Reutilization method of polybenzimidazole production waste liquid

Abstract

The invention relates to the technical field of polybenzimidazole, and discloses a polybenzimidazole production waste liquid recycling method, which comprises the steps (1), (2) and (3A), or comprises the steps (1), (2) and (3B): (1) a reaction liquid containing polybenzimidazole is contacted with a precipitant for precipitation, and a precipitate and a first waste liquid are obtained through solid-liquid separation; (2) washing the precipitate to obtain a second waste liquid; (3A) returning the second waste liquid as at least part of the precipitant to the step (1); (3B) rectifying the first waste liquid and / or the second waste liquid to obtain light components; returning at least part of the light component as a precipitant to the step (1); and / or returning at least part of the light component as the washing liquid to the step (2). According to the method disclosed by the invention, the consumption of the precipitator and / or the washing liquid can be reduced, and the production cost of the polybenzimidazole is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of polybenzimidazole, and in particular to a method for recycling waste liquid produced by polybenzimidazole. Background Art

[0002] Polybenzimidazole (PBI) is a type of aromatic heterocyclic polymer containing repeating structural units of benzimidazole in the main chain. It is a special engineering plastic with excellent comprehensive performance, excellent high temperature resistance, chemical stability and mechanical properties. It can be used at a temperature of 375°C for a long time, has excellent mechanical strength, and also has excellent flame retardancy, radiation stability, mechanical stability, electrical insulation, chemical stability, thermal stability, antioxidant stability, toughness, adhesion, hygroscopicity and other properties. It can be used in extremely high temperatures, harsh chemical and plasma environments, or in application environments that require high durability and wear resistance of the product.

[0003] There are two main ways to synthesize polybenzimidazole materials: melt polymerization and solution polymerization. Among them, solution polymerization can prepare high molecular weight polybenzimidazole, which is applicable to a wider range of monomers and is conducive to the preparation of functional polybenzimidazole materials. However, solution polymerization usually uses acidic solvents such as polyphosphoric acid and methanesulfonic acid, which have low solid content and large amounts of acidic solvents. A large amount of waste liquid with complex components will be generated during post-polymerization treatment and product purification and washing, which is not conducive to treatment and recycling, and increases the production cost of polybenzimidazole. Summary of the invention

[0004] The purpose of the present invention is to provide a method for recycling waste liquid produced by polybenzimidazole, which can reuse the waste liquid produced by solution polymerization, reduce the production cost of polybenzimidazole, and promote the industrialization process of polybenzimidazole solution polymerization process.

[0005] In order to achieve the above object, the present invention provides a method for recycling waste liquid from polybenzimidazole production, the method comprising steps (1), (2) and (3A), or the method comprising steps (1), (2) and (3B):

[0006] (1) contacting a reaction solution containing polybenzimidazole with a precipitant to perform precipitation, and obtaining a precipitate and a first waste liquid through solid-liquid separation;

[0007] (2) washing the precipitate to obtain a second waste liquid;

[0008] (3A) returning the second waste liquid to step (1) as at least part of the precipitating agent;

[0009] (3B) distilling the first waste liquid and / or the second waste liquid to obtain light components; returning at least part of the light components to step (1) as a precipitant; and / or returning at least part of the light components to step (2) as a washing liquid.

[0010] Through the above technical solution, the present invention can achieve the following beneficial effects:

[0011] (1) The present invention reduces the consumption of precipitating agent and / or washing liquid and reduces the production cost of polybenzimidazole by recycling the first waste liquid generated in the precipitation process and / or the second waste liquid generated in the washing process.

[0012] (2) In a preferred embodiment, the present invention controls the contact mode between the polybenzimidazole-containing reaction solution and the precipitant to control the diameter of a single bundle of polybenzimidazole-containing reaction solution within a specific range, thereby reducing the insoluble matter in the polybenzimidazole product and improving the product performance of the polybenzimidazole. DETAILED DESCRIPTION

[0013] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0014] In the present invention, unless otherwise specified, pressure is absolute pressure.

[0015] The present invention provides a method for recycling waste liquid produced by polybenzimidazole, the method comprising steps (1), (2) and (3A), or the method comprising steps (1), (2) and (3B):

[0016] (1) contacting a reaction solution containing polybenzimidazole with a precipitant to perform precipitation, and obtaining a precipitate and a first waste liquid through solid-liquid separation;

[0017] (2) washing the precipitate to obtain a second waste liquid;

[0018] (3A) returning the second waste liquid to step (1) as at least part of the precipitating agent;

[0019] (3B) distilling the first waste liquid and / or the second waste liquid to obtain light components; returning at least part of the light components to step (1) as a precipitant; and / or returning at least part of the light components to step (2) as a washing liquid.

[0020] According to the present invention, when the alkalinity of the second waste liquid is low, the second waste liquid can be directly returned to step (1) as a precipitant, but when the alkalinity of the second waste liquid is high, the second waste liquid can be used as a partial precipitant and mixed with a freshly replenished precipitant and then contacted with the reaction solution containing polybenzimidazole for precipitation. Usually, the pH of the second waste liquid is 7-12. Therefore, preferably, in step (3A), at least part of the precipitant accounts for 50-100% by weight of the total amount of the precipitant used in step (1).

[0021] The present invention can also distill the acidic waste liquid generated during the precipitation process and the alkaline waste liquid generated during the washing process and recycle them. Preferably, in step (3B), the first waste liquid and / or the second waste liquid are distilled separately; or the first waste liquid is mixed with the second waste liquid to obtain a mixed liquid, and the mixed liquid is then distilled.

[0022] According to the present invention, preferably, the distillation process is carried out in a distillation tower, and the distillation tower is a plate distillation tower, preferably a sieve plate tower with a pore size of 3 to 8 mm.

[0023] According to the present invention, preferably, the distillation process is carried out in a distillation tower, and the distillation tower is filled with fillers. Preferably, the fillers are at least one of Raschig rings, ball rings, step rings, arc saddle rectangular saddle fillers, spherical fillers, corrugated fillers, grid fillers and structured fillers.

[0024] According to the present invention, preferably, the conditions of the distillation tower include: an operating pressure of 0.0001-0.1 MPa; a tower top temperature of 10-100°C; and a tower bottom temperature of 50-200°C.

[0025] According to the present invention, preferably, the conditions for the first waste liquid to be subjected to a separate distillation tower include: an operating pressure of 0.0001-0.01 MPa; a tower top temperature of 10-50°C; and a tower bottom temperature of 50-200°C.

[0026] According to the present invention, preferably, the conditions for the second waste liquid to be subjected to a separate distillation tower include: an operating pressure of 0.005-0.1 MPa; a tower top temperature of 30-100°C; and a tower bottom temperature of 50-120°C.

[0027] According to the present invention, preferably, the conditions for the mixed liquid to be distilled in a rectification tower include: an operating pressure of 0.0005-0.1 MPa; a tower top temperature of 10-100°C; and a tower bottom temperature of 50-200°C.

[0028] In the present invention, the light component is obtained at the top of the distillation tower, and the concentrated liquid is obtained at the bottom of the tower. The concentrated liquid is sent to a waste liquid tank for storage or to a sewage treatment plant.

[0029] According to the present invention, preferably, the method further comprises collecting the waste liquid in a waste liquid retention tank and then sending the waste liquid into a distillation tower for distillation.

[0030] According to the present invention, preferably, the light component obtained by distillation is cooled to 10-50° C. and then returned to step (1) and / or step (2).

[0031] According to the present invention, preferably, in step (3B), at least part of the light components returned to step (1) accounts for 50-100 weight % of the total amount of the precipitant used in step (1).

[0032] According to the present invention, preferably, in step (1), the weight ratio of the total amount of the precipitant to the reaction solution containing polybenzimidazole is 0.1-10:1.

[0033] According to the present invention, preferably, the polybenzimidazole-containing reaction solution is contacted with the precipitant in the following manner: the diameter of a single bundle of the polybenzimidazole-containing reaction solution is controlled to be 0.1-2.5 cm (preferably 0.2-1.5 cm), and then gradually contacted with the precipitant.

[0034] In the present invention, when the viscosity of the reaction solution containing polybenzimidazole is relatively low, the reaction solution containing polybenzimidazole can gradually contact with the precipitant by gravity. When the viscosity of the reaction solution containing polybenzimidazole is relatively high, in order to enable the reaction solution containing polybenzimidazole to be discharged smoothly, preferably, a certain pressure can be applied to the reaction kettle (polymerization kettle), for example, by pumping or ventilating to discharge the reaction solution under a certain pressure, so as to achieve the purpose of pressurization, thereby enabling the reaction solution containing polybenzimidazole to be discharged quickly.

[0035] According to the present invention, preferably, the precipitant is water and / or an alkaline aqueous solution. More preferably, the alkaline aqueous solution is at least one of an aqueous solution of an alkali metal hydroxide, an aqueous solution of an alkaline earth metal hydroxide, an aqueous solution of an alkali metal salt, an aqueous solution of an alkaline earth metal salt, and aqueous ammonia; further preferably, it is at least one of aqueous ammonia, a saturated aqueous sodium carbonate solution, an aqueous potassium carbonate solution, an aqueous sodium bicarbonate solution, an aqueous potassium bicarbonate solution, an aqueous magnesium carbonate solution, an aqueous sodium hydroxide solution, and an aqueous potassium hydroxide solution.

[0036] According to the present invention, preferably, when the precipitant is an alkaline aqueous solution, the pH of the alkaline aqueous solution is ≤12.

[0037] According to the present invention, preferably, the polybenzimidazole-containing reaction solution is obtained by polymerizing an aromatic component containing at least two groups of ortho-amino groups with an aromatic or aliphatic component containing at least two carboxyl groups under polymerization reaction conditions in an inert atmosphere to obtain the polybenzimidazole-containing reaction solution.

[0038] According to the present invention, preferably, the aromatic hydrocarbon component containing at least two groups of vicinal amino groups is an aromatic hydrocarbon tetraamine; more preferably, the aromatic hydrocarbon tetraamine contains 1-4 benzene rings; further preferably, the aromatic hydrocarbon tetraamine is selected from one or more of the following structures:

[0039]

[0040] Wherein, X is selected from oxygen atom, sulfur atom, carbonyl group, sulfonyl group, substituted or unsubstituted alkylene group, for example, -O-, -S-,

[0041] According to the present invention, preferably, the aromatic or aliphatic component containing at least two carboxyl groups has a structure shown in formula (1):

[0042]

[0043] Wherein, R is selected from an aromatic hydrocarbon ring, an aromatic heterocyclic ring or a hydrocarbon group (e.g., a chain alkane group, a cycloalkane group, an alkene group, etc.); Y is hydrogen, an aromatic group or a hydrocarbon group;

[0044] More preferably, the aromatic or aliphatic component containing at least two carboxyl groups is selected from one or more of the following structures:

[0045]

[0046] According to the present invention, preferably, the molar ratio of the aromatic component containing at least two groups of ortho-amino groups to the aromatic or aliphatic component containing at least two carboxyl groups is 1:0.8-1.2, more preferably 1:0.95-1.05.

[0047] According to the present invention, preferably, the polymerization reaction conditions include carrying out the polymerization reaction in the presence of a reaction medium, and the total molar amount of an aromatic component containing at least two groups of vicinal amino groups and an aromatic or aliphatic component containing at least two carboxyl groups is 1-160 mmol, preferably 2-100 mmol, per 100 g of the reaction medium.

[0048] According to the present invention, preferably, the reaction medium is a mixed solution of methanesulfonic acid and phosphorus pentoxide or polyphosphoric acid, wherein the mass ratio of methanesulfonic acid to phosphorus pentoxide is 6-16:1, more preferably 8-12:1.

[0049] According to the present invention, the polymerization conditions may be the conditions of solution polymerization commonly used in the art. Preferably, the polymerization conditions include: a temperature of 80-240° C. and a time of 0.25-72 h. More preferably, the polymerization conditions include: first reacting at 100-160° C. for 0.5-4 h, then heating to 120-220° C. for polymerization for 1-24 h. The above polymerization conditions can be used to obtain functional polybenzimidazole with higher molecular weight and less by-products.

[0050] According to the present invention, in order to make the reaction monomers contact more fully and improve the uniformity of the polymerization reaction, preferably, the polymerization is carried out under stirring, and the stirring linear speed is 0.05-1.0 m / s, more preferably 0.1-0.5 m / s.

[0051] According to the present invention, preferably, the washing includes alkali washing and water washing. During the alkali washing process, an alkaline solution can be used to wash the precipitate. More preferably, the alkaline solution is selected from at least one of an aqueous solution of an alkali metal hydroxide, an aqueous solution of an alkaline earth metal hydroxide, an aqueous solution of an alkali metal salt, an aqueous solution of an alkaline earth metal salt, and aqueous ammonia; further preferably, it is at least one of aqueous ammonia, an aqueous sodium carbonate solution, an aqueous potassium carbonate solution, an aqueous sodium bicarbonate solution, an aqueous potassium bicarbonate solution, an aqueous magnesium carbonate solution, an aqueous sodium hydroxide solution, and an aqueous potassium hydroxide solution.

[0052] According to the present invention, preferably, the mass fraction of the alkaline solution used in the washing process is 0.1-60 wt %.

[0053] In the present invention, the number of washings is not particularly limited, and the number of washings with the alkaline solution may be 1-2 times. Preferably, the amount of the alkaline solution used during the washing process is such that the pH of the waste liquid generated by the last alkaline solution washing is 7-8.

[0054] In the present invention, the number of water washings can be 1 to 3. Preferably, the amount of water used during the washing process is such that the pH of the waste liquid generated by the last water washing is 7 to 8.

[0055] According to the present invention, in order to better remove the ions or acids adsorbed on the polymer surface, preferably, the method further comprises crushing the precipitate after washing with the alkaline solution and then washing with water. The crushing and then washing with water can further remove the residual acidic solvent.

[0056] According to the present invention, preferably, the method further comprises drying the washed precipitate at a temperature of 60-100° C.; more preferably, the drying is performed at 0.01-0.1 MPa and / or in an inert atmosphere.

[0057] In the present invention, the inert atmosphere during the polymerization and drying process is not particularly limited, and may be any inert atmosphere commonly used in the art. The inert atmosphere may be provided by an inert gas and / or nitrogen; the inert gas may be at least one of helium, neon, argon, krypton, xenon and radon.

[0058] The present invention will be described in detail below by way of examples. In the following examples,

[0059] The raw materials used are all commercially available products.

[0060] Example 1

[0061] (1) A reaction medium (methanesulfonic acid and phosphorus pentoxide) and reaction monomers 3,3-diaminobenzidine (0.2 mol) and 4,4-dicarboxydiphenyl ether (0.2 mol) are fed into a polymerization reactor through a feed pipeline. Under a nitrogen atmosphere, the stirring line speed is 0.31 m / s, the mixture is stirred at 120° C. for 40 min, the temperature is raised to 140° C. and the reaction is continued for 2 h to obtain a viscous polymerization reaction solution; wherein the total weight of methanesulfonic acid and phosphorus pentoxide is 1.5 kg, and the weight ratio of methanesulfonic acid to phosphorus pentoxide is 10:1.

[0062] A precipitant (water, 2.4 kg) is added from the top of the precipitation kettle, and then the feed diameter and the number of feed bundles of the viscous polymerization reaction solution are controlled by the feed controller at the top, so that it gradually contacts the precipitant in the precipitation kettle to obtain precipitate and waste liquid; wherein, the diameter of a single bundle of polymerization reaction solution when contacting water is controlled to be 1.0 cm-1.5 cm, and the number of feed bundles is 1. The precipitation is carried out under stirring conditions, and the stirring line speed of the precipitation kettle is 0.2 m / s. The upper waste liquid after precipitation is discharged from the side wall outlet of the precipitation kettle and enters the first waste liquid storage tank, and the waste liquid in the first waste liquid storage tank is used as the first waste liquid.

[0063] (2) 2.67 kg of potassium carbonate solution (10 wt%) is added from the top of the precipitation kettle to wash the precipitate. The generated waste liquid (pH 7-8) is discharged through the pipeline on the side wall of the precipitation kettle and sent to the second waste liquid storage tank. The neutralized product enters the pulverizer from the bottom discharge port and is crushed, and then sent to the treatment kettle. Water (2.4 kg) is added to the top feed port of the treatment kettle to continue washing until it is neutral. After washing, the waste liquid is discharged from the side wall to the second waste liquid storage tank. The washed product enters the dryer under a nitrogen atmosphere and is dried at 0.01 MPa and 80°C to obtain the product. The waste liquid in the second waste liquid storage tank is used as the second waste liquid.

[0064] (3) The first waste liquid is mixed with the second waste liquid to obtain a mixed liquid, and the mixed liquid is sent to a distillation tower, which is a 5 mm pore size sieve plate tower, and the conditions of the distillation tower include: an operating pressure of 0.01 MPa; a tower top temperature of 50°C; a tower bottom temperature of 90°C. A light component is obtained at the top of the tower, and the light component is cooled to 30°C and returned to the precipitation kettle for recycling as a precipitant. The heavy component (concentrated liquid) obtained at the bottom of the tower is sent to the third waste liquid tank for storage. The distillation efficiency of the distillation tower is 90%: 90% of the waste liquid can be recycled by distillation in the distillation tower.

[0065] Example 2

[0066] The system and method of Example 1 are implemented, except that the diameter of the single beam of polymerization reaction solution is controlled to be 0.3cm-0.5cm when it contacts water. The first waste liquid is distilled and returned to the precipitation kettle for recycling as a precipitant. The distillation operating conditions of the first waste liquid include: an operating pressure of 0.001MPa; a tower top temperature of 10°C; a tower bottom temperature of 110°C. A light component is obtained at the top of the tower, and the light component is returned to the precipitation kettle as a precipitant for recycling. The second waste liquid is distilled and returned to the treatment kettle as a washing liquid for recycling. The distillation operating conditions of the second waste liquid include: an operating pressure of 0.01MPa; a tower top temperature of 50°C; a tower bottom temperature of 90°C. A light component is obtained at the top of the tower, and the light component is cooled to 30°C and returned to the treatment kettle for recycling as a washing liquid.

[0067] Example 3

[0068] The system and method of Example 1 are implemented, except that after the second waste liquid reaches the waste liquid storage tank, it is directly returned from the waste liquid storage tank to the precipitation kettle for recycling as a precipitant. The first waste liquid is sent to the distillation tower, and the operating conditions of the distillation tower include: operating pressure of 0.0001MPa; tower top temperature of 10°C; tower bottom temperature of 70°C. The light component is obtained at the top of the tower, and the light component is returned to the treatment kettle as washing water for recycling. The heavy component (concentrated liquid) obtained at the bottom of the tower is sent to the third waste liquid tank for storage.

[0069] Example 4

[0070] The system and method of Example 1 are implemented, except that the diameter of the single bundle of polymerization reaction solution is controlled to be 0.7 cm-1.0 cm when contacting water.

[0071] Example 5

[0072] The system and method of Example 1 are implemented, except that the diameter of the single bundle of polymerization reaction solution is controlled to be 2 cm-2.5 cm when contacting water.

[0073] Comparative Example 1

[0074] The method in Example 1 is followed, except that the first waste liquid and the second waste liquid are not treated and are not recycled.

[0075] Comparative Example 2

[0076] The method and system of Comparative Example 1 were followed, except that the discharge diameter was not controlled (>3 cm).

[0077] Test Case

[0078] (1) The intrinsic viscosity of polybenzimidazole (which can reflect the molecular weight) is measured by the Ubbelohde viscosity method: PBI powder is dissolved in concentrated sulfuric acid (98wt%) to prepare a sulfuric acid solution with a concentration of 0.6g / dL. The sulfuric acid solution is added to an Ubbelohde viscometer with a capillary inner diameter of 1.0-1.1mm, and stabilized in a constant temperature water bath at 25°C for 30min. The outflow time of the measured solution is recorded as t1, the outflow time of concentrated sulfuric acid is recorded as t0, and the concentration of the polymer solution is recorded as C. The intrinsic viscosity of PBI is calculated according to Formula 1 and Formula 2.

[0079] Increased viscosity

[0080] Intrinsic viscosity

[0081] (2) Insoluble matter content of polybenzimidazole solution: 0.2 g of polybenzimidazole product and 9.8 g of dimethyl sulfoxide (DMSO) were added to a flask, dissolved at 80°C for 12 hours and then centrifuged. After separating the upper clear solution, the mass of the residual filter residue was weighed. The percentage of the residual filter residue to the total mass of the solution was the insoluble matter content.

[0082] The intrinsic viscosity, insoluble content and total water consumption of the final product after five reactions are shown in Table 1.

[0083] Table 1

[0084]

[0085] Note: The percentage of water saved refers to the amount of water saved compared with the control ratio in which the waste liquid is not recycled.

[0086] It can be seen from the results in Table 1 that the method of the present invention can not only reduce the amount of water used, but also save costs (waste liquid disposal costs are huge).

[0087] Examples 1-4, which use the preferred embodiment of the present invention to control the viscous mixed solution containing the polymerization product to slowly contact with the precipitant, have lower insoluble content, better solubility of the polybenzimidazole product, and significantly better product quality (significantly lower insoluble content).

[0088] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for recycling waste liquid from polybenzimidazole production, characterized in that: The method comprises steps (1), (2) and (3A), or the method comprises steps (1), (2) and (3B): (1) contacting a reaction solution containing polybenzimidazole with a precipitant to perform precipitation, and obtaining a precipitate and a first waste liquid through solid-liquid separation; (2) washing the precipitate to obtain a second waste liquid; (3A) returning the second waste liquid to step (1) as at least part of the precipitating agent; (3B) distilling the first waste liquid and / or the second waste liquid to obtain light components; returning at least part of the light components to step (1) as a precipitant; and / or returning at least part of the light components to step (2) as a washing liquid.

2. The method according to claim 1, wherein: In step (3A), at least part of the precipitant accounts for 50-100 weight % of the total amount of precipitant used in step (1).

3. The method according to claim 1, wherein: In step (3B), the first waste liquid and / or the second waste liquid are distilled in the following manners: the first waste liquid and the second waste liquid are distilled separately; or the first waste liquid is mixed with the second waste liquid to obtain a mixed liquid, and then the mixed liquid is distilled.

4. The method according to any one of claims 1 to 3, wherein: The distillation process is carried out in a distillation tower, and the distillation tower is filled with fillers. Preferably, the fillers are at least one of Raschig rings, ball rings, step rings, arc saddle rectangular saddle fillers, spherical fillers, corrugated fillers, grid fillers and structured fillers; And / or, the distillation process is carried out in a distillation tower, and the distillation tower is a plate distillation tower, preferably a sieve plate tower with a pore size of 3-8 mm; More preferably, the conditions of the distillation tower include: operating pressure of 0.0001-0.1 MPa; tower top temperature of 10-100°C; tower bottom temperature of 50-200°C.

5. The method according to any one of claims 1 to 4, wherein: The conditions for the first waste liquid to be subjected to a separate distillation tower include: an operating pressure of 0.0001-0.01 MPa; a tower top temperature of 10-50°C; a tower bottom temperature of 50-200°C; And / or, the conditions for the second waste liquid to be subjected to a separate distillation tower include: an operating pressure of 0.005-0.1 MPa; a tower top temperature of 30-100° C.; a tower bottom temperature of 50-120° C.; And / or, the conditions for the mixed liquid to be distilled in a rectification tower include: an operating pressure of 0.0005-0.1 MPa; a tower top temperature of 10-100°C; and a tower bottom temperature of 50-200°C.

6. The method according to any one of claims 1 to 5, wherein: The light component obtained by distillation is cooled to 10-50° C. and then returned to step (1) and / or step (2).

7. The method according to any one of claims 1 to 6, wherein: In step (3B), at least part of the light components returned to step (1) accounts for 50-100 weight % of the total amount of precipitant used in step (1).

8. The method according to claim 1, wherein: In step (1), the weight ratio of the total amount of the precipitant to the reaction solution containing polybenzimidazole is 10-0.1:

1.

9. The method according to claim 1, wherein: The precipitant is water and / or an alkaline aqueous solution; And / or, the washing includes alkali washing and water washing.

10. The method according to claim 1, wherein: The method of contacting the reaction liquid containing polybenzimidazole with the precipitant is as follows: the diameter of a single bundle of the reaction liquid containing polybenzimidazole is controlled to be 0.1-2.5 cm, and then the reaction liquid is gradually contacted with the precipitant.

Images