A preparation method of 4,4'-diaminodiphenylmethane and 4,4'-diaminodiphenylmethane

Abstract

The invention discloses a preparation method of 4,4'-diaminodiphenylmethane and 4,4'-diaminodiphenylmethane. The preparation method comprises: under nitrogen protection, adding formaldehyde solution to aniline for reaction to obtain an aminal solution; adding a pre-prepared catalyst to the aminal solution for reaction to obtain a reaction liquid, wherein the catalyst comprises a pre-prepared aniline hydrochloric acid solution and / or an amine salt solution with a pH value less than 7; and purifying the reaction liquid to obtain 4,4'-diaminodiphenylmethane. The preparation method adopts the pre-prepared weakly acidic aniline hydrochloric acid solution and / or the amine salt solution with a pH value less than 7 as a catalyst, thereby avoiding equipment corrosion and environmental pollution caused by directly adding a strong acid into a first reactor.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, and in particular to a preparation method of 4,4'-diaminodiphenylmethane and 4,4'-diaminodiphenylmethane. Background Art

[0002] 4,4'-Diaminodiphenylmethane (4,4'-MDA) is an important organic chemical that can be used in epoxy resin toughening curing agent, chain extender and organic dye synthesis. In the polyurethane production process, 4,4'-MDA is an important intermediate for the synthesis of diphenylmethane diisocyanate (MDI).

[0003] At present, the industry usually uses aniline (AN) and formaldehyde condensation to prepare 4,4'-MDA, which is an acid-catalyzed reaction. The industrial production of 4,4'-MDA uses hydrochloric acid as a catalyst, which has the advantages of mild reaction conditions and high product yield, but there is a problem of serious corrosion of equipment.

[0004] Therefore, technicians in the industry are constantly trying to solve this problem. For example, the Chinese patent CN109851509A has been published, which uses a strong or weak acid styrene or acrylic acid cation exchange resin as a catalyst to prepare 4,4′-MDA. Although this solution avoids the use of hydrochloric acid as a catalyst and effectively avoids equipment corrosion, the disadvantage of this solution is that the production cost is high, the post-processing is more troublesome, and the catalyst reuse rate is not high.

[0005] Therefore, it is urgent to find a method for preparing 4,4′-MDA that can effectively avoid equipment corrosion and effectively reduce production costs. Summary of the invention

[0006] In order to solve the problems of the prior art, the present invention provides a preparation method of 4,4'-diaminodiphenylmethane and 4,4'-diaminodiphenylmethane, which can effectively reduce the acid corrosion degree of equipment.

[0007] In order to solve the above technical problems, the present invention proposes the following technical solutions:

[0008] In a first aspect, a method for preparing 4,4'-diaminodiphenylmethane is provided, the method comprising:

[0009] Under nitrogen protection, formaldehyde solution is added to aniline to react and obtain aminal solution;

[0010] Adding a pre-prepared catalyst to the aminal solution to react and obtain a reaction solution, wherein the catalyst includes a pre-prepared aniline hydrochloric acid solution and / or an amine salt solution with a pH value less than 7;

[0011] The reaction solution is purified to obtain the 4,4'-diaminodiphenylmethane.

[0012] In a preferred embodiment, the step of adding formaldehyde solution to aniline to obtain an aminal solution comprises:

[0013] Aniline is added into the first reactor, and formaldehyde solution is added dropwise into the aniline under stirring at 30-60° C. for reaction for 10-40 minutes to obtain an aminal solution, wherein the molar ratio of the aniline to the formaldehyde is 2-5:1.

[0014] In a preferred embodiment, the step of adding a pre-prepared catalyst to the aminal solution to obtain a reaction solution comprises:

[0015] At 60-90° C., the pre-prepared catalyst is added to the aminal solution in the first reactor under stirring for 4-8 hours to obtain a reaction solution, wherein the molar ratio of the catalyst to the formaldehyde is 0.25-0.85:1.

[0016] In a preferred embodiment, the reaction solution is separated and purified to obtain the 4,4'-diaminodiphenylmethane, comprising:

[0017] Washing the reaction solution with water for multiple times to obtain a washed reaction solution, and combining and collecting the washed solutions to obtain a first aqueous phase;

[0018] The reaction solution after water washing is sequentially subjected to alkali washing and water washing to obtain a first organic phase;

[0019] Aniline was removed from the first organic phase by distillation under reduced pressure to obtain 4,4'-diaminodiphenylmethane.

[0020] In a preferred embodiment, the reaction solution is separated and purified to obtain the 4,4'-diaminodiphenylmethane, comprising:

[0021] Adding a first organic solvent to the reaction solution, washing with water for multiple times to obtain a washed reaction solution, and combining and collecting the washed solutions to obtain a first aqueous phase;

[0022] The reaction solution after water washing is sequentially subjected to alkali washing and water washing to obtain a second organic phase;

[0023] Aniline and the first organic solvent are removed from the first organic phase under reduced pressure to obtain 4,4'-diaminodiphenylmethane.

[0024] In a preferred embodiment, before the reaction solution is purified to obtain the 4,4'-diaminodiphenylmethane, the method further comprises: recovering an amine salt from the reaction solution, comprising:

[0025] Adding a second organic solvent and pure water to the reaction solution to wash the amine salt and collecting the second aqueous phase;

[0026] The second aqueous phase is concentrated and rotary evaporated to obtain an amine salt solution as the catalyst, wherein the concentration of the amine salt solution is 0.36-0.50 mol / l.

[0027] In a preferred embodiment, the volume of the second organic solvent added is 5-10% of the volume of the reaction solution, and the volume of the pure water added is 10-20% of the volume of the reaction solution.

[0028] In a preferred embodiment, the preparation method further comprises: pre-preparing aniline hydrochloric acid, comprising:

[0029] Add aniline into the second reactor, and dropwise add a hydrochloric acid solution with a mass fraction of 31% into the aniline under stirring at 25-45° C. for 10-40 minutes to obtain an aniline hydrochloric acid solution, wherein the molar ratio of the aniline to the hydrochloric acid is 0.5-2:1;

[0030] In a preferred embodiment, the concentration of the aniline hydrochloric acid solution is 0.36-0.50 mol / l.

[0031] In a second aspect, there is also provided 4,4'-diaminodiphenylmethane prepared by the preparation method described in any one of the first aspects.

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

[0033] The invention provides a preparation method of 4,4'-diaminodiphenylmethane and 4,4'-diaminodiphenylmethane. The preparation method comprises: under nitrogen protection, adding formaldehyde solution to aniline to react and obtain an aminal solution; adding a pre-prepared catalyst to the aminal solution to react and obtain a reaction liquid, wherein the catalyst comprises a pre-prepared aniline hydrochloric acid solution and / or an amine salt solution with a pH value less than 7; and purifying the reaction liquid to obtain 4,4'-diaminodiphenylmethane. The preparation method adopts a pre-prepared weakly acidic aniline hydrochloric acid solution and / or an amine salt solution with a pH value less than 7 as a catalyst, thereby avoiding equipment corrosion and environmental pollution caused by directly adding a strong acid into a first reactor.

[0034] Furthermore, the method further comprises preparing aniline hydrochloric acid in advance, and by generating a weakly acidic catalyst in the second reaction vessel, corrosion of the first reactor and the like by the strong acid can be further avoided;

[0035] Furthermore, the method also includes recovering an amine salt solution in the reaction solution, and the recovered weakly acidic amine salt solution can be used as a catalyst for the synthesis of 4,4'-diaminodiphenylmethane, thereby achieving the reuse of the catalyst, and the catalyst recovery process is simple and the cost is low;

[0036] In addition, the entire reaction system is in a low temperature state of 60-95°C and is conducive to the formation of the most valuable 4,4'-diaminodiphenylmethane product, avoiding energy waste and unnecessary product formation caused by high temperature reactions.

[0037] It should be noted that the present invention only needs to achieve at least one of the above-mentioned technical effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 4,4'-diaminodiphenylmethane preparation process flow chart in this embodiment. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution in the embodiment of the present invention will be clearly and completely described below. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] In the description of the present invention, it is to be understood that the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0041] As described in the background technology, 4,4'-diaminodiphenylmethane production requires acid catalysis for condensation reaction, and when hydrochloric acid is used as a catalyst, it is proven that the yield is higher, but the corrosion to the reaction equipment is also greater. For this reason, it is necessary to find a method for preparing 4,4'-diaminodiphenylmethane that can ensure the yield and has little corrosion to the reaction equipment. This embodiment provides a method for preparing 4,4'-diaminodiphenylmethane and 4,4'-diaminodiphenylmethane, which can effectively overcome the above problems.

[0042] like Figure 1 As shown, the preparation method of 4,4'-diaminodiphenylmethane comprises the following steps:

[0043] S1, under nitrogen protection, adding formaldehyde solution to aniline to react and obtain an aminal solution. Step S1 specifically comprises:

[0044] Aniline is added to the first reactor, and formaldehyde solution is added dropwise to the aniline under stirring at 30-60° C. for 10-40 minutes to obtain an aminal solution, wherein the molar ratio of aniline to formaldehyde is 2-5:1.

[0045] Usually, the formaldehyde content in the formaldehyde solution in this step is 31% to 40%, preferably 37%.

[0046] Preferably, the solution temperature is controlled to be below 45° C. during the process of dropwise adding the formaldehyde solution.

[0047] Preferably, the stirring speed in this step is 400 r / min.

[0048] The reaction process of step S1 is shown in the following formula (1):

[0049]

[0050] Therefore, when the ratio of the amount of aniline to formaldehyde is 2-5:1, the excess aniline can promote the reaction to proceed in the forward direction without affecting the subsequent reaction, and there is substantially no formaldehyde residue in the aminal solution obtained after the reaction, effectively avoiding unnecessary side reactions caused by formaldehyde in the subsequent reaction and reducing the yield and purity. Preferably, the ratio of the amount of aniline to formaldehyde is 3:1.

[0051] S2. Add the pre-prepared catalyst to the aminal solution obtained in step S1, and react to obtain a reaction solution.

[0052] Specifically, step S2 includes:

[0053] At 60-90° C., a pre-prepared catalyst is added to the aminal solution in the first reactor under stirring for 4-8 hours to obtain a reaction solution. The catalyst is a weakly acidic acid catalyst, including a pre-prepared aniline hydrochloric acid solution, an amine salt solution with a pH value less than 7, or a mixed solution of the two. When the catalyst is a mixed solution of the two, the aniline hydrochloric acid and the amine salt can be in any ratio.

[0054] The aniline hydrochloric acid solution and the amine salt solution used as catalysts are both weakly acidic, so as to achieve acid catalysis while reducing corrosion to the reactor. It should be noted that in this embodiment, the aniline hydrochloric acid solution needs to be prepared in advance, while the amine salt can be recycled and reused indefinitely after the reaction is completed, which not only reduces the problem of a large amount of alkali required to neutralize the acid, saves resources, reduces production costs, but also reduces problems such as wastewater discharge.

[0055] Preferably, the stirring speed in this step is 400 r / min.

[0056] The reaction process of step S2 is shown in the following formula (2):

[0057]

[0058] In the above formula (2), H + That is, an acid catalyst.

[0059] In step S2, under the action of an acid catalyst, the aminal undergoes transposition rearrangement to form a mixed product of 4,4'-MDA, 2,4'-MDA and 2,2'-MDA, wherein the percentage of 4,4'-MDA in the total MDA product is more than 80%.

[0060] Specifically, the above-mentioned transposition rearrangement process is as follows: under the action of an acid catalyst, first one of the secondary amines in the aminal is transposed to the para or ortho position of the corresponding benzene ring. From the perspective of steric hindrance and molecular stability, the proportion of the para-primary amine structure is much higher than that of the ortho-primary amine structure. Then, taking the para-primary amine structure as an example, the CN bond in the para-aminal is broken to form the p-aniline methyl carbon cation and the aniline nitrogen anion. Finally, according to the positioning effect determined by the molecular structure of aniline, the p-aniline methyl carbon cation is grafted at the ortho or para position of the benzene ring of the aniline nitrogen anion to complete the transposition rearrangement to form 4,4'-MDA and 2,4'-MDA respectively, and from the perspective of steric hindrance and molecular stability, the 4,4'-MDA content of the para-structure after rearrangement is much higher than that of 2,4'-MDA. Similarly, another ortho-primary amine structure is rearranged to form 2,4'-MDA or 2,2'-MDA, both of which have much lower contents than the aforementioned 4,4'-MDA, and finally a higher yield of 4,4'-MDA is obtained.

[0061] Of course, it is inevitable that, during the above rearrangement process, a small amount of 4,4'-MDA and p-aniline methyl carbonium cations are prone to side reactions to generate polyamines and other byproducts, as shown in the following formula (3):

[0062]

[0063] It should be noted that H + The activity and high temperature environment will promote the generation of polyamines. + The solution of using hydrochloric acid with higher activity as the acid catalyst is adopted in this reaction system. + The relatively low-activity hydrochloric acid of this amine is used as an acid catalyst to effectively reduce the amount of polyamines produced. The low temperature environment of this reaction system can also effectively inhibit the production of polyamines. Therefore, the polyamine content in the reaction product of this reaction is low (6-10%), which is much lower than the polyamine content in 4,4'-MDA prepared using hydrochloric acid as a catalyst, effectively improving the purity and yield of the product.

[0064] Preferably, when the amount ratio of the catalyst in step S2 to the formaldehyde in step S1 is 0.25-0.85:1, the reaction efficiency is high. By controlling the amount of the catalyst, not only the reaction efficiency is effectively improved, but also the reaction cost can be further reduced.

[0065] The preparation method further comprises: S0, pre-preparing aniline hydrochloric acid, S0 comprising:

[0066] Aniline is added into the second reactor, and a hydrochloric acid solution with a mass fraction of 31% is added dropwise into the aniline under stirring at 25-45° C. for 10-40 minutes to obtain an aniline hydrochloric acid solution, wherein the molar ratio of aniline to hydrochloric acid is 0.5-2:1.

[0067] In a preferred embodiment, the concentration of the generated aniline hydrochloric acid solution is 0.36-0.50 mol / l.

[0068] Preferably, the stirring speed in this step is 400 r / min.

[0069] S3. The reaction solution is purified to obtain 4,4'-diaminodiphenylmethane.

[0070] In addition to the above-mentioned MDA product, the reaction solution obtained in step S2 also contains impurities such as water, aniline, and excess acidic catalyst. Therefore, it is necessary to separate and purify by multiple washings.

[0071] Specifically, step S3 includes:

[0072] S31, washing the reaction solution with water for multiple times to obtain a washed reaction solution and collecting the washed solution to obtain a first aqueous phase. This step can separate the amine salt in the reaction solution from the reaction solution by washing with water.

[0073] S32, the reaction liquid after water washing is subjected to alkali washing and water washing in sequence to obtain a first organic phase. The acid catalyst that may remain in the reaction liquid after water washing can be effectively neutralized by alkali washing. The waste alkali salt remaining in the organic phase can be washed away by water washing after alkali washing.

[0074] S33, distilling the first organic phase under reduced pressure to remove aniline to obtain 4,4'-diaminodiphenylmethane.

[0075] The boiling point of aniline (184.4°C) is lower than that of 4,4'-diaminodiphenylmethane (242°C) and the difference is quite large, so aniline can be separated and removed by vacuum distillation.

[0076] To achieve better separation and purification effect, in another preferred embodiment, step S3 includes:

[0077] S34, adding a first organic solvent to the reaction solution, washing with water for multiple times to obtain a washed reaction solution, and combining and collecting the washed solutions to obtain a first aqueous phase;

[0078] S35, sequentially performing alkali washing and water washing on the reaction solution after water washing to obtain a second organic phase;

[0079] S36, distilling the second organic phase under reduced pressure to remove aniline and the first organic solvent to obtain 4,4'-diaminodiphenylmethane.

[0080] In this embodiment, the first organic solvent is preferably chloroform. Chloroform, as a high-quality organic solvent, can extract the organic phase from the aqueous phase to improve the yield. Chloroform has a low melting point (61.2° C.) and can be easily removed by distillation.

[0081] Furthermore, the aniline evaporated in the above steps S32 and S34 can be reused as a raw material, which effectively reduces the cost and avoids pollution.

[0082] The reaction solution obtained in the above step S2 includes amine salt, which can be recovered and used as the catalyst in step S2. Therefore, before step S3, the preparation method further includes:

[0083] Sa. recovering the amine salt in the reaction solution, comprising:

[0084] Sa1, adding a second organic solvent (such as toluene, chloroform, or a mixture of toluene and chloroform) and pure water to the reaction solution to wash the amine salt and collect the second aqueous phase;

[0085] Sa2. Concentrate and rotary evaporate the second aqueous phase to obtain an amine salt solution that can be used as a catalyst. The concentration of the amine salt solution is 0.36-0.50 mol / l.

[0086] The amine salt in this embodiment is a strong acid and weak base salt, which is weakly acidic. Using it as the catalyst in step S2 can not only play an acid catalytic role, but also has less corrosion to the reactor. More importantly, it can achieve the reuse of the catalyst to reduce production costs, and the recovery process is simple, the recovery rate is high (more than 90%), and the recovery cost is low. In addition, the distilled water evaporated in step S42 can be reused, such as for washing the amine salt in S41, thereby further reducing costs and reducing the amount of waste liquid.

[0087] In addition, the reaction system in this embodiment is in a low temperature state of 60-95°C, the reaction process is relatively safe and mild, and is conducive to the formation of the product 4,4'-diaminodiphenylmethane, avoiding energy waste and unnecessary product formation caused by high temperature reaction.

[0088] According to high performance liquid chromatography, the content of 4,4'-diaminodiphenylmethane in the product prepared by the preparation method in this embodiment is not less than 80%, and the yield is higher and the purity is better than that of the prior art.

[0089] The preparation method of 4,4'-diaminodiphenylmethane is further described below in conjunction with specific examples.

[0090] Example 1

[0091] This embodiment provides a method for preparing 4,4'-diaminodiphenylmethane, which comprises the following steps:

[0092] S10, prepare aniline hydrochloric acid in advance.

[0093] Under nitrogen protection, 88.98 g of aniline was added to the second reactor, and stirred at a stirring speed of 400 r / min (this stirring speed was used in each step of this embodiment), and 112.5 g of 31% concentrated hydrochloric acid was added dropwise. The temperature was controlled at 27° C. and stirred for 20 min to obtain an aniline hydrochloric acid solution with a concentration of 0.36-0.50 mol / l.

[0094] S20, adding formaldehyde solution to aniline to react and obtain an acetal solution.

[0095] Under nitrogen protection, add 247.73g of aniline, add 107.89g of 37% formaldehyde solution dropwise while stirring, control the temperature below 45°C, and stir for 10-20min. Then add the aniline hydrochloride solution prepared in S10, stir for 10-30min, raise the temperature to 70°C and keep it for 4-8h, and react at 95°C to obtain a reaction solution. The concentration of the added aniline hydrochloride is 0.42mol / l, and the volume is 904ml.

[0096] S30, adding toluene and pure water to the reaction solution to wash the amine salt, and collecting the corresponding aqueous phase and the remaining reaction solution respectively, concentrating the aqueous phase and performing rotary evaporation to recover the amine salt solution.

[0097] S40. Add 50 g of pure water to the remaining reaction liquid obtained in S30 to wash the amine salt, wash three times, collect 150 ml of the washing liquid (aqueous phase), add 50 g of 32% sodium hydroxide solution for alkaline washing, and then add 100 g of water for washing, and separate the layers using a separatory funnel to obtain the aqueous phase and the organic phase.

[0098] The organic phase was distilled to obtain 230 g of product, and the aniline evaporated during the distillation process was recycled.

[0099] According to the detection by high performance liquid chromatography, the percentage of 4'4-MDA in the product is 82.82%, the percentage of 2'4-MDA is 3.56%, the percentage of polyamine is 7.66%, and the percentage of 2'2-MDA is 0.41%.

[0100] Example 2

[0101] The rest of this embodiment is the same as that of Embodiment 1, except that:

[0102] In step S20, 371.60 g of aniline was added.

[0103] According to the detection by high performance liquid chromatography, the percentage of 4'4-MDA in the product is 83.41%, the percentage of 2'4-MDA is 3.17%, the percentage of polyamine is 7.32%, and the percentage of 2'2-MDA is 0.38%.

[0104] Example 3

[0105] The rest of this embodiment is the same as that of Embodiment 1, except that:

[0106] In step S20, 495.46 g of aniline was added.

[0107] According to the detection by high performance liquid chromatography, the percentage of 4'4-MDA in the product is 84.43%, the percentage of 2'4-MDA is 2.98%, the percentage of polyamine is 7.05%, and the percentage of 2'2-MDA is 0.33%.

[0108] Example 4

[0109] The rest of this embodiment is the same as that of Embodiment 3, except that:

[0110] Step S40 is: adding 50 ml of chloroform to the reaction solution, washing with water and alkali for multiple times to obtain an organic phase and an aqueous phase, and distilling the organic phase under reduced pressure to remove aniline and chloroform to obtain the product.

[0111] According to the detection by high performance liquid chromatography, the percentage of 4'4-MDA in the product is 84.66%, the percentage of 2'4-MDA is 3.12%, the percentage of polyamine is 7.15%, and the percentage of 2'2-MDA is 0.41%.

[0112] Example 5

[0113] The rest of this embodiment is the same as that of Embodiment 3, except that:

[0114] In step S20, 619.33 g of aniline was added.

[0115] According to the detection by high performance liquid chromatography, the percentage of 4'4-MDA in the product is 84.13%, the percentage of 2'4-MDA is 3.06%, the percentage of polyamine is 8.21%, and the percentage of 2'2-MDA is 0.30%.

[0116] Example 6

[0117] The rest of this embodiment is the same as that of Embodiment 3, except that:

[0118] In step S10, 177.96 g of aniline was added.

[0119] According to the detection by high performance liquid chromatography, the percentage of 4'4-MDA in the product is 83.05%, the percentage of 2'4-MDA is 3.23%, the percentage of polyamine is 7.65%, and the percentage of 2'2-MDA is 0.26%.

[0120] Example 7

[0121] The rest of this embodiment is the same as that of Embodiment 3, except that:

[0122] In step S10, 133.47 g of aniline was added.

[0123] According to the detection by high performance liquid chromatography, the percentage of 4'4-MDA in the product is 83.28%, the percentage of 2'4-MDA is 3.07%, the percentage of polyamine is 7.95%, and the percentage of 2'2-MDA is 0.31%.

[0124] Example 8

[0125] The rest of this embodiment is the same as that of Embodiment 3, except that:

[0126] In step S10, 44.49 g of aniline was added.

[0127] According to the detection by high performance liquid chromatography, the percentage of 4'4-MDA in the product is 82.05%, the percentage of 2'4-MDA is 2.92%, the percentage of polyamine is 9.14%, and the percentage of 2'2-MDA is 0.26%.

[0128] Example 9

[0129] The rest of this embodiment is the same as that of Embodiment 3, except that:

[0130] Step S10 is not performed, and the catalyst used in step S20 is the aniline solution recovered in Example 3.

[0131] According to the detection by high performance liquid chromatography, the percentage of 4'4-MDA in the product is 81.75%, the percentage of 2'4-MDA is 2.88%, the percentage of polyamine is 7.10%, and the percentage of 2'2-MDA is 0.29%.

[0132] Comparative Example 1

[0133] The rest of this embodiment is the same as that of Embodiment 3, except that:

[0134] Step S10 is not performed, and in step S20, 45 g of 31% hydrochloric acid is used as a catalyst.

[0135] According to the detection by high performance liquid chromatography, the percentage of 4'4-MDA in the product is 78.31%, the percentage of 2'4-MDA is 2.52%, the percentage of polyamine is 6.88%, and the percentage of 2'2-MDA is 0.22%.

[0136] The specific experimental data of the above Examples 1 to 9 and Comparative Example 1 are shown in Table 1 below:

[0137] Table 1

[0138]

[0139]

[0140] Based on the above Table 1, it can be seen that compared with Comparative Example 1, the products prepared in Examples 1-9 have a higher percentage of 4'4-MDA and a lower corrosion capacity for equipment. According to Examples 1 to 3 and 5, when the ratio of the amount of aniline to hydrochloric acid is 1:1 when preparing aniline hydrochloric acid, the percentage of 4'4-MDA in the product is the highest. According to Examples 3, 6 to 8, when the ratio of the amount of aniline to formaldehyde is 4:1 when preparing aminal, the percentage of 4'4-MDA in the product is the highest. According to Examples 3 and 4, when chloroform is used as a solvent for purification, the percentage of 4'4-MDA in the product is higher and the purification effect is better. According to Examples 3 and 9, when the acidic amine salt produced by the recovery reaction is used as a reaction catalyst for catalyst reuse, the catalytic ability is not much different from that of aniline hydrochloric acid.

[0141] In summary, the method for preparing 4,4'-diaminodiphenylmethane provided in this embodiment uses a pre-prepared weakly acidic aniline hydrochloric acid solution and / or an amine salt solution with a pH value less than 7 as a catalyst, thereby avoiding equipment corrosion and environmental pollution caused by directly adding a strong acid into the first reactor;

[0142] Furthermore, the method further comprises preparing aniline hydrochloric acid in advance, and by generating a weakly acidic catalyst in the second reaction vessel, corrosion of the first reactor and the like by the strong acid can be further avoided;

[0143] Furthermore, the method also includes recovering an amine salt solution in the reaction solution, and the recovered weakly acidic amine salt solution can be used as a catalyst for the synthesis of 4,4'-diaminodiphenylmethane, thereby achieving the reuse of the catalyst, and the catalyst recovery process is simple and the cost is low;

[0144] In addition, the entire reaction system is in a low temperature state of 60-95°C and is conducive to the formation of the most valuable 4,4'-diaminodiphenylmethane product, avoiding energy waste and unnecessary product formation caused by high temperature reactions.

[0145] All of the above optional technical solutions can be combined in any way to form optional embodiments of the present invention, that is, any multiple embodiments can be combined to meet the needs of different application scenarios. They are all within the protection scope of this application and will not be described one by one here.

[0146] It should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing 4,4'-diaminodiphenylmethane, characterized in that: The preparation method comprises: S10, preparing aniline hydrochloric acid in advance; Under nitrogen protection, 88.98 g of aniline was added to the reactor, and 112.5 g of 31% concentrated hydrochloric acid was added dropwise while stirring at a stirring speed of 400 r / min. The temperature was controlled at 27°C, and the stirring speed was 400 r / min for 20 min to obtain an aniline hydrochloric acid solution with a concentration of 0.36-0.50 mol / l; S20, adding formaldehyde solution to aniline to react to obtain an aminal solution; Under nitrogen protection, add 247.73g of aniline, add 107.89g of 37% formaldehyde solution dropwise under stirring at a stirring speed of 400r / min, control the temperature below 45°C, stir at a stirring speed of 400r / min for 10-20min, then add the aniline hydrochloride solution prepared in S10, stir at a stirring speed of 400r / min for 10-30min, heat to 70°C and keep warm for 4-8h, react at 95°C to obtain a reaction solution, wherein the concentration of the added aniline hydrochloride is 0.42mol / l and the volume is 904ml; S30, adding toluene and pure water to the reaction solution to wash the amine salt, collecting the corresponding aqueous phase and the remaining reaction solution, concentrating the aqueous phase, and rotary evaporating to recover the amine salt solution; S40, adding 50 g of pure water to the remaining reaction solution obtained in S30 to wash the amine salt, washing three times, collecting 150 ml of the aqueous phase of the washing liquid, adding 50 g of 32% sodium hydroxide solution for alkaline washing, and then adding 100 g of water for washing, and separating by separating funnel to obtain an aqueous phase and an organic phase; The organic phase was distilled to obtain 230 g of product, and the aniline evaporated during the distillation process was recovered and reused; According to the detection by high performance liquid chromatography, the percentage of 4'4-MDA in the product is 82.82%, the percentage of 2'4-MDA is 3.56%, the percentage of polyamine is 7.66%, and the percentage of 2'2-MDA is 0.41%.

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