Method for green synthesis of hexamethylenediamine

Abstract

The invention discloses a green method for synthesizing hexamethylenediamine, which comprises the following steps: by taking adiponitrile and ethanol as solvents as raw materials and taking a porous cobalt-based catalyst and a solid base catalyst which are mixed according to a certain ratio as catalysts, reacting to obtain hexamethylenediamine at the reaction temperature of 70-90 DEG C under the reaction pressure of 2-5MPa H2 and the stirring rotating speed of 500-1000rpm. In the hydrogenation process, the two catalysts are mixed and added according to a certain proportion, and efficient conversion of adiponitrile and high selectivity of hexamethylenediamine can be realized under mild conditions. The catalyst used in the method is simple in preparation process, low in cost and easy to recover, the hexamethylenediamine synthesis process is green, and good economic benefits and application prospects are embodied. The method provided by the invention solves the problem that in the traditional process of synthesizing hexamethylenediamine through adiponitrile hydrogenation, inorganic alkali, such as sodium hydroxide, ammonia water and other strong corrosive additives, needs to be added, so that the conversion efficiency and selectivity are improved, the requirement on equipment is reduced, and meanwhile, the energy consumption of later separation is reduced.

Description

Technical Field

[0001] The invention belongs to the field of hexamethylenediamine synthesis, and particularly relates to a preparation method of a high-efficiency hydrogenation catalyst and a solid base catalyst and applications thereof. Background Art

[0002] Hexamethylenediamine is an important chemical raw material used primarily in the production of key chemicals such as nylon 66, nylon 610, and epoxy resins. It is primarily obtained through the hydrogenation of adiponitrile. To improve conversion efficiency and selectivity of hexamethylenediamine, inorganic bases such as sodium hydroxide, aqueous ammonia, and liquid ammonia are typically added as additives during the adiponitrile hydrogenation process. However, these additives are highly corrosive, requiring high equipment requirements. Furthermore, they dissolve in the reaction solution, complicating subsequent product separation and generating significant amounts of wastewater. Therefore, the development of an alkali-free process for adiponitrile hydrogenation is crucial.

[0003] To replace inorganic bases, patent CN117603161A discloses a method for partially replacing inorganic bases with cycloheximide quaternary ammonium base. However, during use, it still has to be mixed with other inorganic bases or organic bases, which does not fundamentally solve the problem. Patent CN117586130A discloses a method for preparing hexamethylenediamine. Although no inorganic base is added, the reaction solvent is a mixed solvent of liquid ammonia and water, which is still an alkaline solution system. Patent CN116393133B discloses a supported nickel-based catalyst, preparation method and application. Although no inorganic base is used in the reaction system for adiponitrile hydrogenation, the reaction conditions are significantly higher and the performance is weaker than that of commercial alkaline systems. Patent CN104923240B discloses a sepiolite-supported bimetallic nickel-based catalyst, its preparation method, and application. The nickel-based sepiolite-supported catalyst is modified with potassium and lanthanum as additives to increase the catalyst's basic sites, thereby enabling the addition of inorganic bases. However, the catalyst's activity is significantly insufficient, its reaction temperature is relatively high (>100°C), adiponitrile is not fully converted, and the selectivity for hexamethylenediamine is less than 60%. Patent CN107469825B discloses a method for preparing and applying an oxidatively modified carbon nanotube-supported bimetallic copper-magnesium co-doped nickel-based multimetallic catalyst. The introduction of magnesium increases the catalyst's basic sites, enabling an alkali-free process. However, the catalyst's catalytic efficiency is low, failing to meet industrial application requirements. Patent CN115779956B discloses a method for preparing and using an adiponitrile hydrogenation catalyst. The catalyst uses a magnesium-aluminum composite support and is modified with an alkali metal fluoride to increase the basicity of the catalyst. This allows for a higher yield of hexamethylenediamine, but its catalytic efficiency is still not comparable to that of commercial inorganic base systems.

[0004] In view of this, although the development of alkali-free processes has made certain progress, the catalysts developed with solid alkaline sites have limited alkaline sites and lack the degree of matching with the number of hydrogenation sites. The regulation is relatively complex and cannot achieve the high efficiency of inorganic alkaline systems. Therefore, it is particularly important to develop more efficient catalysts and catalysts with adjustable alkaline sites. Summary of the Invention

[0005] The present invention aims to provide a green method for synthesizing hexamethylenediamine, which solves the problems of high equipment requirements and waste liquid generation brought about by traditional inorganic alkali systems, provides a new idea for the development of alkali-free processes, and has important technical value and practical application prospects.

[0006] The technical solution adopted in the present invention is:

[0007] The green method for synthesizing hexamethylenediamine of the present invention comprises the following steps:

[0008] First, a porous cobalt-based catalyst is prepared by a dealloying method, and a super-strong solid base catalyst is prepared by a co-precipitation method. Then, under mild reaction conditions, a certain proportion of the porous cobalt-based catalyst and the solid base catalyst are mixed as the total catalyst, ethanol is used as the solvent, and adiponitrile is hydrogenated to hexamethylenediamine at a reaction temperature of 70-90°C, a reaction pressure of 2-5MPa H2, and a stirring speed of 500-1000rpm. No highly corrosive inorganic base is required during the reaction, and the catalyst can be recycled and reused.

[0009] The preparation process of the porous cobalt-based catalyst includes vacuum melting of a CoFeCrAl alloy, wherein the proportions of the elements in the CoFeCrAl alloy are: Co 10-15%, Fe 0.5-1%, Cr 1-2%, and Al 80-90%; then crushing the alloy into particles of 80-200 mesh; and finally dealloying to produce the porous cobalt-based catalyst, wherein the dealloying is performed using a sodium hydroxide solution with a concentration of 20-30%, a dealloying temperature of 50-80°C, and a dealloying time of 0.5-4 hours.

[0010] The super-strong solid base catalyst is a MgO-SnO2 composite oxide, prepared using a co-precipitation method. MgCl2 and SnCl2 are dissolved in water in a specific ratio, and ammonia is added dropwise as a precipitant to adjust the pH to 10. The reaction is continued for one hour, followed by aging overnight. The precipitate is washed and dried, and then calcined at 500-800°C in an air atmosphere for two hours to obtain the solid base catalyst. The molar ratio of MgCl2 to SnCl2 is 1:1-2:1.

[0011] The porous cobalt-based catalyst has a pore size of 8-12 nm and a specific surface area of ​​20-30 m 2 / g; the strength of the solid superbase is 26.5≤H- <33.0, and the super base content is 0.8-1mmol / g.

[0012] The mixing ratio of the porous cobalt-based catalyst and the solid base catalyst is 2:1 to 1:2.

[0013] The total catalyst proportion of the porous cobalt-based catalyst and the solid base catalyst is 0.5-1 wt%.

[0014] The technical advantages of the present invention are: compared to the inorganic base system of commercial Raney nickel catalysts, the use of solid base instead of soluble inorganic base makes the system non-corrosive, the catalyst recyclable, and the process more environmentally friendly. Furthermore, the matching degree between the number of base sites and the number of hydrogenation sites can be easily adjusted, thereby achieving the dual effects of high conversion efficiency and high hexamethylenediamine selectivity, and having higher catalytic efficiency than traditional systems. The catalyst preparation method involved in the present invention is simple to process and amenable to industrial scale-up production, showing broad application potential in the field of hexamethylenediamine synthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the XRD pattern of the porous cobalt-based catalyst in Example 2.

[0016] Figure 2 This is the XRD pattern of the MgO-SnO2 composite oxide superbase catalyst in Example 6. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is described in detail below with reference to specific embodiments.

[0018] Example 1

[0019] Using various pure metals as raw materials, vacuum melting method is used to melt Co according to atomic ratio. 10 Fe1Cr1Al 88 The alloy is then physically crushed to obtain 80-200 mesh alloy powder; then, the majority of the aluminum is removed by alkali dealloying to form a porous cobalt-based catalyst. The dealloying conditions are: 20% sodium hydroxide, 80°C, 1 hour. Finally, it is washed with pure water until neutral and stored in a water seal to obtain the catalyst, which is labeled as Co-1 catalyst. Its pore size is 11nm and the specific surface area reaches 21m 2 / g.

[0020] Example 2

[0021] Using various pure metals as raw materials, vacuum melting method is used to melt Co according to atomic ratio. 15 Fe 0.5 Cr1Al 83.5The alloy is then physically crushed to obtain 80-200 mesh alloy powder; then, the majority of the aluminum is removed by alkali dealloying to form a porous cobalt-based catalyst. The dealloying conditions are: 20% sodium hydroxide, 80°C, 1 hour. Finally, it is washed with pure water until neutral and stored in a water seal to obtain the catalyst, which is labeled as Co-2 catalyst. Its pore size is 9.6nm and the specific surface area reaches 26m 2 / g. Its crystal phase results are as follows Figure 1 As shown in the figure, only the diffraction peak of Co can be observed, and the intensity is weak.

[0022] Example 3

[0023] Using various pure metals as raw materials, vacuum melting method is used to melt Co according to atomic ratio. 15 Fe 0.5 Cr2Al 82.5 The alloy is then physically crushed to obtain 80-200 mesh alloy powder. Subsequently, the majority of the aluminum is removed by alkali dealloying to form a porous cobalt-based catalyst. The dealloying conditions are: 20% sodium hydroxide, 80°C, 1 hour. Finally, it is washed with pure water until neutral and stored in a water seal to obtain the catalyst, which is labeled as Co-3 catalyst. Its pore size is 9.2nm and the specific surface area reaches 24m 2 / g.

[0024] Example 4

[0025] Using various pure metals as raw materials, vacuum melting method is used to melt Co according to atomic ratio. 15 Fe 0.5 Cr1Al 83.5 The alloy is then physically crushed to obtain 80-200 mesh alloy powder. Subsequently, the majority of the aluminum is removed by alkali dealloying to form a porous cobalt-based catalyst. The dealloying conditions are: 30% sodium hydroxide, 50°C, 0.5h. Finally, it is washed with pure water until neutral and stored in a water seal to obtain the catalyst, which is labeled as Co-4 catalyst. Its pore size is 10.4nm and the specific surface area reaches 22m 2 / g.

[0026] Example 5

[0027] Using various pure metals as raw materials, vacuum melting method is used to melt Co according to atomic ratio. 15 Fe 0.5 Cr1Al 83.5 The alloy is then physically crushed to obtain 80-200 mesh alloy powder; then, the majority of the aluminum is removed by alkali dealloying to form a porous cobalt-based catalyst. The dealloying conditions are: 20% sodium hydroxide, 60°C, 4 hours. Finally, it is washed with pure water until neutral and stored in a water seal to obtain the catalyst, which is labeled as Co-5 catalyst. Its pore size is 9.8nm and the specific surface area reaches 28m2 / g.

[0028] Example 6

[0029] MgCl2 and SnCl4 containing crystal water are used as raw materials with a molar ratio of 1, ammonia water as precipitant, and the pH is adjusted to 10. The reaction is carried out for 1 hour, aged overnight, filtered, washed, and dried, and finally calcined at 600℃ in air for 2 hours to obtain a MgO-SnO2 composite oxide superbase catalyst, which is labeled as MgSn-1 catalyst. The base strength is 26.5≤H - <33.0, the super base content is 0.98mmol / g. Its crystal phase results are as follows Figure 2 As shown in FIG, after calcination, it presents a structure of MgSnO3.

[0030] Example 7

[0031] MgCl2 and SnCl4 containing crystal water are used as raw materials with a molar ratio of 2, ammonia water as precipitant, and the pH is adjusted to 10. The reaction is carried out for 1 hour, aged overnight, filtered, washed, and dried, and finally calcined at 600℃ for 2 hours in an air atmosphere to obtain a MgO-SnO2 composite oxide superbase catalyst, which is labeled as MgSn-2 catalyst. The base strength is 26.5≤H - <33.0, and the super base content is 0.8mmol / g.

[0032] Example 8

[0033] MgCl2 and SnCl4 containing crystal water are used as raw materials with a molar ratio of 1, ammonia water as precipitant, and the pH is adjusted to 10. The reaction is carried out for 1 hour, aged overnight, filtered, washed, and dried, and finally calcined at 800℃ in air for 2 hours to obtain a MgO-SnO2 composite oxide superbase catalyst, which is labeled as MgSn-3 catalyst. The base strength is 26.5≤H - <33.0, and the super base content is 0.86mmol / g.

[0034] Example 9

[0035] The synthesized porous cobalt-based catalyst and MgO-SnO2 solid base catalyst are applied to the adiponitrile hydrogenation reaction, and the ratio of the two catalysts is adjusted to achieve the regulation of conversion rate and selectivity. The adiponitrile hydrogenation reaction conditions are: 33wt% adiponitrile, ethanol as solvent, total catalyst proportion 1wt%, reaction temperature 70-90℃, reaction pressure 2-5MPa H2, and stirring speed 500-1000rpm. Compared with the traditional inorganic alkali process conditions: 33wt% adiponitrile, ethanol as solvent, 6wt% water, Raney nickel catalyst proportion 1wt%, 25wt% (accounting for catalyst dosage) NaOH, reaction temperature 70℃, reaction pressure 2MPa H2, and stirring speed 500rpm. Specific performance comparison is shown in Table 1. The results show that the catalyst system of the present invention still exhibits higher catalytic efficiency even under alkali-free conditions.

[0036] Table 1 Performance comparison of adiponitrile hydrogenation to hexamethylenediamine

[0037] catalyst Reaction conditions Adiponitrile conversion rate (%) Hexamethylenediamine yield (%) Co-1 / MgSn-1=1 70℃, 2MPa, 500rpm, 1.5h 100 86.3 Co-2 / MgSn-1=1 70℃, 2MPa, 500rpm, 1.5h 100 98.6 Co-2 / MgSn-1=2 70℃, 2MPa, 500rpm, 1.5h 100 91.3 Co-2 / MgSn-1=0.5 70℃, 2MPa, 500rpm, 1.5h 100 80.5 Co-3 / MgSn-1=1 70℃, 2MPa, 500rpm, 1.5h 100 90.7 Co-4 / MgSn-1=1 70℃, 2MPa, 500rpm, 1.5h 100 88.4 Co-5 / MgSn-1=1 70℃, 2MPa, 500rpm, 1.5h 100 97.8 Co-2 / MgSn-2=1 70℃, 2MPa, 500rpm, 1.5h 100 79.1 Co-2 / MgSn-3=1 70℃, 2MPa, 500rpm, 1.5h 100 82.6 Commercial Raney Nickel 70℃, 2MPa, 500rpm, 1.5h 97.1 45.2 Co-2 / MgSn-1=1 90℃, 2MPa, 500rpm, 0.5h 100 95.7 Co-2 / MgSn-1=1 70℃, 5MPa, 500rpm, 1h 100 92.3 Co-2 / MgSn-1=1 70℃, 2MPa, 1000rpm, 0.5h 100 98.1

[0038] Example 10

[0039] The synthesized porous cobalt-based catalyst was used in the hydrogenation of adiponitrile with a MgO-SnO2 solid base catalyst (Co-2 / MgSn-1 = 1). The reaction conditions were: 33 wt% adiponitrile, ethanol as the solvent, 1 wt% of the total catalyst, 70°C, 2 MPa H2 pressure, 1000 rpm stirring speed, and 0.5 h. The catalyst's recyclable performance is shown in Table 2. After five cycles, it maintained good catalytic performance.

[0040] Table 2 Catalyst recycling performance

[0041] Number of cycles Adiponitrile conversion rate (%) Hexamethylenediamine yield (%) 1 100 98.1 2 100 97.6 3 100 95.1 4 100 92.6 5 100 91.8

[0042] Based on the above embodiments, the present invention provides a method for the green synthesis of hexamethylenediamine, which is mainly related to the preparation and hydrogenation process of a highly active catalyst, wherein the catalyst comprises a porous cobalt hydrogenation catalyst and a solid base catalyst. During the hydrogenation process, the two catalysts are mixed and added according to a certain proportion. Under mild conditions, efficient conversion of adiponitrile and high selectivity of hexamethylenediamine can be achieved. The present invention adopts a dealloying method to prepare a porous cobalt-based catalyst, and a coprecipitation method to prepare a super-strong solid base catalyst. There is no need to add highly corrosive inorganic alkalis, such as highly corrosive additives such as sodium hydroxide and ammonia, in the reaction, thereby improving conversion efficiency and selectivity, reducing the requirements for equipment, and reducing the energy consumption of later separation. The catalyst preparation process in the method is simple, low in cost, easily recyclable, and the hexamethylenediamine synthesis process is green, reflecting good economic benefits and application prospects.

[0043] It should be further noted that the examples of the above embodiments of the present invention do not cover all combinations of process conditions specified in the technical solution of the present invention. These examples are intended only to facilitate understanding of the technical solution of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, any obvious adjustments and modifications made to the technical solution of the present invention that fall within the technical concept of the present invention are also intended to fall within the scope of protection of the present invention.

Claims

1. A green method for synthesizing hexamethylenediamine, characterized in that: The raw materials are adiponitrile, ethanol is the solvent, and the catalyst is a porous cobalt-based catalyst and a solid base catalyst mixed in a certain proportion. Hexamethylenediamine is obtained after the reaction. The reaction temperature is 70-90°C, the reaction pressure is 2-5MPa H2, and the stirring speed is 500-1000rpm; wherein: The porous cobalt-based catalyst is prepared by vacuum melting to obtain a CoFeCrAl alloy; then crushing the obtained alloy into particles of 80-200 mesh; and finally dealloying to produce the porous cobalt-based catalyst, wherein the dealloying is carried out using a sodium hydroxide solution with a concentration of 20-30%, a dealloying temperature of 50-80°C, and a dealloying time of 0.5-4 hours. The solid superbase is a MgO-SnO2 composite oxide. The preparation process of the solid base catalyst is as follows: MgCl2 and SnCl2 are used as raw materials by a coprecipitation method, dissolved in water according to a certain proportion, and ammonia water is used as a precipitant. Ammonia water is added dropwise to adjust the pH to 10, react for 1 hour, age overnight, wash and dry the precipitate, and then calcine at 500-800°C for 2 hours in an air atmosphere to finally obtain the solid base catalyst.

2. The method according to claim 1, wherein: The mixing ratio of the porous cobalt-based catalyst and the solid base catalyst is 2:1 to 1:

2.

3. The method according to claim 1, wherein: The proportions of each element in the CoFeCrAl alloy are: Co 10-15%, Fe 0.5-1%, Cr 1-2%, and Al 80-90%.

4. The method according to claim 1, wherein: The molar ratio of MgCl2 to SnCl2 is 1:1-2:

1.

5. The method according to claim 1, wherein: The pore size of the porous cobalt-based catalyst is 8-12nm, and the specific surface area reaches 20-30m 2 / g.

6. The method according to claim 1, wherein: The strength of solid superbase is 26.5≤H - <33.0, and the super base content is 0.8-1mmol / g.

7. The method according to claim 1, characterized in that: The total catalyst proportion of the porous cobalt-based catalyst and the solid base catalyst in the reaction is 0.5-1 wt%.

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