A catalyst for the hydrogenation of dinitrotoluene and a method for its preparation and use

Abstract

The application discloses a dinitrotoluene hydrogenation catalyst and a preparation method and application thereof. The preparation method of the hydrogenation catalyst comprises the following steps: placing a MAX material in a mixed acid solution for etching treatment, washing, intercalation treatment, centrifugation and freeze-drying of the product after etching to obtain a precursor MXene powder; dispersing the precursor MXene powder in water, adding a tetravalent platinum salt, stirring, and then freeze-drying to obtain a platinum catalyst with MXene as a carrier, namely a dinitrotoluene hydrogenation catalyst. The platinum catalyst with MXene as a carrier prepared by the application has excellent catalytic performance, can quickly and highly selectively catalyze dinitrotoluene hydrogenation reduction into diaminotoluene under relatively mild conditions, and the selectivity and conversion rate are close to 100%. Meanwhile, the preparation process of the catalyst is simple, the loading amount of the noble metal platinum is low, the preparation cost is low, the catalyst can be recycled, and the catalyst has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of catalytic hydrogenation technology, and in particular to a dinitrotoluene hydrogenation catalyst, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Diaminotoluene (TDA) is a raw material for the synthesis of toluene diisocyanate (TDI), which is mainly used in the preparation of flexible polyurethane foams and elastomers. TDA is usually converted from dinitrotoluene (DNT) through methods such as iron powder reduction, sodium sulfide reduction, electrolytic reduction, and catalytic hydrogenation. Catalytic hydrogenation has attracted widespread attention due to its advantages, including high product quality, high yield, short reaction time, and low pollution.

[0004] Because DNT contains two nitro groups, the reaction involves multi-step hydrogenation. The nitro group at the fourth position has less steric hindrance, making hydrogenation easier, while the nitro group at the second position has greater steric hindrance, making hydrogenation more difficult. The conversion of the nitro group to an amino group also alters the aromatic ring properties. The conversion of the first nitro group (electron-withdrawing group) to an amino group (electron-donating group) reduces electron defects in the benzene ring, hindering further reduction of the second nitro group, thus making complete conversion to diaminotoluene more difficult. Therefore, compared to aromatic nitro compounds containing only one nitro group, the hydrogenation reduction of the nitro group in dinitrotoluene (DNT) is more challenging.

[0005] Currently, two main DNT catalytic hydrogenation technologies are used in industry: one uses supported noble metal catalysts such as Pd / C and Pt / C, which have the advantages of low reaction pressure (1.0 MPa) and high catalyst activity, but the catalysts are expensive and prone to carbon deposition or poisoning and deactivation; the other uses Raney-Ni catalysts, which are inexpensive, but have a high operating pressure (2.0 MPa), and are prone to generating monoamine reduction products during hydrogenation, making it impossible to completely reduce the two nitro groups. Summary of the Invention

[0006] In view of this, the present invention provides a dinitrotoluene hydrogenation catalyst, its preparation method and application. The catalyst prepared by the present invention can rapidly and selectively catalyze the hydrogenation reduction of dinitrotoluene to diaminotoluene under mild conditions, and the catalyst has low cost and simple preparation process.

[0007] In a first aspect, the present invention provides a method for preparing a dinitrotoluene hydrogenation catalyst, comprising the following steps:

[0008] The MAX material was etched in a mixed acid solution, and the etched product was washed, intercalated, centrifuged, and freeze-dried to obtain the precursor MXene powder; the MAX material includes at least three elements: Ti, Al, and C.

[0009] The precursor MXene powder was dispersed in water, a tetravalent platinum salt was added, and after stirring, it was freeze-dried to obtain a platinum catalyst supported by MXene. The platinum catalyst supported by MXene is a dinitrotoluene hydrogenation catalyst.

[0010] Preferably, the MAX material is selected from any one of Ti2AlC, Ti3AlC2, and Ti4AlC3. Ti3AlC2 is easier to etch and has wider applicability, so Ti3AlC2 is preferred.

[0011] Preferably, the mixed acid solution comprises hydrofluoric acid, hydrochloric acid, and water; preferably, the volume ratio of hydrofluoric acid, hydrochloric acid, and water is 2-2.5:2-2.5:1; preferably, the mass fraction of hydrochloric acid is 37%.

[0012] Preferably, the washing is performed by centrifugation with deionized water until the pH is ≥ 6.

[0013] Preferably, the intercalation treatment specifically involves: dispersing the washed product in water, then adding an alkali metal chloride, stirring for a period of time, and then centrifuging; wherein the ratio of the washed product, alkali metal chloride, and water is 1.8-2.2g:1.8-2.2g:30-50mL. The alkali metal chloride includes lithium chloride, sodium chloride, or potassium chloride. Further, in the step of centrifuging after stirring for a period of time, the stirring speed is 300-500 rpm; the stirring time is 10-15 hours. The inherent structure and properties of MXene cause it to exhibit diverse response behaviors when interacting with different metal ions. Alkali metal ions (such as Li...) + Na + K + MXene can be spontaneously or electrochemically intercalated between layers, causing an increase in the interlayer spacing. Subsequent ultrasonic centrifugation can then yield single-layer or few-layer MXene.

[0014] Preferably, the centrifugation speed is 2500-3500 rpm; the centrifugation time is 10-20 min.

[0015] Preferably, in the step of obtaining the precursor MXene powder by freeze-drying, the supernatant after centrifugation is freeze-dried for 20-28 hours.

[0016] Preferably, the precursor MXene powder is dispersed in water, and the ratio of MXene powder to water is 100mg:30-70mL.

[0017] Preferably, the tetravalent platinum salt is selected from any one of chloroplatinic acid, potassium chloroplatinate, and dichlorotetraamineplatinum, and more preferably chloroplatinic acid. Preferably, the mass of platinum in the tetravalent platinum salt is 0.8-1.2 wt% of the MXene powder. In this invention, Ti in the MXene support is oxidized to a higher valence state, and Pt in the tetravalent platinum salt... 4+ It is reduced in situ to Pt during the impregnation preparation process. 2+ , loaded on the MXene surface.

[0018] Preferably, the stirring speed is 300-500 rpm; the stirring time is 8-16 h.

[0019] Preferably, in the MXene-supported platinum catalyst obtained by freeze-drying, the freeze-drying time is 20-28 hours.

[0020] Secondly, the present invention provides a dinitrotoluene hydrogenation catalyst prepared by the above preparation method, wherein the platinum loading is 0.8-1.2 wt% of the MXene support.

[0021] Thirdly, the present invention provides a method for preparing diaminotoluene, comprising the following steps:

[0022] Under the action of the above-mentioned dinitrotoluene hydrogenation catalyst, dinitrotoluene undergoes a hydrogenation reaction in the liquid phase to obtain diaminotoluene.

[0023] Preferably, the temperature of the hydrogenation reaction is 75-85°C.

[0024] Preferably, the pressure of the hydrogenation reaction is 0.8-1.2 MPa.

[0025] Preferably, the hydrogenation reaction takes 0.8-1.5 hours.

[0026] Preferably, the solvent for the hydrogenation reaction includes anhydrous ethanol, methanol, or a mixture of ethyl acetate and water, and more preferably a mixture of ethyl acetate and water. More preferably, the volume ratio of ethyl acetate to water is 1:3-5; and the molar ratio of the catalyst, dinitrotoluene, and solvent is 10 mg: 380-420 mg: 20-30 mL.

[0027] Fourthly, the present invention provides an application of the above-mentioned catalyst in the catalytic hydrogenation of dinitrotoluene to synthesize diaminotoluene.

[0028] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0029] (1) The dinitrotoluene hydrogenation catalyst of the present invention has excellent catalytic performance and can rapidly and selectively catalyze the hydrogenation reduction of dinitrotoluene to diaminotoluene under relatively mild conditions, with selectivity and conversion rate close to 100%; at the same time, the catalyst can be recycled.

[0030] (2) The preparation process of the dinitrotoluene hydrogenation catalyst of the present invention is simple and the loading of the precious metal platinum is low, so the preparation cost is low and it has good prospects for industrial application. Attached Figure Description

[0031] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0032] Figure 1 This is a scanning electron microscope (SEM) image of MXene without lithium chloride intercalation in Example 1;

[0033] Figure 2 These are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of MXene after lithium chloride intercalation in Example 1; A is the SEM image, and B is the TEM image.

[0034] Figure 3 The Ti 2p spectrum of the X-ray photoelectron spectroscopy (XPS) of the precursor MXene powder and 1% Pt-MXene in Example 2 is shown.

[0035] Figure 4 This is the XPS spectrum of Pt 4f of 1% Pt-MXene prepared in Example 2;

[0036] Figure 5 These are TEM images of 1% Pt-MXene prepared in Example 2;

[0037] Figure 6 This is a GCMS spectrum of the substrate and product of the hydrogenation reaction of dinitrotoluene catalyzed by the catalyst of Example 2 of the present invention;

[0038] Figure 7 This is the 1H NMR spectrum of the substrate and product of the hydrogenation reaction of dinitrotoluene catalyzed by the catalyst of Example 2 of the present invention;

[0039] Figure 8 These are the GCMS spectra of the products of the hydrogenation reaction of dinitrotoluene catalyzed by the catalysts of Comparative Examples 1-3 of this invention;

[0040] Figure 9 This is the GCMS spectrum of the product of the hydrogenation reaction of dinitrotoluene catalyzed by the catalyst of Comparative Example 4 of this invention. Detailed Implementation

[0041] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0042] This invention does not impose any special restrictions on the source of the reagents; commercially available products well known to those skilled in the art can be used.

[0043] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0044] Example 1: Preparation of precursor MXene powder

[0045] 2g of titanium aluminum carbide was added to a mixed acid solution consisting of 20mL hydrofluoric acid, 20mL 12M hydrochloric acid, and 10mL water. The mixture was stirred at 30℃ for 24h, cooled to room temperature, and the reaction solution was added to a 50mL centrifuge tube. The solution was centrifuged at 3000rpm for 5 minutes until pH ≥ 6. The centrifuged solid was dispersed in 40mL water, and 2g of lithium chloride was added for intercalation. The intercalated solution was sonicated under an argon atmosphere for 15min. After sonication, the solution was centrifuged at 3000rpm for 15 minutes, and the supernatant was freeze-dried for 24h to obtain the precursor MXene powder.

[0046] Figure 1 This is a scanning electron microscope (SEM) image of MXene without lithium chloride intercalation. Figure 2 (A) is a scanning electron microscope image of MXene after lithium chloride intercalation. Figure 2 (B) is a transmission electron microscope (TEM) image of MXene after lithium chloride intercalation. As can be seen from the image, single-layer or few-layer MXene nanosheets were obtained after lithium chloride intercalation.

[0047] Example 2

[0048] 100 mg of the precursor MXene powder obtained in Example 1 was ultrasonically dispersed in 50 mL of deionized water. 0.5 mL of chloroplatinic acid hexahydrate standard solution with a platinum loading of 1 wt% was added to the solution. The mixture was stirred at room temperature at 400 rpm for 12 h. The resulting liquid was then freeze-dried for 24 h to obtain a platinum catalyst supported on MXene (denoted as 1% Pt-MXene).

[0049] Figure 3The image shows the XPS Ti 2p spectra of the precursor MXene powder and 1% Pt-MXene. As can be seen from the spectra, when Pt is loaded, the Ti 2p spectrum shifts towards higher binding energy. This is because the Ti in MXene is oxidized to a higher valence state.

[0050] Figure 4 This is the XPS spectrum of Pt 4f in 1% Pt-MXene. The graph shows that Pt exists in a divalent form, indicating that Pt... 4+ Reduced to Pt 2+ .

[0051] Figure 5 This is a TEM image of 1% Pt-MXene. As can be seen from the image, no Pt nanoparticles were formed, indicating that Pt did not aggregate. Figure 4 It can be seen that Pt is uniformly loaded on the MXene support in a divalent form.

[0052] Example 3

[0053] 100 mg of the precursor MXene powder obtained in Example 1 was ultrasonically dispersed in 50 mL of deionized water. 0.5 mL of potassium chloroplatinate standard solution with a platinum content of 2 mg / mL (platinum loading of 1 wt%) was added to the solution. The mixture was stirred at room temperature at 400 rpm for 12 h. The resulting liquid was then freeze-dried for 24 h to obtain a platinum catalyst supported on MXene.

[0054] Example 4

[0055] 100 mg of the precursor MXene powder obtained in Example 1 was ultrasonically dispersed in 50 mL of deionized water. 0.5 mL of a standard solution of dichlorotetraammineplatinum with a platinum loading of 1 wt% was added to the solution. The mixture was stirred at room temperature at 400 rpm for 12 h. The resulting liquid was then freeze-dried for 24 h to obtain a platinum catalyst supported on MXene.

[0056] Comparative Example 1

[0057] 100 mg of the precursor MXene powder obtained in Example 1 was ultrasonically dispersed in 50 mL of deionized water. 7.2 mg of ferric nitrate nonahydrate (iron loading of 1 wt%) was added to the water. The mixture was stirred at room temperature at 400 rpm for 12 h. The resulting liquid was then freeze-dried for 24 h to obtain an iron catalyst supported on MXene.

[0058] Comparative Example 2

[0059] 100 mg of the precursor MXene powder obtained in Example 1 was ultrasonically dispersed in 50 mL of deionized water. 5 mg of cobalt nitrate hexahydrate (cobalt loading was 1 wt%) was added to the water. The mixture was stirred at room temperature at 400 rpm for 12 h. The resulting liquid was then freeze-dried for 24 h to obtain a cobalt catalyst supported on MXene.

[0060] Comparative Example 3

[0061] 100 mg of the precursor MXene powder obtained in Example 1 was ultrasonically dispersed in 50 mL of deionized water. 5 mg of nickel nitrate hexahydrate (nickel loading was 1 wt%) was added to the solution. The mixture was stirred at room temperature at 400 rpm for 12 h. The resulting liquid was then freeze-dried for 24 h to obtain a nickel catalyst supported on MXene.

[0062] Comparative Example 4

[0063] 100 mg of the precursor MXene powder obtained in Example 1 was ultrasonically dispersed in 50 mL of deionized water, and 2 mg of rhodium trichloride (rhodium loading was 1 wt%) was added to it. After stirring at room temperature at 400 rpm for 12 h, the reaction liquid was freeze-dried for 24 h to obtain a rhodium catalyst with MXene as the support.

[0064] Test case

[0065] The catalysts from Examples 2 and Comparative Examples 1-4 were used in the catalytic hydrogenation of 2,4-dinitrotoluene. The solution after the catalytic reaction was analyzed by gas chromatography-mass spectrometry (GC-MS). The specific steps were as follows: 400 mg of 2,4-dinitrotoluene, 5 mL of ethyl acetate, 20 mL of water, and 10 mg of catalyst were added to a 100 mL stirred explosion-proof reactor equipped with circulating condensate water. At room temperature, the gas was purged three times with hydrogen. After purging, the pressure was increased to a specified level with hydrogen to check the airtightness for 30 min. If the airtightness was good, the temperature was raised to 80 °C, and the reaction was carried out under stirring at 300 rpm. During the reaction, hydrogen was continuously introduced to maintain a constant pressure of 1 MPa, and the reaction was carried out for 1 h. After the reaction, the reaction mixture and catalyst were separated. The separated catalyst was returned to the reactor for reuse to replenish the lost catalyst.

[0066] The solution after 1 hour of reaction was processed and analyzed by GCMS. Figure 6The substrate and product of the catalyst in Example 2 are shown. The peak time of 2,4-dinitrotoluene in GC-MS was 10.3 min, and the peak time of 2,4-diaminotoluene in GC-MS was 9.5 min. Both the substrate 2,4-dinitrotoluene and the product 2,4-diaminotoluene were very pure, with no other impurity peaks. The substrate before the catalytic reaction of the catalyst in Example 2 and the solution after 1 h of catalytic reaction (after removing the solvent water and ethyl acetate) were analyzed. 1 1H NMR analysis was performed using deuterated DMSO as the solvent. The results are as follows: Figure 7 As shown, 2.500 represents the peak of deuterated DMSO, 3.300 represents the water peak, and other peaks, through analysis and literature review, were confirmed to be the substrate 2,4-dinitrotoluene and the product 2,4-diaminotoluene. GSMS and... 1 1H NMR analysis showed that the platinum catalyst with MXene as support prepared in Example 2 had high catalytic activity and catalytic selectivity, with a selectivity of 99% and a conversion rate of 100%.

[0067] Figure 8 The catalytic reaction products of the catalysts prepared in Comparative Examples 1-3 are shown in the figure. As can be seen from the figure, the GCMS spectrum only shows a single peak at 10.3 min, which is the peak of 2,4-dinitrotoluene. There is no peak of 2,4-diaminotoluene, indicating that Fe, Co and Ni cannot catalyze the hydrogenation reduction of 2,4-dinitrotoluene under mild conditions.

[0068] Figure 9 The catalytic reaction products of the catalyst prepared in Comparative Example 4 are shown in the figure. As can be seen from the GC-MS spectrum, four peaks appear: 2,4-diaminotoluene at 9.5 min, 2,4-dinitrotoluene at 10.3 min, 4-methyl-3-nitroaniline at 10.4 min, and 2-amino-4-nitrotoluene at 10.9 min. These data indicate that the rhodium catalyst supported on MXene can only convert a small amount of 2,4-dinitrotoluene within 1 hour, producing a semi-hydrogenation product and a small amount of 2,4-diaminotoluene.

[0069] As can be seen from the above comparison, the platinum catalyst with MXene as the support prepared in this invention has excellent catalytic activity and high selectivity in the catalytic reaction of 2,4-dinitrotoluene to 2,4-diaminotoluene. Moreover, the loading of the noble metal platinum in this catalyst is low and the preparation process is simple.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing diaminotoluene, characterized in that, Includes the following steps: In the presence of a hydrogenation catalyst, dinitrotoluene undergoes a hydrogenation reaction in the liquid phase to yield diaminotoluene. The preparation method of the dinitrotoluene hydrogenation catalyst includes the following steps: The MAX material was etched in a mixed acid solution, and the etched product was washed, intercalated, centrifuged, and freeze-dried to obtain the precursor MXene powder; the MAX material includes at least three elements: Ti, Al, and C. The precursor MXene powder was dispersed in water, a tetravalent platinum salt was added, and after stirring, it was freeze-dried to obtain a platinum catalyst supported by MXene. The platinum catalyst supported by MXene is a dinitrotoluene hydrogenation catalyst. Pt in tetravalent platinum salts 4+ It is reduced in situ to Pt during the impregnation preparation process. 2+ , loaded on the MXene surface.

2. The method for preparing diaminotoluene according to claim 1, characterized in that, The MAX material is selected from any one of Ti2AlC, Ti3AlC2, and Ti4AlC3; the mixed acid solution includes hydrofluoric acid, hydrochloric acid, and water; The washing process involves centrifuging with deionized water until the pH reaches ≥ 6. The intercalation process specifically involves dispersing the washed product in water, then adding an alkali metal chloride, stirring for a period of time, and then centrifuging. The ratio of the washed product, alkali metal chloride, and water is 1.8-2.2 g: 1.8-2.2 g: 30-50 mL.

3. The method for preparing diaminotoluene according to claim 2, characterized in that, The MAX material is Ti3AlC2.

4. The method for preparing diaminotoluene according to claim 2, characterized in that, The volume ratio of hydrofluoric acid, hydrochloric acid and water is 2~2.5:2~2.5:

1.

5. The method for preparing diaminotoluene according to claim 2, characterized in that, The hydrochloric acid has a mass fraction of 37%.

6. The method for preparing diaminotoluene according to claim 2, characterized in that, The alkali metal chloride is selected from lithium chloride, sodium chloride, or potassium chloride.

7. The method for preparing diaminotoluene according to claim 2, characterized in that, In the centrifugation step after stirring for a period of time, the stirring speed is 300-500 rpm; the stirring time is 10-15 h.

8. The method for preparing diaminotoluene according to claim 1, characterized in that, The centrifugation speed is 2500-3500 rpm; the centrifugation time is 10-20 min; in the step of freeze drying to obtain the precursor MXene powder, the supernatant after centrifugation is freeze dried for 20-28 h.

9. The method for preparing diaminotoluene according to claim 1, characterized in that, The precursor MXene powder is dispersed in water, and the ratio of MXene powder to water is 100mg:30-70mL; The tetravalent platinum salt is selected from either chloroplatinic acid or potassium chloroplatinate.

10. The method for preparing diaminotoluene according to claim 9, characterized in that, The tetravalent platinum salt is chloroplatinic acid.

11. The method for preparing diaminotoluene according to claim 9, characterized in that, The mass of platinum in the tetravalent platinum salt is 0.8-1.2 wt% of MXene powder.

12. The method for preparing diaminotoluene according to claim 1, characterized in that, The stirring speed is 300-500 rpm; the stirring time is 8-16 h; and the freeze-drying time for obtaining the platinum catalyst with MXene as the support is 20-28 h.

13. The method for preparing diaminotoluene according to claim 1, characterized in that, The hydrogenation reaction is carried out at a temperature of 75-85℃; at a pressure of 0.8-1.2 MPa; and for a time of 0.8-1.5 h.

14. The method for preparing diaminotoluene according to claim 1, characterized in that, include: The solvent for the hydrogenation reaction is a mixture of ethyl acetate and water; the ratio of the catalyst, dinitrotoluene, and solvent is 10 mg: 380-420 mg: 20-30 mL.

15. The method for preparing diaminotoluene according to claim 14, characterized in that, The volume ratio of ethyl acetate to water is 1:3-5.

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