Coal direct liquefaction iron series oil slurry catalyst and preparation method thereof

Abstract

The application provides a coal direct liquefaction iron series oil slurry catalyst and a preparation method thereof. The method comprises the following steps: mixing coal powder, ferrous sulfate aqueous solution and ammonia solution, generating a precipitation reaction to obtain a suspension of a precipitation product, and then contacting the suspension with compressed air in countercurrent to generate an oxidation reaction to obtain a suspension of an oxidation product; wherein the pressure of the oxidation reaction is 0.2-1.0 MPa, the temperature is 10-70 DEG C, and the oxidation residence time is 10-30 min; filtering the suspension of the oxidation product to obtain a filter cake and a filtrate; and mixing the filter cake with a circulating solvent to obtain the coal direct liquefaction iron series oil slurry catalyst. Through the defined oxidation reaction conditions, the solubility of oxygen in the liquid phase can be improved, the oxidation reaction can be fully carried out even for the ferrous sulfate aqueous solution and the ammonia solution with a higher concentration, the water treatment amount of the oxidation reaction is greatly reduced, the oxidation reaction efficiency is significantly improved, and the high-activity gamma-FeOOH precipitate can be more efficiently generated.

Description

Technical Field

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

[0002] Direct coal liquefaction (DCL) is one of the effective ways to utilize coal, especially low-rank coal, cleanly and efficiently. DCL is a complex physical and chemical process, and many factors influence its yield and efficiency, including: coal type and properties, reactor type, catalyst, solvent, reaction temperature and time, and atmosphere. DCL generally relies on an oil-coal slurry system containing pulverized coal, a hydrogen-donating solvent, and a catalyst. The catalyst is one of the key raw materials in the DCL process and has a direct impact on its effectiveness.

[0003] In direct coal liquefaction, the catalyst, after a single use, enters the liquefaction residue along with the minerals and unreacted coal. This residue is then burned or gasified, and the catalyst remains as ash. In other words, existing catalysts are discarded after a single reaction. Therefore, even with low activity, iron-based catalysts, represented by iron-containing minerals and iron salts, have been the first to be industrialized due to their low cost, non-toxicity, and lack of need for recycling. That is, iron-based catalysts are widely researched and applied due to their relative efficiency, low cost, and lack of need for recycling. Common iron-based catalysts include red mud, ferrous sulfate, pyrite, ferric hydroxide, and pyrrhotite.

[0004] Smaller particle sizes of iron-based catalysts result in better dispersibility and thus better coal liquefaction performance. However, in existing direct coal liquefaction processes, the iron catalysts used (such as Fe2O3 and FeS2) are prone to agglomeration during the reaction due to their micron-sized particles, affecting their dispersibility and directly impacting coal liquefaction performance. The ideal solution to this problem is to prepare highly active iron-based catalysts, further optimize their composition, and refine the preparation process and methods to reduce operational complexity, thereby developing novel high-pressure oil-slurry coal direct liquefaction catalysts.

[0005] Existing technologies disclose various optimization schemes. For example, Chinese patent application CN110743559 discloses a solid-phase grinding method for preparing highly dispersed multifunctional catalysts. The catalyst uses activated carbon as a support, Ni as the active metal, and MoO2 and CeO2 as auxiliary metals. The highly dispersed multifunctional catalyst is prepared by solid-phase grinding. In the prepared highly dispersed multifunctional catalyst, the metal loading is 0.1~5%, and the particle size of the active metal component is 3~20nm.

[0006] Chinese patent application CN108772064A discloses a method for preparing iron-based catalysts for direct coal liquefaction with low water consumption. The method involves loading an iron-containing soluble salt solution onto a catalyst support by spraying, then adding an alkaline aqueous solution to react and obtain a secondary product. The secondary product is then oxidized and undergoes a crystal phase transformation to obtain an iron-based catalyst. However, this method has low mixing and absorption efficiency, is a static reaction process, and results in uneven catalyst materials.

[0007] Chinese patent application CN1109734C discloses a method for preparing a slurry-like highly dispersed iron-based coal liquefaction catalyst. In this method, an iron salt solution is mixed with ammonia water under high-speed stirring to generate amorphous Fe(OH)2 or Fe(OH)3 ultrafine dispersed particles. These particles are then dehydrated by high-speed centrifugation to generate a hydrogel. Finally, the hydrogel is mixed and dispersed with an appropriate amount of coal powder and a direct coal liquefaction solvent to prepare a slurry-like iron-based catalyst. However, this preparation process makes it difficult to generate highly active γ-FeOOH.

[0008] Existing technologies use ferrous sulfate and ammonia as raw materials to produce ferrous hydroxide, which is then added to ammonium phosphate and oxidized in air at 40°C for 20 hours to obtain γ-FeOOH. γ-FeOOH is dried at 100°C and agglomerates. When used in liquefaction reactions, the agglomerates are pulverized in the process solvent using an ultrafine mill. However, the above method has high grinding energy consumption and is not easy to grind into nanoscale particles.

[0009] Chinese patent application CN1274415C discloses a method for preparing a highly dispersed iron-based coal direct liquefaction catalyst. The method involves adding coal powder to a ferrous salt solution at room temperature and stirring until homogeneous. Then, a certain amount of a weakly alkaline or strongly alkaline solution containing hydroxide ions is added and stirred until homogeneous, resulting in a coal slurry containing a precipitate. The Fe(OH)₂ precipitate in the coal slurry is then oxidized to γ-FeOOH using air or oxygen at 20-50°C. Finally, the coal slurry is centrifuged or pressure filtered to obtain the finished catalyst. To ensure the formation of nano-sized, highly active hydrated iron oxide (γ-FeOOH), the oxidation reaction time in this preparation process is 100 minutes. However, this method is a liquid-phase oxidation reaction, and the slow mass transfer due to low-pressure oxidation leads to low reaction efficiency and a long reaction time.

[0010] Existing iron-based catalysts for direct coal liquefaction typically employ a precipitation reaction using a low-concentration (e.g., 3 wt.%) ferrous sulfate solution and an extremely dilute (e.g., 1 wt.%) ammonia solution. Air is then introduced under atmospheric pressure to oxidize the ferrous precipitate, generating γ-FeOOH. Because oxygen needs to dissolve and penetrate the liquid film, mass transfer in the liquid phase is slow, requiring an oxidation reaction time of over one hour to ensure the generation of nanoscale, highly active γ-FeOOH. Therefore, industrial oxidation reactors are large, limiting the production capacity of industrial plants. Simultaneously, due to the long residence time of the slurry material in the oxidation reactor, calcium and magnesium ions from the ash in the carrier coal are dissolved and displaced, reacting with the large amount of sulfate ions present in the system to generate calcium sulfate and magnesium sulfate. These deposit on the internal components and flow pipes of the oxidation reactor, forming scale, which reduces the production efficiency of industrial plants, and in severe cases, necessitates shutdown for cleaning. Secondly, due to the high water temperature supplied to industrial catalyst production equipment, and the heat generated by mechanical actions such as grinding, rotation, shearing, and conveying, coupled with the exothermic reaction of oxidation, the temperature inside the oxidation reactor often reaches above 60°C. At high temperatures, the reaction rate is fast, but due to the low oxidation mass transfer efficiency, ferrous ions tend to generate less active iron oxides such as Fe3O4 and Fe2O3. Furthermore, at high temperatures, the precipitation and scaling of calcium and magnesium ions become more severe.

[0011] In summary, current methods for preparing iron-based catalysts for direct coal liquefaction typically encounter the following problems: liquid-phase precipitation methods use low concentrations of ferrous sulfate and ammonia, resulting in high water consumption and the generation of significant amounts of difficult-to-treat wastewater; highly active γ-FeOOH is difficult to generate, and agglomeration occurs during drying; the phase transformation of ferrous iron cannot be matched with suitable oxygen supply efficiency and oxidation environment, easily leading to the formation of weaker iron oxides such as Fe3O4 and Fe2O3. Therefore, a method for preparing iron-based slurry catalysts for direct coal liquefaction is urgently needed to address these technical issues. Summary of the Invention

[0012] The main objective of this invention is to provide a direct coal liquefaction iron-based slurry catalyst and its preparation method, in order to solve the problems of low reaction efficiency, easy occurrence of side reactions, easy product agglomeration, high wastewater treatment cost, and low product activity in the preparation process of existing direct coal liquefaction iron-based catalysts.

[0013] To achieve the above objectives, according to one aspect of the present invention, a method for preparing an iron-based slurry catalyst for direct coal liquefaction is provided, comprising the following steps: Step S1, mixing pulverized coal, an aqueous solution of ferrous sulfate, and an aqueous solution of ammonia to undergo a precipitation reaction, generating a suspension of precipitated products; Step S2, contacting the suspension of precipitated products countercurrently with compressed air to obtain a gas-liquid mixture, wherein the gas-liquid mixture undergoes an oxidation reaction to obtain an oxidation product suspension; wherein the oxidation reaction pressure is 0.2~1.0 MPa, the temperature is 10~70℃, and the oxidation residence time is 10~30 min; the oxidation product suspension includes pulverized coal and γ-FeOOH precipitate loaded on the surface of the pulverized coal; Step S3, filtering the oxidation product suspension to obtain a filter cake and a filtrate; mixing the filter cake with a circulating solvent and slurrying to obtain an iron-based slurry catalyst for direct coal liquefaction.

[0014] Further, in step S1, the ferrous sulfate aqueous solution has a weight percentage of 5-15 wt.%; and / or, the ferrous sulfate aqueous solution also includes a first catalytic aid; and / or, the weight ratio of coal powder to iron in the ferrous sulfate aqueous solution is 100:(3-9); and / or, the ammonia aqueous solution has a weight percentage of 1-10 wt.%; and / or, the ammonia aqueous solution also includes a second catalytic aid.

[0015] Further, in step S1, the first catalyst promoter includes one or more of water-soluble salts of alkali metals, transition metals, and aluminum; and / or, the weight ratio of the first catalyst promoter to the iron element in the ferrous sulfate aqueous solution is (0.03~0.08):1; and / or, the second catalyst promoter includes water-soluble silicon salts and / or water-soluble molybdenum salts; and / or, the weight ratio of the second catalyst promoter to the iron element in the ferrous sulfate aqueous solution is (0.02~0.06):1.

[0016] Further, in step S1, the precipitation reaction temperature is 10~70℃ and the time is 0.01~0.3h; and / or, the pH value of the precipitation product suspension is 7.5~9.0.

[0017] Furthermore, in step S2, the gas-liquid ratio of compressed air to the precipitated product suspension is 5~20 Nm. 3 / m 3And / or, the oxidation reaction is carried out in an oxidation reactor, the oxidation reactor including a precipitate suspension inlet, an ammonia inlet, a compressed air inlet, a gas outlet, and an oxidation product suspension outlet. The precipitate suspension inlet and the compressed air inlet are both located on the side wall of the oxidation reactor, and the position of the precipitate suspension inlet is higher than the position of the compressed air inlet in the vertical axis. Preferably, there are 1 to 5 compressed air inlets arranged from top to bottom. Preferably, the ammonia inlet is located on the side wall of the oxidation reactor opposite to the compressed air inlet, and at least one compressed air inlet is located lower than the position of the ammonia inlet. More preferably, there are 1 to 3 ammonia inlets. More preferably, the number of ammonia inlets is the same as the number of compressed air inlets, and the two are arranged alternately along the vertical axis of the oxidation reactor. And / or, the pH difference between the gas-liquid mixture and the oxidation product suspension is ±0.5. And / or, the pH value of the gas-liquid mixture is 7.0 to 8.0. And / or, the pH value of the oxidation product suspension is 7.5 to 8.0.

[0018] Furthermore, in step S2, the oxidation reaction pressure is 0.3~0.8MPa; and / or, the oxidation reaction temperature is 20~60℃; and / or, the oxidation residence time is 15~30min.

[0019] Further, in step S3, the moisture content of the filter cake is 25-40%; and / or, the weight ratio of the filter cake to the circulating solvent is (1-4):1; and / or, the mixing and pulping temperature is 80-150℃.

[0020] Further, in step S3, the circulating solvent includes a high-temperature solvent and / or a medium-temperature solvent; preferably, the weight ratio of the high-temperature solvent to the medium-temperature solvent in the circulating solvent is (0.1~3):1.

[0021] According to another aspect of the present invention, a direct coal liquefaction iron-based slurry catalyst is provided, which is prepared by the above-described method for preparing a direct coal liquefaction iron-based slurry catalyst.

[0022] Furthermore, the solid phase of the coal direct liquefaction iron-based slurry catalyst includes coal powder and γ-FeOOH precipitate supported on the surface of the coal powder, and the liquid phase includes a circulating solvent and water; the weight percentage of iron in the coal direct liquefaction iron-based slurry catalyst is 1~3 wt.%; and / or, the solid content of the coal direct liquefaction iron-based slurry catalyst is 20~50%; and / or, the water content of the coal direct liquefaction iron-based slurry catalyst is 0.2~1%; and / or, the particle size Dv50 of the coal direct liquefaction iron-based slurry catalyst is 20~75 μm; and / or, the γ-FeOOH precipitate is needle-shaped with a diameter of 10~80 nm and a length of 100~500 nm; and / or, the coal direct liquefaction iron-based slurry catalyst also includes auxiliary elements, which include one or more of alkali metal elements, transition metal elements, aluminum elements, silicon elements and molybdenum elements, and the weight percentage of auxiliary elements is 0.05~0.38 wt.%.

[0023] By applying the technical solution of this invention, the solubility of oxygen in the liquid phase is increased by raising the oxidation reaction pressure. Even high-concentration ferrous sulfate and ammonia solutions can undergo sufficient oxidation, significantly reducing the water treatment volume and substantially improving the oxidation reaction efficiency. High oxygen solubility allows for a suitable oxidation environment and oxygen supply efficiency to match the specific phase transformation of ferrous iron at high temperatures, thereby generating highly active γ-FeOOH more efficiently. The improved oxidation efficiency shortens the oxidation reaction time, reducing the residence time of the solid phase in the reactor, thus delaying scaling and extending the operating cycle of the catalyst production unit. Attached Figure Description

[0024] 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:

[0025] Figure 1 A schematic diagram of an apparatus for preparing iron-based slurry catalyst for direct coal liquefaction according to Embodiment 1 of the present invention is shown.

[0026] The above figures include the following reference numerals:

[0027] 1. Ferrous sulfate coal slurry tank; 2. Ferrous salt slurry feed pump; 3. Ammonia solution tank; 4. Ammonia solution feed pump; 5. Dynamic mixing reactor; 6. Oxidation reactor; 61. Precipitated product suspension inlet; 62. Ammonia water inlet; 63. Compressed air inlet; 64. Gas outlet; 65. Oxidation product suspension outlet; 66. Oxidation product suspension recovery port; 7. Oxidation product suspension pump; 8. Oxidation product suspension tank; 9. Filter press feed pump; 10. Filter press; 101. Filtrate outlet; 102. Filter cake outlet; 11. Oil slurry catalyst mixing tank; 12. Oil slurry catalyst transfer pump; 13. Cooler; 14. Gas-liquid separator.

[0028] A. Ferrous sulfate aqueous solution; B. Pulverized coal; C. Ammonia aqueous solution; D. Compressed air; E. Tail gas treatment system; F. Circulating solvent; G. Water treatment system; H. Vacuum system; I. Oil-water separation system; J. Coal direct liquefaction unit. Detailed Implementation

[0029] 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 accompanying drawings and embodiments.

[0030] As described in the background section of this invention, existing technologies suffer from problems such as low reaction efficiency, strong side reactions, easy product agglomeration, high wastewater treatment costs, and low product activity during the preparation of iron-based catalysts for direct coal liquefaction. To address these issues, in a typical embodiment of this invention, a method for preparing an iron-based slurry catalyst for direct coal liquefaction is provided, comprising the following steps: Step S1, mixing pulverized coal, an aqueous solution of ferrous sulfate, and an aqueous solution of ammonia to induce a precipitation reaction, generating a suspension of precipitated products; Step S2, countercurrently contacting the suspension of precipitated products with compressed air to obtain a gas-liquid mixture, which undergoes an oxidation reaction to obtain an oxidation product suspension; wherein the oxidation reaction pressure is 0.2~1.0 MPa, the temperature is 10~70℃, and the oxidation residence time is 10~30 min; the oxidation product suspension includes pulverized coal and γ-FeOOH precipitate loaded on the surface of the pulverized coal; Step S3, filtering the oxidation product suspension to obtain a filter cake and a filtrate; mixing the filter cake with a circulating solvent and slurrying to obtain the iron-based slurry catalyst for direct coal liquefaction.

[0031] First, pulverized coal, ferrous sulfate aqueous solution, and ammonia aqueous solution are mixed and a precipitation reaction occurs to form a suspension of precipitate products. The ferrous sulfate aqueous solution reacts with the ammonia aqueous solution to form ferrous hydroxide precipitate. The pulverized coal acts as a loading medium for the ferrous hydroxide precipitate, which can improve the dispersibility of ferrous hydroxide in the suspension of precipitate products and is more conducive to the subsequent formation of highly dispersed γ-FeOOH precipitate.

[0032] The precipitate suspension is contacted countercurrently with compressed air to form a gas-liquid mixture and undergo an oxidation reaction. During this process, the ferrous ions in ferrous hydroxide are oxidized and undergo a gradual phase change as oxidation progresses, eventually forming γ-FeOOH. The formation conditions for γ-FeOOH are relatively stringent and usually occur at relatively low temperatures of 10–30°C. When the reaction environment is uncontrolled, side reactions inevitably occur. When the oxygen content in the reaction environment is insufficient, the oxidation environment will inevitably be at higher temperatures (e.g., 50–70°C) due to equipment operation and other reasons. At this temperature, the oxidation reaction rate is passively accelerated. Under insufficient oxygen supply, ferrous ions tend to form less reactive iron oxides such as Fe3O4 and Fe2O3. When the pH value of the reaction environment is uncontrolled, hydrogen ions from hydrolysis during the oxidation reaction will accumulate in the gas-liquid mixture as the reaction proceeds, leading to the production of byproducts such as Fe2O3, making it difficult to form the specific oxidation product, namely γ-FeOOH precipitate.

[0033] This invention employs a higher oxidation reaction pressure, which increases the solubility of oxygen in the precipitate product suspension. This allows the oxygen supply efficiency of the environment to match the accelerated oxidation reaction rate at higher equipment temperatures. Consequently, ferrous ions in the precipitate can generate highly active γ-FeOOH over a wider temperature range, increasing their yield and ensuring catalyst activity. Simultaneously, due to the increased oxygen solubility, even high-concentration ferrous sulfate and ammonia solutions can undergo sufficient oxidation, significantly reducing the amount of water required for the oxidation reaction.

[0034] Furthermore, in the gas-liquid mixture, the calcium and magnesium ions contained in the ash of the pulverized coal will dissolve and be displaced into the liquid phase as the residence time increases. These calcium and magnesium ions react with a large amount of sulfate ions present in the system to generate calcium sulfate and magnesium sulfate byproducts, which accumulate in the reaction vessel. Because the oxidation reaction rate of this invention is accelerated and the residence time is shortened, the accumulation of calcium and magnesium ions during the oxidation reaction can be reduced, thus extending the process production cycle.

[0035] The oxidation product suspension is filtered to obtain a filter cake and filtrate. The filter cake is then mixed with a circulating solvent and slurryed to obtain an iron-based oil slurry catalyst for direct coal liquefaction. The filter cake is directly mixed with the circulating solvent to obtain a mixture, which is then evaporated. This allows most of the moisture to be removed directly from the filter cake, reducing the potential for γ-FeOOH crystallization and growth that can occur with gas-solid phase drying. This ensures that γ-FeOOH is highly dispersed in the circulating solvent, enhancing catalyst activity. Furthermore, nano-sized γ-FeOOH is more easily incorporated into the oil phase during rapid stirring and dispersion, leading to the precipitation of the aqueous phase and further improving dehydration efficiency. In addition, the oil slurry catalyst is easy to transport, further improving production efficiency.

[0036] In summary, this invention involves loading ferrous hydroxide precipitate onto the surface of pulverized coal for a controlled oxidation reaction. By increasing the oxidation reaction pressure, the solubility of oxygen in the liquid phase is enhanced. The high oxygen solubility and the controlled pH value, combined with the specific phase transformation of ferrous iron at high temperatures, create a suitable oxidation environment and oxygen supply efficiency, thereby improving the efficiency and selectivity of the oxidation reaction and ultimately generating sufficiently active γ-FeOOH. Using a circulating solvent to separate the precipitate allows for transfer between liquid phases, reducing drying and agglomeration. The increased oxidation efficiency shortens the oxidation reaction time, reducing the residence time of the gas-liquid mixture, thus delaying scaling and extending the operating cycle of the catalyst production unit.

[0037] In a preferred embodiment, in step S1, the ferrous sulfate aqueous solution has a weight percentage of 5-15 wt.%; and / or, the ferrous sulfate aqueous solution further includes a first catalytic aid; and / or, the weight ratio of coal powder to iron in the ferrous sulfate aqueous solution is (10-20):1; and / or, the ammonia aqueous solution has a weight percentage of 1-10 wt.%; and / or, the ammonia aqueous solution further includes a second catalytic aid.

[0038] In existing liquid-phase precipitation oxidation methods, the weight percentages of ferrous sulfate aqueous solution and ammonia aqueous solution are typically in the lower ranges of 2-5% and 0.5-2%, respectively. This invention limits the weight percentages of ferrous sulfate aqueous solution and ammonia aqueous solution to these ranges. Because pressurized oxidation increases oxygen solubility, even higher concentrations of ferrous sulfate and ammonia aqueous solutions can fully undergo the oxidation reaction, significantly reducing the water treatment volume and further lowering production costs while ensuring product activity.

[0039] In some preferred embodiments, a portion of the coal powder used as a direct coal liquefaction feedstock is mixed with an aqueous solution of ferrous sulfate and an aqueous solution of ammonia as a catalyst carrier to further reduce costs and improve the dispersibility of the γ-FeOOH precipitate. The role of adding a first catalytic promoter to the aqueous solution of ferrous sulfate is to improve the dispersibility of iron and promote the formation of more active γ-FeOOH. The role of adding a second catalytic promoter to the aqueous solution of ammonia is to improve the hydrogen activity of iron.

[0040] The method of this application can increase the precipitation reaction rate without the need for a precipitation reactor. In some preferred embodiments, the mixing of pulverized coal, ferrous sulfate aqueous solution, and ammonia aqueous solution is carried out in a dynamic mixing reactor. The dynamic mixing reactor is equipped with an agitator, which causes the mixture to rotate and circulate within the pipes, thereby achieving efficient and uniform mixing of materials. This facilitates the formation of uniform ferrous ion precipitates, while the dynamic precipitation environment further reduces the formation of calcium and magnesium ion scale.

[0041] In a preferred embodiment, in step S1, the first catalyst promoter includes one or more of alkali metals, transition metals, and water-soluble salts of aluminum; and / or, the molar ratio of the first catalyst promoter to iron in the ferrous sulfate aqueous solution is (0.03~0.05):1; and / or, the second catalyst promoter includes water-soluble silicon salts and / or water-soluble molybdenum salts; and / or, the molar ratio of the second catalyst promoter to iron in the ferrous sulfate aqueous solution is (0.02~0.04):1. The alkali metals include one or more of Li, Na, and K; the transition metals include one or more of Zr, Mn, and Zn.

[0042] In some embodiments, the first catalyst promoter includes one or more of Zr(NO3)4·5H2O, Ca(NO3)2, and Al(NO3)3; and / or, the second catalyst promoter includes K2SiO3 and / or (NH4)6Mo7O 24· 4H2O.

[0043] By using a limited variety of first and second catalyst promoters, the particle size of γ-FeOOH can be further refined due to the metal ions present in the first catalyst promoter. In the second catalyst, water-soluble silicon salts (such as K₂SiO₃) and / or water-soluble molybdenum salts (such as (NH₄)₆Mo₇O₇) are used. 24· The addition of 4H2O can further enhance the hydrogen activity of iron, thereby further strengthening its promoting effect on the coal liquefaction catalytic performance of the catalyst. Limiting the addition ratio of the first and second catalysts within the above range is more conducive to promoting the uniform dispersion of the catalyst and iron, thereby further increasing the number of active sites in the catalyst and improving the coal liquefaction catalytic performance of the catalyst.

[0044] In a preferred embodiment, in step S1, the temperature of the precipitation reaction is 10~70°C; and / or, the pH value of the precipitate suspension is 7.5~9.0. Limiting the precipitation reaction conditions to the above range is beneficial for the complete and uniform formation of ferrous hydroxide precipitate. Limiting the pH value of the precipitate suspension to the above range is beneficial for controlling the pH value of the oxidation reaction.

[0045] In a preferred embodiment, in step S2, the gas-liquid ratio of compressed air to the precipitated product suspension is 5~20 Nm. 3 / m 3 That is, the total amount of compressed air introduced into each cubic meter (1000L) of precipitated product suspension is 5~20 Nm³. 3(Standard cubic meters); The oxidation reaction is carried out in oxidation reactor 6, which includes a precipitate suspension inlet 61, an ammonia inlet 62, a compressed air inlet 63, a gas outlet 64, and an oxidation product suspension outlet 65. The precipitate suspension inlet 61 and the compressed air inlet 63 are both located on the side wall of the oxidation reactor 6, and the position of the precipitate suspension inlet 61 is higher than the position of the compressed air inlet 63 in the vertical axis. Preferably, there are 1 to 5 compressed air inlets 63 arranged from top to bottom. Preferably, the ammonia inlet 62 is located in the oxidation reactor. On the side wall of the 6th reactor opposite to the compressed air inlet 63, at least one of the compressed air inlets 63 is positioned lower than the ammonia inlet 62; more preferably, the number of ammonia inlets 62 is 1 to 3; even more preferably, the number of ammonia inlets 62 is the same as the number of compressed air inlets 63, and the two are alternately arranged along the vertical axis of the oxidation reactor 6; and / or, the pH difference between the gas-liquid mixture and the oxidation product suspension is ±0.5; and / or, the pH of the gas-liquid mixture is 7.0 to 8.0; and / or, the pH of the oxidation product suspension is 7.5 to 8.0.

[0046] The oxidation reaction of ferrous iron precipitate is carried out in an oxidation reactor. In some preferred embodiments, the oxidation reactor is a bubble reactor, which is divided into an oxidation reaction section and a gas-liquid separation section. The precipitate suspension enters from the top of the oxidation reaction section and flows out from the bottom of the reactor. Compressed air enters from the middle and lower part of the oxidation reaction section, comes into countercurrent contact with the precipitate suspension, enters the gas-liquid separation section, and then exits from the top of the reactor.

[0047] The pH of the gas-liquid mixture in the reactor is stabilized between 7.0 and 8.0 by adding ammonia water at different gradients, ensuring the stable generation of highly active γ-FeOOH. One to three compressed air inlets are installed on the lower sidewall of the oxidation reactor, each equipped with a gas distributor. Each gas distributor has multiple 3-10 mm orifices facing downwards. An ammonia water injection port is located above the gas distributors on the lower sidewall of the oxidation reactor to replenish the gas-liquid mixture with ammonia water for pH adjustment.

[0048] By setting a limited number of compressed air inlets and forming different reaction zones above them, and introducing compressed air and supplementing ammonia water into different reaction zones, the acidity and alkalinity of the oxidation reaction can be further stabilized, while making it easier for oxygen to fully contact the gas-liquid mixture. This reduces the phenomenon of local reduction of oxygen in the compressed air as the oxidation reaction proceeds in the case of no zone, thereby further optimizing the acidity and alkalinity environment and oxygen supply efficiency of the oxidation reaction, and thus generating highly active γ-FeOOH more efficiently.

[0049] Injecting supplementary ammonia water through a limited amount of ammonia solution inlet can further reduce the overall pH fluctuation of the gas-liquid mixture in the oxidation reactor, and is more conducive to controlling the pH of the gas-liquid mixture and the oxidation product suspension to reach a defined range and difference. A defined pH range makes it easier to neutralize hydrogen ions in the gas-liquid mixture to an appropriate level, promoting the directional progress of the oxidation reaction, further optimizing the selectivity of the oxidation reaction, and thus more efficiently generating sufficiently active γ-FeOOH precipitates. Furthermore, due to pressurized oxidation and zoned injection of compressed air, oxygen solubility and the oxidation reaction rate are further improved, and the water treatment volume is further reduced, thus further increasing the utilization rate of the oxidation reactor per unit volume.

[0050] By adopting a counter-current gas-liquid contact design and precisely controlling the oxidation reaction pressure and pH value, the oxidation reactor of the present invention significantly shortens the reaction residence time, effectively inhibits the formation of calcium sulfate and magnesium sulfate precipitates from calcium and magnesium ions and sulfate ions in pulverized coal ash, thereby greatly reducing scaling on the inner wall of the reactor and pipelines, and extending the continuous operation cycle of the device.

[0051] In a preferred embodiment, in step S2, the oxidation reaction pressure is 0.3~0.8MPa; and / or, the oxidation reaction temperature is 20~60℃; and / or, the oxidation residence time is 15~30min.

[0052] When the oxidation reaction conditions are further limited to the above range, the temperature within the above range makes it easier for the oxidation rate to be passively accelerated, and the oxidation reaction pressure within the above range makes it easier for oxygen to reach a suitable solubility in the liquid phase, thereby improving the oxygen supply efficiency of the environment for the oxidation reaction. This can match a faster oxidation reaction rate at higher equipment temperatures, thereby further improving the catalyst yield while ensuring activity.

[0053] In a preferred embodiment, before step S3, the preparation method further includes dividing the oxidation product suspension into two parts, namely a first part of the oxidation product suspension and a second part of the oxidation product suspension, filtering the first part of the oxidation product suspension, and returning the second part of the oxidation product suspension to step S2 for oxidation reaction; preferably, the volume ratio of the first part of the oxidation product suspension and the second part of the oxidation product suspension is (2~10):1.

[0054] In a preferred embodiment, in step S3, the moisture content of the filter cake is 25-40%; and / or, in the coal direct liquefaction iron-based oil slurry catalyst, the weight ratio of the filter cake to the circulating solvent is (20-70):(20-80); and / or, the mixing and slurrying temperature is 80-150°C; and / or, the filtration method is preferably pressure filtration.

[0055] Limiting the moisture content of the filter cake to the above range can promote the stable dispersion of oxidation products in the filter cake, further reduce agglomeration, and make it more conducive to the uniform dispersion of the oil slurry catalyst in the circulating solvent. This further improves the compatibility of the catalyst with coal liquefaction feedstock in the subsequent direct coal liquefaction reaction, thereby enhancing the coal liquefaction catalytic performance of the catalyst.

[0056] The circulating solvent includes a high-temperature solvent and / or a medium-temperature solvent; preferably, the weight ratio of the high-temperature solvent to the medium-temperature solvent in the circulating solvent is (0.1~3):1.

[0057] Both the high-temperature and medium-temperature solvents are fractions obtained from coal direct liquefaction product oil through sequential hydrogenation and fractionation, with a distillation range of 220–538°C. The high-temperature solvent is obtained from the bottom portion of the hydrogenation-stabilized fractionation column, typically with a temperature range of 270–538°C, while the medium-temperature solvent is obtained from the side stream of the hydrogenation-stabilized fractionation column, typically with a temperature range of 190–350°C. These recycled solvents have higher compatibility with the filter cake, further improving the uniformity of the catalyst's active components in the oil slurry, thereby enhancing the catalyst's coal liquefaction catalytic performance.

[0058] In another typical embodiment of the present invention, a coal direct liquefaction iron-based slurry catalyst is also provided, prepared by the above-described method for preparing the coal direct liquefaction iron-based slurry catalyst. The coal direct liquefaction iron-based slurry catalyst comprises a solid phase and a liquid phase. Because the above preparation method can improve the activity and yield of γ-FeOOH and enhance the dispersibility of the solid phase in the coal direct liquefaction iron-based slurry catalyst, the resulting slurry catalyst has more active sites for the coal direct liquefaction reaction, further improving the catalyst's coal liquefaction catalytic performance.

[0059] In a preferred embodiment, the solid phase of the coal direct liquefaction iron-based slurry catalyst comprises coal powder and γ-FeOOH precipitate supported on the surface of the coal powder, and the liquid phase comprises a circulating solvent and water; the iron content in the coal direct liquefaction iron-based slurry catalyst is 1-3 wt.%; and / or, the solid content of the coal direct liquefaction iron-based slurry catalyst is 20-50%; and / or, the water content of the coal direct liquefaction iron-based slurry catalyst is 0.2-1%; and / or, the particle size Dv50 of the coal direct liquefaction iron-based slurry catalyst is 20-75 μm; and / or, the γ-FeOOH precipitate is needle-shaped with a diameter of 10-80 nm and a length of 100-500 nm; and / or, the coal direct liquefaction iron-based slurry catalyst further comprises an auxiliary element, which includes one or more of alkali metals, transition metals, aluminum, silicon, and molybdenum, and the weight percentage of the auxiliary element is 0.05-0.38 wt.%. In some embodiments, the particle size Dv50 of the iron-based slurry catalyst for direct coal liquefaction is 43-59 μm; and / or, the γ-FeOOH precipitate is needle-shaped with a diameter of 25-75 nm and a length of 129-465 nm; and / or, the weight percentage of the auxiliary element is 0.08-0.38 wt.%.

[0060] Iron-based slurry catalysts for direct coal liquefaction with the aforementioned content range exhibit higher uniformity and dispersibility, further increasing the contact area with the reaction substrate and thus promoting the forward reaction of coal liquefaction. Catalysts with particle sizes within the aforementioned range have higher specific surface areas and greater dispersibility in the slurry, further increasing the contact area between iron and the coal liquefaction feedstock, increasing the active sites for the catalytic reaction, and thereby further improving the catalytic efficiency of direct coal liquefaction. The aforementioned types of auxiliary elements interact with the iron in the catalyst, promoting reduction and inhibiting aggregation, which further enhances catalyst activity and improves the efficiency of the coal liquefaction reaction.

[0061] In some embodiments, a schematic diagram of a coal direct liquefaction iron-based slurry catalyst preparation apparatus is shown below. Figure 1As shown, ferrous sulfate aqueous solution A and pulverized coal B are first fed into ferrous sulfate coal slurry tank 1 for premixing, and then fed into dynamic mixing reactor 5 through iron salt slurry feed pump 2. At the same time, ammonia solution C from ammonia solution tank 3 is fed into dynamic mixing reactor 5 through ammonia solution feed pump 4 for precipitation reaction. The resulting precipitate suspension is fed into oxidation reactor 6 through precipitate suspension inlet 61 on the upper side wall of oxidation reactor 6. Ammonia solution C is divided into three sections and fed into oxidation reactor 6 through three ammonia inlets 62 on the side wall of oxidation reactor 6. Compressed air D is divided into three sections and fed into oxidation reactor 6 through three compressed air inlets 63 on the side wall of oxidation reactor 6. A gas-liquid mixture is obtained in oxidation reactor 6 and undergoes oxidation reaction. The pH of the reaction solution is controlled by the addition of ammonia solution C. The resulting oxidation product suspension is discharged from oxidation product suspension outlet 65 at the bottom of oxidation reactor 6, and the tail gas is discharged from gas outlet 64 and sent to tail gas treatment system E.

[0062] Preferably, the side wall of the oxidation reactor 6 is also provided with an oxidation product suspension recovery port 66, and a portion of the oxidation product suspension is fed into the oxidation product suspension recovery port 66 on the side wall of the oxidation reactor 6. Another portion of the oxidation product suspension is further fed into the oxidation product suspension tank 8 for storage by the oxidation product suspension pump 7, and then fed into the filter press 10 for filtration by the filter press feed pump 9. The filtrate is discharged from the filtrate outlet 101 and sent to the water treatment system G, and the filter cake is discharged from the filter cake outlet 102 and sent to the oil slurry catalyst mixing tank 11. At the same time, the circulating solvent F is sent into the oil slurry catalyst mixing tank 11 for mixing and slurrying, to obtain the coal direct liquefaction iron-based oil slurry catalyst, the residual circulating solvent vapor and the vapor of the displaced water. The coal direct liquefaction iron-based oil slurry catalyst is sent to the coal direct liquefaction unit J by the oil slurry catalyst transfer pump 12; the residual circulating solvent vapor and the vapor of the displaced water are sent to the gas-liquid separator 14 through the cooler 13, where a vacuum is drawn by the vacuum system H, and the feed liquid is sent to the oil-water separation system I.

[0063] In actual operation, it is preferable that the oxidation product suspension recovery port 66 is located on the other side of the oxidation reactor 6 relative to the precipitated product suspension inlet 61.

[0064] Typical, but not limiting, oxidation reaction pressures are 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, 1.0 MPa, or any two of these values. Oxidation reaction temperatures are 10℃, 15℃, 23℃, 28℃, 34℃, 40℃, 45℃, 52℃, 58℃, 65℃, 70℃, or any two of these values. Oxidation residence times are 10 min, 12 min, 14 min, 15 min, 18 min, 20 min, 22 min, 25 min, 26 min, 28 min, 30 min, or any two of these values. The gas-liquid ratio of compressed air to the precipitated product suspension is 5 Nm³. 3 / m 3 7Nm 3 / m 3 9Nm 3 / m 3 10Nm 3 / m 3 12Nm 3 / m 3 14Nm 3 / m 3 15Nm 3 / m 3 17Nm 3 / m 3 19Nm 3 / m 3 20Nm 3 / m 3 Or a range of values ​​consisting of any two of its values.

[0065] 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.

[0066] Example 1

[0067] Step S1: Prepare a 12 wt% ferrous sulfate aqueous solution. Add coal powder (average particle size 50 μm) to the ferrous sulfate aqueous solution and add Zr(NO3)4·5H2O as the first catalyst to make the Zr to Fe weight ratio 4:100 and the coal powder to Fe weight ratio 100:6. Prepare a 5 wt% ammonia aqueous solution and add K2SiO3·nH2O (n=8) as the second catalyst to make the Si to Fe weight ratio 3:100. Feed the ammonia aqueous solution and ferrous sulfate aqueous solution into a dynamic mixing reactor at 500 rpm for 0.1 h of precipitation reaction at 30℃ to obtain a precipitated product suspension with a pH of 8.2.

[0068] In step S2, the precipitated product suspension enters the oxidation reactor through the precipitated product suspension inlet on the upper side wall of the oxidation reactor. Ammonia solution and compressed air are separated into three sections and independently introduced into the oxidation reactor through three ammonia inlets and three compressed air inlets on the side wall of the oxidation reactor. A gas-liquid mixture is obtained in the oxidation reactor, and the pH value of the gas-liquid mixture is controlled at 7.5. The oxidation reaction is carried out, with the reaction temperature controlled at 40℃, the reaction pressure at 0.6MPa, the oxidation reaction residence time at 20min, and the gas-liquid ratio of compressed air to precipitated product suspension at 15Nm. 3 / m 3 The resulting oxidation product suspension is discharged from the bottom of the oxidation reactor, with its pH value controlled at 7.5, and the gas is discharged from the top.

[0069] The oxidation product suspension is divided into a first oxidation product suspension and a second oxidation product suspension. The first oxidation product suspension is processed in step S3, and the second oxidation product suspension is returned to the oxidation reactor for oxidation reaction. The volume ratio of the first oxidation product suspension to the second oxidation product suspension is 3:1.

[0070] In step S3, the first part of the oxidation product suspension is added to a filter press for filtration to separate it into filter cake and filtrate. The water content of the filter cake is controlled to be 25%. The high-temperature solvent and the medium-temperature solvent are mixed at a weight ratio of 1:3 to form a circulating solvent. The filter cake and the circulating solvent are mixed and slurried at 120°C for 1.5 hours. The weight ratio of the filter cake to the circulating solvent is 3:1, thus obtaining the iron-based oil slurry catalyst for direct coal liquefaction.

[0071] Example 2

[0072] The difference from Example 1 is that in step S1, the ferrous sulfate aqueous solution has a weight percentage of 8 wt%.

[0073] Example 3

[0074] The difference from Example 1 is that in step S1, the ammonia solution has a weight percentage of 3 wt%.

[0075] Examples 4 to 16

[0076] The difference from Example 1 is that the oxidation reaction conditions in step S2 are different, as detailed in Table 1.

[0077] Example 17

[0078] The difference from Example 1 is that in step S1, the weight percentage of ferrous sulfate aqueous solution is 5 wt%, the weight percentage of ammonia aqueous solution is 1 wt%, and the weight ratio of coal powder to iron in ferrous sulfate aqueous solution is 100:9.

[0079] Example 18

[0080] The difference from Example 1 is that in step S1, the ferrous sulfate solution has a weight percentage of 15 wt%, the ammonia solution has a weight percentage of 10 wt%, and the weight ratio of iron in the coal powder to the ferrous sulfate solution is 100:3.

[0081] Example 19

[0082] The difference from Example 1 is that in step S2, the ammonia solution and compressed air are divided into two sections and enter the oxidation reactor independently from the two ammonia inlets and the two compressed air inlets on the side wall of the oxidation reactor for oxidation reaction.

[0083] Example 20

[0084] The difference from Example 1 is that in step S2, the ammonia solution and compressed air are introduced into the oxidation reactor independently from one ammonia inlet and one compressed air inlet on the side wall of the oxidation reactor to carry out the oxidation reaction.

[0085] Example 21

[0086] The difference from Example 1 is that,

[0087] In step S1, Zr(NO3)4·5H2O is added to the ferrous sulfate aqueous solution to make the weight ratio of Zr to Fe 3:100, and K2SiO3·nH2O is added to the ammonia aqueous solution to make the weight ratio of Si to Fe 2:100.

[0088] Example 22

[0089] The difference from Example 1 is that,

[0090] In step S1, Zr(NO3)4·5H2O is added to the ferrous sulfate aqueous solution to make the weight ratio of Zr to Fe 8:100, and K2SiO3·nH2O is added to the ammonia aqueous solution to make the weight ratio of Si to Fe 6:100.

[0091] Example 23

[0092] The difference from Example 1 is that,

[0093] In step S1, Ca(NO3)2 is used as the first catalyst promoter, and (NH4)6Mo7O 24· 4H2O was used as the second catalytic agent; the oxidation reaction temperature was 10℃, and the pH of the resulting precipitate suspension was controlled at 7.5.

[0094] In step S3, the moisture content of the filter cake is controlled to be 40% during filtration. The high-temperature solvent and the medium-temperature solvent are mixed at a weight ratio of 0.1:1 to form a circulating solvent. The weight ratio of the filter cake to the circulating solvent is 2:1. The filter cake and the circulating solvent are mixed and slurried at 80°C to obtain the iron-based oil slurry catalyst for direct coal liquefaction.

[0095] Example 24

[0096] The difference from Example 1 is that,

[0097] In step S1, Al(NO3)3 is used as the first catalyst; the precipitation reaction temperature is 70℃; and the pH value of the resulting precipitate suspension is controlled at 9.0.

[0098] In step S3, the moisture content of the filter cake is controlled to be 30% during filtration, and the weight ratio of the filter cake to the circulating solvent is 1:1. The high-temperature solvent and the medium-temperature solvent are mixed at a weight ratio of 3:1 to form the circulating solvent. The filter cake and the circulating solvent are mixed and slurried at 150°C to obtain the iron-based oil slurry catalyst for direct coal liquefaction.

[0099] Example 25

[0100] The difference from Example 1 is that,

[0101] In step S3, a circulating solvent is prepared by mixing a high-temperature solvent and a medium-temperature solvent at a weight ratio of 1:1. The weight ratio of the filter cake to the circulating solvent is 4:1. The filter cake and the circulating solvent are mixed and slurried at 150°C to obtain a coal direct liquefaction iron-based oil slurry catalyst.

[0102] Example 26

[0103] The difference from Example 1 is that,

[0104] In step S3, a circulating solvent is prepared by mixing a high-temperature solvent and a medium-temperature solvent at a weight ratio of 0.1:1. The filter cake and the circulating solvent are mixed and slurried at 150°C to obtain a coal direct liquefaction iron-based oil slurry catalyst.

[0105] Example 27

[0106] The difference from Example 1 is that,

[0107] In step S1, the precipitation reaction time is 0.01 h and the reaction temperature is 70 °C.

[0108] In step S2, the precipitated product suspension enters the oxidation reactor through the precipitated product suspension inlet on the upper side wall of the oxidation reactor. Ammonia solution and compressed air are introduced into the oxidation reactor independently through one ammonia inlet and one compressed air inlet on the side wall of the oxidation reactor, respectively. A gas-liquid mixture is obtained in the oxidation reactor and an oxidation reaction is carried out. The resulting oxidation product suspension is discharged from the bottom of the oxidation reactor and the gas is discharged from the top.

[0109] Example 28

[0110] The difference from Example 1 is that,

[0111] In step S1, the precipitation reaction takes 0.3 hours and the reaction temperature is 10°C.

[0112] In step S2, the precipitated product suspension enters the oxidation reactor through the precipitated product suspension inlet on the upper side wall of the oxidation reactor. The ammonia solution and compressed air are divided into 5 sections and enter the oxidation reactor independently through 5 ammonia inlets and 5 compressed air inlets on the side wall of the oxidation reactor. A gas-liquid mixture is obtained in the oxidation reactor and undergoes an oxidation reaction. The resulting oxidation product suspension is discharged from the bottom of the oxidation reactor, and the gas is discharged from the top.

[0113] Example 29

[0114] The difference from Example 1 is that,

[0115] In step S2, the amount of ammonia added is adjusted so that the pH value of the gas-liquid mixture in the oxidation reactor reaches 7.0 and the pH value of the oxidation product suspension reaches 7.5, with a difference of -0.5.

[0116] Example 30

[0117] The difference from Example 1 is that,

[0118] In step S2, the amount of ammonia added is adjusted so that the pH value of the gas-liquid mixture in the oxidation reactor reaches 8.0 and the pH value of the oxidation product suspension reaches 7.5, with a difference of 0.5.

[0119] Example 31

[0120] The difference from Example 1 is that,

[0121] In step S2, the amount of ammonia added is adjusted so that the pH value of the gas-liquid mixture in the oxidation reactor reaches 7.5 and the pH value of the oxidation product suspension reaches 8.0, with a difference of -0.5.

[0122] Example 32

[0123] The difference from Example 1 is that,

[0124] In step S2, the amount of ammonia added is adjusted so that the pH value of the gas-liquid mixture in the oxidation reactor reaches 7.2 and the pH value of the oxidation product suspension reaches 7.7, with a difference of -0.5.

[0125] Comparative Example 1

[0126] The difference from Example 1 is that in step S2, the oxidation reaction pressure is atmospheric pressure (0.1 MPa) and the oxidation residence time is 1.5 h; the ammonia solution and compressed air are introduced into the oxidation reactor independently from one ammonia inlet and one compressed air inlet on the side wall of the oxidation reactor, respectively, and a gas-liquid mixture is obtained in the oxidation reactor.

[0127] Performance testing:

[0128] 1. Catalyst characterization:

[0129] The following characterization tests were performed on the iron-based oil slurry catalyst for direct coal liquefaction, and the results are shown in Table 2.

[0130] The weight percentage of iron or auxiliary elements: The content of metal elements was determined by inductively coupled plasma (ICP).

[0131] Solid content: Accurately weigh a certain amount of catalyst sample, filter it, wash the filter cake with tetrahydrofuran solvent to remove the oil phase, collect the solid phase, control the temperature of the drying oven at 105~110℃, dry it until the mass is constant, and calculate the solid content.

[0132] Moisture content: Accurately weigh a certain amount of catalyst sample, filter it, collect the oil phase, and then measure the moisture content of the oil phase using GB / T 260-2016 "Determination of Moisture in Petroleum Products" to further calculate the moisture content of the catalyst.

[0133] Oil slurry catalyst particle size Dv50: A certain amount of catalyst sample is accurately weighed, filtered, and the filter cake is washed with tetrahydrofuran solvent to remove the oil phase. The solid phase is then collected, and the particle size distribution of the solid phase is determined by a laser particle size analyzer.

[0134] Size of γ-FeOOH precipitate: observed using scanning electron microscopy.

[0135] 2. Catalyst performance:

[0136] 2.1 Dry Coal Analysis

[0137] The following industrial and elemental analyses were performed on the dry coal in the direct coal liquefaction feedstock, and the results are shown in Table 3.

[0138] Industrial analysis: Determined according to the methods in GB / T211-2017 and GB / T212-2008. Among them, M... ad Refers to the air-dried basis water content; A dAsh content on a dry basis; V daf Refers to dry, ash-free volatile matter.

[0139] Elemental analysis: determined according to the methods in GB / T214-2007, GB / T476-2008 and GB / T19227-2008. Among them, C... ad S ad H ad O ad N ad These refer to the content of the elements C, H, O, N, and S, respectively.

[0140] 2.2 Performance of Coal Liquid in Direct Coal Liquefaction

[0141] The coal liquefaction reaction performance of the iron-based oil slurry catalyst for direct coal liquefaction was tested. The test methods and result calculation methods were in accordance with GB / T 33690-2017 "High-pressure reactor test method for coal liquefaction reactivity". The results are shown in Table 4.

[0142] A high-pressure reactor test was conducted on the iron-based oil slurry catalyst for direct coal liquefaction. The specific steps are as follows: Coal slurry was added to a 500 mL high-pressure reactor for coal liquefaction reaction. The amount of dry coal added to the direct coal liquefaction feedstock (i.e., coal slurry) was 28 g; the weight ratio of iron in the iron-based oil slurry catalyst to dry coal was 0.01:1; coal liquefaction circulating oil (high-temperature solvent: medium-temperature solvent = 1:3) was used as the solvent, with a solvent volume of 42 g; a certain amount of sulfur powder was added, and the atomic ratio of sulfur in the sulfur powder to iron in the iron-based oil slurry catalyst was 2:1. The initial cold hydrogen pressure in the high-pressure reactor was 10 MPa, and the reactor was kept at 455℃ for 1 hour. After the reaction was completed, the reaction system was rapidly cooled, a gas sample was taken to determine its composition, and the liquid and solid phases after the reaction were collected. They were extracted with hexane and tetrahydrofuran for 48 hours, respectively. The extraction residue was burned to ash, and the coal conversion rate, hydrogen consumption rate, gas yield, water yield, bitumen yield, and oil yield were calculated.

[0143] Table 1

[0144]

[0145] In Table 1, " / " means "same as Example 1".

[0146] Table 2

[0147]

[0148]

[0149] Table 3

[0150]

[0151] Table 4

[0152]

[0153]

[0154] It is evident that Comparative Example 1, due to the oxidation reaction being carried out under normal pressure, resulted in low oxidation efficiency, fewer highly active iron species being generated, and thus weaker coal liquefaction.

[0155] As can be seen from the above, the preparation method of the iron-based slurry catalyst for direct coal liquefaction of the present invention achieves efficient mass transfer of oxygen and precise control of the γ-FeOOH crystal phase in a high-concentration raw material system by oxidizing the precipitated product suspension in countercurrent contact with compressed air under a pressure of 0.2~1.0MPa. This not only significantly shortens the oxidation time (10~30 min) and greatly improves the reaction efficiency, but also effectively inhibits the scaling of calcium and magnesium ions due to the shortened reaction residence time. At the same time, it avoids the agglomeration of active components caused by the drying process, fundamentally solving the technical problems of low efficiency, large amount of wastewater, easy scaling and poor product activity of traditional liquid phase oxidation methods.

[0156] Furthermore, it can be seen that the overall effect is better when all process parameters are within the preferred range of the present invention.

[0157] 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 slurry catalyst for direct coal liquefaction, characterized in that, Includes the following steps: Step S1: Coal powder, ferrous sulfate aqueous solution and ammonia aqueous solution are mixed to produce a precipitation reaction and generate a suspension of precipitate products. Step S2: The precipitated product suspension is contacted countercurrently with compressed air to obtain a gas-liquid mixture. The gas-liquid mixture undergoes an oxidation reaction to obtain an oxidation product suspension. The oxidation reaction is carried out at a pressure of 0.2~1.0 MPa, a temperature of 10~70℃, and an oxidation residence time of 10~30 min. The oxidation product suspension includes the coal powder and γ-FeOOH precipitate loaded on the surface of the coal powder. Step S3: Filter the oxidation product suspension to obtain filter cake and filtrate; mix the filter cake with the circulating solvent and slurry to obtain the coal direct liquefaction iron-based oil slurry catalyst.

2. The preparation method of the iron-based slurry catalyst for direct coal liquefaction according to claim 1, characterized in that, In step S1 The ferrous sulfate aqueous solution has a weight percentage of 5-15 wt.%; and / or, The ferrous sulfate aqueous solution also includes a first catalytic aid; and / or, The weight ratio of the pulverized coal to the iron in the ferrous sulfate aqueous solution is 100:(3~9); and / or, The ammonia solution has a weight percentage of 1-10 wt.%; and / or, The ammonia solution also includes a second catalytic aid.

3. The preparation method of the iron-based slurry catalyst for direct coal liquefaction according to claim 2, characterized in that, In step S1 The first catalyst promoter includes one or more water-soluble salts of alkali metals, transition metals, and aluminum; and / or, The weight ratio of the first catalyst to the iron in the ferrous sulfate aqueous solution is (0.03~0.08):1; and / or, The second catalyst promoter comprises a water-soluble silicon salt and / or a water-soluble molybdenum salt; and / or, The weight ratio of the second catalyst to the iron in the ferrous sulfate aqueous solution is (0.02~0.06):

1.

4. The method for preparing the iron-based slurry catalyst for direct coal liquefaction according to any one of claims 1 to 3, characterized in that, In step S1 The precipitation reaction is carried out at a temperature of 10~70℃ for a time of 0.01~0.3h; and / or, The pH value of the precipitated product suspension is 7.5~9.

0.

5. The method for preparing the iron-based slurry catalyst for direct coal liquefaction according to any one of claims 1 to 4, characterized in that, In step S2 The gas-liquid ratio of the compressed air to the precipitated product suspension is 5~20 Nm. 3 / m 3 ; and / or, The oxidation reaction is carried out in an oxidation reactor (6), which includes a precipitate suspension inlet (61), an ammonia inlet (62), a compressed air inlet (63), a gas outlet (64), and an oxidation product suspension outlet (65). The precipitate suspension inlet (61) and the compressed air inlet (63) are both located on the side wall of the oxidation reactor (6), and the position of the precipitate suspension inlet (61) is higher than the position of the compressed air inlet (63) in the vertical axis. Preferably, the compressed air inlet (63) is located at a higher position than the position of the compressed air inlet (65). The number of ammonia inlets (62) is 1 to 5, arranged from top to bottom; preferably, the ammonia inlets (62) are located on the side wall of the oxidation reactor (6) opposite to the compressed air inlets (63), and at least one of the compressed air inlets (63) is positioned lower than the ammonia inlet (62); more preferably, the number of ammonia inlets (62) is 1 to 3; even more preferably, the number of ammonia inlets (62) is the same as the number of compressed air inlets (63), and the two are alternately arranged along the vertical axis of the oxidation reactor (6); and / or, The pH difference between the gas-liquid mixture and the oxidation product suspension is ±0.5; and / or, The pH value of the gas-liquid mixture is 7.0~8.0; and / or, The pH value of the oxidation product suspension is 7.5~8.

0.

6. The method for preparing the iron-based slurry catalyst for direct coal liquefaction according to any one of claims 1 to 5, characterized in that, In step S2 The oxidation reaction is carried out at a pressure of 0.3~0.8 MPa; and / or, The oxidation reaction is carried out at a temperature of 20~60℃; and / or, The oxidation residence time is 15~30 min.

7. The method for preparing the iron-based slurry catalyst for direct coal liquefaction according to any one of claims 1 to 6, characterized in that, In step S3 The moisture content of the filter cake is 25-40%; and / or, The weight ratio of the filter cake to the circulating solvent is (1~4):1; and / or, The mixing and pulping temperature is 80~150℃.

8. The method for preparing the iron-based slurry catalyst for direct coal liquefaction according to any one of claims 1 to 7, characterized in that, In step S3, The circulating solvent includes high-temperature solvents and / or medium-temperature solvents; Preferably, in the circulating solvent, the weight ratio of the high-temperature solvent to the medium-temperature solvent is (0.1~3):

1.

9. A coal direct liquefaction iron-based slurry catalyst, characterized in that, It is prepared by the method for preparing the iron-based slurry catalyst for direct coal liquefaction according to any one of claims 1 to 8.

10. The iron-based slurry catalyst for direct coal liquefaction according to claim 9, characterized in that, The solid phase of the coal direct liquefaction iron-based slurry catalyst comprises coal powder and γ-FeOOH precipitate supported on the surface of the coal powder, and the liquid phase comprises a circulating solvent and water; the iron content in the coal direct liquefaction iron-based slurry catalyst is 1~3 wt.% by weight; and / or, The solid content of the iron-based slurry catalyst for direct coal liquefaction is 20-50%; and / or, the water content of the iron-based slurry catalyst for direct coal liquefaction is 0.2-1%; and / or, The particle size Dv50 of the coal direct liquefaction iron-based slurry catalyst is 20~75μm; and / or, The γ-FeOOH precipitate is needle-shaped, with a diameter of 10-80 nm and a length of 100-500 nm; and / or, The coal direct liquefaction iron-based slurry catalyst also includes auxiliary elements, which include one or more of alkali metal elements, transition metal elements, aluminum elements, silicon elements and molybdenum elements, and the weight percentage of the auxiliary elements is 0.05~0.38 wt.%.

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