Process for the preparation of diamines and polyamines of the diphenylmethane series

Abstract

The application relates to a preparation method of diamines and polyamines in a diphenylmethane series, which comprises the following steps: condensation reaction and transposition reaction of aniline and formaldehyde in the presence of an acid catalyst, neutralization after reaction, and phase separation to obtain diamines and polyamines in the diphenylmethane series; the reaction system contains inorganic salts of sodium and / or potassium, and the content of the inorganic salts of sodium and potassium is 10 ppm-10% of the total mass of the reaction system. The application widens the protonation degree (acid catalyst dosage) range of the condensation reaction, enables the reaction to be carried out under milder conditions, ensures that the macromolecule and impurity contents in the product are at a lower level, increases the phase separation density difference in the neutralization process, is beneficial to the high efficiency and stability of the phase separation process, improves the waste brine concentration, increases the reuse value of the waste brine, and enables the subsequent wastewater refining and treatment process to be carried out under lower energy consumption and a simpler process.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of diamines and polyamines of the diphenylmethane series, in particular to a method for preparing diamines and polyamines of the diphenylmethane series (DAM). BACKGROUND

[0002] Diamines and polyamines of the diphenylmethane series (DAM) generally refer to the following types of amines and mixtures of amines:

[0003]

[0004] Here, n represents a natural number ≥ 0, n = 0 is called diamino diphenylmethane, abbreviated as diamine; n > 0 is called polyamine-based polyphenylmethane, abbreviated as polyamine, and the mixture of the two types is called diamines and polyamines of the diamino diphenylmethane series. The derived product after all NH2 groups in DAM are replaced by NCO groups is a diisocyanate of the diamino diphenylmethane series, a polyisocyanate of the diamino diphenylmethane series, or a polyimino polyphenylene polymethylene polyisocyanate, or a diisocyanate and a polyisocyanate of the diamino diphenylmethane series (hereinafter referred to as MDI).

[0005] DAM is prepared by a continuous, semi-continuous or discontinuous reaction process, and the preparation method generally uses aniline to react with hydrochloric acid to generate aniline acid salt, and then adds formaldehyde in the reactor to generate DAM acid salt. Through neutralization, water washing process and separation of organic phase and inorganic phase, the crude DAM is obtained, and after refining process, DAM is obtained, and then through phosgenation reaction to generate monomer or polymer MDI. This method is described in patents US-A 2009 / 0240077, EP-A-451442 and WO-A-99 / 40059.

[0006] In the traditional large-scale industrial production process, no matter which way to prepare DAM, it is generally necessary to add lye to neutralize the salt product of DAM / aniline and hydrochloric acid, and limited by the reaction quality, stability and density difference between oil and water phases in the neutralization process, the amount of added hydrochloric acid and caustic soda is high, which accounts for more than 10% of the production cost of DAM. At the same time, a large amount of organic amine-containing wastewater is generated, the treatment process is complex, and the treatment cost is high.

[0007] Patent DE16434491A discloses a method for preparing high content 4,4'-MDA by first reacting aniline with acid and then with formaldehyde, the degree of protonation is at least 25%, more suitable at least 50%, 75-100% more suitable. In order to be able to prepare MDA with the desired isomer distribution, sometimes a considerable amount of acid catalyst (corresponding to a high degree of protonation) is added, the amount of which makes the reaction proceed in a homogeneous phase, the water in the reaction and the water from the starting reactants remains in the reaction mixture all the time, which reduces the density difference of the subsequent organic and aqueous phases, increases the energy consumption and difficulty of separation. DE10111337A describes a method for preparing MDA with a degree of protonation <20%, but in this method the content of 2,4'-MDA in MDA increases. Moreover, this method also causes the water in the reaction and the water from the starting reactants to remain in the reaction mixture all the time. Patent CN1721389A discloses a method for preparing diphenyl series polyamines at a low degree of protonation, by removing part of the water from the amination product, ensuring that the obtained acidic mixture contains 1-20% by weight of water, but at the same time as the water is removed from the system, a large amount of HCl salted with organic matter is dissolved in the aqueous phase and taken away, greatly reducing the HCl content in the acidic mixture, causing loss of acidic catalyst, making the subsequent reaction need to be carried out at a higher temperature or longer residence time, at the same time causing the product composition to deviate from the target value, increasing the content of by-products or impurities. SUMMARY

[0008] In view of the above problems existing in the prior art, the purpose of the present application is to provide a method for preparing diphenylmethane series diamines and polyamines (DAM), which makes the condensation reaction proceed in a wider range of protonation degree, especially at a lower degree of protonation, reduces the amount of acidic catalyst in the system, and reduces the amount of lye, reduces the cost of raw materials and the amount of wastewater; at the same time, improves the density difference of neutralization and phase separation, improves the phase separation efficiency, reduces the mutual entrainment of oil and water phases, and reduces the cost of subsequent oil and water phase refining post-treatment process.

[0009] To achieve the above purpose, the present application provides a method for preparing diphenylmethane series diamines and polyamines, which comprises condensation reaction and transposition reaction of aniline and formaldehyde in the presence of an acid catalyst, and then neutralization and phase separation to obtain diphenylmethane series diamines and polyamines.

[0010] Preferably, the reaction system contains sodium and / or potassium inorganic salt, and the content of sodium and potassium inorganic salt is 10 ppm-10% of the total mass of the reaction system, preferably 0.5%-5%.

[0011] The total mass of the reaction system refers to the total mass of all substances in the system during the reaction.

[0012] Preferably, the inorganic salt of sodium and / or potassium is selected from one or more of sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, and the like, and preferably the type of inorganic salt is the same as the type of acid anion in the acid catalyst;

[0013] Preferably, the reaction is carried out in a reaction solvent, and preferably the reaction solvent is water.

[0014] Preferably, the inorganic salt of sodium and / or potassium can be added to the raw materials aniline, formaldehyde, acid catalyst, reaction solvent, and / or aniline salt. The inorganic salt of sodium and / or potassium can be added directly or in the form of an aqueous solution.

[0015] Preferably, the acid catalyst is an organic acid or an inorganic acid, and preferably the inorganic acid includes one or more of hydrochloric acid, sulfuric acid, phosphoric acid, or methanesulfonic acid, and the like.

[0016] Preferably, the acid catalyst is hydrochloric acid, and the inorganic salt of sodium and / or potassium is sodium chloride or potassium chloride.

[0017] The mass fraction of the hydrochloric acid is 25-37%, and preferably 28-35%. In the present application, the amount of acid catalyst used in the condensation reaction after the addition of NaCl to the reaction system can be in a wider range, and the molar ratio of the acid catalyst to aniline is 0.03-1.0, and preferably 0.05-0.30.

[0018] In the present application, the condensation reaction temperature is 40-60°C, and preferably 45-55°C, and the reaction time is 1-2 hours.

[0019] In the present application, the formaldehyde is preferably in the form of an aqueous solution, the mass fraction of formaldehyde is 20-55%, and preferably 30-40%, and the molar ratio of formaldehyde to aniline is 0.2-0.8, and preferably 0.3-0.6.

[0020] Since the inorganic salt of sodium and / or potassium is added to the raw materials, the solubility of the raw materials and the water generated in the reaction in DAM / aniline and its salt product, and the solubility of DAM / aniline salt product in water can be reduced by using salting-out effect, and the loss caused by the acid catalyst being taken away with the water phase can be avoided, therefore the method described in the present application is particularly suitable for preparing DAM at a low protonation degree, i.e. the molar ratio of acid catalyst to aniline is less than or equal to 0.30.

[0021] Preferably, when the molar ratio of acid catalyst to aniline is less than or equal to 0.30, and preferably 0.05-0.2, the rearrangement reaction includes a first-stage rearrangement reaction and a second-stage rearrangement reaction, the rearrangement liquid obtained from the first-stage rearrangement reaction is separated into phases to remove the water phase, and then the second-stage rearrangement reaction is continued.

[0022] Preferably, after the first stage of the transposition reaction, a mixture containing diphenylmethane series diamines and polyamines is obtained, the transposition liquid is subjected to phase separation, the aqueous phase is removed, and an organic phase containing diphenylmethane series diamines and polyamines is obtained, the organic phase is introduced into a reactor for the second stage of the transposition reaction, and the transposition liquid obtained after the second stage of the transposition reaction is subjected to neutralization and phase separation by adding an alkali solution, and an organic phase containing diphenylmethane series diamines and polyamines and a brine phase are obtained after the phase separation; the organic phase containing diphenylmethane series diamines and polyamines is refined to remove aniline and residual water and the like, and a refined DAM product is obtained; and the brine phase is subjected to extraction and stripping treatment to obtain waste brine.

[0023] In the present application, the phase separation process of the first stage of the transposition reaction is carried out in a phase separator, in order to avoid the problem that macromolecules and salt substances in the organic phase are prone to blockage, a cyclone separator or a phase separator with a high-efficiency, anti-blocking inclined plate coalescer and wire mesh is preferably used, the phase separation temperature is 60-90°C, preferably 70-80°C, and the phase separation time is 10-60 min;

[0024] In the present application, the reaction temperature of the first stage of the transposition reaction is 60-90°C, preferably 70-80°C, and the reaction time is 1-2 h;

[0025] In the present application, the reaction temperature of the second stage of the transposition reaction is 90-150°C, preferably 100-140°C, and the reaction time is 1-3 h;

[0026] In the present application, the alkali solution used for neutralization is a hydroxide of an alkali metal or an alkaline earth metal element, such as sodium hydroxide, potassium hydroxide, etc., and sodium hydroxide solution is preferably used, and the mass fraction of sodium hydroxide is 30-55%, preferably 40-50%;

[0027] Preferably, the molar ratio of OH - in the alkali solution to H + in the acid catalyst is 1.05-1.40, preferably 1.10-1.20;

[0028] In the present application, the phase separation reaction temperature after neutralization is 90-110°C, preferably 100-105°C, and the phase separation time is 20-60 min;

[0029] In some preferred embodiments of the present application, the method for preparing diphenylmethane series diamines and polyamines comprises the following steps:

[0030] 1) mixing aniline and an acid catalyst to prepare aniline acid salt;

[0031] 2) mixing the aniline acid salt and formaldehyde to perform condensation reaction and transposition reaction;

[0032] 3) the reaction solution after the transposition reaction is neutralized and separated into phases to obtain an organic phase containing diphenylmethane series diamines and polyamines, which is refined.

[0033] In the present application, the reaction temperature of the aniline and the acid catalyst in step 1) is 20-60°C, preferably 30-40°C, and the reaction time is 10-30 min;

[0034] In the present application, the refining in step 3) can be performed by known means such as resin adsorption and distillation, and the distillation is preferably reduced pressure distillation.

[0035] In some preferred embodiments of the present application, the method for preparing diphenylmethane series diamines and polyamines comprises the following steps:

[0036] a) condensation reaction of aniline and formaldehyde,

[0037] b) transposition reaction of the condensation reaction solution by adding an acid catalyst;

[0038] c) neutralization and phase separation of the transposition solution after the transposition reaction to obtain diphenylmethane series diamines and polyamines.

[0039] The present application has the following beneficial effects:

[0040] (1) The present application widens the range of protonation degree of the condensation reaction by adding sodium and / or potassium inorganic salt such as NaCl to the raw material, reduces the loss of catalyst with the water phase after phase separation, avoids the subsequent transposition reaction process at a higher temperature and for a longer time, and greatly reduces the content of macromolecules and impurities in the product. At the same time, by separating part of the water in the system, the amount of material in the transposition and neutralization process is reduced, which is equivalent to increasing the production capacity under the same equipment conditions;

[0041] (2) In the method for preparing DAM according to the present application, the addition of sodium and / or potassium inorganic salt increases the density difference between the oil and water phases in the neutralization and phase separation process, which is beneficial to the efficiency and stability of the phase separation process, reduces the mutual entrainment of the oil and water phases, increases the concentration of waste salt water, increases the reuse value of waste salt water, and at the same time reduces the solubility of organic components in the water phase, so that the subsequent wastewater refining and treatment process can be carried out at lower energy consumption and simpler process. DETAILED DESCRIPTION

[0042] In order to enable a more detailed understanding of the technical features and content of the present application, the content of the present application is further explained below in combination with the embodiment. Although the preferred embodiment of the present application is described in the embodiment, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiment described herein.

[0043] Raw materials and sources:

[0044] Aniline: Wanhua Chemical Co., Ltd.;

[0045] Formaldehyde: Wanhua Chemical Co., Ltd.;

[0046] Hydrochloric acid: Wanhua Chemical Co., Ltd.;

[0047] Sodium hydroxide: Wanhua Chemical Co., Ltd.;

[0048] Sodium chloride (aqueous solution): Wanhua Chemical Co., Ltd.

[0049] Detection method:

[0050] The composition of DAM was analyzed by liquid chromatography (LC), the sample injection amount was 10 μL, the solvent was acetonitrile (chromatographic grade) and water, the test time was 80 min, the column temperature was 40°C, the ultraviolet wavelength was 271 nm, and the analysis instrument was Agilent 1260 Infinity;

[0051] The wastewater NaCl was analyzed by titration, and the organic matter content in the wastewater was analyzed by liquid chromatography (LC), and the analysis instrument was Agilent 1200.

[0052] Example 1:

[0053] The hydrochloric acid solution (mass concentration of 33%) and aniline (mass concentration of ≥99%) were added to the reactor at a molar ratio of 0.10 to generate aniline hydrochloride, the reaction temperature was 40°C, and the reaction time was 10 min. The NaCl aqueous solution was added to the formaldehyde aqueous solution (mass concentration of 37%), and the amount of NaCl added was 1% of the total mass of aniline, hydrochloric acid, formaldehyde and water. The formaldehyde solution containing NaCl was added dropwise into the reactor containing aniline hydrochloride, the molar ratio of formaldehyde to aniline was 0.4, and the condensation reaction was carried out at 50°C for 1 h. Then it was added to the first stage of the shift kettle and shifted at 75°C for 1 h. The above shift liquid was introduced into the phase separator I at 75°C for 20 min, and the upper aqueous phase was separated. Then the lower organic phase was introduced into the second stage of the shift kettle and shifted at 120°C for 2 h. The obtained shift liquid was mixed with 50% sodium hydroxide solution, the molar ratio of sodium hydroxide to hydrochloric acid was 1.15, the neutralization reaction temperature was 100°C, the reaction time was 30 min, and the upper organic phase was separated in the phase separator II. The upper organic phase was washed with pure water, and the water and aniline were removed through the rectification tower. Finally, the refined DAM was obtained.

[0054] The composition and quality of the DAM and waste brine obtained by the method of the present application are listed in Table 1.

[0055] Example 2:

[0056] An aqueous solution of NaCl is added to the hydrochloric acid solution (mass concentration of 28%), and the amount of NaCl added is 0.5% of the total mass of aniline, hydrochloric acid, formaldehyde and water. The hydrochloric acid solution and aniline (mass concentration of ≥99%) are added to the reactor at a molar ratio of 0.30 to generate aniline hydrochloride, and the reaction temperature is 35°C and the reaction time is 20 min. An aqueous formaldehyde solution (mass concentration of 30%) is added dropwise to the reactor containing aniline hydrochloride, and the molar ratio of formaldehyde to aniline is 0.6. Condensation is carried out at 45°C for 1.5 h, and then the solution is added to the first-stage conversion kettle for conversion at 80°C for 1.5 h. The above-mentioned conversion solution is introduced into a cyclone separator for phase separation at 80°C for 10 min, and after the upper aqueous phase is separated, the lower organic phase is introduced into the second-stage conversion kettle for conversion at 140°C for 1 h. The obtained conversion solution is mixed with a 40 wt% sodium hydroxide solution, and the molar ratio of the alkali solution (calculated as sodium hydroxide) to hydrochloric acid (calculated as hydrogen chloride) is 1.10. The neutralization reaction temperature is 105°C, the reaction time is 20 min, and the upper organic phase is obtained after standing and phase separation in a phase separator. The upper organic phase is washed with pure water, and water and aniline are removed through a rectification tower, and finally refined DAM is obtained.

[0057] The composition and quality of the DAM and waste brine obtained by the method of the present application are listed in Table 1.

[0058] Example 3:

[0059] hydrochloric acid (mass concentration ≥ 99%) in a molar ratio of 0.05 into a reactor to generate aniline hydrochloride, the reaction temperature is 30°C, and the reaction time is 30 min. An aqueous solution of NaCl is added into an aqueous formaldehyde solution (mass concentration 40%), the amount of NaCl added is 5% of the total mass of aniline, hydrochloric acid, formaldehyde and water, the formaldehyde solution is added dropwise into the reactor containing aniline hydrochloride, the molar ratio of formaldehyde to aniline is 0.3, condensation reaction is carried out at 55°C for 2 h, then it is added into a first-stage conversion kettle to be converted at 70°C for 2 h, the above-mentioned conversion liquid is introduced into a phase separator I to be separated at 70°C for 40 min, after the upper aqueous phase is separated, the lower organic phase is introduced into a second-stage conversion kettle to be converted at 100°C for 3 h, the obtained conversion liquid is mixed with a 50wt% sodium hydroxide solution, the molar ratio of the alkali solution (calculated as sodium hydroxide) to hydrochloric acid (calculated as hydrogen chloride) is 1.20, the neutralization reaction temperature is 103°C, the reaction time is 40 min, and the upper organic phase is obtained by standing and separating in a phase separator II, the obtained upper organic phase is washed with pure water, and water and aniline are removed through a rectification tower, finally refined DAM is obtained.

[0060] The composition and quality of DAM and waste brine obtained by the method of the present application are shown in Table 1.

[0061] Example 4:

[0062] An aqueous solution of NaCl is added into aniline, the amount of NaCl added is 10 ppm of the total mass of aniline, hydrochloric acid, formaldehyde and water, a hydrochloric acid solution and the aniline (mass concentration ≥ 99%) are added into a reactor in a molar ratio of 1.00 to generate aniline hydrochloride, the reaction temperature is 20°C, and the reaction time is 20 min. An aqueous formaldehyde solution (mass concentration 55%) is added dropwise into the reactor containing aniline hydrochloride, the molar ratio of formaldehyde to aniline is 0.8, condensation reaction is carried out at 40°C for 2 h, then it is added into a conversion kettle to be converted at 90°C for 3 h, the obtained conversion liquid is mixed with a 55wt% sodium hydroxide solution, the molar ratio of the alkali solution (calculated as sodium hydroxide) to hydrochloric acid (calculated as hydrogen chloride) is 1.05, the neutralization reaction temperature is 90°C, the reaction time is 60 min, and the upper organic phase is obtained by standing and separating in a phase separator, the obtained upper organic phase is washed with pure water, and water and aniline are removed through a rectification tower, finally refined DAM is obtained.

[0063] The composition and quality of DAM and waste brine obtained by the method of the present application are shown in Table 1.

[0064] Example 5:

[0065] hydrochloric acid (mass concentration 37%) and aniline (mass concentration > 99%) were added into a reactor in a molar ratio of 0.50 to generate aniline hydrochloride, the reaction temperature was 60°C, and the reaction time was 15 min. An aqueous solution of NaCl was added into an aqueous solution of formaldehyde (mass concentration 20%), the amount of NaCl added was 10% of the total mass of aniline, hydrochloric acid, formaldehyde and water, the formaldehyde solution was added dropwise into the reactor containing aniline hydrochloride, the molar ratio of formaldehyde to aniline was 0.2, and condensation reaction was carried out at 60°C for 1 h, then the reaction solution was added into a shift kettle and shifted at 150°C for 1 h, the obtained shifted solution was mixed with a 30 wt% sodium hydroxide solution, the molar ratio of the base solution (calculated as sodium hydroxide) to hydrochloric acid (calculated as hydrogen chloride) was 1.40, the neutralization reaction temperature was 110°C, the reaction time was 50 min, and phase separation was carried out in a phase separator, the upper organic phase was taken, washed with pure water, and subjected to a rectification tower to remove water and aniline, and finally refined DAM was obtained.

[0066] The composition and quality of DAM and waste brine obtained by the method of the present application are shown in Table 1.

[0067] Example 6:

[0068] An aqueous solution of Na2SO4 was added into an aqueous solution of formaldehyde (mass concentration 37%), the amount of Na2SO4 added was 5% of the total mass of aniline, sulfuric acid, formaldehyde and water, aniline (mass concentration > 99%) and the aqueous solution of formaldehyde (mass concentration 37%) were added into a reactor in a molar ratio of 0.40 to generate aniline formaldehyde, the reaction temperature was 60°C, and the reaction time was 1 h. A sulfuric acid solution (mass concentration 50%) was added into the reactor containing the condensation reaction solution, the molar ratio of sulfuric acid to aniline was 0.30, and reaction was carried out at 60°C for 30 min, then the reaction solution was added into a first-stage shift kettle and shifted at 70°C for 2 h, the above shifted solution was introduced into a phase separator one and phase separated at 70°C for 40 min, after the upper aqueous phase was separated, the lower organic phase was introduced into a second-stage shift kettle and shifted at 110°C for 2 h, the obtained shifted solution was mixed with a 50 wt% sodium hydroxide solution, the molar ratio of the base solution (calculated as sodium hydroxide) to hydrochloric acid (calculated as hydrogen chloride) was 1.15, the neutralization reaction temperature was 105°C, the reaction time was 30 min, and phase separation was carried out in a phase separator two, the upper organic phase was taken, washed with pure water, and subjected to a rectification tower to remove water and aniline, and finally refined DAM was obtained.

[0069] The composition and quality of DAM and waste brine obtained by the method of the present application are shown in Table 1.

[0070] Comparative Example 1

[0071] Hydrochloric acid solution (mass concentration 33%) and aniline (mass concentration > 99%) are added into the reactor in a molar ratio of 0.1 to form aniline hydrochloride, the reaction temperature is 40°C, and the reaction time is 10 min. Aqueous formaldehyde solution (mass concentration 37%) is added dropwise, the molar ratio of formaldehyde to aniline is 0.4, condensation reaction is carried out at 50°C for 1 h, then it is added into the first-stage conversion kettle to be converted at 75°C for 1 h, the above-mentioned conversion liquid is introduced into phase separator one to be separated at 75°C for 20 min, after the upper aqueous phase is separated, the lower organic phase is introduced into the second-stage conversion kettle to be converted at 180°C for 3 h, the obtained conversion liquid is mixed with 50% sodium hydroxide solution, the molar ratio of the lye (calculated as sodium hydroxide) to hydrochloric acid (calculated as hydrogen chloride) is 1.15, the neutralization reaction temperature is 100°C, the reaction time is 30 min, and the upper organic phase is obtained by standing and separating in phase separator two, the obtained upper organic phase is washed with pure water, and water and aniline are removed through a rectification tower, finally refined DAM is obtained.

[0072] The composition and quality of DAM and waste brine obtained by the method of the present application are listed in Table 1.

[0073] Comparative Example 2:

[0074] Hydrochloric acid solution (mass concentration 25%) and aniline (mass concentration > 99%) are added into the reactor in a molar ratio of 1.00 to form aniline hydrochloride, the reaction temperature is 20°C, and the reaction time is 20 min. Aqueous formaldehyde solution (mass concentration 55%) is added dropwise, the molar ratio of formaldehyde to aniline is 0.8, condensation reaction is carried out at 40°C for 2 h, then it is added into the conversion kettle to be converted at 160°C for 2 h, the obtained conversion liquid is mixed with 55% sodium hydroxide solution, the molar ratio of the lye (calculated as sodium hydroxide) to hydrochloric acid (calculated as hydrogen chloride) is 1.05, the neutralization reaction temperature is 90°C, the reaction time is 60 min, and the upper organic phase is obtained by standing and separating in a phase separator, the obtained upper organic phase is washed with pure water, and water and aniline are removed through a rectification tower, finally refined DAM is obtained.

[0075] The composition and quality of DAM and waste brine obtained by the method of the present application are listed in Table 1.

[0076] Table 1 Effect data of examples and comparative examples

[0077]

Claims

1. A method for preparing diphenylmethane-based diamines and polyamines, characterized in that, Aniline and formaldehyde were subjected to condensation and transposition reactions in the presence of an acid catalyst. After the reaction, neutralization was performed, and phase separation was carried out to obtain a series of diphenylmethane diamines and polyamines. The reaction system contains inorganic salts of sodium and / or potassium, and the content of sodium and potassium inorganic salts is 10 ppm-10% of the total mass of the reaction system. The molar ratio of acid catalyst to aniline is 0.03-1.0; The translocation reaction includes a first-stage translocation reaction and a second-stage translocation reaction. The translocated liquid obtained from the first-stage translocation reaction is subjected to phase separation to remove the aqueous phase, and then the second-stage translocation reaction continues.

2. The preparation method according to claim 1, characterized in that, The content of inorganic salts such as sodium and potassium is 0.5%-5% of the total mass of the reaction system.

3. The preparation method according to claim 1, characterized in that, The inorganic salts of sodium and / or potassium are selected from one or more of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate.

4. The preparation method according to claim 3, characterized in that, The types of inorganic salts are the same as the types of acid radicals in acid catalysts.

5. The preparation method according to claim 1, characterized in that, The reaction is carried out in a reaction solvent.

6. The preparation method according to claim 5, characterized in that, The reaction solvent is water.

7. The preparation method according to claim 1, characterized in that, The inorganic salts of sodium and / or potassium are added to the raw materials aniline, formaldehyde, acid catalyst, reaction solvent and / or aniline salt.

8. The preparation method according to claim 1, characterized in that, The acid catalyst is an organic acid or an inorganic acid.

9. The preparation method according to claim 8, characterized in that, The acid catalyst is an inorganic acid, which includes one or more of hydrochloric acid, sulfuric acid, phosphoric acid, or methanesulfonic acid.

10. The preparation method according to claim 9, characterized in that, The acid catalyst is hydrochloric acid.

11. In the preparation method according to claim 1, the molar ratio of acid catalyst to aniline is 0.05-0.

30.

12. The preparation method according to claim 11, characterized in that, The molar ratio of acid catalyst to aniline is 0.05-0.

2.

13. The preparation method according to claim 1, characterized in that, The condensation reaction temperature is 40-60℃, and the reaction time is 1-2 hours.

14. The preparation method according to claim 13, characterized in that, The condensation reaction temperature is 45-55℃.

15. The preparation method according to claim 1, characterized in that, The formaldehyde is present in the form of an aqueous solution, with a formaldehyde mass fraction of 20-55%.

16. The preparation method according to claim 1, characterized in that, The molar ratio of formaldehyde to aniline is 0.2-0.

8.

17. The preparation method according to claim 16, characterized in that, The molar ratio of formaldehyde to aniline is 0.3-0.

6.

18. The preparation method according to claim 1, characterized in that, After the first-stage transposition reaction, a mixture containing diphenylmethane-based diamines and polyamines is obtained. The transposition liquid is then subjected to phase separation to remove the aqueous phase, yielding an organic phase containing diphenylmethane-based diamines and polyamines. This organic phase is then introduced into a reactor for the second-stage transposition reaction. Alkali solution is added to the transposition reaction liquid obtained after the second-stage transposition reaction for neutralization and phase separation. After separation, an organic phase containing diphenylmethane-based diamines and polyamines and a brine phase are obtained. The organic phase containing diphenylmethane-based diamines and polyamines is purified to remove aniline and residual water, yielding a purified DAM product.

19. The preparation method according to claim 1, characterized in that, The phase separation temperature of the first-stage translocation reaction is 60-90℃, and the phase separation time is 10-60 min.

20. The preparation method according to claim 19, characterized in that, The phase separation temperature of the first-stage translocation reaction is 70-80℃.

21. The preparation method according to claim 1, characterized in that, The reaction temperature for the first stage of the translocation reaction is 60-90℃, and the reaction time is 1-2 hours.

22. The preparation method according to claim 21, characterized in that, The reaction temperature for the first stage of the transposition reaction is 70-80℃.

23. The preparation method according to claim 1, characterized in that, The second stage of the translocation reaction is carried out at a temperature of 90-150℃ for 1-3 hours.

24. The preparation method according to claim 23, characterized in that, The second stage of the transposition reaction is carried out at a temperature of 100-140℃.

25. The preparation method according to claim 18, characterized in that, The alkaline solution used for neutralization is a hydroxide of an alkali metal or alkaline earth metal element.

26. The preparation method according to claim 25, characterized in that, The alkaline solution used for neutralization is sodium hydroxide or potassium hydroxide.

27. The preparation method according to claim 18, characterized in that, OH in alkaline solution - With acid catalyst H + The molar ratio is 1.05-1.

40.

28. The preparation method according to claim 27, characterized in that, OH in alkaline solution - With acid catalyst H + The molar ratio is 1.10-1.

20.

29. The preparation method according to claim 18, characterized in that, The phase separation reaction temperature after neutralization is 90-110℃, and the phase separation time is 20-60 min.

30. The preparation method according to claim 29, characterized in that, The phase separation reaction temperature after neutralization is 100-105℃.

31. The preparation method according to claim 1, characterized in that, Includes the following steps: 1) Aniline is mixed with an acid catalyst to obtain a mixed solution containing aniline salts; 2) A mixed solution containing aniline salts is mixed with formaldehyde to carry out condensation and transposition reactions; 3) The reaction solution obtained after the transposition reaction is neutralized and separated to obtain an organic phase containing diphenylmethane series diamines and polyamines, which is then purified.

32. The preparation method according to claim 31, characterized in that, In step 1), the reaction temperature of aniline with the acid catalyst is 20-60℃, and the reaction time is 10-30 min.

33. The preparation method according to claim 32, characterized in that, In step 1), the reaction temperature of aniline with the acid catalyst is 30-40℃.

34. The preparation method according to claim 31, characterized in that, In step 3), purification is achieved through resin adsorption or distillation.

35. The preparation method according to claim 1, characterized in that, Includes the following steps: a) Aniline and formaldehyde are mixed and subjected to a condensation reaction. b) Add an acid catalyst to the condensation reaction solution to carry out the transposition reaction; c) The transposition solution after the transposition reaction is neutralized and separated to obtain diphenylmethane series diamines and polyamines.

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