Process for the preparation of a high trans 1,4-cyclohexanediamine

Abstract

The application discloses a preparation method of 1,4-cyclohexanediamine with high trans / cis ratio. The method uses 1,4-phenylenediamine as a raw material and an ether compound as a solvent, and through adding a proper amount of benzene and / or a monosubstituted alkylbenzene compound under the action of a metal-supported catalyst, the proportion of the trans body of 1,4-CHDA can be effectively increased in the hydrogenation process of 1,4-PDA, meanwhile, the high selectivity of 1,4-CHDA is maintained, and the application performance of the product in polyurethane is improved.

Description

Technical Field

[0001] This invention relates to a method for hydrogenating 1,4-PDA, and more particularly to a method for preparing 1,4-CHDA with a high trans-cis ratio, belonging to the field of amine compound synthesis. Background Technology

[0002] 1,4-CHDA is an important intermediate in the polyurethane industry. It has excellent light and air stability and can be widely used in the preparation of polyamide resins and aliphatic polyurethanes.

[0003] 1,4-CHDA can be synthesized by hydrogenation of 1,4-PDA. Due to the presence of a cyclohexyl group in its molecular structure, it has two stereoisomers: cis and trans. Numerous studies have found that polyurethane or polyamide products prepared using the trans-isomer of 1,4-CHDA exhibit better elasticity, heat resistance, and stability compared to the cis-isomer. Currently, commercially available 1,4-CHDA products contain approximately 60-80% cis-isomer and 20-40% trans-isomer. Because the two stereoisomers in 1,4-CHDA have similar boiling points, they are difficult to separate through distillation. Furthermore, the cis-isomer generated during the hydrogenation of 1,4-PDA further increases the production cost of 1,4-CHDA products. Therefore, effectively increasing the proportion of trans-isomers during the hydrogenation process of 1,4-PDA has become a key research focus for researchers.

[0004]

[0005] CN102690204B uses o-phenylenediamine, m-phenylenediamine, or p-phenylenediamine as raw materials, and isopropanol aqueous solution or tetrahydrofuran aqueous solution as solvent. It reacts with ammonia, hydrogen, sodium nitrite, and catalyst in a slurry bed reactor, achieving a phenylenediamine conversion rate of over 99% and a cyclohexanediamine selectivity of up to 96.8%. However, it does not mention the control of the ratio of the two cis-trans isomers in 1,4-CHDA.

[0006] Su Chengyan et al. [Study on the synthesis of CHDA by catalytic hydrogenation of PDA and purification process of trans-CHDA [D]. Xiamen University. 2007] used a 5% Ru / C catalyst activated at 500℃ and treated with alkali. In isopropanol solvent, the reaction temperature was 140℃, the reaction pressure was 8MPa, and the reaction time was 20min. With the help of composite sodium salt, the conversion rate of p-phenylenediamine was close to 100%, and the selectivity of 1,4-CHDA reached 90%. However, the amount of catalyst used was 18.5% of the raw material, and it could only be recycled 3 times. Therefore, the catalyst cost was very high, which limited its industrial application.

[0007] The literature [ChemCatChem, 2013, vol. 5, #10, pp. 2905-2912] reports the preparation of 1,4-CHDA from 1,4-cyclohexanediol as a starting material via a reaction in a sealed container at 170°C with a catalyst of dodecacarbonyltriruthenium, a ligand of 4,5-bis(diisopropylphosphinomethyl)acridine, ammonia, and a solvent of tert-butanol, achieving a trans ratio as high as 64.4%. However, the ligand is expensive, and the starting material 1,4-cyclohexanediol lacks a price advantage, making it unsuitable for industrial-scale production. Summary of the Invention

[0008] To address the aforementioned problems in the existing technology, this invention provides a method for preparing high trans-cis 1,4-cyclohexanediamine. This method can effectively increase the 1,4-CHDA trans-cis ratio to above 4:1, while maintaining a 1,4-PDA conversion rate close to 100% and a 1,4-CHDA selectivity of above 98%, thereby improving the product's application performance in polyurethane.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] This invention provides a method for preparing high CHDA reverse-cis ratio, comprising the following steps:

[0011] 1,4-CHDA was prepared by hydrogenation reaction using 1,4-PDA as the reactant and ether compounds as the solvent, with the addition of benzene and / or monosubstituted alkylbenzenes, under the action of a metal-supported catalyst.

[0012] In this invention, the benzene and / or monosubstituted alkylbenzene includes one or more of benzene, toluene, ethylbenzene, and cumene, preferably benzene and / or toluene. The molar amount of the benzene or monosubstituted alkylbenzene added is 0.1-1.0 times the molar amount of 1,4-PDA, preferably 0.2-0.5 times.

[0013] In this invention, the active metal of the metal-supported catalyst includes one or more of Ru, Rh, Ni, Pt, and Pd. The catalyst support is one or more of diatomaceous earth, alumina, activated carbon, lithium aluminate, and zirconium oxide. The active metal content in the metal-supported catalyst is 1-10 wt%, preferably 3-5 wt%, calculated based on the total weight of the metal-supported catalyst.

[0014] As a preferred embodiment, the amount of the metal-supported catalyst is 1-10 wt% of the mass of 1,4-PDA, preferably 3-6 wt%.

[0015] In this invention, the ether compound is selected from one or more of tetrahydrofuran, 1,4-dioxane, methyl ether, diethyl ether and methyl tert-butyl ether, preferably tetrahydrofuran and / or 1,4-dioxane.

[0016] As a preferred embodiment, the mass ratio of 1,4-PDA to solvent is 0.03-0.3, preferably 0.1-0.15.

[0017] In this invention, there are no special requirements for the reaction conditions involved in the hydrogenation reaction process. Those skilled in the art can screen the conditions as needed using existing disclosed methods. For example, the hydrogenation reaction temperature is 100-190℃, such as 100℃, 130℃, 160℃, or 190℃, preferably 110-130℃.

[0018] Preferably, the hydrogenation reaction is carried out at a pressure of 3-15 MPaA, such as 3 MPaA, 5 MPaA, 7 MPaA, 9 MPaA, 11 MPaA, 13 MPaA, or 15 MPaA, and more preferably 5-10 MPaA; specifically, the reaction pressure can be controlled by the amount of hydrogen introduced.

[0019] Preferably, when the hydrogen supply is stopped, the pressure drop of the hydrogen consumed in the reaction is less than 0.01 MPa / min, such as 0.009 MPa / min, 0.008 MPa / min, 0.007 MPa / min, 0.005 MPa / min, etc., at which point the reaction is complete and the hydrogenation reaction ends.

[0020] In this invention, the reactor used in the method is an intermittent high-pressure reactor equipped with a catalyst filtration device; preferably, the catalyst filtration device is an internal filter or an external filter, more preferably an internal filter of the high-pressure reactor.

[0021] In this invention, after the hydrogenation reaction is completed, the metal-supported catalyst can be recycled. Specifically, the metal-supported catalyst is separated and recovered by conventional means such as filtration, and there are no special requirements in this invention. Preferably, the catalyst separation method is as follows: when the temperature of the reaction liquid drops to 50°C or below, N2 with a concentration not exceeding 0.6 MPaA is used to separate the product liquid from the catalyst through an in-reactor catalyst filtration device.

[0022] According to the method of the present invention, the ratio of 1,4-CHDA transcis to 1,4-PDA is greater than 4:1, while the conversion rate of 1,4-PDA is close to 100%, and the selectivity of 1,4-CHDA is greater than 98%.

[0023] The trans-propion of 1,4-CHDA is a thermodynamically stable product. To obtain a higher content of the trans-propion, traditional 1,4-PDA hydrogenation methods employ higher reaction temperatures, which favor the conversion of cis-1,4-CHDA to trans-1,4-CHDA. However, when the 1,4-CHDA trans-cis ratio reaches 4:6, further increasing the reaction temperature to increase the trans-propion content will cause 1,4-CHDA to undergo ammonolysis polymerization, forming a large amount of heavy component tar, thus significantly reducing the selectivity of 1,4-CHDA.

[0024] Compared with existing technologies, the positive effect of the method of this invention lies in the addition of an appropriate amount of benzene or monosubstituted alkylbenzene to the 1,4-PDA hydrogenation reaction system. Due to the electron-donating effect of the alkyl substituent and the low steric hindrance of benzene, benzene or monosubstituted alkylbenzene exhibits higher hydrogenation reactivity than 1,4-PDA. Therefore, at a lower reaction temperature, benzene or monosubstituted alkylbenzene preferentially adsorbs onto the catalyst surface and undergoes hydrogenation, while the large amount of heat generated causes a significant increase in the hot spot temperature on the catalyst surface. At this time, 1,4-PDA enters the high-temperature active region of the catalyst to undergo hydrogenation, which is beneficial to increasing the trans-isomer content in 1,4-CHDA. During this reaction, the liquid phase temperature of the reaction system does not change, but the hot spot temperature on the catalyst surface rises rapidly. Therefore, it is possible to complete the conversion of high-content trans-isomer 1,4-CHDA at a lower liquid phase temperature, while avoiding the generation of a large amount of ammonolytic polymerization tar at high liquid phase temperatures, which would coat the catalyst surface and cause a decrease in activity. This maintains high selectivity for 1,4-CHDA and greatly reduces production costs.

[0025] It is worth noting that the amount of benzene or monosubstituted alkylbenzene added should be 0.1-1.0 times, preferably 0.2-0.5 times, the molar amount of 1,4-PDA. Adding amounts exceeding the range described herein will actually reduce the selectivity of 1,4-CHDA. This is mainly because when the content of benzene or monosubstituted alkylbenzene compounds in the reaction system exceeds the standard, their strong hydrogenation reactivity will cause hydrogen deficiency in the 1,4-PDA reaction, thereby forming unsaturated Schiff base intermediate compounds, which then undergo intermolecular condensation to form heavy component tar, resulting in a decrease in the selectivity of 1,4-CHDA. Detailed Implementation

[0026] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the listed embodiments.

[0027] The main raw materials used in the various embodiments and comparative examples of this invention are sourced as follows. Unless otherwise specified, other raw materials and reagents were obtained through commercially available channels:

[0028] 5 wt% Ru / C and 3 wt% Rh / Al2O3 were purchased from Johnson Matthey.

[0029] Tetrahydrofuran and 1,4-dioxane were purchased from Comio Biosciences, analytical grade;

[0030] 1,4-PDA was purchased from Acros Reagents, with a purity greater than 99%.

[0031] Benzene, toluene, and p-xylene were purchased from Aladdin Reagent Company, with a purity greater than 99%.

[0032] The main equipment information is as follows:

[0033] Test Method: The gas chromatography analysis conditions in the following examples were as follows: an Agilent 7890 and DB-5 column were used, the injector temperature was 280℃, and the detector temperature was 300℃. The temperature program was as follows: initial column temperature 50℃, held for 2 min; temperature increased to 80℃ at 5℃ / min, held for 0 min; temperature increased to 300℃ at 15℃ / min, held for 15 min. The content of each component was determined by normalization.

[0034] Example 1

[0035] In a high-pressure reactor, 0.65 g of 5 wt% Ru / C catalyst, 21.6 g of 1,4-PDA, 216 g of THF, and 3.12 g of benzene were added. After the reactor passed leak testing, it was purged three times with 1 MPaA of N2, followed by three times with 1 MPaA of H2. The temperature was raised to 110℃. During the reaction, H2 was continuously introduced into the reactor through a hydrogen flow controller to maintain the reaction pressure at 3 MPaA. When the hydrogen flow rate reading of the hydrogen flow controller was lower than 100 sccm, the H2 supply was stopped. When the pressure drop in the reactor was less than 0.01 MPa / min, the reaction was stopped, the reactor was cooled and depressurized, and the reaction liquid was filtered out for gas chromatography analysis.

[0036] Example 2

[0037] In a high-pressure reactor, 1.3 g of 3 wt% Rh / Al₂O₃ catalyst, 21.6 g of 1,4-PDA, 144 g of 1,4-dioxane, and 9.2 g of toluene were added. After the reactor passed leak testing, it was purged three times with 1 MPaA of N₂, followed by three times with 1 MPaA of H₂. The temperature was raised to 130°C. During the reaction, H₂ was continuously introduced into the reactor through a hydrogen flow controller to maintain the reaction pressure at 10 MPaA. When the hydrogen flow rate reading of the hydrogen flow controller dropped below 100 sccm, the H₂ supply was stopped. When the pressure drop in the reactor was less than 0.01 MPa / min, the reaction was stopped, the reactor was cooled and depressurized, and the reaction liquid was filtered out for gas chromatography analysis.

[0038] Example 3

[0039] In a high-pressure reactor, 2.16 g of 5 wt% Ru / C catalyst, 21.6 g of 1,4-PDA, 72 g of 1,4-dioxane, and 18.4 g of toluene were added. After the reactor passed leak testing, it was purged three times with 1 MPaA of N2, followed by three times with 1 MPaA of H2. The temperature was raised to 160℃. During the reaction, H2 was continuously introduced into the reactor through a hydrogen flow controller to maintain the reaction pressure at 10 MPaA. When the hydrogen flow rate reading of the hydrogen flow controller dropped below 100 sccm, the H2 supply was stopped. When the pressure drop in the reactor was less than 0.01 MPa / min, the reaction was stopped, the reactor was cooled and depressurized, and the reaction liquid was filtered out for gas chromatography analysis.

[0040] Example 4

[0041] In a high-pressure reactor, 0.22 g of 3wt% Rh / Al₂O₃ catalyst, 21.6 g of 1,4-PDA, 720 g of THF, and 3.12 g of benzene were added. After the reactor passed leak testing, it was purged three times with 1 MPaA of N₂, followed by three times with 1 MPaA of H₂. The temperature was raised to 100℃. During the reaction, H₂ was continuously introduced into the reactor through a hydrogen flow controller to maintain the reaction pressure at 4 MPaA. When the hydrogen flow rate reading of the hydrogen flow controller dropped below 100 sccm, the H₂ supply was stopped. When the pressure drop in the reactor was less than 0.01 MPa / min, the reaction was stopped, the reactor was cooled and depressurized, and the reaction liquid was filtered out for gas chromatography analysis.

[0042] Comparative Example 1

[0043] Except for the absence of benzene, the rest is the same as in Example 1.

[0044] Comparative Example 2

[0045] Except for the absence of toluene, the process is the same as in Example 2.

[0046] Comparative Example 3

[0047] Except for the addition of 21.2g of p-xylene instead of toluene, the rest is the same as in Example 3.

[0048] Comparative Example 4

[0049] Except for increasing the amount of benzene added to 31.2g, the rest is the same as in Example 4.

[0050] The results of the examples and comparative examples are shown in Table 1.

[0051] Table 1 Results of Examples and Comparative Examples

[0052] 1,4-PDA conversion rate / % 1,4-CHDA selectivity / % anti-common Example 1 100 99.5 93:7 Example 2 100 98.9 91:9 Example 3 100 98.1 88:12 Example 4 100 98.3 85:15 Comparative Example 1 100 95.2 42:58 Comparative Example 2 100 94.3 45:55 Comparative Example 3 100 91.1 51:49 Comparative Example 4 100 81.2 61:39

Claims

1. A method for preparing a high trans-cis ratio 1,4-cyclohexanediamine, comprising the following steps: 1,4-cyclohexanediamine is prepared by hydrogenation reaction using 1,4-phenylenediamine as the reactant and an ether compound as the solvent, with the addition of benzene and / or monosubstituted alkylbenzenes, under the action of a metal-supported catalyst; the molar amount of benzene and / or monosubstituted alkylbenzenes added is 0.1-1.0 times the molar amount of 1,4-phenylenediamine; the benzene and / or monosubstituted alkylbenzenes are selected from one or more of benzene, toluene, ethylbenzene and cumene.

2. The method according to claim 1, characterized in that, The molar amount of benzene and / or monosubstituted alkylbenzene added is 0.2-0.5 times the molar amount of 1,4-phenylenediamine.

3. The method according to claim 1, characterized in that, The active metal of the metal-supported catalyst includes one or more of Ru, Rh, Ni, Pt, and Pd; the catalyst support is one or more of diatomaceous earth, alumina, activated carbon, lithium aluminate, and zirconium oxide.

4. The method according to claim 3, characterized in that, The active metal content in the metal-supported catalyst is 1-10 wt%, calculated based on the total weight of the metal-supported catalyst.

5. The method according to claim 3, characterized in that, The active metal content in the metal-supported catalyst is 3-5 wt%, calculated based on the total weight of the metal-supported catalyst.

6. The method according to claim 1, characterized in that, The amount of the metal-supported catalyst is 1-10 wt% of the mass of 1,4-phenylenediamine.

7. The method according to claim 1, characterized in that, The amount of the metal-supported catalyst is 3-6 wt% of the mass of 1,4-phenylenediamine.

8. The method according to claim 1, characterized in that, The ether compound is selected from one or more of tetrahydrofuran, 1,4-dioxane, methyl ether, diethyl ether, and methyl tert-butyl ether, wherein the mass ratio of 1,4-phenylenediamine to solvent is 0.03-0.

3.

9. The method according to claim 1, characterized in that, The ether compound is tetrahydrofuran and / or 1,4-dioxane, wherein the mass ratio of 1,4-phenylenediamine to solvent is 0.1-0.

15.

10. The method according to claim 1, characterized in that, The hydrogenation reaction temperature is 100-190℃; the hydrogenation reaction pressure is 3-15 MPaA.

11. The method according to claim 1, characterized in that, The hydrogenation reaction temperature is 110-130℃; the hydrogenation reaction pressure is 5-10 MPa.

12. The method according to claim 1, characterized in that, The hydrogenation reaction ends when the pressure drop of the hydrogen consumed after the hydrogen supply is stopped is less than 0.01 MPa / min.

13. The method according to claim 1, characterized in that, The high trans-cis ratio 1,4-cyclohexanediamine has a trans-cis ratio of 4:1 or higher.

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