Process for preparing a low alcoholysis degree polyvinyl alcohol

Abstract

The present application relates to a kind of preparation methods of low alcoholysis degree polyvinyl alcohol, and the preparation process and catalytic alcoholysis process of polyvinyl acetate copolymer solution are obtained by the copolymerization of polyvinyl acetate with polybasic monomer;The specific solvent used in the present application, by controlling alcohol content in alcoholysis process, solve the problem of inaccurate control caused by the alcoholysis reaction of polyvinyl alcohol with alcoholysis degree less than 60mol% too fast, in traditional alcoholysis process, with the increase of alcoholysis time, alcoholysis degree is constantly increased, if neutralization is not added midway, alcoholysis degree will increase to about 99mol%;The low alcoholysis degree polyvinyl alcohol of the present application is suitable for auxiliary dispersant of vinyl chloride suspension polymerization.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyvinyl alcohol production, and particularly relates to a preparation method of low alcoholysis degree polyvinyl alcohol. BACKGROUND

[0002] Polyvinyl alcohol (PVA) is an important water-soluble polymer compound developed in the early 1950s, and is widely used. It can be used to produce fibers, and can also be used as a sizing agent for chemical fiber fabrics, a coating material, an adhesive, an emulsifier, a paper processing aid and the like. With the continuous development of science and technology, the demand for polyvinyl alcohol with different polymerization degrees and different alcoholysis degrees is increasingly urgent.

[0003] In the suspension polymerization of vinyl chloride, the alcoholysis degree of the existing auxiliary dispersant for the suspension polymerization of polyvinyl chloride is basically concentrated between 35mol% and 60mol%. The auxiliary dispersant can not only improve the porosity of polyvinyl chloride, but also make the particle distribution more uniform, and is an important component of the polyvinyl chloride suspension polymerization formula in recent years.

[0004] CN102311516B discloses a preparation method of a polyvinyl alcohol auxiliary dispersant for manufacturing polyvinyl chloride by a suspension method. The method is to add methanol into a copolymer solution to obtain a diluted copolymer solution, and then add a terminating agent to terminate the reaction after alcoholysis for a period of time, so as to obtain low alcoholysis degree. If the terminating agent is not added for neutralization in the middle, the alcoholysis degree will continuously increase with the increase of the alcoholysis time, and the alcoholysis degree will increase to about 99mol%.

[0005] CN107474163A points out that in the low alcoholysis degree reaction, deionized water is added. Since there is water in the reaction system, the dissociation degree of the catalyst sodium hydroxide is enhanced, and the direct saponification reaction with polyvinyl acetate is consumed, and the consumption of the catalyst inhibits the ester exchange reaction, so that the alcoholysis degree of the product is reduced, thereby producing low alcoholysis degree polyvinyl alcohol. The addition amount of sodium hydroxide can be adjusted to obtain different low alcoholysis degree polyvinyl alcohol products. However, in the actual production process, the alcoholysis speed is fast due to the high alkali content in the initial alcoholysis, and therefore, when producing low alcoholysis degree PVA, the control timing of neutralization is not good, which will cause the alcoholysis degree control to exceed the product index range. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings in the prior art, to better control the production of low alcoholysis degree PVA, and to more accurately control the alcoholysis degree within the product index range, and to provide a preparation method of low alcoholysis degree polyvinyl alcohol.

[0007] The technical scheme adopted by the present application to achieve the purpose is as follows:

[0008] A method for preparing low alcoholysis degree polyvinyl alcohol, comprising the following steps: a) copolymerization of polyvinyl acetate and a multi-functional monomer: 1) nitrogen is used to replace air in a reaction kettle, and then the components of the copolymerization monomer are added for copolymerization at a set temperature, and after the reaction is completed, a solvent is added to terminate the polymerization; the amount of the solvent added is 40wt%-80wt% of the monomer, and then the temperature is controlled at 60°C-100°C under reduced pressure distillation to remove unreacted copolymerization monomer, to obtain a polyvinyl acetate copolymer solution; 2) dilute solvent is added to the copolymer solution;

[0009] b) catalytic alcoholysis: the polyvinyl acetate copolymer solution obtained in step a) is diluted, and then heated, and after the temperature is raised to the alcoholysis temperature, an alcohol solution of a catalyst is added for alcoholysis reaction, and after the alcoholysis reaction is completed, the organic solvent is removed by reduced pressure distillation, to obtain low alcoholysis degree polyvinyl alcohol.

[0010] Further, the dilute solvent is a benzene series, such as benzene, toluene, ethylbenzene, xylene, or a mixture thereof; as a preferred, the solvent is benzene.

[0011] In step b), the amount of each component is 100 parts by weight of the diluted copolymer solution, and 1.9-16.4 parts by weight of the alcohol solution of the catalyst.

[0012] The solid content of the diluted copolymer solution is 10.0wt%-40.0wt%.

[0013] The applicant found that when the dilute solvent is selected as a benzene series, and the alcohol solution of the catalyst is 1.9-16.4 parts; in the alcoholysis process, the alcoholysis degree does not continuously increase with the increase of the alcoholysis time; the problem of inaccurate control caused by too fast alcoholysis reaction of polyvinyl alcohol with an alcoholysis degree lower than 60mol% is solved.

[0014] The catalyst is at least one of potassium hydroxide and sodium hydroxide, and preferably sodium hydroxide; the concentration of the catalyst is 0.003wt%-20.0wt%.

[0015] The alcohol in the alcohol solution of the catalyst is at least one of methanol, ethanol, isopropyl alcohol, and n-butanol, and preferably methanol.

[0016] The molar ratio of the alcohol in the alcohol solution to the benzene series is between 0.5 and 1.0.

[0017] The alcoholysis reaction time is 0.1-3.0 hours, and preferably the reaction time is 0.2-2.0 hours.

[0018] The alcoholysis reaction temperature is 30°C-50°C, and preferably the reaction temperature is 35°C-45°C.

[0019] The components in step a) include the following components by weight: vinyl acetate: 100 parts, functional monomer A: 0.03-6.0 parts, solvent: 10-70 parts, initiator: 0.01-0.1 parts.

[0020] The functional monomer A is at least one of sodium methyl allyl sulfonate, sodium allyl sulfonate, propenyl chloride, propenyl amine, methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, 2-acrylamido-2-methylpropane sulfonic acid, sodium 2-acrylamido-2-methylpropane sulfonate, or a mixture thereof.

[0021] As a preference, the amount of functional monomer A is 0.05-5.0 parts.

[0022] As a preference, the functional monomer A is at least one of sodium methyl allyl sulfonate and sodium 2-acrylamido-2-methylpropane sulfonate, or a mixture thereof.

[0023] The solvent is benzene, toluene, ethylbenzene, xylene, or a mixture thereof; as a preference, the solvent is benzene.

[0024] As a preference, the amount of solvent is 20-60 parts.

[0025] The initiator is at least one of azobisisobutyronitrile, azobisisoheptyl nitrile, dimethyl azobisisobutyrate, tert-butyl hydroperoxide, tert-butyl peroxypivalate, dibenzoyl peroxide, or a mixture thereof; as a preference, the initiator is azobisisobutyronitrile.

[0026] As a preference, the amount of initiator is 0.01-0.06 parts.

[0027] The reaction temperature is 60-90℃; as a preference, the reaction temperature is 65-85℃.

[0028] The copolymerization reaction is performed for 2-6 hours; as a preference, the reaction time is 3-5 hours.

[0029] The application also provides a low alcoholysis degree polyvinyl alcohol as an auxiliary dispersant for vinyl chloride suspension polymerization.

[0030] The beneficial effects of the basic scheme are:

[0031] The present application adopts specific solvent, and solves the problem of inaccurate control caused by too fast alcoholysis of polyvinyl alcohol with alcoholysis degree less than 60 mol% by controlling alcohol content in alcoholysis process. In traditional alcoholysis process, alcoholysis degree increases with increasing alcoholysis time, and if neutralizer is not added in the middle, alcoholysis degree will increase to about 99 mol%. According to the method of the present application, alcoholysis degree is basically not affected by neutralization time after alcoholysis reaction reaches 35 mol%-60 mol%, and alcoholysis degree can be controlled according to the proportion of alcohol. DETAILED DESCRIPTION

[0032] The technical solutions of the present application are further analyzed and described below through non-limiting examples. It is necessary to point out that the examples are only used for further description of the present application, and cannot be understood as limitation of the protection scope of the present application. Skilled persons in the art can make some non-essential improvements and adjustments according to the content of the above-mentioned application.

[0033] Example 1

[0034] First, nitrogen gas is used to replace air in the reaction kettle, then 100 parts of vinyl acetate and 0.05 parts of sodium methyl allyl sulfonate are subjected to solution polymerization in 20 parts of benzene solvent in the presence of 0.08 parts of azobisisobutyronitrile, and the polymerization temperature is 65℃, and the reaction is carried out for 3 hours. When the polymerization reaction is completed, 80 parts of benzene is added, then the temperature is controlled at 60℃, and the unreacted comonomer is removed by distillation under reduced pressure to obtain a polyvinyl acetate copolymer solution. A part of the polyvinyl acetate copolymer solution is prepared into a 100 part benzene solution with a concentration of 10.0 wt%, then 1.9 parts of 0.003 wt% sodium hydroxide methanol solution is used for alcoholysis at 35℃, and after alcoholysis for 12 min, the alcoholysis solution is divided into three parts, one part is distilled under reduced pressure to remove organic solvent, and the other two parts are distilled under reduced pressure to remove organic solvent after 40 min and 110 min respectively, then deionized water and methanol are added to prepare a solution with a solid content of about 40.0±0.5 wt%, thereby obtaining the polyvinyl alcohol auxiliary dispersant for vinyl chloride suspension polymerization. The low alcoholysis degree polyvinyl alcohol obtained in the present application has the following alcoholysis degree:

[0035] Alcoholysis time, min 12 40 110 Alcoholysis degree, (mol / mol)% 36.82 36.81 36.76

[0036] Example 2

[0037] First, the reaction kettle is purged with nitrogen to replace the air, then 100 parts of vinyl acetate and 5 parts of 2-acrylamide 2-methylpropane sulfonic acid sodium are solution polymerized in 80 parts of ethylbenzene solvent in the presence of 0.06 parts of azobisisobutyronitrile, the polymerization temperature is 80℃, the reaction is carried out for 5 hours, when the polymerization reaction is completed, 60 parts of ethylbenzene is added, then the temperature is controlled at 80℃ under reduced pressure distillation to remove unreacted comonomer, to obtain a polyvinyl acetate copolymer solution, take a part of the polyvinyl acetate copolymer solution to prepare a 100 parts of 40.0wt% ethylbenzene solution, then use 16.4 parts of 0.091wt% sodium hydroxide methanol solution to carry out alcoholysis at 45℃, after alcoholysis for 20min, the alcoholysis solution is divided into three parts, one part is distilled under reduced pressure to remove the organic solvent, the other two parts are distilled under reduced pressure to remove the organic solvent after 60min and 120min respectively, then deionized water and methanol are added to prepare a 40.0±0.5% solid content aqueous solution, thus the polyvinyl alcohol auxiliary dispersant for vinyl chloride suspension polymerization is obtained. The low alcoholysis degree polyvinyl alcohol obtained in the application has the following alcoholysis degree:

[0038] Alcoholysis time, min 20 60 120 Alcoholysis degree, (mol / mol)% 59.52 59.52 59.54

[0039] Example 3

[0040] First, the reaction kettle is purged with nitrogen to replace the air, then 100 parts of vinyl acetate and 5 parts of 2-acrylamide 2-methylpropane sulfonic acid sodium are solution polymerized in 80 parts of ethylbenzene solvent in the presence of 0.06 parts of azobisisobutyronitrile, the polymerization temperature is 80℃, the reaction is carried out for 5 hours, when the polymerization reaction is completed, 60 parts of ethylbenzene is added, then the temperature is controlled at 80℃ under reduced pressure distillation to remove unreacted comonomer, to obtain a polyvinyl acetate copolymer solution, take a part of the polyvinyl acetate copolymer solution to prepare a 100 parts of 40.0wt% ethylbenzene solution, then use 16.4 parts of 0.091wt% sodium hydroxide methanol solution to carry out alcoholysis at 45℃, after alcoholysis for 20min, the alcoholysis solution is divided into three parts, one part is distilled under reduced pressure to remove the organic solvent, the other two parts are distilled under reduced pressure to remove the organic solvent after 60min and 120min respectively, then deionized water and methanol are added to prepare a 40.0±0.5% solid content aqueous solution, thus the polyvinyl alcohol auxiliary dispersant for vinyl chloride suspension polymerization is obtained. The low alcoholysis degree polyvinyl alcohol obtained in the application has the following alcoholysis degree:

[0041] Alcoholysis time, min 15 30 100 Alcoholysis degree, (mol / mol)% 40.47 40.47 40.51

[0042] Example 4

[0043] First, the reaction kettle is purged with nitrogen to replace the air, then 100 parts of vinyl acetate and 1 part of methyl allyl sodium sulfonate are solution polymerized in the presence of 0.05 parts of azobisisobutyronitrile in 30 parts of xylene, 30 parts of ethylbenzene solvent, the polymerization temperature is 80℃, the reaction is 5 hours, when the polymerization reaction is finished, 50 parts of benzene is added, then the temperature is controlled at 90℃ under reduced pressure distillation, to remove unreacted comonomer, to obtain polyvinyl acetate copolymer solution, take a part of polyvinyl acetate copolymer solution to prepare 100 parts of 20.0wt% concentration of benzene solution, then use 6.9 parts of 4.3wt% concentration of sodium hydroxide methanol solution at 38℃ for alcoholysis, after alcoholysis for 20min, the alcoholysis solution is divided into three parts, one part is removed under reduced pressure to remove the organic solvent, the other two parts are removed under reduced pressure to remove the organic solvent after 40min and 100min respectively, then deionized water and methanol are added to prepare a water solution with a solid content of 40.0±0.5wt%, which is the polyvinyl alcohol auxiliary dispersant for vinyl chloride suspension polymerization. The low alcoholysis degree polyvinyl alcohol obtained in the application has the following alcoholysis degree:

[0044] Alcoholysis time, min 20 40 100 Alcoholysis degree, (mol / mol)% 48.11 48.12 48.10

[0045] Comparative example 1

[0046] First, the reaction kettle is purged with nitrogen to replace the air, then 100 parts of vinyl acetate and 0.05 parts of methyl allyl sodium sulfonate are solution polymerized in the presence of 0.08 parts of azobisisobutyronitrile in 20 parts of benzene solvent, the polymerization temperature is 65℃, the reaction is 3 hours, when the polymerization reaction is finished, 80 parts of benzene is added, then the temperature is controlled at 70℃ under reduced pressure distillation, to remove unreacted comonomer, to obtain polyvinyl acetate copolymer solution, take a part of polyvinyl acetate copolymer solution to prepare 100 parts of 10wt% concentration of methanol solution, then use 1.9 parts of 0.003wt% concentration of sodium hydroxide methanol solution at 35℃ for alcoholysis, after alcoholysis for 12min, the alcoholysis solution is divided into three parts, one part is removed under reduced pressure to remove the organic solvent, the other two parts are removed under reduced pressure to remove the organic solvent after 30min and 120min respectively. The low polymerization degree and low alcoholysis degree polyvinyl alcohol obtained in the application has the following alcoholysis degree:

[0047] Alcoholysis time, min 12 30 120 Alcoholysis degree, (mol / mol)% Alcoholysis time, min Alcoholysis degree, (mol / mol)% 36.82 65.41 98.76

Claims

1. A process for the preparation of low alcoholysis degree polyvinyl alcohol, characterized by: a) copolymerization of vinyl acetate: 1) first, replace the air in the reactor with nitrogen, then add vinyl acetate, functional monomer A, initiator and solvent, and carry out copolymerization at a set temperature; after the reaction is completed, continue to add solvent to terminate the polymerization, at this time the amount of solvent added is 40wt%-80wt% of the monomers; then control the temperature at 60℃-100℃ under reduced pressure distillation to remove unreacted comonomers, obtaining polyvinyl acetate copolymer solution; 2) add dilution solvent to the copolymer solution, the dilution solvent is benzene series; b) catalytic alcoholysis: dilute the polyvinyl acetate copolymer solution obtained in step a) and heat it, after the temperature rises to the alcoholysis temperature, add an alcohol solution containing a catalyst to carry out alcoholysis reaction, after the alcoholysis reaction is completed, remove the organic solvent by reduced pressure distillation to obtain low alcoholysis degree polyvinyl alcohol; In the copolymerization reaction of step a) 1), the amount of vinyl acetate added is 100 parts, the amount of functional monomer A added is 0.03-6.0 parts, the amount of solvent added is 10-70 parts, and the amount of initiator added is 0.01-0.1 part; The functional monomer A is at least one of sodium methyl allyl sulfonate, sodium allyl sulfonate, propenyl chloride, propenyl amine, methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, 2-acrylamide-2-methylpropane sulfonic acid, sodium 2-acrylamide-2-methylpropane sulfonate, or a mixture thereof; The initiator is at least one of azobisisobutyronitrile, azobisisoheptyl nitrile, dimethyl azobis isobutyrate, tert-butyl hydroperoxide, tert-butyl peroxypivalate, and dibenzoyl peroxide, or a mixture thereof; In step b), the amount of each component is as follows in parts by weight: 100 parts of the diluted copolymer solution, and 1.9-16.4 parts of the alcohol solution containing the catalyst; The solid content of the diluted copolymer solution is 10.0wt%-40.0wt%; The catalyst is at least one of potassium hydroxide and sodium hydroxide, and the concentration of the catalyst is 0.003wt%-20.0wt%; The solvent in step a) 1) is benzene series, and the benzene series in steps a) 1) and 2) is one of benzene, toluene, ethylbenzene, and xylene, or a mixture thereof.

2. The method of producing low alcoholysis degree polyvinyl alcohol according to claim 1, characterized by: The molar ratio of alcohol to benzene series in the alcohol solution is between 0.5 and 1.

0.

3. The method of producing low alcoholysis degree polyvinyl alcohol according to claim 2, characterized by: The alcohol in the alcohol solution of the catalyst is at least one of methanol, ethanol, isopropanol, and n-butanol.

4. The low alcoholysis degree polyvinyl alcohol according to any one of claims 1-3 for use as an auxiliary dispersant for vinyl chloride suspension polymerization.