Supported epsilon / epsilon '-iron carbide compound as well as preparation method and application thereof

Abstract

The invention relates to a supported epsilon / epsilon '-iron carbide compound as well as a preparation method and application thereof, the method comprises the following steps: (a) carrying out reduction treatment on a supported precursor through hydrogen at the temperature of 350-530 DEG C to obtain a reduction product; (b) treating the reduction product in a first gas atmosphere at 75-185 DEG C to obtain a pretreatment product; and (c) treating the pre-treated product in a second gas atmosphere at 200-300 DEG C to form a product containing epsilon / epsilon '-iron carbide. The epsilon / epsilon '-iron carbide compound disclosed by the embodiment of the invention can be used as a catalyst for a synthesis gas conversion reaction, and halogen ions such as bromine or iodine are introduced into the epsilon / epsilon'-iron carbide compound, so that the reaction has relatively high CO conversion rate and extremely low total CO2 selectivity, and comprehensive optimization of a reaction result is realized.

Description

Technical Field

[0001] The present invention belongs to the field of syngas conversion, and relates to a supported ε / ε'-iron carbide composite that can be used for syngas conversion. Background Art

[0002] Syngas is a mixed gas obtained by gasifying coal, natural gas, and biomass (its composition is CO and H2). 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 syngas conversion 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 syngas conversion. Iron-based catalysts have the advantages of high activity, a wide applicable condition window, strong sulfur resistance, simple online catalyst replacement, and suitability for industrial continuous production. However, one of the bottleneck problems in 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 prior art discloses a high-purity iron carbide catalyst that can reduce the primary CO2 of the Fischer-Tropsch synthesis reaction to nearly zero, and at the same time can achieve a high CO space-time conversion rate, thereby reducing the total CO2 selectivity to <5% at a low CO conversion rate (usually lower than 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 a high CO conversion rate. Summary of the Invention

[0010] To overcome at least one defect of the above-mentioned prior art, in a first aspect, an embodiment of the present invention provides a method for preparing a supported ε / ε'-iron carbide composite, comprising the following steps:

[0011] (a) Reducing a supported precursor at a temperature of 350 to 530 °C with hydrogen to obtain a reduction product;

[0012] (b) Treating the reduction product in a first gas atmosphere at 75 to 185 °C to obtain a pretreated product;

[0013] (c) Treating the pretreated product in a second gas atmosphere at 200 to 300 °C to form a product containing ε / ε'-iron carbide;

[0014] Wherein, the first gas includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide is 1.2:1 to 2.8:1; the second gas includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide is 1:1 to 3.2:1;

[0015] The supported precursor is an iron-containing carrier subjected to a second impregnation treatment with an impregnating solution, and the product containing ε / ε'-iron carbide is the supported ε / ε'-iron carbide composite, and the impregnating solution contains iodide ions and / or bromide ions; alternatively, the supported precursor is an iron-containing carrier, and the product containing ε / ε'-iron carbide is subjected to a third impregnation treatment in the impregnating solution to obtain the supported ε / ε'-iron carbide composite;

[0016] The preparation process of the iron-containing carrier includes: subjecting the carrier to a first impregnation treatment with an aqueous solution containing iron ions, and then drying and calcining the obtained product.

[0017] In a second aspect, an embodiment of the present invention provides an ε / ε'-iron carbide composite prepared by the above-mentioned preparation method.

[0018] In a third aspect, an embodiment of the present invention provides a catalyst, comprising the ε / ε'-iron carbide composite prepared by the above-mentioned preparation method or the above-mentioned ε / ε'-iron carbide composite.

[0019] In a fourth aspect, an embodiment of the present invention provides the application of the ε / ε'-iron carbide composite prepared by the above-mentioned preparation method, the above-mentioned ε / ε'-iron carbide composite or the above-mentioned catalyst in the synthesis gas conversion reaction.

[0020] In a fifth aspect, an embodiment of the present invention provides the use of the ε / ε'-iron carbide composite prepared by the above preparation method, the above ε / ε'-iron carbide composite, or the above catalyst in a reaction for synthesizing C and H fuels and / or chemicals based on the Fischer-Tropsch synthesis principle.

[0021] In a sixth aspect, an embodiment of the present invention provides a syngas conversion process, which includes contacting the above catalyst with syngas under reaction conditions for reaction.

[0022] The ε / ε'-iron carbide composite of an embodiment of the present invention can be used as a catalyst for syngas conversion reactions, especially Fischer-Tropsch synthesis reactions. By introducing halide ions such as bromine or iodine into the ε / ε'-iron carbide composite, the reaction has a high CO conversion rate, an extremely low total CO2 selectivity, and a low CH4 selectivity, achieving an overall optimization of the reaction results. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings are only for the purpose of showing specific embodiments and are not considered to be a limitation of the present invention. Among them:

[0024] Figure 1 is the XRD pattern of the ε / ε'-iron carbide composite CX1 prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] Typical embodiments reflecting 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 changes in different embodiments, all of which do not depart from the scope of the present invention, and the descriptions therein are essentially for illustrative purposes and not for limiting the present invention.

[0026] An embodiment of the present invention provides an ε / ε'-iron carbide composite, which includes ε / ε'-iron carbide, halide ions, and optional promoter cations. The molar ratio of ε / ε'-iron carbide, halide ions, and promoter cations is 100:(0.15 - 46):(0 - 25), and the molar number of ε / ε'-iron carbide is calculated based on the molar number of iron elements contained therein;

[0027] Among them, the halide ions are bromide ions and / or iodide ions. The composite has a hexagonal, pseudo-hexagonal, or trigonal crystal system structure, and its average grain diameter is 4 - 32 nm, and further can be 5 - 27 nm.

[0028] In one embodiment, the molar ratio of ε / ε’-iron carbide to halide ions can be 100:(0.15 - 46), further can be 100:(0.5 - 30), 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.

[0029] In one embodiment, the molar ratio of ε / ε’-iron carbide to promoter cations can be 100:(0.1 - 21), further can be 100:(0.1 - 10), such as 100:0.5, 100:1, 100:5, 100:10, 100:15, 100:20.

[0030] In one embodiment, the ε / ε’-iron carbide complex includes halide cations, and the halide cations can maintain charge balance with halide ions, that is, the total negative charge (or the total valence shown) of halide ions is equal to the total positive charge of halide cations.

[0031] In one embodiment, the ε / ε’-iron carbide complex includes promoter anions, and the promoter cations can maintain charge balance with the promoter anions.

[0032] In one embodiment, the halide cations include one or more of first metal ions and complex cations. Further, the first metal ions include 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), neodymium ions (such as trivalent and tetravalent neodymium ions); the complex cations include one or more of hexaammine manganese ions, hexaammine iron ions, and hexaammine copper ions.

[0033] In one embodiment, the promoter cations include one or more of second metal ions. The second metal ions can include 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 second metal ions can be one or more of 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.

[0034] In one embodiment, the promoter anion includes one or more of oxygen ions, complex ions, and acid radical ions, such as nitrate, citrate, and gluconate.

[0035] One embodiment of the present invention provides a method for preparing a supported ε / ε'-iron carbide composite, comprising the following steps:

[0036] (a) Reducing the supported precursor at a temperature of 350-530 °C with hydrogen to obtain a reduction product;

[0037] (b) Treating the reduction product in a first gas atmosphere at 75-185 °C to obtain a pretreated product;

[0038] (c) Treating the pretreated product in a second gas atmosphere at 200-300 °C to form a product containing ε / ε'-iron carbide;

[0039] Wherein, the first gas includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide is 1.2:1 to 2.8:1; the second gas includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide is 1:1 to 3.2:1;

[0040] The supported precursor is an iron-containing carrier subjected to a second impregnation treatment with an impregnating solution, and the impregnating solution contains bromide ions and / or iodide ions; alternatively, the supported precursor is an iron-containing carrier, and the product containing ε / ε'-iron carbide is subjected to a third impregnation treatment in the impregnating solution;

[0041] The preparation process of the iron-containing carrier includes: subjecting the carrier to a first impregnation treatment in an aqueous solution containing iron ions, and drying and calcining the impregnated carrier.

[0042] In one embodiment, the iron content in the supported precursor is 10-30 wt%, such as 12 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%.

[0043] In one embodiment, the carrier includes one or more of silica, alumina, titanium dioxide, niobium pentoxide, and zirconia. Further, the particle size of the carrier is 30-200 μm, such as 50 μm, 60 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm.

[0044] In one embodiment, an aqueous solution containing iron ions is prepared by dissolving at least one solute in a first solvent, and the at least one solute includes an iron salt, and the iron salt includes one or more of ferric nitrate, ferric chloride, ammonium ferrous sulfate, and ammonium ferric citrate.

[0045] In one embodiment, the first solvent comprises water.

[0046] In one embodiment, the drying treatment performed on the carrier after impregnation comprises the following process: drying the impregnated carrier at 20 - 30 °C for 0.5 - 4 h, then drying it at 35 - 80 °C under a vacuum of 250 - 1200 Pa for 6 - 12 h, and then drying the dried material at 110 - 150 °C for 3 - 24 h.

[0047] In one embodiment, the temperature of the calcination treatment after the drying treatment is 200 - 550 °C, such as 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C; the time is 1 - 10 h, such as 2 h, 4 h, 5 h, 6 h, 8 h.

[0048] In one embodiment, the impregnating solution is prepared by dissolving one or more solutes in a second solvent. The one or more solutes include halides and optionally additives; the halides include water-soluble bromides and / or iodides. The impregnating solutions used for the second impregnation treatment and the third impregnation treatment are the same. Herein, "optionally" means it can include or not include. For example, according to the above description, the one or more solutes can include halides or can include halides and additives.

[0049] In one embodiment, the halides include one or more of bromides and iodides containing copper, manganese, cobalt, rare earth metal elements, iron, and molybdenum; for example, the halides can include 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.

[0050] In one embodiment, the additives 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 additives include 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.

[0051] In one embodiment, no chemical reaction occurs between the solute components of the same solution. For example, the solutes of the impregnating solution do not simultaneously include potassium carbonate and calcium nitrate.

[0052] In one embodiment, the amounts of the halide and the additive can be appropriately selected according to the contents of the respective ions in the composite to be prepared. Further, the concentrations of both the halide and the additive can be 0.7 to 7 mol / L, such as 1 mol / L, 2 mol / L, 3 mol / L, 5 mol / L, 6 mol / L.

[0053] In one embodiment, the second solvent includes water and / or ethanol. For example, the second solvent can be water or a mixture of ethanol and water.

[0054] In one embodiment, the temperature of the first impregnation treatment, the second impregnation treatment, or the third impregnation treatment is 0 to 50 °C, further can be 20 to 30 °C, such as 10 °C, 15 °C, 20 °C, 30 °C, 35 °C, 40 °C, 45 °C; the time of the first impregnation treatment, the second impregnation treatment, or the third impregnation treatment can be 0.1 to 12 h, further can be 0.2 to 10 h, still further can be 0.3 to 9 h, such as 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h.

[0055] In one embodiment, the material after the second impregnation treatment or the third impregnation treatment can be dried at 15 to 40 °C, and further dried under light-shielded conditions. The drying temperature can be, for example, 20 °C, 25 °C, 30 °C, 35 °C; the drying time can be 0.5 to 12 h. The drying treatment can be carried out under normal pressure or reduced pressure conditions.

[0056] In one embodiment, the first impregnation treatment, the second impregnation treatment, or the third impregnation treatment can adopt one of the slurry impregnation method, the saturated impregnation method, the supersaturated impregnation method, or other feasible impregnation methods.

[0057] In one embodiment, the temperature of the reduction and surface purification treatment in step (a) can be 350 to 530 °C, such as 360 °C, 380 °C, 390 °C, 400 °C, 420 °C, 450 °C, 460 °C, 480 °C, 500 °C; the treatment pressure can be 0.1 to 9 atm, further can be 0.3 to 2.1 atm, such as 0.2 atm, 0.5 atm, 0.8 atm, 1 atm, 1.5 atm, 2 atm, 2.5 atm, 5 atm, 8 atm; the treatment time can be 0.7 to 15 h, further can be 1 to 12 h, such as 2 h, 3 h, 5 h, 8 h, 10 h.

[0058] In one embodiment, the gas flow rate of H2 in step (a) can be 600 - 25000 mL / h / g, further can be 2800 - 22000 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, 18000 mL / h / g, 20000 mL / h / g.

[0059] In one embodiment, the first gas in step (b) includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide can be 1.2:1 - 2.8:1, such as 1.5:1, 1.8:1, 2:1, 2.2:1, 2.5:1.

[0060] In one embodiment, the pre-treatment temperature in step (b) can be 75 - 185 °C, such as 80 °C, 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, 150 °C, 160 °C, 180 °C; the treatment pressure can be 0.05 - 5 atm, further can be 0.08 - 2.5 atm, such as 0.1 atm, 0.2 atm, 0.5 atm, 0.8 atm, 1 atm, 1.2 atm, 1.5 atm, 1.8 atm, 2 atm, 3 atm, 4 atm, 5 atm; the treatment time can be 15 - 120 min, further can be 20 - 90 min, such as 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 80 min, 100 min.

[0061] In one embodiment, the gas flow rate of the first gas in step (b) can be 300 - 12000 mL / h / g, further can be 1500 - 9000 mL / h / g, such as 500 mL / h / g, 1000 mL / h / g, 1800 mL / h / g, 2000 mL / h / g, 3000 mL / h / g, 4000 mL / h / g, 5000 mL / h / g, 6000 mL / h / g, 7000 mL / h / g, 10000 mL / h / g.

[0062] In one embodiment, the molar ratio of hydrogen to carbon monoxide in the second gas in step (c) can be 1.2:1, 1.5:1, 1.8:1, 2:1, 2.2:1, 2.5:1, 2.8:1, 3:1. The second gas can be a mixture of hydrogen and carbon monoxide.

[0063] In one embodiment, the treatment temperature in step (c) can be 200 - 300 °C, such as 210 °C, 230 °C, 250 °C, 260 °C, 270 °C, 280 °C; the treatment pressure can be 0.1 - 12 atm, further can be 0.2 - 4.5 atm, such as 0.5 atm, 0.8 atm, 1 atm, 1.2 atm, 1.5 atm, 1.8 atm, 2 atm, 2.2 atm, 2.8 atm, 3 atm, 3.5 atm, 4 atm, 5 atm, 8 atm; the treatment time can be 1.5 - 15 h, further can be 2.5 - 12 h, such as 2 h, 3 h, 4 h, 5 h, 6 h, 9 h, 10 h.

[0064] In one embodiment, the gas flow rate of the second gas in step (c) can be 500 - 30000 mL / h / g, further can be 3000 - 25000 mL / h / g, such as 1000 mL / h / g, 4000 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, 20000 mL / h / g, 22000 mL / h / g.

[0065] In one embodiment, in step (c), the temperature of the system is raised from 75 - 185 °C to 200 - 300 °C at a heating rate of 0.1 - 5.5 °C / min, and further, the temperature of the system is raised from 75 - 185 °C to 210 - 290 °C at a heating rate of 0.15 - 2.0 °C / min; the heating rate in step (c) 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.

[0066] In one embodiment, preferably, steps (a), (b), (c) and the first, second, and third impregnation treatments are all carried out under light - shielding conditions.

[0067] In one embodiment, a method for preparing a supported ε / ε’ - iron carbide composite includes the following steps:

[0068] (a - 0) Perform a first impregnation treatment on the carrier in an aqueous solution containing iron ions, and dry and calcine the impregnated carrier to obtain an iron - containing carrier; perform a second impregnation treatment on the iron - containing carrier in an impregnation solution to obtain a supported precursor; wherein the impregnation solution contains bromide ions and / or iodide ions;

[0069] (a) The supported precursor is reduced by hydrogen at a temperature of 350 - 530 °C to obtain a reduced product;

[0070] (b) The reduced product is treated at 75 - 185 °C in a first gas atmosphere to obtain a pretreated product;

[0071] (c) The pretreated product is treated at 200 - 300 °C in a second gas atmosphere to obtain a supported ε / ε'-iron carbide composite.

[0072] In another embodiment, a method for preparing a supported ε / ε'-iron carbide composite includes the following steps:

[0073] (a-0) The support is subjected to a first impregnation treatment in an aqueous solution containing iron ions, and the impregnated support is dried and calcined to obtain a supported precursor;

[0074] (a) The supported precursor is reduced by hydrogen at a temperature of 350 - 530 °C to obtain a reduced product;

[0075] (b) The reduced product is treated at 75 - 185 °C in a first gas atmosphere to obtain a pretreated product;

[0076] (c) The pretreated product is treated at 200 - 300 °C in a second gas atmosphere to form a product containing ε / ε'-iron carbide;

[0077] (c-1) The product containing ε / ε'-iron carbide obtained in step (c) is subjected to a second impregnation treatment with an impregnating solution to obtain a halogen element-containing ε / ε'-iron carbide composite.

[0078] One embodiment of the present invention provides a catalyst comprising the above-mentioned ε / ε'-iron carbide composite.

[0079] One embodiment of the present invention provides the application of the above-mentioned ε / ε'-iron carbide composite or catalyst in the synthesis gas conversion reaction.

[0080] 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 alcohols as the final product.

[0081] In one embodiment, the synthesis gas comprises CO and H2.

[0082] One embodiment of the present invention provides the application of the above ε / ε'-iron carbide composite or catalyst in the reaction for synthesizing C and 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 the reaction in which syngas (a mixture of CO and H2) is used as a raw material, and through the CO hydrogenation and carbon chain growth reactions under the action of a catalyst and appropriate conditions, to produce chain hydrocarbons and / or their oxygen-containing derivatives.

[0083] In one embodiment, the above reaction is a Fischer-Tropsch synthesis reaction, the reaction temperature can be 250-295 °C, such as 260 °C, 270 °C, 280 °C, 290 °C; the reaction pressure can be 2-3.5 MPa, and the molar ratio of H2 / CO can be 1.7-2.15.

[0084] One embodiment of the present invention provides a syngas conversion process, which includes contacting the above catalyst with syngas for reaction under syngas conversion reaction conditions.

[0085] In one embodiment, the syngas conversion can be carried out in a high-temperature and high-pressure continuous reactor.

[0086] The ε / ε'-iron carbide composite of one embodiment of the present invention can be used as a catalyst for the syngas conversion reaction. By introducing halide ions into the ε / ε'-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 ε / ε'-iron carbide composite catalyst, it shows considerable activity.

[0087] The ε / ε'-iron carbide composite of one embodiment of the present invention can be used as a catalyst for the syngas conversion reaction, which can keep the reaction with an extremely low CO2 selectivity under 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 bottlenecks, and promoting the high-end, diversification and low-carbonization of the clean conversion of syngas, pointing out new trends and directions for the development of modern syngas chemical industry.

[0088] The ε / ε'-iron carbide composite of one embodiment of the present invention, as a catalyst for the Fischer-Tropsch synthesis reaction, can maintain 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%, and further below 3%; the selectivity of its by-product CH4 can be maintained below 8.5%, and further below 5.5%; the utilization efficiency of carbon atoms is maintained above 95%, and further above 97%; the selectivity of effective products can reach above 86.5%, and further above 92%.

[0089] In one embodiment, through the Fischer-Tropsch synthesis reaction catalyzed by the ε / ε’-iron carbide composite, a CO2 selectivity of <5%, a carbon atom utilization efficiency of >95%, and an effective product selectivity of >88% can be achieved at a CO conversion rate of over 70%.

[0090] 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 + interacting with Br - and Br atoms that interact with H atoms by covalent bonds.

[0091] All pressure values involved herein are gauge pressures.

[0092] Hereinafter, in conjunction with the accompanying drawings and specific embodiments, an ε / ε’-iron carbide composite and its application in one embodiment of the present invention will be further described. Among them, the test methods involved are as follows:

[0093] 1. During the reaction process of the examples or comparative examples, an in-situ XRD detector (Rigaku, model D / max-2600 / PC) was used to monitor the phase change of the materials, and the crystal system structure of the ε / ε’-iron carbide composite was measured by the X-ray diffractometer.

[0094] 2. The average grain diameter of the ε / ε’-iron carbide composite was obtained by XRD testing.

[0095] 3. The ε / ε’-iron carbide composite was detected by Mossbauer spectroscopy (Transmission 57Fe, 57Co(Rh) source sinusoidal velocity spectrometer) to obtain the corresponding composition.

[0096] 4. The ε / ε’-iron carbide composite was detected for elements by an inductively coupled plasma emission spectrometer (ICP).

[0097] 5. During the conversion reaction of syngas, the products obtained from the reaction were analyzed by gas chromatography (Agilent 7890 gas chromatography) for calculating conversion rates, selectivities, etc. The products refer to the tail gas collected from the end of the reactor, including the generated hydrocarbon compounds, alcohol compounds, CO2, etc.

[0098] 6. The CO conversion rate %, CO2 selectivity %, CH4 selectivity %, carbon atom utilization efficiency %, and effective product selectivity % were calculated by the following formulas:

[0099] CO conversion rate % = [(moles of CO in feed - moles of CO in product) / moles of CO in feed] × 100%;

[0100] CO2 selectivity % = [moles of CO2 in product / (moles of CO in feed - moles of CO in product)] × 100%;

[0101] CH4 selectivity % = [moles of CH4 in product / (moles of CO in feed - moles of CO in product)] × 100%;

[0102] Carbon atom utilization efficiency % = (1 - CO2 selectivity %) × 100%;

[0103] Effective product selectivity % = (1 - CO2 selectivity % - CH4 selectivity %) × 100%.

[0104] Example 1

[0105] (a - 0) Weigh 30 g of silica as the carrier, and impregnate the carrier in an aqueous solution of ammonium ferric citrate, where the ammonium ferric citrate solution is weighed and prepared according to the content of 30 wt% of iron element in the final carrier; dry the impregnated carrier at 29 °C for 1 h, then dry it in a vacuum drying oven at 40 °C and a vacuum degree of 200 Pa for 12 h, dry the dried material in an oven at 125 °C for 12 h, and then calcine the obtained material in a muffle furnace at 370 °C for 5 h to obtain an iron-containing carrier as the supported precursor.

[0106] (a) At a pressure of 450 °C and 1.0 atm, keep the supported precursor in H2 with a flow rate of 13000 mL / h / g for 3 h for reduction and surface purification treatment to obtain a reduced product.

[0107] (b) Cool the reduced product to 150 °C and contact it with the first gas at this temperature for pre-treatment to obtain a pre-treated product; where the pressure of the system is 1.3 atm, the gas flow rate of the first gas is 7700 mL / h / g, the treatment time is 60 min, and the first gas is a mixture of H2 and CO with a molar ratio of H2:CO = 2.5:1.

[0108] (c) Contact the pre-treated product with the second gas, the pressure of the system is 2.2 atm, the total gas flow rate is 17000 mL / h / g, and under this condition, heat the system from 150 °C to 250 °C at a heating rate of 1.3 °C / min for carbide preparation; where the second gas is a mixture of H2 and CO with a molar ratio of H2:CO = 1.6:1, and the treatment time of the material at 250 °C is 5 h.

[0109] (c-1) Dissolve manganese bromide and potassium nitrate in 50 ml of water to obtain an impregnation solution; weigh the sample obtained in step (c), disperse it in the impregnation solution, 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 35 °C, and the impregnation time is 5.5 h. After the treatment, a supported ε / ε'-iron carbide composite is prepared and labeled as CX1.

[0110] Examples 1-1 to 3-8 are all prepared with substantially the same raw materials and processes as Example 1 to prepare the supported ε / ε'-iron carbide composite, except that: the content or type of halide ions or promoter cations in the impregnation solution is different, and the prepared composites are sequentially labeled as CX1-1 to CX3-8 using the same numbers as in Example 1. Since the loss of materials during the preparation process is extremely small, the content of each substance in the obtained composite is basically the same as the dosage of the corresponding raw materials. For specific content values, see Table 1.

[0111] Example 4

[0112] (a-0) Weigh 30 g of silica as the carrier, impregnate the carrier in an aqueous solution of ammonium ferric citrate, and weigh and prepare the ammonium ferric citrate solution according to the content of 30 wt% of iron element in the final carrier; dry the impregnated carrier at 29 °C for 1 h, then dry it in a vacuum drying oven at 40 °C and a vacuum degree of 200 Pa for 12 h, dry the dried material in an oven at 125 °C for 12 h, and then calcine the obtained material in a muffle furnace at 500 °C for 5 h to obtain an iron-containing carrier as the supported precursor.

[0113] (a) At a pressure of 400 °C and 1.5 atm, keep the supported precursor in H2 with a flow rate of 13000 mL / h / g for 3 h to perform reduction and surface purification treatment to obtain a reduction product.

[0114] (b) Cool the reduction product to 170 °C and contact it with the first gas at this temperature for pre-treatment to obtain a pre-treatment product; wherein, the pressure of the system is 1.3 atm, the gas flow rate of the first gas is 7700 mL / h / g, the treatment time is 60 min, and the first gas is a mixture of H2 and CO, and the molar ratio of the two is H2:CO = 2:1.

[0115] (c) Contact the pre-treatment product with the second gas, the pressure of the system is 2.2 atm, the total gas flow rate is 17000 mL / h / g, and under this condition, heat the system from 150 °C to 280 °C at a heating rate of 1.3 °C / min to prepare the carbide; wherein, the second gas is a mixture of H2 and CO, and the molar ratio of the two is H2:CO = 1.6:1, and the treatment time of the material at 280 °C is 5 h.

[0116] (c-1) Dissolve manganese bromide, potassium citrate, and cobalt nitrate in 50 ml of water to obtain an impregnation solution; weigh the sample obtained in step (c), disperse it in the impregnation solution, and perform impregnation treatment by the slurry impregnation method. The impregnation ratio (molar ratio) is Fe:Br:K:Co = 100:15:3.0:5.0, the impregnation temperature is 35 °C, and the impregnation time is 5.5 h. After the treatment, a supported ε / ε'-iron carbide composite is prepared and labeled as CX4.

[0117] Example 4-1

[0118] This example uses substantially the same raw materials and process as Example 1 to prepare a supported ε / ε'-iron carbide composite, with the only difference being that in step (c), the carbonization temperature is 200 °C. The finally prepared supported ε / ε'-iron carbide composite is labeled as CX4-1.

[0119] Example 4-2

[0120] This example uses substantially the same raw materials and process as Example 1 to prepare a supported ε / ε'-iron carbide composite, with the only difference being that in step (c), the carbonization temperature is 300 °C. The finally prepared supported ε / ε'-iron carbide composite is labeled as CX4-2.

[0121] Example 4-3

[0122] This example uses substantially the same raw materials and process as Example 1 to prepare a supported ε / ε'-iron carbide composite, with the only difference being that in step (c), the molar ratio of hydrogen to carbon monoxide in the second gas is 1:1. The finally prepared supported ε / ε'-iron carbide composite is labeled as CX4-3.

[0123] Example 4-4

[0124] This example uses substantially the same raw materials and process as Example 1 to prepare a supported ε / ε'-iron carbide composite, with the only difference being that in step (c), the molar ratio of hydrogen to carbon monoxide in the second gas is 3.2:1. The finally prepared supported ε / ε'-iron carbide composite is labeled as CX4-4.

[0125] Example 4-5

[0126] This example uses substantially the same raw materials and process as Example 1 to prepare a supported ε / ε'-iron carbide composite, with the only difference being that in step (c), the system pressure is 0.2 atm. The finally prepared supported ε / ε'-iron carbide composite is labeled as CX4-5.

[0127] Example 4-6

[0128] This example uses substantially the same raw materials and process as Example 1 to prepare the supported ε / ε'-iron carbide composite, with the only difference being that: step (a) is carried out under reduction at 220 °C and a pressure of 4.5 atm. The finally prepared supported ε / ε'-iron carbide composite is labeled as CX4-6.

[0129] Examples 4-7

[0130] This example uses substantially the same raw materials and process as Example 1 to prepare the supported ε / ε'-iron carbide composite, with the only difference being that: in step (b), the pressure of the system is 0.08 atm, and the molar ratio of hydrogen to carbon monoxide in the first gas is 1.2:1. The finally prepared supported ε / ε'-iron carbide composite is labeled as CX4-7.

[0131] Examples 4-8

[0132] This example uses substantially the same raw materials and process as Example 1 to prepare the supported ε / ε'-iron carbide composite, with the only difference being that: in step (b), the pressure of the system is 2.5 atm, and the molar ratio of hydrogen to carbon monoxide in the first gas is 2.8:1. The finally prepared supported ε / ε'-iron carbide composite is labeled as CX4-8.

[0133] Examples 4-9

[0134] This example uses substantially the same raw materials and process as Example 1 to prepare the supported ε / ε'-iron carbide composite, with the only difference being that: in step (c), the system pressure is 2.5 atm and the treatment is for 12 h. The finally prepared supported ε / ε'-iron carbide composite is labeled as CX4-9.

[0135] Examples 4-10

[0136] This example uses substantially the same raw materials and process as Example 1 to prepare the supported ε / ε'-iron carbide composite, with the only difference being that: step (a) is carried out at 350 °C for 12 h. The finally prepared supported ε / ε'-iron carbide composite is labeled as CX4-10.

[0137] Examples 4-11

[0138] This example uses substantially the same raw materials and process as Example 1 to prepare the supported ε / ε'-iron carbide composite, with the only difference being that: in step (c), the total gas flow rate is 25000 mL / h / g, and the system is heated from 150 °C to 270 °C at a heating rate of 2 °C / min. The finally prepared supported ε / ε'-iron carbide composite is labeled as CX4-11.

[0139] Example 5

[0140] (a-0) Weigh 30 g of zirconia as the carrier, and impregnate the carrier in an aqueous solution of iron nitrate. Weigh and prepare the aqueous solution of iron nitrate according to the content of 20 wt% of elemental iron in the final carrier. Dry the impregnated carrier at 30 °C for 3 h, then dry it in a vacuum drying oven at 70 °C under a vacuum of 400 Pa for 6 h. Dry the dried material in an oven at 120 °C for 12 h, and then calcine the obtained material in a muffle furnace at 550 °C for 5 h to obtain an iron-containing carrier.

[0141] Dissolve manganese bromide and potassium gluconate in 100 ml of water to prepare an impregnating solution. Weigh 28 g of the above-prepared iron-containing carrier, disperse it in the impregnating solution, 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 35 °C, and the impregnation time is 3 h. Then dry it in a vacuum drying oven at 35 °C under a vacuum of 300 Pa for 12 h to obtain a supported precursor.

[0142] (a) At a temperature of 450 °C and a pressure of 2.0 atm, hold the supported precursor in H2 with a flow rate of 20000 mL / h / g for 10 h to perform reduction and surface purification treatment to obtain a reduced product.

[0143] (b) Cool the reduced product to 180 °C and contact it with the first gas at this temperature for pretreatment to obtain a pretreated product. Among them, the pressure of the system is 2 atm, the gas flow rate of the first gas is 8000 mL / h / g, the treatment time is 40 min, and the first gas is a mixture of H2 and CO, and the molar ratio of the two is H2:CO = 1.5:1.

[0144] (c) Contact the pretreated product with the second gas. The pressure of the system is 4.5 atm, the total gas flow rate is 20000 mL / h / g, and under this condition, the system is heated from 180 °C to 280 °C at a heating rate of 1.5 °C / min to prepare a carbide. Among them, the second gas is a mixture of H2 and CO, and the molar ratio of the two is H2:CO = 2:1. The treatment time of the material at 280 °C is 12 h. After the treatment is completed, a supported ε / ε’-iron carbide composite is prepared and marked as CX5.

[0145] Comparative Example 1

[0146] In this example, an ε / ε’-iron carbide composite was prepared using substantially the same raw materials and process as in Example 1, except that: in step (c-1), the impregnation ratio (molar ratio) was Fe:Br:K = 100:50.0:2.0. The finally prepared supported ε / ε’-iron carbide composite was marked as DX1.

[0147] Comparative Example 2

[0148] In this example, ε / ε'-iron carbide composite was prepared using substantially the same raw materials and process as in Example 1, except that: in the preparation of the impregnation solution in step (c-1), manganese bromide was not added. The finally obtained ε / ε'-iron carbide composite was labeled as D2.

[0149] Comparative Example 3

[0150] In this example, ε / ε'-iron carbide composite was prepared using substantially the same raw materials and process as in Example 1, except that: in the preparation of the impregnation solution in step (c-1), manganese chloride was used to replace manganese bromide in an equimolar amount. The finally obtained ε / ε'-iron carbide composite was labeled as DX3.

[0151] Comparative Example 4

[0152] ε / ε'-iron carbide was prepared using exactly the same raw materials and steps as in steps (a-0) to (c) of Example 1, but the impregnation step of (c-1) was not carried out. It was labeled as D4.

[0153] Comparative Example 5

[0154] Supported ε / ε'-iron carbide composite was prepared using exactly the same raw materials and steps as in steps (a-0) to (c-1) of Example 1, except that: in the second gas in step (c), the molar ratio of H2 and CO was H2:CO = 0.5:1. The finally obtained supported ε / ε'-iron carbide composite was labeled as DX5.

[0155] The ε / ε'-iron carbide composites, ε / ε'-iron carbide, etc. prepared in each example and comparative example were subjected to XRD, Mössbauer spectroscopy and ICP measurements. The content of ε / ε'-iron carbide was calculated based on 100 mol, and the relevant contents all refer to the number of moles. The specific results are shown in Table 1.

[0156] In a slurry bed continuous reactor, the catalytic reaction performance of the ε / ε'-iron carbide composites, ε / ε'-iron carbide, etc. prepared in each example and comparative example was evaluated respectively. The catalyst loading was 9.0 g. Evaluation conditions: T = 257 °C, P = 2.75 MPa, H2:CO = 2.0:1, (H2 + CO) total amount = 13000 mL / h / g- Fe (standard state flow rate, relative to 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 are shown in Tables 2 and 3.

[0157] Table 1

[0158]

[0159]

[0160] Table 2

[0161]

[0162]

[0163] Table 3

[0164]

[0165]

[0166] Based on the above results, when the ε / ε’-iron carbide composite containing halogen ions such as bromine or iodine prepared in the examples of the present invention is used as a catalyst for the syngas conversion reaction under industrial conditions, it can exhibit ultra-low CO2 selectivity, relatively low CH4 selectivity, extremely high carbon atom utilization efficiency, and effective product selectivity while 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 ε / ε’-iron carbide composite in the examples of the present invention was continuously operated for a long period in a stirred tank 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 operating stability. Therefore, by using the ε / ε’-iron carbide composite in the examples of the present invention as a catalyst for the syngas conversion reaction, comprehensive optimization of the reaction results can be achieved.

[0167] Unless otherwise specified, the terms used in the present invention have the meanings commonly understood by those skilled in the art.

[0168] The embodiments described in the present invention are for illustrative purposes only 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 preparation method of a supported ε / ε’-iron carbide composite, comprising the following steps: (a) Reducing a supported precursor at a temperature of 350 - 530 °C with hydrogen to obtain a reduction product; (b) Treating the reduction product in a first gas atmosphere at 75 - 185 °C to obtain a pretreated product; (c) Treating the pretreated product in a second gas atmosphere at 200 - 300 °C to form a product containing ε / ε’-iron carbide; Wherein, The first gas includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide is from 1.2:1 to 2.8:1; the second gas includes hydrogen and carbon monoxide, and the molar ratio of hydrogen to carbon monoxide is from 1:1 to 3.2:1; The supported precursor is an iron-containing carrier subjected to a second impregnation treatment with an impregnating solution, and the product containing ε / ε’-iron carbide is the supported ε / ε’-iron carbide composite, and the impregnating solution contains iodide ions and / or bromide ions; or, the supported precursor is an iron-containing carrier, and the product containing ε / ε’-iron carbide is subjected to a third impregnation treatment in the impregnating solution to obtain the supported ε / ε’-iron carbide composite; The preparation process of the iron-containing carrier includes: subjecting the carrier to a first impregnation treatment with an aqueous solution containing iron ions, and then drying and calcining the obtained product.

2. The preparation method according to claim 1, wherein, The preparation raw materials of the aqueous solution containing iron ions include a first solvent and at least one solute, the at least one solute includes an iron salt, and the iron salt includes one or more of ammonium ferrous sulfate, ferric chloride, ferric nitrate, and ammonium ferric citrate; and / or, The carrier includes one or more of titanium dioxide, alumina, silica, zirconia, and niobium pentoxide; and / or, The preparation raw materials of the impregnating solution include one or more solutes, the one or more solutes include halides and optional auxiliaries; the halides include water-soluble bromides and / or iodides.

3. The preparation method according to claim 2, wherein, The halides include one or more of bromides and iodides containing copper, manganese, cobalt, rare earth metal elements, iron, and molybdenum; and / or, The particle size of the carrier is from 30 μm to 200 μm; and / or, The auxiliaries include one or more of salts of manganese, molybdenum, cobalt, copper, alkaline earth metals, rare earth metals, and alkali metals.

4. The preparation method according to claim 1, wherein, The material after the second impregnation treatment or the third impregnation treatment is dried at 15 - 40 °C; and / or, The temperature of the calcination treatment is from 200 °C to 550 °C; and / or, The temperature of the first impregnation treatment, the second impregnation treatment, or the third impregnation treatment is from 0 to 50 °C, and the time is from 0.1 to 12 h.

5. The preparation method according to claim 1, wherein, The treatment pressure of step (a) is from 0.1 to 9 atm, preferably from 0.3 to 2.1 atm; the treatment time is from 0.7 to 15 h, preferably from 1 to 12 h; and / or, The treatment pressure of step (b) is from 0.05 to 5 atm, preferably from 0.08 to 2.5 atm; the treatment time is from 15 to 120 min, preferably from 20 to 90 min; and / or, The treatment pressure of step (c) is from 0.1 to 12 atm, preferably from 0.2 to 4.5 atm; the treatment time is from 1.5 to 15 h.

6. An ε / ε’-iron carbide composite prepared by the preparation method according to any one of claims 1 to 5.

7. The composite according to claim 6, comprising ε / ε’-iron carbide, halide ions and optional promoter cations, and the molar ratio of ε / ε’-iron carbide, the halide ions and the promoter cations is 100:(0.15 - 46):(0 - 25), and the molar number of ε / ε’-iron carbide is calculated based on the molar number of iron element contained therein; wherein, The halide ion is bromide ion and / or iodide ion.

8. The composite according to claim 7, wherein, The molar ratio of ε / ε’-iron carbide to the halogen element is 100:(0.5 - 30); and / or, The molar ratio of ε / ε’-iron carbide to the auxiliary cation is 100:(0.1 - 21); and / or, The promoter cations include one or more of the second metal ions. Further, the promoter cations include one or more of cobalt ions, copper ions, chromium ions, alkaline earth metal ions, alkali metal ions, molybdenum ions, rare earth ions, and manganese ions.

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

10. Use of an ε / ε'-iron carbide composite prepared by the preparation method according to any one of claims 1 to 5, an ε / ε'-iron carbide composite according to any one of claims 6 to 8, or the catalyst according to claim 9 in a syngas conversion reaction.

11. Use of an ε / ε'-iron carbide composite prepared by the preparation method according to any one of claims 1 to 5, an ε / ε'-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, H fuels and / or chemicals based on the Fischer-Tropsch synthesis principle.

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

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