Method for removing 3-cyanobenzylamine in m-xylylenediamine

Abstract

The invention discloses a method for removing 3-cyanobenzylamine in m-xylylenediamine, which comprises the following steps: pumping a m-xylylenediamine crude product solution containing 3-cyanobenzylamine into a fixed bed reactor, mixing with hydrogen, and carrying out reduction reaction under the action of a nickel-based catalyst to obtain high-purity m-xylylenediamine. According to the method, 3-cyanobenzylamine is reduced and converted into m-xylylenediamine by adopting hydrogen under the selective catalytic action of a nickel-based catalyst; the process is simple, the impurity 3-cyanobenzylamine is effectively removed, the product purity is improved, and the yield of m-xylylenediamine is increased.

Description

Technical Field

[0001] This invention relates to a method for removing 3-cyanobenzylamine from m-phenylenediamine, specifically a method for purifying and removing 3-cyanobenzylamine from m-phenylenediamine. It belongs to the field of m-phenylenediamine purification technology. Background Technology

[0002] m-Xylylenediamine, also known as 1,3-phenylenediamine, m-dimethylaminobenzene, or 1,3-dimethylaminobenzene, is a colorless liquid at room temperature. Its molecular formula is C8H12N2, and its relative molecular weight is 136.19. It is readily soluble in water, ethanol, acetone, chloroform, toluene, and other organic reagents. m-Xylylenediamine is an important chemical raw material, a high-performance and widely used epoxy resin curing agent, and an important fine chemical intermediate. It can be used to synthesize polyurethane, xylene nylon resin, 1,3-di(aminomethyl)cyclohexane, a series of epoxy resins, rubber additives, pesticides, fiber finishing agents, rust inhibitors, chelating agents, lubricants, paper processing agents, and electronic chemicals. It is an important fine petrochemical that urgently needs development in China.

[0003] Industrially, m-phenylenediamine is typically produced from isophthalonitrile using a batch autoclave or continuous fixed-bed hydrogenation process under the action of a catalyst. During the hydrogenation reaction of isophthalonitrile, highly reactive imine intermediates are generated, which readily undergo further polycondensation reactions with intermediates and the target product, producing 3-methylbenzylamine, 3-cyanobenzylamine, m-xylene, secondary amines, tertiary amines, and other high-boiling polymerization byproducts. Industrially, after hydrogenation, evaporation is typically used to remove the solvent and low-boiling byproducts, followed by distillation to remove higher-boiling impurities, yielding high-purity m-phenylenediamine.

[0004] 3-Cyanobenzylamine is a semi-hydrogenation product of isophthalonitrile with a boiling point of 263°C, which is very close to the boiling point of m-phenylenediamine (274°C). It is difficult to separate it using common distillation methods, and its separation is a challenge in the current industrial production of high-quality MXDA in China.

[0005] Patent CN101379021A discloses a method for preparing pure phenylenediamine. This method uses a distillation column with a side feed port. Under conditions of a bottom pressure of 200 mbar or lower and a bottom temperature of 185°C or lower, phenylenediamine is extracted through the side feed port. Low-boiling-point substances such as water, methylbenzylamine, and ammonia are removed through the top. The unevaporated portion at the bottom contains high-boiling-point substances such as amides, amidines, bis-XDA (XDA dimer), and other oligomers. Under these operating conditions, 3-cyanobenzylamine and m-phenylenediamine are both collected at the side feed port, making the separation of 3-cyanobenzylamine impossible.

[0006] Patent CN1849291A discloses a method for preparing and purifying m-phenylenediamine. This method involves removing low-boiling-point substances such as solvents by distillation after hydrogenation, followed by solvent extraction to remove inorganic impurities such as those carried over from the raw materials or catalysts. However, it does not mention methods for removing organic substances with boiling points similar to m-phenylenediamine.

[0007] Patent CN104326920A discloses a method for removing impurities from m-phenylenediamine. This method involves using ammonia gas in a hydrogen atmosphere to react with 3-aminomethylbenzyl alcohol in m-phenylenediamine, converting it into m-phenylenediamine for removal. 3-Aminomethylbenzyl alcohol is a product of the hydrolysis of m-phenylenediamine and can be avoided by drying the raw materials. However, 3-cyanobenzylamine, as a byproduct, cannot be avoided through raw material purification, and there are currently no reports on the separation of this compound. Summary of the Invention

[0008] To address the shortcomings of existing technologies in the purification of intermediate-phenylenediamine, the present invention aims to provide a method for removing 3-cyanobenzylamine from intermediate-phenylenediamine. This method involves pumping an intermediate-phenylenediamine solution containing 3-cyanobenzylamine impurities into a reactor, and using a nickel-based catalyst and selective reduction with hydrogen to completely convert the 3-cyanobenzylamine impurities into intermediate-phenylenediamine, thereby achieving the purpose of removing impurities and purification.

[0009] To achieve the above-mentioned technical objectives, this invention provides a method for removing 3-cyanobenzylamine from m-phenylenediamine. The method involves pumping a crude m-phenylenediamine solution containing 3-cyanobenzylamine into a fixed-bed reactor and mixing it with hydrogen gas. A reduction reaction is then carried out under the action of a nickel-based catalyst to obtain high-purity m-phenylenediamine. The temperature of the reduction reaction is 50–80°C, and the mass hourly space velocity (MSV) of the crude m-phenylenediamine solution is 1–15 h⁻¹. -1 .

[0010] The key to this invention lies in the selective reduction reaction of 3-cyanobenzylamine with hydrogen in the presence of a nickel-based catalyst to convert it into m-phenylenediamine, thus removing impurities and improving the purity of the m-phenylenediamine product. The main reaction in this invention is as follows: First, hydrogen and 3-cyanobenzylamine molecules are adsorbed onto the surface of a nickel-based catalyst. The nickel-based catalyst effectively activates the adsorbed hydrogen molecules, decomposing the molecular hydrogen into two hydrogen atoms. These activated hydrogen atoms have high activity and can react with the adsorbed substrate molecules. The activated hydrogen atoms react with the cyano group of 3-cyanobenzylamine adsorbed on the catalyst surface, gradually hydrogenating and reducing it to an imine (-CH=NH) and then to an amine (-CH2NH2). The reduced product desorbs from the catalyst surface, releasing the final m-phenylenediamine. In this process, the nickel-based catalyst plays a crucial role, not only effectively activating the hydrogen molecules but also providing the necessary surface active centers to facilitate the smooth conversion of the cyano group to the amine. Furthermore, the selective reduction properties of nickel ensure the selective reduction of specific groups, thereby improving the selectivity and yield of the reaction.

[0011] The inventors discovered that the temperature of the reduction reaction directly affects the purity of the product and the effectiveness of removing 3-cyanobenzylamine. If the temperature is too low, 3-cyanobenzylamine cannot be completely converted to m-phenylenediamine; while if the temperature is too high, m-phenylenediamine will undergo heat sensitization and transform into other high-boiling-point impurities. Further preferred temperature is 55–80°C, more preferably 60–80°C.

[0012] The inventors also discovered that the mass hourly space velocity (MHSV) of the crude m-phenylenediamine solution directly affects the removal efficiency. When the MHSV is too high, the reaction of 3-cyanobenzylamine is incomplete; when the MHSV is too low, m-phenylenediamine will undergo further hydrogenation. A further preferred MHSV is 1–10 h. -1 More preferably 4-8h -1 .

[0013] As a preferred embodiment, the pressure of the reduction reaction is 3.0 to 8.0 MPa, more preferably 4.0 to 6.0 MPa.

[0014] As a preferred embodiment, the crude m-phenylenediamine solution is prepared by mixing crude m-phenylenediamine and liquid ammonia at a mass ratio of (10-50):(50-90). If the concentration of crude m-phenylenediamine is too high, the solution viscosity will be too high, easily causing blockage of the inlet and outlet pipelines. A further preferred ratio is (15-40):(60-85), and even more preferred is (20-30):(70-80).

[0015] As a preferred embodiment, the molar ratio of hydrogen to crude m-phenylenediamine solution is (10-50):1, more preferably (10-30):1. When the hydrogen-to-amine ratio is too high, m-phenylenediamine undergoes complete hydrogenation, producing impurities such as 1,3-cyclohexanedimethylamine. When the hydrogen-to-amine ratio is low, the conversion of 3-cyanobenzylamine is incomplete. More preferably, the ratio is (10-20):1.

[0016] As a preferred embodiment, the crude m-phenylenediamine contains 0.1–10 mol% 3-cyanobenzylamine. m-Phenylenediamine is prepared by hydrogenation of isophthalonitrile; the 3-cyanobenzylamine is a byproduct of the isophthalonitrile hydrogenation process.

[0017] As a preferred embodiment, the nickel-based catalyst comprises the active component metallic nickel, an additive, and a support.

[0018] As a preferred embodiment, the additive is selected from at least one of magnesium, iron, copper, zinc, manganese and their oxides, and more preferably magnesium nitrate.

[0019] As a preferred embodiment, the carrier is selected from at least one of alumina, silicon oxide, titanium oxide and zirconium oxide, more preferably alumina and / or silicon oxide, and even more preferably alumina.

[0020] As a preferred embodiment, the nickel-based catalyst is composed of active component metallic nickel, promoter, and support in a mass ratio of (50–80):(20–50):(0.5–15), more preferably (60–70):(30–40):(1.5–10). When the mass ratio of metallic nickel, promoter, and support is within this range, both the catalytic activity of the nickel-based catalyst and the stability of its structure can be guaranteed.

[0021] As a preferred embodiment, the preparation method of the nickel-based catalyst is as follows: adding the auxiliary agent solution to the aqueous solution of the support, precipitating to obtain the modified support, then adding the modified support to the salt solution of metallic nickel and the auxiliary agent solution, stirring vigorously, and then filtering, washing, drying and calcining to obtain the catalyst.

[0022] As a preferred embodiment, the m-phenylenediamine is prepared by hydrogenation of isophthalonitrile.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1) This invention employs a selective reduction method using a nickel-based catalyst, which enables the conversion of 3-cyanobenzylamine to m-phenylenediamine under relatively mild temperature and pressure conditions. Furthermore, due to precise control of the reaction conditions, the formation of byproducts can be minimized. This means that the obtained m-phenylenediamine has high purity, reducing the complexity and cost of subsequent purification steps.

[0025] 2) The preparation process of this invention is simple. Under preferred conditions, 3-cyanobenzylamine can be completely converted into m-phenylenediamine, which improves the purity of the product and increases the yield of m-phenylenediamine. Detailed Implementation

[0026] 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 to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by those skilled in the art without creative effort are still within the scope of protection of the present invention.

[0027] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0028] Catalyst preparation:

[0029] 20.5g of Mg(NO3)2·6H2O was dissolved in 100ml of water, 4g of NaOH was dissolved in 100ml of water, and 1.2g of alumina was placed in 100ml of water. Magnesium nitrate solution and sodium hydroxide solution were simultaneously added dropwise to the alumina solution, and after precipitation, modified alumina support was obtained. 23.2g of Ni(NO3)2·6H2O was dissolved in 100ml of water, 12.7g of Na2CO3 was dissolved in 100ml of water, and 4g of modified alumina was placed in 200ml of water. Nickel nitrate solution and sodium carbonate solution were precipitated simultaneously. The precipitate was filtered, washed, dried, and then subjected to hydrogen space velocity (HHSV) of 800 h⁻¹. -1 The catalyst was obtained by reducing it at 500℃ for 2 hours, followed by passivation with water at room temperature.

[0030] Example 1

[0031] 100 ml of the prepared catalyst was packed into the middle of a 50 mm diameter fixed-bed reactor. The reactor was filled with quartz sand or wire mesh packing material at both ends. After nitrogen purging, the catalyst was activated by continuously exchanging low-pressure hydrogen at 500 °C for 24 h. 700 g of liquid ammonia and 300 g of crude m-phenylenediamine were added to a 2 L stirred tank and stirred until a 30% (w / w) crude m-phenylenediamine-liquid ammonia solution was prepared. The content of 3-cyanobenzylamine in the crude m-phenylenediamine was 3.2 mol%. The reactor temperature was set to 80 °C and the hydrogen pressure to 6 MPa. The crude m-phenylenediamine-liquid ammonia solution was pumped into the reactor using a metering pump, mixing with hydrogen as it passed through the catalyst bed. The mass hourly space velocity (MSV) of the crude m-phenylenediamine solution was 6 h⁻¹. -1The molar ratio of hydrogen to crude m-phenylenediamine solution was 10:1. After the reaction, hydrogen and ammonia were separated by a high-precision separator. The resulting solution was sampled and analyzed by gas chromatography, and the residual amount of 3-cyanobenzylamine was 0%.

[0032] Examples 2-11 are the same as Example 1, using the catalyst prepared in Example 1. Reactions were carried out under different concentrations of crude m-phenylenediamine-liquid ammonia solution, 3-cyanobenzylamine content, reaction temperature, pressure, molar ratio of hydrogen to m-phenylenediamine, and mass hourly space velocity of m-phenylenediamine. 3-Cyanobenzylamine was almost completely converted, with no other byproducts generated. Specific experimental conditions and removal effects are shown in Table 1.

[0033] Comparative Example 1

[0034] The reactor temperature was set at 90°C, and other conditions were the same as in Example 1. After the reaction, samples were taken for gas chromatography analysis. The residual amount of 3-cyanobenzylamine was 0%, and the content of 3-methylbenzylamine increased from 0.2% in the raw material to 0.65%. The m-phenylenediamine underwent a partial deamination side reaction at high temperature.

[0035] Comparative Example 2

[0036] The reactor temperature was set at 110°C, and other conditions were the same as in Example 1. After the reaction, samples were taken for gas chromatography analysis. The residual amount of 3-cyanobenzylamine was 0%, and the content of m-xylene increased from 0.04% in the raw material to 0.43%. The m-phenylenediamine underwent a complete deamination side reaction at high temperature.

[0037] Comparative Example 3

[0038] The mass hourly space velocity of m-phenylenediamine was set to 20 h⁻¹. -1 Other conditions were the same as in Example 1. After the reaction, a sample was taken for gas chromatography analysis. The residual amount of 3-cyanobenzylamine was 0.59%, indicating that 3-cyanobenzylamine did not react completely under high space velocity.

[0039] Comparative Example 4

[0040] The reaction pressure was set to 9 MPa, and other conditions were the same as in Example 1. After the reaction, samples were taken for gas chromatography analysis. The residual amount of 3-cyanobenzylamine was 0.02%, but the content of 3-methylbenzylamine increased by 2.46% from 0.2% in the raw material. A large amount of m-phenylenediamine under high pressure underwent deamination.

[0041] Comparative Example 5

[0042] The reaction pressure was set to 2 MPa, and other conditions were the same as in Example 1. After the reaction, samples were taken for gas chromatography analysis. The residual amount of 3-cyanobenzylamine was 3.12%. Under low pressure, 3-cyanobenzylamine hardly underwent hydrogenation conversion.

[0043] Table 1 shows the experimental conditions and removal effects of comparative examples 1 to 5.

[0044] Table 1

[0045]

[0046] Note: The solution concentration in the table refers to the mass concentration of crude m-phenylenediamine in the crude m-phenylenediamine solution; the hydrogen-amine ratio is the molar ratio of hydrogen to crude m-phenylenediamine in the crude m-phenylenediamine solution.

Claims

1. A method for removing 3-cyanobenzylamine from m-phenylenediamine, characterized in that: A crude m-phenylenediamine solution containing 3-cyanobenzylamine is pumped into a fixed-bed reactor and mixed with hydrogen gas. A reduction reaction is then carried out under the action of a nickel-based catalyst to obtain high-purity m-phenylenediamine. The reduction reaction temperature is 50–80°C, and the mass hourly space velocity (HSV) of the crude m-phenylenediamine solution is 1–15 h⁻¹. -1 .

2. The method for removing 3-cyanobenzylamine from m-phenylenediamine according to claim 1, characterized in that: The pressure of the reduction reaction is 3.0–8.0 MPa.

3. The method for removing 3-cyanobenzylamine from m-phenylenediamine according to claim 2, characterized in that: The crude m-phenylenediamine solution was prepared by mixing crude m-phenylenediamine and liquid ammonia in a mass ratio of (10-50):(50-90).

4. The method for removing 3-cyanobenzylamine from m-phenylenediamine according to claim 3, characterized in that: The molar ratio of hydrogen gas to crude m-phenylenediamine solution is (10-50):

1.

5. A method for removing 3-cyanobenzylamine from m-phenylenediamine according to any one of claims 1 to 4, characterized in that: The crude m-phenylenediamine contains 0.1–10 mol of 3-cyanobenzylamine.

6. The method for removing 3-cyanobenzylamine from m-phenylenediamine according to claim 1, characterized in that: The nickel-based catalyst includes the active component metallic nickel, an additive, and a support.

7. The method for removing 3-cyanobenzylamine from m-phenylenediamine according to claim 6, characterized in that: The additive is selected from at least one of magnesium, iron, copper, zinc, manganese and their oxides.

8. The method for removing 3-cyanobenzylamine from m-phenylenediamine according to claim 6, characterized in that: The carrier is selected from at least one of alumina, silicon dioxide, titanium dioxide, and zirconium oxide.

9. A method for removing 3-cyanobenzylamine from m-phenylenediamine according to claim 7 or 8, characterized in that: The nickel-based catalyst is composed of active component metallic nickel, additives and support in a mass ratio of (50-80):(20-50):(0.5-15).

10. The method for removing 3-cyanobenzylamine from m-phenylenediamine according to claim 9, characterized in that: The preparation method of the nickel-based catalyst is as follows: the auxiliary agent solution is added to the aqueous solution of the support, and the modified support is obtained by precipitation. The modified support is then added to the salt solution of metallic nickel and the auxiliary agent salt solution. After vigorous stirring, the catalyst is filtered, washed, dried and calcined to obtain the final product.

11. The method for removing 3-cyanobenzylamine from m-phenylenediamine according to claim 1, characterized in that: The m-phenylenediamine in the crude m-phenylenediamine solution is prepared by hydrogenation of isophthalonitrile.

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