Lanthanum oxide catalyst, method for preparing the same, and use thereof

Abstract

The present application relates to the technical field of catalyst preparation, and relates to a lanthanum oxide catalyst and a preparation method and application thereof, which comprises the following steps: (1) mixing lanthanum oxide powder and a doped element precursor, and then drying to obtain a doped powder; the doped element precursor is selected from soluble compounds containing Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Ce and Zn; (2) mixing the doped powder, silica sol, carbon nanotubes, polyethylene glycol and porous polyurethane, and then granulating to obtain a granular semi-finished product; and (3) calcining and cooling the granular semi-finished product under air isolation to obtain the catalyst. The lanthanum oxide catalyst provided in the present application can uniformly disperse active sites in the catalyst through the synergistic effect of the doped elements, silicon dioxide and carbon nanotubes, and meanwhile, the rich pores in the lanthanum oxide catalyst can enhance heat dissipation, thereby solving the problem of temperature runaway of the catalyst bed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalyst preparation, and particularly relates to a lanthanum oxide catalyst and a preparation method and application thereof. BACKGROUND

[0002] Methane oxidative coupling reaction is one of the methods for preparing ethylene by directly reacting methane, and one of the most common methane oxidative coupling reaction catalysts is a lanthanum oxide catalyst. Methane oxidative coupling reaction is a strong exothermic reaction. If the activity of the lanthanum oxide catalyst is unstable and the activity of some sites suddenly increases during the reaction process, the reaction will be intensified, thereby causing local overheating and triggering a temperature runaway. The temperature runaway not only destroys the structural stability of the catalyst, causes the catalyst to sinter and the catalytic activity to decrease, but also damages the reactor and affects the service life of the reactor, thereby bringing serious safety hazards.

[0003] Therefore, it is urgent to provide a lanthanum oxide catalyst with stable activity and capable of avoiding temperature runaway and a preparation method thereof. SUMMARY

[0004] The application aims to solve the problem of temperature runaway of the catalyst bed layer in methane oxidative coupling reaction, and provides a lanthanum oxide catalyst and a preparation method and application thereof.

[0005] To achieve the above-mentioned purpose, the first aspect of the application provides a preparation method of a lanthanum oxide catalyst, and the method comprises the following steps:

[0006] (1) mixing lanthanum oxide powder and a doped element precursor and then drying to obtain a doped powder; wherein the doped element precursor is selected from soluble compounds containing Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Ce, Zn elements;

[0007] (2) mixing the doped powder, silica sol, carbon nanotubes, polyethylene glycol and porous polyurethane and then granulating to obtain a granular semi-finished product;

[0008] (3) calcining and cooling the granular semi-finished product in an air-isolated environment to obtain a catalyst.

[0009] The second aspect of the application provides a lanthanum oxide catalyst, wherein the catalyst comprises lanthanum oxide, a doped element, silicon dioxide and carbon nanotubes.

[0010] The molar ratio of the lanthanum oxide and the doped element is 1:0.02-0.15 in terms of the molar amount of lanthanum element and the doped element; and the mass ratio of the lanthanum oxide, the silicon dioxide and the carbon nanotubes is 1:1-20:0.001-0.5.

[0011] The third aspect of the present application provides application of the lanthanum oxide catalyst of the second aspect of the present application in a methane oxidative coupling reaction.

[0012] By the above technical solution, the present application has the following beneficial technical effects:

[0013] 1) The lanthanum oxide catalyst provided in the present application has the synergistic effect of doping elements, silicon dioxide and carbon nanotubes, which can uniformly disperse the active sites in the catalyst, and the rich pores in the lanthanum oxide catalyst can further enhance heat dissipation, thereby solving the problem of flying temperature of the catalyst bed.

[0014] 2) The preparation method of the lanthanum oxide particles provided in the present application is simple in operation and mild in conditions, and is suitable for industrial popularization. DETAILED DESCRIPTION

[0015] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are understood to be approximate values. The endpoints of the ranges of values and the values thereof can be combined with one another even though not expressly stated in the application. The endpoints of the ranges of values and the values thereof can be combined with one another to create a new range of values.

[0016] The first aspect of the present application provides a preparation method of a lanthanum oxide catalyst, which comprises the following steps:

[0017] (1) mixing lanthanum oxide powder and a doping element precursor, and then drying to obtain a doped powder; wherein the doping element precursor is selected from soluble compounds containing Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Ce, Zn elements;

[0018] (2) mixing the doped powder, silica sol, carbon nanotubes, polyethylene glycol and porous polyurethane, and then granulating to obtain a granular semi-finished product;

[0019] (3) calcining and cooling the granular semi-finished product in an air-tight environment to obtain a catalyst.

[0020] In step (1),

[0021] In a preferred embodiment, the purity of the lanthanum oxide powder is ≥95%, preferably ≥99%. The lanthanum oxide powder in the present application can be a commercially available product, such as general analytical purity and / or higher 6N grade lanthanum oxide.

[0022] In a preferred embodiment, the doping element precursor is selected from soluble compounds containing Ba, Al, Zn, Mg, Ca, Ce elements. In the present application, the soluble compounds of the doping element precursor are not particularly limited, including but not limited to nitrate, sulfate, chloride and the like of the doping element.

[0023] In a preferred embodiment, in order to improve the mixing uniformity of the lanthanum oxide powder and the doping element precursor, the lanthanum oxide powder and the doping element precursor are mixed in an aqueous solution. In the present application, the doping element precursor can be first dissolved in water, and then the lanthanum oxide powder is added to the water, and the mixture is stirred thoroughly.

[0024] In a preferred embodiment, the molar ratio of the lanthanum oxide powder to the doping element, based on the molar amount of lanthanum element and the doping element, is 1:0.02-0.15, preferably 1:0.05-0.08.

[0025] In a preferred embodiment, the drying temperature is 80-150°C, preferably 90-110°C; and the drying time is 2-10h, preferably 4-6h.

[0026] In step (2),

[0027] In a preferred embodiment, the content of silicon dioxide in the silica sol is 10-40wt%, preferably 20-30wt%.

[0028] In a preferred embodiment, the carbon nanotube is selected from single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0029] In a preferred embodiment, the molecular weight of the polyethylene glycol is 1000-30000, preferably 6000-20000. In the present application, the mechanical strength and stability of the lanthanum oxide catalyst prepared by using polyethylene glycol with a molecular weight within the above range are better.

[0030] In a preferred embodiment, the pore size of the porous polyurethane is 15-60PPI, preferably 25-40PPI.

[0031] In the present application, the polyethylene glycol and the porous polyurethane work together to enrich the internal pore structure of the catalyst particles and improve the heat transfer performance of the catalyst.

[0032] In a preferred embodiment, the mass ratio of the doped powder, the silica sol (calculated as SiO2), the carbon nanotube, the polyethylene glycol, and the porous polyurethane is 1:1-20:0.001-0.5:0.001-10:0.05-5; preferably 1:1-5.5:0.05-0.15:0.5-5.5:0.1-1.

[0033] In comparison with dilution by adding inert materials such as glass beads when packing the catalyst bed, the active sites in the catalyst can be more uniformly diluted without packing inert materials by adding a large amount of silica sol during the preparation of the catalyst, and the polyethylene glycol and the porous polyurethane can form a large number of pores in the interior of the catalyst particles, avoiding covering of the active components by silica, thereby obtaining a catalyst with high stability and high activity.

[0034] In a preferred embodiment, the granulation is performed in a granulator. In the present application, the granulation is not specially limited and can be performed according to conventional operations. In the granulation, an appropriate amount of water can be added to the mixture of the doped powder, the silica sol, the carbon nanotube, the polyethylene glycol, and the porous polyurethane for adjustment. The amount of water is not specially limited in the present application and can be adjusted according to the conventional amount used in the granulation.

[0035] In a preferred embodiment, the granular semi-product is a spherical particle, and the average diameter of the spherical particle is 100-1000 μm, preferably 500-800 μm.

[0036] In step (3),

[0037] In a preferred embodiment, the granular semi-product is preferably subjected to standing and drying before calcination. The standing is performed at room temperature for 12-36 h, and the drying is performed at 100-150 ℃ for 10-16 h.

[0038] In a preferred embodiment, the granular semi-product is calcined and cooled under nitrogen protection to obtain the lanthanum oxide catalyst.

[0039] In a preferred embodiment, the calcination includes one-stage calcination and two-stage calcination. The one-stage calcination has a one-stage heating rate of 2-5 ℃ / min, a one-stage calcination temperature of 500-700 ℃, and a one-stage calcination time of 2-6 h. The two-stage calcination has a two-stage heating rate of 3-8 ℃ / min, a two-stage calcination temperature of 750-1000 ℃, and a two-stage calcination time of 2-4 h.

[0040] The second aspect of the present application provides a lanthanum oxide catalyst, wherein the catalyst comprises lanthanum oxide, a doping element, silica, and a carbon nanotube.

[0041] wherein the molar ratio of the lanthanum oxide and the doping element is 1:0.02-0.15 in terms of the molar amount of the lanthanum element and the doping element; and the mass ratio of the lanthanum oxide, the silicon dioxide and the carbon nanotube is 1:0.05-20:0.001-0.5.

[0042] In a preferred embodiment, the molar ratio of the lanthanum oxide and the doping element is 1:0.05-0.08 in terms of the molar amount of the lanthanum element and the doping element; and the mass ratio of the lanthanum oxide, the silicon dioxide and the carbon nanotube is 1:1-5.5:0.05-0.15.

[0043] In a preferred embodiment, the pore volume of the catalyst is 0.3-0.8 cm 3 / g, preferably 0.3-0.6 cm 3 / g; the pore size is 10-50 nm, preferably 10-35 nm; and the BET specific surface area is 200-300 m 2 / g, preferably 210-280 m 2 / g.

[0044] In a preferred embodiment, the mechanical strength of the catalyst is 30-60 N / particle, preferably 35-60 N / particle.

[0045] The third aspect of the present application provides the use of the catalyst according to the second aspect of the present application in the oxidative coupling reaction of methane.

[0046] The present application will be described in detail below by way of examples.

[0047] In the examples and comparative examples, the lanthanum oxide powder is a commercially available product with a purity of 5N and an average particle size of 50 nm; and the silicon sol contains 30 wt% of silicon dioxide with an average particle size of 10-20 nm.

[0048] Example 1

[0049] (1) 5 g of barium nitrate was dissolved in 50 g of deionized water, and after stirring until the barium nitrate was completely dissolved, 40 g of lanthanum oxide powder was added, and then dried at 100°C for 4 h to obtain a doped powder;

[0050] (2) The doped powder, 400 g of silicon sol, 4 g of single-walled carbon nanotubes, 200 g of polyethylene glycol (molecular weight 6000), 20 g of porous polyurethane (pore size 30 PPI) and water were mixed and then put into a granulator to obtain a spherical particle semi-finished product with an average particle size of 500 μm;

[0051] (3) The obtained granular semi-product is placed in a muffle furnace under nitrogen protection, first heated to 650°C at a heating rate of 2°C / min, calcined for 2h to complete the first-stage calcination, then heated to 850°C at a heating rate of 5°C / min, calcined for 3h to complete the second-stage calcination, and then cooled to room temperature under nitrogen protection to obtain the lanthanum oxide-based catalyst.

[0052] Example 2

[0053] (1) 4g of zinc nitrate hexahydrate is dissolved in 50g of deionized water, 40g of lanthanum oxide powder is added after stirring until the zinc nitrate is completely dissolved, and then dried at 100°C for 4h to obtain a doped powder;

[0054] (2) The above doped powder, 200g of silica sol, 3g of multi-walled carbon nanotubes, 40g of polyethylene glycol (molecular weight 20000), 10g of porous polyurethane (pore size 30PPI), and water are uniformly mixed and then placed in a granulator to obtain spherical granular semi-products with an average particle size of 800μm;

[0055] (3) The obtained granular semi-product is placed in a muffle furnace under nitrogen protection, first heated to 650°C at a heating rate of 2°C / min, calcined for 2h to complete the first-stage calcination, then heated to 850°C at a heating rate of 5°C / min, calcined for 3h to complete the second-stage calcination, and then cooled to room temperature under nitrogen protection to obtain the lanthanum oxide-based catalyst.

[0056] Example 3

[0057] (1) 6g of cerium nitrate hexahydrate is dissolved in 50g of deionized water, 40g of lanthanum oxide powder is added after stirring until the cerium nitrate is completely dissolved, and then dried at 100°C for 4h to obtain a doped powder;

[0058] (2) The above doped powder, 650g of silica sol, 2g of single-walled carbon nanotubes, 100g of polyethylene glycol (molecular weight 10000), 30g of porous polyurethane (pore size 30PPI), and water are uniformly mixed and then placed in a granulator to obtain spherical granular semi-products with an average particle size of 800μm;

[0059] (3) The obtained granular semi-product is placed in a muffle furnace under nitrogen protection, first heated to 650°C at a heating rate of 2°C / min, calcined for 2h to complete the first-stage calcination, then heated to 850°C at a heating rate of 5°C / min, calcined for 3h to complete the second-stage calcination, and then cooled to room temperature under nitrogen protection to obtain the lanthanum oxide-based catalyst.

[0060] Example 4

[0061] The same as Example 1, except that the molecular weight of the polyethylene glycol is 15000 and the pore size of the porous polyurethane is 15 PPI.

[0062] Comparative Example 1

[0063] (1) 5 g of barium nitrate was dissolved in 50 g of deionized water, and after stirring until the barium nitrate was completely dissolved, 40 g of lanthanum oxide powder was added, and then dried at 100°C for 4 h to obtain a doped powder;

[0064] (2) The doped powder, 400 g of silica sol, 200 g of polyethylene glycol (molecular weight 10000), and water were mixed uniformly and then put into a granulator to obtain spherical granular semi-products with an average particle size of 500 μm;

[0065] (3) The granular semi-products obtained were left to stand at room temperature for 24 h and then dried at 120°C for 12 h. The dried granular semi-products were placed in a muffle furnace, and under nitrogen protection, first heated to 650°C at a heating rate of 2°C / min, and calcined for 2 h to complete the first stage of calcination, and then heated to 850°C at a heating rate of 5°C / min, and calcined for 3 h to complete the second stage of calcination, and then cooled to room temperature under nitrogen protection to obtain a lanthanum oxide-based catalyst.

[0066] Test Example 1

[0067] The mechanical strength, pore size, pore volume, and specific surface area of the lanthanum oxide catalyst granules in Examples 1-4 and Comparative Example 1 were tested, and the test results are shown in Table 1.

[0068] Among them, the mechanical strength was tested by using a particle strength tester purchased from Jiangyan City, Jiangsu Province, China, model KC-2A, seven lanthanum oxide catalyst particles were randomly selected for testing, and the average value was taken as the test result; the pore size, pore volume, and specific surface area were tested by using a chemical adsorption instrument of Micromeritics Corporation, model AutoChem 2920.

[0069] Table 1

[0070] No. Mechanical strength N / grain Pore size / nm Pore volume / cm 3 / g]] Specific surface area / m 2 / g]] Example 1 43 17 0.45 252 Example 2 46 15 0.43 257 Example 3 41 12 0.42 261 Example 4 47 18 0.49 263 Comparative Example 1 Comparative Example 2 45 13 0.33 223

[0071] Test Example 2

[0072] The lanthanum oxide catalyst granules in Examples 1-4 and Comparative Example 1 were respectively loaded in a fixed bed reactor with an inner diameter of 26 mm and a bed thickness of 25 mm, and under the conditions of a methane space velocity of 80000 mL / g h, an alkoxy volume ratio of 4, and a temperature of 700°C, continuous reaction was carried out for 2 h, and the temperature in the middle of the catalyst bed was recorded.

[0073] From the recording results, it can be seen that the catalyst bed temperature in Examples 1-4 is relatively stable throughout the reaction process, and is basically maintained at 700-720℃, indicating that the active sites of the catalyst are uniformly dispersed and have good stability. However, the catalyst bed in Comparative Example 1 has temperature fluctuations after running for 1 min, and the temperature sharply rises from 700℃ to 810℃, resulting in a temperature runaway, indicating that the active sites of the catalyst are not uniformly dispersed.

[0074] The above describes the preferred embodiments of the present application in detail, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A method for preparing a lanthanum oxide catalyst, characterized in that, The method includes the following steps: (1) Lanthanum oxide powder and dopant precursor are mixed and dried to obtain doped powder; wherein the dopant precursor is selected from soluble compounds containing Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Ce and Zn. (2) The doped powder, silica sol, carbon nanotubes, polyethylene glycol and porous polyurethane are mixed and then granulated to obtain a particle semi-finished product; (3) The granular semi-finished product is roasted and cooled in an air-isolated environment to obtain a catalyst; Based on silica in the silica sol, the mass ratio of the doped powder, silica sol, carbon nanotubes, polyethylene glycol, and porous polyurethane is 1:1-20:0.001-0.5:0.001-10:0.05-5.

2. The preparation method according to claim 1, wherein, The molar ratio of the lanthanum oxide powder to the dopant element is 1:0.02-0.15, based on the molar amounts of lanthanum and the dopant element.

3. The preparation method according to claim 1, wherein, The molar ratio of the lanthanum oxide powder to the dopant element is 1:0.05-0.08, based on the molar amounts of lanthanum and the dopant element.

4. The preparation method according to claim 1, wherein, The silica sol contains 10-40 wt% silica.

5. The preparation method according to claim 1, wherein, The silica sol contains 20-30 wt% silica.

6. The preparation method according to claim 1, wherein, The carbon nanotubes are selected from single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

7. The preparation method according to claim 1, wherein, The molecular weight of the polyethylene glycol is 1000-30000.

8. The preparation method according to claim 1, wherein, The molecular weight of the polyethylene glycol is 6000-20000.

9. The preparation method according to claim 1, wherein, The porous polyurethane has a pore size of 15-60 PPI.

10. The preparation method according to claim 1, wherein, The porous polyurethane has a pore size of 25-40 PPI.

11. The preparation method according to claim 1, wherein, Based on silica in the silica sol, the mass ratio of the doped powder, silica sol, carbon nanotubes, polyethylene glycol, and porous polyurethane is 1:1-5.5:0.05-0.15:0.5-5.5:0.1-1.

12. The preparation method according to any one of claims 1-11, wherein, The roasting includes a first-stage roasting and a second-stage roasting. The first-stage roasting has a heating rate of 2-5℃ / min, a roasting temperature of 500-700℃, and a roasting time of 2-6h. The second-stage roasting has a heating rate of 3-8℃ / min, a roasting temperature of 750-1000℃, and a roasting time of 2-4h.

13. A lanthanum oxide catalyst, characterized in that, The catalyst comprises lanthanum oxide, a dopant element, silicon dioxide, and carbon nanotubes; wherein, based on the molar amounts of lanthanum oxide and the dopant element, the molar ratio of lanthanum oxide to the dopant element is 1:0.02-0.15; and the mass ratio of lanthanum oxide, silicon dioxide, and carbon nanotubes is 1:1-20:0.001-0.

5. The catalyst has a pore volume of 0.3-0.8 cm. 3 / g; pore size 10-50nm; BET specific surface area 200-300m² 2 / g.

14. The lanthanum oxide catalyst according to claim 13, wherein, The molar ratio of lanthanum oxide to dopant is 1:0.05-0.08, based on the molar amounts of lanthanum and dopant.

15. The lanthanum oxide catalyst according to claim 13, wherein, The mass ratio of lanthanum oxide, silicon dioxide, and carbon nanotubes is 1:1-5.5:0.05-0.

15.

16. The lanthanum oxide catalyst according to claim 13, wherein, The catalyst has a pore volume of 0.3-0.6 cm. 3 / g.

17. The lanthanum oxide catalyst according to claim 13, wherein, The catalyst has a pore size of 10-35 nm.

18. The lanthanum oxide catalyst according to claim 13, wherein, The catalyst has a BET specific surface area of ​​210-280 m². 2 / g.

19. The use of the lanthanum oxide catalyst according to any one of claims 13-18 in the oxidative coupling reaction of methane.