An oxidation drying method of a water-saving coal direct liquefaction iron-based catalyst

Abstract

The present application relates to a kind of water-saving coal direct liquefaction iron-based catalyst preparation process in oxidation drying method.The method includes the following steps: (1) the ferrous salt solution, alkaline solution and coal powder are mixed, to prepare the wet catalyst of coal powder load Fe (OH) 2 with ≤30% water content;(2) the wet catalyst of step (1) is sent into first rotary drum oxidizing dryer, with the first oxygen-containing gas sent into the temperature lower than 70 ℃ to carry out first oxidation and pre-drying treatment, obtain pretreatment catalyst;(3) the pretreatment catalyst of step (2) is sent into second rotary drum oxidizing dryer, with the second oxygen-containing gas sent into the temperature higher than 190 ℃ to carry out supplementary oxidation and secondary drying treatment, obtain coal powder load FeOOH iron-based catalyst.The oxidation, drying method in preparation process can make the oxidation and drying of wet catalyst required time short, iron oxidation efficiency is high, preparation process is easy to continuous stable operation, and the coal direct liquefaction activity of prepared catalyst is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of direct coal liquefaction, in particular, to an oxidation drying method of a water-saving type direct coal liquefaction iron-based catalyst. BACKGROUND

[0002] Generally, direct liquefaction is a technology of converting coal into liquid products such as gasoline and diesel by directly hydrogenating coal powder, catalyst and solvent into coal slurry at high temperature and high pressure. Coal liquefaction catalyst is one of the key factors affecting the performance of direct coal liquefaction, and plays an important role in improving the coal conversion rate and oil yield. Coal direct liquefaction catalysts are mainly divided into three categories according to the active components: (1) iron-based catalysts with low price, high activity and no need to recover waste catalysts; (2) cobalt, molybdenum, nickel and tungsten-based catalysts with high cost, high activity and waste catalysts needing to be recovered; (3) metal halide catalysts with high activity and strong corrosion to the device. Relatively speaking, iron-based catalysts with high cost performance are the focus and direction of research and development in the field of coal direct liquefaction catalysts.

[0003] Since the birth of direct coal liquefaction process, in order to improve the performance of direct coal liquefaction, many researchers use natural pyrite or various iron-containing waste residues to prepare direct coal liquefaction catalysts by crushing and grinding. However, due to the limitation of mechanical grinding level, the particle size of the catalyst can only reach micron level, which has the disadvantages of large amount of catalyst addition, low catalytic activity, high energy consumption and poor dispersion in coal slurry, etc., which limits the industrial application of this type of catalyst.

[0004] In order to improve the activity of iron-based catalyst, many researchers have developed high-dispersion synthetic iron-based catalysts. Japan New Energy Development Organization (NEDO) uses iron sulfate and sulfur as raw materials to synthesize iron sulfide (SIS) in a continuous fluidized bed reactor at 480-500℃. The catalyst has higher liquefaction activity than pyrite, but the catalyst is easy to agglomerate and needs to be dispersed by ultrasonic vibration. In addition, due to the use of ferric salt, the cost is relatively high (I. Mochida, Progresses of coal liquefaction catalysts in Japan. Catalysis Surveys from Japan 1998, 2: 17-30).

[0005] CN 101947472 A discloses a preparation method of an oil-soluble direct coal liquefaction catalyst. The invention prepares a direct coal liquefaction catalyst by coating iron oxide nanocrystals with oleic acid. The catalyst has the characteristics of high dispersion, good oil solubility, non-toxicity, high catalytic activity, good selectivity, high oil yield and high conversion rate, but has the disadvantages of high catalyst cost and complex preparation process.

[0006] CN03153377.9 uses ferrous sulfate and ammonia as raw materials, mixes ferrous sulfate solution and coal powder, then adds a certain amount of ammonia solution to prepare coal slurry loaded with Fe(OH)2precipitate, and then prepares a high-dispersion iron-based coal direct liquefaction catalyst through oxidation and filtration. The catalyst is a nano catalyst, the catalyst particle width is 20-50 nm, the length is 60-150 nm, the catalytic activity is higher than that of natural pyrite, the preparation process is simple, the operation is convenient, and the catalyst is easy to scale up. However, there are also disadvantages such as long preparation process, high energy consumption for filtration, and large water consumption for preparation.

[0007] CN108772064 A discloses a preparation method of an iron-based catalyst, which comprises loading an iron-containing soluble salt solution on a catalyst carrier by spraying, then spraying an alkaline aqueous solution onto the carrier, oxidizing the secondary product, and then obtaining the iron-based catalyst through crystal phase transformation. The preparation process is complex, involves two spraying processes, and it is difficult to ensure uniform loading for mixing reaction.

[0008] CN108970614 A discloses a preparation method of an iron-based catalyst for coal direct liquefaction, which comprises mixing and reacting an iron-containing soluble salt solution and an alkaline aqueous solution to obtain a slurry primary product, then loading the primary product on a solid carrier by spraying in an oxygen-containing atmosphere to obtain a secondary product with FeOOH loaded on the surface of the solid carrier, and then drying under a nitrogen atmosphere to obtain the catalyst. The preparation method has short process flow, low production cost, low water consumption, and no wastewater, but also has the following disadvantages: the slurry primary product reacts in an oxygen-containing atmosphere to increase the viscosity, which easily blocks the spray head and affects the uniform dispersion and loading effect of the solid carrier; drying is carried out in a nitrogen atmosphere, and the catalyst is easily oxidized when using ferrous solution as raw material.

[0009] CN 109433210 A discloses a preparation method of a coal direct liquefaction iron-based catalyst, which comprises the following steps: reacting an iron salt solution and ammonia water through a static mixer to obtain a slurry mixture containing iron precipitate, then the slurry mixture containing iron precipitate enters an absorption oxidation reactor and is atomized into mist droplets, and the mist droplets are mixed with coal powder and absorbed by the coal powder, and then the coal powder absorbing the mist droplets is subjected to rapid oxidation in the absorption oxidation reactor to generate an iron oxide precursor under the action of a first hot air with 4-12% oxygen at 80-120 DEG C, and then the iron oxide precursor is dried in a ball mill dryer under the action of a second hot air at 180-260 DEG C to obtain the catalyst. The method has low cost, low water consumption and low energy consumption, and the catalyst has high activity. However, the method also has the following disadvantages: the viscosity of the slurry at the nozzle increases due to the action of the hot air with 4-12% oxygen at 80-120 DEG C when the slurry mixture containing iron precipitate enters the absorption oxidation reactor and is atomized into mist droplets, which easily causes the nozzle to be blocked and affects the stable operation of the production; the slurry mixture containing iron precipitate is subjected to the hot air before being mixed with the coal powder, which easily causes the slurry to be dehydrated and hardened and affects the mixing and absorption effect with the coal powder; the high temperature and low oxygen content of the hot air in the absorption oxidation reactor easily cause the slurry containing divalent iron precipitate to be rapidly dehydrated and insufficiently oxidized, which causes the iron oxidation efficiency of the catalyst to be poor, etc.

[0010] CN107349948A discloses an iron-alkali composite catalyst for coal direct liquefaction, which is prepared by mixing and stirring coal powder, an iron salt solution, an alkali solution and an additive, and then drying the mixture to obtain a supported iron-alkali composite catalyst. However, the method has large water consumption and high energy consumption, and the properties of the dried product are difficult to guarantee.

[0011] In view of the problems of large water consumption, long process flow, easy blockage and non-uniformity in the preparation process of the existing industrial coal direct liquefaction iron-based catalyst, it is necessary to develop a new water-saving preparation technology of a coal direct liquefaction iron-based catalyst using a high-concentration raw material solution. SUMMARY

[0012] The purpose of the present application is to provide an oxidation and drying method of a water-saving coal direct liquefaction iron-based catalyst, which can save water and shorten the time required for oxidation and drying of the wet catalyst, thereby improving the efficiency.

[0013] To achieve the above-mentioned purpose, the present application adopts the following technical solution:

[0014] An oxidation and drying method of a water-saving coal direct liquefaction iron-based catalyst, characterized in that the oxidation and drying method comprises the following steps:

[0015] (1) mixing a ferrous salt solution, an alkali solution and coal powder to prepare a wet catalyst with a water content of ≤30% and the coal powder loaded with Fe(OH)2;

[0016] (2) the wet catalyst of step (1) is sent into a first rotary drum oxidizing dryer, and is contacted with a first oxygen-containing gas with a temperature lower than 70°C to perform a first oxidation and pre-drying treatment, to obtain a pretreated catalyst;

[0017] (3) the pretreated catalyst of step (2) is sent into a second rotary drum oxidizing dryer, and is contacted with a second oxygen-containing gas with a temperature higher than 190°C to perform a supplementary oxidation and secondary drying treatment, to obtain a coal-powder loaded FeOOH iron-based catalyst.

[0018] In step (1) of the present application, when mixing the ferrous salt solution, the alkaline solution and the coal powder, the ferrous salt solution and the alkaline solution can be first mixed and reacted in an inert atmosphere to generate a slurry containing Fe(OH)2precipitate, and then the slurry is mixed uniformly with the coal powder in a mixing machine under an inert atmosphere such as nitrogen atmosphere, and the slurry is uniformly absorbed on the coal powder by rotating stirring, to obtain a wet catalyst. In some embodiments, the particle size of the coal powder is less than 200 mesh, i.e., can pass through a 200 mesh Tyler standard sieve, to better disperse in the direct coal liquefaction reaction.

[0019] Preferably, in step (1), the concentration of the ferrous salt solution is 15% to 35%, such as 18%, 20%, 25% or 30%; and the ferrous salt solution is a divalent iron inorganic salt solution, preferably a ferrous sulfate solution.

[0020] Preferably, in step (1), the concentration of the alkaline solution is 15% to 35%, such as 18%, 20%, 25% or 30%; and the alkaline solution is a weak alkaline solution containing hydroxyl or a strong alkaline solution, preferably ammonia water.

[0021] In some embodiments, preferably, in step (1), the water content of the wet catalyst is 15% to 30%, such as 20%, 24%, 26% or 28%, to maintain the loose state of the wet catalyst.

[0022] In step (2) of the present application, the wet catalyst is pre-dried and first oxidized in the first rotary drum oxidizing dryer using the first oxygen-containing gas; and the use of rotary kiln type equipment to process the material therein is well known in the art, and to improve the processing effect, the inner wall of the drum of the first rotary drum oxidizing dryer can be provided with a uniform distribution type scraper, and the inside of the drum can be provided with a coaxially rotating dispersing tooth rod, specifically, the rotary kiln type equipment used can be a dispersing rotary dryer.

[0023] To ensure the effect of primary oxidation, the oxygen content of the first oxygen-containing gas is preferably 15-30 vol%, such as 18 vol%, 20 vol% or 25 vol%, and the temperature is 30-60°C, such as 40°C or 50°C, preferably air is used to reduce the cost while ensuring the effect of oxidation; and further preferably, in step (2), the volume ratio of the first oxygen-containing gas to the wet catalyst is 500:1-1000:1, such as 600:1 or 800:1; and the residence time of the wet catalyst in the first rotary drum oxidation dryer is 5-15 minutes, such as 8, 10 or 12 minutes, to improve the oxidation efficiency while ensuring the effect of oxidation. It is known in the art that the residence time of the material in the rotary drum can be adjusted by adjusting the relative height of the discharge end of the rotary drum, which will not be described here.

[0024] In step (3) of the present application, the pretreated catalyst is subjected to secondary drying and supplemental oxidation in a second rotary drum oxidation dryer using a second oxygen-containing gas; of course, it is understood in the art that the inner wall of the drum of the second rotary drum oxidation dryer can also be provided with uniform distribution paddles and dispersing toothed bars; in some embodiments, the catalyst after secondary drying and supplemental oxidation can be further subjected to ball milling to achieve better dispersion.

[0025] To control the effect of secondary drying and supplemental oxidation and ensure uniform and sufficient oxidation, the oxygen content of the second oxygen-containing gas is preferably 2-8 vol%, such as 3 vol%, 5 vol% or 7 vol%, and the temperature is 200-250°C, such as 220°C or 240°C; further preferably, in step (3), the volume ratio of the second oxygen-containing gas to the pretreated catalyst is 5000:1-10000:1; and the residence time of the pretreated catalyst in the second rotary drum oxidation dryer is 5-15 minutes, such as 8, 10 or 12 minutes, to improve the oxidation efficiency while ensuring the effect of oxidation.

[0026] In the present application, unless otherwise specified, the percentages or percentages referred to are mass percentages or mass percentages.

[0027] Compared with the prior art, the present application has the following advantages:

[0028] The research finds that the preparation method of the water-saving coal direct liquefaction iron-based catalyst in the prior art has the defects that the slurry containing iron is prone to viscosity increase and nozzle blockage in an oxygen-containing atmosphere, the slurry containing iron precipitate is prone to dehydration and hardening under hot air before being contacted with the coal powder, the high temperature and low oxygen content of the hot air for oxidation result in poor iron oxidation efficiency of the catalyst, and the like. The present application uses a concentrated solution to prepare a wet catalyst with coal powder loaded with Fe(OH)2 and a water content of less than or equal to 30%, and in view of the problems of large particle size of Fe(OH)2 in the prepared catalyst due to the concentrated solution and the difficulty in uniform and sufficient oxidation, the wet catalyst with coal powder loaded with Fe(OH)2 is first subjected to rapid partial oxidation and pre-drying in a first rotary drum oxidation dryer under low temperature but high oxygen content such as flowing air, and then is subjected to supplemental oxidation and drying in a flowing gas with high temperature and low oxygen content to prepare a dry catalyst with coal powder loaded with FeOOH. Through the mutual cooperation of the above two-step oxidation drying, the wet catalyst can be uniformly and fully oxidized, the oxidation and drying time is short, the iron oxidation efficiency is high, and the preparation process is easy to continuously and stably operate. At the same time, it has been verified that the prepared catalyst has high coal direct liquefaction activity and is not weaker than the corresponding catalyst prepared by a dilute solution, and effectively solves the problems of the preparation method of the water-saving coal direct liquefaction iron-based catalyst in the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 Flowchart of the oxidation drying method suitable for the present application;

[0030] BRIEF DESCRIPTION OF DRAWINGS

[0031] 1 is a mixing reactor, 2 is a mixer, 3 is a first rotary drum oxidation dryer, 4 is a first temperature regulator, 5 is a first cyclone dust collector, 6 is a second rotary drum oxidation dryer, 7 is a catalyst bin, 8 is an induced draft fan, 9 is a second temperature regulator, and 10 is a second cyclone dust collector. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0033] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the properties. The endpoints of the ranges and any numerical values should be interpreted as approximately as the range of values in some amount intended for expression as a preciseness. The endpoints of the ranges of values, the endpoints of the ranges of values and separate points, and separate points can be combined with one another to create one or more new ranges of values, which are to be construed as being explicitly included in the present disclosure. In the event of a contradiction, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0034] It should be noted that the terms "first", "second" and the like in the description and in the claims of the present application and in the above-described drawings are intended to distinguish similar objects and not necessarily describe a particular order or sequence. It should be understood that the data thus used can be interchanged, where appropriate, to describe embodiments of the application described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or apparatus that includes a list of steps or units not necessarily limited to those clearly listed, but can include other steps or units not clearly listed or inherent to such processes, methods, products or apparatus.

[0035] The present application provides an oxidation drying method of a water-saving coal direct liquefaction iron-based catalyst, comprising the following steps:

[0036] (1) mixing a ferrous salt solution, an alkaline solution and coal powder to prepare a wet catalyst of coal powder loaded with Fe(OH)2 with a water content of ≤30%;

[0037] (2) feeding the wet catalyst of step (1) into a first rotary drum oxidation dryer, and contacting with a first oxygen-containing gas with a temperature lower than 70℃ to perform a first oxidation and pre-drying treatment, to obtain a pretreated catalyst;

[0038] (3) feeding the pretreated catalyst of step (2) into a second rotary drum oxidation dryer, and contacting with a second oxygen-containing gas with a temperature higher than 180℃ to perform a supplemental oxidation and secondary drying treatment, to obtain an iron-based catalyst of coal powder loaded with FeOOH.

[0039] Specifically, it can be as follows Figure 1As shown, first, the ferrous salt solution and the alkaline solution are mixed in a mixing reactor 1 to prepare a slurry containing Fe(OH)2precipitate, and then the slurry is mixed with coal powder in a mixer 2 under a nitrogen atmosphere to prepare a wet catalyst with Fe(OH)2-loaded coal powder having a water content of ≤30%; the wet catalyst is then continuously fed into a first rotary drum oxidation dryer 3 and a first oxygen-containing gas (air) contact continuously fed after being adjusted in temperature by a first temperature regulator 4 to a temperature of, for example, 30-60°C, to perform a first oxidation and pre-drying treatment, to obtain a pretreated catalyst (the tail gas is discharged after being separated from the pretreated catalyst entrained by a first cyclone 5), and the pretreated catalyst separated from the first cyclone 5 is fed into a second rotary drum oxidation dryer 6 and a second oxygen-containing gas (for example, a mixture of air and nitrogen) contact continuously fed after being adjusted in temperature by a second temperature regulator 9 to a temperature of, for example, 200-250°C, to perform a supplemental oxidation and supplemental drying treatment, to obtain an iron-based catalyst fed into a catalyst bin 7, and the tail gas is discharged after being separated from the pretreated catalyst entrained by a second cyclone 10, and then is partially vented and partially recycled to the second temperature regulator for reuse; the iron-based catalyst separated from the second cyclone 10 is fed into the catalyst bin 7 for standby use.

[0040] The present application is further illustrated by the following examples / Comparative Examples.

[0041] Example 1

[0042] A ferrous sulfate aqueous solution with a mass fraction of 25% and an aqueous ammonia solution with a mass fraction of 25% are respectively fed into a mixing reactor at flow rates of 40.8 kg / h and 9.2 kg / h under a nitrogen atmosphere, and the reaction temperature is maintained at 50°C; the reaction generates a slurry containing Fe(OH)2precipitate with a pH value of 7.5, and then the slurry is mixed with coal powder (coal powder with a particle size of less than 200 mesh and a water content of 3%) at a flow rate of 80 kg / h in a mixer to obtain a wet catalyst with Fe(OH)2-loaded coal powder having a water content of about 30%; the wet catalyst is fed into a first rotary drum oxidation dryer (the same as the following rotary drum oxidation dryer) at a flow rate of 130 kg / h, and flowing air heated to 50°C by a heating furnace at a flow rate of about 100 Nm 3 / h is fed into the first rotary drum oxidation dryer to perform rapid oxidation and pre-drying on the wet catalyst, and the residence time (t1) of the wet catalyst in the first rotary drum oxidation dryer is about 10 minutes; the generated pretreated catalyst with FeOOH-loaded coal powder is fed into a second rotary drum oxidation dryer; an air and nitrogen mixture with an oxygen content of 5 vol% is fed into the second rotary drum oxidation dryer at a flow rate of about 1000 Nm 3The flow rate of 1.5 m3 / h of air is heated to 225°C by a heating furnace and then enters the second rotary drum oxidation dryer to supplement the oxidation and drying of the pre-dried catalyst. The residence time (t2) of the pre-dried catalyst in the second rotary drum oxidation dryer is about 15 minutes, and a dry catalyst loaded with FeOOH is obtained. The analysis of the dry catalyst shows that the water content is about 2.5%, the total iron content is about 4.0%, and the oxidation efficiency (i.e., the percentage of ferric iron in the total iron content) is about 92.5%.

[0043] Examples 2 to 9

[0044] The catalyst preparation and oxidation drying conditions of Examples 2 to 9 are shown in Table 1, and the rest are the same as in Example 1.

[0045] Comparative Example 1

[0046] The catalyst preparation and oxidation drying conditions of Comparative Example 1 are shown in Table 1, and the rest are the same as in Example 1.

[0047] Comparative Example 2

[0048] In Comparative Example 2, the wet catalyst of coal powder loaded with Fe(OH)2 with a water content of about 30% from the mixer does not enter the first rotary drum oxidation dryer for oxidation and pre-drying, but directly enters the second rotary drum oxidation dryer for oxidation and drying. The specific parameters are shown in Table 1.

[0049] Comparative Example 3

[0050] Comparative Example 3 differs from Example 1 in that no second rotary drum oxidation dryer is provided, and the relevant specific parameters are shown in Table 1.

[0051] Comparative Example 4

[0052] A high-dispersion iron-based catalyst for direct coal liquefaction and its preparation method (CN03153377.9) provided in the patent CN03153377.9 is used for preparation. The specific process is as follows: 5.70 kg of ferrous sulfate heptahydrate is dissolved in 46.88 kg of tap water, and then added to 15.78 kg of coal powder to prepare a ferrous sulfate coal slurry. 1.27 kg of concentrated ammonia water is added to 17.38 kg of tap water. Under stirring, the above-mentioned ammonia water is added to the above-mentioned ferrous sulfate coal slurry, and after the addition is completed, the stirring is continued for 10 seconds. When the reaction is completed, the pH value is 7.8. The above-mentioned reaction product is oxidized at 40°C and under an air flow rate of 3 m3 / h for 100 minutes. After the oxidation reaction is completed, centrifugal filtration is performed, and the obtained filter cake is the catalyst of Comparative Example 4. 3 / h air flow rate for 100 minutes. After the oxidation reaction is completed, centrifugal filtration is performed, and the obtained filter cake is the catalyst of Comparative Example 4.

[0053]

[0054] Catalyst performance evaluation

[0055] A certain amount of the catalyst prepared in the above examples and comparative examples was weighed and subjected to coal liquefaction autoclave test, and the coal liquefaction reaction performance test conditions were as follows: the experimental device was a 500 mL autoclave. The coal sample used in the test was Shendong coal (basic properties are shown in Table 2), and the total dry coal powder amount including the dry coal powder in the catalyst was 28 g; the coal liquefaction cycle oil was used as the solvent, the solvent addition amount was 42 g, the catalyst was added according to the Fe / dry coal weight ratio of 1:100, and the molar ratio of the added catalyst to the total iron in the catalyst was 2. The autoclave reaction cold hydrogen initial pressure was 10 MPa, the constant temperature was 455 ℃ for 1 h, and after the reaction was completed, the temperature was lowered to room temperature. The gas sample composition was analyzed by gas chromatography, and the liquid and solid phases were analyzed by solvent extraction, and the coal liquefaction conversion rate and coal liquefaction oil yield were calculated. The specific data are shown in Table 1 above.

[0056] Table 2 Shendong coal analysis data

[0057]

[0058] From the above catalyst preparation oxidation and drying process conditions and the properties of the obtained catalyst and the performance evaluation results of Shendong coal direct liquefaction, it can be seen that the oxidation and drying method provided by the water-saving type coal direct liquefaction iron-based catalyst preparation process of the present application can shorten the oxidation and drying time of the wet catalyst, improve the iron oxidation efficiency, and make the preparation process easy to continuously and stably operate, and the prepared catalyst has high coal direct liquefaction activity.

[0059] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An oxidative drying method of a water-saving coal direct liquefaction iron-based catalyst, characterized by, The oxidation drying method comprises the following steps: (1) mixing a ferrous salt solution, an alkaline solution and coal powder to prepare a wet catalyst of coal powder loaded with Fe(OH)2 with a water content of ≤30%; (2) feeding the wet catalyst of step (1) into a first rotary drum oxidation dryer to contact with a first oxygen-containing gas with a temperature of 30-60℃ to perform a first oxidation and pre-drying treatment, to obtain a pretreated catalyst; wherein the oxygen content of the first oxygen-containing gas is 15-30vol%; (3) feeding the pretreated catalyst of step (2) into a second rotary drum oxidation dryer to contact with a second oxygen-containing gas with a temperature of 200-250℃ to perform a supplemental oxidation and secondary drying treatment, to obtain a coal powder loaded FeOOH iron-based catalyst; wherein the oxygen content of the second oxygen-containing gas is 2-8vol%.

2. The oxidative drying process according to claim 1, characterized in that, In step (1), when the ferrous salt solution, the alkaline solution and the coal powder are mixed, first, the ferrous salt solution and the alkaline solution are mixed and reacted under an inert atmosphere to generate a slurry containing Fe(OH)2precipitate, and then the slurry is mixed with the coal powder in a mixer to obtain the wet catalyst.

3. The oxidative drying process according to claim 1, characterized in that, In step (1), the concentration of the ferrous salt solution is 15%-35%; the ferrous salt solution is a divalent iron inorganic salt solution; The concentration of the alkaline solution is 15%-35%; the alkaline solution is a weak alkaline solution or a strong alkaline solution containing hydroxyl ions.

4. The oxidative drying method according to claim 2, characterized in that, In step (1), the concentration of the ferrous salt solution is 15%-35%; the ferrous salt solution is a ferrous sulfate solution; The concentration of the alkaline solution is 15%-35%; the alkaline solution is ammonia water.

5. The oxidative drying process according to any one of claims 1 to 4, characterized in that, In step (1), the water content of the wet catalyst is 15%-30%.

6. The oxidative drying process according to claim 1, characterized in that, In step (2), the first oxygen-containing gas is air.

7. The oxidative drying process according to claim 6, characterized in that, In step (2), the flow rate of the first oxygen-containing gas based on the mass of the wet catalyst is 0.5 to 1 Nm 3 / kg / h; and the residence time of the wet catalyst in the first rotary drum oxidation dryer is 5 to 15 minutes.

8. The oxidative drying process according to claim 7, characterized in that, In step (3), the flow rate of the second oxygen-containing gas based on the mass of the pretreatment catalyst is 5 to 10 Nm 3 / kg / h; and the residence time of the pretreatment catalyst in the second rotary drum oxidation dryer is 5 to 15 minutes.

9. The oxidation drying method according to any one of claims 1-4 and 6-8, characterized in that, In step (1), the particle size of the coal powder is less than 200 mesh.

10. The oxidative drying process according to claim 1, wherein, The first and second rotary drum oxidation dryers are scattering rotary dryers.

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