Metal type theta-iron carbide compound as well as preparation method and application thereof

Abstract

The invention relates to a metal type theta-iron carbide compound and a preparation method and application thereof.The method comprises the steps that S1, a precursor is subjected to reduction and surface purification treatment at the temperature of 300-500 DEG C under the action of hydrogen, and an intermediate product is obtained; and S2, the intermediate product is subjected to carbide preparation treatment in a mixed gas atmosphere at the temperature of 300-470 DEG C. The metal type theta-iron carbide compound disclosed by the invention is used as a catalyst for a synthesis gas conversion reaction, so that the reaction has extremely low total CO2 selectivity.

Description

Technical Field

[0001] The present invention relates to the conversion of syngas, and particularly to a θ-iron carbide composite capable of being used for the conversion of syngas and a preparation method thereof. Background Art

[0002] The primary energy structure in China is characterized by rich coal, scarce oil, and little gas. With the development of China's economy, the external dependence on oil has been continuously climbing. Syngas is a mixed gas obtained by gasifying coal, natural gas, and biomass (its composition is CO and H2). The syngas conversion technology is an increasingly important energy conversion route in recent years. After carbon-containing substances such as coal, natural gas, and biomass are gasified to obtain syngas, it can be further converted into liquid fuels and high-value chemicals.

[0003] Among them, the reaction equations for the conversion of syngas are as follows:

[0004] (2n + 1)H2 + nCO → C n H 2n+2 + nH2O (a)

[0005] 2nH2 + nCO → C n H 2n + nH2O (b)

[0006] (n + 1)H2 + 2nCO → C n H 2n+2 + nCO2 (c)

[0007] nH2 + 2nCO → C n H 2n + nCO2 (d)

[0008] Iron-based catalysts are the cheapest and most readily available catalysts for the conversion of syngas. Iron-based catalysts have the advantages of high activity, a wide applicable condition window, strong sulfur resistance, simple on-line catalyst replacement, and suitability for industrial continuous production. However, one of the bottleneck problems in the traditional iron-based catalyst syngas conversion technology is the excessively high CO2 selectivity (usually accounting for 35 - 45% of the converted raw material CO).

[0009] The paper published by Professor Enrique Iglesia, "Pathways for CO2 Formation and Conversion During Fischer-Tropsch Synthesis on Iron-Based Catalysts" (Catalysis Letters volume 80, pages 77-86 (2002)), elaborates that in the reaction of syngas conversion achieved by the Fischer-Tropsch synthesis principle, there are two sources of CO2 generation: (1) primary CO2 directly from the primary Fischer-Tropsch synthesis reaction (see the above equations (c) and (d)); and (2) secondary CO2 generated by the water-gas-shift reaction (WGS reaction, CO + H2O → CO2 + H2) between H2O and CO at higher CO conversion rates.

[0010] The prior art discloses a high-purity iron carbide catalyst that can reduce the primary CO2 of the Fischer-Tropsch synthesis reaction to nearly zero, while achieving a high CO space-time conversion rate, thereby reducing the total CO2 selectivity to <5% at low CO conversion rates (usually below 35%). However, when the CO conversion rate increases, as the H2O content in the reaction environment increases, the WGS reaction becomes intense, resulting in an increase in secondary CO2, and ultimately causing an increase in the total CO2 selectivity at high CO conversion rates.

[0011] In addition, reducing the CO2 selectivity will significantly improve the carbon atom utilization efficiency and essentially enhance the economy and environmental friendliness of the syngas conversion technology. Therefore, how to suppress the water-gas-shift side reaction, reduce the CO2 selectivity, and improve the carbon atom utilization efficiency at high CO conversion rates has become one of the common key problems in the field of syngas conversion. On the other hand, in addition to CO2, another main by-product in the field of syngas conversion is methane. In the reaction, a high CH4 selectivity and a high CO2 selectivity will jointly reduce the selectivity of the effective products of the reaction. Summary of the Invention

[0012] To overcome at least one defect of the above prior art, on the one hand, an embodiment of the present invention provides a preparation method of a metal-type θ-iron carbide composite, comprising the following steps:

[0013] S0: Provide a precursor, the precursor being nano-iron and / or nano-iron compound or the nano-iron and / or nano-iron compound containing bromide ions and / or iodide ions; the nano-iron compound can be prepared into nano-iron through a reduction reaction;

[0014] S1: Under the action of hydrogen, reduce and surface-purify the precursor at 300-500 °C to obtain an intermediate product;

[0015] S2: Carry out the preparation treatment of carbide on the intermediate product in a mixed gas atmosphere at 300 - 470 °C;

[0016] Wherein, the mixed gas includes hydrogen and carbon monoxide with a molar ratio of (5:1 - 110):1;

[0017] Carry out the first impregnation treatment on the nano - iron and / or nano - iron compound through an impregnating solution to obtain the nano - iron and / or nano - iron compound containing bromide ions and / or iodide ions; wherein, when the precursor is the nano - iron and / or the nano - iron compound, carry out the second impregnation treatment on the product of step S2 through the impregnating solution.

[0018] In a second aspect, an embodiment of the present invention provides a θ - iron carbide composite prepared by the above - mentioned preparation method.

[0019] In a third aspect, an embodiment of the present invention provides a catalyst, which includes the θ - iron carbide composite prepared by the above - mentioned preparation method or the above - mentioned θ - iron carbide composite.

[0020] In a fourth aspect, an embodiment of the present invention provides the application of the θ - iron carbide composite prepared by the above - mentioned preparation method, the above - mentioned θ - iron carbide composite or the above - mentioned catalyst in the synthesis gas conversion reaction.

[0021] In a fifth aspect, an embodiment of the present invention provides the application of the θ - iron carbide composite prepared by the above - mentioned preparation method, the above - mentioned θ - iron carbide composite or the above - mentioned catalyst in the reaction of synthesizing C, H fuels and / or chemicals based on the Fischer - Tropsch synthesis principle.

[0022] In a sixth aspect, an embodiment of the present invention provides a synthesis gas conversion process, which includes contacting the above - mentioned catalyst with synthesis gas under reaction conditions for reaction.

[0023] The θ - iron carbide composite of an embodiment of the present invention can be used as a catalyst for the synthesis gas conversion reaction, especially the Fischer - Tropsch synthesis reaction. By introducing halogen ions such as bromine or iodine into the θ - iron carbide composite, the reaction has a high CO conversion rate, an extremely low total CO2 selectivity and a low CH4 selectivity, realizing the comprehensive optimization of the reaction results. Description of the Drawings

[0024] The drawings are only for the purpose of showing specific embodiments and are not considered as a limitation of the present invention. Among them:

[0025] Figure 1 It is the XRD pattern of the θ - iron carbide composite CX1 prepared in Example 1 of the present invention. Detailed Embodiments

[0026] Typical embodiments embodying the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different embodiments, all of which do not depart from the scope of the present invention, and the description herein is for illustrative purposes in nature and not intended to limit the present invention.

[0027] An embodiment of the present invention provides a θ-iron carbide composite, comprising θ-iron carbide and a halogen element, and the molar ratio of θ-iron carbide to the halogen element is 100:(0.1 - 40);

[0028] Among them, the halogen element is bromine element and / or iodine element; the composite has an orthorhombic crystal structure, and its average grain diameter is 7 - 42 nm, further can be 9 - 35 nm; herein, the molar number of θ-iron carbide is counted based on the molar number of iron element contained therein.

[0029] In one embodiment, the halogen element exists in the form of halide ions, which can be bromide ions and / or iodide ions. The molar ratio of θ-iron carbide to the halogen element (or halide ions) can be 100:(0.1 - 40), further can be 100:(0.35 - 32), still further can be 100:(7 - 20), such as 100:0.5, 100:1, 100:5, 100:10, 100:15, 100:20, 100:25, 100:30, 100:40.

[0030] In one embodiment, the θ-iron carbide composite comprises a halide cation, and the halide cation can maintain charge balance with the halide ion, that is, the total negative charge (or the total valence shown) of the halide ion is equal to the total positive charge of the halide cation.

[0031] In one embodiment, the θ-iron carbide composite further comprises other cationic elements, and the other cationic elements exist in the form of other cations. The molar ratio of θ-iron carbide to the other cationic elements (or other cations) can be 100:(0.1 - 22), further can be 100:(0.1 - 18), still further can be 100:(0.1 - 10), such as 100:0.5, 100:1, 100:3, 100:5, 100:7, 100:10, 100:15, 100:20.

[0032] In one embodiment, the other cation is the halide cation, or the θ-iron carbide composite comprises both the halide cation and other cations.

[0033] In one embodiment, the θ-iron carbide composite further comprises other anions, which can maintain charge balance with other cations when the composite comprises both halide cations and other cations simultaneously.

[0034] In one embodiment, the other cationic elements may be selected from one or more of manganese, copper, cobalt, molybdenum, chromium, rare earth elements, alkali metal elements, and alkaline earth metal elements; preferably, the other cationic elements are selected from one or more of manganese, copper, cobalt, molybdenum, chromium, lanthanum, cerium, neodymium, sodium, potassium, calcium, and barium. Correspondingly, the other cations may be selected from one or more of manganese ions, copper ions, cobalt ions, molybdenum ions, chromium ions, rare earth ions, alkali metal ions, and alkaline earth metal ions; for example, the other cations may be manganese ions (such as divalent, trivalent, and tetravalent manganese ions), copper ions (such as monovalent and divalent copper ions), cobalt ions (such as divalent cobalt ions), molybdenum ions (such as divalent, trivalent, and tetravalent molybdenum ions), chromium ions (such as trivalent chromium ions), lanthanum ions (such as trivalent and tetravalent lanthanum ions), cerium ions (such as trivalent and tetravalent cerium ions), neodymium ions (such as trivalent and tetravalent neodymium ions), sodium ions, potassium ions, calcium ions, and barium ions.

[0035] In one embodiment, the halide cations include one or more of a first metal ion and a complex cation. Further, the first metal ion includes one or more of iron ions (such as divalent and trivalent iron ions), manganese ions (such as divalent manganese ions), copper ions (such as monovalent and divalent copper ions), cobalt ions (such as divalent cobalt ions), molybdenum ions (such as divalent, trivalent, and tetravalent molybdenum ions), lanthanum ions (such as trivalent and tetravalent lanthanum ions), cerium ions (such as trivalent and tetravalent cerium ions), and neodymium ions (such as trivalent and tetravalent neodymium ions); the complex cation includes one or more of hexaammine manganese ions, hexaammine iron ions, and hexaammine copper ions.

[0036] In one embodiment, the other anions include one or more of oxygen ions, complex ions, and acid radical ions, such as oxygen ions, nitrate ions, citrate ions, and gluconate ions.

[0037] One embodiment of the present invention provides a method for preparing the above-mentioned θ-iron carbide composite, comprising the following steps:

[0038] S1: Under the action of hydrogen, the precursor is subjected to reduction and surface purification treatment at 300-500 °C to obtain an intermediate product;

[0039] S2: The intermediate product is subjected to carbide preparation treatment at 300-470 °C in a mixed gas atmosphere;

[0040] wherein, the mixed gas includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide is 5:1-110:1;

[0041] The precursor is nano-iron and / or nano-iron compound that has undergone a first impregnation treatment with an impregnation solution. The nano-iron compound can be obtained by a reduction reaction to produce nano-iron, and the impregnation solution includes bromide ions and / or iodide ions; or,

[0042] The precursor is nano-iron and / or the nano-iron compound, and the product of step S2 is subjected to a second impregnation treatment with the impregnation solution.

[0043] In one embodiment, the nano-iron compound includes one or more of nano-iron oxide, nano-magnetite, nano-goethite, and nano-iron hydroxide oxide.

[0044] In one embodiment, the nano-iron or nano-iron compound can be nano-iron powder and / or nano-iron particles.

[0045] In one embodiment, the average grain diameter of the nano-iron or nano-iron compound is 6 - 35 nm, further it can be 9 - 28 nm, such as 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, 22 nm, 25 nm, 30 nm, 32 nm.

[0046] In one embodiment, the impregnation solution is prepared by dissolving an impregnation compound in a solvent. The impregnation compound can include water-soluble halides, and the halides include bromides and / or iodides. Further, the halides include one or more of manganese, molybdenum, cobalt, rare earth metal elements, iron, and copper bromides and iodides. For example, the halide can be one or more of manganese bromide, ferrous bromide, copper bromide, cobalt bromide, molybdenum bromide, manganese iodide, ferrous iodide, copper iodide, rare earth bromides, rare earth iodides, hexaammine manganese bromide, hexaammine iron bromide, hexaammine copper bromide, hexaammine manganese iodide, hexaammine iron iodide, and hexaammine copper iodide.

[0047] In one embodiment, the concentration of the halide in the impregnation solution can be 0.7 - 7 mol / L, such as 1 mol / L, 2 mol / L, 3 mol / L, 5 mol / L, 6 mol / L.

[0048] In one embodiment, the solvent of the impregnation solution includes water and / or ethanol. For example, the solvent can be water or a mixture of ethanol and water.

[0049] In one embodiment, the solute of the impregnating solution further includes other compounds, and the other compounds include one or more of salts (organic salts and / or inorganic salts) of manganese, copper, cobalt, molybdenum, rare earth metals, alkali metals, and alkaline earth metals. For example, the other compounds may be one or more of potassium nitrate, sodium nitrate, manganese nitrate, copper nitrate, cobalt nitrate, molybdenum nitrate, calcium nitrate, barium nitrate, rare earth nitrates, potassium carbonate, sodium carbonate, potassium citrate, sodium citrate, manganese citrate, copper citrate, cobalt citrate, molybdenum citrate, calcium citrate, barium citrate, potassium gluconate, sodium gluconate, lithium gluconate, rubidium gluconate, cesium gluconate, manganese gluconate, copper gluconate, and calcium gluconate.

[0050] In one embodiment, no chemical reaction occurs between the solute components of the impregnating solution. For example, the solute does not include potassium carbonate and calcium nitrate at the same time.

[0051] In one embodiment, the dosages of the halide and other compounds can be appropriately selected according to the contents of various ions in the composite to be prepared. Further, the concentration of the halide or other compound can be 0.7 - 7 mol / L, such as 1 mol / L, 2 mol / L, 3 mol / L, 5 mol / L, 6 mol / L.

[0052] In one embodiment, the precursor is nano - iron or nano - iron compound subjected to the first impregnation treatment with the impregnating solution. The temperature of the first impregnation treatment or the second impregnation treatment is 0 - 50 °C, further preferably 20 - 30 °C, such as 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C; the time of the first impregnation treatment or the second impregnation treatment can be 0.1 - 12 h, further preferably 0.2 - 10 h, and still further preferably 0.3 - 9 h, such as 0.5 h, 1 h, 2 h, 3 h, 5 h, 6 h, 8 h.

[0053] In one embodiment, the material after the first impregnation treatment or the second impregnation treatment can be dried at 15 - 40 °C, and further dried under light - shielding conditions. The drying temperature can be, for example, 20 °C, 25 °C, 30 °C, 35 °C; the drying time can be 0.5 - 12 h. The drying treatment can be carried out under normal pressure or reduced pressure.

[0054] In one embodiment, the first impregnation treatment or the second impregnation treatment can adopt one of slurry impregnation method, saturated impregnation method, supersaturated impregnation method or other feasible impregnation methods.

[0055] In one embodiment, the temperature for the reduction and surface purification treatment in step S1 can be 300 to 500 °C, such as 350 °C, 400 °C, 420 °C, 450 °C, 460 °C, 480 °C, 500 °C; the treatment pressure can be 0.13 to 9.5 atm, further can be 0.22 to 2.5 atm, such as 0.15 atm, 0.2 atm, 0.5 atm, 0.8 atm, 1 atm, 1.5 atm, 2 atm, 5 atm, 8 atm, 9 atm; the treatment time can be 1.2 to 26 h, further can be 2 to 12 h, such as 5 h, 8 h, 10 h, 15 h, 20 h, 25 h.

[0056] In one embodiment, the gas flow rate of H2 in step S1 can be 600 to 21000 mL / h / g, further can be 1200 to 16000 mL / h / g, such as 1000 mL / h / g, 1500 mL / h / g, 2000 mL / h / g, 3000 mL / h / g, 5000 mL / h / g, 6000 mL / h / g, 8000 mL / h / g, 10000 mL / h / g, 12000 mL / h / g, 15000 mL / h / g.

[0057] In one embodiment, the mixed gas in step S2 includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide can be 5:1 to 110:1, such as 10:1, 20:1, 30:1, 36:1, 40:1, 50:1, 60:1, 80:1, 100:1. The mixed gas can be a mixture of hydrogen and carbon monoxide.

[0058] In one embodiment, the pre-treatment temperature in step S2 can be 300 to 470 °C, such as 300 °C, 320 °C, 330 °C, 350 °C, 380 °C, 400 °C, 420 °C; the treatment pressure can be 0 to 21 atm, further can be 0.01 to 17 atm, such as 0.1 atm, 0.2 atm, 0.5 atm, 0.8 atm, 1 atm, 1.5 atm, 2 atm, 3 atm, 5 atm, 8 atm, 10 atm, 12 atm, 15 atm, 18 atm, 20 atm; the treatment time can be 3 to 72 h, further can be 5 to 48 h, such as 10 h, 20 h, 25 h, 30 h, 40 h, 45 h, 50 h, 55 h, 60 h, 70 h.

[0059] In one embodiment, the gas flow rate of the mixed gas in step S2 can be 500 - 31000 mL / h / g, further can be 1500 - 17000 mL / h / g, such as 1000 mL / h / g, 3000 mL / h / g, 5000 mL / h / g, 6000 mL / h / g, 7000 mL / h / g, 8000 mL / h / g, 10000 mL / h / g, 12000 mL / h / g, 15000 mL / h / g, 18000 mL / h / g, 25000 mL / h / g, 30000 mL / h / g.

[0060] In one embodiment, in step S2, the temperature of the system is raised or lowered from 300 - 500 °C to 300 - 470 °C at a heating or cooling rate of 0.2 - 5 °C / min. Further, the temperature of the system is raised or lowered from 300 - 500 °C to 300 - 400 °C at a variable temperature rate of 0.2 - 2.5 °C / min; the variable temperature rate in step S2 can be, for example, 0.5 °C / min, 0.8 °C / min, 1 °C / min, 1.2 °C / min, 1.5 °C / min, 1.8 °C / min, 2 °C / min, 2.2 °C / min, 3 °C / min, 4 °C / min.

[0061] In one embodiment, preferably, steps S1, S2, and the first or second impregnation treatment are all carried out under light - shielding conditions.

[0062] In one embodiment, the preparation method of the metal - type θ - iron carbide composite includes the following steps:

[0063] S0: The nano - iron and / or nano - iron compound is subjected to a first impregnation treatment with an impregnating solution to obtain a precursor to be treated;

[0064] S1: Under the action of hydrogen, the precursor is subjected to reduction and surface purification treatment at 300 - 500 °C to obtain an intermediate product;

[0065] S2: The intermediate product is treated at 300 - 470 °C in a mixed - gas atmosphere to obtain a halogen - containing θ - iron carbide composite.

[0066] In another embodiment, the preparation method of the metal - type θ - iron carbide composite includes the following steps:

[0067] S1: Under the action of hydrogen, the precursor (nano - iron and / or nano - iron compound) is subjected to reduction and surface purification treatment at 300 - 500 °C to obtain an intermediate product;

[0068] S2: The intermediate product is treated at 300 - 470 °C in a mixed - gas atmosphere;

[0069] S21: Perform a second impregnation treatment on the product of step S2 to obtain a halogen element-containing θ-iron carbide composite.

[0070] An embodiment of the present invention provides a catalyst comprising the above-mentioned θ-iron carbide composite.

[0071] An embodiment of the present invention provides the application of the above-mentioned θ-iron carbide composite or catalyst in the synthesis gas conversion reaction.

[0072] In one embodiment, the synthesis gas conversion reaction can be a Fischer-Tropsch synthesis reaction or other reactions based on the Fischer-Tropsch synthesis principle, such as a reaction using synthesis gas as the starting material and the final product being alcohol.

[0073] In one embodiment, the synthesis gas comprises CO and H2.

[0074] An embodiment of the present invention provides the application of the above-mentioned θ-iron carbide composite or catalyst in the reaction for synthesizing C, H fuels and / or chemicals based on the Fischer-Tropsch synthesis principle. Among them, the reaction based on the Fischer-Tropsch synthesis principle refers to a reaction using synthesis gas (a mixture of CO and H2) as the raw material, under the action of a catalyst and appropriate conditions, through CO hydrogenation and carbon chain growth reactions to generate hydrocarbons and / or their oxygen-containing derivatives.

[0075] In one embodiment, the above reaction is a Fischer-Tropsch synthesis reaction, the reaction temperature can be 280 - 340 °C, such as 290 °C, 300 °C, 310 °C, 320 °C; the reaction pressure can be 2 - 3.5 MPa, and the molar ratio of H2 / CO can be 1.7 - 2.15.

[0076] An embodiment of the present invention provides a synthesis gas conversion process, which includes bringing the above-mentioned catalyst into contact with synthesis gas for reaction under synthesis gas conversion reaction conditions.

[0077] In one embodiment, the synthesis gas conversion can be carried out in a high-temperature and high-pressure continuous reactor.

[0078] The θ-iron carbide composite of an embodiment of the present invention can be used as a catalyst for the synthesis gas conversion reaction. By introducing halogen ions into θ-iron carbide, the reaction has a high CO conversion rate, an extremely low total CO2 selectivity, and a low CH4 selectivity. At the same time, benefiting from the very high CO space-time conversion rate of the θ-iron carbide composite catalyst, it shows considerable activity.

[0079] A θ-iron carbide composite of an embodiment of the present invention can be used as a catalyst for the synthesis gas conversion reaction, enabling the reaction to maintain an extremely low CO2 selectivity at a high CO conversion rate, while maintaining a low CH4 selectivity and a high reaction stability, greatly improving the utilization efficiency of carbon atoms and the selectivity of effective products, breaking through the key technical bottleneck, and promoting the high-end, diversification, and low-carbonization of the clean conversion of synthesis gas, indicating a new trend and direction for the development of modern synthesis gas chemistry.

[0080] A θ-iron carbide composite of an embodiment of the present invention, as a catalyst for the Fischer-Tropsch synthesis reaction, can maintain a continuous and stable reaction for more than 300 h using a high-pressure continuous reactor under industrial Fischer-Tropsch synthesis reaction conditions. Its CO2 selectivity is below 5%, further below 3%; the selectivity of its by-product CH4 can be maintained below 8.5%, further below 5.5%; the utilization efficiency of carbon atoms is maintained above 95%, further above 97%; the selectivity of effective products can reach above 86.5%, further above 92%.

[0081] In one embodiment, through the Fischer-Tropsch synthesis reaction catalyzed by the θ-iron carbide composite, a CO2 selectivity of <5%, a carbon atom utilization efficiency of >95%, and an effective product selectivity of >90% can be achieved at a CO conversion rate of above 70%.

[0082] As used herein, the "ions" contained in the composite include all particles that are combined with other particles by covalent bonds and / or ionic bonds. For example, the bromide ions in the composite include both Br that interacts with K by ionic bonds + interactions - and Br atoms that interact with H atoms by covalent bonds.

[0083] All pressure values involved herein are gauge pressures.

[0084] Hereinafter, in conjunction with the accompanying drawings and specific embodiments, a θ-iron carbide composite of an embodiment of the present invention and its applications will be further described. Among them, the test methods involved are as follows:

[0085] 1. During the reaction process of the examples or comparative examples, an in-situ XRD detector was used to monitor the phase changes of the materials with an X-ray diffractometer (Rigaku Corporation, model D / max-2600 / PC), and the crystal system structure of the θ-iron carbide composite was measured by the X-ray diffractometer.

[0086] 2. The average grain diameter of the θ-iron carbide composite was obtained through XRD testing.

[0087] 3. A Mössbauer spectrometer (Transmission 57 Fe, 57The Mössbauer spectroscopy of the θ-iron carbide complex was detected by a Co(Rh) source sinusoidal velocity spectrometer to obtain the composition of the complex.

[0088] 4. The elemental detection of the θ-iron carbide complex was carried out by an Inductive Coupled Plasma Emission Spectrometer (ICP).

[0089] 5. During the conversion reaction of syngas, the products obtained from the reaction were analyzed by gas chromatography (Agilent 7890 gas chromatography) to calculate the conversion rate, selectivity, etc. The products refer to the tail gas collected from the end of the reactor, including the generated hydrocarbon compounds, alcohol compounds, CO2, etc.

[0090] 6. The CO conversion rate %, CO2 selectivity %, CH4 selectivity %, carbon atom utilization efficiency %, and effective product selectivity % were calculated by the following formulas:

[0091] CO conversion rate % = [(moles of CO in the feed - moles of CO in the product) / moles of CO in the feed] × 100%;

[0092] CO2 selectivity % = [moles of CO2 in the product / (moles of CO in the feed - moles of CO in the product)] × 100%;

[0093] CH4 selectivity % = [moles of CH4 in the product / (moles of CO in the feed - moles of CO in the product)] × 100%;

[0094] Carbon atom utilization efficiency % = (1 - CO2 selectivity %) × 100%;

[0095] Effective product selectivity % = (1 - CO2 selectivity % - CH4 selectivity %) × 100%.

[0096] Example 1

[0097] S1: At a pressure of 430 °C and 2.0 atm, 5.6 g of nano-iron particles with an average grain diameter of 20 nm were taken and maintained in H2 with a flow rate of 12000 mL / h / g for 2 h for reduction and surface purification treatment to obtain an intermediate product.

[0098] S2: The intermediate product was cooled to 420 °C and contacted with the mixed gas at this temperature to prepare the pre-carbide; among them, the pressure of the system was 2.0 atm, the flow rate of the mixed gas was 10000 mL / h / g, and the treatment time was 6 h; the mixed gas was a mixed gas of H2 and CO, and the molar ratio of H2 to CO was 30:1.

[0099] S21: Dissolve manganese bromide and potassium nitrate in 50 ml of water to obtain an impregnation solution; mix the impregnation solution with the product of step S2 and perform impregnation treatment by the slurry impregnation method. The impregnation ratio (molar ratio) is Fe:Br:K = 100:7.0:2.0, the impregnation temperature is 32 °C, and the impregnation time is 2 h; dry the impregnated solid material at 35 °C for 7 h. After the treatment is completed, an iron theta-carbide complex is obtained and labeled as CX1.

[0100] Examples 1-1 to 3-8 all use basically the same raw materials and processes as in Example 1 to prepare the metal-type iron theta-carbide complex, except that: the content or type of halide ions or other cations in the impregnation solution is different, and the prepared complexes are sequentially labeled as CX1-1 to CX3-8 using the same numbering as in Example 1. Since the loss of materials during the preparation process is extremely small, the content of each substance in the obtained complex is basically the same as the dosage of the corresponding raw materials. For specific content values, see Table 1.

[0101] Example 4

[0102] S0: Dissolve 0.035 mol of manganese bromide, 0.03 mol of potassium citrate, and 0.05 mol of copper nitrate in 50 ml of water to obtain an impregnation solution; take 8.0 g of nano-iron oxide particles with an average grain diameter of 16 nm, mix the impregnation solution with the nano-iron oxide particles, and perform impregnation treatment by the slurry impregnation method. The impregnation ratio (molar ratio) is Fe:Br:K:Cu = 100:7.0:3.0:5.0, the impregnation temperature is 37 °C, and the impregnation time is 3 h; dry the impregnated solid material at 25 °C for 8 h to obtain a precursor.

[0103] S1: At a temperature of 430 °C and a pressure of 3.0 atm, keep the precursor prepared in step S0 in H2 with a flow rate of 15000 mL / h / g for 2 h to perform reduction and surface purification treatment to obtain an intermediate product.

[0104] S2: Cool the intermediate product to 350 °C and contact it with a mixed gas at this temperature to prepare pre-carbide; wherein, the pressure of the system is 3.0 atm, the flow rate of the mixed gas is 12000 mL / h / g, and the treatment time is 6 h; the mixed gas is a mixed gas of H2 and CO, and the molar ratio of H2 to CO is 30:1. After the treatment is completed, an iron theta-carbide complex is obtained and labeled as CX4.

[0105] Example 4-1

[0106] This example uses basically the same raw materials and processes as in Example 1 to prepare the iron theta-carbide complex, except that: the H2 flow rate in step S1 is 1200 mL / h / g. The finally obtained iron theta-carbide complex is labeled as CX4-1.

[0107] Example 4-2

[0108] In this example, the θ-iron carbide composite is prepared using substantially the same raw materials and process as in Example 1, with the only difference being that the H2 flow rate in step S1 is 16000 mL / h / g. The finally obtained θ-iron carbide composite is labeled as CX4-2.

[0109] Example 4-3

[0110] In this example, the θ-iron carbide composite is prepared using substantially the same raw materials and process as in Example 1, with the only difference being that the H2 flow rate in step S1 is 10000 mL / h / g. The finally obtained θ-iron carbide composite is labeled as CX4-3.

[0111] Example 4-4

[0112] In this example, the θ-iron carbide composite is prepared using substantially the same raw materials and process as in Example 1, with the only difference being that the carbonization temperature in step S2 is 300 °C. The finally obtained θ-iron carbide composite is labeled as CX4-4.

[0113] Example 4-5

[0114] In this example, the θ-iron carbide composite is prepared using substantially the same raw materials and process as in Example 1, with the only difference being that the carbonization temperature in step S2 is 470 °C. The finally obtained θ-iron carbide composite is labeled as CX4-5.

[0115] Example 4-6

[0116] In this example, the θ-iron carbide composite is prepared using substantially the same raw materials and process as in Example 1, with the only difference being that the carbonization temperature in step S2 is 400 °C. The finally obtained θ-iron carbide composite is labeled as CX4-6.

[0117] Example 4-7

[0118] In this example, the θ-iron carbide composite is prepared using substantially the same raw materials and process as in Example 1, with the only difference being that the reduction temperature in step S1 is 500 °C. The finally obtained θ-iron carbide composite is labeled as CX4-7.

[0119] Example 4-8

[0120] In this example, the θ-iron carbide composite is prepared using substantially the same raw materials and process as in Example 1, with the only difference being that the carbonization pressure in step S2 is 17 atm. The finally obtained θ-iron carbide composite is labeled as CX4-8.

[0121] Example 4-9

[0122] This example uses substantially the same raw materials and process as Example 1 to prepare the θ-iron carbide composite, with the only difference being that the reduction time in step S1 is 12 h. The finally prepared θ-iron carbide composite is labeled as CX4-9.

[0123] Examples 4 - 10

[0124] This example uses substantially the same raw materials and process as Example 1 to prepare the θ-iron carbide composite, with the only difference being that the carbonization time in step S2 is 48 h. The finally prepared θ-iron carbide composite is labeled as CX4-10.

[0125] Example 5

[0126] S0: Dissolve 0.035 mol of manganese bromide and 0.02 mol of potassium gluconate in 50 ml of water to prepare an impregnating solution; take 8.0 g of nano-iron oxide particles with an average grain diameter of 20 nm, mix the impregnating solution with the nano-iron oxide particles, and perform impregnation treatment by the slurry impregnation method. The impregnation ratio (molar ratio) is Fe:Br:K = 100:7.0:2.0, the impregnation temperature is 37 °C, and the impregnation time is 2 h; dry the impregnated solid material at 25 °C for 6 h to obtain a precursor.

[0127] S1: At a temperature of 430 °C and a pressure of 2.0 atm, keep the precursor prepared in step S0 in H2 with a flow rate of 12000 mL / h / g for 2 h to perform reduction and surface purification treatment to obtain an intermediate product.

[0128] S2: Cool the intermediate product to 350 °C and contact it with a mixed gas at this temperature to prepare pre-carbide; wherein, the pressure of the system is 2.0 atm, the flow rate of the mixed gas is 10000 mL / h / g, and the treatment time is 6 h; the mixed gas is a mixed gas of H2 and CO, and the molar ratio of H2 to CO is 30:1. After the treatment is completed, the θ-iron carbide composite is prepared and labeled as CX5.

[0129] Comparative Example 1

[0130] This example uses substantially the same raw materials and process as Example 1 to prepare the θ-iron carbide composite, with the only difference being that in step S21, the impregnation ratio is Fe:Br:K = 100:50:2. The finally prepared θ-iron carbide composite is labeled as DX1.

[0131] Comparative Example 2

[0132] This example uses substantially the same raw materials and process as Example 1 to prepare the θ-iron carbide composite, with the only difference being that in step S21, when preparing the impregnating solution, manganese bromide is not added, and only potassium nitrate is added. The finally prepared θ-iron carbide composite is labeled as D2.

[0133] Comparative Example 3

[0134] In this example, a θ-iron carbide composite was prepared using substantially the same raw materials and process as in Example 1, except that: in step S21, manganese chloride in an equimolar amount was used instead of manganese bromide to prepare an impregnating solution, and the nano-iron particles were impregnated with this impregnating solution. The finally prepared θ-iron carbide composite was labeled DX3.

[0135] Comparative Example 4

[0136] The same raw materials and steps as in steps S1 to S2 of Example 1 were used, but the impregnation step S21 was not carried out to prepare θ-iron carbide, which was labeled D4.

[0137] Comparative Example 5

[0138] In this example, a θ-iron carbide composite was prepared using substantially the same raw materials and process as in Example 1, except that: in step S2, the temperature was lowered to 270 °C for the operation. The finally prepared θ-iron carbide composite was labeled DX5.

[0139] The θ-iron carbide composites, θ-iron carbide, etc. prepared in each example and comparative example were subjected to XRD, Mössbauer spectroscopy and ICP measurements. The content of θ-iron carbide was calculated based on 100 mol, and the relevant contents refer to the number of moles. The specific results are shown in Table 1.

[0140] In a slurry bed continuous reactor, the catalytic reaction performance of the θ-iron carbide composites, θ-iron carbide, etc. prepared in each example and comparative example was evaluated respectively. The catalyst loading was 9.0 g. Evaluation conditions: T = 283 °C, P = 2.70 MPa, H2:CO = 2.1:1, (H2+CO) total amount = 15000 mL / h / g- Fe (standard state flow rate, relative to the Fe element), and the circulation ratio was 1.2. The reaction was carried out, and the reaction products were analyzed by gas chromatography. The reaction performance evaluation data at 24 h and 300 h of the reaction are shown in Tables 2 and 3.

[0141] Table 1

[0142]

[0143]

[0144] Table 2

[0145]

[0146] Table 3

[0147]

[0148] From the results of each example, comparative example, and Tables 1-3, it can be seen that compared with Example 1, the impregnating solution of Comparative Example 2 does not contain manganese bromide, indicating that the composite prepared in Comparative Example 2 does not contain manganese ions and bromide ions. The results in Table 2 show that although the CO conversion rate of Comparative Example 2 is higher than that of Example 1, its CO2 selectivity of 40.6% is much higher than the CO2 selectivity of 3.0% in Example 1, and the carbon atom utilization rate (59.4%) and the effective product selectivity (55.8%) are much lower than the carbon atom utilization rate (97.0%) and the effective product selectivity (92.4%) in Example 1. Therefore, the composite in Example 1 can improve the overall efficiency of the reaction compared with the composite in Comparative Example 2 and achieve the optimization of the comprehensive reaction results.

[0149] Furthermore, the difference between Example 1-1 and Example 1 is that the halide used is ferrous bromide. The results in Table 2 show that the reaction performance data of Example 1-1 and Example 1 are not very different, indicating that the improvement in performance of Example 1 compared with Comparative Example 2 is mainly brought about by the addition of bromide ions rather than manganese ions.

[0150] Even further, the main difference between Example 2 and Example 1-2 is that iodide ions are introduced into the prepared composite instead of bromide ions. The results in Table 2 show that the reaction performance data of Example 2 and Example 1-2 are not very different, indicating that introducing iodide ions into iron carbide can also play a role in improving the comprehensive reaction performance. In addition, the difference between Comparative Example 3 and Example 1 is that chloride ions are introduced into the prepared composite instead of bromide ions. The results in Table 2 show that all the reaction performances of Comparative Example 3 are significantly lower than those of Example 1 and cannot achieve the optimization of the comprehensive reaction results.

[0151] Even further, bromide ions are also introduced into the iron carbide in Comparative Example 1, but its bromide ion content is too high, exceeding the range of the molar ratio of θ-iron carbide to halide ions of 100:(0.1-40) defined in an embodiment of the present invention. According to the results in Table 2, the CO conversion rate of Comparative Example 1 is only 35.2%, far lower than the CO conversion rate of 82.7% in Example 1, and the carbon atom utilization rate and the effective product selectivity of Comparative Example 1 are also significantly lower than those in Example 1. Thus, when the bromide ions in the iron carbide composite exceed a certain range, the comprehensive optimization of the reaction results cannot be achieved either.

[0152] Even further, the main difference between Examples 1 to 1-7 is mainly the different contents of bromide ions. Combining the results in Tables 2 and 3, the molar ratio of iron carbide (or iron element) to bromide ions in the prepared composite is preferably 100:(7-20).

[0153] Furthermore, the main difference between Examples 3 to 3-8 lies in the different contents of other cations. Combining the results in Tables 2 and 3, the molar ratio of iron carbide (or iron element) to other cations in the prepared composite is preferably 100:(0.1-10).

[0154] In addition, according to the results in Table 3, it can be seen that the reactions catalyzed by the composites of each example of the present invention can keep the CO conversion rate, product selectivity, etc. stable for a long time. Thus, by making the θ-iron carbide composite contain halide ions such as bromine or iodine and limiting the halide ion content within a specific range, and using it as a catalyst for the Fischer-Tropsch synthesis reaction, the overall efficiency of the reaction can be improved, and the comprehensive results of the reaction can be optimized.

[0155] Based on the above description, using the θ-iron carbide composite containing halide ions such as bromine or iodine prepared in the examples of the present invention as a catalyst for the syngas conversion reaction under industrial conditions can exhibit ultra-low CO2 selectivity, relatively low CH4 selectivity, extremely high carbon atom utilization efficiency and effective product selectivity on the premise of maintaining a high CO conversion rate (>60%). Further long-term experiments were carried out. From the data of the reaction for 300 h in Table 3, it can be seen that after the θ-iron carbide composite of the examples of the present invention was continuously operated in a stirred tank for a long period as a catalyst, its CO conversion rate, product selectivity, carbon atom utilization efficiency and effective product selectivity all remained stable without obvious changes, showing good operation stability. Thus, by using the θ-iron carbide composite of the examples of the present invention as a catalyst for the syngas conversion reaction, the comprehensive optimization of the reaction results can be achieved.

[0156] Unless otherwise specified, the terms used in the present invention have the meanings commonly understood by those skilled in the art.

[0157] The embodiments described in the present invention are only for illustrative purposes and are not intended to limit the protection scope of the present invention. Those skilled in the art can make various other substitutions, changes and improvements within the scope of the present invention. Therefore, the present invention is not limited to the above embodiments but is only defined by the claims.

Claims

1. A method for preparing a metal-type θ-iron carbide composite, comprising the following steps: S0: Provide a precursor, which is nano-iron and / or nano-iron compound or the nano-iron and / or nano-iron compound containing bromide ion and / or iodide ion; the nano-iron compound can be prepared into nano-iron through a reduction reaction; S1: Under the action of hydrogen, subject the precursor to reduction and surface purification treatment at 300-500 °C to obtain an intermediate product; S2: Subject the intermediate product to carbide preparation treatment in a mixed gas atmosphere at 300-470 °C; Wherein, The mixed gas includes hydrogen and carbon monoxide with a molar ratio of (5:1 to 110):1; The nano-iron and / or nano-iron compound is subjected to a first impregnation treatment with an impregnation solution to obtain the nano-iron and / or nano-iron compound containing bromide ions and / or iodide ions; wherein, when the precursor is the nano-iron and / or the nano-iron compound, the product of step S2 is subjected to a second impregnation treatment with the impregnation solution.

2. The preparation method according to claim 1, wherein, The impregnation solution includes bromide ions and / or iodide ions; and / or, The nano-iron compound includes one or more of nano-iron oxide, nano-magnetite, nano-goethite, and nano-iron hydroxide oxide; and / or, The average grain diameter of the nano-iron or nano-iron compound is 6 nm to 35 nm.

3. The preparation method according to claim 1, wherein, The raw materials for preparing the impregnation solution include an impregnation compound, and the impregnation compound includes water-soluble bromide and / or iodide; further, the impregnation compound includes one or more of bromides and iodides containing manganese, molybdenum, cobalt, rare earth metal elements, iron, and copper; and / or, The first impregnation treatment or the second impregnation treatment adopts slurry impregnation method, saturated impregnation method or supersaturated impregnation method.

4. The preparation method according to claim 3, wherein, The impregnation compound further includes other compounds, and the other compounds are selected from one or more of salts of copper, molybdenum, alkali metals, manganese, rare earth metals, alkaline earth metals, and cobalt.

5. The preparation method according to claim 1, wherein, The treatment pressure of step S1 is 0.13 to 9.5 atm, the treatment time is 1.2 to 26 h, and the gas flow rate of hydrogen is 600 to 21000 mL / h / g; and / or, The treatment pressure of step S2 is 0 to 21 atm, the treatment time is 3 to 72 h, and the gas flow rate of the mixed gas is 500 to 31000 mL / h / g.

6. A θ-iron carbide composite prepared by the preparation method according to any one of claims 1 to 5.

7. The θ-iron carbide composite according to claim 6, comprising θ-iron carbide and a halogen element, and the molar ratio of the θ-iron carbide to the halogen element is 100:(0.1-40); wherein, The halogen element is bromine element and / or iodine element; the molar number of θ-iron carbide is based on the molar number of iron element contained therein; the average grain diameter of the composite is 7 to 42 nm.

8. The θ-iron carbide composite according to claim 7, wherein, The molar ratio of θ-iron carbide to the halogen element is 100:(0.35 to 32); and / or, The composite includes other cationic elements, and the molar ratio of θ-iron carbide to the other cationic elements is 100:(0.1 to 22), further 100:(0.1 to 18); The other cationic elements are selected from one or more of molybdenum ions, rare earth ions, chromium ions, alkali metal ions, alkaline earth metal ions, cobalt ions, manganese ions, and copper ions.

9. A catalyst, comprising the θ-iron carbide composite prepared by the preparation method according to any one of claims 1 to 5 or the θ-iron carbide composite according to any one of claims 6 to 8.

10. Application of the θ-iron carbide composite prepared by the preparation method according to any one of claims 1 to 5, the θ-iron carbide composite according to any one of claims 6 to 8 or the catalyst according to claim 9 in the synthesis gas conversion reaction.

11. Use of the θ-iron carbide composite prepared by the preparation method according to any one of claims 1 to 5, the θ-iron carbide composite according to any one of claims 6 to 8, or the catalyst according to claim 9 in a reaction for synthesizing C and H fuels and / or chemicals based on the Fischer-Tropsch synthesis principle.

12. A syngas conversion process comprising contacting the catalyst according to claim 9 with syngas under reaction conditions for reaction.

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