fields. PVP-K30 has good solubility and film-forming properties and can be used in pharmaceuticals, cosmetics, food additives, textile auxiliaries and other fields. PVP-K60 has good thickening and stabilizing effects and can be used in water treatment, textile finishing, papermaking industry, medicine and personal care products and other fields. PVP-K90 has extremely high viscosity and excellent thickening properties and can be used in high viscosity colloids, coatings, inks, adhesives, medicine and other fields.

[0005] Some application fields require polyvinyl pyrrolidone to be white to ensure the appearance, performance and quality of the product. However, the prior art generally uses ammonia and hydrogen peroxide as initiators to polymerize the raw material N-vinyl pyrrolidone (NVP), and the prepared polyvinyl pyrrolidone tends to be light yellow, making it unable to meet the application requirements of white.

[0006] Therefore, it is necessary to provide a method for preparing polyvinyl pyrrolidone to avoid yellowing of the prepared polyvinyl pyrrolidone so as to make it meet the application requirements of white color. Summary of the invention

[0007] 1. Technical issues to be resolved

[0008] In view of the above technical problems, in order to solve the problem in the prior art that polyvinyl pyrrolidone prepared using ammonia water and hydrogen peroxide as initiators tends to appear light yellow and cannot meet the application requirements of white, the present invention provides a preparation process of polyvinyl pyrrolidone.

[0009] (II) Technical solution

[0010] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0011] The present invention provides a process for preparing polyvinyl pyrrolidone, comprising the following steps:

[0012] S1: dissolving N-vinyl pyrrolidone in deionized water to obtain an N-vinyl pyrrolidone solution;

[0013] S2: adding a composite catalyst and a composite initiator to the N-vinyl pyrrolidone solution, and performing a first polymerization reaction at a certain temperature; the composite catalyst comprises a soluble cobalt salt and a soluble cerium salt, and the composite initiator comprises a redox initiator composed of a persulfate and a sulfite, and an azo initiator;

[0014] S3: raising the temperature to carry out a second polymerization reaction, and lowering the temperature after the reaction to obtain a polyvinyl pyrrolidone liquid;

[0015] S4: post-treating the polyvinyl pyrrolidone liquid to obtain polyvinyl pyrrolidone powder.

[0016] In the above-mentioned process for preparing polyvinyl pyrrolidone, preferably, in step S1, the mass ratio of deionized water to N-vinyl pyrrolidone is 1.5:1-2.5:1.

[0017] In the above-mentioned process for preparing polyvinyl pyrrolidone, preferably, in step S2, the added amount of the composite catalyst is 0.01-0.02‰ of the mass of N-vinyl pyrrolidone, and the added amount of the composite initiator is 0.25-0.6% of the mass of N-vinyl pyrrolidone.

[0018] In the above-mentioned process for preparing polyvinyl pyrrolidone, preferably, in step S2, the temperature of the first polymerization reaction is 25-30° C., and the time of the first polymerization reaction is 50-70 min.

[0019] In the above-mentioned process for preparing polyvinyl pyrrolidone, preferably, in step S2, the molar ratio of persulfate to sulfite in the composite catalyst is 1:1-1:3.

[0020] In the above-mentioned process for preparing polyvinyl pyrrolidone, preferably, in step S2, the molar ratio of the redox initiator to the azo initiator is 1:2-2:1.

[0021] In the preparation process of polyvinyl pyrrolidone as described above, preferably, in step S2, the soluble cobalt salt is one or more of cobalt nitrate, cobalt chloride, cobalt sulfate and cobalt acetate, and the soluble cerium salt is one or more of cerium nitrate, cerium chloride, cerium sulfate and cerium acetate.

[0022] In the above-mentioned process for preparing polyvinyl pyrrolidone, preferably, in step S2, the azo initiator is azobisisoheptanenitrile.

[0023] In the above-mentioned process for preparing polyvinyl pyrrolidone, preferably, in step S3, the temperature of the second polymerization reaction is 40-45° C., and the time of the second polymerization reaction is 40-60 min.

[0024] In the above-mentioned process for preparing polyvinyl pyrrolidone, preferably, in step S4, the polyvinyl pyrrolidone liquid is subjected to a dry spray treatment at 100-110° C. and a pressure of -0.03 MPa to -0.06 MPa to obtain polyvinyl pyrrolidone powder.

[0025] (III) Beneficial effects

[0026] The composite catalyst of the present invention comprises a soluble cobalt salt and a soluble cerium salt. The cobalt ions and the cerium ions can jointly promote the decomposition of the initiator, generate free radicals, and thus significantly improve the initiation efficiency, accelerate the polymerization reaction rate of the NVP monomer, improve the conversion rate of the monomer, reduce the monomer residue, and shorten the polymerization reaction time.

[0027] The composite catalyst of the present invention can also lower the temperature of the polymerization reaction, so that the initiator can effectively initiate the polymerization reaction at a lower temperature, which helps to reduce the risk of thermal degradation, reduce energy consumption, and can reduce the occurrence of side reactions, thereby improving the purity and uniformity of PVP.

[0028] The composite initiator of the present invention comprises a redox initiator and an azo initiator. The composite initiator can generate different free radicals, synergistically accelerate the polymerization reaction rate of the NVP monomer, and can also reduce the usage of the initiator.

[0029] Under the combined action of the composite catalyst and the composite initiator, the preparation process of polyvinyl pyrrolidone of the present invention can significantly accelerate the polymerization reaction rate of NVP monomer, reduce the temperature and time of the polymerization reaction, reduce the occurrence of monomer residues and side reactions, and prepare polyvinyl pyrrolidone with a white appearance. DETAILED DESCRIPTION

[0030] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below in conjunction with specific implementation methods.

[0031] The present invention provides a process for preparing polyvinyl pyrrolidone, comprising the following steps:

[0032] S1: dissolving N-vinyl pyrrolidone in deionized water to obtain an N-vinyl pyrrolidone solution.

[0033] S2: Adding a composite catalyst and a composite initiator to the N-vinyl pyrrolidone solution, and performing a first polymerization reaction at a certain temperature. In this step, the composite catalyst includes a soluble cobalt salt and a soluble cerium salt, and the composite initiator includes a redox initiator composed of a persulfate and a sulfite, and an azo initiator.

[0034] S3: Continue to raise the temperature under the temperature condition of the first polymerization reaction to carry out a second polymerization reaction, and cool down after the reaction to obtain polyvinyl pyrrolidone liquid.

[0035] S4: post-treating the polyvinyl pyrrolidone liquid to obtain polyvinyl pyrrolidone powder.

[0036] Preferably, in the above step S1, the mass ratio of deionized water to N-vinyl pyrrolidone is 1.5:1-2.5:1. The present invention adopts deionized water to dissolve N-vinyl pyrrolidone, and impurity ions have been removed in the deionized water, which can avoid the influence of impurities on the polymerization reaction. The present invention controls the mass ratio of deionized water to N-vinyl pyrrolidone to 1.5:1-2.5:1. By adjusting the ratio of NVP monomer and deionized water, the concentration of the monomer in the reaction system can be effectively controlled to ensure good mass transfer efficiency, promote uniform dispersion of NVP monomer, and maintain an ideal reaction rate of NVP monomer.

[0037] Preferably, in the above step S2, the added amount of the composite catalyst is 0.01-0.02‰ of the mass of N-vinyl pyrrolidone, and the added amount of the composite initiator is 0.25-0.6% of the mass of N-vinyl pyrrolidone.

[0038] The composite catalyst of the present invention comprises a soluble cobalt salt and a soluble cerium salt, and there is a synergistic effect between the cobalt ion and the cerium ion, and has a high catalytic efficiency. The addition amount is low, and the decomposition of the initiator can be promoted by maintaining it at 0.01-0.02‰ of the mass of N-vinyl pyrrolidone, generating free radicals, and then significantly improving the initiation efficiency, accelerating the polymerization reaction rate of the NVP monomer, improving the conversion rate of the monomer, reducing the monomer residue, reducing the time of the polymerization reaction, and saving the catalyst cost. In addition, the composite catalyst of the present invention can also reduce the temperature of the polymerization reaction, so that the initiator effectively initiates the polymerization reaction at a relatively low temperature, which helps to reduce the risk of thermal degradation, reduce energy consumption, and can reduce the occurrence of side reactions, and improve the purity and uniformity of PVP.

[0039] The composite initiator of the present invention comprises a redox initiator and an azo initiator. The composite initiator can generate different free radicals to synergistically accelerate the polymerization reaction rate of the NVP monomer. The amount of the initiator used in the present invention is relatively small, and can be maintained at 0.25-0.6% of the mass of N-vinyl pyrrolidone.

[0040] In the present invention, cobalt ions and cerium ions have a synergistic effect, so the composite catalyst must contain both soluble cobalt salt and soluble cerium salt. If only one of them is used, the catalytic efficiency will be reduced, the improvement of the initiation efficiency will not be obvious, and the color of the prepared polyvinyl pyrrolidone will be yellow.

[0041] Similarly, the composite initiator in the present invention must also include both a redox initiator and an azo initiator. The redox initiator is more inclined to decompose and generate free radicals at a lower temperature (in the first polymerization reaction), and the azo initiator is more inclined to decompose and generate free radicals at a higher temperature (in the second polymerization reaction). Compared with a single redox initiator or a single azo initiator, the amount of the composite initiator used is lower.

[0042] Further preferably, under the action of the composite catalyst and the composite initiator of the present invention, in the above step S2, the temperature of the first polymerization reaction only needs to be maintained at 25-30°C, and the first polymerization reaction only needs to be carried out for 50-70 minutes. In the above step S3, the temperature of the second polymerization reaction only needs to be maintained at 40-45°C, and the second polymerization reaction only needs to be carried out for 40-60 minutes to prepare polyvinyl pyrrolidone. After the composite catalyst and the composite initiator are added to the N-vinyl pyrrolidone solution, under the catalytic action of the composite catalyst and the temperature condition of 25-30°C, the composite initiator generates free radicals, and the free radicals initiate the NVP monomer to undergo the first polymerization reaction. After the first polymerization reaction is completed, the temperature is raised to 40-45°C, and the composite initiator further generates free radicals, which initiate the NVP monomer to undergo a second polymerization reaction, and finally white polyvinyl pyrrolidone is prepared.

[0043] Preferably, in step S2, in the composite catalyst, the molar ratio of persulfate to sulfite is 1:1-1:3, and the molar ratio of redox initiator to azo initiator is 1:2-2:1.

[0044] In the composite catalyst of the present invention, persulfate is used as an oxidant, sulfite is used as a reducing agent, and the molar ratio of persulfate to sulfite is controlled at 1:1-1:3, which can maintain the free radical generation rate at a high level, improve the initiation efficiency, and avoid initiating side reactions. If the molar ratio is too high or too low, insufficient or excessive free radical generation will result, affecting the control of the polymerization reaction. When the persulfate is excessive, for example, the molar ratio is higher than 1:1, too many free radicals may be generated, causing side reactions, thereby affecting the molecular weight distribution and quality of the product. When the sulfite is excessive, for example, the molar ratio exceeds 1:3, the reducing agent may not react completely, and the residual reducing agent may affect the purity and performance of the product.

[0045] Preferably, in the above step S2, the soluble cobalt salt may be one or more of cobalt nitrate, cobalt chloride, cobalt sulfate and cobalt acetate, the soluble cerium salt may be one or more of cerium nitrate, cerium chloride, cerium sulfate and cerium acetate. The persulfate may be one or more of ammonium persulfate, potassium persulfate and sodium persulfate, the sulfite may be potassium sulfite and / or sodium sulfite, and the azo initiator may be azobisisoheptanenitrile (ABVN).

[0046] Preferably, in step S4, the polyvinyl pyrrolidone liquid is subjected to a drying spray treatment at 100-110° C. and a pressure of -0.03 MPa to -0.06 MPa to remove moisture therein to obtain a polyvinyl pyrrolidone powder having a moisture content of less than 5%. The dried polyvinyl pyrrolidone powder and water vapor can be separated by a bag separator, then enter a vibrating screen for screening, and then mixed by a double cone mixer, and finally packaged and stored.

[0047] In general, the reasons why the color of the prepared PVP product is light yellow include that the polymerization temperature is too high, the polymerization time is long at high temperature, the occurrence of side reactions and the residual amount of NVP monomer is high. Under the joint action of the composite catalyst and the composite initiator, the preparation process of the polyvinyl pyrrolidone of the present invention can significantly accelerate the polymerization reaction rate of the NVP monomer, reduce the temperature and time of the polymerization reaction, reduce the occurrence of monomer residues and side reactions, and thus can prepare a polyvinyl pyrrolidone with a white appearance.

[0048] In addition, the vinyl pyrrolidone prepared by the prior art is easy to change from white to light yellow in a short period of time, such as within a few months, during storage, thereby affecting its use. Under the combined action of the composite catalyst, composite initiator, reaction temperature and time in different polymerization reactions of the present invention, the present invention can not only prepare white polyvinyl pyrrolidone, but also prepare white polyvinyl pyrrolidone that can maintain white color during long-term storage, is not easy to turn yellow, and does not change color for more than 1.5 years of storage at room temperature.

[0049] In addition, the K value of the polyvinyl pyrrolidone prepared by the present invention can be controlled between K12-K90, for example, K12, K15, K17, K25, K30, K45, K60, K70, K80, K85 and K90, etc. Specifically, the K value of polyvinyl pyrrolidone can be controlled by controlling the mass ratio of deionized water to N-vinyl pyrrolidone, the amount of the composite initiator added, the temperature and time of the two polymerization reactions, thereby realizing customized production of polyvinyl pyrrolidone.

[0050] In order to further clarify the scheme of the present invention and its technical advancement, the following is a description in conjunction with specific embodiments and technical effects.

[0051] Example 1

[0052] This embodiment provides a process for preparing polyvinyl pyrrolidone, comprising the following steps:

[0053] S1: dissolving N-vinyl pyrrolidone in deionized water to obtain an N-vinyl pyrrolidone solution. In this step, the mass ratio of deionized water to N-vinyl pyrrolidone is 2:1.

[0054] S2: Add a composite catalyst and a composite initiator to the N-vinyl pyrrolidone solution, and perform the first polymerization reaction at 30°C for 70 minutes. In this step, the composite catalyst includes cobalt nitrate and cerium nitrate, and the composite initiator includes a redox initiator composed of persulfate and sulfite, and azobisisoheptanenitrile. In this step, the amount of the composite catalyst added is 0.015‰ of the mass of N-vinyl pyrrolidone, and the amount of the composite initiator added is 0.28% of the mass of N-vinyl pyrrolidone. The persulfate is ammonium persulfate, the sulfite is potassium sulfite, the molar ratio of persulfate to sulfite is 1:2, and the molar ratio of the redox initiator to the azo initiator is 1:1.

[0055] S3: The second polymerization reaction was carried out at 45°C for 60 minutes. After the reaction was completed, the temperature was lowered to obtain polyvinyl pyrrolidone liquid.

[0056] S4: Drying and spraying the polyvinyl pyrrolidone liquid at 105° C. and a pressure of −0.04 MPa to obtain polyvinyl pyrrolidone powder.

[0057] Example 2

[0058] This embodiment provides a process for preparing polyvinyl pyrrolidone, comprising the following steps:

[0059] S1: dissolving N-vinyl pyrrolidone in deionized water to obtain an N-vinyl pyrrolidone solution. In this step, the mass ratio of deionized water to N-vinyl pyrrolidone is 1.5:1.

[0060] S2: Add a composite catalyst and a composite initiator to the N-vinyl pyrrolidone solution, and perform the first polymerization reaction at 27°C for 60 minutes. In this step, the composite catalyst includes cobalt chloride and cerium chloride, and the composite initiator includes a redox initiator composed of persulfate and sulfite, and azobisisoheptanonitrile. In this step, the amount of the composite catalyst added is 0.01‰ of the mass of N-vinyl pyrrolidone, and the amount of the composite initiator added is 0.3% of the mass of N-vinyl pyrrolidone. The persulfate is potassium persulfate, the sulfite is sodium sulfite, the molar ratio of persulfate to sulfite is 1:1, and the molar ratio of the redox initiator to the azo initiator is 1:2.

[0061] S3: The second polymerization reaction was carried out at 42°C for 50 minutes. After the reaction was completed, the temperature was lowered to obtain polyvinyl pyrrolidone liquid.

[0062] S4: Drying and spraying the polyvinyl pyrrolidone liquid at 100° C. and a pressure of −0.03 MPa to obtain polyvinyl pyrrolidone powder.

[0063] Example 3

[0064] This embodiment provides a process for preparing polyvinyl pyrrolidone, comprising the following steps:

[0065] S1: dissolving N-vinyl pyrrolidone in deionized water to obtain an N-vinyl pyrrolidone solution. In this step, the mass ratio of deionized water to N-vinyl pyrrolidone is 2.5:1.

[0066] S2: Add a composite catalyst and a composite initiator to the N-vinyl pyrrolidone solution, and perform the first polymerization reaction at 25°C for 50 minutes. In this step, the composite catalyst includes cobalt sulfate and cerium sulfate, and the composite initiator includes a redox initiator composed of persulfate and sulfite, and azobisisoheptanonitrile. In this step, the amount of the composite catalyst added is 0.02‰ of the mass of N-vinyl pyrrolidone, and the amount of the composite initiator added is 0.35% of the mass of N-vinyl pyrrolidone. The persulfate is sodium persulfate, the sulfite is potassium sulfite, the molar ratio of persulfate to sulfite is 1:3, and the molar ratio of the redox initiator to the azo initiator is 2:1.

[0067] S3: The second polymerization reaction was carried out at 40°C for 40 minutes. After the reaction was completed, the temperature was lowered to obtain polyvinyl pyrrolidone liquid.

[0068] S4: Drying and spraying the polyvinyl pyrrolidone liquid at 110° C. and a pressure of −0.06 MPa to obtain polyvinyl pyrrolidone powder.

[0069] Example 4

[0070] This embodiment provides a process for preparing polyvinyl pyrrolidone, comprising the following steps:

[0071] S1: dissolving N-vinyl pyrrolidone in deionized water to obtain an N-vinyl pyrrolidone solution. In this step, the mass ratio of deionized water to N-vinyl pyrrolidone is 1.8:1.

[0072] S2: Add a composite catalyst and a composite initiator to the N-vinyl pyrrolidone solution, and perform the first polymerization reaction at 28°C for 55 minutes. In this step, the composite catalyst includes cobalt acetate and cerium acetate, and the composite initiator includes a redox initiator composed of persulfate and sulfite, and azobisisoheptanonitrile. In this step, the amount of the composite catalyst added is 0.018‰ of the mass of N-vinyl pyrrolidone, and the amount of the composite initiator added is 0.4% of the mass of N-vinyl pyrrolidone. The persulfate is ammonium persulfate, the sulfite is potassium sulfite, the molar ratio of persulfate to sulfite is 1:1.5, and the molar ratio of the redox initiator to the azo initiator is 1:2.

[0073] S3: The second polymerization reaction was carried out at 43°C for 45 minutes. After the reaction was completed, the temperature was lowered to obtain polyvinyl pyrrolidone liquid.

[0074] S4: Drying and spraying the polyvinyl pyrrolidone liquid at 106° C. and a pressure of −0.05 MPa to obtain polyvinyl pyrrolidone powder.

[0075] Example 5

[0076] This embodiment provides a process for preparing polyvinyl pyrrolidone, comprising the following steps:

[0077] S1: dissolving N-vinyl pyrrolidone in deionized water to obtain an N-vinyl pyrrolidone solution. In this step, the mass ratio of deionized water to N-vinyl pyrrolidone is 2.1:1.

[0078] S2: Add a composite catalyst and a composite initiator to the N-vinyl pyrrolidone solution, and perform the first polymerization reaction at 26°C for 65 minutes. In this step, the composite catalyst includes cobalt nitrate and cerium nitrate, and the composite initiator includes a redox initiator composed of persulfate and sulfite, and azobisisoheptanenitrile. In this step, the amount of the composite catalyst added is 0.016‰ of the mass of N-vinyl pyrrolidone, and the amount of the composite initiator added is 0.5% of the mass of N-vinyl pyrrolidone. The persulfate is ammonium persulfate, the sulfite is potassium sulfite, the molar ratio of persulfate to sulfite is 1:2.5, and the molar ratio of the redox initiator to the azo initiator is 1:1.

[0079] S3: The second polymerization reaction was carried out at 41°C for 55 minutes. After the reaction was completed, the temperature was lowered to obtain polyvinyl pyrrolidone liquid.

[0080] S4: Drying and spraying the polyvinyl pyrrolidone liquid at 105° C. and a pressure of −0.04 MPa to obtain polyvinyl pyrrolidone powder.

[0081] Example 6

[0082] This embodiment provides a process for preparing polyvinyl pyrrolidone, comprising the following steps:

[0083] S1: dissolving N-vinyl pyrrolidone in deionized water to obtain an N-vinyl pyrrolidone solution. In this step, the mass ratio of deionized water to N-vinyl pyrrolidone is 2.3:1.

[0084] S2: Add a composite catalyst and a composite initiator to the N-vinyl pyrrolidone solution, and perform the first polymerization reaction at 29°C for 53 minutes. In this step, the composite catalyst includes cobalt nitrate and cerium nitrate, and the composite initiator includes a redox initiator composed of persulfate and sulfite, and azobisisoheptanenitrile. In this step, the amount of the composite catalyst added is 0.014‰ of the mass of N-vinyl pyrrolidone, and the amount of the composite initiator added is 0.45% of the mass of N-vinyl pyrrolidone. The persulfate is ammonium persulfate, the sulfite is potassium sulfite, the molar ratio of persulfate to sulfite is 1:1.8, and the molar ratio of the redox initiator to the azo initiator is 2:1.

[0085] S3: The second polymerization reaction was carried out at 44°C for 49 minutes. After the reaction was completed, the temperature was lowered to obtain polyvinyl pyrrolidone liquid.

[0086] S4: Drying and spraying the polyvinyl pyrrolidone liquid at 105° C. and a pressure of −0.04 MPa to obtain polyvinyl pyrrolidone powder.

[0087] Example 7

[0088] This embodiment provides a process for preparing polyvinyl pyrrolidone, comprising the following steps:

[0089] S1: dissolving N-vinyl pyrrolidone in deionized water to obtain an N-vinyl pyrrolidone solution. In this step, the mass ratio of deionized water to N-vinyl pyrrolidone is 1.9:1.

[0090] S2: Add a composite catalyst and a composite initiator to the N-vinyl pyrrolidone solution, and perform the first polymerization reaction at 30°C for 50 minutes. In this step, the composite catalyst includes cobalt nitrate and cerium nitrate, and the composite initiator includes a redox initiator composed of persulfate and sulfite, and azobisisoheptanonitrile. In this step, the amount of the composite catalyst added is 0.019‰ of the mass of N-vinyl pyrrolidone, and the amount of the composite initiator added is 0.6% of the mass of N-vinyl pyrrolidone. The persulfate is ammonium persulfate, the sulfite is potassium sulfite, the molar ratio of persulfate to sulfite is 1:2.2, and the molar ratio of the redox initiator to the azo initiator is 1.5:1.

[0091] S3: The second polymerization reaction was carried out at 45°C for 55 minutes. After the reaction was completed, the temperature was lowered to obtain polyvinyl pyrrolidone liquid.

[0092] S4: Drying and spraying the polyvinyl pyrrolidone liquid at 105° C. and a pressure of −0.04 MPa to obtain polyvinyl pyrrolidone powder.

[0093] Example 8

[0094] This embodiment provides a process for preparing polyvinyl pyrrolidone, comprising the following steps:

[0095] S1: dissolving N-vinyl pyrrolidone in deionized water to obtain an N-vinyl pyrrolidone solution. In this step, the mass ratio of deionized water to N-vinyl pyrrolidone is 2.2:1.

[0096] S2: Add a composite catalyst and a composite initiator to the N-vinyl pyrrolidone solution, and perform the first polymerization reaction at 28°C for 55 minutes. In this step, the composite catalyst includes cobalt nitrate and cerium nitrate, and the composite initiator includes a redox initiator composed of persulfate and sulfite, and azobisisoheptanonitrile. In this step, the amount of the composite catalyst added is 0.017‰ of the mass of N-vinyl pyrrolidone, and the amount of the composite initiator added is 0.55% of the mass of N-vinyl pyrrolidone. The persulfate is ammonium persulfate, the sulfite is potassium sulfite, the molar ratio of persulfate to sulfite is 1:1.4, and the molar ratio of the redox initiator to the azo initiator is 1.8:1.

[0097] S3: The second polymerization reaction was carried out at 45°C for 40 minutes. After the reaction was completed, the temperature was lowered to obtain polyvinyl pyrrolidone liquid.

[0098] S4: Drying and spraying the polyvinyl pyrrolidone liquid at 105° C. and a pressure of −0.04 MPa to obtain polyvinyl pyrrolidone powder.

[0099] Comparative Example 1

[0100] This comparative example provides a process for preparing polyvinyl pyrrolidone, which differs from Example 1 in that no composite catalyst is used.

[0101] Comparative Example 2

[0102] This comparative example provides a process for preparing polyvinyl pyrrolidone, which is different from Example 1 in that the initiator is a redox initiator composed of persulfate and sulfite.

[0103] Comparative Example 3

[0104] This comparative example provides a preparation process of polyvinyl pyrrolidone, which is different from Example 1 in that the initiator is azobisisoheptanenitrile.

[0105] The K value and the residual monomer content of the polyvinyl pyrrolidone prepared in Examples 1-8 and Comparative Examples 1-3 were tested, and the product colors were observed and recorded to obtain Table 1.

[0106] Table 1 K value, color and residual monomer content of the products of Examples 1-8 and Comparative Examples 1-3

[0107]

[0108]

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for preparing polyvinyl pyrrolidone, characterized in that: The steps include: S1: dissolving N-vinyl pyrrolidone in deionized water to obtain an N-vinyl pyrrolidone solution; S2: adding a composite catalyst and a composite initiator to the N-vinyl pyrrolidone solution, and performing a first polymerization reaction at a certain temperature; the composite catalyst comprises a soluble cobalt salt and a soluble cerium salt, and the composite initiator comprises a redox initiator composed of a persulfate and a sulfite, and an azo initiator; S3: raising the temperature to carry out a second polymerization reaction, and lowering the temperature after the reaction to obtain a polyvinyl pyrrolidone liquid; S4: post-treating the polyvinyl pyrrolidone liquid to obtain polyvinyl pyrrolidone powder.

2. The process for preparing polyvinyl pyrrolidone according to claim 1, characterized in that: In step S1, the mass ratio of deionized water to N-vinyl pyrrolidone is 1.5:1-2.5:

1.

3. The process for preparing polyvinyl pyrrolidone according to claim 1, characterized in that: In step S2, the added amount of the composite catalyst is 0.01-0.02‰ of the mass of N-vinyl pyrrolidone, and the added amount of the composite initiator is 0.25-0.6% of the mass of N-vinyl pyrrolidone.

4. The process for preparing polyvinyl pyrrolidone according to claim 1, characterized in that: In step S2, the temperature of the first polymerization reaction is 25-30° C., and the time of the first polymerization reaction is 50-70 min.

5. The process for preparing polyvinyl pyrrolidone according to claim 1, characterized in that: In step S2, in the composite catalyst, the molar ratio of persulfate to sulfite is 1:1-1:

3.

6. The process for preparing polyvinyl pyrrolidone according to claim 1, characterized in that: In step S2, the molar ratio of the redox initiator to the azo initiator is 1:2-2:

1.

7. The process for preparing polyvinyl pyrrolidone according to claim 1, characterized in that: In step S2, the soluble cobalt salt is one or more of cobalt nitrate, cobalt chloride, cobalt sulfate and cobalt acetate, and the soluble cerium salt is one or more of cerium nitrate, cerium chloride, cerium sulfate and cerium acetate.

8. The process for preparing polyvinyl pyrrolidone according to claim 1, characterized in that: In step S2, the azo initiator is azobisisoheptanonitrile.

9. The process for preparing polyvinyl pyrrolidone according to claim 1, characterized in that: In step S3, the temperature of the second polymerization reaction is 40-45° C., and the time of the second polymerization reaction is 40-60 min.

10. The process for preparing polyvinyl pyrrolidone according to claim 1, characterized in that: In step S4, the polyvinyl pyrrolidone liquid is subjected to a dry spray treatment at 100-110° C. and a pressure of -0.03 MPa to -0.06 MPa to obtain polyvinyl pyrrolidone powder.

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