Process for the preparation of polyvinylpyrrolidone

Abstract

The application relates to the field of fine chemical synthesis, and relates to a preparation method of polyvinylpyrrolidone. Pure water, N-vinylpyrrolidone and ammonia water are continuously introduced into a micro-mixer, uniformly mixed in the micro-mixer, and then introduced into a preheater to be preheated to a reaction temperature; the obtained mixture is sequentially and continuously introduced into a micro-channel reactor and a delay reactor together with an aqueous hydrogen peroxide solution, and the reaction is carried out at normal pressure at 55-80 DEG C; and the product continuously coming out of the delay reactor is a polyvinylpyrrolidone solution. The application is a continuous preparation method which is easy to control in temperature, high in safety, narrow in molecular weight distribution, short in reaction time and easy to industrialize.

Description

Technical Field

[0001] This invention relates to the field of fine chemical synthesis, and more particularly to a method for preparing polyvinylpyrrolidone. Background Technology

[0002] Polyvinylpyrrolidone (PVP) is an important water-soluble polymer material with excellent biocompatibility, solubility (soluble in both water and many organic solvents), complexing properties, dispersibility, film-forming properties, solubilizing properties, adhesive properties, chemical stability, biological inertness, and safety and non-toxicity. It is widely used in cosmetics, pharmaceuticals, food, textile printing and dyeing, papermaking, adhesives, coatings, pigments, detergents, metal processing, energy, polymer polymerization, electronics, separation membranes, lithium batteries, photovoltaics, medical polymer materials, nanomaterials, graphene, catalysts, adsorbent materials, and agriculture and animal husbandry.

[0003] Currently, polyvinylpyrrolidone (PVP) is prepared via batch production in a stirred reactor. The most common process uses N-vinylpyrrolidone as the monomer and water as the solvent, undergoing free radical polymerization in the presence of hydrogen peroxide as an initiator. Hydrogen peroxide decomposition acidifies the solution, leading to monomer decomposition. Therefore, ammonia is added during the polymerization process to adjust the pH and maintain it within the alkaline range; ammonia also acts as a co-catalyst. Because the polymerization of N-vinylpyrrolidone is a strongly exothermic reaction, temperature spikes are common, making temperature control difficult. This results in a wide molecular weight distribution in the polymer and a colored product. This problem becomes more pronounced with increasing reactor volume, potentially leading to reactor overflow. Furthermore, batch production in a stirred reactor results in a long reaction time.

[0004] Chinese patent CN115093498B discloses a method for preparing low-residual-monomer and low-color-ratio PVP. Under nitrogen protection, pure water, NVP, hydrogen peroxide as an initiator, and ammonia as a pH adjuster are used as the reaction solution. A high-temperature polymerization reaction is carried out in a reactor at 50℃~90℃. A pH interlock control device monitors the pH environment of the polymerization solution in real time, ensuring that the pH of the reaction environment is continuously controlled between 7 and 9, ultimately obtaining PVP with low residual monomer and low color. However, this method does not solve the problem of a wide molecular weight distribution of the polymer product, and the reaction time is also long, lasting several hours. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems in the prior art and provide a method for preparing polyvinylpyrrolidone, which is a continuous preparation method that is easy to control in temperature, has high safety, narrow molecular weight distribution, short reaction time and is easy to industrialize.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing polyvinylpyrrolidone, which uses a continuous flow microchannel reactor to polymerize N-vinylpyrrolidone to synthesize polyvinylpyrrolidone, includes the following steps:

[0008] 1) Pure water, N-vinylpyrrolidone, and ammonia are continuously fed into a micro mixer via their respective horizontal flow pumps to premix at room temperature to form a homogeneous mixed solution;

[0009] 2) The mixed solution from the micro mixer is fed into the preheater for preheating;

[0010] 3) The mixed solution from the preheater is fed into the microchannel reactor, and hydrogen peroxide is continuously fed into the microchannel reactor via a horizontal flow pump. The material from the microchannel reactor is then fed into the delayed reactor and reacted at a temperature of 55-80℃ for 30-45 minutes to obtain polyvinylpyrrolidone.

[0011] In step 2), the preheating temperature is 55-80℃.

[0012] The mass flow rate ratio of the purified water to N-vinylpyrrolidone is 1 to 4:1.

[0013] The mass flow rate ratio of ammonia to N-vinylpyrrolidone is 0.003 to 0.05:1.

[0014] The mass flow rate ratio of hydrogen peroxide to N-vinylpyrrolidone is 0.005~0.08∶1.

[0015] The polyvinylpyrrolidone prepared by the method of the present invention has a molecular weight distribution index ≤2.0 and a color Hazen ≤15.

[0016] Compared with the prior art, the beneficial effects achieved by the technical solution of this invention are:

[0017] The method provided by this invention utilizes a continuous flow microchannel reactor to synthesize polyvinylpyrrolidone (PVP) via N-vinylpyrrolidone polymerization, with the operation proceeding continuously. Due to the micro-size and interfacial effects of the microchannels, the microreactor possesses a high specific surface area and a very short material diffusion distance, thereby achieving rapid heat and mass transfer. This not only ensures stable and uniform reaction temperature but also significantly improves reaction efficiency, greatly shortens reaction time, and ensures inherent safety in the PPVP preparation process, while enabling a high degree of automation and intelligence in the production process. The PPVP product prepared by the method of this invention has better quality, with a molecular weight distribution index ≤2.0 and a Hazen color ≤15 (10% aqueous solution). Attached Figure Description

[0018] Figure 1This is a schematic diagram of the process flow of the present invention.

[0019] Figure reference numerals: 1-Pure water storage tank; 2-N-Vinylpyrrolidone storage tank; 3-Ammonia storage tank; 4-Hydrogen peroxide storage tank; 5, 6, 7, 8-Horizontal flow pump; 9-Micro mixer; 10-Preheater; 11-Microchannel reactor; 12-Delayed reactor. Detailed Implementation

[0020] To make the technical problems, technical solutions and beneficial effects of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0021] See Figure 1 The reaction apparatus of the present invention includes a pure water storage tank 1, an N-vinylpyrrolidone storage tank 2, an ammonia storage tank 3, a hydrogen peroxide storage tank 4, a horizontal flow pump 5-8, a micro mixer 9, a preheater 10, a microchannel reactor 11, and a delayed reactor 12.

[0022] The horizontal flow pumps 5-7 are respectively connected to the storage tanks 1-3 and the three inlets of the micro mixer 9; the outlet of the micro mixer 9 is connected to the inlet of the preheater 10; the outlet of the preheater 10 is connected to one inlet of the microchannel reactor 11; the hydrogen peroxide storage tank 4 is connected to the other inlet of the microchannel reactor 11 through the horizontal flow pump 8; the outlet of the microchannel reactor 11 is connected to the inlet of the delayed reactor 12; the preheater 10, the microchannel reactor 11, and the delayed reactor 12 are all provided with interfaces for hot water inlet and hot water outlet, and the pressure in the delayed reactor can be 0.01-0.5 MPa.

[0023] Specifically, the micromixer has an internally cross-flow microchannel structure with a microchannel size not exceeding 0.6 mm; the internal structure of the microchannel reactor is a branched recombinant microchannel with each branch microchannel having a size not exceeding 0.25 mm and each composite microchannel having a size below 0.5 mm; the delayed reactor is a coil reactor with an inner diameter of no more than 10 mm.

[0024] In this invention, the mass concentration of the ammonia water is 25%, and the mass concentration of the hydrogen peroxide is 30%.

[0025] Example 1

[0026] use Figure 1 The process flow shown for synthesizing polyvinylpyrrolidone includes the following steps:

[0027] 1) Pure water, N-vinylpyrrolidone, and 25% ammonia were continuously fed into a micro mixer via their respective horizontal flow pumps to premix at room temperature to form a homogeneous mixed solution; the mass flow rates of pure water, N-vinylpyrrolidone, and 25% ammonia were 150 g / h, 75 g / h, and 0.375 g / h, respectively.

[0028] 2) The mixed solution from the micro mixer is preheated to 65°C in a preheater and then fed into the microchannel reactor. At the same time, 30% hydrogen peroxide is continuously fed into the microchannel reactor via a horizontal flow pump at a flow rate of 0.75 g / h.

[0029] 3) The material from the microchannel reactor is then fed into the delayed reactor, where the reaction is carried out at a temperature of 65℃ and a pressure of 0.1MPa. The microchannels inside the micromixer have a size of 0.2mm × 0.5mm; each branch channel of the microchannel reactor has a size of 0.15mm × 0.1mm, and each composite channel has a size of 0.3mm × 0.1mm; the inner diameter of the coil in the delayed reactor is 2mm, the length is 32m, and the total reaction time is 30min. The product discharged from the delayed reactor is polyvinylpyrrolidone. The obtained polyvinylpyrrolidone has a weight-average molecular weight of 51,000, a monomer residue of 89ppm, a molecular weight distribution index of 1.8, and a Hazen color value of 10 for a 10% solution.

[0030] Example 2

[0031] The process flow and steps are the same as in Example 1. The difference lies in the preheating temperature and reaction temperature, which are both 80°C. The obtained polyvinylpyrrolidone had a weight-average molecular weight of 47,000, a monomer residue of 50 ppm, a molecular weight distribution index of 1.7, and a Hazen color value of 15 for a 10% solution.

[0032] Example 3

[0033] The process flow and steps are the same as in Example 1. The difference lies in the preheating temperature and reaction temperature, which are 55°C. The obtained polyvinylpyrrolidone had a weight-average molecular weight of 53,000, a monomer residue of 150 ppm, a molecular weight distribution index of 1.9, and a Hazen color value of 5 for a 10% solution.

[0034] Example 4

[0035] The process flow and steps are the same as in Example 1. The difference lies in the mass flow rate of 30% hydrogen peroxide being 2.25 g / h and the mass flow rate of 25% ammonia being 1.13 g / h. The weight-average molecular weight of polyvinylpyrrolidone was determined to be 29,000, the monomer residue was 61 ppm, the molecular weight distribution index was 1.7, and the Hazen color value of the 10% solution was 10.

[0036] Example 5

[0037] The process flow and steps are the same as in Example 1. The difference lies in the mass flow rate of 30% hydrogen peroxide being 4.5 g / h and the mass flow rate of 25% ammonia being 2.5 g / h. The weight-average molecular weight of polyvinylpyrrolidone was determined to be 4500, the monomer residue was 93 ppm, the molecular weight distribution index was 1.4, and the Hazen color value of the 10% solution was 10.

[0038] Example 6

[0039] The process flow and steps for synthesizing polyvinylpyrrolidone were the same as in Example 1. The difference was that the mass flow rates of purified water and N-vinylpyrrolidone were 100 g / h and 50 g / h, respectively, and the total reaction time was 43 min. The weight-average molecular weight of polyvinylpyrrolidone was determined to be 49,000, the monomer residue was 68 ppm, the molecular weight distribution index was 1.7, and the Hazen value of the 10% solution was 10.

[0040] Comparative Example 1

[0041] In a 1L three-necked flask equipped with a stirrer and placed in a constant-temperature water bath, 400g of water, 200g of N-vinylpyrrolidone, and 1g of 25% ammonia were added. Nitrogen gas was purged to remove air from the flask, stirring was started, and the mixture was heated to 65°C in the water bath and maintained at that temperature. 2g of 30% hydrogen peroxide was added to initiate the polymerization reaction. The reaction temperature was observed to rise from 65°C to 85°C, and then slowly decrease back to 65°C. Timing was started from the addition of hydrogen peroxide, and the reaction was stopped after 8 hours. The weight-average molecular weight of polyvinylpyrrolidone was determined to be 49,000, the monomer residue was 990 ppm, the molecular weight distribution index was 3.5, and the Hazen color value of a 10% solution was 100.

Claims

1. A method for preparing polyvinylpyrrolidone, characterized in that, Includes the following steps: 1) Pure water, N-vinylpyrrolidone, and ammonia are continuously fed into a micro-mixer via their respective horizontal flow pumps to premix at room temperature, forming a homogeneous mixed solution; the mass flow ratio of pure water to N-vinylpyrrolidone is 1~4:1; the mass flow ratio of ammonia to N-vinylpyrrolidone is 0.003~0.05:

1. 2) The mixed solution from the micro mixer is passed into a preheater and preheated to 55~80℃; 3) The mixed solution from the preheater is fed into a microchannel reactor, while hydrogen peroxide is continuously fed into the microchannel reactor via a horizontal flow pump. The material from the microchannel reactor is then fed into a delayed reactor, and the reaction is carried out at a temperature of 55-80℃ for 30-45 minutes to obtain polyvinylpyrrolidone; the mass flow ratio of hydrogen peroxide to N-vinylpyrrolidone is 0.005-0.08:

1. The micromixer is an internally cross-flow microchannel structure with a microchannel size not exceeding 0.6 mm; the internal structure of the microchannel reactor is a branched recombinant microchannel, with each branch microchannel having a size not exceeding 0.25 mm and each composite microchannel having a size below 0.5 mm; the delayed reactor is a coil reactor with an inner diameter of no more than 10 mm. The obtained polyvinylpyrrolidone has a molecular weight distribution index ≤ 2.0 and a color Hazen ≤ 15 for a 10% aqueous solution of polyvinylpyrrolidone.

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