Preparation method of Ru-based catalyst for catalyzing one-step hydrogenation of 2,4-dinitrotoluene to prepare 1-methyl-2,4-cyclohexanediamine

Abstract

The present invention discloses a method for preparing a Ru-based catalyst for catalyzing the one-step hydrogenation of 2,4-dinitrotoluene to prepare 1-methyl-2,4-cyclohexanediamine, and relates to the field of catalysts. The preparation steps of the Ru-based catalyst include preparing a PS template, preparing a carrier, preparing a modified carrier and a loaded catalyst. The present invention utilizes three-dimensional ordered polystyrene microspheres as a template in combination with a dual solvent-assisted induction method to prepare an ordered multi-level porous MOFs material 3D-ZIF-8, and after high-temperature carbonization, successfully constructs a modified carrier NHPC, and successfully synthesizes a Ru / NHPC catalyst using an impregnation precipitation method. The results show that the N site in the carbon skeleton plays a significant anchoring role for the metal species, facilitating the formation and high dispersion of ultrafine Ru NPs. The Ru / NHPC catalyst of the present invention is applied to catalyze the one-step hydrogenation reaction of DNT to prepare HTDA, which solves the problem of high activation energy barrier for benzene ring hydrogenation, and the reaction activity is much higher than that of common Ru-based catalysts in industry, with a DNT conversion rate of 100% and a HTDA selection rate of up to 92.20%.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and in particular to a method for preparing a Ru-based catalyst for catalyzing the one-step hydrogenation of 2,4-dinitrotoluene to prepare 1-methyl-2,4-cyclohexanediamine. Background Art

[0002] 1-Methyl-2,4-cyclohexanediamine (HTDA) is an important organic compound. In the field of materials synthesis, it can be used as an epoxy resin curing agent to give epoxy resin good mechanical properties, corrosion resistance, and heat resistance. It can also be used to synthesize polyamide resins and to manufacture a variety of engineering products. In the field of pharmaceutical chemicals, it is a key intermediate for the synthesis of various drugs such as antibacterial and antihistamine drugs. It can also be used to construct bioactive molecules to assist biomedical research. In the field of surfactants, it can be used to prepare cationic surfactants with emulsifying and bactericidal properties, as well as amphoteric surfactants with good biocompatibility and low irritation. It is also widely used in detergents, cosmetics and other industries.

[0003] Currently, the main HTDA preparation processes include the one-step hydrogenation method of dinitrotoluene (DNT) and the two-step hydrogenation method of DNT. The former uses DNT as raw material and uses Ru catalyst to hydrogenate to directly produce HTDA. This route has many advantages such as high raw material utilization, simple process, and low cost. The latter requires DNT to be reduced to toluenediamine (TDA) using a Ni-based catalyst, and then TDA is hydrogenated to HTDA using Ru catalyst. It has serious shortcomings such as complex process, high cost investment, and low raw material utilization.

[0004] The one-step hydrogenation of DNT involves not only the reduction of the nitro group but also the reduction of the benzene ring. Due to the high energy barrier for benzene ring hydrogenation, high requirements are placed on the catalyst for this one-step hydrogenation. Therefore, a solution to the challenges hindering the industrial production of HTDA lies in the development of high-performance Ru-based hydrogenation catalysts. Experimental DNT hydrogenation studies have shown that conventional Ru-based catalysts are difficult to achieve with this one-step hydrogenation to HTDA. The main reasons for this are: ① uneven distribution of Ru active sites, low utilization of active centers, high cost, and poor activity; ② the uncontrollable adsorption and desorption characteristics of reactants and products on the catalyst surface, resulting in severe deamination side reactions during the catalytic reaction and low HTDA selectivity; and ③ the catalytic hydrogenation reaction conditions are very demanding, especially when the reaction pressure exceeds 10 MPa. Therefore, the development of high-performance Ru-based hydrogenation catalysts is crucial for achieving high HTDA selectivity. Summary of the Invention

[0005] The present invention aims to overcome the deficiencies of existing catalysts in the background technology and provides a method for preparing a Ru-based catalyst for catalyzing the one-step hydrogenation of 2,4-dinitrotoluene to produce 1-methyl-2,4-cyclohexanediamine. The Ru-based catalyst prepared by this method has the characteristics of high catalytic activity, good dispersion, and relatively mild reaction conditions.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for preparing a Ru-based catalyst for catalyzing the one-step hydrogenation of 2,4-dinitrotoluene to prepare 1-methyl-2,4-cyclohexanediamine, comprising the following steps:

[0008] (1) Preparation of PS template: 125.0 mL of styrene was washed with NaOH solution and deionized water in sequence. The washed styrene was added to 500 mL of deionized water containing PVP. Under high-purity Ar bubbling, K2S2O8 aqueous solution was added. The mixture was heated to reflux under magnetic stirring and then stirred at a constant temperature for 24 h. After cooling, polystyrene microspheres were obtained. The PS template was obtained by centrifugation.

[0009] (2) Preparation of the carrier: Zn(NO3)2·6H2O and 2-methylimidazole were dissolved in 125 mL of methanol to form a mixed solution. The PS template was then immersed in the mixed solution and degassed for 5 min. The impregnated complex was taken out and dried at 50 °C. The dried product was immersed in 200 mL of CH3OH / NH3·H2O mixed solution and vacuum degassed for 1 min. The product was allowed to stand at room temperature and atmospheric pressure for 12 h. The product was then washed with a large amount of anhydrous methanol, ethanol, and deionized water until there was no ammonia smell. The fragments were collected by filtration and dried in air. The product was then immersed in 500 mL of THF for 1 day, centrifuged and washed, and dried. The THF was replaced and the above operation was repeated to remove the template to obtain the carrier 3D-ZIF-8.

[0010] (3) Preparation of modified support: 1.0 g of 3D-ZIF-8 was calcined at 900 °C for 6 h in a tube furnace. After cooling to room temperature, it was washed with 1-10 mol / L dilute sulfuric acid at 80 °C for 24 h under reflux. It was then washed with deionized water until neutral. The product was vacuum dried overnight and passed through a 200-mesh sieve to obtain the modified support NHPC.

[0011] (4) Loading catalyst: Place the modified carrier NHPC in a three-necked flask, add appropriate amount of distilled water and polyethylene glycol, heat in an oil bath at 60-90 °C and stir continuously, slowly add the Ru metal precursor aqueous solution to the above three-necked flask, continue stirring for 4 hours after the solution is added, then add 1 mol / L alkaline solution drop by drop, adjust the pH to 10-12, and continue stirring for 1 hour; wash the impregnated catalyst precursor to neutrality, place the filter cake at 110 °C and vacuum dry for 12 hours; then place it in a fixed bed reactor and reduce it in a hydrogen atmosphere for 4 hours to obtain a Ru-based catalyst with a Ru loading of 1-5 wt%.

[0012] As a preferred embodiment of the present invention, in step (1), the concentration of the NaOH solution is 1 to 5 mol / L, and the amount used is 40 mL; the concentration of the K2S2O8 aqueous solution is 1 to 5 mol / L, and the amount used is 75 mL; the heating reflux temperature is 70 to 100°C, and the time is 30 min; the centrifugation is to centrifuge the polystyrene microspheres at a speed of 800 to 1000 rpm for 12 h.

[0013] As a preferred embodiment of the present invention, in step (1), the amount of PVP used is 10 to 20 g.

[0014] As a preferred embodiment of the present invention, in step (2), the molar ratio of Zn(NO3)2·6H2O to 2-methylimidazole is 3 to 8:1.

[0015] As a preferred embodiment of the present invention, in step (2), the molar ratio of the CH3OH / NH3·H2O mixed solution is 1:1-3.

[0016] As a preferred embodiment of the present invention, in step (4), the molecular weight of the polyethylene glycol is 400-1000, and the mass ratio of the polyethylene glycol to the modified carrier NHPC is 1:5-10.

[0017] As a preferred embodiment of the present invention, in step (4), the Ru-containing metal precursor aqueous solution is a 1 mol / L ruthenium chloride aqueous solution, and the total amount of metal Ru is 2% to 5% of the modified support NHPC.

[0018] As a preferred embodiment of the present invention, in step (4), the alkaline solution is an aqueous solution of one of lithium hydroxide, sodium hydroxide, sodium carbonate, and ammonium carbonate.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] This study used three-dimensional ordered polystyrene microspheres as templates and a dual-solvent-assisted induction method to prepare the ordered hierarchically porous MOF material 3D-ZIF-8. After high-temperature carbonization, 3D ordered macroporous ZIF-8-derived N-doped carbon (NHPC) was successfully constructed. A Ru / NHPC catalyst was then synthesized using an impregnation precipitation method. Results demonstrated that the nitrogen sites within the carbon framework significantly anchored the metal species, facilitating the formation and high dispersion of ultrafine Ru NPs. The Ru / NHPC catalyst was applied to the one-step hydrogenation of DNT to produce HTDA, overcoming the high activation barrier for benzene ring hydrogenation. The reaction activity was significantly higher than that of common industrial Ru-based catalysts, achieving 100% DNT conversion and 92.20% HTDA selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the XRD pattern of Ru / NHPC prepared in Example 1;

[0022] Figure 2 is a scanning electron microscope image of Ru / NHPC prepared in Example 1;

[0023] Figure 3 is a high-resolution transmission electron microscope image of Ru / NHPC prepared in Example 1;

[0024] Figure 4 is a transmission electron microscope image of the Ru / AC catalyst prepared in Comparative Example 2. DETAILED DESCRIPTION

[0025] The following is a clear and complete description of the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] First, 125.0 mL of styrene was washed sequentially with 40 mL of a 2.5 mol / L NaOH solution and deionized water. The washed styrene was then added to a round-bottom flask containing 500 mL of deionized water containing 15 g of PVP. Under high-purity Ar bubbling, 75 mL of a 2.5 mol / L aqueous K₂S₂O₂ solution was rapidly added to the flask. The mixture was heated to 80°C under reflux for 30 minutes with magnetic stirring, followed by continuous stirring at 80°C for 24 hours. After cooling, milky white monodisperse colloidal polystyrene microspheres were obtained. The polystyrene microspheres were centrifuged for 12 hours to obtain a three-dimensional PS template. 20g Zn(NO3)2·6H2O and 15g 2-methylimidazole were dissolved in 125mL methanol to prepare a mixed solution. Then, 2g PS template was immersed in the above solution. After degassing for 5 minutes, the impregnated complex was removed, transferred to a beaker, and dried at 50°C to obtain an intermediate product. The block intermediate product was immersed in 200mL CH3OH / NH3·H2O (mixing ratio of 1:2) mixed solution and degassed under vacuum for 1 minute. The product was allowed to stand at room temperature and atmospheric pressure for 12 hours, and then washed with a large amount of anhydrous methanol, ethanol, and deionized water until there was no ammonia smell. Finally, the fragments were collected by filtration, dried in air, and then immersed in 500mL THF for 1 day, centrifuged and washed, and dried. Then, the THF was replaced and the above steps were repeated to remove the template to obtain the support 3D-ZIF-8. 1.0 g of the support 3D-ZIF-8 was calcined at 900°C for 6 h in a tube furnace. After cooling to room temperature, it was washed with 3M H2SO4 under reflux at 80°C for 24 h, then washed with deionized water until neutral, and vacuum dried overnight. The product was then passed through a 200-mesh sieve to obtain the modified support NHPC. The modified carrier NHPC was placed in a three-necked flask, 30 mL of distilled water and 2.5 mL of polyethylene glycol 400 were added, and the mixture was heated in an oil bath at 80°C with continuous stirring. An aqueous solution containing RuCl3 (wherein Ru was 5% of the NHPC loading) was slowly added dropwise. After the addition of the solution was completed, stirring was continued for 4 hours. Then, a 1 mol / L aqueous lithium hydroxide solution was added dropwise, and the pH was adjusted to 10-12, and stirring was continued for 1 hour. Then, heating and stirring were stopped, and the impregnated catalyst precursor was washed to neutrality. The filter cake was placed in a vacuum dryer at 110°C for 12 hours. It was placed in a fixed bed reactor and reduced in a hydrogen atmosphere for 4 hours to obtain a Ru-based catalyst with a Ru loading of 5 wt%, which was recorded as Ru5 / NHPC.

[0028] Example 2

[0029] Unlike Example 1, the RuCl3 aqueous solution used in this example has a metal loading of 4% of the NHPC carrier. The Ru-based catalyst obtained in this example is denoted as Ru4 / NHPC.

[0030] Example 3

[0031] Unlike Example 1, the RuCl3 aqueous solution used in this example has a metal loading of 3% of the NHPC carrier. The Ru-based catalyst obtained in this example is denoted as Ru3 / NHPC.

[0032] Example 4

[0033] Unlike Example 1, the RuCl3 aqueous solution used in this example has a metal loading of 2% of the NHPC carrier. The Ru-based catalyst obtained in this example is denoted as Ru2 / NHPC.

[0034] Comparative Example 1

[0035] Different from Example 1, this comparative example does not load Ru metal.

[0036] Comparative Example 2

[0037] Different from Example 1, the carrier used in this comparative example is commercial activated carbon AC, and Ru / AC catalyst is finally obtained.

[0038] Comparative Example 3

[0039] Different from Example 1, the carrier used in this comparative example is alumina.

[0040] Comparative Example 4

[0041] The catalyst used in this comparative example is a commercial 20% Ru / C catalyst purchased from Shanghai Maclean Reagent Factory.

[0042] Comparative Example 5

[0043] The catalyst used in this comparative example was a commercial 20% Pt / C catalyst purchased from Shanghai MacLean Reagent Factory.

[0044] Comparative Example 6

[0045] The catalyst used in this comparative example is a commercial Raney nickel catalyst purchased from Shanghai Maclean Reagent Factory.

[0046] Comparative Example 7

[0047] The catalyst used in this comparative example was a commercial 20% Pd / C catalyst purchased from Shanghai MacLean Reagent Factory.

[0048] The Ru-based catalysts prepared in Examples 1-4 and Comparative Example 1 were characterized using X-ray diffraction, transmission electron microscopy, and inductively coupled plasma optical emission spectroscopy. X-ray diffraction (XRD) was performed using a Rigaku Ultima IV diffractometer to determine the powder X-ray diffraction spectra of the catalysts. Transmission electron microscopy (TEM) was performed using a JEOL JEM-F200 field transmission electron microscope to observe the catalyst morphology and the particle size of the metal nanoparticles. The results are shown in Figure 2. Figure 1-4 As shown in Table 1.

[0049] Table 1 ICP-OES data results

[0050]

[0051] Figure 1 This indicates that Example 1 successfully prepared the corresponding highly active Ru-based catalyst, as can be seen from the ICP-OES data analysis in Table 1. The Ru content of the Ru-based catalysts in Examples 1 to 4 was 1% to 4%, which is basically consistent with the theoretical loading of 2% to 5%. This shows that the metallic Ru in Examples 1 to 4 was successfully loaded on the support with almost no loss, indicating that the catalyst preparation method is efficient and feasible. Figure 2 It is further shown that Example 1 successfully prepared the Ru / NHPC catalyst. Figure 3 and 4 This shows that the catalyst prepared by this method has better dispersion than the catalyst prepared by the traditional method, and ultrafine Ru NPS particles are formed, so its catalytic activity is better than that of the traditional method.

[0052] Application Examples

[0053] The highly active Ru-based catalysts prepared in Examples 1-4 were used to catalyze the one-step hydrogenation of DNT to produce HTDA.

[0054] Catalytic method: In a hydrogen atmosphere at a temperature of 180°C and a pressure of 6.0 MPa, 0.01 g of a highly active Ru-based catalyst, 0.50 g of DNT, 0.02 g of LiOH, and 0.01 g of NaBH4 were dissolved in 60 mL of HTDA and stirred at a stirring rate of 1000 r / min to carry out the reaction.

[0055] Test Case

[0056] The catalysts of Examples 1-4 and Comparative Examples 1-7 were used to catalyze the one-step hydrogenation reaction of DNT to prepare HTDA, and catalyst performance evaluation tests were performed. The method for catalyzing the one-step hydrogenation of DNT to prepare HTDA using the catalysts of Comparative Examples 1-7 was the same as the catalytic method of Examples 1-4 in the application examples.

[0057] Testing Method: Product distribution was quantitatively analyzed using an Agilent 8860 gas chromatograph, and reaction products were qualitatively analyzed using an Agilent 8860GC / 5077 MSD gas spectrometer. Gas chromatography conditions were as follows: vaporizer temperature 280°C; detector temperature 280°C; temperature program: column temperature 60°C, initial dwell time 3 min, ramp rate 10°C / min, end temperature 200°C, dwell time 10 min; high-purity N₂ carrier gas at a flow rate of 30 mL / min, split ratio 1:45.

[0058] The reaction products were qualitatively analyzed using an Agilent 8860 GC / 5077 MSD gas chromatograph. The analytical conditions were the same as those for the Agilent 8860 gas chromatograph.

[0059] Liquid Chromatography Test Method: The content of coupling byproducts (tar) was determined using a Shimadzu LC2030 HPLC equipped with a reversed-phase C18 column. Analytical conditions were as follows: the mobile phase was a 40 / 60 (volume ratio) methanol / water mixture, the flushing rate was 1.0 mL / min, and the UV detection wavelength was 200-220 nm.

[0060] Standard curve determined by external standard method:

[0061] (1) Preparation of standard substances: TDA was selected as the standard substance, and the evaluation reaction solvent HTDA was used as the solvent to prepare standard solutions of 14.32 mg / mL, 28.62 mg / mL, 42.92 mg / mL, and 57.22 mg / mL, respectively.

[0062] (2) Draw a standard curve: Inject the standard solutions into the gas chromatograph respectively and record the peak area of each standard solution; draw a standard curve with the concentration of the standard solution as the horizontal axis and the peak area of TDA in the standard solution as the vertical axis.

[0063] (3) Sample determination: Inject the sample to be tested into the gas chromatograph and record the peak area of TDA.

[0064] (4) Calculation of results: Substitute the peak area of the sample to be tested into the standard curve to determine the concentration of TDA in the sample; then calculate the total amount of TDA in the sample. Based on the actual amount of TDA and the theoretical amount of TDA obtained by complete conversion of DNT, the selectivity of the intermediate product TDA can be obtained.

[0065] Calculation formula:

[0066]

[0067]

[0068] Since there are no other by-products except deamination by-products (including tar) in the reaction

[0069]

[0070] The test data results are shown in Table 2.

[0071] Table 2 Performance evaluation test data of different catalysts

[0072]

[0073] The data in Table 2 show that the Ru / NHPC catalysts prepared in Examples 1 to 4 using three-dimensional ordered polystyrene microspheres as templates in combination with a dual solvent-assisted induction method exhibit excellent catalytic performance. This is because the metal loading of the catalysts prepared by this preparation method is uniform, so the reaction activity and selectivity are relatively high. The catalyst performance is significantly better than that of the traditional catalysts (Comparative Examples 1-7), and the active component loading rate is extremely high, proving that this method is effective and feasible. Figures 1 to 4 This indicates that the highly active Ru-based catalyst successfully prepared by this method has active components that are highly dispersed in the pores of the carrier and on its surface, thereby enhancing the catalytic activity of the catalyst and solving the problem of high activation energy barrier of the benzene ring in the hydrogenation process. The reaction activity far exceeds that of commonly used commercial hydrogenation catalysts, with a DNT conversion rate of 100% and an HTDA selectivity of up to 92.20%, showing obvious catalytic performance advantages.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the technical solution and conceptual invention of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a Ru-based catalyst for catalyzing the one-step hydrogenation of 2,4-dinitrotoluene to produce 1-methyl-2,4-cyclohexanediamine, characterized in that: The following steps are involved: (1) Preparation of PS template: 125.0 mL of styrene was washed with NaOH solution and deionized water in sequence. The washed styrene was added to 500 mL of deionized water containing PVP. Under high-purity Ar bubbling, K2S2O8 aqueous solution was added. The mixture was heated to reflux under magnetic stirring and then stirred at a constant temperature for 24 h. After cooling, polystyrene microspheres were obtained. The PS template was obtained by centrifugation. (2) Preparation of the carrier: Zn(NO3)2·6H2O and 2-methylimidazole were dissolved in 125 mL of methanol to form a mixed solution. The PS template was then immersed in the mixed solution and degassed for 5 min. The impregnated complex was taken out and dried at 50 °C. The dried product was immersed in 200 mL of CH3OH / NH3·H2O mixed solution and vacuum degassed for 1 min. The product was allowed to stand at room temperature and atmospheric pressure for 12 h. The product was then washed with a large amount of anhydrous methanol, ethanol, and deionized water until there was no ammonia smell. The fragments were collected by filtration and dried in air. The product was then immersed in 500 mL of THF for 1 day, centrifuged and washed, and dried. The THF was replaced and the above operation was repeated to remove the template to obtain the carrier 3D-ZIF-8. (3) Preparation of modified support: 1.0 g of 3D-ZIF-8 was calcined at 900 °C for 6 h in a tube furnace. After cooling to room temperature, it was washed with 1-10 mol / L dilute sulfuric acid at 80 °C for 24 h under reflux. It was then washed with deionized water until neutral. The product was vacuum dried overnight and passed through a 200-mesh sieve to obtain the modified support NHPC. (4) Loading catalyst: Place the modified carrier NHPC in a three-necked flask, add appropriate amount of distilled water and polyethylene glycol, heat in an oil bath at 60-90 °C and stir continuously, slowly add the Ru metal precursor aqueous solution to the above three-necked flask, continue stirring for 4 hours after the solution is added, then add 1 mol / L alkaline solution drop by drop, adjust the pH to 10-12, and continue stirring for 1 hour; wash the impregnated catalyst precursor to neutrality, place the filter cake at 110 °C and vacuum dry for 12 hours; then place it in a fixed bed reactor and reduce it in a hydrogen atmosphere for 4 hours to obtain a Ru-based catalyst with a Ru loading of 1-5 wt%.

2. The preparation method according to claim 1, wherein: In step (1), the concentration of the NaOH solution is 1-5 mol / L, and the amount used is 40 mL; the concentration of the K2S2O8 aqueous solution is 1-5 mol / L, and the amount used is 75 mL; the heating reflux temperature is 70-100°C, and the time is 30 min; the centrifugation is to centrifuge the polystyrene microspheres at a speed of 800-1000 rpm for 12 h.

3. The preparation method according to claim 1, wherein: In step (1), the amount of PVP used is 10-20 g.

4. The preparation method according to claim 1, wherein: In step (2), the molar ratio of Zn(NO3)2·6H2O to 2-methylimidazole is 3 to 8:

1.

5. The preparation method according to claim 1, wherein: In step (2), the molar ratio of CH3OH to NH3·H2O in the CH3OH / NH3·H2O mixed solution is 1:1-3.

6. The preparation method according to claim 1, wherein: In step (4), the molecular weight of the polyethylene glycol is 400-1000, and the mass ratio of the polyethylene glycol to the modified carrier NHPC is 1:5-10.

7. The preparation method according to claim 1, wherein: In step (4), the Ru-containing metal precursor aqueous solution is a 1 mol / L ruthenium chloride aqueous solution, and the total amount of metal Ru is 2% to 5% of the modified support NHPC.

8. The preparation method according to claim 1, wherein: In step (4), the alkaline solution is an aqueous solution of one of lithium hydroxide, sodium hydroxide, sodium carbonate, and ammonium carbonate.

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