A nitrogen-containing catalyst for the dehydrogenation of cyclohexane to benzene, its preparation method and application

Abstract

This application discloses a nitrogen-containing catalyst for the dehydrogenation of cyclohexane to benzene, its preparation method, and its application. The catalyst comprises a hierarchical porous molecular sieve and a nitride supported on the surface of the sieve; the nitride is selected from FeN and / or Fe₂N. The catalyst provided in this application can be applied to the dehydrogenation reaction of cyclohexane to produce benzene and improves the conversion rate of cyclohexane and the selectivity of the benzene produced. The preparation method is stable, controllable, and reproducible. The method for the dehydrogenation reaction of cyclohexane to produce benzene provided in this application uses the catalyst provided in this application, resulting in a fast reaction rate, high yield, and applicability to large-scale production.

Description

Technical Field

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

[0002] Reversible hydrogen storage and release technology based on organic liquid hydrides in cyclohexane-benzene-hydrogen or methylcyclohexane-toluene-hydrogen storage systems is considered an effective means for large-scale storage and long-distance transportation of hydrogen energy. Currently, dehydrogenation of hydrogen supports such as cyclohexane generally uses Pt / γ-Al₂O₃ and its modified catalysts. However, under unsteady conditions with no hydrogen circulation, low pressure, and fluctuating temperature and feed rate, these catalysts generally suffer from high dehydrogenation temperatures, easy deactivation due to carbon deposition, and low efficiency of the dehydrogenation system. Therefore, one of the prerequisites for the industrialization of this reversible hydrogen storage and release technology is the development of low-temperature, high-efficiency dehydrogenation catalysts.

[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 catalyst performance. Nitrides have attracted attention in recent years due to their catalytic performance similar to precious metals. Nitrides and precious metals share similar d-band electron characteristics below the Fermi level, and compared to precious metals, nitrides are inexpensive and exhibit excellent resistance to sulfur poisoning, thus showing broad application prospects in the field of catalysts. Summary of the Invention

[0004] This application describes the preparation of metal nitrides supported on hierarchical porous molecular sieves. The method is inexpensive, simple, and produces well-dispersed nitrides on the sieves. When applied to the dehydrogenation of cyclohexane to benzene, the catalyst exhibits good activity, high cyclohexane conversion and benzene selectivity, and good stability.

[0005] 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;

[0006] According to one aspect of this application, a nitrogen-containing catalyst for the dehydrogenation of cyclohexane to benzene is provided, the nitrogen-containing catalyst 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 FeN and / or Fe2N.

[0008] The multi-level porous molecular sieve is made from mordenite molecular sieve and / or ZSM-5 molecular sieve;

[0009] The silica-to-alumina ratio of the multi-level porous molecular sieve is 10–30;

[0010] Optionally, the silica-alumina ratio of the hierarchical porous molecular sieve is any value among 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, and 30, or a range between any two.

[0011] The multi-stage porous molecular sieve undergoes alkali treatment, ammonium ion exchange treatment, and crushing and sieving treatment.

[0012] The alkaline treatment includes the following steps:

[0013] The mordenite zeolite molecular sieve and / or ZSM-5 molecular sieve were impregnated in an alkaline solution, dried, and calcined to obtain an alkaline-treated hierarchical porous molecular sieve.

[0014] The alkaline solution is selected from NaOH aqueous solution and / or KOH aqueous solution;

[0015] The concentration of the alkaline solution is 0.1–0.3 mol / L;

[0016] The solid-liquid ratio of the silicate zeolite molecular sieve and / or ZSM-5 molecular sieve to the alkaline solution is 1:(10-30)g / ml;

[0017] The temperature of the impregnation I is 65–90°C;

[0018] Optionally, the temperature of the impregnation I is any value among 65°C, 70°C, 75°C, 80°C, 85°C, and 90°C, or a range between any two.

[0019] The immersion time for the first stage is 0.5 to 1.5 hours.

[0020] Optionally, the immersion time I is any value among 0.5 hours, 0.75 hours, 1 hour, 1.25 hours, and 1.5 hours, or a range between any two.

[0021] The temperature of the drying process I is 80–130°C;

[0022] 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.

[0023] The drying time for step I is 8–24 hours;

[0024] 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.

[0025] The calcination temperature I is 450–650°C;

[0026] 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.

[0027] The calcination time is 1 to 6 hours.

[0028] Optionally, the calcination time I is any value among 1h, 2h, 3h, 4h, 5h, and 6h, or a range between any two.

[0029] The ammonium ion exchange treatment includes the following steps:

[0030] The alkali-treated molecular sieve was impregnated with ammonium salt solution, dried, and calcined. This yielded a molecular sieve that had undergone both alkali treatment and ammonium ion exchange treatment.

[0031] The ammonium salt solution is selected from NH4NO3 solution;

[0032] The concentration of the ammonium salt solution is 0.4–1.2 mol / L;

[0033] 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.

[0034] The solid-liquid ratio of the alkali-treated molecular sieve to the ammonium salt solution is 1:(10-30)g / ml;

[0035] Optionally, the solid-liquid ratio of the alkali-treated molecular sieve to the ammonium salt solution is any value among 1:10, 1:20, and 1:30, or any range between the two.

[0036] The temperature for impregnation II is 65–90°C;

[0037] Optionally, the temperature of the impregnation II is any value among 65°C, 70°C, 75°C, 80°C, 85°C, and 90°C, or a range between any two.

[0038] The immersion time for the second stage is 4–8 hours;

[0039] Optionally, the immersion time II is any value among 4h, 5h, 6h, 7h, and 8h, or a range between any two.

[0040] The temperature of the drying II process is 80–130°C;

[0041] 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.

[0042] The drying time for step II is 8–24 hours;

[0043] Optionally, the drying time II is any value among 8h, 12h, 16h, 20h, and 24h, or a range between any two.

[0044] The calcination temperature II is 450–650°C;

[0045] 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.

[0046] The calcination time II is 1 to 6 hours.

[0047] Optionally, the upper limit of the calcination time II is selected from any value of 1h, 2h, 3h, 4h, 5h, 6h or any range between two.

[0048] The molecular sieve that has undergone alkali treatment and ammonium ion exchange treatment, after being crushed and sieved, has a particle size of 16-32 mesh, which is the multi-stage porous molecular sieve.

[0049] 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:

[0050] The multi-level porous molecular sieve III is impregnated in an aqueous solution containing iron salt, dried, calcined, and nitrided to obtain the nitrogen-containing catalyst for the dehydrogenation of cyclohexane to benzene.

[0051] The iron salt is selected from at least one of ferric chloride, ferric sulfate, and ferric nitrate.

[0052] The mass ratio of iron in the iron salt to the mass of the hierarchical porous molecular sieve is (0.6–2.1):100;

[0053] Optionally, the mass ratio of iron in the iron salt to the mass of the hierarchical porous molecular sieve is any value from 0.6:100, 1:100, 1.5:100, 2:100, 2.1:100, or any range between two.

[0054] The solid-liquid ratio of the multi-level porous molecular sieve to the aqueous solution containing iron salt is 1:(0.6~0.8)g / ml;

[0055] Optionally, the solid-liquid ratio of the multi-level porous molecular sieve to the aqueous solution containing iron 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.

[0056] The temperature for impregnation III is 23–30°C;

[0057] Optionally, the temperature of the impregnation III is any value among 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, and 30°C, or a range between any two.

[0058] The soaking time for the third stage is 0.5 to 1 hour;

[0059] Optionally, the impregnation time III is any value among 0.5h, 0.75h, and 1h, or a range between any two.

[0060] The temperature of the drying III process is 80–130°C;

[0061] 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.

[0062] The drying time for step III is 6–24 hours;

[0063] 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.

[0064] The calcination temperature III is 450–650°C;

[0065] 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.

[0066] The calcination time for the third stage is 1 to 6 hours.

[0067] Optionally, the calcination time III is any value among 1h, 2h, 3h, 4h, 5h, and 6h, or a range between any two.

[0068] The atmosphere for the nitriding treatment is an ammonia atmosphere;

[0069] The nitriding treatment temperature is 600–700°C;

[0070] Optionally, the nitriding temperature is any value among 600°C, 650°C, and 700°C, or a range between any two.

[0071] The nitriding treatment time is 0.5 to 4 hours;

[0072] 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.

[0073] The heating rate for the nitriding treatment is 4–10 °C / min.

[0074] 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.

[0075] According to another aspect of this application, a method for preparing the above-mentioned nitrogen-containing catalyst is provided, comprising the following steps:

[0076] (1) The initial molecular sieve is subjected to alkali treatment and ammonium ion exchange treatment to obtain a multi-level porous molecular sieve;

[0077] (2) The multi-level porous molecular sieve is immersed in an iron salt solution to obtain a catalyst precursor, and the obtained catalyst precursor is calcined to obtain a multi-level porous molecular sieve loaded with Fe2O3.

[0078] (3) The multi-level porous molecular sieve loaded with Fe2O3 is subjected to nitriding treatment in an ammonia atmosphere to obtain the catalyst.

[0079] Specifically, the above-mentioned calcined mixture is placed in an open tube furnace, and the temperature is raised under the condition of a nitrogen source to obtain the catalyst FeN, Fe2N / hierarchical porous molecular sieve.

[0080] Impregnation III is an equal-volume impregnation.

[0081] According to another aspect of this application, a method for preparing benzene by dehydrogenation of cyclohexane is provided, wherein a raw material containing hydrogen and cyclohexane is introduced into a fixed-bed reactor and reacted with a catalyst to obtain a product containing benzene.

[0082] 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.

[0083] The reaction temperature is 280–340°C;

[0084] 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.

[0085] The reaction time is 2-3 hours;

[0086] Optionally, the reaction time is any value among 2h, 2.5h, and 3h, or a range between any two.

[0087] The reaction pressure is 0.1–0.4 MPa;

[0088] 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.

[0089] In the raw materials,

[0090] The flow rate of the hydrogen gas is 5–10 ml / min;

[0091] 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.

[0092] The mass hourly space velocity of the cyclohexane is 2–4 h⁻¹. -1 .

[0093] 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.

[0094] The beneficial effects that this application can produce include:

[0095] 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.

[0096] 2) The preparation method of the catalyst provided in this application is stable, controllable and reproducible.

[0097] 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

[0098] Figure 1 Catalyst 1 # X-ray powder diffraction pattern of the FeN and Fe2N mixture. Detailed Implementation

[0099] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0100] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0101] Examples 1-28

[0102] Preparation of catalysts

[0103] Taking item 1 in Tables 1-3 as an example, maintaining the solution temperature at I 65℃, the mordenite molecular sieve (silicon-to-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 I 12 h, and calcined at 550℃ for I 3 h to obtain Na-type hierarchical porous molecular sieve material. Maintaining the solution temperature at II 80℃, the Na-type hierarchical porous molecular sieve material with a solid-liquid ratio (g / ml) of 1:20 was subjected to ammonium ion exchange with a 0.8 mol / L NH4NO3 solution for 6 h, washed, dried at 100℃ II 12 h, and calcined at 550℃ II After 3 hours, hydrogen-type hierarchical porous molecular sieve material was obtained; it was crushed and sieved to 20 mesh to prepare hierarchical porous molecular sieve material; ferric chloride was dissolved in deionized water, poured into the hierarchical porous molecular sieve material and stirred with a glass plate (the mass ratio of iron element in the synthesized Fe2O3 to the mass of the hierarchical porous molecular sieve was 2:100, and the solid-liquid ratio of the hierarchical porous molecular sieve material to the iron salt solution was 1:0.7 g / ml), placed at 25℃ for 1 hour, dried in an oven at 100℃ for 6 hours, and calcined at 500℃ for 4 hours. The calcined mixture was placed in an open tube furnace, heated to 650℃ with a heating rate of 4℃ / min under ammonia gas, and then heated at this temperature for 0.5 hours to obtain catalyst FeN,Fe2N / hierarchical porous molecular sieve material, denoted as catalyst 1. # .

[0104] 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:

[0105] Table 1

[0106]

[0107]

[0108] Table 2

[0109]

[0110]

[0111] Table 3

[0112]

[0113]

[0114]

[0115] The explanations for columns 1 to 3 above are as follows:

[0116] The silica-to-alumina ratio of ZSM-5 molecular sieve (Z) is 20–30.

[0117] The silica-to-alumina ratio of mordenite molecular sieve (S) is 10–20.

[0118] 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).

[0119] Iron salts: ferric chloride (Fe1), ferric sulfate (Fe2), ferric nitrate (Fe3).

[0120] XRD characterization

[0121] 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 FeN and Fe2N mixture in the sample conform to the characteristic peaks of the FeN and Fe2N mixture (e.g., Figure 1 (As shown).

[0122] Gas chromatography characterization

[0123] The composition of the acetaldehyde condensation reaction products was analyzed using an Agilent 7890B gas chromatograph (FID detector, HP-5 capillary column).

[0124] Application Example 1

[0125] The catalyst is used in the dehydrogenation reaction of cyclohexane to prepare benzene.

[0126] Catalysts 1 to 28 prepared in Examples 1-3 # ~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.

[0127] After the reaction stabilized, both the reactants and products were analyzed using online gas chromatography. The results are shown in Table 4.

[0128] Table 4

[0129]

[0130]

[0131] As can be seen from the table, the prepared catalyst, when applied to this reaction, exhibits high conversion rate and selectivity.

[0132] Application Example 2

[0133] Catalyst 1 prepared using the catalysts 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.

[0134] Table 5

[0135]

[0136]

[0137] The table shows that the reaction temperature has a significant impact on the reaction conversion rate.

[0138] 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, In a fixed-bed reactor, a feedstock containing hydrogen and cyclohexane is introduced and reacted with a nitrogen-containing catalyst to obtain a product containing benzene. 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 FeN and / or Fe2N; The multi-level porous molecular sieve is made from mordenite molecular sieve and / or ZSM-5 molecular sieve; The silicon-to-aluminum atomic ratio of the hierarchical porous molecular sieve is 10~30; The reaction temperature is 280~320℃; The reaction pressure is 0.1~0.4 MPa.

2. The method for preparing benzene by dehydrogenation of cyclohexane according to claim 1, characterized in that, The particle size of the multi-stage porous molecular sieve is 16~32 mesh.

3. A method for producing benzene from cyclohexane by dehydrogenation according to claim 1, characterized in that, The method for preparing the catalyst includes the following steps: The multi-level porous molecular sieve III is impregnated in an aqueous solution containing iron salt, dried, calcined, and nitrided to obtain the nitrogen-containing catalyst for the dehydrogenation of cyclohexane to benzene.

4. The method according to claim 3, characterized in that, The multi-stage porous molecular sieve undergoes alkali treatment, ammonium ion exchange treatment, and crushing and sieving treatment.

5. The method according to claim 4, characterized in that, The alkaline treatment includes the following steps: The mordenite zeolite molecular sieve and / or ZSM-5 molecular sieve are impregnated in an alkaline solution, dried, and calcined to obtain an alkaline-treated molecular sieve. The alkaline solution is selected from NaOH aqueous solution and / or KOH aqueous solution; The concentration of the alkaline solution is 0.1~0.3 mol / L; The solid-liquid ratio of the silicate zeolite molecular sieve and / or ZSM-5 molecular sieve to the alkaline solution is 1:(10~30)g / ml; The temperature of the impregnation I is 65~90℃; The immersion time for I is 0.5~1.5h; The temperature of the drying process I is 80~130℃; The drying time for step I is 8~24 hours; The calcination temperature I is 450~650℃; The calcination time is 1-6 hours.

6. The method according to claim 5, characterized in that, The ammonium ion exchange treatment includes the following steps: The alkali-treated molecular sieve was impregnated with ammonium salt solution, dried, and calcined to obtain the alkali-treated and ammonium ion-exchange-treated molecular sieve. The ammonium salt solution is selected from NH4NO3 solution; The concentration of the ammonium salt solution is 0.4~1.2 mol / L; The solid-liquid ratio of the alkali-treated molecular sieve to the ammonium salt solution is 1:(10~30)g / ml; The temperature for impregnation II is 65~90℃; The immersion time for the second stage is 4-8 hours; The temperature of the drying II process is 80~130℃; The drying time for step II is 8-24 hours; The calcination temperature II is 450~650℃; The calcination time II is 1~6 hours.

7. The method according to claim 3, characterized in that, The iron salt is selected from at least one of ferric chloride, ferric sulfate, and ferric nitrate. The mass ratio of iron in the iron salt to the mass of the multi-level porous molecular sieve is (0.6-2.1):100; The solid-liquid ratio of the multi-level porous molecular sieve to the aqueous solution containing iron salt is 1:(0.6~0.8) g / ml; The temperature for impregnation III is 23~30℃; The soaking time for the third stage is 0.5 to 1 hour; The temperature of the drying III process is 80~130℃; The drying time for step III is 6-24 hours; The calcination temperature III is 450~650℃; The calcination time for the third stage is 1 to 6 hours.

8. The method according to claim 3, characterized in that, The atmosphere for the nitriding treatment is an ammonia atmosphere; The nitriding treatment temperature is 600~700℃; The nitriding treatment time is 0.5~4h; The heating rate for the nitriding treatment is 4~10℃ / min.

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