Fischer-Tropsch synthesis method for catalyst containing epsilon / epsilon'iron carbide and chi iron carbide

Abstract

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

Description

Technical Field

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

[0002] Synthesis gas (H2+CO) is the most common inlet gas in the coal chemical industry. Many products can be obtained through different reaction pathways. The most common method is to use the synthesis gas through the Fischer-Tropsch synthesis reaction to obtain low-carbon hydrocarbons, gasoline, diesel, wax and other fuels and chemicals. Fischer-Tropsch synthesis can be divided into low-temperature Fischer-Tropsch (220-280°C) and high-temperature Fischer-Tropsch (300-350°C) according to the reaction temperature. Among them, low-temperature Fischer-Tropsch generally uses precipitated or supported iron catalysts, and the products are mainly low-carbon hydrocarbons, diesel and wax, while CO2 and CH4 are also produced as by-products.

[0003] The current common coal indirect liquefaction technology route is: coal gasification → syngas purification → CO2 shift (producing CO2) → Fischer-Tropsch synthesis reaction → gas-liquid separation → CO2 removal (producing CO2) → light hydrocarbon recovery → hydrogen recovery → CH4 conversion → recycle gas back to the reactor. The purpose of the CO2 shift is to adjust the hydrogen-to-carbon ratio of the syngas to meet the requirements of the Fischer-Tropsch synthesis reaction, which produces CO2. Furthermore, traditional iron catalysts generate CO2 and CH4 as byproducts during the Fischer-Tropsch synthesis reaction (with an overall selectivity of 15-30%, depending on catalyst performance and process conditions). CO2 must be removed from the recycle gas via a decarbonization unit, while CH4 is generally converted into syngas and returned to the reactor for combustion or emission. Overall, the coal indirect liquefaction process is lengthy, with complex process control parameters and large fixed asset investments. Furthermore, approximately 50% of the carbon atoms in coal are emitted into the atmosphere as CO2 and CH4, which is both a waste of raw materials and a significant environmental burden (CO2 and CH4 are greenhouse gases). How to reduce the production of CO2 and CH4 in the Fischer-Tropsch synthesis process to achieve carbon emission reduction is an important challenge in the coal chemical industry.

[0004] Patent 1 (CN102614764B) describes a process for treating non-condensable gases from Fischer-Tropsch synthesis. This process removes CO2 from the converted mixed gas, and then subjects the decarbonized mixed gas to pressure swing adsorption to produce high-purity hydrogen. Patent 2 (CN200610140020.4) describes a two-stage Fischer-Tropsch synthesis process. This process involves removing CO2 from the non-condensable gas using an alkaline wash method, followed by a water-gas shift and decarbonization process to convert it into synthesis gas, which then enters the Fischer-Tropsch synthesis reactor.

[0005] Generally speaking, the traditional Fischer-Tropsch synthesis process is generally designed with circulating gas decarbonization and CH4 reforming systems due to its high selectivity for CO2 and CH4, which complicates the process flow and increases investment and operating costs.

[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] This series of catalysts exhibits unprecedented high activity, ultra-low CO2 selectivity, low CH4 selectivity, and high stability. The composite catalysts containing ε / ε' iron carbide and χ iron carbide are characterized by high catalytic activity at relatively low temperatures, a wide temperature range, and very low CO2 selectivity, making them particularly suitable for low-temperature slurry bed reactors. The exceptional performance of these catalysts has made their large-scale industrial application imperative. However, unlike laboratory testing and evaluation of catalysts, industrial applications require re-evaluation due to the mismatch between existing processes and the activity and selectivity characteristics of iron carbide catalysts. This is particularly important for industrial applications that fully exploit the catalyst's potential and require specific advantages or breakthroughs. It is necessary to re-integrate the catalyst's unique characteristics and develop a new, targeted process for industrial application.

[0015] If a composite catalyst containing ε / ε' iron carbide and χ iron carbide can be used to develop a breakthrough Fischer-Tropsch synthesis process that can achieve CO2-free removal, it will greatly improve carbon utilization and reduce equipment investment costs, while also meeting the goal of carbon emission reduction. The economic benefits and social effects will be very obvious. Summary of the Invention

[0016] The purpose of the present invention is to propose a Fischer-Tropsch synthesis method for a catalyst containing ε / ε' iron carbide and χ iron carbide. The process does not require CO2 removal and is a new carbon emission reduction process with a simple process, high carbon utilization rate and low cost.

[0017] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0018] A Fischer-Tropsch synthesis method for a catalyst containing ε / ε' iron carbide and χ iron carbide, wherein the catalyst containing ε / ε' iron carbide and χ iron carbide is a composite catalyst containing supported and / or precipitated ε / ε' iron carbide and χ iron carbide; the Fischer-Tropsch synthesis method comprises:

[0019] The inlet gas containing synthesis gas is contacted with a composite catalyst containing ε / ε' iron carbide and χ iron carbide, and a Fischer-Tropsch synthesis reaction is carried out in a gas-liquid-solid three-phase reactor. The reaction conditions are as follows: temperature 230-275°C, pressure 1-5 MPa; total space velocity in the reactor 10000-38000 Nm 3 / h / t, superficial gas velocity 0.15-0.55m / s, catalyst concentration 5-20%;

[0020] The light component products after the reaction and the unreacted gas flow out from the top of the reactor as the outlet gas, and after heat exchange and condensation, the light oil and water as the liquid phase and the non-condensable gas as the gas phase are obtained through gas-liquid separation.

[0021] The heavy component products after the reaction are discharged after separation of the catalyst by filtration, and heavy oil and wax are obtained after fractionation;

[0022] A portion of the non-condensable gas is used as the first circulating gas; the remaining portion of the non-condensable gas is subjected to light hydrocarbon recovery, the gas depleted of light hydrocarbons after light hydrocarbon recovery is further subjected to hydrogen recovery, and the H2-rich gas obtained after hydrogen recovery is used as the second circulating gas; the circulating gas composed of the first circulating gas and the second circulating gas is pressurized and used as part of the inlet gas; wherein the volume ratio of the non-condensable gas used as the first circulating gas to the non-condensable gas subjected to light hydrocarbon recovery is 0.7-6.0;

[0023] The inlet gas includes fresh synthesis gas, the recycle gas and optionally pure hydrogen for adjusting the hydrogen-carbon ratio of the feed gas; the hydrogen-carbon ratio of the inlet gas is 1.5-5;

[0024] Wherein, the gas-liquid-solid three-phase reactor is a bubbling slurry bed reactor with a gas distributor.

[0025] In the present invention, the Fischer-Tropsch synthesis reaction temperature may be 230-275°C, such as 235, 240, 245, 255, 265 or 270°C; preferably, the reaction temperature is 240-265°C, such as 245, 250, 255 or 260°C.

[0026] Fischer-Tropsch synthesis is usually carried out under high pressure. In the present invention, the reaction pressure of the Fischer-Tropsch synthesis reaction can be 1-5.5 MPa, such as 1.5, 1.8, 2, 2.5, 3, 3.2, 3.5, 4, 4.5 or 5 MPa; preferably, the reaction pressure is 1.7-3.0 MPa, such as 2, 2.5 or 2.8 MPa.

[0027] In the present invention, when the Fischer-Tropsch synthesis reaction is carried out, the total space velocity in the reactor can be 10000-38000 Nm 3 / h / t, such as 15000, 19000, 21000, 23000, 30000 or 35000 Nm 3 / h / t; preferably, the total space velocity in the reactor is 14000-30000Nm 3 / h / t.

[0028] In the present invention, when the Fischer-Tropsch synthesis reaction is carried out, the superficial gas velocity in the reactor can be 0.15-0.55 m / s, such as 0.2, 0.3, 0.37, 0.45 or 0.5 m / s; preferably, the superficial gas velocity in the reactor is 0.25-0.4 m / s.

[0029] In the present invention, when the Fischer-Tropsch synthesis reaction is carried out, the catalyst concentration in the reactor can be 5-20%, such as 6%, 8%, 9%, 10%, 12%, 15%, 18% or 20%. Preferably, the catalyst concentration is 8-14%.

[0030] In a preferred embodiment, the gas-liquid-solid three-phase reactor includes a first gas distributor located at the bottom lower head of the reactor cylinder and a second gas distributor arranged at the lower part of the reactor, and the gas outlet holes of the first and second gas distributors are both open downward, so that fresh synthesis gas can be passed downward from the lower second gas distributor. On the one hand, it is beneficial to the reverse contact with the rising flow from the bottom to improve the degree of gas-liquid-solid three-phase mixing, thereby improving the conversion rate. On the other hand, the buffering of the downward air intake is used to reduce the collision wear of the catalyst.

[0031] In a preferred embodiment, the first gas distributor is used to receive the circulating gas in the raw gas, and the second gas distributor is used to receive the remaining gas in the raw gas; by introducing the circulating gas at the bottom of the reactor and utilizing the higher catalyst concentration at the bottom of the reactor, the effective re-conversion of the circulating gas is promoted to improve the yield, and at the same time, the relatively low effective gas concentration in the circulating gas is utilized to avoid the bottom temperature runaway and thus limit the dilemma of further increasing the intake volume to increase production capacity, thereby improving the applicability of the reactor to high-activity catalysts.

[0032] In a preferred embodiment, the distance between the second gas distributor and the first gas distributor is 1 / 8-1 / 6, for example, 1 / 7, of the height of the reactor. Studies have found that when the two are set too far apart, it is not conducive to the reverse contact of the rising flow from the bottom and the improvement of the degree of gas-liquid-solid three-phase mixing; when they are set too close, it is not conducive to controlling the bottom temperature.

[0033] In the present invention, the hydrogen-to-carbon ratio of the inlet gas is 1.5-5, such as 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5.5, preferably 2-4, such as 2.5, 3 or 3.5; the inlet gas includes synthesis gas from the outside and the circulating gas; of course, it can be understood in the art that in order to maintain the total hydrogen-to-carbon ratio of the inlet gas, CO or hydrogen can be further introduced into the inlet gas to adjust the hydrogen-to-carbon ratio.

[0034] In a preferred embodiment, the volume ratio of the non-condensable gas used as the first circulating gas to the non-condensable gas for light hydrocarbon recovery is 2-3.7, such as 2.2, 2.5, 3 or 3.5.

[0035] In a preferred embodiment, the volume ratio of CO2 in the feed gas is 2-10%, such as 3%, 5% or 7%, preferably 4-8%.

[0036] In the present invention, it can be understood that before entering the reactor, the raw gas can first be heat exchanged with the reactor outlet logistics to increase the temperature; according to the Fischer-Tropsch synthesis method of the present invention, preferably, the logistics after the reaction undergoes two or more stages of heat exchange and gas-liquid separation, the first stage heat exchange temperature is 136-230°C, the last stage heat exchange temperature is 2-55°C, and the middle stage heat exchange temperature is between the first stage heat exchange temperature and the last stage heat exchange temperature; preferably, two stages of heat exchange, the first stage heat exchange temperature is preferably 150-175°C, and the second stage heat exchange temperature is preferably 8-51°C.

[0037] In the present invention, another part of the obtained non-condensable gas is subjected to light hydrocarbon recovery to obtain a light hydrocarbon product and a de-light hydrocarbon gas; light hydrocarbon recovery is well known in the art, and for example, deep cooling, pressure swing adsorption or oil washing can be used to separate the light hydrocarbons therein, and the recovery ratio can reach 90%-99%, which will not be described in detail.

[0038] In the present invention, the hydrogen recovery can be carried out in a hydrogen recovery unit. Those skilled in the art will appreciate that hydrogen enrichment can be achieved in the hydrogen recovery unit by pressure swing adsorption or membrane separation, which is well known in the art and will not be described in detail here. Those skilled in the art will appreciate that since impurities are difficult to avoid in the recovered hydrogen, it is referred to as H2-rich gas. This H2-rich gas can be circulated to the reactor as part of the feed gas to adjust the hydrogen-to-carbon ratio of the feed gas.

[0039] Optionally, in the present invention, 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. Specific reforming methods are well known in the art, so that the methane and ethane therein are steam reformed to obtain hydrogen and CO, and then hydrogen recovery 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.

[0040] In the present invention, the catalyst containing supported ε / ε' iron carbide and χ iron carbide is preferably a composition containing supported ε / ε' iron carbide and χ iron carbide disclosed in CN 112569978A, which is incorporated into this application by reference. Specifically, the composition containing supported ε / ε' iron carbide and χ iron carbide comprises 55-90 wt% of a carrier and 10-45 wt% of an iron component, based on the total amount of the composition, wherein the iron component comprises 95-100 mol% of ε / ε' iron carbide and χ iron carbide, and 0-5 mol% of Fe-containing impurities, based on the total amount of the iron component, wherein the Fe-containing impurities are iron-containing substances other than ε / ε' iron carbide and χ iron carbide; preferably, the specific surface area of ​​the composition is 40-450 m2 / g, preferably 45-350 m2 / g, such as 50-350 m2 / g. The preparation method of the composition containing supported ε / ε' iron carbide and χ iron carbide comprises:

[0041] The carrier is impregnated in an aqueous solution of an iron salt, and the impregnated carrier is dried and calcined to obtain a precursor;

[0042] (1) Preparing supported ε / ε' iron carbide, comprising:

[0043] (1-1) performing a first reduction on the precursor with H2 at a temperature of 300-550°C;

[0044] (1-2) pre-treating the material obtained in step (1-1) with H2 and CO at a temperature of 90-185°C, wherein the molar ratio of H2 to CO is 1.2-2.8:1;

[0045] (1-3) preparing a first carbide by reacting the material obtained in step (1-2) with H2 and CO at a temperature of 200-300°C, wherein the molar ratio of H2 to CO is 1-3.2:1, to obtain supported ε / ε' iron carbide;

[0046] (2) preparing supported x iron carbide, comprising:

[0047] (2-1) subjecting the precursor to a second reduction reaction with H2 at a temperature of 350-610°C;

[0048] (2-2) performing a surface passivation treatment on the material obtained in step (2-1) 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%;

[0049] (2-3) preparing a second carbide by reacting the material obtained in step (2-2) 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;

[0050] (3) The supported ε / ε' iron carbide and χ iron carbide are mixed with Fe-containing impurities under the protection of an inert gas.

[0051] In a preferred embodiment, the composition comprises 60-85 wt% of a support and 15-40 wt% of an iron component, based on the total weight of the composition. Preferably, the iron component comprises 97-100 mol% of ε / ε' iron carbide and χ iron carbide, and 0-3 mol% of Fe-containing impurities, based on the total weight of the iron component. Further preferably, the molar ratio of the supported ε / ε' iron carbide to the χ iron carbide is a:b, wherein 0 < a ≤ 85 and 0 < b ≤ 85, such as 15:85 - 85 - 15, for example 82:17.

[0052] In the present invention, the catalyst containing precipitated ε / ε' iron carbide and χ iron carbide is preferably the composition containing precipitated ε / ε' iron carbide and χ iron carbide disclosed in CN 112569980A, which is incorporated into this application by reference. Specifically, the composition containing precipitated ε / ε' iron carbide and χ iron carbide, based on the total amount of the composition, contains 95-100 mol% of precipitated ε / ε' iron carbide and χ iron carbide, and 0-5 mol% of Fe-containing impurities, wherein the Fe-containing impurities are iron-containing substances other than ε / ε' iron carbide and χ iron carbide; preferably, the specific surface area of ​​the composition is 40-320 m2 / g, preferably 50-270 m2 / g, such as 250 m2 / g. The preparation method of the composition containing precipitated ε / ε' iron carbide and χ iron carbide comprises:

[0053] The aqueous solution containing the iron salt is mixed with an alkaline precipitant for co-precipitation, and the obtained precipitate is washed and separated, and the obtained solid is dried and calcined to obtain a precursor;

[0054] (1) Preparing precipitated ε / ε' iron carbide, comprising:

[0055] (1-1) performing a first reduction on the precursor with H2 at a temperature of 450-580°C;

[0056] (1-2) pre-treating the material obtained in step (1-1) with H2 and CO at a temperature of 90-185°C, wherein the molar ratio of H2 to CO is 1.2-2.8:1;

[0057] (1-3) preparing a first carbide by reacting the material obtained in step (1-2) with H2 and CO at a temperature of 200-300°C, wherein the molar ratio of H2 to CO is 1-3.2:1; obtaining precipitated ε / ε' iron carbide;

[0058] (2) Preparing precipitated x iron carbide, comprising:

[0059] (2-1) performing a second reduction on the precursor with H2 at a temperature of 450-610°C;

[0060] (2-2) performing a surface passivation treatment on the material obtained in step (2-1) 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%;

[0061] (2-3) preparing a second carbide by reacting the material obtained in step (2-2) with H2 and CO at a temperature of 260-430°C, wherein the molar ratio of H2 to CO is 7-110:1; obtaining precipitated χ iron carbide;

[0062] (3) mixing 95-100 mol parts of precipitated ε / ε' iron carbide and χ iron carbide and 0-5 mol parts of Fe-containing impurities under inert gas conditions;

[0063] In a preferred embodiment, the composition comprises 97-100 mol% of precipitated ε / ε' iron carbide and χ iron carbide, and 0-3 mol% of Fe-containing impurities, based on the total amount of the composition; further preferably, the molar ratio of the precipitated ε / ε' iron carbide and χ iron carbide is a:b, wherein 0<a≤75, 0<b≤75, such as 25:75-75-25, for example 72:27.

[0064] In a preferred embodiment, the Fe-containing impurities are at least one of iron carbide, iron, iron oxide, iron hydroxide, iron sulfide, and iron salt other than ε / ε' iron carbide and χ iron carbide.

[0065] Unless otherwise specified, the concentrations or percentages referred to in the present invention are mass concentrations or mass percentages.

[0066] Through the above technical solution, the present invention has the following technical effects compared with the traditional Fischer-Tropsch synthesis process:

[0067] (1) Simple process and easy operation. The present invention does not require circulating gas decarbonization and CH4 conversion equipment, shortens the process flow, reduces the difficulty of operation, and reduces the cost.

[0068] (2) High carbon utilization rate: The carbon utilization rate of the present invention is high, and the raw materials are utilized more thoroughly.

[0069] (3) New process for carbon emission reduction: The present invention can significantly reduce greenhouse gas (CO2+CH4) emissions in the coal indirect liquefaction process.

[0070] (4) The process of the present invention can be applied to inlet gas with a lower hydrogen-to-carbon ratio, and is particularly applicable to the production process of producing fuels and chemicals using coal as raw material.

[0071] (5) 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.

[0072] (6) The present invention introduces circulating gas at the bottom of the reactor, utilizing the higher catalyst concentration at the bottom of the reactor to promote the effective re-conversion of the circulating gas to improve the yield. At the same time, the relatively low effective gas concentration in the circulating gas is utilized to avoid the bottom temperature runaway, which would limit the further increase in the intake volume to increase the production capacity. This improves the applicability of the reactor to high-activity catalysts.

[0073] (7) In the present invention, fresh synthesis gas is introduced downward from the lower gas distributor, which is conducive to countercurrent contact with the rising flow from the bottom to improve the degree of gas-liquid-solid three-phase mixing, thereby improving the conversion rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 This is a schematic diagram of the process of Fischer-Tropsch synthesis in Example 1. DETAILED DESCRIPTION

[0075] 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.

[0076] 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.

[0077] 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 slurry bed reactor 1; then, the light components and unreacted gases generated by the reaction flow out from the top of the reactor as outlet gas, and after heat exchange condensation in the heat exchange unit 2, gas-liquid separation is carried out by the gas-liquid separation unit 3 to obtain light oil and water as liquid phase and non-condensable gas as gas phase respectively; the liquid phase can further enter the oil-water separation unit 7 for oil-water separation to obtain light oil and water.

[0078] The heavy component products generated by the reaction are filtered out of the catalyst through the internal filter installed in the reactor and then discharged from the side of the reactor. After the heavy oil is separated, heavy wax is obtained.

[0079] A portion of the non-condensable gas is pressurized by compressor 5 as the first circulating gas and returned to the reactor to continue the Fischer-Tropsch synthesis reaction; the rest of the non-condensable gas is sent to the low-carbon hydrocarbon recovery unit 4 for low-carbon hydrocarbon recovery to obtain low-carbon hydrocarbon products and low-carbon hydrocarbon-free gas; the low-carbon hydrocarbon-free gas is further sent to the hydrogen recovery unit 6 for hydrogen recovery to obtain recovered H2-rich gas and residual tail gas; the obtained H2-rich gas is pressurized by compressor 5 as the second circulating gas and returned to the reactor to continue the Fischer-Tropsch synthesis reaction; wherein the inlet gas contains fresh synthesis gas, circulating gas and optional hydrogen or CO for adjusting the hydrogen-carbon ratio of the inlet gas, and the circulating gas is a mixture of the first circulating gas and the second circulating gas.

[0080] The present invention is further described below with reference to Examples / Comparative Examples.

[0081] Example 1

[0082] Use Figure 1 The Fischer-Tropsch synthesis system shown in the figure contacts the inlet gas with the catalyst and performs the Fischer-Tropsch synthesis reaction in a gas-liquid-solid three-phase reactor. The reaction conditions are as follows: temperature 260°C, pressure 3 MPa; total space velocity in the reactor 23000 Nm 3 / h / t, superficial gas velocity 0.26m / s, catalyst concentration 9%;

[0083] The inlet gas first exchanges heat with the reactor outlet stream and then enters the reactor from the bottom; the hydrogen-to-carbon ratio of the inlet gas is 2;

[0084] The light components and unreacted gases generated by the reaction flow out from the top of the reactor as outlet gas, and after heat exchange condensation, light oil and water as liquid phase and non-condensable gas as gas phase are obtained respectively through gas-liquid separation; part of the non-condensable gas is returned to the reactor after pressurization as the first circulating gas to continue the Fischer-Tropsch synthesis reaction; the rest of the non-condensable gas is returned to the reactor after pressurization as the second circulating gas after low-carbon hydrocarbon recovery and hydrogen recovery to continue the Fischer-Tropsch synthesis reaction; wherein, the inlet gas contains fresh synthesis gas and circulating gas; the volume ratio of the non-condensable gas as the first circulating gas to the non-condensable gas for low-carbon hydrocarbon recovery is 2.0; during normal operation, the volume proportion of CO2 in the raw gas is about 5-7%.

[0085] The slurry bed reactor includes a first gas distributor located at the bottom end cap of the reactor cylinder and a second gas distributor located at the lower portion of the reactor, with the gas outlets of the first and second gas distributors both opening downward. The distance between the second gas distributor and the first gas distributor is 1 / 7 of the reactor height. The first gas distributor is used to receive the recycled gas from the inlet gas, and the second gas distributor is used to receive the remaining gas from the inlet gas.

[0086] The catalyst used is a composition containing supported ε / ε' iron carbide and χ iron carbide, which is prepared according to Example 1 in CN112569978A.

[0087] Example 2

[0088] The difference from Example 1 is that during the reaction, the relevant parameters are as follows:

[0089] Temperature 240°C, pressure 2 MPa; total space velocity in the reactor 16000 Nm 3 / h / t, superficial gas velocity of 0.35m / s, catalyst concentration of 12%; the feed gas has a hydrogen-to-carbon ratio of 3.5; the volume ratio of the non-condensable gas used as the first recycle gas to the non-condensable gas used for light hydrocarbon recovery is 3.5. During normal operation, the volume proportion of CO2 in the feed gas is approximately 4-6%.

[0090] The catalyst used is a composition containing precipitated ε / ε' iron carbide and χ iron carbide, which is prepared according to Example 1 in CN112569980A.

[0091] Example 3

[0092] The difference from Example 1 is that during the reaction, the relevant parameters are as follows:

[0093] Temperature 230°C, pressure 1.8 MPa; total space velocity in the reactor 23000 Nm 3 / h / t, the superficial gas velocity is 0.37m / s, the catalyst concentration is 8%; and the hydrogen-to-carbon ratio of the inlet gas is 1.5.

[0094] Example 4

[0095] The difference from Example 2 is that, during the reaction, the relevant parameters are as follows:

[0096] Temperature 270°C, pressure 3.2 MPa; total space velocity in the reactor 19000 Nm 3 / h / t, the superficial gas velocity is 0.28m / s, the catalyst concentration is 12%; and the hydrogen-to-carbon ratio of the inlet gas is 4.5.

[0097] Example 5

[0098] The difference from Example 1 is that no second gas distributor is provided in the reactor, and all the inlet gas enters the first gas distributor.

[0099] Comparative Example 1

[0100] The difference from Example 1 is that during the reaction, the relevant parameters are as follows:

[0101] The reaction conditions are as follows: temperature 290°C, pressure 1.7 MPa; total space velocity in the reactor 16500 Nm 3 / h / t, superficial gas velocity 0.35m / s, catalyst concentration 9%.

[0102] Comparative Example 2

[0103] The difference from Example 1 is that the temperature is 220°C, the pressure is 2 MPa, and the total air velocity in the reactor is 16500 Nm 3 / h / t, superficial gas velocity 0.35m / s, catalyst concentration 12%.

[0104] After analyzing the product out of the reactor, the reaction evaluation results of the above embodiment / comparative example are as follows:

[0105]

[0106]

[0107] In the table, CH4 and C5+ selectivities refer to the weight percentage of the total hydrocarbon products.

[0108] As can be seen from the above examples and comparative examples, compared to the comparative examples, the present process fully utilizes the high catalytic activity, extremely low CO2 selectivity, low CH4 selectivity, and high C5+ selectivity of supported and precipitated iron carbide composite catalysts, making them particularly suitable for low-temperature slurry bed reactors. The reaction achieved CO conversion rates >89%, CO2 selectivity <10%, CH4 selectivity <5.5%, and C5+ selectivity >82%. Furthermore, compared to the comparative examples, the present process maintained a high degree of catalytic stability, with minimal change in reaction values ​​after 400 hours.

Claims

1. A Fischer-Tropsch synthesis method for a catalyst containing ε / ε' iron carbide and χ iron carbide, wherein the catalyst containing ε / ε' iron carbide and χ iron carbide is a composite catalyst containing supported and / or precipitated ε / ε' iron carbide and χ iron carbide; the Fischer-Tropsch synthesis method comprises: The inlet gas containing synthesis gas is contacted with a composite catalyst containing ε / ε' iron carbide and χ iron carbide, and a Fischer-Tropsch synthesis reaction is carried out in a gas-liquid-solid three-phase reactor. The reaction conditions are as follows: temperature 230-275°C, pressure 1-5 MPa; total space velocity in the reactor 10000-38000 Nm 3 / h / t, superficial gas velocity 0.15-0.55m / s, catalyst concentration 5-20%; The light component products and unreacted gas after the reaction flow out from the top of the reactor as the outlet gas. After heat exchange and condensation, they are separated by gas-liquid separation to obtain light oil and water as the liquid phase and non-condensable gas as the gas phase. The heavy component products after the reaction are discharged after filtering and separating the catalyst. After fractionation, heavy oil and wax are obtained. A portion of the non-condensable gas is used as the first circulating gas; the remaining portion of the non-condensable gas is subjected to light hydrocarbon recovery, the gas depleted of light hydrocarbons after light hydrocarbon recovery is further subjected to hydrogen recovery, and the H2-rich gas obtained after hydrogen recovery is used as the second circulating gas; the circulating gas composed of the first circulating gas and the second circulating gas is pressurized and used as part of the inlet gas; wherein the volume ratio of the non-condensable gas used as the first circulating gas to the non-condensable gas subjected to light hydrocarbon recovery is 0.7-6.0; The inlet gas includes fresh synthesis gas, the recycle gas and optionally pure hydrogen for adjusting the hydrogen-carbon ratio of the feed gas; the hydrogen-carbon ratio of the inlet gas is 1.5-5; Wherein, the gas-liquid-solid three-phase reactor is a bubbling slurry bed reactor with a gas distributor.

2. The method according to claim 1, characterized in that The volume ratio of the non-condensable gas used as the first circulating gas to the non-condensable gas for recovering low-carbon hydrocarbons is 2.0-3.7; and the hydrogen-to-carbon ratio of the gas entering the tower is 2-4.

3. The Fischer-Tropsch synthesis method according to claim 1 or 2, characterized in that: The reaction temperature of the Fischer-Tropsch synthesis is 240-265° C.; and the reaction pressure is 1.7-3.0 MPa.

4. The Fischer-Tropsch synthesis method according to any one of claims 1 to 3, characterized in that: The total space velocity in the reactor is 14000-30000Nm 3 / h / t; the superficial gas velocity in the reactor is 0.25-0.4 m / s; and the catalyst concentration is 8-14%.

5. The Fischer-Tropsch synthesis method according to any one of claims 1 to 4, characterized in that: The slurry bed reactor comprises a first gas distributor located at the bottom lower head of the reactor cylinder and a second gas distributor arranged at the lower part of the reactor, and the gas outlet holes of the first and second gas distributors are both open downward; Preferably, the distance between the second gas distributor and the first gas distributor is 1 / 8-1 / 6 of the height of the reactor.

6. The Fischer-Tropsch synthesis method according to claim 5, characterized in that The first gas distributor is used to receive the circulating gas, and the second gas distributor is used to receive the remaining gas in the tower inlet gas.

7. The Fischer-Tropsch synthesis method according to any one of claims 1 to 6, characterized in that: in, Before entering the reactor, the inlet gas is heat exchanged with the reactor outlet stream to increase its temperature, and then enters the reactor for Fischer-Tropsch synthesis reaction.

8. The Fischer-Tropsch synthesis method according to any one of claims 1 to 7, characterized in that: The composition containing supported ε / ε' iron carbide and χ iron carbide comprises, based on the total amount of the composition, 55-90 wt% of a support 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 ε / ε' iron carbide and χ iron carbide, and 0-5 mol% of Fe-containing impurities; The Fe-containing impurities are at least one of iron carbide, iron, iron oxide, iron hydroxide, iron sulfide and iron salt other than ε / ε' iron carbide and χ iron carbide.

9. The Fischer-Tropsch synthesis method according to any one of claims 1 to 8, characterized in that: The composition containing precipitated ε / ε' iron carbide and χ iron carbide comprises 95-100 mol% of precipitated ε / ε' iron carbide and χ iron carbide, and 0-5 mol% of Fe-containing impurities, based on the total amount of the composition; The Fe-containing impurities are at least one of iron carbide, iron, iron oxide, iron hydroxide, iron sulfide and iron salt other than ε / ε' iron carbide and χ iron carbide.

10. The Fischer-Tropsch synthesis method according to any one of claims 1 to 9, characterized in that: The volume ratio of CO2 in the inlet gas is 2-10%, preferably 4-8%.

Images