Method for preparing 1, 4-cyclohexanediamine with high trans-cis ratio

Abstract

The invention relates to a method for preparing 1, 4-cyclohexanediamine with a high trans-cis ratio, which is characterized in that a small amount of PPDA hydrogenated tar is recycled to improve the pore structure of a catalyst, so that trans-CHDA is easier to pass through, the selectivity of trans-form is increased, and the performance of polyurethane is improved.

Description

Technical Field

[0001] The present invention relates to a method for preparing cyclohexanediamine, and particularly to a method for preparing 1,4-cyclohexanediamine with a high trans-cis ratio, belonging to the field of synthesis of amine compounds. Background Art

[0002] Currently, aromatic diamines and their hydrogenation products are traditional chemical intermediates and can be widely used in the pharmaceutical, rubber, and polyurethane industries. Among them, p-phenylenediamine (hereinafter referred to as PPDA) is a derivative organic compound of aniline, and it can be hydrogenated to prepare an important polyurethane raw material 1,4-cyclohexanediamine (hereinafter referred to as CHDA). In the polyurethane industry, the polyurethane polymer prepared from PPDA will slowly change color due to the molecular structure, thus limiting its application. However, compared with PPDA aromatic diamines, the polyurethane prepared from CHDA has a more stable molecular structure against light and air and better performance.

[0003] Regarding the catalytic hydrogenation of PPDA to synthesize CHDA, from existing literature and patent reports, the main achievements are to use specific noble metal catalysts such as rhodium Rh and ruthenium Ru for the reaction. US Patents US2606924 and US3697449 reported the effects of supported Ru catalysts in the hydrogenation of the benzene ring of aromatic amine compounds. The reaction is mainly carried out under the conditions of P = 10 - 35 MPa, T = 80 - 230 °C, using an inert solvent, and the catalyst is alkali-modified. Research shows that high pressure and alkali modification of the catalyst can both improve the catalytic activity and the reaction yield. US Patent US3586862 reported that the Rh catalyst also shows high activity in the hydrogenation of PPDA, but due to its high price, the further use of the Rh catalyst is limited.

[0004] For this saturated cyclic compound CHDA, it mainly includes two conformations, namely the boat form and the chair form, in which six carbon atoms exist in a non-planar structure and basically in the chair configuration. However, the chemical bonds do not break during the mutual conversion between conformations, so the conformational conversion will not affect the molecular configuration. Therefore, when paying attention to the stereoisomerism of CHDA, conformational isomerism can be ignored, and only cis-trans isomerism needs to be concerned. In addition, due to the different spatial structures of cis-trans isomers, their physical and chemical properties are also different. Among them, the structural symmetry of the trans form is better than that of the cis form, so the boiling point and melting point are also higher than those of the cis form.

[0005] The two amino groups of CHDA are respectively located on the 1,4-carbon atoms of cyclohexane. CHDA has two isomers, trans-1,4-cyclohexanediamine (hereinafter referred to as trans-CHDA) and cis-1,4-cyclohexanediamine (hereinafter referred to as cis-CHDA), and their structures are as follows:

[0006]

[0007] Generally, the larger the proportion of trans-CHDA, the better the performance of the prepared polyurethane. Therefore, in order to improve the performance of the polyurethane, the proportion of trans-CHDA should be increased as much as possible.

[0008] In the current CHDA preparation process, the active metals used are basically noble metal Ru. Currently, the activity mainly affects the conversion rate of raw material PPDA and does not affect the selectivity of trans-CHDA. Since CHDA has two configurations, cis and trans, and the molecular sizes of the two configurations are also different, among which the molecular structure of trans-CHDA is more symmetrical than that of cis-CHDA and is more likely to pass through the catalyst pores. Therefore, regulating the appropriate pore size of the catalyst can improve the selectivity of trans-CHDA.

[0009] In the present invention, a small part of the tar after hydrogenation of PPDA is premixed with the raw material liquid to disperse the tar in the pores of the catalyst, reducing the pore size of the catalyst. Compared with cis-CHDA, the passing rate of trans-CHDA molecules is increased. At the same time, due to the presence of the tar, the generation of side reactions is inhibited. Therefore, the reaction temperature can be increased to increase the selectivity of trans-CHDA. Summary of the Invention

[0010] In order to increase the content of trans in current CHDA and thus improve the performance of the polyurethane, the object of the present invention is to provide a process for liquid-phase catalytic hydrogenation of PPDA with high trans-CHDA selectivity.

[0011] The present invention provides a method for preparing 1,4-cyclohexanediamine, the method comprising the following steps: using p-phenylenediamine as a raw material, reacting p-phenylenediamine with hydrogen in a solution of a solvent, an auxiliary agent and p-phenylenediamine tar under a hydrogenation catalyst to form 1,4-cyclohexanediamine.

[0012] In the present invention, the catalyst mainly comprises a carrier and an active metal. Preferably, the active metal is selected from one or more of Ru, Rh, Ni, Pt, Pd. The mass ratio of the active metal of the catalyst to the carrier is 0.5%-8%.

[0013] In the present invention, the carrier is selected from one or more of activated carbon, Al2O3, SiO2, and its specific surface area is 100-300m 2 / g, and the pore size is 10-50nm.

[0014] The auxiliary agent is selected from one or more of metal oxides or hydroxides such as Li, K, Ca, and the addition amount of the auxiliary agent is 0.1%-5% of the mass of PPDA.

[0015] In the present invention, the composition of the p-phenylenediamine tar is 20-28% cyclohexylaniline, 1-5% naphthalene, 9-12% cyclohexane, 6-10% diphenylamine, 40-50% p-phenylenediamine, 4-8% dimethylamine and other compounds.

[0016] In the present invention, taking PPDA as 100%, the addition amount of tar is 1%-5% of the mass of PPDA, the addition amount of solvent is 500%-2000% of the mass of PPDA, and the addition amount of catalyst is 4%-16% of the mass of PPDA.

[0017] In the present invention, the solvent is selected from one or more of tetrahydrofuran, methanol, ethanol, propanol, isopropanol, n-butanol, ethyl acetate, and butyl acetate.

[0018] The preparation method of CHDA in the present invention uses a batch reactor for operation. The reaction conditions are as follows:

[0019] The reaction temperature is 100-190°C, the hydrogen pressure is 5-10 MPa, the reaction time is 30-300 min, and hydrogen is fed continuously. First, add PPDA, solvent, additives, and PPDA tar into the reactor, premix for 0-120 min, and the premixing temperature is 30-50°C. React for a certain time under the corresponding reaction pressure and temperature. After the temperature in the reactor drops to room temperature, filter out the reaction solution for gas chromatography analysis.

[0020] Specifically, the present invention has the following advantages compared with the prior art:

[0021] 1. By recycling a small amount of the tar from the hydrogenation of PPDA, the present invention improves the pore structure of the catalyst, makes trans-CHDA more likely to pass through, increases the selectivity of the trans form, and makes the performance of the polyurethane more excellent.

[0022] 2. By adding a small amount of the tar from the hydrogenation of PPDA, the present invention inhibits the generation of side reactions, and thus can increase the selectivity of trans-CHDA. Specific embodiments

[0023] To further illustrate, the following examples are listed.

[0024] Raw materials and sources: All raw materials are purchased commercially from InnoChem. The sources of the main raw materials used in the following examples or comparative examples are as follows. Others, if not otherwise specified, are ordinary commercially available raw materials. Among them, PPDA tar is obtained by rectification and separation of the reaction solution, and its composition is 28% cyclohexylaniline, 5% naphthalene, 9% cyclohexane, 10% diphenylamine, 40% p-phenylenediamine, 8% dimethylamine and other compounds. The γ-Al2O3 powder is purchased from Yangzhou Zhongtianli New Materials Co., Ltd., and its BET is 212 m 2 / g, and the pore diameter is 17 nm.

[0025] Testing method: The conditions for gas chromatography analysis in the following examples are as follows: Agilent 7890 and DB-5 are used. The injector temperature is 280 °C and the detector temperature is 300 °C. The temperature programming is as follows: The initial column temperature is 50 °C and is held for 2 min; it is heated to 80 °C at a rate of 5 °C / min and held for 0 min; it is heated to 300 °C at a rate of 15 °C / min and held for 15 min. The content of each component is determined by the normalization method.

[0026] Determination method of saturated water absorption rate: The carrier is vacuum-dried at 130 °C for 4 h, cooled to room temperature. Weigh 5 g of γ-Al2O3 powder and place it in a 50 mL beaker, add 10 mL of distilled water, immerse it in a water bath at 60 °C for 40 min, cool to room temperature, and directly pour out the excess water (assuming the volume is V). Then the saturated water absorption rate of the carrier is α=(50 - V) / 5 mL / g.

[0027] Example 1

[0028] The catalyst used is Ru / Al2O3, where the mass fraction of Ru relative to Al2O3 is 5%: The carrier uses commercial γ-Al2O3. The catalyst active component Ru is loaded on the carrier by the equal-volume impregnation method. The steps are as follows: Weigh 5 g of γ-Al2O3 and measure its saturated water absorption, which is 4.2 mL. Dissolve 0.5 g of RuCl3 in 4.2 mL of dilute hydrochloric acid solution, add this impregnation solution to 5 g of alumina powder, and impregnate for 4 h to obtain the catalyst precursor. Roast this precursor in a muffle furnace at 250 °C for 4 h to obtain the unactivated catalyst.

[0029] Activation process: In a high-pressure reactor with stirring, add 3 g of the unactivated catalyst and 300 g of tetrahydrofuran, heat to 160 °C, and activate for 4 h. Wait for the reactor to cool to room temperature and filter out the tetrahydrofuran in the reactor.

[0030] Reaction process: 3 g of the activated catalyst is already in the reactor. Add 25 g of 1,4-phenylenediamine, 278 g of tetrahydrofuran, 0.5 g of auxiliary agent LiOH, and 1.0 g of PPDA tar (the components are 28% cyclohexylaniline, 5% naphthalene, 9% cyclohexane, 10% diphenylamine, 40% phenylenediamine, 8% dimethylamine and other compounds) into the reactor. Close the reactor, displace the air in the reactor three times with 0.6 MPa of nitrogen, and then displace the nitrogen in the reactor three times with 1 MPa of hydrogen. Charge hydrogen to 8 MPa and stir and premix for 1 h. Turn on the reactor heater to the reaction temperature of 140 °C and keep the temperature constant for 2 h. Wait for the temperature in the reactor to drop to room temperature, filter out the reaction solution and conduct gas chromatography analysis.

[0031] Example 2

[0032] The catalyst used is 5% Ru / Al2O3. The support uses commercial γ-Al2O3, and the catalyst active component Ru is loaded onto the support by the equal-volume impregnation method. Activation process: In a high-pressure reaction kettle with stirring, add 3 g of catalyst and 300 g of tetrahydrofuran, heat up to 160 °C, and activate for 4 h. Wait for the reaction kettle to cool down to room temperature, and filter out the tetrahydrofuran in the kettle. Reaction process: In the reaction kettle, add 25 g of 1,4-phenylenediamine, 278 g of tetrahydrofuran, 0.5 g of LiOH, and 1.0 g of PPDA tar. Close the reaction kettle, displace the air in the kettle three times with 0.6 MPa of nitrogen, and then displace the nitrogen in the kettle three times with 1 MPa of hydrogen. Pressurize the hydrogen to 8 MPa, stir and premix for 1 h. Open the reaction kettle and heat it to the reaction temperature of 140 °C, and carry out the constant-temperature reaction for 2 h. Wait for the temperature in the kettle to drop to room temperature, filter out the reaction solution and conduct gas chromatography analysis.

[0033] Example 3

[0034] The catalyst used is 5% Ru / Al2O3. The support uses commercial γ-Al2O3, and the catalyst active component Ru is loaded onto the support by the equal-volume impregnation method. Activation process: In a high-pressure reaction kettle with stirring, add 3 g of catalyst and 300 g of tetrahydrofuran, heat up to 160 °C, and activate for 4 h. Wait for the reaction kettle to cool down to room temperature, and filter out the tetrahydrofuran in the kettle. Reaction process: In the reaction kettle, add 25 g of 1,4-phenylenediamine, 278 g of tetrahydrofuran, 0.5 g of LiOH, and 0.5 g of PPDA tar. Close the reaction kettle, displace the air in the kettle three times with 0.6 MPa of nitrogen, and then displace the nitrogen in the kettle three times with 1 MPa of hydrogen. Pressurize the hydrogen to 8 MPa, stir and premix for 1 h. Open the reaction kettle and heat it to the reaction temperature of 140 °C, and carry out the constant-temperature reaction for 2 h. Wait for the temperature in the kettle to drop to room temperature, filter out the reaction solution and conduct gas chromatography analysis.

[0035] Example 4

[0036] The catalyst used is 5% Ru / Al2O3. The support uses commercial γ-Al2O3, and the catalyst active component Ru is loaded onto the support by the equal-volume impregnation method. Activation process: In a high-pressure reaction kettle with stirring, add 3 g of catalyst and 300 g of tetrahydrofuran, heat up to 160 °C, and activate for 4 h. Wait for the reaction kettle to cool down to room temperature, and filter out the tetrahydrofuran in the kettle. Reaction process: In the reaction kettle, add 25 g of 1,4-phenylenediamine, 278 g of tetrahydrofuran, 0.5 g of LiOH, and 1.0 g of PPDA tar. Close the reaction kettle, displace the air in the kettle three times with 0.6 MPa of nitrogen, and then displace the nitrogen in the kettle three times with 1 MPa of hydrogen. Pressurize the hydrogen to 8 MPa, stir and premix for 2 h. Open the reaction kettle and heat it to the reaction temperature of 140 °C, and carry out the constant-temperature reaction for 2 h. Wait for the temperature in the kettle to drop to room temperature, filter out the reaction solution and conduct gas chromatography analysis.

[0037] Example 5

[0038] The catalyst used was 5% Ru / Al2O3. The carrier used was commercial γ-Al2O3, and the active component Ru of the catalyst was loaded onto the carrier by the equal-volume impregnation method. Activation process: In a high-pressure reactor with stirring, 3 g of the catalyst and 300 g of tetrahydrofuran were added, and the temperature was raised to 160 °C and activated for 4 h. After the reactor cooled to room temperature, the tetrahydrofuran in the reactor was filtered out. Reaction process: In the reactor, 25 g of 1,4-phenylenediamine, 278 g of tetrahydrofuran, 0.5 g of LiOH, and 1.0 g of PPDA tar were added. The reactor was closed, and the air in the reactor was replaced three times with 0.6 MPa of nitrogen, and then the nitrogen in the reactor was replaced three times with 1 MPa of hydrogen. The hydrogen was pressurized to 8 MPa and stirred and premixed for 1 h. The reactor was opened and heated to a reaction temperature of 160 °C and reacted at a constant temperature for 2 h. After the temperature in the reactor dropped to room temperature, the reaction solution was filtered out for gas chromatography analysis.

[0039] Example 6

[0040] The catalyst used was 5% Ru / Al2O3. The carrier used was commercial γ-Al2O3, and the active component Ru of the catalyst was loaded onto the carrier by the equal-volume impregnation method. Activation process: In a high-pressure reactor with stirring, 3 g of the catalyst and 300 g of tetrahydrofuran were added, and the temperature was raised to 160 °C and activated for 4 h. After the reactor cooled to room temperature, the tetrahydrofuran in the reactor was filtered out. Reaction process: In the reactor, 25 g of 1,4-phenylenediamine, 278 g of tetrahydrofuran, 0.5 g of LiOH, and 1.0 g of PPDA tar were added. The reactor was closed, and the air in the reactor was replaced three times with 0.6 MPa of nitrogen, and then the nitrogen in the reactor was replaced three times with 1 MPa of hydrogen. The hydrogen was pressurized to 8 MPa and stirred and premixed for 1 h. The reactor was opened and heated to a reaction temperature of 180 °C and reacted at a constant temperature for 2 h. After the temperature in the reactor dropped to room temperature, the reaction solution was filtered out for gas chromatography analysis.

[0041] Example 7

[0042] The catalyst used is 5% Ru / Al2O3. The carrier uses commercial γ-Al2O3, and the catalyst active component Ru is loaded onto the carrier by the equal-volume impregnation method. Activation process: In a high-pressure reactor with stirring, add 3 g of the catalyst and 300 g of tetrahydrofuran, heat up to 160 °C, and activate for 4 h. Wait for the reactor to cool to room temperature, and filter out the tetrahydrofuran in the reactor. Reaction process: Add 25 g of 1,4-phenylenediamine, 278 g of tetrahydrofuran, 0.5 g of LiOH, and 1.0 g of PPDA tar into the reactor. Close the reactor, replace the air in the reactor with 0.6 MPa of nitrogen three times, and then replace the nitrogen in the reactor with 1 MPa of hydrogen three times. Pressurize the hydrogen to 8 MPa, stir and premix for 1 h. Open the reactor and heat it to the reaction temperature of 140 °C, and keep the temperature constant for reaction for 1 h. Wait for the temperature in the reactor to drop to room temperature, filter out the reaction solution for gas chromatography analysis.

[0043] Example 8

[0044] The catalyst used is 5% Ru / Al2O3. The carrier uses commercial γ-Al2O3, and the catalyst active component Ru is loaded onto the carrier by the equal-volume impregnation method. Activation process: In a high-pressure reactor with stirring, add 3 g of the catalyst and 300 g of tetrahydrofuran, heat up to 160 °C, and activate for 4 h. Wait for the reactor to cool to room temperature, and filter out the tetrahydrofuran in the reactor. Reaction process: Add 25 g of 1,4-phenylenediamine, 278 g of tetrahydrofuran, 0.5 g of LiOH, and 1.0 g of PPDA tar into the reactor. Close the reactor, replace the air in the reactor with 0.6 MPa of nitrogen three times, and then replace the nitrogen in the reactor with 1 MPa of hydrogen three times. Pressurize the hydrogen to 8 MPa, stir and premix for 1 h. Open the reactor and heat it to the reaction temperature of 140 °C, and keep the temperature constant for reaction for 3 h. Wait for the temperature in the reactor to drop to room temperature, filter out the reaction solution for gas chromatography analysis.

[0045] Example 9

[0046] The catalyst used is 5% Ru / Al2O3. The carrier uses commercial γ-Al2O3, and the catalyst active component Ru is loaded onto the carrier by the equal-volume impregnation method. Activation process: In a high-pressure reactor with stirring, add 3 g of the catalyst and 300 g of tetrahydrofuran, heat up to 160 °C, and activate for 4 h. Wait for the reactor to cool to room temperature, and filter out the tetrahydrofuran in the reactor. Reaction process: Add 25 g of 1,4-phenylenediamine, 278 g of tetrahydrofuran, 0.5 g of LiOH, and 1.0 g of PPDA tar into the reactor. Close the reactor, replace the air in the reactor with 0.6 MPa of nitrogen three times, and then replace the nitrogen in the reactor with 1 MPa of hydrogen three times. Pressurize the hydrogen to 8 MPa, stir and premix at 50 °C for 1 h. Open the reactor and heat it to the reaction temperature of 140 °C, and keep the temperature constant for reaction for 2 h. Wait for the temperature in the reactor to drop to room temperature, filter out the reaction solution for gas chromatography analysis.

[0047] Comparative Example 1

[0048] The catalyst used was 5% Ru / Al₂O₃. The support used was commercial γ-Al₂O₃, and the active component Ru of the catalyst was loaded on the support by the equal-volume impregnation method. Activation process: In a high-pressure reactor with stirring, 3 g of the catalyst and 300 g of tetrahydrofuran were added, heated to 160 °C, and activated for 4 h. After the reactor cooled to room temperature, the tetrahydrofuran in the reactor was filtered out. Reaction process: In the reactor, 25 g of 1,4-phenylenediamine, 278 g of tetrahydrofuran, 0.5 g of LiOH, and 0 g of PPDA tar were added. The reactor was closed, and the air in the reactor was replaced three times with 0.6 MPa of nitrogen, and then the nitrogen in the reactor was replaced three times with 1 MPa of hydrogen. The hydrogen was pressurized to 8 MPa, and the reactor was heated to the reaction temperature of 140 °C and kept at a constant temperature for 2 h. After the temperature in the reactor dropped to room temperature, the reaction solution was filtered out for gas chromatography analysis.

[0049] Comparative Example 2

[0050] The catalyst used was 5% Ru / Al₂O₃. The support used was commercial γ-Al₂O₃, and the active component Ru of the catalyst was loaded on the support by the equal-volume impregnation method. Activation process: In a high-pressure reactor with stirring, 3 g of the catalyst and 300 g of tetrahydrofuran were added, heated to 160 °C, and activated for 4 h. After the reactor cooled to room temperature, the tetrahydrofuran in the reactor was filtered out. Reaction process: In the reactor, 25 g of 1,4-phenylenediamine, 278 g of tetrahydrofuran, 0.5 g of LiOH, and 2 g of PPDA tar were added. The reactor was closed, and the air in the reactor was replaced three times with 0.6 MPa of nitrogen, and then the nitrogen in the reactor was replaced three times with 1 MPa of hydrogen. The hydrogen was pressurized to 8 MPa, and stirred and premixed for 1 h. The reactor was heated to the reaction temperature of 140 °C and kept at a constant temperature for 2 h. After the temperature in the reactor dropped to room temperature, the reaction solution was filtered out for gas chromatography analysis.

[0051]

Claims

1. A method for preparing 1,4 - cyclohexanediamine, the method comprising the following steps: Using p-phenylenediamine as a raw material, in a solution of a solvent, an auxiliary agent, and p-phenylenediamine tar, p-phenylenediamine reacts with hydrogen under a hydrogenation catalyst to produce 1,4-cyclohexanediamine. The p-phenylenediamine tar contains 20-28% cyclohexyl aniline, 1-5% naphthalene, 9-12% cyclohexane, 6-10% diphenylamine, 40-50% p-phenylenediamine, and 4-8% dimethylamine.

2. The preparation method according to claim 1, characterized in that, The catalyst mainly includes a carrier and an active metal. Preferably, the active metal is selected from one or more of Ru, Rh, Ni, Pt, and Pd; wherein the mass ratio of the active metal to the carrier of the catalyst is 0.5%-8%; and / or, the addition amount of the catalyst is 4%-16% of the mass of PPDA.

3. The preparation method according to claim 1 or 2, characterized in that, The carrier is selected from one or more of activated carbon, Al2O3, and SiO2, and has a specific surface area of 100-300 m 2 / g and a pore size of 10-50 nm.

4. The preparation method according to any one of claims 1-3, characterized in that, The auxiliary agent is selected from one or more of metal oxides or hydroxides such as Li, K, Ca, etc., and the addition amount of the auxiliary agent is 0.1%-5% of the mass of PPDA.

5. The preparation method according to any one of claims 1-4, characterized in that, Based on PPDA being 100%, the addition amount of tar is 1%-5% of the mass of PPDA, and the addition amount of the solvent is 500%-2000% of the mass of PPDA.

6. The preparation method according to any one of claims 1-5, characterized in that, The solvent is selected from one or more of tetrahydrofuran, methanol, ethanol, propanol, isopropanol, n-butanol, ethyl acetate, and butyl acetate.

7. The preparation method according to any one of claims 1-6, characterized in that, The reaction temperature is 100-190 °C, the hydrogen pressure is 5-10 MPa, and the reaction time is 30-300 min.

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