CN112569982A

CN112569982A - Composition containing precipitated epsilon/epsilon' iron carbide, preparation method, catalyst and application thereof, and Fischer-Tropsch synthesis method

Info

Publication number: CN112569982A
Application number: CN202011059151.6A
Authority: CN
Inventors: 王鹏; 林泉; 张冰; 门卓武; 程萌; 徐文强; 李为真
Original assignee: China Energy Investment Corp Ltd; National Institute of Clean and Low Carbon Energy
Current assignee: China Energy Investment Corp Ltd; National Institute of Clean and Low Carbon Energy
Priority date: 2019-09-30
Filing date: 2020-09-30
Publication date: 2021-03-30
Anticipated expiration: 2040-09-30
Also published as: CN112569982B

Abstract

The invention relates to the field of Fischer-Tropsch synthesis reaction, and discloses a composition containing precipitated epsilon/epsilon' iron carbide, a preparation method, a catalyst and application thereof, and a Fischer-Tropsch synthesis method. A precipitated epsilon/epsilon ' iron carbide-containing composition comprising 95 to 100 mol% of precipitated epsilon/epsilon ' iron carbide and 0 to 5 mol% of Fe-containing impurities, based on the total amount of the composition, said Fe-containing impurities being iron-containing substances other than epsilon/epsilon ' iron carbide; wherein the specific surface area of the composition is 20-260m²(ii) in terms of/g. Can simply prepare the epsilon/epsilon' carbonizationIron is used as an active component to obtain continuous and stable Fischer-Tropsch synthesis reaction, and the selectivity of effective products is high.

Description

Composition containing precipitated epsilon/epsilon' iron carbide, preparation method, catalyst and application thereof, and Fischer-Tropsch synthesis method

Technical Field

The invention relates to the field of Fischer-Tropsch synthesis reaction, in particular to a composition containing precipitated epsilon/epsilon' iron carbide, a preparation method, a catalyst and application thereof, and a Fischer-Tropsch synthesis method.

Background

The primary energy structure of China is characterized by rich coal, lack of oil and little gas. With the development of economy in China, the dependence of petroleum on the outside is continuously rising.

Fischer-Tropsch synthesis is an increasingly important energy conversion way in recent years, and can convert carbon monoxide and H₂The syngas is converted into liquid fuels and chemicals.

The reaction equation for fischer-tropsch synthesis is as follows:

(2n+1)H₂+nCO→C_nH_2n+2+nH₂O (1)，

2nH₂+nCO→C_nH_2n+nH₂O (2)。

in addition to alkanes and alkenes, industrial fischer-tropsch synthesis can also produce carbon dioxide (CO) as a by-product₂) And methane (CH)₄). The Fischer-Tropsch synthesis reaction has complex mechanism and multiple steps, such as CO dissociation, carbon (C) hydrogenation and CH_xChain growth, and hydrogenation and dehydrogenation reactions that result in hydrocarbon product desorption and oxygen (O) removal.

Iron is the cheapest transition metal used in making fischer-tropsch synthesis catalysts. The traditional iron-based catalyst has high water gas shift (CO + H)₂O→CO₂+H₂) Active, therefore, conventional iron-based catalysts typically have a higher CO by-product₂Selectivity, typically 25% to 45% of the carbon monoxide of the conversion feedstock. This is one of the major disadvantages of iron-based fischer-tropsch catalysts.

The active phase of the iron-based catalyst is very complicated to change, which causes considerable debate between the nature of the active phase and the Fischer-Tropsch synthesis reaction mechanism of the iron-based catalyst.

CN104399501A discloses epsilon-Fe suitable for low-temperature Fischer-Tropsch synthesis reaction₂C, a preparation method of the nano-particles. The initial precursor is skeleton iron, and the reaction system is intermittent discontinuous reaction of polyethylene glycol solvent. CO of this catalyst₂Selectivity 18.9%, CH₄The selectivity of (2) is 17.3%. The disadvantage is that the method can only be applied to low temperature below 200 ℃, and the reaction can not be continuously completed. This means that such catalysts are not suitable for continuous production under modern Fischer-Tropsch synthesis industrial conditions. However, since the skeleton iron cannot be completely carbonized, epsilon-Fe described in the above document₂The nanoparticles of C contain a considerable amount of iron impurity components of the non-iron carbide type, and in fact, the prior art cannot obtain epsilon-Fe free of iron impurities₂C pure phase substance, where Fe impurity is non-epsilon-Fe₂Various Fe (element) -containing phase components of C.

Accordingly, there is a need for an improved iron-based catalyst for use in fischer-tropsch synthesis reactions.

Disclosure of Invention

The invention aims to solve the problem of how to obtain a pure-phase iron carbide substance without Fe impurities by using an iron-based catalyst, improve the stability of Fischer-Tropsch synthesis reaction, and simultaneously reduce CO₂Or CH₄The problem of overhigh selectivity of byproducts, provides a composition containing precipitated epsilon/epsilon' iron carbide, a preparation method, a catalyst and application thereof, and a Fischer-Tropsch synthesis method.

In order to achieve the above object, the first aspect of the present invention provides a precipitated epsilon/epsilon ' iron carbide-containing composition comprising 95 to 100 mol% of precipitated epsilon/epsilon ' iron carbide and 0 to 5 mol% of Fe-containing impurities, which are iron-containing substances other than epsilon/epsilon ' iron carbide, based on the total amount of the composition; wherein the specific surface area of the composition is 20-260m²/g。

In a second aspect, the present invention provides a method for preparing a precipitated epsilon/epsilon' iron carbide-containing composition comprising:

(1) mixing an aqueous solution containing ferric salt with an alkaline precipitator for coprecipitation, washing and separating the obtained precipitate, and drying and roasting the obtained solid to obtain a precursor;

(2) reacting the precursor with H₂The precursor is reduced at the temperature of 450-580 ℃;

(3) mixing the material obtained in the step (2) with H₂Pre-treating CO at 90-185 deg.C, and H₂The molar ratio to CO is 1.2-2.8: 1;

(4) mixing the material obtained in the step (3) with H₂CO at a temperature of 200-₂The molar ratio to CO is 1-3.2: 1, obtaining precipitate type epsilon/epsilon' iron carbide;

(5) mixing 95-100 molar parts of precipitation type epsilon/epsilon' iron carbide and 0-5 molar parts of Fe-containing impurities under the protection of inert gas;

wherein the Fe-containing impurities are iron-containing substances except epsilon/epsilon' iron carbide.

In a third aspect, the invention provides a precipitated epsilon/epsilon' iron carbide-containing composition prepared by the method provided by the invention.

In a fourth aspect, the invention provides a catalyst comprising a precipitated epsilon/epsilon' iron carbide-containing composition provided by the invention.

In a fifth aspect, the invention provides an application of the composition or the catalyst containing the precipitated epsilon/epsilon' iron carbide in Fischer-Tropsch synthesis reaction.

In a sixth aspect, the invention provides a use of the precipitated epsilon/epsilon' iron carbide-containing composition or catalyst provided by the invention in synthesis reactions of C, H fuel and/or chemicals based on the fischer-tropsch principle.

In a seventh aspect, the invention provides a fischer-tropsch synthesis process comprising: under the condition of Fischer-Tropsch synthesis reaction, the synthetic gas is contacted with the composition or the catalyst containing the sediment type epsilon/epsilon' iron carbide provided by the invention.

An eighth aspect of the present invention provides a fischer-tropsch synthesis method, comprising: contacting the synthesis gas with a Fischer-Tropsch catalyst under Fischer-Tropsch synthesis reaction conditions, wherein the Fischer-Tropsch catalyst comprises a Mn component and the precipitated epsilon/epsilon' iron carbide-containing composition provided by the invention.

Through the technical scheme, the invention has the following technical effects:

(1) the required raw materials are simple and easy to obtain, and the cost is low: the iron source of the main raw material for synthesizing the precursor can be commercial iron salt, and when active phase carbide is synthesized, only original reaction gas (carbon monoxide and hydrogen) of a Fischer-Tropsch synthesis reaction system is used, so that no inorganic or organic reaction raw material is involved, and the method is greatly simplified compared with the prior art;

(2) the operation steps are simple and convenient, and in the preferred embodiment, the whole process of preparing the precipitation type epsilon/epsilon' iron carbide only needs three steps of precursor reduction, pretreatment and carbide preparation, and the preparation of the active phase can be realized in situ in the same reactor.

(3) The method comprises the steps of preparing the precipitation type epsilon/epsilon' iron carbide with the purity of 100 percent, and forming a composition with Fe-containing impurities and further forming a catalyst with an auxiliary agent. The 100% purity precipitated epsilon/epsilon' iron carbide or combinationThe product or the catalyst can be used for a high-temperature high-pressure (for example, the temperature of 235-_CThe theoretical technical barrier that the epsilon/epsilon' iron carbide needs to stably exist at the temperature of less than 200 ℃ under mild conditions can realize the stable temperature of up to 250 ℃ and CO₂Very low selectivity: under the condition of industrial Fischer-Tropsch synthesis reaction, a high-pressure continuous reactor can be used for keeping continuous and stable reaction for more than 400h, and CO is generated₂The selectivity is less than 5% (preferably, less than 2.5%); at the same time, its by-product CH₄The selectivity is kept at 13.5 percent (preferably, the selectivity can reach below 9.5 percent), the selectivity of the effective product can reach above 80 percent (preferably, the selectivity can reach above 88 percent), and the method is very suitable for the high-efficiency production of oil wax products in the Fischer-Tropsch synthesis industry of the modern coal chemical industry.

Drawings

FIG. 1 is an in situ XRD spectrum of a precipitated ε/ε' iron carbide preparation process of example 1 as provided in the present invention; wherein, the preparation of the D-iron carbide is completed before the reduction of the A-precursor, after the reduction of the B-precursor and the pretreatment of the C-.

Detailed Description

The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

The invention provides a composition containing precipitated epsilon/epsilon ' iron carbide, which comprises 95 to 100mol percent of precipitated epsilon/epsilon ' iron carbide and 0 to 5mol percent of Fe-containing impurities based on the total amount of the composition, wherein the Fe-containing impurities are substances containing iron elements except epsilon/epsilon ' iron carbide; wherein the specific surface area of the composition is 20-260m²/g。

The invention provides a composition containing precipitated epsilon/epsilon ' iron carbide, wherein the epsilon/epsilon ' iron carbide comprises epsilon-iron carbide with the purity of 100 percent and epsilon ' -iron carbide with the purity of 100 percent. Further, the precipitated epsilon/epsilon' iron carbide may be combined with other Fe-containing impurities. At the upper partUnder the limit of the content, the composition containing the precipitated epsilon/epsilon' iron carbide provided by the invention can be used alone or combined with other components when being applied to a Fischer-Tropsch synthesis catalyst, can improve the stability of the Fischer-Tropsch synthesis reaction of the Fischer-Tropsch synthesis catalyst, and greatly reduce CO₂Or CH₄Selectivity of by-products.

In some embodiments of the invention, the composition comprises precipitated high purity epsilon/epsilon 'iron carbide and XRD and mossbauer spectroscopy analyses are performed to observe that the crystalline phase is pure epsilon/epsilon' iron carbide as a result of the obtained XRD and mossbauer spectroscopy. Preferably, the composition has a specific surface area of 25 to 200m²(ii) in terms of/g. The specific surface area may be represented by N₂The BET adsorption and desorption method (2). The composition comprises hexagonal, pseudohexagonal or trigonal epsilon/epsilon' iron carbide.

In some embodiments of the invention, it is further preferred that the composition comprises 97 to 100 mol% precipitated epsilon/epsilon' iron carbide and 0 to 3 mol% Fe-containing impurities, based on the total amount of the composition. Can be determined by XRD and Mossbauer spectrometry analysis, and can also be determined according to the preparation charge of the composition.

In some embodiments of the invention, the Fe-containing impurities are at least one of iron carbide, iron oxides, iron hydroxides, iron sulfides, iron salts other than epsilon/epsilon' iron carbide. The Fe-containing impurities may be introduced by solution impregnation, sputtering, atomic deposition or mixing.

In some embodiments of the present invention, the iron salt may be a water-soluble iron salt commonly used in the art, and may be selected from water-soluble iron salts, and may be commercially available, for example, the iron salt is at least one of ferric nitrate, ferric chloride, ferrous ammonium sulfate, and ferric ammonium citrate.

In some embodiments of the present invention, the basic precipitant may be conventionally selected in the art, for example, the basic precipitant is at least one of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, sodium hydroxide, potassium hydroxide, and ammonia water.

In a preferred embodiment of the present invention, the drying and baking process comprises: firstly, drying the solid for 6-10h at the temperature of 35-80 ℃ and the vacuum degree of 250-1200 Pa; drying the dried material at 75-180 ℃ for 3-24h, and roasting the obtained material at the temperature of 250-580 ℃ for 1-10 h. The above drying process can be performed in an oven, and the roasting process can be performed in a muffle furnace.

In some embodiments of the present invention, step (2) may perform the functions of in-situ generating nano iron powder from iron element in the precursor and reducing the generated nano iron powder.

In some embodiments of the invention, H in step (2)₂Can be represented by H₂Introducing the mixture into the reaction system in the form of a flow, and simultaneously controlling H₂The pressure of the flow is used to control the pressure of the precursor reduction, preferably, in the step (2), the pressure of the precursor reduction is 0.1-15atm, preferably 0.3-2.6atm, and the time is 0.7-15h, preferably 1-12 h.

The invention isIn some embodiments, H₂The amount of H used may be selected according to the amount of the precursor to be treated, preferably, in step (2), H₂The gas flow rate of (b) is 600-25000mL/h/g, more preferably 2800-22000 mL/h/g.

In step (3) of the process provided by the present invention, H₂And CO may be (H)₂+ CO) mixed gas flow to participate in the pretreatment process; at the same time, by controlling (H)₂+ CO) mixed gas stream pressure to control the pressure of the pretreatment process. Preferably, in the step (3), the pressure of the pretreatment is 0.05-7atm, preferably 0.08-4.5atm, and the time is 15-120min, preferably 20-90 min.

In some embodiments of the present invention, preferably, in step (3), H₂The total gas flow rate with CO is 300-12000mL/h/g, more preferably 1500-9000 mL/h/g.

In step (4) of the method provided by the invention, conditions for realizing the preparation of the carbide are provided so as to obtain the precipitation type epsilon/epsilon' iron carbide. H₂And CO may be (H)₂+ CO) in the form of a mixed gas stream into the carbide production process; at the same time, by controlling (H)₂+ CO) mixed gas stream pressure to control the pressure of the carbide making process. Preferably, in the step (4), the carbide is prepared at a pressure of 0.1 to 10atm, preferably 0.2 to 4.5atm, for a time of 1.5 to 15 hours, preferably 2.5 to 12 hours.

In some embodiments of the present invention, preferably, in step (4), H₂The total gas flow rate with CO is 500-30000mL/h/g, more preferably 3000-25000 mL/h/g.

In a preferred embodiment of the present invention, the carbide preparation further comprises: in the step (4), the temperature is simultaneously raised from the pretreatment temperature to 200-300 ℃ at a temperature raising rate of 0.2-5 ℃/min. In this preferred embodiment, the resulting precipitated epsilon/epsilon' iron carbide may have better effective product selectivity in the fischer-tropsch synthesis reaction. Further preferably, the temperature is raised from the temperature of the pretreatment to 210-290 ℃ at a temperature raising rate of 0.2-2.5 ℃/min. In the temperature raising operation, the temperature of the pretreatment is 90-185 ℃ in the step (3). Namely, the temperature raising operation is: raising the temperature from 90-185 ℃ to 200-300 ℃ at a temperature raising rate of 0.2-5 ℃/min in the step (4), preferably raising the temperature from 90-185 ℃ to 210-290 ℃ at a temperature raising rate of 0.2-2.5 ℃/min.

In the present invention, "mL/h/g" in the iron carbide production process means the volume of gas introduced per gram of the material per hour, unless otherwise specified.

In a preferred embodiment of the present invention, the precursor reduction, pretreatment and carbide preparation processes can be performed continuously in the same reactor. In-situ characterization equipment can be used to track the crystal phase transition of the material during the preparation process. In-situ characterization equipment can be used to track the crystal phase transition of the material during the preparation process.

In some embodiments of the present invention, the precipitation type epsilon/epsilon' iron carbide can be obtained by the process of the steps (1) to (4). As determined by XRD and/or mossbauer spectroscopy.

In some embodiments of the present invention, the precipitated epsilon/epsilon' iron carbide-containing composition may contain Fe-containing impurities incorporated by means of external addition. Preferably, in the step (5), 97 to 100 parts by mole of the precipitated epsilon/epsilon' iron carbide is mixed with 0 to 3 parts by mole of the Fe-containing impurities.

In one embodiment of the present invention, in the step (5), the mixing is performed by mixing the precipitated epsilon/epsilon' iron carbide powder and the Fe-containing impurity powder in a glove box under the protection of inert gas according to the dosage requirement.

In a third aspect, the present invention provides a precipitated epsilon/epsilon' iron carbide-containing composition produced by the process of the present invention. The composition comprises 95 to 100 mol% of precipitation type epsilon/epsilon 'iron carbide and 0 to 5 mol% of Fe-containing impurities, wherein the Fe-containing impurities are substances containing iron elements except the epsilon/epsilon' iron carbide, based on the total amount of the composition.

Preferably, the composition comprises 97 to 100 mol% precipitated epsilon/epsilon' iron carbide and 0 to 3 mol% Fe-containing impurities.

Preferably, the specific surface area of the composition is between 20 and 260m²Per g, preferably from 25 to 200m²/g。

In a fourth aspect, the invention provides a catalyst comprising a precipitated epsilon/epsilon' iron carbide-containing composition provided by the invention. Preferably, the catalyst may also comprise other components, such as promoters.

In the embodiment provided by the present invention, preferably, the precipitated epsilon/epsilon' iron carbide-containing composition is contained in an amount of 75 wt% or more and less than 100 wt% and the auxiliary in an amount of more than 0 wt% and 25 wt% or less, based on the total amount of the catalyst.

In the embodiment provided by the invention, preferably, the catalyst can be prepared by introducing the auxiliary agent by a method of impregnation, atomic deposition, sputtering or chemical deposition.

The composition or the catalyst containing the precipitated epsilon/epsilon' iron carbide is used for carrying out the Fischer-Tropsch synthesis reaction, and the Fischer-Tropsch synthesis reaction can be carried out at high temperature and high pressure, for example, the conditions of the Fischer-Tropsch synthesis reaction comprise: the temperature is 235 ℃ and 250 ℃, and the pressure is 2.3-2.5 MPa.

In the present invention, the pressure refers to gauge pressure unless otherwise specified.

In some embodiments of the invention, preferably, the fischer-tropsch synthesis reaction is carried out in a high temperature, high pressure continuous reactor. The composition or the catalyst containing the precipitation type epsilon/epsilon' iron carbide can realize that the Fischer-Tropsch synthesis reaction can be continuously and stably carried out for more than 400 hours in a high-temperature high-pressure continuous reactor.

In a specific embodiment provided by the present invention, the composition of the fischer-tropsch catalyst may further comprise, based on the total amount of the fischer-tropsch catalyst, a content of the precipitated epsilon/epsilon' iron carbide-containing composition of 75 wt% or more and less than 100 wt%, and a content of Mn of more than 0 wt% and 25 wt% or less. In the fischer-tropsch catalyst, Mn may be present as an oxide and may be incorporated into the fischer-tropsch catalyst by methods including, but not limited to, impregnation, chemical deposition, sputtering, atomic deposition.

The present invention will be described in detail below by way of examples. In the following examples and comparative examples,

in-situ XRD detection in the process of preparing the iron carbide, an X-ray diffractometer (Rigaku company, model D/max-2600/PC) is used for monitoring the crystal phase change of the material;

the obtained iron carbide and iron carbide composition were subjected to Mossbauer spectrometer (Transmission)⁵⁷Fe，⁵⁷A Co (Rh) source sinusoidal velocity spectrometer) to perform Mossbauer spectrum detection;

the BET specific surface area of the iron carbide composition was measured by a nitrogen adsorption method;

carrying out Fischer-Tropsch synthesis reaction:

carrying out gas chromatography (Agilent 6890 gas chromatography) on the product obtained by the reaction;

the effect of the reaction is calculated by the following formula:

CO₂selectivity%₂Mole number/(moles of CO in feed-moles of CO in discharge)]×100％；

CH₄Selectivity%₄Mole/(mole of CO in the feed x CO conversion% (1-CO)₂Selectivity%))]×100％；

Effective product selectivity ═ 1-CO₂Selective% CH₄Selectivity%]×100％

Space-time conversion rate (mmol/h/g) of raw material CO_Fe) (moles of CO in feed-moles of CO in discharge)/reaction time/weight of Fe element;

space-time yield (mmol/h/g) for efficient product formation_Fe) Reaction of C₂And C₂The above number of moles of hydrocarbon/reaction time/weight of Fe element.

Example 1

(1) Mixing ferric ammonium citrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 60 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(2) Mixing the precursor with H₂At a pressure of 2.6atm, H₂The flow of the precursor is 22000mL/h/g, and the precursor is reduced for 1h at the temperature of 580 ℃;

(3) cooling the product obtained in the step (2) to 160 ℃, and reacting the product with H at 160 DEG C₂Mixed gas with CO (pressure 4.5atm, total gas flow 9000mL/H/g, H₂Contacting with CO at a molar ratio of 2:1) for pretreatment for 20 min;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 4.5atm, total gas flow 25000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is increased from 160 ℃ to 290 ℃ at the temperature increase rate of 2.5 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3), the carbonization time is 2.5h, and precipitated iron carbide is obtained, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide determined by Mossbauer spectroscopy and is marked as iron carbide 1;

(5) 97 parts by mole of precipitated iron carbide 1 was mixed with 3 parts by mole of ferrous oxide (i.e., Fe-containing impurities) under Ar gas. After mixing, it is designated as iron carbide composition 1.

Example 2

(1) Mixing ferric nitrate with the concentration of 0.7mol/L and sodium carbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 40 ℃ and under the condition that the pH value is 7.0 to obtain precipitation slurry, washing by deionized water, filtering to obtain a filter cake, drying at the temperature of 120 ℃ for 24 hours, and roasting at the temperature of 350 ℃ for 7 hours to obtain a precursor.

(2) Mixing the precursor with H₂At a pressure of 0.3atm, H₂The flow rate of the precursor is 28000mL/h/g, and the precursor is reduced for 12h at the temperature of 450 ℃;

(3) cooling the product obtained in the step (2) to 160 ℃, and reacting the product with H at 160 DEG C₂Mixed gas with CO (pressure 0.08atm, total gas flow 1500mL/H/g, H)₂Contacting with CO at a molar ratio of 2:1) for pretreatment for 90 min;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 0.2atm, total gas flow 3000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 160 ℃ to 210 ℃ at the temperature rise rate of 0.2 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 12 hours to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide measured by Mossbauer spectroscopy and is marked as iron carbide 2;

(5) 99 molar parts of precipitated iron carbide 2 are mixed with 1 molar part of ferrous oxide (i.e. Fe-containing impurities) under Ar gas protection. After mixing, it is designated as iron carbide composition 2.

Example 3

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonium bicarbonate solution with the concentration of 0.5mo1/L at the temperature of 70 ℃ and the pH value of 6.2 to obtain precipitation slurry, washing by deionized water, filtering to obtain a filter cake, drying at the temperature of 110 ℃ for 20 hours, and roasting at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(2) Mixing the precursor with H₂At a pressure of 1.5atm, H₂The flow rate of the precursor is 12000mL/h/g, and the precursor is reduced for 6h at the temperature of 500 ℃;

(3) cooling the product obtained in the step (2) to 150 ℃, and reacting the product with H at 150 DEG C₂Mixed gas with CO (pressure 2.0atm, total gas flow 6000mL/H/g, H)₂Contacting with CO at a molar ratio of 2:1) for pretreatment for 45 min;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide measured by Mossbauer spectroscopy and is marked as iron carbide 3;

(5) 98 molar parts of precipitated iron carbide 3 are mixed with 2 molar parts of ferrous oxide (i.e. Fe-containing impurities) under Ar gas protection. After mixing, it was designated as iron carbide composition 3.

Example 4

(1) - (4) Process according to example 1, except that "precursor and H" are used₂Replacement of "precursor with H" at a pressure of 3atm₂At a pressure of 2.6atm 'to obtain precipitated iron carbide, which is determined by Mossbauer spectroscopy to be pure epsilon/epsilon' iron carbide and is marked as iron carbide 4.

(5) 98 molar parts of precipitated iron carbide 4 are mixed with 2 molar parts of ferrous oxide (i.e. Fe-containing impurities) under Ar gas protection. After mixing, it was designated as iron carbide composition 4.

Example 5

(1) - (4) Process according to example 1, except that "precursor and H" are used₂Replacement of "precursor with H" at a pressure of 0.08atm₂At a pressure of 2.6atm 'to obtain precipitated iron carbide, which is determined by Mossbauer spectroscopy to be pure epsilon/epsilon' iron carbide and is marked as iron carbide 5.

(5) 97 parts by mole of precipitated iron carbide 5 was mixed with 3 parts by mole of ferrous oxide (i.e., Fe-containing impurities) under Ar gas. After mixing, it was designated as iron carbide composition 5.

Example 6

(1) Mixing ammonium ferrous sulfate with the concentration of 1.2mol/L and potassium carbonate solution with the concentration of 0.3mo1/L at the temperature of 50 ℃ and the pH value of 5.8 to obtain precipitation slurry, washing with deionized water, filtering to obtain a filter cake, drying at the temperature of 120 ℃ for 24 hours, and roasting at the temperature of 390 ℃ for 5 hours to obtain a precursor.

(2) Mixing the precursor with H₂At a pressure of 1.5atm, H₂The flow rate of the precursor is 12000mL/h/g, and the precursor is reduced for 13h at the temperature of 500 ℃;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of CO to CO is 1.5:1, and then the temperature is 2.0 DEG CHeating the temperature to 250 ℃ from 150 ℃ at a heating rate/min, then carrying out carbide preparation with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and marking the precipitated iron carbide as pure epsilon/epsilon' iron carbide 6 by Mossbauer spectroscopy;

(5) 99 molar parts of precipitated iron carbide 6 are mixed with 1 molar part of ferrous oxide (i.e. Fe-containing impurities) under Ar gas protection. After mixing, it was designated as iron carbide composition 6.

Example 7

(1) Mixing ferric chloride with the concentration of 1.0mol/L and potassium hydroxide solution with the concentration of 0.7mo1/L at the temperature of 70 ℃ and the pH value of 7.2 to obtain precipitation slurry, washing with deionized water, filtering to obtain a filter cake, drying at the temperature of 120 ℃ for 24 hours, and roasting at the temperature of 350 ℃ for 5 hours to obtain the precursor.

(2) Mixing the precursor with H₂At a pressure of 1.5atm, H₂The flow rate of the precursor is 12000mL/h/g, and the precursor is reduced for 0.5h at the temperature of 500 ℃;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide measured by Mossbauer spectroscopy and is marked as iron carbide 7;

(5) 98 molar parts of precipitated iron carbide 7 are mixed with 2 molar parts of ferrous oxide (i.e. Fe-containing impurities) under Ar gas protection. After mixing, it was designated as iron carbide composition 7.

Example 8

(1) Mixing ferric chloride with the concentration of 1.5mol/L and sodium bicarbonate solution with the concentration of 0.5 mol/L of 1/L at the temperature of 50 ℃ and under the condition of pH value of 7.2 to obtain precipitation slurry, washing with deionized water, filtering to obtain a filter cake, drying at the temperature of 120 ℃ for 24 hours, and roasting at the temperature of 450 ℃ for 7 hours to obtain a precursor.

(2) Mixing the precursor with H₂At a pressure of 1.5atm, H₂The flow rate of the precursor is 23000mL/h/g, and the precursor is reduced for 6h at the temperature of 500 ℃;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide measured by Mossbauer spectroscopy and is marked as iron carbide 8;

(5) 97 parts by mole of precipitated iron carbide 8 was mixed with 3 parts by mole of ferrous oxide (i.e., Fe-containing impurities) under Ar gas. After mixing, it was designated as iron carbide composition 8.

Example 9

(1) Mixing ferric nitrate with the concentration of 2.0mol/L and potassium bicarbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 60 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing by deionized water, filtering to obtain a filter cake, drying at the temperature of 120 ℃ for 24 hours, and roasting at the temperature of 350 ℃ for 5 hours to obtain the precursor.

(2) Mixing the precursor with H₂At a pressure of 1.5atm, H₂The flow rate of the precursor is 400mL/h/g, and the precursor is reduced for 6 hours at the temperature of 500 ℃;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3), the carbonization time is 6 hours, and precipitated iron carbide is obtained, and the iron carbide is determined by Mossbauer spectroscopy to bePure epsilon/epsilon' iron carbide, marked as iron carbide 9;

(5) 98 molar parts of precipitated iron carbide 9 are mixed with 2 molar parts of ferrous oxide (i.e. Fe-containing impurities) under Ar gas protection. After mixing, it was designated as iron carbide composition 9.

Example 10

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 60 ℃ and under the condition that the pH value is 7.5 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(3) cooling the product obtained in the step (2) to 150 ℃, and reacting the product with H at 150 DEG C₂Mixed gas with CO (pressure 6atm, total gas flow 6000mL/H/g, H)₂Contacting with CO at a molar ratio of 2:1) for pretreatment for 45 min;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide determined by Mossbauer spectroscopy and is marked as iron carbide 10;

(5) 99 molar parts of precipitated iron carbide 10 are mixed with 1 molar part of ferrous oxide (i.e. Fe-containing impurities) under Ar gas protection. After mixing, this is designated as iron carbide composition 10.

Example 11

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and sodium hydroxide solution with the concentration of 0.8mo1/L at the temperature of 60 ℃ and the pH value of 7.2 to obtain precipitation slurry, washing with deionized water, filtering to obtain a filter cake, drying at the temperature of 120 ℃ for 24 hours, and roasting at the temperature of 350 ℃ for 8 hours to obtain the precursor.

(3) obtained in the step (2)Cooling the obtained product to 150 deg.C, and reacting with H at 150 deg.C₂Mixed gas with CO (pressure 0.04atm, total gas flow 6000mL/H/g, H)₂Contacting with CO at a molar ratio of 2:1) for pretreatment for 45 min;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide measured by Mossbauer spectroscopy and is marked as iron carbide 11;

(5) 98 molar parts of precipitated iron carbide 11 were mixed with 2 molar parts of ferrous oxide (i.e. Fe-containing impurities) under Ar gas protection. After mixing, this was designated as iron carbide composition 11.

Example 12

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.3 mol/L of 1 at the temperature of 60 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing by deionized water, filtering to obtain a filter cake, drying at the temperature of 120 ℃ for 24 hours, and roasting at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(3) cooling the product obtained in the step (2) to 150 ℃, and reacting the product with H at 150 DEG C₂Mixed gas with CO (pressure 2.0atm, total gas flow 6000mL/H/g, H)₂Contacting with CO at a molar ratio of 2:1) for pretreatment for 100 min;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide measured by Mossbauer spectroscopy and is marked as iron carbide 12;

(5) 98 molar parts of precipitated iron carbide 12 were mixed with 2 molar parts of ferrous oxide (i.e. Fe-containing impurities) under Ar gas. After mixing, this was designated as iron carbide composition 12.

Example 13

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonia water solution with the concentration of 0.8mo1/L at the temperature of 60 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing by deionized water, filtering to obtain a filter cake, drying at the temperature of 120 ℃ for 24 hours, and roasting at the temperature of 550 ℃ for 5 hours to obtain a precursor.

(3) cooling the product obtained in the step (2) to 150 ℃, and reacting the product with H at 150 DEG C₂Mixed gas with CO (pressure 2.0atm, total gas flow 6000mL/H/g, H)₂Contacting with CO at a molar ratio of 2:1) for pretreatment for 10 min;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide measured by Mossbauer spectroscopy and is marked as iron carbide 13;

(5) 98 molar parts of precipitated iron carbide 13 are mixed with 2 molar parts of ferrous oxide (i.e. Fe-containing impurities) under Ar gas protection. After mixing, this was designated as iron carbide composition 13.

Example 14

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 60 ℃ and under the condition that the pH value is 6.2 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(3) cooling the product obtained in the step (2) to 150 ℃, and reacting the product with H at 150 DEG C₂Mixed gas with CO (pressure 2.0atm, total gas flow 10000mL/H/g, H)₂Contacting with CO at a molar ratio of 2:1) for pretreatment45min；

(4) H is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide measured by Mossbauer spectroscopy and is marked as iron carbide 14;

(5) 98 molar parts of precipitated iron carbide 14 are mixed with 2 molar parts of ferrous oxide (i.e. Fe-containing impurities) under Ar gas. After mixing, is designated as iron carbide composition 14.

Example 15

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 60 ℃ and under the condition that the pH value is 6.3 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(3) cooling the product obtained in the step (2) to 150 ℃, and reacting the product with H at 150 DEG C₂Mixed gas with CO (pressure 2.0atm, total gas flow 200mL/H/g, H)₂Contacting with CO at a molar ratio of 2:1) for pretreatment for 45 min;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3), the carbonization time is 6 hours, and precipitated iron carbide is obtained, wherein v is marked as iron carbide 15;

(5) 97 parts by mole of precipitated iron carbide 15 was mixed with 3 parts by mole of ferrous oxide (i.e., Fe-containing impurities) under Ar gas. After mixing, this was designated as iron carbide composition 15.

Example 16

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 60 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 100 ℃ for 24 hours, and roasting the filter cake at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 5atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide measured by Mossbauer spectroscopy and is marked as iron carbide 16;

(5) 97 parts by mole of precipitated iron carbide 16 was mixed with 3 parts by mole of ferrous oxide (i.e., Fe-containing impurities) under Ar gas. After mixing, it was designated as iron carbide composition 16.

Example 17

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 30 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 0.08atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon dioxide to the CO is 1.5:1, and the temperature is raised at the speed of 2.0 ℃/min under the conditionHeating to 250 ℃ from 150 ℃, then carrying out carbide preparation with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and marking the precipitated iron carbide as pure epsilon/epsilon 'iron carbide through Mossbauer spectroscopy, wherein the pure epsilon/epsilon' iron carbide is marked as iron carbide 17;

(5) 98 molar parts of precipitated iron carbide 17 are mixed with 2 molar parts of ferrous oxide (i.e. Fe-containing impurities) under Ar gas protection. After mixing, this was designated as iron carbide composition 17.

Example 18

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1 at the temperature of 50 ℃ and under the condition that the pH value is 7.8 to obtain precipitation slurry, washing by deionized water, filtering to obtain a filter cake, drying at the temperature of 120 ℃ for 24 hours, and roasting at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 13h to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide measured by Mossbauer spectroscopy and is marked as iron carbide 18;

(5) the precipitated iron carbide 18 was mixed with 2 molar parts of ferrous oxide (i.e., Fe-containing impurities) at 98 molar parts under Ar gas. After mixing, is designated as iron carbide composition 18.

Example 19

(1) Mixing ferric nitrate with the concentration of 1.2mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1 at the temperature of 40 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 1h to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide measured by Mossbauer spectroscopy and is marked as iron carbide 19;

(5) 98 molar parts of precipitated iron carbide 19 are mixed with 2 molar parts of ferrous oxide (i.e. Fe-containing impurities) under Ar gas protection. After mixing, this is designated iron carbide composition 19.

Example 20

(1) Mixing ferric nitrate with the concentration of 1.2mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 60 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 26000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' carbonized through Mossbauer spectroscopyIron, denoted as iron carbide 20;

(5) 99 molar parts of precipitated iron carbide 20 are mixed with 1 molar part of ferrous oxide (i.e. Fe-containing impurities) under Ar gas protection. After mixing, the mixture was designated as iron carbide composition 20.

Example 21

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 60 ℃ and under the condition that the pH value is 7.0 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 400mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide measured by Mossbauer spectroscopy and is marked as iron carbide 21;

(5) 98 molar parts of precipitated iron carbide 21 are mixed with 2 molar parts of ferrous oxide (i.e. Fe-containing impurities) under Ar gas protection. After mixing, the mixture was designated as iron carbide composition 21.

Example 22

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 60 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 350 ℃ for 10 hours to obtain a precursor.

(3) cooling the product obtained in the step (2)To 150 ℃ and reacting with H at 150 DEG C₂Mixed gas with CO (pressure 2.0atm, total gas flow 6000mL/H/g, H)₂Contacting with CO at a molar ratio of 2:1) for pretreatment for 45 min;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 295 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide measured by Mossbauer spectroscopy and is marked as iron carbide 22;

(5) the precipitated iron carbide 22 was mixed with 3 molar parts of ferrous oxide (i.e., Fe-containing impurities) at 97 molar parts under Ar gas. After mixing, the mixture was designated as iron carbide composition 22.

Example 23

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 60 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 450 ℃ for 5 hours to obtain a precursor.

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 190 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide measured by Mossbauer spectroscopy and is marked as iron carbide 23;

(5) 98 molar parts of precipitated iron carbide 23 are mixed with 2 molar parts of ferrous oxide (i.e. Fe-containing impurities) under Ar gas protection. After mixing, this was designated as iron carbide composition 23.

Example 24

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 60 ℃ and under the condition that the pH value is 5.9 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 4.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide, and the precipitated iron carbide is pure epsilon/epsilon' iron carbide measured by Mossbauer spectroscopy and is marked as iron carbide 24;

(5) 98 molar parts of precipitated iron carbide 24 are mixed with 2 molar parts of ferrous oxide (i.e. Fe-containing impurities) under Ar gas. After mixing, the mixture is designated as iron carbide composition 24.

Comparative example 1

(1) Mixing ferric nitrate with the concentration of 1.7mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 60 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(2) Mixing the precursor with H₂At a pressure of 1.5atm, H₂The flow rate of the precursor is 12000mL/h/g, and the precursor is reduced for 6h at the temperature of 430 ℃;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, and then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide which is marked as iron carbide D1;

(5) 98 molar parts of precipitated iron carbide D1 were mixed with 2 molar parts of ferrous oxide (i.e., Fe-containing impurities) under Ar gas. After mixing, it was designated as iron carbide composition D1.

Comparative example 2

(1) (1) mixing ferric nitrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.9 mol/L of 1/L at the temperature of 60 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 350 ℃ for 3 hours to obtain the precursor.

(3) cooling the product obtained in the step (2) to 190 ℃, and reacting the product with H at 190 DEG C₂Mixed gas with CO (pressure 2.0atm, total gas flow 6000mL/H/g, H)₂Contacting with CO at a molar ratio of 2:1) for pretreatment for 45 min;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 190 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, and then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide which is marked as iron carbide D2;

(5) 98 molar parts of precipitated iron carbide D2 were mixed with 2 molar parts of ferrous oxide (i.e., Fe-containing impurities) under Ar gas. After mixing, it was designated as iron carbide composition D2.

Comparative example 3

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 50 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 380 ℃ for 5 hours to obtain a precursor.

(3) cooling the product obtained in the step (2) to 150 ℃, and reacting the product with H at 150 DEG C₂Mixed gas with CO (pressure 2.0atm, total gas flow 6000mL/H/g, H)₂Contacting with CO at a molar ratio of 3:1) for pretreatment for 45 min;

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 2.0 ℃/min under the condition, then the carbon is prepared with the material obtained in the step (3), the carbonization time is 6 hours, and the obtained precipitated iron carbide is marked as iron carbide D3;

(5) 99 molar parts of precipitated iron carbide D3 was mixed with 1 molar part of ferrous oxide (i.e. Fe-containing impurities) under Ar gas. After mixing, it was designated as iron carbide composition D3.

Comparative example 4

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.9 mol/L of 1/L at the temperature of 50 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The mol ratio of the carbon to CO is 0.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature raising rate of 2.0 ℃/min under the condition, and then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain a precipitation typeIron carbide, noted as iron carbide D4;

(5) 98 molar parts of precipitated iron carbide D4 were mixed with 2 molar parts of ferrous oxide (i.e., Fe-containing impurities) under Ar gas. After mixing, it was designated as iron carbide composition D4.

Comparative example 5

(1) Mixing ferric nitrate with the concentration of 1.1mol/L and ammonium carbonate solution with the concentration of 0.3 mol/L of 1 at the temperature of 60 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 350 ℃ for 5 hours to obtain a precursor.

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 250 ℃ at the temperature rise rate of 0.1 ℃/min under the condition, and then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide which is marked as iron carbide D5;

(5) 97 parts by mole of precipitated iron carbide D5 was mixed with 3 parts by mole of ferrous oxide (i.e., Fe-containing impurities) under Ar gas. After mixing, it was designated as iron carbide composition D5.

Comparative example 6

(1) Mixing ferric nitrate with the concentration of 1.0mol/L and ammonium carbonate solution with the concentration of 0.8 mol/L of 1/L at the temperature of 50 ℃ and under the condition that the pH value is 7.2 to obtain precipitation slurry, washing the precipitation slurry by deionized water, filtering the precipitation slurry to obtain a filter cake, drying the filter cake at the temperature of 120 ℃ for 24 hours, and roasting the filter cake at the temperature of 390 ℃ for 5 hours to obtain a precursor.

(4) h is to be₂The conditions of the mixed gas with CO are firstly changed as follows: pressure 2.0atm, total gas flow 12000mL/H/g, H₂The molar ratio of the carbon to CO is 1.5:1, the temperature is raised from 150 ℃ to 310 ℃ at the temperature rise rate of 1.5 ℃/min under the condition, and then the carbon is prepared with the material obtained in the step (3) for 6 hours to obtain precipitated iron carbide which is marked as iron carbide D6;

(5) 98 molar parts of precipitated iron carbide D6 were mixed with 2 molar parts of ferrous oxide (i.e., Fe-containing impurities) under Ar gas. After mixing, it was designated as iron carbide composition D6.

Comparative example 7

The procedure of example 1 was followed except that (5) 92 parts by mole of iron carbide 1 was mixed with 8 parts by mole of ferrous oxide (i.e., Fe-containing impurities) under Ar gas. After mixing, it was designated as iron carbide composition D7.

Examples 25 to 48

Respectively taking 1-24 parts of iron carbide composition in N₂Adding manganese citrate solution by immersion method under protection, and adding N at 25 deg.C₂And drying the gas flow for 24 hours to obtain the Fischer-Tropsch catalyst 1-24 correspondingly. Wherein the amount of the added manganese citrate solution is impregnated, so that the obtained Fischer-Tropsch catalysts 1-24 respectively contain 85 wt% of iron carbide composition 1-24 and 15 wt% of MnO₂。

Comparative examples 8 to 14

Respectively taking iron carbide compositions D1-D7 as the balance of N₂Adding manganese citrate solution by immersion method under protection, and adding N at 25 deg.C₂And drying the gas flow for 24h to obtain the Fischer-Tropsch catalysts D1-D7. Wherein the added manganese citrate solution is impregnated in an amount which enables the obtained Fischer-Tropsch catalysts D1-D7 to respectively contain 85 wt% of iron carbide composition D1-D7 and 15 wt% of MnO₂。

Test example

XRD and Mossbauer spectroscopy were performed on iron carbides 1-24 and D-D6, and the results of the determination of the Fe compound content are shown in Table 1. Wherein the content of the Fe compound is expressed in mol percent.

TABLE 1

Iron carbide numbering	Content of Epsilon/Epsilon' iron carbide (mol%)	Other Fe-containing impurities content (mol%)
			1-24	100.0	0.0
D1	54.0	46.0
			D2	43.0	57.0
D3	37.0	63.0
			D4	47.0	53.0
D5	37.0	63.0
			D6	45.0	55.0

In the method, the whole process of preparing the iron carbide 1 in the example 1 adopts an in-situ XRD detection technology, and an X-ray diffractometer (Rigaku company, model D/max-2600/PC) is used for monitoring the crystal phase change of the material. As shown in FIG. 1, curve A is before the reduction of the precursor in step (1), curve B is after the reduction of the precursor in step (1), curve C is after the pretreatment in step (2), and curve D is after the preparation of the carbide in step (3). Wherein curve A is alpha-Fe₂O₃The characteristic peak 2 theta is 33.3 degrees, 35.7 degrees, 41.0 degrees, 49.5 degrees, 54.2 degrees, 57.6 degrees and 62.7 degrees, which are completely consistent with the standard card PDF-02-0919. B is an α -Fe crystal phase, and curve C is an α -Fe crystal phase with a very small number of carbon atom layers formed on the surface, and their characteristic peaks 2 θ are 44.7 °, 65.0 °, 82.3 °, which are consistent with the XRD standard card PDF-65-4899 of α -Fe. Curve D is ε -Fe with a purity of 100%₂C and epsilon-Fe_2.2C, i.e. epsilon/epsilon' iron carbide, and together with an XRD standard card PDF-89-2005, curve D shows that 2 θ is 37.7 °, 41.4 °, 43.2 °, 57.2 °, 68.0 °, 76.8 °, 82.9 ° exactly in accordance with the standard card. The obtained spectrogram can clearly see the change process from the nanometer iron powder to the target carbide. The crystallinity of the generated target product epsilon/epsilon 'iron carbide is good, all characteristic peaks of the epsilon/epsilon' iron carbide are well corresponded, the purity is extremely high, and no other impurities exist.

The pure phase epsilon/epsilon' iron carbide obtained in other examples also has a similar spectrum as described above and will not be described in detail. The iron carbides obtained in comparative examples 1 to 6 could not have pure phases of epsilon/epsilon' iron carbide and the spectra as shown in fig. 1 could not be obtained.

Mossbauer spectra and BET specific surface area measurements were performed for iron carbide compositions 1-24 and D1-D7, respectively, and the results are shown in Table 2.

TABLE 2

Evaluation example

In a fixed bed continuous reactor, the performance evaluation of the catalytic reaction is respectively carried out on Fischer-Tropsch catalysts 1-24, D1-D7 and iron carbide compositions 1-3. The catalyst loading was 10.0 g.

Evaluation conditions were as follows: t248 deg.C, P2.45 MPa, H₂：CO＝1.8：1，(H₂+ CO) total amount 42000mL/h/g-_Fe(standard state flux, relative to Fe element). The reaction was carried out, the reaction product was analyzed by gas chromatography, and the evaluation data of the reaction performance for the reactions of 24 hours and 400 hours are shown in tables 3 and 4.

TABLE 3

TABLE 4

As can be seen from the above examples, comparative examples and data in tables 1 to 4, the precipitated epsilon/epsilon' iron carbide or the composition or the catalyst prepared by the invention has high space-time conversion rate of raw material CO, better reaction performance and ultralow CO in limited condition range when the Fischer-Tropsch synthesis reaction is carried out under industrial conditions₂And (4) selectivity. At the same time, CH₄Low selectivity, effective product selectivityHigh.

Further long-period experiments are carried out, and the data of the reaction time of 400h in the table 4 show that after the precipitated epsilon/epsilon' iron carbide-containing composition or the catalyst prepared under the limited conditions provided by the invention runs for a long time, the CO conversion rate and the product selectivity are stable and have no obvious change, and the stability is greatly superior to that of the iron carbide in the prior art.

The precipitated epsilon/epsilon' iron carbide or the composition or the catalyst prepared under the limited conditions of the invention can be suitable for a high-temperature high-pressure continuous reactor, has high reaction stability, and CO₂Very low selectivity: under the condition of industrial Fischer-Tropsch synthesis reaction, a high-pressure continuous reactor can be used for keeping continuous and stable reaction for more than 400h, and CO is generated₂The selectivity is less than 5 percent (preferably, 2.5 percent or less can be achieved); at the same time, its by-product CH₄The selectivity is also kept below 13.5 percent (preferably below 9.5 percent), and the selectivity of the effective product can reach more than 80 percent (preferably above 88 percent). Wherein the catalyst effective product formation space-time yield of the preferred conditions (catalysts 1-3) can reach 125mmol/h/g-_FeThe method is very suitable for producing oil and wax products efficiently in the Fischer-Tropsch synthesis industry of the modern coal chemical industry.

The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, numerous simple modifications can be made to the technical solution of the invention, including combinations of the individual specific technical features in any suitable way. The invention is not described in detail in order to avoid unnecessary repetition. Such simple modifications and combinations should be considered within the scope of the present disclosure as well.

Claims

1. A precipitated epsilon/epsilon ' iron carbide-containing composition comprising 95 to 100 mol% of precipitated epsilon/epsilon ' iron carbide and 0 to 5 mol% of an Fe-containing impurity which is an iron-containing substance other than epsilon/epsilon ' iron carbide, based on the total amount of the composition;

wherein the specific surface area of the composition is 20-260m²/g。

2. The composition according to claim 1, wherein the composition has a specific surface area of 25-200m²/g。

3. The composition according to claim 1 or 2, wherein the composition comprises 97-100 mol% of precipitated epsilon/epsilon' iron carbide and 0-3 mol% of Fe-containing impurities, based on the total amount of the composition.

4. The composition of any of claims 1-3, wherein the Fe-containing impurities are at least one of iron carbide other than epsilon/epsilon' iron carbide, iron oxide, iron hydroxide, iron sulfide, iron salt.

5. A method of preparing a precipitated epsilon/epsilon' iron carbide-containing composition comprising:

(4) subjecting the product obtained in step (3)Materials and H₂CO at a temperature of 200-₂The molar ratio to CO is 1-3.2: 1, obtaining precipitate type epsilon/epsilon' iron carbide;

6. The method according to claim 5, wherein the iron salt is selected from water soluble iron salts, preferably at least one of ferric nitrate, ferric chloride, ferrous ammonium sulfate and ferric ammonium citrate;

the alkaline precipitator is at least one of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, sodium hydroxide, potassium hydroxide and ammonia water;

preferably, the drying and roasting process comprises the following steps: firstly, drying the solid for 6-10h at the temperature of 35-80 ℃ and the vacuum degree of 250-1200 Pa; drying the dried material at 75-180 ℃ for 3-24h, and roasting the obtained material at the temperature of 250-580 ℃ for 1-10 h.

7. The process according to claim 5 or 6, wherein in step (2), the pressure of the precursor reduction is 0.1-15atm, preferably 0.3-2.6atm, and the time is 0.7-15h, preferably 1-12 h;

further preferably, in step (2), H₂The gas flow rate of (b) is 600-25000mL/h/g, more preferably 2800-22000 mL/h/g.

8. The method according to claim 5 or 6, wherein in step (3), the pressure of the pretreatment is 0.05-7atm, preferably 0.08-4.5atm, and the time is 15-120min, preferably 20-90 min;

further preferably, in step (3), H₂The total gas flow rate with CO is 300-12000mL/h/g, more preferably 1500-9000 mL/h/g.

9. The method according to claim 5 or 6, wherein in step (4), the carbide is prepared at a pressure of 0.1-10atm, preferably 0.2-4.5atm, for a time of 1.5-15h, preferably 2.5-12 h;

further preferably, in step (4), H₂The total gas flow rate with CO is 500-30000mL/h/g, more preferably 3000-25000 mL/h/g.

10. The method of claim 5 or 6, wherein the carbide preparation further comprises: simultaneously performing temperature rise operation in the step (4), and raising the temperature from the pretreatment temperature to 200-300 ℃ at the temperature rise rate of 0.2-5 ℃/min;

preferably, the temperature is raised from the temperature of the pretreatment to 210-290 ℃ at a temperature raising rate of 0.2-2.5 ℃/min.

11. The method as claimed in claim 5 or 6, wherein 97 to 100 molar parts of the precipitated epsilon/epsilon' iron carbide is mixed with 0 to 3 molar parts of the Fe-containing impurities in the step (5).

12. A precipitated epsilon/epsilon' iron carbide-containing composition produced by the method of any one of claims 5-11.

13. A catalyst comprising the precipitated epsilon/epsilon' iron carbide-containing composition of any of claims 1-4 and 12.

14. Use of a precipitated epsilon/epsilon' iron carbide-containing composition according to any one of claims 1 to 4 and 12 or a catalyst according to claim 13 in a fischer-tropsch synthesis reaction.

15. Use of a precipitated epsilon/epsilon' iron carbide-containing composition according to any one of claims 1 to 4 and 12 or a catalyst according to claim 13 in the synthesis of C, H fuels and/or chemicals based on the fischer-tropsch principle.

16. A process for fischer-tropsch synthesis comprising: contacting synthesis gas with a precipitated epsilon/epsilon' iron carbide-containing composition of any one of claims 1-4 and 12 or a catalyst of claim 13 under fischer-tropsch synthesis reaction conditions;

preferably, the fischer-tropsch synthesis is carried out in a high temperature high pressure continuous reactor.

17. A process for fischer-tropsch synthesis comprising: contacting synthesis gas with a fischer-tropsch catalyst under fischer-tropsch synthesis reaction conditions, wherein the fischer-tropsch catalyst comprises a Mn component and the precipitated form e/e' containing iron carbide composition of any one of claims 1 to 4 and 12.