Method for directly preparing aviation kerosene fraction hydrocarbon from carbon dioxide hydrogenation

Abstract

The present application provides a method for directly preparing aviation kerosene fraction hydrocarbon from carbon dioxide hydrogenation, under the reaction conditions of temperature 260-420 DEG C, pressure 0.01-10.0 MPa, space velocity 500-50000 mL / (h.g cat ), H2 / CO2 molar ratio 0.8-7.0, the mixed gas of carbon dioxide and hydrogen is directly converted to aviation kerosene fraction hydrocarbon under the catalysis of a multifunctional composite catalyst. The composite catalyst is composed of the first component of iron-based carbon dioxide hydrogenation catalyst supported on carrier and the second component of composite molecular sieve with the functions of olefin polymerization and heavy hydrocarbon hydrogen cracking. In the method, the single-pass CO2 conversion rate can reach more than 30%, the methane selectivity in the hydrocarbon product can be less than 10%, and the aviation kerosene fraction hydrocarbon with carbon atom number 8-16 can have a selectivity of more than 50%. The present application opens up a new route for producing aviation kerosene from carbon dioxide.

Description

Technical Field

[0001] This invention relates to a method for producing aviation kerosene by hydrogenating carbon dioxide, and more specifically to a method for directly producing high-quality aviation kerosene by hydrogenating carbon dioxide. Background Technology

[0002] Aviation kerosene is an indispensable transportation fuel in modern society. Currently, it is mainly produced from petroleum through technologies such as direct crude oil fractionation and catalytic cracking. However, petroleum reserves are limited, and developing non-petroleum resource sources for aviation kerosene has become a competitive research goal for countries worldwide. CO2, as the cheapest and most abundant resource in the C1 family, is extremely plentiful on Earth. With the continuous development of human society, the use of fossil fuels has increased dramatically, leading to a rise in atmospheric CO2 levels. This not only exacerbates the greenhouse effect but also results in a huge waste of carbon resources. A circular model that utilizes CO2 captured from industrial waste gases or the atmosphere to produce hydrogen using renewable energy, and then catalytically hydrogenates CO2 to produce liquid hydrocarbons, is of great significance for simultaneously addressing the two major challenges facing human society today: climate change and the energy crisis.

[0003] Studies have shown that the preparation of hydrocarbons by carbon dioxide hydrogenation generally involves two steps: first, CO2 undergoes a reverse water-gas shift reaction to produce CO, and then CO undergoes Fischer-Tropsch synthesis to produce hydrocarbons. The traditional Fischer-Tropsch synthesis process for hydrocarbons by CO hydrogenation is limited by the Anderson-Schulz-Flory (ASF) law. According to the ASF distribution, the product selectivity of aviation kerosene fractions (C8-C9) is... 16 The selectivity for hydrocarbons (C2) is generally no more than 30%. Unlike CO hydrogenation, CO2 hydrogenation results in a low C / H ratio on the catalyst surface due to the slow adsorption of CO2 on the catalyst surface. This phenomenon favors the hydrogenation of surface-adsorbed species, reduces the probability of chain growth in the product, and thus improves the selectivity for methane. However, it makes the preparation of long-chain hydrocarbons by CO2 hydrogenation more difficult. Therefore, current research on CO2 hydrogenation mainly focuses on low-molecular-weight hydrocarbons or oxygen-containing compounds such as methanol, dimethyl ether, methane, and low-carbon olefins, while research on the preparation of long-chain hydrocarbons by CO2 hydrogenation is relatively limited. Although recent studies have shown that the direct synthesis of gasoline fraction hydrocarbons (C2) by carbon dioxide hydrogenation... 5～11 Breakthroughs have been achieved in the process of synthesizing hydrocarbons from gasoline fractions, with selectivity for hydrocarbon products exceeding 70% (Wei Jian, et al. Nature Communications, 2017, 8, 15174; Gao Peng, et al. Nature Chemistry, 2017, 9: 1019-1024). However, the direct synthesis of aviation kerosene fraction hydrocarbons from carbon dioxide hydrogenation (C...) remains a challenge. 8～16Research on CO2 hydrogenation for producing aviation kerosene has not yet yielded significant breakthroughs. The target product, aviation kerosene, has a low hydrocarbon yield, while the byproducts CO and methane exhibit high selectivity. Therefore, finding a high-conversion, high-selectivity process for producing aviation kerosene via CO2 hydrogenation has become an urgent problem to be solved in the production of aviation kerosene using CO2. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that the target product aviation kerosene fraction has low hydrocarbon selectivity, the by-products CO and methane have high selectivity, and the CO2 utilization rate is low in the prior art. The present invention provides a new method for producing aviation kerosene by hydrogenating carbon dioxide.

[0005] This invention provides a method for directly producing aviation kerosene distillate hydrocarbons by hydrogenation of carbon dioxide, characterized in that: a mixture of carbon dioxide and hydrogen is used as the feed gas, and aviation kerosene distillate hydrocarbons are directly generated under the catalytic action of a multifunctional composite catalyst; the composite catalyst consists of a supported iron-based catalyst as the first component, and a catalyst with low-carbon olefin polymerization function and heavy hydrocarbon (C) 16+ The first component is composed of two molecular sieves with hydrocracking function as a second component, which are mixed or combined; the mass ratio of the first component to the second component is 1:8 to 8:1, preferably 1:2 to 4:1, and more preferably 1:2 to 2:1.

[0006] The reaction conditions for producing aviation kerosene fraction hydrocarbons by carbon dioxide hydrogenation are as follows: reaction temperature of 260–420℃ (preferably 300–400℃, more preferably 320–360℃), reaction pressure of 0.01–10.0 MPa (preferably 0.1–8.0 MPa, more preferably 1.0–6.0 MPa), and feed gas space velocity of 500–50000 mL / (h·g) cat (Preferred value: 1000–20000 mL / (h·g)) cat More preferably, it is 1000–10000 mL / (h·g) cat The H2 / CO2 molar ratio in the feed gas is 0.8 to 7.0 (preferably 2.0 to 6.0, more preferably 3.0 to 6.0).

[0007] The main active component of the supported iron-based catalyst is Fe supported on carbon materials. x C(2≤x≤3), Fe x The mass percentage of component C in the supported iron catalyst is 20-60% (preferably 30-50%, more preferably 30-40%).

[0008] The supported iron-based catalyst may or may not contain an additive, which is an oxide and accounts for 0-20% of the total mass of the iron-based catalyst. The additive is one or more of Na oxide, K oxide, Zr oxide, V oxide, Zn oxide, and Ce oxide. The preferred content of the additive in the catalyst is 0.5-9% of the total mass of the iron-based catalyst.

[0009] The product has low-carbon olefin polymerization function and heavy hydrocarbons (C 16+ The composite molecular sieve with hydrocracking function refers to a molecular sieve that has the function of low-carbon olefin polymerization and a molecular sieve that has the function of heavy olefin hydrocracking. The molecular sieve with the function of low-carbon olefin polymerization is preferably one or two of ZSM-5 and Y, and the molecular sieve with the function of heavy hydrocarbon hydrocracking is preferably one or two of Beta and MCM-22. Among them, it is preferred that Y molecular sieve with a silicon-aluminum ratio of 10 to 150 and Beta molecular sieve with a silicon-aluminum ratio of 20 to 200 are mixed or combined. The mass ratio of the two functional molecular sieves (low-carbon olefin polymerization molecular sieve / heavy hydrocarbon hydrocracking molecular sieve) is 1:5 to 5:1, preferably 1:3 to 3:1, and more preferably 1:2 to 2:1.

[0010] The composite molecular sieve containing heavy olefin hydrogenation cracking functional molecular sieve may or may not be metal modified. The modified metals used include one or more of Mo, Zn, Ga, Ni, Na, Co, Cu, and La. The metal element accounts for less than 10% of the mass of the modified molecular sieve, preferably 0.5% to 5%, and more preferably 0.5% to 2%.

[0011] The calcined iron-based catalyst precursor is mixed with two types of molecular sieves as the second component, or supported on an iron-based catalyst, a molecular sieve with low-carbon olefin polymerization function, and heavy hydrocarbons (C14-C24-C24). 16+ After the hydrocracking functional molecular sieves are stacked sequentially to form a composite catalyst, it needs to be reduced at 300-400℃ for 2-12 hours in H2 gas for 0.5-6 hours before the reaction. Then, it needs to be carbonized at 300-420℃ in H2 / CO2 gas (molar ratio H2 / CO2 = 0.05-5 (preferably 0.15-2), where H2+CO2 accounts for more than 70% of the total gas volume, and the H2 / CO2 gas does not contain or contains one or more of nitrogen, CO and inert gases) for 0.5-6 hours. After the treatment, an iron-based multifunctional composite catalyst composed of a supported iron-based catalyst and two types of molecular sieves can be obtained.

[0012] The multifunctional composite catalyst can be prepared using any one of the following three processes;

[0013] A. The catalyst is synthesized using a one-step method, including the following steps:

[0014] (1) Prepare a soluble Fe(III) salt and an auxiliary salt to form a salt solution, or prepare a soluble Fe(III) salt to form a salt solution, wherein the Fe(III) concentration in the salt solution is 0.05-2 mol / L, and an HCl solution with a concentration of 5-12.1 mol / L is added to adjust the pH value to 0-3; the soluble Fe(III) salt refers to a salt compound that can be dissolved in water, preferably one or more of chloride, nitrate, and acetate; the auxiliary salt is a salt compound that can be dissolved in water, preferably one or more of chloride, nitrate, and acetate;

[0015] (2) Add an alkaline solution to the salt solution in step (1); adjust the pH of the solution from 0 to 3 to an alkaline pH of 8 to 11; after the addition is complete, add carbon material to the solution and age it for 1 to 3 hours; the alkaline solution refers to an alkaline solution that can adjust the pH of the solution, preferably one or more of NaOH, KOH, Na2CO3, NaHCO3, K2CO3, KHCO3, Na2C2O4, K2C2O4, RCOONa, RCOOK, and ammonia water; the concentration of the alkaline solution is 0.1 to 8 mol / L; where R refers to an organic functional group, including C1 to C2. 20 Alkyl, C1-C 20 alkenyl or C6~C 20 Aryl, preferably methyl, ethyl or phenyl; carbon material refers to one or more of carbon fiber, carbon nanotube, graphite carbon and graphene, preferably one or more of carbon fiber, carbon nanotube and graphite carbon;

[0016] (3) After the reaction is completed, the deposited product is separated from the solution in step (2) by centrifugation or filtration, and the deposited product is washed with water, dried at 60-130℃, and calcined at 250-500℃ for 2-8 hours to obtain the supported iron-based catalyst precursor containing the promoter.

[0017] (4) The calcined iron-based catalyst precursor is mixed with two types of molecular sieves as the second component, or supported on iron-based catalysts, molecular sieves with low-carbon olefin polymerization function, and heavy hydrocarbons (C 16+ After the hydrocracking functional molecular sieves are stacked sequentially to form a composite catalyst, it needs to be reduced at 300-400℃ for 2-12 hours in H2 gas for 0.5-6 hours before the reaction. Then, it needs to be carbonized at 300-420℃ in H2 / CO2 gas (molar ratio H2 / CO2 = 0.05-5 (preferably 0.15-2), where H2+CO2 accounts for more than 70% of the total gas volume in H2 / CO2 gas, and H2 / CO2 gas does not contain or contains one or more of nitrogen, CO and inert gases) for 0.5-6 hours. After the treatment, an iron-based multifunctional composite catalyst composed of a supported iron-based catalyst and two kinds of molecular sieves can be obtained.

[0018] B. Alternatively, the catalyst is prepared using a one-step synthesis method, comprising the following steps:

[0019] (1) Form a salt solution of soluble Fe(III) salt with a Fe(III) concentration of 0.05-2 mol / L, and add HCl solution with a concentration of 5-12.1 mol / L to adjust the pH value to 0-3;

[0020] (2) Add the alkaline solution containing Na and / or K described in step (2) of process A to the salt solution in step (1); gradually adjust the pH value of the solution from 0 to 3 to an alkaline pH value from 8 to 11; after the addition is complete, add carbon material to the solution and age it for 1 to 3 hours;

[0021] (3) After the reaction is completed, the deposited product is separated from the solution in step (2) by centrifugation or filtration, and the deposited product is washed with water. The content of residual Na or K in the catalyst is controlled by controlling the number of washings and the amount of water used for each washing. The product is dried and calcined at 250-500℃ for 2-8 hours to obtain an iron-based catalyst precursor containing Na and / or K promoters.

[0022] (4) The calcined iron-based catalyst precursor is mixed with two types of molecular sieves as the second component, or supported on iron-based catalysts, molecular sieves with low-carbon olefin polymerization function, and heavy hydrocarbons (C 16+ After the hydrocracking functional molecular sieves are stacked sequentially to form a composite catalyst, it needs to be reduced at 300-400℃ for 2-12 hours with H2 gas before the reaction, and then carbonized at 300-420℃ for 0.5-6 hours with H2 / CO2 gas (molar ratio H2 / CO2 = 0.05-5 (0.15-2), H2+CO2 in the H2 / CO2 gas accounts for more than 70% of the total gas volume content, and the H2 / CO2 gas does not contain or contains one or more of nitrogen, CO and inert gases). After the treatment, an iron-based multifunctional composite catalyst composed of a supported iron-based catalyst and two kinds of molecular sieves can be obtained.

[0023] C. Alternatively, the catalyst is first synthesized using a co-precipitation method to obtain Fe2O3 supported on carbon materials, and then additives are added using an impregnation method, including the following steps:

[0024] (1) Mix soluble Fe(III) salts to form a salt solution with a Fe(III) concentration of 0.05-2 mol / L, and add HCl solution with a concentration of 5-12.1 mol / L to adjust the pH value to 0-3;

[0025] (2) Add the alkaline solution described in step (2) of process A to the salt solution in step (1); gradually adjust the pH value of the solution from 0 to 3 to an alkaline pH value from 8 to 11; after the addition is complete, add carbon material and age for 1 to 3 hours;

[0026] (3) After the reaction is completed, the deposited product is separated from (2) by centrifugation or filtration, and the deposited product is thoroughly washed with deionized water, dried at 60-130℃, and calcined at 250-500℃ for 2-8 hours to obtain the active component Fe2O3 loaded on carbon material.

[0027] (4) The catalyst is formed by combining the auxiliary salt with the active ingredient by the impregnation method. The specific process is as follows: calculate the theoretical amount of auxiliary salt according to the required auxiliary content, prepare an aqueous solution of auxiliary salt, impregnate the carbon material supported Fe3O4 prepared in (3) in the solution, and after stirring, standing, drying and calcining, the calcination temperature is 250~500℃ and the calcination time is 2~8h, thus obtaining the supported iron-based catalyst precursor containing auxiliary.

[0028] (5) The calcined iron-based catalyst precursor is mixed with two molecular sieves as the second component, or supported on an iron-based catalyst, a molecular sieve with low-carbon olefin polymerization function, and heavy hydrocarbons (C 16+ After the hydrocracking functional molecular sieves are stacked sequentially to form a composite catalyst, it needs to be reduced at 300-400℃ for 2-12 hours with H2 gas before the reaction, and then treated at 300-420℃ for 0.5-6 hours with H2 / CO2 gas (molar ratio H2 / CO2 = 0.05-5 (0.15-2), H2+CO2 in the H2 / CO2 gas accounts for more than 70% of the total gas content, and the H2 / CO2 gas does not contain or contains one or more of nitrogen, CO and inert gases). After treatment, an iron-based multifunctional composite catalyst composed of a supported iron catalyst and two types of molecular sieves can be obtained.

[0029] When modifying molecular sieves with heavy olefin hydrocracking capabilities, the metal component can be loaded onto the molecular sieve using one of the following two methods:

[0030] (1) Prepared by impregnation method, the specific process is as follows: calculate the theoretical amount of metal salt required according to the required metal content, prepare an aqueous solution of metal salt, wherein the metal salt is selected from any one or more of the following: nitrate, chloride, bromide, acetate, acetylacetone, citrate, oxalate, benzoate; impregnate the molecular sieve to be modified in the solution, and after stirring, standing, drying and calcining, the calcination temperature is 300-700℃ and the calcination time is 2-10h, thus obtaining the metal modified molecular sieve;

[0031] (2) Prepared by ion exchange method, the specific process is as follows: calculate the theoretical amount of metal salt required according to the required metal content, prepare an aqueous solution of metal salt, the metal salt is selected from any one or more of the following: nitrate, chloride, bromide, acetate, acetylacetone, citrate, oxalate, benzoate; mix the molecular sieve to be modified with a solid-liquid mass ratio of 1:(10-200), ion exchange for 2-24 hours, wash with water, dry, and calcine at a temperature of 300-700℃ for 2-10 hours, and the metal-modified molecular sieve is obtained.

[0032] The components of the multifunctional composite catalyst can be mixed or combined in one of the following three ways, with the layered packing method being preferred:

[0033] (1) Powder mixing method: Weigh iron-based catalyst and two kinds of molecular sieve catalyst powders respectively, grind and mix them evenly according to the required mass ratio, then press them into tablets, crush and sieve them (sieve hole size is 0.1-2.0mm, preferably 0.3-0.8mm) to obtain a composite catalyst with a particle size of 0.1-2.0mm, preferably 0.3-0.8mm;

[0034] (2) Particle mixing method: Weigh the iron-based catalyst and the two molecular sieve catalyst powders separately, press them into tablets, crush and sieve them (sieve hole size is 0.1-2.0 mm, preferably 0.3-0.8 mm), mix the particles evenly according to the required mass ratio of iron-based catalyst and two molecular sieves to form a composite catalyst with a particle size of 0.1-2.0 mm (preferably 0.3-0.8 mm);

[0035] (3) Layered packing method: The catalyst bed is sequentially packed with the required mass of supported iron-based catalyst bed with a particle size of 0.1-2.0 mm (0.3-0.8 mm), molecular sieve bed with low-carbon olefin polymerization function, and heavy hydrocarbon (C) in the order of catalyst contact with feed gas. 16+ The hydrogenation cracking functional di-molecular sieve bed catalyst has no or no inert material isolation layer between adjacent bed components. The mass ratio of the inert material isolation layer to the active component of the composite catalyst is 0.01 to 10 (preferably 0.1 to 5). The inert material isolation layer material is an inert material that does not react with the catalyst and the feed gas components, preferably one or two of inert SiO2 microspheres and quartz sand, and the particle size ratio of its particle size to the particle size of the catalyst is 1:0.8 to 1:3 (preferably 1:1 to 1:1.5).

[0036] In the production of aviation kerosene by hydrogenation of carbon dioxide, the catalyst performance is evaluated as follows: A composite catalyst consisting of a multifunctional composite catalyst precursor and a molecular sieve is packed into the isothermal section of a fixed-bed reactor. Before the reaction, it undergoes reduction at 300–400℃ for 2–12 hours with H2 gas, followed by carbonization at 300–420℃ for 0.5–6 hours with H2 / CO2 gas (H2 / CO2 = 0.05–5 (0.15–2), the H2+CO2 mixture accounting for more than 70% of the total gas content, with or without CO and inert gases). The temperature is then adjusted to the reaction temperature, and the carbonized gas is switched to the reaction gas. The reaction products are introduced into the chromatogram for analysis in gaseous or liquid form. CO, N2, CH4, and CO2 are detected by TCD, while hydrocarbons and oxygen-containing compounds are detected by FID.

[0037] This invention applies to gases containing carbon dioxide, wherein the gas refers to any one or more of the following: industrial waste gas containing carbon dioxide, automobile exhaust, coal-fired waste gas, and carbon dioxide absorbed from the atmosphere and seawater.

[0038] This invention has the following characteristics:

[0039] (1) The catalyst used in this invention is simple to prepare, the raw materials are cheap and readily available, the mechanical strength is high, the stability is good, and it is suitable for fixed bed, fluidized bed and slurry bed applications, and is suitable for large-scale industrial production.

[0040] (2) The present invention can directly obtain aviation kerosene fuel in one step. The aviation kerosene does not contain pollutants such as sulfur and nitrogen, has low olefin content and high calorific value.

[0041] (3) The present invention uses a one-step method to directly produce gasoline. The reaction device is simple, the process flow is short, the equipment investment is low, and the energy consumption is low.

[0042] (4) This invention utilizes carbon dioxide, a greenhouse gas, as a carbon resource, which helps to realize the recycling of carbon resources and reduce dependence on fossil energy, while also reducing the environmental burden. Detailed Implementation

[0043] The technical details of this invention are described in detail in the following embodiments. It should be noted that the embodiments are only intended to further illustrate the technical features of this invention, and are not intended to limit the invention.

[0044] HY (SiO2 / Al2O3=18), HMCM-22 (SiO2 / Al2O3=30), and HZSM-5 molecular sieves with SiO2 / Al2O3 ratios of 50 and 150 respectively, purchased from Nankai University Molecular Sieve Factory, and HBeta (SiO2 / Al2O3=75) molecular sieve purchased from Zeolyst Company were calcined in air at 500℃ for 4 hours. The samples were then ground, pressed, pulverized, and sieved to form molecular sieve particles with a particle size of 0.35-0.71 mm for later use (in the following examples).

[0045] Example 1

[0046] 24.34 g of FeCl3·6H2O was mixed with water to form an iron salt solution with a Fe(III) concentration of 1.64 mol / L, and 2.5 mL of 12.1 mol / L HCl solution was added. Under stirring at 60 °C, 180 mL of 1.5 mol / L NaOH solution was added at a uniform rate, adjusting the pH of the solution from 0.6 to approximately 10 over 1.5 h. After the addition was complete, 6.0 g of carbon nanofibers (0.5–5 mm in length, 20–300 nm in diameter) were added to the solution, and the temperature was maintained while stirring continued for 1 h. Finally, the solution was cooled to room temperature. After the reaction was completed, the deposited product was separated by centrifugation and washed once with 400 mL of deionized water. The product was then dried at 60 °C and calcined at 350 °C for 3 h under a nitrogen atmosphere to obtain the Na-Fe2O3-C(N) catalyst sample. The sample was then ground, pressed into tablets, pulverized, and sieved to form Na-Fe2O3-C(N) particles with a particle size of 0.35-0.71 mm for later use.

[0047] Catalyst Evaluation: 0.5g of Na–Fe2O3-C(N) particles and 0.5g of composite molecular sieve particles (0.4g HY molecular sieve + 0.1g HBeta) were weighed and layered according to the order of contact with the feed gas (the feed gas passed through Na-Fe2O3-C, HY, and HBeta in sequence). The catalyst was layered in a fixed-bed reactor according to the Na-Fe2O3-C / HY / HBeta sequence for 3 hours of pre-reaction reduction and carbonization, followed by CO2 hydrogenation reaction evaluation. Reduction conditions: Atmospheric pressure, in pure H2 (25mL / min), reduction at 350℃ for 8 hours. Carbonization conditions: Carbonization gas (molar ratio) composition: H2 / CO2 = 1.0, CO: 10%, 330℃, 0.5MPa. Analysis and calculation of the Mössbauer spectroscopy characterization results of the carbonized sample showed that Fe was the main active component of the supported iron-based catalyst after carbonization. x The mass percentage of C (2≤x≤3) is 30.3%.

[0048] Reaction conditions: H2 / CO2 = 3.0 (molar ratio), pressure 4.0 MPa, space velocity 5000 mL / (h·g) cat The effect of reaction temperature on the performance of Na–Fe2O3-C / HY-HBeta catalyst in CO2 hydrogenation was investigated. The results (see Table 1) show that the Na–Fe2O3-C / HY-HBeta catalyst exhibits good performance in the synthesis of aviation kerosene distillate hydrocarbons via CO2 hydrogenation within the experimental temperature range. The CO2 conversion rate gradually increases with increasing reaction temperature, reaching a maximum of 38%. 8-16 The hydrocarbon content in the product remains relatively stable at 42-47% between 260-360℃, then gradually decreases, while the selectivity of CO, a byproduct affecting aviation kerosene yield, gradually increases. Taking all factors into consideration, the optimal temperature for CO2 hydrogenation to synthesize aviation kerosene fraction hydrocarbons should be between 300 and 360℃.

[0049] Table 1 Effect of reaction temperature on CO2 hydrogenation performance of Na–Fe2O3-C(N) / HY-HBeta catalyst

[0050]

[0051] Example 2

[0052] The Na–Fe₂O₃-C(N) catalyst and the multifunctional composite molecular sieve HY+HBeta prepared in Example 1 were weighed according to different mass ratios to form a catalyst with a total mass of 1.0 g, which was used for the CO₂ hydrogenation reaction as in Example 1. The catalyst evaluation procedure was the same as in Example 1, except that the following conditions were replaced: Reduction conditions: at atmospheric pressure, in pure H₂ (25 mL / min), reduction time of 12 h at 300 °C. Carbonization conditions: carbonization gas composition: H₂ / CO₂ = 0.15, CO: 30%, 300 °C, 0.1 MPa, carbonization treatment for 4 h; after analysis and calculation of the Mössbauer spectroscopy characterization results of the carbonized sample, it was found that the main active component of the supported iron-based catalyst after carbonization was Fe. x The mass percentage of C (2≤x≤3) is 49.9%.

[0053] Reaction conditions: H2 / CO2 = 3.0, temperature 320℃, pressure 2.0 MPa, space velocity 8000 mL / (h·g) catThe effect of different mass ratios of the active components of the catalyst on the CO2 hydrogenation performance of the Na–Fe2O3-C(N) / HY-HBeta catalyst was investigated. The results (see Table 2) show that different proportions of the components in the multifunctional composite catalyst result in different reaction performances. Only under suitable component ratios can the catalyst exhibit synergistic effects and better synthesis of aviation kerosene distillate hydrocarbons. The higher the proportion of iron in the catalyst, the higher the carbon dioxide conversion rate of the catalytic reaction, the more molecular sieves with olefin polymerization function, and the higher the selectivity of aviation kerosene distillate hydrocarbons. When the mass ratio of Na-Fe-C:HY:HBeta is 0.52:0.40:0.08, the proportion of aviation kerosene distillate hydrocarbons in the hydrocarbons reaches 50.1%.

[0054] Table 2. Effect of different component mass ratios on CO2 hydrogenation performance of Na–Fe2O3-C(N) / HY-HBeta catalyst

[0055]

[0056] Example 3

[0057] The process and conditions were the same as in Example 1, except that “HZSM-5 (SiO2 / Al2O3=100) molecular sieve” was used instead of “HY molecular sieve” and “MCM-22 molecular sieve” was used instead of “HBeta”, and the resulting catalyst was Na-Fe2O3-C(N) / HZSM-5-MCM-22.

[0058] The catalyst loading method, reduction treatment, carbonization treatment, and evaluation conditions were the same as in Example 1, except that the carbonization conditions were changed to: carbonization gas composition: H2 / CO2 = 2, CO: 5%, 350℃, 0.1MPa, carbonization treatment for 6h. Analysis and calculation of the Mössbauer spectroscopy characterization results of the carbonized sample showed that the main active component of the supported iron-based catalyst after carbonization was Fe. x The mass percentage of C (2≤x≤3) is 32.1%. The feed gas pressure, space velocity, and temperature for reaction evaluation are changed to "6.0MPa" and "3000mL / (h·g)" respectively. cat The evaluation results for “300℃” and “300℃” are listed in Table 3.

[0059] Example 4

[0060] The catalyst preparation steps are the same as in Example 1, except that "36.38g Fe(NO3)3·9H2O" is used instead of "24.34g FeCl3·6H2O", and "1.5mol / L KOH solution" is used instead of "1.5mol / L NaOH solution". The resulting catalyst is K-Fe2O3-C(N) / HY-HBeta.

[0061] The catalyst loading method, reduction treatment, carbonization treatment, and evaluation conditions were the same as in Example 1, except that the carbonization conditions were changed to: carbonization gas composition: H2 / CO2 = 1, CO: 20%, 320℃, 1.0 MPa, carbonization treatment for 0.5 h. Analysis and calculation of the Mössbauer spectroscopy characterization results of the carbonized sample showed that the mass percentage of the main active component FexC (2≤x≤3) in the carbonized supported iron-based catalyst was 37.5%. The feed gas pressure, space velocity, and temperature for reaction evaluation were changed to "1.0 MPa" and "7000 mL / (h·g)", respectively. cat The evaluation results for “340℃” and “340℃” are listed in Table 3.

[0062] Example 5

[0063] The catalyst preparation steps are the same as in Example 1, except that "17.19g ferric acetate Fe(OH)(CH3COO)2" is used instead of "24.34g FeCl3·6H2O", and "8g carbon nanotubes (length 0.5-5mm, inner diameter 4-20nm, wall thickness 0.05-1nm)" is used instead of "6.0g carbon nanofibers". The resulting catalyst is Na-Fe2O3-C(T) / HY-HBeta.

[0064] The catalyst loading method, reduction treatment, carbonization treatment, and evaluation conditions were the same as in Example 1, except that the carbonization conditions were changed to: carbonization gas composition: H2 / CO2 = 3, CO: 20%, Ar: 5%, 400℃, 1.0 MPa, carbonization treatment for 1 h; analysis and calculation of the Mössbauer spectrum characterization results of the carbonized sample showed that Fe was the main active component of the supported iron-based catalyst after carbonization. x The mass percentage of C (2≤x≤3) is 34.5%. The feed gas pressure, space velocity, and temperature for reaction evaluation are changed to "3.0MPa" and "9000mL / (h·g)" respectively. cat The evaluation results for “310℃” and “310℃” are listed in Table 3.

[0065] Example 6

[0066] The catalyst preparation steps are the same as in Example 1, except that "4g graphite carbon" is used to replace "6.0g carbon nanofibers" and "2% Co-HBeta" is used to replace "HBeta". The resulting catalyst is Na-Fe2O3-C(G) / HY-Co-HBeta.

[0067] The catalyst loading method, reduction treatment, carbonization treatment, and evaluation conditions were the same as in Example 1, except that the carbonization conditions were changed to: carbonization gas composition: H2 / CO2 = 0.5, 320℃, 1.0 MPa, carbonization treatment for 5 h; analysis and calculation of the Mössbauer spectroscopy characterization results of the carbonized sample showed that the mass percentage of the main active component FexC (2≤x≤3) in the carbonized supported iron-based catalyst was 59.5%. The feed gas pressure, space velocity, and temperature for reaction evaluation were changed to "0.5 MPa" and "4000 mL / (h·g)", respectively. cat The evaluation results for “350℃” and “350℃” are listed in Table 3.

[0068] Table 3. Effects of different composite multifunctional catalysts on the performance of CO2 hydrogenation to aviation kerosene fraction hydrocarbons.

[0069]

[0070] Table 3 shows that the various supported iron-based composite multifunctional catalysts prepared in this invention all exhibit good performance in the production of aviation kerosene distillate hydrocarbons by CO2 hydrogenation. Among them, Na-Fe2O3-C(G) / HY-Co-HBeta shows high selectivity for aviation kerosene distillate hydrocarbons (46.0%), which is related to the graphite carbon support material contained in its supported iron catalyst and the Co auxiliary agent contained in the HBeta molecular sieve.

[0071] Example 7

[0072] The process and conditions were the same as in Example 1, except that 0.5g of the Na–Fe2O3-C(N) catalyst prepared by the method in Example 1 was weighed and mixed evenly with 0.4g of HY molecular sieve and 0.1g of HBeta molecular sieve particles, and then used for the CO2 hydrogenation reaction. Reduction conditions: at atmospheric pressure, in pure H2 (25mL / min), reduction at 350℃ for 8h. Carbonization conditions: carbonization gas composition: H2 / CO2 = 2, CO: 5%, 320℃, 1.0MPa, carbonization treatment for 3h. Analysis and calculation of the Mössbauer spectroscopy characterization results of the carbonized sample showed that the main active component of the supported iron-based catalyst after carbonization was Fe. x The mass percentage of C (2≤x≤3) is 31.0%. Reaction conditions: Feed gas: H2 / CO2 = 1.0–6.0, 5% N2, temperature 310℃, pressure 4.0 MPa, space velocity 2000 mL / (h·g) catThe effect of the hydrogen-to-carbon ratio of the feed gas on the CO2 hydrogenation performance of the Na–Fe2O3-C(N)-HY-HBeta composite multifunctional catalyst was investigated. The results (see Table 4) show that the CO2 conversion rate increases significantly with the increase of the hydrogen-to-carbon ratio of the feed gas. Within the range of hydrogen-to-carbon ratios investigated, the hydrocarbon selectivity of aviation kerosene fraction decreases with the increase of the hydrogen-to-carbon ratio, but always remains at a high value (hydrocarbon product proportion > 40%).

[0073] Table 4. Effect of the hydrogen-to-carbon ratio of the feed gas on the catalytic performance of Na–Fe2O3-C(N)-HY-HBeta for CO2 hydrogenation

[0074]

[0075] Example 8

[0076] The process and conditions were the same as in Example 1, except that 0.5g of the Na–Fe2O3-C(N) catalyst prepared by the method in Example 1 was weighed and layered with a composite molecular sieve (0.4g of HY molecular sieve and 0.1g of HBEA molecular sieve particles mixed evenly) and then packed into a fixed-bed reactor for CO2 hydrogenation reaction. Reduction conditions: at atmospheric pressure, in pure H2 (25mL / min), reduction at 400℃ for 6h. Carbonization conditions: carbonization gas composition: H2 / CO2 = 1, CO: 10%, 340℃, 0.1MPa, carbonization treatment for 3h. Analysis and calculation of the Mössbauer spectroscopy characterization results of the carbonized sample showed that the main active component of the supported iron-based catalyst after carbonization was Fe. x The mass percentage of C (2≤x≤3) is 35.5%. Reaction conditions: H2 / CO2 = 3.5, temperature 320℃, pressure 4.0 MPa, space velocity 6000 mL / (h·g) cat The stability of the Na–Fe2O3-C(N) / / HY-HBEA catalyst for CO2 hydrogenation was investigated. The results (see Table 5) show that the catalyst consistently exhibited excellent CO2 hydrogenation performance throughout the 200-h reaction time, with no significant deactivation. Analysis of the aviation kerosene product composition (after 200 h of reaction) (see Table 6) shows that the aviation kerosene fraction hydrocarbons (C... 8-16 The hydrocarbons mainly consist of alkanes (including n-alkanes, isoalkanes, and cycloalkanes) and aromatics, with a low olefin content. The by-product hydrocarbons of the reaction, besides containing a small amount of methane, also include low-carbon distillate hydrocarbons (C64-C64) mainly composed of alkanes. 2-7 ).

[0077] Table 5. Stability of CO2 hydrogenation reaction on Fe2O3-C(N) / / HY-HBeta catalyst.

[0078]

[0079] Table 6. Analysis of hydrocarbon fraction composition of the product after 200 hours of reaction.

[0080] Content (C-mol%) <![CDATA[Jet fuel fraction hydrocarbon (C 8-16 )]]> <![CDATA[Low-carbon fraction hydrocarbons (C 2～7 )]]> Alkanes 76.0 83.5 Olefins 5.0 8.0 Aromatics 19.0 9.0

[0081] In this method, the single-pass CO2 conversion rate can reach 30%, the methane selectivity in the hydrocarbon products is less than 11%, and the hydrocarbon selectivity of the aviation kerosene fraction with 8-16 carbon atoms is as high as 42%, with the aviation kerosene fraction mainly composed of alkanes and aromatics. This invention opens up a new route for producing aviation kerosene from carbon dioxide.

[0082] Comparative Examples

[0083] The catalyst preparation, processing, and reaction evaluation steps are the same as in Example 1, except that the following steps are different. Two experiments are designed to be conducted: (1) Remove the catalyst reduction step and carbonization treatment step, that is, directly conduct catalyst evaluation tests on the catalyst sample after layered packing.

[0084] (2) The carbonization step of the catalyst was removed, meaning the reduced catalyst sample was directly subjected to catalyst evaluation tests; the reaction evaluation temperature of the catalyst was changed to 300℃. The evaluation results of the two catalysts, combined with the results in Table 1, are listed in Table 7.

[0085] Table 7. Effects of different pretreatment conditions on the CO2 hydrogenation performance of Na–Fe2O3-C(N) / HY-HBeta catalyst

[0086]

[0087] As shown in Table 7, the Na–Fe2O3-C(N) / HY-HBeta catalyst only exhibits high catalytic activity and selectivity for aviation kerosene fractions after calcination, reduction, and carbonization treatment. Compared to this process, the catalyst without carbonization treatment shows reduced catalytic activity and significantly lower selectivity for aviation kerosene fractions, with the reaction mainly producing low-carbon hydrocarbons (C). 2-7 Without reduction and carbonization treatment, the main product of the catalytic hydrogenation of carbon dioxide is CO, and almost no hydrocarbons from aviation kerosene distillate are generated.

[0088] The supported iron-based catalyst samples were characterized by XRD and Mössbauer spectroscopy after calcination, reduction, carbonization, reaction, and 200 hours of reaction. The iron phase composition was analyzed, and the results are listed in Table 8. Analysis of the results in Table 8 shows that Na-Fe... x The iron-active phase composition of CC(N) catalytic carbon dioxide hydrogenation to aviation kerosene fraction hydrocarbons is Fe. xC(x=2,2.5,3). The composition of the iron phase after carbonization and after reaction is almost the same. Only a small amount of Fe3O4 phase is formed after reaction. However, the composition of the iron phase remains unchanged after 200 hours of reaction. This is one of the main reasons why the catalyst system maintains good reaction stability.

[0089] Table 8. XRD and Mössbauer spectroscopy results of iron phase composition of Na–Fe2O3-C(N) / HY-HBeta catalyst

[0090]

[0091] In summary, this invention not only provides a new route for the synthesis of aviation kerosene distillate hydrocarbons by carbon dioxide hydrogenation, but also invents a new, highly efficient and stable catalytic system for the synthesis of aviation kerosene distillate hydrocarbons by carbon dioxide hydrogenation.

Claims

1. A method for directly producing aviation kerosene fraction hydrocarbons by hydrogenation of carbon dioxide, characterized in that: Using a mixture of carbon dioxide and hydrogen as feedstock, aviation kerosene distillate hydrocarbons are directly converted under the catalysis of an iron-based multifunctional composite catalyst; the carbon dioxide is a gas containing carbon dioxide. The composite catalyst consists of a supported iron-based catalyst as the first component, combined with a catalyst possessing low-carbon olefin polymerization capabilities and C... 16+ Two molecular sieves with heavy hydrocarbon hydrocracking capabilities are mixed or combined as the second component; the mass ratio of the first component to the second component is 1:8 to 8:

1. The second component possesses low-carbon olefin polymerization capabilities and C... 16+ The two types of molecular sieves with heavy hydrocarbon hydrocracking capabilities refer to molecular sieves that have low-carbon olefin polymerization capabilities and those that have heavy hydrocarbon hydrocracking capabilities, respectively. Molecular sieves with low-carbon olefin polymerization capabilities are one or both of ZSM-5 and Y, while molecular sieves with heavy hydrocarbon hydrocracking capabilities are one or both of Beta and MCM-22. The calcined iron-based catalyst precursor is mixed with two types of molecular sieves as the second component, or supported on an iron-based catalyst, a molecular sieve with low-carbon olefin polymerization function, and C. 16+ After functional molecular sieves for heavy hydrocarbon hydrocracking are sequentially stacked to form a composite catalyst, it needs to be reduced in H2 gas at 300-400 °C for 2-12 h before the reaction, and then carbonized in H2 / CO2 gas at 300-420 °C for 0.5-6 h. After treatment, an iron-based multifunctional composite catalyst composed of a supported iron-based catalyst and two types of molecular sieves can be obtained. The H2 / CO2 molar ratio in the H2 / CO2 gas is 0.05~5, H2+CO2 accounts for more than 70% of the total gas volume in the H2 / CO2 gas, and the H2 / CO2 gas does not contain nitrogen, CO and inert gases, or contains one or more of nitrogen, CO and inert gases.

2. The method according to claim 1, characterized in that: The reaction temperature is 260~420℃, the reaction pressure is 0.01~10.0MPa, and the feed gas hourly space velocity is 500~50000mL / (h∙g). cat The H2 / CO2 molar ratio in the feed gas is 0.8~7.

0.

3. The method according to claim 1, characterized in that: The main active component of the supported iron-based catalyst is Fe supported on carbon materials. x C, where 2≤x≤3, Fe x The mass percentage of component C in the supported iron-based catalyst is 20-60%. The supported iron-based catalyst may or may not contain an additive, which is an oxide and accounts for 0-20% of the total mass of the iron-based catalyst; the additive is one or more of Na oxide, K oxide, Zr oxide, V oxide, Zn oxide, and Ce oxide.

4. The method according to claim 3, characterized in that: The content of promoters in supported iron-based catalysts accounts for 0.5-9% of the total mass of the iron-based catalyst.

5. The method according to claim 3, characterized in that: The mass ratio of the first component to the second component of the composite catalyst is 1:2 to 4:1, the molar ratio of H2 / CO2 in the H2 / CO2-containing gas is 0.15 to 2, and Fe... x Component C accounts for 30-50% of the mass of the supported iron-based catalyst. The reaction temperature is 300~400℃, the reaction pressure is 0.1~8.0MPa, and the feed gas hourly space velocity is 1000~20000mL / (h∙g). cat The H2 / CO2 molar ratio in the feed gas is 2.0~6.

0.

6. The method according to claim 5, characterized in that: The mass ratio of the first component to the second component of the composite catalyst is 1:2 to 2:1, Fe x Component C accounts for 30-40% of the mass of the supported iron-based catalyst. The reaction temperature is 320~360℃, the reaction pressure is 1.0~6.0MPa, and the feed gas hourly space velocity is 1000~10000mL / (h∙g). cat The molar ratio of H2 / CO2 in the feed gas is 3.0~6.

0.

7. The method according to claim 1, characterized in that: The molecular sieve with low-carbon olefin polymerization function refers to a Y molecular sieve with a silica-to-alumina ratio of 10-150, possessing C 16+ Molecular sieves with heavy hydrocarbon hydrocracking capabilities refer to Beta molecular sieves with a silica-to-alumina ratio of 20-200; among the two types of molecular sieves, low-carbon olefin polymerization molecular sieves / C 16+ The mass ratio of molecular sieves used in the hydrogenation and cracking of heavy hydrocarbons is 1:5 to 5:

1. Two types of molecular sieves containing heavy hydrocarbon hydrogenation cracking function are modified with metal or not. The modified metals include one or more of Mo, Zn, Ga, Ni, Na, Co, Cu, and La, and the metal element accounts for less than 10% of the mass of the modified molecular sieve.

8. The method according to claim 7, characterized in that: Two types of molecular sieves, low-carbon olefin polymerization molecular sieves / C 16+ The mass ratio of molecular sieves for heavy hydrocarbon hydrogenation cracking is 1:3 to 3:

1. Metal elements account for 0.5% to 5% of the mass of the modified molecular sieve.

9. The method according to claim 8, characterized in that: Two types of molecular sieves, low-carbon olefin polymerization molecular sieves / C 16+ The mass ratio of molecular sieves for heavy hydrocarbon hydrogenation cracking is 1:2 to 2:1; Metal elements account for 0.5-2% of the mass of the modified molecular sieve.

10. The method according to claim 1 or 3, characterized in that: The iron-based multifunctional composite catalyst was prepared using any one of the following three processes; A. The catalyst is synthesized using a one-step method, including the following steps: (1) Prepare a soluble Fe(III) salt and an auxiliary salt to form a salt solution, or prepare a soluble Fe(III) salt to form a salt solution, wherein the Fe(III) concentration in the salt solution is 0.05~2 mol / L, and add HCl solution with a concentration of 5~12.1 mol / L to adjust the pH value to 0~3; the soluble Fe(III) salt refers to a salt compound that can be dissolved in water, and is one or more of chloride, nitrate, and acetate; the auxiliary salt is a salt compound that can be dissolved in water, and is one or more of chloride, nitrate, and acetate; (2) Add an alkaline solution to the salt solution in step (1); adjust the pH of the solution from 0 to 3 to an alkaline pH of 8 to 11; after the addition is complete, add carbon material to the solution and age for 1 to 3 hours; the alkaline solution refers to an alkaline solution that can adjust the pH of the solution, and is one or more of NaOH, KOH, Na2CO3, NaHCO3, K2CO3, KHCO3, Na2C2O4, K2C2O4, RCOONa, RCOOK, and ammonia water; the concentration of the alkaline solution is 0.1 to 8 mol / L; where R refers to an organic functional group, including C1 to C2. 20 Alkyl, C1~C 20 alkenyl or C6~C 20 Aryl carbon materials refer to one or more of the following: carbon fiber, carbon nanotubes, graphitic carbon, and graphene. (3) After the reaction is completed, the deposited product is separated from the solution in step (2) by centrifugation or filtration, and the deposited product is washed with water, dried at 60~130℃, and calcined at 250~500℃ for 2~8h to obtain the supported iron-based catalyst precursor containing the promoter. (4) The calcined iron-based catalyst precursor is mixed with two types of molecular sieves as the second component, or supported on an iron-based catalyst, a molecular sieve with low-carbon olefin polymerization function, and C 16+ After the functional molecular sieves for heavy hydrocarbon hydrogenation cracking are stacked in sequence to form a composite catalyst, it needs to be reduced at 300~400 ℃ for 2~12 h in H2 gas and carbonized at 300~420 ℃ in H2 / CO2 gas for 0.5~6 h before the reaction. After the treatment, an iron-based multifunctional composite catalyst composed of a supported iron-based catalyst and two kinds of molecular sieves can be obtained. B. Alternatively, the catalyst is prepared using a one-step synthesis method, comprising the following steps: (1) Form a salt solution of soluble Fe(III) salt with a Fe(III) concentration of 0.05~2 mol / L, and add HCl solution with a concentration of 5~12.1 mol / L to adjust the pH value to 0~3; (2) Add the alkaline solution containing Na and / or K in step (2) of process A to the salt solution in step (1); gradually adjust the pH value of the solution from 0 to 3 to an alkaline pH value of 8 to 11; after the addition is complete, add carbon material to the solution and age it for 1 to 3 hours. (3) After the reaction is completed, the deposited product is separated from the solution in step (2) by centrifugation or filtration, and the deposited product is washed with water. The content of residual Na or K in the catalyst is controlled by controlling the number of washings and the amount of water used for each washing. After drying, the product is calcined at 250~500℃ for 2~8h to obtain an iron-based catalyst precursor containing Na and / or K promoters. (4) The calcined iron-based catalyst precursor is mixed with two types of molecular sieves as the second component, or supported on an iron-based catalyst, a molecular sieve with low-carbon olefin polymerization function, and C 16+ After the functional molecular sieves for heavy hydrocarbon hydrogenation cracking are stacked in sequence to form a composite catalyst, it needs to be reduced at 300~400 ℃ for 2~12 h in H2 gas and carbonized at 300~420 ℃ in H2 / CO2 gas for 0.5~6 h before the reaction. After the treatment, an iron-based multifunctional composite catalyst composed of a supported iron-based catalyst and two kinds of molecular sieves can be obtained. C. Alternatively, the catalyst is first synthesized using a co-precipitation method to obtain Fe2O3 supported on carbon materials, and then an additive is added using an impregnation method, including the following steps: (1) Mix soluble Fe(III) salts to form a salt solution with a Fe(III) concentration of 0.05~2 mol / L, and add HCl solution with a concentration of 5~12.1 mol / L to adjust the pH value to 0~3; (2) Add the alkaline solution described in step (2) of process A to the salt solution in step (1); gradually adjust the pH value of the solution from 0 to 3 to an alkaline pH value of 8 to 11; after the addition is complete, add carbon material and age for 1 to 3 hours; (3) After the reaction is completed, the deposited product is separated from (2) by centrifugation or filtration, and the deposited product is thoroughly washed with deionized water, dried at 60~130℃, and calcined at 250~500℃ for 2~8h to obtain the active component Fe2O3 loaded on carbon material. (4) The catalyst is formed by combining the auxiliary salt with the active ingredient by the impregnation method. The specific process is as follows: calculate the theoretical amount of auxiliary salt according to the required auxiliary content, prepare an aqueous solution of auxiliary salt, impregnate the carbon material supported Fe2O3 prepared in (3) in the solution, and after stirring, standing, drying and calcining, the calcination temperature is 250~500℃ and the calcination time is 2~8h, thus obtaining the supported iron-based catalyst precursor containing auxiliary. (5) The calcined iron-based catalyst precursor is mixed with two types of molecular sieves as the second component, or supported on an iron-based catalyst, a molecular sieve with low-carbon olefin polymerization function, and C 16+ After the functional molecular sieves for heavy hydrocarbon hydrogenation cracking are stacked in sequence to form a composite catalyst, it needs to be reduced at 300~400 °C for 2~12 h with H2 gas and treated at 300~420 °C with H2 / CO2 gas for 0.5~6 h before the reaction. After treatment, an iron-based multifunctional composite catalyst composed of a supported iron-based catalyst and two kinds of molecular sieves can be obtained.

11. The method according to claim 10, characterized in that: In step (2) of preparation process A, R is selected from methyl, ethyl or phenyl; the carbon material is one or more of carbon fiber, carbon nanotubes or graphite carbon.

12. The method according to claim 10, characterized in that: With C 16+ During the metal modification of functional molecular sieves for heavy hydrocarbon hydrocracking, the metal component is loaded onto the molecular sieve using one of the following two methods: (1) Prepared by impregnation method, the specific process is as follows: calculate the theoretical amount of metal salt required according to the required metal content, prepare an aqueous solution of metal salt, wherein the metal salt is selected from any one or more of the following: nitrate, chloride, bromide, acetate, acetylacetone, citrate, oxalate, benzoate; impregnate the molecular sieve to be modified in the solution, and after stirring, standing, drying and calcining, the calcination temperature is 300~700℃ and the calcination time is 2~10 h, thus obtaining the metal modified molecular sieve; (2) Prepared by ion exchange method. The specific process is as follows: calculate the theoretical amount of metal salt required according to the required metal content, prepare an aqueous solution of metal salt, wherein the metal salt is selected from any one or more of the following: nitrate, chloride, bromide, acetate, acetylacetone, citrate, oxalate, benzoate; mix the molecular sieve to be modified with the aqueous solution at a solid-liquid mass ratio of 1: (10~200), ion exchange for 2~24 h, wash with water, dry, and calcine at a calcine temperature of 300~700℃ for 2~10 h, and the metal-modified molecular sieve is obtained.

13. The method according to claim 3, characterized in that: The components of the composite catalyst are mixed or combined in one of the following three ways. (1) Powder mixing method: Weigh out iron-based catalyst and two kinds of molecular sieve catalyst powders respectively, grind and mix them evenly according to the required mass ratio, then press them into tablets, crush and sieve them with a sieve hole size of 0.1~2.0mm to obtain a particle size of 0.1-2.0mm; (2) Particle mixing method: Weigh the iron-based catalyst and the two molecular sieve catalyst powders respectively, press them into tablets, crush them and sieve them with a sieve hole size of 0.1~2.0mm, mix the particles evenly according to the required mass ratio of iron-based catalyst and two molecular sieves to form a composite catalyst with a particle size of 0.1-2.0mm; (3) Layered packing method: The catalyst bed is filled sequentially with the required mass of supported iron-based catalyst bed with a particle size of 0.1-2.0 mm, molecular sieve bed with low carbon olefin polymerization function, and C in the order of catalyst contact with feed gas. 16+ The heavy hydrocarbon hydrocracking functional dimolecular sieve bed catalyst has no or no inert material isolation layer between adjacent bed components. The mass ratio of the inert material isolation layer to the active component of the composite catalyst is 0.01~10. The inert material isolation layer is an inert material that does not react with the catalyst and the feed gas components. Its particle size ratio to the catalyst particle size is 1:0.8~1:

3.

14. The method according to claim 1, characterized in that: The components of the composite catalyst are combined using a layered packing method.

15. The method according to claim 13 or 14, characterized in that: In methods (1) and (2), the components of the composite catalyst are pulverized and sieved with a sieve aperture size of 0.3~0.8 mm during mixing to obtain a composite catalyst with a particle size of 0.3-0.8 mm. Method (3) Layered filling method: The catalyst bed is filled sequentially with the required mass of supported iron-based catalyst bed with a particle size of 0.3-0.8 mm, molecular sieve bed with low carbon olefin polymerization function, and C in the order of catalyst contact with feed gas. 16+ The heavy hydrocarbon hydrocracking functional dimolecular sieve bed catalyst has no or no inert material isolation layer between adjacent bed components. The mass ratio of the inert material isolation layer to the active component of the composite catalyst is 0.1~5. The inert material isolation layer material is one or two of inert SiO2 microspheres and quartz sand, and its particle size ratio to the catalyst particle size is 1:1~1:1.

5.

16. The method according to claim 1, characterized in that: The gas containing carbon dioxide refers to any one or more of the following: industrial waste gas, automobile exhaust, and atmospheric gases containing carbon dioxide.

17. The method according to claim 16, characterized in that: Gases containing carbon dioxide are either coal-fired exhaust or vehicle exhaust.

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