Recycling method of polyvinyl alcohol

Abstract

The invention provides a polyvinyl alcohol recovery method, which comprises: S1, adding a reducing agent to a to-be-treated liquid with a temperature maintained at 40-60 DEG C, completely reacting, removing solid substances, and filtering to obtain a filtration liquid, the to-be-treated liquid comprising polyvinyl alcohol and an iodine-containing compound; and S2, drying the filtration liquid in the step S1 so as to realize the recovery of the polyvinyl alcohol. According to the method, the target of recovering the polyvinyl alcohol from the polyvinyl alcohol waste liquid containing the iodine-containing compound is achieved through oxidation reaction, filtering and drying operation in sequence at the specific temperature, and good economic benefits and environmental benefits are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of waste liquid purification, and in particular to a recovery method for extracting polyvinyl alcohol from waste films in a polarizer manufacturing process. Background Art

[0002] The traditional process of producing polarizers is mainly to make the polyvinyl alcohol film undergo dipping, cross-linking, and stretching processes in sequence to prepare a polarizer and achieve polarization performance. In the above process, the polyvinyl alcohol film is immersed in a solution containing boric acid, iodine, potassium iodide, etc. The stretching process is a high-ratio stretching and extension. Although the polyvinyl alcohol film itself has a certain toughness, the toughness is limited. The polyvinyl alcohol film will break at a certain frequency during the stretching process. The polyvinyl alcohol film material after stretching and breaking cannot be collected or processed in subsequent production. Therefore, there will be a serious waste of the original film material, which reduces the production cost.

[0003] However, there is currently no precedent for recycling the broken polyvinyl alcohol waste film in the polarizer manufacturing process. In order to reduce environmental pollution and realize the recycling and reuse of waste film, it is very necessary to study a practical process for recycling the broken polyvinyl alcohol waste film in the polarizer manufacturing process. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a polyvinyl alcohol recovery method and recovery system in view of the shortcomings of the prior art.

[0005] To solve the above technical problems, the present invention can be implemented through the following technical solutions:

[0006] In the first aspect, the present application provides a method for recovering polyvinyl alcohol, the method comprising the following steps: S1, adding a reducing agent to a liquid to be treated at a temperature maintained at 40°C to 60°C, removing solid matter after sufficient reaction, filtering, and obtaining a filtrate, wherein the liquid to be treated comprises polyvinyl alcohol and an iodine-containing compound; S2, drying the filtrate in step S1 to achieve recovery of the polyvinyl alcohol. Through the above steps, polyvinyl alcohol can be recovered from waste liquid containing iodine impurities, and iodine can also be recovered.

[0007] As a further improvement of the present application, in step S1, the reducing agent includes one or more of potassium hypochlorite, potassium permanganate, potassium chlorate, manganese dioxide, nitric acid, concentrated sulfuric acid, hypochlorous acid, and sodium peroxide. The function of the reducing agent is to oxidize the iodine ions in the iodine-containing compound in the liquid to be treated into elemental iodine, so as to recover solid iodine.

[0008] As a further improvement of the present application, the following steps are also included before step S1: S01, dissolving the waste polyvinyl alcohol film obtained in the polarizer process with ultrapure water to obtain a dissolving solution; S02, passing the dissolving solution through a first filter and a first heat exchanger in sequence, filtering and cooling them respectively, to obtain the liquid to be treated. The purpose of ultrapure water dissolution is to dissolve all the waste polyvinyl alcohol films in the polarizer process into water, which is convenient for impurity removal to achieve the recovery of high-purity polyvinyl alcohol. The function of the first filter is to separate impurities such as solid particles that do not participate in the reaction from the dissolving solution, so as to facilitate subsequent chemical reactions and the separation of useful substances. The function of the first heat exchanger is to cool the dissolving solution to a preset temperature, so as to facilitate the oxidation of iodine ions into elemental iodine, while preventing polyvinyl alcohol from being oxidized into resin.

[0009] As a further improvement of the present application, in step S01, the degree of polymerization of the waste polyvinyl alcohol film obtained in the polarizer manufacturing process is between 1700 and 2500, and the degree of hydrolysis is not less than 95%.

[0010] As a further improvement of the present application, in step S01, the weight percentage of the waste polyvinyl alcohol film obtained in the polarizer manufacturing process is 1 to 1.2 parts, and the weight percentage of the ultrapure water is 200 to 400 parts. The design of the above component contents facilitates the complete dissolution of the waste polyvinyl alcohol film in water, and the concentration of the polyvinyl alcohol after dissolution is 5 g / L to 10 g / L.

[0011] As a further improvement of the present application, in step S01, the temperature for dissolving the waste polyvinyl alcohol film is controlled to be 90°C to 95°C, and the time for dissolving the waste polyvinyl alcohol film is controlled to be 40 to 50 minutes. The design of the above temperature and time facilitates the complete dissolution of the waste polyvinyl alcohol film in water. In step S02, the temperature of the dissolved solution after cooling is controlled to be 40°C to 60°C. This temperature range facilitates the oxidation of iodine ions into elemental iodine, while preventing polyvinyl alcohol from being oxidized into resin. The filter diameter of the dissolved solution is controlled to be 5μm to 10μm, so as to filter out solid particles that do not participate in the reaction as much as possible.

[0012] As a further improvement of the present application, before step S1, the method further includes the step: S0, adding an oxidant to the liquid to be treated. Preferably, the oxidant includes potassium sulfite. The function of the oxidant is to reduce the solid iodine element in the liquid to be treated to iodine ions, so as to determine the reaction node when the iodine ions are oxidized to the element again, so as to facilitate the smooth progress of the reaction.

[0013] As a further improvement of the present application, the liquid to be treated also includes boric acid. In step S2, before the filtrate is dried, the following steps are also included: heating the filtrate, adjusting the pH value, and adsorbing boric acid in sequence. Preferably, after heating, the temperature of the filtrate is 55°C to 65°C; after adjusting the pH value, the pH value of the filtrate is 3 to 5. Boric acid in the treatment liquid can be removed by the above process.

[0014] In the second aspect, the present application also provides a polyvinyl alcohol recovery system, the system comprising: a treatment liquid reaction module, an iodine filtering module and a first recovery module, wherein: the treatment liquid reaction module is used to react the treatment liquid with a reducing agent, and the treatment liquid includes polyvinyl alcohol and an iodine-containing compound; the iodine filtering module is connected to the treatment liquid reaction module, and is used to screen out the solid matter in the treatment liquid after the oxidation reaction to obtain a filtrate; the first recovery module is connected to the iodine filtering module, and is used to dry the filtrate to achieve the recovery of the polyvinyl alcohol. The above system can recover the polyvinyl alcohol in the iodine-containing compound and polyvinyl alcohol waste liquid, and realize the recovery of iodine element, avoiding environmental pollution and waste of resources.

[0015] As a further improvement of the present application, a treatment liquid preparation module is also included before the treatment liquid reaction module, including: a dissolution unit, a first filter and a first heat exchanger, wherein: the dissolution unit is used to dissolve the polyvinyl alcohol waste film obtained in the polarizer process by ultrapure water to obtain a solution; the first filter is connected to the output end of the dissolution unit, and is used to filter the solution; the first heat exchanger is connected to the output end of the first filter, and is used to cool the filtered solution to obtain a filtrate. The treatment liquid reaction module can be used to prepare the polyvinyl alcohol waste film in the polarizer process into a treatment liquid, which is convenient for the subsequent recovery of polyvinyl alcohol.

[0016] As a further improvement of the present application, the filter diameter of the first filter is set to 5 μm to 10 μm, so as to filter the insoluble impurities in the dissolving solution.

[0017] As a further improvement of the present application, the iodine filtration module includes: a crude iodine dehydration unit and a second filter, wherein: the crude iodine dehydration unit is connected to the output end of the reaction module for the liquid to be treated, and is used to remove the solid iodine in the liquid to be treated; the second filter is connected to the output end of the crude iodine dehydration unit, and is used to filter the liquid to be treated after the solid iodine is removed to obtain the filtrate. The function of the iodine filtration module is to recover the iodine element.

[0018] As a further improvement of the present application, the crude iodine dehydration unit includes a crude iodine dehydrator and a crude iodine collecting tank. The crude iodine dehydrator is connected to the output end of the treated liquid reaction module and is used to separate the solid crude iodine in the treated liquid; the crude iodine collecting tank is connected to the output end of the crude iodine dehydrator and is used to collect the separated solid crude iodine.

[0019] As a further improvement of the present application, the filter diameter of the second filter is set to 0.1 μm to 5 μm, so as to filter out other solid substances after the crude iodine is removed.

[0020] As a further improvement of the present application, the recovery system also includes a boric acid treatment module for removing boric acid in the liquid to be treated.

[0021] As a further improvement of the present application, the boric acid treatment module includes: a second heat exchanger and a boric acid adsorption module, wherein: the second heat exchanger is connected to the output end of the iodine filtration module to heat the filtrate; the boric acid adsorption module is connected to the output end of the second heat exchanger to adsorb boric acid in the liquid to be treated to obtain the filtrate.

[0022] As a further improvement of the present application, the boric acid adsorption module comprises a column filled with a boron adsorbent, and the height of the boron adsorbent in the column is ≥850 mm.

[0023] The present application provides a polyvinyl alcohol recovery method and recovery system, and its beneficial effects are at least:

[0024] The polyvinyl alcohol recovery method achieves the goal of recovering polyvinyl alcohol from polyvinyl alcohol waste liquid containing iodine compounds by sequentially undergoing oxidation reaction, filtration and drying operations at a specific temperature, and has good economic and environmental benefits. On the one hand, by treating the polyvinyl alcohol waste liquid containing iodine compounds, the recycling of polyvinyl alcohol is achieved, which helps to reduce resource waste, improve the reuse rate of polyvinyl alcohol, and reduce costs. On the other hand, the iodine-containing compounds in the waste film can also be converted into solid iodine elemental substance and recovered through the recovery method, which helps to reduce pollution to the environment and improve the utilization rate and environmental protection of the waste film. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the structure of a polyvinyl alcohol recovery system used in Example 1. DETAILED DESCRIPTION

[0026] The present invention will be described in detail below in conjunction with the various embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and any structural, methodological, or functional changes made by a person skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0027] Currently, there is no precedent for recycling the broken polyvinyl alcohol waste film in the polarizer manufacturing process. In order to solve this problem, the present invention provides a polyvinyl alcohol recycling method and recycling system, which realizes the recycling of polyvinyl alcohol and solves the above-mentioned problem.

[0028] The following will first describe the recycling method and then describe the recycling system. It should be noted that the description order of the following embodiments is not intended to limit the preferred order of the embodiments.

[0029] Method Embodiment

[0030] This embodiment provides a method for recovering polyvinyl alcohol, including steps S1 and S2.

[0031] Step S1, adding a reducing agent to a liquid to be treated whose temperature is maintained at 40°C to 60°C, removing solid matter after sufficient reaction, filtering to obtain a filtrate, wherein the liquid to be treated includes polyvinyl alcohol and an iodine-containing compound.

[0032] The liquid to be treated can be waste film generated in the process of polarizer production, including polyvinyl alcohol and iodine-containing compounds. Oxidizing the liquid to be treated at a temperature of 40°C to 60°C helps to oxidize the iodine-containing compounds into solid iodine elements, while avoiding oxidation of polyvinyl alcohol into resin, making it easier to screen out solid iodine elements and other impurities, and then recover polyvinyl alcohol.

[0033] Step S2, drying the filtrate in step S1 to recover the polyvinyl alcohol. The water in the filtrate can be evaporated through the drying process to finally obtain pure polyvinyl alcohol.

[0034] The polyvinyl alcohol recovery method achieves the goal of recovering polyvinyl alcohol from polyvinyl alcohol waste liquid containing iodine compounds by sequentially undergoing oxidation reaction, filtration and drying operations at a specific temperature, and has good economic and environmental benefits. On the one hand, by treating the polyvinyl alcohol waste liquid containing iodine compounds, the recycling of polyvinyl alcohol is achieved, which helps to reduce resource waste, improve the reuse rate of polyvinyl alcohol, and reduce costs. On the other hand, the iodine-containing compounds in the waste film can also be converted into solid iodine elemental substance and recovered through the recovery method, which helps to reduce pollution to the environment and improve the utilization rate and environmental protection of the waste film.

[0035] Preferably, in step S1, the reducing agent includes one or more of potassium hypochlorite, potassium permanganate, potassium chlorate, manganese dioxide, nitric acid, concentrated sulfuric acid, hypochlorous acid, and sodium peroxide. The function of the reducing agent is to oxidize iodine ions into elemental iodine, and the amount of the reducing agent added can be based on the fact that no granular objects are produced in the solution. When the reducing agent is potassium hypochlorite, the reaction equation is as follows: KClO+2KI+H2O→I2+2KOH+KCl.

[0036] In some embodiments, the following steps are also included before step S1:

[0037] S01. Dissolving the waste polyvinyl alcohol film obtained in the polarizer manufacturing process by ultrapure water to obtain a solution.

[0038] In the above dissolution process, the waste film generated in the polarizer manufacturing process is mixed with ultrapure water, that is, the polyvinyl alcohol and iodine-containing compounds in the waste film are dissolved into the water to form a uniform solution to be treated, which is beneficial for treating the polyvinyl alcohol waste film and iodine-containing compounds in the raw materials. Specifically, the polyvinyl alcohol in the waste film is the main recycling object, and the iodine-containing compounds are produced by compounds such as potassium iodide used in the polarizer manufacturing process. The waste film is effectively converted through the dissolution process, providing a suitable solution state for subsequent recycling.

[0039] At the same time, the uniform dissolution process helps the subsequent process steps to proceed smoothly, ensuring that the useful substances are fully dissolved in the solution and improving the recovery efficiency. After the waste membrane is converted into the liquid to be treated, its volume may be reduced relative to the waste membrane, which helps to reduce the storage and treatment costs of the waste membrane.

[0040] Preferably, the temperature for dissolving the waste polyvinyl alcohol film is controlled to be 90° C. to 95° C., and the heating and melting time is 40 to 50 minutes.

[0041] By treating the waste film within the appropriate temperature and heating melting time parameters, it helps to promote the dissolution of components such as polyvinyl alcohol and iodine-containing compounds. High temperature can increase the thermal motion between molecules, making the polyvinyl alcohol molecules in the waste film more likely to interact with water molecules, accelerating the dissolution rate and also improving the recovery rate. Controlling the dissolution temperature and heating time within the appropriate range can effectively save energy and reduce the energy consumption cost in the recycling process. Appropriate temperature and time control can ensure that the dissolution process does not over-treat the waste film and avoid unnecessary waste of resources that may be caused.

[0042] Preferably, in terms of weight percentage, the weight portion of the waste polyvinyl alcohol film obtained in the polarizer manufacturing process is 1 to 1.2 parts, and the weight portion of the ultrapure water is 200 to 400 parts.

[0043] By controlling the weight ratio of waste membrane and ultrapure water, a reasonable ratio of waste membrane and solvent can be achieved to ensure the stability and uniformity of the liquid to be treated during the recovery process. It can be considered that the above appropriate ratio can improve the dissolution efficiency and ensure that the components such as polyvinyl alcohol and iodine-containing compounds in the waste membrane are fully dissolved in ultrapure water. By controlling the amount of waste membrane and ultrapure water, the rational use and conservation of resources can be achieved. Appropriately reducing the amount of ultrapure water can not only reduce costs, but also help reduce the generation of wastewater, thereby reducing the impact on the environment.

[0044] At the same time, the above weight ratio can ensure that useful components such as polyvinyl alcohol in the waste film are dissolved and recovered to the greatest extent possible. Properly increasing the amount of ultrapure water can increase the volume of the solution, which is beneficial to subsequent filtration and treatment steps and improves recovery efficiency.

[0045] In summary, the appropriate weight ratio can reduce the complexity of the mixing process, simplify the operation steps and processes, make it easier for operators to handle the liquid to be treated, reduce the probability of error, and improve process stability.

[0046] Preferably, the degree of polymerization of the waste polyvinyl alcohol film obtained in the polarizer manufacturing process is between 1700 and 2500, and the degree of hydrolysis is not less than 95%. According to the characteristics of the waste film in the polarizer manufacturing process, that is, the degree of polymerization is between 1700 and 2500, and the degree of hydrolysis is not less than 95%, the recycling process has certain advantages in environmental protection, economy and technical implementation, which has positive significance for the efficient recycling of waste films and the effective utilization of resources.

[0047] S02. The dissolved liquid is sequentially passed through a first filter and a first heat exchanger for filtering and cooling, respectively, to obtain the liquid to be treated.

[0048] This embodiment does not limit the first filter and the second filter mentioned below, which can be, for example, a belt filter, using filter cloth or filter paper belt, and retaining solid particles in the liquid on the belt through continuous movement of the belt, thereby achieving filtration; it can also be, for example, a membrane filter, using a microporous membrane or a porous membrane, which can efficiently filter tiny particles and impurities to obtain a relatively pure filtrate.

[0049] This embodiment does not limit the first heat exchanger and the second heat exchanger mentioned below, which are mainly used for heat exchange, transferring the heat in the liquid to be treated to the cooling medium or absorbing heat from the cooling medium, so as to achieve cooling or heating of the liquid to be treated. For example, a shell and tube heat exchanger is composed of a shell and a tube bundle, wherein the shell is filled with a cooling medium, and the liquid to be treated passes through the pipes in the tube bundle and exchanges heat with the cooling medium through the shell; another example is a plate heat exchanger, which is composed of a series of parallel metal plates, and the liquid to be treated and the cooling medium exchange heat through the interlayer between the plates; another example is a tube heat exchanger, which is composed of multiple parallel pipes, and the liquid to be treated and the cooling medium pass through different pipes to achieve heat exchange.

[0050] In the cooling and filtering steps, the obtained solution is filtered and cooled in sequence through the first filter and the first heat exchanger. In the first filter, solid particles, impurities and other substances in the solution are separated to obtain a solution to be treated. In the first heat exchanger, the temperature of the solution to be treated is reduced, which helps to solidify some substances therein or reduce their solubility.

[0051] Preferably, in step S02, the temperature of the dissolved solution after cooling is controlled to be between 40°C and 60°C, and the filter diameter of the dissolved solution filtered is controlled to be between 5 μm and 10 μm.

[0052] Controlling the cooling temperature of the dissolved solution within the range of 40°C to 60°C helps prevent the dissolved solution from cooling too quickly and avoids damage to equipment or materials that may be caused by rapid temperature changes. At the same time, the above temperature range is also conducive to ensuring the stability of the physical properties of the liquid to be treated, which is conducive to the smooth progress of subsequent steps. Controlling the filter diameter of the dissolved solution filtration within the range of 5μm to 10μm can effectively remove solid particles and impurities in the dissolved solution. Reasonable selection of the filter diameter can ensure the filtering effect without causing excessive filtrate loss, thereby improving the recovery efficiency. By controlling the cooling temperature and the filter diameter, overly complex process condition adjustments can be avoided, the operating steps are simplified, and the complexity and technical threshold of the process implementation are reduced. In summary, the control of the cooling temperature and the filter diameter helps to ensure the stability and efficiency of the recovery process, and ultimately achieves the effective recovery and reuse of polyvinyl alcohol.

[0053] In some embodiments, before step S1, the method further includes the following steps: S0, adding an oxidant to the liquid to be treated.

[0054] In the above steps, the iodine element in the liquid to be treated (usually in the form of yellow iodine molecules) can be converted into iodide ions (usually in the form of colorless ions) by an oxidant. This process can be achieved by adding a suitable oxidant, which will provide the required electron transfer to reduce the iodine molecules to iodide ions. The oxidant can be SO2, H2S, Na2S2O3, K2S2O3, etc.

[0055] Preferably, potassium sulfite with a purity of not less than 98% is used to reduce the iodine in the liquid to be treated. Preferably, the amount of potassium sulfite used can be based on the critical point at which the color of the liquid to be treated changes from yellow to clear and transparent.

[0056] In some embodiments, the liquid to be treated also includes boric acid. In step S2, before the filtrate is dried, the following steps are also included: heating the filtrate, adjusting the pH value, and adsorbing boric acid in sequence. Preferably, after heating, the temperature of the filtrate is 55°C to 65°C; after adjusting the pH value, the pH value of the filtrate is 3 to 5. Further preferably, after heating, the temperature of the filtrate is 60°C.

[0057] In the process of polarizer manufacturing, boric acid is often used as a cross-linking agent to enhance the ductility of polyvinyl alcohol film. Therefore, the boric acid contained in the waste film is sometimes treated to improve the purity of polyvinyl alcohol. By adjusting the pH value of the filtrate to the range of 3 to 5, the boric acid component therein can be precipitated in solid or ionic form, thereby achieving the separation of boric acid. Boric acid adsorption devices usually use specific adsorbent materials, such as ortho-dihydroxy functional group materials, boron removal resins prepared by grafting polystyrene microspheres with N-methyl-D-glucosamine functional groups, adsorbents after grafting and shrinking cross-linked polystyrene resins, or silica-polyamine composite materials as carriers. Functionalized grafted ortho-dihydroxy compounds are used as boron adsorbents. These adsorbents have good selectivity and can effectively adsorb and remove boric acid.

[0058] Thus, by adjusting the pH value of the filtrate to a certain range, the boric acid is separated and removed, the purity of polyvinyl alcohol is further improved, and a purer product is obtained. On the other hand, the method of removing boric acid using a boric acid adsorption device does not require the use of chemical agents, does not generate waste liquid and waste gas, and does not pollute the environment. On the other hand, by removing impurities such as boric acid, the quality of the obtained polyvinyl alcohol product is higher, the added value is greater, and the market competitiveness of the product is increased.

[0059] In certain embodiments, polyvinyl alcohol can be purified from filtrate by the method for salting-out separation, and an amount of salt (such as potassium chloride or potassium sulfate etc.) can be added in polyvinyl alcohol liquid, and by adjusting the temperature and concentration of the solution, polyvinyl alcohol is reacted with salt to form solid-state polyvinyl alcohol salts. Subsequently, by separation operations such as filtering or centrifugation, solid-state polyvinyl alcohol salts are separated from solvents. In the drying step, the polyvinyl alcohol salts obtained by separation are heat-treated to evaporate the water therein, thereby obtaining solid-state polyvinyl alcohol. The temperature and time of drying can be adjusted according to actual conditions to obtain required solid state form.

[0060] Preferably, potassium sulfate can be added to the filtrate to maintain the temperature of the filtrate at 60°C, and then the filtrate is sieved and dried to achieve the recovery of the target polyvinyl alcohol. Further preferably, the concentration of K2SO4 in the filtrate is ≥61g / L.

[0061] System Example

[0062] The embodiment of the present application also provides a recycling system for use in the recycling method in the method embodiment. The specific embodiment is consistent with the embodiment described in the above-mentioned embodiment 1 and the technical effects achieved, and some contents will not be repeated here.

[0063] A polyvinyl alcohol recovery system, the system comprising: a treatment liquid reaction module, an iodine filtering module and a first recovery module, wherein: the treatment liquid reaction module is used to react the treatment liquid with a reducing agent, the treatment liquid comprising polyvinyl alcohol and an iodine-containing compound; the iodine filtering module is connected to the treatment liquid reaction module, and is used to screen out the solid matter in the treatment liquid after the oxidation reaction to obtain a filtrate; the first recovery module is connected to the iodine filtering module, and is used to dry the filtrate to achieve the recovery of the polyvinyl alcohol. The above system can recover the polyvinyl alcohol in the iodine-containing compound and polyvinyl alcohol waste liquid, and realize the recovery of iodine element, avoiding environmental pollution and waste of resources.

[0064] In some embodiments, a treatment liquid preparation module is further included before the treatment liquid reaction module, including: a dissolution unit, a first filter and a first heat exchanger, wherein: the dissolution unit is used to dissolve the polyvinyl alcohol waste film obtained in the polarizer process by ultrapure water to obtain a dissolved liquid; the first filter is connected to the output end of the dissolution unit to filter the dissolved liquid; the first heat exchanger is connected to the output end of the first filter to cool the filtered dissolved liquid to obtain a filtrate. The treatment liquid reaction module can be used to prepare the polyvinyl alcohol waste film in the polarizer process into a treatment liquid, which is convenient for the subsequent recovery of polyvinyl alcohol.

[0065] In some embodiments, the filter diameter of the first filter is set to 5 μm to 10 μm, so as to filter insoluble impurities in the dissolving solution.

[0066] In some embodiments, the iodine filtration module includes: a crude iodine dehydration unit and a second filter, wherein: the crude iodine dehydration unit is connected to the output end of the treated liquid reaction module to remove solid iodine in the treated liquid; the second filter is connected to the output end of the crude iodine dehydration unit to filter the treated liquid after removing the solid iodine to obtain the filtrate. The function of the iodine filtration module is to recover the iodine element.

[0067] In some embodiments, the crude iodine dehydration unit includes a crude iodine dehydrator and a crude iodine collection tank. The crude iodine dehydrator is connected to the output end of the treated liquid reaction module and is used to separate solid crude iodine from the treated liquid; the crude iodine collection tank is used to collect the separated solid crude iodine.

[0068] In some embodiments, the filter diameter of the second filter is set to 0.1 μm to 5 μm, so as to filter out other solid substances after the crude iodine is removed.

[0069] In some embodiments, the recovery system further includes a boric acid treatment module for removing boric acid from the liquid to be treated.

[0070] In some embodiments, the boric acid treatment module includes: a second heat exchanger and a boric acid adsorption module, wherein: the second heat exchanger is connected to the output end of the iodine filtration module to heat the filtrate; the boric acid adsorption module is connected to the output end of the second heat exchanger to adsorb boric acid in the liquid to be treated to obtain the filtrate.

[0071] In some embodiments, the boric acid adsorption module comprises a column filled with a boron adsorbent, and the height of the boron adsorbent in the column is ≥850 mm.

[0072] In order to better understand the technical solution of the present application, the beneficial effects of the present application will be further illustrated below in combination with embodiments and comparative examples.

[0073] Example 1

[0074] A method for recovering polyvinyl alcohol comprises the following steps:

[0075] (1) dissolving the waste polyvinyl alcohol film obtained in the polarizer manufacturing process with ultrapure water, wherein, by weight percentage, 1 part by weight of the waste polyvinyl alcohol film and 200 parts by weight of ultrapure water are mixed and put into a mixing and dissolving barrel with a stirrer having a jacketed water bath heating device, and the stirring speed is 70 r / min. The temperature is raised while stirring until the temperature reaches 95° C., and the raised temperature is kept constant for 45 minutes until the waste film is completely dissolved to obtain a dissolved solution;

[0076] (2) passing the above-mentioned dissolved liquid into a first filter (primary filter tank) having filtering and screening functions, and then passing through a first plate heat exchanger to treat the temperature of the dissolved liquid to 50° C., and then entering a solution oxidation tank;

[0077] (3) Adding an excess of potassium sulfite to the above-mentioned solution until the color of the solution changes from yellow to a clear color is optimal. Further, adding an excess of potassium hypochlorite to the above-mentioned clear solution to convert the iodide ions in the above-mentioned solution into iodine element. The reaction equation is as follows:

[0078] KClO+2KI+H2O→I2+2KOH+KCl;

[0079] (4) recovering the iodine element in the above-mentioned solution, that is, passing the above-mentioned solution into a crude iodine dehydrator, and the obtained solid crude iodine is discharged into a crude iodine collection tank, and the remaining solution flows into a second filter (secondary filter tank), the filter diameter of the second filter is 1 μm, and after filtering out excess impurities through the second filter, a filtrate is obtained;

[0080] (5) passing the filtrate into a second plate heat exchanger, maintaining the temperature of the filtrate at 60° C., adjusting the pH of the filtrate to 4 with sulfuric acid, and passing the filtrate after the pH value is adjusted through a column filled with a boron adsorbent (boron removal resin column), wherein the boron adsorbent is a silica gel-polyamine composite material with a functionalized grafted o-dihydroxy compound as a carrier, the height of the adsorption resin in the column is 1500 mm, and the flow rate of the filtrate per hour is 10 times the volume of the adsorption resin in the column;

[0081] (6) introducing the above-mentioned filtrate after boron removal into a recovery barrel or a salting-out recovery barrel, adding K2SO4 or evaporating water to the above-mentioned filtrate after boric acid removal, the concentration of K2SO4 in the filtrate is 80 g / L, maintaining the temperature of the filtrate after boron removal at 60° C., directly drying or drying through a sieve, and the target polyvinyl alcohol can be recovered;

[0082] (7) The relative molecular weight of polyvinyl alcohol was measured by viscosity measurement. The intrinsic viscosity η of the polymer dilute solution was measured using an Ubbelohde viscometer. According to the Mark-HouwiIlk formula [η] = kMα, the k and α values ​​were found in the literature or relevant manuals, and the polymer degree of polymerization was calculated to be 1832.

[0083] In summary, the polyvinyl alcohol with excellent polymerization degree recovered by the present application, in addition, the iodine extracted by simultaneous recovery is of high purity, which realizes the multi-level efficient utilization of waste into treasure and resource recovery, and is highly environmentally friendly; after the iodine is extracted, a boric acid flocculant is further added to realize the recycling of polyvinyl alcohol, which is safe and pollution-free; the system for extracting iodine has a simple structure, which improves the treatment efficiency of the waste solution and the added value of the waste material.

[0084] It should be pointed out that the above is only used to explain the preferred embodiments of the present invention, and is not intended to limit the present invention in any form. Therefore, any modifications or changes made to the present invention under the same inventive spirit should still be included in the scope of protection intended by the present invention.

Claims

1. A method for recovering polyvinyl alcohol, characterized in that: The method comprises the following steps: S1, adding a reducing agent to the liquid to be treated at a temperature maintained at 40°C to 60°C, removing solid matter after sufficient reaction, filtering, and obtaining a filtrate, wherein the liquid to be treated includes polyvinyl alcohol and an iodine-containing compound; S2. Drying the filtrate in step S1 to recover the polyvinyl alcohol.

2. The recycling method according to claim 1, characterized in that: In step S1, the reducing agent includes one or more of potassium hypochlorite, potassium permanganate, potassium chlorate, manganese dioxide, nitric acid, concentrated sulfuric acid, hypochlorous acid, and sodium peroxide.

3. The recycling method according to claim 1, characterized in that: Before step S1, the method further includes the following steps: S01, dissolving the waste polyvinyl alcohol film obtained in the polarizer manufacturing process by ultrapure water to obtain a dissolving solution; S02. The dissolved liquid is sequentially passed through a first filter and a first heat exchanger for filtering and cooling, respectively, to obtain the liquid to be treated.

4. The recycling method according to claim 3, characterized in that: In step S01, the degree of polymerization of the waste polyvinyl alcohol film obtained in the polarizer manufacturing process is between 1700 and 2500, and the degree of hydrolysis is not less than 95%.

5. The recycling method according to claim 4, characterized in that: In step S01, in terms of weight percentage, the weight of the waste polyvinyl alcohol film obtained in the polarizer manufacturing process is 1 to 1.2 parts, and the weight of the ultrapure water is 200 to 400 parts.

6. The recycling method according to claim 5, characterized in that: In step S01, the temperature of dissolving the waste polyvinyl alcohol film is controlled to be 90° C. to 95° C., and the time of dissolving the waste polyvinyl alcohol film is controlled to be 40 to 50 minutes; In step S02, the temperature of the dissolved solution after cooling is controlled to be between 40°C and 60°C, and the filter diameter of the dissolved solution is controlled to be between 5 μm and 10 μm.

7. The recycling method according to claim 1, characterized in that: Before step S1, the method further includes the following steps: S0. Adding an oxidant to the liquid to be treated.

8. The recycling method according to claim 7, characterized in that: The oxidizing agent includes potassium sulfite.

9. The recycling method according to claim 1, characterized in that: The liquid to be treated also includes boric acid. In step S2, before the filtrate is dried, the following steps are also included: The filtrate is heated, the pH value is adjusted, and the boric acid is adsorbed in sequence.

10. The recycling method according to claim 9, characterized in that: After heating, the temperature of the filtrate is 55°C to 65°C; After adjusting the pH value, the pH value of the filtrate is 3-5.

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