Preparation method of polyvinyl alcohol with low sodium acetate content

Abstract

The invention discloses a preparation method of polyvinyl alcohol with low sodium acetate content, and belongs to the technical field of polyvinyl alcohol preparation, the preparation method comprises the following steps: S1, adding methyl acetate into a methanol solution of polyvinyl acetate, and uniformly mixing to obtain a mixed solution; adding a methanol solution of sodium hydroxide into the mixed solution, uniformly mixing, transferring to a belt alcoholysis machine, and carrying out alcoholysis reaction to obtain a polyvinyl alcohol solid product after the reaction is finished; s2, the polyvinyl alcohol solid product is smashed, liquid removal and drying are conducted, and polyvinyl alcohol with the low sodium acetate content is obtained.The method only needs to conduct simple technical improvement on an original production line and is easy to implement; through optimization of process parameters, production is stable, continuous production is easy to realize, and the purpose of producing a polyvinyl alcohol product with low alcoholysis degree and low sodium acetate content is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyvinyl alcohol preparation, and particularly relates to a preparation method of low-sodium acetate content polyvinyl alcohol. BACKGROUND

[0002] Polyvinyl alcohol (PVA) is a widely used high molecular compound, and is applied in the fields of textile, food, medicine, building, wood processing, papermaking, printing, agriculture, steel, high polymer chemical industry, liquid crystal display and the like. The production process mainly includes synthesis, refining and polymerization of vinyl acetate (VAC) and alcoholysis of polyester (PVAC), and is in the form of white (or slightly yellow) sheet or flocculation. The alcoholysis degree of PVA is mainly realized by adjusting the addition amount of alkali. In the production process of polyvinyl alcohol, sodium acetate is one of the inevitable by-products, and the content thereof is usually between 1% and 2%. In the subsequent use, the sodium acetate must be washed away (less than 0.5%) with water, which not only increases the loss of PVA in the washing process, but also needs to be matched with a large water washing machine, and a large amount of sewage containing PVA and sodium acetate is generated, the COD of the sewage is high, and the sewage cannot be directly discharged and needs to be treated twice, thereby increasing the cost.

[0003] The residual sodium acetate in polyvinyl alcohol may bring the following side effects, depending on the application scenarios such as medicine, industry or food packaging, etc.

[0004] 1. Influence on biocompatibility (medical field)

[0005] Local irritation: Sodium acetate may cause slight irritation to mucous membranes or tissues (such as the eye, wound) at high concentrations, causing redness or discomfort; pH fluctuation: Sodium acetate is weakly alkaline, and if the residual amount is high, it may change the pH value of the solution, affecting the stability of the drug or the tolerance of human tissues.

[0006] 2. Influence on material performance (industrial field)

[0007] Hygroscopicity: Sodium acetate is easy to absorb moisture, which may increase the moisture sensitivity of PVA film or fiber, affecting the mechanical strength or transparency; Processing stability: During high-temperature processing, sodium acetate may decompose to produce acetic acid, which may corrode the equipment or cause PVA degradation.

[0008] 3. Safety and toxicity

[0009] Low toxicity but needs to be controlled: Sodium acetate itself is a low-toxicity substance (LD50 is about 3.5g / kg, oral administration in rats), but excessive intake may cause electrolyte imbalance (such as hypernatremia).

[0010] 4. Other potential problems

[0011] Crystallization: If sodium acetate is not completely dissolved, it can form tiny particles in the PVA solution, affecting the uniformity of film formation or the safety of injectable agents. Reaction with ingredients: Combined with some metal ions (such as calcium and aluminum), it may affect the cross-linking reaction or product performance.

[0012] Currently, the treatment method for high sodium acetate content in polyvinyl alcohol products is purification treatment, which specifically reduces the residual sodium acetate by washing, dialysis or ultrafiltration. However, there are problems such as large amount of wastewater treatment difficulty. There are also other alkaline substances (such as sodium carbonate) instead of sodium hydroxide (to reduce the generation of sodium acetate) in the synthesis of PVA. However, sodium carbonate is a weak base (pH≈11), while sodium hydroxide is a strong base (pH≈14). The alcoholysis reaction requires a high alkaline environment to promote the removal of acetate (OAc-), and the alkalinity of sodium carbonate is insufficient, resulting in a significant reduction in reaction rate. Incomplete alcoholysis, increased residual acetyl (CHCOO-), affecting the purity and performance of PVA (such as solubility, film formation).

[0013] There is also a method of adjusting the parameters of the polyvinyl alcohol alcoholysis process to achieve the purpose of low sodium acetate content, such as the production process of low alcoholysis degree polyvinyl alcohol disclosed in Chinese patent CN1330090A, which selects esters, ethers, ketones, hydrocarbons and other substances as solvent additives, and is miscible with methanol in proportion to form a mixed solvent. However, the ash content of the obtained polyvinyl alcohol product is high, which is difficult to reach the ideal state; for example, CN111072824A discloses a preparation method of low-ash low-alcoholysis-degree polyvinyl alcohol, which uses only ester compounds as solvent additives, but the sodium acetate content in the product is 0.41-0.85%, which is still at a high level. SUMMARY

[0014] The present application provides a preparation method of low-sodium acetate content polyvinyl alcohol, which can solve the problem of high sodium acetate content in polyvinyl alcohol products in the prior art.

[0015] The object of the present application can be achieved by the following technical solutions:

[0016] A preparation method of low-sodium acetate content polyvinyl alcohol, comprising the following steps:

[0017] S1, adding methyl acetate to the methanol solution of polyvinyl acetate, mixing uniformly to obtain a mixed solution; adding a methanol solution of sodium hydroxide to the mixed solution, mixing uniformly, and then transferring to a belt alcoholysis machine for alcoholysis reaction; after the reaction is completed, a polyvinyl alcohol solid product is obtained;

[0018] S2, crushing, dehydrating and drying the polyvinyl alcohol solid product to obtain low-sodium acetate content polyvinyl alcohol.

[0019] In some embodiments, the mass fraction of the methanol solution of polyvinyl acetate is 32-36%.

[0020] In some embodiments, the purity of the methyl acetate is ≥ 99.5%.

[0021] In some embodiments, the mass ratio of the methyl acetate and the methanol solution of polyvinyl acetate in S1 is 1:12.

[0022] In some embodiments, the concentration of the methanol solution of sodium hydroxide is 6-15 g / L.

[0023] In some embodiments, the molar ratio of sodium hydroxide and polyvinyl acetate in S1 is 0.0010-0.0015:1.

[0024] In some embodiments, the alcoholysis reaction temperature in S1 is 51-55℃, and the alcoholysis reaction time is 36-50 min.

[0025] In some embodiments, the polyvinyl alcohol solid product is subjected to a crushing process in sequence through a first crusher and a second crusher, and methyl acetate is added during the crushing process of the second crusher to terminate the alcoholysis reaction, and the addition amount of methyl acetate is 2000-3000 L / h.

[0026] In some embodiments, the liquid removal process of the polyvinyl alcohol solid product is performed using a screw extruder, and the extruder filter screen is cleaned with methanol before liquid removal, and the addition amount of methanol is 1000-2000 L / h.

[0027] In some embodiments, the drying temperature is 95-98℃.

[0028] Advantages of the present application:

[0029] 1. The method provided by the present application only needs to make simple technical improvements to the original production line, is easy to implement, and through optimization of process parameters, production is stable, continuous production is easy to realize, and the purpose of producing polyvinyl alcohol products with low alcoholysis degree and low sodium acetate content is achieved.

[0030] 2. The present application adds simple ester compounds to the methanol solution of polyvinyl acetate, replacing the water required in the original process. Due to the decrease in water content, the side reactions of alcoholysis are reduced, and the required NaOH is also reduced, thereby reducing the generation of by-product sodium acetate.

[0031] 3. Since methyl acetate is a byproduct of the alcoholysis of polyvinyl acetate, the introduction of methyl acetate does not introduce new impurities, avoiding the unknown component contamination of the product that may be left by other esters (such as ethyl acetate). At the same time, methyl acetate is highly miscible with methanol, which can optimize the rheology of the polyvinyl acetate solution, ensure uniform mixing with the lye, and reduce local over-reaction, which is unmatched by other esters with poor solubility.

[0032] 4. The present application strictly controls the mass addition ratio of methyl acetate and polyvinyl acetate methanol solution to achieve the purpose of low sodium acetate, high purity, and continuous and stable polyvinyl alcohol production. If the amount of methyl acetate added is too high, the amount of base for alcoholysis reaction will be too low, the alcoholysis reaction cannot be terminated in time, and the alcoholysis degree of the finished product will be too high. If the amount of methyl acetate added is too low, the amount of base consumed by the alcoholysis reaction will be too high, the alcoholysis reaction will be incomplete, production will be interrupted, and the alcoholysis degree of the finished product will be too low.

[0033] 5. In the process of polyvinyl acetate alcoholysis reaction, the reduction of the amount of sodium hydroxide will inevitably cause the increase of residual acetate, which will seriously affect the viscosity and solubility of the polyvinyl alcohol product. However, the introduction of methyl acetate allows the ester group in polyvinyl acetate that is not substituted by hydroxyl to be further substituted, and the reduction of the amount of sodium hydroxide does not generate a large amount of sodium acetate in the process of substituting carboxyl with hydroxyl. Therefore, the reduction of the amount of sodium hydroxide and the use of methyl acetate together solve the problem of high residual sodium acetate and overcome the adverse effects introduced by the reduction of the amount of sodium hydroxide in the prior art.

[0034] 6. In the present application, methyl acetate is added to terminate the alcoholysis reaction during the crushing of the polyvinyl alcohol solid product, and methanol is added as a cleaning liquid before extrusion. These measures can effectively prevent the sticking of the crusher and the clogging of the mesh of the extruder, increase the production stability, and prolong the production cycle.

[0035] 7. The present application significantly improves the concentration of polyvinyl acetate in the production process, which is beneficial to improving the production efficiency. The reason is that when the concentration of polyvinyl acetate is low, the produced polyvinyl alcohol product is in a flocculent state, the mesh is clogged, the belt material does not form, and continuous production cannot be achieved. DETAILED DESCRIPTION

[0036] In order to make the technical problems, technical solutions and beneficial effects of the present application more clear and explicit, the following embodiments are used to further explain the present application. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0037] It should be understood that the magnitude of the serial number of each process in various embodiments of the present application does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence, and the execution order of each process should be determined according to its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0038] The weight of the related components mentioned in the embodiments of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of each component. Therefore, as long as the content of the related components in the embodiments of the present application is enlarged or reduced in proportion, it is within the scope disclosed in the embodiments of the present application. Specifically, the mass mentioned in the embodiments of the present application can be μg, mg, g, kg and other mass units commonly known in the chemical field.

[0039] Unless otherwise defined, all professional terms used herein have the same meaning as generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present application.

[0040] In order to solve the problem of high sodium acetate content in the polyvinyl alcohol product in the prior art, the present application provides a preparation method of low-sodium acetate content polyvinyl alcohol, comprising the following steps:

[0041] S1, adding methyl acetate to the methanol solution of polyvinyl acetate, mixing uniformly to obtain a mixed solution; adding a methanol solution of sodium hydroxide to the mixed solution, mixing uniformly, and then transferring to a belt alcoholysis machine for alcoholysis reaction. After the reaction is completed, a polyvinyl alcohol solid product is obtained;

[0042] S2, crushing, dehydrating and drying the polyvinyl alcohol solid product to obtain low-sodium acetate content polyvinyl alcohol.

[0043] In some embodiments, the mass fraction of the methanol solution of polyvinyl acetate is 32-36%.

[0044] In some embodiments, the purity of the methyl acetate is ≥99.5%.

[0045] In some embodiments, the mass ratio of methyl acetate to the methanol solution of polyvinyl acetate in S1 is 1:12.

[0046] In some embodiments, the concentration of the methanol solution of sodium hydroxide is 6-15 g / L.

[0047] In some embodiments, the molar ratio of sodium hydroxide to polyvinyl acetate in S1 is 0.0010-0.0015:1.

[0048] In some embodiments, the alcoholysis reaction temperature in S1 is 51-55℃, and the alcoholysis reaction time is 36-50 min.

[0049] In some embodiments, the polyvinyl alcohol solid product is subjected to a crushing process in sequence by a first crusher and a second crusher, and methyl acetate is added in the crushing process of the second crusher to terminate the alcoholysis reaction, and the addition amount of methyl acetate is 2000-3000 L / h.

[0050] In some embodiments, the liquid removal process of the polyvinyl alcohol solid product is performed using a screw extruder, and the extruder filter screen is cleaned with methanol before liquid removal, and the addition amount of methanol is 1000-2000 L / h.

[0051] In some embodiments, the drying temperature is 95-98℃.

[0052] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or prepared by existing methods.

[0053] The technical solutions of the present application are illustrated below by specific examples and comparative examples.

[0054] Example 1

[0055] A preparation method of a low-sodium acetate content polyvinyl alcohol includes the following steps:

[0056] 200 kg of methyl acetate (purity 99.5%), a methanol solution of sodium hydroxide with a concentration of 6 g / L, and a methanol solution of polyvinyl acetate with a mass fraction of 35% are fed into a mixer, the degree of polymerization of the polyvinyl acetate is 2250, the mass ratio of methyl acetate to the methanol solution of polyvinyl acetate is controlled to be 1:12, and the molar ratio of sodium hydroxide to polyvinyl acetate is 0.0015:1, after uniform mixing, they are transferred to a belt alcoholysis machine, and reacted at 52℃ for 38 min, after the reaction is completed, a polyvinyl alcohol solid product and a mother liquor are obtained, the polyvinyl alcohol solid product is treated by a first crusher, then enters a second crusher, methyl acetate is added in the crushing process of the second crusher to terminate the alcoholysis reaction, the addition amount of methyl acetate is 3000 L / h, then a screw extruder is used for liquid removal, methanol is used to clean the extruder filter screen before liquid removal, the addition amount of methanol is 2000 L / h, and finally drying is performed at 98℃ to obtain a polyvinyl alcohol PVA20-92 product.

[0057] Example 2

[0058] A preparation method of a low-sodium acetate content polyvinyl alcohol includes the following steps:

[0059] 200kg of methyl acetate (purity 99.5%), 6g / L of sodium hydroxide methanol solution and 35% polyvinyl acetate methanol solution with a polyvinyl acetate polymerization degree of 2300 were fed into a mixer, the mass ratio of methyl acetate and polyvinyl acetate methanol solution was controlled to be 1:12, the molar ratio of sodium hydroxide and polyvinyl acetate was 0.0014:1, after uniform mixing, they were transferred to a belt alcoholysis machine, reacted at 51°C for 36min, after the reaction was completed, polyvinyl alcohol solid product was obtained and the mother liquor was separated out, the polyvinyl alcohol solid product was treated by a first crusher, then entered a second crusher, methyl acetate was added in the second crusher to terminate the alcoholysis reaction, the addition amount of methyl acetate was 3000L / h, then a screw extruder was used for liquid removal, before liquid removal, the extruder filter screen was cleaned with methanol, the addition amount of methanol was 2000L / h, finally, drying was carried out at 98°C, and polyvinyl alcohol PVA20-92 product was obtained.

[0060] Example 3

[0061] A method for preparing a low-sodium acetate content polyvinyl alcohol, comprising the following steps:

[0062] 200kg of methyl acetate (purity 99.5%), 6g / L of sodium hydroxide methanol solution and 35% polyvinyl acetate methanol solution with a polyvinyl acetate polymerization degree of 2320 were fed into a mixer, the mass ratio of methyl acetate and polyvinyl acetate methanol solution was controlled to be 1:12, the molar ratio of sodium hydroxide and polyvinyl acetate was 0.0015:1, after uniform mixing, they were transferred to a belt alcoholysis machine, reacted at 53°C for 38min, after the reaction was completed, polyvinyl alcohol solid product was obtained and the mother liquor was separated out, the polyvinyl alcohol solid product was treated by a first crusher, then entered a second crusher, methyl acetate was added in the second crusher to terminate the alcoholysis reaction, the addition amount of methyl acetate was 3000L / h, then a screw extruder was used for liquid removal, before liquid removal, the extruder filter screen was cleaned with methanol, the addition amount of methanol was 2000L / h, finally, drying was carried out at 98°C, and polyvinyl alcohol PVA20-92 product was obtained.

[0063] Example 4

[0064] A method for preparing a low-sodium acetate content polyvinyl alcohol, comprising the following steps:

[0065] Put 250 kg of methyl acetate (purity 99.5%), 8 g / L sodium hydroxide methanol solution and 36% polyvinyl acetate methanol solution with a polyvinyl acetate polymerization degree of 1850 into a mixer, control the mass ratio of methyl acetate and polyvinyl acetate methanol solution to be 1:12, the molar ratio of sodium hydroxide and polyvinyl acetate to be 0.0010:1, mix uniformly, and then transfer to a belt alcoholysis machine, react at 52°C for 45 min, after the reaction is completed, obtain polyvinyl alcohol solid product and mother liquor, after the polyvinyl alcohol solid product is treated by a first crusher, it enters a second crusher, methyl acetate is added in the second crusher crushing process to terminate the alcoholysis reaction, the addition amount of methyl acetate is 2500 L / h, then use a screw extruder to perform liquid removal, use methanol to clean the filter screen of the extruder before liquid removal, the addition amount of methanol is 1500 L / h, and finally dry at 98°C to obtain polyvinyl alcohol PVA17-88 product.

[0066] Example 5

[0067] A method for preparing a low-sodium acetate content polyvinyl alcohol, comprising the following steps:

[0068] Put 250 kg of methyl acetate (purity 99.5%), 8 g / L sodium hydroxide methanol solution and 36% polyvinyl acetate methanol solution with a polyvinyl acetate polymerization degree of 1850 into a mixer, control the mass ratio of methyl acetate and polyvinyl acetate methanol solution to be 1:12, the molar ratio of sodium hydroxide and polyvinyl acetate to be 0.0010:1, mix uniformly, and then transfer to a belt alcoholysis machine, react at 52°C for 45 min, after the reaction is completed, obtain polyvinyl alcohol solid product and mother liquor, after the polyvinyl alcohol solid product is treated by a first crusher, it enters a second crusher, methyl acetate is added in the second crusher crushing process to terminate the alcoholysis reaction, the addition amount of methyl acetate is 2500 L / h, then use a screw extruder to perform liquid removal, use methanol to clean the filter screen of the extruder before liquid removal, the addition amount of methanol is 1500 L / h, and finally dry at 98°C to obtain polyvinyl alcohol PVA17-88 product.

[0069] Example 6

[0070] A method for preparing a low-sodium acetate content polyvinyl alcohol, comprising the following steps:

[0071] Put 250 kg of methyl acetate (purity 99.5%), 8 g / L sodium hydroxide methanol solution and 36% polyvinyl acetate methanol solution with a mass fraction of 36% into a mixer, the polyvinyl acetate polymerization degree is 2000, the mass ratio of methyl acetate and polyvinyl acetate methanol solution is controlled to be 1:12, the molar ratio of sodium hydroxide and polyvinyl acetate is 0.0012:1, after uniform mixing, it is transferred to a belt alcoholysis machine, reacted at 54°C for 45 min, after the reaction is completed, polyvinyl alcohol solid product is obtained and the mother liquor is separated out, the polyvinyl alcohol solid product is treated by a first crusher, then enters a second crusher, methyl acetate is added in the second crushing process to terminate the alcoholysis reaction, the addition amount of methyl acetate is 2500 L / h, then a screw extruder is used for liquid removal, methanol is used for cleaning the filter screen of the extruder before liquid removal, the addition amount of methanol is 1500 L / h, finally dried at 98°C to obtain polyvinyl alcohol PVA17-88 product.

[0072] Example 7

[0073] A method for preparing a low-sodium acetate content polyvinyl alcohol, comprising the following steps:

[0074] Put 260 kg of methyl acetate (purity 99.5%), 10 g / L sodium hydroxide methanol solution and 33% polyvinyl acetate methanol solution with a mass fraction of 33% into a mixer, the polyvinyl acetate polymerization degree is 2250, the mass ratio of methyl acetate and polyvinyl acetate methanol solution is controlled to be 1:12, the molar ratio of sodium hydroxide and polyvinyl acetate is 0.0011:1, after uniform mixing, it is transferred to a belt alcoholysis machine, reacted at 53°C for 42 min, after the reaction is completed, polyvinyl alcohol solid product is obtained and the mother liquor is separated out, the polyvinyl alcohol solid product is treated by a first crusher, then enters a second crusher, methyl acetate is added in the second crushing process to terminate the alcoholysis reaction, the addition amount of methyl acetate is 2500 L / h, then a screw extruder is used for liquid removal, methanol is used for cleaning the filter screen of the extruder before liquid removal, the addition amount of methanol is 1500 L / h, finally dried at 98°C to obtain polyvinyl alcohol PVA20-88 product.

[0075] Example 8

[0076] A method for preparing a low-sodium acetate content polyvinyl alcohol, comprising the following steps:

[0077] 260 kg of methyl acetate (purity 99.5%), a methanol solution of sodium hydroxide with a concentration of 10 g / L, and a methanol solution of polyvinyl acetate with a mass fraction of 33% are fed into a mixer, the polyvinyl acetate has a degree of polymerization of 2250, the mass ratio of methyl acetate to the methanol solution of polyvinyl acetate is controlled to be 1:12, and the molar ratio of sodium hydroxide to polyvinyl acetate is 0.0013:1, after being uniformly mixed, the mixture is transferred to a belt alcoholysis machine, and reacted at 54°C for 42 min, after the reaction is completed, polyvinyl alcohol solid products are obtained and a mother liquor is separated out, the polyvinyl alcohol solid products are treated by a first pulverizer, then enter a second pulverizer, methyl acetate is added in the pulverizing process of the second pulverizer to terminate the alcoholysis reaction, the addition amount of methyl acetate is 2500 L / h, then a screw extruder is used for liquid removal, methanol is used for cleaning the filter screen of the extruder before liquid removal, the addition amount of methanol is 1500 L / h, and finally drying is performed at 98°C to obtain polyvinyl alcohol PVA20-88 products.

[0078] Example 9

[0079] A method for preparing polyvinyl alcohol with low sodium acetate content, comprising the following steps:

[0080] 260 kg of methyl acetate (purity 99.5%), a methanol solution of sodium hydroxide with a concentration of 10 g / L, and a methanol solution of polyvinyl acetate with a mass fraction of 33% are fed into a mixer, the polyvinyl acetate has a degree of polymerization of 2250, the mass ratio of methyl acetate to the methanol solution of polyvinyl acetate is controlled to be 1:12, and the molar ratio of sodium hydroxide to polyvinyl acetate is 0.0013:1, after being uniformly mixed, the mixture is transferred to a belt alcoholysis machine, and reacted at 54°C for 42 min, after the reaction is completed, polyvinyl alcohol solid products are obtained and a mother liquor is separated out, the polyvinyl alcohol solid products are treated by a first pulverizer, then enter a second pulverizer, methyl acetate is added in the pulverizing process of the second pulverizer to terminate the alcoholysis reaction, the addition amount of methyl acetate is 2500 L / h, then a screw extruder is used for liquid removal, methanol is used for cleaning the filter screen of the extruder before liquid removal, the addition amount of methanol is 1500 L / h, and finally drying is performed at 98°C to obtain polyvinyl alcohol PVA20-88 products.

[0081] Comparative Example 1

[0082] A method for preparing polyvinyl alcohol with low sodium acetate content, compared with Example 1, the only difference is that the methyl acetate in Example 1 is replaced by an equal amount of ethyl acetate.

[0083] Comparative Example 2

[0084] A method for preparing polyvinyl alcohol with low sodium acetate content, compared with Example 1, the only difference is that the mass ratio of methyl acetate to the methanol solution of polyvinyl acetate is controlled to be 1:11.

[0085] Comparative Example 3

[0086] A method for preparing a low sodium acetate content polyvinyl alcohol, which differs from Example 1 only in that the mass ratio of methyl acetate and the methanol solution of polyvinyl acetate is controlled to be 1:13.

[0087] Comparative Example 4

[0088] A method for preparing a low sodium acetate content polyvinyl alcohol, which differs from Example 1 only in that the methyl acetate in Example 1 is removed.

[0089] The polyvinyl alcohol products obtained in Examples 1-9 and Comparative Examples 1-4 were detected, and the detection process was as follows:

[0090] (1) Determination of residual acetate, purity, volatile matter, and alcoholysis degree

[0091] Analysis steps: 1.2 g of the sample was accurately weighed on an analytical balance, transferred into a 500 mL ground-mouth triangular flask, 200 mL of distilled water was added, and completely dissolved on an electric heating stirrer. 20 mL of 0.5000 mol / L NaOH solution was added to the sample solution using an alkaline automatic burette, and after standing at room temperature for 20 min, 2 drops of phenolphthalein indicator was added, and titrated with 0.5000 mol / L H2SO4 until a light red end point was reached. The consumption of milliliters was a, and a blank test was performed, and the consumption of milliliters was b. The volatile matter was also measured, and the analysis method was according to the "Determination of volatile matter of finished PVA".

[0092] The residual acetate content calculation formula is as follows:

[0093]

[0094] In the formula, 0.5000 is the molar concentration of H2SO4;

[0095] G is the sample weight (g);

[0096] The purity calculation formula is as follows:

[0097] PVA purity, i.e. 1 is a constant.

[0098] The alcoholysis degree calculation formula is as follows:

[0099]

[0100] (2) Determination of sodium acetate content

[0101] Weigh 7.5g sample on balance to the nearest 10mg, put into a pre-prepared flask, add 200ml distilled water, heat on electric stove while shaking, cool to room temperature, add 0.5ml of 1:1 methylene blue and dimethyl yellow mixed indicator, titrate with sulfuric acid standard solution [C(1 / 2H2SO4) = 0.1mol / L] to blue purple end point. At the same time, use 200ml distilled water as a blank test. If the pH of distilled water = 5-7, no blank test is needed.

[0102] The sodium acetate content is calculated according to the following formula:

[0103]

[0104] In the formula, X3 is the sodium acetate content, %;

[0105] V0 is the volume of sulfuric acid standard solution consumed by the blank titration, mL;

[0106] V1 is the volume of sulfuric acid standard solution consumed by the sample titration, mL;

[0107] C is the concentration of the sulfuric acid standard solution, mol / L;

[0108] 0.0820 represents the mass of sodium acetate in grams corresponding to 1.00ml of sulfuric acid standard solution [C(1 / 2H2SO4) = 1.0mol / L];

[0109] m is the mass of the sample, g;

[0110] 82.0 is the molar mass of sodium acetate, g / mol;

[0111] 40.0 is the molar mass of sodium hydroxide, g / mol;

[0112] X2 is the sodium hydroxide content, %.

[0113] The arithmetic mean of the average test results is taken as the test result, to two decimal places.

[0114] (3) Ash % = Sodium acetate % * 0.378

[0115] The test results are shown in Table 1:

[0116] Table 1

[0117]

[0118] It can be seen from the recorded data in Table 1 that the sodium acetate content of the PVA20-92 prepared in Example 1-Example 3, the PVA17-88 prepared in Example 4-Example 6 and the PVA20-88 product prepared in Example 7-Example 9 is ≤0.3, the volatile content is <3.9% and the purity is ≥95.9%, indicating that the polyvinyl alcohol obtained by the preparation method has the characteristics of low sodium acetate content, low volatile content and high purity. As can be seen from the test results in Example 1 and Comparative Example 1, after replacing the methyl acetate with an equal amount of ethyl acetate, the alcoholysis degree decreases more obviously, and other indicators do not change much, but the addition of methyl acetate in the system requires additional separation measures, additional equipment and improved process flow. As can be seen from the test results in Example 1 and Comparative Example 2, after modifying the mass ratio of the methyl acetate and polyvinyl acetate methanol solution to 1:11, which is equivalent to increasing the amount of methyl acetate, the alcoholysis degree increases, but the product color decreases and the solution is slightly turbid. As can be seen from the test results in Example 1 and Comparative Example 3, after modifying the mass ratio of the methyl acetate and polyvinyl acetate methanol solution to 1:13, which is equivalent to reducing the amount of methyl acetate, the alcoholysis degree decreases. As can be seen from the test results in Example 1 and Comparative Example 4, compared with the conventional polyvinyl alcohol preparation method, only the amount of sodium hydroxide is reduced, and the addition of any ester substance is stopped, the alcoholysis degree of the product is difficult to decrease, and the product color decreases significantly and the solution is turbid.

[0119] It should be noted that the relational terms herein such as first and second and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any such actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0120] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A process for the preparation of low sodium acetate content polyvinyl alcohol, characterized by, The method comprises the following steps: S1, adding methyl acetate into a methanol solution of polyvinyl acetate, mixing uniformly to obtain a mixed solution; adding a methanol solution of sodium hydroxide into the mixed solution, mixing uniformly, and then transferring to a belt alcoholysis machine to perform alcoholysis reaction; after the reaction is completed, a polyvinyl alcohol solid product is obtained; S2, crushing, deliquoring and drying the polyvinyl alcohol solid product to obtain a polyvinyl alcohol with low sodium acetate content.

2. The process for the preparation of low sodium acetate content polyvinyl alcohol as claimed in claim 1, wherein, The mass fraction of the methanol solution of polyvinyl acetate is 32-36%.

3. The process for the preparation of low sodium acetate content polyvinyl alcohol as claimed in claim 1, wherein, The purity of the methyl acetate is greater than or equal to 99.5%.

4. The process for the preparation of low sodium acetate content polyvinyl alcohol as claimed in claim 1, wherein, The mass ratio of the methyl acetate to the methanol solution of polyvinyl acetate in S1 is 1:

12.

5. The process for the preparation of low sodium acetate content polyvinyl alcohol as claimed in claim 1, wherein, The concentration of the methanol solution of sodium hydroxide is 6-15 g / L.

6. The process for the preparation of low sodium acetate content polyvinyl alcohol as claimed in claim 1, wherein, The molar ratio of sodium hydroxide to polyvinyl acetate in S1 is 0.0010-0.0015:

1.

7. The process for the preparation of low sodium acetate content polyvinyl alcohol as claimed in claim 1, wherein, The alcoholysis reaction temperature in S1 is 51-55 ℃, and the alcoholysis reaction time is 36-50 min.

8. The process for the preparation of low sodium acetate content polyvinyl alcohol as claimed in claim 1, wherein, The crushing process of the polyvinyl alcohol solid product is sequentially performed in a first crusher and a second crusher; the second crusher is added with methyl acetate during the crushing process, and the addition amount of the methyl acetate is 2000-3000 L / h.

9. The process for the preparation of low sodium acetate content polyvinyl alcohol as claimed in claim 1, wherein, The deliquoring process of the polyvinyl alcohol solid product is performed by using a screw extruder; the extruder filter screen is cleaned with methanol before deliquoring, and the addition amount of the methanol is 1000-2000 L / h.

10. The process for the preparation of low sodium acetate content polyvinyl alcohol as claimed in claim 1, wherein, The drying temperature is 95-98 ℃.

Images