Method for directly synthesizing heavy hydrocarbon through carbon dioxide hydrogenation

Abstract

The invention provides a method for directly synthesizing heavy hydrocarbon with the carbon number of 5-16 through hydrogenation of carbon dioxide, which comprises the following step of: under the reaction conditions that the temperature is 280-350 DEG C, the pressure is 0.02-9.0 MPa, the air speed is 500-30000 mL / (h.gcat) and the molar ratio of H2 to CO2 is 0.9-6.0, directly converting mixed gas consisting of carbon dioxide and hydrogen into the heavy hydrocarbon with the carbon number of 5-16 under the catalytic action of a multifunctional composite catalyst. The composite catalyst is prepared by mixing a supported iron-based catalyst containing carbon and alkali metal as a first component and a molecular sieve with olefin polymerization and heavy hydrocarbon hydrocracking functions as a second component. In the method, the one-way CO2 conversion rate can reach more than 40%, and the selectivity of the heavy hydrocarbon with the carbon atom number of 5-16 can reach more than 70%. The invention develops a new route for producing the heavy hydrocarbon with the carbon atom number of 5-16 from carbon dioxide.

Description

Technical Field

[0001] The invention relates to a method for preparing heavy hydrocarbons by hydrogenating carbon dioxide, and in particular to a method for directly preparing heavy hydrocarbons with a carbon number of 5 to 16 by hydrogenating carbon dioxide. Background Art

[0002] Heavy hydrocarbons with carbon numbers of 5 to 16, including the main hydrocarbon fractions of transportation fuels such as gasoline and aviation kerosene, occupy an important position in modern energy and chemical industry. At present, heavy hydrocarbons with carbon numbers of 5 to 16 are mainly produced from petroleum through direct crude oil fractionation and catalytic cracking. However, the reserves of petroleum resources are limited, and the development of non-petroleum resources to obtain heavy hydrocarbons with carbon numbers of 5-16 has become a goal of research and development by countries around the world. CO2 is the cheapest and most abundant resource in the carbon family, and its reserves are extremely abundant. With the continuous development of human society, the use of fossil energy has increased dramatically, and the content of CO2 in the atmosphere has increased day by day, which not only aggravates the greenhouse effect, but also causes a huge waste of carbon resources. The cycle mode of using industrial waste gas or CO2 captured in the atmosphere to produce hydrogen with renewable energy and catalytic hydrogenation of CO2 to produce liquid hydrocarbons is of great significance for simultaneously solving the two new challenges of climate change and energy crisis facing human society today.

[0003] Studies have shown that the production of hydrocarbons by hydrogenation of carbon dioxide generally involves two steps: first, CO2 undergoes a reverse water-gas shift to produce CO, and then CO is converted to hydrocarbons by Fischer-Tropsch synthesis. The product selectivity of the traditional Fischer-Tropsch synthesis process for the hydrogenation of CO to hydrocarbons is limited by the Anderson-Schulz-Flory (ASF) law. 16 The selectivity of hydrocarbons is low. Unlike the CO hydrogenation process, the CO2 hydrogenation process has a low C / H ratio on the catalyst surface due to the slow adsorption of CO2 on the catalyst surface. This phenomenon is conducive to the hydrogenation of surface adsorbed species, reducing the chain growth probability of the product, thereby improving the methane selectivity. However, it makes it more difficult to produce long-chain hydrocarbons by CO2 hydrogenation. Therefore, the target products of CO2 hydrogenation research are currently mainly concentrated on products such as small molecular weight hydrocarbons or oxygen-containing compounds such as methanol, dimethyl ether, methane and light olefins, while there are fewer studies on the preparation of long-chain hydrocarbons by CO2 hydrogenation. Therefore, finding a high conversion rate and high selectivity CO2 hydrogenation to produce heavy hydrocarbons with a carbon number of 5-16 has become an urgent problem that needs to be solved in the conversion and utilization of CO2. Summary of the invention

[0004] The technical problem to be solved by the present invention is that the target product C 5-16 The problems of low hydrocarbon selectivity, high selectivity of byproducts CO and methane, and low CO2 utilization rate are provided. 5-16 Heavy hydrocarbons method.

[0005] The present invention provides a method for directly preparing heavy hydrocarbons with a carbon number of 5-16 by hydrogenating carbon dioxide, which is characterized in that: a mixed gas consisting of carbon dioxide and hydrogen is used as a raw material gas, and is directly converted into heavy hydrocarbons with a carbon number of 5-16 under the catalytic action of a multifunctional composite catalyst; the composite catalyst comprises a supported iron-based catalyst containing carbon and alkali metal as a first component, and a catalyst having a light olefin polymerization function and a heavy hydrocarbon (C 16+ ) The molecular sieve with hydrocracking function is mixed or layered and filled as the second component; the mass ratio of the first component to the second component is 1:6 to 6:1, preferably 1:3 to 3:1.

[0006] The reaction conditions for preparing heavy hydrocarbons with a carbon number of 5-16 by hydrogenation of carbon dioxide in the present invention are as follows: the reaction temperature is 280-350°C (preferably 290-340°C, more preferably 300-330°C), the reaction pressure is 0.02-9.0MPa (preferably 1.5-7.0MPa, more preferably 2.5-5.0MPa), the raw gas space velocity is 500-30000mL / (h·g cat ) (preferably 1000 to 20000 mL / (h·g cat ), more preferably 2000 to 15000h -1 ), the H2 / CO2 molar ratio in the raw gas is 0.9 to 6.0 (preferably 1.5 to 5.0, more preferably 2.5 to 4.0).

[0007] The main active component of the supported iron-based catalyst containing carbon and alkali metal is Fe x C (2≤x≤3), the mass of the active component iron element in the catalyst accounts for 25-65% (preferably 30-60%, more preferably 40-60%) in the loaded iron catalyst, the mass ratio of the auxiliary alkali metal element to the active component element Fe is 0.01-5:1 (preferably 0.05-1:1, more preferably 0.05-0.8:1), the alkali metal auxiliary element is one or more of Na, K, Li, and the rest is carbon material.

[0008] The low-carbon olefin polymerization function and the heavy hydrocarbon (C 16+ ) The molecular sieve with hydrocracking function refers to a molecular sieve with both light olefin polymerization function and heavy olefin hydrocracking function, preferably ZSM-22, wherein the ZSM-22 molecular sieve with a silicon-aluminum ratio of 20 to 150 is preferred. The molecular sieve can be modified with metals, and the metals used include one or more of Co, Ga, and La. The metal element accounts for less than 5% of the mass of the modified molecular sieve, preferably 0.5% to 3%, and more preferably 0.5% to 2%.

[0009] The supported iron-based catalyst containing carbon and alkali metal can be prepared by the following process:

[0010] (1) Prepare soluble Fe salt and alkali metal additive salt to form 100 mL of salt solution, the Fe concentration in the salt solution is 0.1-1.0 mol / L, and the mass ratio of alkali metal additive element to active Fe element is 0.01-5:1 (preferably 0.05-1:1, more preferably 0.05-0.8:1). Take a certain volume of the above solution and impregnate it on 2.0 g of carbon material at 20-50°C, let it stand for 2-30 hours, dry it at 60-120°C for 4-8 hours, and calcine the obtained sample at 350-500°C under N2 for 2-8 hours. The obtained sample is marked as MFe@C, where M is the alkali metal additive and C is the carbon material.

[0011] In the above preparation steps, the soluble Fe salt refers to an organic iron salt compound soluble in water, preferably one or more of ferric acetate, ferric oxalate, and ferric acetylacetonate; the auxiliary salt is a salt compound soluble in water, preferably one or more of nitrate and acetate. The carbon material refers to carbon fiber, carbon nanotube, graphite carbon, preferably carbon nanotube, more preferably multi-walled carbon nanotube.

[0012] (2) After the calcined MFe@C is combined with the molecular sieve to form a composite catalyst, it needs to be reduced at 300-400°C with H2 gas for 2-12 h before the reaction, and treated at 300-420°C with H2 / CO2 gas (H2 / CO2=0.05-5 (preferably 0.15-2), the H2+CO2 mixed gas accounts for more than 70% of the total gas content, and the mixed gas may or may not contain CO and inert gas) for 0.5-6 h. After the treatment, an iron-based multifunctional composite catalyst containing carbon material and alkali metal composed of MFe@C and molecular sieve can be obtained.

[0013] When metal modification is performed on molecular sieves with heavy olefin hydrocracking function, the metal component can be loaded onto the molecular sieve by one of the following two methods:

[0014] (1) Prepared by equal volume impregnation method, the specific process is: according to the required metal content, the amount of metal salt required theoretically is calculated, and an aqueous solution of metal salt is prepared, wherein the metal salt is selected from any one or more of nitrate, chloride, bromide, acetate, acetylacetonate, citrate, oxalate, and benzoate; an equal volume of the molecular sieve to be modified is impregnated in the solution, and after stirring, standing, drying, and calcining, the calcination temperature is 300-600°C, and the calcination time is 2-8h, the metal-modified molecular sieve is obtained;

[0015] Or, (2) prepared by ion exchange method, the specific process is: according to the required metal content, the amount of metal salt required theoretically is calculated, and an aqueous solution of the metal salt is prepared, wherein the metal salt is selected from any one or more of nitrate, chloride, bromide, acetate, acetylacetonate, citrate, oxalate, and benzoate; the molecular sieve to be modified is mixed at a solid-liquid mass ratio of 1:(10-200), ion exchange is performed for 2-24 hours, and then washed, dried, and calcined at a temperature of 300-600°C for a calcination time of 2-8 hours to obtain a metal-modified molecular sieve.

[0016] The two components of the multifunctional composite catalyst can be mixed in one of the following three ways or in two or three ways, among which the layered filling method is preferred:

[0017] (1) Powder mixing method: Weigh the iron-based catalyst and molecular sieve catalyst powders respectively, grind and mix them in a mortar according to the required mass ratio, press them into tablets, crush and sieve (the sieve size is 0.1-2.0 mm, preferably 0.3-0.8 mm), and obtain a composite catalyst with a particle size of 0.1-2.0 mm (0.3-0.8 mm);

[0018] (2) Particle mixing method: Weigh the iron-based catalyst and molecular sieve catalyst powders respectively, press them into tablets, crush and sieve them (the sieve size is 0.1-2.0 mm, preferably 0.3-0.8 mm), mix the particles evenly according to the required mass ratio, and form a composite catalyst with a particle size of 0.1-2.0 mm (0.3-0.8 mm);

[0019] (3) Layered filling method: The catalyst bed is filled with the required mass of loaded iron-based catalyst and composite molecular sieve catalyst with a particle size of 0.1-2.0 mm (0.3-0.8 mm) in the order of contact between the catalyst and the raw gas. There may or may not be an inert material isolation layer between the catalyst bed components. The mass ratio of the inert material isolation layer to the active component of the composite catalyst is 0.01-10 (preferably 0.1-5). The material of the inert material isolation layer is an inert material that does not react with the catalyst and the raw gas components, preferably an inert SiO2 ball or quartz sand, and the ratio of its particle size to the particle size of the catalyst is 1:0.8-1:3 (preferably 1:1-1:1.5).

[0020] When heavy hydrocarbons with a carbon number of 5-16 are produced by hydrogenation of carbon dioxide, the catalyst performance is evaluated as follows: the prepared iron-based multifunctional catalyst is filled in the constant temperature section of a fixed bed reactor, and before the reaction, it is reduced at 300-400°C with H2 gas for 2-12 hours, and carbonized at 300-420°C with H2 / CO2 gas (H2 / CO2=0.05-5 (0.15-2), H2+CO2 mixed gas accounts for more than 70% of the total gas content, and the mixed gas may or may not contain CO and inert gas) for 0.5-6 hours, and then adjusted to the reaction temperature, and the carbonized gas is switched to the reaction gas. The reaction products are introduced into the chromatogram in gaseous or liquid form for analysis. Among them, CO, N2, CH4 and CO2 are detected by TCD, and hydrocarbons and oxygen-containing compounds are detected by FID.

[0021] The present invention is applied to gas containing carbon dioxide, which refers to any one or more of industrial waste gas containing carbon dioxide, automobile exhaust, coal combustion waste gas, and carbon dioxide absorbed from the atmosphere and seawater.

[0022] In the method, the single-pass CO2 conversion rate can reach more than 40%, and the selectivity of heavy hydrocarbons with carbon atoms of 5 to 16 can reach more than 70%. The present invention has opened up a new route for producing heavy hydrocarbons with carbon atoms of 5 to 16 from carbon dioxide.

[0023] The present invention has the following characteristics:

[0024] (1) The present invention can directly obtain heavy hydrocarbons with a carbon number of 5-16 in one step, wherein the heavy hydrocarbon components are mainly isoparaffins and heavy olefins, and the aromatic hydrocarbon component is relatively low (<15%);

[0025] (2) The present invention adopts a one-step method to directly produce heavy hydrocarbons with a carbon number of 5-16, with a simple reaction device, a short process flow, low equipment investment and low energy consumption;

[0026] (3) The present invention utilizes carbon dioxide, a greenhouse gas, as a carbon resource, which helps to achieve the recycling of carbon resources and reduce dependence on fossil energy, while alleviating the environmental burden. DETAILED DESCRIPTION

[0027] The technical details of the present invention are described in detail by the following examples. It should be noted that the examples are only used to further illustrate the technical features of the present invention, rather than to limit the present invention.

[0028] Example 1

[0029] 35.317g of ferric acetylacetonate (Fe(C5H7O2)3, molecular weight: 353.17) and 1.6998g of sodium nitrate (NaNO3, molecular weight: 84.99) were mixed with water to form 100mL of iron salt solution. 20mL of the above solution was impregnated into 0.5g of multi-walled carbon nanotubes (MWCNT, nanotube inner diameter of 0.5-2nm, outer diameter of 3-20nm, nanotube length / outer diameter ratio of 70-130) at 25°C, allowed to stand for 20 hours, dried at 80°C for 8 hours, and the obtained sample was calcined at 450°C for 3 hours under N2. The obtained sample was marked as NaFe@C, and the sample was ground, tableted, crushed, and sieved to form NaFe@C particles with a particle size of 0.35-0.71mm.

[0030] The NaFe@C particles were reduced and carbonized according to the following process. The electron microscopy results showed that the particles were carbon-coated active iron (mainly FexC (2≤x≤3)). The carbon material existed in the form of nano-microspheres (with a diameter of 50-100 nanometers). The active iron was evenly distributed in the micro-sphere carbon material. The mass content of iron in the catalyst was 56.3%, and the mass ratio of Na / Fe was 0.08:1.

[0031] The processed HZSM-22 (SiO2 / Al2O3=33, molar ratio) purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. was calcined at 450°C for 3h. The sample was ground, tableted, crushed and sieved to form molecular sieve particles with a particle size of 0.35-0.71mm for use.

[0032] Weigh 0.5g of the NaFe@C particles and 0.5g of the HZSM-22 molecular sieve particles prepared above, and load them into a fixed bed reactor (with an inner diameter of 10mm, a tube wall thickness of 3mm, and a length of 30cm) in layers according to the order of contact with the raw gas, and carry out reduction and carbonization treatment for 3h before reaction and CO2 hydrogenation reaction evaluation in the order of NaFe@C / HZSM-22. Reduction conditions: under normal pressure, in pure H2 (35mL / min), at 360℃ for 8h. Carbonization conditions: Carbonization gas composition: molar ratio H2 / CO2=1.0, the rest is volume content CO: 10%, 330℃, 0.5MPa; reaction conditions: molar ratio H2 / CO2=3.0, 300℃, pressure of 4.0MPa, space velocity of 4000mL / (h·g cat ), the CO2 hydrogenation reaction performance of NaFe@C / HZSM-22 catalyst was investigated, and the results are listed in Tables 1 and 2.

[0033] Example 2

[0034] The implementation scheme is the same as Example 1, except that 0.5 g NaFe@C particles (particle size 0.35-0.71 mm) and 0.5 g HZSM-22 molecular sieve particles (particle size 0.35-0.71 mm) are uniformly mixed (NaFe@C + HZSM-22) and loaded into the reactor as in Example 1 for CO2 hydrogenation reaction. The reduction conditions are: under normal pressure, pure H2 (35 mL / min), 300°C reduction time 12 h. Carbonization conditions: carbonization gas composition: molar ratio H2 / CO2 = 0.15, the rest is volume content CO: 30%, 300°C, 0.1 MPa, carbonization treatment 6 h; reaction conditions: molar ratio H2 / CO2 = 5.0, temperature 350°C, pressure 1.0 MPa, space velocity 8000 mL / (h·g cat ), the CO2 hydrogenation performance results of NaFe@C+HZSM-22 catalyst are listed in Table 1 and Table 2.

[0035] Example 3

[0036] The catalyst preparation steps are the same as those in Example 1, except that "NaZSM-22" is used instead of "HZSM-22", and the obtained catalyst is NaFe@C / NaZSM-22.

[0037] The catalyst loading method, reduction treatment, carbonization treatment and evaluation conditions are the same as those in Example 1, except that the catalyst reduction conditions are changed to: normal pressure, pure H2 (35 mL / min), 400°C reduction time 2 h; the carbonization conditions are changed to: carbonization gas composition: molar ratio H2 / CO2=2, 400°C, 0.1 MPa, carbonization treatment 3 h; the reaction conditions are changed to: molar ratio H2 / CO2=6.0, 350°C, pressure 7.0 MPa, space velocity 1000 mL / (h·g cat The reaction results are listed in Table 1 and Table 2.

[0038] Example 4

[0039] The catalyst preparation steps are the same as those in Example 1, except that only "19.094 g of ferric acetate Fe(OH)(CH3COO)2 (molecular weight: 190.94)" is used instead of "35.317 g of ferric acetylacetonate (Fe(C5H7O2)3), and the obtained catalyst is NaFe@C / HZSM-22-A.

[0040] The catalyst loading method, reduction treatment, carbonization treatment and evaluation conditions are the same as those in Example 1, except that the carbonization conditions of the catalyst are changed to: carbonization gas composition: molar ratio H2 / CO2=3, the rest is volume content CO: 20%, Ar: 5%, 300°C, 0.05MPa, carbonization treatment 1h; the raw gas pressure, space velocity and temperature of the reaction evaluation are changed to "2.0MPa", "9000mL / (h·g cat )" and "310℃", the evaluation results are listed in Table 1 and Table 2.

[0041] Example 5

[0042] The catalyst preparation steps are the same as those in Example 1, except that only "0.3 g NaFe@C particles (particle size 0.35-0.71 mm) and 0.7 g HZSM-22 particles (particle size 0.35-0.71 mm)" are used instead of "0.5 g NaFe@C particles and 0.5 g HZSM-22 particles", and the obtained catalyst is 3-NaFe@C / 7-HZSM-22.

[0043] The catalyst loading method, reduction treatment, carbonization treatment and evaluation conditions are the same as those in Example 1, except that the carbonization conditions of the catalyst are changed to: carbonization gas composition: molar ratio H2 / CO2=0.5, 320°C, 1.0MPa, carbonization treatment for 5h; the raw gas pressure, space velocity and temperature of the reaction evaluation are changed to "2.5MPa", "4000mL / (h·g cat )" and "350°C", the evaluation results are listed in Tables 1 and 2.

[0044] Example 6

[0045] The catalyst preparation steps are the same as those in Example 1, except that only "0.7 g NaFe@C particles (particle size 0.35-0.71 mm) and 0.3 g HZSM-22 particles (particle size 0.35-0.71 mm)" are used instead of "0.5 g NaFe@C particles and 0.5 g HZSM-22 particles", and the obtained catalyst is 7-NaFe@C / 3-HZSM-22.

[0046] The catalyst loading method, reduction treatment, carbonization treatment and evaluation conditions are the same as those in Example 1, except that the carbonization conditions of the catalyst are changed to: carbonization gas composition: molar ratio H2 / CO2=0.5, 320°C, 1.0MPa, carbonization treatment for 5h; the raw gas pressure, space velocity and temperature of the reaction evaluation are changed to "2.5MPa", "4000mL / (h·g cat )" and "350°C", the evaluation results are listed in Tables 1 and 2.

[0047] Table 1. Performance of NaFe@C-based composite catalysts for the hydrogenation of carbon dioxide to heavy hydrocarbons

[0048]

[0049] Table 2. C5~C prepared by carbon dioxide hydrogenation over NaFe@C based composite catalyst 16 Heavy hydrocarbon composition distribution

[0050]

[0051]

[0052] *: Other heavy hydrocarbons include straight-chain alkanes, cycloalkanes and other heavy fraction hydrocarbons with carbon numbers of 5-16. Isoalkanes refer to alkanes with branched chains;

[0053] The results in Table 1 show that the NaFe@C-based composite catalysts composed of NaFe@C and ZSM-22 molecular sieves all show good carbon dioxide hydrogenation conversion to synthesize heavy hydrocarbons with a carbon number of 5-16. Under the experimental conditions of operation, the CO2 conversion rate of the reaction can be basically maintained at more than 40%, and the selectivity of hydrocarbon products is maintained at about 90%, of which the heavy hydrocarbons with a carbon number of 5-16 account for 70%. From the distribution of heavy hydrocarbons with a carbon number of 5-16 in Table 2, its main components are olefins and isoparaffins, accounting for more than 80% of the mass of heavy hydrocarbons. The above reaction results show that the excellent carbon dioxide hydrogenation performance exhibited by the NaFe@C / ZSM-22 composite catalyst prepared by the present invention is different from the traditional carbon dioxide hydrogenation synthesis of gasoline (mainly isoparaffins and aromatics) and aviation kerosene fraction hydrocarbons (mainly isoparaffins) of the traditional iron-based molecular sieve composite catalyst. The reason for this is that it is related to the unique structural characteristics of NaFe@C and ZSM-22 in the NaFe@C / ZSM-22 catalyst. The experimental characterization results prove that NaFe@C is a carbon-coated active iron structure. The carbon material exists in the form of nano-microspheres (diameter 50-100 nanometers). The active iron is evenly distributed in the microsphere carbon material, which is conducive to the efficient activation of carbon dioxide and the directional conversion to low-carbon olefins. The ZSM-22 molecular sieve is composed of a ten-membered ring with a mesoporous one-dimensional pore channel with a pore diameter of 0.47×0.55nm. This structure is conducive to the formation of heavy olefins. Therefore, the NaFe@C / ZSM-22 catalyst is used in the hydrogenation of carbon dioxide to show excellent synthesis of heavy hydrocarbons with a carbon number of 5-16, especially the synthesis of heavy olefins.

[0054] Example 7

[0055] 0.5 g NaFe@C catalyst (particle size 0.35-0.71 mm) and 0.5 g HZSM-22 molecular sieve particles (particle size 0.35-0.71 mm) prepared by the method of Example 1 were weighed separately and loaded into a fixed bed reactor (with an inner diameter of 10 mm, a tube wall thickness of 3 mm, and a length of 30 cm) in the order of NaFe@C / HZSM-22 according to the order of contact with the raw gas for CO2 hydrogenation reaction. Reduction conditions: under normal pressure, in pure H2 (25 mL / min), 400 ° C reduction time 6 h. Carbonization treatment conditions: carbonization gas composition: molar ratio H2 / CO2 = 1, the rest is volume content CO: 10%, 340 ° C, 0.1 MPa, carbonization treatment 3 h; reaction conditions: molar ratio H2 / CO2 = 3.5, temperature is 300 ° C, pressure is 3.0 MPa, space velocity is 4000 mL / (h·g cat ), the stability of the CO2 hydrogenation reaction of NaFe@C / HZSM-22 catalyst was investigated. The results (see Table 3 and Table 4) show that the catalyst always exhibits excellent CO2 hydrogenation performance within 100h reaction time, and the catalyst has no obvious deactivation phenomenon. The composition of heavy hydrocarbon products with carbon numbers of 5-16 (after 100h reaction) is shown in Table 4. 5-16 Hydrocarbons) are mainly composed of isoparaffins and olefins, with low aromatic content. In addition to a small amount of methane, the by-product hydrocarbons of the reaction also include low-carbon fraction hydrocarbons (C 2-4 ).

[0056] Table 3 Stability of CO2 hydrogenation reaction over NaFe@C / HZSM-22 catalyst

[0057]

[0058] Table 4 Analysis of hydrocarbon fraction composition of products after 100 h of reaction

[0059] Content (C-mol%) <![CDATA[Heavy hydrocarbon fraction hydrocarbon (C 5-16 )]]> <![CDATA[Low-carbon fraction hydrocarbons (C 2～4 )]]> Olefins 36.9 53.0 Isoalkanes 45.2 17.0 Aromatics 10.8 --- Other hydrocarbon components 7.1 30.0

[0060] In the method, the single-pass CO2 conversion rate can reach more than 40%, the methane selectivity in the hydrocarbon product is less than 11%, the selectivity of the heavy hydrocarbon fraction with a carbon number of 5 to 16 is as high as more than 70%, and the heavy hydrocarbon fraction is mainly isoparaffins and olefins. The present invention has opened up a new route for producing heavy hydrocarbons with a carbon number of 5-16 from carbon dioxide.

[0061] Comparative Example 1

[0062] The steps of catalyst preparation, treatment and reaction evaluation were the same as those in Example 1, except that in the catalyst evaluation step, only 1.0 g of NaFe@C catalyst (particle size 0.35-0.71 mm) prepared by the method of Example 1 was loaded into the reactor instead of "0.5 g of NaFe@C and 0.5 g of HZSM-22 catalyst". The reaction results are listed in Tables 5 and 6.

[0063] Comparative Example 2

[0064] The steps of catalyst preparation, treatment and reaction evaluation are the same as those in Example 1, except that the steps of preparing the iron-based catalyst are changed as follows: 24.34 g of FeCl3·6H2O is mixed with 75 mL of water to form an iron salt solution, and 2.5 mL of 12.1 mol / L HCl solution is added. At 60° C. and under stirring conditions, about 180 mL of 1.5 mol / L NaOH solution is added at a uniform rate. Within about 1.5 h, the pH value of the solution is adjusted from acidic to about 10. After the addition is complete, the temperature is maintained and stirred for 1 h, and finally cooled to room temperature. After the reaction is completed, the deposited product is separated by centrifugation, washed once with 400 mL of deionized water, dried at 60° C., and calcined at 350° C. for 3 h under a nitrogen atmosphere to obtain a Na-Fe2O3 catalyst sample (particle size is 0.35-0.71 mm).

[0065] The molecular sieve was changed to HZSM-5 molecular sieve (produced by Nankai University, SiO2 / Al2O3=48) (particle size 0.35-0.71 mm).

[0066] The reaction results of the obtained Na-Fe2O3 / HZSM-5 catalyst are listed in Tables 5 and 6.

[0067] Table 5. Carbon dioxide hydrogenation performance of comparative catalysts

[0068]

[0069] Table 6. Fractional composition analysis of heavy hydrocarbons in the carbon dioxide hydrogenation product of the comparative catalyst

[0070]

[0071] *: Other heavy hydrocarbons include heavy distillate hydrocarbons with carbon numbers of 5-16, such as paraffins and cycloalkanes.

[0072] From the results in Tables 5 and 6, it can be seen that although NaFe@C exhibits a high carbon dioxide conversion rate and selectivity for hydrocarbon products, its C 5-16The selectivity of heavy hydrocarbons is not high, only 47.5%, and the selectivity of heavy hydrocarbons is mainly olefins, the selectivity of isoparaffins is low, and it contains a large amount of straight-chain alkanes. Only when it is combined with HZSM-22 to form a composite catalyst can it show a higher C 5-16 Heavy hydrocarbon selectivity.

[0073] Na-Fe2O3 / HZSM-5 catalyst is a traditional iron-based composite molecular sieve catalyst. Although it shows good performance in the hydrogenation of carbon dioxide to C 5-16 The heavy hydrocarbons have good performance, but the heavy hydrocarbons contain more isoparaffins and aromatics, while the olefins are relatively small, only 5.3%.

[0074] Compared with the above two catalysts, the catalyst of the present invention is applied to the process of carbon dioxide hydrogenation to generate highly selective C 5-16 Heavy hydrocarbons can be produced, and heavy hydrocarbons mainly composed of isoparaffins and olefins can be produced.

[0075] In general, the present invention not only provides a method for synthesizing C 5-16 A new route for heavy hydrocarbons, and the invention of carbon dioxide hydrogenation to C 5-16 A new catalytic system with high efficiency and stability for heavy hydrocarbons.

Claims

1. A method for directly preparing heavy hydrocarbons with a carbon number of 5 to 16 by hydrogenating carbon dioxide, characterized in that: A mixed gas consisting of carbon dioxide and hydrogen is used as raw gas, and is directly converted into heavy hydrocarbons with a carbon number of 5-16 under the catalytic action of a multifunctional composite catalyst; The composite catalyst comprises a supported iron-based catalyst containing carbon and alkali metal as the first component, and a catalyst having a light olefin polymerization function and a heavy hydrocarbon (C 16+ ) The molecular sieve with hydrocracking function is mixed or layered as the second component; the mass ratio of the first component to the second component is 1:6 to 6:1, preferably 1:3 to 3:1, and more preferably 1:2 to 2:

1.

2. The method according to claim 1, characterized in that: The reaction temperature is 280-350°C (preferably 290-340°C, more preferably 300-330°C), the reaction pressure is 0.02-9.0 MPa (preferably 1.5-7.0 MPa, more preferably 2.5-5.0 MPa), and the raw gas space velocity is 500-30000 mL / (h·g cat ) (preferably 1000 to 20000 mL / (h·g cat ), more preferably 2000 to 15000h -1 ), the H2 / CO2 molar ratio in the raw gas is 0.9 to 6.0 (preferably 1.5 to 5.0, more preferably 2.5 to 4.0).

3. The method according to claim 1, characterized in that: The main active component of the supported iron-based catalyst containing carbon and alkali metal is Fe x C (2≤x≤3), the mass of the active component iron element in the catalyst accounts for 25-65% (preferably 30-60%, more preferably 40-60%) in the loaded iron catalyst, the mass ratio of the auxiliary alkali metal element to the active component element Fe is 0.01-5:1 (preferably 0.05-1:1, more preferably 0.05-0.8:1), the alkali metal auxiliary element is one or more of Na, K, Li, and the rest is carbon material.

4. The method according to claim 1, characterized in that: The low-carbon olefin polymerization function and the heavy hydrocarbon (C 16+ ) The molecular sieve with hydrocracking function refers to a molecular sieve with both light olefin polymerization function and heavy olefin hydrocracking function, preferably ZSM-22, wherein the ZSM-22 molecular sieve with a silicon-aluminum molar ratio of 20 to 150 is more preferred, the molecular sieve does not use or can use metal modification, the metal used includes one or more of Co, Ga, and La, and the metal element accounts for less than 5% of the mass of the modified molecular sieve, preferably 0.5% to 3%, and more preferably 0.5% to 2%.

5. According to any one of claims 1 to 4, the method uses an iron-based CO2 hydrogenation catalyst component having the following characteristics: The catalyst was prepared by impregnation method: (1) A soluble Fe salt and an alkali metal auxiliary salt are prepared to form a salt solution of 100 mL, wherein the Fe concentration in the salt solution is 0.1 to 1.0 mol / L, and the mass ratio of the alkali metal auxiliary element to the active Fe element is 0.01 to 5:1 (preferably 0.05 to 1:1, more preferably 0.05 to 0.8:1). A certain volume of the above solution is impregnated onto 2.0 g of a carbon material at 20 to 50° C., allowed to stand for 2 to 30 hours, dried at 60 to 120° C. for 4 to 8 hours, and the obtained sample is calcined at 350 to 500° C. under N2 for 2 to 8 hours; the obtained sample is labeled as MFe@C, wherein M is an alkali metal auxiliary and C is a carbon material; In the above preparation steps, the soluble Fe salt refers to an organic iron salt compound soluble in water, preferably one or more of iron acetate, iron oxalate, and iron acetylacetonate; the auxiliary salt is a salt compound soluble in water, preferably one or more of nitrate and acetate; the carbon material refers to carbon fiber, carbon nanotube, graphite carbon, preferably carbon nanotube, more preferably multi-walled carbon nanotube; (2) After the calcined MFe@C is combined with the molecular sieve to form a composite catalyst, it is required to be reduced at 300-400°C containing H2 gas for 2-12 hours before the reaction, and treated at 300-420°C containing H2 / CO2 mixed gas (H2 / CO2 = 0.05-5 (preferably 0.15-2, molar ratio), the H2+CO2 mixed gas accounts for more than 70% of the total gas content, and the mixed gas may or may not contain one or more of CO and inert gases) for 0.5-6 hours. After the treatment, an iron-based multifunctional composite catalyst composed of MFe@C and molecular sieve can be obtained.

6. The method according to claim 4, characterized in that: When metal modification is performed on molecular sieves with heavy olefin hydrocracking function, the metal component can be loaded onto the molecular sieve by one or both of the following two methods: (1) Prepared by equal volume impregnation method, the specific process is: according to the required metal content, the amount of metal salt required theoretically is calculated, and an aqueous solution of metal salt is prepared, wherein the metal salt is selected from any one or more of nitrate, chloride, bromide, acetate, acetylacetonate, citrate, oxalate, and benzoate; an equal volume of the molecular sieve to be modified is impregnated in the solution, and after stirring, standing, drying, and calcining, the calcination temperature is 300-600°C, and the calcination time is 2-8h, the metal-modified molecular sieve is obtained; Or, (2) prepared by ion exchange method, the specific process is: according to the required metal content, the amount of metal salt required theoretically is calculated, and an aqueous solution of the metal salt is prepared, wherein the metal salt is selected from any one or more of nitrate, chloride, bromide, acetate, acetylacetonate, citrate, oxalate, and benzoate; the molecular sieve to be modified is mixed at a solid-liquid mass ratio of 1:(10-200), ion exchange is performed for 2-24 hours, and then washed, dried, and calcined at a temperature of 300-600°C for a calcination time of 2-8 hours to obtain a metal-modified molecular sieve.

7. The method according to claim 1, characterized in that: The two components of the multifunctional composite catalyst can be composited in one, two or three of the following three ways, among which the layered filling method is preferred: (1) Powder mixing method: Weigh the iron-based catalyst and molecular sieve catalyst powders respectively, grind and mix them in a mortar according to the required mass ratio, press them into tablets, crush and sieve (the sieve size is 0.1-2.0 mm, preferably 0.3-0.8 mm), and obtain a composite catalyst with a particle size of 0.1-2.0 mm (0.3-0.8 mm); (2) Particle mixing method: Weigh the iron-based catalyst and molecular sieve catalyst powders respectively, press them into tablets, crush and sieve them (the sieve size is 0.1-2.0 mm, preferably 0.3-0.8 mm), mix the particles evenly according to the required mass ratio, and form a composite catalyst with a particle size of 0.1-2.0 mm (0.3-0.8 mm); (3) Layered filling method: The catalyst bed is filled with the required mass of loaded iron-based catalyst and composite molecular sieve catalyst with a particle size of 0.1-2.0 mm (0.3-0.8 mm) in the order in which the catalyst contacts the raw gas. The catalyst bed components may or may not contain an inert material isolation layer. The mass ratio of the inert material isolation layer to the active component of the composite catalyst is 0.01-10 (preferably 0.1-5). The inert material isolation layer is made of an inert material that does not react with the catalyst and the raw gas components, preferably an inert SiO2 ball or quartz sand, and the ratio of its particle size to the particle size of the catalyst is 1:0.8-1:3 (preferably 1:1-1:1.5).

8. The method according to claim 1 or 2, characterized in that: The carbon dioxide is a gas containing carbon dioxide, and the gas refers to any one or more of industrial waste gas containing carbon dioxide, automobile exhaust, coal combustion waste gas, and carbon dioxide absorbed in the atmosphere and seawater.

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