Fluidized bed Fischer-Tropsch synthesis method for catalyst containing chi iron carbide

Abstract

The invention discloses a fluidized bed Fischer-Tropsch synthesis method for an chi-containing iron carbide catalyst, the chi-containing iron carbide catalyst is a supported and / or precipitated chi-containing iron carbide catalyst, a CO2 removal device is not needed in the technological process, and the method is a novel carbon emission reduction process which is simple in process, high in carbon utilization rate and low in cost.

Description

Technical Field

[0001] The present invention relates to the field of coal chemical Fischer-Tropsch synthesis, and in particular to a fluidized bed Fischer-Tropsch synthesis process method for a chi-iron carbide catalyst, wherein the chi-iron carbide catalyst is a supported and / or precipitated chi-iron carbide catalyst. Background Art

[0002] Carbon-containing raw materials such as natural gas, coal, or biomass can be converted into synthesis gas (H2+CO) through certain processes. A variety of products can be obtained through different reaction pathways. The most common method is to convert synthesis gas into low-carbon hydrocarbons, fuels such as gasoline, diesel, and wax, as well as chemicals through the Fischer-Tropsch synthesis reaction. Fischer-Tropsch synthesis can generally be divided into low-temperature Fischer-Tropsch (200-280°C) and high-temperature Fischer-Tropsch (300-350°C) according to the reaction temperature. Among them, high-temperature Fischer-Tropsch generally uses molten iron catalysts, and the products are mainly low-carbon hydrocarbons, gasoline, oxygen-containing compounds, and chemicals, while H2O, CO2, and CH4 are also produced as by-products.

[0003] The current common Fischer-Tropsch synthesis (FTS) process involves: feedstock conversion to syngas → syngas purification → water-gas shift (adjusting the hydrogen-to-carbon ratio) → FTS reaction → gas-liquid separation to obtain liquid products → gas removal and separation of the CO2 byproduct → recovery of low-carbon hydrocarbons → tail gas conversion and hydrogen recovery → compressed recycle gas returned to the reactor, with the remainder (containing CO2 and CH4) discharged. The FTS product must be further upgraded and processed downstream to become the final product. Conventional iron catalysts generate CO2 and CH4 as byproducts during the FTS reaction (with an overall selectivity of 15-30%, depending on catalyst performance and process conditions). Some of the CO2 must be removed from the recycle gas via a decarbonization unit, while the CH4 can be converted into syngas or hydrogen and returned to the reactor for combustion or discharge. Overall, the process from feedstock to product is lengthy, with complex process control parameters and significant fixed asset investment. Approximately 50% of the carbon atoms are emitted into the atmosphere as CO2 and CH4, representing both a waste of raw materials and a significant environmental burden (CO2 and CH4 are greenhouse gases). How to reduce the amount of CO2 and CH4 in the Fischer-Tropsch synthesis process to achieve carbon emission reduction is an important challenge.

[0004] In high-temperature Fischer-Tropsch synthesis (FTS), the WGS reaction is essentially near equilibrium, and CO2 selectivity is primarily controlled by thermodynamics. However, high-temperature FTS also exhibits high CH4 selectivity, necessitating the design of a CH4 reforming and recovery system. This complicates the process flow and increases investment and operating costs. CN102746870B describes a FTS process that separates CO2 and CH4 from tail gas, venting the CO2 and reforming the CH4 into H2 and CO.

[0005] Generally speaking, the traditional high-temperature Fischer-Tropsch synthesis process uses a molten iron catalyst. For example, CN200810202454.1 and CN200510024821.X disclose microspherical precipitated iron catalysts for high-temperature Fischer-Tropsch synthesis. The specific surface area of ​​the catalyst is less than 10m 2 / g. The specific surface area of ​​the molten iron catalyst disclosed in CN03115226.0 is 13m 2 / g, and at a space velocity of 2000 h-1, the space-time yield of C5+ is only 0.05g / (g.cat.h). Therefore, molten iron catalysts generally have disadvantages such as high preparation temperature, high energy consumption, poor catalyst sphericity, easy wear, high methane selectivity, and low space-time yield.

[0006] The applicant has previously applied for a series of patent applications related to iron carbide catalysts, including:

[0007] CN112569993B and CN112569982B disclose supported and precipitated ε / ε' iron carbide, preparation methods thereof, catalysts prepared therefrom, and applications of the catalysts in Fischer-Tropsch reactions, respectively.

[0008] CN112569983B and CN112569992A disclose supported and precipitated χ iron carbide, preparation methods thereof, catalysts prepared therefrom, and applications of the catalysts in Fischer-Tropsch reactions, respectively.

[0009] CN112569984B and CN112569981B disclose supported and precipitated θ iron carbide, preparation methods thereof, catalysts prepared therefrom, and applications of the catalysts in Fischer-Tropsch reactions, respectively.

[0010] CN112569978B and CN112569980B disclose respectively supported and precipitated ε / ε' iron carbide and χ iron carbide compositions and preparation methods thereof, catalysts prepared therefrom, and applications of the catalysts in Fischer-Tropsch reactions;

[0011] CN112569990B and CN112569988B disclose respectively supported and precipitated ε / ε' iron carbide and θ iron carbide compositions and preparation methods thereof, catalysts prepared therefrom, and applications of the catalysts in Fischer-Tropsch reactions;

[0012] CN112569976B and CN112569977B disclose respectively supported and precipitated χ iron carbide and θ iron carbide compositions and preparation methods thereof, catalysts prepared therefrom, and applications of the catalysts in Fischer-Tropsch reactions;

[0013] CN112569979B and CN112569975B disclose respectively supported and precipitated ε / ε' iron carbide, χ iron carbide and θ iron carbide compositions and preparation methods thereof, catalysts prepared therefrom and applications of the catalysts in Fischer-Tropsch reactions.

[0014] Among them, the supported and precipitated χ iron carbide composite catalysts proposed in CN 112569983B and CN 112569992B are not only simple to prepare but also have low CH4 selectivity. In addition, the light olefin products have high added value, but a mature high-yield light olefin Fischer-Tropsch synthesis process has not yet been developed in this field. Therefore, if the χ iron carbide catalysts invented in patents CN 112569983B and CN 112569992B can be used to develop a high-yield light olefin Fischer-Tropsch synthesis process, it will have high social and economic benefits. Summary of the Invention

[0015] The purpose of the present invention is to propose a fluidized bed Fischer-Tropsch synthesis method for a chi iron carbide catalyst, which does not require CO2 removal in the process flow and has a high yield of light olefins. It is a new carbon emission reduction process with a simple process, high carbon utilization rate and low cost.

[0016] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0017] A fluidized bed Fischer-Tropsch synthesis method for a chi-iron carbide catalyst, wherein the chi-iron carbide catalyst is a supported and / or precipitated chi-iron carbide catalyst; the fluidized bed Fischer-Tropsch synthesis method comprises:

[0018] The inlet gas is subjected to a Fischer-Tropsch synthesis reaction in a gas-solid fluidized bed reactor under the action of the catalyst, wherein the conditions for the Fischer-Tropsch synthesis reaction are as follows: a temperature of 280-330°C, a pressure of 1-5.2 MPa, an inlet gas space velocity of 5000-45000 Nm 3 / h / t, the superficial gas velocity is 0.2-0.8m / s, and the hydrogen-carbon ratio of the inlet gas is 1.8-5;

[0019] After the reaction product is separated by the catalyst, heat exchange and cooling are performed to condense and separate the heavy hydrocarbons therein; the reaction product after the heavy hydrocarbons are separated is further cooled to condense and separate the water and light hydrocarbons therein; then the non-condensable gas after the condensed water and light hydrocarbons are separated is subjected to light hydrocarbon recovery to obtain a light hydrocarbon product and a gas depleted of light hydrocarbons;

[0020] A portion of the depleted low-carbon hydrocarbon gas is pressurized and then circulated to the inlet gas as a circulating gas; the inlet gas includes fresh synthesis gas, CO2 feed gas and the circulating gas; the volume proportion of CO2 in the inlet gas is 3-10%.

[0021] In the present invention, fresh synthesis gas is mixed with the circulating gas from the circulating compressor and the CO2 feed gas to form the tower gas; of course, it can be understood in the art that in order to maintain the total hydrogen-carbon ratio of the tower gas, CO or hydrogen can be further introduced into the raw gas to adjust the hydrogen-carbon ratio.

[0022] The inlet gas can undergo heat exchange with the high-temperature oil and gas exiting the top of the reactor in a heat exchanger before entering the Fischer-Tropsch synthesis gas-solid fluidized bed reactor from the bottom. It forms a gas-solid fluidized bed with the supported or precipitated iron carbide catalyst within the reactor, allowing the Fischer-Tropsch synthesis reaction to proceed at elevated temperatures. Hydrocarbons, oxygenates, CO₂, water, and unreacted gases generated by the Fischer-Tropsch synthesis reaction are discharged from the top of the reactor in the form of a gas phase. For example, a cyclone separator can be positioned below the top outlet of the fluidized bed reactor to remove any solid catalyst entrained in the gas phase and return the catalyst to the lower portion of the fluidized bed.

[0023] After heat exchange and cooling separation with the inlet gas in the heat exchanger, heavy Fischer-Tropsch synthesis oil (heavy hydrocarbons) can be obtained; the remaining gas phase enters the cooler for further cooling (for example, cooling to 5-50°C under normal pressure) to further condense the water and light oil therein, and the light oil component and water dissolved with oxygen-containing organic matter can be obtained in the oil-water separator respectively; the non-condensable gas after separation of water and light oil (light hydrocarbons) is further subjected to low-carbon hydrocarbon recovery, and the low-carbon hydrocarbon product and the de-low-carbon hydrocarbon gas in the gas are separated; wherein, the recovery of low-carbon hydrocarbons is well known in the art, and deep cooling, pressure swing adsorption or oil washing can be used to separate the low-carbon hydrocarbons therein, and the details will not be repeated. Most of the de-low-carbon hydrocarbon gas remaining after the recovery of low-carbon hydrocarbons enters the circulating gas compressor as circulating gas, and re-enters the Fischer-Tropsch synthesis reactor after being pressurized by the compressor, without the need for decarbonization treatment.

[0024] According to the fluidized bed Fischer-Tropsch synthesis method of the present invention, preferably, the circulating gas accounts for 60%-90% of the decarbonized low-carbon gas, preferably 65%-85%, such as 70% or 75%.

[0025] In some embodiments, the remaining depleted low-carbon hydrocarbon gas in the depleted low-carbon hydrocarbon gas is further processed, such as by hydrogen recovery, and the recovered H2-rich gas is recycled to the inlet gas. H2 recovery can be achieved by pressure swing adsorption (PSA), membrane separation, or cryogenic methods. Those skilled in the art will appreciate that the recovered hydrogen is H2-rich because impurities are unavoidable. This H2-rich gas can be recycled as part of the inlet gas to adjust the hydrogen-to-carbon ratio of the inlet gas.

[0026] Optionally, the gas depleted of low-carbon hydrocarbons after low-carbon hydrocarbon recovery can be subjected to catalytic reforming before hydrogen recovery to obtain reformed gas. It is understood in the art that, due to the recovery of low-carbon hydrocarbons, the remaining hydrocarbons in the gas depleted of low-carbon hydrocarbons are mainly methane and ethane, which can be converted through reforming. The specific reforming process is well known in the art and will not be described in detail here, so that the methane and ethane therein are steam reformed to obtain hydrogen and CO, and then hydrogen recovery treatment is carried out. The catalytic reforming can be used according to actual needs. Reforming can increase the hydrogen content in the gas. If there is sufficient hydrogen entering the system, it is understood in the art that reforming can be omitted.

[0027] In the present invention, in order to increase the proportion of olefins in the product, CO2 inlet gas is also provided to the fluidized bed reactor. Preferably, the volume proportion of CO2 in the inlet gas is 4-8%, such as 5% or 6%.

[0028] In order to better exert the performance of the catalyst, in the present invention, when performing fluidized bed Fischer-Tropsch synthesis, the reaction temperature is controlled at 280-330°C, such as 285, 300 or 325°C. Preferably, the reaction temperature is 290-320°C, such as 300 or 310°C.

[0029] In the present invention, when fluidized bed Fischer-Tropsch synthesis is carried out, the reaction pressure may be 1-5.2 MPa, such as 1.2, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5 MPa; preferably, the reaction pressure is 2.5-3.9 MPa.

[0030] In the present invention, when the fluidized bed Fischer-Tropsch synthesis is carried out, the air velocity of the inlet gas is 5000-45000Nm 3 / h / tFor example, 8000, 10000, 15000, 20000, 25000, 30000, 35000, 40000 or 42000 Nm 3 / h / t, the air velocity in the tower is 0.2-0.8m / s, such as 0.25, 0.35, 0.4, 0.5, 0.55, 0.7 or 0.75m / s, preferably, the air velocity of the inlet gas is 12000-28000Nm 3 / t / h, more preferably 15000-23000Nm 3 / t / h, the air velocity in the empty tower is 0.3-0.6m / s.

[0031] In the present invention, when fluidized bed Fischer-Tropsch synthesis is carried out, the hydrogen-to-carbon ratio of the inlet gas is 1.8-5, such as 2.5, 4 or 4.5. Preferably, the hydrogen-to-carbon ratio of the inlet gas is 2-3, such as 2.2, 2.5 or 2.8.

[0032] In the fluidized bed Fischer-Tropsch synthesis method of the present invention, the supported χ iron carbide catalyst used is known in the art, see the supported χ iron carbide composition disclosed in CN 112569983A, which is incorporated into this application by reference. Specifically, the supported χ iron carbide catalyst, based on the total weight of the composition, comprises 55-90 wt% of a carrier and 10-45 wt% of an iron component, wherein, based on the total weight of the iron component, the iron component comprises 95-100 mol% of the χ iron carbide catalyst and 0-5 mol% of Fe-containing impurities, wherein the Fe-containing impurities are iron-containing substances other than χ iron carbide. The preparation method of the supported χ iron carbide composition comprises:

[0033] (1) impregnating the support in an aqueous solution of an iron salt, and drying and calcining the impregnated support to obtain a precursor;

[0034] (2) reducing the precursor with H2 at a temperature of 350-610°C;

[0035] (3) subjecting the material obtained in step (2) to surface passivation treatment with an O2-containing gas at a temperature of 0-50° C., wherein the volume concentration of O2 in the O2-containing gas is 1-5%;

[0036] (4) preparing carbide by reacting the material obtained in step (3) with H2 and CO at a temperature of 260-430°C, wherein the molar ratio of H2 to CO is 7-110:1, to obtain supported χ iron carbide;

[0037] (5) Mixing the supported χ iron carbide with Fe-containing impurities under the protection of inert gas.

[0038] According to the Fischer-Tropsch synthesis method of the present invention, preferably, the specific surface area of ​​the supported iron carbide catalyst composition is 40-450 m 2 / g, preferably 50-350m 2 / g; based on the total amount of the composition, the supported chi-iron carbide catalyst composition comprises 60-85 wt% of a carrier and 15-40 wt% of an iron component; preferably, based on the total amount of the iron component, the iron component comprises 97-100 mol% of chi-iron carbide and 0-3 mol% of Fe-containing impurities; wherein the Fe-containing impurities are at least one of iron carbide, iron, iron oxide, iron hydroxide, iron sulfide, and iron salt other than chi-iron carbide.

[0039] In the fluidized bed Fischer-Tropsch synthesis method of the present invention, the precipitated χ iron carbide catalyst used is known in the art, see the precipitated χ iron carbide composition disclosed in CN 112569992A, which is incorporated into this application by reference. Specifically, the precipitated χ iron carbide catalyst comprises 95-100 mol% of precipitated χ iron carbide and 0-5 mol% of Fe-containing impurities, based on the total amount of the composition, wherein the Fe-containing impurities are iron-containing substances other than χ iron carbide; wherein the specific surface area of ​​the precipitated χ iron carbide catalyst composition is 30-350 m 2 / g; the preparation method of the precipitated x iron carbide composition comprises:

[0040] (1) mixing an aqueous solution containing an iron salt with an alkaline precipitant for co-precipitation, washing and separating the obtained precipitate, and then drying and calcining the obtained solid to obtain a precursor;

[0041] (2) reducing the precursor with H2 at a temperature of 450-610°C;

[0042] (3) subjecting the material obtained in step (2) to surface passivation treatment with an O2-containing gas at a temperature of 0-50° C., wherein the volume concentration of O2 in the O2-containing gas is 1-5%;

[0043] (4) preparing carbide by reacting the material obtained in step (3) with H2 and CO at a temperature of 260-430°C, wherein the molar ratio of H2 to CO is 7-110:1, to obtain precipitated χ iron carbide;

[0044] (5) 95-100 mol parts of precipitated χ iron carbide and 0-5 mol parts of Fe-containing impurities are mixed under the protection of an inert gas.

[0045] Preferably, the specific surface area of ​​the precipitated iron carbide catalyst composition is 35-250 m 2 / g; based on the total amount of the composition, the precipitated χ iron carbide-containing catalyst composition comprises 97-100 mol% of precipitated χ iron carbide and 0-3 mol% of Fe-containing impurities; wherein the Fe-containing impurities are at least one of iron carbide, iron, iron oxide, iron hydroxide, iron sulfide, and iron salt other than χ iron carbide.

[0046] In the present invention, unless otherwise specified, the percentages or percents involved are mass percentages or mass percents.

[0047] Through the above technical solution, the present invention has the following technical effects compared with the traditional Fischer-Tropsch synthesis process:

[0048] (1) The present invention has successfully developed a new Fischer-Tropsch synthesis process for high-yield low-carbon olefins. Based on the existing chi-containing iron carbide catalyst, by adding CO2 to the raw gas and selecting a suitable fluidized bed Fischer-Tropsch process, the product has a high content of high-value-added low-carbon olefins and a high carbon utilization rate. There is no need for decarbonization of the circulating gas, the process flow is shortened, the operation difficulty is reduced, and the cost is low.

[0049] (2) The present invention has a high carbon element utilization rate, more thorough utilization of raw materials, and can significantly reduce greenhouse gas (CO2+CH4) emissions in the coal indirect liquefaction process.

[0050] (3) After the Fischer-Tropsch process of the present invention is promoted, it will help achieve a breakthrough in the industry, have a significant impact on the industry, and have considerable economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a schematic diagram of the fluidized bed Fischer-Tropsch synthesis system in Example 1. DETAILED DESCRIPTION

[0052] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0053] It should be noted that the terms "first," "second," and the like in the specification and claims of the present invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate for the embodiments of the present invention described herein. In addition, the terms "including," "having," and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to these processes, methods, products, or apparatuses.

[0054] like Figure 1As shown, when the Fischer-Tropsch synthesis method of the present invention is used for Fischer-Tropsch synthesis, the inlet gas is contacted with the catalyst, and the Fischer-Tropsch synthesis reaction is carried out in the fluidized bed reactor 1; then, the product generated by the reaction and the unreacted gas are separated as the outlet gas at the top of the reactor by a cyclone to remove the entrained solid catalyst and then leave the fluidized bed reactor 1, firstly, after heat exchange and cooling in the heat exchange unit 2, the heavy hydrocarbons therein are condensed and separated; the reaction product after the heavy hydrocarbons are separated is further sent to the cooling unit 3 for cooling, so that the water and light hydrocarbons therein are condensed and separated, and then the oil-water separation can be further carried out in the oil-water separator 8; then, the non-condensable gas after the condensed water and light hydrocarbons are separated is sent to the low-carbon hydrocarbon recovery unit 5 for low-carbon hydrocarbon recovery to obtain a low-carbon hydrocarbon product and a low-carbon hydrocarbon-free gas;

[0055] A portion of the depleted low-carbon hydrocarbon gas is pressurized by a compressor 6 and then circulated to the inlet gas. To further recover hydrogen, in some embodiments, the remaining depleted low-carbon hydrocarbon gas is sent to a hydrogen recovery unit 7 for hydrogen recovery, and the recovered H2-rich gas is used as part of the inlet gas to adjust the hydrogen-to-carbon ratio. The tail gas remaining after hydrogen recovery can be used as purge gas.

[0056] The present invention is further described below with reference to Examples / Comparative Examples.

[0057] Example 1

[0058] Use Figure 1 The fluidized bed Fischer-Tropsch synthesis system shown in the figure performs Fischer-Tropsch synthesis reaction in a gas-solid fluidized bed reactor 1 under the action of a catalyst. The conditions of the Fischer-Tropsch synthesis reaction are as follows: temperature 300°C, pressure 2.5MPa, gas velocity 15000Nm 3 / h / t, the superficial gas velocity is 0.3m / s;

[0059] The gaseous product after the reaction is discharged from the top of the sub-reactor after the catalyst is removed, and the condensed heavy hydrocarbons are separated in the heat exchange unit 2; the reaction product after the heavy hydrocarbons are separated is further separated from the condensed water and light hydrocarbons in the cooling unit 3; the resulting non-condensable gas is then sent to the light hydrocarbon recovery unit 5 for light hydrocarbon recovery to obtain light hydrocarbon products and light hydrocarbon-free gas;

[0060] 85% of the depleted low-carbon hydrocarbon gas is pressurized by compressor 6 and then recycled to the inlet gas. The inlet gas comprises fresh synthesis gas, CO2 feed gas, and recycle gas. The remaining depleted low-carbon hydrocarbon gas is further fed to hydrogen recovery unit 7 for hydrogen recovery. The recovered H2-rich gas is pressurized by compressor 6 and then recycled to the inlet gas. The inlet gas has a hydrogen-to-carbon ratio of 2 and a CO2 content of 8% by volume.

[0061] The catalyst used is a supported χ iron carbide catalyst, which is prepared according to Example 1 in CN 112569983A.

[0062] Example 2

[0063] The difference from Example 1 is that during the reaction, the relevant parameters are as follows:

[0064] The temperature is 315℃, the pressure is 3.5MPa, and the air velocity of the inlet gas is 23000Nm 3 / h / t, the empty tower gas velocity is 0.5m / s; the circulating gas accounts for 70% of the decarbonized gas; the hydrogen-carbon ratio of the gas entering the tower is 3; and the CO2 volume content is 4%.

[0065] The catalyst used is a precipitated χ iron carbide catalyst, which is prepared according to Example 1 in CN 112569992A.

[0066] Example 3

[0067] The difference from Example 1 is that during the reaction, the relevant parameters are as follows:

[0068] The temperature is 330℃, the pressure is 4.5MPa, and the air velocity of the inlet gas is 30000Nm 3 / h / t, the empty tower gas velocity is 0.7m / s; the circulating gas accounts for 80% of the decarbonized gas; the hydrogen-carbon ratio of the gas entering the tower is 2, and the CO2 volume content is 3.5%.

[0069] Example 4

[0070] The difference from Example 2 is that, during the reaction, the relevant parameters are as follows:

[0071] The temperature is 280℃, the pressure is 2MPa, and the air velocity of the inlet gas is 12000Nm 3 / h / t, the empty tower gas velocity is 0.2m / s; the circulating gas accounts for 70% of the decarbonized gas; the hydrogen-carbon ratio of the gas entering the tower is 3; and the CO2 volume content is 4%.

[0072] Comparative Example 1

[0073] The difference from Example 1 is that the reaction temperature is 260°C.

[0074] Comparative Example 2

[0075] The difference from Example 1 is that the reaction temperature is 340°C.

[0076] Comparative Example 3

[0077] The difference from Example 1 is that no additional CO2 is added to the inlet gas during the reaction.

[0078] By analyzing the outlet gas, the reaction product parameters of the above embodiments / comparative examples are shown in Table 1 below:

[0079] Table 1

[0080]

[0081]

[0082] The CH4 and C5+ selectivities in the table refer to the weight percentage of the specific product in the total hydrocarbon products;

[0083] C 2-4 Olefins / C 2-4 The total hydrocarbon ratio is C 2-4 C in total hydrocarbons 2-4 The mass ratio of olefins.

[0084] From the above examples / comparative examples, it can be seen that by controlling the reaction temperature, the selectivity of CO2 and CH4 can be effectively reduced and the selectivity of C5+ can be improved; by adding CO2 to the feed gas, the selectivity of light olefins (C 2-4 olefins), which are 2-4 The proportion of total hydrocarbons increased significantly.

Claims

1. A fluidized bed Fischer-Tropsch synthesis method for a chi-iron carbide catalyst, wherein the chi-iron carbide catalyst is a supported and / or precipitated chi-iron carbide catalyst; the fluidized bed Fischer-Tropsch synthesis method comprises: The inlet gas is subjected to a Fischer-Tropsch synthesis reaction in a gas-solid fluidized bed reactor under the action of the catalyst, wherein the conditions for the Fischer-Tropsch synthesis reaction are as follows: a temperature of 280-330°C, a pressure of 1-5.2 MPa, an inlet gas space velocity of 5000-45000 Nm 3 / h / t, the superficial gas velocity is 0.2-0.8m / s, and the hydrogen-carbon ratio of the inlet gas is 1.8-5; After the reaction product is separated by the catalyst, heat exchange and cooling are performed to condense and separate the heavy hydrocarbons therein; the reaction product after the heavy hydrocarbons are separated is further cooled to condense and separate the water and light hydrocarbons therein; then the non-condensable gas after the condensed water and light hydrocarbons are separated is subjected to light hydrocarbon recovery to obtain a light hydrocarbon product and a gas depleted of light hydrocarbons; A portion of the depleted low-carbon hydrocarbon gas is pressurized and then circulated to the inlet gas as a circulating gas; the inlet gas includes fresh synthesis gas, CO2 feed gas and the circulating gas; the volume proportion of CO2 in the inlet gas is 3-10%.

2. The fluidized bed Fischer-Tropsch synthesis method according to claim 1, characterized in that: The recycle gas accounts for 60%-90% of the decarbonized gas, preferably 65%-85%.

3. The fluidized bed Fischer-Tropsch synthesis method according to claim 1, characterized in that: The hydrogen-to-carbon ratio of the inlet gas is 2-3.

4. The fluidized bed Fischer-Tropsch synthesis method according to claim 1, characterized in that: The volume proportion of CO2 in the inlet gas is 4-8%.

5. The fluidized bed Fischer-Tropsch synthesis method according to claim 1, characterized in that: When performing fluidized bed Fischer-Tropsch synthesis, the reaction temperature is 290-320° C.; the reaction pressure is 2.5-3.9 MPa.

6. The fluidized bed Fischer-Tropsch synthesis method according to claim 1, characterized in that: When performing fluidized bed Fischer-Tropsch synthesis, the inlet gas space velocity is 15000-23000Nm 3 / t / h, the air velocity in the empty tower is 0.3-0.6m / s.

7. The fluidized bed Fischer-Tropsch synthesis method according to claim 1, characterized in that: The remaining decarbonized gas in the decarbonized gas is further subjected to hydrogen recovery treatment to obtain H2-rich gas and residual tail gas, and the recovered H2-rich gas is circulated to the fluidized bed reactor as part of the inlet gas.

8. The fluidized bed Fischer-Tropsch synthesis method according to claim 1, characterized in that: Before entering the reactor, the inlet gas is heat exchanged with the logistics leaving the reactor to increase its temperature, and then enters the reactor to carry out the Fischer-Tropsch synthesis reaction.

9. The fluidized bed Fischer-Tropsch synthesis method according to claim 1, characterized in that: The supported χ iron carbide catalyst comprises, based on the total amount of the composition, 55-90 wt% of a carrier and 10-45 wt% of an iron component, wherein, based on the total amount of the iron component, the iron component comprises 95-100 mol% of the χ iron carbide catalyst and 0-5 mol% of Fe-containing impurities, wherein the Fe-containing impurities are iron-containing substances other than the χ iron carbide; The specific surface area of ​​the composition is 40-450m 2 / g, preferably 50-350m 2 / g; Based on the total amount of the composition, the composition comprises 60-85 wt% of a carrier and 15-40 wt% of an iron component; preferably, based on the total amount of the iron component, the iron component comprises 97-100 mol% of χ iron carbide and 0-3 mol% of Fe-containing impurities; Wherein, the Fe-containing impurities are at least one of iron carbide, iron, iron oxide, iron hydroxide, iron sulfide, and iron salt other than x-iron carbide.

10. The fluidized bed Fischer-Tropsch synthesis method according to claim 1, characterized in that: The precipitated χ iron carbide catalyst comprises, based on the total amount of the composition, 95-100 mol% of precipitated χ iron carbide and 0-5 mol% of Fe-containing impurities, wherein the Fe-containing impurities are iron-containing substances other than χ iron carbide; wherein the specific surface area of ​​the composition is 30-350 m 2 / g; the specific surface area of ​​the composition is 35-250m 2 / g; based on the total amount of the composition, the composition comprises 97-100 mol% of precipitated χ iron carbide, and 0-3 mol% of Fe-containing impurities; Wherein, the Fe-containing impurities are at least one of iron carbide, iron, iron oxide, iron hydroxide, iron sulfide, and iron salt other than x-iron carbide.

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