A method for preparing hexamethylenediamine by hydrogenation of cyclohexanone and adiponitrile

Abstract

This invention discloses a method for hydrogenating adiponitrile. The method involves quaternizing cyclohexylimine to obtain a quaternary ammonium base, which is then reused as a base auxiliary in the hydrogenation of adiponitrile. Compared to existing hydrogenation processes, this method can reduce the total content of other byproducts, 1,2-cyclohexanediamine (DCH) and dihexyltriamine (BHT), by approximately 50%, thereby improving reaction efficiency.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a cyclohexylimine quaternary ammonium base and its application as an auxiliary agent in the hydrogenation of adiponitrile to prepare hexamethylenediamine. Background Technology

[0002] Hydrogenation of adiponitrile is currently the main route for the preparation of hexamethylenediamine, with the low-pressure method being the mainstream process worldwide due to its mild reaction conditions and low equipment investment. During the low-pressure synthesis of hexamethylenediamine, various byproducts are generated, such as cyclohexylimine (HMI), 1,2-cyclohexanediamine (DCH), and dihexyltriamine (BHT). To reduce the content of these byproducts, inorganic bases such as sodium hydroxide and potassium hydroxide are often added to the Raney catalytic system. Increasing the amount of inorganic base generally reduces the content of these byproducts. However, because inorganic bases cause a series of post-processing problems, such as the need for additional equipment for alkali removal and the need for periodic cleaning of tar from the distillation column, the content of inorganic bases in the reaction system cannot be too high. Therefore, using inorganic bases cannot further reduce the content of byproducts.

[0003] Therefore, new technologies need to be developed to reduce the formation of byproducts such as DCH and BHT during the hydrogenation reaction of adiponitrile. Summary of the Invention

[0004] To address the problem that the byproducts of DCH and BHT cannot be further reduced in existing technologies, the present invention aims to provide a cyclohexylimine quaternary ammonium base. By using this quaternary ammonium base to replace inorganic base additives, the total content of DCH and BHT in the adiponitrile hydrogenation reaction can be reduced by about 50% compared with existing hydrogenation processes, thereby improving reaction efficiency.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0006] First, the present invention provides a cyclohexylimine quaternary ammonium base.

[0007] A method for preparing a cyclohexylimine quaternary ammonium base includes: using cyclohexylimine as a raw material to prepare a cyclohexylimine quaternary ammonium base;

[0008] The cyclohexylimine may be a cyclohexylimine produced as a byproduct of the hydrogenation of adiponitrile;

[0009] The structure of the cyclohexylimine quaternary ammonium base is as follows: R can be a group such as methyl, ethyl, n-propyl, isopropyl, tert-butyl, etc.

[0010] In one specific embodiment of the present invention, the method for preparing the cyclohexylimine quaternary ammonium base includes the following steps:

[0011] S1: A certain amount of cycloheximine, haloalkanes, and sodium alkoxides are dispersed in a solvent and subjected to a reflux reaction;

[0012] S2: The mother liquor obtained from the reflux reaction is cooled, filtered, and concentrated under reduced pressure to obtain a cycloheximine quaternary ammonium base solution.

[0013] Wherein, the haloalkane mentioned in step (S1) can be a monochloro, monobromo, or monoiodide-substituted product of alkanes such as methane, ethane, propane, and isobutane, preferably a monobromo and monoiodide-substituted product;

[0014] The sodium alkoxide can be sodium methoxide, sodium ethoxide, sodium isopropoxide, sodium tert-butoxide, etc., with sodium methoxide and sodium ethoxide being preferred;

[0015] The solvent can be methanol, ethanol, isopropanol, n-butanol, tetrahydrofuran, etc., and preferably isopropanol, n-butanol, etc., which are alcohol solvents with higher boiling points.

[0016] The molar ratio of cycloheximine to haloalkanes is 1:1.7 to 2, preferably 1:1.95 to 2;

[0017] The molar ratio of haloalkanes to sodium alkoxides is 1:1 to 1.1:1;

[0018] The preferred concentration of the substrate cyclohexylimine is 0.5–1 mol / L;

[0019] The reflux reaction temperature is determined by the boiling point of the solvent, and the reaction time is 5 to 24 hours, with the preferred time being 8 to 12 hours.

[0020] In step (S2), the preferred temperature for cooling and filtration is 5–60°C, and the preferred concentration of the cycloheximine quaternary ammonium alkali solution after vacuum concentration is 1–3 mol / L.

[0021] This invention also relates to the application of the above-mentioned cyclohexylimine quaternary ammonium base in the hydrogenation reaction of adiponitrile.

[0022] A method for preparing hexamethylenediamine by hydrogenation of adiponitrile, wherein the raw material is adiponitrile, the catalyst is Raney nickel, and the auxiliary agent is a mixture of cycloheximine quaternary ammonium base and optional other organic or inorganic bases. Other bases may include LiOH, NaOH, KOH, tetramethylammonium hydroxide hydrate, tetraethylammonium hydroxide hydrate, etc., with NaOH and tetramethylammonium hydroxide being preferred.

[0023] The hydrogenation reaction can be carried out using batch or semi-continuous processes, with batch processes being preferred.

[0024] The preferred amount of catalyst relative to adiponitrile is 10–20 wt%.

[0025] The amount of alkali additive (including cycloheximine quaternary ammonium base and other bases) relative to the catalyst is 10-50 wt%; the mass ratio of cycloheximine quaternary ammonium base to other bases is 10-1:1.

[0026] The preferred temperature for hydrogenation reaction is 70–90°C, and the preferred pressure is 2–6 MPa.

[0027] The beneficial effects of this invention are as follows:

[0028] This invention uses hexamethyleneimine quaternary ammonium base to replace inorganic base additives in the hydrogenation reaction of adiponitrile. Compared with existing hydrogenation processes, it can significantly reduce the total content of DCH and BHT, preferably by about 50%, thereby improving reaction efficiency. Detailed Implementation

[0029] To better understand the technical solution of the present invention, the following embodiments will further illustrate the method provided by the present invention. However, the present invention is not limited to the listed embodiments, but should also include any other known modifications within the scope of the claims of the present invention.

[0030] The present invention will be further explained and illustrated below through more specific embodiments, but these do not constitute any limitation.

[0031] Raw material source:

[0032]

[0033]

[0034] The gas chromatographic analysis conditions for the reaction solution components in the following examples were as follows: Agilent DB-5 column, injection port temperature 280°C, FID detector temperature 300°C, column flow rate 1.5 ml / min, hydrogen flow rate 30 ml / min, air flow rate 400 ml / min, and the temperature program was 50°C held for 2 min, then increased to 80°C at 5°C / min, and then increased to 280°C at 15°C / min and held for 10 min.

[0035] Reactor parameters: tube length 1000mm, inner diameter 22mm, wall thickness 5mm, heated by electric heating jacket.

[0036] Example 1

[0037] S1: Preparation of cyclohexylimine quaternary ammonium base.

[0038] 50 g of cycloheximine, 85 g of methyl bromo, and 48 g of sodium methoxide were added to a glass container as substrates and dissolved in 817 g of isopropanol. The mixture was mechanically stirred at 300 rpm and refluxed at 83 °C for 12 h. After the reaction was complete, the mother liquor was cooled to 50 °C and filtered to remove the precipitated sodium bromide. The mother liquor was further concentrated under reduced pressure to obtain 400 mL of an alcoholic solution of cycloheximine quaternary ammonium base with a concentration of 1 mol / L.

[0039] S2: Hydrogenation reaction of adiponitrile.

[0040] 200g adiponitrile, 20g Raney nickel catalyst (wet weight), 13.8mL of cycloheximine quaternary ammonium alkali alcohol solution prepared in S1, and 2g NaOH were added to the reactor for hydrogenation reaction. The reaction conditions were: 90℃, 2MPa. After hydrogen absorption was stopped, the mother liquor was sampled and analyzed. The HMD content was 98.75%, the DCH content was 0.02%, and the BHT content was 1.13%.

[0041] Example 2

[0042] S1: Preparation of cyclohexylimine quaternary ammonium base.

[0043] 50 g of cycloheximine, 142 g of iodomethane, and 68 g of sodium ethoxide were added to a glass container as substrates and dissolved in 740 g of n-butanol. The mixture was mechanically stirred at 300 rpm and refluxed at 118 °C for 8 h. After the reaction, the mother liquor was cooled to 60 °C and filtered to remove the precipitated sodium iodide. The mother liquor was further concentrated under reduced pressure to obtain 147 mL of an alcoholic solution of cycloheximine quaternary ammonium base with a concentration of 3 mol / L.

[0044] S2: Hydrogenation reaction of adiponitrile.

[0045] 300g of adiponitrile, 45g of Raney nickel catalyst (wet weight), 46.3mL of cycloheximine quaternary ammonium alkali alcohol solution prepared in S1, and 2.3g of NaOH were added to the reactor for hydrogenation reaction. The reaction conditions were: 70℃, 6MPa. After hydrogen absorption was stopped, the mother liquor was sampled and analyzed. The HMD content was 98.97%, the DCH content was 0.03%, and the BHT content was 0.91%.

[0046] Example 3

[0047] S1: Preparation of cyclohexylimine quaternary ammonium base.

[0048] 50 g of cycloheximine, 104 g of bromoethane, and 48 g of sodium methoxide were added to a glass container as substrates and dissolved in 798 g of n-butanol. The mixture was mechanically stirred at 300 rpm and refluxed at 118 °C for 12 h. After the reaction, the mother liquor was cooled to 60 °C and filtered to remove the precipitated sodium bromide. The mother liquor was further concentrated under reduced pressure to obtain 218 mL of an alcoholic solution of cycloheximine quaternary ammonium base with a concentration of 2 mol / L.

[0049] S2: Hydrogenation reaction of adiponitrile.

[0050] 250 g of adiponitrile, 50 g of Raney nickel catalyst (wet weight), 25.9 mL of cycloheximine quaternary ammonium alkali alcohol solution prepared in S1, and 1.5 g of NaOH were added to the reactor for hydrogenation reaction. The reaction conditions were: 80 °C, 4 MPa. After hydrogen absorption was stopped, the mother liquor was sampled and analyzed. The HMD content was 98.66%, the DCH content was 0.03%, and the BHT content was 1.18%.

[0051] Comparative Example 1

[0052] Compared with Example 2, the difference of this invention is that the hydrogenation reaction does not involve the addition of a cycloheximine quaternary ammonium base, but only NaOH is added as an auxiliary agent:

[0053] 300g of adiponitrile, 45g of Raney nickel catalyst (wet weight), and 22.7g of NaOH were added to the reactor for hydrogenation. The reaction conditions were 70℃ and 6MPa. After hydrogen absorption was stopped, the mother liquor was sampled and analyzed. The HMD content was 97.25%, the DCH content was 0.08%, and the BHT content was 2.63%.

[0054] Comparative Example 2

[0055] Compared with Example 2, the difference of this invention is that only cycloheximine quaternary ammonium base is added as an auxiliary agent in the hydrogenation reaction:

[0056] 300g of adiponitrile, 45g of Raney nickel catalyst (wet weight), and 52.3mL of the cycloheximine quaternary ammonium base prepared in step 1 of Example 2 were added to the reactor for hydrogenation. The reaction conditions were: 70℃, 6MPa. After hydrogen absorption was stopped, the mother liquor was sampled and analyzed. The HMD content was 98.23%, the DCH content was 0.04%, and the BHT content was 2.21%.

[0057] 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 method for preparing hexamethylenediamine by hydrogenation of adiponitrile, wherein the raw material is adiponitrile, the catalyst is Raney nickel, and the auxiliary agent is a mixture of cycloheximine quaternary ammonium base and other organic or inorganic bases; The structure of the cyclohexylimine quaternary ammonium base is as follows: in, R is selected from methyl, ethyl, n-propyl, isopropyl, and tert-butyl; The other organic or inorganic bases are selected from LiOH, NaOH, KOH, tetramethylammonium hydroxide hydrate, and tetraethylammonium hydroxide hydrate.

2. The method according to claim 1, wherein, The catalyst is used in a relative amount of adiponitrile of 10–20 wt%.

3. The method according to claim 1, wherein, The relative amount of alkali additive to catalyst is 10-50 wt%; the mass ratio of cycloheximine quaternary ammonium base to other bases is 10-1:

1.

4. The method according to any one of claims 1-3, wherein, The hydrogenation reaction temperature is 70–90℃ and the pressure is 2–6 MPa.

5. The method according to claim 1, wherein, The preparation method of the cyclohexylimine quaternary ammonium base includes the following steps: S1: A certain amount of cycloheximine, haloalkanes, and sodium alkoxides are dispersed in a solvent and subjected to a reflux reaction; S2: The mother liquor obtained from the reflux reaction is cooled, filtered, and concentrated under reduced pressure to obtain a cycloheximine quaternary ammonium base solution.

6. The method according to claim 5, wherein, The haloalkane mentioned in step (S1) is a monochloro, monobromine, or monoiodine substituted product of methane, ethane, propane, or isobutane; The molar ratio of cycloheximine to haloalkanes is 1:1.7 to 2.

7. The method according to claim 5, wherein, The sodium alkoxide mentioned in step (S1) is selected from sodium methoxide, sodium ethoxide, sodium isopropoxide, and sodium tert-butoxide; The molar ratio of haloalkanes to sodium alkoxides is 1:1 to 1.1:

1.

8. The method according to claim 5, wherein, The solvent used in step (S1) is selected from methanol, ethanol, isopropanol, n-butanol and tetrahydrofuran.

9. The method according to claim 5, wherein, The reflux reaction time in step (S1) is 5 to 24 hours.

10. The method according to claim 5, wherein, In step (S2), the cooling filtration temperature is 5–60°C; The concentration of the cyclohexylimine quaternary ammonium base solution after vacuum concentration is 1–3 mol / L.

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