Preparation method of polyvinylpyrrolidone

Abstract

The invention discloses a preparation method of polyvinylpyrrolidone, and relates to the field of fine chemical synthesis. The method comprises the following steps: continuously introducing purified water, N-vinyl pyrrolidone and ammonia water into a micro-mixer, uniformly mixing by the micro-mixer, introducing the obtained mixture into a preheater, preheating to a reaction temperature, sequentially and continuously introducing the mixture and a hydrogen peroxide aqueous solution into a micro-channel reactor and a delay reactor, and reacting at the normal pressure of 55-80 DEG C, the product continuously discharged from the delayed reactor is the polyvinylpyrrolidone solution. The continuous preparation method provided by the invention has the advantages of easy temperature control, high safety, narrow molecular weight distribution, short reaction time and easy industrialization.

Description

Technical Field

[0001] The invention relates to the field of fine chemical synthesis, in particular to a method for preparing polyvinyl pyrrolidone. Background Art

[0002] Polyvinyl pyrrolidone is an important water-soluble polymer material with excellent biocompatibility, solubility (soluble in water and many organic solvents), complexation, dispersibility, film-forming, solubilization, adhesion, chemical stability, biological inertness and safety and non-toxicity. It is widely used in cosmetics, medicine and health, 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, adsorption materials, agriculture and animal husbandry and other fields.

[0003] At present, the preparation method of polyvinyl pyrrolidone is to use a stirred reactor for intermittent production. The most commonly used process is to use N-vinyl pyrrolidone as a monomer and water as a solvent, and to obtain polyvinyl pyrrolidone by free radical polymerization under the action of initiator hydrogen peroxide. The decomposition of hydrogen peroxide will make the solution acidic, and the acidity will cause the monomer to decompose. Therefore, ammonia water is added during the polymerization reaction to adjust the pH value to maintain it in the alkaline range, and ammonia water also plays a role in promoting catalysis. Since the polymerization of N-vinyl pyrrolidone is a strong exothermic reaction, the temperature is prone to soar during the reaction process, and the reaction temperature is difficult to control, resulting in a wide distribution of polymer molecular weight and coloring of the product. As the volume of the reactor increases, this situation becomes more prominent, and may even lead to the danger of the reactor being impacted. In addition, the intermittent production using a stirred reactor requires a long reaction time.

[0004] Chinese patent CN115093498B discloses a method for preparing low-residual monomer and low-color PVP, which uses pure water, NVP, initiator hydrogen peroxide and acid-base regulator ammonia as reaction liquids under nitrogen protection, and performs high-temperature polymerization in a reactor at 50°C to 90°C. The pH interlocking control device is used to monitor the pH environment of the polymerization liquid in real time online to ensure that the pH of the reaction environment is continuously controlled between 7 and 9, and finally obtains low-residual monomer and low-color PVP. However, this method does not solve the problem of wide molecular weight distribution of polymer products, and the reaction time is also as long as several hours. Summary of the invention

[0005] The object of the present invention is to solve the above problems in the prior art and provide a method for preparing polyvinyl pyrrolidone, which is a continuous preparation method with easy temperature control, high safety, narrow molecular weight distribution, short reaction time and easy industrialization.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] The method for preparing polyvinyl pyrrolidone comprises the following steps:

[0008] 1) Purified water, N-vinyl pyrrolidone and ammonia water are continuously introduced into a micro mixer through respective horizontal flow pumps, and pre-mixed at room temperature to form a uniform mixed solution;

[0009] 2) The mixed solution coming out of the micro mixer is passed into a preheater for preheating;

[0010] 3) The mixed solution from the preheater is passed into the microchannel reactor, and at the same time, hydrogen peroxide is continuously passed into the microchannel reactor through a horizontal flow pump. The material from the microchannel reactor is then passed into a delayed reactor and reacted at a temperature of 55 to 80° C. for 30 to 45 minutes to obtain polyvinyl pyrrolidone.

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

[0012] The mass flow ratio of the pure water to the N-vinyl pyrrolidone is 1-4:1.

[0013] The mass flow ratio of the ammonia water to the N-vinyl pyrrolidone is 0.003-0.05:1.

[0014] The mass flow ratio of the hydrogen peroxide to N-vinyl pyrrolidone is 0.005-0.08:1.

[0015] The molecular weight distribution index of the polyvinyl pyrrolidone obtained by the preparation method of the invention is ≤2.0, and the chromaticity Hazen is ≤15.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0017] The method provided by the present invention uses a continuous flow microchannel reactor to carry out the polymerization reaction of N-vinyl pyrrolidone to synthesize polyvinyl pyrrolidone, and the operation is carried out continuously. The microreactor has a high specific surface area and a very short material diffusion distance due to the micro-size effect and interface effect of its microchannel, so that rapid heat transfer and mass transfer can be achieved, which can not only ensure the stability and uniformity of the reaction temperature, but also greatly improve the reaction efficiency, greatly shorten the reaction time, and realize the intrinsic safety of the polyvinyl pyrrolidone preparation process, and make the production process highly automated and intelligent. The polyvinyl pyrrolidone product prepared by the method of the present invention has better quality, a molecular weight distribution index ≤2.0, and a chromaticity Hazen ≤15 (10% aqueous solution). BRIEF DESCRIPTION OF THE DRAWINGS

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

[0019] Figure numerals: 1-pure water storage tank; 2-N-vinyl pyrrolidone 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-delay reactor. DETAILED DESCRIPTION

[0020] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0021] See also Figure 1 The reaction device of the present invention comprises a pure water storage tank 1, an N-vinyl pyrrolidone storage tank 2, an ammonia water storage tank 3, a hydrogen peroxide storage tank 4, horizontal flow pumps 5 to 8, a micro mixer 9, a preheater 10, a microchannel reactor 11, and a delay reactor 12;

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

[0023] Specifically, the micromixer is an internal cross-flow microchannel structure, and the scale of the microchannel does not exceed 0.6mm; the internal structure of the microchannel reactor is a branched and recombinant microchannel, the scale of each branch microchannel does not exceed 0.25mm, and the scale of each composite microchannel is kept below 0.5mm; the delayed reactor is a coil reactor, and the inner diameter of the coil is not more than 10mm.

[0024] In the present 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 in the figure for synthesizing polyvinyl pyrrolidone comprises the following steps:

[0027] 1) Pure water, N-vinyl pyrrolidone and 25% ammonia water are continuously introduced into a micro mixer through respective horizontal flow pumps to be pre-mixed at room temperature to form a uniform mixed solution; the mass flow rates of pure water, N-vinyl pyrrolidone and 25% ammonia water are 150 g / h, 75 g / h and 0.375 g / h respectively;

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

[0029] 3) The material coming out of the microchannel reactor is then passed into the delay reactor to react at a reaction temperature of 65°C and a reaction pressure of 0.1MPa; the size of the microchannel inside the micromixer is 0.2mm×0.5mm; the size of each branch channel of the microchannel reactor is 0.15mm×0.1mm, and the size of each composite channel is 0.3mm×0.1mm; the inner diameter of the coil of the delay reactor is 2mm, the length is 32m, the total reaction time is 30min, and the product discharged from the delay reactor is polyvinyl pyrrolidone. After measurement, the weight average molecular weight of the obtained polyvinyl pyrrolidone is 51000, the monomer residue is 89ppm, the molecular weight distribution index is 1.8, and the color Hazen value of the 10% solution is 10.

[0030] Example 2

[0031] The process and steps are the same as those in Example 1. The difference is that the preheating temperature and the reaction temperature are 80° C. After measurement, the weight average molecular weight of the obtained polyvinyl pyrrolidone is 47,000, the residual monomer content is 50 ppm, the molecular weight distribution index is 1.7, and the color Hazen value of the 10% solution is 15.

[0032] Example 3

[0033] The process and steps are the same as those in Example 1. The difference is that the preheating temperature and the reaction temperature are 55° C. After measurement, the weight average molecular weight of the obtained polyvinyl pyrrolidone is 53,000, the residual monomer content is 150 ppm, the molecular weight distribution index is 1.9, and the color Hazen value of the 10% solution is 5.

[0034] Example 4

[0035] The process and steps are the same as those in Example 1. The difference is that the mass flow rate of 30% hydrogen peroxide is 2.25 g / h, and the mass flow rate of 25% ammonia water is 1.13 g / h. After measurement, the weight average molecular weight of polyvinyl pyrrolidone is 29000, the residual monomer content is 61 ppm, the molecular weight distribution index is 1.7, and the color Hazen value of 10% solution is 10.

[0036] Example 5

[0037] The process and steps are the same as those in Example 1. The difference is that the mass flow rate of 30% hydrogen peroxide is 4.5 g / h, and the mass flow rate of 25% ammonia water is 2.5 g / h. After measurement, the weight average molecular weight of polyvinyl pyrrolidone is 4500, the residual monomer content is 93 ppm, the molecular weight distribution index is 1.4, and the color Hazen value of 10% solution is 10.

[0038] Example 6

[0039] The process and steps for synthesizing polyvinyl pyrrolidone are the same as those in Example 1. The difference is that the mass flow rates of purified water and N-vinyl pyrrolidone are 100 g / h and 50 g / h, respectively, and the total reaction time is 43 min. After measurement, the weight average molecular weight of polyvinyl pyrrolidone is 49,000, the residual monomer content is 68 ppm, the molecular weight distribution index is 1.7, and the chromaticity Hazen value of the 10% solution is 10.

[0040] Comparative Example 1

[0041] 400g water, 200g N-vinyl pyrrolidone and 1g 25% ammonia water were added to a 1L three-necked flask placed in a constant temperature water bath with stirring, nitrogen was passed to drive out the air in the flask, stirring was started, and the mixture was heated to 65°C in a water bath and kept warm. 2g of 30% hydrogen peroxide was added to start the polymerization reaction. It can be observed that the reaction temperature rose from 65°C to 85°C, and then slowly dropped to 65°C. The timing was started from the time of adding hydrogen peroxide, and the reaction was terminated after 8h of reaction. After measurement, the weight average molecular weight of polyvinyl pyrrolidone was 49,000, the residual monomer content was 990ppm, the molecular weight distribution index was 3.5, and the color Hazen value of the 10% solution was 100.

Claims

1. A method for preparing polyvinyl pyrrolidone, characterized in that: The following steps are involved: 1) Purified water, N-vinyl pyrrolidone and ammonia water are continuously introduced into a micro mixer through respective horizontal flow pumps, and pre-mixed at room temperature to form a uniform mixed solution; 2) The mixed solution coming out of the micro mixer is passed into a preheater for preheating; 3) The mixed solution from the preheater is passed into the microchannel reactor, and at the same time, hydrogen peroxide is continuously passed into the microchannel reactor through a horizontal flow pump. The material from the microchannel reactor is then passed into a delayed reactor and reacted at a temperature of 55 to 80° C. for 30 to 45 minutes to obtain polyvinyl pyrrolidone.

2. The method for preparing polyvinyl pyrrolidone according to claim 1, wherein: In step 2), the preheating temperature is 55-80°C.

3. The method for preparing polyvinyl pyrrolidone according to claim 1, wherein: The mass flow ratio of the pure water to the N-vinyl pyrrolidone is 1-4:

1.

4. The method for preparing polyvinyl pyrrolidone according to claim 1, wherein: The mass flow ratio of the ammonia water to the N-vinyl pyrrolidone is 0.003-0.05:

1.

5. The method for preparing polyvinyl pyrrolidone according to claim 1, wherein: The mass flow ratio of the hydrogen peroxide to N-vinyl pyrrolidone is 0.005-0.08:1.

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