A method for continuously producing N,N'-(4,4'-methylene diphenyl) bismaleimide

Abstract

The present application belongs to the field of chemical industry, and particularly relates to a method for preparing bismaleimide by continuously dehydrating and closing a ring in a continuous reactor with N,N'-(4,4'-methylene diphenyl) bismaleimide acid (referred to as BMA) as raw material. The method comprises the following steps: continuously adding a mixture of BMA and flux into a reactor which is sequentially filled with inert fillers and catalysts from top to bottom, and under the atmosphere of inert gas (including nitrogen), the mixture is first melted to form a liquid state when passing through the inert fillers of the reactor, and then enters the catalyst bed layer of the reactor to generate a dehydrating and closing ring reaction to generate BMI. The present application has the technical advantages of simple operation, efficient reaction, less side reaction, and suitability for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering, specifically relating to a method for preparing bismaleimide by continuous dehydration and ring-closure in a continuous reactor using N,N'-(4,4'-methylenediphenyl)bismaleimide acid (BMA) as a raw material. Background Technology

[0002] N,N'-(4,4'-methylenediphenyl)bismaleimide (BMI) is a bifunctional compound containing maleimide functional groups. It combines high temperature resistance, radiation resistance, chemical corrosion resistance, and excellent mechanical properties. It is an important monomer for high-performance thermosetting resins and is widely used in aerospace, electronics, rail transportation, advanced composite materials and other fields. It is one of the key basic materials for achieving lightweight and high temperature resistance of materials.

[0003] Currently, the main methods for synthesizing bismaleimide are: US Patent 4154737A discloses a method for synthesizing maleimide using acetic anhydride dehydration. This method uses maleic anhydride and aromatic diamines (or other primary amines or diamines) as raw materials, and acetone as a solvent to synthesize a maleamic acid intermediate. The maleamic acid intermediate is then used to synthesize maleimide under the action of a dehydrating agent (acetic anhydride) and a metal salt catalyst (such as magnesium salt, lithium salt, manganese(II) salt, or cobalt(II) salt). This acetic anhydride dehydration method has significant drawbacks: it generates a large amount of acidic organic wastewater, solvent recovery is difficult, and the resulting product has poor quality and a wide melting range, leading to high production costs.

[0004] Patent JPH06116235A discloses an azeotropic distillation method for synthesizing bismaleimide. Using maleic anhydride and 4,4'-diaminodiphenylmethane (MDA) as raw materials, and toluene and DMF as a mixed solvent, a bismaleimide acid intermediate is synthesized. This intermediate undergoes a dehydration and ring-closure reaction catalyzed by p-toluenesulfonic acid to generate bismaleimide. After repeated washing, crystallization, filtration, and drying, the target product, bismaleimide, is obtained. The disadvantages of this azeotropic distillation method are: long reaction time, low production efficiency, and difficulty in consistently ensuring product quality.

[0005] The reaction equation is as follows:

[0006] Existing synthesis methods mainly rely on batch reactors, which not only have long reaction times, leading to a decline in product quality, but also cause the acid and metal salt catalysts used to remain in the product. In addition, unreasonable washing processes further affect product quality. All of the above problems indicate that the existing BMI synthesis process has obvious shortcomings. Therefore, there is an urgent need to develop a BMI synthesis method that is simple to operate, highly efficient, has few side reactions, and is suitable for continuous industrial production.

[0007] The existing methods for preparing BMI using BMA as a raw material are as follows: Invention CN119462471A, entitled "A process and system for synthesizing bismaleimide compounds," discloses: S2, closed-loop dehydration reaction: Add polymerization inhibitor and catalyst to the BMA solution obtained in step S1, heat to 110-140℃ and boil, reflux to remove the water generated in the reaction, and the reflux reaction time is 3-6 hours. S3. Recover organic solvents: Spray dry the solution obtained in step S2 to remove the organic solvents from the solution and obtain the crude powder product BMI, while recovering the solvents therein. S4. Hot washing with toluene: Add toluene to the crude BMI obtained in step S3, heat to boiling temperature until most of the powder in the system dissolves, filter while hot to remove the residue generated by the reaction, and collect the filtrate. S5. Cooling and crystallization: Cool the filtrate obtained in step S4, filter the precipitated crystals, and obtain yellow coarse crystals; S6. Alkali washing: The crystals obtained in step S5 are washed with sodium bicarbonate solution and heated to remove the organic acids produced in the side reaction. After cooling, crystallization and filtration, light yellow crystals are obtained. S7. Hot water washing: Wash the crystals obtained in step S6 with hot water until neutral, and filter to obtain light yellow crystals; S8. Drying: The crystals obtained in step S7 are dried to obtain light yellow powdery crystals, which is the product BMI.

[0008] The above reaction is a batch reaction, which also has the disadvantages of long reaction time, high impurities and low yield. In addition, it requires a large amount of solvent, and the solvent needs to be evaporated in the later stage, resulting in high cost. Summary of the Invention

[0009] The problem to be solved by the present invention is to provide a simple and continuous method for preparing N,N'-(4,4'-methylenediphenyl)bismaleimide.

[0010] To address the aforementioned technical problems, this invention provides a method for the continuous preparation of N,N'-(4,4'-methylenediphenyl)bismaleimide (BMI), comprising the following steps: A mixture of BMA and flux is continuously added to a reactor that is filled with inert packing material and catalyst from top to bottom, wherein the mass ratio of flux to BMA is 0.05~0.2:1 (preferably 0.1~0.2:1). In an inert gas (including nitrogen) atmosphere, the mixture is first melted into a liquid state when passing through the inert packing of the reactor, and then enters the catalyst bed of the reactor to undergo a dehydration and closed-loop reaction to generate BMI; The crude BMI obtained from the reaction was post-processed to obtain BMI; BMA is N,N'-(4,4'-methylenediphenyl)bismaleimide acid. BMI is N,N'-(4,4'-methylenediphenyl)bismaleimide.

[0011] Note: Under the action of heating and flux, BMA melts to form a homogeneous liquid.

[0012] As an improvement to the method of the present invention: The feed mass hourly space velocity (HHSV) of the mixture is 3.5~10 h⁻¹. -1 The reaction temperature in the catalyst bed is 130℃~170℃.

[0013] Mass space velocity of the mixture = mass feed rate of the mixture / mass of catalyst.

[0014] The temperature of the inert packing section is 140~170℃.

[0015] As a further improvement to the method of the present invention, the catalyst is prepared by: The support is placed in an acid solution with a mass fraction of 5%~15% and impregnated at a constant temperature of 60~80℃ for 2~4 hours. After filtration, it is dried in an oven at 100~120℃ for 2~3 hours, then calcined at 300~400℃ for 2~3 hours and cooled to room temperature to obtain the catalyst.

[0016] Note: Drying only removes free moisture, while acidic substances remain adsorbed on the support; after calcination, all three acidic substances react chemically with the hydroxyl groups on the support surface, transforming into chemically bonded active functional groups / acid radical sites. Therefore, the final catalyst obtained contains no free acid, only bonded acidic groups, and does not dissolve or contaminate the material during the catalytic process.

[0017] As a further improvement to the method of the present invention: The support is γ-Al2O3 or hydrogen-form silica-alumina molecular sieve; The acid is p-toluenesulfonic acid, phosphoric acid, or sulfuric acid.

[0018] As a further improvement to the method of the present invention: The hydrogen-type silica-alumina molecular sieves are H-ZSM-5, H-Beta, and H-USY.

[0019] The silicon-to-aluminum ratio (SiO2 / Al2O3) is 25-50, and the morphology is spherical (approximately 1 mm in diameter) or strip-shaped (φ1×3-5 mm).

[0020] That is, the catalyst of the present invention is γ-Al2O3 (i.e., γ-Al2O3-) treated with p-toluenesulfonic acid, phosphoric acid, or sulfuric acid.p -TsOH, γ-Al2O3-H3PO4 and γ-Al2O3-H2SO4) or treated hydrogen-type silica-alumina molecular sieves (H-ZSM-5, H-Beta or H-USY, with a silica-alumina ratio of SiO2 / Al2O3 of 25~50), in spherical (1 mm in diameter) or strip-shaped (φ1×3~5 mm).

[0021] As a further improvement to the method of the present invention: The flux is any one of the following: N,N'-(4,4'-methylenediphenyl)bismaleimide (BMI), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), or N-methylpyrrolidone (NMP). The inert packing material is any one of the following: glass packing, ceramic packing, high-temperature resistant plastic packing, or graphite packing.

[0022] As a further improvement to the method of the present invention, the post-processing method for crude BMI product is as follows: The crude BMI product was added to deionized water (appropriate amount of deionized water) and dispersed into powder by wet grinding. After thorough washing with water, BMI was obtained after solid-liquid separation.

[0023] As a further improvement to the method of the present invention: crude BMI is fed into a wet mill, and 2 to 4 times the mass of crude BMI is added to deionized water. The grinding temperature is controlled at 60 to 80°C, and constant temperature wet grinding is performed for 1 to 2 hours (grinding speed is 1000 to 2000 rpm). After grinding, solid-liquid separation is performed. The resulting filter cake is added to 2 to 4 times the mass of crude BMI to deionized water again, and wet grinding is repeated for 1 to 2 hours before solid-liquid separation. The resulting solid material is vacuum dried at 60 to 80°C for 2 to 4 hours to obtain N,N'-(4,4'-methylenediphenyl)bismaleimide (high-purity bismaleimide finished product).

[0024] This invention addresses the shortcomings of existing technologies, such as low reaction efficiency, numerous side reactions, large solvent consumption, and unreasonable washing processes, by providing a method for the continuous synthesis of bismaleimide that is simple to operate, highly efficient, has few side reactions, and is suitable for industrial production.

[0025] In this invention, for a mixture of 100g BMA and an appropriate amount of flux, the reactor can be a reaction tube with an inner diameter of 2cm and a height of 30cm. A 5cm high layer of inert packing is placed in the upper layer of the reaction tube, and a 25cm high layer of catalyst is placed in the lower layer. The feeding rate of the feeder is controlled to be 200~500g / h.

[0026] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in: 1) The reaction time is significantly shortened and energy consumption is significantly reduced.

[0027] 2) The catalyst is supported on γ-Al2O3 and molecular sieves and will not enter the product, so it will not affect the purity and quality of the product.

[0028] Conventional reactions use acids (such as phosphoric acid and sulfuric acid) and metal salts (such as sodium acetate). Some of the catalyst enters the reaction solution and is carried into the product, which will cause a decline in product quality.

[0029] 3) The short residence time of raw materials and products at high temperatures can effectively suppress side reactions.

[0030] In contrast, batch reactors, where raw materials and products exist at high temperatures for extended periods, will produce more byproducts and decrease yield and product quality because both raw materials and products undergo polymerization reactions.

[0031] 4) It requires less flux, is environmentally friendly, easy to operate, has a high yield, and is low in cost.

[0032] 5) The constant-temperature wet grinding and washing process ensures more thorough washing, effectively removing residual impurities (reaction byproducts) and improving product purity and quality, resulting in excellent product stability. Furthermore, due to the low solvent consumption, less wastewater is generated, contributing to low cost.

[0033] Existing washing methods mainly involve water washing, which generates a large amount of wastewater through repeated washing. Furthermore, the impurities encapsulated in the solids of the product cannot be washed away, resulting in low product content. Attached Figure Description

[0034] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0035] Figure 1 This is a schematic diagram of a BMI synthesis device. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto: Example 1: An apparatus for continuous preparation of BMI, such as... Figure 1 As shown, it includes: a reactor, a collection bottle, a feeder assembly (including a solid hopper, a gas pipe and a solid pusher), heaters H1 and H2, valves Q1 and Q2, inert packing, a catalyst, an insulation layer and a cooling tank.

[0037] The feeder assembly includes a solid hopper with a stopper with valve Q1 at the top opening. The side wall opening of the solid hopper is connected to the gas inlet of the three-way pipe via a gas pipe (sealed connection). The bottom opening of the solid hopper is connected to the solid inlet of the three-way pipe. A solid pusher is installed in the solid inlet pipe. The outlet of the three-way pipe is connected to the top inlet of the reaction tube.

[0038] The inside of the reaction tube is filled with inert packing and catalyst sequentially from top to bottom (i.e., from inlet to outlet).

[0039] A heating device H1 is installed on the outer wall of the reaction tube corresponding to the inert packing. The function of the heating device H1 is to control the temperature of the inert packing section so that the BMA can melt. A heating device H2 is installed on the outer wall of the reaction tube corresponding to the catalyst. The function of the heating device H2 is to control the reaction temperature.

[0040] An insulation layer is installed on the outermost periphery of the entire reaction tube (i.e., heating devices H1 and H2 are located between the outer wall of the reaction tube and the insulation layer).

[0041] The bottom outlet of the reaction tube is connected to the collection bottle, which is equipped with valve Q2 and is placed in the cooling tank.

[0042] The reaction process of this invention: A mixture of BMA and flux is added to the solid hopper. Nitrogen valve Q1 is opened, and the temperature of the inert packing section is controlled by heater H1 to allow BMA to melt. The temperature of the catalyst section is controlled by heater H2 to the set reaction temperature. The feeder assembly is turned on, and the mixture is continuously and stably fed into the reaction tube under the action of the solid pusher. After the mixture is heated to a molten state in the inert packing section, it enters the catalyst section. BMA undergoes a dehydration and closed-loop reaction to generate BMI. The reaction product and the water generated in the reaction are continuously discharged from the reactor and enter the collection bottle to form crude BMI.

[0043] The specific work process is as follows: S1. Inert packing and catalyst are sequentially filled inside the reaction tube from top to bottom (i.e., from inlet to outlet); then the outlet of the three-way pipe is sealed to the top inlet of the reaction tube.

[0044] Open the bottle stopper and add a mixture of N,N'-(4,4'-methylenediphenyl)bismaleimide (BMA) and flux into the solids hopper; Open valve Q1, and nitrogen gas enters the reaction tube through the gas pipe and the three-way pipe, thereby venting the air in the reaction tube; throughout the entire reaction process, nitrogen gas is always in working condition, the purpose of which is to ensure that the reaction is carried out under nitrogen protection.

[0045] S2. Start the heating device H1 to make the temperature of the inert filler section 140~170℃, so that BMA can melt. Start the heating device H2 to control the reaction temperature corresponding to the catalyst section; S3. Start the solid pusher. The mixture of BMA and flux enters the reaction tube through the outlet of the three-way pipe under the action of the solid pusher.

[0046] After the mixture is heated to a molten state in the inert packing section, it enters the catalyst section, where BMA undergoes a dehydration and ring-closing reaction to generate BMI. The reaction product and the water generated in the reaction are continuously discharged from the reactor and enter a collection bottle to form crude BMI.

[0047] Note: The solid pusher is a conventional sealed screw-type feeding mechanism. The rotation of the screw pushes the mixed material in the solid hopper.

[0048] S4. Place the crude BMI product in the collection bottle into a wet mill, add 2-4 times the mass of the crude BMI product in deionized water, control the grinding temperature at 60-80℃, and perform constant temperature wet milling for 1-2 hours (grinding speed at 1000-2000 rpm). After milling, perform solid-liquid separation, add 2-4 times the mass of the crude BMI product in deionized water to the obtained filter cake again, repeat wet milling for 1-2 hours and filter; place the obtained solid material in a vacuum oven and vacuum dry at 60-80℃ for 2-4 hours to finally obtain high-purity bismaleimide product.

[0049] Note: The fluxes N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP) are all soluble in water.

[0050] Catalyst preparation examples The preparation method of catalyst T-1 is as follows: γ-Al2O3 (as support) is placed in a 10% p-toluenesulfonic acid aqueous solution (as treatment solution), and impregnated at 70℃ for 3h. After filtration, it is dried in an oven at 110℃ for 2.5h, then calcined at 350℃ for 2.5h, and cooled to room temperature to obtain catalyst T-1.

[0051] Note: It is necessary to ensure that the carrier remains submerged in the treatment solution after the impregnation is completed.

[0052] Compared to the preparation method of catalyst T-1, by changing the catalyst treatment conditions (support, treatment solution, impregnation temperature and time, drying temperature and time, calcination temperature and time), the catalysts shown in Table 1 were obtained accordingly.

[0053] Table 1

[0054] Note: The morphology of γ-Al2O3 or hydrogen-type silica-alumina molecular sieves is spherical (1 mm in diameter). The silica-alumina ratio of H-ZSM-5 and H-Beta is 25.

[0055] Example 1:

[0056] The reactor is a reaction tube with an inner diameter of 2cm and a height of 30cm. A 5cm high ceramic packing is placed in the upper layer of the reaction tube and a 25cm high catalyst T-1 is placed in the lower layer. A mixture of 100g BMA and 10g DMAC (which has been mixed evenly before being added) is added to the feeder. The nitrogen valve Q1 is opened and the nitrogen flow rate is controlled to be about 100ml / min.

[0057] Turn on heating devices H1 and H2 to raise the temperature of the inert packing section to approximately 150°C (T1, °C) and the temperature of the catalyst section to approximately 150°C (T2, °C). Turn on the feeder assembly and adjust the feed rate of the feeder assembly to 350 g / h (w, g / h). Continue working for a certain period of time until no more material flows out from the lower end of the reaction tube. Turn off heating devices H1 and H2 and turn off the nitrogen gas. The experiment is now complete.

[0058] Post-processing: The crude BMI product in the collection bottle was put into a wet mill, 300g of deionized water was added, and the milling temperature was controlled at 70℃. The mixture was wet milled at a constant temperature for 1.5h. After milling, solid-liquid separation was performed. The resulting filter cake was put back into the wet mill, 300g of deionized water was added, and the wet milling was repeated for 1.5h and then filtered. The resulting solid material was placed in a vacuum oven and vacuum dried at 80℃ for 3h. The molar yield (y,%) was 96.0% and the purity was 99.1% (HPLC).

[0059] Product molar yield = (number of moles of BMI obtained) / (number of moles of BMA added) × 100%.

[0060] Examples 2-14: The amount of BMA used remained constant at 100g. The types of catalysts, the feed rate of the feeder (w, g / h), the type and mass of the flux (m, g), the temperature of the inert packing section (T1, ℃), and the temperature of the catalyst section (T2, ℃) were changed, while the rest remained the same as in Example 1. Specific process parameters are shown in Table 2 below; the results are also shown in Table 2 below.

[0061] Table 2

[0062] Note: The feed mass hourly velocity of the mixture corresponding to Example 1 is approximately 6.4.

[0063] Comparative Examples 1-9: The amount of BMA remained constant at 100g; only the type of catalyst, the feed rate of the feeder (w, g / h), the type and mass of the flux (m, g), the temperature of the inert packing section (T1, °C), and the temperature of the catalyst section (T2, °C) were changed, while the rest were the same as in Example 1. Specific process parameters are shown in Table 3 below; the results are also shown in Table 3 below.

[0064] Table 3

[0065] Note: The temperature of the inert packing section in Comparative Example 6 was too high. When passing through the inert packing, more impurities were generated by the BMA reaction (the probability of BMA self-polymerization and decomposition increased), resulting in a decrease in yield.

[0066] Comparative Example 10: The amount of water used in each post-treatment was changed to 100g, while the rest remained the same as in Example 1. The results were: yield 97.7% and purity 96.2% (HPLC).

[0067] The amount of water used in each post-treatment was changed to 600g, while the rest remained the same as in Example 1. The results were: yield 95.9% and purity 99.0% (HPLC).

[0068] Comparative Example 11: The grinding temperature in the post-processing was changed to 40°C, and the rest was the same as in Example 1. The results were: yield 98.4% and purity 95.2% (HPLC).

[0069] Comparative Example 12: The post-processing grinding time was changed to 0.5 h, and the rest was the same as in Example 1. The results were: yield 98.1% and purity 95.5% (HPLC).

[0070] The post-processing grinding time was changed to 3 hours, and the rest was the same as in Example 1. The results were: yield 95.8% and purity 99.0% (HPLC).

[0071] Comparative Example 13: 100g BMA, 500g toluene, 10g DMAC and 5g p-toluenesulfonic acid were added to a 1L three-necked flask. The mixture was heated to reflux and subjected to azeotropic distillation to remove water. The reaction was carried out for 8 hours. The experiment was stopped and the solvent (toluene) was distilled off to obtain crude BMI. The crude BMI was post-processed according to the method in Example 1. The results were: yield of 80.5% and purity of 99.0% (HPLC).

[0072] Finally, it should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the content disclosed in this invention should be considered within the scope of protection of this invention.

Claims

1. A method for the continuous preparation of N,N'-(4,4'-methylenediphenyl)bismaleimide, characterized in that... Includes the following steps: A mixture of BMA and flux is continuously added to a reactor that is sequentially filled with inert packing and catalyst from top to bottom, with the mass ratio of flux to BMA being 0.05~0.2:1; In an inert gas atmosphere, the mixture is first melted into a liquid state when passing through the inert packing of the reactor, and then enters the catalyst bed of the reactor to undergo a dehydration and closed-loop reaction to generate BMI; The crude BMI obtained from the reaction was post-processed to obtain BMI; BMA is N,N'-(4,4'-methylenediphenyl)bismaleimide acid. BMI is N,N'-(4,4'-methylenediphenyl)bismaleimide.

2. The method according to claim 1, characterized in that: The feed mass hourly space velocity (HHSV) of the mixture is 3.5~10 h⁻¹. -1 The reaction temperature in the catalyst bed is 130℃~170℃.

3. The method according to claim 2, characterized in that... The catalyst is prepared by: The support is placed in an acid solution with a mass fraction of 5%~15% and impregnated at a constant temperature of 60~80℃ for 2~4 hours. After filtration, it is dried in an oven at 100~120℃ for 2~3 hours, then calcined at 300~400℃ for 2~3 hours and cooled to room temperature to obtain the catalyst.

4. The method according to claim 3, characterized in that: The support is γ-Al2O3 or hydrogen-form silica-alumina molecular sieve; The acid is p-toluenesulfonic acid, phosphoric acid, or sulfuric acid.

5. The method according to claim 4, characterized in that: The hydrogen-type silica-alumina molecular sieves are H-ZSM-5, H-Beta, and H-USY.

6. The method according to claim 5, characterized in that: The flux is any one of the following: N,N'-(4,4'-methylenediphenyl)bismaleimide, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, or N-methylpyrrolidone. The inert packing material is any one of the following: glass packing, ceramic packing, high-temperature resistant plastic packing, or graphite packing.

7. The method according to any one of claims 1 to 6, characterized in that... The post-processing method for BMI crude products is as follows: The crude BMI product was dispersed into powder by wet milling and thoroughly washed with water. After solid-liquid separation, BMI was obtained.

8. The method according to claim 7, characterized in that: The crude BMI product was fed into a wet mill, and 2-4 times the mass of the crude BMI product was added with deionized water. The grinding temperature was controlled at 60-80℃, and the product was wet-milled at a constant temperature for 1-2 hours. After grinding, solid-liquid separation was performed. The resulting filter cake was then added to 2-4 times the mass of the crude BMI product with deionized water, and the wet milling was repeated for 1-2 hours, followed by solid-liquid separation. The resulting solid material was vacuum-dried at 60-80℃ for 2-4 hours to obtain N,N'-(4,4'-methylenediphenyl)bismaleimide.

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