Catalyst for producing olefin through Fischer-Tropsch synthesis and preparation method and application thereof

Abstract

The invention discloses a preparation method and application of a catalyst for producing olefin through Fischer-Tropsch synthesis. The catalyst comprises an active component, an auxiliary component and a hydrophobic carbon layer, the active component is a Co simple substance, an oxide or a carbide, the auxiliary component is a Na simple substance or an oxide, and reaction active sites are a Co-Na nano-alloy coated by the hydrophobic carbon layer and independent Co and Na species. The preparation method comprises the following steps: uniformly mixing a precursor solution of Co and a precursor solution of Na, adding a carbon source, adding a mixture of ammonia water and ammonium carbonate for coprecipitation, adding ethanol for heating evaporation, and carrying out hydrothermal and calcination treatment to obtain the hydrophobic carbon layer coated Co-Na alloy catalyst (Co-Na C). The catalyst has the advantages of stable structure, good heat-conducting property, high active component utilization rate, high synthesis gas conversion rate, high olefin selectivity, stable reaction performance and the like, the preparation steps are simple, the raw materials are easy to obtain, the repeatability is good, and large-scale production is easy to realize.

Description

Technical Field

[0001] The present invention relates to a highly efficient Fischer-Tropsch synthesis catalyst with a special structure, which is used for catalyzing synthesis gas to directly prepare olefins, and belongs to the field of energy chemical industry. In particular, it relates to a preparation method and application of a Co-Na nano alloy structure catalyst coated with a hydrophobic carbon layer. Background Art

[0002] Fischer-Tropsch synthesis is the process of using synthesis gas (H 2 A common technology that further converts olefins (CO and CO) into various fuels and chemicals through catalytic reactions. The olefins in the products are important raw materials for the production of plastics and basic chemicals in the chemical industry. At present, olefins are mainly produced by naphtha cracking or light alkane pyrolysis. Among them, the production of olefins by Fischer-Tropsch reaction is an efficient technology for producing olefins directly from synthesis gas. However, the proportion of C1 small molecules (methane, carbon dioxide) in traditional Fischer-Tropsch synthesis products is too high, resulting in a decrease in the selectivity of olefins. Therefore, it is necessary to change the structure, composition and reaction conditions of the catalyst to improve the selectivity of olefins.

[0003] Patent CN112619691B reported a method of preparing a catalyst composed of iron, VIIB group elements, IIB group elements, silicon dioxide, and ZSM-5 molecular sieve by pulping, mixing, and spraying. The catalyst activity and selectivity of light olefins were improved by rapid diffusion of light olefins by the molecular sieve. Patent CN112007655A reported an iron-manganese oxide coated with an amorphous silicon oxide shell, which was then alkylated to obtain a hydrophobic silicon oxide-coated iron-manganese oxide catalyst, which can inhibit the CO generated by the Fischer-Tropsch reaction. 2 Patent CN113171775A reported a hydrophobic carbon-encapsulated iron-based catalyst obtained by calcining the organic framework material MIL-101(Fe)@NPG, which inhibited the water-gas shift reaction and improved the selectivity of hydrocarbons. However, the composition and preparation method of the above catalyst are complicated, the pretreatment steps are cumbersome, and the reaction conditions are harsh, which still needs further improvement. Summary of the invention

[0004] The purpose of the present invention is to adopt a simple method for preparing a hydrophobic carbon layer, introduce a bimetallic alloy structure, improve the conversion rate of CO and the selectivity of light olefins, and form a CoNa alloy by adding an appropriate amount of Na additive to enhance the CC coupling reaction and inhibit the hydrogenation reaction, thereby reducing CH 4 The hydrophobicity of the catalyst carbon layer is used to rapidly desorb water molecules from the catalyst surface, thereby reducing the competitive adsorption capacity of water molecules and CO on the catalyst surface and promoting CO conversion. The rapid desorption of water molecules can also weaken the water-gas shift reaction, resulting in CO 2 Significantly reduced.

[0005] Preparation process of Co-Na nanoalloy catalyst coated with a hydrophobic carbon layer:

[0006] (1) A mixture is prepared by dissolving a soluble salt of Co with a molar content of Co of 0.01 mol / L - 10 mol / L and a soluble salt of Na with a molar content of Na of 0.001 mol / L - 5 mol / L in 200 - 500 ml of deionized water;

[0007] The soluble salt of Co is one or more of cobalt nitrate, cobalt acetate, cobalt sulfate, and cobalt chloride; the soluble salt of Na is one or more of sodium nitrate, sodium chloride, sodium acetate, sodium sulfite, and sodium thiosulfate;

[0008] (2) The mixture obtained in step (1) is ultrasonically treated at room temperature for 5 - 10 h, vigorously stirred at 1500 - 3000 revolutions per minute for 5 - 10 h, and then a hydrophobic carbon layer precursor is added; the hydrophobic carbon layer precursor is one or more of glucose, citric acid, polyvinyl alcohol, polyethylene glycol, and aniline; after stirring is completed, ammonia water and ammonium carbonate solution are added for precipitation reaction.

[0009] (3) The mixture treated in step (2) is added to 50 - 100 ml of an ethanol solution, heated and evaporated at 70 - 95 °C for 4 - 12 hours, and then deionized water is added and placed in a hydrothermal reaction kettle for treatment at 120 - 200 °C for 3 - 8 h;

[0010] (4) The mixture treated in step (3) is filtered and then washed with deionized water to obtain a filter cake;

[0011] (5) The filter cake obtained in step (4) is dried in air at 120 - 150 °C for 6 - 24 h, and then calcined at 600 - 1200 °C in an inert gas atmosphere for 5 - 15 h to obtain a Co-Na@C catalyst; the inert gas used is one or more of helium, argon, and nitrogen; the gas hourly space velocity is 2000 - 4000 h -1 .

[0012] The Co-Na nanoalloy structure catalyst coated with a hydrophobic carbon layer can be applied to the Fischer-Tropsch synthesis reaction to prepare olefins. It is characterized in that before the reaction, it is first activated in hydrogen or a hydrogen-inert gas mixture at 300 - 600 °C for 4 - 10 h, and then syngas with a volume ratio of H 2 to CO of 1 - 10 is introduced for reaction. The reaction temperature is 180 - 350 °C, the reaction pressure is 0.5 - 5 MPa, and the syngas hourly space velocity is 500 - 8000 h -1 .

[0013] The beneficial effects of the present invention are as follows: A catalyst with a structure of Co-Na alloy coated with a hydrophobic carbon layer was successfully prepared, a new preparation method was proposed, and this catalyst was applied to the Fischer-Tropsch reaction for the preparation of olefins. Due to the unique hydrophobicity of the carbon layer and the excellent C-C coupling ability of the CoNa alloy, the catalytic activity of CO hydrogenation was improved, the selectivity of olefins was significantly enhanced, and the catalyst had good stability, with a stability of >200 h.

[0014] This catalyst has the advantages of stable structure, good thermal conductivity, high utilization rate of active components, high syngas conversion rate and olefin selectivity, and stable reaction performance. Moreover, its preparation steps are simple, raw materials are easy to obtain, the repeatability is good, and it is easy to realize large-scale production. Brief Description of the Drawings

[0015] Figure 1 It is a photograph of the water contact angle of the Co-Na@C catalyst in Example 1. It can be seen from the figure that the catalyst is a hydrophobic catalyst;

[0016] Figure 2 It is a TEM image of the Co-Na@C catalyst in Example 1. It can be clearly seen from the figure that the carbon-coated Co-Na alloy structure is the active site of the reaction;

[0017] Figure 3 It is a test chart of the stability performance of the Co-Na@C catalyst in Example 1. The catalyst maintained a high conversion rate of CO and a high selectivity of olefins throughout the test process of more than 200 h, indicating that the catalyst structure is stable;

[0018] Figure 4 It is the XRD pattern (a) of the Co-Na@C catalyst after reduction and the XRD pattern (b) after the reaction in Example 1. It can be seen from the figure that the main active components of the Co-Na@C catalyst are elemental Co, oxides and carbides, and highly dispersed elemental Na or oxides. Detailed Embodiments

[0019] To better understand the present invention, the technical solutions of the present invention will be elaborated in detail below in conjunction with embodiments. The embodiments cited do not limit the protection scope of the present invention.

[0020] Example 1

[0021] (1) Take 35 g of cobalt nitrate hexahydrate and 1.0 g of sodium nitrate and dissolve them in 300 ml of deionized water;

[0022] (2) After subjecting the obtained mixture to ultrasonic treatment for 6 h, vigorously stir it at 1600 revolutions per minute for 6 h, add 10 g of glucose, and stir evenly. After the stirring is completed, add 200 ml of ammonia water with a mass concentration of 25% and an ammonium carbonate solution with a mass concentration of 30% in a total volume, and react for 5 h at a volume ratio of 5:1 for the two components of ammonia water and ammonium carbonate;

[0023] (3) Add 50 ml of ethanol solution to the obtained reaction product, evaporate it at 80 °C for 8 h until it becomes colloidal or paste-like (no obvious liquid), and then add 300 ml of deionized water and place it in a hydrothermal reaction kettle for treatment at 150 °C for 5 h;

[0024] (4) Filter, wash the solid with water again, and obtain a filter cake after washing the product;

[0025] (5) Dry the obtained filter cake in air at 120 °C for 12 h, and finally calcine it in a helium atmosphere at a space velocity of 2000 h -1 to obtain a Co-Na@C catalyst by calcining at 1000 °C for 10 h.

[0026] This catalyst is first activated at 400 °C for 5 h under hydrogen conditions, and then under the conditions where the volume ratio of H 2 to CO is 5, the reaction temperature is 260 °C, the reaction pressure is 3 MPa, and the space velocity of the syngas is 4000 h -1 Carry out the reaction, and the results are shown in Table 1.

[0027] Example 2

[0028] (1) Take 40 g of cobalt nitrate hexahydrate and 1.2 g of sodium chloride and dissolve them in 200 ml of deionized water;

[0029] (2) After subjecting the obtained mixture to ultrasonic treatment for 7 h, vigorously stir it at 1600 revolutions per minute for 6 h, add 10 g of aniline, stir evenly, add 200 ml of ammonia water with a mass concentration of 28% and an ammonium carbonate solution with a mass concentration of 40% in a total volume, and react for 6 h at a volume ratio of 3:1 for the two components of ammonia water and ammonium carbonate;

[0030] (3) Add 70 ml of ethanol solution to the obtained reaction product, evaporate it at 85 °C for 10 h until it becomes colloidal or paste-like (no obvious liquid), and then add 400 ml of deionized water and place it in a hydrothermal reaction kettle for treatment at 150 °C for 5 h;

[0031] (4) Filter, wash the solid with water again, and obtain a filter cake after washing the product;

[0032] (5) Dry the obtained filter cake in air at 120 °C for 12 h, and finally calcine it in a nitrogen atmosphere at a space velocity of 2500 h -1 to obtain a Co-Na@C catalyst by calcining at 900 °C for 8 h.

[0033] The catalyst was first activated at 550 °C for 4 h under hydrogen, and then in H 2 The volume ratio of to CO was 4, the reaction temperature was 240 °C, the reaction pressure was 2 MPa, and the syngas space velocity was 4000 h -1 The reaction was carried out under the conditions of, and the results are shown in Table 1.

[0034] Example 3

[0035] (1) 38 g of cobalt nitrate hexahydrate and 1.6 g of sodium nitrate were dissolved in 300 ml of deionized water;

[0036] (2) After ultrasonic treatment of the obtained mixture for 6 h, it was vigorously stirred at 1800 rpm for 8 h, 15 g of aniline was added and stirred evenly. 300 ml of ammonia water with a mass concentration of 25% and ammonium carbonate solution with a mass concentration of 25% were added, and the reaction was carried out for 4 h with the volume ratio of ammonia water and ammonium carbonate being 7:1;

[0037] (3) 70 ml of ethanol solution was added to the obtained reaction product, and it was evaporated at 95 °C for 8 h until it became a gel or paste (no obvious liquid), and then 300 ml of deionized water with a total volume was added and placed in a hydrothermal reaction kettle for treatment at 130 °C for 6 h;

[0038] (4) Filter, wash the solid with water again, and obtain a filter cake after washing the product; (5) The obtained filter cake was dried in air at 140 °C for 18 h, and finally the space velocity was 2500 h under a nitrogen atmosphere -1 , and calcined at 1000 °C for 12 h to obtain the Co-Na@C catalyst.

[0039] The catalyst was first activated at 600 °C for 8 h under hydrogen, and then in H 2 The volume ratio of to CO was 8, the reaction temperature was 300 °C, the reaction pressure was 3 MPa, and the syngas space velocity was 4000 h -1 The reaction was carried out under the conditions of, and the results are shown in Table 1.

[0040] Example 4

[0041] (1) 42 g of cobalt nitrate hexahydrate and 1.8 g of sodium nitrate were dissolved in 400 ml of deionized water;

[0042] (2) After ultrasonic treatment of the obtained mixture for 8 h, it was vigorously stirred at 1600 rpm for 6 h, 15 g of citric acid was added and stirred evenly. 400 ml of ammonia water with a mass concentration of 28% and ammonium carbonate solution with a mass concentration of 30% with a total volume were added, and the reaction was carried out for 5 h with the volume ratio of ammonia water and ammonium carbonate being 5:1;

[0043] (3) 100 mL of ethanol solution was added to the obtained reaction product, and it was evaporated at 95 °C for 10 h until it became a gel or paste (no obvious liquid), and then 250 mL of deionized water was added and placed in a hydrothermal reaction kettle for treatment at 180 °C for 5 h;

[0044] (4) Filter, wash the solid with water again, and a filter cake was obtained after washing the product; (5) The obtained filter cake was dried in air at 140 °C for 24 h, and finally calcined at 700 °C for 11 h in an argon atmosphere with a space velocity of 3000 h -1 , and the Co-Na@C catalyst was obtained.

[0045] This catalyst was first activated at 500 °C for 5 h under hydrogen conditions, and then in H 2 The volume ratio of to CO was 8, the reaction temperature was 280 °C, the reaction pressure was 2 MPa, and the syngas space velocity was 4000 h -1 The reaction was carried out under the conditions, and the results are shown in Table 1.

[0046] Example 5

[0047] (1) 40 g of cobalt acetate and 2.6 g of sodium nitrate were dissolved in 300 mL of deionized water;

[0048] (2) After the obtained mixture was ultrasonically treated for 7 h, it was vigorously stirred at 1600 revolutions per minute for 6 h, 20 g of polyethylene glycol was added, and it was stirred evenly. 500 mL of ammonia water with a mass concentration of 24% and ammonium carbonate solution with a mass concentration of 15% were added, and the volume ratio of the two components of ammonia water and ammonium carbonate was 5:1 and reacted for 5 h;

[0049] (3) 80 mL of ethanol solution was added to the obtained reaction product, and it was evaporated at 90 °C for 10 h until it became a gel or paste (no obvious liquid), and then 300 mL of deionized water was added and placed in a hydrothermal reaction kettle for treatment at 200 °C for 5 h;

[0050] (4) Filter, wash the solid with water again, and a filter cake was obtained after washing the product; (5) The obtained filter cake was dried in air at 130 °C for 24 h, and finally calcined at 1200 °C for 8 h in a nitrogen atmosphere with a space velocity of 3000 h -1 , and the Co-Na@C catalyst was obtained.

[0051] This catalyst was first activated at 450 °C for 6 h under hydrogen conditions, and then in H 2 The volume ratio of to CO was 5, the reaction temperature was 320 °C, the reaction pressure was 4 MPa, and the syngas space velocity was 7000 h -1 The reaction was carried out under the conditions, and the results are shown in Table 1.

[0052] Example 6

[0053] (1) Dissolve 38 g of cobalt nitrate hexahydrate and 2.8 g of sodium nitrate in 500 ml of deionized water;

[0054] (2) After ultrasonic treatment of the obtained mixture for 10 h, vigorously stir it at 1600 revolutions per minute for 8 h, add 25 g of glucose, and stir evenly. Add 400 ml of a solution of ammonia water with a mass concentration of 25% and ammonium carbonate solution with a mass concentration of 30%, and react for 5 h with a volume ratio of ammonia water to ammonium carbonate of 7:1;

[0055] (3) Add 50 ml of ethanol solution to the obtained reaction product, evaporate it at 90 °C for 10 h until it becomes a gel or paste (no obvious liquid), and then add 400 ml of deionized water and place it in a hydrothermal reaction kettle for treatment at 200 °C for 8 h;

[0056] (4) Filter, wash the solid with water again, and obtain a filter cake after washing the product;

[0057] (5) Dry the obtained filter cake in air at 130 °C for 12 h, and finally calcine it in a nitrogen atmosphere at a space velocity of 3500 h -1 , at a temperature of 1200 °C for 15 h to obtain the Co-Na@C catalyst.

[0058] This catalyst is first activated at 550 °C for 6 h under hydrogen conditions, and then under the condition that the volume ratio of H 2 to CO is 4, the reaction temperature is 240 °C, the reaction pressure is 2 MPa, and the syngas space velocity is 4000 h -1 to carry out the reaction, and the results are shown in Table 1.

[0059] Comparative Example 1

[0060] (1) Take 35 g of cobalt nitrate hexahydrate and 2.5 g of sodium nitrate and dissolve them in deionized water;

[0061] (2) After ultrasonic treatment of the obtained mixture for 10 h, vigorously stir it at 1800 revolutions per minute for 8 h and add 20 g of activated carbon carrier (coconut shell carbon, Beijing Guanghua Jingke Activated Carbon Co., Ltd.). After stirring is completed, add a precipitant with a volume ratio of ammonia water to ammonium carbonate of 5:1 for reaction;

[0062] (3) Filter and wash the product to obtain a filter cake;

[0063] (4) Dry the obtained filter cake in air at 120 °C for 13 h, and finally calcine it in a nitrogen atmosphere at a space velocity of 3000 h -1 , at a temperature of 800 °C for 12 h to obtain the CoNa / C catalyst.

[0064] This catalyst is first activated at 450 °C for 4 h under hydrogen conditions, and then under the condition that the volume ratio of H 2 to CO is 5, the reaction temperature is 280 °C, the reaction pressure is 4 MPa, and the syngas space velocity is 3000 h-1 The reaction was carried out under the conditions shown in Table 1.

[0065] Comparative Example 2

[0066] (1) Dissolve 5.2 g of cobalt nitrate hexahydrate and 0.1 g of sodium nitrate in deionized water.

[0067] (2) Add 15 g of activated carbon support (coconut shell carbon, Beijing Guanghua Jingke Activated Carbon Co., Ltd.)

[0068] for impregnation.

[0069] (3) The obtained solid was dried in air at 120 °C for 10 h, and finally calcined in a nitrogen atmosphere at a space velocity of 3000 h -1 at a temperature of 600 °C for 10 h to obtain the CoNa / C-IM catalyst.

[0070] The catalyst was first activated at 550 °C for 4 h under hydrogen conditions, and then in H 2 The volume ratio of H to CO was 4, the reaction temperature was 270 °C, the reaction pressure was 4 MPa, and the syngas space velocity was 2500 h -1 The reaction was carried out under the conditions shown in Table 1.

[0071] Table 1 Catalyst CO hydrogenation reaction performance evaluation and product analysis.

[0072]

[0073] The results show that: compared with the ordinary Co-Na catalysts obtained by traditional precipitation or impregnation in Comparative Examples 1 and 2, the Co-Na nanoalloy catalysts with hydrophobic carbon layer coating prepared by the special method in Examples 1-6 have a 4-fold increase in the conversion rate of CO and the selectivity of the main product olefins, and at the same time significantly reduce the formation of methane, carbon dioxide and other by-products.

Claims

1. A preparation method of a catalyst for Fischer-Tropsch synthesis to produce olefins, characterized in that: The specific preparation process is as follows: (1) Dissolve soluble salts of Co with a final molar content of Co of 0.01 mol / L - 10 mol / L (preferably 0.05 mol / L - 5 mol / L, more preferably 0.1 mol / L - 3 mol / L) and soluble salts of Na with a final molar content of Na of 0.001 mol / L - 5 mol / L (preferably 0.005 mol / L - 3 mol / L, more preferably 0.01 mol / L - 1 mol / L) in 200 - 500 ml of deionized water and mix to prepare a mixture; (2) Ultrasonically treat the mixture obtained in step (1) at room temperature for 5 - 10 h, vigorously stir at 1500 - 3000 revolutions per minute for 5 - 10 h, then add a hydrophobic carbon layer precursor in a mass ratio to metallic Co of 1:1 - 10:1 (preferably 1:1 - 7:1, more preferably 2:1 - 6:1) and stir; after stirring is completed, add a mixed solution of ammonia water (mass concentration 20% - 30%) and ammonium carbonate (mass concentration 10% - 50%) with a total volume of 50 - 500 ml and a molar ratio of ammonium ions to metallic Co of 2:1 - 20:1, and the volume ratio of ammonia water to ammonium carbonate is 2:1 - 10:1 (preferably 2:1 - 8:1, more preferably 4:1 - 7:1), and carry out a precipitation reaction for 2 - 10 h; (3) Add 50 - 100 ml of an ethanol solution to the mixture treated in step (2), heat and evaporate at 70 - 95 °C for 4 - 12 hours until it becomes colloidal or pasty (no obvious liquid), then add 200 - 500 ml of water, place it in a hydrothermal reaction kettle, and treat it at 120 - 200 °C (preferably 130 - 180 °C, more preferably 140 - 170 °C) for 3 - 8 h (preferably 4 - 7 h, more preferably 4 - 6 h); (4) Filter the mixture treated in step (3), wash the solid with water to obtain a filter cake; (5) Dry the filter cake obtained in step (4) in air at 120 - 150 °C for 6 - 24 h, and then calcine it at 600 - 1200 °C (preferably 700 - 1100 °C, more preferably 800 - 1000 °C) in an inert gas atmosphere for 5 - 15 h (preferably 6 - 13 h, more preferably 7 - 11 h) to obtain a Co-Na@C catalyst.

2. According to the preparation method described in claim 1, characterized in that: The inert gas used is one or more of helium, argon, and nitrogen; the gas hourly space velocity is 2000 - 4000 h -1 .

3. According to the preparation method described in claim 1, characterized in that: Among them, the soluble salt of Co is one or more of cobalt nitrate, cobalt acetate, cobalt sulfate, and cobalt chloride; the soluble salt of Na is one or more of sodium nitrate, sodium chloride, sodium acetate, sodium sulfite, and sodium thiosulfate; The carbon layer precursor is one or more of glucose, citric acid, polyvinyl alcohol, polyethylene glycol, and aniline.

4. A catalyst prepared by the preparation method described in any one of claims 1 - 3.

5. According to the catalyst described in claim 4, characterized in that: The catalyst is composed of an active component, a promoter component and a hydrophobic carbon layer. The active component is one or more of Co in the form of elemental, oxide or carbide, the promoter component is one or two of Na in the form of elemental or oxide, and the high-activity sites are one or more of Co-Na nanoalloys coated with a hydrophobic carbon layer and individual Co and Na species.

6. Use of the catalyst according to claim 4 or 5 in the production of olefins by Fischer-Tropsch synthesis.

7. The use according to claim 6, characterized in that: characterized in that: First, load the catalyst into the reaction tube. Before use, activate the catalyst in a hydrogen or hydrogen-inert gas mixture at 300 - 600 °C for 4 - 10 h. After activation, adjust to the reaction conditions, which are as follows: The volume ratio of H 2 to CO in the syngas is 1 - 10, the reaction temperature is 180 - 350 °C, the reaction pressure is 0.5 - 5 MPa, and the syngas space velocity is 500 - 8000 h -1 .

8. The use according to claim 7, characterized in that: the inert gas used is one or more of helium, argon and nitrogen; the volume concentration of hydrogen in the activation atmosphere is 1% - 100%.

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