Preparation method for diphenylmethane series diamine and polyamine

Abstract

A preparation method for diphenylmethane series diamine and polyamine (DAM). During the preparation of DAM by means of said method, wastewater generated in a DAM production process can achieve relatively low TOC content without complex treatment. The preparation method comprises: reacting a formaldehyde solution with aniline in the presence of an acidic catalyst to prepare the DAM. The formaldehyde solution used in the reaction system is a formaldehyde solution satisfying characteristic parameter A<2000, and the characteristic parameter A is calculated by means of the following formula (I): A=-5×P×(100×CHCHO-25)2×log2(t) / (log10(CCH3O-500)×log10(CFe3+)), wherein P is the pH value of the formaldehyde solution, and CHCHO is the mass percentage concentration of formaldehyde in the formaldehyde solution; CFe3+ is the content of Fe3+ in the formaldehyde solution; CCH3O is the mass concentration of methanol in the formaldehyde solution; and t is the storage time of the formaldehyde solution.

Description

A preparation method of diphenylmethane series diamines and polyamines Technical Field

[0001] The present invention relates to the technical field of diphenylmethane series diamines and polyamines (DAM) preparation, and in particular to a method for preparing diphenylmethane series diamines and polyamines and a method for reducing the TOC content of wastewater generated during the preparation of diphenylmethane series diamines and polyamines. Background Art

[0002] In the process of preparing diphenylmethane series diamines and polyamines (DAM), the main raw materials for the condensation reaction are aniline and formaldehyde, and hydrochloric acid is usually used as a catalyst. Among them, the raw material formaldehyde is obtained by oxidizing methanol and is generally present in the form of formaldehyde solution. There are two common industrial methods for preparing formaldehyde from methanol: the iron-molybdenum method and the silver method. The formaldehyde gas obtained after oxidation is diluted with water to obtain formaldehyde solutions of different concentrations, generally 30% to 50%. In the reaction process of preparing formaldehyde, impurities including but not limited to formic acid will be generated, and polymerization reactions will occur to obtain different polymers, and the content of these impurities is closely related to the storage conditions of formaldehyde. At the same time, in order to avoid large-scale polymerization of the formaldehyde solution, a portion of polymerization inhibitor can be added, and the raw material methanol is a common polymerization inhibitor.

[0003] In the prior art, there is no systematic research on formaldehyde storage; generally, only the storage temperature is controlled. It is generally believed that the optimal temperature for formaldehyde storage is: T = C(CH2O) + 5. At this temperature, the formaldehyde solution will not increase the formic acid content due to excessively high temperatures, nor will it polymerize significantly due to excessively low temperatures.

[0004] Researchers have discovered that during the storage of formaldehyde solutions, not only temperature and concentration affect their quality, but also specific reactions that occur during storage, leading to the formation of a range of undesirable impurities. These include formaldehyde undergoing disproportionation, which significantly increases formic acid content, and the generation of acetic acid, dimethyl ether, maleic anhydride, and acrylic acid, among other impurities, by the influence of iron and hydrogen ions during storage. When formaldehyde is stored for a long time and used in condensation reactions, these impurities enter the condensation system and ultimately the brine. Normal extraction and stripping processes are unable to remove these impurities, ultimately leading to a significant increase in the TOC content of the brine, making chlor-alkali recycling and discharge to the sea impossible.

[0005] In addition, the researchers found that the amount of impurities in the formaldehyde solution during storage is closely related to the concentration of formaldehyde itself. The lower the concentration, the less impurities are generated during the storage of formaldehyde. Furthermore, the researchers also found that during the storage of formaldehyde solution, H + The presence of H can effectively inhibit a series of undesirable reactions such as disproportionation reaction, but too high H +content, will cause the accelerated polymerization of the formaldehyde solution, and eventually a large amount of solid precipitation in the formaldehyde solution will make it unusable; Specifically, the researchers found that Fe + This will accelerate further reactions of formaldehyde in the formaldehyde solution, resulting in the formation of a series of impurities. In traditional production processes, polymerization inhibitors are often used to prevent the polymerization of formaldehyde solutions and the formation of impurities. Methanol is a commonly used inhibitor, but excess methanol does not participate in the reaction and is ultimately carried out of the system as waste, resulting in a large amount of raw material waste.

[0006] However, during the condensation reaction in the DAM production process, aniline and formaldehyde solution react under the catalysis of hydrochloric acid and are then neutralized with caustic soda. During this reaction, the large amount of water introduced by the formaldehyde solution affects the load increase. Furthermore, the increased water content reduces the density difference between the brine and organic phases during neutralization, affecting the neutralization and stratification. Therefore, in the actual DAM production process, it is often desirable to use a higher concentration of formaldehyde solution for the condensation reaction, rather than a lower concentration.

[0007] Summary of the Invention

[0008] The present invention provides a method for preparing diphenylmethane series diamines and polyamines. The method of the present invention is used to prepare diphenylmethane series diamines and polyamines (DAM). Wastewater generated during the DAM production process can have a low TOC content without complicated treatment.

[0009] To achieve its purpose, the present invention provides the following technical solutions:

[0010] The present invention provides a method for preparing diphenylmethane series diamines and polyamines, comprising reacting a formaldehyde solution and aniline in the presence of an acidic catalyst to prepare the diphenylmethane series diamines and polyamines, wherein the formaldehyde solution used in the reaction system is a formaldehyde solution that satisfies a characteristic parameter A < 2000, and the characteristic parameter A is calculated by the following formula (I): A = -5 × P × (100 × C HCHO -25) 2 ×log2(t) / (log 10 (C CH3O -500)×log 10 (C Fe3+ ))

[0011] Wherein, P is the pH value of the formaldehyde solution, C HCHO is the formaldehyde concentration in the formaldehyde solution; C Fe3+ is the Fe in the formaldehyde solution 3+ Content, unit is mmol / L; C CH3O is the methanol mass concentration in the formaldehyde solution, in ppm; t is the storage time of the formaldehyde solution, in days.

[0012] In some embodiments, the formaldehyde concentration C in the formaldehyde solution is HCHO 30-55%, preferably 37-50%;

[0013] The pH value of the formaldehyde solution is 1-7, preferably 1-4;

[0014] Fe in the formaldehyde solution 3+ Ion content C Fe3+ 0.0000001-0.0001mmol / L, preferably 0.0000001-0.00005mmol / L;

[0015] The methanol mass concentration C in the formaldehyde solution CH3O 1000~50000ppm, preferably 5000~10000pm;

[0016] The storage time t of the formaldehyde solution is 0 to 80 days, preferably 0 to 60 days.

[0017] Furthermore, the initial content of formic acid and corresponding esters in the formaldehyde solution is less than 200 ppm, and the formaldehyde is prepared, for example, by methanol oxidation.

[0018] In some embodiments, the storage temperature of the formaldehyde solution is controlled to be 30-80°C, preferably 40-65°C.

[0019] In some embodiments, the preparation method comprises the following steps:

[0020] (1) contacting a formaldehyde solution satisfying the characteristic parameter A < 2000 with aniline in the presence of an acidic catalyst to obtain a reaction solution;

[0021] (2) neutralizing the reaction solution obtained in step (1), and then separating the phases to obtain an aqueous phase and an organic phase containing diphenylmethane series diamines and polyamines, washing the organic phase with water, and distilling the washed organic phase to obtain diphenylmethane series diamines and polyamines;

[0022] (3) The aqueous phase obtained in step (2) and the washing water produced by the water washing are combined to obtain wastewater to be treated, and the wastewater to be treated is subjected to extraction and stripping treatment to obtain treated wastewater; preferably, the treated wastewater is directly reused in the chlor-alkali industry for salt production.

[0023] In some embodiments, in step (3), the extraction agent used for the extraction is selected from one or more of aniline, chlorobenzene, and dichlorobenzene, preferably aniline; the mass ratio of the extraction agent to the wastewater to be treated is 0.15 to 0.3, preferably 0.16 to 0.25;

[0024] In some embodiments, the mass ratio of the stripping gas used for the stripping to the stripped material is 0.13 to 0.3, preferably 0.16 to 0.25; preferably, the stripping gas is water vapor, preferably 2S steam; preferably, the stripping is carried out at normal pressure.

[0025] In some embodiments, the acidic catalyst is selected from hydrochloric acid.

[0026] In some embodiments, the molar ratio of formaldehyde to aniline is 0.3 to 0.5;

[0027] The acidic catalyst is H + The molar ratio of the aniline to the aniline is 0.05 to 0.4.

[0028] In some embodiments, in step (2), the neutralization is performed with an alkaline solution;

[0029] Preferably, the alkali solution is selected from a sodium hydroxide aqueous solution; preferably, the mass concentration of the alkali solution is 30 to 50%;

[0030] Preferably, OH - The alkali solution is calculated as H + The molar amount of the acidic catalyst is 1.05 to 1.3 times.

[0031] The present invention also provides a method for reducing the TOC content of wastewater generated during the preparation of diphenylmethane series diamines and polyamines. The diphenylmethane series diamines and polyamines are prepared using the preparation method described above.

[0032] The technical solution provided by the present invention has the following beneficial effects:

[0033] The method of the present invention is used to prepare diphenylmethane series diamines and polyamines (DAM). Wastewater generated in the DAM production process can be treated with simple extraction and stripping to obtain treated wastewater with a lower TOC content. DETAILED DESCRIPTION

[0034] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. The term "and / or" as may be used herein includes any and all combinations of one or more of the associated listed items.

[0036] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in the art can be used. Reagents or instruments used without specifying the manufacturer are all commercially available conventional products.

[0037] The present invention provides a method for preparing diphenylmethane series diamines and polyamines, comprising reacting a formaldehyde solution and aniline in the presence of an acidic catalyst to prepare the diphenylmethane series diamines and polyamines, wherein the formaldehyde solution used in the reaction system is a formaldehyde solution that satisfies a characteristic parameter A < 2000, and the characteristic parameter A is calculated by the following formula (I): A = -5 × P × (100 × C HCHO -25) 2 ×log2(t) / (log 10 (C CH3O -500)×log 10 (C Fe3+ ))

[0038] Wherein, P is the pH value of the formaldehyde solution, C HCHO is the formaldehyde concentration in the formaldehyde solution; C Fe3+ is the Fe in the formaldehyde solution 3+ Content, unit is mmol / L; C CH3O is the methanol mass concentration in the formaldehyde solution, in ppm; t is the storage time of the formaldehyde solution, in days.

[0039] The inventors have discovered that in the process of preparing diphenylmethane series diamines and polyamines, the raw material formaldehyde solution used is controlled to meet specific requirements, that is, a formaldehyde solution that meets the characteristic parameter A < 2000 is used in the reaction system. Compared with the use of formaldehyde solution that does not meet this characteristic requirement, the waste brine generated in the production process can be obtained into wastewater with a lower TOC content after simple treatment.

[0040] In the present invention, in the process of preparing diphenylmethane series diamines and polyamines, a formaldehyde solution satisfying a characteristic parameter A <2000 is used. In some embodiments, the characteristic parameter A of the formaldehyde solution used in the reaction system is 1980, 1950, 1900, 1850, 1920, 1800, 1550, 1500, 1450, 1400, 1200, 1000, 950, 900, 850, 800, 700, 600, 500, 100, etc. The characteristic parameter A of the formaldehyde solution is preferably <1800, more preferably <1600, more preferably <1500, more preferably <1400, more preferably <1000, and more preferably <900. Using a formaldehyde solution that meets the requirements of the preferred characteristic parameter A is conducive to obtaining brine with a lower TOC content.

[0041] In a preferred embodiment, the formaldehyde concentration C in the formaldehyde solution is HCHO The pH value of the formaldehyde solution is 1-7, such as 1, 2, 3, 4, 5, 6, 7, etc., preferably 1-4; the Fe content of the formaldehyde solution is 30-55%, such as 30%, 35%, 37%, 40%, 45%, 50%, 55%, etc., preferably 37-50%; the ... 3+ Ion content C Fe3+ 0.0000001-0.0001mmol / L, such as 0.0000001, 0.000001, 0.00001, 0.00003, 0.00005, 0.00008, 0.0001mmol / L, etc., preferably 0.0000001-0.00005mmol / L; the methanol mass concentration C in the formaldehyde solution CH3O The formaldehyde concentration is 1000-50000 ppm, for example, 1000, 2000, 3000, 4000, 4600, 5000, 6000, 7000, 8000, 9000, 10000, 30000, 50000 ppm, etc., preferably 5000-10000 ppm; the storage time t of the formaldehyde solution is 0-80 days, for example, 0, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80 days, etc., preferably 0-60 days; on this basis, the formaldehyde solution used in the reaction system is controlled to adopt a formaldehyde solution that meets the characteristic parameter A <2000. In the process of preparing diphenylmethane series diamines and polyamines, controlling the formaldehyde solution used while meeting the above requirements can significantly improve the TOC content of the waste brine generated during the production process. Only simple extraction and stripping treatment is required to obtain wastewater with a low TOC content that can be directly reused in the chlor-alkali process or directly discharged into the sea.

[0042] In the actual industrial process, the production and storage of formaldehyde solution are inevitably affected by many conditions, such as storage time, methanol content in formaldehyde, etc. These factors work together to produce impurities in the formaldehyde solution, which ultimately affects the reaction of the condensation system. After extensive research, the inventors found that the characteristic parameter A can effectively characterize the acceptance of formaldehyde solution to the condensation system. Formaldehyde solution with A < 2000 can significantly improve the TOC content of the wastewater produced when used in the condensation system prepared by DAM. The characteristic parameter A is closely related to the formaldehyde concentration, pH value and Fe 3+The TOC content of the formaldehyde solution is related to the concentration of the formaldehyde solution, the content of methanol in the formaldehyde solution, and the storage time. It is best to keep each of the above parameters within a reasonable range simultaneously. The DAM preparation method of the present invention achieves integrated regulation of multiple factors through characteristic parameter A. The formaldehyde solution used does not need to have an excessively low formaldehyde concentration. Even with a relatively high-concentration formaldehyde solution, wastewater with a relatively low TOC content can be obtained through simple treatment. Furthermore, the increase in byproducts caused by long-term storage of the formaldehyde solution will not affect the condensation reaction and result in an excessively high TOC content in the final wastewater. For example, even with formaldehyde solutions stored for 60 days or longer, wastewater with a relatively low TOC content can still be obtained through simple treatment.

[0043] The formaldehyde solution used is a formaldehyde solution having an initial content of formic acid and its corresponding esters of less than 200 ppm, for example, 10, 50, 100, 150, 190 ppm, etc. The formaldehyde is prepared, for example, by a methanol oxidation process. "Initial content" refers to the mass content of the corresponding substances initially contained in the freshly prepared formaldehyde solution before storage. The formaldehyde can be, for example, but not limited to, prepared by methods such as the iron-molybdenum process or the silver process.

[0044] Furthermore, the storage temperature of the formaldehyde solution is controlled to be 30-80° C., such as 30° C., 40° C., 50° C., 60° C., 70° C., 80° C., etc., preferably 40-65° C. The storage temperature refers to the temperature condition of the formaldehyde solution during storage.

[0045] Herein, "storage time of formaldehyde solution" refers to the time that the formaldehyde solution prepared upstream spends in storage before use.

[0046] The specific process of the preparation method of diphenylmethane series diamines and polyamines (DAM) can be carried out using corresponding processes known in the art. In some preferred embodiments, the preparation method specifically includes the following steps:

[0047] (1) contacting a formaldehyde solution satisfying the characteristic parameter A < 2000 with aniline in the presence of an acidic catalyst to obtain a reaction solution;

[0048] (2) neutralizing the reaction solution obtained in step (1), and then separating the phases to obtain an aqueous phase and an organic phase containing diphenylmethane series diamines and polyamines, washing the organic phase with water, and distilling the washed organic phase to obtain diphenylmethane series diamines and polyamines;

[0049] (3) The aqueous phase obtained in step (2) and the washing water produced by the water washing are combined to obtain wastewater to be treated, and the wastewater to be treated is subjected to extraction and stripping treatment to obtain treated wastewater; preferably, the treated wastewater is directly reused in the chlor-alkali industry for salt production, and sodium chloride is electrolyzed in the chlor-alkali industry to produce sodium hydroxide and chlorine.

[0050] In some embodiments, in step (3), the extraction agent used for the extraction is selected from one or more of aniline, chlorobenzene, and dichlorobenzene, preferably aniline; the mass ratio of the extraction agent to the wastewater to be treated is 0.15 to 0.3, for example, 0.15, 0.16, 0.20, 0.25, 0.30, etc., preferably 0.16 to 0.25.

[0051] In some embodiments, the mass ratio of the stripping gas used for the stripping to the stripped material is 0.13 to 0.3, for example, 0.13, 0.16, 0.20, 0.25, 0.30, etc., preferably 0.16 to 0.25; preferably, the stripping gas is water vapor, preferably 2S steam, i.e., saturated steam of 0.3 MPa; preferably, the stripping is carried out at normal pressure.

[0052] In some embodiments, the acidic catalyst is selected from hydrochloric acid; the mass concentration of the hydrochloric acid is, for example, 25% to 34%, such as 25%, 28%, 30%, 32%, 34%, etc.

[0053] In some embodiments, the molar ratio of formaldehyde to aniline is 0.3 to 0.5, for example, 0.3, 0.4, or 0.5; the acidic catalyst is H + The molar ratio of aniline to the aniline is 0.05 to 0.4, for example, 0.05, 0.1, 0.2, 0.3, 0.4, etc.

[0054] In some embodiments, in step (2), the neutralization is performed with an alkaline solution;

[0055] In some embodiments, the alkali solution is selected from an aqueous sodium hydroxide solution; preferably, the mass concentration of the alkali solution is 30% to 50%, such as 30%, 40%, 50%, etc.;

[0056] In some embodiments, OH - The amount of the alkali solution is calculated as H + The molar amount of the acidic catalyst is 1.05 to 1.3 times, for example, 1.05, 1.10, 1.20, 1.30 times, etc.

[0057] In some embodiments, in step (1), the formaldehyde solution, aniline, and acidic catalyst are contacted and reacted at 40-80°C (e.g., 40°C, 50°C, 60°C, 80°C, etc.) for a residence time of, for example, 5-60 min (e.g., 5, 10, 20, 30, 40, 50, 60 min, etc.) to obtain a reaction mixture containing a polyaminobenzylaniline salt; the temperature is then raised to 100-140°C (e.g., 100°C, 120°C, 130°C, 140°C, etc.) to continue the reaction for a reaction time of, for example, 60-180 min (e.g., 60 min, 80 min, 100 min, 140 min, 180 min, etc.) to obtain a polyamine.

[0058] The present invention also provides a method for reducing the TOC content of wastewater generated during the preparation of diphenylmethane-series diamines and polyamines. Specifically, the diphenylmethane-series diamines and polyamines are prepared using the above-described method, thereby reducing the TOC content of wastewater generated during the preparation of diphenylmethane-series diamines and polyamines. Specifically, in a process for preparing DAM based on the reaction of a formaldehyde solution, aniline, and an acidic catalyst, by controlling the formaldehyde solution used in the reaction system to satisfy a characteristic parameter A less than 2000, the wastewater generated during the preparation process can be treated to produce wastewater with a low TOC content without undergoing complex treatment steps. The calculation formula and related details regarding the characteristic parameter A are described above and are not further elaborated.

[0059] Preferably, the formaldehyde mass percentage concentration C in the formaldehyde solution is HCHO 30-55%, preferably 37-50%; the pH value of the formaldehyde solution is 1-7, preferably 1-4; Fe in the formaldehyde solution 3+ Ion content C Fe3+ The methanol mass concentration C in the formaldehyde solution is 0.0000001-0.0001mmol / L, preferably 0.0000001-0.00005mmol / L; CH3O The formaldehyde concentration is 1,000 to 50,000 ppm, preferably 5,000 to 10,000 ppm; the storage time t of the formaldehyde solution is 0 to 80 days, preferably 0 to 60 days; and on this basis, the formaldehyde solution used in the reaction system is controlled to meet the characteristic parameter A < 2,000. In the process of preparing diphenylmethane series diamines and polyamines, by controlling the formaldehyde solution used to meet the above requirements, the TOC content of the waste brine generated during the production process can be significantly improved. Through simple extraction and stripping treatment, wastewater with a low TOC content can be obtained, which can be directly reused in the chlor-alkali process or discharged directly into the sea.

[0060] The contents of formaldehyde solution can refer to the corresponding description in the above “Preparation method of diphenylmethane series diamines and polyamines”, which will not be repeated here. The contents of formaldehyde solution can refer to the corresponding description in the above “Preparation method of diphenylmethane series diamines and polyamines”, which will not be repeated here.

[0061] In some embodiments, the method of the present invention is used to prepare DAM. After simple extraction and stripping treatment, the generated wastewater has a low TOC content, for example, less than 25 ppm, and can be directly reused as chlorine alkali for salt production.

[0062] The present invention is further illustrated below with reference to the embodiments, but the present invention is not limited thereto.

[0063] Raw material information

[0064] Aniline: Produced by the Ningbo Aniline Plant in Ningbo Wanhua Industrial Park, industrial product;

[0065] Formaldehyde aqueous solution: Produced by Ningbo Formaldehyde Plant in Ningbo Wanhua Industrial Park, industrial product.

[0066] Hydrochloric acid: a by-product of the Ningbo MDI unit in Ningbo Wanhua Industrial Park, an industrial product.

[0067] Detection method

[0068] The determination method of each component in the formaldehyde aqueous solution was carried out by liquid chromatography derivatization method, and the analytical instrument was Agilent 1260.

[0069] Method for determining TOC content in wastewater: Take 1g of wastewater, dilute it 20 times with 0.1wt% hydrochloric acid, then filter it through a 0.45um aqueous filter membrane. Place the filtrate into a TOC sample tube and analyze it using a Jena 3100 TOC analyzer.

[0070] Example 1

[0071] The formaldehyde mass percentage concentration, pH, Fe 3+ The information on content, methanol mass concentration, storage time, storage temperature, initial content of formic acid and corresponding esters is shown in Table 1.

[0072] Hydrochloric acid (mass concentration 33%), aniline material (mass concentration 94%), and formaldehyde aqueous solution (formaldehyde mass percentage concentration 37%) enter the reactor to react, wherein hydrochloric acid (H +The molar ratio of formaldehyde to aniline was 0.11:1, the molar ratio of formaldehyde to aniline was 0.40:1, the residence time was 60 min, and the reaction temperature was 55°C. A reaction mixture containing polyaminobenzylaniline salt was generated, and the temperature was raised to 120°C and the residence time was 2 hours to obtain a transfer liquid; subsequently, the reaction liquid was neutralized with a NaOH aqueous solution (mass concentration 50%) in a mixer, and the NaOH aqueous solution (as OH) was added to the mixture. - The amount of hydrochloric acid (in H + The molar ratio of the diamines and polyamines in the diphenylmethane series is 1.2, and the mixture obtained after neutralization enters a separator and is separated into a brine phase and an organic phase comprising diamines and polyamines of the diphenylmethane series; the organic phase is fed into a stirring tank, and the organic phase comprising diamines and polyamines of the diphenylmethane series and 0.2 times the mass of washing water are fully mixed under stirring, and the washed organic phase and washed water are obtained by oil-water separation; the brine phase produced in the separator and the washed water produced in the stirring tank are combined as treated wastewater, extracted using aniline as an extractant, the mass ratio of the extractant to the treated wastewater being 0.18, and the extracted wastewater is stripped using 2s steam as a stripping gas, the mass ratio of the stripping gas to the extracted wastewater being 0.25, and brine is obtained after stripping, wherein the TOC content is shown in Table 1.

[0073] Examples 2-6

[0074] The method was carried out in accordance with Example 1, except that the formaldehyde mass percentage concentration, pH, Fe 3+ The content, methanol mass concentration, storage time and storage temperature are different. Please refer to Table 1 for details.

[0075] Comparative Examples 1-4

[0076] The method was carried out in accordance with Example 1, except that the formaldehyde mass percentage concentration, pH, Fe 3+ The content, methanol mass concentration, storage time and storage temperature are different. Please refer to Table 1 for details.

[0077] The characteristic parameter A of the aqueous formaldehyde solution used in each example and comparative example is shown in Table 1, and is calculated according to the formula (I) described above. The TOC content of the brine obtained in each example and comparative example is shown in Table 1.

[0078] Table 1

[0079] It will be readily understood that the above embodiments are merely examples for clarity of description and are not intended to limit the present invention to these examples. Those skilled in the art will readily appreciate that other variations or modifications based on the above description are possible. It is not necessary and impossible to provide an exhaustive list of all possible implementations. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing diphenylmethane series diamines and polyamines, which comprises reacting a formaldehyde solution with aniline in the presence of an acidic catalyst to prepare the diphenylmethane series diamines and polyamines, characterized in that, The formaldehyde solution used in the reaction system is a formaldehyde solution that satisfies the characteristic parameter A < 2000, and the characteristic parameter A is calculated by the following formula (I): A = -5 × P × (100 × C HCHO -25) 2 × log2(t) / (log 10 (C CH3O -500) × log 10 (C Fe3+ )) wherein, P is the pH value of the formaldehyde solution, C HCHO is the mass percentage concentration of formaldehyde in the formaldehyde solution; C Fe3+ is the Fe 3+ content in the formaldehyde solution, with the unit of mmol / L; C CH3O is the mass concentration of methanol in the formaldehyde solution, in ppm; t is the storage time of the formaldehyde solution, with the unit of days.

2. The preparation method according to claim 1, characterized in that, The mass percentage concentration C of formaldehyde in the formaldehyde solution HCHO is 30 to 55%, preferably 37 to 50%; The pH value of the formaldehyde solution is 1 - 7, preferably 1 - 4; The Fe in the formaldehyde solution 3+ ion content C Fe3+ is 0.0000001 - 0.0001 mmol / L, preferably 0.0000001 - 0.00005 mmol / L; The mass concentration C of methanol in the formaldehyde solution CH3O is 1000 to 50000 ppm, preferably 5000 to 10000 ppm; The storage time t of the formaldehyde solution is 0 - 80 days, preferably 0 - 60 days.

3. The preparation method according to claim 1 or 2, characterized in that, The initial content of formic acid and its corresponding esters in the formaldehyde solution is <200 ppm. The formaldehyde is prepared, for example, by the methanol oxidation method.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The storage temperature of the formaldehyde solution is controlled at 30 - 80°C, preferably 40 - 65°C.

5. The preparation method according to any one of claims 1-4, characterized in that, The preparation method comprises the following steps: (1) Contact and react a formaldehyde solution with a characteristic parameter A < 2000 and aniline in the presence of an acidic catalyst to obtain a reaction solution; (2) Neutralize the reaction solution obtained in step (1), then phase-separate to obtain an aqueous phase and an organic phase containing diphenylmethane series diamines and polyamines. Wash the organic phase, and distill the washed organic phase to obtain diphenylmethane series diamines and polyamines; (3) Combine the aqueous phase obtained in step (2) and the washing water generated from the washing to obtain wastewater to be treated. The wastewater to be treated is subjected to extraction and stripping treatments to obtain treated wastewater. Preferably, the treated wastewater is directly recycled and used in the chlor-alkali industry for salt dissolution.

6. The preparation method according to claim 5, characterized in that, In step (3), the extractant used for the extraction is selected from one or more of aniline, chlorobenzene, and dichlorobenzene, preferably aniline; the mass ratio of the extractant to the wastewater to be treated is 0.15 - 0.3, preferably 0.16 - 0.25; And / or, the mass ratio between the stripping gas used for the stripping and the material to be stripped is 0.13 - 0.3, preferably 0.16 - 0.25; preferably, the stripping gas is steam, preferably 2S steam; preferably, the stripping is carried out under atmospheric pressure.

7. The preparation method according to any one of claims 1-6, characterized in that, The acidic catalyst is selected from hydrochloric acid.

8. The preparation method according to any one of claims 1-7, characterized in that, The molar ratio of the formaldehyde to the aniline is 0.3 - 0.5; The molar ratio of the acid catalyst calculated as H + to the aniline is 0.05 to 0.

4.

9. The preparation method according to claim 5 or 6, characterized in that, In step (2), the neutralization is carried out with an alkali solution; Preferably, the alkali solution is selected from an aqueous sodium hydroxide solution; preferably, the mass concentration of the alkali solution is 30 - 50%; Preferably, the lye in terms of OH - is 1.05 to 1.3 times the molar amount of the acidic catalyst in terms of H + count.

10. A method for facilitating the reduction of the TOC content of wastewater generated during the preparation of diphenylmethane series diamines and polyamines, characterized in that, The diphenylmethane series diamines and polyamines are prepared by using the preparation method according to any one of claims 1 - 9.

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