CN114276478B

CN114276478B - Preparation method and device of polyvinyl alcohol with high alcoholysis degree

Info

Publication number: CN114276478B
Application number: CN202111676351.0A
Authority: CN
Inventors: 姜维; 张飞雄; 吴远友; 徐晓云; 余德宝; 景雁凤
Original assignee: Inner Mongolia Shuangxin Environment Friendly Material Co ltd; Inner Mongolia Shuangxin Polymer Materials Technology Research Institute Co ltd
Current assignee: Inner Mongolia Shuangxin Environment Friendly Material Co ltd; Inner Mongolia Shuangxin Polymer Materials Technology Research Institute Co ltd
Priority date: 2021-12-31
Filing date: 2021-12-31
Publication date: 2024-02-02
Anticipated expiration: 2041-12-31
Also published as: CN114276478A; CN118165148A

Abstract

The invention discloses a preparation method and a device of high alcoholysis degree polyvinyl alcohol, which are characterized in that anion exchange resin and cation exchange resin are introduced into aqueous solution of the polyvinyl alcohol to improve the alcoholysis degree of the polyvinyl alcohol, and the preparation method comprises the steps of treating the ion exchange resin, saponification reaction of the polyvinyl alcohol and the like, so that the alcoholysis degree of the polyvinyl alcohol reaches more than 99.9%, and meanwhile, the sodium acetate content of a product is lower than 0.5wt%.

Description

Preparation method and device of polyvinyl alcohol with high alcoholysis degree

Technical Field

The invention belongs to the field of polyvinyl alcohol preparation, and particularly relates to a preparation method and a device of polyvinyl alcohol with high alcoholysis degree, in particular to preparation of polyvinyl alcohol special for an optical film.

Background

Polyvinyl alcohol (PVA) is an important chemical raw material for manufacturing optical films, the polyvinyl alcohol is obtained by alcoholysis reaction of polyvinyl acetate (PVAC) and methanol, and NaOH is a catalyst, however, the existing side reaction produces impurity sodium acetate, and the product quality is affected. The existing PVA special for the optical film must meet the requirements that the alcoholysis degree is above 99.9%, the sodium acetate content is lower than 0.5wt%, and the existing method basically introduces a new additive during polymerization or adjusts the amount of alkali to reach the target during alcoholysis, so that the process is complex and not well controlled, the cost is high, and the index cannot meet the requirements.

Chinese patent CN 111647104a discloses a method for preparing polyvinyl alcohol for optical film, which comprises regulating the polymerization degree of polyvinyl alcohol product by changing solvent amount, initiator addition amount and/or polymerization reaction temperature in polymerization process, wherein the polymerization degree is only regulated in polymerization stage, and the content of impurity sodium acetate cannot be reduced.

Disclosure of Invention

Aiming at the problems of low alcoholysis degree and high sodium acetate content of the polyvinyl alcohol special for the optical film in the prior art, the invention provides a preparation method of the polyvinyl alcohol with high alcoholysis degree, in particular to a preparation method of the polyvinyl alcohol special for the optical film, and the alcoholysis degree of the polyvinyl alcohol is more than 99.9 percent by introducing ion exchange resin into an aqueous solution of the polyvinyl alcohol, and meanwhile, the sodium acetate content of a product is lower than 0.5 weight percent, so that the index requirement of the polyvinyl alcohol for the optical film is met.

According to a first embodiment of the present invention, there is provided a method for producing a polyvinyl alcohol having a high degree of alcoholysis, comprising the steps of:

(1) Treating the anion exchange resin to obtain a regenerated anion exchange resin;

(2) Preparing a polyvinyl alcohol solution;

(3) And (3) conveying the polyvinyl alcohol solution in the step (2) to the anion exchange resin regenerated in the step (1) for reaction to obtain the polyvinyl alcohol solution with improved alcoholysis degree.

Further, in the step (1), a cation exchange resin is treated to obtain a regenerated cation exchange resin.

Further, the method also comprises a step (4) of conveying the polyvinyl alcohol solution obtained in the step (3) into the cation exchange resin regenerated in the step (1) for reaction to obtain the polyvinyl alcohol solution with improved alcoholysis degree.

Further, the polyvinyl alcohol solution in the step (2) is a polyvinyl alcohol aqueous solution.

In the step (3), the polyvinyl alcohol solution in the step (2) is conveyed into the anion exchange resin regenerated in the step (1), and the polyvinyl alcohol solution with improved alcoholysis degree is obtained after the reaction.

Further, in the step (3), the reacted polyvinyl alcohol solution is returned to the anion exchange resin to react until the alcoholysis degree of the polyvinyl alcohol reaches a set value, or the polyvinyl alcohol solution in the step (2) is conveyed to the anion exchange resin treated in the step (1) to perform a cyclic reaction until the alcoholysis degree of the polyvinyl alcohol reaches the set value.

Further, the reaction in the step (3) includes an anion exchange reaction and an ester saponification reaction.

Further, the reaction in step (4) includes a cation exchange reaction.

According to still another embodiment of the present invention, there is provided a method for preparing a high alcoholysis degree polyvinyl alcohol, comprising the steps of:

(1) Respectively treating the anion exchange resin and the cation exchange resin to obtain regenerated anion exchange resin and cation exchange resin;

(2) Preparing a polyvinyl alcohol solution;

(3) Conveying the polyvinyl alcohol solution in the step (2) to the regenerated anion exchange resin in the step (1) for reaction until the alcoholysis degree of the polyvinyl alcohol reaches a set value;

(4) And (3) conveying the polyvinyl alcohol solution obtained in the step (3) to the regenerated cation exchange resin in the step (1) for reaction until the pH value of the polyvinyl alcohol solution reaches a set value, and obtaining the polyvinyl alcohol solution with improved alcoholysis degree.

Further, in the step (3), the polyvinyl alcohol solution after the contact reaction with the anion exchange resin is returned to the dissolution tank of the original polyvinyl alcohol, and then the polyvinyl alcohol solution in the dissolution tank is conveyed to the anion exchange resin to realize the reciprocating circulation of the polyvinyl alcohol solution, so as to promote the sufficient contact between the polyvinyl alcohol solution and the anion exchange resin, and the repeated circulation is carried out for one or more times (for example, 5-30 times, preferably 7-25 times, preferably 8-20 times, preferably 9-18 times, more preferably 10-15 times), during the repeated process, periodic sampling is carried out, the alcoholysis degree of the polyvinyl alcohol in the polyvinyl alcohol solution is detected, and the repeated is ended when the alcoholysis degree of the polyvinyl alcohol in the polyvinyl alcohol solution reaches more than 99.9%, preferably 99.95% or more preferably 99.98% or more, most preferably 99.99% or more, and the polyvinyl alcohol solution is obtained, otherwise, the repeated is continued.

Further, in the step (4), the polyvinyl alcohol solution after the contact reaction with the cation exchange resin is returned to the dissolution tank of the polyvinyl alcohol, and then the polyvinyl alcohol solution in the dissolution tank is conveyed to the cation exchange resin to realize the reciprocating circulation of the polyvinyl alcohol solution, so as to promote the sufficient contact between the polyvinyl alcohol solution and the cation exchange resin, and the repeated circulation is carried out for one or more times (for example, 5-30 times, preferably 7-25 times, preferably 8-20 times, preferably 9-18 times, more preferably 10-15 times), and during the repeated process, periodic sampling is carried out, and the repeated is finished when the pH of the solution is 6-7, preferably the pH is 6.5-7, so that the polyvinyl alcohol solution with improved alcoholysis degree is obtained, otherwise, the repeated is continued.

Further, in the step (1), the anion exchange resin and the cation exchange resin are repeatedly washed with water before being treated, respectively.

Further, in the step (1), the regeneration of the anion exchange resin includes: soaking the anion exchange resin with an alkali solution (soaking time, for example, 10 to 120 minutes, preferably 20 to 60 minutes, more preferably 25 to 40 minutes, for example, 30 minutes), and then washing with water (for example, one or more times, for example, 3 to 6 times), the alkali solution being used in an amount of 0.5 to 10 times, preferably 0.7 to 8 times, preferably 0.8 to 5 times, more preferably 1 to 3 times, the volume of the anion resin, and the alkali solution being, for example, a sodium hydroxide solution or a potassium hydroxide solution having a concentration of 0.5 to 6mol/L, preferably 1 to 5mol/L, preferably 3 to 5 mol/L;

Regeneration of the cation exchange resin includes: the cationic resin is soaked with an acid solution (soaking time, for example, 10 to 120 minutes, preferably 20 to 60 minutes, more preferably 25 to 40 minutes, for example, 30 minutes), and then washed with water (for example, one or more times, for example, 3 to 6 times), the acid solution being used in an amount of 0.5 to 10 times, preferably 0.7 to 8 times, preferably 0.8 to 5 times, more preferably 1 to 3 times the volume of the cationic resin, and the acid solution may be, for example, a hydrochloric acid or sulfuric acid solution having a concentration of 0.1 to 7mol/L, preferably 0.5 to 6mol/L, preferably 3 to 5 mol/L.

Further, when regenerating the anion exchange resin, washing the anion exchange resin with water to a pH of the water wash of preferably 7 to 9, more preferably 7.5 to 8.5, most preferably 8; the cation exchange resin is washed with water to a pH of the water wash preferably in the range of 5 to 7, more preferably in the range of 5.5 to 6.5, most preferably 6, when the cation exchange resin is regenerated.

Further, in the step (2), the concentration of the polyvinyl alcohol solution is 5 to 20wt%, preferably 8 to 18wt%, more preferably 10 to 15wt%, and the dissolution temperature of the polyvinyl alcohol is 80 to 100 ℃, preferably 85 to 95 ℃, more preferably about 90 ℃ and the dissolution time is 1 to 5 hours.

Further, the polyvinyl alcohol solution in the step (2) is transferred to the anion exchange resin when being cooled to 10-60 ℃, preferably cooled to 20-60 ℃.

Further, in the step (3), 0.2 to 2.0 parts, preferably 0.6 to 1.6 parts, more preferably 0.8 to 1.5 parts, most preferably 1 to 1.2 parts of an anion exchange resin (dry basis) are required per part of polyvinyl alcohol (dry basis) by weight,

in step (4), 0.1 to 1.0 parts, preferably 0.3 to 0.8 parts, more preferably 0.4 to 0.7 parts, and most preferably 0.5 to 0.6 parts of cation exchange resin (dry basis) are required per part of polyvinyl alcohol (dry basis) by weight.

Further, the reaction temperature of all the reactions in the step (3) is 10 to 60 ℃, more preferably 20 to 60 ℃, and the reaction pressure is normal pressure.

Further, the reaction temperature of all the reactions in the step (4) is 10 to 60 ℃, more preferably 20 to 60 ℃, and the reaction pressure is normal pressure.

Further, the polyvinyl alcohol solution with improved alcoholysis degree obtained in the step (4) is directly used as a final product in the next process, for example, the process of preparing an optical film.

Further, the anion exchange resin of step (1) is a strong base, for example, may be a quaternary amine group (-NR) ₃ OH), preferably selected from-N ⁺ Cl ^- 、-NH ⁺ Cl ^- 、-NH ⁺ ₂ Cl ^- 、-NH ⁺ ₃ Cl ^- 、-NH ₄ ⁺ Cl ^- Any one or more of the following; the cation exchange resin is weak acid type or strong acid type, and can be, for example, sulfonic acid group (-SO) ₃ H) Preferably the acidic groups are selected from the group consisting of-SO ₃ ^- H ⁺ (having active groups-SO on the surface) ₃ ^- H ⁺ The cation exchange resin of (2) is directly reacted with polyvinyl alcohol solution) and-SO without acid liquor treatment ₃ ^- Na ⁺ Either or both of the anion exchange resins and the cation exchange resins herein are conventional resins well known to those skilled in the art.

With surface carrying chloride ions (Cl) ^- ) And the surface of the anion exchange resin is provided with hydrogen ions (H) ⁺ ) The reaction principle is illustrated by using sodium hydroxide solution as the cation exchange resin and alkali solution:

in the present application, the anion exchange resin is treated with sodium hydroxide solution, and the anion exchange resin is mixed with sodium hydroxide solution and then left to stand, so that chloride ions (Cl) carried on the surface of the anion exchange resin ^- ) By hydroxide ions (OH) ^- ) Substituted to form a surface carrying hydroxyl ions (OH ^- ) Simultaneously generating sodium chloride (NaCl);

in the step (3), hydroxide ions (OH) are carried on the surface ^- ) And sodium acetate in polyvinyl alcohol solution (inWhen polyvinyl alcohol is dissolved, sodium acetate contained in the polyvinyl alcohol is dissolved into the solution) to react, and acetate ions (CH) are formed on the surface ₃ COO ^- ) The anion exchange resin and sodium hydroxide of (1) and the generated sodium hydroxide and polyvinyl alcohol are subjected to saponification reaction (the alcoholysis degree of the polyvinyl alcohol is not 100 percent and the polyvinyl alcohol has ester groups which are not alcoholyzed) to obtain sodium acetate and a polyvinyl alcohol solution with improved alcoholysis degree, and the obtained sodium acetate and the surface of the polyvinyl alcohol carry hydroxyl ions (OH) ^- ) The anion exchange resin of (2) continuously reacts, the reaction is repeated, and finally, the polyvinyl alcohol solution with the alcoholysis degree improved is obtained, meanwhile, the content of sodium acetate is reduced, and the polyvinyl alcohol solution with the alcoholysis degree improved contains sodium hydroxide;

in the step (4), the surface is provided with hydrogen ions (H ⁺ ) The cation exchange resin of (2) is reacted with sodium hydroxide contained in the polyvinyl alcohol solution with improved alcoholysis degree in the step (3) to produce a catalyst having sodium ions (Na ⁺ ) Removing sodium hydroxide from the polyvinyl alcohol solution with improved alcoholysis degree to obtain a purer polyvinyl alcohol product;

if a material with sodium ions (Na ⁺ ) The cation exchange resin of (2) is reacted with an acid solution to produce a catalyst having hydrogen ions (H) ⁺ ) And sodium chloride.

Further, the polyvinyl alcohol used in step (2) may be any polyvinyl alcohol product having an alcoholysis degree of 80 to 99.8%, particularly an alcoholysis degree of 99% or more, prepared according to a method known in the art, for example, acetylene is prepared by a calcium carbide acetylene method, acetylene is reacted with acetic acid to produce vinyl acetate, a polymerization reaction of vinyl acetate produces polyvinyl acetate, and the polyvinyl alcohol product obtained after alcoholysis of polyvinyl acetate.

Further, the water is distilled water or deionized water, preferably secondary distilled water.

In the present application, the ion exchange resin is a polymer matrix with a cross-linked structure, and the inside of the polymer matrix is a net-shaped structure, and has all-around pore channels filled with water molecules, and a plurality of chemical bonds are combined on the position of a certain part of the pore channelsTo provide exchanged exchange groups consisting of two parts, divided into fixed groups (e.g. NH on anion exchange resin ₄ ⁺ Sulfonate SO on the surface of cation exchange resin ₃ ^- ) And mobile moieties (e.g. chloride (Cl) on the surface of anion exchange resins ^- ) Hydroxy (OH) ^- ) Na on the surface of cation exchange resin ⁺ And H ⁺ ). The fixed part of the exchange group is bound on the matrix of the macromolecule and cannot move freely, and is called as fixed ion; the mobile part of the exchange group becomes free mobile ions in the solution, and under certain conditions, the mobile part can exchange with ions with the same sign.

The invention uses the ion exchange resin fixed group as carrier to make the hydroxyl ion on the anion exchange resin and acetate ion in the polyvinyl alcohol exchange, the hydrogen ion and sodium ion on the cation exchange resin exchange, and prepares the polyvinyl alcohol with alcoholysis degree above 99.9% and sodium acetate content below 0.5 wt%.

In the present application, the anion exchange resin and the cation exchange resin after use can be regenerated and reused. The regeneration step of the anion exchange resin comprises the following steps: carrying the waste of step (3), for example with acetate ions (CH) ₃ COO ^- ) The anion exchange resin of step (4) and the cation exchange resin used in step (1) are washed with a large amount of water and regenerated using step (1).

According to still another embodiment of the present invention, it further relates to a polyvinyl alcohol solution for optical films prepared by the above method, in which the degree of alcoholysis of polyvinyl alcohol is 99.9% or more, preferably 99.95% or more, and the sodium acetate content is less than 0.50% by weight, even less than 0.15% by weight, even less than 0.10% by weight.

According to still another embodiment of the present invention, there is provided an apparatus for preparing polyvinyl alcohol having a high alcoholysis degree, comprising an alkali liquor tank for storing alkali liquor, an acid liquor tank for storing the acid liquor, a water tank for storing the water, an anion exchange resin tank filled with anion exchange resin, a polyvinyl alcohol dissolution tank for filling polyvinyl alcohol dissolution liquid, a cation exchange resin tank filled with cation exchange resin, wherein an alkali liquor output pipe of the alkali liquor tank is connected to the anion exchange resin tank after passing through an alkali liquor valve, an acid liquor output pipe of the acid liquor tank is connected to the cation exchange resin tank after passing through an acid liquor valve, a water output pipe of the water tank is connected to the polyvinyl alcohol dissolution tank after passing through a water valve in sequence after separating a first branch pipe and a second branch pipe, the first branch pipe is connected to the anion exchange resin tank, the anion exchange resin tank is provided with a waste alkali liquor output pipe for outputting waste alkali liquor, and the cation exchange resin tank is provided with a waste acid liquor output pipe for outputting waste acid liquor;

The polyvinyl alcohol dissolving liquid is divided into a third branch pipe and a fourth branch pipe by the polyvinyl alcohol dissolving tank after passing through a dissolving liquid valve, the fourth branch pipe is divided into a fifth branch pipe and a sixth branch pipe, the third branch pipe and the fifth branch pipe are connected with an anion exchange resin tank, and the sixth branch pipe is connected with a cation exchange resin tank.

Further, a first valve is arranged on the first branch pipe, a second valve is arranged on the second branch pipe, a third valve is arranged on the water output pipeline after the second branch pipe is separated, a fourth valve is arranged on the third branch pipe, a fifth valve is arranged on the fifth branch pipe, a sixth valve is arranged on the sixth branch pipe, a waste lye valve is arranged on the waste lye output pipeline, and a waste acid liquor valve is arranged on the waste acid liquor output pipeline.

Further, the first branch pipe is connected to the liquid inlet of the anion exchange resin tank after being converged with the alkali liquor output pipeline of the alkali liquor tank, and the second branch pipe is connected to the liquid inlet of the cation exchange resin tank after being converged with the acid liquor output pipeline of the acid liquor tank.

Further, the third branch pipe and the fifth branch pipe are respectively connected with the waste alkali liquor output pipeline of the anion exchange resin tank in a converging way, the sixth branch pipe is connected with the waste alkali liquor output pipeline of the cation exchange resin tank in a converging way, and the fifth branch pipe and the sixth branch pipe are respectively provided with a first liquid pump and a second liquid pump.

Further, the anion exchange resin tank, the cation exchange resin tank and the polyvinyl alcohol dissolving tank can be respectively, for example, vertical storage tanks, an upper layer of silk screen and a lower layer of silk screen are respectively arranged in the anion exchange resin tank and the cation exchange resin tank, a space for storing resin is formed between the silk screens, the silk screens can be made of 304 stainless steel meshes, the pore diameter of the silk screens is smaller than the particle size of the resin, the pore diameter of the silk screens can be 0.2-0.4mm, for example, the pore diameter ratio of the anion exchange resin tank and the cation exchange resin tank is more than 1.5, and the polyvinyl alcohol dissolving liquid is ensured to be fully contacted in the anion exchange resin tank or in the circulating process of the cation exchange resin tank and the polyvinyl alcohol dissolving tank. The anion exchange resin tank and the cation exchange resin tank are respectively provided with a resin inlet for resin to be put in and a resin outlet for resin to be taken out, and the resin inlet and the resin outlet are preferably positioned between the two layers of silk screens.

Further, the polyvinyl alcohol dissolution tank is provided with a feed inlet for inputting a polyvinyl alcohol solution into the polyvinyl alcohol dissolution tank.

Further, a sampling port is formed in the anion exchange resin tank, a polyvinyl alcohol solution is periodically adopted, and the alcoholysis degree of the polyvinyl alcohol in the polyvinyl alcohol solution is analyzed; the cation exchange resin tank is provided with a sampling port, and a polyvinyl alcohol solution is periodically adopted and the pH value is detected.

Further, the volume of the anion exchange resin tank is consistent with that of the cation exchange resin tank, the volume of the polyvinyl alcohol dissolving tank is larger than that of the anion exchange resin tank or the cation exchange resin tank, the volume of the polyvinyl alcohol dissolving tank can be 1.2-3 times that of the anion exchange resin tank or the cation exchange resin tank, so that the polyvinyl alcohol solution is circulated between the polyvinyl alcohol dissolving tank and the anion exchange resin tank or the cation exchange resin tank under the power of the first liquid pump or the second liquid pump, namely, circulating liquid is input into the anion exchange resin tank or the cation exchange resin tank from the polyvinyl alcohol dissolving tank, and the liquid of the anion exchange resin tank or the cation exchange resin tank returns to the polyvinyl alcohol dissolving tank in an overflow mode.

Further, the alkali liquor tank is preferably located above the anion exchange resin tank, the alkali liquor enters the anion exchange resin tank under the action of self gravity, the acid liquor tank is preferably located above the cation exchange resin tank, and the water tank is preferably located above the anion exchange resin tank, the cation exchange resin tank and the polyvinyl alcohol dissolution tank.

All valves are in a closed state before the device is used, and in the using process, the feed inlet of the polyvinyl alcohol dissolving tank is in an open state.

The method for improving the alcoholysis degree of the polyvinyl alcohol by using the device comprises the following steps:

(1) Opening the alkali liquor valve, and inputting alkali liquor (such as sodium hydroxide solution) into the anion exchange resin (such as chloride ion (Cl) carried on the surface ^- ) The anion exchange resin) and closing an alkali liquor valve after the alkali liquor passes through the anion exchange resin;

opening the acid valve, and introducing acid (such as hydrochloric acid solution) into the cation exchange resin (such as sodium ion (Na) ⁺ ) The cation exchange resin) and closing an acid valve after the acid solution passes through the cation exchange resin;

then opening a waste lye valve and a waste acid liquor valve, discharging waste lye and waste acid liquor after resin soaking through a waste lye output pipeline and a waste acid liquor output pipeline respectively, opening a water valve, a first valve and a second valve, respectively conveying water in a water tank to an anion exchange resin tank and a cation exchange resin tank through a first branch pipe and a second branch pipe after passing through the water output pipeline respectively to flush the anion exchange resin and the cation exchange resin, wherein the pH value of the water for washing the anion exchange resin to the water is preferably 7-9, more preferably 7.5-8.5, most preferably 8, the first valve and the waste lye valve are closed, the pH value of the water for washing the cation exchange resin to the water is preferably 5-7, more preferably 5.5-6.5, most preferably 6, and finally closing the water valve;

(2) Inputting the dissolved polyvinyl alcohol solution from a feed inlet of a polyvinyl alcohol dissolving tank, opening a dissolving liquid valve, a fifth valve, a first liquid pump, the first valve and the third valve, continuously pumping the dissolving liquid into an anion exchange resin tank through the first liquid pump to carry out ion exchange reaction (acetate ions in the solution are exchanged with hydroxyl ions of the anion exchange resin to generate sodium hydroxide, sodium hydroxide and ester groups in the polyvinyl alcohol are subjected to saponification reaction to improve the alcoholysis degree of the polyvinyl alcohol), continuously entering the anion exchange resin tank along with the dissolving liquid, overflowing the dissolving liquid into a first branch pipe and a water output pipeline from the anion exchange resin tank after filling the whole anion exchange resin tank, then entering the polyvinyl alcohol dissolving tank, circulating, periodically (for example, every half hour, 1 hour, or 2 hours) sampling the polyvinyl alcohol solution at a sampling port of the anion exchange resin tank, analyzing whether the alcoholysis degree of the polyvinyl alcohol meets the requirement, if so, stopping circulating, closing the dissolving liquid valve, the first liquid pump and the fifth valve to obtain the polyvinyl alcohol solution for improving the alcoholysis degree, otherwise, continuously circulating,

(3) Opening a second liquid pump, a fourth valve and a sixth valve, pumping the polyvinyl alcohol solution (containing sodium hydroxide and presenting alkalinity) in the anion exchange resin tank in the step (2) into a cation exchange resin tank through the second liquid pump to carry out ion exchange reaction (inorganic salt ions such as sodium ions in the solution are exchanged with hydrogen ions in the cation exchange resin to remove the inorganic salt, and simultaneously, the hydrogen ions react with hydroxyl ions in the solution to generate water), continuously entering the cation exchange resin tank along with the polyvinyl alcohol solution, filling the whole cation exchange resin tank with the solution, overflowing the solution from the cation exchange resin tank, then entering a polyvinyl alcohol dissolution tank through a second branch pipe and a water output pipeline, closing the fourth valve and the first valve at the moment, simultaneously opening the dissolution liquid valve, pumping the solution in the polyvinyl alcohol dissolution tank into the cation exchange resin tank through the second liquid pump to circulate, periodically (for example, every 2 hours) sampling a sampling port of the cation exchange resin tank, analyzing whether the pH value of the polyvinyl alcohol solution meets the requirement (pH is 6-7), if not, ending the circulation, otherwise, continuing the circulation;

(4) Opening a waste acid liquid valve, outputting the polyvinyl alcohol solution in the cation exchange resin tank and the polyvinyl alcohol dissolving tank in the step (4), obtaining a finished product of the polyvinyl alcohol solution with improved alcoholysis degree, detecting the alcoholysis degree and the sodium acetate content of the finished product, and entering the preparation process of the optical film, wherein the anion exchange resin in the anion exchange resin tank and the cation exchange resin in the cation exchange resin tank are subjected to alkali treatment and acid treatment after being washed by water.

The invention has the beneficial effects that:

1) The invention can prepare the polyvinyl alcohol or the polyvinyl alcohol solution with high alcoholysis degree, can prepare PVA with different alcoholysis degree grade requirements, is especially suitable for preparing the polyvinyl alcohol special for the optical film, and can realize one-step continuous production of the polyvinyl alcohol solution raw material suitable for the polyvinyl alcohol special for the optical film. The solution of PVA is introduced into ion exchange resin, the efficient removal of acetate ions of sodium acetate impurities in PVA is realized through the ion exchange function of anion exchange resin, meanwhile, sodium hydroxide is generated after the exchange, and the saponification reaction of polyvinyl alcohol is promoted, so that the alcoholysis degree of PVA can be improved to more than 99.9%, and meanwhile, the content of impurity sodium acetate is reduced to be lower than 0.5wt%.

2) The process for preparing the polyvinyl alcohol or the polyvinyl alcohol solution with high alcoholysis degree has the advantages of mild operation condition, environment friendliness, easy acquisition of ion exchange resin, low input cost, simple process, easy realization of industrial scale production and remarkable effect.

3) After the anion exchange resin and the cation exchange resin for preparing the polyvinyl alcohol with high alcoholysis degree or the polyvinyl alcohol solution are used, the anion exchange resin and the cation exchange resin can be regenerated and reused by using water washing, alkali treatment and acid treatment, so that the production and operation cost is reduced.

4) The polyvinyl alcohol solution with high alcoholysis degree can directly enter the preparation process of the PVA optical film without further treatment, thereby realizing the integration of polyvinyl alcohol purification and PVA optical film material preparation and reducing the production cost of PVA optical film material preparation.

Drawings

FIG. 1 is a schematic diagram of the reaction of an anion exchange resin with chloride ions on the surface thereof treated with sodium hydroxide;

FIG. 2 is a schematic diagram of the reaction of an anion exchange resin with hydroxide ions on the surface thereof, treated with sodium hydroxide, with sodium acetate in a polyvinyl alcohol solution;

FIG. 3 is a schematic diagram of saponification of an ester group in sodium hydroxide and polyvinyl alcohol;

FIG. 4 is a schematic illustration of the reaction of a cation exchange resin with sodium ions on its surface treated with hydrochloric acid;

FIG. 5 is a schematic diagram of the reaction of a cation exchange resin with hydrogen ions on the surface thereof, treated with hydrochloric acid, with sodium hydroxide in an alcoholyzed polyvinyl alcohol solution;

FIG. 6 is a schematic structural view of an apparatus for preparing high degree of alcoholysis of polyvinyl alcohol according to the invention;

FIG. 7 is a schematic structural view of another apparatus for preparing high degree of alcoholysis of polyvinyl alcohol according to the invention;

FIG. 8 is a schematic structural view of another apparatus for preparing high degree of alcoholysis of polyvinyl alcohol according to the invention.

Reference numerals:

1-an alkali liquid tank, 2-an acid liquid tank, 3-a water tank, 4-an anion exchange resin tank, 5-a polyvinyl alcohol dissolution tank, 6-a cation exchange resin tank, 7-a first liquid pump, 8-a second liquid pump, 9-a feed inlet, 10-a sampling port and 11-a sampling port;

l1-alkali liquor output pipeline, L2-acid liquor output pipeline, L3-water output pipeline, L4-first branch pipe, L5-dissolution liquor output pipeline, L6-second branch pipe, L7-waste alkali liquor output pipeline, L8-waste acid liquor output pipeline, L9-fifth branch pipe, L10-sixth branch pipe, L11-third branch pipe and L12-fourth branch pipe;

f1-alkali liquor valve, F2-acid liquor valve, F3-water valve, F4-first valve, F5-third valve, F6-second valve, F7-fifth valve, F8-sixth valve, F9-waste alkali liquor valve, F10-waste acid liquor valve, F11-fourth valve and F12-dissolution liquor valve.

Detailed Description

The invention is further described below with reference to the drawings and examples.

As shown in fig. 6, the present invention provides an apparatus for preparing polyvinyl alcohol having high alcoholysis degree, comprising an anion exchange resin tank 4 for filling anion exchange resin, a polyvinyl alcohol dissolution tank 5 for filling polyvinyl alcohol solution, and a cation exchange resin tank 6 for filling cation exchange resin, wherein a first branch pipe L4 is connected to the anion exchange resin tank 4, a second branch pipe L6 is connected to the cation exchange resin tank 6, the anion exchange resin tank 4 is provided with a waste lye output pipe L7 for outputting waste lye, the cation exchange resin tank 6 is provided with a waste lye output pipe L8 for outputting waste lye, the dissolution liquid output pipe L5 of the polyvinyl alcohol dissolution tank 5 is divided into a fifth branch pipe L9 and a sixth branch pipe L10 via a dissolution liquid valve F12, the fifth branch pipe L9 is connected to the anion exchange resin tank 4, and the sixth branch pipe L10 is connected to the cation exchange resin tank 6.

The first branch pipe L4 is provided with a first valve F4, the second branch pipe L6 is provided with a second valve F6, a pipeline connected with the polyvinyl alcohol dissolving tank 5 after the first branch pipe L4 and the second branch pipe L6 are converged is provided with a third valve F5, the fifth branch pipe L9 is provided with a fifth valve F7, the sixth branch pipe L10 is provided with a sixth valve F8, the waste lye output pipeline L7 is provided with a waste lye valve F9, and the waste lye output pipeline L8 is provided with a waste lye valve F10.

The fifth branch pipe L9 is connected with the waste lye output pipeline L7 of the anion exchange resin tank 4 in a converging way, the sixth branch pipe L10 is connected with the waste lye output pipeline L8 of the cation exchange resin tank in a converging way, the fifth branch pipe L9 and the sixth branch pipe L10 are respectively provided with a first liquid pump 7 and a second liquid pump 8, and the first liquid pump 7 and the second liquid pump 8 can be unidirectional pumps or bidirectional pumps.

The anion exchange resin tank 4 is provided with an inlet for the alkali liquor and/or water, and the cation exchange resin tank 6 is provided with an inlet for the acid liquor and/or water.

In the apparatus shown in fig. 6, the anion exchange resin and the cation exchange resin were regenerated using the following methods:

(1) Through the inlet of the anion exchange resin tank for the alkaline solution (e.g. sodium hydroxide solution), the anion exchange resin is charged with (e.g. surface carried chloride ions (Cl) ^- ) The anion exchange resin of (2) is filled with alkali liquor, and the alkali liquor stops being filled after the alkali liquor passes through the anion exchange resin;

by cation exchange resinsThe acid solution (for example, hydrochloric acid solution) is introduced into the tank and is charged with a cation exchange resin (for example, sodium ion (Na) ⁺ ) The cation exchange resin of (2) and acid liquor is introduced into the cation exchange resin tank, and the introduction of the acid liquor is stopped after the acid liquor passes through the cation exchange resin;

Then opening the waste lye valve and the waste lye valve, discharging the waste lye and the waste lye after the resin is soaked through the waste lye output pipeline and the waste lye output pipeline respectively, opening the water (water can be secondary distilled water for example) inlets of the anion exchange resin tank and the cation exchange resin tank to respectively convey water to flush the anion exchange resin and the cation exchange resin, wherein the pH value of the water to flush the anion exchange resin is preferably 7-9, more preferably 7.5-8.5, most preferably 8, closing the water inlet and the waste lye valve, stopping conveying, the pH value of the water to flush the cation exchange resin is preferably 5-7, more preferably 5.5-6.5, most preferably 6, closing the water inlet and the waste lye valve, and stopping conveying.

As shown in fig. 7, the present invention provides another apparatus for preparing polyvinyl alcohol with high alcoholysis degree, which comprises an alkali liquor tank 1 for storing alkali liquor, an acid liquor tank 2 for storing acid liquor, a water tank 3 for storing water, an anion exchange resin tank 4 for filling with anion exchange resin, a polyvinyl alcohol dissolution tank 5 for filling with polyvinyl alcohol solution, and a cation exchange resin tank 6 for filling with cation exchange resin, wherein an alkali liquor output pipe L1 of the alkali liquor tank 1 is connected with the anion exchange resin tank 4 after passing through an alkali liquor valve F1, an acid liquor output pipe L2 of the acid liquor tank 2 is connected with the cation exchange resin tank 6 after passing through an acid liquor valve F2, a water output pipe of the water tank 3 is sequentially separated into a first branch pipe L4 and a second branch pipe L6 after passing through a water valve F3 and then is connected with the polyvinyl alcohol dissolution tank 5, the first branch pipe L4 is connected with the anion exchange resin tank 4, the second branch pipe L6 is connected with the cation exchange resin tank 6, the anion exchange resin tank 4 is provided with a waste alkali liquor output pipe L7 for outputting waste alkali liquor, the cation exchange resin tank 6 is provided with a waste liquor output pipe L8, and a third branch pipe L10 is connected with a fifth branch pipe L10 and a sixth branch pipe L12 after passing through a water valve F3, and a fifth branch pipe 10 is connected with the fifth branch pipe 11L 12, and a fifth branch pipe 10 is connected with the fifth branch pipe 11.

The first branch pipe L4 is provided with a first valve F4, the second branch pipe L6 is provided with a second valve F6, a third valve F5 is arranged on a water output pipeline after the first branch pipe L4 and the second branch pipe L6 are separated, the third branch pipe L11 is provided with a fourth valve F11, the fifth branch pipe L9 is provided with a fifth valve F7, the sixth branch pipe L10 is provided with a sixth valve F8, the waste lye output pipeline L7 is provided with a waste lye valve F9, and the waste lye output pipeline L8 is provided with a waste lye valve F10.

The first branch pipe L4 is connected to the liquid inlet of the anion exchange resin tank 4 after being converged with the alkali liquid output pipeline L1 of the alkali liquid tank, and the second branch pipe L6 is connected to the liquid inlet of the cation exchange resin tank 6 after being converged with the acid liquid output pipeline L2 of the acid liquid tank.

The third branch pipe L11 and the fifth branch pipe L9 are respectively connected with the waste lye output pipeline L7 of the anion exchange resin tank 4 in a converging way, the sixth branch pipe L10 is connected with the waste lye output pipeline L8 of the cation exchange resin tank in a converging way, the fifth branch pipe L9 and the sixth branch pipe L10 are respectively provided with a first liquid pump 7 and a second liquid pump 8, and the first liquid pump 7 and the second liquid pump 8 can be unidirectional pumps or bidirectional pumps.

The anion exchange resin tank 4, the cation exchange resin tank 6 and the polyvinyl alcohol dissolving tank 5 can be respectively, for example, vertical storage tanks, an upper layer of silk screen and a lower layer of silk screen are respectively arranged in the anion exchange resin tank 4 and the cation exchange resin tank 6, a space for storing resin is formed between the silk screens, for example, a 304 stainless steel mesh is formed between the silk screens, the pore diameter of the silk screens is smaller than the particle diameter of the resin and is used for preventing the resin from flowing out along with circulating liquid, the pore diameter can be, for example, 0.2-0.4mm, the length-diameter ratio of the anion exchange resin tank 4 to the cation exchange resin tank 6 is more than 1.5, and the polyvinyl alcohol dissolving liquid is ensured to be fully contacted in the circulating process of the anion exchange resin tank or the cation exchange resin tank and the polyvinyl alcohol dissolving tank.

The polyvinyl alcohol dissolving tank 5 is provided with a feed inlet 9 for feeding the polyvinyl alcohol product into the polyvinyl alcohol dissolving tank.

The anion exchange resin tank 4 is provided with a sampling port 10, and a polyvinyl alcohol solution is periodically adopted to analyze the alcoholysis degree of the polyvinyl alcohol in the polyvinyl alcohol solution; the cation exchange resin tank 6 is provided with a sampling port 11, and a polyvinyl alcohol solution is periodically collected and the pH is detected.

The volume of the anion exchange resin tank 4 is consistent with the volume of the cation exchange resin tank 6, the volume of the polyvinyl alcohol dissolving tank 5 is larger than the volume of the anion exchange resin tank 4 or the cation exchange resin tank 6, the volume of the polyvinyl alcohol dissolving tank 5 can be 1.2-3 times that of the anion exchange resin tank 4 or the cation exchange resin tank 6, for example, so that the liquid is circulated between the polyvinyl alcohol dissolving tank 6 and the anion exchange resin tank 4 or the cation exchange resin tank 6 under the power of the first liquid pump 7 or the second liquid pump 8, namely, the circulating liquid is input into the anion exchange resin tank 4 or the cation exchange resin tank 6 from the polyvinyl alcohol dissolving tank 5, and the liquid of the anion exchange resin tank 4 or the cation exchange resin tank 6 returns to the polyvinyl alcohol dissolving tank 5 in an overflow mode.

The alkali solution tank 1 is preferably positioned above the anion exchange resin tank 4, alkali solution enters the anion exchange resin tank under the action of self gravity, the acid solution tank 2 is preferably positioned above the cation exchange resin tank 6, and the water tank 3 is preferably positioned above the anion exchange resin tank 4, the cation exchange resin tank 6 and the polyvinyl alcohol dissolving tank 5.

As shown in fig. 8, the present invention provides another embodiment of an apparatus for preparing polyvinyl alcohol with high alcoholysis degree, which is different from the embodiment of fig. 7 in that the dissolution liquid output pipe L5 of the polyvinyl alcohol dissolution tank 5 is not separated into the third branch pipe L11 connected to the anion exchange resin tank 4 and the fourth valve F11 after passing through the dissolution liquid valve F12, and the first liquid pump 7 and/or the second liquid pump 8 are bi-directional pumps, so that the forward and backward flow of the fluid in the branch pipes can be realized.

The following describes the method for improving the alcoholysis of polyvinyl alcohol with reference to the apparatus of FIG. 7:

(1) Opening alkali liquor valve F1, alkaliThe liquid (such as sodium hydroxide solution) is fed under gravity to the anion exchange resin (such as chloride (Cl) carried on the surface ^- ) The anion exchange resin of (2) and closing an alkali liquor valve F1 after alkali liquor passes through the anion exchange resin in an anion exchange resin tank 4;

opening acid valve F2, and introducing acid (such as hydrochloric acid solution) into the cation exchange resin (such as sodium ion (Na) ⁺ ) The cation exchange resin of (2) and closing the acid valve F2 after the acid solution has passed through the cation exchange resin;

then opening a waste lye valve F9 and a waste lye valve F10, discharging waste lye and waste lye after resin soaking through a waste lye output pipeline L7 and a waste lye output pipeline L8 respectively, opening a water valve F3, a first valve F4 and a second valve F6, respectively conveying water in a water tank 3 to an anion exchange resin tank 4 and a cation exchange resin tank 6 through a first branch pipe L4 and a second branch pipe L6 after the water is discharged through the water output pipeline L3, flushing the anion exchange resin and the cation exchange resin, wherein the pH value of the water for washing the anion exchange resin to the water is preferably 7-9, more preferably 7.5-8.5, most preferably 8, closing the first valve F4 and the waste lye valve F9, the pH value of the water for washing the cation exchange resin to the water is preferably 5-7, more preferably 5.5-6.5, most preferably 6, closing the second valve F6 and the waste lye valve F10, and finally closing the water valve F3;

(2) The dissolved polyvinyl alcohol solution is input from a feed port 9 of a polyvinyl alcohol dissolving tank 5, a dissolving solution valve F12, a fifth valve F7, a first liquid pump 7, a first valve F4 and a third valve F5 are opened, the dissolving solution is continuously pumped into the anion exchange resin tank 4 through the first liquid pump 7 to carry out ion exchange reaction (acetate ions in the solution and hydroxyl ions of the anion exchange resin are exchanged to generate sodium hydroxide, the sodium hydroxide and ester groups in the polyvinyl alcohol are saponified to improve the alcoholysis degree of the polyvinyl alcohol), as the dissolving solution continuously enters the anion exchange resin tank 4, the dissolving solution overflows from the anion exchange resin tank to enter the first branch pipe L4 and a water output pipeline after entering the polyvinyl alcohol dissolving tank 5, so that circulation is carried out, a sampling port 10 of the anion exchange resin tank 4 periodically (for example, every half hour, 1 hour or 2 hours) is carried out, whether the alcoholysis degree of the polyvinyl alcohol in the polyvinyl alcohol solution is satisfied or not is analyzed, if the alcoholysis degree of the polyvinyl alcohol solution is satisfied, circulation is stopped, the dissolving solution F12, the first valve F7 and the fifth valve F7 are closed, and the circulation of the polyvinyl alcohol solution is continuously obtained,

(3) Opening a second liquid pump 8, a fourth valve F11 and a sixth valve F8, pumping the polyvinyl alcohol solution (containing sodium hydroxide and being alkaline) of the anion exchange resin tank 4 in the step (2) into a cation exchange resin tank through the second liquid pump 8 to perform ion exchange reaction (inorganic salt ions such as sodium ions in the solution and hydrogen ions in the cation exchange resin are exchanged to remove the inorganic salt, and simultaneously the hydrogen ions and the hydroxyl ions in the solution react to generate water), continuously entering the cation exchange resin tank 6 along with the polyvinyl alcohol solution, overflowing the solution from the cation exchange resin tank 6 after the whole cation exchange resin tank 6 is filled with the solution, then entering the polyvinyl alcohol dissolution tank 5 through a second branch pipe L6 and a water output pipeline, closing the fourth valve F11 and the first valve F4 at the moment, simultaneously opening a dissolving liquid valve F12, pumping the reaction liquid in the polyvinyl alcohol dissolution tank 5 into the cation exchange resin tank 6 through the second liquid pump 8 to perform circulation, and periodically (for example, for 1 hour or every 2 hours) at a sampling port 10 of the cation exchange resin tank to perform sampling to meet the requirement of the cycle, if the cycle is satisfied, otherwise, continuing to analyze whether the cycle pH is satisfied or not;

(4) Opening a waste acid liquid valve F10, outputting the polyvinyl alcohol solution in the cation exchange resin tank 6 and the polyvinyl alcohol dissolution tank 5 in the step (4), obtaining a finished polyvinyl alcohol solution product with improved alcoholysis degree, detecting the alcoholysis degree and sodium acetate content of the finished polyvinyl alcohol solution product, and entering the preparation process of an optical film, wherein the anion exchange resin and the cation exchange resin in the anion exchange resin tank 4 and the cation exchange resin tank 6 are subjected to alkali treatment and acid treatment after being washed by water.

In another embodiment of the present invention, for the step (4), the polyvinyl alcohol solution obtained in the step (3) may be led out, the polyvinyl alcohol may be separated by cooling crystallization, and then sodium hydroxide or sodium salt generated in the step (3) of the polyvinyl alcohol may be removed by washing with water at a low temperature, thereby obtaining a polyvinyl alcohol solution with improved alcoholysis degree and impurity removal.

Next, the surface carries chloride ions (Cl ^- ) And the surface of the anion exchange resin is provided with sodium ions (Na ⁺ ) The reaction principle of the present invention is illustrated by using sodium hydroxide as the cation exchange resin and alkali solution:

in the present application, the anion exchange resin is treated with sodium hydroxide, and the anion exchange resin is mixed with sodium hydroxide solution and then left to stand, so that chloride ions (Cl) carried on the surface of the anion exchange resin ^- ) By hydroxide ions (OH) ^- ) Substituted to form a surface carrying hydroxyl ions (OH ^- ) Sodium chloride (NaCl) is simultaneously generated, and the reaction process is shown in fig. 1;

in the step of increasing the alcoholysis degree, hydroxide ions (OH ^- ) The anionic resin of (2) reacts with sodium acetate in the polyvinyl alcohol solution (sodium acetate contained in the polyvinyl alcohol dissolves out into the solution when the polyvinyl alcohol dissolves) to generate a solution with acetate ions (CH) on the surface ₃ COO ^- ) The anion exchange resin and sodium hydroxide of (1) and the generated sodium hydroxide and polyvinyl alcohol are subjected to saponification reaction (the alcoholysis degree of the polyvinyl alcohol is not 100 percent and the polyvinyl alcohol has ester groups which are not alcoholyzed) to obtain sodium acetate and polyvinyl alcohol solution, and the obtained sodium acetate and the surface of the sodium acetate carry hydroxyl ions (OH) ^- ) The anionic resin of (2) is reacted again, the reaction is repeated, finally, the polyvinyl alcohol solution with the alcoholysis degree improved is obtained, meanwhile, the content of sodium acetate is reduced, the polyvinyl alcohol solution with the alcoholysis degree improved contains sodium hydroxide, and the reaction process is shown in figures 2 and 3;

with hydrogen ions (H) ⁺ ) The cation exchange resin of (2) is reacted with sodium hydroxide contained in the polyvinyl alcohol solution for improving alcoholysis degree in the above step to produce a catalyst having sodium ions (Na ⁺ ) Removing sodium hydroxide from the polyvinyl alcohol solution with improved alcoholysis degree to obtain purer polyvinyl alcohol product, wherein the reaction process is shown in figure 5;

if a material with sodium ions (Na ⁺ ) The cation exchange resin of (2) is reacted with an acid solution to produce a catalyst having hydrogen ions (H) ⁺ ) The reaction process of the cation exchange resin and sodium chloride is shown in figure 4.

The method for improving the alcoholysis degree of polyvinyl alcohol according to the present invention is described below by way of specific examples.

The ion exchange resin used in the examples was newly purchased, and a large amount of distilled water was used to suck up impurity groups on the surface of the resin before use.

Example 1

An alcoholysis-degree polyvinyl alcohol solution was prepared using the apparatus of FIG. 6.

(1) 100Kg of anion exchange resin (anion resin with immobilized active groups-NH) ₄ ⁺ Placing Cl-) into an anion exchange resin tank 4, soaking for 40 minutes by using 2.5mol/L sodium hydroxide solution with 3 times of volume, discharging waste alkali liquid, washing the anion exchange resin at least 3 times by using secondary distilled water until the pH of the washing liquid is about 8, and obtaining treated anion exchange resin;

50Kg of cation exchange resin (cation resin has immobilized active groups-SO) ₃ ^- H ⁺ ) Placing the mixture into a cation exchange resin tank 6, and repeatedly washing the mixture with secondary distilled water until the pH of the washing liquid is about 6 to obtain treated cation exchange resin;

(2) Taking 500Kg of polyvinyl alcohol particles (alcoholysis degree is 98.27%, sodium acetate content is about 0.84 wt%) and adding 2000Kg of secondary distilled water, dissolving at about 80 ℃ for 2h, cooling to about 35 ℃ and conveying to a polyvinyl alcohol dissolving tank 5;

(3) Inputting the polyvinyl alcohol solution obtained in the step (2) into the anion exchange resin prepared in the step (1) for reaction, wherein the reaction temperature is about 35 ℃, overflowing the polyvinyl alcohol solution from the anion exchange resin tank 4 to the original polyvinyl alcohol dissolution tank 5, conveying the solution in the polyvinyl alcohol dissolution tank 5 into the anion exchange resin tank 4, repeating the process for a plurality of times, periodically sampling in the repeated process, detecting the alcoholysis degree of the polyvinyl alcohol in the polyvinyl alcohol solution, ending the repetition when the alcoholysis degree of the polyvinyl alcohol reaches 99.99%, otherwise continuing the repetition to obtain the polyvinyl alcohol solution with the alcoholysis degree improved, and the content of sodium acetate is about 0.35wt%;

(4) And (3) conveying the polyvinyl alcohol solution obtained in the step (3) to the cation exchange resin treated in the step (1) for reaction, wherein the reaction temperature is 35 ℃, the solution overflows from the cation exchange resin tank 6 and is conveyed back to the polyvinyl alcohol dissolving tank 5, repeating the process for a plurality of times, periodically sampling in the repeating process, ending repeating when the pH value of the polyvinyl alcohol solution is detected to be 6.5, otherwise, continuing repeating, and finally outputting a finished product of the polyvinyl alcohol solution with the alcoholysis degree improved from the cation exchange resin tank 6, and directly entering the preparation process of the optical film.

Example 2

An alcoholysis-degree polyvinyl alcohol solution was prepared using the apparatus of FIG. 7.

(1) 250Kg of anion exchange resin (anion exchange resin with immobilized active group-NH) ⁺ ₂ Cl ^- ) Placing into an anion exchange resin tank 4, soaking with 2 times volume of 4mol/L sodium hydroxide solution for 35 min, discharging waste alkali liquid, washing anion exchange resin with secondary distilled water for at least 3 times until the pH of the water washing liquid is about 7.5, and obtaining treated anion exchange resin;

150Kg of cation exchange resin (the surface of the cation exchange resin has fixed active groups-SO) ₃ ^- Na ⁺ ) Soaking in 2 times volume of 4mol/L HCl solution for 35 min, discharging acid pickle, washing cation exchange resin at least 4 times with secondary distilled water, and repeatedly washing with secondary distilled water until pH of water washing solution is about 5.5 to obtain treated cation exchange resin;

(2) 500Kg of polyvinyl alcohol particles (alcoholysis degree is 98.22%, sodium acetate content is about 0.77 wt%) are taken, 4500Kg of secondary distilled water is added, the dissolution temperature is about 90 ℃ and dissolved for 2.5h, then the temperature is reduced to about 40 ℃ and the mixture is conveyed into a polyvinyl alcohol dissolution tank 5;

(3) Inputting the polyvinyl alcohol solution obtained in the step (2) into the anion exchange resin prepared in the step (1) for reaction, wherein the reaction temperature is about 40 ℃, overflowing the polyvinyl alcohol solution from the anion exchange resin tank 4 and returning the polyvinyl alcohol solution to the original polyvinyl alcohol dissolving tank 5, then conveying the polyvinyl alcohol solution in the polyvinyl alcohol dissolving tank 5 into the anion exchange resin tank 4, repeating the process for a plurality of times, periodically sampling in the repeating process, detecting the alcoholysis degree of the polyvinyl alcohol in the polyvinyl alcohol solution, ending the repetition when the alcoholysis degree of the polyvinyl alcohol reaches 99.98%, otherwise continuing the repetition to obtain the polyvinyl alcohol solution with the alcoholysis degree improved, and the content of sodium acetate is about 0.13wt%;

(4) And (3) conveying the polyvinyl alcohol solution obtained in the step (3) to the cation exchange resin treated in the step (1) for reaction, wherein the reaction temperature is 40 ℃, the solution overflows from the cation exchange resin tank 6 and is conveyed back to the polyvinyl alcohol dissolving tank 5, repeating the process for a plurality of times, periodically sampling in the repeating process, ending repeating when the pH value of the polyvinyl alcohol solution is detected to be 6, otherwise, continuing repeating, outputting a finished product of the polyvinyl alcohol solution with the alcoholysis degree improved from the cation exchange resin tank 6, and directly entering the preparation process of the optical film.

Example 3

An alcoholysis-degree polyvinyl alcohol solution was prepared using the apparatus of FIG. 8.

(1) 500Kg of anion exchange resin (the surface of the anion exchange resin is provided with fixed active groups-NH) ⁺ ₃ Cl ^- ) Placing into an anion exchange resin tank 4, soaking with 2.5 times volume of 3.5mol/L sodium hydroxide solution for 40 minutes, discharging waste alkali liquid, washing anion exchange resin with secondary distilled water for at least 3 times until the pH of the washing liquid is about 8.5, and obtaining treated anion exchange resin;

250Kg of cation exchange resin (the surface of the cation exchange resin is provided with fixed active groups-SO) ₃ ^- Na ⁺ ) Placing the mixture into a cation exchange resin tank 6, soaking the mixture in 3.5mol/L HCl solution with the volume of 2.5 times for 40 minutes, discharging waste acid liquid, washing the cation exchange resin at least 4 times by using secondary distilled water, and repeatedly washing the cation exchange resin with the secondary distilled water until the pH of the washing liquid is about 6 to obtain treated cation exchange resin;

(2) Adding 3667Kg of secondary distilled water into 500Kg of polyvinyl alcohol particles (the alcoholysis degree is 99.68 percent and the sodium acetate content is about 0.54 weight percent), dissolving for 3 hours at the dissolution temperature of about 90 ℃, cooling to about 40 ℃, and conveying to a polyvinyl alcohol dissolving tank 5;

(3) Inputting the polyvinyl alcohol solution obtained in the step (2) into the anion exchange resin prepared in the step (1) for reaction, wherein the reaction temperature is about 40 ℃, overflowing the polyvinyl alcohol solution from the anion exchange resin tank 4 and returning the overflow to the original polyvinyl alcohol dissolving tank 5, then conveying the solution in the polyvinyl alcohol dissolving tank 5 into the anion exchange resin tank 4, repeating the process for a plurality of times, periodically sampling in the repeating process, detecting the alcoholysis degree of the polyvinyl alcohol in the polyvinyl alcohol solution, ending the repetition when the alcoholysis degree of the polyvinyl alcohol reaches 99.99%, otherwise continuing the repetition to obtain the polyvinyl alcohol solution with the alcoholysis degree improved, and the content of sodium acetate is about 0.07wt%;

(4) And (3) conveying the polyvinyl alcohol solution obtained in the step (3) to the cation exchange resin treated in the step (1) for reaction, wherein the reaction temperature is 40 ℃, the solution overflows from the cation exchange resin tank 6 and is conveyed back to the polyvinyl alcohol dissolving tank 5, repeating the process for a plurality of times, periodically sampling in the repeating process, ending repeating when the pH value of the polyvinyl alcohol solution is detected to be 6.5, otherwise, continuing repeating, and finally outputting a finished product of the polyvinyl alcohol solution with the alcoholysis degree improved from the cation exchange resin tank 6, and directly entering the preparation process of the optical film.

Example 4

(1) 1000Kg of anion exchange resin (the surface of the anion exchange resin is provided with fixed active groups-N) ⁺ Cl ^- ) Placing into an anion exchange resin tank 4, soaking with 3 times of 2.5mol/L sodium hydroxide solution for 45 minutes, discharging waste alkali liquid, washing the anion exchange resin with secondary distilled water for at least 3 times until the pH of the water washing liquid is about 7.5, and obtaining treated anion exchange resin;

500Kg of cation exchange resin (cation resin has immobilized active groups-SO) ₃ ^- H ⁺ ) Placing into cation exchange resin tank 6, repeatedly washing with secondary distilled water until pH of water washing solution is about 5.5 Obtaining a treated cation exchange resin;

(2) Adding 2833Kg of secondary distilled water into 500Kg of polyvinyl alcohol particles (the alcoholysis degree is 99.36 percent and the sodium acetate content is about 0.68 weight percent), dissolving for 3 hours at the dissolution temperature of about 85 ℃, cooling to about 30 ℃, and conveying to a polyvinyl alcohol dissolution tank 5;

(3) Inputting the polyvinyl alcohol solution obtained in the step (2) into the anion exchange resin prepared in the step (1) for reaction, wherein the reaction temperature is about 35 ℃, overflowing the polyvinyl alcohol solution from the anion exchange resin tank 4 and returning the overflow to the original polyvinyl alcohol dissolving tank 5, then conveying the solution in the polyvinyl alcohol dissolving tank 5 into the anion exchange resin tank 4, repeating the process for a plurality of times, periodically sampling in the repeating process, detecting the alcoholysis degree of the polyvinyl alcohol in the polyvinyl alcohol solution, ending the repetition when the alcoholysis degree of the polyvinyl alcohol reaches 99.99%, otherwise continuing the repetition to obtain the polyvinyl alcohol solution with the alcoholysis degree improved, and the content of sodium acetate is about 0.10wt%;

(4) And (3) conveying the polyvinyl alcohol solution obtained in the step (3) to the cation exchange resin treated in the step (1) for reaction, wherein the reaction temperature is 35 ℃, the solution overflows from the cation exchange resin tank 6 and is conveyed back to the polyvinyl alcohol dissolving tank 5, repeating the process for a plurality of times, periodically sampling in the repeating process, ending repeating when the pH value of the polyvinyl alcohol solution is detected to be 6, otherwise, continuing repeating, outputting a finished product of the polyvinyl alcohol solution with the alcoholysis degree improved from the cation exchange resin tank 6, and directly entering the preparation process of the optical film.

Comparative examples 1 to 4

For comparison, the applicant examined the alcoholysis degree and sodium acetate content of the polyvinyl alcohol not treated with the ion exchange resin according to the polyvinyl alcohol raw materials of examples 1 to 4, and compared the polyvinyl alcohol treated in examples 1 to 4, respectively. The comparative results of the alcoholysis degree of the obtained polyvinyl alcohol and the sodium acetate content are shown in the following Table 1:

table 1 comparison of the results of the measurements of the polyvinyl alcohol products of comparative examples 1 to 4 with those of examples 1 to 4

Sequence number	Resin treatment	Alcoholysis degree/%	Sodium acetate/wt%
				Comparative example 1	Untreated process	98.27	0.84
Example 1	Treated with	99.99	0.35
				Comparative example 2	Untreated process	98.22	0.77
Example 2	Treated with	99.98	0.13
				Comparative example 3	Untreated process	99.68	0.54
Example 3	Treated with	99.99	0.07
				Comparative example 4	Untreated process	99.36	0.68
Example 4	Treated with	99.99	0.10

In the above experiment, the method for determining the alcoholysis degree and the sodium acetate uses national standard, the polyvinyl alcohol solution is firstly dried, the alcoholysis degree of the dried polyvinyl alcohol product is determined according to the rule of annex D in GB/T12010.2-2010, and the sodium acetate is determined according to the rule of annex B in GB/T12010.2-2010.

As can be seen from the results in Table 1, the alcoholysis degree of the polyvinyl alcohol treated by the ion exchange resin is improved, the sodium acetate content is obviously reduced, and the quality requirement of the polyvinyl alcohol special for the PVA optical film can be completely met.

It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. And obvious variations or modifications thereof are contemplated as falling within the scope of the present invention.

Claims

1. The preparation method of the polyvinyl alcohol with high alcoholysis degree is characterized by comprising the following steps:

(1) Separate treatment of anion exchange resinsAnd cation exchange resin to obtain regenerated surface-carried hydroxyl ions (OH ^- ) Anion exchange resin and cation exchange resin of (a);

(2) Preparing a polyvinyl alcohol solution;

(3) Conveying the polyvinyl alcohol solution in the step (2) to the regenerated anion exchange resin in the step (1) for reaction to obtain the polyvinyl alcohol solution with improved alcoholysis degree;

(4) And (3) conveying the polyvinyl alcohol solution obtained in the step (3) to the regenerated cation exchange resin in the step (1) for reaction, and returning the reacted polyvinyl alcohol solution to the anion exchange resin for reaction until the alcoholysis degree of the polyvinyl alcohol reaches a set value, or conveying the polyvinyl alcohol solution obtained in the step (2) to the anion exchange resin treated in the step (1) for cyclic reaction until the alcoholysis degree of the polyvinyl alcohol reaches the set value, and the pH value of the polyvinyl alcohol solution reaches the set value of 6-7, so as to obtain the polyvinyl alcohol solution with improved alcoholysis degree.

2. The method according to claim 1, wherein the set value of the alcoholysis degree of the polyvinyl alcohol is 99.9% or more, and the set value of the pH of the solution is 6 to 7.

3. The method according to claim 1, wherein in the step (3), the reacted polyvinyl alcohol solution is returned to the anion exchange resin to react until the alcoholysis degree of the polyvinyl alcohol reaches a set value, or the polyvinyl alcohol solution in the step (2) is fed to the anion exchange resin treated in the step (1) to perform a cyclic reaction until the alcoholysis degree of the polyvinyl alcohol reaches a set value.

4. The preparation method according to claim 1, wherein in the step (3), the polyvinyl alcohol solution after the contact reaction with the anion exchange resin is returned to the dissolution tank of the original polyvinyl alcohol, and then the solution in the dissolution tank is conveyed to the anion exchange resin to realize the repeated circulation of the polyvinyl alcohol solution, and in the repeated process, the sample is taken, the alcoholysis degree of the polyvinyl alcohol in the polyvinyl alcohol solution is detected, and the repetition is ended when the alcoholysis degree of the polyvinyl alcohol in the polyvinyl alcohol solution reaches a set value, otherwise the repetition is continued.

5. The method according to claim 1, wherein in the step (4), the polyvinyl alcohol solution after the reaction with the cation exchange resin is returned to the dissolution tank of the polyvinyl alcohol, and then the polyvinyl alcohol solution in the dissolution tank is conveyed to the cation exchange resin, so that the repetition of the polyvinyl alcohol solution is realized, and in the repetition process, the sampling is performed, and the repetition is ended when the pH of the solution is set, otherwise, the repetition is continued.

6. The process according to any one of claims 1 to 5, wherein in step (1), the anion exchange resin and the cation exchange resin are each repeatedly washed with water before being treated;

regeneration of the anion exchange resin includes: treating the anion exchange resin with alkali liquor, and then washing with water;

regeneration of the cation exchange resin includes: the cation exchange resin is treated with an acid solution and then washed with water.

7. The process according to claim 6, wherein the anion exchange resin is washed with water until the pH of the washing solution is 7 to 9 when the anion exchange resin is regenerated; and when the cation exchange resin is regenerated, washing the cation exchange resin with water until the pH of the water washing liquid is 5-7.

8. The method according to any one of claims 1 to 5, wherein in the step (2), the concentration of the polyvinyl alcohol solution is 5 to 20wt%, the dissolution temperature of the polyvinyl alcohol is 80 to 100 ℃, and the dissolution time is 1 to 5 hours; and then the dissolved polyvinyl alcohol solution is conveyed to anion exchange resin for reaction when the temperature is reduced to 10-60 ℃.

9. The process according to any one of claims 1 to 5, wherein the reaction temperature of all the reactions in step (3) and step (4) is 10 to 60 ℃.

10. The process according to any one of claims 1 to 5, wherein in step (3), 0.2 to 2.0 parts of anion exchange resin is required per part of polyvinyl alcohol on a dry weight basis, and/or

In the step (4), each part of polyvinyl alcohol needs 0.1-1.0 part of cation exchange resin calculated by dry weight.

11. The process of any one of claims 1-5, wherein the anion exchange resin of step (1) is a strongly basic anion exchange resin; and/or

The cation exchange resin is weak acid cation exchange resin or strong acid cation exchange resin; and/or

The alcoholysis degree of the polyvinyl alcohol used in the step (2) is 80 to 99.8%.

12. The process according to claim 10, wherein the anion exchange resin is a quaternary amine group-containing resin, and/or

The cation exchange resin is a resin containing sulfonic acid groups.

13. The device for preparing the high alcoholysis degree polyvinyl alcohol solution is characterized by comprising an anion exchange resin tank for filling anion exchange resin, a polyvinyl alcohol dissolving tank for filling polyvinyl alcohol solution and a cation exchange resin tank for filling cation exchange resin, wherein the anion exchange resin tank is provided with a waste alkali liquor output pipeline for outputting waste alkali liquor, the cation exchange resin tank is provided with a waste acid liquor output pipeline for outputting waste acid liquor, the dissolution liquor output pipeline of the polyvinyl alcohol dissolving tank is divided into a third branch pipe and a fourth branch pipe after passing through a dissolution liquor valve, the fourth branch pipe is divided into a fifth branch pipe and a sixth branch pipe, the third branch pipe and the fifth branch pipe are connected with the anion exchange resin tank, and the sixth branch pipe is connected with the cation exchange resin tank;

The device also comprises an alkali liquor tank for storing alkali liquor, an acid liquor tank for storing acid liquor and a water tank for storing water, wherein an alkali liquor output pipeline of the alkali liquor tank is connected with the anion exchange resin tank after passing through an alkali liquor valve, an acid liquor output pipeline of the acid liquor tank is connected with the cation exchange resin tank after passing through an acid liquor valve, and a water output pipeline of the water tank is connected with the polyvinyl alcohol dissolution tank after sequentially separating a first branch pipe and a second branch pipe after passing through a water valve, wherein the first branch pipe is connected with the anion exchange resin tank, and the second branch pipe is connected with the cation exchange resin tank.

14. The device according to claim 13, wherein the first branch pipe is provided with a first valve, the second branch pipe is provided with a second valve, the water output pipeline after separating the first branch pipe and the second branch pipe is provided with a third valve, the third branch pipe is provided with a fourth valve, the fifth branch pipe is provided with a fifth valve, the sixth branch pipe is provided with a sixth valve, the waste lye output pipeline is provided with a waste lye valve, and/or

The fifth branch pipe and the sixth branch pipe are respectively provided with a first liquid pump and a second liquid pump.

15. The apparatus according to claim 13, wherein the inside of the anion exchange resin tank and the cation exchange resin tank are provided with upper and lower screens, respectively, between which a space for storing the resin is formed, and/or,

The volume of the anion exchange resin tank is consistent with that of the cation exchange resin tank, and the volume of the polyvinyl alcohol dissolving tank is larger than that of the anion exchange resin tank or the cation exchange resin tank; the alkali solution tank is positioned above the anion exchange resin tank, the acid liquor tank is positioned above the cation exchange resin tank, and the water tank is positioned above the anion exchange resin tank, the cation exchange resin tank and the polyvinyl alcohol dissolution tank.

16. The apparatus according to claim 13, wherein the polyvinyl alcohol dissolution tank is provided with a feed port for feeding a polyvinyl alcohol solution into the polyvinyl alcohol dissolution tank, and/or

The anion exchange resin tank and the cation exchange resin tank are respectively provided with sampling ports.

17. The apparatus of claim 14, wherein the first liquid pump and/or the second liquid pump is a bi-directional gear pump.