Process for the preparation of ethylene modified polyvinyl alcohol

Abstract

The present application relates to the field of ethylene modified polyvinyl alcohol preparation, in particular to a method for preparing ethylene modified polyvinyl alcohol. The method comprises: (1) polymerizing ethylene ester monomer and ethylene in the presence of solvent and initiator to obtain a polymerization liquid; (2) sequentially performing alcoholysis treatment and separation treatment on the polymerization liquid to obtain ethylene modified polyvinyl alcohol; wherein the polymerization reaction system used in the polymerization reaction comprises: sequentially connected oxygen removal device and reaction device; the oxygen removal device comprises an oxygen remover tank body, a liquid monomer feeding port and a bubbling gas feeding port arranged at the top of the oxygen remover tank body; the reaction device comprises a reactor tank body, a deoxygenated liquid monomer feeding port and a gas phase monomer feeding port arranged at the top of the reactor tank body, and a heat exchanger arranged in the reactor tank body. The problems of low heat removal efficiency and high safety risk in the polymerization process of ethylene ester monomer and ethylene can be solved.

Description

Technical Field

[0001] This invention relates to the field of ethylene-modified polyvinyl alcohol preparation, and more specifically to a method for preparing ethylene-modified polyvinyl alcohol. Background Technology

[0002] Ethylene-modified polyvinyl alcohol (PVA) is a modified PVA product obtained by alcoholysis of ethylene-vinyl acetate copolymer. The ethylene-vinyl acetate copolymer is obtained by copolymerizing ethylene and vinyl acetate in solution. This copolymerization reaction is exothermic, and to ensure its smooth progress, the heat generated during the reaction needs to be removed promptly. Because ethylene participates in the reaction, the raw material solvent and vinyl acetate cannot reach an azeotropic state, and conventional external heat removal methods cannot meet the heat removal requirements.

[0003] Current methods involve removing the reactants from the reaction system and exchanging heat externally, which requires additional reaction system conveying devices, resulting in complex equipment and potential leakage risks.

[0004] There is an urgent need to develop a production method that can efficiently and safely deheat the reaction in order to achieve the safe preparation of ethylene-modified polyvinyl alcohol. Summary of the Invention

[0005] This invention addresses the problems of complex heat removal equipment for polymerization reactions, easy leakage at equipment connections, and high safety risks in the existing preparation process of ethylene-modified polyvinyl alcohol, and provides a method for preparing ethylene-modified polyvinyl alcohol.

[0006] To achieve the above objectives, the present invention provides a method for preparing ethylene-modified polyvinyl alcohol, the method comprising:

[0007] (1) In the presence of a solvent and an initiator, ethylene ester monomer is polymerized with ethylene to obtain a polymer solution;

[0008] (2) The polymer solution is subjected to alcoholysis and separation treatment in sequence to obtain ethylene-modified polyvinyl alcohol;

[0009] The polymerization system used in the polymerization reaction includes: a deoxygenation device and a reaction device connected in sequence;

[0010] The deoxygenation device includes a deoxygenator tank, and a liquid phase monomer inlet and a bubbling gas inlet located at the top of the deoxygenator tank.

[0011] The reaction apparatus includes a reactor tank, a deoxygenated liquid-phase monomer inlet and a gas-phase monomer inlet located at the top of the reactor tank, and a heat exchanger located inside the reactor tank.

[0012] The method for preparing ethylene-modified polyvinyl alcohol provided by this invention employs an in-reactor heat removal method during the polymerization of ethylene ester and ethylene. This method offers high heat removal efficiency, low leakage risk, and high safety, facilitating the smooth progress of the polymerization reaction and improving the stability of the reaction process. Using this method, the ethylene-modified polyvinyl alcohol obtained has a degree of polymerization of 300-2800, a degree of alcoholysis of 80-99.5 mol%, an ethylene content of 0.5-10 mol%, and a viscosity of 4% by weight aqueous solution of 4-70 mPa·s. Attached Figure Description

[0013] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0014] Figure 1 This is a schematic diagram of the polymerization reaction system used in the ethylene-modified polyvinyl alcohol method of the present invention.

[0015] Explanation of reference numerals in the attached figures

[0016] A-Deoxygenation device B-Reaction device 1-Deoxygenator tank

[0017] 2-Liquid phase monomer inlet; 3-Blowing gas inlet; 4-Blower.

[0018] 5-Deaerator agitator; 6-Condenser; 7-Deaeratored liquid monomer discharge port. 8-Reactor tank; 9-Deoxygenated liquid monomer inlet; 10-Solvent inlet

[0019] 11-Initiator inlet; 12-Gas phase monomer inlet; 13-Heat exchange coil

[0020] 13-1-Cooling medium inlet 13-2-Cooling medium outlet 14-Reaction stirrer

[0021] 15-Temperature detector 16-Pressure detector 17-Explosion-proof disc

[0022] 18-Polymerization product outlet Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0025] This invention provides a method for preparing ethylene-modified polyvinyl alcohol, the method comprising:

[0026] (1) In the presence of a solvent and an initiator, ethylene ester monomer is polymerized with ethylene to obtain a polymer solution;

[0027] (2) The polymer solution is subjected to alcoholysis and separation treatment in sequence to obtain ethylene-modified polyvinyl alcohol;

[0028] The polymerization system used in the polymerization reaction includes: a deoxygenation device and a reaction device connected in sequence;

[0029] The deoxygenation device includes a deoxygenator tank, and a liquid phase monomer inlet and a bubbling gas inlet located at the top of the deoxygenator tank.

[0030] The reaction apparatus includes a reactor tank, a deoxygenated liquid-phase monomer inlet and a gas-phase monomer inlet located at the top of the reactor tank, and a heat exchanger located inside the reactor tank.

[0031] In the production of ethylene-modified polyvinyl alcohol, the polymerization reaction between ethylene ester monomers and ethylene monomers releases a large amount of heat. Based on existing process equipment, at least a portion of the reactants are typically removed from the reaction system for external heat exchange before being returned to the reaction system. This requires corresponding material conveying devices, complicating the process and resulting in low heat removal efficiency, affecting reaction efficiency, and posing a risk of leakage during material transfer. This invention employs an in-reactor heat removal method, which offers high heat removal efficiency, low leakage risk, and high safety, ensuring the smooth progress of the polymerization reaction and improving the stability of the reaction process.

[0032] According to the present invention, in the method for preparing ethylene-modified polyvinyl alcohol, the polymerization reaction is carried out in a reaction apparatus equipped with an internal heat exchanger, and the heat of reaction is carried out of the reaction apparatus by the heat exchanger. The heat exchanger is located inside the reaction apparatus and is in direct contact with the materials of the polymerization reaction. Through contact heat exchange, the heat of reaction released during the reaction is carried away in a timely manner, achieving efficient heat removal. In the present invention, the limitation on the heat exchanger is relatively broad; conventional heat exchangers can be used, as long as the structure of the heat exchanger allows it to be installed inside the reactor and in direct contact with the reactants. Preferably, the heat exchanger can be selected from immersion coil heat exchangers, plate heat exchangers, or shell-and-tube heat exchangers.

[0033] According to a preferred embodiment of the present invention, the heat exchanger is an immersed serpentine heat exchange coil, which has excellent heat exchange effect, simple structure, and shape that is more compatible with the reaction device. It also facilitates the installation of a stirrer inside the reaction device, thereby improving the material mixing effect.

[0034] According to the present invention, in the method for preparing ethylene-modified polyvinyl alcohol, the amount of ethylene fed into the polymerization reaction satisfies the following conditions: the ethylene pressure in the polymerization reaction is 0.5-15 bar, preferably 1-12 bar.

[0035] In this invention, ethylene pressure refers to the pressure of ethylene in the reaction environment (e.g., a polymerization reactor), which can be read from the pressure gauge of the polymerization reactor.

[0036] According to the present invention, in the stated application, the amount of raw materials fed into the polymerization reaction can be selected conventionally in the art. Preferably, the weight ratio of the ethylene ester monomer:solvent:initiator is (250-6500):(100-3500):0.1.

[0037] According to the present invention, in the method for preparing ethylene-modified polyvinyl alcohol, the conditions for the polymerization reaction are broadly defined, and conventional conditions for polymerization reactions of ethylene ester monomers with ethylene in the art can be used. Preferably, the conditions for the polymerization reaction include: a reaction temperature of 40-80°C, more preferably 45-75°C; and a reaction time of 2-6.5 h, more preferably 2.5-5.5 h.

[0038] According to the present invention, in the method for preparing ethylene-modified polyvinyl alcohol, the ethylene ester monomer can be selected from conventional ethylene ester monomers in the art, for example, it can be selected from at least one of vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate and vinyl lauryl ester, preferably vinyl acetate.

[0039] According to the present invention, in the method for preparing ethylene-modified polyvinyl alcohol, the initiator can be a conventional initiator selected in the art, for example, it can be selected from at least one of azobisisobutyronitrile, azobisisoheptanenitrile, bis(4-tert-butylcyclohexyl) peroxydicarbonate, tert-pentyl peroxydipentanoate, bis(2-ethylhexyl) peroxydicarbonate, bis(3,5,5-trimethylacetyl) peroxydicarbonate, potassium persulfate, ammonium persulfate, sodium bisulfite and tartaric acid, preferably azobisisobutyronitrile.

[0040] According to the present invention, in the method for preparing ethylene-modified polyvinyl alcohol, the solvent can be a conventional solvent selected in the art, for example, it can be selected from at least one of methanol, ethanol, propanol and isobutanol, preferably methanol.

[0041] According to the present invention, in the method for preparing ethylene-modified polyvinyl alcohol, the reaction apparatus used to prepare the polymerization liquid is relatively broadly defined, as long as the reaction apparatus is equipped with the aforementioned heat exchanger and can remove the heat of reaction released during the reaction process from the reaction apparatus in a timely manner through contact heat exchange.

[0042] According to a preferred embodiment of the present invention, the polymerization liquid can be prepared by a polymerization reaction system such as... Figure 1 As shown, the polymerization reaction system includes: a deoxygenation device A and a reaction device B connected in sequence;

[0043] The deoxygenation device A includes a deoxygenator tank 1, and a liquid phase monomer inlet 2 and a bubbling gas inlet 3 located on the top of the deoxygenator tank 1.

[0044] The reaction device B includes a reactor tank 8, a deoxygenated liquid phase monomer inlet 9 and a gas phase monomer inlet 12 located at the top of the reactor tank 8, and a heat exchanger 13 located inside the reactor tank 8.

[0045] According to the present invention, in the polymerization reaction system, the deoxygenation device A is used to deoxygenate the ethylene ester monomer using bubbling gas to obtain deoxygenated ethylene ester monomer. The deoxygenation device A can reduce or remove oxygen in the liquid monomer (e.g., ethylene ester monomer) to facilitate the efficient and smooth progress of subsequent polymerization reactions. In the deoxygenation device A, both the liquid monomer inlet 2 and the bubbling gas inlet 3 can be connected to the outside via corresponding pipelines. For example, the liquid monomer inlet 2 can be connected to a liquid monomer storage tank via a liquid monomer inlet pipe. Figure 1 (Not shown in the image); the bubbling gas inlet 3 can be connected to the bubbling gas storage tank via the bubbling gas inlet pipe. Figure 1 (Not shown in the image).

[0046] According to the present invention, in the polymerization reaction system, preferably, a bubbler 4 is provided inside the deaerator tank 1, and the bubbler 4 is connected to the bubbling gas inlet 3. The bubbling gas enters the bubbler 4 through the bubbling gas inlet 3, and a large number of bubbles are generated by the bubbler 4, so as to better perform the functions of bubbling and deaeration.

[0047] According to the present invention, the bubbler 4 is broadly defined in the polymerization reaction system, and any bubbling device can be used, preferably a bubbler with a ring structure.

[0048] According to the present invention, the bubbling gas can be an inert gas, such as helium, neon, or argon, or a non-inert gas that does not participate in the above-mentioned polymerization reaction, such as nitrogen. In a preferred embodiment of the present invention, the bubbling gas is nitrogen.

[0049] According to the present invention, in the polymerization reaction system, preferably, the deaerator tank 1 is provided with a deaerator agitator 5, which performs bubbling under stirring conditions to obtain a better deaerator effect.

[0050] According to the present invention, in the polymerization reaction system, preferably, a condenser 6 is connected to the top of the deaerator tank 1 for condensing the bubbling gas that rises to the top of the deaerator tank 1 after the deaeration treatment, and incorporating the condensed product into the deoxygenated ethylene ester monomer.

[0051] According to the present invention, preferably, the condenser 6 is disposed on the top of the deaerator tank 1 and located outside the deaerator tank 1.

[0052] According to the present invention, the condenser 6 is broadly defined in the polymerization reaction system, and any condensation device capable of condensing gaseous substances to obtain liquid-phase condensation products can be used.

[0053] According to the present invention, in the polymerization reaction system, the bottom of the deaerator tank 1 is provided with a deoxygenated liquid monomer outlet 7.

[0054] According to the present invention, in the polymerization reaction system, the reaction device B is used to polymerize the deoxygenated ethylene ester monomer and ethylene to obtain the polymerization liquid.

[0055] According to the present invention, in the polymerization reaction system, in the reaction device B, preferably, the reactor tank 8 is provided with a jacket.

[0056] According to the present invention, in the polymerization reaction system, the jacket of the reactor tank 8 is relatively wide, and a conventional reactor jacket structure can be adopted. Heat can be provided for the start-up of the polymerization reaction by circulating hot oil, hot water, or hot steam in the jacket, while simultaneously providing thermal insulation for the polymerization process.

[0057] According to the present invention, in the polymerization reaction, preferably in the initial stage of the polymerization reaction, the jacket temperature is set 2-15°C higher than the reaction temperature, which is beneficial for initiating the polymerization reaction. More preferably, the jacket temperature is set 5-10°C higher than the reaction temperature.

[0058] According to the present invention, in the polymerization reaction system, the deoxidized liquid monomer inlet 9 of the reaction device B is connected to the deoxidized liquid monomer outlet 7 of the deoxygenation device A.

[0059] According to the present invention, in the polymerization reaction system, the top of the reactor tank 8 is further provided with a solvent inlet 10 and an initiator inlet 11. Both the solvent inlet 10 and the initiator inlet 11 can be connected to the outside via corresponding pipelines. For example, the solvent inlet 10 can be connected to a solvent storage tank via a solvent inlet pipe. Figure 1 (Not shown in the image); the initiator inlet 11 can be connected to the initiator storage tank via an initiator inlet pipe. Figure 1 (Not shown in the image).

[0060] According to the present invention, in the polymerization reaction system, in the reaction device B, a gas phase monomer feed valve is provided at the gas phase monomer feed inlet 12. Figure 1 (Not shown in the diagram). The feed rate of ethylene and the reaction pressure inside reactor tank 8 are adjusted by controlling the opening degree of the gas phase monomer feed valve.

[0061] According to the present invention, in the polymerization reaction system, in the reaction device B, the bottom of the reactor tank 8 is provided with a polymerization product outlet 18 for discharging the polymerization liquid.

[0062] According to the present invention, the heat exchanger 13 preferably adopts a spiral heat exchange coil.

[0063] According to the present invention, preferably, the cooling medium inlet 13-1 and the cooling medium outlet 13-2 of the heat exchanger 13 are both located at the top of the deaerator tank 1.

[0064] According to the present invention, preferably, a cooling medium inlet valve is provided at the cooling medium inlet 13-1. The flow rate of the cooling medium is adjusted by controlling the opening degree of the cooling medium inlet valve, thereby adjusting the heat dissipation process and the heat in the reaction system.

[0065] According to the present invention, in the polymerization reaction system, preferably, a reaction stirrer 14 is provided inside the reactor tank 8 in the reaction device B.

[0066] According to the present invention, in the polymerization reaction system, preferably in the reactor tank 8 of the reaction apparatus B, a temperature detector 15 is provided for monitoring temperature changes during the polymerization reaction. The definition of the temperature detector 15 in this invention is relatively broad; any conventional temperature detector, such as a thermometer, can be used.

[0067] According to the present invention, preferably, the temperature detector 15 is connected to the cooling medium feed valve through a temperature regulating valve, so as to automatically control the opening of the cooling medium feed valve according to the temperature change during the polymerization reaction, thereby controlling the temperature of the reaction system.

[0068] According to the present invention, in the polymerization reaction system, preferably, a pressure detector 16 is provided at the top of the reactor tank 8 in the reaction apparatus B. The present invention provides a broad definition for the pressure detector 16, and any conventional pressure detector, such as a pressure gauge, can be used.

[0069] According to the present invention, preferably, the pressure detector 16 is connected to the gas phase monomer feed valve through a solenoid valve, so that when the pressure of the reaction system (reaction pressure) is lower than the set pressure value, the opening of the gas phase monomer feed valve is automatically increased, and vice versa.

[0070] According to the present invention, in the polymerization reaction system, preferably, the top of the reactor tank 8 is further provided with an explosion-proof plate 17 in the reaction device B. The explosion-proof plate 17 is used to release pressure when the reaction pressure exceeds the limit, ensuring equipment safety.

[0071] According to the present invention, the material of the cooling medium used in the heat exchanger 13 is broadly defined, for example, water, reaction solvent (i.e., the solvent used in the polymerization reaction), or liquid monomer (e.g., ethylene ester monomer) can be used. Preferably, the ethylene ester monomer can be used as the cooling medium to preheat the ethylene ester monomer while cooling the reaction system through heat exchange.

[0072] According to the present invention, in the polymerization reaction system, the cooling medium inlet 13-1 is optionally connected to the deaerator tank 1, and when the cooling medium inlet 13-1 is connected to the deaerator tank 1, the cooling medium outlet 13-2 is connected to the deoxidized liquid monomer inlet 9. By adopting this connection method, a portion of the deoxidized ethylene ester monomer can be used as the cooling medium.

[0073] In this invention, the cooling medium inlet 13-1 is connected to the deaerator tank 1. Specifically, it is preferable to connect the cooling medium inlet 13-1 to the liquid phase monomer outlet 7 of the deaerator tank 1.

[0074] According to the present invention, the process of preparing the polymerization liquid using the polymerization reaction system includes:

[0075] (1) In the deoxygenation device A, ethylene ester monomer enters the deoxygenator tank 1 through the liquid monomer inlet 2. The deoxygenation agitator 5 is turned on. Under agitation conditions, bubbling gas (e.g., nitrogen) enters the bubbler 4 through the bubbling gas inlet 3. A large number of bubbles are generated by the bubbler 4. The bubbling action removes oxygen from the ethylene ester monomer, resulting in deoxygenated ethylene ester monomer. Then, the bubbling gas (carrying some ethylene ester monomer) rises to the upper part of the deoxygenator tank 1 and enters the condenser 6. Through condensation, the ethylene ester monomer carried in the bubbling gas is cooled and condensed into a liquid stream, which returns to the deoxygenator tank 1 and is incorporated into the deoxygenated ethylene ester monomer. The deoxygenated ethylene ester monomer leaves the deoxygenation device A through the liquid monomer outlet 7 at the bottom of the deoxygenator tank 1.

[0076] (2) In the reaction device B, the deoxygenated ethylene ester monomer, ethylene, solvent and initiator enter the reactor tank 8 through the deoxygenated liquid-phase monomer inlet 9, gas-phase monomer inlet 12, solvent inlet 10 and initiator inlet 11, respectively. The reaction stirrer 14 is turned on to make the above raw materials uniformly mixed to obtain a reaction system. Then, the polymerization reaction is carried out at the reaction temperature. During the reaction, when the temperature of the reaction system is higher than the set reaction temperature, the cooling medium inlet valve in the heat exchanger 13 is automatically opened. The cooling medium carries away the heat in the reaction system through the heat exchanger 13. After heat exchange, the temperature of the reaction system drops. When the temperature of the reaction system is lower than the set temperature, the cooling medium inlet valve in the heat exchanger 13 is automatically closed. The heat of the reaction system is maintained and the reaction continues, realizing continuous feeding and continuous polymerization. The polymerization liquid leaves the reaction device B through the polymerization product outlet 18 at the bottom of the reactor tank 8.

[0077] According to the present invention, the alcoholysis treatment in the method for preparing ethylene-modified polyvinyl alcohol is broadly defined and can be carried out in a manner known in the art. For example, the polymerization liquid can be alcoholyzed in the presence of a catalyst, followed by neutralization with a terminator to end the alcoholysis.

[0078] According to the present invention, for the alcoholysis, preferably, the catalyst may be selected from at least one of sodium hydroxide, potassium hydroxide, sulfuric acid, hydrochloric acid and p-toluenesulfonic acid, and more preferably sodium hydroxide.

[0079] According to the present invention, preferably, for the alcoholysis, the molar ratio of the catalyst to the target polymerization product in the polymerization liquid is (0.001-0.1):1.

[0080] According to the present invention, preferably, the temperature of the alcoholysis treatment is 30-50°C, more preferably 35-45°C.

[0081] According to the present invention, in the method for preparing ethylene-modified polyvinyl alcohol, before the alcoholysis treatment, the concentration of the polymerization solution is adjusted so that the concentration of the polymerization product in the polymerization solution is 5-50% by weight.

[0082] According to the present invention, the concentration adjustment can be achieved by adding a polymerization reaction solvent (e.g., methanol) to the polymerization solution. By adjusting the concentration of the polymer product resin in the polymerization solution to 5-50% by weight, it is more conducive to pelletizing after alcoholysis.

[0083] According to the present invention, the separation process in the method for preparing ethylene-modified polyvinyl alcohol is broadly defined and can be carried out in a manner known in the art. For example, the alcoholysis product can be washed with a solvent (preferably the same substance as the polymerization solvent), followed by centrifugation and drying to obtain ethylene-modified polyvinyl alcohol.

[0084] The present invention will be described in detail below through embodiments. In the following embodiments and comparative examples,

[0085] Unless otherwise specified, all materials used are common commercially available products.

[0086] Degree of alcoholysis of polyvinyl alcohol: determined according to the method specified in Appendix D of GB / T 12010.2-2010.

[0087] Viscosity of polyvinyl alcohol aqueous solution: determined according to the method specified in Appendix E of GB / T 12010.2-2010 and using a Brookfield viscometer.

[0088] Degree of polymerization of polyvinyl alcohol: determined according to the method specified in GB / T 12010.5-2010.

[0089] Ethylene content in polyvinyl alcohol: determined by proton nuclear magnetic resonance spectroscopy.

[0090] Example 1

[0091] (1) Adopt Figure 1The system shown undergoes a polymerization reaction. In deoxygenation device A, vinyl acetate enters deoxygenator tank 1 through liquid monomer inlet 2, and deoxygenation agitator 5 is turned on, with the stirring speed controlled at 100 rpm. Nitrogen gas enters annular bubbler 4 through bubbling gas inlet 3, generating a large number of bubbles. The bubbling action removes oxygen from the vinyl acetate, resulting in deoxygenated vinyl acetate. Then, nitrogen gas (carrying some vinyl acetate) rises to the upper part of deoxygenator tank 1 and enters condenser 6. After condensation, the vinyl acetate carried by the nitrogen gas is cooled and condensed into a liquid stream, which returns to deoxygenator tank 1 and is mixed with the deoxygenated vinyl acetate. The liquid then leaves deoxygenation device A through liquid monomer outlet 7 at the bottom of deoxygenator tank 1 and enters reaction device B.

[0092] (2) In reaction apparatus B, deoxygenated vinyl acetate, ethylene, methanol, and azobisisobutyronitrile (AIBN) enter reactor tank 8 through the deoxygenated liquid monomer inlet 9, gaseous monomer inlet 12, solvent inlet 10, and initiator inlet 11, respectively. The weight ratio of AIBN:methanol:deoxygenated vinyl acetate is 0.014:42.85:100, and the ethylene pressure (polymerization pressure, i.e., reactor gauge pressure) is 12 bar. (Nitrogen is pre-purified sequentially in reactor tank 8 before the ethylene feedstock is introduced.) After two gas purgings and three ethylene purgings, the reaction stirrer 14 is turned on (stirring speed controlled at 80 rpm) to ensure uniform mixing of the above raw materials to obtain the reaction system. Circulating hot water at 70°C is then introduced into the outer jacket of the reactor tank 8, and the polymerization reaction is carried out at the set reaction temperature (65°C). During the reaction, temperature detector 15 (connected to the cooling medium feed valve via a temperature control valve) and pressure detector 16 (connected to the gaseous monomer feed valve via a solenoid valve) are monitored. The system monitors temperature and pressure changes during the reaction process. The explosion-proof plate 17 can release pressure when the reaction pressure exceeds the limit, ensuring system safety. During the reaction, when the temperature of the reaction system exceeds 65℃, the cooling medium inlet valve at the cooling medium inlet 13-1 of the heat exchange coil 13 automatically opens, allowing the cooling medium (secondary demineralized water) to flow into the heat exchange coil 13 (immersion coil heat exchange coil) and out through the cooling medium outlet 13-2. This heat exchange removes heat from the reaction system, causing the temperature to drop. When the temperature drops below 65℃, the cooling medium inlet valve automatically closes, maintaining the heat in the reaction system. When the reaction pressure is below 12 bar, the opening of the gaseous monomer inlet valve automatically increases; conversely, it automatically decreases to maintain the reaction pressure. The reaction continues, and after 5 hours, the polymerization liquid continuously leaves the reaction device B through the polymerization product outlet 18. By adjusting the outflow rate of the polymerization liquid, the liquid level in the reaction device B remains constant, thus maintaining the reaction time.

[0093] (3) The unreacted residual monomers in the polymerization liquid were blown out, and methanol was added to adjust the polymer concentration to 40% by weight. Sodium hydroxide methanol solution (sodium hydroxide methanol solution was prepared by mixing methanol and sodium hydroxide, wherein the molar ratio of sodium hydroxide to polymer product was 0.03:1) was added for alcoholysis (alcoholysis temperature was 40℃, alcoholysis time was 1h). Then, acetic acid was added to terminate the reaction. The product was washed with methanol, and then centrifuged and dried (drying temperature was 110℃, drying time was 3.5h) to obtain a white ethylene-modified polyvinyl alcohol product (denoted as P1).

[0094] The product P1 has a degree of polymerization of 988, a degree of alcoholysis of 98.5 mol%, an ethylene content of 8.5 mol%, and a viscosity of 13.4 mPa·s for a 4% by weight P1 aqueous solution.

[0095] The polymerization and alcoholysis conditions and results in the above preparation process are detailed in Table 1, and the parameters of the ethylene-modified polyvinyl alcohol product are detailed in Table 2.

[0096] Examples 2-5

[0097] The method of Example 1 was followed, except that different raw material feeding ratios and polymerization conditions were used in the polymerization stage, and different alcoholysis conditions were used in the alcoholysis stage. All other steps and conditions were the same as in Example 1, yielding ethylene-modified polyvinyl alcohol products (denoted as P2-P5).

[0098] The polymerization and alcoholysis conditions and results in the above preparation process are detailed in Table 1, and the parameters of the ethylene-modified polyvinyl alcohol product are detailed in Table 2.

[0099] Table 1

[0100]

[0101]

[0102] Continued from Table 1

[0103]

[0104] Note: In Table 1, for the heat removal effect, if the difference between the measured temperature inside the reaction device and the set heat-generating reaction temperature does not exceed ±1.0℃ when the polymerization is carried out continuously for no less than 3 hours, it is considered to be effective heat removal.

[0105] Table 2

[0106]

[0107] As can be seen from the above embodiments, the method of the present invention for preparing ethylene-modified polyvinyl alcohol has high heat removal efficiency, low leakage risk, and high safety during the preparation process, which is conducive to the smooth progress of the polymerization reaction and thus can improve the stability of the reaction process.

[0108] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing ethylene-modified polyvinyl alcohol, characterized in that, The method includes: (1) In the presence of a solvent and an initiator, ethylene ester monomer is polymerized with ethylene to obtain a polymer solution; (2) The polymer solution is subjected to alcoholysis and separation treatment in sequence to obtain ethylene-modified polyvinyl alcohol; The polymerization system used in the polymerization reaction includes: a deoxygenation device and a reaction device connected in sequence; The deoxygenation device includes a deoxygenator tank, and a liquid phase monomer inlet and a bubbling gas inlet located at the top of the deoxygenator tank. The reaction apparatus includes a reactor tank, a deoxygenated liquid-phase monomer inlet and a gas-phase monomer inlet located at the top of the reactor tank, and a heat exchanger located inside the reactor tank.

2. The method according to claim 1, wherein, The heat exchanger is selected from immersion coil heat exchangers, plate heat exchangers, or shell and tube heat exchangers, preferably immersion coil heat exchangers.

3. The method according to claim 1 or 2, wherein, In the polymerization reaction, the ethylene pressure is 0.5-15 bar, preferably 1-12 bar.

4. The method according to any one of claims 1-3, wherein, The conditions for the polymerization reaction include: a reaction temperature of 40-80℃, preferably 45-75℃; and a reaction time of 2-6.5h, preferably 2.5-5.5h.

5. The method according to any one of claims 1-4, wherein, The vinyl ester monomer is selected from at least one of vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, and vinyl lauryl ester, preferably vinyl acetate; And / or, the initiator is selected from at least one of azobisisobutyronitrile, azobisisoheptanenitrile, bis(4-tert-butylcyclohexyl) peroxydicarbonate, tert-pentyl peroxypentanoate, bis(2-ethylhexyl) peroxydicarbonate, bis(3,5,5-trimethylacetyl) peroxide, potassium persulfate, ammonium persulfate, sodium bisulfite and tartaric acid, preferably azobisisobutyronitrile; And / or, the solvent is selected from at least one of methanol, ethanol, propanol and isobutanol, preferably methanol.

6. The method according to any one of claims 1-5, wherein, The reactor tank is equipped with a jacket on its exterior. Preferably, in the polymerization reaction, the jacket temperature is set 2-15°C higher than the reaction temperature.

7. The method according to any one of claims 1-6, wherein, The alcoholysis process is carried out in the presence of a catalyst.

8. The method according to claim 7, wherein, The catalyst is selected from at least one of sodium hydroxide, potassium hydroxide, sulfuric acid, hydrochloric acid and p-toluenesulfonic acid, preferably sodium hydroxide.

9. The method according to claim 8, wherein, The alcoholysis treatment is carried out at a temperature of 30-50°C, preferably 35-45°C.

10. The method according to any one of claims 1-9, wherein, Prior to the alcoholysis treatment, the concentration of the polymerization solution is adjusted so that the concentration of the polymerization product in the polymerization solution is 5-50% by weight.

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