CN112569977A - Composition containing precipitated X-type iron carbide and theta-type iron carbide, preparation method, catalyst and application thereof, and Fischer-Tropsch synthesis method - Google Patents
Composition containing precipitated X-type iron carbide and theta-type iron carbide, preparation method, catalyst and application thereof, and Fischer-Tropsch synthesis method Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims abstract description 58
- 238000002360 preparation method Methods 0.000 title claims abstract description 35
- 238000001308 synthesis method Methods 0.000 title abstract description 9
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 177
- 229910052742 iron Inorganic materials 0.000 claims abstract description 66
- 238000003786 synthesis reaction Methods 0.000 claims abstract description 54
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- 230000015572 biosynthetic process Effects 0.000 claims description 23
- 239000000463 material Substances 0.000 claims description 18
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- UQSXHKLRYXJYBZ-UHFFFAOYSA-N iron oxide Inorganic materials [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims description 15
- 238000002161 passivation Methods 0.000 claims description 14
- 230000008569 process Effects 0.000 claims description 14
- 229910052799 carbon Inorganic materials 0.000 claims description 9
- 230000008859 change Effects 0.000 claims description 9
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- -1 iron carbides Chemical class 0.000 claims description 9
- 239000007787 solid Substances 0.000 claims description 9
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 8
- VCJMYUPGQJHHFU-UHFFFAOYSA-N iron(3+);trinitrate Chemical compound [Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VCJMYUPGQJHHFU-UHFFFAOYSA-N 0.000 claims description 8
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- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 6
- 238000010438 heat treatment Methods 0.000 claims description 6
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- 238000001816 cooling Methods 0.000 claims description 5
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- 239000002244 precipitate Substances 0.000 claims description 4
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 4
- 235000017550 sodium carbonate Nutrition 0.000 claims description 4
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- 159000000014 iron salts Chemical class 0.000 claims description 3
- 150000003839 salts Chemical class 0.000 claims description 3
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 2
- MBMLMWLHJBBADN-UHFFFAOYSA-N Ferrous sulfide Chemical class [Fe]=S MBMLMWLHJBBADN-UHFFFAOYSA-N 0.000 claims description 2
- 229910021578 Iron(III) chloride Inorganic materials 0.000 claims description 2
- UIIMBOGNXHQVGW-DEQYMQKBSA-M Sodium bicarbonate-14C Chemical compound [Na+].O[14C]([O-])=O UIIMBOGNXHQVGW-DEQYMQKBSA-M 0.000 claims description 2
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 2
- 229960004642 ferric ammonium citrate Drugs 0.000 claims description 2
- IMBKASBLAKCLEM-UHFFFAOYSA-L ferrous ammonium sulfate (anhydrous) Chemical compound [NH4+].[NH4+].[Fe+2].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O IMBKASBLAKCLEM-UHFFFAOYSA-L 0.000 claims description 2
- 239000004313 iron ammonium citrate Substances 0.000 claims description 2
- 235000000011 iron ammonium citrate Nutrition 0.000 claims description 2
- 235000014413 iron hydroxide Nutrition 0.000 claims description 2
- RBTARNINKXHZNM-UHFFFAOYSA-K iron trichloride Chemical compound Cl[Fe](Cl)Cl RBTARNINKXHZNM-UHFFFAOYSA-K 0.000 claims description 2
- NCNCGGDMXMBVIA-UHFFFAOYSA-L iron(ii) hydroxide Chemical class [OH-].[OH-].[Fe+2] NCNCGGDMXMBVIA-UHFFFAOYSA-L 0.000 claims description 2
- 239000011736 potassium bicarbonate Substances 0.000 claims description 2
- 235000015497 potassium bicarbonate Nutrition 0.000 claims description 2
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- 235000011181 potassium carbonates Nutrition 0.000 claims description 2
- TYJJADVDDVDEDZ-UHFFFAOYSA-M potassium hydrogencarbonate Chemical compound [K+].OC([O-])=O TYJJADVDDVDEDZ-UHFFFAOYSA-M 0.000 claims description 2
- 235000011118 potassium hydroxide Nutrition 0.000 claims description 2
- 235000011121 sodium hydroxide Nutrition 0.000 claims description 2
- FRHBOQMZUOWXQL-UHFFFAOYSA-L ammonium ferric citrate Chemical compound [NH4+].[Fe+3].[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O FRHBOQMZUOWXQL-UHFFFAOYSA-L 0.000 claims 1
- 235000013980 iron oxide Nutrition 0.000 claims 1
- VBMVTYDPPZVILR-UHFFFAOYSA-N iron(2+);oxygen(2-) Chemical class [O-2].[Fe+2] VBMVTYDPPZVILR-UHFFFAOYSA-N 0.000 claims 1
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 79
- 229910002092 carbon dioxide Inorganic materials 0.000 description 46
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- OAVRWNUUOUXDFH-UHFFFAOYSA-H 2-hydroxypropane-1,2,3-tricarboxylate;manganese(2+) Chemical compound [Mn+2].[Mn+2].[Mn+2].[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O.[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O OAVRWNUUOUXDFH-UHFFFAOYSA-H 0.000 description 4
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
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- NUJOXMJBOLGQSY-UHFFFAOYSA-N manganese dioxide Chemical compound O=[Mn]=O NUJOXMJBOLGQSY-UHFFFAOYSA-N 0.000 description 4
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 3
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- AUALKMYBYGCYNY-UHFFFAOYSA-E triazanium;2-hydroxypropane-1,2,3-tricarboxylate;iron(3+) Chemical compound [NH4+].[NH4+].[NH4+].[Fe+3].[Fe+3].[Fe+3].[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O.[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O.[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O.[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O AUALKMYBYGCYNY-UHFFFAOYSA-E 0.000 description 1
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Images
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/20—Carbon compounds
- B01J27/22—Carbides
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
- B01J35/61—Surface area
- B01J35/613—10-100 m2/g
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
- B01J35/61—Surface area
- B01J35/615—100-500 m2/g
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
- C10G2/00—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon
- C10G2/30—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen
- C10G2/32—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen with the use of catalysts
- C10G2/33—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen with the use of catalysts characterised by the catalyst used
- C10G2/331—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen with the use of catalysts characterised by the catalyst used containing group VIII-metals
- C10G2/332—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon from carbon monoxide with hydrogen with the use of catalysts characterised by the catalyst used containing group VIII-metals of the iron-group
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Materials Engineering (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- General Chemical & Material Sciences (AREA)
- Carbon And Carbon Compounds (AREA)
- Catalysts (AREA)
Abstract
The invention relates to the field of Fischer-Tropsch synthesis reaction, and discloses a composition containing precipitated X-type iron carbide and theta-type iron carbide, a preparation method, a catalyst and application thereof, and a Fischer-Tropsch synthesis method. The composition comprises 95-100 mol% of precipitated X-iron carbide and theta-iron carbide and 0-5 mol% of Fe-containing impurities, wherein the Fe-containing impurities are iron-containing substances except the X-iron carbide and the theta-iron carbide; wherein the specific surface area of the composition is 60 to 300m2(ii) in terms of/g. Can simply and conveniently prepare the chi iron carbide and the theta iron carbide which are used as active components to obtain continuous and stable Fischer-Tropsch synthesis reaction, and the effective product has high selectivity.
Description
Technical Field
The invention relates to the field of Fischer-Tropsch synthesis reaction, in particular to a composition containing precipitated X-type iron carbide and theta-type 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→CnH2n+2+nH2O (1)，
2nH2+nCO→CnH2n+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 CHxChain 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 pure phase materials of iron carbide free of iron impurities, which are various Fe (element) -containing phase components of non-iron carbide.
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 pure-phase carbon without Fe impurities by using an iron-based catalystIron-melting substance, and improving the stability of Fischer-Tropsch synthesis reaction while reducing CO2Or CH4The problem of overhigh selectivity of byproducts provides a composition containing precipitated X-type iron carbide and theta-type iron carbide, a preparation method thereof, 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 composition containing precipitated x iron carbide and theta iron carbide, the composition comprising 95 to 100 mol% of the precipitated x iron carbide and theta iron carbide, and 0 to 5 mol% of Fe-containing impurities, the Fe-containing impurities being iron-containing substances other than the x iron carbide and the theta iron carbide, based on the total amount of the composition; wherein the specific surface area of the composition is 60 to 300m2/g。
In a second aspect, the present invention provides a method of preparing a composition comprising precipitated iron chi carbide and iron theta carbide, comprising:
mixing and coprecipitating an aqueous solution containing ferric salt and an alkaline precipitator, washing and separating the obtained precipitate to obtain a solid, and drying and roasting the solid to obtain a precursor;
(1) preparing precipitated theta iron carbide, comprising:
(1-1) reacting the precursor with H2At a temperature T1Performing a first reduction at 470-620 ℃;
(1-2) mixing the material obtained in the step (1-1) with H2CO at temperature T2The first carbide preparation is carried out at the temperature of 280-420 ℃ for 20-120H, wherein H2The molar ratio to CO is 5-120: 1; obtaining precipitated theta iron carbide;
(2) preparing precipitated X-type iron carbide, which comprises the following steps:
(2-1) reacting the precursor with H2Performing a second reduction at a temperature of 450-610 ℃;
(2-2) mixing the material obtained in the step (2-1) with O2The gas is subjected to surface passivation treatment at a temperature of 0-50 ℃, and the gas contains O2O in gas2The volume concentration of (A) is 1-5%;
(2-3) mixing the material obtained in the step (2-2) with H2CO is carried out at the temperature of 260 ℃ to 430 DEG CPreparation of the second carbide H2The molar ratio to CO is 7-110: 1; obtaining the precipitated X-shaped iron carbide;
(3) mixing 95-100 molar parts of precipitated x-type iron carbide and theta-type iron carbide and 0-5 molar parts of Fe-containing impurities under the condition of inert gas;
wherein the Fe-containing impurities are iron-containing substances except X iron carbide and theta iron carbide.
In a third aspect, the invention provides a composition containing precipitated x iron carbide and theta iron carbide prepared by the method provided by the invention.
In a fourth aspect, the invention provides a catalyst comprising the composition containing precipitated x iron carbide and theta iron carbide provided by the invention.
In a fifth aspect, the invention provides an application of the composition or the catalyst containing the precipitated x iron carbide and the theta iron carbide in Fischer-Tropsch synthesis reaction.
In a sixth aspect, the invention provides a composition or catalyst containing precipitated x iron carbide and theta iron carbide, and application of the composition or catalyst in synthesis reaction 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 synthesis gas is contacted with the composition or the catalyst containing the precipitated iron chi carbide and the iron theta carbide provided by the invention.
An eighth aspect of the present invention provides a fischer-tropsch synthesis method, comprising: and (2) contacting the synthesis gas with a Fischer-Tropsch catalyst under the Fischer-Tropsch synthesis reaction condition, wherein the Fischer-Tropsch catalyst comprises a Mn component and the composition containing the precipitated x iron carbide and the theta iron carbide.
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 in a preferred embodiment, the whole process of preparing each crystal phase iron carbide can be realized in the same reactor, and then the crystal phase iron carbide and the active phase iron carbide are mixed to form the composition.
(3) According to the invention, through the steps provided by the method, the theta iron carbide and the chi iron carbide with the purity of 100% can be prepared by a precipitation method respectively, and then the theta iron carbide and the chi iron carbide and Fe-containing impurities form a composition to further prepare the catalyst. The above iron carbide or composition or catalyst can be used at high temperatures and pressures (e.g., 245 ℃ C., 340 ℃ C., 1.5-2.5MPa, H)21.5-2.0) continuous reactor, the reaction stability is extremely high, and the traditional literature theory that the chemical potential mu of carbon is higher is broken throughCThe theoretical technical barrier that pure iron carbide cannot exist stably is that stable temperature up to 340 ℃ and CO can be realized2Very 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 below 14% (preferably, 7% or below can be achieved); at the same time, its by-product CH4The selectivity is also kept below 14 percent (preferably below 8 percent), the selectivity of the effective product can reach above 73 percent (preferably above 86 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 XRD spectrum of a precipitated X-type iron carbide prepared in preparation example 1 provided by the present invention;
fig. 2 is an XRD spectrum of the precipitated iron theta carbide prepared in preparation example 2 provided in the present invention.
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, in a first aspect, a composition comprising precipitated iron chi-carbide and iron theta-carbide, said composition being based on the total amount of the compositionThe compound comprises 95-100 mol% of precipitated X-type iron carbide and theta-type iron carbide, and 0-5 mol% of Fe-containing impurities, wherein the Fe-containing impurities are iron-containing substances except the X-type iron carbide and the theta-type iron carbide; wherein the specific surface area of the composition is 60 to 300m2/g。
The invention provides a composition, which comprises theta iron carbide with the purity of 100% and chi iron carbide with the purity of 100%. Further, precipitated x and θ iron carbides may be combined with other Fe-containing impurities to form the composition. Under the limitation of the composition content of the composition, the composition containing the precipitated x iron carbide and the theta iron carbide provided by the invention can be used alone or combined with other components when being applied to a Fischer-Tropsch synthesis catalyst, so that the stability of the Fischer-Tropsch synthesis reaction of the Fischer-Tropsch synthesis catalyst is improved, and CO is reduced2Or CH4Selectivity of by-products.
In some embodiments of the invention, the composition comprises precipitated high purity iron chi carbide and iron theta carbide, and Mossbauer spectroscopy is performed to observe that the crystalline phase comprises pure iron chi carbide and pure iron theta carbide based on the Mossbauer spectroscopy results obtained. Preferably, the composition has a specific surface area of 70 to 190m2(ii) in terms of/g. The specific surface area may be represented by N2The BET adsorption and desorption method (2). The composition includes orthorhombic theta iron carbide and monoclinic chi iron carbide.
In some embodiments of the present invention, it is further preferred that the composition comprises 97 to 100 mol% of precipitated x and θ iron carbides and 0 to 3 mol% of 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 present invention, preferably, the Fe-containing impurity is at least one of iron carbide, iron oxide, iron hydroxide, iron sulfide, and iron salt other than χ iron carbide and θ iron carbide. The Fe-containing impurities may be introduced by solution impregnation, sputtering, atomic deposition or mixing.
In the specific embodiment provided by the invention, the molar ratio of the precipitated X-type iron carbide to the precipitated theta-type iron carbideIs a: b, wherein a is more than 0 and less than 100, b is more than 0 and less than 100, preferably, a is more than 0 and less than or equal to 75, and b is more than 0 and less than or equal to 75. The molar ratio of the iron carbides of the two phases in the above range can produce a synergistic effect, optimizing the dissociation path of CO and the hydrogenation path of the C species and CHxIncrease the catalytic activity and decrease CH4With CO2And adjusting the product distribution.
In a second aspect, the present invention provides a method of preparing a composition comprising precipitated iron chi carbide and iron theta carbide, comprising:
mixing and coprecipitating an aqueous solution containing ferric salt and an alkaline precipitator, washing and separating the obtained precipitate to obtain a solid, and drying and roasting the solid to obtain a precursor;
(1) preparing precipitated theta iron carbide, comprising:
(1-1) reacting the precursor with H2At a temperature T1Performing a first reduction at 470-620 ℃;
(1-2) mixing the material obtained in the step (1-1) with H2CO at temperature T2The first carbide preparation is carried out at the temperature of 280-420 ℃ for 20-120H, wherein H2The molar ratio to CO is 5-120: 1; obtaining precipitated theta iron carbide;
(2) preparing precipitated X-type iron carbide, which comprises the following steps:
(2-1) reacting the precursor with H2Performing a second reduction at a temperature of 450-610 ℃;
(2-2) mixing the material obtained in the step (2-1) with O2The gas is subjected to surface passivation treatment at a temperature of 0-50 ℃, and the gas contains O2O in gas2The volume concentration of (A) is 1-5%;
(2-3) mixing the material obtained in the step (2-2) with H2CO at a temperature of 260-2The molar ratio to CO is 7-110: 1; obtaining the precipitated X-shaped iron carbide;
(3) mixing 95-100 molar parts of precipitated x-type iron carbide and theta-type iron carbide and 0-5 molar parts of Fe-containing impurities under the condition of inert gas;
wherein the Fe-containing impurities are iron-containing substances except X iron carbide and theta iron carbide.
One embodiment provided by the present invention first prepares the precursor. In the preparation process, preferably, the iron salt may be a water-soluble iron salt commonly used in the art, and the iron salt is selected from water-soluble iron salts, which may be commercially available products, for example, 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.
In the preparation process of the precursor, preferably, the precipitation conditions include: the pH value is 5.5-8.5, and the temperature is 45-75 ℃.
In the preparation process of the precursor, the precipitate is washed, and can be washed by deionized water for multiple times until the conductivity of the washing filtrate is lower than 300 muS/cm. And (3) carrying out solid-liquid separation for many times in the washing process to obtain a solid. Preferably, the solid is dried for 6 to 10 hours at the temperature of between 35 and 80 ℃ and the vacuum degree of between 250 and 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. Obtaining the precursor.
The invention provides another embodiment for preparing precipitated theta iron carbide.
In some embodiments of the present invention, step (1-1) may simultaneously perform in-situ generation of nano iron powder from iron element in the precursor and reduction of the generated nano iron powder.
Preferably, H in step (1-1)2Can be represented by H2Introducing the mixture into the reaction system in the form of a flow, and simultaneously controlling H2The pressure of the stream to control the pressure of the first reduction, preferably, in step (1-1), the pressure of the first reduction is 0.1 to 15atm, preferably 0.3 to 2.6 atm; the time is 0.7-15h, preferably 1-12 h.
In some embodiments of the invention, H2The amount of H to be used may be selected depending on the amount of the precursor to be treated, and preferably, in step (1-1), H2The gas flow rate of (b) is 600-25000mL/h/g,more preferably 2800 and 22000 mL/h/g.
In step (1-2) of the method provided by the present invention, conditions for achieving the production of the second carbide are provided to obtain precipitated theta iron carbide. H2And CO may be (H)2+ CO) in the form of a mixed gas stream into the first carbide production process; at the same time, by controlling (H)2+ CO) mixed gas stream pressure to control the pressure of the first carbide making process. Preferably, in the step (1-2), the first carbide is prepared at a pressure of 0 to 28atm, preferably 0.01 to 20atm, for a time of 20 to 120 hours, preferably 24 to 80 hours.
In some embodiments of the present invention, preferably, in step (1-2), H2The total gas flow rate with CO is 200-.
In the step (1-2) of the method provided by the invention, temperature change treatment is also carried out. Preferably, the first carbide preparation further comprises: in the step (1-2), the temperature change operation is carried out at the same time from the temperature T1Cooling or heating to temperature T at variable temperature rate of 0.2-5 deg.C/min2(ii) a Preferably, from the temperature T1Cooling or heating to 300-400 ℃ at a temperature change rate of 0.2-2.5 ℃/min.
The invention provides an embodiment for preparing precipitated X-shaped iron carbide.
In some embodiments of the present invention, step (2-1) may simultaneously perform in-situ generation of nano iron powder from iron element in the precursor and reduction of the generated nano iron powder.
Preferably, H in step (2-1)2Can be represented by H2Introducing the mixture into the reaction system in the form of a flow, and simultaneously controlling H2The pressure of the stream to control the pressure of the second reduction, preferably, in step (2-1), the pressure of the second reduction is 0.1 to 15atm, preferably 0.3 to 2.6 atm; the time is 0.7-15h, preferably 1-12 h.
In some embodiments of the invention, H2The amount of the precursor to be used can be selected according to the amount of the precursor to be treated, preferably, H2The gas flow rate of (b) is 600-25000mL/h/g, more preferably 2800-22000 mL/h/g.
In the step (2-2) of the process of the present invention, O is contained2The gas being O2Mixed gas with inert gas. The inert gas may be at least one of nitrogen, helium, argon, krypton, and xenon. Said oxygen-containing group2Introducing gas to participate in the surface passivation treatment process; at the same time, by controlling the content of O2The pressure of the gas controls the pressure of the surface passivation treatment. Preferably, in the step (2-2), the pressure of the surface passivation treatment is 0-1.6atm, preferably 0-0.09atm, and the time is 5-72h, preferably 10-56 h.
In some embodiments of the present invention, preferably, in the step (2-2), the O-containing compound is2The gas flow rate of the gas is 400-12000mL/h/g, and more preferably 1400-8500 mL/h/g.
In the step (2-3) of the method provided by the invention, conditions for realizing the preparation of the second carbide are provided so as to obtain pure x-shaped iron carbide. H2And CO may be (H)2+ CO) in the form of a mixed gas stream into the second carbide production process; at the same time, by controlling (H)2+ CO) mixed gas stream to control the pressure of the second carbide making process. Preferably, in the step (2-3), the second carbide is prepared at a pressure of 0.08 to 12atm, preferably 0.15 to 2.5atm, for a time of 0.3 to 30 hours, preferably 0.5 to 2.4 hours.
In some embodiments of the present invention, preferably, in step (2-3), H2The total gas flow rate with CO is 250-21000mL/h/g, more preferably 2000-18000 mL/h/g.
According to a preferred embodiment of the present invention, the second carbide preparation further comprises: and (4) simultaneously performing temperature rise operation in the step (2-3), wherein the temperature is raised from the surface passivation treatment temperature to 250-430 ℃ at the temperature rise rate of 0.2-5 ℃/min. In the preferred embodiment, the obtained precipitated chi-type iron carbide can have better effective product selectivity in the Fischer-Tropsch synthesis reaction. Further preferably, the temperature is raised from the temperature of the surface passivation treatment to 260-400 ℃ at a temperature raising rate of 0.2-2.5 ℃/min. In the heating operation, the temperature of the surface passivation treatment is 0-50 ℃ in the step (2-2). Namely, the temperature raising operation is: raising the temperature from 0-50 ℃ to the temperature in step (2-3) of 250 ℃ to 430 ℃ at a temperature raising rate of 0.2-5 ℃/min, preferably from 0-50 ℃ to 260 ℃ to 400 ℃ 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 another preferred embodiment of the present invention, the first reduction and the first carbide preparation may be performed in the same fischer-tropsch synthesis reactor in the preparation of precipitated iron theta carbides. In the process of preparing the precipitated chi-type iron carbide, the second reduction, the surface passivation treatment and the second carbide preparation can be carried out in the same Fischer-Tropsch synthesis reactor. In-situ characterization equipment can be used to track the crystal phase transition of the material during the preparation process.
In the invention, the precipitation type theta iron carbide and the precipitation type chi iron carbide can be obtained through the steps (1) and (2) in the method provided by the invention.
In the step (3) of the method provided by the invention, the precipitated theta iron carbide and the chi iron carbide are mixed into the precipitated iron carbide. The mixing result satisfies that preferably, the molar ratio of the precipitated X iron carbide to the theta iron carbide is a: b, wherein a is more than 0 and less than 100, b is more than 0 and less than 100, preferably, a is more than 0 and less than or equal to 75, and b is more than 0 and less than or equal to 75.
In some embodiments of the present invention, the composition comprising precipitated iron chi carbide and iron theta carbide may comprise Fe-containing impurities incorporated by external means. Preferably, in the step (3), 97 to 100 molar parts of the precipitated chi iron carbide and the theta iron carbide are mixed with 0 to 3 molar parts of the Fe-containing impurities.
In the step (3) of the method provided by the invention, the mixing is carried out under the protection of inert gas, and the powders of the precipitated X-type iron carbide and the theta-type iron carbide and the Fe-containing impurity powder are mixed in a glove box according to the dosage requirement.
In a third aspect, the present invention provides a composition comprising precipitated iron chi carbide and iron theta carbide made by the method of the present invention. The composition comprises 95-100 mol% of precipitated X-type iron carbide and theta-type iron carbide and 0-5 mol% of Fe-containing impurities, wherein the Fe-containing impurities are iron-containing substances except the X-type iron carbide and the theta-type iron carbide.
Preferably, the composition comprises 97 to 100 mol% of precipitated chi iron carbide and theta iron carbide, and 0 to 3 mol% of Fe-containing impurities, based on the total amount of the composition.
Preferably, the specific surface area of the composition is 60 to 300m2A/g, preferably from 70 to 190m2/g。
Preferably, the molar ratio of the precipitated x iron carbide to the theta iron carbide is a: b, wherein a is more than 0 and less than 100, b is more than 0 and less than 100, preferably, a is more than 0 and less than or equal to 75, and b is more than 0 and less than or equal to 75.
In a fourth aspect, the invention provides a catalyst comprising the composition containing precipitated x iron carbide and theta iron carbide provided by the invention. Preferably, the catalyst may also comprise other components, such as promoters.
In the specific embodiment provided by the present invention, preferably, the content of the composition containing precipitated x iron carbide and θ iron carbide is 75 wt% or more and less than 100 wt%, and the content of the auxiliary agent is 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.
In a fifth aspect, the invention provides an application of the composition or the catalyst containing the precipitated x iron carbide and the theta iron carbide in Fischer-Tropsch synthesis reaction.
The invention provides an application of the composition or the catalyst containing the precipitated x iron carbide and the theta iron carbide in C, H fuel and/or chemical synthesis based on the Fischer-Tropsch synthesis principle.
In a seventh aspect, the present invention provides a fischer-tropsch synthesis reaction process, comprising: under the condition of Fischer-Tropsch synthesis reaction, the synthesis gas is contacted with the composition or the catalyst containing the precipitated iron chi carbide and the iron theta carbide provided by the invention.
The composition or the catalyst containing the precipitated x iron carbide and the theta iron carbide is adopted for carrying out Fischer-Tropsch synthesisThe synthesis reaction can be carried out under high temperature and high pressure, for example, the conditions of the Fischer-Tropsch synthesis reaction include: the temperature is 235 ℃ and 250 ℃, and the pressure is 2.3-2.5 MPa. But also can be used for realizing better effective product selectivity; the effective product is prepared from CO and H2Produced by the reaction, except for CH4With CO2Products containing carbon other than C, including but not limited to2And C2The above hydrocarbons, alcohols, aldehydes, ketones, esters, and the like.
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 precipitated x iron carbide and the theta 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.
An eighth aspect of the present invention provides a fischer-tropsch synthesis method, comprising: and (2) contacting the synthesis gas with a Fischer-Tropsch catalyst under the Fischer-Tropsch synthesis reaction condition, wherein the Fischer-Tropsch catalyst comprises a Mn component and the composition containing the precipitated x iron carbide and the theta iron carbide.
In a specific embodiment provided by the present invention, the composition of the fischer-tropsch catalyst may further include, based on the total amount of the fischer-tropsch catalyst, 75 wt% or more and less than 100 wt% of the composition containing precipitated x iron carbide and θ iron carbide, and more than 0 wt% and less than 25 wt% of Mn. 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 COFe) (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 formationFe) Reaction of C2And C2The above number of moles of hydrocarbon/reaction time/weight of Fe element.
Preparation example 1
(1) Mixing ferric nitrate with the concentration of 1.2mol/L and sodium carbonate solution with the concentration of 0.9 mol/L of 1 at the temperature of 65 ℃ and under the condition of pH value of 6.5 to obtain precipitation slurry, washing by deionized water, filtering to obtain a filter cake, drying at the temperature of 110 ℃ for 24 hours, and roasting at the temperature of 400 ℃ for 10 hours to obtain a precursor.
(2) Mixing the precursor with H2At a pressure of 1.8atm, H2The flow rate of the second reduction is 15000mL/h/g, and the temperature is 470 ℃ for 1 h;
(3) cooling the product obtained in the step (2) to 35 ℃, and reacting with O-containing at the temperature2Performing surface passivation treatment by contact of inert gas, wherein O is contained in the gas2The volume concentration of the catalyst is 1 percent, the pressure is 0.08atm, the gas flow is 7500mL/h/g, and the treatment time is 20 h;
(4) will contain O2OfChanging the resultant gas into H2And CO, with the conditions: pressure 2.0atm, total gas flow 18000mL/H/g, H2And (3) heating the mixture to 360 ℃ from 35 ℃ at a heating rate of 2.0 ℃/min under the condition that the molar ratio of the mixture to CO is 35:1, then carrying out second carbide preparation on the product obtained in the step (3), wherein the carbonization time is 2.5h, so as to obtain precipitated iron carbide, and the precipitated iron carbide is pure chi iron carbide determined by Mossbauer spectroscopy and is marked as iron carbide 1.
The preparation method of the precipitated x iron carbide provided by the invention is not limited to preparation example 1, and the specific implementation method for preparing the precipitated x iron carbide is described in the embodiment of the Chinese patent application 'composition containing the precipitated x iron carbide, preparation method thereof, catalyst and application thereof, and Fischer-Tropsch synthesis method', and the entire content of the method is introduced into the invention.
Preparation example 2
(a) Mixing ferric nitrate with the concentration of 1.1mol/L and sodium carbonate solution with the concentration of 0.7 mol/L of 1 at the temperature of 55 ℃ and under the condition of pH value of 6.2 to obtain precipitation slurry, washing by deionized water, filtering to obtain a filter cake, drying at the temperature of 125 ℃ for 24 hours, and roasting at the temperature of 400 ℃ for 10 hours to obtain a precursor.
(b) The precursor is subjected to hydrogen generation at 490 ℃, under the pressure of 2.0atm and the gas flow of 12000mL/H/g2Carrying out first reduction for 3.5 h;
(2) cooling the product obtained in the step (1) to 400 ℃ at the speed of 2.1 ℃/min, and reacting with H at the temperature2And the first carbide is prepared by contacting with CO mixed gas, and the conditions are as follows: pressure 20atm, total gas flow 18000mL/H/g, H2The molar ratio of the obtained product to CO is 60:1, the treatment time is 10 hours, and the obtained product is pure theta iron carbide determined by Mossbauer spectroscopy and is marked as iron carbide 2.
The preparation method of the precipitated theta iron carbide provided by the invention is not limited to the preparation example 2, and the specific implementation method for preparing the precipitated theta iron carbide is described in the embodiment of the Chinese patent application 'composition containing the precipitated theta iron carbide, the preparation method, the catalyst and the application thereof, and the Fischer-Tropsch synthesis method', and the whole content of the method is introduced into the invention.
Example 1
72 parts by mole (in terms of iron element, the same applies hereinafter) of iron carbide 1, 27 parts by mole of iron carbide 2 and 1 part by mole of ferrous oxide (i.e., Fe-containing impurities) were mixed under protection of Ar gas. After mixing, it is designated as iron carbide composition 1.
Example 2
Under the protection of Ar gas, 26 molar parts of iron carbide 1, 72 molar parts of iron carbide 2 and 2 molar parts of ferrous oxide (namely Fe-containing impurities) are mixed. After mixing, it is designated as iron carbide composition 2.
Example 3
Under the protection of Ar gas, 79 mol parts of iron carbide 1, 20 mol parts of iron carbide 2 and 1mol part of ferrous oxide (namely Fe-containing impurities) are mixed. After mixing, it was designated as iron carbide composition 3.
Example 4
Under the protection of Ar gas, 20 molar parts of iron carbide 1, 77 molar parts of iron carbide 2 and 3 molar parts of ferrous oxide (namely Fe-containing impurities) are mixed. After mixing, it was designated as iron carbide composition 4.
Comparative example 1
Under the protection of Ar gas, 79 mol parts of iron carbide 1, 14 mol parts of iron carbide 2 and 7 mol parts of ferrous oxide (namely Fe-containing impurities) are mixed. After mixing, it was designated as iron carbide composition D1.
Comparative example 2
Under the protection of Ar gas, 14 molar parts of iron carbide 1, 80 molar parts of iron carbide 2 and 6 molar parts of ferrous oxide (namely Fe-containing impurities) are mixed. After mixing, it was designated as iron carbide composition D2.
Examples 5 to 8
Respectively taking 1-4 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 1-4 correspondingly. Wherein the amount of the added manganese citrate solution is impregnated, so that the obtained Fischer-Tropsch catalysts 1-4 respectively and correspondingly contain 85 wt% of iron carbide composition 1-6 and 15 wt% of MnO2。
Comparative examples 3 to 4
Respectively taking iron carbide compositions D1-D2 as the balance of N2Adding manganese citrate solution by immersion method under protection, and adding N at 25 deg.C2Drying the obtained product for 24 hours by airflow to obtain the Fischer-Tropsch catalystD1-D2. Wherein the added manganese citrate solution is impregnated in an amount which enables the obtained Fischer-Tropsch catalysts D1-D2 to respectively contain 85 wt% of iron carbide composition D1-D2 and 15 wt% of MnO2。
Test example
Mossbauer spectroscopy was performed on iron carbide 1-2, 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
In the preparation examples 1 and 2, in-situ XRD detection technology is adopted, and an X-ray diffractometer (Rigaku company, model D/max-2600/PC) is used for monitoring the crystal phase change of the material. The XRD test result of preparation example 1 is shown in FIG. 1, in which the curve is such that carbide 1 having a crystal phase of ε -Fe with a purity of 100% is obtained after all the carbonization steps are completed2C and epsilon-Fe2.2C, i.e. epsilon/epsilon' iron carbide, and together an XRD standard card PDF-89-2005 showing 2 theta equal to 37.7 °, 41.4 °, 43.2 °, 57.2 °, 68.0 °, 76.8 °, 82.9 ° in full agreement with the standard card. 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 XRD test result of preparation example 2 is shown in FIG. 2, in which the curve is that carbide 2 obtained after completion of all the carbonization steps has a crystal phase of 100% purity of the orthorhombic system theta-Fe3C, that is, θ iron carbide, has all characteristic peaks at 36.6 °, 37.8 °, 42.9 °, 43.8 °, 44.6 °, 45.0 °, 45.9 °, 48.6 °, and 49.1 ° of 2 θ main peak, and θ -Fe3The C standard card PDF-65-2142 is completely consistent. The generated target product theta iron carbide has good crystallinity, well corresponds to all characteristic peaks of the theta iron carbide, has extremely high purity and does not contain any other impurities.
Mossbauer spectra and BET specific surface area measurements were performed for iron carbide compositions 1-4 and D1-D2, 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 1-4, D1-D2 and iron carbide compositions 1-2. The catalyst loading was 10.0 g.
Evaluation conditions were as follows: t310 deg.C, P2.3 MPa, H2：CO＝1.8：1，(H2+ CO) total amount 42000mL/h/g-Fe(standard state flux, relative to Fe element). The reaction products were 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 composition or catalyst containing precipitated iron chi carbide and iron theta carbide prepared by the invention has high space-time conversion rate of raw material CO, better reaction performance and ultralow CO under limited conditions when the Fischer-Tropsch synthesis reaction is carried out under industrial conditions2And (4) selectivity. At the same time, CH4Low selectivity and high selectivity of effective products.
Further, after long-period experiments, as can be seen from the data of the reaction time of 400 hours in table 4, after the composition or the catalyst containing the precipitated iron chi carbide and the precipitated iron theta carbide prepared under the limited conditions of the present invention is operated for a long time, both the CO conversion rate and the product selectivity are stable, no obvious change is generated, and the stability is greatly superior to that of the iron carbide in the prior art.
The composition or the catalyst containing the precipitated X-type iron carbide and the theta-type iron carbide prepared by the invention can be suitable for a high-temperature high-pressure continuous reactor, has high reaction stability, and contains 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 below 14% (preferably, 7% or below can be achieved); at the same time, its by-product CH4The selectivity is also kept below 14 percent (preferably below 8 percent), and the selectivity of the effective product can reach above 73 percent (preferably above 86 percent). Wherein the space-time yield of the catalyst effective product under the preferred conditions can reach 220mmol/h/g-FeThe method is very suitable for the high-efficiency production of products such as gasoline and diesel oil in the large modern chemical Fischer-Tropsch synthesis 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 (22)
1. A composition containing precipitated x iron carbide and theta iron carbide, wherein the composition comprises 95-100 mol% of the precipitated x iron carbide and the theta iron carbide and 0-5 mol% of Fe-containing impurities, and the Fe-containing impurities are iron-containing substances except the x iron carbide and the theta iron carbide;
wherein the specific surface area of the composition is 60 to 300m2/g。
2. The composition of claim 1, which isWherein the specific surface area of the composition is 70 to 190m2/g。
3. Composition according to claim 1 or 2, wherein the composition comprises 97-100 mol% precipitated x and Θ iron carbides, and 0-3 mol% Fe-containing impurities, based on the total amount of the composition.
4. The composition of any one of claims 1-3, wherein the Fe-containing impurities are at least one of iron carbides other than X and θ iron carbides, iron oxides, iron hydroxides, iron sulfides, iron salts.
5. The composition according to any one of claims 1 to 4, wherein the molar ratio of precipitated χ iron carbide to Θ iron carbide is a: b, wherein a is more than 0 and less than 100, b is more than 0 and less than 100, preferably, a is more than 0 and less than or equal to 75, and b is more than 0 and less than or equal to 75.
6. A method of preparing a composition comprising precipitated iron chi carbide and iron theta carbide, comprising:
mixing and coprecipitating an aqueous solution containing ferric salt and an alkaline precipitator, washing and separating the obtained precipitate to obtain a solid, and drying and roasting the solid to obtain a precursor;
(1) preparing precipitated theta iron carbide, comprising:
(1-1) reacting the precursor with H2At a temperature T1Performing a first reduction at 470-620 ℃;
(1-2) mixing the material obtained in the step (1-1) with H2CO at temperature T2The first carbide preparation is carried out at the temperature of 280-420 ℃ for 20-120H, wherein H2The molar ratio to CO is 5-120: 1; obtaining precipitated theta iron carbide;
(2) preparing precipitated X-type iron carbide, which comprises the following steps:
(2-1) reacting the precursor with H2Performing a second reduction at a temperature of 450-610 ℃;
(2-2) mixing the material obtained in the step (2-1) with O2Gas (es)Surface passivation treatment is carried out at a temperature of 0-50 ℃, and the O-containing2O in gas2The volume concentration of (A) is 1-5%;
(2-3) mixing the material obtained in the step (2-2) with H2CO at a temperature of 260-2The molar ratio to CO is 7-110: 1; obtaining the precipitated X-shaped iron carbide;
(3) mixing 95-100 molar parts of precipitated x-type iron carbide and theta-type iron carbide and 0-5 molar parts of Fe-containing impurities under the condition of inert gas;
wherein the Fe-containing impurities are iron-containing substances except X iron carbide and theta iron carbide.
7. The method according to claim 6, wherein in the step (3), the molar ratio of the precipitated X iron carbide to the theta iron carbide is a: b, wherein a is more than 0 and less than 100, b is more than 0 and less than 100, preferably, a is more than 0 and less than or equal to 75, and b is more than 0 and less than or equal to 75.
8. The method according to claim 6 or 7, 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 solid is dried for 6 to 10 hours at the temperature of between 35 and 80 ℃ and the vacuum degree of between 250 and 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.
9. The process according to any one of claims 6 to 8, wherein in step (1-1), the pressure of the first reduction is 0.1 to 15atm, preferably 0.3 to 2.6 atm; the time is 0.7 to 15 hours, preferably 1 to 12 hours;
further preferably, in step (1-1), H2The gas flow rate of (b) is 600-25000mL/h/g, more preferably 2800-22000 mL/h/g.
10. The method according to any one of claims 6 to 8, wherein, in the step (1-2), the first carbide is prepared at a pressure of 0 to 28atm, preferably 0.01 to 20atm, for a time of 20 to 120h, preferably 24 to 80 h;
further preferably, in step (1-2), H2The total gas flow rate with CO is 200-.
11. The method of any of claims 6-8, wherein the first carbide making further comprises: in the step (1-2), the temperature change operation is carried out at the same time from the temperature T1Heating or cooling to T at a variable temperature rate of 0.2-5 deg.C/min2；
Preferably, from the temperature T1The temperature is raised or lowered to 300-400 ℃ at the temperature change rate of 0.2-2.5 ℃/min.
12. The process according to any one of claims 6 to 8, wherein in step (2-1), the pressure of the second reduction is 0.1 to 15atm, preferably 0.3 to 2.6 atm; the time is 0.7 to 15 hours, preferably 1 to 12 hours;
further preferably, in step (2-1), H2The gas flow rate of (b) is 600-25000mL/h/g, more preferably 2800-22000 mL/h/g.
13. The method according to any one of claims 6 to 8, wherein in the step (2-2), the pressure of the surface passivation treatment is 0 to 1.6atm, preferably 0 to 0.09atm, and the time is 5 to 72h, preferably 10 to 56 h;
further preferably, in the step (2-2), the O-containing compound2The gas flow rate of the gas is 400-12000mL/h/g, and more preferably 1400-8500 mL/h/g.
14. The method according to any one of claims 6 to 8, wherein in step (2-3), the second carbide is prepared at a pressure of 0.08 to 12atm, preferably 0.15 to 2.5atm, for a time of 0.3 to 30h, preferably 0.5 to 2.4 h;
further preferably, in step (2-3), H2The total gas flow rate with CO is 250-21000mL/h/g, more preferably 2000-18000 mL/h/g.
15. The method of any of claims 6-8, wherein the second carbide preparation further comprises: in the step (2-3), the temperature is simultaneously raised from the temperature of the surface passivation treatment to 250-430 ℃ at a temperature raising rate of 0.2-5 ℃/min;
preferably, the temperature is raised from the temperature of the surface passivation treatment to 260-400 ℃ at a temperature raising rate of 0.2-2.5 ℃/min.
16. The method according to any one of claims 6 to 15, wherein in step (3), 97 to 100 molar parts of precipitated χ and Θ iron carbides, 0 to 3 molar parts of Fe-containing impurities are mixed.
17. A composition comprising precipitated x and theta iron carbides, obtainable by a process according to any one of claims 6 to 16.
18. A catalyst comprising the composition comprising precipitated iron chi-carbide and iron theta-carbide of any one of claims 1-5 and 17.
19. Use of a composition comprising precipitated iron χ carbide and iron θ carbide according to any one of claims 1-5 and 17 or a catalyst according to claim 18 in a fischer-tropsch synthesis reaction.
20. Use of a composition comprising precipitated iron χ carbide and iron θ carbide according to any one of claims 1 to 5 and 17 or a catalyst according to claim 18 in a fischer-tropsch based synthesis of C, H fuels and/or chemicals.
21. A process for fischer-tropsch synthesis comprising: contacting synthesis gas with a composition comprising precipitated iron chi carbide and iron theta carbide according to any one of claims 1 to 5 and 17 or a catalyst according to claim 18 under fischer-tropsch synthesis reaction conditions;
preferably, the fischer-tropsch synthesis is carried out in a high temperature high pressure continuous reactor.
22. 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 a composition comprising precipitated iron carbides according to any one of claims 1 to 5 and 17.
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| EP0361349A2 (en) * | 1988-09-26 | 1990-04-04 | Seisan Kaihatsu Kagaku Kenkyusho | Magnetic fine particles of epsilon' iron carbide |
| US20160045901A1 (en) * | 2013-03-19 | 2016-02-18 | Korea Institute Of Energy Research | Iron-based catalyst and method for preparing the same and use thereof |
| CN110075844A (en) * | 2019-04-30 | 2019-08-02 | 上海师范大学 | Nanometer iron-based fischer-tropsch synthetic catalyst of mesoporous carbon-loaded and its preparation method and application |
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| EP0361349A2 (en) * | 1988-09-26 | 1990-04-04 | Seisan Kaihatsu Kagaku Kenkyusho | Magnetic fine particles of epsilon' iron carbide |
| US20160045901A1 (en) * | 2013-03-19 | 2016-02-18 | Korea Institute Of Energy Research | Iron-based catalyst and method for preparing the same and use thereof |
| CN110075844A (en) * | 2019-04-30 | 2019-08-02 | 上海师范大学 | Nanometer iron-based fischer-tropsch synthetic catalyst of mesoporous carbon-loaded and its preparation method and application |
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| PENG WANG ET AL.: "Synthesis of stable and low-CO2 selective ε-iron carbide Fischer-Tropsch catalysts" * |
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