A method and system for the synthesis of alpha-olefins by fischer-tropsch synthesis

Abstract

The application discloses a Fischer-Tropsch synthesis method and system for synthesizing alpha-olefins from synthesis gas. The method comprises the following process route: adding a high-boiling-point solvent into a slurry bed reactor through a solvent inlet located at the upper part of the slurry bed reactor, adding an activated Fischer-Tropsch synthesis catalyst into the slurry bed reactor through a catalyst inlet located at the upper part of the slurry bed reactor, and then adding synthesis gas into the slurry bed reactor through a synthesis gas inlet located at the bottom of the slurry bed reactor, so that the synthesis gas is subjected to a Fischer-Tropsch synthesis reaction under the action of the activated Fischer-Tropsch synthesis catalyst; and in the reaction process, the Fischer-Tropsch synthesis catalyst is intermittently added by the following manner, and inorganic potassium salt, potassium oxide or potassium hydroxide, and organic potassium salt and concentrated synthetic water are simultaneously added.

Description

Technical Field

[0001] This invention belongs to the field of coal chemical industry, and specifically relates to a Fischer-Tropsch synthesis method and system for producing α-olefins from syngas. Background Technology

[0002] Syngas (H2 + CO) is the most common feedstock gas in the coal chemical industry. It can yield numerous products through different reaction pathways, the most common being the Fischer-Tropsch synthesis reaction, which produces fuels such as gasoline, diesel, and waxes, as well as chemicals. Fischer-Tropsch synthesis can be classified into low-temperature Fischer-Tropsch (220–270℃) and high-temperature Fischer-Tropsch (320–350℃) based on reaction temperature. Low-temperature Fischer-Tropsch typically uses precipitated iron catalysts or supported iron catalysts, and the reactor can be a fixed bed or a slurry bed, with diesel and waxes being the main products. High-temperature Fischer-Tropsch synthesis commonly uses molten iron catalysts, with gasoline and low-carbon olefins being the main products, and the reactor is a fluidized bed. Among all Fischer-Tropsch synthesis products, low-carbon olefins produced by high-temperature Fischer-Tropsch have higher added value, with α-olefins being a high-quality fine chemical feedstock that is difficult or impossible to produce in other coal chemical and petrochemical industries. Slurry bed reactors are gas-liquid-solid three-phase systems. Compared with fluidized bed and fixed bed reactors, they have the following advantages: (1) lower cost and easier installation, and easier scale-up; (2) higher yield per unit reactor volume, with catalyst consumption per ton of product being only 20% to 30% of that in fixed bed reactors; (3) catalyst can be loaded and unloaded online, which is especially important for iron-based catalysts with shorter service life. Currently, large-scale coal indirect liquefaction plants in the world all use slurry bed reactors. If slurry bed reactors are used for Fischer-Tropsch synthesis with the production of α-olefins as the target product, their economic efficiency will be significantly higher than other Fischer-Tropsch synthesis processes. To achieve the above goals, the following key issues need to be addressed: (1) Slurry bed reactors need to maintain a certain liquid level during operation. The solvent in the reactor is generally the liquid wax produced by the Fischer-Tropsch reaction itself. Under typical medium-high temperature Fischer-Tropsch reaction conditions (>280℃), the liquid wax will vaporize, making it impossible to maintain the liquid level in the reactor; (2) The α-olefin selectivity of the product obtained by using a slurry bed reactor for the Fischer-Tropsch reaction is low. In order to improve the economic added value, it is necessary to improve the α-olefin selectivity; (3) The reaction products obtained by the slurry bed reactor are unstable, which brings many problems to the reactor and subsequent separation; (4) The catalyst used in the slurry bed reactor is generally also reduced by slurry bed. The iron catalyst obtained by this reduction method has high selectivity for CO2 and CH4. Almost all of these CO2 are emitted into the atmosphere, resulting in a large amount of carbon emissions.

[0003] There are already some reports on the use of slurry beds for Fischer-Tropsch synthesis. For example, the literature "The Influence of High Temperature on the Performance of Fe-Cu-K-Si Catalyst in Fischer-Tropsch Synthesis in Slurry Beds" (Clean Coal Technology, 2017(3):p.51-55) studied the effect of high temperature on the performance of Fischer-Tropsch iron catalysts in stirred tank reactors. It was found that the reactor liquid level decreased with increasing reaction temperature, indicating that the liquid level in the slurry bed cannot be stably maintained under high temperature conditions, especially when the reaction temperature reaches 320℃. Moreover, the technology described in the article is still the traditional Fischer-Tropsch reaction with high carbon oil and wax as the target product, which is not economically viable. In general, it only uses the traditional low-temperature Fischer-Tropsch iron catalyst at a higher temperature (maximum only 320℃) without involving the production of α-olefins with higher economic value.

[0004] CN101928194A discloses a fixed-bed Fischer-Tropsch synthesis method that addresses the catalyst bed temperature control issue by returning a portion of the gaseous hydrocarbon products and a portion of the liquid products to the inlet of the Fischer-Tropsch reactor. However, this causes olefins to be returned to the reactor for secondary reactions, resulting in low olefin selectivity. Since olefins are high-value-added products, this negatively impacts the overall economics of the process. Furthermore, this method is only applicable to fixed-bed reactors; the preferred reaction temperature mentioned is 190–250°C, which falls within the low-temperature Fischer-Tropsch range. Its primary objective is to obtain more high-carbon-number products such as oils and waxes, but the economic added value of the resulting products remains low.

[0005] CN103170284A discloses a high-temperature, high-pressure slurry bed reactor Fischer-Tropsch synthesis system, employing a high-temperature, high-pressure slurry bed reactor. However, the reaction temperature is only 260–290°C, which does not fall within the generally accepted "high-temperature Fischer-Tropsch" range (300–350°C). Furthermore, the highest activation temperature is only 320°C, making it unsuitable for all Fischer-Tropsch iron catalysts (such as fused iron catalysts). The economic viability of the resulting product needs improvement.

[0006] Therefore, there is an urgent need for a method to produce high-value-added α-olefins from syngas in order to improve economic efficiency. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention aims to provide a method for the efficient production of α-olefins from syngas. It realizes the Fischer-Tropsch synthesis reaction with α-olefins as the main product in a slurry bed reactor under medium and high temperature conditions. The catalyst has high activity (i.e., high conversion rate of reactants), high selectivity for α-olefins, low selectivity for CO2 and CH4, and significant economic benefits.

[0008] During their long-term research, the inventors of this invention discovered that the decline in catalyst performance during Fischer-Tropsch synthesis in a slurry bed is partly due to the loss of some key elements, such as potassium (K), which dissolves in the synthesis water and is discharged with the effluent. Furthermore, the inventors found that the catalyst's reactivity varies significantly along the axial direction, and the temperature difference along the axial direction is also substantial. This is caused by the uneven reaction of the catalyst along the axial direction of the slurry bed reactor. Specifically, due to the uneven distribution of the catalyst along the axial direction, and the high catalyst concentration at the bottom of the reactor, the synthesis gas, after entering from the bottom, is continuously consumed along the axial direction. By the time unreacted gas reaches the top of the reactor, the reaction rate is already very low. Since Fischer-Tropsch synthesis is a strongly exothermic reaction, this also leads to uneven temperature distribution along the axial direction; that is, the reaction is vigorous and the temperature is high at the bottom of the reactor, while the reaction is weaker and the temperature is lower at the top. Especially when replacing the catalyst, the catalyst concentration at the bottom of the reactor is generally higher, which makes the difference in reaction performance and temperature along the reactor's axial direction even more pronounced. Based on this, this invention was made.

[0009] Therefore, according to one aspect of the present invention, a Fischer-Tropsch synthesis method for preparing α-olefins from syngas is provided, comprising the following process route:

[0010] 1) A high-boiling-point solvent is added to the slurry bed reactor through the solvent inlet located at the top of the slurry bed reactor, an activated Fischer-Tropsch synthesis catalyst is added through the catalyst inlet located at the top of the slurry bed reactor, and then syngas is added through the syngas inlet located at the bottom of the slurry bed reactor, so that the syngas undergoes a Fischer-Tropsch synthesis reaction under the action of the activated Fischer-Tropsch synthesis catalyst.

[0011] 2) The gas phase discharged through the gas phase outlet at the top of the slurry bed reactor enters the condenser, wherein the temperature of the condenser is 8 to 18°C ​​lower than the temperature of the slurry bed reactor, resulting in condensed high-boiling-point solvent and gas phase.

[0012] 3) The high-boiling-point solvent condensed in 2) is mixed with an optional high-boiling-point solvent for replenishing the slurry bed reactor in a high-boiling-point solvent mixing tank and then added to the slurry bed reactor via the solvent inlet;

[0013] 4) The gas phase discharged from the condenser enters the three-phase separator, where synthetic water, light oil and gas phase are separated. The gas phase separated by the three-phase separator enters the low-carbon olefin separator to obtain α-olefins.

[0014] In the reaction process, the Fischer-Tropsch synthesis catalyst in the slurry bed reactor is intermittently replaced in the following manner, while inorganic potassium salts, potassium oxide or potassium hydroxide, organic potassium salts and concentrated synthesis water are added:

[0015] Based on 100 wt% of the Fischer-Tropsch synthesis catalyst present in the slurry bed reactor, 1 wt% to 50 wt% of the activated Fischer-Tropsch synthesis catalyst and 0.5 wt% to 10 wt% of an organopotassium salt are added to the high-boiling solvent mixing tank, mixed with the high-boiling solvent therein, and then introduced into the slurry bed reactor through the solvent inlet; and

[0016] Based on 100 wt% of the Fischer-Tropsch synthesis catalyst present in the slurry bed reactor, 0.5 wt% to 10 wt% of inorganic potassium salt, potassium oxide, or potassium hydroxide, and 10 wt% to 50 wt% of concentrated synthesis water are added to a water mixing tank and mixed. The mixture is then introduced into the slurry bed reactor through a synthesis water inlet located at the top of the reactor. The concentrated synthesis water is obtained by concentrating the synthesis water separated by the three-phase separator to 10% to 30% of its original volume.

[0017] Based on 100 wt% of the Fischer-Tropsch synthesis catalyst present in the slurry bed reactor, optionally 1 wt% to 90 wt%, preferably 1 wt% to 50 wt% of the activated Fischer-Tropsch synthesis catalyst is added to the slurry bed reactor via the catalyst inlet.

[0018] Preferably, the Fischer-Tropsch synthesis catalyst is selected from one or more of Fischer-Tropsch molten iron catalysts, precipitated iron catalysts, or supported iron catalysts, and can be a Fischer-Tropsch synthesis catalyst conventionally used in the art, such as precipitated iron catalyst CNFT-1 (produced by Hebei Xinpeng New Material Technology Co., Ltd.).

[0019] Preferably, the Fischer-Tropsch synthesis reaction conditions are as follows: reaction temperature above 280°C, preferably 285–330°C; pressure 1.0–6.0 MPa, preferably 1.5–3.5 MPa; gas velocity 0.1–0.5 m / s, preferably 0.12–0.45 m / s; and the volume ratio of H2 to CO in the synthesis gas 0.7–2.5, preferably 1.2–2.2.

[0020] Preferably, the organic potassium salt is one or more selected from potassium citrate, potassium oxalate, and potassium acetate.

[0021] Preferably, the inorganic potassium salt is one or more selected from potassium carbonate, potassium sulfate, potassium nitrate, potassium oxide, and potassium borate.

[0022] Preferably, the Fischer-Tropsch synthesis catalyst is replaced every 50 to 150 hours of reaction.

[0023] Preferably, the high-boiling-point solvent is a solvent with a boiling point greater than 330°C, for example, it can be selected from polyalphaolefin base oil or high-melting-point paraffin.

[0024] Preferably, the waste catalyst is discharged via a waste catalyst outlet located at the top of the slurry bed reactor.

[0025] Preferably, the Fischer-Tropsch synthesis catalyst is activated by the following steps:

[0026] a) The reduction reaction is carried out in a fluidized bed reactor under a reducing atmosphere.

[0027] b) The reduced catalyst obtained in step a) is carbonized in a fluidized bed reactor in the presence of a carbon source to obtain an activated Fischer-Tropsch synthesis catalyst.

[0028] Preferably, step a) is carried out in a fluidized bed reactor in the following manner:

[0029] First stage: starting temperature to 200℃, heating rate 30~70℃ / h, preferably 40~60℃ / h, pure N2 atmosphere, space velocity 2~20L / g / h, pressure 0.05~0.5MPa (preferably 0.1MPa~0.3MPa), ensuring gas velocity >0.45m / s;

[0030] Second stage: 200℃ to 270℃, heating rate 10~30℃ / h, preferably 15~25℃ / h, using a mixed gas atmosphere of 50%~70% N2 and 30%~50% H2 by volume, space velocity 3~18L / g / h, pressure 0.1~1.5MPa, preferably 0.3MPa~1.0MPa, ensuring gas velocity greater than 0.3m / s;

[0031] The third stage: from 270℃ to the final reduction temperature of 280~450℃, preferably 260~440℃, with a heating rate of 5~15℃ / h, preferably 8~12℃ / h. During this stage, a mixed gas atmosphere of 10%~30% N2 and 70%~90% H2 by volume is used, with a space velocity of 3~17L / g / h and a pressure of 0.5~1.5MPa, preferably 0.7MPa~1.3MPa, ensuring a gas velocity greater than 0.2m / s.

[0032] Fourth stage: Maintain the final reduction temperature for 4-12 hours, preferably 5-10 hours, in a pure H2 atmosphere, with a space velocity of 4-15 L / g / h and a pressure of 1-2.5 MPa, preferably 1.2 MPa-2.0 MPa, ensuring a gas velocity greater than 0.15 m / s;

[0033] Fifth stage: The reduction temperature is lowered to the carbonization temperature of 200-380℃, preferably 240-360℃. Then, a mixed gas atmosphere of 2.5%-10% N2 and 90%-97.5% H2 by volume is used, with a space velocity of 4-15 L / g / h and the pressure is reduced to 0.5-2.0 MPa, preferably 0.7 MPa-1.5 MPa, to ensure that the gas velocity is greater than 0.15 m / s.

[0034] The first stage is the drying and effluent stage. Using low-pressure, high-space-velocity pure N2 facilitates rapid removal of moisture and saves on H2 usage. The second stage is the initial effluent stage of reduction. Using medium pressure (N2 + H2) helps control the reduction rate and ensure reduction quality. The third stage is the final effluent stage of reduction. Using a reducing gas dominated by H2 helps improve the degree of reduction. The fourth stage is the final stage of reduction. Using pure H2 helps to completely reduce the catalyst and increase the concentration of active components.

[0035] Preferably, step b) is carried out in a fluidized bed reactor in the following manner:

[0036] In the fifth stage, N2 in the mixed gas atmosphere is gradually replaced with CO at a temperature of 200–380°C, preferably 240–360°C, a space velocity of 4–15 L / g / h, and a pressure of 0.5–2.0 MPa, preferably 0.7 MPa–1.5 MPa, ensuring a gas velocity greater than 0.15 m / s. After each 20% replacement, the gas is held for 1–2 hours. Replacement is stopped when the volume ratio of H2 to CO is 5–50, preferably 10–40. Carbonization is continued for 4–12 hours, preferably 6–10 hours, under the condition of a mixed gas atmosphere with a volume ratio of 2.5%–10% CO and 90%–97.5% H2.

[0037] Then, the temperature is lowered to the Fischer-Tropsch synthesis reaction temperature, and pure N2 is used to replace H2+CO in the reactor until the H2+CO content in the reactor is less than 0.2% of the total gas volume, at which point carbonization is complete.

[0038] According to a second aspect of the present invention, a system for preparing α-olefins from syngas is provided, the system comprising:

[0039] A slurry bed reactor for carrying out Fischer-Tropsch synthesis has a synthesis gas inlet at the bottom of the slurry bed reactor, a catalyst inlet at the top of the slurry bed reactor, a solvent inlet at the top of the slurry bed reactor, a synthesis water inlet at the top of the slurry bed reactor, a gas phase outlet at the top of the slurry bed reactor, and a spent catalyst outlet at the top of the slurry bed reactor.

[0040] A condenser for separating the gas phase discharged via the gas phase outlet of the slurry bed reactor, the condenser having a gas phase inlet, an upper outlet and a lower outlet, the gas phase inlet of the condenser being connected to the gas phase outlet of the slurry bed reactor via a pipeline;

[0041] A three-phase separator is used to separate material from the upper outlet of the condenser into synthetic water, light oil and gas phase. The three-phase separator has a feed inlet, a gas phase outlet, a light oil outlet and a synthetic water outlet. The feed inlet of the three-phase separator is connected to the upper outlet of the condenser through a pipeline.

[0042] A low-carbon olefin separator for separating the gas phase from the three-phase separator to obtain α-olefins, the low-carbon olefin separator having a feed inlet, a tail gas outlet and a low-carbon olefin outlet, the feed inlet of the low-carbon olefin separator being connected to the gas phase outlet of the three-phase separator.

[0043] A synthetic water concentration tank is connected to the synthetic water outlet from a three-phase separator via a pipeline to concentrate the synthetic water separated by the three-phase separator. The synthetic water concentration tank is also connected to the water phase inlet of a water mixing tank via a pipeline.

[0044] A water mixing tank for mixing synthetic water and inorganic potassium salts, potassium oxide, or potassium hydroxide, and having an aqueous phase inlet, an inorganic potassium salt inlet, and an outlet, wherein the aqueous phase inlet is connected via a pipeline to the synthetic water concentration tank to receive concentrated synthetic water, the inorganic potassium salt inlet is used to feed inorganic potassium salts, potassium oxide, or potassium hydroxide, and the outlet of the water mixing tank is connected via a pipeline to the synthetic water inlet of the slurry bed reactor; and

[0045] A high-boiling-point solvent mixing tank for mixing high-boiling-point solvents, activated Fischer-Tropsch synthesis catalysts, and organopotassium salts has one outlet and one or more inlets. The outlet of the high-boiling-point solvent mixing tank is connected to the solvent inlet of the slurry bed reactor via a pipeline. The one or more inlets are used to feed organopotassium salts, high-boiling-point solvents from the lower outlet of the condenser, activated Fischer-Tropsch synthesis catalysts, and high-boiling-point solvents from the solvent storage tank.

[0046] Preferably, the system further includes a fluidized bed reactor for activating the Fischer-Tropsch synthesis catalyst, and is connected by pipelines to the feed inlet of the high-boiling-point solvent mixing tank and the catalyst inlet of the slurry bed reactor, respectively, to supply the activated Fischer-Tropsch synthesis catalyst.

[0047] Preferably, valves are provided on the pipelines connecting the components of the system to control the opening and closing of the pipelines and / or control the flow rate of the pipelines.

[0048] Preferably, the light oil outlet of the three-phase separator is connected to a light oil storage tank via a pipeline to collect light oil in the light oil storage tank.

[0049] Preferably, the exhaust outlet of the low-carbon olefin separator is connected to a treatment device for further treatment of the exhaust gas, or directly connected to the atmosphere for direct discharge.

[0050] Preferably, the low-carbon olefin outlet of the low-carbon olefin separator is connected to an α-olefin storage tank via a pipeline to collect α-olefins.

[0051] Beneficial technical effects

[0052] The product prepared by the method according to the present invention has a high proportion of α-olefins; no dewaxing system is required; the steam generated by the reaction has a high grade; the problem of uneven activity and temperature along the axial direction in the reactor is solved, and there are fewer side reactions; the reduced catalyst treated with appropriate amounts of synthetic water and potassium salt has higher activity, more stable performance, lower methane selectivity, and lower oxygen-containing compound selectivity.

[0053] The method for efficiently producing α-olefins from syngas according to the present invention has the following advantages:

[0054] 1. The product has a high proportion of α-olefins, resulting in excellent economic efficiency of the entire process. Furthermore, the product has low selectivity for CO2 and CH4, which reduces carbon emissions.

[0055] 2. The slurry bed reactor was applied to the medium- and high-temperature Fischer-Tropsch synthesis reaction (>280℃). The slurry bed level was maintained by recovering and replenishing high-boiling-point solvents (boiling point >320℃), thus realizing the operation of the medium- and high-temperature slurry bed reactor.

[0056] 3. During the reaction process, adding appropriate amounts of potassium citrate and potassium carbonate can compensate for the performance loss caused by the loss of key catalyst components (such as K), thus maintaining the stability of the catalyst's performance.

[0057] 4. Recycle the synthesis water produced by the Fischer-Tropsch reaction, so that the active components of the catalyst (Fe, K, etc.) dissolved in the water can be returned to the reactor. In addition, the addition of an appropriate amount of water can also improve the catalyst activity and reduce the selectivity of oxygen-containing compounds in the product.

[0058] 5. Adding the activated Fischer-Tropsch synthesis catalyst from the top of the reactor can effectively solve the problem of uneven distribution of reactor activity and reaction temperature along the axial direction.

[0059] 6. Compared with traditional slurry bed reactors, the products of medium- and high-temperature Fischer-Tropsch reactions contain virtually no wax, eliminating the need for a wax filtration system. This makes the reactor simpler and reduces production and operating costs.

[0060] 7. Compared with traditional slurry bed reactors, the reaction temperature is higher, the product is lighter, the separation from the catalyst is simpler, the catalyst replacement is more convenient, the generated steam has a higher grade, and the overall process has higher energy efficiency.

[0061] 8. Discharging spent catalyst from the top of the reactor helps maintain stable operation of the reactor and subsequent separation sections. This is because most of the finely ground catalyst powder in the reactor flows with the bulk liquid phase to the upper part of the reactor.

[0062] 9. Using a fluidized bed reactor to activate the Fischer-Tropsch synthesis catalyst. Compared with a slurry bed reactor, a fluidized bed reactor can reduce and carbonize the Fischer-Tropsch synthesis catalyst at a higher temperature, thereby improving the selectivity of the activated Fischer-Tropsch synthesis catalyst to α-olefins and reducing the selectivity to CH4 and CO2. Attached Figure Description

[0063] Figure 1 A schematic diagram illustrating the process flow of the method for producing α-olefins from syngas according to the present invention.

[0064] Figure Labels

[0065] 1-Slurry bed reactor, 2-Condenser, 3-Three-phase separator, 4-Fluidized bed reactor, 5-Low-carbon olefin separator, 6-Synthetic water concentration tank, 7-High-boiling-point solvent mixing tank, 8-Water mixing tank Detailed Implementation

[0066] The present invention will be further described below with reference to embodiments. It should be understood that the embodiments provided in this invention are for illustrative purposes only and are not intended to limit the scope of the invention.

[0067] The following describes a system for preparing α-olefins from syngas according to a preferred embodiment of the present invention, with reference to the accompanying drawings. The system comprises:

[0068] A slurry bed reactor 1 for carrying out Fischer-Tropsch synthesis reaction has a synthesis gas inlet at the bottom of the slurry bed reactor 1, a Fischer-Tropsch synthesis catalyst inlet at the top of the slurry bed reactor 1, a solvent inlet at the top of the slurry bed reactor 1, a synthesis water inlet at the top of the slurry bed reactor 1, a gas phase outlet at the top of the slurry bed reactor 1, and a waste catalyst outlet at the top of the slurry bed reactor 1.

[0069] Condenser 2 is used to separate the gas phase discharged through the gas phase outlet of slurry bed reactor 1. Condenser 2 has a gas phase inlet, an upper outlet and a lower outlet. The gas phase inlet of condenser 2 is connected to the gas phase outlet of slurry bed reactor 1 through a pipeline.

[0070] Three-phase separator 3 is used to separate the material from the upper outlet of condenser 2 into synthetic water, light oil and gas phase. Three-phase separator 3 has a feed inlet, a gas phase outlet, a light oil outlet and a synthetic water outlet. The feed inlet of the three-phase separator 3 is connected to the upper outlet of condenser 2 through a pipeline, and the light oil outlet is connected to a light oil storage tank (not shown) through a pipeline to collect light oil.

[0071] The low-carbon olefin separator 5 is used to separate the gas phase from the three-phase separator 3 to obtain α-olefins. The low-carbon olefin separator 5 has a feed inlet, a tail gas outlet and a low-carbon olefin outlet. The feed inlet of the low-carbon olefin separator 5 is connected to the gas phase outlet of the three-phase separator 3. The low-carbon olefin outlet is connected to the α-olefin storage tank (not shown) through a pipeline to collect α-olefin products. The tail gas discharged through the tail gas outlet is discharged for further processing.

[0072] Synthetic water concentration tank 6 is connected to the synthetic water outlet from the three-phase separator 3 via a pipeline to concentrate the synthetic water from the three-phase separator 3. The synthetic water concentration tank 6 is connected to the water phase inlet of the water mixing tank 8 via a pipeline, so that a portion of the concentrated water enters the water mixing tank 8 and the remaining concentrated water enters the water treatment device (not shown) for further processing.

[0073] Water mixing tank 8 is used to mix synthetic water and inorganic potassium salt, potassium oxide or potassium hydroxide, and has an aqueous phase inlet, an inorganic potassium salt inlet and an outlet. The aqueous phase inlet is connected to the synthetic water concentration tank 6 through a pipeline to receive the concentrated synthetic water therefrom. The inorganic potassium salt inlet is used to feed inorganic potassium salt, potassium oxide or potassium hydroxide. The outlet of water mixing tank 8 is connected to the synthetic water inlet of slurry bed reactor 1 through a pipeline.

[0074] A high-boiling-point solvent mixing tank 7, used for mixing high-boiling-point solvents, activated Fischer-Tropsch synthesis catalysts, and organopotassium salts, has one outlet and four inlets. The outlet of the high-boiling-point solvent mixing tank 7 is connected to the solvent inlet of the slurry-bed reactor 1 via a pipeline. The four inlets are used to feed the organopotassium salts, the high-boiling-point solvent from the lower outlet of the condenser 2, the activated Fischer-Tropsch synthesis catalyst, and the high-boiling-point solvent from a solvent storage tank (not shown), respectively.

[0075] Fluidized bed reactor 4 is used to activate the Fischer-Tropsch synthesis catalyst and is connected to the feed inlet of the high-boiling-point solvent mixing tank 7 and the catalyst inlet of the slurry bed reactor 1 respectively through pipelines to supply the activated Fischer-Tropsch synthesis catalyst.

[0076] Example 1

[0077] Catalyst reduction: Precipitated iron catalyst (CNFT-1 catalyst produced by Hebei Xinpeng New Material Technology Co., Ltd., main components Fe-Cu-K-Si-B, spherical, bulk density 0.7~1.2g / cm³). 3 Particle size distribution 30–200 μm, specific surface area 100–300 m² 2 / g, with a wear rate of less than 4%, was reduced in a fluidized bed (15cm in diameter).

[0078] The restoration process is as follows:

[0079] First stage: starting temperature to 200℃, heating rate 50℃ / h, pure N2 atmosphere, space velocity 18L / g / h, pressure 0.2MPa, gas velocity 0.48m / s;

[0080] Second stage: 200℃ to 270℃, heating rate 20℃ / h, 60% N2-40% H2 atmosphere, space velocity 16L / g / h, pressure 0.5MPa, gas velocity 0.35m / s;

[0081] Third stage: 270℃ to the final reduction temperature of 410℃, heating rate 10℃ / h, 20% N2-80% H2 atmosphere, space velocity 15L / g / h, pressure 0.8MPa, gas velocity 0.25m / s;

[0082] Fourth stage: Maintain the final reduction temperature for 6 hours, in a pure H2 atmosphere, with a space velocity of 13 L / g / h, a pressure of 1.35 MPa, and a gas velocity of 0.2 m / s;

[0083] Fifth stage: The reduction temperature is lowered to the carbonization temperature of 350℃, and then the atmosphere is changed to 5% N2-95% H2. The space velocity remains unchanged, the pressure is reduced to 1.0 MPa, and the gas velocity is 0.25 m / s. The reduction ends.

[0084] Catalyst carbonization: CO was gradually replaced with N2, with a 1.5-hour pause after each 20% replacement. Replacement was stopped when the H2 to CO ratio reached 1:9. Carbonization continued for 7 hours under a 5% CO-95% H2 atmosphere at a pressure of 1.0 MPa and a gas velocity of 0.25 m / s. After carbonization, the temperature was lowered to the reaction temperature, and pure N2 was used to replace the (H2+CO) in the reactor until the (H2+CO) content in the reactor was below 0.2%. Carbonization was then complete, yielding an activated Fischer-Tropsch synthesis catalyst.

[0085] Fischer-Tropsch synthesis reaction: 1200g of polyalphaolefin base oil (PAO100) is added to slurry bed reactor 1 as a solvent through the solvent inlet, and 30g of the activated Fischer-Tropsch synthesis catalyst prepared above is added through the catalyst inlet. Then, syngas (H2 / CO=2) is added through the syngas inlet to carry out the Fischer-Tropsch synthesis reaction. The reaction temperature is 290℃, the pressure is 2.0MPa, and the gas velocity is 0.2m / s. The gas phase in slurry bed reactor 1 enters condenser 2 (temperature controlled at 280℃) to obtain condensed PAO100 and gas phase. The condensed PAO100 enters high-boiling-point solvent mixing tank 7 and then enters slurry bed reactor 1 through the solvent inlet. The gas phase discharged from the upper outlet of condenser 2 enters three-phase separator 3, where it is separated to obtain synthetic water, light oil, and gas phase. The synthetic water enters water concentration tank 6 to be concentrated to 15% of its original volume and finally enters the subsequent water treatment unit (not shown). The light oil is collected as a product in a light oil storage tank (not shown). The gas phase separated from the three-phase separator 3 enters the low-carbon olefin separator 5, and the gaseous product mainly composed of α-olefins is obtained and collected in the α-olefin storage tank (not shown). The remaining gas is discharged as tail gas.

[0086] At the beginning of the reaction, the catalyst activity does not decrease, and there is no need to replace the catalyst or add potassium salts. When the catalyst performance deteriorates, the old catalyst in the reactor needs to be replaced with fresh, activated Fischer-Tropsch synthesis catalyst. Organic and inorganic potassium salts (or potassium oxide or potassium hydroxide) are added to the reactor along with the activated Fischer-Tropsch synthesis catalyst.

[0087] The catalyst in the reactor is replaced intermittently every 100 hours. During replacement, 1.5 g of activated Fischer-Tropsch synthesis catalyst and 1 g of potassium citrate are added to the high-boiling solvent mixing tank 7, mixed with condensed (or replenished) polyalphaolefin base oil (PAO100), and then introduced into the slurry bed reactor 1 through the solvent inlet. Additionally, 1.2 g of potassium carbonate is added to the water mixing tank 8, mixed with 10 g of concentrated synthesis water from the synthesis water concentration tank 6, and then introduced into the slurry bed reactor 1 through the synthesis water inlet. 1.5 g of activated Fischer-Tropsch synthesis catalyst is introduced into the slurry bed reactor 1 through the catalyst inlet, and the old catalyst is discharged from the waste catalyst outlet.

[0088] Reaction performance: continuous operation time > 500 h, axial temperature difference of reactor < 2 ℃, high and stable catalyst activity, CO conversion rate basically did not decrease within 500 h, and the conversion rate of reactants and the selectivity of reaction products detected at different time points are shown in Table 1.

[0089] Table 1: Conversion rate of reactants and selectivity of reaction products detected at different time points (Example 1)

[0090] CO conversion rate (%) 54.4 53.8 54.1 53.6 53.5 54.1 53.6 <![CDATA[H2 conversion rate (%)]]> 38.2 37.7 38.1 37.6 37.7 38.0 37.7 <![CDATA[CO2 selectivity (%)]]> 22.0 22.2 22.1 22.4 22.4 22.1 22.3 <![CDATA[CH4 selectivity (%)]]> 7.8 7.9 8.0 7.9 8.0 8.0 8.1 <![CDATA[C2-C4 selectivity (%)]]> 38.1 38.2 38.2 38.3 38.4 38.5 38.6 <![CDATA[C5 + Selectivity (%) 47.8 47.70 47.70 47.50 47.5 47.4 47.3 Selectivity of oxygen-containing compounds (%) 6.3 6.2 6.1 6.3 6.1 6.10 6.0 α-Olefin selectivity (%) 40.4 40.6 40.5 40.4 40.7 40.6 40.5

[0091] Comparative Example 1

[0092] Except for using a slurry bed reactor instead of a fluidized bed reactor for the activation of the precipitated iron catalyst, the Fischer-Tropsch synthesis reaction was carried out in the same manner as in Example 1.

[0093] The conditions for catalyst activation using a slurry bed reactor are as follows:

[0094] Catalyst reduction: Polyalphaolefin base oil (PAO100) was used as the solvent in the slurry bed reactor. The first and second stages were the same as in Example 1. Because the slurry bed level gradually decreased after the temperature exceeded 290°C, the final reduction temperature in the third stage was 290°C. After reaching 290°C, the fourth stage began, using a pure H2 atmosphere with a space velocity of 13 L / g / h, a pressure of 1.35 MPa, and a gas velocity of 0.2 m / s, maintained for 6 hours. Fifth stage: At the final reduction temperature of 290°C, the atmosphere was changed to 5% N2-95% H2, with the space velocity remaining constant, but the pressure was reduced to 1.0 MPa and the gas velocity to 0.25 m / s, ending the reduction.

[0095] Catalyst carbonization: Consistent with Example 1, but because the slurry bed reactor cannot maintain the liquid level under high temperature (e.g., 420°C), the reduction and carbonization temperature is 290°C, and other conditions remain unchanged.

[0096] Reaction performance: The reaction time was 500 h, the axial temperature difference of the reactor was <4.2℃, and the conversion rate and selectivity of the reaction products were detected at different time points as shown in Table 2.

[0097] The catalyst in the comparative example had low activity and poor stability, high selectivity for CH4 and CO2, but lower selectivity for α-olefins than in Example 1.

[0098] Table 2: Conversion rates of reactants and selectivity of reaction products detected at different time points (Comparative Example 1)

[0099] CO conversion rate (%) 50.6 49.9 48.3 47.2 46.7 45.8 45.5 <![CDATA[H2 conversion rate (%)]]> 33.8 33.2 31.4 30.1 29.8 29.0 28.9 <![CDATA[CO2 selectivity (%)]]> 25.0 25.6 26.0 26.5 26.7 26.9 27.3 <![CDATA[CH4 selectivity (%)]]> 10.3 10.4 10.7 10.9 11.2 11.6 11.8 <![CDATA[C2-C4 selectivity (%)]]> 38.4 38.7 38.9 39.2 39.6 40 40.2 <![CDATA[C5 + Selectivity (%) 45.1 44.8 44.1 43.7 43.1 42.2 41.7 Selectivity of oxygen-containing compounds (%) 6.2 6.1 6.3 6.2 6.1 6.2 6.3 α-Olefin selectivity (%) 29.3 29.2 29.1 28.9 28.7 28.6 28.4

[0100] Comparative Example 2

[0101] The Fischer-Tropsch synthesis reaction was carried out in the same manner as in Example 1, except that 10 wt% of the activated Fischer-Tropsch synthesis catalyst was replaced at the catalyst inlet, and potassium carbonate, potassium citrate and synthesis water were not added.

[0102] Reaction performance: continuous operation time > 500 h, reactor axial temperature difference < 5.2 ℃, the conversion rate of reactants and the selectivity of reaction products detected at different time points are shown in Table 3.

[0103] Table 3: Conversion rates of reactants and selectivity of reaction products detected at different time points (Comparative Example 2)

[0104] CO conversion rate (%) 52.4 52.2 52.3 51.9 51.6 51.2 50.8 <![CDATA[H2 conversion rate (%)]]> 37.0 36.7 36.7 36.4 36.0 35.7 35.4 <![CDATA[CO2 selectivity (%)]]> 21.0 21.1 21.3 21.4 21.5 21.7 21.8 <![CDATA[CH4 selectivity (%)]]> 9.1 9.3 9.4 9.6 9.8 10.0 10.3 <![CDATA[C2-C4 selectivity (%)]]> 38.3 38.4 38.6 38.8 39.0 39.3 39.7 <![CDATA[C5 + Selectivity (%) 43.8 43.3 43.1 42.8 42.2 41.7 41.1 Selectivity of oxygen-containing compounds (%) 8.8 9.0 8.9 8.8 9.0 9.0 8.9 α-Olefin selectivity (%) 33.7 33.6 33.5 33.5 33.4 33.6 33.4

[0105] Because no potassium component and synthetic water were added, the catalyst activity decreased, the selectivity of CH4 and α-olefins decreased significantly, the selectivity of oxygen-containing compounds increased, the economy deteriorated, and the effect was not as good as in Example 1.

Claims

1. A Fischer-Tropsch synthesis method for preparing α-olefins from syngas, comprising the following process route: 1) A high-boiling-point solvent is added to the slurry bed reactor through the solvent inlet located at the top of the slurry bed reactor, an activated Fischer-Tropsch synthesis catalyst is added through the catalyst inlet located at the top of the slurry bed reactor, and then syngas is added through the syngas inlet located at the bottom of the slurry bed reactor, so that the syngas undergoes a Fischer-Tropsch synthesis reaction under the action of the activated Fischer-Tropsch synthesis catalyst. 2) The gas phase discharged via the top gas phase outlet of the slurry bed reactor enters the condenser, wherein, The temperature of the condenser is 8-18°C lower than that of the slurry bed reactor, resulting in condensed high-boiling-point solvent and gas phase. 3) The high-boiling-point solvent condensed in 2) is mixed with an optional high-boiling-point solvent for replenishing the slurry bed reactor in a high-boiling-point solvent mixing tank and then added to the slurry bed reactor via the solvent inlet; 4) The gas phase discharged from the condenser enters the three-phase separator, where synthetic water, light oil and gas phase are separated. The gas phase separated by the three-phase separator enters the low-carbon olefin separator to obtain α-olefins. During the reaction, the Fischer-Tropsch synthesis catalyst in the slurry bed reactor is intermittently replaced in the following manner, while inorganic potassium salts, potassium oxide or potassium hydroxide, organic potassium salts and concentrated synthesis water are added: Based on 100 wt% of the Fischer-Tropsch synthesis catalyst present in the slurry bed reactor, 1 wt% to 50 wt% of the activated Fischer-Tropsch synthesis catalyst and 0.5 wt% to 10 wt% of an organopotassium salt are added to the high-boiling solvent mixing tank, mixed with the high-boiling solvent therein, and then introduced into the slurry bed reactor through the solvent inlet; and Based on 100 wt% of the Fischer-Tropsch synthesis catalyst present in the slurry bed reactor, 0.5 wt% to 10 wt% of inorganic potassium salt, potassium oxide or potassium hydroxide, and 10 wt% to 50 wt% of concentrated synthesis water are added to a water mixing tank and mixed, and then enter the slurry bed reactor through a synthesis water inlet located at the top of the slurry bed reactor, wherein the concentrated synthesis water is obtained by concentrating the synthesis water separated by the three-phase separator to 10% to 30% of its original volume; as well as Based on 100 wt% of the Fischer-Tropsch synthesis catalyst present in the slurry bed reactor, optionally 1 wt% to 90 wt% of the activated Fischer-Tropsch synthesis catalyst is added to the slurry bed reactor via the catalyst inlet.

2. The Fischer-Tropsch synthesis method for preparing α-olefins from syngas according to claim 1, wherein, The Fischer-Tropsch synthesis catalyst is selected from one or more of the following: Fischer-Tropsch molten iron catalyst, precipitated iron catalyst, or supported iron catalyst.

3. The Fischer-Tropsch synthesis method for preparing α-olefins from syngas according to claim 2, wherein, The Fischer-Tropsch synthesis reaction conditions are as follows: reaction temperature above 280℃; pressure 1.0~6.0MPa; gas velocity 0.1~0.5m / s; and volume ratio of H2 to CO in the synthesis gas 0.7~2.

5.

4. The Fischer-Tropsch synthesis method for preparing α-olefins from syngas according to claim 2, wherein, The reaction conditions for Fischer-Tropsch synthesis are: The reaction temperature is 285~330℃; And / or, the pressure is 1.5~3.5MPa; And / or, the air velocity is 0.12~0.45m / s; And / or, the volume ratio of H2 to CO in the synthesis gas is 1.2 to 2.

2.

5. The Fischer-Tropsch synthesis method for preparing α-olefins from syngas according to claim 1 or 2, wherein, The organic potassium salt is selected from one or more of potassium citrate, potassium oxalate, and potassium acetate; The inorganic potassium salt is selected from one or more of potassium carbonate, potassium sulfate, potassium nitrate, and potassium borate; And / or, the Fischer-Tropsch catalyst is replaced every 50 to 150 hours of reaction; And / or, the high-boiling solvent is a solvent with a boiling point greater than 330°C; And / or, the spent catalyst is discharged via a spent catalyst outlet located at the top of the slurry bed reactor.

6. The Fischer-Tropsch synthesis method for preparing α-olefins from syngas according to claim 1 or 2, wherein, The Fischer-Tropsch synthesis catalyst is activated through the following steps: a) The reduction reaction is carried out in a fluidized bed reactor under a reducing atmosphere. b) The reduced catalyst obtained in step a) is carbonized in a fluidized bed reactor in the presence of a carbon source to obtain an activated Fischer-Tropsch synthesis catalyst.

7. The Fischer-Tropsch synthesis method for preparing α-olefins from syngas according to claim 6, wherein, Step a) is carried out in a fluidized bed reactor in the following manner: First stage: starting temperature to 200℃, heating rate 30~70℃ / h, pure N2 atmosphere, space velocity 2~20L / g / h, pressure 0.05~0.5MPa, ensuring gas velocity >0.45m / s; Second stage: 200℃ to 270℃, heating rate 10~30℃ / h, using a mixed gas atmosphere of 50%~70% N2 and 30%~50% H2 by volume, space velocity 3~18L / g / h, pressure 0.1~1.5MPa, ensuring gas velocity greater than 0.3m / s; The third stage: from 270℃ to the final reduction temperature of 280~450℃, with a heating rate of 5~15℃ / h. During this stage, a mixed gas atmosphere of 10%~30% N2 and 70%~90% H2 by volume is used, with a space velocity of 3~17L / g / h and a pressure of 0.5~1.5MPa, ensuring a gas velocity greater than 0.2m / s. Fourth stage: Maintain the final reduction temperature for 4~12h, pure H2 atmosphere, space velocity 4~15L / g / h, pressure 1~2.5MPa, and ensure gas velocity is greater than 0.15m / s; Fifth stage: Reduce the final reduction temperature to the carbonization temperature of 200~380℃, and then use a mixed gas atmosphere of 2.5%~10% N2 and 90%~97.5% H2 by volume, with a space velocity of 4~15 L / g / h and the pressure reduced to 0.5~2.0 MPa, ensuring that the gas velocity is greater than 0.15 m / s; And / or, step b) is carried out in a fluidized bed reactor in the following manner: In the fifth stage, N2 in the mixed gas atmosphere is gradually replaced with CO at a temperature of 200-380℃, a space velocity of 4-15 L / g / h, and a pressure of 0.5-2.0 MPa, ensuring a gas velocity greater than 0.15 m / s. After each 20% replacement, the gas is held for 1-2 hours. Replacement is stopped when the volume ratio of H2 to CO is 5-50. Carbonization is continued for 4-12 hours under the condition of a mixed gas atmosphere with a volume ratio of 2.5%-10% CO and 90%-97.5% H2. Then, the temperature is lowered to the Fischer-Tropsch synthesis reaction temperature, and pure N2 is used to replace H2+CO in the reactor until the H2+CO content in the reactor is less than 0.2% of the total gas volume, at which point carbonization is complete.

8. The Fischer-Tropsch synthesis method for preparing α-olefins from syngas according to claim 7, wherein, In the first phase, The heating rate is 40~60℃ / h; And / or, the pressure is 0.1MPa~0.3MPa.

9. The Fischer-Tropsch synthesis method for preparing α-olefins from syngas according to claim 7, wherein, In the second phase, The heating rate is 15~25℃ / h; And / or, the pressure is 0.3MPa~1.0MPa.

10. The Fischer-Tropsch synthesis method for preparing α-olefins from syngas according to claim 7, wherein, In the third phase, The heating rate is 8~12℃ / h; And / or, the pressure is 0.7MPa~1.3MPa.

11. The Fischer-Tropsch synthesis method for preparing α-olefins from syngas according to claim 7, wherein, In the fourth phase, Maintain the final reduction temperature for 5-10 hours; And / or, pressure 1.2MPa~2.0MPa.

12. The Fischer-Tropsch synthesis method for preparing α-olefins from syngas according to claim 7, wherein, In the fifth stage, The carbonization temperature is 240~360℃; And / or, the pressure drops to 0.7MPa~1.5MPa.

13. The Fischer-Tropsch synthesis method for preparing α-olefins from syngas according to claim 7, wherein, The N2 in the mixed gas atmosphere in the fifth stage is gradually replaced with CO, wherein... The temperature is 240~360℃; And / or, the pressure is 0.7MPa~1.5MPa; And / or, stop the replacement when the volume ratio of H2 to CO is 10~40; And / or, carbonization is carried out continuously for 6 to 10 hours under a mixed gas atmosphere of 2.5% to 10% CO and 90% to 97.5% H2 by volume.

14. A system for preparing α-olefins from syngas, the system comprising: A slurry bed reactor for carrying out Fischer-Tropsch synthesis has a synthesis gas inlet at the bottom of the slurry bed reactor, a catalyst inlet at the top of the slurry bed reactor, a solvent inlet at the top of the slurry bed reactor, a synthesis water inlet at the top of the slurry bed reactor, a gas phase outlet at the top of the slurry bed reactor, and a spent catalyst outlet at the top of the slurry bed reactor. A condenser for separating the gas phase discharged via the gas phase outlet of the slurry bed reactor, the condenser having a gas phase inlet, an upper outlet and a lower outlet, the gas phase inlet of the condenser being connected to the gas phase outlet of the slurry bed reactor via a pipeline; A three-phase separator is used to separate material from the upper outlet of the condenser into synthetic water, light oil and gas phase. The three-phase separator has a feed inlet, a gas phase outlet, a light oil outlet and a synthetic water outlet. The feed inlet of the three-phase separator is connected to the upper outlet of the condenser through a pipeline. A low-carbon olefin separator for separating the gas phase from the three-phase separator to obtain α-olefins, the low-carbon olefin separator having a feed inlet, a tail gas outlet and a low-carbon olefin outlet, the feed inlet of the low-carbon olefin separator being connected to the gas phase outlet of the three-phase separator. A synthetic water concentration tank is connected via a pipeline to the synthetic water outlet of a three-phase separator to concentrate the synthetic water separated by the three-phase separator. The synthetic water concentration tank is also connected via a pipeline to the water phase inlet of a water mixing tank. A water mixing tank is used to mix synthetic water with inorganic potassium salts, potassium oxide, or potassium hydroxide. It has an aqueous phase inlet, an inorganic potassium salt inlet, and an outlet. The aqueous phase inlet of the water mixing tank is connected via a pipeline to a synthetic water concentration tank to receive concentrated synthetic water. The inorganic potassium salt inlet is used to feed inorganic potassium salts, potassium oxide, or potassium hydroxide. The outlet of the water mixing tank is connected via a pipeline to the synthetic water inlet of the slurry bed reactor. A high-boiling-point solvent mixing tank for mixing high-boiling-point solvents, activated Fischer-Tropsch synthesis catalysts, and organopotassium salts has one outlet and one or more inlets. The outlet of the high-boiling-point solvent mixing tank is connected to the solvent inlet of the slurry bed reactor via a pipeline. The one or more inlets are used to feed organopotassium salts, high-boiling-point solvents from the lower outlet of the condenser, activated Fischer-Tropsch synthesis catalysts, and high-boiling-point solvents from the solvent storage tank.

15. The system for preparing α-olefins from syngas according to claim 14, wherein, The system also includes a fluidized bed reactor for activating the Fischer-Tropsch synthesis catalyst, and is connected via pipelines to the feed inlet of the high-boiling-point solvent mixing tank and the catalyst inlet of the slurry bed reactor to supply the activated Fischer-Tropsch synthesis catalyst.

16. The system for preparing α-olefins from syngas according to claim 14 or 15, wherein, Valves are installed on the pipelines connecting the components of the system to control the opening and closing of the pipelines and / or control the flow rate of the pipelines; And / or, the light oil outlet of the three-phase separator is connected to a light oil storage tank via a pipeline to collect light oil in the light oil storage tank.

17. The system for preparing α-olefins from syngas according to claim 14 or 15, wherein, The exhaust outlet of the low-carbon olefin separator is connected to a treatment device for further treatment of the exhaust gas, or it is directly connected to the atmosphere for direct discharge.

18. The system for preparing α-olefins from syngas according to claim 14 or 15, wherein, The low-carbon olefin outlet of the low-carbon olefin separator is connected to an α-olefin storage tank via a pipeline to collect α-olefins.

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