A catalyst for preparing benzene from cyclohexane by dehydrogenation and a preparation method and application thereof

Abstract

The application discloses a catalyst for preparing benzene through cyclohexane dehydrogenation and a preparation method and application thereof, which comprises gamma-Al2O3 and VN supported on the surface of the gamma-Al2O3. 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 high in reaction speed and yield, and can be applied to large-scale production.

Description

Technical Field

[0001] This application relates to a catalyst for the dehydrogenation of cyclohexane to benzene, its preparation method and application, and belongs to the field of chemical engineering. Background Technology

[0002] Cyclohexane is an important chemical raw material and intermediate with a wide range of applications. Approximately 20% is used as a solvent and adhesive, and 80% is used in organic synthesis, primarily for the production of cyclohexanol, cyclohexanone, adipic acid, and caprolactam. Before 2010, the domestic cyclohexane market consumed more than it produced, resulting in tens of thousands of tons of imports annually despite lower exports. In 2011, domestic cyclohexane imports experienced a sharp decline and have since remained below 5,000 tons, while exports have remained relatively stable.

[0003] The dehydrogenation of cyclohexane is called catalytic reforming in the petroleum refining industry. The active component of the catalyst is a noble metal such as platinum, the acidic component is mainly a halogen (chlorine or fluorine), and the support is alumina. The noble metal constitutes the active dehydrogenation center. Raney nickel or other non-noble metal catalysts are also used. In operating units, bimetallic or multimetallic catalysts are often used, with the multimetallic component acting as a co-catalyst to improve catalyst performance. Among existing catalysts, Ni, Ir, Pd, and Pt are commonly used as the active components of dehydrogenation catalysts. Pt exhibits high activity for cycloalkanes due to its high activation ability for CH bonds. Under the same active component content, the higher the metal dispersion, the higher the catalyst activity. However, the recovery of noble metals used in catalysts is difficult and expensive. Summary of the Invention

[0004] This patent describes the preparation of metal nitrides supported on alumina, which is inexpensive, simple to prepare, and exhibits good dispersion of the nitrides on alumina. When applied to the dehydrogenation of cyclohexane to benzene, it demonstrates good catalyst activity, high cyclohexane conversion and benzene selectivity, and good stability.

[0005] According to one aspect of this application, a catalyst for the dehydrogenation of cyclohexane to benzene is provided, which can improve the conversion rate of cyclohexane and the selectivity of benzene; comprising γ-Al2O3 and VN supported on the surface of said γ-Al2O3.

[0006] The molar ratio of VN to γ-Al2O3 is (1-2):178, in terms of the molar amounts of vanadium and aluminum.

[0007] Optionally, the molar ratio of VN to γ-Al2O3 is any value among 1:178, 1.5:178, and 2:178, or any range between the two.

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

[0009] The catalyst was obtained by impregnating γ-Al2O3 in a solution containing vanadium salt, drying, calcining, and nitriding.

[0010] The vanadium salt is selected from at least one of vanadium tetrachloride, vanadium oxalate, and vanadium oxalate.

[0011] The solid-liquid ratio of the γ-Al2O3 to the vanadium-containing solution is 1:(0.6~0.8)g / ml;

[0012] Optionally, the solid-liquid ratio of the γ-Al2O3 to the vanadium salt-containing solution 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.

[0013] The molar ratio of vanadium in the vanadium-containing solution to aluminum in the γ-Al2O3 is (1-2):178.

[0014] Optionally, the molar ratio of vanadium in the vanadium-containing solution to aluminum in the γ-Al2O3 is any value from 1:178, 1.5:178, 2:178, or any range between both.

[0015] The drying temperature is 90–110°C;

[0016] Optionally, the drying temperature is any value among 90°C, 100°C, and 110°C, or a range between any two.

[0017] The drying time is 4 to 8 hours.

[0018] Optionally, the drying time is any value among 4h, 5h, 6h, 7h, and 8h, or a range between any two.

[0019] The calcination temperature is 450–550°C;

[0020] Optionally, the calcination temperature is any value or a range between 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, and 550℃.

[0021] The calcination time is 2 to 6 hours.

[0022] Optionally, the calcination time is any value among 2h, 3h, 4h, 5h, and 6h, or a range between any two.

[0023] The nitriding process includes:

[0024] In a nitrogen-containing atmosphere, the temperature is increased to 400–600℃ at a heating rate of 4–10℃ / min, and calcined for 0.5–4 hours.

[0025] Optionally, the nitrogen-containing atmosphere is an ammonia atmosphere.

[0026] Optionally, the heating rate is any value among 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, and 10℃ / min, or a range between any two.

[0027] Optionally, the temperature at the end of the heating process can be any value among 400℃, 450℃, 500℃, 550℃, and 600℃, or a range between any two.

[0028] Optionally, the roasting time is any value among 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, and 4h, or a range between any two.

[0029] 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 VN / γ-Al2O3.

[0030] The impregnation is an equal-volume impregnation; specifically, vanadium salt is dissolved in a certain amount of deionized water, γ-Al2O3 is poured in and stirred with a glass plate, placed at room temperature, dried in an oven and calcined.

[0031] According to another aspect of this application, a method for preparing benzene by dehydrogenation reaction of cyclohexane is provided, comprising the following steps: introducing a raw material containing hydrogen and cyclohexane into a reactor, reacting it with a catalyst to obtain a product containing benzene;

[0032] The catalyst is selected from the catalysts described above or the catalysts prepared by the preparation method described above.

[0033] The reaction temperature is 280–340°C;

[0034] 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.

[0035] The reaction time is 2-3 hours;

[0036] Optionally, the reaction time is any value among 2h, 2.5h, and 3h, or a range between any two.

[0037] The reaction pressure is 0.1–0.4 MPa.

[0038] 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.

[0039] In the raw materials,

[0040] The flow rate of the hydrogen gas is 5–10 ml / min;

[0041] 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.

[0042] The mass hourly space velocity of the cyclohexane is 2–4 h⁻¹. -1 .

[0043] 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.

[0044] The reactor is a fixed-bed reactor.

[0045] The beneficial effects that this application can produce include:

[0046] 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.

[0047] 2) The preparation method of the catalyst provided in this application is stable, controllable, and reproducible.

[0048] 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

[0049] Figure 1 Catalyst 1 # X-ray powder diffraction pattern of VN in the image. Detailed Implementation

[0050] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0051] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased commercially.

[0052] The gas chromatograph used was an Agilent 7890B gas chromatograph.

[0053] Example 1

[0054] Preparation of catalysts

[0055] Taking item 1 in Table 1 as an example, vanadium oxalate was dissolved in deionized water, γ-Al₂O₃ was added, and the mixture was stirred with a glass plate (the molar ratio of vanadium to aluminum was 1:178, and the solid-liquid ratio of γ-Al₂O₃ to the vanadium salt-containing solution was 1:0.7 g / ml). The mixture was left at room temperature for 6 hours, dried in an oven at 100°C for 6 hours, and calcined at 500°C for 4 hours. The calcined mixture was then placed in an open tube furnace, heated to 500°C at a rate of 4°C / min under ammonia gas, and heated at this temperature for 2 hours to obtain catalyst VN / γ-Al₂O₃, denoted as catalyst 1. # .

[0056] 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:

[0057] Table 1

[0058]

[0059]

[0060] The explanations for each column in Table 1 above are as follows:

[0061] Vanadium salts: vanadium tetrachloride (V1), vanadium oxalate (V2), vanadium oxalate (V3).

[0062] XRD characterization

[0063] Catalyst 1 was analyzed using a Miniflex 600 X-ray diffractometer with a Cu target. # Powder diffraction yielded catalyst 1. # The VN diffraction peaks in the image conform to the characteristic peaks of VN (e.g., Figure 1 (As shown).

[0064] Gas chromatography characterization

[0065] The composition of the acetaldehyde condensation reaction products was analyzed using an Agilent 7890B gas chromatograph (FID detector, HP-5 capillary column).

[0066] Example 2

[0067] The catalyst is used in the dehydrogenation reaction of cyclohexane to prepare benzene.

[0068] Catalysts 1 to 28 prepared in Example 1 # ~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.

[0069] After the reaction stabilized, both the reactants and products were analyzed using online gas chromatography. The results are shown in Table 2.

[0070] Table 2

[0071]

[0072]

[0073] As can be seen from the table, the synthesized catalyst is used in the cyclohexane dehydrogenation reaction, and the reaction conversion and selectivity are both high.

[0074] Example 3

[0075] Catalyst 1 prepared in Table 1 # 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 3.

[0076] Table 3

[0077]

[0078]

[0079] The table shows that the reaction temperature has a significant impact on the conversion rate of the dehydrogenation reaction.

[0080] 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 catalyst to obtain a product containing benzene. The reaction temperature is 300~340℃; The catalyst comprises γ-Al2O3 and VN supported on the surface of the γ-Al2O3; The molar ratio of VN to γ-Al2O3 is (1-2):178, in terms of the molar amounts of vanadium and aluminum.

2. A method for preparing benzene by dehydrogenation of cyclohexane according to claim 1, characterized in that, The method for preparing the catalyst includes the following steps: The catalyst was obtained by impregnating γ-Al2O3 in a solution containing vanadium salt, drying, calcining, and nitriding.

3. The method according to claim 2, characterized in that, The vanadium salt is selected from at least one of vanadium tetrachloride, vanadium oxalate, and vanadium oxalate. The solid-liquid ratio of the γ-Al2O3 to the vanadium-containing solution is 1:(0.6-0.8) g / ml; The molar ratio of vanadium in the vanadium-containing solution to aluminum in the γ-Al₂O₃ is (1-2):

178.

4. The method according to claim 2, characterized in that, The drying temperature is 90~110℃; The drying time is 4 to 8 hours.

5. The method according to claim 2, characterized in that, The calcination temperature is 450~550℃; The calcination time is 2-6 hours.

6. The method according to claim 2, characterized in that, The nitriding process includes: In a nitrogen-containing atmosphere, the temperature is increased to 400-600 °C at a heating rate of 4-10 °C / min, and calcined for 0.5-4 h.

7. The method according to claim 6, characterized in that, The nitrogen-containing atmosphere is an ammonia atmosphere.

8. The method for preparing benzene by dehydrogenation of cyclohexane according to claim 1, characterized in that, The reaction time is 2-3 hours; The reaction pressure is 0.1~0.4 MPa.

9. The method for preparing benzene by dehydrogenation of cyclohexane according to claim 1, characterized in that, In the raw materials, The flow rate of the hydrogen gas is 5~10 ml / min; The mass hourly space velocity of the cyclohexane is 2-4 h⁻¹. -1 .

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