Ethylene-vinyl acetate copolymer alcoholysis method, ethylene-vinyl alcohol copolymer and application of ethylene-vinyl alcohol copolymer

Abstract

The invention relates to the field of resin, and discloses an alcoholysis method of an ethylene-vinyl acetate copolymer, the ethylene-vinyl alcohol copolymer and application of the ethylene-vinyl alcohol copolymer. The method comprises the following steps: (1) an ethylene-vinyl acetate copolymer, alkali and an alcohol solvent are mixed to obtain a mixed solution, first alcoholysis is carried out, and the dosage of the alkali enables the pH value of the mixed solution to be not lower than 10; and (2) carrying out second alcoholysis on the product of the first alcoholysis under a heating condition. The ethylene-vinyl alcohol prepared by the method has the alcoholysis degree of not less than 99.5%, and has lower yellow index and alkali residue.

Description

Technical Field

[0001] The present invention relates to the field of resins, and specifically to a method for alcoholysis of ethylene-vinyl acetate copolymer and ethylene-vinyl alcohol copolymer and their applications. Background Art

[0002] Ethylene-vinyl alcohol copolymer (abbreviated as EVOH) is a new type of polymer synthetic material that combines the processability of ethylene polymers and the gas barrier properties of vinyl alcohol polymers. It has excellent gas barrier properties, water resistance, oil resistance, ammonia resistance and other properties. EVOH, polyvinylidene chloride (PVDC) and polyamide (PA) are known as the world's three major high-barrier resins. In the 1950s, DuPont in the United States first obtained EVOH resin by copolymerizing ethylene with vinyl acetate (VAc) and then alcoholysis.

[0003] In the existing EVOH production process, EVOH can generally be prepared by polymerizing ethylene and vinyl acetate through conventional methods such as emulsion polymerization, solution polymerization or suspension polymerization and then saponification. In the solution polymerization process, alcohols with no more than 4 carbons are usually used as solvents, and methanol is preferably used. The ethylene-vinyl acetate copolymer solution obtained by polymerization contains solvent methanol and unreacted vinyl acetate monomer. By utilizing the characteristic that methanol and vinyl acetate form an azeotrope in the distillation column, unreacted vinyl acetate is removed by adding methanol solution or blowing in methanol vapor, and then it enters the alcoholysis device. Methyl acetate formed by the reaction is removed by distillation, and EVOH with an alcoholysis degree of more than 99% is obtained at the bottom, but generally below 99.5%. The alcoholysis of ethylene-vinyl acetate copolymer can adopt kettle alcoholysis. CN104098733A discloses a method for alcoholysis of ethylene-vinyl acetate copolymer. Under the conditions of -4 to 0 atmospheres, the reaction temperature is 40 - 85 °C, and the reaction time is 4 - 7 hours for alcoholysis. Then, neutralization and washing are carried out to obtain the EVOH product, which mainly has the problems of long alcoholysis reaction time and low production efficiency. The alcoholysis of ethylene-vinyl acetate copolymer can also adopt tower alcoholysis. CN1196724C discloses a method for manufacturing saponified ethylene-vinyl acetate copolymer. Alcoholysis catalysts usually adopt methanol solutions of sodium hydroxide, potassium hydroxide, etc. CN11543301A discloses the use of an acidic deep eutectic solvent of choline chloride-p-toluenesulfonic acid for alcoholysis, which can effectively reduce the problem that the presence of metal ions affects the product quality when using sodium hydroxide, and the solvent can be recycled multiple times, but no specific recovery method for the solvent is mentioned. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems existing in the prior art, such as low alcoholysis degree, high yellow index and high alkali residue content of ethylene-vinyl alcohol products, and to provide a method for alcoholysis of ethylene-vinyl acetate copolymer and ethylene-vinyl alcohol copolymer and their applications.

[0005] To achieve the above object, a first aspect of the present invention provides a method for alcoholysis of ethylene-vinyl acetate copolymer, the method comprising:

[0006] (1) Mixing ethylene-vinyl acetate copolymer, an alkali and an alcohol solvent to obtain a mixed solution, and performing a first alcoholysis, wherein the amount of the alkali is such that the pH of the mixed solution is not lower than 10;

[0007] (2) Performing a second alcoholysis on the product of the first alcoholysis under heating conditions.

[0008] A second aspect of the present invention provides an ethylene-vinyl alcohol copolymer prepared by the above method.

[0009] A third aspect of the present invention provides the use of the above ethylene-vinyl alcohol copolymer in at least one of packaging materials, automobile fuel tanks, oxygen barrier floor heating pipes, textile materials and medical materials.

[0010] Through the above technical solution, the present invention adopts the method that after a first alcoholysis reaction, an EVOH with an alcoholysis degree of less than 99% is obtained, and then this solution is further subjected to an alcoholysis reaction of ethylene-vinyl acetate copolymer under heating conditions to obtain an EVOH product with an alcoholysis degree of not less than 99.5%, and has a lower yellowness index and alkali residue. Description of the Drawings

[0011] Figure 1 is the production process flow of the present invention.

[0012] Description of the Reference Numerals

[0013] 01 is the first alcoholysis reactor; 02 is the motor; 03 is the mixing area; 04 is the first reaction area; 05 is the second reaction area; 06 is the extrusion area; 101, 102, 104 and 108 are material input pipelines; 103 and 107 are gas output pipelines; 105 is the connection pipeline for 01 to output to 03; 106 is the pipeline for transporting the gas in the reaction product of 04 to 01; 109 is the extrusion pipeline. Detailed Embodiments

[0014] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0015] A first aspect of the present invention provides a method for alcoholysis of ethylene-vinyl acetate copolymer, the method comprising:

[0016] (1) Mix ethylene-vinyl acetate copolymer, an alkali, and an alcohol solvent to obtain a mixed solution, and perform the first alcoholysis. The dosage of the alkali is such that the pH of the mixed solution is not lower than 10;

[0017] (2) Under heating conditions, perform the second alcoholysis on the product of the first alcoholysis.

[0018] In the present invention, when the above method is used for the alcoholysis of ethylene-vinyl acetate copolymer, due to the addition of the second alcoholysis, the alcoholysis method can improve the alcoholysis degree of ethylene-vinyl alcohol, thereby increasing the barrier performance when the ethylene-vinyl acetate copolymer is made into a product and improving the product quality.

[0019] The inventors of the present invention found that for the above-mentioned first alcoholysis, the alcoholysis degree of the obtained product is less than 99 mol%. After heating the product of the first alcoholysis for the second alcoholysis, a product with an alcoholysis degree not lower than 99.5 mol% can be obtained.

[0020] In the present invention, in order to alcoholyze ethylene-vinyl acetate copolymer, ethylene-vinyl acetate copolymer and an alcohol solvent need to be alcoholyzed under alkaline conditions.

[0021] In the present invention, controlling the pH of the mixed solution to be not lower than 10 can not only meet the conditions for the first alcoholysis, but also prepare for the second alcoholysis to obtain a higher alcoholysis degree, and can also reduce the alkali residue in the product.

[0022] In the present invention, there is no limitation on the type of the alkali. Conventional types of alkali in the art can be used as long as the pH of the mixed system can be made not lower than 10. For example, the alkali is sodium hydroxide and / or potassium hydroxide.

[0023] In the present invention, in order to alcoholyze ethylene-vinyl acetate copolymer, the weight ratio of ethylene-vinyl acetate copolymer to alcohol solvent is 1:1 - 4, and it can be 1:1, 1:2, 1:3, 1:4 or any range formed by any two of the above values and the values within the range.

[0024] In the present invention, controlling the weight ratio of ethylene-vinyl acetate copolymer to alcohol solvent to meet the above range can not only reduce the solvent, but also reduce the recovery cost.

[0025] In the present invention, there are no restrictions on the conditions for mixing, as long as the alcoholysis of ethylene-vinyl acetate copolymer can proceed smoothly. Preferably, the conditions for mixing include: the temperature is 50-120 °C, which can be 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, 100 °C, 110 °C, 120 °C or any range formed by any two of the above values and the values within the range, and the time is 0.1-1 hour, which can be 0.1 hour, 0.2 hour, 0.3 hour, 0.4 hour, 0.5 hour, 0.6 hour, 0.7 hour, 0.8 hour, 0.9 hour, 1 hour or any range formed by any two of the above values and the values within the range.

[0026] In the present invention, controlling the mixing conditions within the above range can not only be easily controlled in production, reduce the usage amount of alkali and solvent, but also increase the alcoholysis degree of ethylene-vinyl alcohol product.

[0027] In the present invention, there are no restrictions on the alcohol solvent, as long as the alcoholysis of ethylene-vinyl acetate copolymer can proceed smoothly. Preferably, the alcohol solvent is an alcohol solvent with 1-4 carbon atoms, more preferably at least one of methanol, ethanol, propanol, ethylene glycol, n-butanol and tert-butanol, and more preferably methanol.

[0028] In the present invention, based on the total molar amount of the ethylene-vinyl acetate copolymer, the content of the structural unit derived from ethylene in the ethylene-vinyl acetate copolymer is 20-60 mol%, which can be 20 mol%, 25 mol%, 30 mol%, 35 mol%, 40 mol%, 45 mol%, 50 mol%, 55 mol%, 60 mol% or any range formed by any two of the above values and the values within the range, and preferably 25-50 mol%.

[0029] In the present invention, the weight-average molecular weight of the ethylene-vinyl acetate copolymer is 20,000-250,000 g / mol, which can be 20,000 g / mol, 50,000 g / mol, 100,000 g / mol, 150,000 g / mol, 200,000 g / mol, 250,000 g / mol or any range formed by any two of the above values and the values within the range. Preferably, the weight-average molecular weight of the ethylene-vinyl acetate copolymer is 30,000-150,000 g / mol, and the molecular weight distribution is 1.1-3, which can be 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3 or any range formed by any two of the above values and the values within the range.

[0030] In the present invention, in order to obtain a higher degree of alcoholysis, the heating conditions include: the temperature is 120 - 250 °C, which can be 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, 250 °C or any range formed by any two of the above values and the values within the range, and the time is 0.5 - 2 h, which can be 0.5 h, 1 h, 1.5 h, 2 h or any range formed by any two of the above values and the values within the range.

[0031] In the present invention, controlling the heating conditions within the above range can not only improve the alcoholysis degree of ethylene - vinyl alcohol, but also prevent the yellowness index from being too high, thus improving the barrier property of the product.

[0032] Preferably, the heating includes primary heating and secondary heating.

[0033] In the present invention, controlling the heating to be primary heating and secondary heating can achieve zone temperature control, and further achieve precise regulation of the production process and product quality.

[0034] In the present invention, the temperature of the primary heating is 120 - 200 °C, which can be 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C or any range formed by any two of the above values and the values within the range, and the time is 0.2 - 1 h, which can be 0.2 h, 0.3 h, 0.4 h, 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1 h or any range formed by any two of the above values and the values within the range.

[0035] In the present invention, controlling the conditions of the primary heating within the above range can not only improve the alcoholysis degree of ethylene - vinyl alcohol and control the yellowness index from being too high, but also further improve the alcoholysis degree of ethylene - vinyl alcohol.

[0036] More preferably, the temperature of the secondary heating is 140 - 250 °C, which can be 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, 250 °C or any range formed by any two of the above values and the values within the range, and the time is 0.2 - 1 h, which can be 0.2 h, 0.3 h, 0.4 h, 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1 h or any range formed by any two of the above values and the values within the range.

[0037] In the present invention, controlling the conditions of the secondary heating within the above range can not only further improve the alcoholysis degree of ethylene - vinyl alcohol and control the yellowness index from being too high, but also further improve the alcoholysis degree of ethylene - vinyl alcohol.

[0038] In the present invention, the temperature of the second heating is higher than that of the first heating.

[0039] In the present invention, the temperature of the second heating is 10 - 100 °C higher than that of the first heating, and it can be 10 °C, 20 °C, 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, 100 °C or any range formed by any two of the above values and the values within the range.

[0040] In the present invention, the first heating is carried out first and then the second heating.

[0041] In the present invention, controlling to carry out low-temperature heating first and then high-temperature heating can further improve the degree of alcoholysis of ethylene-vinyl alcohol.

[0042] In the present invention, there is no limitation on the equipment for carrying out the above-mentioned second alcoholysis, and it can meet the above-mentioned heating conditions. Preferably, for continuous processing and suitable for industrial production such as kettle alcoholysis, alcoholysis in an extruder, etc., the above-mentioned second alcoholysis can be carried out in an extruder, preferably in a twin-screw extruder.

[0043] In the present invention, when using an extruder, the rotation speed of the extruder is controlled to be 30 - 100 revolutions per minute, and it can be 30 revolutions per minute, 40 revolutions per minute, 50 revolutions per minute, 60 revolutions per minute, 70 revolutions per minute, 80 revolutions per minute, 90 revolutions per minute, 100 revolutions per minute or any range formed by any two of the above values and the values within the range; preferably, the speed at which the product of the first alcoholysis enters the extruder is 80 - 1500 kg / h, and it can be 80 kg / h, 90 kg / h, 100 kg / h, 110 kg / h, 120 kg / h, 130 kg / h, 140 kg / h, 150 kg / h, 200 kg / h, 300 kg / h, 400 kg / h, 500 kg / h, 600 kg / h, 700 kg / h, 800 kg / h, 900 kg / h, 1000 kg / h, 1100 kg / h, 1200 kg / h, 1300 kg / h, 1400 kg / h, 1500 kg / h or any range formed by any two of the above values and the values within the range.

[0044] In the present invention, controlling the rotation speed of the extruder and the speed at which the product of the first alcoholysis enters the extruder within the above ranges can control the residence time of the material and improve the degree of alcoholysis of the ethylene-vinyl alcohol product.

[0045] In the present invention, in order to obtain a higher degree of alcoholysis, the method further includes: adjusting the pH of the second alcoholysis product to 2 - 6, and it can be 2, 3, 4, 5, 6 or any range formed by any two of the above values and the values within the range.

[0046] In the present invention, controlling the pH of the second alcoholysis product within the above range can further improve the degree of alcoholysis.

[0047] In the present invention, the method further includes: extruding, strand forming, cooling, washing, and drying the product after pH adjustment.

[0048] Preferably, the temperature of the cooling is 10 - 25°C, which can be 10°C, 12°C, 14°C, 16°C, 18°C, 20°C, 22°C, 24°C, 25°C or any range formed by any two of the above values and the values within the range, and the time is 0.2 - 1 h, which can be 0.2 h, 0.3 h, 0.4 h, 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1 h or any range formed by any two of the above values and the values within the range.

[0049] In the present invention, the method for adjusting the pH includes: contacting the second alcoholysis product with an acid. There is no limitation on the acid, and conventional types of acids in the art can be used as long as the pH of the mixed system can be made to be 2 - 6. Preferably, it is at least one of acetic acid, propionic acid, and carbon dioxide, and more preferably acetic acid.

[0050] Combined Figure 1 , a specific embodiment of the present invention includes the following steps:

[0051] (1) Respectively introducing the alcohol solution of ethylene - vinyl acetate copolymer and the alcohol solution of the base into 01 through 101 and 102 for mixing, and introducing alcohol solvent gas through 104 and discharging gas through 105 to perform the first alcoholysis. Among them, the weight ratio of the ethylene - vinyl acetate copolymer to the alcohol solvent is 1:1 - 4, and the amount of the base is such that the pH of the mixed solution is not lower than 10;

[0052] (2) Feeding the product of the first alcoholysis into an extruder (02 - 06) at a speed of 80 - 1500 kg / h, controlling the rotation speed of the extruder at 30 - 100 revolutions per minute through 02, and performing the second alcoholysis under the conditions of the first heating (temperature: 120 - 200°C, time: 0.2 - 1 h) at 04 and the second heating (temperature: 140 - 250°C, time: 0.2 - 1 h) at 05 to obtain an ethylene - vinyl alcohol copolymer solution;

[0053] (3) Returning the gas generated by the first heating to 01 through 106 with a reflux ratio of 0.1 - 1; discharging the gas generated by the second heating through 107;

[0054] (4) Adding an acid to the product after the second heating from which the gas has been discharged in step (3) through 108 to make the pH of the product after the second heating 2 - 6;

[0055] (5) Extruding, strand forming, cooling, washing, and drying the product of step (4) through 06.

[0056] The second aspect of the present invention provides an ethylene-vinyl alcohol copolymer prepared by the above method.

[0057] The degree of alcoholysis of the ethylene-vinyl alcohol copolymer obtained in the present invention is not less than 99.5 mol%, and can be 99.5 mol%, 99.6 mol%, 99.7 mol%, 99.8 mol%, 99.9 mol%, 100 mol% or any range formed by any two values above and the values within the range.

[0058] According to the present invention, the structural unit derived from ethylene in the ethylene-vinyl alcohol copolymer is consistent with that in the ethylene-vinyl acetate copolymer in the raw material. Based on the total molar amount of the ethylene-vinyl alcohol copolymer, the content of the structural unit derived from ethylene is 20-60 mol%, and can be 20 mol%, 25 mol%, 30 mol%, 35 mol%, 40 mol%, 45 mol%, 50 mol%, 55 mol%, 60 mol% or any range formed by any two values above and the values within the range, preferably 25-50 mol%.

[0059] According to the present invention, the weight-average molecular weight and molecular weight distribution of the ethylene-vinyl alcohol copolymer are consistent with those of the ethylene-vinyl acetate copolymer in the raw material. The weight-average molecular weight of the ethylene-vinyl alcohol copolymer is 20,000-250,000 g / mol, and can be 20,000 g / mol, 50,000 g / mol, 100,000 g / mol, 150,000 g / mol, 200,000 g / mol, 250,000 g / mol or any range formed by any two values above and the values within the range. Preferably, the molecular weight distribution is 1.1-3, and can be 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3 or any range formed by any two values above and the values within the range.

[0060] According to the present invention, the residual amount of alkali in the ethylene-vinyl alcohol copolymer is 1000 ppm or less.

[0061] According to the present invention, the yellowness index of the ethylene-vinyl alcohol copolymer is 6-16, and can be 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 or any range formed by any two values above and the values within the range.

[0062] In the present invention, the residual amount of alkali is the content of acetate salts such as sodium acetate and / or potassium acetate of metal cations in the above alkali.

[0063] The third aspect of the present invention provides the application of the above ethylene-vinyl alcohol copolymer in at least one of packaging materials, automobile fuel tanks, oxygen barrier floor heating pipes, textile materials and medical materials.

[0064] The present invention will be described in detail below with reference to embodiments. In the following embodiments, the content of the structural unit derived from ethylene in the ethylene-vinyl acetate copolymer is 32 mol%; the weight-average molecular weight of the ethylene-vinyl acetate copolymer is 75,000 g / mol, and the molecular weight distribution is 1.6.

[0065] Test method for weight-average molecular weight and molecular weight distribution: Measured by GPC method;

[0066] Product chromaticity analysis: Hunter Lab colorimeter, model: UltraScan VIS, mode type: RSIN including specular reflection, measurement method: general, observation area: 1 square inch, 3 holes, simulated light: natural light at 2 pm.

[0067] The test method for degree of alcoholysis is as follows: The dried EVOH is crushed to 100 mesh, sequentially extracted and purified with deionized water, and dried at 120 °C. The obtained ethylene-vinyl alcohol copolymer is subjected to NMR measurement under the following conditions, and the degree of alcoholysis is obtained by the following analysis method:

[0068] Analysis method: The integral value (I 1 ) of the peak at the chemical shift of 3.7 - 4 ppm and the integral value (I 2 ) of the peak at the chemical shift of 0.6 - 1.8 ppm are obtained from the spectrum measured at 40 °C. The integral value (I 3 ) of the peak at the chemical shift of 3.1 - 3.7 ppm, the integral value (I 4 ) of the peak at the chemical shift of 0.6 - 1.8 ppm, and the integral value (I 5 ) of the peak at the chemical shift of 1.9 - 2.1 ppm are obtained from the spectrum measured at 95 °C. Here, the peak at the chemical shift of 0.6 - 1.8 ppm is mainly from methylene protons, and the peak at the chemical shift of 1.9 - 2.1 ppm is from the protons of the methyl in the unhydrolyzed vinyl acetate unit. The degree of alcoholysis is calculated by the following formula 1 from these integral values:

[0069] Formula 1:

[0070] Test method and calculation method for alkali residue content: Place the dry sample particles (10 g) in 100 mL of 0.01 M hydrochloric acid aqueous solution, stir at 95 °C for 3 hours, and quantitatively analyze the stirred aqueous solution by ion chromatography. The measurement is carried out using a standard curve prepared for an aqueous solution of metal chloride, and the amount of sodium acetate is calculated in g. The calculation formula is: amount of sodium acetate / 10 × 100%.

[0071] Example 1

[0072] (1) The ethylene-vinyl acetate copolymer methanol solution enters the first alcoholysis reactor 01 through pipeline 101, and the methanol solution containing sodium hydroxide enters through 102. The weight ratio of the ethylene-vinyl acetate copolymer to methanol is 1:3, and the pH of the material is 12. The methanol gas phase enters the first alcoholysis reactor 01 through 104 with a flow rate of 200 kg / h. The temperature of the first alcoholysis is 90 °C and the time is 0.5 h. The resin solution after alcoholysis is discharged from 105, and the flow rate of the copolymer solution obtained is 98 kg / h. After analysis, the alcoholysis degree of the product is 98.5%.

[0073] (2) Feed the product of step (1) into the second alcoholysis reactor (02 - 06). Control the rotation speed of the extruder at 40 revolutions per minute through 02, and control the temperature of the first reaction zone 04 at 160 °C (time is 0.3 h). After passing through the first reaction zone 04, return the gaseous methanol and the methyl acetate generated by the reaction to the first alcoholysis reactor 01 with a reflux ratio of 0.8 through pipeline 106. Then the copolymer solution enters the second reaction zone 05, and control the temperature of the second reaction zone 05 at 180 °C (time is 0.4 h). After passing through the second reaction zone, discharge the gaseous methyl acetate and methanol through the second exhaust port 108. Then add acetic acid solution through pipeline 108 to make the pH of the material 6. After extrusion through the extrusion zone 06, it is formed into strips through a perforated plate with 12 holes of φ3 mm, and passed through a cooling water tank. Control the temperature of the cooling water tank at 20 °C (time is 0.4 h), and then obtain EVOH particles through a pelletizer. Then obtain EVOH products through water washing and drying. The various parameters of the EVOH products are shown in Table 1.

[0074] Example 2

[0075] (1) The ethylene-vinyl acetate copolymer methanol solution enters the first alcoholysis reactor 01 through pipeline 101, and the methanol solution containing sodium hydroxide enters through 102. The weight ratio of the ethylene-vinyl acetate copolymer to methanol is 1:4, making the pH of the material 13. The methanol gas phase enters the first alcoholysis reactor 01 through 104 with a flow rate of 150 kg / h. The temperature of alcoholysis is 100 °C and the time is 0.5 h. The resin solution after alcoholysis is discharged from 105, and the flow rate of the copolymer solution obtained is 94 kg / h. After analysis, the alcoholysis degree of the product is 98.2%.

[0076] (2) Feed the product of step (1) into the second alcoholysis reactor (02 - 06). Control the rotation speed of the extruder through 02 to be 40 revolutions per minute, and control the temperature of the first reaction zone 04 to be 140 °C (for 0.6 h). After passing through the first reaction zone 04, return gaseous methanol and the generated methyl acetate to the first alcoholysis reactor 01 with a reflux ratio of 1 through pipeline 106. Then the resin liquid enters the second reaction zone 05. Control the temperature of the second reaction zone 05 to be 170 °C (for 0.5 h). After passing through the second reaction zone, discharge gaseous methyl acetate and methanol through the second exhaust port 108. Then add acetic acid solution through pipeline 108 to obtain a material pH of 6. After extrusion through the extrusion zone 06, it is formed into strips through a 12 - hole perforated plate with a diameter of φ3 mm, and passed through a cooling water tank. Control the temperature of the cooling water tank to be 20 °C (for 0.5 h), and then obtain EVOH particles through a pelletizer. After that, obtain the EVOH product through multi - stage water washing and drying. Analyze the various parameters of the EVOH product as shown in Table 1.

[0077] Example 3

[0078] (1) The ethylene - vinyl acetate copolymer methanol solution enters the first alcoholysis reactor 01 through pipeline 101, and the methanol solution containing sodium hydroxide enters through 102. The weight ratio of the ethylene - vinyl acetate copolymer to methanol is 1:3, obtaining a material pH of 12. Methanol gas phase enters the first alcoholysis reactor 01 through 104 with a flow rate of 200 kg / h. The temperature of the first alcoholysis is 90 °C, and the time is 0.5 h. The alcoholyzed resin liquid is discharged from 105, obtaining a copolymer solution flow rate of 98 kg / h. After analysis, the alcoholysis degree of the product is 98.5%.

[0079] (2) Feed the product of step (1) into the second alcoholysis reactor (02 - 06). Control the rotation speed of the extruder through 02 to be 40 revolutions per minute, and control the temperature of the first reaction zone 04 to be 180 °C (for 0.3 h). After passing through the first reaction zone 04, return gaseous methanol and the generated methyl acetate to the first alcoholysis reactor 01 with a reflux ratio of 0.8 through pipeline 106. Then the copolymer solution enters the second reaction zone 05. Control the temperature of the second reaction zone 05 to be 210 °C (for 0.4 h). After passing through the second reaction zone, discharge gaseous methyl acetate and methanol through the second exhaust port 108. Then add acetic acid solution through pipeline 108 to make the material pH 6. After extrusion through the extrusion zone 06, it is formed into strips through a 12 - hole perforated plate with a diameter of φ3 mm, and passed through a cooling water tank. Control the temperature of the cooling water tank to be 20 °C (for 0.4 h), and then obtain EVOH particles through a pelletizer. After that, obtain the EVOH product through water washing and drying. Analyze the various parameters of the EVOH product as shown in Table 1.

[0080] Example 4

[0081] (1) The methanol solution of ethylene-vinyl acetate copolymer enters the first alcoholysis reactor 01 through pipeline 101, and the methanol solution containing sodium hydroxide enters through 102. The weight ratio of ethylene-vinyl acetate copolymer to methanol is 1:3, and the pH of the material obtained is 12. The methanol gas phase enters the first alcoholysis reactor 01 through 104, with a flow rate of 200 kg / h. The temperature of the first alcoholysis is 90 °C, and the time is 0.5 h. The resin solution after alcoholysis is discharged from 105, and the flow rate of the copolymer solution obtained is 98 kg / h. After analysis, the degree of alcoholysis of the product is 98.5%.

[0082] (2) The product of step (1) is sent to the second alcoholysis reactor (02-06). The rotation speed of the extruder is controlled at 40 revolutions per minute through 02, and the temperature of the first reaction zone 04 is controlled at 160 °C (time is 0.3 h). After passing through the first reaction zone 04, the gaseous methanol and methyl acetate generated by the reaction are refluxed to the first alcoholysis reactor 01 with a reflux ratio of 0.8 through pipeline 106. Then the copolymer solution enters the second reaction zone 05, and the temperature of the second reaction zone 05 is controlled at 160 °C (time is 0.4 h). After passing through the second reaction zone, the gaseous methyl acetate and methanol are discharged through the second exhaust port 108. Then acetic acid solution is added through pipeline 108 to make the pH of the material 6. After extrusion through the extrusion zone 06, it is formed into strips through a perforated plate with 12 holes of φ3 mm, and passed through a cooling water tank. The temperature of the cooling water tank is controlled at 20 °C (time is 0.4 h), and then EVOH particles are obtained through a pelletizer. Then the EVOH product is obtained through water washing and drying. The various parameters of the EVOH product are shown in Table 1.

[0083] Example 5

[0084] (1) The methanol solution of ethylene-vinyl acetate copolymer enters the first alcoholysis reactor 01 through pipeline 101, and the methanol solution containing sodium hydroxide enters through 102. The weight ratio of ethylene-vinyl acetate copolymer to methanol is 1:3, and the pH of the material obtained is 12. The methanol gas phase enters the first alcoholysis reactor 01 through 104, with a flow rate of 200 kg / h. The temperature of the first alcoholysis is 90 °C, and the time is 0.5 h. The resin solution after alcoholysis is discharged from 105, and the flow rate of the copolymer solution obtained is 98 kg / h. After analysis, the degree of alcoholysis of the product is 98.5%.

[0085] (2) Feed the product of step (1) into the second alcoholysis reactor (02 - 06). Control the rotation speed of the extruder through 02 to be 40 revolutions per minute, and control the temperature of the first reaction zone 04 to be 180 °C (for a time of 0.3 h). After passing through the first reaction zone 04, return gaseous methanol and the generated methyl acetate to the first alcoholysis reactor 01 with a reflux ratio of 0.8 through pipeline 106. Then the copolymer solution enters the second reaction zone 05. Control the temperature of the second reaction zone 05 to be 180 °C (for a time of 0.4 h). After passing through the second reaction zone, discharge gaseous methyl acetate and methanol through the second exhaust port 108. Then add acetic acid solution through pipeline 108 to make the pH of the material 6. After extrusion through the extrusion zone 06, it is formed into strips through a 12-hole perforated plate with a diameter of φ3 mm, and passed through a cooling water tank. Control the temperature of the cooling water tank to be 20 °C (for a time of 0.4 h), and then obtain EVOH particles through a pelletizer. After that, obtain the EVOH product through water washing and drying. Analyze the various parameters of the EVOH product as shown in Table 1.

[0086] Example 6

[0087] (1) The methanol solution of ethylene - vinyl acetate copolymer enters the first alcoholysis reactor 01 through pipeline 101, and the methanol solution containing sodium hydroxide enters through 102. The weight ratio of ethylene - vinyl acetate copolymer to methanol is 1:3, and the pH of the obtained material is 12. The methanol gas phase enters the first alcoholysis reactor 01 through 104 with a flow rate of 200 kg / h. The temperature of the first alcoholysis is 90 °C, and the time is 0.5 h. The resin solution after alcoholysis is discharged from 105, and the flow rate of the obtained copolymer solution is 98 kg / h. After analysis, the alcoholysis degree of the product is 98.5%.

[0088] (2) Feed the product of step (1) into the second alcoholysis reactor (02 - 06). Control the rotation speed of the extruder through 02 to be 40 revolutions per minute, and control the temperature of the first reaction zone 04 to be 180 °C (for a time of 0.3 h). After passing through the first reaction zone 04, return gaseous methanol and the generated methyl acetate to the first alcoholysis reactor 01 with a reflux ratio of 0.8 through pipeline 106. Then the copolymer solution enters the second reaction zone 05. Control the temperature of the second reaction zone 05 to be 160 °C (for a time of 0.4 h). After passing through the second reaction zone, discharge gaseous methyl acetate and methanol through the second exhaust port 108. Then add acetic acid solution through pipeline 108 to make the pH of the material 6. After extrusion through the extrusion zone 06, it is formed into strips through a 12-hole perforated plate with a diameter of φ3 mm, and passed through a cooling water tank. Control the temperature of the cooling water tank to be 20 °C (for a time of 0.4 h), and then obtain EVOH particles through a pelletizer. After that, obtain the EVOH product through water washing and drying. Analyze the various parameters of the EVOH product as shown in Table 1.

[0089] Example 7

[0090] (1) The ethylene-vinyl acetate copolymer methanol solution enters the first alcoholysis reactor 01 through pipeline 101, and the methanol solution containing sodium hydroxide enters through 102. The weight ratio of the ethylene-vinyl acetate copolymer to methanol is 1:3, and the pH of the material obtained is 12. Methanol gas phase enters the first alcoholysis reactor 01 through 104, with a flow rate of 200 kg / h. The temperature of the first alcoholysis is 90 °C and the time is 0.5 h. The resin solution after alcoholysis is discharged from 105, and the flow rate of the copolymer solution obtained is 98 kg / h. After analysis, the alcoholysis degree of the product is 98.5%.

[0091] (2) Feed the product of step (1) into the second alcoholysis reactor (02-06). Control the rotation speed of the extruder to be 40 revolutions per minute through 02, and control the temperature of the first reaction zone 04 to be 160 °C (time is 0.3 h). After passing through the first reaction zone 04, gas methanol and methyl acetate generated by the reaction are refluxed to the first alcoholysis reactor 01 with a reflux ratio of 0.8 through pipeline 106. Then the copolymer solution enters the second reaction zone 05, and control the temperature of the second reaction zone 05 to be 260 °C (time is 0.4 h). After passing through the second reaction zone, gas methyl acetate and methanol are discharged through the second exhaust port 108. Then acetic acid solution is added through pipeline 108 to make the pH of the material 6. After extrusion through the extrusion zone 06, it is formed into strips through a perforated plate with 12 holes of φ3 mm, and passed through a cooling water tank. Control the temperature of the cooling water tank to be 20 °C (time is 0.4 h), and then obtain EVOH particles through a pelletizer. Then, EVOH products are obtained through water washing and drying. The parameters of the EVOH products are analyzed as shown in Table 1.

[0092] Example 8

[0093] (1) The ethylene-vinyl acetate copolymer methanol solution enters the first alcoholysis reactor 01 through pipeline 101, and the methanol solution containing sodium hydroxide enters through 102. The weight ratio of the ethylene-vinyl acetate copolymer to methanol is 1:3, and the pH of the material obtained is 12. Methanol gas phase enters the first alcoholysis reactor 01 through 104, with a flow rate of 200 kg / h. The temperature of the first alcoholysis is 90 °C and the time is 0.5 h. The resin solution after alcoholysis is discharged from 105, and the flow rate of the copolymer solution obtained is 98 kg / h. After analysis, the alcoholysis degree of the product is 98.5%.

[0094] (2) Feed the product of step (1) into the second alcoholysis reactor (02-06). Control the rotation speed of the extruder at 80 rpm through 02, and control the temperature of the first reaction zone 04 at 160 °C (for 0.3 h). After passing through the first reaction zone 04, return gaseous methanol and the generated methyl acetate to the first alcoholysis reactor 01 with a reflux ratio of 0.8 through pipeline 106. Then the copolymer solution enters the second reaction zone 05. Control the temperature of the second reaction zone 05 at 180 °C (for 0.4 h). After passing through the second reaction zone, discharge gaseous methyl acetate and methanol through the second exhaust port 108. Then add acetic acid solution through pipeline 108 to make the pH of the material 6. After extrusion in the extrusion zone 06, it is formed into strips through a perforated plate with 12 holes of φ3 mm, and passed through a cooling water tank. Control the temperature of the cooling water tank at 20 °C (for 0.4 h). Then obtain EVOH particles through a pelletizer, and then obtain EVOH products through water washing and drying. Analyze the various parameters of the EVOH products as shown in Table 1.

[0095] Comparative Example 1

[0096] According to the method of Example 1, except that the second alcoholysis reactor is cancelled, analyze the various parameters of the EVOH products as shown in Table 1.

[0097] Comparative Example 2

[0098] According to the method of Example 1, except that the second alcoholysis reactor is cancelled and the pH of the material is made 13, analyze the various parameters of the EVOH products as shown in Table 1.

[0099] Comparative Example 3

[0100] (1) The ethylene-vinyl acetate copolymer methanol solution enters the first alcoholysis reactor 01 through pipeline 101, and the methanol solution containing sodium hydroxide enters through 102. The weight ratio of the ethylene-vinyl acetate copolymer to methanol is 1:3, and the pH of the material is made 8. The methanol gas phase enters the first alcoholysis reactor 01 through 104 with a flow rate of 200 kg / h. The temperature of the first alcoholysis is 90 °C and the time is 0.5 h. The resin solution after alcoholysis is discharged from 105, and the flow rate of the copolymer solution obtained is 98 kg / h.

[0101] (2) Feed the product of step (1) into the second alcoholysis reactor (02-06), control the rotation speed of the extruder at 40 revolutions per minute through 02, control the temperature of the first reaction zone 04 at 160 °C (for 0.3 h). After passing through the first reaction zone 04, reflux gaseous methanol and the methyl acetate generated by the reaction back to the first alcoholysis reactor 01 with a reflux ratio of 0.8 through pipeline 106. Then the copolymer solution enters the second reaction zone 05, control the temperature of the second reaction zone 05 at 180 °C (for 0.4 h). After passing through the second reaction zone, discharge gaseous methyl acetate and methanol through the second exhaust port 108. Then add acetic acid solution through pipeline 108 to make the pH of the material 6. After extrusion through the extrusion zone 06, it is formed into strips through a perforated plate with 12 holes of φ3 mm, and passed through a cooling water tank, control the temperature of the cooling water tank at 20 °C (for 0.4 h), and then obtain EVOH particles through a pelletizer. Then obtain EVOH products through water washing and drying. Analyze the various parameters of the EVOH products as shown in Table 1.

[0102] Table 1

[0103]

[0104]

[0105] Continued Table 1

[0106]

[0107] It can be seen from the results in Table 1 that the ethylene-vinyl alcohol copolymer obtained by using the method of the present invention has a degree of alcoholysis of more than 99.5 mol%, and has a lower yellow index and alkali residue.

[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 technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for alcoholysis of ethylene-vinyl acetate copolymer, characterized in that, the method comprises: (1) Mixing ethylene-vinyl acetate copolymer, alkali and alcohol solvent to obtain a mixed solution, and performing first alcoholysis, wherein the dosage of the alkali is such that the pH of the mixed solution is not lower than 10; (2) Performing second alcoholysis on the product of the first alcoholysis under heating conditions.

2. The method according to claim 1, wherein, the weight ratio of the ethylene-vinyl acetate copolymer to the alcohol solvent is 1:1 - 4; and / or, the conditions for mixing include: temperature is 50 - 120 °C, time is 0.1 - 1 hour; and / or, the alkali is sodium hydroxide and / or potassium hydroxide.

3. The method according to claim 1 or 2, wherein, the alcohol solvent is an alcohol solvent with 1 - 4 carbon atoms, more preferably at least one of methanol, ethanol, propanol, ethylene glycol, n-butanol and tert-butanol, and more preferably methanol.

4. The method according to claim 1 or 2, wherein, based on the total molar amount of the ethylene-vinyl acetate copolymer, the content of the structural unit derived from ethylene in the ethylene-vinyl acetate copolymer is 20 - 60 mol%, preferably 25 - 50 mol%; and / or, the weight-average molecular weight of the ethylene-vinyl acetate copolymer is 20,000 - 250,000 g / mol, and the molecular weight distribution is 1.1 - 3.

5. The method according to claim 1 or 2, wherein, the conditions for heating include: temperature is 120 - 250 °C, time is 0.5 - 2 h; preferably, the heating includes first heating and second heating; preferably, the temperature of the first heating is 120 - 200 °C, time is 0.2 - 1 h; preferably, the temperature of the second heating is 140 - 250 °C, time is 0.2 - 1 h; preferably, the temperature of the second heating is higher than that of the first heating; preferably, the temperature of the second heating is 10 - 100 °C higher than that of the first heating.

6. The method according to claim 1 or 2, wherein, the second alcoholysis is carried out in an extruder; preferably in a twin-screw extruder; preferably, the rotation speed of the extruder is 30 - 100 revolutions per minute; preferably, the speed at which the product of the first alcoholysis enters the extruder is 80 - 1500 kg / h.

7. The method according to claim 1 or 2, wherein, the method further comprises: adjusting the pH of the product of the second alcoholysis to 2 - 6; preferably, the method for adjusting pH includes: contacting the product of the second alcoholysis with an acid.

8. Ethylene-vinyl alcohol copolymer prepared by the method according to any one of claims 1 - 7.

9. The ethylene-vinyl alcohol copolymer according to claim 8, wherein, the degree of alcoholysis of the ethylene-vinyl alcohol copolymer is not lower than 99.5 mol%; and / or, based on the total molar amount of the ethylene-vinyl alcohol copolymer, the content of the structural unit derived from ethylene is 20 - 60 mol%, preferably 25 - 50 mol%; and / or, the weight-average molecular weight of the ethylene-vinyl alcohol copolymer is 20,000 - 250,000 g / mol, and the molecular weight distribution is 1.1 - 3; And / or, the residual amount of alkali in the ethylene-vinyl alcohol copolymer is 1000 ppm or less; And / or, the yellowness index of the ethylene-vinyl alcohol copolymer is 6-16.

10. Use of the ethylene-vinyl alcohol copolymer according to claim 8 or 9 in at least one of packaging materials, automobile fuel tanks, oxygen-barrier floor heating pipes, textile materials, and medical materials.

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