Iron carbide catalyst, method for its preparation and its use in the synthesis of hydrocarbons from synthesis gas

Abstract

The application provides an iron-carbide catalyst, a preparation method thereof and application of the iron-carbide catalyst in synthesis gas hydrocarbon synthesis, wherein the catalyst contains 50-88% of iron, 5-10% of carbon, 2-10% of aluminum and 0-35% of element X in terms of percentage by weight; iron substantially exists in the form of active epsilon-Fe2C nanoparticles, X is one or more of potassium, calcium, barium, manganese, cobalt, nickel, copper, zirconium, molybdenum, lanthanum and cerium, the specific surface area of the catalyst is 20-105 m 2 / g, and the average pore size is 5-25 nm. The main phase of the catalyst is an epsilon-Fe2C phase, has a mesoporous structure, can enhance the reaction stability when applied in a Fischer-Tropsch synthesis reaction, reduces the selectivity of by-products CO2 and CH4, and is beneficial to the generation of long-chain alkanes.

Description

Technical Field

[0001] This invention belongs to the field of Fischer-Tropsch synthesis catalysts, specifically relating to an iron carbide catalyst with high stability and high activity, its preparation method, and its application in syngas to hydrocarbon production. Background Technology

[0002] Fischer-Tropsch synthesis technology provides a pathway for the conversion of coal into liquid fuels, specifically by transforming coal-based syngas into clean liquid fuels primarily composed of straight-chain alkanes and olefins. This process offers advantages such as being sulfur-free, nitrogen-free, and aromatic-free, making it a crucial technology for the clean and efficient utilization of coal. Iron-based catalysts hold an important position among Fischer-Tropsch synthesis catalysts due to their low cost, high catalytic activity and water-gas shift reaction activity, and significant auxiliary effects.

[0003] The Fischer-Tropsch synthesis is a high-temperature, high-pressure, and strongly exothermic reaction, requiring timely heat exchange to ensure the stable operation of the catalytic system. Fischer-Tropsch slurry bed reactors offer advantages such as ease of control, uniform temperature, and online catalyst replacement, making them widely used in industrial production. However, the catalyst is prone to breakage and pulverization during the vigorous movement of the slurry bed, leading to filter clogging and affecting the stable operation of the reaction system. Furthermore, iron-based catalysts exist in multiple phases, which can interconvert under certain conditions (Journal of American Chemical Society, 2010, 132, 14928). This interconversion process can easily damage the catalyst structure, leading to catalyst breakage and accelerated deactivation. Therefore, slurry bed catalysts need to possess very high wear resistance and structural stability.

[0004] Traditional iron-based catalysts exhibit high activity in the water-gas shift reaction, resulting in high CO2 selectivity (20%-45%). Under the new development trend, new catalyst technologies are needed to achieve emission reduction and efficiency improvement. The literature (Science Advance, 2018, 4, eaau2947) reports Fe2C / Fe... 2.2The C phase exhibits low CO2 selectivity. Patent CN110339848A discloses a method for preparing supported Fe2C carbides. This method involves preparing an iron salt precursor via impregnation, followed by H2 reduction to form an intermediate Fe phase, which is then carbonized with syngas to form a supported Fe2C catalyst. The catalyst prepared by this method exhibits high CH4 selectivity (13.5%) but poor mechanical strength, making it difficult to meet the requirements for long-term slurry bed operation. Patents CN1803281A, CN1495148A, CN101164693A, and CN101190412A disclose methods for preparing Raney iron or framework iron catalysts (with Fe in a metallic state). However, these two types of catalysts have high CO2 product selectivity (30%-45%), low carbon utilization, and high energy consumption. Patent CN104399501A describes a method for carbonizing skeletal iron into Fe2C catalyst in polyethylene glycol solvent. However, the catalyst synthesized by this method has high CH4 selectivity (17.3%) and high CO2 selectivity (18.9%), and the reaction is a discontinuous reaction, which can only be applied to low temperatures below 200°C, resulting in low production efficiency.

[0005] In summary, the catalysts prepared in the prior art have problems such as low reaction efficiency, high selectivity for CH4 byproducts, poor wear resistance, and poor catalyst stability. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides an iron carbide catalyst, its preparation method, and its application in the Fischer-Tropsch synthesis reaction. The catalyst of this invention has an ε-Fe₂C phase as its main phase and a mesoporous structure. When applied to the Fischer-Tropsch synthesis reaction, it can enhance reaction stability and reduce the selectivity of byproducts CO₂ and CH₄.

[0007] In a first aspect, the present invention provides an iron carbide catalyst, wherein, by weight percentage, the catalyst comprises 50-88% iron, 5-10% carbon, 2-10% aluminum, and 0-35% element X, or is composed of 50-88% iron, 5-10% carbon, 2-10% aluminum, and 0-35% element X; wherein the iron exists substantially in the form of active ε-Fe2C nanoparticles, and X is one or more of potassium, calcium, barium, manganese, cobalt, nickel, copper, zirconium, molybdenum, lanthanum, and cerium, and the specific surface area of ​​the catalyst is 20-105 m². 2 / g, with an average pore size of 5-25nm.

[0008] Secondly, the present invention provides a method for preparing the above-mentioned catalyst, wherein the preparation method includes:

[0009] (1) The iron block, aluminum block and any metal X are melted evenly and cooled to obtain precursor A, wherein X is one or more of calcium, barium, manganese, cobalt, nickel, copper, zirconium, molybdenum, lanthanum and cerium;

[0010] (2) Precursor A is crushed and sieved to obtain precursor B;

[0011] (3) Dealuminize the precursor B to form a precursor C containing skeletal iron;

[0012] (4) Wash and dry the precursor C, or wash, impregnate and dry the precursor C to obtain the precursor D; when the catalyst contains potassium, the impregnation is carried out with a methanol solution of potassium carbonate.

[0013] (5) The precursor D was carbonized in an atmosphere of H2 and CO to obtain an iron carbide catalyst.

[0014] Thirdly, this invention provides an application of the above-mentioned catalyst in the Fischer-Tropsch synthesis reaction, wherein the reaction conditions are: H2 / CO = 1-50:1, and space velocity is 1000-25000 h⁻¹. -1 The temperature is 200-350℃ and the pressure is 1-5Mpa.

[0015] Fourthly, the present invention provides a method for preparing C2 or higher alkanes via Fischer-Tropsch synthesis using the above-mentioned catalyst, wherein the reaction conditions are: H2 / CO = 1-50:1, and space velocity is 1000-25000 h⁻¹. -1 The temperature is 200-350℃ and the pressure is 1-5Mpa.

[0016] The catalyst, its preparation method, and its application described in this invention have the following beneficial effects:

[0017] (1) The preparation method of the Fischer-Tropsch synthesis iron-based catalyst provided by the present invention is simple, does not involve complex synthesis operations, and is suitable for large-scale production.

[0018] (2) The catalyst prepared by the present invention, after being repeatedly smelted at high temperature (for example, 5 times), not only has high mechanical strength, but also has a mesoporous structure, which is conducive to the generation of long-chain alkanes and is suitable for fixed bed and slurry bed reactors.

[0019] (3) Unlike ε-Fe2C low-temperature Fischer-Tropsch synthesis technology, Raney iron or skeletal iron catalysts, the iron carbide catalyst prepared in this invention can meet the requirements of medium-temperature (200-350℃) Fischer-Tropsch synthesis, with low selectivity for CO2 and CH4 and high stability. Attached Figure Description

[0020] The accompanying drawings are part of the specification and, together with the detailed description, provide a further explanation of the invention, but are not intended to limit the invention.

[0021] Figure 1 The X-ray diffraction patterns are those of the catalysts obtained in Examples 1-8 of this invention.

[0022] Figure 2 The pore size distribution diagrams are of the catalysts obtained in Examples 1-8 of this invention. Detailed Implementation

[0023] The specific embodiments of the present invention will be described in detail below. The specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0024] In some embodiments, the present invention provides an iron carbide catalyst, wherein, by weight percentage, the catalyst comprises 50-88% iron, 5-10% carbon, 2-10% aluminum, and 0-35% element X, or is composed of 50-88% iron, 5-10% carbon, 2-10% aluminum, and 0-35% element X; wherein the iron is substantially present in the form of active ε-Fe2C nanoparticles, and X is one or more of potassium, calcium, barium, manganese, cobalt, nickel, copper, zirconium, molybdenum, lanthanum, and cerium, and the specific surface area of ​​the catalyst is 20-105 m². 2 / g, with an average pore size of 5-25nm.

[0025] In some preferred embodiments, the catalyst contains 55-88% iron, 5-10% carbon, 2-5% aluminum and 5-30% element X.

[0026] In some preferred embodiments, element X is one or more of potassium, calcium, barium, manganese, cobalt, nickel, and copper, preferably one or more of potassium, manganese, and copper.

[0027] In some preferred embodiments, the catalyst has a specific surface area of ​​70-105 m². 2 / g (e.g., 70-85mg) 2 / g), with an average pore size of 6.5-8.5 nm (e.g., 6.5-8.3 nm).

[0028] In some embodiments, the present invention provides a method for preparing the above-mentioned catalyst, wherein the preparation method includes:

[0029] (1) The iron block, aluminum block and any metal X are melted evenly and cooled to obtain precursor A, wherein X is one or more of calcium, barium, manganese, cobalt, nickel, copper, zirconium, molybdenum, lanthanum and cerium;

[0030] (2) Precursor A is crushed and sieved to obtain precursor B;

[0031] (3) Dealuminize the precursor B to form a precursor C containing skeletal iron;

[0032] (4) Wash and dry the precursor C, or wash, impregnate, and dry the precursor C and then store it in liquid paraffin to obtain the precursor D; when the catalyst contains potassium, the impregnation is carried out with a methanol solution of potassium carbonate.

[0033] (5) The precursor D was carbonized in an atmosphere of H2 and CO to obtain an iron carbide catalyst.

[0034] In a preferred embodiment, in step (1), the mass ratio of the iron block, aluminum block and metal X particles is (40-70):(30-60):(0-35), for example (40-50):(50-60):(0-10) or (40-45):(50-55):(3-5).

[0035] In a preferred embodiment, in step (1), the smelting is performed by melting the alloy raw materials into a uniform bulk alloy using an electric arc furnace, a smelting furnace, or an induction furnace, or by atomizing the alloy powder using an induction furnace.

[0036] In a preferred embodiment, in step (1), the melting process is repeated 4-6 times (e.g., 5 times).

[0037] In a preferred embodiment, in step (1), the cooling method for the molten alloy is one of natural cooling, spray cooling, cooling after suction casting, and cooling after casting.

[0038] In a preferred embodiment, in step (2), the crushing or sieving involves crushing or sieving the precursor A to a particle size of 6.5-850 μm, preferably to a particle size of 48-150 μm (e.g., 48-106 μm), to obtain precursor B.

[0039] In a preferred embodiment, in step (3), the precursor B is dealuminized by alkaline washing with an alkaline solution; the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution, preferably a potassium hydroxide solution; the concentration of the alkaline solution is 2-12 mol / L, preferably 3-9 mol / L; the amount of alkaline solution added is based on a molar ratio of aluminum to alkali in precursor B of 1:2-9, preferably 1:4-6; the temperature of the alkaline washing is 0-95℃, preferably 5-50℃ (e.g., 5-10℃); the time of the alkaline washing is 1-15h, preferably 3-6h (e.g., 3-5h); the alkaline washing is carried out under an inert gas atmosphere, preferably under argon, nitrogen or helium.

[0040] In a preferred embodiment, in step (4), the washing is performed by water washing, ethanol washing and cyclohexane washing, wherein the water washing is performed 1-20 times; the ethanol washing is performed 1-5 times; and the cyclohexane washing is performed 0-5 times, and the solid to liquid mass ratio is 1:5-15.

[0041] In a preferred embodiment, in step (4), the drying is carried out under argon, nitrogen or helium, at a temperature of 50-300°C, for a time of 3-20 hours.

[0042] In a preferred embodiment, in step (5), the precursor D is flushed into a reactor with liquid paraffin, and the carbonization is carried out in the reactor.

[0043] In a preferred embodiment, in step (5), the carbonization is carried out in an atmosphere of H2 and CO, the temperature is 180-350℃, for example 180-250℃; the heating rate is 2.5℃ / min; the pressure is 1-5MPa, for example 1-3MPa; H2 / CO = (1-70):1, preferably (1-50):1, for example (1-20):1; and the carbonization time is 5-20h, preferably 8-15h.

[0044] In some embodiments, the present invention provides an application of the above-described catalyst in a Fischer-Tropsch synthesis reaction, wherein the reaction conditions are: H2 / CO = (1-50):1, for example (1-5):1 or (1-2):1; space velocity is 1000-25000 h⁻¹. -1 For example, 1000-15000h -1 1000-12000h -1 Or 1000-6000h -1 Temperature is 200-350℃, for example 240-270℃ or 250-270℃; pressure is 1-5Mpa, for example 1-3Mpa.

[0045] In some embodiments, the present invention provides a method for preparing C2 or higher alkanes via Fischer-Tropsch synthesis using the above-described catalyst, wherein the reaction conditions are: H2 / CO = 1-50:1, for example (1-5):1 or (1-2):1; space velocity of 1000-25000 h⁻¹. -1 For example, 1000-15000h -1 1000-12000h -1 Or 1000-6000h -1 Temperature is 200-350℃, for example 240-270℃ or 250-270℃; pressure is 1-5Mpa, for example 1-3Mpa.

[0046] The invention is further illustrated by the following examples, but the invention is not limited thereto.

[0047] Example

[0048] Unless otherwise stated, the reagents, materials and apparatus involved in the following examples are all commercially available in the art; the routine operations involved in the following examples can be found in patents, patent applications and publications disclosed in the art (e.g., He Yongde, ed., Modern Coal Chemical Technology Handbook, Chemical Industry Press, 2003, but not limited thereto).

[0049] Example 1

[0050] (1) Weigh the iron blocks and aluminum blocks in a weight ratio of 45:55, mix them, and add them to the vacuum arc furnace. Evacuate the arc furnace to a vacuum level of 6×10. -4 Pa, argon gas is introduced, DC power is turned on to start electric arc heating, the current is adjusted to melt the raw material, and electromagnetic stirring is turned on to stir the melt evenly. The melting is repeated 5 times, cast into a mold and cooled to obtain precursor A. Then, alloy precursor A is crushed and sieved to 48-106μm to obtain precursor B.

[0051] (2) Add 590 mL of 9 mol / L potassium hydroxide solution to a round-bottom flask, maintain the water bath temperature at 10 °C, and replace the air in the flask with nitrogen three times. Slowly add 45 g of alloy powder precursor B to the alkaline solution, and continue the reaction for 5 h to form precursor C. Wash 15 times with an equal volume of deionized water, rinse 3 times with 100 mL of anhydrous ethanol, and wash twice with 100 mL of cyclohexane. Dry under a nitrogen atmosphere at 120 °C for 12 h. Store the dried catalyst in liquid paraffin to obtain precursor D.

[0052] (3) Take 10g of catalyst precursor D and weigh 450g of liquid paraffin. Wash the catalyst precursor into a 1L reactor with the liquid paraffin. Use syngas with a H2 / CO ratio of 20 and pressurize to 3MPa. Heat to 250℃ and carbonize in situ for 15h. This catalyst is named FA1 (iron content 88%, carbon content 10%, aluminum content 2%), and its phase XRD pattern is shown in [reference needed]. Figure 1 Aperture distribution is seen in Figure 2 After carbonization, the reaction gas is switched to a syngas mixture with H2 / CO = 2, the reaction pressure is 3 MPa, the temperature is raised to 270℃, and the space velocity is 6000 h⁻¹. -1 The evaluation results are listed in Table 1.

[0053] Example 2

[0054] (1) Same as Example 1.

[0055] (2) Same as Example 1.

[0056] (3) Take 10g of alkali-washed catalyst precursor D, weigh 450g of liquid paraffin, and rinse the catalyst precursor into a 1L reactor with the liquid paraffin. Use syngas with an H2 / CO ratio of 20 and pressurize to 3MPa. Heat to 250℃ and carbonize in situ for 15h. This catalyst is named FA1-1 (iron content 88%, carbon content 10%, aluminum content 2%), and its structure is the same as FA1. After carbonization, switch to syngas with an H2 / CO ratio of 2, with a reaction pressure of 3MPa, temperature of 240℃, and space velocity of 6000h⁻¹. -1 The evaluation results are listed in Table 1.

[0057] Example 3

[0058] (1) Prepare bulk alloy according to the method of Example 1, except that iron particles, aluminum particles and manganese sheets are weighed in a weight ratio of 43:52:5 and then put into an electric arc furnace.

[0059] (2) Same as Example 1.

[0060] (3) Take 10g of alkali-washed catalyst precursor D, weigh 450g of liquid paraffin, and rinse the catalyst precursor into a 1L reactor with the liquid paraffin. Use syngas with a H2 / CO ratio of 20, and pressurize to 3MPa. Heat to 270℃ and carbonize in situ for 15h. The catalyst is named FA2 (iron content 79%, carbon content 8%, aluminum content 4%, manganese content 9%), and its phase XRD pattern is shown in [reference needed]. Figure 1 Aperture distribution is seen in Figure 2 After carbonization, the reaction gas is switched to a syngas mixture of H2 / CO = 2, with a reaction pressure of 3 MPa, a temperature of 270 °C, and a space velocity of 15000 h⁻¹. -1 The evaluation results are listed in Table 1.

[0061] Example 4

[0062] (1) Prepare bulk alloy according to the method of Example 1, except that iron particles, aluminum particles and copper particles are weighed in a weight ratio of 43:52:5 and then put into the electric arc furnace.

[0063] (2) Same as Example 1.

[0064] (3) Take 10g of alkali-washed catalyst precursor D, weigh 450g of liquid paraffin, and rinse the catalyst precursor into a 1L reactor with the liquid paraffin. Use syngas with a H2 / CO ratio of 20, and pressurize to 3MPa. Heat to 270℃ and carbonize in situ for 15h. This catalyst is named FA3 (iron content 78%, carbon content 8%, aluminum content 4%, copper content 10%), and its phase XRD pattern is shown in [reference needed]. Figure 1 Aperture distribution is seen in Figure 2After carbonization, the reaction gas is switched to a syngas mixture with H2 / CO = 2, at a pressure of 3 MPa, a temperature of 270°C, and a space velocity of 6000 h⁻¹. -1 The evaluation results are listed in Table 1.

[0065] Example 5

[0066] (1) Same as Example 4.

[0067] (2) Same as Example 1.

[0068] (3) Take 10g of the alkaline-washed catalyst precursor and weigh 450g of liquid paraffin. Wash the catalyst precursor into a 1L reactor with the liquid paraffin. Use syngas with a H2 / CO ratio of 20 and pressurize to 3MPa. Raise the temperature to 270℃ and carbonize in situ for 15h. This catalyst is named FA3-1 (iron content 78%, carbon content 8%, aluminum content 4%, copper content 10%), and its structure is the same as FA3. After carbonization, switch to syngas with a H2 / CO ratio of 2, with a reaction pressure of 3MPa, a temperature of 250℃, and a space velocity of 12000h. -1 The evaluation results are listed in Table 1.

[0069] Example 6

[0070] (1) Prepare bulk alloy according to the method of Example 1, except that iron particles, aluminum particles, manganese flakes and copper particles are weighed in a weight ratio of 42:51:4:3 and then put into an electric arc furnace.

[0071] (2) Same as Example 1.

[0072] (3) Take 10g of the alkaline-washed catalyst precursor and weigh 450g of liquid paraffin. Wash the catalyst precursor into a 1L reactor with the liquid paraffin. Use syngas with a H2 / CO ratio of 20 and pressurize to 3MPa. Heat to 270℃ and carbonize in situ for 15h. This catalyst is named FA4 (iron content 73%, carbon content 7%, aluminum content 5%, manganese content 10%, copper content 5%). Its phase XRD pattern is shown in [reference needed]. Figure 1 Aperture distribution is seen in Figure 2 After carbonization, the reaction gas is switched to a syngas mixture of H2 / CO = 2, with a reaction pressure of 3 MPa, a temperature of 270 °C, and a space velocity of 15000 h⁻¹. -1 The evaluation results are listed in Table 1.

[0073] Example 7

[0074] (1) Same as Example 6.

[0075] (2) Same as Example 6.

[0076] (3) Take 10g of the alkaline-washed catalyst precursor and weigh 450g of liquid paraffin. Wash the catalyst precursor into a 1L reactor with the liquid paraffin. Use syngas with a H2 / CO ratio of 20 and pressurize to 3MPa. Raise the temperature to 270℃ and carbonize in situ for 15h. Name the catalyst FA4-1 (iron content 73%, carbon content 7%, aluminum content 5%, manganese content 10%, copper content 5%). After carbonization, switch to syngas with a H2 / CO ratio of 2, with a reaction pressure of 3MPa, a temperature of 250℃, and a space velocity of 12000h. -1 The evaluation results are listed in Table 1.

[0077] Example 8

[0078] (1) Same as Example 6.

[0079] (2) Add 590 ml of 9 mol / L potassium hydroxide solution to a round-bottom flask, maintain the water bath temperature at 10°C, replace the air in the flask with nitrogen three times, slowly add 45 g of alloy powder precursor B to the alkaline solution, and let the reaction continue for 5 h to form precursor C.

[0080] (3) Wash precursor C 15 times with an equal volume of deionized water and rinse 3 times with 100 mL of anhydrous ethanol. Mix 30 mL of potassium carbonate methanol solution with the alkaline filtered catalyst precursor, dry at 200 °C for 12 h under N2 atmosphere, and then store in liquid paraffin to obtain precursor D.

[0081] (4) Take 10g of alkali-washed catalyst precursor D, weigh 450g of liquid paraffin, and rinse the catalyst precursor into a 1L reactor with the liquid paraffin. Use syngas with an H2 / CO ratio of 20 and pressurize to 3MPa. Heat to 270℃ and carbonize in situ for 15h. Name this catalyst FA5 (iron content 69%, carbon content 7%, aluminum content 5%, manganese content 12%, copper content 5%, potassium content 2%). After carbonization, switch to syngas with an H2 / CO ratio of 2, maintain a reaction pressure of 3MPa, a temperature of 250℃, and a space velocity of 12000h⁻¹. -1 The evaluation results are listed in Table 1.

[0082] Comparative Example 1

[0083] (1) The preparation method of this catalyst is derived from the reference (J. Catal. 2011, 279, 111). Ferric nitrate was used as the iron source (concentration 3 mol / L), and diluted ammonia (1:1 dilution) was used as the precipitant. Continuous co-precipitation was performed at 80℃ and pH = 8.5. The precipitate was filtered and washed several times, dried at 120℃ for 12 h, and calcined in a muffle furnace at 500℃ for 5 h. Subsequently, the precursor was pressed into tablets and granulated, with a sieve particle size of 6.5-150 μm.

[0084] (2) Take 14.3g of the calcined catalyst precursor and weigh 450g of liquid paraffin. Wash the catalyst precursor into a 1L reactor with the liquid paraffin. Reduce the catalyst at 270℃ for 10h with pure hydrogen pressurized to 3MPa. Then switch to syngas with an H2 / CO ratio of 20. Heat to 270℃ and carbonize in situ for 15h. This catalyst is named D1. After carbonization, switch to syngas with an H2 / CO ratio of 2, with a reaction pressure of 3MPa, a temperature of 270℃, and a space velocity of 6000h⁻¹. -1 The evaluation results are listed in Table 1.

[0085] Comparative Example 2

[0086] (1) Similar to Comparative Example 1, except that a mixed solution of ferric nitrate and manganese nitrate was continuously co-precipitated with ammonia water to prepare a precipitated FeMn catalyst with a Fe:Mn ratio of 10:1.

[0087] (2) Same as Comparative Example 1, this catalyst was named D2. After carbonization, the synthesis gas was switched to H2 / CO = 2, the reaction pressure was 3 MPa, the temperature was 270℃, and the space velocity was 15000 h⁻¹. -1 .

[0088] Comparative Example 3

[0089] (1) Same as Example 6.

[0090] (2) Same as in Example 6, this catalyst is named D3.

[0091] (3) Take 10g of the alkaline-washed catalyst precursor and weigh 450g of liquid paraffin. Wash the catalyst precursor into a 1L reactor with the liquid paraffin. Set the pressure of pure H2 to 3MPa and the temperature to 270℃. After H2 reduction for 5h, switch to syngas with H2 / CO = 2. The reaction pressure is 3MPa, the temperature is 270℃, and the space velocity is 15000h⁻¹. -1 .

[0092] Table 1. Specific surface area and average pore size of catalysts in Examples 1-8

[0093] FA1 72 8.14 FA2 84 7.63 FA3 75 6.57 FA4 74 8.06 FA5 68 8.23

[0094] As can be seen from Table 1, the iron carbide catalysts invented in this invention have a large specific surface area, all exceeding 70 μm. 2 / g (preferably higher than 84m) 2 / g), forming a mesoporous structure with an average pore size of 6.5-8.5 nm, which is conducive to the formation of long-chain alkanes.

[0095] Table 2. Results of Fischer-Tropsch synthesis reactions in the examples and comparative examples.

[0096]

[0097] As shown in Table 2, the iron carbide catalyst prepared by the method of this invention exhibits high reactivity under industrial conditions. Under the same reaction conditions, its reactivity is superior to that of similar precipitated and framework iron catalysts. Its preferred reactivity reaches 273.5 mmol / h / g-Fe.

[0098] Meanwhile, the methane selectivity of the iron carbide catalyst provided by this invention is low, preferably below 5.4% after 24 hours of reaction; C 2+ The selectivity of effective hydrocarbon products is higher than 80%, with 94.6% being the preferred selectivity.

[0099] Compared with skeletal iron catalysts, the iron carbide catalyst prepared by the method of the present invention has a lower CO2 selectivity, preferably as low as 7.4%.

[0100] Stability comparison revealed that the iron carbide catalyst prepared by the method of the present invention maintained high stability in both CO conversion and product selectivity after 360 h of reaction, and its stability was higher than that of precipitated and framework iron catalysts D1-D3.

Claims

1. An iron carbide catalyst for use in Fischer-Tropsch synthesis reactions at temperatures of 250-350°C, wherein, The reaction conditions for the Fischer-Tropsch synthesis reaction are: H2 / CO = (1-50):1; space velocity 1000-25000 h⁻¹ -1 Temperature: 250-350℃; Pressure: 1-5 MPa; Specific surface area of ​​the catalyst: 70-105 m² 2 / g, with an average pore size of 6.5-8.5 nm; the catalyst is obtained by a preparation method including the following steps: (1) Iron blocks, aluminum blocks and one or more metals selected from manganese and copper are melted and smelted evenly, and the precursor A is obtained after cooling; (2) Precursor A is crushed and sieved to obtain precursor B; (3) Dealuminize precursor B to form precursor C containing skeletal iron; (4) Wash and dry the precursor C, and then store it in liquid paraffin to obtain the precursor D; or wash the precursor C, impregnate it with a methanol solution of potassium carbonate, dry it, and then store it in liquid paraffin to obtain the precursor D. (5) The precursor D is carbonized in an atmosphere of H2 and CO at a temperature of 250-350℃ for 5-20h to obtain an iron carbide catalyst. In the iron carbide catalyst, iron exists mainly in the form of active ε-Fe2C nanoparticles. In step (5), the carbonization conditions are: heating rate 2.5℃ / min, pressure 1-5MPa, H2 / CO=(1-70):1, time 5-20h.

2. The application as described in claim 1, wherein, The catalyst contains, by weight percentage, 50-88% iron, 5-10% carbon, 2-10% aluminum and 5-35% element X, wherein element X is one or more of manganese and copper, or element X is one or more of manganese and copper and potassium.

3. The application as described in claim 1 or 2, wherein, The catalyst contains, by weight percentage, 55-88% iron, 5-10% carbon, 2-5% aluminum and 5-30% element X, wherein element X is one or more of manganese and copper, or element X is one or more of manganese and copper and potassium.

4. The application as described in claim 1 or 2, wherein, In step (1), the mass ratio of the iron block, aluminum block and one or more metals selected from manganese and copper is (40-70):(30-60):(5-35).

5. The application as described in claim 1 or 2, wherein, In step (1), the smelting is to smelt the alloy raw materials into a uniform bulk alloy using an electric arc furnace, a smelting furnace, or an induction furnace, or to atomize the alloy raw materials into alloy powder using an induction furnace.

6. The application as described in claim 1 or 2, wherein, In step (1), the melting process is repeated 4-6 times.

7. The application as described in claim 1 or 2, wherein, In step (1), the cooling is performed by one of the following: natural cooling, spray cooling, cooling after suction casting, and cooling after casting.

8. The application as described in claim 1 or 2, wherein, In step (2), the precursor A is crushed and sieved to a particle size of 6.5-850 μm.

9. The application as described in claim 8, wherein, In step (2), the precursor A is crushed and sieved to a particle size of 48-150 μm.

10. The application as described in claim 1 or 2, wherein, In step (3), the precursor B is dealuminized by alkaline washing with alkaline solution.

11. The application as described in claim 10, wherein, The alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution.

12. The application as described in claim 11, wherein, The alkaline solution is a potassium hydroxide solution.

13. The application as described in claim 10, wherein, The concentration of the alkaline solution is 2-12 mol / L.

14. The application as described in claim 13, wherein, The concentration of the alkaline solution is 3-9 mol / L.

15. The application as described in claim 10, wherein, The alkaline solution is added according to a molar ratio of aluminum in precursor B to alkaline solution of 1:2 to 1:

9.

16. The application as described in claim 15, wherein, The alkaline solution is added according to a molar ratio of aluminum in precursor B to alkaline solution of 1:4 to 1:

6.

17. The application as described in claim 10, wherein, The alkaline washing temperature is 0-95℃.

18. The application as described in claim 17, wherein, The temperature of the alkaline washing is 5-50℃.

19. The application as described in claim 10, wherein, The alkaline washing time is 1-15 hours.

20. The application as described in claim 19, wherein, The alkaline washing time is 3-6 hours.

21. The application as described in claim 10, wherein, The alkaline washing is carried out under an inert gas atmosphere.

22. The application as described in claim 21, wherein, The alkaline washing is performed under argon, nitrogen, or helium atmosphere.

23. The application as described in claim 1 or 2, wherein, In step (4), the washing is performed by water washing, ethanol washing and cyclohexane washing, wherein water washing is performed 1-20 times, ethanol washing is performed 1-5 times, and cyclohexane washing is performed 0-5 times; the drying is performed under argon, nitrogen or helium, the drying temperature is 50-300℃, and the time is 3-20h.

24. The application as described in claim 1 or 2, wherein, In step (5), the precursor D is flushed into the reactor with liquid paraffin, and the carbonization is carried out in the reactor.

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