3D-printed iron-based fischer-tropsch synthesis catalyst and method of making

Abstract

The application provides a 3D printing iron-based fischer-tropsch synthesis catalyst and a preparation method, the catalyst is connected by a plurality of standardized units obtained by direct writing 3D printing through a mortise-tenon structure, and the catalyst is internally distributed with a through hole structure; the standardized unit comprises an inlet unit, a transition unit and an outlet unit which are sequentially connected, wherein the pore size of the hole in the inlet unit is greater than the pore size of the hole in the outlet unit; the catalyst is designed as a standardized unit, the units are connected through a mortise-tenon structure, precise stacking and close contact can be realized, and the voidage fluctuation problem of a traditional granular catalyst is avoided. When amplification is needed, only the number of units needs to be increased, and the unit structure and the preparation process do not need to be changed; through path design of direct writing 3D printing, the large hole of the inlet unit is coupled with high Fe / high additive content, and the small hole of the outlet section is coupled with low Fe / low additive content, so that the structure and the component are synergistically optimized.

Description

Technical Field

[0001] This invention relates to the field of iron-based Fischer-Tropsch synthesis catalysts and their preparation technology, and particularly to a 3D-printed iron-based Fischer-Tropsch synthesis catalyst and its preparation method. Background Technology

[0002] Low-carbon olefins (ethylene, propylene, and butene) are among the most important basic raw materials in the chemical industry, widely used in the production of plastics, synthetic rubber, solvents, pharmaceuticals, and fine chemicals. Currently, the production of low-carbon olefins mainly relies on naphtha steam cracking, a process highly dependent on petroleum resources. my country has relatively abundant coal resources; therefore, developing a technological route for producing low-carbon olefins using coal-based syngas as a feedstock is of significant strategic importance for ensuring national energy security and the supply of chemical raw materials.

[0003] Fischer-Tropsch synthesis (FTS) is an important catalytic process for converting syngas (a mixture of CO and H2) into liquid hydrocarbons or olefins. Iron-based catalysts are widely used in Fischer-Tropsch to olefin (FTO) reactions due to their advantages such as wide operating conditions, high product tunability, and strong adaptability to the H2 / CO ratio in the syngas. However, traditional iron-based Fischer-Tropsch synthesis catalysts are typically used in powder or microsphere form, which presents significant technical bottlenecks.

[0004] In recent years, 3D printing (additive manufacturing) technology has offered new possibilities for the design and preparation of structured catalysts. Through 3D printing, the macroscopic geometry and internal pore distribution of catalysts can be precisely controlled, enabling "on-demand" catalyst configurations. However, current 3D printing catalyst technology is still in the early exploratory stage in the Fischer-Tropsch synthesis field, and a complete solution capable of meeting industrial needs has not yet been formed. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention provides a 3D-printed iron-based Fischer-Tropsch synthesis catalyst and its preparation method. The catalyst has a multi-level pore structure with gradient distribution inside, which meets the requirements for industrial-scale use.

[0006] The specific details of the invention are as follows: In a first aspect, the present invention provides a 3D-printed iron-based Fischer-Tropsch synthesis catalyst, wherein the catalyst is formed by connecting multiple standardized units obtained by direct-write 3D printing through a tenon-and-mortise structure, and the catalyst has a through-hole structure distributed axially inside. The standardized unit includes an inlet unit, a transition unit, and an outlet unit connected in sequence, wherein the diameter of the orifice in the inlet unit is larger than the diameter of the orifice in the outlet unit.

[0007] Optionally, the channels in the inlet unit are distributed in a straight line along the catalyst axis, and the channels in the outlet unit are distributed in a spiral or serpentine pattern along the catalyst axis.

[0008] Optionally, the catalyst comprises: a support component, an iron-based active phase, and an auxiliary component; The carrier comprises an inorganic oxide, or a composite of the inorganic oxide and a ceramic material, wherein the inorganic oxide is selected from at least one of alumina, silicon oxide, zirconium oxide and titanium oxide, and the ceramic material is selected from any one of cordierite, silicon carbide and mullite. The iron-based active phase includes iron carbides; The additive components include alkali metals and transition metals; The mass percentage of the iron-based active phase and auxiliary components located in the inlet unit is greater than the mass percentage of the iron-based active phase and auxiliary components located in the outlet unit.

[0009] Optionally, the iron carbide located in the inlet unit is mainly χ-Fe5C2, and the iron carbide located in the outlet unit is mainly θ-Fe3C.

[0010] Optionally, the alkali metal is selected from at least one of K, Na, and Li; The transition metal is selected from at least one of Mn, Cu, Zn, and Cr.

[0011] Optionally, the catalyst further includes a halogen control layer modified on the inner wall of the pore structure, the halogen control layer comprising at least one of Br, Cl and I.

[0012] In a second aspect, the present invention provides a method for preparing the 3D-printed iron-based Fischer-Tropsch synthesis catalyst described in the first aspect above, the preparation method comprising: The raw materials for catalyst preparation are powder materials that constitute the carrier, precursor powder materials that constitute the iron-based active phase, and precursor powder materials that constitute the auxiliary components. After being mixed with binder, dispersant and deionized water, the mixture is wet-milled to obtain a slurry. The slurry is loaded into the barrel of a direct-write 3D printer, and 3D printing is performed according to the pre-designed three-dimensional model of the catalyst to obtain the inlet unit green body, the transition unit green body and the outlet unit green body that make up the catalyst. After drying the green body obtained from 3D printing, it is transferred to a carbon-containing atmosphere for programmed temperature-controlled carbonization to obtain the inlet unit, transition unit and outlet unit that make up the catalyst. The inlet unit, transition unit, and outlet unit are assembled using a tenon-mortise structure to form the 3D-printed iron-based Fischer-Tropsch synthesis catalyst.

[0013] Optionally, the slurry has a solid content of 35-65 vol%, a viscosity of 20-300 Pa·s, and a yield stress of 10-100 Pa. The slurry used for printing the inlet unit preform has a higher iron content and additive component content than the slurry used for printing the outlet unit preform.

[0014] Optionally, the programmed temperature-controlled carbonization process includes: Increase the temperature to 200-300 °C at a rate of 1-5 °C / min, hold for 2-4 h, then continue to increase the temperature to 350-450 °C at a rate of 1-3 °C / min, hold for 2-6 h, and then increase the temperature to 500-650 °C at a rate of 2-5 °C / min, hold for 2-6 h.

[0015] Optionally, after the programmed temperature-controlled carbonization treatment, the method further includes: The carbonized green body is placed in an atmosphere containing halogen compounds and kept at 500-650 °C for 0.5-4 hours to modify the inner wall of the pores in the green body with halogen elements to form a halogen control layer.

[0016] Compared with the prior art, the present invention has the following advantages: This invention provides a 3D-printed iron-based Fischer-Tropsch synthesis catalyst. The catalyst is formed by connecting multiple standardized units obtained through direct-write 3D printing via a mortise and tenon joint structure. The catalyst has a permeable pore structure distributed internally. Each standardized unit includes an inlet unit, a transition unit, and an outlet unit connected in sequence. The pore diameter of the pores in the inlet unit is larger than that in the outlet unit. This invention designs the catalyst as standardized units, with the units connected by mortise and tenon joints, enabling precise stacking and close contact, avoiding the porosity fluctuation problem of traditional particulate catalysts. Scale-up only requires increasing the number of units without changing the unit structure or preparation process. Through the path design of direct-write 3D printing, this invention couples the large pores of the inlet unit with high Fe / high additive content, and the small pores of the outlet section with low Fe / low additive content, achieving synergistic optimization of structure and composition. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating the preparation method of the 3D-printed iron-based Fischer-Tropsch synthesis catalyst provided in an embodiment of the present invention is shown. Figure 2 A schematic diagram of the structure of the 3D-printed iron-based Fischer-Tropsch synthesis catalyst provided in an embodiment of the present invention is shown. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention. Furthermore, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of the present invention.

[0020] Specific experimental steps or conditions are not specified in the embodiments; they can be performed according to the conventional experimental steps or conditions described in the prior art. Reagents and other instruments used, unless otherwise specified, are all commercially available conventional reagent products. Furthermore, the accompanying drawings are merely illustrative diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore, repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0021] Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of this specification.

[0022] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] To facilitate understanding of the technical solution of this invention, the relevant technologies of iron-based Fischer-Tropsch synthesis catalysts are described as follows: (1) Traditional powdered iron-based Fischer-Tropsch synthesis catalyst Traditional powdered catalysts are prepared using co-precipitation or impregnation methods to form the Fe-Mn-K / Al2O3 system, which is then compressed into 2 mm diameter particles and packed into a fixed-bed reactor for use. This is currently the most widely used form of Fischer-Tropsch synthesis catalyst in industry. However, this technology has the following problems: 1) Low mass transfer efficiency; when powdered catalysts are packed in a fixed-bed reactor, gas must navigate through numerous tortuous channels between particles to reach the active sites, resulting in high internal diffusion resistance. This is particularly problematic for low-carbon olefin products, making rapid desorption difficult and leading to secondary hydrogenation of olefins to form alkanes or cracking to form small molecules, severely limiting olefin selectivity.

[0024] 2) High pressure drop: The low porosity of the powder bed (usually <0.4) results in high gas flow resistance, which increases compressor energy consumption and operating costs, and limits the single-tower capacity of the reactor.

[0025] 3) Uneven heat transfer: Fischer-Tropsch synthesis is a strongly exothermic reaction (ΔH is about -165 kJ / mol CO). The thermal conductivity of the powder bed is low (usually <0.5 W / (m·K)), which easily generates local hot spots. The local temperature can be 50-100 ℃ higher than the average temperature, leading to catalyst sintering deactivation and deterioration of product selectivity.

[0026] 4) Scale-up difficulties: When laboratory-scale powdered catalysts are scaled up to industrial scale, they face problems such as uneven packing, deterioration of heat and mass transfer caused by scale-up effects, and difficulty in accurately controlling catalyst packing density, resulting in channeling and wall effects.

[0027] 5) Fixed distribution of active components: The active components of catalysts prepared by traditional impregnation or co-precipitation methods are uniformly distributed, and cannot be optimized according to the reaction characteristics of different locations in the reactor (high CO conversion rate at the inlet and high selectivity at the outlet).

[0028] The root cause of the above problems is that the geometry of the powdered catalyst is determined by the tableting or extrusion mold, and cannot be optimized in a directional manner according to the flow field and reaction characteristics in the reactor; the voids between the particles are formed by random stacking, which cannot be precisely controlled, resulting in the inability to design the bed structure.

[0029] (2) Metal 3D Printed Autocatalytic Reactor (SCR) This technology involves directly 3D printing metals (Fe / Co / Ni) using selective laser melting (SLM), with the metal bulk serving as an integrated catalyst and reactor structure. However, this technology has the following drawbacks: 1) Low specific surface area; the BET specific surface area of ​​the metallic material is <1 m². 2 / g, the active sites are severely underexposed, resulting in catalyst activity that is much lower than that of powder catalysts; 2) Acid etching is required, which involves using a mixture of HCl and HNO3 to etch the inner surface to increase roughness. The process has poor controllability, and the etching depth and uniformity are difficult to control precisely. 3) The equipment is expensive. The cost of SLM equipment is 10-20 times that of direct-write printers, which limits the promotion and application of the technology. 4) In the additive-free system, the metal matrix lacks the synergistic effect of additives, resulting in limited product selectivity and making it impossible to optimize product distribution through additive regulation.

[0030] The root cause of the above problems is that the metal material printed by SLM is dense and cannot form a porous structure; acid etching is a remedial measure after the fact and cannot accurately control the surface morphology and pore structure.

[0031] (3) Direct-writing 3D printing of denitrification catalyst For example, CN108283944A discloses the use of extrusion 3D printing to prepare honeycomb or lattice structured denitration catalysts. This technology has the following problems: 1) Limited application scope: It is only used for SCR denitration reaction. The catalytic reaction mechanism is completely different from Fischer-Tropsch synthesis, and the technical solution cannot be directly transferred to the FTS field.

[0032] 2) The pore structure is simple, mostly a straight honeycomb structure, without gradient design, and cannot be optimized in a directional manner according to the reaction characteristics of different locations in the reactor.

[0033] 3) The active components are uniformly distributed without a gradient distribution design of additives, which cannot meet the differentiated needs of high activity at the inlet and high selectivity at the outlet.

[0034] 4) Without in-situ carbonization-halogen synergistic regulation, it can be used directly after calcination. Without carbonization crystal phase control and halogen modification, it is impossible to achieve fine control of the selectivity of Fischer-Tropsch synthesis products.

[0035] The root cause of the above problems lies in the significant differences in reaction mechanisms and catalyst requirements between denitration and Fischer-Tropsch synthesis. The design of denitration catalysts failed to consider key requirements in Fischer-Tropsch synthesis, such as product diffusion, chain growth, selectivity control, and carbon deposition inhibition.

[0036] In view of the aforementioned problems with existing solutions, this invention discloses a 3D-printed iron-based Fischer-Tropsch synthesis catalyst and its preparation method. The core of the catalyst utilizes a direct-writing 3D printing process to prepare modular standardized units, which are then assembled integrally using a tenon-and-mortise structure. This results in a continuous gradient pore structure within the catalyst, achieving both axial iron-carbon active phase gradient distribution and component gradient distribution. Furthermore, catalytic performance is regulated by halogen modification of the pore inner walls. This effectively solves the technical defects of traditional iron-based Fischer-Tropsch catalysts, such as high randomness in molding, pore blockage, uneven distribution of active phase, and poor catalytic selectivity and stability. Specific implementation methods are as follows: In a first aspect, the present invention provides a 3D-printed iron-based Fischer-Tropsch synthesis catalyst, wherein the catalyst is formed by connecting multiple standardized units obtained by direct-write 3D printing through a tenon-and-mortise structure, and the catalyst has a through-hole structure distributed inside. The standardized unit includes an inlet unit, a transition unit, and an outlet unit connected in sequence, wherein the diameter of the orifice in the inlet unit is larger than the diameter of the orifice in the outlet unit.

[0037] In practical implementation, the catalyst in this embodiment is assembled from multiple standardized functional units through a mortise and tenon joint structure that allows for disassembly and precise splicing. The overall structure is well-organized, with high assembly precision, enabling modular replacement and large-scale stacking. The standardized unit is divided into an inlet unit, a transition unit, and an outlet unit along the catalyst airflow axis. These three units are integrated and matched with a printed structure, and their ends are equipped with mutually compatible tenons and mortises. After splicing, there are no gaps or air leaks, resulting in high overall structural strength.

[0038] In this embodiment, the catalyst features a continuous gradient pore structure. The core gradient characteristic is that the inlet unit pore diameter is larger than the outlet unit pore diameter. Specifically, the inlet unit pores are straight, regular channels along the catalyst axis, resulting in low airflow resistance and enabling rapid and uniform distribution of the feed gas. This allows reactants to quickly reach the active sites, preventing airflow congestion and localized carbon buildup at the inlet. The outlet unit pores are spirally or serpentinely distributed along the catalyst axis, extending the residence time of the reactant gas, enhancing secondary catalytic reactions, and improving feed conversion. The transition unit features a gradually changing pore structure, achieving a smooth transition from large-diameter straight channels to small-diameter spiral / serpentine channels, avoiding airflow turbulence and sudden pressure drop problems caused by abrupt pore changes.

[0039] In one specific implementation, the inlet unit channel diameter is set to 1.5–3.0 mm, and the outlet unit channel diameter is set to 0.5–1.2 mm. The diameter gradually changes uniformly along the axial direction to ensure the overall channel continuity and airflow stability.

[0040] In one specific embodiment, the catalyst comprises: a support component, an iron-based active phase, and an auxiliary component; The carrier comprises an inorganic oxide, or a composite of the inorganic oxide and a ceramic material, wherein the inorganic oxide is selected from at least one of alumina, silicon oxide, zirconium oxide and titanium oxide, and the ceramic material is selected from any one of cordierite, silicon carbide and mullite. The iron-based active phase includes iron carbides; The additive components include alkali metals and transition metals.

[0041] In specific implementation, the support in this embodiment can be composed of inorganic oxides or inorganic oxide-ceramic composites with high specific surface area and high thermal stability. The inorganic oxide is selected from at least one of alumina, silicon oxide, zirconium oxide, and titanium oxide; the ceramic material is selected from any one of cordierite, silicon carbide, and mullite. The support serves as a framework support, disperses active components, and resists high-temperature sintering. The ceramic component further enhances the overall mechanical strength and thermal stability of the catalyst, adapting to the high-temperature and high-pressure reaction conditions of fixed-bed Fischer-Tropsch synthesis. The promoter is composed of a complex of alkali metals and transition metals, synergistically regulating the phase evolution, surface alkalinity, and electronic structure of active sites of iron carbides. The alkali metal is selected from at least one of K, Na, and Li, with K being preferred, as it significantly enhances CO adsorption activation, inhibits methane formation, and promotes long-chain hydrocarbon formation. The transition metal is selected from at least one of Mn, Cu, Zn, and Cr, with Mn and Cu being preferred. Mn optimizes the dispersion of the active phase, while Cu lowers the reduction temperature of iron species and enhances low-temperature catalytic activity.

[0042] In practice, the mass percentage of iron carbides in the inlet unit (iron content 10-40 wt%) is greater than that in the outlet unit (iron content 5-15 wt%). Similarly, the mass percentage of additive components in the inlet unit is greater than that in the outlet unit. The total additive component content in the inlet unit is 8-15 wt%, while the total additive component content in the outlet unit is 0.5-7 wt%. This gradient trend aligns with the iron-based activity. The high proportion of active phase and high additive component in the inlet unit ensures efficient conversion of the feed gas, while the low proportion of active phase and low additive component in the outlet unit avoids excessive hydrogenation, optimizes product distribution, and achieves staged catalysis throughout the entire process.

[0043] In one specific implementation, the iron carbide located in the inlet unit is mainly composed of χ-Fe5C2, and the iron carbide located in the outlet unit is mainly composed of θ-Fe3C.

[0044] In specific implementation, the iron-based active phase in this embodiment is an iron carbide system, which is the core active site for Fischer-Tropsch synthesis. This invention achieves a precise axial phase gradient distribution: the iron carbide in the catalyst inlet unit is mainly composed of highly active χ-Fe5C2, with the χ-Fe5C2 content accounting for 60-90% of the total weight of the iron-based active phase in this section. χ-Fe5C2 has high olefin selectivity and high chain growth probability, suitable for the high CO conversion requirements of the inlet section; the iron carbide in the outlet unit is mainly composed of highly stable θ-Fe3C, with the θ-Fe3C content accounting for 50-80% of the total weight of the iron-based active phase in this section. θ-Fe3C has moderate olefin selectivity and strong anti-carbon deposition ability, suitable for the long-term stable operation requirements of the outlet section.

[0045] In one specific embodiment, the catalyst further includes a halogen control layer modified on the inner wall of the pore structure, the halogen control layer comprising at least one of Br, Cl and I.

[0046] In this embodiment, the inner wall of the catalyst channel is uniformly modified with a halogen regulation layer. Under Fischer-Tropsch synthesis conditions, halogen atoms (Br, Cl, I) can be dynamically adsorbed and desorbed on the catalyst surface, promoting surface oxygen cycling, inhibiting excessive CO dissociation (inhibiting CH4 generation), and promoting CO bond retention (promoting olefin generation).

[0047] Secondly, the present invention provides a method for preparing the 3D-printed iron-based Fischer-Tropsch synthesis catalyst described in the first aspect above. Figure 1 A flowchart illustrating the preparation method of the 3D-printed iron-based Fischer-Tropsch synthesis catalyst provided in an embodiment of the present invention is shown, as follows: Figure 1 As shown, the preparation method includes: S1. Using precursor powder materials that form the carrier, precursor powder materials that form the iron-based active phase, and precursor powder materials that form the auxiliary components as catalyst preparation raw materials, the raw materials are mixed with binder, dispersant and deionized water and then wet-milled to obtain slurry. S2. The slurry is loaded into the barrel of a direct-write 3D printer, and 3D printing is performed according to the pre-designed three-dimensional model of the catalyst to obtain the inlet unit green body, transition unit green body and outlet unit green body that make up the catalyst. S3. After drying the green body obtained by 3D printing, transfer it to a carbon-containing atmosphere for programmed temperature-controlled carbonization to obtain the inlet unit, transition unit and outlet unit that make up the catalyst. S4. The inlet unit, transition unit and outlet unit are modularly assembled using a tenon-mortise structure to form the 3D printed iron-based Fischer-Tropsch synthesis catalyst.

[0048] The first step in this embodiment is the 3D printing of a catalyst framework with multi-level channels. These channels are axially distributed throughout the catalyst and formed by a gradient change in the direct-write 3D printing path. The framework itself possesses a mesoporous / microporous multi-level structure. Furthermore, the iron-based active phase and promoter components are distributed in a gradient along the axial direction within the catalyst framework. Specifically, a three-dimensional model of the overall catalyst structure can be designed based on the geometry of the target reactor, reaction conditions, and syngas flow rate distribution. The three-dimensional model includes an inlet unit, an outlet unit, and a transition unit. Along the catalyst axis, the channels within the inlet unit are straight-through channels, the outlet unit has a spiral or serpentine channel structure, and the transition unit between them has a gradually changing channel structure that bridges the gap between the inlet and outlet units. CFD simulations are used to optimize the geometric parameters (channel diameter, wall thickness, and stagger angle) and the gradient distribution parameters of the active phase and promoter components for each channel segment. Simultaneously, a tenon-and-mortise connection structure between the catalyst units is designed.

[0049] In practice, the inlet unit (near the reactant gas inlet) has a parallel straight-through channel structure with a channel diameter of 1.0-5.0 mm and a channel wall thickness of 0.5-2.0 mm. The high syngas concentration and fast reaction rate are addressed by the large straight-through channels, which ensure low diffusion resistance and allow reactants to quickly reach the active sites. The outlet unit (near the reactant gas outlet) has a serpentine / spiral channel structure with a channel diameter of 0.1-2.0 mm and a channel wall thickness of 0.3-1.0 mm. As the CO concentration decreases, the staggered small channels enhance turbulent mixing, promote product diffusion and desorption, and suppress secondary hydrogenation. The transition unit, located between the inlet and outlet units, gradually transitions from straight-through channels to serpentine / spiral channels, achieving a smooth transition from laminar to turbulent flow.

[0050] In specific implementation, the precursor powder material constituting the iron-based active phase can be selected from at least one of iron-containing soluble salts, such as ferric nitrate, ferric chloride, ferric citrate, ferric acetylacetone, ferric sulfate, and ferrous oxalate; the powder material constituting the carrier can be selected from Al2O3, SiO2, ZrO2, or TiO2; the precursor powder material constituting the auxiliary component can be selected from soluble salts containing auxiliary metal components, such as manganese nitrate, manganese chloride, copper nitrate, copper chloride, zinc nitrate, zinc chloride, chromium nitrate, potassium nitrate, potassium carbonate, potassium hydroxide, sodium nitrate, and sodium carbonate; the binder is selected from polyvinyl alcohol or hydroxypropyl methylcellulose; and the dispersant is selected from ammonium polyacrylate or ammonium citrate.

[0051] In one specific implementation scheme, based on the total mass of the printing slurry, the following components are used: carrier powder 25-45 wt%, iron-based active phase precursor powder 25-45 wt%, auxiliary agent precursor powder 8-15 wt%, binder 1-5 wt%, dispersant 0.5-3 wt%, and the balance being deionized water; the slurry solid content is 35-65 vol%, viscosity is 20-300 Pa·s, and yield stress is 10-100 Pa. Furthermore, the iron content and auxiliary agent content in the slurry used for printing the inlet unit green body are greater than those in the slurry used for printing the outlet unit green body. Therefore, during 3D printing, two sets of slurries can be prepared for printing the inlet and outlet unit green bodies respectively. The transition unit green body can be printed using either of these slurries, or the two sets of slurries can be mixed in a specific ratio before printing the transition unit.

[0052] During the printing process, the slurry used for printing the inlet unit green body, outlet unit green body, and transition unit green body is sequentially loaded into the multi-cylinder system (2-5 cylinders) of the direct-write 3D printer. Segmented direct-write 3D printing is performed according to the designed 3D model; axial gradient changes in the content of active components are achieved by switching cylinders; radial gradient changes in the pore structure are achieved by adjusting the movement path of the printing nozzles; printing parameters include: nozzle diameter 0.2-2.0 mm, printing speed 2-40 mm / s, extrusion pressure 0.2-4.0 MPa, and layer thickness 0.2-1.5 mm.

[0053] Furthermore, the 3D-printed green body was dried for 24-72 hours under programmed temperature and humidity control conditions with a temperature gradient of 20-80℃ and a relative humidity gradient of 90%-40%. An example drying program was as follows: 25℃, 85% relative humidity, static drying for 12 hours; temperature increased to 35℃, 70% relative humidity, static drying for 12 hours; temperature further increased to 50℃, 55% relative humidity, static drying for 12 hours; temperature further increased to 70℃, 45% relative humidity, static drying for 12 hours; temperature further increased to 80℃, 40% relative humidity, static drying for 12 hours.

[0054] Furthermore, the dried green body is subjected to in-situ carbonization in a carbon-containing atmosphere. The carbon-containing atmosphere includes at least one of CO, CH4, and C2H4, and may also include a reducing gas H2 or a N2-H2 mixture (H2 volume fraction 5-30%). The carbonization rate of different carbonization stages is controlled by adjusting the molar ratio of CO / CH4 in the carbon-containing atmosphere.

[0055] In practical implementation, this invention utilizes segmented programmed heating for in-situ carbonization. Taking advantage of the natural difference in iron content between the inlet and outlet sections, the carbonization temperature is controlled to directionally regulate the iron carbide crystal phase composition in different sections, eliminating the need for additional crystal phase control steps. The segmented programmed heating includes: a first stage: heating at 1-5°C / min to 200-300°C and holding for 2-4 hours. This stage primarily involves nitrate decomposition and iron oxide reduction. A second stage: heating at 1-3°C / min to 350-450°C and holding for 2-6 hours. This stage marks the beginning of iron carbide crystal nuclei formation. A third stage: heating at 2-5°C / min to 500-650°C and holding for 2-6 hours. This stage allows for the full growth of the iron carbide crystal phase. During in-situ carbonization, the inlet unit, with its higher iron content and stronger reducing atmosphere, preferentially forms iron carbides with χ-Fe5C2 as the main phase; the outlet section, with its lower iron content, forms iron carbides with θ-Fe3C as the main phase.

[0056] Furthermore, during the later stage of the third stage of in-situ carbonization or after the end of the heat preservation process (at an ambient temperature of 500-650°C), a halogen-containing compound is introduced into the reaction atmosphere for in-situ modification of the pore inner wall. The halogen-containing compound is selected from CH3Br, CH3Cl, CH3I, HBr, and HCl. The introduction rate is 0.1-100 ppmv, and the modification time is 0.5-4 hours. A pulsed introduction method is preferred, with a pulse period of 5-30 minutes, a pulse duration of 1-5 minutes, a halogen-containing compound concentration of 5-50 ppmv during the pulse, and a concentration of 0.1-5 ppmv during the pulse interval. Pulsed introduction can reduce the amount of halogen used while ensuring the modification effect.

[0057] Furthermore, the catalyst components are modularly assembled using a tenon-mortise structure. During assembly, the contact surfaces of adjacent units are coated with an Al2O3-SiO2 high-temperature binder to obtain an industrial-scale catalyst assembly.

[0058] To enable those skilled in the art to more clearly understand the present invention, the following embodiments are provided to illustrate in detail a 3D-printed iron-based Fischer-Tropsch synthesis catalyst and its preparation method.

[0059] Example 1 (1) 3D model design See Figure 2The schematic diagram shows a columnar monolithic catalyst assembled from two inlet units, one transition unit, and one outlet unit (each unit φ50 mm × 100 mm) using mortise and tenon joints. Each unit features a gradient pore structure; the inlet unit contains 49 parallel straight-through pores with a diameter of 3.0 mm and a wall thickness of 1.0 mm. The transition unit features gradually decreasing and increasing numbers of straight-through pores, then arranged in a serpentine pattern, with the pore diameter gradually decreasing from 3.0 mm to 1.5 mm and the number of pores increasing to 98. The outlet unit maintains the serpentine pore distribution with a diameter of 1.5 mm and a wall thickness of 0.6 mm. CFD simulation optimization confirmed that the straight-through pores in the inlet section resulted in a pressure drop of <0.05 MPa / m, while the staggered pores in the outlet section increased turbulence intensity by 40%.

[0060] (2) Slurry preparation Slurry for inlet unit preparation: 40 g α-Al₂O₃ powder (particle size 10 μm), 45 g ferric nitrate (Fe(NO₃)₃·9H₂O), 8 g manganese nitrate (Mn(NO₃)₂·4H₂O), 5 g potassium nitrate (KNO₃), 3 g copper nitrate (Cu(NO₃)₂·3H₂O), 6 g polyvinyl alcohol (PVA), 1.5 g ammonium polyacrylate, and 35 g deionized water. Ball milling for 6 hours resulted in a solid content of 50 vol% and a viscosity of 120 Pa·s.

[0061] Slurry for the outlet and transition units: 55 g α-Al₂O₃ powder, 12 g ferric nitrate, 2 g manganese nitrate, 0.5 g potassium nitrate, 0.3 g copper nitrate, and other additives as in the inlet section. Solid content: 50 vol%, viscosity: 80 Pa·s.

[0062] (3) Segmented direct writing 3D printing A dual-tube printer is used. Tube A contains the printing paste for the inlet unit, and tube B contains the printing paste for the outlet and transition units. The printing parameters are as follows: nozzle diameter 1.0 mm, printing speed 15 mm / s, layer thickness 0.6 mm, and extrusion pressure 1.2 MPa.

[0063] (4) Programmable temperature and humidity controlled drying The printed green blanks were placed in a constant temperature and humidity chamber for drying for 60 hours. The temperature and humidity control process was as follows: at 25℃ and 85% relative humidity, the blanks were left to dry for 12 hours; the temperature was increased to 35℃ and 70% relative humidity, and the blanks were left to dry for 12 hours; the temperature was further increased to 50℃ and 55% relative humidity, and the blanks were left to dry for 12 hours; the temperature was further increased to 70℃ and 45% relative humidity, and the blanks were left to dry for 12 hours; the temperature was further increased to 80℃ and 40% relative humidity, and the blanks were left to dry for 12 hours.

[0064] (5) Segmented programmed heating in-situ carbonization The dried green billets were placed in a tube furnace and a CO / H2 / N2 mixture (volume ratio 20:5:75) was introduced. The heating process consisted of three stages: Stage 1: heating at 1 °C / min to 250 °C and holding for 3 hours; Stage 2: heating at 2 °C / min to 400 °C and holding for 6 hours; Stage 3: heating at 3 °C / min to 600 °C and holding for 4 hours.

[0065] (6) In-situ modification in a halogen atmosphere During the last hour of the third stage of carbonization at 600 °C, CH3Br was introduced into the atmosphere at a concentration of 10 ppmv.

[0066] (7) Mortise and tenon assembly Four catalyst units are connected by a tenon-mortise joint, and the contact surfaces are coated with Al2O3-SiO2 high-temperature binder to assemble a whole catalyst with a diameter of 50 mm × 400 mm.

[0067] The active phase and promoter content of the inlet unit obtained by catalyst composition analysis are as follows: Fe 32 wt%, Mn 5 wt%, K 3 wt%, Cu 1.5 wt%; The active phase and additive content of the outlet unit obtained by catalyst composition analysis are as follows: Fe 10 wt%, Mn 1 wt%, K 0.3 wt%, Cu 0.2 wt%.

[0068] XRD analysis showed that the iron-carbon compounds in the inlet unit were mainly χ-Fe5C2 (relative content of about 75%), with small amounts of θ-Fe3C and α-Fe; the iron-carbon compounds in the outlet unit were mainly θ-Fe3C (relative content of about 65%), with small amounts of χ-Fe5C2 and Fe3O4.

[0069] Catalytic performance evaluation: The assembled catalyst was packed into a fixed-bed reactor, and syngas (H2 / CO = 2.0) was introduced. The reaction temperature was 340 °C, the pressure was 2.0 MPa, and the volumetric space velocity was 2000 h⁻¹. -1 .

[0070] After 200 hours of reaction, the CO conversion rate was 95%; the C2-C4 olefin selectivity was 76%; the methane selectivity was 5%; the CO2 selectivity was 2.5%; and the bed pressure drop was 1 / 15 of that of traditional powder catalysts.

[0071] Example 2 (1) 3D model design Same as Example 1.

[0072] (2) Slurry preparation 45 g of γ-Al₂O₃ powder (5 μm particle size), 25 g of Fe₂O₃ nanoparticles (50 nm particle size), 4 g of MnO₂ powder, 2 g of K₂CO₃ powder, 1.5 g of CuO powder, 5 g of ZrO₂ powder, 7 g of hydroxypropyl methylcellulose (HPMC), 2 g of ammonium citrate, and 30 g of deionized water were mixed and ball-milled for 8 hours. The slurry was divided into two portions: one portion was supplemented with an additional 20 g of Fe₂O₃ nanoparticles as the inlet unit slurry (high Fe), and the other portion was used as the outlet unit slurry (low Fe).

[0073] Steps (3)-(7) are the same as in Example 1.

[0074] Catalytic performance evaluation: The reaction conditions were the same as in Example 1. After 200 hours of reaction, the CO conversion rate was 85%, the C2-C4 olefin selectivity was 72%, the methane selectivity was 6%, and the CO2 selectivity was 3.2%.

[0075] Example 2 simplifies the slurry preparation process, but the accuracy of the gradient control of active components is slightly lower than that of the segmented independent preparation method in Example 1.

[0076] Example 3 (1) 3D model design and Figure 2 The difference between the structural schematic diagrams shown is that the three-dimensional model designed in this embodiment is an integral catalyst suitable for small experimental reactors, which does not require mortise and tenon assembly; the design size is φ20 mm × 50 mm, the diameter of the straight channel in the inlet section is 1.0 mm, and the number of channels is 25; the straight channels in the transition section gradually decrease in size and increase in number, and then are distributed in a serpentine pattern, with the channel diameter gradually decreasing from 1.0 mm to 0.5 mm, and the number of channels increasing to 50; the diameter of the serpentine channel in the outlet section is 0.5 mm, and the number of channels increases to 50.

[0077] (2) Slurry preparation Same as Example 1.

[0078] (3) Printing parameters Nozzle diameter 0.6 mm, printing speed 8 mm / s, layer thickness 0.3 mm.

[0079] Steps (4)-(6) are the same as in Example 1.

[0080] Catalytic performance evaluation: The reaction conditions were the same as in Example 1, but the volume hourly space velocity was increased to 5000 h⁻¹. -1 (Due to the reduced catalyst volume, the space velocity needs to be increased to maintain a sufficient residence time.) After 200 hours of reaction, the CO conversion rate was 80%, and the C conversion rate was... 2-The C4 olefin selectivity was 78% (high pore density facilitates rapid product desorption), the methane selectivity was 4%, and the CO2 selectivity was 2%.

[0081] Example 4 (1) 3D model design The industrial-scale catalyst is designed with an overall size of φ200 mm × 2000 mm and is assembled from 20 standardized catalyst units (9 inlet units, 9 outlet units and 2 transition units, each unit φ200 mm × 100 mm) through mortise and tenon joints.

[0082] The inlet unit contains 1600 parallel straight-through channels with a diameter of 4.0 mm and a wall thickness of 1.5 mm. The transition unit features a gradual decrease in the size and increase in the number of straight-through channels, which then form a serpentine distribution. The channel diameter gradually decreases from 4.0 mm to 2 mm, and the number of channels increases to 3200. The outlet unit maintains a serpentine channel distribution with a diameter of 2 mm and a wall thickness of 0.8 mm. CFD simulation optimization confirmed that the straight-through channels in the inlet section resulted in a pressure drop of <0.03 MPa / m, while the staggered channels in the outlet section increased the turbulence intensity by 35%.

[0083] (2) Segmented slurry preparation The slurry for the inlet unit preparation consisted of: 4.0 kg of α-Al₂O₃ powder (15 μm particle size), 4.5 kg of ferric nitrate, 0.8 kg of manganese nitrate, 0.5 kg of potassium nitrate, 0.3 kg of copper nitrate, 0.6 kg of polyvinyl alcohol, 0.15 kg of ammonium polyacrylate, and 3.5 kg of deionized water. After ball milling for 8 hours, the solid content was 55 vol%, and the viscosity was 150 Pa·s.

[0084] Slurry for the outlet and transition units: 5.5 kg α-Al₂O₃ powder, 1.2 kg ferric nitrate, 0.2 kg manganese nitrate, 0.05 kg potassium nitrate, 0.03 kg copper nitrate, and other additives as in the inlet section. Solid content 55 vol%, viscosity 100 Pa·s.

[0085] (3) Segmented direct writing 3D printing It uses a large-format direct-write 3D printer with a dual-barrel system. Printing parameters: nozzle diameter 1.5 mm, printing speed 10 mm / s, extrusion pressure 2.0 MPa, layer thickness 0.8 mm.

[0086] (4) Programmable temperature and humidity controlled drying The green body was placed in a large constant temperature and humidity drying kiln and dried for 72 hours. The temperature and humidity control process was as follows: at 25℃ and 90% relative humidity, it was left to dry for 18 hours; the temperature was increased to 35℃ and 75% relative humidity, and it was left to dry for 18 hours; the temperature was further increased to 55℃ and 55% relative humidity, and it was left to dry for 18 hours; the temperature was further increased to 80℃ and 40% relative humidity, and it was left to dry for 18 hours.

[0087] (5) Segmented programmed heating in-situ carbonization The dried green billets were placed in an industrial tube furnace, and a CO / H2 / N2 mixture (volume ratio 20:5:75) was introduced. The heating process consisted of three stages: Stage 1: heating to 250 °C at 0.8 °C / min and holding for 4 hours; Stage 2: heating to 400 °C at 1.5 °C / min and holding for 8 hours; Stage 3: heating to 600 °C at 2.5 °C / min and holding for 6 hours.

[0088] (6) In-situ modification in a halogen atmosphere During the last 2 hours of the third stage of carbonization at 600℃, CH3Br was introduced into the atmosphere at a concentration of 8 ppmv using a pulsed method (pulse cycle of 15 minutes, pulse duration of 2 minutes, concentration of 20 ppmv during the pulse, and concentration of 2 ppmv during the intermittent period).

[0089] (7) Mortise and tenon modular assembly Twenty catalyst units are connected by tenons and mortises, with the contact surfaces coated with Al2O3-SiO2 high-temperature binder, and assembled into an industrial-scale monolithic catalyst with a diameter of φ200 mm × 2000 mm. The overall compressive strength of the assembled catalyst was tested: axial compressive strength >10 MPa, radial compressive strength >8 MPa.

[0090] The active phase and promoter content of the inlet unit obtained by catalyst composition analysis are as follows: Fe 30 wt%, Mn 4.8 wt%, K 2.8 wt%, Cu 1.2 wt%. The active phase and additive content of the outlet unit obtained by catalyst composition analysis are as follows: Fe 9.5 wt%, Mn 0.9 wt%, K 0.25 wt%, Cu 0.15 wt%.

[0091] XRD analysis showed that the iron-carbon compounds in the inlet unit were mainly χ-Fe5C2 (relative content of about 72%), while those in the outlet unit were mainly θ-Fe3C (relative content of about 68%).

[0092] Catalytic performance evaluation The assembled industrial-scale catalyst was loaded into an industrial pilot-scale fixed-bed reactor, and syngas (H2 / CO = 2.0) was introduced. The reaction temperature was 340 °C, the pressure was 2.5 MPa, and the volume hourly space velocity was 2500 h⁻¹. -1 .

[0093] After 500 hours of reaction (long-term industrial-scale evaluation), the CO conversion rate was 94%, the C2-C4 olefin selectivity was 75%, the methane selectivity was 5.2%, the CO2 selectivity was 2.6%, and the bed pressure drop was 0.08 MPa (only 1 / 12 of the pressure drop of a conventional powder bed of the same scale).

[0094] Magnification verification conclusion: Comparing performance data of Example 1 (laboratory scale, φ50 mm × 400 mm) and Example 5 (industrial scale, φ200 mm × 2000 mm): Table 1 Catalyst Performance Indicators

[0095] The comparison in Table 1 shows that the performance deviations of the laboratory-scale catalyst and the industrial-scale catalyst are all within 1%, proving that the mortise and tenon modular assembly strategy of this invention can achieve direct digital scale-up from laboratory to industrial scale, and the scale-up effect is negligible.

[0096] Comparative Example 1 is a traditional powdered catalyst Fe-Mn-K-Cu / Al2O3 powder catalyst (Fe:Mn:K:Cu:Al2O3=25:4:2.5:1:67.5, weight ratio) was prepared by co-precipitation and then pressed into granules with a diameter of 2 mm.

[0097] Catalytic performance evaluation: The reaction conditions were the same as in Example 1. After 200 hours of reaction, the CO conversion rate was 60%, the C2-C4 olefin selectivity was 48%, the methane selectivity was 15%, the CO2 selectivity was 18%, and the bed pressure drop was 15 times that of Example 1. Comparative Example 2 The difference between the 3D model design and Example 1 is that the internal pore structure of the catalyst is a uniform straight channel (same as the internal pore structure of the inlet unit in Example 1). The same preparation process as Example 1 is used, and the printing slurry used is the same as the slurry used to prepare the inlet unit in Example 1 (Fe content 20 wt uniformly distributed).

[0098] The catalytic performance was evaluated under the same reaction conditions as in Example 1. After 200 hours of reaction, the CO conversion rate was 75%, the C2-C4 olefin selectivity was 62%, the methane selectivity was 8%, the CO2 selectivity was 8%, and the pressure drop was twice that of Example 1.

[0099] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0100] For the sake of simplicity, the method embodiments are described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0101] The foregoing has provided a detailed description of a 3D-printed iron-based Fischer-Tropsch synthesis catalyst and its preparation method. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only intended to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A 3D-printed iron-based Fischer-Tropsch synthesis catalyst, characterized in that, The catalyst is formed by connecting multiple standardized units obtained by direct writing 3D printing through a mortise and tenon joint structure, and the catalyst has a through-hole structure distributed along the axial direction. The standardized unit includes an inlet unit, a transition unit, and an outlet unit connected in sequence, wherein the diameter of the orifice in the inlet unit is larger than the diameter of the orifice in the outlet unit.

2. The 3D-printed iron-based Fischer-Tropsch synthesis catalyst according to claim 1, characterized in that, The channels in the inlet unit are distributed in a straight line along the catalyst axis, while the channels in the outlet unit are distributed in a spiral or serpentine pattern along the catalyst axis.

3. The 3D-printed iron-based Fischer-Tropsch synthesis catalyst according to claim 1, characterized in that, The catalyst comprises: a support component, an iron-based active phase, and an auxiliary component; The carrier comprises an inorganic oxide, or a composite of the inorganic oxide and a ceramic material, wherein the inorganic oxide is selected from at least one of alumina, silicon oxide, zirconium oxide and titanium oxide, and the ceramic material is selected from any one of cordierite, silicon carbide and mullite. The iron-based active phase includes iron carbides; The additive components include alkali metals and transition metals; The mass percentage of the iron-based active phase and auxiliary components located in the inlet unit is greater than the mass percentage of the iron-based active phase and auxiliary components located in the outlet unit.

4. The 3D-printed iron-based Fischer-Tropsch synthesis catalyst according to claim 3, characterized in that, The iron carbides located in the inlet unit are mainly χ-Fe5C2 phase, while the iron carbides located in the outlet unit are mainly θ-Fe3C phase.

5. The 3D-printed iron-based Fischer-Tropsch synthesis catalyst according to claim 3, characterized in that, The alkali metal is selected from at least one of K, Na and Li; The transition metal is selected from at least one of Mn, Cu, Zn, and Cr.

6. The 3D-printed iron-based Fischer-Tropsch synthesis catalyst according to claim 1, characterized in that, The catalyst further includes a halogen control layer, which is modified on the inner wall of the pore structure, and the composition of the halogen control layer includes at least one of Br, Cl and I.

7. A method for preparing a 3D-printed iron-based Fischer-Tropsch synthesis catalyst according to any one of claims 1-6, characterized in that, The preparation method includes: The raw materials for catalyst preparation are powder materials that constitute the carrier, precursor powder materials that constitute the iron-based active phase, and precursor powder materials that constitute the auxiliary components. After being mixed with binder, dispersant and deionized water, they are wet-milled and mixed to prepare a slurry. The slurry is loaded into the barrel of a direct-write 3D printer, and 3D printing is performed according to the pre-designed three-dimensional model of the catalyst to obtain the inlet unit green body, the transition unit green body and the outlet unit green body that make up the catalyst. After drying the green body obtained from 3D printing, it is transferred to a carbon-containing atmosphere for programmed temperature-controlled carbonization to obtain the inlet unit, transition unit and outlet unit that make up the catalyst. The inlet unit, transition unit, and outlet unit are modularly assembled using a tenon-mortise structure to form the 3D-printed iron-based Fischer-Tropsch synthesis catalyst.

8. The method for preparing the 3D-printed iron-based Fischer-Tropsch synthesis catalyst according to claim 7, characterized in that, The slurry has a solid content of 35-65 vol%, a viscosity of 20-300 Pa·s, and a yield stress of 10-100 Pa. The slurry used for printing the inlet unit preform has a higher iron content and additive component content than the slurry used for printing the outlet unit preform.

9. The method for preparing the 3D-printed iron-based Fischer-Tropsch synthesis catalyst according to claim 7, characterized in that, The programmed temperature-controlled carbonization process includes: Increase the temperature to 200-300 °C at a rate of 1-5 °C / min, hold for 2-4 h, then continue to increase the temperature to 350-450 °C at a rate of 1-3 °C / min, hold for 2-6 h, and then increase the temperature to 500-650 °C at a rate of 2-5 °C / min, hold for 2-6 h.

10. The method for preparing the 3D-printed iron-based Fischer-Tropsch synthesis catalyst according to claim 7, characterized in that, After the programmed temperature-controlled carbonization treatment, the method further includes: The carbonized green body is placed in an atmosphere containing halogen compounds and kept at 500-650 °C for 0.5-4 h to modify the inner wall of the pores in the green body with halogen elements to form a halogen control layer.

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