Preparation method of partially alcoholyzed polyvinyl alcohol
By using a specific solvent to add two solvents in the alcoholylation process of polyvinyl alcohol, the problem of difficulty in controlling alcoholylation in traditional alcoholylation processes is solved, and the stable control of alcoholylation within the appropriate range is achieved, and the process control accuracy and product quality are improved.
Patent Information
- Application Number
- CN202311491982.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-11-10
- Publication Date
- 2025-05-13
AI Technical Summary
In traditional alcoholylation processes, the increase in alcoholylation time leads to a continuous increase in alcoholylation. If the terminator is not neutralized, the alcoholylation may reach more than 99 mol%, making it difficult to control the alcoholylation within the appropriate range.
A specific solvent is added in two times, and the alcohol content is controlled during the alcoholylation process. A partial alcoholylated polyvinyl alcohol is prepared by reacting a mixed solution of alkali and alcohol with a polyvinyl acetate polymer solution. The alcoholylation degree is between 70% mol/mol-95% mol/mol, and no terminator is required.
The stable control of alcoholylation is achieved, which is basically not affected by neutralization time, avoiding the problem of excessive alcoholylation, and improving the process control accuracy and product quality.
Smart Images
Figure SMS_1 
Figure SMS_2
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of polyvinyl alcohol production, and specifically relates to a preparation method of partially alcoholysed polyvinyl alcohol. Background Art
[0002] Polyvinyl alcohol is classified according to the degree of alcoholysis, and is mainly divided into three types: complete alcoholysis type polyvinyl alcohol, partial alcoholysis type polyvinyl alcohol and low alcoholysis type polyvinyl alcohol. Partial alcoholysis type polyvinyl alcohol mainly refers to the alcoholysis degree between 70% mol / mol and 95% mol / mol. Usually, sodium hydroxide is used as a catalyst for alcoholysis in industrial production, which has a fast reaction speed and good product quality. Under the catalysis of sodium hydroxide, the methanol solution of polyvinyl acetate mainly undergoes the following three reactions: transesterification reaction, saponification reaction and methyl ester decomposition side reaction. When the system is anhydrous, the main transesterification reaction is carried out, and the alkali plays a catalytic role, so the dosage is also small, so less sodium acetate is generated. However, the saponification reaction proceeds very slowly, and the entire alcoholysis reaction is slow. When water is present in the system, the saponification reaction rate is greatly increased. At the same time, due to the presence of water, the alkali dissociation degree is large, the catalytic effect is strengthened, and the transesterification reaction rate is accelerated, and the entire alcoholysis reaction proceeds very quickly. In actual production, as the reaction time increases, the degree of alcoholysis will increase. In order to obtain partially alcoholyzed polyvinyl alcohol, acid will be added at an appropriate time to terminate the reaction.
[0003] Chinese patent document CN111100228A discloses a polyvinyl alcohol and a preparation method thereof, wherein raw materials including vinyl acetate monomer, solvent and initiator are polymerized, and then polyvinyl acetate obtained by the polymerization reaction is subjected to alcoholysis, and a terminator needs to be added to stop the reaction during the alcoholysis reaction. This technology is not easy to explode during the polymerization process, and will not cause the problem of difficult removal of vinyl acetate monomer wrapped in particles.
[0004] The prior art has the following disadvantages: In the traditional alcoholysis process, as the alcoholysis time increases, the alcoholysis degree continues to increase. If no terminator is added for neutralization in the middle, the alcoholysis degree will increase to about 99 mol%. Summary of the invention
[0005] Based on the above problems, the present invention provides a method for preparing partially alcoholyzed polyvinyl alcohol, which does not require the addition of a terminator after alcoholysis and in which the alcoholysis degree is substantially unaffected by the neutralization time.
[0006] On the one hand, the present invention provides a method for preparing partially alcoholysed polyvinyl alcohol, comprising: obtaining a polyvinyl acetate polymer solution by reacting vinyl acetate monomer, a solvent and an initiator, and performing an alcoholysis reaction with a mixed solution of alkali and alcohol to obtain the polyvinyl acetate polymer solution; the molar ratio of the alcohol in the mixed solution of alkali and alcohol to the polyvinyl acetate polymer solution is 1.4-2.0; and the solvent is added twice during the reaction process of obtaining the polyvinyl acetate polymer solution.
[0007] Furthermore, the second addition of the solvent is performed after the unreacted monomers are removed by distillation under reduced pressure.
[0008] Furthermore, the solvent is an ester.
[0009] Furthermore, the solvent is one or more of methyl acetate, ethyl acetate, butyl acetate, methoxyethyl acetate, ethoxyethyl acetate and isoamyl acetate.
[0010] Furthermore, the alcohol in the mixed solution of alkali and alcohol is one or more of methanol, ethanol, isopropanol and n-butanol.
[0011] Furthermore, the vinyl acetate monomer added to the polyvinyl acetate polymer solution reaction includes 5-120 parts of solvent and 0.01-1.0 parts of initiator, calculated as mass percentage, based on 100 parts of vinyl acetate monomer.
[0012] Furthermore, the polyvinyl acetate polymer solution reaction process also includes adding a polymerization inhibitor.
[0013] Furthermore, the initiator includes an organic peroxide or azo initiator.
[0014] Furthermore, the added amount of the solvent is 40wt%-80wt% of the monomer.
[0015] Furthermore, the method comprises the following steps: adding vinyl acetate monomer, solvent and initiator to carry out polymerization reaction, reacting at 60-70°C for 2-6 hours, adding inhibitor, and distilling under reduced pressure to obtain polyvinyl acetate polymer solution; diluting the polyvinyl acetate polymer solution to 20.0-60.0wt%, adding a mixed solution of alkali and alcohol to carry out alcoholysis reaction to obtain the obtained product.
[0016] The present invention has the following beneficial effects: 1) The present invention adopts a specific solvent to be added twice and controls the alcohol content during the alcoholysis process, thereby solving the problem of inaccurate control caused by excessively fast reaction of alcoholysis of some alcoholysis-type polyvinyl alcohol, and no terminator needs to be added after alcoholysis.
[0017] 2) In the traditional alcoholysis process, the alcoholysis degree increases with the increase of alcoholysis time. If no terminator is added to neutralize it, the alcoholysis degree will increase to about 99 mol%. According to the method of the present invention, after the alcoholysis reaction reaches 70% mol / mol-95% mol / mol, the alcoholysis degree is basically not affected by the alcoholysis time, and the alcoholysis degree can be controlled by controlling the alcohol ratio. DETAILED DESCRIPTION
[0018] The examples are provided to better illustrate the content of the present invention, but the content of the present invention is not limited to the examples. Therefore, those skilled in the art can make non-essential improvements and adjustments to the implementation scheme according to the above content of the invention, which still fall within the protection scope of the present invention.
[0019] The average polymerization degree of the polyvinyl alcohol prepared by the invention is 200-4000, and the alcoholysis degree is 70% mol / mol-95% mol / mol.
[0020] The product of the polyvinyl alcohol of the present invention has an average degree of polymerization of less than 1000, and the initiator comprises an organic peroxide initiator, preferably one or more of bis(2-ethylhexyl) peroxydicarbonate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, bis(3,5,5-trimethylhexanoyl) peroxide, dipropyl peroxydicarbonate and tert-pentyl peroxypivalate, and further preferably bis(2-ethylhexyl) peroxydicarbonate.
[0021] The polyvinyl alcohol product of the present invention has an average polymerization degree higher than 1000, and the initiator is at least one of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, tert-butyl hydroperoxide, tert-butyl peroxypivalate, and dibenzoyl peroxide; preferably, the initiator is azobisisobutyronitrile.
[0022] The alkali used in the present invention is at least one of potassium hydroxide and sodium hydroxide, preferably sodium hydroxide; the molar ratio of the alkali to the polyvinyl acetate is 0.005-0.2.
[0023] The polymerization inhibitor used in the present invention is at least one of hydroquinone, hydroquinone, p-tert-butylcatechol and 2,4-diphenyl-4-methylpentene.
[0024] The alcoholysis reaction time of the present invention is 0.15-4.0 hours, preferably 0.2-2 hours.
[0025] The alcoholysis reaction temperature of the present invention is 25°C-55°C, and the preferred reaction temperature is 30°C-50°C.
[0026] Example 1 First, nitrogen was introduced into the reactor to replace the air, and then 100 parts of vinyl acetate and 0.02 parts of azobisisobutyronitrile were polymerized in 5 parts of methyl acetate solvent at a polymerization temperature of 60°C for 3 hours. When the polymerization reaction was completed, hydroquinone inhibitor was added, and then the temperature was controlled at 50°C for reduced pressure distillation to remove unreacted monomers, and then 80 parts of methyl acetate were added for reduced pressure distillation to obtain a polyvinyl acetate polymer solution. A portion of the polyvinyl acetate polymer solution was taken to adjust to 100 parts of methyl acetate alcoholysis solution with a concentration of 20wt% (including 20 parts of polyvinyl acetate resin and 80 parts of methyl acetate). Methanol and sodium hydroxide were prepared into a methanol alkaline solution, the molar ratio of sodium hydroxide to polyvinyl acetate resin was 0.005, and the molar ratio of methanol to polyvinyl acetate resin was 1.4. The methanol alkali solution was added to the alcoholysis solution at 50°C and mixed evenly for alcoholysis. The alcoholysis solution was divided into three parts. After alcoholysis for 30 minutes, one part was pelletized, washed with methanol, filtered and dried at 85°C-100°C to obtain a PVA sample. The other two parts were pelletized after 50 minutes and 80 minutes respectively, washed, filtered and dried at 85°C-100°C to obtain PVA samples. The average polymerization degree of PVA obtained under this condition was 3983, and its alcoholysis degree was shown in Table 1: Table 1 Example 2 First, nitrogen was introduced into the reactor to replace the air, and then 100 parts of vinyl acetate and 1.0 part of bis(2-ethylhexyl)peroxydicarbonate were polymerized in 120 parts of butyl acetate solvent at a polymerization temperature of 65°C for 5 hours. When the polymerization reaction was finished, hydroquinone inhibitor was added, and then the temperature was controlled at 65°C for vacuum distillation to remove the unreacted monomers, and then 60 parts of methyl acetate were added for vacuum distillation to obtain a polyvinyl acetate polymer solution. A portion of the polyvinyl acetate polymer solution was taken to adjust to 100 parts of methyl acetate alcoholysis solution with a concentration of 60wt% (including 60 parts of polyvinyl acetate resin, 39 parts of methyl acetate, and 1 part of water). Methanol and sodium hydroxide were prepared into a methanol alkaline solution, the molar ratio of sodium hydroxide to polyvinyl acetate resin was 0.2, and the molar ratio of methanol to polyvinyl acetate resin was 2.0. The methanol alkali solution was added to the alcoholysis solution at 40°C and mixed evenly for alcoholysis. The alcoholysis solution was divided into three parts. After alcoholysis for 12 minutes, one part was pelletized, washed and filtered, and then dried at 85°C-100°C to obtain a PVA sample. The other two parts were pelletized after 40 minutes and 80 minutes respectively, washed and filtered, and then dried at 85°C-100°C to obtain PVA samples. The average polymerization degree of PVA obtained under this condition was 205, and its alcoholysis degree was shown in Table 2: Table 2 Alcoholysis time, min 12 40 80 Alcoholysis degree, (mol / mol)% 94.8 94.9 94.8 Example 3 First, nitrogen was passed into the reactor to replace the air, and then 100 parts of vinyl acetate and 0.08 parts of azobisisobutyronitrile were polymerized in 20 parts of methyl acetate and solvent at a polymerization temperature of 62°C for 4 hours. When the polymerization reaction was completed, 2,4-diphenyl-4-methylpentene was added as a polymerization inhibitor, and then the temperature was controlled at 40°C for reduced pressure distillation to remove the unreacted monomers, and then 40 parts of methyl acetate were added for reduced pressure distillation to obtain a polyvinyl acetate polymer solution. A portion of the polyvinyl acetate polymer solution was taken to adjust to 100 parts of a methyl acetate alcoholysis solution with a concentration of 35wt% (including 35 parts of polyvinyl acetate resin, 63.8 parts of methyl acetate, and 1.2 parts of water). Methanol and sodium hydroxide were prepared into a methanol alkaline solution, the molar ratio of sodium hydroxide to polyvinyl acetate resin was 0.02, and the molar ratio of methanol to polyvinyl acetate resin was 1.63. The methanol alkali solution was added to the alcoholysis solution at 30°C and mixed evenly for alcoholysis. The alcoholysis solution was divided into three parts. After alcoholysis for 25 minutes, one part was pelletized, washed and filtered, and then dried at 85°C-100°C to obtain a PVA sample. The other two parts were pelletized after 60 minutes and 120 minutes respectively, washed and filtered, and then dried at 85°C-100°C to obtain PVA samples. The average polymerization degree of PVA obtained under this condition was 1746, and its alcoholysis degree was shown in Table 3: Table 3 Example 4 First, nitrogen was introduced into the reactor to replace the air, and then 100 parts of vinyl acetate and 0.04 parts of azobisisobutyronitrile were used to carry out solution polymerization in 5 parts of ethyl acetate, 3 parts of ethoxyethyl acetate and 3 parts of isoamyl acetate solvents. The polymerization temperature was 70°C and the reaction was carried out for 5 hours. When the polymerization reaction was completed, 2,4-diphenyl-4-methylpentene inhibitor was added, and then the temperature was controlled at 65°C and the unreacted monomers were removed by vacuum distillation. Then 60 parts of methoxyethyl acetate were added and vacuum distilled at 65°C to obtain a polyvinyl acetate polymer solution. A portion of the polyvinyl acetate polymer solution was taken to adjust to 100 parts of a mixed solvent solution with a concentration of 30wt% (including 30 parts of polyvinyl acetate resin, 69.5 parts of methyl acetate and 0.5 parts of water). Methanol and sodium hydroxide were prepared into a methanol alkaline solution, and the molar ratio of sodium hydroxide to polyvinyl acetate resin was 0.05, and the molar ratio of methanol to polyvinyl acetate resin was 1.9. The methanol alkali solution was added to the alcoholysis solution at 35°C and mixed evenly for alcoholysis. The alcoholysis solution was divided into three parts. After alcoholysis for 20 minutes, one part was pelletized, washed and filtered, and then dried at 85°C-100°C to obtain a PVA sample. The other two parts were pelletized after 55 minutes and 120 minutes respectively, washed and filtered, and then dried at 85°C-100°C to obtain PVA samples. The average polymerization degree of PVA obtained under this condition was 2420, and its alcoholysis degree was shown in Table 4: Table 4 Alcoholysis time, min 20 55 90 Alcoholysis degree, (mol / mol)% 87.81 87.89 87.78 Example 5 First, nitrogen was introduced into the reactor to replace the air, and then 100 parts of vinyl acetate and 0.8 parts of di(3,5,5-trimethylhexanoyl)peroxide were polymerized in 90 parts of methyl acetate solvent at a polymerization temperature of 64°C for 3.5 hours. When the polymerization reaction was completed, p-tert-butylcatechol was added as a polymerization inhibitor, and then the temperature was controlled at 70°C for reduced pressure distillation to remove the unreacted monomers, and then 70 parts of methyl acetate were added for reduced pressure distillation to obtain a polyvinyl acetate polymer solution. A portion of the polyvinyl acetate polymer solution was taken to adjust to 100 parts of methyl acetate alcoholysis solution with a concentration of 50wt% (including 50 parts of polyvinyl acetate resin, 48 parts of methyl acetate, and 2 parts of water). Methanol and sodium hydroxide were prepared into a methanol alkaline solution, the molar ratio of sodium hydroxide to polyvinyl acetate resin was 0.1, and the molar ratio of methanol to polyvinyl acetate resin was 1.8. The methanol alkali solution was added to the alcoholysis solution at 40°C and mixed evenly for alcoholysis. The alcoholysis solution was divided into three parts. After alcoholysis for 15 minutes, one part was pelletized, washed and filtered, and then dried at 85°C-100°C to obtain a PVA sample. The other two parts were pelletized after 40 minutes and 80 minutes respectively, washed and filtered, and then dried at 85°C-100°C to obtain PVA samples. The average polymerization degree of PVA obtained under this condition was 543, and its alcoholysis degree was shown in Table 5: Table 5 Alcoholysis time, min 15 40 80 Alcoholysis degree, (mol / mol)% 88.1 88.1 88.1 Comparative Example 1 This comparative example is the same as Example 1 except that “the temperature is controlled at 50°C for reduced pressure distillation to remove unreacted monomers, 80 parts of methanol are added for reduced pressure distillation to obtain a polyvinyl acetate polymer solution, and a portion of the polyvinyl acetate polymer solution is taken to prepare 100 parts of a methanol solution with a concentration of 20wt% (comprising 20 parts of polyvinyl acetate resin and 80 parts of methanol)”.
[0027] The average polymerization degree of PVA obtained under this condition is 3988, and its alcoholysis degree is shown in Table 6: Table 6 Alcoholysis time, min 30 50 80 Alcoholysis degree, (mol / mol)% 72.5 85.5 89.1 Comparative Example 2 This comparative example is the same as Example 2 except that "the temperature is controlled at 65°C for reduced pressure distillation to remove unreacted monomers, and 60 parts of methanol are added for reduced pressure distillation" and "the molar ratio of methanol to polyvinyl acetate resin is 3.0".
[0028] The average polymerization degree of PVA obtained under this condition is 206, and its alcoholysis degree is shown in Table 7: Table 7 Alcoholysis time, min 12 40 80 Alcoholysis degree, (mol / mol)% 95.6 97.3 99.0 As can be seen from Tables 1-7 above, the specific means of adding a specific solvent twice and controlling the alcohol content during the alcoholysis process are adopted in the polyvinyl acetate polymer solution in Examples 1-5 of the present invention, while the specific means of adding a specific solvent only for the first time is not adopted in Comparative Example 1-2. The results obtained thereby show that the alcoholysis degree of Examples 1-5 is substantially unaffected by the alcoholysis time, while the alcoholysis degree of Comparative Example 1-2 increases with the increase of the alcoholysis time; thus, it can be seen that the technical solution of adding a specific solvent twice and controlling the alcohol content during the alcoholysis process in the polyvinyl acetate polymer solution can ensure that the alcoholysis degree of the obtained polyvinyl alcohol is not affected by the alcoholysis time.
[0029] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.
Claims
1. A method for preparing partially alcoholysed polyvinyl alcohol, characterized in that: The invention comprises a polyvinyl acetate polymer solution obtained by reacting vinyl acetate monomer, solvent and initiator, and alcoholysis reaction with a mixed solution of alkali and alcohol; the molar ratio of alcohol in the mixed solution of alkali and alcohol to the polyvinyl acetate polymer solution is 1.4-2.0; and the solvent is added twice in the reaction process of preparing the polyvinyl acetate polymer solution.
2. The method for preparing partially alcoholyzed polyvinyl alcohol according to claim 1, characterized in that: The second addition of the solvent is performed after the unreacted monomers are removed by distillation under reduced pressure.
3. The method for preparing partially alcoholyzed polyvinyl alcohol according to claim 1 or 2, characterized in that: The solvent is an ester.
4. The method for preparing partially alcoholyzed polyvinyl alcohol according to claim 3, characterized in that: The solvent is one or more of methyl acetate, ethyl acetate, butyl acetate, methoxyethyl acetate, ethoxyethyl acetate and isoamyl acetate.
5. The method for preparing partially alcoholyzed polyvinyl alcohol according to any one of claims 1 to 4, characterized in that: The alcohol in the mixed solution of alkali and alcohol is one or more of methanol, ethanol, isopropanol and n-butanol.
6. The method for preparing partially alcoholyzed polyvinyl alcohol according to any one of claims 1 to 5, characterized in that: The vinyl acetate monomer added to the polyvinyl acetate polymer solution reaction includes 5-120 parts of solvent and 0.01-1.0 parts of initiator, calculated by mass percentage, based on 100 parts of vinyl acetate monomer.
7. The method for preparing partially alcoholyzed polyvinyl alcohol according to claim 6, characterized in that: The polyvinyl acetate polymer solution reaction process also includes adding a polymerization inhibitor.
8. The method for preparing partially alcoholyzed polyvinyl alcohol according to claim 1 or 7, characterized in that: The initiator includes an organic peroxide or azo initiator.
9. The method for preparing partially alcoholyzed polyvinyl alcohol according to claim 8, characterized in that: The amount of the solvent added is 40 wt% to 80 wt% of the monomer.
10. The method for preparing partially alcoholyzed polyvinyl alcohol according to any one of claims 1 to 9, characterized in that: The following steps are involved: Vinyl acetate monomer, solvent and initiator are added to carry out polymerization reaction, and after reacting at 60-70° C. for 2-6 hours, a polymerization inhibitor is added, and then vacuum distillation is carried out to obtain a polyvinyl acetate polymer solution; the polyvinyl acetate polymer solution is diluted to 20.0-60.0wt%, and a mixed solution of alkali and alcohol is added to carry out alcoholysis reaction to obtain the product.
Citation Information
Patent Citations
Polyvinyl alcohol and preparation method thereof
CN111100228A