Method for preparing diphenylmethane series diamine and polyamine

Abstract

The invention relates to a method for preparing diphenylmethane series diamine and polyamine (DAM for short), which comprises the following steps of: catalyzing aniline and formaldehyde to carry out condensation reaction under higher pressure by using carbonic acid or carbon dioxide as an acid catalyst, and heating reaction liquid under higher pressure to promote a transposition reaction of a reaction intermediate product, thereby obtaining the diphenylmethane series diamine and polyamine. And reducing the pressure of the reaction system after transposition, decomposing the ammonium carbonate in the reaction liquid and releasing carbon dioxide at a relatively high temperature, and finally refining the obtained reaction liquid containing diaminodiphenylmethane to prepare DAM. By adopting the method disclosed by the invention, the neutralization process of the traditional acid catalysis condensation process can be avoided, the consumption of alkali liquor is avoided, and no byproduct waste brine is produced, so that the process treatment flow of byproduct wastewater in the DAM production process is greatly simplified, and meanwhile, the quality of the prepared DAM is stable.

Description

Technical Field

[0001] This invention belongs to the field of DAM preparation technology, specifically relating to an acidic catalyst whose amine salt is easily decomposed, avoiding the need for alkali neutralization in traditional processes, and its application in the DAM preparation process. Background Technology

[0002] MDI is one of the main raw materials in the polyurethane industry. The method of preparing diphenylmethane series diamines and polyamines (DAM) by reacting aniline and formaldehyde under an acidic catalyst, and then synthesizing MDI by reacting DAM with phosgene, is a well-known method in the industry.

[0003] In traditional DAM preparation processes, aniline and formaldehyde undergo a condensation reaction under an acid catalyst to obtain an acidic reaction mixture containing DAM. The reaction solution containing DAM salts is then completely neutralized with an alkaline solution, resulting in separation into an organic phase and a brine phase. The organic phase is further purified to obtain crude DAM. The neutralization process typically uses NaOH solution. In the complete neutralization of diphenylmethane series diamine and polyamine salts to obtain diphenylmethane series diamines and polyamines, a large amount of acid catalyst, such as hydrochloric acid, is used in the initial condensation reaction of aniline and formaldehyde. To fully neutralize the hydrochloric acid, a large amount of caustic soda is consumed, with caustic soda costs accounting for approximately 5% of the DAM manufacturing cost. Simultaneously, the addition of caustic soda generates a large amount of waste brine containing organic amines, placing significant pressure on environmental emissions and recycling. Many factories have had to invest heavily and implement complex and lengthy treatment processes to address this issue. Furthermore, due to the special nature of the neutralization reaction, if the amount of caustic soda added is insufficient or the control is unstable, the excessive acidic reaction solution can also cause corrosion to downstream equipment, affecting the long-term stable operation of the DAM production unit.

[0004] To address this long-standing industry challenge, numerous patents both domestically and internationally have been published related to solving the problem. For example, patent CN201711450846.5 mentions a composite catalyst for catalyzing the decomposition of amine salts and its preparation method, as well as a method for preparing MDA. The acidic catalyst mentioned is hydrochloric acid or sulfuric acid. While the catalyst developed using this technology can catalyze the decomposition of amine salts in hydrochloride or sulfate, experiments have shown that the amine salt decomposition conversion rate is low, and the hydrochloric acid or sulfuric acid produced during decomposition cannot be effectively separated and recovered, limiting its application to small-scale laboratory research. Another example is patent CN202010793516.1, which mentions a catalyst for catalyzing the conversion of amine salts and its preparation method, as well as a method for preparing DAM. This method can separate DAM from the reaction solution and recover aniline salts through catalytic conversion and extraction. However, similarly, experiments have shown that the amine salt conversion rate is low, and it requires a large amount of extractant and multi-stage extraction, resulting in a complex process and high energy consumption for extractant recovery. For example, patent CN202080085270.0 mentions the heterogeneous synthesis of methylenediamine. This technology has been studied in the industry for decades. As the latest report on this technology, the patent mentions that there are still problems such as short catalyst life and difficulty in regeneration, as well as high impurity content in the prepared DAM.

[0005] In conclusion, there is still no reliable way to solve this industry problem, and therefore a new technology is urgently needed to help the industry achieve a breakthrough in this direction. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing diphenylmethane series diamines and polyamines. This method uses carbonic acid or carbon dioxide as an acidic catalyst. After the reaction, only the reaction system needs to be controlled at a low pressure. The ammonium carbonate or carbonic acid in the reaction solution can be completely decomposed. This avoids the need for adding alkali to neutralize, which consumes a large amount of alkali solution, produces a large amount of amine-containing brine as a byproduct, and involves complex subsequent processing. At the same time, the prepared DAM has stable quality indicators and meets the requirements for downstream isocyanate preparation.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] A method for preparing diphenylmethane series diamines and polyamines, using carbonic acid and / or carbon dioxide as acidic catalysts to catalyze the reaction of aniline with formaldehyde.

[0009] One specific implementation includes the following steps:

[0010] a) A mixture of aniline, carbonic acid and / or carbon dioxide, and formaldehyde is subjected to a pre-condensation reaction to obtain a reaction solution;

[0011] b) Heat the reaction solution obtained in step a) to cause the intermediate generated by the pre-condensation reaction to undergo a displacement reaction;

[0012] c) Reduce the pressure of the reaction system while maintaining it at a certain temperature to promote the decomposition of carbonic acid and its salts in the reaction system;

[0013] d) The reaction solution obtained in step c) is purified to obtain DAM.

[0014] In the method of the present invention, in step a), the catalyst is carbonic acid and / or carbon dioxide.

[0015] When using carbon dioxide, aniline and the catalyst carbon dioxide can be mixed first to undergo a salt-forming reaction. The pressure of the mixing system should be controlled above 10 barg (e.g., 10-80 barg, preferably 15-60 barg, more preferably 20-30 barg). Before mixing, a certain amount of water needs to be added to the aniline, and the amount of water introduced should be such that the molar ratio of carbon dioxide to water is 1 / 2-1 / 10, which promotes the formation of carbonic acid from carbon dioxide and its ionization to produce H₂. + This avoids the formation of carbonic acid and aniline under high pressure, which would cause salt precipitation and blockage and affect the stable operation of the process. Carbon dioxide can be injected from the bottom distributor and stirred at the same time, so that the aniline and carbonic acid in the reaction system can form salt under high pressure.

[0016] When carbonic acid is used as a catalyst, high-concentration carbonic acid needs to be prepared before mixing with aniline. That is, carbon dioxide and water are mixed at a molar ratio of 1 / 2 to 1 / 10, and the pressure of the mixing system is controlled at more than 10 barg (e.g., 10-80 barg, preferably 15-60 barg, more preferably 20-30 barg). Then, the high-concentration carbonic acid formed after mixing is mixed with aniline to undergo a salt formation reaction.

[0017] The temperature of the reaction system is controlled at 30-100℃, preferably 50-80℃;

[0018] In step a), carbonic acid / carbon dioxide is introduced into the reaction system to provide H₂. + The amount is based on the production of one mole of H+ per mole of carbonic acid ionized. + Calculation, H + The molar ratio of carbon dioxide to aniline is between (0.04-0.5):1. The amount of carbon dioxide introduced can be increased by increasing the pressure of the reaction system.

[0019] In the preferred embodiment, the residence time for the salt formation reaction in step a) of introducing carbonic acid / carbon dioxide is 4-8 min;

[0020] After the salt formation reaction is completed, the reaction solution and formaldehyde solution can be mixed in any mixing method, such as static mixer, stirred tank, high shear, super gravity suspension bed, etc. The mixed reaction solution is kept under a pressure not lower than that of the salt formation reaction, the reaction temperature is controlled at 50-100℃, and the reaction residence time is 10-50min.

[0021] The molar ratio of formaldehyde to aniline is 0.25-0.60, preferably 0.35-0.50; more preferably, the mass concentration of formaldehyde is 30-50 wt%. A large amount of heat is released during the reaction, which can be removed by means of an in-reactor heat exchanger or an external circulation heat exchanger to control the reaction system between 50-100°C.

[0022] In step b), the condensation reaction solution of aniline and formaldehyde obtained in a) is heated to cause the intermediate reaction product in the reaction solution to undergo a rearrangement reaction.

[0023] In a preferred embodiment, the reaction temperature in step b) is controlled at 90-150°C, preferably 100-130°C; the reaction pressure is 10-90 barg, preferably 20-65 barg; and the transposition reaction time is 50-200 min, preferably 80-150 min. The transposition reaction in step b) can be carried out in any type of reactor, such as a stirred mixed reactor, a tower-type plug flow reactor, etc.

[0024] In step c), the pressure of the reaction system is reduced while the reaction system is kept at a certain temperature to promote the decomposition of carbonic acid and its salts in the reaction system;

[0025] In a preferred embodiment, the decomposition reaction pressure of the ammonium carbonate in step c) is 0.8-2.0 barg, preferably 1.0-1.5 barg; the reaction temperature is 80-130°C, preferably 90-120°C. In this step, most of the ammonium carbonate decomposes rapidly, yielding a mixture containing DAM, aniline, and water.

[0026] In a preferred embodiment, in step d), the mixture containing DAM, aniline, and water can be separated into phases, and the separated organic phase can be distilled under reduced pressure to obtain purified DAM. In this step, even if a small amount of carbonic acid and its salts remain in step c), they can be further decomposed, which has no impact on the quality of DAM or the processing procedure.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) Carbonic acid or carbon dioxide reacting with water to form carbonic acid can be used directly as a catalyst for the reaction of aniline and formaldehyde. Under high pressure and in the presence of amino groups and water in the reaction system, carbonic acid can provide sufficient H2O. + This catalyzes the reaction between aniline and formaldehyde, resulting in DAM of better quality.

[0029] (2) Carbonic acid is a weak acid, and aniline and DAM are both weak bases. Under near-normal pressure, ammonium carbonate is easily decomposed. Therefore, after the rearrangement reaction is completed, only the pressure of the reaction system needs to be reduced, and no caustic soda needs to be added for neutralization to obtain DAM in a non-salt state. This avoids the consumption of a large amount of caustic soda, and does not generate a large amount of saline wastewater or the post-treatment process and cost of the wastewater. As a result, the industrial process is greatly simplified, and the manufacturing cost of DAM is significantly reduced.

[0030] (3) The DAM preparation method of the present invention produces DAM with stable quality under carbonic acid catalysis, which meets the needs of various downstream applications. Detailed Implementation

[0031] The present invention will be further illustrated below with more specific embodiments, but these do not constitute any limitation on the scope of the invention.

[0032] The raw materials used in the following examples, such as aniline (analytical grade), formaldehyde aqueous solution, hydrochloric acid, and caustic soda with a mass concentration of 50%, were all produced by Wanhua. The composition of DAM was analyzed by GC chromatography.

[0033] High-pressure nitrogen is supplied by the nitrogen pipeline network of Wanhua (Yantai) Industrial Park.

[0034] Example 1

[0035] Step a): Add 150.0 g of aniline (99.9 wt%) to a high-pressure reactor equipped with a stirring and cooling / heating jacket, then add 30.5 g of water (so that the molar ratio of carbon dioxide to water during the reaction is 1 / 3). After that, seal the high-pressure reactor and purge the space above the liquid surface in the reactor with nitrogen gas for 10 min. Then pressurize with high-pressure nitrogen gas until the pressure of the reaction system reaches 25 barg and stop. Wait 100 min. If the system pressure is still within the range of 25 ± 0.1 barg, the system is considered to be sealed well.

[0036] After starting the stamping process, the agitator in the reactor is set to 300 rpm. Then, high-pressure carbon dioxide is continuously introduced from the bottom feed distribution plate of the reactor using a high-pressure carbon dioxide cylinder. The process is based on the principle that each mole of carbon dioxide ionizes to produce one mole of H₂. + Calculation, until the provided H + The reaction was stopped when the molar ratio of aniline to aniline was 0.35. The reaction temperature was controlled at 50°C by heat transfer through a jacket, and stirring was continued for 4 minutes.

[0037] Subsequently, 54.4 g of a 40 wt% formaldehyde aqueous solution (molar ratio of formaldehyde to aniline was 0.45) was added to the reactor using a high-pressure pump. The formaldehyde addition rate was controlled at 3 mL / min. During the addition, the reactor temperature was continuously controlled at 60 °C and the stirring speed was 300 rpm. After the formaldehyde addition was completed, the reaction was continued at a constant temperature for 10 min.

[0038] Step b): Raise the temperature of the reactor to 110°C, stir at 300 rpm, maintain a pressure of 70 barg, and keep the temperature constant for 2 hours to complete the displacement reaction.

[0039] Step c): Slowly open the exhaust and pressure relief valve of the reactor, maintain the reactor stirring speed at 300 rpm, maintain the reactor pressure at 1.2 barg, and the temperature at 110℃, so that the gas in the reactor is cooled by the cooling equipment and the tail gas is captured and absorbed before being discharged into the air. Continue for 30 minutes and then stop.

[0040] Step d): Lower the temperature of the reaction solution to 90°C to allow the reaction solution to separate into two phases. Take 80g of the lower oil phase and then distill it under reduced pressure to obtain 57.1g of purified DAM.

[0041] The catalyst type, alkali consumption, amine brine content, and DAM composition data for this embodiment are detailed in Table 1.

[0042] Example 2

[0043] Step a): Add 150.0 g of aniline (99.9 wt%) to a high-pressure reactor equipped with a stirring and cooling / heating jacket. Then seal the high-pressure reactor and purge the space above the liquid level inside the reactor with nitrogen for 10 min. Then pressurize with high-pressure nitrogen until the system pressure reaches 20 barg and stop. Wait 100 min. If the system pressure is still within the range of 20 ± 0.1 barg, the system is considered to be well sealed.

[0044] First, high-pressure carbon dioxide cylinder gas is used to ionize carbon dioxide (based on the principle that each mole of carbon dioxide produces one mole of H₂ after carbon dioxide is introduced to produce carbonic acid). + Calculation, until the provided H + Carbonic acid was produced by passing 43.6 g of water through the mixture (the molar ratio of carbon dioxide to water during the reaction was 0.25, and the reaction was stopped) at a pressure of 20 barg.

[0045] Then, start the stirring of the reaction vessel after stamping, set the speed to 450 rpm, add all the prepared carbonic acid, and carry out the salt formation reaction with aniline. Control the reaction temperature to 50℃ by jacket heat transfer and continue stirring for 6 minutes.

[0046] Subsequently, 64.5 g of a 30 wt% formaldehyde aqueous solution (molar ratio of formaldehyde to aniline was 0.40) was added to the reactor using a high-pressure pump. The formaldehyde addition rate was controlled at 2 mL / min. During the addition, the reactor temperature was continuously controlled at 70 °C and the stirring speed was 450 rpm. After the formaldehyde addition was completed, the reaction was continued at a constant temperature for 10 min.

[0047] Step b): Raise the temperature of the reactor to 100℃, stir at 350 rpm, maintain a pressure of 40 barg, and keep the temperature constant for 3 hours to complete the displacement reaction.

[0048] Step c): Slowly open the exhaust and pressure relief valve of the reactor, maintain the reactor stirring speed at 350 rpm, maintain the reactor pressure at 1.0 barg, and the temperature at 100℃, so that the gas in the reactor is cooled by the cooling equipment and the tail gas is captured and absorbed before being discharged into the air. Continue for 20 minutes and then stop.

[0049] Step d): Lower the temperature of the reaction solution to 90°C to allow the reaction solution to separate into two phases. Take 80.0g of the lower oil phase and then distill it under reduced pressure to obtain 52.6g of purified DAM.

[0050] The catalyst type, alkali consumption, amine brine content, and DAM composition data for this embodiment are detailed in Table 1.

[0051] Example 3

[0052] Step a): Add 150.0 g of aniline (99.9 wt%) to a high-pressure reactor equipped with a stirring and cooling / heating jacket, then add 39.2 g of water (so that the molar ratio of carbon dioxide to water during the reaction is 1 / 9). Seal the high-pressure reactor and purge the space above the liquid level in the reactor with nitrogen for 10 min. Then pressurize with high-pressure nitrogen until the system pressure reaches 12 barg and stop. Wait 100 min. If the system pressure is still within the range of 12 ± 0.1 barg, the system is considered to be well sealed.

[0053] After starting the stamping process, the agitator in the reactor is set to 500 rpm. Then, high-pressure carbon dioxide is continuously introduced from the bottom feed distribution plate of the reactor using a high-pressure carbon dioxide cylinder. The process is based on the principle that each mole of carbon dioxide ionizes to produce one mole of H₂. + Calculation, until the provided H + The reaction was stopped when the molar ratio of aniline to aniline was 0.15. The reaction temperature was controlled at 65°C by heat transfer through a jacket, and stirring was continued for 8 minutes.

[0054] Subsequently, 35.3 g of a 48 wt% formaldehyde aqueous solution (molar ratio of formaldehyde to aniline was 0.35) was added to the reactor using a high-pressure pump. The formaldehyde addition rate was controlled at 2.5 mL / min, and the reactor temperature was continuously controlled at 80 °C during the addition. After the formaldehyde addition was completed, the reaction was continued at a constant temperature for 10 min.

[0055] Step b): Raise the temperature of the reactor to 120°C, stir at 200 rpm, maintain a pressure of 20 barg, and keep the temperature constant for 2.5 hours to complete the displacement reaction.

[0056] Step c): Slowly open the exhaust and pressure relief valve of the reactor, maintain the reactor stirring speed at 200 rpm, maintain the reactor pressure at 1.5 barg and the temperature at 100℃, and allow the gas inside the reactor to be cooled by the cooling equipment and the tail gas to be captured and absorbed before being discharged. Continue for 50 minutes and then stop.

[0057] Step d): Lower the temperature of the reaction solution to 90°C to allow the reaction solution to separate into two phases. Take 80g of the lower oil phase and then distill it under reduced pressure to obtain 47.3g of purified DAM.

[0058] The catalyst type, alkali consumption, amine brine content, and DAM composition data for this embodiment are detailed in Table 1.

[0059] Comparative Example 1

[0060] In order to compare and evaluate the carbonation catalytic process of the present invention, this comparative example uses hydrochloric acid, which is currently widely used in industrial applications, as an acidic catalyst.

[0061] Step a): Add 150.0 g of aniline (99.9 wt%) to a pressure-resistant reactor equipped with a stirring and cooling / heating jacket. Then, purge the space above the liquid level in the reactor with nitrogen for 10 min, setting the rotation speed to 300 rpm. Add 62.4 g of 33% hydrochloric acid (hydrochloric acid with H2 content...). + The formaldehyde-aniline molar ratio was 0.35. The reaction temperature was controlled at 50℃ by jacket heat transfer and stirring was continued for 4 min. Then, 54.4 g of 40 wt% formaldehyde aqueous solution was added to the reactor at a rate of 3 mL / min. The molar ratio of formaldehyde to aniline was 0.45. During the addition, the reactor temperature was continuously controlled at 60℃ and the stirring speed was 300 rpm. After the formaldehyde addition was completed, the reaction was continued at a constant temperature for 10 min.

[0062] Step b): Raise the temperature of the reactor to 110°C, stir at 300 rpm, and maintain the temperature for 2 hours to complete the displacement reaction.

[0063] Step c): Add 47.9g of 50% sodium hydroxide solution to the reaction system, stir the reaction vessel at 300rpm, maintain the reaction vessel at normal pressure, and stop stirring after 5min.

[0064] Step d): Lower the temperature of the reaction solution to 90°C to allow the reaction solution to separate into two phases. After washing the upper oil phase, 167.2g of washed oil phase is obtained. Then, it is subjected to vacuum distillation to obtain 117.9g of purified DAM.

[0065] The catalyst type, alkali consumption, amine brine content, and DAM composition data for this comparative example are detailed in Table 1.

[0066] Comparative Example 2

[0067] This comparative example only uses the 33% hydrochloric acid from Comparative Example 1 according to H... + The same molar ratio as aniline was replaced with 92.2g of 30% dilute sulfuric acid, and the remaining steps and process parameters were completely consistent with Comparative Example 1. In step d), 165.5g of washed oil phase was obtained, which was then subjected to vacuum distillation to obtain 115.8g of purified DAM.

[0068] The catalyst type, alkali consumption, amine brine content, and DAM composition data for this comparative example are detailed in Table 1.

[0069] Table 1. Example / Comparative Data

[0070]

[0071] *Note: The amount of alkali consumed is calculated based on a 50% concentration of sodium hydroxide solution.

[0072] As can be seen from the experimental results in the table above, the method for preparing diphenylmethane series diamines and polyamines of the present invention, using carbonic acid or carbon dioxide as an acidic catalyst, yielded DAMs that met the index requirements in Examples 1-3. Compared with Comparative Examples 1 and 2, the method of the present invention does not involve an alkali neutralization process, thus avoiding the consumption of alkali solution and the generation of amine-containing wastewater. Only conventional salt-free amine-containing wastewater needs to be treated, eliminating the entire process and treatment cost of amine-containing wastewater treatment. The process flow is greatly simplified, and the overall manufacturing cost of DAM is significantly reduced.

[0073] Although the present invention has been described in detail through the preferred embodiments described above, it should be understood that the above description should not be considered as a limitation of the present invention. Those skilled in the art will understand that modifications or adjustments can be made to the present invention based on the teachings of this specification. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A process for the preparation of diphenylmethane series diamines and polyamines, characterized in that, Carbonic acid and / or carbon dioxide is used as an acidic catalyst to catalyze the reaction of aniline and formaldehyde.

2. The method of claim 1, wherein, The method comprises the following steps: a) mixing aniline, carbonic acid and / or carbon dioxide, and formaldehyde to perform a pre-condensation reaction to obtain a reaction solution; b) heating the reaction solution obtained in step a) to perform a rearrangement reaction of the intermediate produced in the pre-condensation reaction; c) reducing the pressure of the reaction system while maintaining the reaction system at a certain temperature to promote the decomposition of carbonic acid and its salts in the reaction system; d) refining the reaction solution obtained in step c) to obtain DAM.

3. The method of claim 2, wherein, In step a), when carbon dioxide is used as the catalyst, aniline is first mixed with carbon dioxide to perform a salt formation reaction, the pressure of the mixed system is controlled to be higher than 10 barg, a certain amount of water is added to aniline before mixing, and the amount of water is controlled such that the molar ratio of carbon dioxide to water is 1 / 2-1 / 10; and / or When carbonic acid is used as the catalyst, carbon dioxide is first mixed with water at a molar ratio of 1 / 2-1 / 10 before mixing with aniline, the pressure of the mixed system is controlled to be higher than 10 barg, and then the high-concentration carbonic acid formed after mixing is mixed with aniline to perform a salt formation reaction.

4. The method according to claim 2 or 3, characterized in that, In step a), carbonic acid / carbon dioxide is introduced into the reaction system to provide H₂. + The amount is based on the production of one mole of H+ per mole of carbonic acid ionized. + Calculation, H + The molar ratio of aniline to aniline is between (0.04-0.5):

1.

5. The method according to any one of claims 2-4, characterized in that, In step a), the temperature of the salt formation reaction system is controlled to be 30-100℃, preferably 50-80℃; and the residence time of the carbonic acid / carbon dioxide salt formation reaction is 4-8 min.

6. The method according to any one of claims 2-5, characterized in that, In step a), the molar ratio of formaldehyde to aniline is 0.25-0.60, preferably 0.35-0.

50.

7. The method according to any one of claims 2 to 6, characterized in that, In step a), after mixing with formaldehyde, the reaction temperature is controlled to be 50-100℃, and the residence time is 10-50 min.

8. The method according to any one of claims 2 to 7, characterized in that, In step b), the reaction temperature is controlled to be 90-150℃, preferably 100-130℃; the reaction pressure is 10-90 barg, preferably 20-65 barg; and the residence time of the rearrangement reaction is 50-200 min, preferably 80-150 min.

9. The method according to any one of claims 2-8, characterized in that, In step c), the reaction pressure is 0.8-2.0 barg, preferably 1.0-1.5 barg; and the reaction temperature is 80-130℃, preferably 90-120℃.

10. The method according to any one of claims 2 to 9, characterized in that, In step d), the mixture containing DAM, aniline, and water is first phase-separated, and then the organic phase after phase separation is distilled under reduced pressure to obtain refined DAM.

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