Preparation method and application of alumina supported ruthenium catalyst

Abstract

The invention provides a preparation method of a novel aluminum oxide supported ruthenium catalyst, which is used in a reaction for preparing cyclohexene by partial hydrogenation of benzene. The preparation method comprises the following steps: mixing aluminum sulfate octadecahydrate serving as a raw material with dicyandiamide and alpha-alanine, roasting to prepare defective aluminum oxide, and loading ruthenium onto the defective aluminum oxide by adopting an impregnation method to prepare the Ru / Al2O3-x catalyst. The aluminum oxide prepared by the synthetic route has higher penta-coordinated aluminum concentration and higher specific surface area, is used for anchoring ruthenium atoms, can inhibit the growth of ruthenium clusters in catalytic partial hydrogenation reaction of benzene, and has higher catalytic activity and stability.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical engineering, and specifically relates to a preparation method and application of a novel alumina-supported ruthenium catalyst. Background Art

[0002] Cyclohexene is an important chemical raw material that can be used to produce nylon, feed, medicine, polyester and pesticides, etc., and has broad application prospects. At present, there are two process routes for producing nylon-6 and nylon-66. The traditional production route is benzene→cyclohexane→cyclohexanol+cyclohexanone→cyclohexanone→nylon. In this route, cyclohexane oxidation is a free radical reaction. For safety reasons, the conversion rate can only be controlled below 5%. There are disadvantages such as many by-products, high energy consumption, low yield and low raw material utilization. The process route for partial hydrogenation of benzene to produce cyclohexene is benzene→cyclohexene→cyclohexanone→nylon. This process avoids the cyclohexane oxidation process and can consume 1 / 3 less hydrogen. At the same time, the by-product cyclohexane can be reused. It is an environmentally friendly, atomic-economical, energy-saving and efficient process route.

[0003] The catalyst commonly used in the partial hydrogenation of benzene to produce cyclohexene is a ruthenium-based catalyst, which is mostly a high-load catalyst with a high cost of use, and the selectivity of cyclohexene is also low. In order to reduce costs, low-load ruthenium-based catalysts have become a research hotspot. CN109331821A modifies sepiolite with zirconium oxide, and then loads metallic ruthenium. The load used is 8%. When the conversion rate of benzene is 55%, the selectivity of cyclohexene reaches 58%. Although the ruthenium load is reduced, the selectivity of cyclohexene is not ideal. CN116764629A discloses a method for preparing a graphene-supported ruthenium-based catalyst, which is a supported catalyst, but with graphene as a carrier, the cost is relatively high. The hydrotalcite carrier, which has been studied more, is prepared by double titration method, which will produce a large amount of alkaline wastewater, is unfriendly to the environment, and the selectivity of cyclohexene is also low.

[0004] γ-Al2O3 is a commonly used catalyst carrier, but when it is used as a carrier to load metal ruthenium for partial hydrogenation of benzene, the conversion rate of benzene and the selectivity of cyclohexene are low, and the stability is also poor. The reason is that during the reaction, metal ruthenium is easy to aggregate and grow into ruthenium clusters, resulting in reduced activity. 3-x The carrier, due to being mixed with dicyandiamide and α-alanine and then calcined, has an increased concentration of pentacoordinated aluminum, which can be used to anchor metallic ruthenium and inhibit the growth of ruthenium clusters. Summary of the invention

[0005] The purpose of the present invention is to provide a preparation method of a novel alumina-supported ruthenium catalyst and its application, and its application in the reaction of partial hydrogenation of benzene to produce cyclohexene.

[0006] The present invention adopts the following technical solution: A preparation method of a novel alumina-supported ruthenium catalyst and its application, characterized in that the catalyst carrier is defective alumina, comprising the following steps: (1) Mix dicyandiamide C2H4N4, α-C3H7NO2 and Al2(SO4)3·18H2O and grind them evenly; The addition ratio of C2H4N4, α-C3H7NO2 and Al2(SO4)3·18H2O is 1:0.8-1.2:1.

[0007] (2) The ground mixture is first heated to 100°C-140°C in a muffle furnace and kept at this temperature for 20 min-40 min, then heated to 400°C-700°C and kept at this temperature for 2-3 h. The heating rate of the muffle furnace is 5°C / min. The calcined solid is collected and ground to obtain defective Al2O 3-x ; (3) Al2O 3-x Add to pure water and stir to disperse evenly, then add anhydrous RuCl3, stir in a 60-80℃ water bath for 2-6 h, the Ru loading is 1-5wt%; (4) Add potassium borohydride solution dropwise to the mixed solution obtained in step (3), stir for 20-40 min, filter and wash with pure water until no chloride ions are detected, and dry to obtain Ru / Al2O 3-x catalyst.

[0008] The present invention provides a method for preparing the above-mentioned alumina-supported ruthenium catalyst and its application in the reaction of partial hydrogenation of benzene to produce cyclohexene, comprising the following steps: Add catalyst, pure water and ZnSO4·7H2O to the lining of the autoclave, and add benzene to the feed tank. Then, repeatedly purge with hydrogen 3-5 times to expel the air in the autoclave, introduce hydrogen and pressurize to 4.0-6.0 MPa, raise the temperature to 140-160℃, adjust the speed to 700-1000 rpm, and when the temperature in the autoclave reaches the set temperature, add the benzene in the feed tank to the lining, start the reaction, and take samples every 10 minutes. All products are analyzed by gas chromatography, the chromatographic column is a PEG capillary column, and the detector is FID.

[0009] The beneficial effects of the present invention are: Compared with alumina prepared by conventional methods, the alumina prepared by the present invention has a higher concentration of penta-coordinated aluminum in the prepared alumina due to the addition of α-alanine during the calcination process, and has a higher specific surface area, which is used to anchor ruthenium atoms, and can inhibit the growth of ruthenium clusters in the catalytic partial hydrogenation reaction of benzene, and has higher catalytic activity and stability. At the same time, the ruthenium loading amount used in the present invention is 1.75%, which is much lower than the loading amount of the catalyst used in industry (greater than 10%), greatly reducing the use cost, and does not generate a large amount of alkaline wastewater during the preparation process, which is environmentally friendly. DETAILED DESCRIPTION

[0010] The embodiments of the present invention are described in detail below. The embodiments are intended to explain the present invention but are not to be construed as limiting the present invention.

[0011] Example 1 6.0 g C2H4N4, 4.8 g α-C3H7NO2 and 6.0 g Al2(SO4)3·18H2O were mixed and ground evenly, then heated to 120℃ in a muffle furnace at a heating rate of 5℃ / min and kept warm for 30 min, then heated to 550℃ and kept warm for 2 h. The calcined solid was collected and ground and recorded as AO1.

[0012] Add 0.1109 g KBH4 to 10 mL pure water to prepare potassium borohydride solution, disperse 3 g AO1 in 100 mL pure water, add 0.1096 g RuCl3, stir in an 80 °C water bath for 3 h, then drop the potassium borohydride solution, continue stirring for 0.5 h, filter and wash, and dry to obtain the target catalyst, recorded as Ru / AO1.

[0013] Example 2 The other conditions were the same as those in Example 1, except that the mass of C2H4N4 was changed to 0 g, and the target catalyst was recorded as Ru / AO2.

[0014] Example 3 The other conditions were the same as in Example 1, except that the mass of α-C3H7NO2 was changed to 0g, and the target catalyst was recorded as Ru / AO3 Example 4 The other conditions were the same as those in Example 1, except that the mass of α-C3H7NO2 was changed to 2.4 g, and the target catalyst was recorded as Ru / AO4.

[0015] Example 5 The other conditions were the same as those in Example 1, except that the mass of α-C3H7NO2 was changed to 7.2 g, and the target catalyst was recorded as Ru / AO5.

[0016] Comparative Example 1 The other conditions were the same as those in Example 1, except that the calcination process was changed to a one-step calcination, that is, the temperature was increased from room temperature to 550°C at a rate of 5°C / min and maintained for 2 h. The target catalyst was recorded as Ru / AO6.

[0017] Comparative Example 2 The other conditions were the same as those in Example 1, except that the masses of C2H4N4 and α-C3H7NO2 were changed to 0 g, and the target catalyst was recorded as Ru / AO7.

[0018] Comparative Example 3 Add 0.1109 g KBH4 to 10 mL pure water to prepare potassium borohydride solution, disperse 3 g γ-Al2O3 in 100 mL pure water, add 0.1096 g RuCl3, stir in a water bath at 80°C for 3 h, then drop the potassium borohydride solution, continue stirring for 0.5 h, filter and wash, and dry to obtain the target catalyst, which is recorded as Ru / AO8.

[0019] Performance Test: Add catalyst, pure water and ZnSO4·7H2O to the lining of the autoclave, and add benzene to the feed tank. Then, purge with hydrogen repeatedly for 5 times to expel the air in the autoclave, introduce hydrogen and pressurize to 5.0 MPa, raise the temperature to 155℃, adjust the speed to 1000 rpm, and when the temperature in the autoclave reaches the set temperature, add the benzene in the feed tank to the lining, start the reaction, and take samples every 10 minutes. All products are analyzed by gas chromatography, the chromatographic column is a PEG capillary column, and the detector is FID.

[0020] Table 1, benzene conversion, cyclohexene selectivity and yield when the catalysts prepared in Examples 1-5 and Comparative Examples 1-3 were used for partial hydrogenation of benzene for 15 min.

[0021]

[0022] Stability test: After the catalyst was tested for performance, the catalyst in the autoclave was centrifuged and collected for the second cycle, and the collected catalyst was added to the autoclave, and the other conditions were the same as the performance test method, and repeated once, i.e., one cycle. The catalysts prepared in Example 1, Example 3 and Comparative Example 1 were tested for stability.

[0023] Table 2, Stability test of the catalyst prepared in Example 1 for partial hydrogenation of benzene

[0024] Table 3, Stability test of the catalyst prepared in Example 3 for partial hydrogenation of benzene

[0025] Table 4, stability test of the catalyst prepared in Comparative Example 1 for partial hydrogenation of benzene

[0026] The above description is only a typical implementation of the present invention, and all improvements and modifications made according to the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. A method for preparing an alumina-supported ruthenium catalyst, characterized in that: The following steps are involved: (1) Mix dicyandiamide C2H4N4, α-C3H7NO2 and Al2(SO4)3·18H2O and grind them evenly; (2) The ground mixture is calcined in a muffle furnace to obtain defective Al2O 3-x ; (3) Al2O 3-x Add to pure water and stir to disperse evenly, then add anhydrous RuCl3 and stir in a water bath for 2-6 h; (4) Add potassium borohydride solution dropwise to the mixed solution obtained in step (3), stir for 20-40 min, filter and wash until no chloride ions are detected, and dry to obtain Ru / Al2O 3-x catalyst.

2. The method for preparing an alumina-supported ruthenium catalyst according to claim 1, characterized in that: The addition ratio of C2H4N4, α-C3H7NO2 and Al2(SO4)3·18H2O is 1:0.8-1.2:

1.

3. The method for preparing the alumina-supported ruthenium catalyst according to claim 1, characterized in that: In step (2), the first stage of the two-stage heating program is to heat the temperature to 100-140°C and keep it warm for 20-40 min, and the second stage is to heat the temperature to 500-600°C and keep it warm for 2-3 h.

4. The method for preparing an alumina-supported ruthenium catalyst according to claim 1, characterized in that: In step (2), the heating rate of the muffle furnace is 3-5°C / min.

5. The method for preparing the alumina-supported ruthenium catalyst according to claim 1, characterized in that: In step (3), the loading amount of Ru is 1-5 wt %, and the water bath temperature is 60-90° C.

6. The method for preparing an alumina-supported ruthenium catalyst according to claim 1, characterized in that: In step (4), the drying temperature is 60-100°C and the drying time is 8-16 h.

7. Use of the catalyst obtained by the preparation method according to any one of claims 1 to 6 in the preparation of cyclohexene by partial hydrogenation of benzene, characterized in that: The steps include: Catalyst, pure water and ZnSO4·7H2O are added into the reactor, and after the air is exhausted, hydrogen is introduced and pressurized to 4.0-6.0 MPa, the temperature is raised to 140-160°C, the rotation speed is adjusted to 700-1000 rpm, and benzene is added to react to prepare cyclohexene.

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