The invention relates to 3, 3apos; 4, 4 apos, 4, 4 apos; tetraaminobiphenyl as well as purification method and application thereof

Abstract

The invention relates to a purification method of low-purity 3, 3 ', 4, 4'-tetraaminobiphenyl used for synthesis of polybenzimidazole. The method is composed of two sequential purification steps of pre-purification and fine purification, the novel purification method of low-purity 3, 3 ', 4, 4'-tetraaminobiphenyl for polybenzimidazole synthesis is simple in purification process and low in material cost, has the potential of large-scale production and application, and compared with similar technologies in the field, the novel purification method of low-purity 3, 3 ', 4, 4'-tetraaminobiphenyl for polybenzimidazole synthesis has the advantages that the purification process is simple, and the cost is low. The method has the obvious advantages of high purity and low loss rate, can be applied to the field of polybenzimidazole synthesis, and has wide application prospects in the fields of water electrolysis, fuel cells, flow batteries and the like.

Description

Technical Field

[0001] The present invention relates to a novel purification method of low-purity 3,3',4,4'-tetraaminobiphenyl for synthesizing high-molecular polybenzimidazole, specifically a method for removing impurities such as metal ions, halogen ions and compounds with similar structures in 3,3',4,4'-tetraaminobiphenyl through two purification steps of dilute acid solution and carbon powder adsorption. Background Art

[0002] Polybenzimidazole has excellent properties such as high temperature resistance, strong acid resistance, and strong alkali resistance. It can be widely used in water electrolysis cells, liquid flow batteries, fuel cells and other electrochemical devices. As a key material for polymer membranes, adhesives, etc., it is a high molecular polymer material with broad application prospects.

[0003] The synthesis of polybenzimidazole is usually achieved by polycondensation reaction. The typical synthesis process is to use 3,3'4,4'-tetraaminobiphenyl and small molecules of dicarboxylic acid to carry out high-temperature condensation reaction to form polybenzimidazole polymers. However, the existing industrial raw material 3,3'4,4'-tetraaminobiphenyl may have more metal ions or organic impurities. For example, the Chinese patent (publication number: CN109735293A) discloses a method for preparing 3,3'4,4'-tetraaminobiphenyl. This method uses dichlorobiphenyl diamine as a raw material and copper, zinc and other metals as catalysts to prepare 3,3'4,4'-tetraaminobiphenyl. The metal catalyst or organic reactant used in the synthesis process may remain in the industrial raw material 3,3'4,4'-tetraaminobiphenyl. Our research work found that the polybenzimidazole synthesis reaction has very high requirements for the purity of tetraaminobiphenyl, otherwise it is difficult to generate polybenzimidazole with sufficient molecular weight, and thus it is difficult to apply it in the film forming field.

[0004] According to market quotations, the price of domestic tetraaminobiphenyl is RMB 3,000 per kilogram, but its purity is only about 94%, while the cost of imported tetraaminobiphenyl with a purity of 99% is RMB 93,200 per kilogram. If low-cost domestic tetraaminobiphenyl can be used to synthesize polybenzimidazole, the cost of polybenzimidazole will be greatly reduced, thereby promoting the application of polybenzimidazole in electrochemical devices such as water electrolysis, liquid flow batteries, and high-temperature fuel cells.

[0005] At present, there are relatively few reports on the use of low-cost domestic raw materials to synthesize polybenzimidazole. Therefore, the present invention is committed to optimizing the purification process of low-cost domestic tetraaminobiphenyl so that its purity meets the needs of polymer polybenzimidazole synthesis and is successfully applied to polybenzimidazole synthesis. In our previous research work, we reported a high-temperature dissolution purification method for removing impurities with similar chemical structures in tetraaminobiphenyl (Journal of The Electrochemical Society, 2023, 170, 084510). The results show that the purity of tetraaminobiphenyl can be increased from 94.4% to 97% by high-temperature dissolution purification, and the residual impurities may form small particles during the preparation of polybenzimidazole membranes. Based on this work, the present invention proposes a novel purification method for low-purity 3,3′,4,4′-tetraaminobiphenyl for polybenzimidazole synthesis. Compared with the prior art, this method can further reduce the content of substances in 3,3′,4,4′-tetraaminobiphenyl that are not conducive to the synthesis reaction of polybenzimidazole. Furthermore, in the context that domestically produced 3,3′,4,4′-tetraaminobiphenyl still has a relatively low purity, a two-step purification method including a pre-purification step and a fine purification step was proposed to effectively remove various impurities in 3,3′,4,4′-tetraaminobiphenyl, enabling it to be used in the synthesis of high molecular weight polybenzimidazole resins. Summary of the invention

[0006] The present invention relates to a purification method of low-purity 3,3′,4,4′-tetraaminobiphenyl for the synthesis of polybenzimidazole. The purification method is composed of dilute acid pre-purification and carbon powder high-temperature adsorption fine purification as two consecutive main purification steps, characterized in that: the dilute acid pre-purification step uses dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid and one or more mixture solutions thereof as dispersed phases, dissolves 3,3′,4,4′-tetraaminobiphenyl at room temperature, and uses a metal alkali solution to adjust the pH value, precipitates, and vacuum filtration or normal pressure filtration or centrifugal separation to obtain solids to obtain a 3,3′,4,4′-tetraaminobiphenyl primary product; the carbon powder high-temperature adsorption fine purification step uses deionized water as a dispersed phase, uses the adsorption effect of activated carbon powder, and re-dissolves the 3,3′,4,4′-tetraaminobiphenyl primary product at high temperature, stands for recrystallization, vacuum filtration or normal pressure filtration or centrifugal separation again to obtain solids, and dries to obtain a 3,3′,4,4′-tetraaminobiphenyl final product.

[0007] The present invention is specifically described as follows: A novel purification method for low-purity 3,3′,4,4′-tetraaminobiphenyl for the synthesis of high-molecular polybenzimidazole, characterized in that: dilute acid pre-purification and carbon powder high-temperature adsorption fine purification are two consecutive main purification steps; wherein the chemical formula of 3,3′,4,4′-tetraaminobiphenyl is C 12 H 14 N 4, CAS No. 91-95-2; wherein the dilute acid is dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid and one or more mixtures thereof in an aqueous solution with a concentration of less than 1M; wherein the carbon powder is activated carbon powder including but not limited to XC-72, Ketjen black and other carbon-based powders with high specific surface area and strong adsorption capacity; wherein the metal alkali solution is an aqueous solution with strong alkalinity including but not limited to NaOH, KOH, LiOH and the like.

[0008] A purification method as described above, characterized in that the process is as follows: using 0.2-1M hydrochloric acid aqueous solution as a dispersant, adding low-purity 3,3′,4,4′-tetraaminobiphenyl, and stirring at room temperature for 5-10 minutes. The mixed solution is vacuum filtered or filtered at normal pressure or centrifuged to remove solid impurities to obtain a brown-red clear solution; the brown-red clear solution obtained above is placed on a magnetic stirrer, and a 0.5-10M NaOH or KOH or LiOH solution is prepared and added dropwise to the obtained brown-red clear solution, and the pH value is adjusted to 7-13, and then stirring is continued for 0.5-1 hour to precipitate, and then vacuum filtered or filtered at normal pressure or centrifuged to obtain a solid to obtain the initial product of 3,3′,4,4′-tetraaminobiphenyl; XC-72 or Ketjen black activated carbon powder / deionized water mixture is used. The solid or deionized water is used as a dispersant, and the mass ratio of the solid to the liquid is 0 to 1:200. The mixed solution is stirred and heated at 80-130°C for 3-6 hours to obtain a high-temperature mixed solution; the high-temperature mixed solution obtained above is quickly filtered by vacuum filtration to remove XC-72 or Ketjen black activated carbon powder and other impurities to obtain a light brown clear solution; the obtained light brown clear solution is allowed to stand at room temperature for 12-48 hours, and a light-colored solid slowly precipitates from the solution, and the solution is converted into a reddish-brown suspension. The reddish-brown suspension is obtained by vacuum filtration or atmospheric pressure filtration or centrifugation to obtain a light red solid. The light red solid obtained above is washed with deionized water 1-3 times, and then vacuum dried or blown dried at 60-100°C for 3-5 hours to obtain the final product of 3,3′,4,4′-tetraaminobiphenyl. The simplified schematic diagram of the process can be seen. Figure 1 The novel purification method of low-purity 3,3′,4,4′-tetraaminobiphenyl for the synthesis of polybenzimidazole proposed in the present invention has a simple purification process and low material cost, has the potential for large-scale production and application, and compared with similar technologies in this field, has the obvious advantages of high purity and low loss rate, can be applied to the field of polybenzimidazole synthesis, and has broad application prospects in the fields of water electrolysis, fuel cells, liquid flow batteries, etc.

[0009] The invention provides a method for purifying low-purity 3,3′,4,4′-tetraaminobiphenyl for the synthesis of polybenzimidazoles. The purification process is simple and the cost is low, and the method has the potential for large-scale production and application. Compared with similar technologies in the field, the final product 3,3′,4,4′-tetraaminobiphenyl has ultra-high purity (more than 99.9%) and can be applied to the synthesis of various polybenzimidazole resins. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 : Schematic diagram of the purification method of low-purity 3,3′,4,4′-tetraaminobiphenyl for the synthesis of polybenzimidazole proposed in the present invention;

[0011] Figure 2 : The HPLC chromatogram obtained in Example 1;

[0012] Figure 3 : Molecular weight distribution curve obtained based on gel permeation chromatography in Example 1;

[0013] Figure 4 : PBI synthesized from unpurified 3,3′,4,4′-tetraaminobiphenyl cannot produce a uniform film (a), while PBI synthesized from 3,3′,4,4′-tetraaminobiphenyl purified by this method can produce a uniform film (b). DETAILED DESCRIPTION

[0014] The chemical formula of 3,3′,4,4′-tetraaminobiphenyl is C 12 H 14 N 4 , CAS No. 91-95-2.

[0015] The technical solution of the present invention is further described below in conjunction with the embodiments, but the technical content of the present invention is not limited to the described scope.

[0016] Example 1

[0017] A method for purifying low-purity 3,3',4,4'-tetraaminobiphenyl for the synthesis of polybenzimidazole, comprising the following steps:

[0018] 1. Add 10 g of low-purity 3,3′,4,4′-tetraaminobiphenyl (with a mass purity of 95.7%) to 200 mL of 0.5 M hydrochloric acid aqueous solution, stir at room temperature for 5 min, and vacuum filter the mixed solution to obtain a brown-red clear solution;

[0019] 2. Place the brown-red clear solution obtained above on a magnetic stirrer, prepare a 1M NaOH solution and add it dropwise to the obtained brown-red clear solution, adjust the pH value to 8, and then continue stirring for 0.5 hours to precipitate, then perform vacuum filtration, take the powder and dry it to obtain 8.5 g of the initial product of 3,3′,4,4′-tetraaminobiphenyl;

[0020] 3. Add 3,3′,4,4′-tetraaminobiphenyl primary product and 0.2 g carbon powder (XC-72 activated carbon) to 400 mL of deionized water, and stir and heat the mixed solution at 110° C. for 4 hours to obtain a high-temperature mixed solution;

[0021] 4. Use vacuum filtration to quickly filter the high-temperature mixed solution obtained above to remove XC-72 activated carbon powder and other impurities to obtain a light brown clear solution;

[0022] 5. The light brown clear solution obtained above was allowed to stand at room temperature for 24 hours, and the obtained reddish brown suspension was vacuum filtered to obtain a light red solid;

[0023] 6. The light red solid obtained above was washed with deionized water and then vacuum dried at 80°C for 3 hours to obtain 6.5 g of 3,3′,4,4′-tetraaminobiphenyl final product with a purity of 99.99%. Its HPLC analysis showed Figure 2 .

[0024] Synthesis of polybenzimidazole:

[0025] Add 66.0g polyphosphoric acid (PPA) and 2.14g (0.01mol) of the purified 3,3′,4,4′-tetraaminobiphenyl in a three-necked flask, place the three-necked flask in an oil bath (dimethyl silicone oil), and make the PPA liquid level lower than the dimethyl silicone oil liquid level. Pass nitrogen into the flask for protection, and use a glass rotor flowmeter to control the nitrogen flow rate at 200mLmin -1 . Turn on the oil bath and set the temperature to 180°C. Turn on the electric mechanical stirrer and control the stirring rate to 400 rpm. Stir for more than 1 hour until 3,3',4,4'-tetraaminobiphenyl is completely dispersed in the polyphosphoric acid. Add 1.66g (0.01mol) of isophthalic acid (Isophtalic acid, IPA) to the three-necked flask and continue stirring for 1.5 hours. Then add 2.8g of phosphorus pentoxide (P 2 O 5), and set the oil bath temperature to 205°C. After reaching 205°C, maintain this temperature for polycondensation reaction, and the reaction lasts for 6 hours. After reaching the reaction time, stop mechanical stirring, slowly pour the polymer solution into 700mL deionized water to obtain the initial product. At room temperature, soak the initial product in deionized water for 12 hours. Filter the initial product, then pour it into 700mL 5wt% sodium bicarbonate solution and soak it for 36 hours to remove excess phosphoric acid. After testing the solution with PH test paper and it is still alkaline (to ensure that excess acid is removed), filter the solution, crush the initial product to obtain the solid, and wash the polymer three times with ethanol and deionized water respectively. Finally, the polymer was vacuum dried at 150°C for 5 hours, and PBI resin powder A was finally obtained after infrared and nuclear magnetic identification. The polybenzimidazole resin obtained has a weight average molecular weight of 70639g mol -1 The molecular weight distribution curve is shown in Figure 3 .

[0026] Comparative Example of Synthesis of Polybenzimidazole: The process and conditions are the same as those of the above synthesis of polybenzimidazole, except that the same mass of low-purity 3,3′,4,4′-tetraaminobiphenyl (raw material in step 1) in the above synthesis of polybenzimidazole is used instead of the purified 3,3′,4,4′-tetraaminobiphenyl for comparative experiment. The corresponding PBI resin powder B (weight average molecular weight of 35320 g mol -1 ).

[0027] Preparation of polybenzimidazole membrane:

[0028] Add 10g N,N-dimethylacetamide (DMAc) and 0.25g PBI resin powder A or B to the PTFE liner in sequence. After placing the liner in a hydrothermal reactor, put it in a vacuum drying oven and heat it at 220℃ for 10h. The PBI resin is completely dissolved to obtain a 1-2.5wt.% PBI solution. Pour the PBI solution into a glass plate with a 10cm×10cm flat groove and place it in an oven. Set the oven temperature to 120℃. After keeping warm for 0.5h, lower the temperature to 80℃ and dry for 12h. Keep the vacuum state during the drying process. Take out the mold, soak the mold in deionized water, peel off the film, dry it, and finally obtain a PBI membrane with a thickness of 25μm.

[0029] The PBI resin powder B synthesized with unpurified 3,3′,4,4′-tetraaminobiphenyl could not produce a uniform film, while the PBI resin powder A synthesized with 3,3′,4,4′-tetraaminobiphenyl purified by this method could produce a uniform film ( Figure 4 ).

[0030] Example 2

[0031] A method for purifying low-purity 3,3',4,4'-tetraaminobiphenyl for the synthesis of polybenzimidazole, comprising the following steps:

[0032] 1. Add 10 g of low-purity 3,3',4,4'-tetraaminobiphenyl (mass purity is 95%) to 200 mL of 1 M hydrochloric acid aqueous solution, stir at room temperature for 5 min, and vacuum filter the mixed solution to obtain a brown-red clear solution;

[0033] 2. The brown-red clear solution obtained above was placed on a magnetic stirrer, and a 1M NaOH solution was prepared and added dropwise to the obtained brown-red clear solution, and the pH value was adjusted to 8, and then the stirring was continued for 0.5 hours to precipitate, and then vacuum filtered, and the powder was dried to obtain 8.8 g of the initial product of 3,3′,4,4′-tetraaminobiphenyl;

[0034] 3. Add the initial product of 3,3′,4,4′-tetraaminobiphenyl and 0.2 g of carbon powder to 400 mL of deionized water, and stir and heat the mixed solution at 110°C for 4 hours to obtain a high-temperature mixed solution;

[0035] 4. Use vacuum filtration to quickly filter the high-temperature mixed solution obtained above to remove XC-72 activated carbon powder and other impurities to obtain a light brown clear solution;

[0036] 5. The light brown clear solution obtained above was allowed to stand at room temperature for 24 hours, and the resulting reddish brown suspension was vacuum filtered to obtain a light red solid;

[0037] 6. The light red solid obtained above was washed with deionized water and then dried by air blowing at 80°C for 3 hours to obtain 6.7 g of the final product 3,3′,4,4′-tetraaminobiphenyl with a purity of 98.57%.

[0038] Synthesis of polybenzimidazole: The process and conditions are the same as those of the synthesis of polybenzimidazole in Example 1, except that in the synthesis of polybenzimidazole, the obtained 3,3′,4,4′-tetraaminobiphenyl final product reacts with isophthalic acid in the presence of polyphosphoric acid as a dispersant and nitrogen protection at 205° C. for 6 hours to obtain a polybenzimidazole resin with a weight average molecular weight of 60557 gmol -1 .

[0039] Example 3

[0040] A method for purifying low-purity 3,3′,4,4′-tetraaminobiphenyl for the synthesis of polybenzimidazole comprises the following steps:

[0041] 1. Add 10 g of low-purity 3,3′,4,4′-tetraaminobiphenyl (mass purity is 94.5%) to 200 mL of 0.5 M hydrochloric acid aqueous solution, stir at room temperature for 5 min, and vacuum filter the mixed solution to obtain a brown-red clear solution;

[0042] 2. The brown-red clear solution obtained above was placed on a magnetic stirrer, and a 1M KOH solution was prepared and added dropwise to the obtained brown-red clear solution, and the pH value was adjusted to 8, and then the stirring was continued for 0.5 hours to precipitate, and then vacuum filtered, and the powder was dried to obtain 7.5 g of the initial product of 3,3′,4,4′-tetraaminobiphenyl;

[0043] 3. Add the initial product of 3,3′,4,4′-tetraaminobiphenyl and 0.2 g of carbon powder to 400 mL of deionized water, and stir and heat the mixed solution at 110°C for 4 hours to obtain a high-temperature mixed solution;

[0044] 4. Use vacuum filtration to quickly filter the high-temperature mixed solution obtained above to remove XC-72 activated carbon powder and other impurities to obtain a light brown clear solution;

[0045] 5. The light brown clear solution obtained above was allowed to stand at room temperature for 24 hours, and the resulting reddish brown suspension was vacuum filtered to obtain a light red solid;

[0046] 6. The light red solid obtained above was washed with deionized water and then dried in vacuum at 80°C for 3 hours to obtain 5.4 g of the final product 3,3′,4,4′-tetraaminobiphenyl with a purity of 97.57%.

[0047] Synthesis of polybenzimidazole: The process and conditions are the same as those of the synthesis of polybenzimidazole in Example 1, except that in the synthesis of polybenzimidazole, the obtained 3,3′,4,4′-tetraaminobiphenyl final product reacts with isophthalic acid in the presence of polyphosphoric acid as a dispersant and nitrogen protection at 205° C. for 6 hours to obtain a polybenzimidazole resin with a weight average molecular weight of 55801 gmol -1 .

[0048] Example 4

[0049] A method for purifying low-purity 3,3′,4,4′-tetraaminobiphenyl for the synthesis of polybenzimidazole comprises the following steps:

[0050] 1. Add 10 g of low-purity 3,3′,4,4′-tetraaminobiphenyl (mass purity is 94%) to 200 mL of 0.5 M hydrochloric acid aqueous solution, stir at room temperature for 5 min, and vacuum filter the mixed solution to obtain a brown-red clear solution;

[0051] 2. The brown-red clear solution obtained above was placed on a magnetic stirrer, and a 1M NaOH solution was prepared and added dropwise to the obtained brown-red clear solution, and the pH value was adjusted to 13, and then the stirring was continued for 0.5 hours to precipitate, and then vacuum filtered, and the powder was dried to obtain 9.1 g of the initial product of 3,3′,4,4′-tetraaminobiphenyl;

[0052] 3. Add the initial product of 3,3′,4,4′-tetraaminobiphenyl and 0.2 g of carbon powder to 400 mL of deionized water, and stir and heat the mixed solution at 110°C for 4 hours to obtain a high-temperature mixed solution;

[0053] 4. Use vacuum filtration to quickly filter the high-temperature mixed solution obtained above to remove XC-72 activated carbon powder and other impurities to obtain a light brown clear solution;

[0054] 5. The light brown clear solution obtained above was allowed to stand at room temperature for 24 hours, and the resulting reddish brown suspension was vacuum filtered to obtain a light red solid;

[0055] 6. The light red solid obtained above was washed with deionized water and then vacuum dried at 80°C for 3 hours to obtain 8.3 g of the final product 3,3′,4,4′-tetraaminobiphenyl with a purity of 96.57%.

[0056] Synthesis of polybenzimidazole: The process and conditions are the same as those of the synthesis of polybenzimidazole in Example 1, except that in the synthesis of polybenzimidazole, the obtained 3,3′,4,4′-tetraaminobiphenyl final product reacts with isophthalic acid in the presence of polyphosphoric acid as a dispersant and nitrogen protection at 205° C. for 6 hours to obtain a polybenzimidazole resin with a weight average molecular weight of 50887 gmol -1 .

Claims

1. A method for purifying 3,3',4,4'-tetraaminobiphenyl, characterized in that: It consists of two steps: pre-purification and fine purification. 1) Acid pre-purification: First, an inorganic acid is used as a dispersed phase to dissolve 3,3',4,4'-tetraaminobiphenyl; then, an inorganic base solution is used to adjust the pH value of the system to 7-13 (preferably 7-10, more preferably 7-8), precipitate, and separate the solid and liquid to obtain a solid 3,3',4,4'-tetraaminobiphenyl primary product; 2) Purification by carbon powder adsorption: using water as the dispersed phase, adding activated carbon powder and 3,3',4,4'-tetraaminobiphenyl initial product thereto, dissolving 3,3',4,4'-tetraaminobiphenyl initial product at 80-130°C (preferably 100-130°C, more preferably 120-130°C) to obtain a high-temperature mixed liquid, separating the solid and the liquid to obtain a clear solution; the clear solution is allowed to stand for recrystallization, the solid and the liquid are separated, and the solid is dried to obtain the final product of 3,3',4,4'-tetraaminobiphenyl.

2. The purification method according to claim 1, characterized in that: The acid pre-purification process is carried out at room temperature. In this step, the inorganic acid is an aqueous solution of one or a mixture of two or more of hydrochloric acid, sulfuric acid and nitric acid. The concentration of the inorganic acid is 0.2-1.0M, preferably in the range of 0.5-1.0M, and more preferably in the range of 0.8-1.0M.

3. The purification method according to claim 1 or 2, characterized in that: The ratio of 3,3',4,4'-tetraaminobiphenyl to the inorganic acid solution is 1 g:20-400 mL, preferably in the range of 1 g:100-400 mL, and more preferably in the range of 1 g:200-400 mL.

4. The purification method according to claim 1, characterized in that: First, 3,3',4,4'-tetraaminobiphenyl is added to the dispersant and stirred at room temperature for 5-10 minutes; the mixed solution is separated into solid and liquid, and solid impurities are removed to obtain a clear 3,3',4,4'-tetraaminobiphenyl solution; then, under stirring conditions, an alkali solution is added dropwise to the obtained clear 3,3',4,4'-tetraaminobiphenyl solution, and the pH value thereof is adjusted to 7-13 using the alkali solution, and then stirring is continued for 0.5-1 hour, precipitation is precipitated, and solid-liquid separation is performed to obtain a solid 3,3',4,4'-tetraaminobiphenyl primary product.

5. The purification method according to claim 1 or 4, characterized in that: The inorganic alkaline solution is an aqueous solution of one or more of NaOH, KOH, LiOH, etc., including but not limited to, and the concentration of the alkaline solution is 0.5-10M, preferably in the range of 0.5-2M, and more preferably in the range of 0.5-1M.

6. The purification method according to claim 1, characterized in that: The activated carbon powder is one or more of carbon-based powders including but not limited to XC-72, Ketjen Black, etc., which have high specific surface area and strong adsorption capacity.

7. The purification method according to claim 1, characterized in that: In the process of purification by carbon powder adsorption, the mass ratio of the initial product of 3,3',4,4'-tetraaminobiphenyl to the carbon powder is 200:1-10:1, preferably in the range of 100:1-10:1, and more preferably in the range of 50:1-10:1; the mass ratio of the initial product of 3,3',4,4'-tetraaminobiphenyl to water is 1:400-1:20, preferably in the range of 1:400-1:200, and more preferably in the range of 1:100; in the process of purification by carbon powder adsorption, the mixed solution is stirred and heated at 80-130° C. for 3-6 hours to obtain a high-temperature mixed solution; the clarified solution is allowed to stand at room temperature for 12-48 hours, a solid is precipitated in the solution, the solid and the liquid are separated, the solid is washed with deionized water for 1-3 times, and then vacuum dried or forced air dried at 60-100° C. for 3-5 hours to obtain a final product of 3,3',4,4'-tetraaminobiphenyl.

8. The purification method according to claim 1, 4 or 7, characterized in that: The solid-liquid separation process is vacuum filtration or normal pressure filtration or centrifugal separation to obtain solids.

9. 3,3',4,4'-tetraaminobiphenyl obtained by the purification method according to any one of claims 1 to 8.

10. Use of the 3,3',4,4'-tetraaminobiphenyl according to claim 9 in the synthesis of polybenzimidazole.

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