Method for preparing heavy hydrocarbon by hydrogenating carbon dioxide

Abstract

The invention relates to a method for preparing heavy hydrocarbon by hydrogenation of carbon dioxide. The method comprises the following steps: in the presence of hydrogen, carbon dioxide and a catalyst, completing a reaction for preparing the heavy hydrocarbon by hydrogenation of carbon dioxide, wherein the catalyst comprises a carrier, an active metal and an auxiliary agent, and the carrier is silicon nitride; the active metal is iron; the auxiliary agent is potassium. The method for preparing heavy hydrocarbon through hydrogenation of carbon dioxide provided by the invention has the advantages of high carbon dioxide conversion rate, good carbon monoxide selectivity and good product selectivity, and has better technical effects compared with other methods in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of catalytic reaction, and in particular to a method for preparing heavy hydrocarbons by hydrogenating carbon dioxide. Background Art

[0002] The continuous consumption of fossil fuels around the world has led to the continuous intensification of the greenhouse effect, which has had a negative and even irreversible impact on the climate. Therefore, there is an urgent need to reduce the concentration of CO2 in the atmosphere. Efficient processing and utilization of carbon resources will play a huge role in reducing CO2 emissions, alleviating the greenhouse effect, and reducing carbon emissions. The conversion of CO2 into high-value-added fuels and chemicals through processes such as thermal catalysis, electrocatalysis or photocatalysis reduces greenhouse gas emissions and fossil resource consumption. The efficient conversion and utilization of greenhouse gas carbon dioxide to produce hydrocarbon products is of great significance for alleviating the pressure of the oil resource crisis.

[0003] The hydrogenation of carbon dioxide is easy to produce C1 products such as CO and CH4, but it is difficult to produce C2+ products through CC coupling. The development of efficient catalysts is still a huge challenge. At present, iron-based catalysts are considered to be suitable catalysts for the hydrogenation of CO2 to produce hydrocarbon products because they have two phases, Fe3O4 and Fe5C2. It is generally believed that the hydrogenation of CO2 to C2+ hydrocarbon products on iron-based catalysts mainly goes through two steps, namely the reverse water gas shift reaction (CO2+H2→CO+H2O) and the hydrogenation of CO to hydrocarbons (CO+H2→-(CH2)-+H2O). However, the single Fe catalyst has weak adsorption of CO2, and the CO2 / H2 ratio on the catalyst surface is low, resulting in continuous hydrogenation of the catalyst to produce CH4 instead of C2+ products. Doping with a variety of promoters has been explored to improve the selectivity of C2+ olefins on iron-based catalysts. Alkali metals (such as Na, K) or non-metallic elements (such as N, S) are added to modify the reducibility and carbonization of Fe catalysts. In addition, the carrier is also a key factor affecting the performance of the catalyst. It can effectively anchor the metal, improve the metal dispersion, and significantly improve the performance of the catalyst. It is particularly important to choose a suitable carrier.

[0004] The Chinese invention patent application disclosure CN111185180A provides a method for preparing a single-walled carbon nanotube-loaded iron potassium catalyst and its application in the hydrogenation of carbon dioxide to produce higher carbon olefins. Under certain conditions, the catalyst has a CO2 conversion rate of more than 62% and a hydrocarbon selectivity of more than 62%. However, there is a strong interaction between the carrier and the metal, which makes it difficult for the metal to be reduced and carbonized.

[0005] The literature (Ru catalysts supported by Si3N4 for Fischer-Tropsch synthesis, Applied Surface Science, 2020, 526, 146631) uses silicon nitride for Ru-based catalyst Fischer-Tropsch reaction. Compared with SiO2 carrier, silicon nitride has less interaction with the metal active phase and higher metal dispersion, showing excellent catalytic performance. However, silicon nitride has a low specific surface area and limited metal dispersion.

[0006] Patent ZL201810088867.5 provides a carbon dioxide hydrogenation oil production catalyst, which has high selectivity for C2-C4 olefins and C5+ hydrocarbons at low temperatures, but low carbon dioxide conversion rate, and the auxiliary agent is Pd, which has a high cost. Summary of the invention

[0007] In order to overcome the problems existing in the prior art, the inventors of the present invention have conducted extensive and in-depth research and provided a method for producing heavy hydrocarbons by hydrogenating carbon dioxide. By using high-surface-area silicon nitride as a carrier and K as an auxiliary Fe-based carbon dioxide hydrogenation catalyst for producing heavy hydrocarbons, the carbon dioxide conversion rate is high and the selectivity for heavy hydrocarbons is good.

[0008] In order to achieve the above object, the present invention provides a method for preparing heavy hydrocarbons by hydrogenating carbon dioxide, which comprises the steps of: carrying out a reaction of hydrogenating carbon dioxide to prepare heavy hydrocarbons in the presence of hydrogen, carbon dioxide and a catalyst; wherein the catalyst comprises a carrier, an active metal and an additive. The carrier is silicon nitride; the active metal is iron; and the additive is potassium.

[0009] In the present invention, heavy hydrocarbons refer to C5+ hydrocarbon substances.

[0010] According to the present invention, the silicon nitride carrier, wherein, relative to all the pores in the silicon nitride carrier, macropores with a pore size greater than 50 nm account for 1% to 5%, mesopores with a pore size of 2 to 50 nm account for 95% to 99%, and the porosity of the silicon nitride carrier is 50% to 95%.

[0011] In some embodiments of the present invention, the specific surface area of ​​the carrier is not less than 300 m 2 / g, more preferably 400 to 700 m 2 / g, for example 400m 2 / g、500m 2 / g, 550m 2 / g, 580m 2 / g、600m 2 / g, 650m 2 / g、700m 2 / g.

[0012] In some embodiments of the present invention, the method for preparing a silicon nitride carrier comprises the steps of:

[0013] (1) dispersing a silicon precursor in an organic solvent under normal pressure, an inert atmosphere and a low temperature of 0 to 10° C., introducing a reaction gas into the organic solvent while stirring the organic solvent to react with the silicon precursor to obtain a silicon nitride precursor solution, wherein the reaction gas is ammonia gas or a mixture of ammonia gas and an inert gas;

[0014] (2) centrifuging the silicon nitride precursor solution to obtain a silicon nitride precursor;

[0015] (3) The silicon nitride precursor is subjected to high-temperature pyrolysis at 400-1800° C. in a flowing oxygen-free atmosphere to obtain the silicon nitride carrier.

[0016] In some embodiments of the present invention, in the above step (1), the low temperature condition is 2-10°C.

[0017] In some embodiments of the present invention, in the above step (1), the silicon precursor may be one or more of silicon chloride (also known as "silicon tetrachloride"), silicon fluoride (also known as "silicon tetrafluoride"), silicon bromide (also known as "silicon tetrabromide"), silicon iodide (also known as "silicon tetraiodide"), and silicon imine. In some preferred embodiments, in the above step (a), the silicon imine is prepared by ammonolysis of silicon halide.

[0018] In some embodiments of the present invention, in the above step (1), the organic solvent may be one or more of normal alkanes, cycloalkanes and aromatic hydrocarbons. Among them, normal alkanes are, for example, normal pentane, normal hexane, normal heptane or normal octane, cycloalkanes are, for example, cyclopentane or cyclohexane, and aromatic hydrocarbons are, for example, toluene or xylene, but are not limited thereto.

[0019] In some embodiments of the present invention, in the above step (1), the inert gas may be one or more of nitrogen, helium, neon, and argon, but is not limited thereto.

[0020] In some embodiments of the present invention, in the above step (1), the mass ratio of the silicon precursor to the organic solvent is 1:(1-30), preferably 1:(2.5-25).

[0021] In some embodiments of the present invention, in the above step (1), the reaction gas is a mixture of ammonia and an inert gas, wherein the volume ratio of ammonia to inert gas is (0.1-10):1, preferably (0.5-8):1.

[0022] In some embodiments of the present invention, in the above step (1), the reaction is carried out at a temperature of 0-10°C, preferably 2-8°C (e.g., 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, 8°C).

[0023] In some embodiments of the present invention, in the above step (3), the oxygen-free atmosphere can be one or more of ammonia, an inert gas (e.g., nitrogen, helium, neon, argon), and hydrogen. In this article, the volume ratio of ammonia to the inert gas can be any ratio, such as 10:90, 20:80, 50:50, 80:20. In some other more preferred embodiments, the volume ratio of hydrogen to the inert gas can be (1-100):100, preferably (5-50):100, more preferably (5-15):100, and the volume ratio of ammonia to the inert gas can be (0.1-10):1, preferably (0.4-4):1, and more preferably (0.6-1.5):1.

[0024] In some embodiments of the present invention, in the above step (3), the temperature of the high temperature pyrolysis is 600-1400°C, preferably 800-1100°C, for example 800°C, 900°C, 1000°C, 1100°C.

[0025] In some embodiments of the present invention, in the above step (3), the specific surface area of ​​the silicon nitride carrier is not less than 300m 2 / g, more preferably 400-700m 2 / g, for example 400m 2 / g、500m 2 / g, 550m 2 / g, 580m 2 / g、600m 2 / g, 650m 2 / g,700m 2 / g.

[0026] In some embodiments of the present invention, in the above step (3), the high temperature pyrolysis is roasting.

[0027] In some embodiments of the present invention, in the catalyst, the mass ratio of the active metal to the carrier is (5-50):100, preferably (5-30):100.

[0028] In some embodiments of the present invention, the mass ratio of the auxiliary agent to the carrier is (0.1-5):100, preferably (0.5-3):100.

[0029] In some embodiments of the present invention, the specific surface area of ​​the catalyst is 400 to 700 m 2 / g.

[0030] In some embodiments of the present invention, the dispersion of the active metal in the catalyst is 30-90%; the metal particle size of the catalyst is 1.5-4.0 nm. In the present invention, the dispersion of the active metal in the catalyst can be 40%-50%.

[0031] The catalyst of the present invention utilizes the excellent thermal conductivity, high specific surface area and anchoring effect of amino groups of silicon nitride to greatly improve the metal dispersion and reduce the metal particle size, so that the catalyst anchored on the silicon nitride carrier of the present invention has high dispersion, high metal utilization, high catalytic reaction activity and selectivity for the target product.

[0032] The catalyst of the present invention exhibits the characteristics of easy reduction and carbonization, which can improve the reaction activity and target product selectivity. At the same time, the catalyst exhibits good wear resistance and high hydrothermal stability, which is beneficial to enhancing the stability of the catalytic reaction.

[0033] In the present invention, the active metal and the auxiliary agent can be anchored on the surface of the carrier by impregnation, coprecipitation, chemical vapor deposition, precipitation deposition and the like.

[0034] In some embodiments of the present invention, the method for preparing the catalyst comprises the steps of:

[0035] S1, providing a catalyst precursor I containing an active metal source and the carrier; providing a catalyst precursor II containing a potassium source;

[0036] S2, performing a first calcination treatment on the catalyst precursor I to obtain a catalyst intermediate I;

[0037] S3, mixing the catalyst precursor II and the catalyst intermediate I, and obtaining the catalyst intermediate II after drying;

[0038] S4, performing a second calcination treatment on the catalyst intermediate II to obtain the catalyst.

[0039] In some embodiments of the present invention, in step S1, the active metal source is selected from one or more of ferric nitrate (preferably ferric nitrate nonahydrate), ferric chloride (preferably ferric chloride hexahydrate), ferrous chloride, ferrous acetate, ammonium oxalate iron salt trihydrate and ammonium ferric citrate.

[0040] In some embodiments of the present invention, the potassium source is selected from soluble potassium salts; preferably, the soluble potassium salts are selected from one or more of potassium sulfate, potassium nitrate, potassium carbonate and potassium chloride.

[0041] In the present invention, after the active metal source is anchored on the surface of the silicon nitride carrier to obtain the catalyst precursor I, it is dried at 40 to 180°C to obtain the catalyst precursor I. Preferably, the drying can be carried out in air, inert gas atmosphere or vacuum, and the drying time is 4 to 24 hours. Similarly, after the catalyst precursor II containing the auxiliary agent source is obtained, it is dried at 40 to 180°C.

[0042] In some embodiments of the present invention, in step S2, the conditions of the first calcination treatment include: a temperature of 300°C to 900°C; a time of 1 to 12 hours; preferably, the first calcination treatment is carried out under an inert gas atmosphere; preferably, the inert gas is selected from one or more of nitrogen, argon, neon, and helium.

[0043] In some embodiments of the present invention, in step S3, the drying process comprises: a temperature of 40°C to 180°C; and a time of 4 to 24 hours. Preferably, the drying process can be performed in air, an inert gas atmosphere or a vacuum.

[0044] In some embodiments of the present invention, in step S4, the conditions of the second calcination treatment include: a temperature of 300° C. to 900° C., preferably 300° C. to 600° C.; and a time of 1 to 12 hours.

[0045] In some embodiments of the present invention, the molar ratio of hydrogen to carbon dioxide is 1 to 4:1.

[0046] In some embodiments of the present invention, the conditions of the hydrogenation reaction include: a reaction temperature of 200°C to 500°C, preferably 260°C to 400°C; a space velocity of 1000-20000 NL kg -1 1 -1 , preferably 2000-10000NLkg -1 1 -1 ; The pressure is 0.1~5MPa, preferably 1~4MPa.

[0047] In some embodiments of the present invention, the catalyst is subjected to activation treatment before the hydrogenation reaction.

[0048] In some embodiments of the present invention, the activation treatment conditions include: the activation atmosphere is hydrogen, carbon monoxide or synthesis gas; wherein the molar ratio of hydrogen to carbon monoxide in the synthesis gas is (1-500):1, preferably (1-200):1;

[0049] The activation pressure is 0.1 to 4 MPa, preferably 0.1 to 3 MPa;

[0050] The activation temperature is 200°C to 800°C, preferably 250°C to 600°C;

[0051] The activation time is 2 to 48 hours, preferably 6 to 48 hours.

[0052] In the present invention, before the hydrogenation reaction, the catalyst is activated and reduced to generate metal active sites.

[0053] According to the present invention, the reaction progress of hydrogenating carbon dioxide to produce carbon monoxide can be analyzed online by gas chromatography to monitor the reaction.

[0054] In some embodiments of the present invention, the method for preparing heavy hydrocarbons by hydrogenating carbon dioxide includes the steps of: granulating the catalyst obtained by the above preparation method to obtain catalyst particles of 20 to 40 mesh, and then placing 0.1 to 1 g of the catalyst in the constant temperature zone of a fixed bed reactor, and filling quartz sand on both sides; using hydrogen or synthesis gas to activate the catalyst at 250°C to 600°C and 0.1 to 3 MPa for 2 to 48 hours, and after the activation, the temperature is reduced to 100°C, and the gas is switched to a H2 / CO2 mixed gas with a H2 / CO2 (molar ratio) of 3, a reaction pressure of 0.1 to 5 MPa, and a reaction temperature of 200 to 500°C to react, and using gas chromatography to analyze the product composition online.

[0055] Compared with the prior art, the method for preparing heavy hydrocarbons by hydrogenating carbon dioxide provided by the present invention has a high carbon dioxide conversion rate, good carbon monoxide selectivity and product selectivity, and has better technical effects than other methods of the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 The XRD pattern of the catalyst Exam-2 prepared in Example 2 of the present invention is shown;

[0057] Figure 2 The TEM image of the catalyst Exam-2 prepared in Example 2 of the present invention is shown;

[0058] Figure 3 The curve showing the reaction activity variation over time of the catalyst Exam-1 prepared in Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0059] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0060] In the present invention, unless otherwise specified, the terms "active component", "active phase metal" and "metal active phase" are used interchangeably and all refer to the metal component used as the active phase of the hydrogenation catalyst.

[0061] In the present invention, unless otherwise specified, the term "crystal size" refers to the size of the crystal phase particles of the catalyst, which can be measured by scanning electron microscopy or transmission electron microscopy, but is not limited thereto.

[0062] In the present invention, unless otherwise specified, the term "normal pressure" refers to one standard atmospheric pressure.

[0063] In the following examples, in the composition of the obtained catalyst, such as 10Fe0.5K / SiN, the number 10 represents that the iron content is 10 wt% of the mass of the silicon nitride carrier, and the number 0.5 represents that the potassium content is 0.5 wt% of the mass of the silicon nitride carrier.

[0064] The present invention is described in detail below by way of examples, but the protection scope of the present invention is not limited to the following description.

[0065] In the present invention, the specific surface area is measured by the BET method (Brubauer-Emmet-Teller), and the measurement method is described in, for example, standard NFX11-62.

[0066] In the present invention, the dispersion degree can be measured by CO chemical adsorption, H2 chemical adsorption, hydrogen oxygen titration, TEM, etc., but is not limited thereto. In the following examples, the dispersion degree is measured by TEM.

[0067] In the present invention, the calculation method of CO selectivity is:

[0068]

[0069] In the formula, n(CO out ) represents the amount of CO in the exhaust gas; Indicates the amount of CO2 in the raw gas; Indicates the amount of CO2 in the exhaust gas.

[0070] In the present invention, the calculation method of CO2 conversion rate is:

[0071]

[0072] In the formula, Indicates the amount of CO2 in the raw gas; Indicates the amount of CO2 in the exhaust gas.

[0073] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or the conditions recommended by the manufacturer. The raw materials, reagents or instruments used without specifying the manufacturer are all conventional products that can be obtained through commercial channels or prepared according to the preparation methods disclosed in the prior art.

[0074] In the following examples, the specific surface area is 500m 2 The preparation method of silicon nitride of 1000 g / kg is as follows:

[0075] (1) The air in a 2000 mL three-necked flask was replaced with argon, and then 900 g of n-heptane and 280 g of silicon tetrachloride were weighed and placed in the three-necked flask at normal pressure and 4° C. to obtain a mixed solution.

[0076] (2) While mechanically stirring, ammonia gas (50 mL / min) and Ar gas (10 mL / min) were introduced into the mixed solution of step (1) at a mechanical stirring rate of 400 r / min, and reacted with silicon tetrachloride at a temperature of 4° C. for 36 hours to obtain a silicon nitride precursor solution.

[0077] (3) After the reaction is completed, the silicon nitride precursor solution generated in the reaction in step (2) is centrifuged at a centrifugal speed of 8000 r / min to obtain a silicon nitride precursor.

[0078] (4) The silicon nitride precursor was placed in a high-temperature tube furnace, 5% H2 / 95% N2 (volume ratio, flow rate of 300 mL / min) was introduced, and calcined at 1200°C for 2 h to obtain a specific surface area of ​​500 m 2 / g of silicon nitride carrier; wherein, macropores with a pore size greater than 50nm account for 4.0%, and mesopores with a pore size of 2-50nm account for 96.0%; the porosity of the silicon nitride carrier is 91.0%.

[0079] In the following examples, the specific surface area is 700m 2 The preparation method of silicon nitride of 1000 g / kg is as follows:

[0080] (1) The air in a 2000 mL three-necked flask was replaced with argon, and then 900 g of n-pentane and 100 g of silicon tetrachloride were weighed and placed in the three-necked flask at normal pressure and 5° C. to obtain a mixed solution.

[0081] (2) While mechanically stirring, ammonia gas (50 mL / min) and Ar gas (10 mL / min) were introduced into the mixed solution of step (1) at a mechanical stirring rate of 500 r / min, and reacted with silicon tetrachloride at a temperature of 5° C. for 24 h to obtain a silicon nitride precursor solution.

[0082] (3) After the reaction is completed, the silicon nitride precursor solution generated in the reaction in step (2) is centrifuged at a centrifugal speed of 10000 r / min to obtain a silicon nitride precursor.

[0083] (4) The silicon nitride precursor was placed in a high-temperature tube furnace, ammonia gas (flow rate of 300 mL / min) was introduced, and calcined at 800°C for 2 h to obtain a silicon nitride precursor with a specific surface area of ​​700 m 2 / g of silicon nitride carrier; among which, macropores with a pore size greater than 50nm account for 1.3%, and mesopores with a pore size of 2-50nm account for 98.7%; the porosity of the silicon nitride carrier is 94.6%.

[0084] In the following examples, fumed silica was purchased from Aladdin, CAS: 112945-52-5.

[0085] Example 1

[0086] In this embodiment, the preparation method of the catalyst used comprises the steps of:

[0087] (1) Weigh 4.02 g of ferric nitrate nonahydrate into a container, add 60 mL of anhydrous ethanol, and dissolve it completely to prepare an iron salt solution;

[0088] (2) Then weigh 5g of silicon nitride (500m 2 / g) carrier in a beaker, drop the iron salt solution onto the carrier, stir evenly, and let stand for 24h;

[0089] (3) The beaker in step (2) was placed in an oven at 120° C. and dried for 12 h to obtain catalyst precursor I;

[0090] (4) placing the catalyst precursor I in a tube furnace, introducing argon gas, raising the temperature to 400°C, staying for 5 hours for calcination, and then naturally cooling to room temperature to obtain the catalyst intermediate I;

[0091] (5) Weigh 0.065 g of potassium nitrate into a beaker, add 45 ml of anhydrous ethanol, and dissolve it completely to prepare a potassium salt solution;

[0092] (6) Place the catalyst intermediate I in a beaker, add the potassium salt solution dropwise therein, stir evenly, and let stand for 24 hours;

[0093] (7) The beaker in step (6) was placed in an oven at 120° C. and dried for 12 h to obtain catalyst intermediate II;

[0094] (8) Catalyst intermediate II is placed in a tubular furnace, argon is introduced, the temperature is raised to 400 °C, and the temperature is kept for 5 h for calcination. After naturally cooling to room temperature, the sample is taken out to obtain an iron-potassium metal catalyst with a composition of 10Fe0.5K / SiN, which is recorded as Exam-1.

[0095] The relevant parameters of catalyst Exam-1 are shown in Table 1 below.

[0096] The method for preparing heavy hydrocarbons by hydrogenating carbon dioxide in this embodiment comprises the following steps:

[0097] The catalyst Exam-1 obtained by the above preparation method was granulated to obtain catalyst particles of 20 to 40 mesh, and then 1g of the catalyst was placed in the constant temperature zone of a fixed bed reactor, and quartz sand was filled on both sides; the catalyst was activated for 24 hours using H2 / CO with a molar ratio of 10 at 280°C and 0.1MPa, and the temperature was reduced to 100°C after the activation, and the gas was switched to a H2 / CO2 mixed gas with a molar ratio of 3, the reaction pressure was 3MPa, the reaction temperature was 340°C, and the temperature was 2000NL·kg -1 ·h -1 The CO2 hydrogenation reaction was carried out under the conditions of

[0098] The product composition was analyzed online by gas chromatography. The activity and selectivity results of the hydrogenation reaction are shown in Table 2. The hydrogenation reaction of this example was continued, and the reaction activity curve over time was as shown in Table 2. Figure 3 As shown, it can be seen that the reaction activity of catalyst Exam-1 has not changed significantly, indicating that the catalyst exhibits good anti-wear ability and high hydrothermal stability.

[0099] Example 2

[0100] In this embodiment, the preparation method of the catalyst used comprises the steps of:

[0101] (1) Weigh 15.50 g of ferric nitrate nonahydrate and dissolve it in 60 mL of ethanol to form a metal precursor solution;

[0102] (2) Weigh 5 g of silicon nitride (500 m 2 / g) carrier, drop the metal precursor solution onto the carrier, stir evenly, and let stand for 24h;

[0103] (3) The sample obtained in step (2) was placed in an oven at 80° C. and dried for 1 h;

[0104] (4) placing the sample obtained in step (3) in a tube furnace and introducing 10% ammonia / nitrogen (volume ratio) at a flow rate of 100 mL / min for 8 h;

[0105] (5) taking out the sample in step (4), washing it with ethanol, and drying it in an oven at 100° C. for 24 h to obtain catalyst precursor I;

[0106] (6) placing the catalyst precursor I in a tube furnace, heating it to 500° C. under a nitrogen atmosphere, and calcining it at this temperature for 5 h to obtain a catalyst intermediate I;

[0107] (7) Weigh 0.130 g of potassium nitrate into a beaker, add 45 ml of anhydrous ethanol and dissolve it completely to prepare a potassium salt solution;

[0108] (8) Then, catalyst intermediate I is placed in a beaker, potassium salt solution is added dropwise thereto, stirred evenly, and allowed to stand for 24 hours;

[0109] (9) The beaker of step (8) was placed in an oven at 100° C. and dried for 12 h to obtain catalyst intermediate II;

[0110] (10) Catalyst intermediate II was placed in a tubular furnace, nitrogen was introduced, the temperature was raised to 450 °C, and the temperature was kept for 6 h for calcination. After cooling naturally to room temperature, the sample was taken out to obtain an iron potassium metal catalyst with a composition of 30Fe1K / SiN, which was recorded as Exam-2.

[0111] The relevant parameters of catalyst Exam-2 are shown in Table 1. The XRD and TEM images of catalyst Exam-2 are shown in Table 1. Figure 1 and Figure 2 As shown. Figure 1 and Figure 2 It can be seen that the prepared metal particles have a smaller size.

[0112] The process of hydrogenating carbon dioxide to produce heavy hydrocarbons in this embodiment comprises the following steps:

[0113] The catalyst Exam-2 obtained by the above preparation method was granulated to obtain catalyst particles of 20 to 40 mesh, and then 1g of the catalyst was placed in the constant temperature zone of a fixed bed reactor, and quartz sand was filled on both sides; the catalyst was activated at 300°C and 0.1MPa using H2 / CO with a molar ratio of 20 for 24h, and after the activation, the temperature was reduced to 100°C, and the gas was switched to a H2 / CO2 mixed gas with a molar ratio of 3, the reaction pressure was 2MPa, the reaction temperature was 320°C, and the temperature was 5000NL·kg -1 ·h -1 The CO2 hydrogenation reaction was carried out under the conditions of

[0114] The product composition was analyzed online by gas chromatography. The activity and selectivity results of the hydrogenation reaction are shown in Table 2 below.

[0115] Example 3

[0116] This example is basically the same as Example 2, except that 0.195 g potassium nitrate is used instead of 0.130 g potassium nitrate to obtain catalyst Exam-3, which has a composition of 30Fe1.5K / SiN. The relevant parameters of catalyst Exam-3 are shown in Table 1 below.

[0117] Using catalyst Exam-3, carbon dioxide was hydrogenated to produce heavy hydrocarbons under the same conditions as in Example 2. The product composition was analyzed online by gas chromatography. The activity and selectivity results of the hydrogenation reaction are shown in Table 2 below.

[0118] Example 4

[0119] This example is substantially the same as Example 2, except that 0.650 g of potassium nitrate is used instead of 0.130 g of potassium nitrate to obtain catalyst Exam-4, which has a composition of 30Fe5K / SiN. The relevant parameters of catalyst Exam-4 are shown in Table 1 below.

[0120] Using catalyst Exam-4, carbon dioxide was hydrogenated to produce heavy hydrocarbons under the same conditions as in Example 2. The product composition was analyzed online by gas chromatography. The activity and selectivity results of the hydrogenation reaction are shown in Table 2 below.

[0121] Example 5

[0122] This embodiment is basically the same as embodiment 2, except that 5g of silicon nitride (700m 2 / g) replaces 5g of silicon nitride (500m 2 / g), and catalyst Exam-5 was obtained, and the composition was 30Fe1K / SiN. The relevant parameters of catalyst Exam-5 are shown in Table 1 below.

[0123] Using catalyst Exam-5, carbon dioxide was hydrogenated to produce heavy hydrocarbons under the same conditions as in Example 2, except that 10000 NL·kg -1 ·h -1 Replace 5000NL kg -1 ·h -1 The product composition was analyzed online by gas chromatography. The activity and selectivity results of the hydrogenation reaction are shown in Table 2 below.

[0124] Example 6

[0125] This example is basically the same as Example 2, except that 9.02 g of ferric nitrate nonahydrate is used instead of 15.50 g of ferric nitrate nonahydrate to obtain catalyst Exam-6, which has a composition of 20Fe1K / SiN. The relevant parameters of catalyst Exam-6 are shown in Table 1 below.

[0126] Using catalyst Exam-6, carbon dioxide was hydrogenated to produce heavy hydrocarbons under the same conditions as in Example 1, except that 5000 NL·kg -1 ·h -1 Replace 2000NL kg -1 ·h -1 The product composition was analyzed online by gas chromatography. The results of hydrogenation reaction activity and selectivity are shown in Table 2 below.

[0127] Example 7

[0128] This example is basically the same as Example 2, except that 15.50 g of ferric nitrate nonahydrate is replaced by 1.81 g of ferric nitrate nonahydrate, and 0.130 g of potassium nitrate is replaced by 0.065 g of potassium nitrate to obtain catalyst Exam-7, which has a composition of 5Fe0.5K / SiN. The relevant parameters of catalyst Exam-7 are shown in Table 1 below.

[0129] Using catalyst Exam-7, carbon dioxide was hydrogenated to produce heavy hydrocarbons under conditions substantially the same as those in Example 1. The product composition was analyzed online by gas chromatography. The hydrogenation reaction activity and selectivity results are shown in Table 2 below.

[0130] Example 8

[0131] This example is basically the same as Example 2, except that 9.02 g of ferric nitrate nonahydrate is used instead of 15.50 g of ferric nitrate nonahydrate, and 0.390 g of potassium nitrate is used instead of 0.130 g of potassium nitrate, to obtain catalyst Exam-8, with a composition of 20Fe3K / SiN. The relevant parameters of catalyst Exam-8 are shown in Table 1 below.

[0132] Using catalyst Exam-8, carbon dioxide was hydrogenated to produce heavy hydrocarbons under the same conditions as in Example 1, except that 5000 NL·kg -1 ·h -1 Replace 2000NL kg -1 ·h -1 The product composition was analyzed online by gas chromatography. The results of hydrogenation reaction activity and selectivity are shown in Table 2 below.

[0133] Comparative Example 1

[0134] Comparative Example 1 is substantially the same as Example 6, except that: fumed silica (470 m 2 / g) was used to replace the silicon nitride carrier in Example 1 to obtain catalyst CE-1, which had a composition of 20Fe1K / SiO2. The relevant parameters of catalyst CE-1 are shown in Table 1 below.

[0135] Catalyst CE-1 was used to hydrogenate carbon dioxide to produce heavy hydrocarbons under the same conditions as in Example 6. The product composition was analyzed online by gas chromatography. The activity and selectivity results of the hydrogenation reaction are shown in Table 2 below.

[0136] Comparative Example 2

[0137] In this comparative example, the preparation method of the catalyst used comprises the steps of:

[0138] (1) Weigh 4.02 g of ferric nitrate nonahydrate into a container, add 60 mL of anhydrous ethanol, and dissolve it completely to prepare an iron salt solution;

[0139] (2) Then weigh 5g of silicon nitride (500m 2 / g) carrier in a beaker, drop the iron salt solution onto the carrier, stir evenly, and let stand for 24h;

[0140] (3) The beaker in step (2) was placed in an oven at 120° C. and dried for 12 h to obtain catalyst precursor I;

[0141] (4) Catalyst precursor I was placed in a tubular furnace, argon gas was introduced, the temperature was raised to 400°C, and the mixture was kept for 5 hours for calcination. After naturally cooling to room temperature, the iron metal catalyst was taken out to obtain a composition of 10Fe / SiN, which was recorded as CE-2.

[0142] The relevant parameters of catalyst CE-2 are shown in Table 1 below.

[0143] Catalyst CE-2 was used to hydrogenate carbon dioxide to produce heavy hydrocarbons under the same conditions as in Example 1. The product composition was analyzed online by gas chromatography. The activity and selectivity results of the hydrogenation reaction are shown in Table 2 below.

[0144] Comparative Example 3

[0145] The catalyst used in this comparative example is Exam-2 obtained in Example 2.

[0146] The method for preparing heavy hydrocarbons by hydrogenating carbon dioxide in this comparative example comprises the following steps:

[0147] The catalyst Exam-2 obtained by the above preparation method was granulated to obtain catalyst particles of 20 to 40 mesh, and then 1g of the catalyst was placed in the constant temperature zone of a fixed bed reactor, and quartz sand was filled on both sides; the catalyst was activated at 300°C and 0.1MPa using H2 / CO with a molar ratio of 20 for 24h, and after the activation, the temperature was reduced to 100°C, and the gas was switched to a H2 / CO2 mixed gas with a molar ratio of 4, the reaction pressure was 2MPa, the reaction temperature was 280°C, and the temperature was 5000NL·kg -1 ·h -1 The CO2 hydrogenation reaction was carried out under the conditions of

[0148] The product composition was analyzed online by gas chromatography. The activity and selectivity results of the hydrogenation reaction are shown in Table 2 below.

[0149]

[0150]

[0151]

[0152] As can be seen from the above table, compared with Comparative Examples 1-3, Examples 1-8 use high specific surface area silicon nitride as a carrier and add an appropriate amount of K as an additive to the Fe-based carbon dioxide hydrogenation to heavy hydrocarbons catalyst, which effectively improves the carbon dioxide conversion rate and the selectivity of heavy hydrocarbons.

[0153] Any numerical value mentioned in the present invention, if there is only an interval of two units between any minimum value and any maximum value, includes all values ​​from the minimum value to the maximum value each time increasing by one unit. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, time, etc. is declared to be 50-90, in this specification it means that 51-89, 52-88... and 69-71 and 70-71 are specifically listed. For non-integer values, 0.1, 0.01, 0.001 or 0.0001 can be appropriately considered as a unit. These are just some specially specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0154] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A method for hydrogenating carbon dioxide to produce heavy hydrocarbons, comprising the steps of: hydrogenating carbon dioxide to produce heavy hydrocarbons in the presence of hydrogen, carbon dioxide and a catalyst; wherein: The catalyst comprises a carrier, an active metal and an additive. The carrier is silicon nitride; the active metal is iron; and the auxiliary agent is potassium.

2. The method according to claim 1, characterized in that In the catalyst, the mass ratio of the active metal to the carrier is (5-50):100, preferably (5-30):100; And / or, the mass ratio of the auxiliary agent to the carrier is (0.1-5):100, preferably (0.5-3):

100.

3. The method according to claim 1 or 2, characterized in that: The specific surface area of ​​the catalyst is 400 to 700 m 2 / g.

4. The method according to any one of claims 1 to 3, characterized in that The dispersion degree of active metal in the catalyst is 30-90%; the metal particle size of the catalyst is 1.5-4.0nm.

5. The method according to any one of claims 1 to 4, characterized in that In the silicon nitride carrier, macropores with a pore size greater than 50 nm account for 1% to 5%, and mesopores with a pore size of 2 to 50 nm account for 95% to 99%; the porosity of the silicon nitride carrier is 50% to 95%; And / or, the specific surface area of ​​the carrier is not less than 300m 2 / g, preferably 400 to 700 m 2 / g.

6. The method according to any one of claims 1 to 5, characterized in that The preparation method of the catalyst comprises the steps of: S1, providing a catalyst precursor I containing an active metal source and the carrier; providing a catalyst precursor II containing a potassium source; S2, performing a first calcination treatment on the catalyst precursor I to obtain a catalyst intermediate I; S3, mixing the catalyst precursor II and the catalyst intermediate I, and obtaining the catalyst intermediate II after drying; S4, performing a second calcination treatment on the catalyst intermediate II to obtain the catalyst.

7. The method according to claim 6, characterized in that In step S1, the active metal source is selected from one or more of ferric nitrate, ferric chloride, ferrous chloride, ferrous acetate, ammonium oxalate iron salt trihydrate and ammonium ferric citrate; And / or, the potassium source is selected from soluble potassium salts; preferably, the soluble potassium salts are selected from one or more of potassium sulfate, potassium nitrate, potassium carbonate and potassium chloride.

8. The method according to claim 6 or 7, characterized in that: In step S2, the conditions of the first calcination treatment include: a temperature of 300° C. to 900° C.; a time of 1 to 12 hours; preferably, the first calcination treatment is performed under an inert gas atmosphere; preferably, the inert gas is selected from one or more of nitrogen, argon, neon, and helium; And / or, in step S3, the drying conditions include: temperature of 40°C to 180°C; time of 4 to 24 hours; And / or, in step S4, the conditions of the second calcination treatment include: a temperature of 300° C. to 900° C., preferably 300° C. to 600° C.; and a time of 1 to 12 hours.

9. The method according to any one of claims 1 to 8, characterized in that The molar ratio of hydrogen to carbon dioxide is 1 to 4:1; And / or, the conditions of the hydrogenation reaction include: reaction temperature of 200°C to 500°C, preferably 260°C to 400°C; space velocity of 1000 to 20000 NL kg -1 1 -1 , preferably 2000~10000NLkg -1 1 -1 ; The pressure is 0.1~5Mpa, preferably 1~4MPa.

10. The method according to any one of claims 1 to 9, characterized in that Before the hydrogenation reaction, the catalyst is activated; the conditions of the activation treatment include: The activation atmosphere is hydrogen, carbon monoxide or synthesis gas; wherein the molar ratio of hydrogen to carbon monoxide in the synthesis gas is (1-500):1, preferably (1-200):1; The activation pressure is 0.1 to 4 MPa, preferably 0.1 to 3 MPa; The activation temperature is 200°C to 800°C, preferably 250°C to 600°C.

Images