CN117282463B

CN117282463B - Preparation method of high-added-value liquid fuel composite catalyst prepared by carbon dioxide hydrogenation

Info

Publication number: CN117282463B
Application number: CN202311227119.8A
Authority: CN
Inventors: 孙松; 吴昊; 郭立升; 魏宇学; 周雯杰; 蔡梦蝶; 刘海城
Original assignee: Anhui University
Current assignee: Anhui University
Priority date: 2023-09-21
Filing date: 2023-09-21
Publication date: 2024-06-28
Anticipated expiration: 2043-09-21
Also published as: CN117282463A

Abstract

The invention discloses a preparation method of a liquid fuel composite catalyst with high added value by carbon dioxide hydrogenation, which realizes the directional synthesis of a target product liquid fuel by regulating and controlling the types and arrangement modes of shell molecular sieve catalysts; modifying by adopting a potassium auxiliary agent to obtain an iron-based catalyst with high selectivity to olefin; the modified Fischer-Tropsch synthesis catalyst and the molecular sieve catalyst are coupled through a physical coating method to form a composite catalyst with a core-shell structure, the types and arrangement modes of the molecular sieve catalyst with a modulated shell layer are regulated and controlled to catalyze olefin to generate aromatic hydrocarbon and long-chain heterogeneous hydrocarbon, and a new idea is provided for the efficient conversion process of preparing high-added-value chemicals through selective hydrogenation of carbon dioxide.

Description

Preparation method of high-added-value liquid fuel composite catalyst prepared by carbon dioxide hydrogenation

Technical Field

The invention relates to the technical field of composite catalyst preparation, in particular to a preparation method of a composite catalyst for preparing liquid fuel with high added value by carbon dioxide hydrogenation.

Background

The large-scale industrialized development accelerates the modern process, but the large-scale use of fossil fuels, which are main sources of energy, greatly increases the concentration of carbon dioxide in the air, and causes a series of ecological environmental problems such as greenhouse effect, ocean acidification and the like. The capture and utilization of converted carbon dioxide is a great concern for human society, wherein the catalytic conversion of carbon dioxide into chemical raw materials and important chemicals with high added value is of great significance for realizing carbon neutralization and promoting long-term sustainable development of the environment. The efficient conversion of carbon dioxide to prepare liquid fuel has important significance for meeting social production requirements and relieving economic pressure and for countries with deficient petroleum resources.

Catalytic conversion of carbon dioxide to produce liquid fuels is often limited by reaction kinetics and thermodynamics. Firstly, carbon dioxide is taken as an inert molecule, is not easy to react under the general condition, and needs higher energy to break the chemical energy barrier; secondly, in the process of converting into hydrocarbon products, the carbon chain growth capacity is weak, so that the selectivity of byproducts such as methane, carbon monoxide and the like is high. Currently, the hydroconversion of carbon dioxide mainly comprises the following steps: firstly, in the reaction process of the methanol intermediate, the carbon dioxide is converted into the methanol, and the generated methanol reacts on an acidic molecular sieve to generate a high-carbon product, wherein in the process, the selectivity of the product is higher, but more carbon monoxide is often generated, so that the catalytic activity is reduced; secondly, in the modified Fischer-Tropsch synthesis reaction process, fe ₃O₄ used for activating carbon dioxide molecules and Fe ₅C₂ used for chain growth reaction can exist in the reaction process at the same time, so that the catalyst is widely applied to the carbon dioxide hydrogenation process, but the product distribution is limited by ASF distribution, and is often unfavorable for large-scale application.

Disclosure of Invention

In view of the above, the invention aims to provide a simple and functional preparation method of a liquid fuel composite catalyst with high added value by hydrogenating carbon dioxide, wherein the shell catalyst composition of a capsule catalyst is regulated by introducing one or more molecular sieves, and the selective orientation of different molecular sieves on products is utilized to further improve the directional synthesis of the products, promote the hydrogenation catalytic activity of the carbon dioxide and realize the selective hydrogenation directional synthesis of the carbon dioxide into the liquid fuel.

In order to achieve the above purpose, the present invention adopts the following technical scheme: a preparation method of a liquid fuel composite catalyst with high added value by carbon dioxide hydrogenation comprises the following steps:

(1) Ferric nitrate nonahydrate and zinc nitrate hexahydrate are dissolved in potassium hydroxide solution and stirred for 1-2 hours, then transferred into a hydrothermal synthesis kettle, subjected to hydrothermal synthesis for 6-10 hours at 160-200 ℃, washed and dried, and the potassium auxiliary agent modified iron-based catalyst is obtained.

(2) Pretreating a molecular sieve;

(3) The composite catalyst with one or more layers is obtained by physically coating the iron-based catalyst modified by the coupling potassium auxiliary agent and one or more molecular sieves and calcining the iron-based catalyst in a muffle furnace.

Preferably, in the step (1), the mass ratio of the raw materials of the iron-based catalyst is: iron nitrate nonahydrate 2.02g, zinc nitrate hexahydrate 0.74g, and iron to zinc ratio of 2:1.

Preferably, in the step (1), the concentration of the potassium hydroxide solution is 2.0mol/L; the configuration process comprises the following steps: weighing 5.60g of flaky potassium hydroxide, dissolving in 50mL of deionized water, and uniformly stirring to obtain the product.

Preferably, in the step (1), the optimal hydrothermal synthesis temperature is 180 ℃, and the optimal hydrothermal synthesis time is 8h.

Preferably, in the step (1), the uniform washing mode is 500mL deionized water suction filtration, so as to ensure the same potassium ion content.

Preferably, in the step (2), the molecular sieve pretreatment is as follows: grinding molecular sieves with different silicon-aluminum ratios and different configurations into powder, placing the powder in a muffle furnace, calcining for 4-6 hours at 500-600 ℃, and cooling to room temperature for standby.

Preferably, the molecular sieve is one or more of H-ZSM-5 (Si/al=25-30), H-ZSM-5 (Si/al=35-40), SAPO-11 (Si/al=0.6-0.8), SSZ-13 (Si/al=25-30).

Preferably, in the step (3), the physical coating method is as follows: particle infiltration coating spin coating is used.

Preferably, in the step (3), the mass composition ratio of the pretreated molecular sieve to the potassium auxiliary modified iron-based catalyst is between 0.75 and 1.5.

Further, according to different sequences and physical mixing modes, molecular sieves are physically coated on the surface of the potassium auxiliary agent modified iron-based catalyst, and a molecular sieve single-layer or multi-molecular sieve multi-layer molecular sieve wrapped composite catalyst with a capsule structure is obtained.

Correspondingly, the invention also discloses a composite catalyst prepared by the preparation method.

Correspondingly, the invention also claims the application of the composite catalyst prepared by the preparation method in preparing gasoline and aviation kerosene by carbon dioxide hydrogenation regulation.

Compared with the prior art, the technical scheme of the invention has the following beneficial effects and innovations:

1. The invention designs a composite catalyst with a capsule structure, and the directional synthesis of a liquid fuel product with high added value is realized by adjusting an outer molecular sieve catalyst to realize the hydrogenation catalytic reaction of carbon dioxide. The catalytic performance of the iron-based catalyst is improved by adopting electronic auxiliary potassium; the molecular sieves with different configurations are selected, the types and the sequences of the shell catalyst molecular sieves are regulated, and the catalytic characteristics of unique acid sites and pore channel structures of a plurality of different molecular sieves are connected in series to secondarily catalyze olefin, so that a hydrocarbon product with longer carbon chain is obtained from a low-carbon hydrocarbon intermediate product.

2. According to the invention, the modified Fischer-Tropsch synthesis catalyst and one or more acidic molecular sieve catalysts are coupled by a physical coating method to form a composite catalyst with a multi-layer core-shell structure, and a plurality of catalytic active sites are connected in series, so that the mass transfer process of reactants and the directional synthesis of target products, such as gasoline, diesel oil and the like, are enhanced, the selectivity of liquid fuel products in the catalytic reaction process is improved, and a new thought is provided for designing a high-efficiency catalytic carbon dioxide hydrogenation catalyst.

Drawings

FIG. 1 is a schematic illustration of the catalyst preparation principle of the present invention;

FIG. 3 is an X-ray diffraction pattern of the pretreated H-ZSM-5 and SAPO-11 molecular sieves;

FIG. 2 is a drawing showing the temperature programmed ammonia stripping of the pretreated H-ZSM-5 and SAPO-11 molecular sieves.

Detailed Description

The invention will be further illustrated with reference to specific examples. The technical scheme of the invention is conventional in the field unless specifically stated otherwise, and the reagents or materials are commercially available unless specifically stated otherwise.

In the invention, an X-ray polycrystalline diffractometer is adopted to measure the phase structure of the molecular sieve catalyst, and a programmed temperature chemical adsorption instrument is used to measure the acid strength of the molecular sieve catalyst.

The catalyst activity evaluation process adopted by the invention is as follows:

Before the hydrogenation reaction of carbon dioxide, the prepared catalyst is activated in situ for 6 hours under the condition of 400 ℃ hydrogen. The temperature is reduced to 280-320 ℃ after the reduction. The catalytic reaction is carried out in a fixed bed reactor, and the ratio of raw material synthesis gas is CO ₂/H₂ =1:2-1:5. The W/F value is defined as the ratio of catalyst weight to flow rate, and is controlled in the experiment at 5-15. N-octane is added to the cold trap as a solvent for collecting the heavy hydrocarbon components. The CO, CO ₂ and CH ₄ components of the gas phase product were analyzed by on-line gas chromatography with TCD detector and the light hydrocarbon component (C ₁-C₇) content was analyzed by another on-line gas chromatography with FID detector. After the reaction is finished, collecting heavy hydrocarbon components in the octane cold trap, and adding n-dodecane as an internal standard. The resulting liquid components were analyzed by off-line gas chromatography with FID detector. And (3) carrying out normalization treatment on the results after the analysis of the gas-phase products and the liquid-phase products to obtain the selectivity of various components and the conversion rate of CO ₂.

The following examples selected commercial H-ZSM-5 (Si/al=25-30), SAPO-11 (Si/al=0.6-0.8) molecular sieves. Before use, the commercial H-ZSM-5 (Si/Al=25-30) and SAPO-11 (Si/Al=0.6-0.8) were pretreated separately, and the pretreatment process was: grinding into powder, placing into a muffle furnace, calcining at 550 ℃ for 5 hours, and cooling to room temperature for later use.

FIG. 2 is an X-ray diffraction pattern of the pretreated H-ZSM-5 and SAPO-11 molecular sieves, showing that the H-ZSM-5 and SAPO-11 molecular sieve catalysts correspond to the respective crystal structures. H-ZSM-5 is a three-dimensional pore structure, SAPO-11 is a one-dimensional straight pore, H-ZSM-5 is often applied to olefin aromatization, SAPO-11 is used for olefin isomerization, and the two molecular sieves are selected to improve the selectivity of the gasoline product and simultaneously improve the quality of the gasoline product. FIG. 3 is a drawing of the temperature programmed ammonia stripping of the pretreated H-ZSM-5 and SAPO-11 molecular sieves, showing that SAPO-11 has an obvious NH ₃ desorption peak at low temperature, i.e. SAPO-11 is weakly acidic, while H-ZSM-5 has an obvious NH ₃ desorption peak at low temperature and high temperature, showing that H-ZSM-5 is more acidic than SAPO-11. On the molecular sieve catalyst, the strong acid site has strong adsorption capacity to small molecules, and the aromatization of olefins is promoted.

Example 1

The preparation process of the carbon dioxide hydrogenation composite catalyst comprises the following steps:

Firstly, preparing a high-performance modified Fischer-Tropsch synthesis catalyst with potassium auxiliary introduced, which comprises the following specific steps: 2.02g of ferric nitrate nonahydrate, 0.74g of zinc nitrate hexahydrate were dissolved in 50mL of potassium hydroxide solution (2 mol/L), stirred for 1 hour, and then transferred into a 100mL polytetrafluoroethylene liner. And then placing the polytetrafluoroethylene lining into a hydrothermal reaction kettle, performing hydrothermal synthesis for 8 hours at 180 ℃, washing the obtained product with 500mL of deionized water for 3 times, drying at 60 ℃, grinding, granulating into particles with the size of 20-40 meshes for later use, and marking the product as K-ZnFe ₂O₄.

The 0.20g K-ZnFe ₂O₄ catalyst was weighed into a round bottom flask, and a silica sol solution (mass concentration 10%) was dropped into the round bottom flask using a rubber head dropper to infiltrate the K-ZnFe ₂O₄ catalyst. Then 0.20g of the pretreated H-ZSM-5 molecular sieve catalyst is weighed and added into a round bottom flask, and the mixture is subjected to spin coating to form the multifunctional composite catalyst with a core-shell structure, which is marked as H-ZSM-5@K-ZnFe ₂O₄.

It should be noted that: the spin coating in all embodiments of the invention comprises the following specific operation processes: the granulated modified fischer-tropsch catalyst was placed in a flask by hand, and was wetted by dropwise addition of a silica sol solution (binder). And adding the pretreated and dried molecular sieve, and rotating the flask to wrap the modified Fischer-Tropsch catalyst.

In order to examine the advantages of the capsule catalysts coupled with different molecular sieves in the catalytic performance of carbon dioxide hydrogenation, 0.20g K-ZnFe ₂O₄ catalyst was weighed and transferred into a round-bottom flask, and a silica sol solution (with the mass concentration of 10%) was dripped into the round-bottom flask by using a rubber head dropper to infiltrate the K-ZnFe ₂O₄ catalyst. Then 0.20g of the pretreated SAPO-11 molecular sieve catalyst is weighed into a round bottom flask, and spin-coated to form a multifunctional composite catalyst with a core-shell structure, which is marked as SAPO-11@K-ZnFe ₂O₄. The catalytic properties of the two catalysts are shown in Table 1.

The carbon dioxide hydrogenation catalytic reaction experiment shows that the capsule catalyst with the core-shell structure formed by physical coating can show good catalytic performance to improve the selectivity of products in the range of liquid fuel, the coupling H-ZSM-5 molecular sieve can obviously cause olefin to undergo aromatization reaction, the coupling SAPO-11 molecular sieve can obviously cause olefin to undergo isomerization reaction, and the catalyst has higher catalytic yield for target products with high added value.

Example 2

To examine the advantages of the serial application of various molecular sieves to the hydrogenation catalytic performance of carbon dioxide. Firstly, preparing a high-performance modified Fischer-Tropsch synthesis catalyst with potassium auxiliary introduced, which comprises the following specific steps: 2.02g of ferric nitrate nonahydrate, 0.74g of zinc nitrate hexahydrate were dissolved in 50mL of potassium hydroxide solution (2 mol/L), stirred for 1 hour, and then transferred into a 100mL polytetrafluoroethylene liner. And then placing the polytetrafluoroethylene lining into a hydrothermal reaction kettle, performing hydrothermal synthesis for 8 hours at 180 ℃, washing the obtained product with 500mL of deionized water for 3 times, drying at 60 ℃, grinding, granulating into particles with the size of 20-40 meshes for later use, and marking the product as K-ZnFe ₂O₄.

The 0.20g K-ZnFe ₂O₄ catalyst is weighed and transferred into a round-bottom flask, and a silica sol solution (the mass concentration is 10%) is dripped into the round-bottom flask by using a rubber head dropper to infiltrate the K-ZnFe ₂O₄ catalyst. Then 0.10g of the pretreated SAPO-11 molecular sieve catalyst is weighed into a round bottom flask, and spin-coated to form a multifunctional composite catalyst with a core-shell structure, which is marked as SAPO-11@K-ZnFe2O4. After the SAPO-11@K-ZnFe ₂O₄ composite catalyst is dried in a round-bottom flask, a silica sol solution (with the mass concentration of 10%) is dripped into the round-bottom flask for infiltration, 0.10g of the pretreated H-ZSM-5 molecular sieve catalyst is weighed and added into the round-bottom flask, and the mixture is subjected to spin coating to form the multifunctional composite catalyst with a core-shell structure, which is shown in the figure 1 and is marked as H-ZSM-5@SAPO-11@K-ZnFe ₂O₄. The catalytic properties of the catalysts are listed in table 1.

Carbon dioxide hydrogenation catalytic reaction experiments show that the capsule catalyst with the core-shell structure formed by physical coating can show good catalytic performance, the Fischer-Tropsch synthesis catalyst is modified by coupling a plurality of molecular sieves in series, the intermediate product olefin can improve the catalytic activity through the SAPO-11 molecular sieve, the ratio of a gasoline product (C ₅ ⁺) in the product is improved, the proportion of an isomerism product is increased, and the aromatization reaction further occurs through the outer layer H-ZSM-5 molecular sieve, so that the selectivity of aromatic compounds in the product is improved. It is illustrated that the series connection of two molecular sieves promotes the catalytic reaction, which is beneficial to improving the activity of the target product.

Example 3

Firstly, preparing a high-performance potassium modified Fischer-Tropsch synthesis catalyst, which comprises the following specific steps: 2.02g of ferric nitrate nonahydrate, 0.74g of zinc nitrate hexahydrate were dissolved in 50mL of potassium hydroxide solution (2 mol/L), stirred for 1 hour, and then transferred into a 100mL polytetrafluoroethylene liner. And then placing the polytetrafluoroethylene lining into a hydrothermal reaction kettle, performing hydrothermal synthesis for 8 hours at 180 ℃, washing the obtained product with 500mL of deionized water for several times, drying at 60 ℃, grinding, granulating into particles with the size of 20-40 meshes for later use, and marking the product as K-ZnFe ₂O₄.

The coating order of the pretreated H-ZSM-5 and SAPO-11 molecular sieve catalysts is adjusted, 0.20g of K-ZnFe ₂O₄ catalyst is weighed and transferred into a round-bottom flask, and a silica sol solution (with the mass concentration of 10%) is dripped into the round-bottom flask by using a rubber head dropper to infiltrate the K-ZnFe ₂O₄ catalyst. Then 0.10g of the pretreated H-ZSM-5 molecular sieve catalyst is weighed and added into a round bottom flask, and the mixture is subjected to spin coating to form the multifunctional composite catalyst with a core-shell structure, which is marked as H-ZSM-5@K-ZnFe ₂O₄. After the H-ZSM-5@K-ZnFe ₂O₄ composite catalyst is dried in a round-bottom flask, a silica sol solution (with the mass concentration of 10%) is dripped into the round-bottom flask for infiltration, 0.10g of the pretreated SAPO-11 molecular sieve catalyst is weighed and added into the round-bottom flask, and the mixture is subjected to rotary coating to form the multifunctional composite catalyst with a core-shell structure, namely the SAPO-11@H-ZSM-5@K-ZnFe ₂O₄.

To compare and examine the advantages of the capsule catalysts with different molecular sieve arrangement modes in the application of the catalyst to the hydrogenation of carbon dioxide, 0.10g of pretreated H-ZSM-5 and 0.10g of pretreated SAPO-11 molecular sieve catalyst are physically mixed uniformly, added into a round-bottomed flask which is soaked with K-ZnFe ₂O₄ by adopting a silica sol solution (the mass concentration is 10%), and spin-coated to form a composite catalyst, which is recorded as SAPO-11+H-ZSM-5@K-ZnFe ₂O₄. The catalytic properties of the three catalysts are listed in table 1.

TABLE 1 carbon dioxide hydrogenation catalytic Performance for different catalysts

Note that: A/I represents the ratio of aromatic hydrocarbons in the product to the isomerised product.

The specific reaction conditions in the catalyst activity evaluation process are as follows: the reaction raw material gas space velocity is 3000 ml/(g _cat. Multidot. H) under the normal pressure of 50ml/min hydrogen flow and the reduction time is 6 hours and 2MPa at 300 ℃.

Experiments of carbon dioxide hydrogenation catalytic reaction show that the iron-based catalyst acts on the first part of the series reaction, and the carbon dioxide passes through the iron-based catalyst to generate olefin, low-carbon unsaturated hydrocarbon and the like. The molecular sieve catalyst acts on the second part of the series reaction, the product generated on the iron-based catalyst is diffused to the molecular sieve catalyst for secondary reaction, and the intermediate product can be ensured to achieve sufficient mass transfer between the iron-based catalyst and the molecular sieve catalyst by wrapping the iron-based catalyst with the molecular sieve catalyst. The coupling of H-ZSM-5 and SAPO-11 molecular sieves can obviously lead the olefin to undergo secondary reactions such as aromatization, isomerization and the like. By coupling different molecular sieves, the intermediate product is subjected to further polymerization reaction on a molecular sieve catalyst through the unique MFI structure of the H-ZSM-5 molecular sieve and the straight-chain pore canal of the SAPO-11 molecular sieve, so that the selectivity of the gasoline product is improved. Through different acid sites on the molecular sieve, H-ZSM-5 is easy to aromatize olefin, and SAPO-11 is easy to isomerize. The octane number in the liquid fuel product is improved, and the method has important significance for obtaining the liquid fuel with high added value.

Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims

1. The preparation method of the liquid fuel composite catalyst with high added value by hydrogenating carbon dioxide is characterized by comprising the following steps:

(1) Dissolving ferric nitrate nonahydrate and zinc nitrate hexahydrate in potassium hydroxide solution, stirring for 1-2 hours, then transferring into a hydrothermal synthesis kettle, performing hydrothermal synthesis for 6-10 hours at 160-200 ℃, washing and drying to obtain a potassium auxiliary agent modified iron-based catalyst K-ZnFe ₂O₄;

(2) Pretreating a molecular sieve;

(3) Coating a plurality of molecular sieves on the surface of the iron-based catalyst modified by the potassium auxiliary agent infiltrated with the silica sol solution layer by layer through physical coating, and calcining the catalyst in a muffle furnace to obtain a multi-layer composite catalyst; the molecular sieve is a plurality of H-ZSM-5 with Si/Al=25-30, H-ZSM-5 with Si/Al=35-40, SAPO-11 with Si/Al=0.6-0.8 and SSZ-13 with Si/Al=25-30;

in the step (3), the physical coating method comprises the following steps: particle infiltration, coating and spin coating are adopted, and the mass ratio of the pretreated molecular sieve to the potassium auxiliary agent modified iron-based catalyst is between 0.75 and 1.5; the molecular sieves are physically coated on the surface of the potassium auxiliary agent modified iron-based catalyst according to different sequences, and the composite catalyst with a capsule structure and wrapped by a plurality of molecular sieves and a plurality of layers of molecular sieves is obtained.

2. The method for preparing the liquid fuel composite catalyst with high added value by hydrogenating carbon dioxide according to claim 1, wherein in the step (1), the mass of the raw materials of the iron-based catalyst is as follows: 2.02g of ferric nitrate nonahydrate and 0.74g of zinc nitrate hexahydrate.

3. The method for preparing the liquid fuel composite catalyst with high added value by hydrogenating carbon dioxide according to claim 1, wherein in the step (1), the concentration of the potassium hydroxide solution is 2.0mol/L; the hydrothermal synthesis temperature is 180 ℃, and the hydrothermal synthesis time is 8h.

4. The method for preparing the liquid fuel composite catalyst with high added value by hydrogenating carbon dioxide according to claim 1, wherein in the step (2), the molecular sieve pretreatment is as follows: grinding molecular sieves with different silicon-aluminum ratios and different configurations into powder, placing the powder in a muffle furnace, calcining for 4-6 hours at 500-600 ℃, and cooling to room temperature for standby.

5. A composite catalyst characterized by being prepared according to the preparation method of any one of claims 1 to 4.

6. Use of the composite catalyst according to claim 5 in the carbon dioxide hydrogenation regulation of transportation liquid fuel.

7. Use of the composite catalyst according to claim 5 in preparing gasoline and aviation kerosene by carbon dioxide hydrogenation regulation.