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

Abstract

The invention discloses a Fischer-Tropsch synthesis method for a catalyst containing epsilon / epsilon ', chi and theta iron carbide, the catalyst containing epsilon / epsilon', chi and theta iron carbide is a catalyst containing a supported and / or precipitated epsilon / epsilon 'iron carbide, chi iron carbide and theta iron carbide composition, CO2 removal is not needed in the subsequent treatment of tower outlet gas, and the catalyst containing epsilon / epsilon', chi and theta iron carbide is not needed. 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 catalyst containing ε / ε', χ and θ iron carbide, wherein the ε / ε' iron carbide, χ iron carbide and θ iron carbide catalysts are supported and / or precipitated ε / ε' iron carbide, χ iron carbide and θ iron carbide catalysts. Background Art

[0002] Synthesis gas (H2+CO) is the most common feedstock gas in the coal chemical industry. Many products can be obtained through different reaction pathways. The most common method is to use syngas through the Fischer-Tropsch synthesis reaction to obtain low-carbon hydrocarbons, fuels such as gasoline, diesel, and wax, as well as 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 Fischer-Tropsch synthesis tail gas, which 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, characterized by removing CO2 from the tail gas using alkaline washing, followed by water-gas shift and decarbonization steps to convert it into synthesis gas before entering 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 has unprecedented high activity, ultra-low CO2 selectivity, low CH4 selectivity and high stability. Among them, the composite catalysts of supported and precipitated ε / ε' iron carbide, χ iron carbide and θ iron carbide are characterized by high catalytic activity from low to high temperatures and very low CO2 selectivity, making them particularly suitable for low-temperature slurry bed reactors.

[0015] Due to the excellent performance of these catalysts, their large-scale industrial application is imperative. However, unlike laboratory testing and evaluation of catalysts, industrial applications require re-examination of their industrial application processes due to incompatibility with the activity and selectivity characteristics of iron carbide catalysts. In particular, to fully tap the potential of the catalysts and to achieve specific advantages or breakthroughs in industrial applications, it is necessary to re-integrate the catalyst's unique characteristics and develop a new set of targeted industrial application processes.

[0016] If a composite catalyst of supported and precipitated ε / ε' iron carbide, χ iron carbide and θ 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

[0017] The purpose of the present invention is to propose a Fischer-Tropsch synthesis method for a catalyst containing ε / ε', χ and θ iron carbides. The process does not require CO2 removal and CH4 conversion equipment, and is a new carbon emission reduction process with a simple process, high carbon utilization rate and low cost.

[0018] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0019] A Fischer-Tropsch synthesis method for a catalyst containing ε / ε', χ and θ iron carbides, wherein the catalyst containing ε / ε', χ and θ iron carbides is a catalyst containing a combination of supported and / or precipitated ε / ε' iron carbides, χ iron carbides and θ iron carbides;

[0020] Wherein, the Fischer-Tropsch synthesis is carried out in a Fischer-Tropsch synthesis system, which includes a slurry bed reactor, a condensing unit, a gas-liquid separator, a light hydrocarbon recovery unit, a hydrogen recovery unit and a compressor; wherein, the condensing unit is connected to the top outlet of the slurry bed reactor to receive the light components and unreacted gases generated by the reaction as the outlet gas discharged from the top of the slurry bed reactor and condense them; the gas-liquid separator is connected to the condensing unit and performs gas-liquid separation on the condensed product from the condensing unit to obtain light oil and water as the liquid phase and non-condensable gas as the gas phase; the top of the gas-liquid separator is respectively connected to the compressor The inlet of the hydrogen recovery unit is connected to the low-carbon hydrocarbon recovery unit, so as to feed part of the non-condensable gas into the compressor as the first circulating gas and feed part of the non-condensable gas into the low-carbon hydrocarbon recovery unit; the low-carbon hydrocarbon recovery unit is used to recover low-carbon hydrocarbons from the received non-condensable gas and discharge the de-low-carbon hydrocarbon gas; the inlet of the hydrogen recovery unit is connected to the low-carbon hydrocarbon recovery unit, and the outlet is connected to the inlet of the compressor, for enriching and recovering the hydrogen in the de-low-carbon hydrocarbon gas to obtain H2-rich gas and residual tail gas, and feeding the recovered H2-rich gas as the second circulating gas to the compressor; the compressor is used to pressurize the first circulating gas and the second circulating gas and feed them back to the slurry bed reactor as circulating gas;

[0021] The reaction conditions in the slurry bed reactor are as follows: temperature 220-295°C, pressure 1.2-4.7 MPa; total space velocity in the reactor 11000-38000 Nm 3 / h / t, superficial gas velocity 0.15-0.55m / s, catalyst concentration 5-20%;

[0022] Among them, 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 0.8-6.3; the raw gas for Fischer-Tropsch synthesis using the catalyst in the slurry bed reactor includes fresh synthesis gas and the circulating gas; the hydrogen-carbon ratio of the raw gas is 1.5-5; the slurry bed reactor is a bubbling slurry bed reactor with a gas distributor.

[0023] In order to better exert the performance of the catalyst, in the present invention, the reaction temperature in the Fischer-Tropsch synthesis can be 220-295°C, such as 225, 230, 235, 240, 245, 275, 285 or 290°C; preferably, the reaction temperature of the Fischer-Tropsch synthesis is 250-275°C, such as 255, 260, 265 or 270°C.

[0024] In the present invention, the reaction pressure of the Fischer-Tropsch synthesis reaction can be 1.2-4.7 MPa, such as 1.5, 2, 2.2, 3, 3.2, 4 or 4.5 MPa; preferably, the reaction pressure is 2.1-3.0 MPa, such as 2.5, 2.8 or 3.0 MPa.

[0025] In the present invention, when the Fischer-Tropsch synthesis reaction is carried out, the total space velocity in the reactor can be 11000-38000 Nm 3 / h / t, such as 12000, 15000, 20000, 24000, 30000 or 35000 Nm 3 / h / t; preferably, the total space velocity in the reactor is 15000-32000Nm 3 / h / t.

[0026] 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, 0.35, 0.39 or 0.45 m / s, and the superficial gas velocity in the reactor is 0.25-0.4 m / s.

[0027] 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%, 7%, 9%, 10%, 12%, 15%, 18% or 20%. Preferably, the catalyst concentration is 8-14%.

[0028] In some preferred embodiments, the slurry bed 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 outlets 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.

[0029] In some preferred embodiments, 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 into 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 increase 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 the production capacity, thereby improving the applicability of the reactor to high-activity catalysts.

[0030] In some preferred embodiments, 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.

[0031] In the present invention, the hydrogen-to-carbon ratio of the raw gas is 1.5-5, such as 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5.5, preferably 2-4; the raw gas includes synthesis gas from the outside and the recycled gas; of course, it can be understood in the art that in order to maintain the total hydrogen-to-carbon ratio of the raw gas, CO or hydrogen can be further introduced into the raw gas to adjust the hydrogen-to-carbon ratio.

[0032] In some preferred embodiments, the volume ratio of the non-condensable gas used as the first circulating gas to the non-condensable gas for light hydrocarbon recovery is 1.8-4.2, such as 2, 3 or 3.5, preferably 2-4.

[0033] In some preferred embodiments, the volume ratio of CO2 in the feed gas is 4-12%, such as 6%, 8% or 10%, preferably 5-9%. It is understood that before entering the reactor, the feed gas can first be heat exchanged with the reactor outlet stream to increase its temperature; in some preferred embodiments, the reacted stream undergoes two or more heat exchange and gas-liquid separation stages, with the first stage at a temperature of 136-230°C, the last stage at a temperature of 2-55°C, and the intermediate stage at a temperature between the first and last stages; preferably, two stages of heat exchange are performed, with the first stage at a temperature of 150-175°C and the second stage at a temperature of 8-51°C.

[0034] In the present invention, the other part of the obtained non-condensable gas is subjected to low-carbon hydrocarbon recovery in the low-carbon hydrocarbon recovery unit to obtain a low-carbon hydrocarbon product and a low-carbon hydrocarbon-free gas; the low-carbon hydrocarbon recovery can be carried out by deep cooling, pressure swing adsorption or oil washing, which are well known in the art, and the recovery ratio can reach 90%-99%, which will not be described in detail.

[0035] In the present invention, when hydrogen is enriched and recovered in the hydrogen recovery unit, those skilled in the art will understand that hydrogen enrichment and recovery can be achieved by pressure swing adsorption or membrane separation, which are well known in the art. Optionally, a reforming unit may be provided before the hydrogen recovery unit to catalytically reform the gas depleted of low-carbon hydrocarbons after recovery of low-carbon hydrocarbons to obtain reformed gas. The reforming unit may be used according to actual needs. The hydrogen content in the gas may be increased by reforming. If the hydrogen entering the system is sufficient, it may be understood in the art that a reforming subunit may not be provided. The hydrogen separation subunit is used to enrich and separate the reformed gas or the gas depleted of low-carbon hydrocarbons after recovery of low-carbon hydrocarbons to obtain H2-rich gas and residual tail 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 by reforming. The specific reforming 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.

[0036] In the present invention, the catalyst containing supported ε / ε' iron carbide, χ iron carbide and θ iron carbide is preferably the supported ε / ε' iron carbide, χ iron carbide and θ iron carbide composition disclosed in CN112569979 A, ​​which is incorporated into this application by reference. Specifically, the supported ε / ε' iron carbide, χ iron carbide and θ iron carbide catalyst, based on the total amount of the composition, comprises 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 ε / ε' iron carbide, χ iron carbide and θ iron carbide catalyst, and 0-5 mol% of Fe-containing impurities, wherein the Fe-containing impurities are iron-containing substances other than ε / ε' iron carbide, χ iron carbide and θ iron carbide; the preparation method of the supported ε / ε' iron carbide, χ iron carbide and θ iron carbide composition comprises:

[0037] The carrier is impregnated in an aqueous solution of an iron salt, and the impregnated carrier is dried and calcined to obtain a precursor;

[0038] (1) Preparing supported ε / ε' iron carbide, comprising:

[0039] (1-1) performing a first reduction on the precursor with H2 at a temperature of 300-550°C;

[0040] (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;

[0041] (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;

[0042] (2) preparing supported θ iron carbide, comprising:

[0043] (2-1) performing a second reduction on the precursor with H2 at a temperature T1 of 340-600°C;

[0044] (2-2) preparing a second carbide by reacting the material obtained in step (2-1) with H2 and CO at a temperature T2 of 280-430°C for 20-120 hours, wherein the molar ratio of H2 to CO is 5-120:1, to obtain supported θ iron carbide;

[0045] (3) preparing supported x iron carbide, comprising:

[0046] (3-1) performing a third reduction on the precursor with H2 at a temperature of 350-610°C;

[0047] (3-2) performing a surface passivation treatment on the material obtained in step (3-1) 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%;

[0048] (3-3) preparing carbides by reacting the material obtained in step (3-2) 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;

[0049] (4) The supported ε / ε' iron carbide, χ iron carbide and θ iron carbide are mixed with Fe-containing impurities under the protection of an inert gas.

[0050] In some preferred embodiments, the specific surface area of ​​the catalyst composition containing supported ε / ε' iron carbide, χ iron carbide and θ iron carbide is 40-450 m 2 / g, preferably 50-350m 2 / g;

[0051] In some preferred embodiments, the catalyst composition containing supported ε / ε' iron carbide, χ iron carbide and θ iron carbide comprises 60-85 wt% of a carrier and 15-40 wt% of an iron component, based on the total amount of the composition; preferably, the iron component comprises 97-100 mol% of ε / ε' iron carbide, χ iron carbide and θ iron carbide, and 0-3 mol% of Fe-containing impurities, based on the total amount of the iron component; wherein 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, χ iron carbide and θ iron carbide.

[0052] In some preferred embodiments, in the catalyst composition containing supported ε / ε' iron carbide, χ iron carbide and θ iron carbide, the molar ratio of ε / ε' iron carbide, χ iron carbide and θ iron carbide is a:b:c, wherein 0<a≤90, such as a is 1, 5, 10, 20, 40, 60 or 85, 0<b≤72, such as b is 1, 5, 10, 20, 40, 60 or 70, 0<c≤90, such as c is 1, 5, 10, 20, 40, 60, 70 or 80, for example, a:b:c is 88:5:6.

[0053] In the present invention, the catalyst containing precipitated ε / ε' iron carbide, χ iron carbide and θ iron carbide is preferably the precipitated ε / ε' iron carbide, χ iron carbide and θ iron carbide composition disclosed in CN112569975 A, which is incorporated into this application by reference. Specifically, in some preferred embodiments, the catalyst containing precipitated ε / ε' iron carbide, χ iron carbide and θ iron carbide, based on the total amount of the composition, contains 95-100 mol% of precipitated ε / ε' iron carbide, χ iron carbide and θ 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, χ iron carbide and θ iron carbide; wherein the specific surface area of ​​the catalyst composition containing precipitated ε / ε' iron carbide, χ iron carbide and θ iron carbide is 30-350 m 2 / g; the specific surface area of ​​the catalyst composition containing precipitated ε / ε 'iron carbide, χ iron carbide and θ iron carbide is 35-250m 2 / g; the preparation method of the composition containing precipitated ε / ε' iron carbide, χ iron carbide and θ iron carbide comprises:

[0054] 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;

[0055] (1) Preparing precipitated ε / ε' iron carbide, comprising:

[0056] (1-1) performing a first reduction on the precursor with H2 at a temperature of 450-580°C;

[0057] (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;

[0058] (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;

[0059] (2) Preparing precipitated θ iron carbide, comprising:

[0060] (2-1) subjecting the precursor to a second reduction reaction with H2 at a temperature T1 of 470-620°C;

[0061] (2-2) preparing a second carbide by reacting the material obtained in step (2-1) with H2 and CO at a temperature T2 of 280-420°C for 20-120 hours, wherein the molar ratio of H2 to CO is 5-120:1; obtaining precipitated θ iron carbide;

[0062] (3) Preparing precipitated x iron carbide, comprising:

[0063] (3-1) performing a third reduction on the precursor with H2 at a temperature of 450-610°C;

[0064] (3-2) performing a surface passivation treatment on the material obtained in step (3-1) 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%;

[0065] (3-3) preparing a third carbide by reacting the material obtained in step (3-2) 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;

[0066] (4) 95-100 mol parts of precipitated ε / ε' iron carbide, χ iron carbide and θ iron carbide and 0-5 mol parts of Fe-containing impurities are mixed under inert gas conditions.

[0067] In some preferred embodiments, the catalyst composition containing precipitated ε / ε' iron carbide, χ iron carbide and θ iron carbide contains 97-100 mol% of precipitated ε / ε' iron carbide, χ iron carbide and θ iron carbide, and 0-3 mol% of Fe-containing impurities, based on the total amount of the composition; wherein 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, χ iron carbide and θ iron carbide.

[0068] In some preferred embodiments, in the catalyst composition containing precipitated ε / ε' iron carbide, χ iron carbide and θ iron carbide, the molar ratio of ε / ε' iron carbide, χ iron carbide and θ iron carbide is a:b:c, wherein 0<a≤90, such as a is 1, 5, 10, 20, 40, 60 or 85, 0<b≤75, such as b is 1, 5, 10, 20, 40, 60 or 70, 0<c≤90, such as c is 1, 5, 10, 20, 40, 60, 70 or 80, for example, a:b:c is 88:5:6.

[0069] In the present invention, unless otherwise specified, the percentages or percents involved are mass percentages or mass percents.

[0070] Through the above technical solution, the present invention has the following technical effects compared with the traditional Fischer-Tropsch synthesis process:

[0071] (1) Simple process and easy operation. The present invention does not require circulating gas decarbonization and CH4 conversion equipment, which shortens the process flow, reduces the difficulty of operation, and reduces the cost.

[0072] (2) High carbon utilization rate: The carbon element utilization rate of the present invention is high, and the utilization of raw materials is more thorough.

[0073] (3) New process for carbon emission reduction: The present invention can significantly reduce greenhouse gas (CO2+CH4) emissions in the coal indirect liquefaction process.

[0074] (4) The process of the present invention can be applied to raw gas with a lower hydrogen-to-carbon ratio, and is particularly suitable for production processes of fuels and chemicals using coal as raw material.

[0075] (5) The promotion of the Fischer-Tropsch process of the present invention will help achieve industrial breakthroughs, have a significant impact on the industry, and have considerable economic and social benefits;

[0076] (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.

[0077] (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

[0078] Figure 1 Schematic diagram of the Fischer-Tropsch synthesis system in Example 1. DETAILED DESCRIPTION

[0079] 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.

[0080] 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.

[0081] like Figure 1 As shown, when Fischer-Tropsch synthesis is carried out according to the method of the present invention, the Fischer-Tropsch synthesis system adopted includes a slurry bed reactor 1, a condensing unit 2, a gas-liquid separator 3, a low-carbon hydrocarbon recovery unit 4, a hydrogen recovery unit 6 and a compressor 5; wherein, the condensing unit 2 is connected to the top outlet of the slurry bed reactor 1 to receive the light components and unreacted gases generated by the reaction as the outlet gas discharged from the top of the slurry bed reactor and condense them; the gas-liquid separator 3 is connected to the condensing unit 2, and performs gas-liquid separation on the condensed product from the condensing unit 2 to obtain light oil and water as the liquid phase and non-condensable gas as the gas phase; wherein the liquid phase can further enter the oil-water separation unit 7 for oil-water separation to obtain light oil and water.

[0082] The top of the gas-liquid separator is respectively connected to the inlet of the compressor and the low-carbon hydrocarbon recovery unit, so as to send part of the non-condensable gas into the compressor as the first circulating gas and send part of the non-condensable gas into the low-carbon hydrocarbon recovery unit; the low-carbon hydrocarbon recovery unit is used to recover low-carbon hydrocarbons from the received non-condensable gas and discharge the de-low-carbon hydrocarbon gas; the inlet of the hydrogen recovery unit is connected to the low-carbon hydrocarbon recovery unit, and the outlet is connected to the inlet of the compressor, for enriching and recovering the hydrogen in the de-low-carbon hydrocarbon gas to obtain H2-rich gas and residual tail gas, and sending the recovered H2-rich gas as the second circulating gas to the compressor; the compressor is used to pressurize the first circulating gas and the second circulating gas and send them back to the slurry bed reactor as circulating gas.

[0083] When carrying out Fischer-Tropsch synthesis, the raw gas is contacted with the catalyst and the Fischer-Tropsch synthesis reaction is carried out in a slurry bed reactor; then, the light components and unreacted gases generated by the reaction flow out from the top of the slurry bed reactor as outlet gas, are condensed by heat exchange in the heat exchange condensation unit, and are then separated by gas-liquid separation in the gas-liquid separation unit to obtain light oil and water as liquid phase and non-condensable gas as gas phase.

[0084] 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.

[0085] Part of the non-condensable gas is used as the first circulating gas through a first pipeline and is pressurized by a compressor and then returned to the slurry bed reactor to continue the Fischer-Tropsch synthesis reaction; the rest of the non-condensable gas is sent to a low-carbon hydrocarbon recovery unit through a second pipeline for low-carbon hydrocarbon recovery, and the remaining low-carbon hydrocarbon-free gas is sent to a hydrogen recovery unit for hydrogen enrichment and recovery, and the obtained H2-rich gas is used as the second circulating gas and is pressurized by a compressor and then returned to the slurry bed reactor to continue the Fischer-Tropsch synthesis reaction; wherein the raw gas comprises fresh synthesis gas, circulating gas and optional hydrogen or CO for adjusting the hydrogen-carbon ratio of the raw gas, and the circulating gas is a mixture of the first circulating gas and the second circulating gas.

[0086] The present invention is further described below with reference to Examples / Comparative Examples.

[0087] Example 1

[0088] Use Figure 1 The Fischer-Tropsch synthesis system shown in FIG2 is a system in which the feed gas is contacted with a composite catalyst containing ε / ε' iron carbide, χ iron carbide, and θ iron carbide, and the Fischer-Tropsch synthesis reaction is carried out in a slurry bed reactor under the following reaction conditions: temperature 270°C, pressure 3 MPa; total space velocity in the reactor 24000 Nm 3 / h / t, superficial gas velocity 0.28m / s, catalyst concentration 9%;

[0089] The feed gas first exchanges heat with the reactor outlet stream and then enters the reactor from the bottom; the hydrogen-to-carbon ratio of the feed gas is 4;

[0090] 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 raw gas contains fresh synthesis gas and circulating gas; during normal operation, the volume ratio of the non-condensable gas as the first circulating gas to the non-condensable gas for low-carbon hydrocarbon recovery is 3.5; the volume proportion of CO2 in the raw gas is about 6-8%.

[0091] 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. The gas outlets of the first and second gas distributors are both downward-facing. The distance between the second gas distributor and the first gas distributor is 1 / 7 of the reactor height. The first gas distributor receives recycled gas from the feed gas, and the second gas distributor receives the remaining gas from the feed gas.

[0092] The catalyst used is a catalyst containing supported ε / ε' iron carbide, χ iron carbide and θ iron carbide, which is prepared according to Example 1 in CN112569979 A.

[0093] Example 2

[0094] The difference from Example 1 is that during the reaction, the relevant parameters are as follows:

[0095] Temperature 255°C, pressure 2.2 MPa; total space velocity in the reactor 18500 Nm 3 / h / t, an superficial gas velocity of 0.38 m / s, and a catalyst concentration of 12%. The feed gas has a hydrogen-to-carbon ratio of 2.5. 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 2. During normal operation, the volume proportion of CO2 in the feed gas is approximately 5-7%.

[0096] The catalyst used is a catalyst containing precipitated ε / ε' iron carbide, χ iron carbide and θ iron carbide, which is prepared according to Example 1 in CN112569975 A.

[0097] Example 3

[0098] The difference from Example 1 is that during the reaction, the relevant parameters are as follows:

[0099] Temperature 225°C, pressure 2MPa; total space velocity in the reactor 22000Nm 3 / h / t, superficial gas velocity 0.35m / s, catalyst concentration 9%; and the hydrogen-to-carbon ratio of the raw gas is 1.5.

[0100] Example 4

[0101] The difference from Example 2 is that, during the reaction, the relevant parameters are as follows:

[0102] Temperature 290°C, pressure 3.2 MPa; total space velocity in the reactor 20,000 Nm 3 / h / t, superficial gas velocity 0.3m / s, catalyst concentration 12%; and the hydrogen-to-carbon ratio of the raw gas is 4.5.

[0103] Example 5

[0104] The difference from Example 1 is that no second gas distributor is provided in the reactor, and all the raw gas enters the first gas distributor.

[0105] Comparative Example 1

[0106] The difference from Example 1 is that during the reaction, the relevant parameters are as follows:

[0107] The reaction conditions are as follows: temperature 310°C, pressure 1.6 MPa; total space velocity in the reactor 16000 Nm 3 / h / t, superficial gas velocity 0.38m / s, catalyst concentration 9%.

[0108] Comparative Example 2

[0109] The difference from Example 1 is that during the reaction, the relevant parameters are as follows:

[0110] The reaction conditions are as follows: temperature 210°C, pressure 3 MPa; total space velocity in the reactor 18500 Nm 3 / h / t, superficial gas velocity 0.38m / s, catalyst concentration 12%.

[0111] The reaction evaluation results of the above examples / comparative examples are as follows:

[0112]

[0113] In the table, CH4 and C5+ selectivities refer to the weight percentage of the total hydrocarbon products.

[0114] 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 / or precipitated iron carbide composite catalysts, making them particularly suitable for low-temperature slurry bed reactors. Furthermore, compared to the comparative examples, the present process maintains a high degree of catalytic stability, with minimal change in reaction values ​​after 400 hours.

Claims

1. A slurry bed Fischer-Tropsch synthesis process for a catalyst containing ε / ε', χ and θ iron carbides, wherein the catalyst containing ε / ε', χ and θ iron carbides is a catalyst containing a combination of supported and / or precipitated ε / ε' iron carbides, χ iron carbides and θ iron carbides; It is characterized in that The Fischer-Tropsch synthesis is carried out in a Fischer-Tropsch synthesis system, which includes a slurry bed reactor, a condensing unit, a gas-liquid separator, a light hydrocarbon recovery unit, a hydrogen recovery unit and a compressor; wherein the condensing unit is connected to the top outlet of the slurry bed reactor to receive the light components and unreacted gases generated by the reaction as the outlet gas discharged from the top of the slurry bed reactor and condense them; the gas-liquid separator is connected to the condensing unit and performs gas-liquid separation on the condensed product from the condensing unit to obtain light oil and water as the liquid phase and non-condensable gas as the gas phase; the top of the gas-liquid separator is respectively connected to the inlet of the compressor The inlet of the hydrogen recovery unit is connected to the low-carbon hydrocarbon recovery unit, so as to feed part of the non-condensable gas into the compressor as the first circulating gas and feed part of the non-condensable gas into the low-carbon hydrocarbon recovery unit; the low-carbon hydrocarbon recovery unit is used to recover low-carbon hydrocarbons from the received non-condensable gas and discharge the de-low-carbon hydrocarbon gas; the inlet of the hydrogen recovery unit is connected to the low-carbon hydrocarbon recovery unit, and the outlet is connected to the inlet of the compressor, for enriching and recovering the hydrogen in the de-low-carbon hydrocarbon gas to obtain H2-rich gas and residual tail gas, and sending the recovered H2-rich gas as the second circulating gas to the compressor; the compressor is used to pressurize the first circulating gas and the second circulating gas and return them to the slurry bed reactor as circulating gas; The reaction conditions in the slurry bed reactor are as follows: temperature 220-295°C, pressure 1.2-4.7 MPa; total space velocity in the reactor 11000-38000 Nm 3 / h / t, superficial gas velocity 0.15-0.55m / s, catalyst concentration 5-20%; Among them, 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 0.8-6.3; the raw gas for Fischer-Tropsch synthesis using the catalyst in the slurry bed reactor includes fresh synthesis gas and the circulating gas; the hydrogen-carbon ratio of the raw gas is 1.5-5; the slurry bed reactor is a bubbling slurry bed reactor with a gas distributor.

2. The Fischer-Tropsch synthesis method according to claim 1, wherein The reaction temperature of the Fischer-Tropsch synthesis is 250-275° C.; and the reaction pressure is 2.1-3.0 MPa.

3. The Fischer-Tropsch synthesis method according to claim 1 or 2, characterized in that: The total space velocity in the reactor is 15000-32000Nm 3 / h / t; the superficial gas velocity in the reactor is 0.25-0.4 m / s; and the catalyst concentration is 8-14%.

4. The Fischer-Tropsch synthesis method according to any one of claims 1 to 3, 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 1.6-3.6; and the hydrogen-to-carbon ratio of the raw gas is 2-4.

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 method according to claim 5, wherein: 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.

7. The method according to any one of claims 1 to 6, characterized in that 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 method according to any one of claims 1 to 7, characterized in that The supported ε / ε' iron carbide, χ iron carbide and θ 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 ε / ε' iron carbide, χ iron carbide and θ iron carbide catalysts, and 0-5 mol% of Fe-containing impurities, wherein the Fe-containing impurities are iron-containing substances other than ε / ε' iron carbide, χ iron carbide and θ iron carbide; The specific surface area of ​​the composition is 40-450m 2 / g, preferably 50-350m 2 / g; Preferably, the composition comprises 60-85 wt% of a carrier and 15-40 wt% of an iron component, based on the total amount of the composition; preferably, the iron component comprises 97-100 mol% of ε / ε' iron carbide, χ iron carbide and θ iron carbide, and 0-3 mol% of Fe-containing impurities, based on the total amount of the iron component; 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, χ iron carbide and θ iron carbide.

9. The Fischer-Tropsch method according to any one of claims 1 to 8, characterized in that The catalyst containing precipitated ε / ε' iron carbide, χ iron carbide and θ iron carbide comprises, based on the total amount of the composition, 95-100 mol% of precipitated ε / ε' iron carbide, χ iron carbide and θ 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, χ iron carbide and θ 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 ε / ε' iron carbide, χ iron carbide and θ iron carbide, and 0-3 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, χ iron carbide and θ 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 raw gas is 4-12%, preferably 5-9%.

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