A nitrogen-containing catalyst, a preparation method thereof and application thereof in preparing benzene from cyclohexane dehydrogenation

Abstract

The application discloses a nitrogen-containing catalyst and a preparation method and application thereof in preparing benzene through cyclohexane dehydrogenation, which comprises a hierarchical porous molecular sieve and a nitride supported on the surface of the hierarchical porous molecular sieve; the nitride is selected from WN. The catalyst provided by the application can be applied to the preparation of benzene through cyclohexane dehydrogenation reaction and can improve the conversion rate of cyclohexane and the selectivity of generated benzene. The preparation method of the catalyst provided by the application is stable, controllable and good in reproducibility. The method for preparing benzene through cyclohexane dehydrogenation reaction provided by the application adopts the catalyst provided by the application, is fast in reaction speed, high in yield and capable of being applied to large-scale production.

Description

Technical Field

[0001] This application relates to a nitrogen-containing catalyst, its preparation method, and its application in the dehydrogenation of cyclohexane to benzene, belonging to the field of chemical engineering. Background Technology

[0002] Cyclohexane is an important chemical raw material and intermediate with a wide range of applications. About 20% is used as a solvent and adhesive, and 80% is used in organic synthesis, mainly for the production of products such as cyclohexanol, cyclohexanone, adipic acid, and caprolactam.

[0003] Organic hydrogen carrier dehydrogenation often employs supported industrial reforming catalysts with γ-Al₂O₃ as the support and Pt as the active component. These catalysts suffer from drawbacks such as high cost, susceptibility to coking, and carbon buildup. Raney nickel or other non-precious metal catalysts are also used. In operating units, bimetallic or multimetallic catalysts are commonly employed, with the multimetallic component acting as a co-catalyst to improve catalyst performance. Among existing catalysts, Ni, Ir, Pd, and Pt are frequently used as active components in dehydrogenation catalysts. Pt, in particular, exhibits high activity for cycloalkanes due to its high activation capacity for CH bonds. Under the same active component content, higher metal dispersion results in higher catalyst activity. However, precious metals used in catalysts are difficult to recover and expensive. The active component determines the quality of the catalyst.

[0004] Nitrogen compounds have attracted attention in recent years because they have catalytic properties similar to those of noble metals. Nitrogen compounds and noble metals have similar d-band electron characteristics below the Fermi level. Moreover, compared with noble metals, nitrides are inexpensive and have excellent resistance to sulfur poisoning. Therefore, they have broad application prospects in the field of catalysts. Summary of the Invention

[0005] This patent describes the preparation of metal nitrides supported on hierarchical porous molecular sieves. This method is inexpensive, simple, and produces well-dispersed nitrides on the sieves. When applied to the dehydrogenation of cyclohexane to benzene, it exhibits good catalyst activity, high cyclohexane conversion and benzene selectivity, and good stability.

[0006] According to one aspect of this application, a nitrogen-containing catalyst for the dehydrogenation of cyclohexane to benzene is provided, which can improve the conversion rate of cyclohexane and the selectivity of benzene; comprising a hierarchical porous molecular sieve and a nitride supported on the surface of the hierarchical porous molecular sieve;

[0007] The nitride is selected from WN.

[0008] According to another aspect of this application, a method for preparing the above-mentioned nitrogen-containing catalyst for the dehydrogenation of cyclohexane to benzene is provided, comprising the following steps:

[0009] (1) The initial molecular sieve was subjected to alkali treatment and ammonium ion exchange treatment to obtain a hierarchical porous molecular sieve;

[0010] (2) The multi-level porous molecular sieve obtained in (1) is immersed in a solution containing a tungsten source to obtain a catalyst precursor, which is dried (III) and calcined (III) to obtain a multi-level porous molecular sieve loaded with WO3.

[0011] (3) The multi-level porous molecular sieve loaded with WO3 obtained in (2) is subjected to nitriding treatment in an ammonia atmosphere to obtain the nitrogen-containing catalyst.

[0012] The alkaline treatment includes:

[0013] The initial molecular sieve was treated with alkali solution, dried (I), and calcined (I) to obtain the alkali-treated initial molecular sieve.

[0014] The initial molecular screening was performed using silica-alumina molecular sieves;

[0015] The silica-aluminum molecular sieve is selected from mordenite molecular sieve and / or ZSM-5 molecular sieve;

[0016] The temperature for alkaline treatment is 65–90°C;

[0017] Optionally, the temperature of the alkaline treatment is any value among 65°C, 70°C, 75°C, 80°C, 85°C, and 90°C, or a range between any two.

[0018] The alkaline treatment time is 0.5 to 1.5 hours;

[0019] Optionally, the alkali treatment time is any value among 0.5h, 0.75h, 1h, 1.25h, and 1.5h, or any range between two of them.

[0020] The alkaline solution is selected from NaOH solution and / or KOH solution;

[0021] The solid-liquid ratio of the molecular sieve to the alkaline solution is 1:(10-30)g / ml;

[0022] Optionally, the solid-liquid ratio of the molecular sieve to the alkaline solution is any value among 1:10 g / ml, 1:20 g / ml, and 1:30 g / ml, or any range between two of them.

[0023] The concentration of the alkaline solution is 0.1–0.3 mol / L;

[0024] Optionally, the concentration of the alkaline solution is selected from any value of 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, or any range between two of them.

[0025] The temperature of the drying process I is 80–130°C;

[0026] Optionally, the temperature of the drying I is any value among 80°C, 90°C, 100°C, 110°C, 120°C, and 130°C, or a range between any two.

[0027] The drying time for step I is 8–24 hours;

[0028] Optionally, the drying time I is any value or a range between 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, and 24h.

[0029] The calcination temperature I is 450–650°C;

[0030] Optionally, the calcination temperature I is any value among 450°C, 500°C, 550°C, 600°C, and 650°C, or a range between any two.

[0031] The calcination time is 1 to 6 hours.

[0032] Optionally, the calcination time I is any value among 1h, 2h, 3h, 4h, 5h, and 6h, or a range between any two.

[0033] The ammonium ion exchange treatment includes:

[0034] The initial molecular sieve obtained after alkali treatment is subjected to ammonium ion exchange in an ammonium salt solution, followed by drying (II) and calcination (II) to obtain the hierarchical porous molecular sieve.

[0035] The temperature for ammonium ion exchange is 65–90°C;

[0036] Optionally, the temperature of the ammonium ion exchange treatment is any value among 65°C, 70°C, 75°C, 80°C, 85°C, and 90°C, or a range between any two.

[0037] The ammonium ion exchange time is 4–8 hours;

[0038] Optionally, the ammonium ion exchange treatment time is any value among 4h, 5h, 6h, 7h, and 8h, or a range between any two.

[0039] The ammonium salt is NH4NO3;

[0040] The concentration of the ammonium salt solution is 0.4–1.2 mol / L;

[0041] Optionally, the concentration of the ammonium salt solution is any value or a range between 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, and 1.2 mol / L.

[0042] The solid-liquid ratio of the molecular sieve to the ammonium salt solution is 1:(10-30)g / ml;

[0043] Optionally, the solid-liquid ratio of the molecular sieve to the ammonium salt solution is any value among 1:10 g / ml, 1:20 g / ml, and 1:30 g / ml, or any range between two of them.

[0044] The temperature of the drying II process is 80–130°C;

[0045] Optionally, the temperature of the drying II is any value among 80°C, 90°C, 100°C, 110°C, 120°C, and 130°C, or a range between any two.

[0046] The drying time for step II is 8–24 hours;

[0047] Optionally, the drying time II is any value among 8h, 12h, 16h, 20h, and 24h, or a range between any two.

[0048] The calcination temperature II is 450–650°C;

[0049] Optionally, the calcination temperature II is any value among 450°C, 500°C, 550°C, 600°C, and 650°C, or a range between any two.

[0050] The calcination time for II is 1–6 hours;

[0051] Optionally, the calcination time II is selected from any value of 1h, 2h, 3h, 4h, 5h, 6h or any range between two.

[0052] The multi-stage porous molecular sieve is crushed and sieved.

[0053] The particle size of the multi-stage porous molecular sieve obtained after crushing and sieving is 16-32 mesh.

[0054] Optionally, the particle size of the multi-stage porous molecular sieve obtained after crushing and sieving is any value among 16 mesh, 18 mesh, 20 mesh, 22 mesh, 24 mesh, 26 mesh, 28 mesh, 30 mesh, and 32 mesh, or any value between two of them.

[0055] The tungsten source is selected from tungsten hexachloride and / or amine metatungstate;

[0056] The solid-liquid ratio of the hierarchical porous molecular sieve to the solution containing tungsten salt is 1:(0.6~0.8)g / ml;

[0057] Optionally, the solid-liquid ratio of the multi-level porous molecular sieve to the solution containing tungsten salt is any value among 1:0.6 g / ml, 1:0.7 g / ml, and 1:0.8 g / ml, or any range between two of them.

[0058] The temperature of the drying III process is 80–130°C;

[0059] Optionally, the temperature of the drying III is any value among 80°C, 90°C, 100°C, 110°C, 120°C, and 130°C, or a range between any two.

[0060] The drying time for step III is 6–24 hours;

[0061] Optionally, the drying time III is any value among 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, and 24h, or a range between any two.

[0062] The calcination temperature III is 450–650°C;

[0063] Optionally, the calcination temperature III is any value or a range between any two of 450°C, 470°C, 490°C, 510°C, 530°C, 550°C, 570°C, 590°C, 610°C, 630°C, and 650°C.

[0064] The calcination time for III is 1–6 hours;

[0065] Optionally, the calcination time III is any value among 1h, 2h, 3h, 4h, 5h, and 6h, or a range between any two.

[0066] In the multi-level porous molecular sieve loaded with WO3, the mass ratio of WO3 to the multi-level porous molecular sieve is (1-3):100.

[0067] Optionally, in the multi-level porous molecular sieve loaded with WO3, the mass ratio of WO3 to the multi-level porous molecular sieve is any value among 1:100, 2:100, and 3:100, or any range between the two.

[0068] The nitriding treatment temperature is 650–750°C;

[0069] Optionally, the nitriding temperature is any value among 650°C, 700°C, and 750°C, or a range between any two.

[0070] The nitriding treatment time is 0.5 to 4 hours;

[0071] Optionally, the nitriding treatment time is any value among 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, and 4h, or a range between any two.

[0072] The heating rate for the nitriding treatment is 4–10 °C / min.

[0073] Optionally, the heating rate of the nitriding treatment is any value or a range between 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, and 10℃ / min.

[0074] Specifically, the above-mentioned calcined mixture is placed in an open tube furnace, and the temperature is raised while a nitrogen source is introduced to obtain the catalyst WN / multi-level porous molecular sieve.

[0075] The impregnation is an equal-volume impregnation; specifically, tungsten salt is dissolved in a certain amount of deionized water, poured into a multi-porous molecular sieve and stirred with a glass plate, placed at room temperature, dried in an oven and calcined.

[0076] According to another aspect of this application, a method for preparing benzene by the dehydrogenation reaction of cyclohexane is provided.

[0077] Includes the following steps:

[0078] In a reactor, a raw material containing hydrogen and cyclohexane is introduced and reacted with a catalyst to obtain a product containing benzene.

[0079] The catalyst is selected from the nitrogen-containing catalyst for the dehydrogenation of cyclohexane to benzene described above or the nitrogen-containing catalyst for the dehydrogenation of cyclohexane to benzene prepared by the above preparation method.

[0080] The reaction temperature is 280–340°C;

[0081] Optionally, the reaction temperature is any value or a range between 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, and 340°C.

[0082] The reaction time is 2-3 hours;

[0083] Optionally, the reaction time is any value among 2h, 2.5h, and 3h, or a range between any two.

[0084] The reaction pressure is 0.1–0.4 MPa.

[0085] Optionally, the pressure of the reaction is any value among 0.1 MPa, 0.2 MPa, 0.3 MPa, and 0.4 MPa, or a range between any two.

[0086] In the raw materials,

[0087] The flow rate of the hydrogen gas is 5–10 ml / min;

[0088] Optionally, the flow rate of the hydrogen gas is any value among 5 ml / min, 6 ml / min, 7 ml / min, 8 ml / min, 9 ml / min, and 10 ml / min, or a range between any two.

[0089] The mass hourly space velocity of the cyclohexane is 2–4 h⁻¹. -1 .

[0090] Optionally, the mass hourly space velocity (MSV) of the cyclohexane is 2 h⁻¹. -1 3h -1 4h -1 Any value in the range or any value between the two.

[0091] The reactor is a fixed-bed reactor.

[0092] The beneficial effects that this application can produce include:

[0093] 1) The catalyst provided in this application can be applied to the dehydrogenation reaction of cyclohexane to prepare benzene and improve the conversion rate of cyclohexane and the selectivity of the benzene produced.

[0094] 2) The preparation method of the catalyst provided in this application is stable, controllable, and reproducible.

[0095] 3) The method for preparing benzene by dehydrogenation of cyclohexane provided in this application uses the catalyst provided in this application, which has a fast reaction rate and high yield, and can be applied to large-scale production. Attached Figure Description

[0096] Figure 1 Catalyst 1 # X-ray powder diffraction pattern of WN mixture in the sample. Detailed Implementation

[0097] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0098] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0099] The gas chromatograph used was an Agilent 7890B gas chromatograph.

[0100] Example 1

[0101] Preparation of catalysts

[0102] Taking item 1 in Tables 1-3 as an example, while maintaining the solution temperature at 65℃, the silicate zeolite molecular sieve (silicon-aluminum atomic ratio of 12.5) with a solid-liquid ratio (g / ml) of 1:30 was treated with a 0.3 mol / L NaOH solution for 1.5 h, washed until neutral, dried at 100℃ for 12 h, and calcined at 550℃ for 3 h to obtain Na-type hierarchical porous molecular sieve material; while maintaining the solution temperature at 80℃, the Na-type hierarchical porous molecular sieve material with a solid-liquid ratio (g / ml) of 1:20 was treated with a 0.8 mol / L NH4NO3 solution. The solution underwent ammonium ion exchange for 6 hours, followed by washing and drying at 100℃ for 12 hours, and calcination at 550℃ for 3 hours to obtain a hydrogen-type hierarchical porous molecular sieve material. This material was then crushed and sieved to a 20-mesh size to obtain a hierarchical porous molecular sieve material. Ammonium metatungstate was dissolved in deionized water, and the hierarchical porous molecular sieve material was added and stirred with a glass plate (the mass ratio of synthesized WO3 to hierarchical porous molecular sieve was 2:100, and the solid-liquid ratio of the hierarchical porous molecular sieve material to the tungsten salt solution was 1:0.7 g / ml). The mixture was left at room temperature for 6 hours, dried in an oven at 100℃ for 6 hours, and calcined at 500℃ for 4 hours. The calcined mixture was then placed in an open tube furnace, heated to 700℃ at a rate of 4℃ / min under ammonia gas, and heated at this temperature for 3 hours to obtain catalyst WN / hierarchical porous molecular sieve material, denoted as catalyst 1. # .

[0103] Following the steps below, adjust the type and amount of each raw material and the reaction parameters to obtain a series of catalysts numbered 2 to 28, denoted as catalyst 2. # ~Catalyst 28 # As shown in Table 1 below:

[0104] Table 1

[0105]

[0106]

[0107] Table 2

[0108]

[0109]

[0110] Table 3

[0111]

[0112]

[0113] The explanations for columns 1 to 3 above are as follows:

[0114] The ZSM-5 molecular sieve (Z) has a silica-to-alumina ratio of 25;

[0115] The silica-to-alumina ratio of the mordenite molecular sieve (S) is 30.

[0116] Solid-liquid ratio: Solid-liquid ratio of molecular sieve to alkaline solution (solid-liquid ratio 1), solid-liquid ratio of multi-level porous molecular sieve to NH4NO3 solution (solid-liquid ratio 2).

[0117] Tungsten salts: tungsten hexachloride (W1, dissolved in ethanol), ammonium metatungstate (W2, dissolved in deionized water).

[0118] XRD characterization

[0119] Catalyst 1 was analyzed using a Miniflex 600 X-ray diffractometer with a Cu target. # Powder diffraction yielded catalyst 1. # The diffraction peaks of the WN mixture in the image conform to the characteristic peaks of the WN mixture (e.g., Figure 1 (As shown).

[0120] Gas chromatography characterization

[0121] The composition of the acetaldehyde condensation reaction products was analyzed using an Agilent 7890B gas chromatograph (FID detector, HP-5 capillary column).

[0122] Example 2

[0123] The catalyst is used in the dehydrogenation reaction of cyclohexane to prepare benzene.

[0124] Catalysts 1 to 28 prepared in Examples 1 to 3 # ~Catalyst 28 # The catalyst was used to prepare benzene from cyclohexane via dehydrogenation. The reaction proceeded at 310°C and 0.2 MPa for 3 hours, with the feedstock contacting the catalyst in the reactor to produce a benzene-containing product. The mass hourly space velocity (WHSV) was 3 h⁻¹. -1 The H2 flow rate was 8 ml / min. The feedstock was fed into a fixed-bed reactor containing 3 g of the catalyst, and benzene was prepared by dehydrogenation.

[0125] After the reaction stabilized, both the reactants and products were analyzed using online gas chromatography. The results are shown in Table 4.

[0126] Table 4

[0127]

[0128]

[0129] As can be seen from the table, the prepared catalyst, when applied to this reaction, exhibits high conversion rate and selectivity.

[0130] Example 3

[0131] Catalyst 1 prepared using the catalysts listed in Tables 1-3 # The dehydrogenation of cyclohexane to prepare benzene was carried out. After the reaction parameters were varied and the reaction stabilized, both the reactants and products were analyzed using online gas chromatography. The results are shown in Table 5.

[0132] Table 5

[0133]

[0134] The table shows that the reaction temperature has a significant impact on the reaction conversion rate.

[0135] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing benzene by dehydrogenation of cyclohexane, characterized in that, Includes the following steps: In a reactor, a raw material containing hydrogen and cyclohexane is introduced and reacted with a nitrogen-containing catalyst to obtain a product containing benzene. The reaction temperature is 280~340℃; The reaction pressure is 0.1~0.4 MPa; The flow rate of the hydrogen gas is 5~10 ml / min; The nitrogen-containing catalyst comprises a hierarchical porous molecular sieve and a nitride supported on the surface of the hierarchical porous molecular sieve; The nitride is selected from WN; The method for preparing the nitrogen-containing catalyst is characterized in that, Includes the following steps: (1) The initial molecular sieve was subjected to alkali treatment and ammonium ion exchange treatment to obtain a multi-level porous molecular sieve; (2) The multi-level porous molecular sieve obtained in (1) is immersed in a solution containing a tungsten source to obtain a catalyst precursor, which is dried (III) and calcined (III) to obtain a multi-level porous molecular sieve loaded with WO3. (3) The hierarchical porous molecular sieve loaded with WO3 obtained in (2) is subjected to nitriding treatment in an ammonia atmosphere to obtain the nitrogen-containing catalyst; The initial molecular sieve is selected from mordenite molecular sieve and / or ZSM-5 molecular sieve; In the multi-level porous molecular sieve loaded with WO3, the mass ratio of WO3 to the multi-level porous molecular sieve is (1-3):

100.

2. The method for preparing benzene by dehydrogenation of cyclohexane according to claim 1, characterized in that, The alkaline treatment includes: The initial molecular sieve was treated with alkali solution, dried (I), and calcined (I) to obtain the alkali-treated initial molecular sieve. The temperature for alkaline treatment is 65~90 °C; The alkaline treatment time is 0.5~1.5h; The alkaline solution is selected from NaOH solution and / or KOH solution; The solid-liquid ratio of the molecular sieve to the alkaline solution is 1:(10~30)g / ml; The concentration of the alkaline solution is 0.1~0.3 mol / L; The temperature of the drying process I is 80~130 °C; The drying time for step I is 8~24 hours; The calcination temperature I is 450~650 °C; The calcination time is 1-6 hours.

3. The method for preparing benzene by dehydrogenation of cyclohexane according to claim 1, characterized in that, The ammonium ion exchange treatment includes: The initial molecular sieve obtained after alkali treatment is subjected to ammonium ion exchange in an ammonium salt solution, followed by drying (II) and calcination (II) to obtain the hierarchical porous molecular sieve. The temperature for ammonium ion exchange is 65~90 °C; The ammonium ion exchange time is 4-8 hours; The ammonium salt is NH4NO3; The concentration of the ammonium salt solution is 0.4~1.2 mol / L; The solid-liquid ratio of the molecular sieve to the ammonium salt solution is 1:(10~30)g / ml; The temperature of the drying II process is 80~130°C; The drying time for step II is 8-24 hours; The calcination temperature II is 450~650°C; The calcination time for II is 1-6 hours; The multi-stage porous molecular sieve is crushed and sieved. The particle size of the multi-stage porous molecular sieve obtained after crushing and sieving is 16~32 mesh.

4. The method for preparing benzene by dehydrogenation of cyclohexane according to claim 1, characterized in that, The tungsten source is selected from tungsten hexachloride and / or ammonium metatungstate; The solid-liquid ratio of the hierarchical porous molecular sieve to the solution containing tungsten salt is 1:(0.6-0.8) g / ml; The temperature of the drying III process is 80~130°C; The drying time for step III is 6-24 hours; The calcination temperature III is 450~650°C; The calcination time for the third stage is 1 to 6 hours.

5. The method for preparing benzene by dehydrogenation of cyclohexane according to claim 1, characterized in that, The nitriding treatment temperature is 650~750℃; The nitriding treatment time is 0.5~4h; The heating rate for the nitriding treatment is 4~10℃ / min.

6. The method for preparing benzene by dehydrogenation of cyclohexane according to claim 1, characterized in that, The reaction time is 2-3 hours.

7. The method for preparing benzene by dehydrogenation of cyclohexane according to claim 1, characterized in that, In the raw materials, the mass hourly space velocity (MSV) of the cyclohexane is 2-4 h⁻¹. -1 .

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