Iron-based catalyst, method for preparing the same, and use thereof

Abstract

This invention provides an iron-based catalyst, its preparation method, and its application. The preparation method includes: Step S1, continuously feeding pulverized coal into an absorption reactor, while simultaneously continuously feeding an iron salt solution, an alkaline solution, and compressed gas into a three-fluid mixing nozzle within the absorption reactor, spraying droplets of iron-containing precipitate with a diameter ≤1000μm, so that the droplets of iron-containing precipitate are loaded onto the surface of the pulverized coal to obtain a precursor; wherein, the three-fluid mixing nozzle includes, from top to bottom, a feeding zone, an atomization zone, and a precipitation reaction zone, and the feeding zone includes, from inside to outside, a central channel, an inner annular channel, and an outer annular channel; the iron salt solution is fed into the atomization zone through the central channel, and the alkaline solution is fed into the atomization zone through the outer annular channel; or, the alkaline solution is fed into the atomization zone through the central channel, and the iron salt solution is fed into the atomization zone through the outer annular channel; the compressed gas is fed into the atomization zone through the inner annular channel; Step S2, ball milling and drying the precursor to obtain the iron-based catalyst.

Description

Technical Field

[0001] This invention relates to the field of direct coal liquefaction technology, and more specifically, to an iron-based catalyst, its preparation method, and its application. Background Technology

[0002] Direct coal liquefaction (DCL) is an important coal conversion technology that directly converts coal into liquid hydrocarbon products under high temperature, high pressure, and in the presence of a hydrogen-donating solvent and catalyst. Over the past century, DCL technology has seen hydrogen pressure decrease from 70 MPa to 17–30 MPa, while the reaction temperature needs to be maintained at around 450°C. Further reducing these stringent conditions remains a highly challenging task. Besides operating conditions, which can alter DCL efficiency, the catalyst also plays an equivalent role and is one of the key factors influencing DCL performance, significantly contributing to improved coal conversion and oil yield.

[0003] Existing literature (publication number CN1122511252A) discloses a direct coal liquefaction catalyst and a direct coal liquefaction method. The direct coal liquefaction catalyst comprises a carrier coal and an active metal element supported on the carrier coal, wherein the vitrinite content of the carrier coal is ≥70 wt%, and the active metal element includes iron. The literature also discloses a method for preparing the coal liquefaction catalyst: (1) in the presence of an aqueous solvent, an iron source and carrier coal are stirred evenly, and then an alkaline solution is added to adjust the pH of the system to 6–12 to obtain a coal slurry; (2) the coal slurry is oxidized; (3) the oxidized coal slurry is centrifuged or pressurized for filtration. However, this preparation method has high requirements for coal powder, is not suitable for coal powder with low vitrinite content, and the catalyst preparation process does not involve water conservation and requires a large amount of water.

[0004] To address the issues of high water consumption and long process flow in the preparation of iron-based catalysts for direct coal liquefaction in existing industrial applications, researchers have developed a new water-saving preparation technology for iron-based catalysts for direct coal liquefaction using a high-concentration feedstock solution.

[0005] Existing literature (publication number CN108772064A) discloses a method for preparing an iron-based catalyst. The active component of this iron-based catalyst is FeOOH, and the preparation method includes: loading an iron-soluble salt solution onto a catalyst support by spraying to obtain a primary product; reacting the primary product with an alkaline aqueous solution to obtain a secondary product; and selectively oxidizing the secondary product according to the valence state of iron ions in the iron-soluble salt solution, followed by a crystal phase transformation to obtain the iron-based catalyst. However, this preparation method has low mixing and absorption efficiency, is a static reaction process, and results in an unevenly distributed iron-based catalyst material.

[0006] In existing catalysts and their preparation technologies, iron-containing soluble salt solutions are mixed with alkaline aqueous solutions to obtain slurry-like initial products, which are then loaded onto catalyst supports by spraying. However, the spray nozzles are prone to clogging during spraying, affecting stable production operation. Furthermore, the atomized iron-containing precipitate droplets have a relatively large particle size, resulting in uneven mixing with coal powder. These factors lead to poor catalyst dispersibility and low activity. Additionally, the industrial catalyst process is long and energy consumption is high.

[0007] Based on this, the research and development of an iron-based catalyst and its preparation method are of great significance for improving coal conversion rate and oil yield. Summary of the Invention

[0008] The main objective of this invention is to provide an iron-based catalyst, its preparation method, and its application, in order to solve the problems in the preparation process of iron-based catalysts in the prior art, where the nozzle used to spray the product system obtained by mixing iron-containing soluble salt solution with alkaline aqueous solution is prone to clogging, and the iron-containing precipitate obtained by atomization has a large particle size and is not uniformly mixed with coal powder, resulting in poor dispersibility and activity of the iron-based catalyst and low production efficiency.

[0009] To achieve the above objectives, the present invention provides a method for preparing an iron-based catalyst, comprising: step S1, continuously feeding pulverized coal into an absorption reactor, and simultaneously continuously feeding an iron salt solution, an alkaline solution, and compressed gas into a three-fluid mixing nozzle within the absorption reactor, spraying droplets of iron-containing precipitate with a diameter ≤1000μm, thereby loading the iron-containing precipitate droplets onto the surface of the pulverized coal to obtain a precursor; wherein, the three-fluid mixing nozzle comprises, from top to bottom, a feeding zone, an atomization zone, and a precipitation reaction zone, and the feeding zone comprises, from inside to outside, a central channel, an inner annular channel, and an outer annular channel; the iron salt solution is fed into the atomization zone through the central channel, and the alkaline solution is fed into the atomization zone through the outer annular channel; or, the alkaline solution is fed into the atomization zone through the central channel, and the iron salt solution is fed into the atomization zone through the outer annular channel; the compressed gas is fed into the atomization zone through the inner annular channel; step S2, ball milling and drying the precursor to obtain the iron-based catalyst.

[0010] Furthermore, the jetting velocity of the fluid outlet in the central channel is 10–100 m / s; and / or, the jetting velocity of the fluid outlet in the outer annular channel is 5–50 m / s; and / or, the jetting velocity of the fluid outlet in the inner annular channel is 5–100 m / s; and / or, the velocity of the droplets containing iron precipitates ejected from the three-fluid mixing nozzle is 100–1000 m / s.

[0011] Furthermore, the compressed gas is mixed with the iron salt solution and the alkali solution in the atomization zone, and the ratio of the volume of the compressed gas to the total weight of the iron salt solution and the alkali solution is (10-200) L:1kg; preferably, the three-fluid mixing nozzle also includes a variable diameter connecting cavity located between the feeding zone and the precipitation reaction zone, the lower end of the central channel extends into the variable diameter connecting cavity, and the cavity of the variable diameter connecting cavity located below the central channel is the atomization zone; a blocking part is provided around the outer periphery of one end of the central channel extending into the variable diameter connecting cavity, and flow gaps are provided between the blocking part and the lower port of the inner annular channel, and between the blocking part and the inner wall of the variable diameter connecting cavity; more preferably, the radial diameter of the upper end of the variable diameter connecting cavity is 3 to 8 times the radial diameter of the lower end outlet of the central channel.

[0012] Furthermore, the ratio of the total weight of pulverized coal to iron salt solution and alkali solution introduced into the absorption reactor is (1-3):1, and the residence time of pulverized coal in the absorption reactor is 1-60 min; preferably, the average particle size of pulverized coal is ≤3 mm and the water content is ≤4 wt%; preferably, the absorption reactor is selected from a horizontal mixer, which is equipped with a stirring component inside; preferably, the stirring component is a plow blade, or a screw, or a stirring shaft combining a plow blade and a screw.

[0013] Further, the mass concentration of the iron salt solution is 10-30 wt%; preferably, the mass concentration of the alkali solution is 10-30 wt%; preferably, the iron salt in the iron salt solution is selected from ferrous sulfate and / or ferric sulfate; preferably, the ratio of the inflow rate of the iron salt solution to the alkali solution is (2-6):1; preferably, the alkali solution is an aqueous solution of an alkaline substance, preferably selected from one or more of the group consisting of ammonia water, sodium carbonate aqueous solution, sodium hydroxide aqueous solution, ammonium sulfide aqueous solution, and sodium sulfide aqueous solution; preferably, the iron salt solution further includes a first auxiliary agent, the first auxiliary agent being selected from one or more of the group consisting of water-soluble salts containing alkali metal elements, transition metal elements, and aluminum elements; preferably, the alkali solution further includes a second auxiliary agent, the second auxiliary agent being selected from silicates and / or molybdenum salts; more preferably, the weight percentage of the first auxiliary agent is 0.1-5 wt% based on the total weight of the iron salt solution; more preferably, the weight percentage of the second auxiliary agent is 0.1-3 wt% based on the total weight of the alkali solution.

[0014] Furthermore, the diameter of the iron-containing precipitate droplets is ≤500μm; preferably, the pH of the iron-containing precipitate droplets is 6.0 to 9.0, more preferably 6.5 to 8.0.

[0015] Furthermore, the compressed gas is selected from compressed air or compressed nitrogen; preferably compressed air.

[0016] Further, the water content of the precursor is ≤30wt%; preferably, the ball milling drying temperature is 120~220℃, and the ball milling speed is 30~150rpm; preferably, the above preparation method further includes: using a scraper conveyor to transport the precursor to a ball mill dryer for ball milling drying, and then using a powder classifier for sieving to obtain coarse powder with a particle size >150μm and fine powder with a particle size ≤150μm; then sending the fine powder into a bag filter for separation to obtain an iron-based catalyst and hot air; collecting the heat of the hot air for heating the ball mill dryer; more preferably, using a tail gas recirculator to send the hot air into a hot air furnace, the hot air furnace using hot air and combustion gas to generate heat, and the generated heat is transported to the ball mill dryer.

[0017] To achieve the above objectives, another aspect of the present invention provides an iron-based catalyst, which is prepared by the method described above for preparing the iron-based catalyst provided in this application; preferably, by weight percentage, the iron-based catalyst comprises 0.5–5 wt% Fe and 80–95 wt% pulverized coal; the average particle size of the iron-based catalyst is ≤150 μm; preferably, the iron-based catalyst further comprises a first element and / or a second element, wherein the first element is selected from one or more of the group consisting of alkali metal elements, transition metal elements, and aluminum elements, and the second element is selected from one or more of the group consisting of silicon elements and molybdenum elements; more preferably, by weight percentage, the iron-based catalyst comprises 0.1–1 wt% of the first element and / or the second element.

[0018] Another aspect of the present invention provides an application of the iron-based catalyst provided in this application in direct coal liquefaction.

[0019] Applying the technical solution of this invention and the preparation method described above, in step S1, the iron salt solution and the alkaline solution are dispersed into extremely fine droplets within the same nozzle through changes in the flow channel. These droplets are further torn into micron-sized droplets and accelerated under the impact of compressed gas. The formed micron-sized droplets undergo ultra-high-speed collisions in the atomization zone, causing the precipitation reaction of iron ions to occur in numerous reactors similar to the micron scale. The resulting iron precipitate can have a particle size as low as a few nanometers. Simultaneously, under the highly efficient mixing and impacting action, the iron ions can achieve a near 100% reaction efficiency, thus the final iron-containing active material exhibits extremely high activity. The iron precipitate is atomized and ejected at high speed from the nozzle orifice under the drive of compressed gas. This process forms extremely fine micron-sized iron-containing droplets, and the nozzle is less prone to accumulation, resulting in a very low risk of clogging.

[0020] Meanwhile, in step S1, pulverized coal is continuously fed into the absorption reactor, where it comes into contact with the droplets of iron-containing precipitate. This causes the droplets to be loaded onto the surface of the pulverized coal. Due to the rapid turnover of pulverized coal and the small size of the droplets, the pulverized coal forms a thin layer of adsorption on the droplets. The iron precipitate does not easily accumulate on the surface of the pulverized coal, thus maintaining its nanoscale size and ensuring its ultra-high activity.

[0021] Moreover, the preparation method provided in this application features a short production process for iron-based catalysts, with the reaction and absorption occurring continuously within a single reactor. In particular, the iron precipitation is a millisecond-level reaction occurring within the nozzle, resulting in extremely high efficiency and minimizing nozzle clogging. Compared to traditional liquid-phase precipitation methods, this method reduces precipitation reaction and filtration steps, and also minimizes the need for extensive conveying and stirring equipment and their energy consumption, significantly improving the continuous production efficiency of the iron-based catalysts presented in this application. Attached Figure Description

[0022] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0023] Figure 1 A process flow diagram of the preparation method of iron-based catalysts is shown;

[0024] Figure 2 A schematic cross-sectional view of the three-fluid mixing nozzle inside the absorption reactor is shown.

[0025] The above figures include the following reference numerals:

[0026] 100. Absorption reactor; 101. Agitator; 200. Three-fluid mixing nozzle; 201. Central channel; 202. Inner annular channel; 203. Outer annular channel; 204. Atomization zone; 205. Sedimentation reaction zone; 206. Baffle; 300. Scraper conveyor; 400. Ball mill dryer; 500. Air classifier; 600. Bag filter; 700. Exhaust gas recirculator; 800. Hot air furnace. Detailed Implementation

[0027] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0028] As described in the background art, existing methods for preparing iron-based catalysts suffer from several drawbacks. First, the nozzles used for spraying the product system obtained from the reaction of an iron-containing soluble salt solution and an alkaline aqueous solution are prone to clogging. Second, the iron-containing precipitate obtained from atomization has a relatively large particle size, resulting in uneven mixing with coal powder. This leads to poor dispersibility and activity of the prepared iron-based catalyst, as well as low production efficiency. To address these technical problems, this application provides a method for preparing an iron-based catalyst, comprising: step S1, as follows... Figure 1 As shown, pulverized coal is continuously fed into the absorption reactor 100, while iron salt solution, alkali solution, and compressed gas are continuously fed into the three-fluid mixing nozzle 200 within the absorption reactor 100. This sprays out droplets of iron-containing precipitates with a diameter ≤1000μm, allowing the iron-containing precipitate droplets to be loaded onto the surface of the pulverized coal, thus obtaining the precursor; wherein, as... Figure 2 As shown, the three-fluid mixing nozzle 200 includes, from top to bottom, a feeding zone, an atomization zone 204, and a precipitation reaction zone 205. The feeding zone includes, from inside to outside, a central channel 201, an inner annular channel 202, and an outer annular channel 203. The iron salt solution is conveyed to the atomization zone 204 through the central channel 201, and the alkali solution is conveyed to the atomization zone 204 through the outer annular channel 203; or, the alkali solution is conveyed to the atomization zone 204 through the central channel 201, and the iron salt solution is conveyed to the atomization zone 204 through the outer annular channel 203. The compressed gas is conveyed to the atomization zone 204 through the inner annular channel 202. In step S2, the precursor is ball-milled and dried to obtain an iron-based catalyst.

[0029] Using the preparation method described in this application, in step S1, the iron salt solution and alkali solution are dispersed into extremely fine droplets within the same nozzle through changes in the flow channel. These droplets are further torn into micron-sized droplets and accelerated under the impact of compressed gas. The resulting micron-sized droplets undergo ultra-high-speed collisions in the atomization zone 204, causing the precipitation reaction of iron ions to occur in numerous reactors similar to the micron scale. The resulting iron precipitate can have a particle size as low as a few nanometers. Simultaneously, under the highly efficient mixing and impacting action, the iron ions can achieve a near 100% reaction efficiency, thus the final iron-containing active material exhibits extremely high activity. The iron precipitate is atomized and ejected at high speed from the nozzle orifice under the drive of compressed gas. This process forms extremely fine micron-sized iron-containing droplets, and the nozzle is less prone to accumulation, resulting in a very low risk of clogging.

[0030] Meanwhile, in step S1, pulverized coal is continuously fed into the absorption reactor 100, where it comes into contact with the droplets of iron-containing precipitate. This causes the droplets of iron-containing precipitate to be loaded onto the surface of the pulverized coal. Due to the rapid turnover of pulverized coal and the small size of the droplets of iron-containing precipitate, the pulverized coal forms a thin layer of adsorption on the droplets of iron-containing precipitate. The iron precipitate does not easily accumulate on the surface of the pulverized coal, thus maintaining its nanoscale size and ensuring its ultra-high activity.

[0031] Moreover, the preparation method provided in this application features a short production process for iron-based catalysts, with the reaction and absorption occurring continuously within a single reactor. In particular, the iron precipitation is a millisecond-level reaction occurring within the nozzle, resulting in extremely high efficiency and minimizing nozzle clogging. Compared to traditional liquid-phase precipitation methods, this method reduces precipitation reaction and filtration steps, and also minimizes the need for extensive conveying and stirring equipment and their energy consumption, significantly improving the continuous production efficiency of the iron-based catalysts presented in this application.

[0032] In a preferred embodiment, the jetting rate of the fluid outlet of the central channel 201 is 10–100 m / s. The jetting rate of the fluid outlet of the central channel 201 includes, but is not limited to, the above range. Limiting it to the above range is beneficial to improve the atomization efficiency of the iron salt solution or alkali solution, thereby obtaining droplets of iron-containing precipitates with smaller diameters, which are convenient for subsequent loading onto the surface of pulverized coal.

[0033] In a preferred embodiment, the jetting rate of the fluid outlet of the outer annular channel 203 is 5–50 m / s. The jetting rate of the fluid outlet of the outer annular channel 203 includes, but is not limited to, the above range. Limiting it to the above range is beneficial to improve the atomization efficiency of the iron salt solution or alkali solution, thereby obtaining droplets of iron-containing precipitates with smaller diameters, which are convenient for subsequent loading onto the surface of pulverized coal.

[0034] In a preferred embodiment, the injection rate of the fluid outlet of the inner annular channel 202 is 5 to 100 m / s. The injection rate of the fluid outlet of the inner annular channel 202 includes, but is not limited to, the above range. Limiting it to the above range is beneficial to make the compressed gas injection form a more powerful impact on the droplets of iron salt solution and alkali solution, thereby reducing the particle size of iron precipitate.

[0035] In order to improve the loading rate of iron-containing precipitate droplets on the surface of pulverized coal, thereby improving the dispersibility and activity of iron-based catalysts, preferably, the rate at which the three-fluid mixing nozzle 200 sprays iron-containing precipitate droplets is 100-1000 m / s.

[0036] In a preferred embodiment, compressed gas is mixed with iron salt solution and alkali solution in atomization zone 204, and the volume ratio of compressed gas to the total weight of iron salt solution and alkali solution is (10-200) L:1 kg. The volume ratio of compressed gas to the total weight of iron salt solution and alkali solution includes, but is not limited to, the above range. Limiting it to this range is beneficial to increasing the loading rate of iron-containing precipitate droplets on the coal powder surface, thereby improving the dispersibility and activity of the iron-based catalyst.

[0037] In a preferred embodiment, such as Figure 2As shown, the three-fluid mixing nozzle 200 also includes a variable-diameter connecting cavity located between the feeding zone and the precipitation reaction zone 205. The lower end of the central channel 201 extends into the variable-diameter connecting cavity, and the cavity below the central channel 201 is the atomizing zone 204. A blocking part 206 is arranged around the outer periphery of the end of the central channel 201 extending into the variable-diameter connecting cavity. Flow gaps are provided between the blocking part 206 and the lower port of the inner annular channel 202, and between the blocking part 206 and the inner wall of the variable-diameter connecting cavity. The three-fluid mixing nozzle 200 with the above structure facilitates the improvement of the atomization efficiency of iron salt solution or alkali solution, thereby obtaining droplets of iron-containing precipitates with smaller diameters, which are convenient for subsequent loading onto the surface of pulverized coal.

[0038] To further obtain smaller diameter iron-containing precipitate droplets, preferably, the radial diameter of the upper end of the variable diameter connecting cavity is 3 to 8 times the radial diameter of the lower end outlet of the central channel 201.

[0039] In a preferred embodiment, the total weight ratio of pulverized coal to iron salt solution and alkali solution introduced into the absorption reactor 100 is (1-3):1, and the residence time of pulverized coal in the absorption reactor 100 is 1-60 min. The rate at which pulverized coal is introduced into the absorption reactor 100 and the residence time are not limited to the above ranges. Limiting them to the above ranges is beneficial to increasing the loading rate of iron-containing precipitate droplets on the surface of pulverized coal, thereby improving the dispersibility and activity of the iron-based catalyst.

[0040] Compared to existing methods, the preparation method provided in this application has greater adaptability to raw materials and is suitable for using coal powder with relatively large particle size as an absorbent carrier. In a preferred embodiment, the average particle size of the coal powder is ≤3mm and the water content is ≤4wt%.

[0041] In a preferred embodiment, the absorption reactor 100 includes, but is not limited to, a horizontal mixer, which is equipped with an agitator 101 inside. The agitator 101 enables the pulverized coal to be continuously agitated and crushed within the absorption reactor 100 and pushed towards the discharge zone. Preferably, the agitator 101 is a plow blade, a screw, or a combination of a plow blade and a screw.

[0042] In a preferred embodiment, the mass concentration of the iron salt solution is 10–30 wt%. The mass concentration of the iron salt solution includes, but is not limited to, the above range, and limiting it within the above range is beneficial to increasing the formation rate of iron precipitate.

[0043] In a preferred embodiment, the mass concentration of the alkaline solution is 10–30 wt%. The mass concentration of the alkaline solution includes, but is not limited to, the above range, and limiting it within the above range is beneficial to increasing the formation rate of iron precipitate.

[0044] In this application, the iron salt solution may be an aqueous solution of iron salts commonly used in the art. In a preferred embodiment, the iron salt in the iron salt solution includes, but is not limited to, ferrous sulfate and / or ferrous sulfate.

[0045] To improve the formation rate of iron precipitate, the ratio of the rate of introduction of iron salt solution to the rate of introduction of alkali solution is preferably (2-6):1.

[0046] In this application, the alkaline solution can be an aqueous solution of an alkaline substance commonly used in the art. In a preferred embodiment, the alkaline solution includes, but is not limited to, one or more of the following groups: ammonia water, sodium carbonate aqueous solution, sodium hydroxide aqueous solution, ammonium sulfide aqueous solution, and sodium sulfide aqueous solution.

[0047] To improve the dispersibility of iron-based catalysts, reduce the crystal size of the active phase, and enhance their catalytic activity in direct coal liquefaction, the iron salt solution preferably further includes a first additive. The first additive includes, but is not limited to, one or more water-soluble salts containing alkali metals, transition metals, and aluminum. More preferably, the weight percentage of the first additive, based on the total weight of the iron salt solution, is 0.1–5 wt%.

[0048] To reduce the grain size of the active phase of the iron-based catalyst and improve its hydrogen activation capability, the alkaline solution preferably further includes a second additive, which includes, but is not limited to, silicates and / or molybdenum salts. More preferably, the weight percentage of the second additive, based on the total weight of the alkaline solution, is 0.1–3 wt%.

[0049] The preparation method described above in this application facilitates the efficient production of iron-containing precipitate droplets with small diameters. In a preferred embodiment, the diameter of the iron-containing precipitate droplets is ≤500 μm.

[0050] In a preferred embodiment, the pH of the iron-containing precipitate droplets is 6.0–9.0. The pH of the iron-containing precipitate droplets includes, but is not limited to, the above range. Limiting it to this range is beneficial for the formation of smaller-grained hydrated iron oxide crystals, thereby facilitating its transformation into the active phase and improving its catalytic activity in direct coal liquefaction. Preferably, the pH of the iron-containing precipitate droplets is 6.5–8.0.

[0051] In a preferred embodiment, the compressed gas includes, but is not limited to, compressed air or compressed nitrogen; compressed air is preferred.

[0052] In a preferred embodiment, the water content of the precursor is ≤30wt%. The water content of the precursor includes, but is not limited to, the above range. Limiting it to the above range is beneficial to improving the loading effect of iron precipitates on the surface of pulverized coal, thereby improving the activity of the iron-based catalyst subsequently prepared.

[0053] In a preferred embodiment, the ball milling drying process is carried out at a temperature of 120–220°C and a ball milling speed of 30–150 rpm. The ball milling drying temperature and speed include, but are not limited to, the above-mentioned ranges; limiting them within these ranges is beneficial for improving the removal rate of moisture from the iron-based catalyst. Preferably, the ball milling drying process is carried out at a temperature of 150–220°C.

[0054] In a preferred embodiment, the preparation method of the above-mentioned iron-based catalyst provided in this application further includes: using a scraper conveyor 300 to transport the precursor to a ball mill dryer 400 for ball milling and drying, and then using a classifier 500 for sieving to obtain coarse powder with a particle size >150μm and fine powder with a particle size ≤150μm; then feeding the fine powder into a bag filter 600 to obtain the iron-based catalyst and hot air; collecting the heat of the hot air to heat the ball mill dryer 400.

[0055] The above treatment method is beneficial for obtaining iron-based catalysts with more suitable particle size, and it also helps to recover waste heat and reduce energy consumption.

[0056] To further recover waste heat and further reduce energy consumption, preferably, a tail gas recirculator 700 is used to send hot air into a hot air furnace 800. The hot air furnace 800 uses hot air and combustion gas to generate heat through combustion, and the generated heat is transported to a ball mill dryer 400.

[0057] The second aspect of this application also provides an iron-based catalyst, which is prepared using the method described above. The iron-based catalyst prepared in this application exhibits high activity and high dispersibility, and the iron-containing precipitate is uniformly loaded on the surface of the pulverized coal. It should be noted that, due to the specific nature of the catalyst field and limitations of existing testing and characterization methods, a comprehensive quantitative characterization of the complex microstructure of the obtained iron-based catalyst is difficult. However, experiments show that the iron-based catalyst obtained in this application possesses higher activity and dispersibility.

[0058] In a preferred embodiment, the iron-based catalyst comprises 0.5–5 wt% Fe and 80–95 wt% pulverized coal by weight percentage; the average particle size of the iron-based catalyst is ≤150 μm.

[0059] In a preferred embodiment, the iron-based catalyst further includes a first element and / or a second element, wherein the first element includes, but is not limited to, one or more elements selected from the group consisting of alkali metals, transition metals, and aluminum, and the second element includes, but is not limited to, one or more elements selected from the group consisting of silicon and molybdenum. The introduction of the first element is beneficial for improving the dispersibility of the iron-based catalyst and reducing the crystallite size of the active phase, thereby improving its catalytic activity in direct coal liquefaction. The introduction of the second element is beneficial for reducing the crystallite size of the active phase of the iron-based catalyst, thereby improving its hydrogen activation capacity.

[0060] To further improve the catalytic activity of iron-based catalysts and enhance their cost-effectiveness, the iron-based catalysts further include 0.1 to 1 wt% of a first element and / or a second element by weight percentage.

[0061] The third aspect of this application also provides an application of the iron-based catalyst provided in this application in direct coal liquefaction. The iron-based catalyst prepared in this application has the characteristics of high activity and high dispersibility, and the iron-containing precipitate is uniformly loaded on the surface of coal powder. Its application in direct coal liquefaction can significantly improve indicators such as coal conversion rate, bitumen yield, and oil yield, while reducing hydrogen consumption.

[0062] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0063] The coal powder raw material used in the embodiments and comparative examples of this application is Shendong coal, which is initially crushed to less than 3cm. The results of its industrial analysis and elemental analysis are shown in Table 1.

[0064] Table 1

[0065]

[0066] In Table 1, the symbols represent the following meanings:

[0067] Industrial Analysis Section: M ad Refers to the air-dried basis water content; A d Ash content on a dry basis; V daf Refers to the volatile matter on a dry, ash-free basis. Determined according to the methods in GB / T 211-2017 and GB / T 212-2008.

[0068] Elemental analysis section: C daf Refers to dry, ash-free fixed carbon; C, H, O, N, and S refer to the content of each element; determined according to the methods in GB / T214-2007, GB / T 476-2008, and GB / T 19227-2008.

[0069] Example 1

[0070] A method for preparing an iron-based catalyst, comprising:

[0071] (1) Prepare a 22wt% ferrous sulfate solution by adding the first auxiliary agent Al(NO3)3, so that the weight percentage of the first auxiliary agent Al(NO3)3 in the ferrous sulfate solution is 3.08wt%;

[0072] Prepare a 22wt% ammonia solution by adding a second additive, K2SiO3, so that the weight percentage of the second additive, K2SiO3, in the ammonia solution is 2.05wt%.

[0073] (2) The prepared ferrous sulfate solution, ammonia, and compressed air are continuously fed into the three-fluid mixing nozzle 200 in the absorption reactor 100. Ammonia is fed to the atomization zone 204 via the central channel 201 at a spray rate of 50 m / s; the ferrous sulfate solution is fed to the atomization zone 204 via the outer annular channel 203 at a spray rate of 60 m / s; the three-fluid mixing nozzle 200 sprays droplets containing iron precipitates at a rate of 600 m / s; the volume of compressed air is equal to that of the ferrous sulfate solution and ammonia. The total weight ratio is 120L:1kg; simultaneously, pulverized coal with an average particle size of 3mm is introduced into the absorption reactor 100, and the total weight ratio of the pulverized coal to the ferrous sulfate solution and ammonia is 2:1; the frequency of the plow-shaped agitator in the absorption reactor 100 is adjusted to 15Hz, and the sprayed ferrous sulfate solution droplets and ammonia droplets undergo a precipitation reaction to generate iron-containing precipitate droplets with a diameter of 300μm, which are loaded onto the surface of the pulverized coal to obtain the precursor; the pH of the iron-containing precipitate droplets is 7.0;

[0074] (3) The above-mentioned precursor is discharged from the outlet of the absorption reactor 100 and conveyed to the ball mill dryer 400 by the scraper conveyor 300; the inlet air temperature of the hot air furnace 800 is controlled at 200℃ to grind and dry the precursor to obtain powder;

[0075] (4) The powder obtained in step (3) is carried by hot air from the outlet of ball mill dryer 400 into powder classifier 500 to obtain coarse powder with a particle size >150μm and fine powder with a particle size ≤150μm.

[0076] The coarse powder is returned to the scraper conveyor 300 and transported together with the precursor to the ball mill dryer 400 for further ball milling and drying. The fine powder enters the bag filter 600 with the gas for separation and is collected to obtain the iron-based catalyst, which is designated as catalyst 1#.

[0077] Example 2

[0078] The difference from Example 1 is that in step (2), the ratio of the volume of compressed air to the total weight of ferrous sulfate solution and ammonia is 10L:1kg; the remaining steps are the same as in Example 1, and the resulting iron-based catalyst is designated as catalyst 2#.

[0079] Example 3

[0080] The difference from Example 1 is that in step (2), the ratio of the volume of compressed air to the total weight of ferrous sulfate solution and ammonia is 80L:1kg; the remaining steps are the same as in Example 1, and the resulting iron-based catalyst is designated as catalyst 3#.

[0081] Example 4

[0082] The difference from Example 1 is that in step (2), the ratio of the volume of compressed air to the total weight of ferrous sulfate solution and ammonia is 150L:1kg; the remaining steps are the same as in Example 1, and the resulting iron-based catalyst is designated as catalyst 4#.

[0083] Example 5

[0084] The difference from Example 1 is that in step (2), the ratio of the volume of compressed air to the total weight of ferrous sulfate solution and ammonia is 200L:1kg; the remaining steps are the same as in Example 1, and the resulting iron-based catalyst is designated as catalyst 5#.

[0085] Example 6

[0086] The difference from Example 1 is that in step (2), the pH of the iron-containing precipitate droplets is 6.5; the remaining steps are the same as in Example 1, and the resulting iron-based catalyst is designated as catalyst 6#.

[0087] Example 7

[0088] The difference from Example 1 is that in step (2), the pH of the iron-containing precipitate droplets is 7.5; the remaining steps are the same as in Example 1, and the resulting iron-based catalyst is designated as catalyst 7#.

[0089] Example 8

[0090] The difference from Example 1 is that in step (2), the pH of the iron-containing precipitate droplets is 8.0; the remaining steps are the same as in Example 1, and the resulting iron-based catalyst is designated as catalyst 8#.

[0091] Example 9

[0092] The difference from Example 1 is that in step (2), the pH of the iron-containing precipitate droplets is 9.0; the remaining steps are the same as in Example 1, and the resulting iron-based catalyst is designated as catalyst 9#.

[0093] Example 10

[0094] The difference from Example 1 is that in step (2), the particle size of the coal powder is 2 mm; the remaining steps are the same as in Example 1, and the resulting iron-based catalyst is designated as catalyst 10#.

[0095] Example 11

[0096] The difference from Example 1 is that in step (2), the particle size of the coal powder is 0.85 mm; the remaining steps are the same as in Example 1, and the resulting iron-based catalyst is designated as catalyst 11#.

[0097] Example 12

[0098] The difference from Example 1 is that in step (2), the ratio of the total weight of coal powder, ferrous sulfate solution and ammonia water introduced into the absorption reactor 100 is 3:1; the remaining steps are the same as in Example 1, and the resulting iron-based catalyst is designated as catalyst 12#.

[0099] Example 13

[0100] The difference from Example 1 is that in step (2), the ratio of the total weight of coal powder, ferrous sulfate solution and ammonia water introduced into the absorption reactor 100 is 1:1; the remaining steps are the same as in Example 1, and the resulting iron-based catalyst is designated as catalyst 13#.

[0101] Example 14

[0102] The difference from Example 1 is that in step (2), the ratio of the total weight of coal powder, ferrous sulfate solution and ammonia water introduced into the absorption reactor 100 is 0.8:1; the remaining steps are the same as in Example 1, and the resulting iron-based catalyst is designated as catalyst 14#.

[0103] Comparative Example 1

[0104] The preparation of pulverized coal-supported FeOOH catalysts using a liquid-phase precipitation oxidation method includes:

[0105] At 60℃, 360g of a 22wt% ferrous sulfate solution was prepared, and 1kg of dry coal powder with a particle size of less than 150μm was added. A 22wt% ammonia solution was also prepared and added concurrently to the ferrous sulfate, coal powder mixture, and ammonia solution until all were added. The flow rate of the ferrous sulfate to coal powder mixture was controlled at a ratio of 2:1, the slurry temperature was controlled at 60℃, the stirring speed at 300rpm, and air was simultaneously introduced for oxidation. The reaction time was 60min, and the pH was maintained at 7.5. After the reaction was complete, the mixture was centrifuged to obtain a filter cake. This cake was then washed with deionized water and dried in a nitrogen drying oven at 110℃ for 12h. After drying, the solid was ground to below 100μm to obtain a coal powder-supported FeOOH catalyst, designated as control catalyst 1#.

[0106] Catalyst performance evaluation

[0107] A certain amount of the iron-based catalyst prepared in the above examples and the FeOOH catalyst supported on coal powder prepared in the comparative example were weighed and subjected to high-pressure reactor tests for coal liquefaction. The coal liquefaction reaction performance test conditions were as follows: the iron-based catalysts in the above examples and the comparative example were accurately weighed and added to the coal liquefaction reaction in a 500 mL high-pressure reactor; the amount added was 28 g of dry coal; coal liquefaction circulating oil was used as the solvent, and the amount of solvent added was 42 g; a certain amount of sulfur powder was added, and the sulfur powder was added at an S / Fe atomic ratio of 2; the initial cold hydrogen pressure of the high-pressure reactor reaction was 10 MPa, and the temperature was kept constant at 455℃ for 1 h; after the reaction was completed, the reaction system was rapidly cooled, gas samples were taken to determine their composition, and the liquid and solid phases after the reaction were collected. They were extracted by hexane and tetrahydrofuran for 48 h, respectively. The extraction residues were burned to ash, and the coal conversion rate, hydrogen consumption, gas yield, water yield, bitumen yield, and oil yield were calculated. The test data are shown in Table 2.

[0108] Table 2

[0109]

[0110] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0111] Using the preparation method described in this application, in step S1, the iron salt solution and alkali solution are dispersed into extremely fine droplets within the same nozzle through changes in the flow channel. These droplets are further torn into micron-sized droplets and accelerated under the impact of compressed gas. The resulting micron-sized droplets undergo ultra-high-speed collisions in the atomization zone 204, causing the precipitation reaction of iron ions to occur in numerous reactors similar to the micron scale. The resulting iron precipitate can have a particle size as low as a few nanometers. Simultaneously, under the highly efficient mixing and impacting action, the iron ions can achieve a near 100% reaction efficiency, thus the final iron-containing active material exhibits extremely high activity. The iron precipitate is atomized and ejected at high speed from the nozzle orifice under the drive of compressed gas. This process forms extremely fine micron-sized iron-containing droplets, and the nozzle is less prone to accumulation, resulting in a very low risk of clogging.

[0112] Meanwhile, in step S1, pulverized coal is continuously fed into the absorption reactor 100, where it comes into contact with the droplets of iron-containing precipitate. This causes the droplets of iron-containing precipitate to be loaded onto the surface of the pulverized coal. Due to the rapid turnover of pulverized coal and the small size of the droplets of iron-containing precipitate, the pulverized coal forms a thin layer of adsorption on the droplets of iron-containing precipitate. The iron precipitate does not easily accumulate on the surface of the pulverized coal, thus maintaining its nanoscale size and ensuring its ultra-high activity.

[0113] Moreover, the preparation method provided in this application features a short production process for iron-based catalysts, with the reaction and absorption occurring continuously within a single reactor. In particular, the iron precipitation is a millisecond-level reaction occurring within the nozzle, resulting in extremely high efficiency and minimizing nozzle clogging. Compared to traditional liquid-phase precipitation methods, this method reduces precipitation reaction and filtration steps, and also minimizes the need for extensive conveying and stirring equipment and their energy consumption, significantly improving the continuous production efficiency of the iron-based catalysts presented in this application.

[0114] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0115] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an iron-based catalyst, characterized in that, The preparation method includes: Step S1: Powdered coal is continuously fed into the absorption reactor (100), while iron salt solution, alkaline solution and compressed gas are continuously fed into the three-fluid mixing nozzle (200) in the absorption reactor (100) to spray out droplets of iron-containing precipitate with a diameter ≤1000μm, so that the droplets of iron-containing precipitate are loaded on the surface of the powdered coal to obtain the precursor. The three-fluid mixing nozzle (200) includes, from top to bottom, a feeding zone, an atomizing zone (204), and a precipitation reaction zone (205). The feeding zone includes, from inside to outside, a central channel (201), an inner annular channel (202), and an outer annular channel (203). The iron salt solution is transported to the atomizing zone (204) through the central channel (201), and the alkali solution is transported to the atomizing zone (204) through the outer annular channel (203). Alternatively, the alkali solution is transported to the atomizing zone (204) through the central channel (201), and the iron salt solution is transported to the atomizing zone (204) through the outer annular channel (203). The compressed gas is transported to the atomizing zone (204) through the inner annular channel (202). Step S2: The precursor is ball-milled and dried to obtain the iron-based catalyst.

2. The method for preparing the iron-based catalyst according to claim 1, characterized in that, The jetting rate of the fluid outlet of the central channel (201) is 10–100 m / s; and / or, The jet velocity at the fluid outlet of the outer annular channel (203) is 5–50 m / s; and / or, The jet velocity at the fluid outlet of the inner annular channel (202) is 5–100 m / s; and / or, The three-fluid mixing nozzle (200) sprays droplets of the iron-containing precipitate at a rate of 100-1000 m / s.

3. The method for preparing the iron-based catalyst according to claim 1, characterized in that, The compressed gas is mixed with the iron salt solution and the alkali solution in the atomization zone (204), and the ratio of the volume of the compressed gas to the total weight of the iron salt solution and the alkali solution is (10~200) L:1kg.

4. The method for preparing the iron-based catalyst according to claim 3, characterized in that, The three-fluid mixing nozzle (200) also includes a variable-diameter connecting cavity located between the feeding zone and the sedimentation reaction zone (205). The lower end of the central channel (201) extends into the variable-diameter connecting cavity, and the cavity below the central channel (201) of the variable-diameter connecting cavity is the atomizing zone (204). A blocking part (206) is provided around the outer periphery of one end of the central channel (201) extending into the variable-diameter connecting cavity. Flow gaps are provided between the blocking part (206) and the lower port of the inner annular channel (202), and between the blocking part (206) and the inner wall of the variable-diameter connecting cavity.

5. The method for preparing the iron-based catalyst according to claim 4, characterized in that, The radial diameter of the upper end of the variable diameter connecting cavity is 3 to 8 times the radial diameter of the lower end outlet of the central channel (201).

6. The method for preparing the iron-based catalyst according to any one of claims 1 to 5, characterized in that, The ratio of the total weight of the coal powder, the iron salt solution, and the alkaline solution introduced into the absorption reactor (100) is (1-3):1, and the residence time of the coal powder in the absorption reactor (100) is 1-60 min.

7. The method for preparing the iron-based catalyst according to claim 6, characterized in that, The average particle size of the pulverized coal is ≤3mm, and the water content is ≤4wt%.

8. The method for preparing the iron-based catalyst according to claim 6, characterized in that, The absorption reactor (100) is selected from a horizontal mixer, and an agitator (101) is provided inside it; the agitator (101) is a plow blade, or a screw, or a combination of a plow blade and a screw.

9. The method for preparing the iron-based catalyst according to any one of claims 1 to 5, characterized in that, The iron salt solution has a mass concentration of 10–30 wt%.

10. The method for preparing the iron-based catalyst according to claim 9, characterized in that, The mass concentration of the alkaline solution is 10–30 wt%.

11. The method for preparing the iron-based catalyst according to claim 9, characterized in that, The iron salt in the iron salt solution is selected from ferrous sulfate and / or ferric sulfate.

12. The method for preparing the iron-based catalyst according to claim 9, characterized in that, The ratio of the rate of introduction of the iron salt solution to the rate of introduction of the alkaline solution is (2-6):

1.

13. The method for preparing the iron-based catalyst according to claim 9, characterized in that, The alkaline solution is an aqueous solution of an alkaline substance, and the alkaline solution is selected from one or more of the group consisting of ammonia water, sodium carbonate aqueous solution, sodium hydroxide aqueous solution, ammonium sulfide aqueous solution, and sodium sulfide aqueous solution.

14. The method for preparing the iron-based catalyst according to claim 9, characterized in that, The iron salt solution further includes a first auxiliary agent, which is selected from one or more water-soluble salts containing alkali metal elements, transition metal elements, and aluminum elements.

15. The method for preparing the iron-based catalyst according to claim 9, characterized in that, The alkaline solution also includes a second auxiliary agent, which is selected from silicates and / or molybdenum salts.

16. The method for preparing the iron-based catalyst according to claim 14, characterized in that, The weight percentage of the first auxiliary agent is 0.1 to 5 wt% based on the total weight of the iron salt solution.

17. The method for preparing the iron-based catalyst according to claim 15, characterized in that, The second auxiliary agent comprises 0.1 to 3 wt% of the total weight of the alkaline solution.

18. The method for preparing the iron-based catalyst according to claim 9, characterized in that, The diameter of the droplets of the iron-containing precipitate is ≤500μm.

19. The method for preparing the iron-based catalyst according to claim 18, characterized in that, The pH of the iron-containing precipitate droplets is 6.0–9.

0.

20. The method for preparing the iron-based catalyst according to claim 19, characterized in that, The pH of the iron-containing precipitate droplets is 6.5–8.

0.

21. The method for preparing the iron-based catalyst according to claim 9, characterized in that, The compressed gas is selected from compressed air or compressed nitrogen.

22. The method for preparing the iron-based catalyst according to claim 21, characterized in that, The compressed gas is compressed air.

23. The method for preparing the iron-based catalyst according to claim 9, characterized in that, The water content of the precursor is ≤30wt%.

24. The method for preparing the iron-based catalyst according to claim 23, characterized in that, The temperature of the ball milling drying process is 120–220°C, and the ball milling speed is 30–150 rpm.

25. The method for preparing the iron-based catalyst according to claim 23, characterized in that, The preparation method further includes: The precursor is conveyed to a ball mill dryer (400) by a scraper conveyor (300) for ball milling and drying, and then screened by a classifier (500) to obtain coarse powder with a particle size >150μm and fine powder with a particle size ≤150μm. The fine powder is then fed into a bag filter (600) for separation to obtain the iron-based catalyst and hot air; The heat collected from the hot air is used to heat the ball mill dryer (400).

26. The method for preparing the iron-based catalyst according to claim 25, characterized in that, The hot air is fed into the hot air furnace (800) by the exhaust gas recirculation machine (700), and the hot air furnace (800) uses the hot air and combustion gas to generate heat through combustion, and the generated heat is transported to the ball mill dryer (400).

27. An iron-based catalyst, characterized in that, The iron-based catalyst is prepared by the method of any one of claims 1 to 26; by weight percentage, the iron-based catalyst comprises 0.5 to 5 wt% Fe and 80 to 95 wt% coal powder; the average particle size of the iron-based catalyst is ≤150 μm.

28. The iron-based catalyst according to claim 27, characterized in that, The iron-based catalyst further includes a first element and / or a second element, wherein the first element is selected from one or more of the group consisting of alkali metal elements, transition metal elements, and aluminum elements, and the second element is selected from one or more of the group consisting of silicon elements and molybdenum elements.

29. The iron-based catalyst according to claim 28, characterized in that, The iron-based catalyst comprises 0.1 to 1 wt% of the first element and / or the second element by weight percentage.

30. The use of an iron-based catalyst according to any one of claims 27 to 29 in direct coal liquefaction.

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