A system and method for directly producing olefins from synthesis gas

Abstract

This invention provides a scheme for the direct preparation of olefins from syngas. A reaction apparatus is used to prepare hydrocarbons with a carbon number distribution of 1-7, which are then separated using a gas-liquid separator to obtain C1-C3 and C4-C7 hydrocarbons. The C1-C3 hydrocarbons are then separated into C2-C3 olefins using a gas-gas separator. The C4-C7 hydrocarbons are dehydrated using a liquid-liquid separator, indirectly heated by a gas-liquid separator, and then converted back into C2-C3 olefins by a hydrocarbon recycling converter. These C2-C3 olefins are then combined with the C2-C3 olefins obtained in the previous step and collected. This two-step olefin preparation process allows for reasonable control of product distribution, significantly improving olefin selectivity to 85-95% and increasing syngas conversion rate to 96%. Furthermore, the entire preparation process is simple to operate, significantly reduces the number of equipment units, and substantially lowers production costs. In addition, the room-temperature C4-C7 hydrocarbons obtained from the separation process are indirectly heated by the high-temperature material from the reaction apparatus outlet in a separation unit before being used for hydrocarbon recycling, resulting in energy savings of 3%-5%.

Description

Technical Field

[0001] This invention relates to the fields of clean coal chemical industry and clean natural gas chemical industry, and in particular to a system and method for directly preparing olefins from syngas. Background Technology

[0002] C2-C4 olefins are among the most important chemical raw materials, providing the foundation for the synthesis of various plastics, fibers, and medical devices. China's current ethylene and propylene production both exceed 50 million tons per year, forming a vast chemical and materials product network. Currently, C2-C4 olefins are mainly obtained through the cracking of petroleum feedstocks. Other developing routes include coal-to-methanol olefin production and ethane dehydrogenation to ethylene production. The bottleneck of the petroleum route lies in its resource dependence. Coal-to-methanol olefin production, on the other hand, is characterized by a long route, large equipment investment, and high carbon emissions.

[0003] In comparison, directly producing olefins from syngas without passing through methanol has the advantages of a shorter route and lower investment. Current research focuses on: how to limit the product to high-yield olefin varieties such as C2-C3 olefins; and how to simplify catalyst design to achieve higher single-pass conversion rates and better process continuity, thereby extending single-pass life and reducing the amount of recycled materials. However, since the direct production of olefins from syngas couples hydrogenation with functions such as carbon-carbon chain growth and suppression of hydrogen transfer side reactions, it is often impossible to simultaneously achieve optimal product distribution and catalyst life. Taking relatively inexpensive iron-based catalysts as an example, the resulting olefins can range from C2 to C7. Although the price of C4-C7 olefins is currently very competitive, there is still a need to flexibly adjust the product composition to cope with the complex and ever-changing market. In addition, due to differences in product composition and boiling points, the order of subsequent separations and separation energy consumption have not yet been optimized, and much work remains to be done. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, this invention discloses a system for directly preparing olefins from syngas. The system includes: a reaction apparatus 1, used to directly react syngas under the action of a metal-supported catalyst to obtain a mixture 1 containing C4-C7 hydrocarbons, C1-C3 hydrocarbons, and CO2;

[0005] The gas-liquid separation device 2, which is connected to the outlet of the reaction device 1, is used to cool the mixed substance 1 discharged from the reaction device 1, so that the C4-C7 hydrocarbons and water vapor therein are liquefied and separated to obtain a mixed gas 1 containing C1-C3 hydrocarbons and CO2 and a mixed liquid 1 containing C4-C7 hydrocarbons and water, respectively.

[0006] A gas-gas separation device 5, connected to the gas outlet 9 of the separation device 2, is used to separate the mixed gas 1 discharged from the separation device 2 to obtain C2-C3 olefins and mixed gas 2, respectively; the mixed gas 2 contains unreacted syngas, CO2 and CH4;

[0007] The liquid-liquid separation device 3, connected to the liquid outlet 10 of the separation device 2, is used to separate the mixed liquid 1 discharged from the gas-liquid separation device 2 to obtain C4-C7 hydrocarbons and water respectively; the liquid-liquid separation device 3 is provided with an organic liquid outlet 15, which is connected to the heat exchange medium inlet 11 of the gas-liquid separation device 2 through a pipeline, and transports the separated C4-C7 hydrocarbons to the gas-liquid separation device 2 for indirect heat exchange.

[0008] The olefin recycling conversion unit 4, which is connected to the heat exchange medium outlet 12 of the gas-liquid separation unit 2, is used to receive C4-C7 hydrocarbons after indirect heat exchange and, under the action of molecular sieve catalyst, cause the C4-C7 hydrocarbons to react to obtain C2-C3 olefins.

[0009] The olefin recycling conversion unit 4 and the gas-gas separation unit 5 are respectively equipped with C2-C3 olefin outlet a17 and C2-C3 olefin outlet b19; the C2-C3 olefin outlet a17 and C2-C3 olefin outlet b19 are connected by a pipeline to combine the C2-C3 olefins generated in the two-step reaction.

[0010] Optionally, the bottom of the liquid-liquid separation device 3 is provided with a water outlet 14 for discharging water from the mixed liquid 1 separated by the liquid-liquid separation device 3.

[0011] Optionally, the gas-gas separator 5 is provided with a gas outlet b20 at the top for discharging the mixed gas 2 separated by the gas-gas separator 5.

[0012] To address the aforementioned problems, this invention also discloses a method for directly preparing olefins from syngas, applicable to any of the systems described above, the method comprising:

[0013] S1. Syngas is introduced into reaction device 1 through raw material gas inlet 6. Under the action of metal supported catalyst, the syngas reacts directly to obtain a mixture 1 containing C4-C7 hydrocarbons, C1-C3 hydrocarbons and CO2.

[0014] S2. The mixture 1 is discharged from the product gas outlet 7 of the reaction device 1 and passed into the gas-liquid separation device 2 through the gas inlet a8 for cooling, so that the C4-C7 hydrocarbons and water vapor in it are liquefied and separated to obtain a mixed gas 1 containing C1-C3 hydrocarbons and CO2 and a mixed liquid 1 containing C4-C7 hydrocarbons and water, respectively.

[0015] S3. The mixed gas 1 is discharged from the gas outlet a9 of the gas-liquid separator 2 and passed into the gas-gas separator 5 through the gas inlet b18. The gas is separated to obtain C2-C3 olefins and mixed gas 2. The C2-C3 olefins are discharged from the C2-C3 hydrocarbon outlet b19. The remaining mixed gas 2 is discharged from the gas outlet b20 and recycled.

[0016] S4. Mixed liquid 1 is discharged from the liquid outlet 10 of gas-liquid separator 2 and fed into liquid-liquid separator 3 through liquid inlet 13 for separation, obtaining C4-C7 hydrocarbons and water respectively; then the C4-C7 hydrocarbons are discharged from the organic liquid outlet 15 and fed into separator 2 through heat exchange medium inlet 11 for indirect heat exchange, and then discharged from the heat exchange medium outlet 12 and fed into olefin recycling converter 4 through organic matter inlet 16. Under the action of molecular sieve catalyst, the C4-C7 hydrocarbons react to obtain C2-C3 olefins;

[0017] S5. Combine the C2-C3 olefins discharged from the C2-C3 olefin outlet a17 of the olefin recycling converter 4 and the C2-C3 olefin outlet b19 of the gas-gas separator 5 for later use.

[0018] Optionally, in step S1, the reactor of the reaction device 1 is a fixed bed or a fluidized bed; when the reactor of the reaction device 1 is a fixed bed, the catalyst diameter in the fixed bed is 0.3-6 mm, and the applicable syngas space velocity range is 1000-5000 ml / gcat / h; when the reactor of the reaction device 1 is a fluidized bed, the catalyst diameter in the fluidized bed is 0.03-1 mm, and the applicable syngas space velocity range is 1000-16000 ml / gcat / h.

[0019] Optionally, in step S1, the reaction device 1 is filled with a metal-supported catalyst; the operating temperature of the metal catalyst is 250-350°C; and the operating pressure of the metal catalyst is 2-6 MPa.

[0020] Optionally, in step S1, the metal component of the metal-supported catalyst is one or at least two of iron, cobalt, zinc, and copper; the promoter of the metal-supported catalyst is one or at least two of sodium, potassium, and calcium; and the support of the metal-supported catalyst is one of alumina, silicon oxide, and carbon.

[0021] Optionally, in step S1, the mass fraction of the metal component is 1-50%; the mass fraction of the metal auxiliary is 1-20%; the mass fraction of the support for the metal-supported catalyst is 30-98%; and the specific surface area of ​​the support for the metal-supported catalyst is 50-2000 m². 2 / g.

[0022] Optionally, in step S1, the synthesis gas is H2 and CO; the volume ratio of H2 to CO is 1.25-2:1; and the olefin selectivity in the mixture 1 is 85-95%.

[0023] Optionally, in step S5, the olefin recycling conversion device 4 is filled with a molecular sieve catalyst for converting C4-C7 hydrocarbons into C2-C3 olefins; the molecular sieve catalyst is any one of the SAPO series and the MFI series or a mixture of the two series.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] This application provides a scheme for the direct preparation of olefins from syngas. A reaction apparatus is used to prepare hydrocarbons with a carbon number distribution of 1-7, which are then separated using a gas-liquid separator to obtain C1-C3 and C4-C7 hydrocarbons. The C1-C3 hydrocarbons are then separated into C2-C3 olefins using a gas-gas separator. The C4-C7 hydrocarbons are dehydrated using a liquid-liquid separator, and after indirect heat exchange in the gas-liquid separator, they are converted back into C2-C3 olefins by a hydrocarbon recycling converter. These C2-C3 olefins are then combined with the C2-C3 olefins obtained in the previous step and collected. Compared to the conventional route of preparing olefins from syngas via methanol, this application involves a two-step reaction, allowing for reasonable control of product distribution and significantly improving olefin selectivity to 85-95%, with a syngas conversion rate of 96%. Furthermore, the entire preparation process is simple to operate, significantly reducing the number of devices and production costs. In addition, the room-temperature C4-C7 hydrocarbons obtained through the separation are indirectly heated with the high-temperature material from the reaction apparatus outlet in a separation unit before being used for hydrocarbon recycling, resulting in a significant energy saving of 3%-5%. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A schematic diagram of the system structure for the direct preparation of olefins from syngas provided in an embodiment of the present invention is shown.

[0028] Figure 2 A flowchart of a method for directly preparing olefins from syngas according to an embodiment of the present invention is shown.

[0029] Explanation of reference numerals in the attached figures:

[0030] 1-Olefin preparation reaction unit, 2-Cooling and separation unit, 3-Liquid-liquid separation unit, 4-Olefin recycling conversion unit, 5-Gas-gas separation unit, 6-Raw material gas inlet, 7-Product gas outlet, 8-Gas inlet a, 9-Gas outlet a, 10-Liquid outlet, 11-Heat exchange medium inlet, 12-Heat exchange medium outlet, 13-Liquid inlet, 14-Water outlet, 15-Organic liquid outlet, 16-Organic matter inlet, 17-C2-C3 hydrocarbon outlet a, 18-Gas inlet b, 19-C2-C3 hydrocarbon outlet b, 20-Gas outlet b. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, any product that is the same as or similar to the present invention, derived by anyone under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention. Furthermore, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of the present invention.

[0032] When directly preparing olefins from syngas using existing technologies, problems arise due to the coupling of functions such as hydrogenation, carbon-carbon chain growth, and suppression of hydrogen transfer side reactions. This leads to a trade-off between achieving a reasonable product distribution and catalyst lifetime, as well as cumbersome separation processes. This invention provides a system and method for directly preparing olefins from syngas. A reaction apparatus is used to prepare hydrocarbons with a carbon number distribution of 1-7, which are then separated using a gas-liquid separator to obtain C1-C3 and C4-C7 hydrocarbons. The C1-C3 hydrocarbons are then separated using a gas-gas separator to obtain C2-C3 olefins. The C4-C7 hydrocarbons are dehydrated using a liquid-liquid separator, indirectly heated by a gas-liquid separator, and then converted back to C2-C3 olefins by a hydrocarbon recycling converter. These C2-C3 olefins are then combined with the C2-C3 olefins obtained in the previous step and collected. Specific implementation methods are as follows:

[0033] In a first aspect, embodiments of the present invention provide a system for the direct preparation of olefins from syngas, the structural relationship of which is as follows: Figure 1As shown, the system includes: a reaction device 1, used to directly react syngas under the action of a metal-supported catalyst to obtain a mixture 1 containing C4-C7 hydrocarbons, C1-C3 hydrocarbons, and CO2; a gas-liquid separator 2 connected to the product gas outlet 7 of the reaction device 1, used to cool the mixture 1 discharged from the reaction device 1, liquefying and separating the C4-C7 hydrocarbons and water vapor therein, to obtain a mixed gas 1 containing C1-C3 hydrocarbons and CO2 and a mixed liquid 1 containing C4-C7 hydrocarbons and water; a gas-gas separator 5 connected to the gas outlet 9 of the separator 2, used to separate the mixed gas 1 discharged from the separator 2 to obtain C2-C3 olefins and a mixed gas 2; the mixed gas 2 contains unreacted syngas, CO2, and CH4; and a liquid-liquid separator 3 connected to the liquid outlet 10 of the separator 2 for separating the gas and liquid components. The mixed liquid 1 discharged from the separation device 2 is separated to obtain C4-C7 hydrocarbons and water respectively. The liquid-liquid separation device 3 is provided with an organic liquid outlet 15, which is connected to the heat exchange medium inlet 11 of the gas-liquid separation device 2 through a pipeline, and the separated C4-C7 hydrocarbons are transported to the gas-liquid separation device 2 for indirect heat exchange. The olefin recycling conversion device 4, which is connected to the heat exchange medium outlet 12 of the gas-liquid separation device 2, is used to receive the C4-C7 hydrocarbons after indirect heat exchange, and under the action of the molecular sieve catalyst, the C4-C7 hydrocarbons react to obtain C2-C3 olefins. The olefin recycling conversion device 4 and the gas-gas separation device 5 are respectively provided with C2-C3 olefin outlet a17 and C2-C3 olefin outlet b19. The C2-C3 olefin outlet a17 and C2-C3 olefin outlet b19 are connected by a pipeline to combine the C2-C3 olefins. In addition, a water outlet 14 is provided at the bottom of the liquid-liquid separator 3 for discharging water from the mixed liquid 1 separated by the liquid-liquid separator 3; a gas outlet b20 is provided at the top of the gas-gas separator 5 for discharging the mixed gas 2 separated by the gas-gas separator 5.

[0034] Secondly, the present invention provides a method for directly preparing olefins from syngas. Figure 2 A flowchart of a method for directly preparing olefins from syngas according to an embodiment of the present invention is shown, as follows: Figure 2 As shown, it includes the following steps:

[0035] S1. Syngas is introduced into reaction device 1 through raw material gas inlet 6. Under the action of metal supported catalyst, the syngas reacts directly to obtain a mixture 1 containing C4-C7 hydrocarbons, C1-C3 hydrocarbons and CO2.

[0036] In this step, devices 1-5 are first connected to form a system. Then, syngas H2 and CO are introduced into reaction device 1. Under the catalysis of a metal-supported catalyst, H2 and CO react directly at a volume ratio of 1.25-2:1 to obtain a mixture 1 containing H2, CO, C4-C7 hydrocarbons, C1-C3 olefins, and CO2. In mixture 1, the CO conversion rate is 92-96%, and the olefin selectivity is 85-95%. The reactor in reaction device 1 is either a fixed bed or a fluidized bed. When the reactor in reaction device 1 is a fixed bed, the catalyst diameter is 0.3-6 mm, and the applicable syngas space velocity range is 1000-5000 ml / gcat / h. When the reactor in reaction device 1 is a fluidized bed, the catalyst diameter is 0.03-1 mm, and the applicable syngas space velocity range is 1000-16000 ml / gcat / h. The reaction apparatus 1 is filled with a metal-supported catalyst; the operating temperature of the metal catalyst is 250–350℃, and the operating pressure of the metal catalyst is 2–6 MPa; the metal catalyst consists of a metal component, a metal promoter, and a support; the metal component is one or more of iron, cobalt, zinc, and copper, with a mass fraction of 1–50%; the metal promoter is one or more of sodium, potassium, and calcium, with a mass fraction of 1–20%; the support is one of alumina, silicon dioxide, and carbon, with a mass fraction of 30–98% and a specific surface area of ​​50–2000 m². 2 / g.

[0037] S2. The mixture 1 is discharged from the product gas outlet 7 of the reaction device 1 and passed into the gas-liquid separation device 2 through the gas inlet a8 for cooling, so that the C4-C7 hydrocarbons and water vapor in it are liquefied and separated to obtain a mixed gas 1 containing C1-C3 hydrocarbons and CO2 and a mixed liquid 1 containing C4-C7 hydrocarbons and water, respectively.

[0038] In this specific step, the mixture 1 is introduced into the gas-liquid separation device 2 and cooled to 10-20℃. The C4-C7 hydrocarbons and water vapor in the mixture 1 are liquefied, and the gas and liquid are separated to obtain a mixed gas 1 containing C1-C3 hydrocarbons and CO2 and a mixed liquid 1 containing C4-C7 hydrocarbons and water, respectively.

[0039] S3. The mixed gas 1 is discharged from the gas outlet a9 of the gas-liquid separator 2 and passed into the gas-gas separator 5 through the gas inlet b18. The gas is separated to obtain C2-C3 olefins and mixed gas 2. The C2-C3 olefins are discharged from the C2-C3 hydrocarbon outlet b19. The remaining mixed gas 2 is discharged from the gas outlet b20 and recycled.

[0040] S4. The mixed liquid 1 is discharged from the liquid outlet 10 of the gas-liquid separator 2 and fed into the liquid-liquid separator 3 through the liquid inlet 13 for separation, obtaining C4-C7 hydrocarbons and water respectively; then the C4-C7 hydrocarbons are discharged from the organic liquid outlet 15 and fed into the separator 2 through the heat exchange medium inlet 11 for indirect heat exchange, and then discharged from the heat exchange medium outlet 12 and fed into the olefin recycling conversion device 4 through the organic matter inlet 16. Under the action of the molecular sieve catalyst, the C4-C7 hydrocarbons react to obtain C2-C3 olefins;

[0041] In this specific step, the mixed liquid 1 containing C4-C7 hydrocarbons and water is allowed to stand and separate into layers, yielding water and C4-C7 hydrocarbons. The C4-C7 hydrocarbons, acting as a heat exchange medium, enter the gas-liquid separation device 2 through the heat exchange medium inlet 11 for heat exchange. The heat-exchanged C4-C7 hydrocarbons are then fed into the fluidized bed or fixed bed reactor of the olefin recycling conversion device 4. Under conditions of 480-545℃, and with the action of a molecular sieve catalyst, the C4-C7 hydrocarbons are converted into C2-C3 olefins. The molecular sieve catalyst can be any one of the SAPO series and the MFI series, or a mixture of both.

[0042] S5. Combine the C2-C3 olefins discharged from the C2-C3 olefin outlet a17 of the olefin recycling converter 4 and the C2-C3 olefin outlet b19 of the gas-gas separator 5 for later use.

[0043] In this specific step, the C2-C3 olefins obtained from the olefin recycling unit 4 and the gas-gas separation unit 5 are combined at the pipeline junction.

[0044] This application provides a method for directly preparing olefins from syngas. A reaction apparatus is used to prepare hydrocarbons with a carbon number distribution of 1-7, followed by a separation device to separate C1-C3 and C4-C7 hydrocarbons. The C1-C3 hydrocarbons are then separated into C2-C3 olefins via a gas-to-gas separation device. The C4-C7 hydrocarbons are dehydrated via a liquid-to-liquid separation device, indirectly heated via a gas-to-liquid separation device, and then converted back into C2-C3 olefins via a hydrocarbon recycling conversion device. These C2-C3 olefins are then combined with the C2-C3 olefins obtained in the previous step and collected. Compared to the conventional route of preparing olefins from syngas via methanol, this application involves a two-step olefin preparation process, allowing for reasonable control of product distribution, significantly improving olefin selectivity to 85-95%, and increasing the syngas conversion rate to 96%. Furthermore, the entire preparation process is simple to operate, significantly reduces the number of devices, and substantially lowers production costs. In addition, the room-temperature C4-C7 hydrocarbons obtained through separation are indirectly heated with the high-temperature material from the reaction apparatus outlet in a separation device before being used for hydrocarbon recycling, resulting in a significant energy saving of 3%-5%.

[0045] To enable those skilled in the art to more clearly understand the present invention, the following embodiments will be used to provide a detailed description of a system and method for directly preparing olefins from syngas according to the present invention.

[0046] Example 1

[0047] Connect devices 1-5 to form a complete unit.

[0048] Syngas (CO and H2) is introduced into reaction unit 1 (using a fluidized bed reactor) through feed gas inlet 6. Under reaction conditions of 2 MPa and 280-350℃, a metal-supported catalyst (50% iron, 1% sodium, 49% alumina, with a support specific surface area of ​​50 m²) is used. 2 The catalyst diameter is 0.03-1 mm. The catalyst directly reacts with syngas to produce product gases (C1-C3 hydrocarbons, C4-C7 hydrocarbons, H2, CO, CO2). The syngas space velocity ranges from 1000-10000 ml / gcat / h, the volume ratio of H2 to CO is 1.5-2:1, the carbon number distribution of the resulting hydrocarbons is 1-7, the olefin selectivity is 90-95%, and the CO conversion rate is 92-96%. The product gases exit the reaction unit 1 from product gas outlet 7 and enter the gas-liquid separation unit 2 through gas inlet a8.

[0049] In the gas-liquid separation device 2, the temperature of the product gas is reduced to 10-20℃, causing H2O and C4-C7 hydrocarbons to liquefy into a mixed liquid 1, which is separated from the mixed gas 1 containing H2, CO, CO2 and C1-C3 hydrocarbons. The mixed liquid 1 (H2O, C4-C7 hydrocarbons) exits the gas-liquid separation device 2 from the liquid outlet 10; the mixed gas 1 (H2, CO, CO2 and C1-C3 hydrocarbons) exits the gas-liquid separation device 2 from the gas outlet a9.

[0050] The mixed liquid 1 (H2O, C4-C7 hydrocarbons) from the gas-liquid separator 2 enters the liquid-liquid separator 3 through the liquid inlet 13. The liquid phase is allowed to stand, allowing the H2O and C4-C7 hydrocarbons in the mixed liquid 1 to separate into layers. Water is discharged from the water outlet 14; the C4-C7 hydrocarbons exit the gas-liquid separator 3 through the organic liquid outlet 15.

[0051] The obtained C4-C7 hydrocarbons are used as a heat exchange medium and enter the gas-liquid separation unit 2 through the heat exchange medium inlet 11 for heat exchange. After heat exchange, the C4-C7 hydrocarbons exit the gas-liquid separation unit 2 through the heat exchange medium outlet 12 and are then fed into the olefin recycling conversion unit 4 (using a fluidized bed reactor) through the organic matter inlet 16. Under the action of a molecular sieve catalyst, they are converted into C2-C3 olefins at 480-545℃. The resulting C2-C3 olefin gas exits the olefin recycling conversion unit 4 through the C2-C3 olefin outlet a17.

[0052] Mixed gas 1 (H2, CO, CO2, and C1-C3 hydrocarbons) enters gas-gas separator 5 through gas inlet b18 for separation, yielding C2-C3 olefins and mixed gas 2 (H2, CO, CO2, CH4). Mixed gas 2 (H2, CO, CO2, CH4) exits gas-gas separator 5 through gas outlet b20 for further processing and recycling.

[0053] C2-C3 olefins are discharged from the C2-C3 olefin outlet b19 of the gas-gas separation unit 5. The C2-C3 streams from the C2-C3 olefin outlet b19 of the gas-gas separation unit 5 and the C2-C3 hydrocarbon outlet a17 of the olefin recycling unit 4 are combined and then separated for further processing.

[0054] Example 2:

[0055] Connect devices 1-5 to form a complete unit.

[0056] Syngas (CO and H2) is introduced into reaction unit 1 (using a fixed-bed reactor) through feed gas inlet 6. Under reaction conditions of 3 MPa and 300-350℃, a metal-supported catalyst (10% iron, 5% cobalt, 10% zinc, 20% sodium, 55% carbon, with a support specific surface area of ​​2000 m²) is used. 2 The catalyst diameter is 0.3-3 mm. The catalyst directly reacts with the syngas to produce product gases (C1-C3 hydrocarbons, C4-C7 hydrocarbons, H2, CO, CO2). The syngas space velocity ranges from 1000-2000 ml / gcat / h, the volume ratio of H2 to CO is 1.25-1.65:1, the carbon number distribution of the resulting hydrocarbons is 1-7, the olefin selectivity is 85-88%, and the CO conversion rate is 90-92%. The product gases exit the reaction unit 1 from product gas outlet 7 and enter the gas-liquid separation unit 2 through gas inlet a8.

[0057] In the gas-liquid separation device 2, the temperature of the product gas is reduced to 20-30℃, causing H2O and C4-C7 hydrocarbons to liquefy into a mixed liquid 1, which is separated from the mixed gas 1 containing H2, CO, CO2 and C1-C3 hydrocarbons. The mixed liquid 1 (H2O, C4-C7 hydrocarbons) exits the gas-liquid separation device 2 from the liquid outlet 10; the mixed gas 1 (H2, CO, CO2 and C1-C3 hydrocarbons) exits the gas-liquid separation device 2 from the gas outlet a9.

[0058] The mixed liquid 1 (H2O, C4-C7 hydrocarbons) from the gas-liquid separator 2 enters the liquid-liquid separator 3 through the liquid inlet 13. The liquid phase is allowed to stand, allowing the H2O and C4-C7 hydrocarbons in the mixed liquid 1 to separate into layers. Water is discharged from the water outlet 14; the C4-C7 hydrocarbons exit the gas-liquid separator 3 through the organic liquid outlet 15.

[0059] The obtained C4-C7 hydrocarbons are used as a heat exchange medium and enter the gas-liquid separation unit 2 through the heat exchange medium inlet 11 for heat exchange. After heat exchange, the C4-C7 hydrocarbons exit the gas-liquid separation unit 2 through the heat exchange medium outlet 12 and are then fed into the olefin recycling conversion unit 4 (using a fluidized bed reactor) through the organic matter inlet 16. Under the action of a molecular sieve catalyst (SAPO type molecular sieve), they are converted into C2-C3 olefins at 450-550℃. The resulting C2-C3 olefin gas exits the olefin recycling conversion unit 4 through the C2-C3 olefin outlet a17.

[0060] Mixed gas 1 (H2, CO, CO2, and C2-C3 hydrocarbons) enters gas-gas separator 5 through gas inlet b18 for separation, yielding C2-C3 olefins and mixed gas 2 (H2, CO, CO2, CH4). Mixed gas 2 (H2, CO, CO2, CH4) exits gas-gas separator 5 through gas outlet b20 for further processing and recycling.

[0061] C2-C3 olefins are discharged from the C2-C3 olefin outlet b19 of the gas-gas separation unit 5. The C2-C3 streams from the C2-C3 olefin outlet b19 of the gas-gas separation unit 5 and the C2-C3 hydrocarbon outlet a17 of the olefin recycling unit 4 are combined and then separated for further processing.

[0062] Example 3:

[0063] Connect devices 1-5 to form a complete unit.

[0064] Syngas CO and H2 are introduced into reaction unit 1 (using a fixed-bed reactor) through feed gas inlet 6. Under reaction conditions of 6 MPa and 350 °C, a metal-supported catalyst (35% iron, 15% copper, 2% sodium, 1% potassium, 47% carbon, with a support specific area of ​​1600 m²) is used. 2 / g, catalyst diameter 2-5mm. Catalytic synthesis gas reacts directly to produce product gases (C1-C3 hydrocarbons, C4-C7 hydrocarbons, H2, CO, CO2, CH4). The synthesis gas space velocity ranges from 3000-5000 ml / gcat / h, the volume ratio of H2 to CO is 2:1, the carbon number distribution of the resulting hydrocarbons is 1-7, with an olefin selectivity of 92-95% and a CO conversion rate of 95-96%. The product gases exit the reaction unit 1 from product gas outlet 7 and enter the gas-liquid separation unit 2 via gas inlet a8.

[0065] In the gas-liquid separation device 2, the temperature of the product gas is reduced to 15-20℃, causing H2O and C4-C7 hydrocarbons to liquefy into a mixed liquid 1, which is separated from the mixed gas 1 containing H2, CO, CO2 and C1-C3 hydrocarbons. The mixed liquid 1 (H2O, C4-C7 hydrocarbons) exits the gas-liquid separation device 2 from the liquid outlet 10; the mixed gas 1 (H2, CO, CO2 and C2-C3 hydrocarbons) exits the gas-liquid separation device 2 from the gas outlet a9.

[0066] The mixed liquid 1 (H2O, C4-C7 hydrocarbons) from the gas-liquid separator 2 enters the liquid-liquid separator 3 through the liquid inlet 13. The liquid phase is allowed to stand, allowing the H2O and C4-C7 hydrocarbons in the mixed liquid 1 to separate into layers. Water is discharged from the water outlet 14; the C4-C7 hydrocarbons exit the gas-liquid separator 3 through the organic liquid outlet 15.

[0067] The obtained C4-C7 hydrocarbons are used as a heat exchange medium and enter the gas-liquid separation unit 2 through the heat exchange medium inlet 11 for heat exchange. After heat exchange, the C4-C7 hydrocarbons exit the gas-liquid separation unit 2 through the heat exchange medium outlet 12 and are then fed into the olefin recycling conversion unit 4 (using a fluidized bed reactor) through the organic matter inlet 16. Under the action of molecular sieve catalysts (50% MFI type molecular sieve and 50% SAPO type molecular sieve), they are converted into C2-C3 olefins at 540-560℃. The resulting C2-C3 olefin gas exits the olefin recycling conversion unit 4 through the C2-C3 olefin outlet a17.

[0068] Mixed gas 1 (H2, CO, CO2, and C1-C3 hydrocarbons) enters gas-gas separator 5 through gas inlet b18 for separation, yielding C2-C3 olefins and mixed gas 2 (H2, CO, CO2, CH4). Mixed gas 2 (H2, CO, CO2, CH4) exits gas-gas separator 5 through gas outlet b20 for further processing and recycling.

[0069] C2-C3 olefins are discharged from the C2-C3 olefin outlet b19 of the gas-gas separation unit 5. The C2-C3 streams from the C2-C3 olefin outlet b19 of the gas-gas separation unit 5 and the C2-C3 hydrocarbon outlet a17 of the olefin recycling unit 4 are combined and then separated for further processing.

[0070] Example 4:

[0071] Connect devices 1-5 to form a complete unit.

[0072] Syngas (CO and H2) is introduced into reaction unit 1 (using a fixed-bed reactor) through feed gas inlet 6. Under reaction conditions of 4 MPa and 330 °C, a metal-supported catalyst (3% cobalt, 10% copper, 10% sodium, 77% carbon, with a support specific surface area of ​​1000 m²) is used. 2(The catalyst diameter is 2-6 mm.) Catalytic synthesis gas reacts directly to produce product gases (C1-C3 hydrocarbons, C4-C7 hydrocarbons, H2, CO, CO2). The synthesis gas space velocity ranges from 3000-5000 ml / gcat / h, the volume ratio of H2 to CO is 1.5:1, the carbon number distribution of the resulting hydrocarbons is 1-7, the olefin selectivity is 89-93.5%, and the CO conversion rate is 94.5-95.5%. The product gases exit the reaction unit 1 from product gas outlet 7 and enter the gas-liquid separation unit 2 through gas inlet a8.

[0073] In the gas-liquid separation device 2, the temperature of the product gas is reduced to 10-15℃, causing H2O and C4-C7 hydrocarbons to liquefy into a mixed liquid 1, which is then separated from the mixed gas 1 containing H2, CO, CO2 and C1-C3 hydrocarbons. The mixed liquid 1 (H2O, C4-C7 hydrocarbons) exits the gas-liquid separation device 2 from the liquid outlet 10; the mixed gas 1 (H2, CO, CO2 and C1-C3 hydrocarbons) exits the gas-liquid separation device 2 from the gas outlet a9.

[0074] The mixed liquid 1 (H2O, C4-C7 hydrocarbons) from the gas-liquid separator 2 enters the liquid-liquid separator 3 through the liquid inlet 13. The liquid phase is allowed to stand, allowing the H2O and C4-C7 hydrocarbons in the mixed liquid 1 to separate into layers. Water is discharged from the water outlet 14; the C4-C7 hydrocarbons exit the gas-liquid separator 3 through the organic liquid outlet 15.

[0075] The obtained C4-C7 hydrocarbons are used as a heat exchange medium and enter the gas-liquid separation unit 2 through the heat exchange medium inlet 11 for heat exchange. After heat exchange, the C4-C7 hydrocarbons exit the gas-liquid separation unit 2 through the heat exchange medium outlet 12 and are then fed into the olefin recycling conversion unit 4 (using a fluidized bed reactor) through the organic matter inlet 16. Under the action of a molecular sieve catalyst (MFI type molecular sieve), they are converted into C2-C3 olefins at 520-580℃. The resulting C2-C3 olefin gas exits the olefin recycling conversion unit 4 through the C2-C3 olefin outlet a17.

[0076] Mixed gas 1 (H2, CO, CO2, and C1-C3 hydrocarbons) enters gas-gas separator 5 through gas inlet b18 for separation, yielding C2-C3 olefins and mixed gas 2 (H2, CO, CO2, CH4). Mixed gas 2 (H2, CO, CO2, CH4) exits gas-gas separator 5 through gas outlet b20 for further processing and recycling.

[0077] C2-C3 olefins are discharged from the C2-C3 olefin outlet b19 of the gas-gas separation unit 5. The C2-C3 streams from the C2-C3 olefin outlet b19 of the gas-gas separation unit 5 and the C2-C3 hydrocarbon outlet a17 of the olefin recycling unit 4 are combined and then separated for further processing.

[0078] Example 5

[0079] Connect devices 1-5 to form a complete unit.

[0080] Syngas (CO and H2) is introduced into reaction unit 1 (using a fixed-bed reactor) through feed gas inlet 6. The reaction is carried out under reaction conditions of 2.6 MPa and 340-350 °C, using a metal-supported catalyst (30% iron, 20% zinc, 1.75% sodium, 0.5% calcium, 48% silica, with a specific surface area of ​​260 m²). 2 (The catalyst diameter is 3-6 mm.) Catalytic synthesis gas reacts directly to produce product gases (C1-C3 hydrocarbons, C4-C7 hydrocarbons, H2, CO, CO2). The synthesis gas space velocity ranges from 3000-5000 ml / gcat / h, the volume ratio of H2 to CO is 1.75:1, the carbon number distribution of the resulting hydrocarbons is 1-7, the olefin selectivity is 92-95%, and the CO conversion rate is 95-96%. The product gases exit the reaction unit 1 from product gas outlet 7 and enter the gas-liquid separation unit 2 through gas inlet a8.

[0081] In the gas-liquid separation device 2, the temperature of the product gas is reduced to 10-15℃, causing H2O and C4-C7 hydrocarbons to liquefy into a mixed liquid 1, which is separated from the mixed gas 1 containing H2, CO, CO and C1-C3 hydrocarbons. The mixed liquid 1 (H2O, C4-C7 hydrocarbons) exits the gas-liquid separation device 2 from the liquid outlet 10; the mixed gas 1 (H2, CO, CO2 and C1-C3 hydrocarbons) exits the gas-liquid separation device 2 from the gas outlet a9.

[0082] The mixed liquid 1 (H2O, C4-C7 hydrocarbons) from the gas-liquid separator 2 enters the liquid-liquid separator 3 through the liquid inlet 13. The liquid phase is allowed to stand, allowing the H2O and C4-C7 hydrocarbons in the mixed liquid 1 to separate into layers. Water is discharged from the water outlet 14; the C4-C7 hydrocarbons exit the gas-liquid separator 3 through the organic liquid outlet 15.

[0083] The obtained C4-C7 hydrocarbons are used as a heat exchange medium and enter the gas-liquid separation unit 2 through the heat exchange medium inlet 11 for heat exchange. After heat exchange, the C4-C7 hydrocarbons exit the gas-liquid separation unit 2 through the heat exchange medium outlet 12 and are then fed into the olefin recycling conversion unit 4 (using a fluidized bed reactor) through the organic matter inlet 16. Under the action of a molecular sieve catalyst (MFI type molecular sieve), they are converted into C2-C3 olefins at 480-550℃. The resulting C2-C3 olefin gas exits the olefin recycling conversion unit 4 through the C2-C3 olefin outlet a17.

[0084] Mixed gas 1 (H2, CO, CO2, and C1-C3 hydrocarbons) enters gas-gas separator 5 through gas inlet b18 for separation, yielding C2-C3 olefins and mixed gas 2 (H2, CO, CO2, CH4). Mixed gas 2 (H2, CO, CO2, CH4) exits gas-gas separator 5 through gas outlet b20 for further processing and recycling.

[0085] C2-C3 olefins are discharged from the C2-C3 olefin outlet b19 of the gas-gas separation unit 5. The C2-C3 streams from the C2-C3 olefin outlet b19 of the gas-gas separation unit 5 and the C2-C3 hydrocarbon outlet a17 of the olefin recycling unit 4 are combined and then separated for further processing.

[0086] Example 6

[0087] Connect devices 1-5 to form a complete unit.

[0088] Syngas (CO and H2) is introduced into reaction unit 1 (using a fluidized bed reactor) through feed gas inlet 6. The reaction is carried out under reaction conditions of 2.5 MPa and 300-330 °C, using a metal-supported catalyst (15% iron, 3% cobalt, 1% potassium, 71% carbon, with a specific area of ​​600 m²). 2 / g, catalyst diameter 0.1-0.25mm. Catalytic synthesis gas reacts directly to produce product gases (C1-C3 hydrocarbons, C4-C7 hydrocarbons, H2, CO, CO2). The synthesis gas space velocity ranges from 1000-2500 ml / gcat / h, the volume ratio of H2 to CO is 1.5-1.8:1, the carbon number distribution of the resulting hydrocarbons is 1-7, with an olefin selectivity of 88-91.5% and a CO conversion rate of 94-96%. The product gas exits the reaction unit 1 from product gas outlet 7 and enters the gas-liquid separation unit 2 via gas inlet a8.

[0089] In the gas-liquid separation device 2, the temperature of the product gas is reduced to 12-18℃, causing H2O and C4-C7 hydrocarbons to liquefy into a mixed liquid 1, which is separated from the mixed gas 1 containing H2, CO, CO2 and C1-C3 hydrocarbons. The mixed liquid 1 (H2O, C4-C7 hydrocarbons) exits the gas-liquid separation device 2 from the liquid outlet 10; the mixed gas 1 (H2, CO, CO2 and C1-C3 hydrocarbons) exits the gas-liquid separation device 2 from the gas outlet a9.

[0090] The mixed liquid 1 (H2O, C4-C7 hydrocarbons) from the gas-liquid separator 2 enters the liquid-liquid separator 3 through the liquid inlet 13. The liquid phase is allowed to stand, allowing the H2O and C4-C7 hydrocarbons in the mixed liquid 1 to separate into layers. Water is discharged from the water outlet 14; the C4-C7 hydrocarbons exit the gas-liquid separator 3 through the organic liquid outlet 15.

[0091] The obtained C4-C7 hydrocarbons are used as a heat exchange medium and enter the gas-liquid separation unit 2 through the heat exchange medium inlet 11 for heat exchange. After heat exchange, the C4-C7 hydrocarbons exit the gas-liquid separation unit 2 through the heat exchange medium outlet 12 and are then fed into the olefin recycling conversion unit 4 (using a fluidized bed reactor) through the organic matter inlet 16. Under the action of molecular sieve catalysts (80% MFI type molecular sieve and 20% SAPO type molecular sieve), they are converted into C2-C3 olefins at 550-600℃. The resulting C2-C3 olefin gas exits the olefin recycling conversion unit 4 through the C2-C3 olefin outlet a17.

[0092] Mixed gas 1 (H2, CO, CO2, and C1-C3 hydrocarbons) enters gas-gas separator 5 through gas inlet b18 for separation, yielding C2-C3 olefins and mixed gas 2 (H2, CO, CO2, CH4). Mixed gas 2 (H2, CO, CO2, CH4) exits gas-gas separator 5 through gas outlet b20 for further processing and recycling.

[0093] C2-C3 olefins are discharged from the C2-C3 olefin outlet b19 of the gas-gas separation unit 5. The C2-C3 streams from the C2-C3 olefin outlet b19 of the gas-gas separation unit 5 and the C2-C3 hydrocarbon outlet a17 of the olefin recycling unit 4 are combined and then separated for further processing.

[0094] Example 7

[0095] Connect devices 1-5 to form a complete unit.

[0096] Syngas (CO and H2) is introduced into reaction unit 1 (using a fluidized bed reactor) through feed gas inlet 6. Under reaction conditions of 3 MPa and 310-340℃, a metal-supported catalyst (1% iron, 20% sodium, 79% carbon, with a specific surface area of ​​800 m²) is used. 2 The catalyst (with a diameter of 0.03-0.15 mm) directly reacts with syngas to produce product gases (C1-C3 hydrocarbons, C4-C7 hydrocarbons, H2, CO, CO2). The syngas space velocity ranges from 1000-1600 ml / gcat / h, the volume ratio of H2 to CO is 1.5-2:1, the carbon number distribution of the resulting hydrocarbons is 1-7, the olefin selectivity is 85-87%, and the CO conversion rate is 94-96%. The product gases exit the reaction unit 1 from product gas outlet 7 and enter the gas-liquid separation unit 2 through gas inlet a8.

[0097] In the gas-liquid separation device 2, the temperature of the product gas is reduced to 15-20℃, causing H2O and C4-C7 hydrocarbons to liquefy into a mixed liquid 1, which is separated from the mixed gas 1 containing H2, CO, CO2 and C1-C3 hydrocarbons. The mixed liquid 1 (H2O, C4-C7 hydrocarbons) exits the gas-liquid separation device 2 from the liquid outlet 10; the mixed gas 1 (H2, CO, CO2 and C1-C3 hydrocarbons) exits the gas-liquid separation device 2 from the gas outlet a9.

[0098] The mixed liquid 1 (H2O, C4-C7 hydrocarbons) from the gas-liquid separator 2 enters the liquid-liquid separator 3 through the liquid inlet 13. The liquid phase is allowed to stand, allowing the H2O and C4-C7 hydrocarbons in the mixed liquid 1 to separate into layers. Water is discharged from the water outlet 14; the C4-C7 hydrocarbons exit the gas-liquid separator 3 through the organic liquid outlet 15.

[0099] The obtained C4-C7 hydrocarbons are used as a heat exchange medium and enter the gas-liquid separation unit 2 through the heat exchange medium inlet 11 for heat exchange. After heat exchange, the C4-C7 hydrocarbons exit the gas-liquid separation unit 2 through the heat exchange medium outlet 12 and are then fed into the olefin recycling conversion unit 4 (using a fluidized bed reactor) through the organic matter inlet 16. Under the action of molecular sieve catalysts (40% MFI type molecular sieve and 60% SAPO type molecular sieve), they are converted into C2-C3 olefins at 520-550℃. The resulting C2-C3 olefin gas exits the olefin recycling conversion unit 4 through the C2-C3 olefin outlet a17.

[0100] Mixed gas 1 (H2, CO, CO2, and C1-C3 hydrocarbons) enters gas-gas separator 5 through gas inlet b18 for separation, yielding C2-C3 olefins and mixed gas 2 (H2, CO, CO2, CH4). Mixed gas 2 (H2, CO, CO2, CH4) exits gas-gas separator 5 through gas outlet b20 for further processing and recycling.

[0101] C2-C3 olefins are discharged from the C2-C3 olefin outlet b19 of the gas-gas separation unit 5. The C2-C3 streams from the C2-C3 olefin outlet b19 of the gas-gas separation unit 5 and the C2-C3 hydrocarbon outlet a17 of the olefin recycling unit 4 are combined and then separated for further processing.

[0102] This application provides a method for directly preparing olefins from syngas. A reaction apparatus is used to prepare hydrocarbons with a carbon number distribution of 1-7, which are then separated using a gas-liquid separator to obtain C1-C3 and C4-C7 hydrocarbons. The C1-C3 hydrocarbons are then separated using a gas-gas separator to obtain C2-C3 olefins. The C4-C7 hydrocarbons are dehydrated using a liquid-liquid separator, indirectly heated by a gas-liquid separator, and then converted back to C2-C3 olefins by a hydrocarbon recycling converter. These C2-C3 olefins are then combined with the C2-C3 olefins obtained in the previous step and collected. As can be seen from Examples 1-7, this method can reasonably control the product distribution, significantly improving the olefin selectivity to 85-95%. Furthermore, the entire preparation process is simple to operate, the number of devices is greatly reduced, and production costs are significantly lowered, demonstrating potential for practical application.

[0103] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0104] For the sake of simplicity, the method embodiments are described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0105] The above provides a detailed description of the system and method for directly preparing olefins from syngas provided by the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A system for directly preparing olefins from syngas, characterized in that, The system includes: a reaction device (1) for reacting the synthesis gas directly under the action of a metal-supported catalyst to obtain a mixture 1 containing C4-C7 hydrocarbons, C1-C3 hydrocarbons and CO2; A gas-liquid separation device (2) connected to the product gas outlet (7) of the reaction device (1) is used to cool the mixed substance 1 discharged from the reaction device (1), so that the C4-C7 hydrocarbons and water vapor therein are liquefied and separated to obtain a mixed gas 1 containing C1-C3 hydrocarbons and CO2 and a mixed liquid 1 containing C4-C7 hydrocarbons and water, respectively. A gas-gas separation device (5) connected to the gas outlet (9) of the separation device (2) is used to separate the mixed gas 1 discharged from the separation device (2) to obtain C2-C3 olefins and mixed gas 2 respectively; the mixed gas 2 contains unreacted synthesis gas, CO2 and CH4; The liquid-liquid separation device (3) connected to the liquid outlet (10) of the separation device (2) is used to separate the mixed liquid 1 discharged from the gas-liquid separation device (2) to obtain C4-C7 hydrocarbons and water respectively; the liquid-liquid separation device (3) is provided with an organic liquid outlet (15), which is connected to the heat exchange medium inlet (11) of the gas-liquid separation device (2) through a pipeline, and transports the separated C4-C7 hydrocarbons to the gas-liquid separation device (2) for indirect heat exchange; The olefin recycling conversion device (4) is connected to the heat exchange medium outlet (12) of the gas-liquid separation device (2) to receive C4-C7 hydrocarbons after indirect heat exchange, and under the action of molecular sieve catalyst, the C4-C7 hydrocarbons react to obtain C2-C3 olefins. The olefin recycling conversion unit (4) and the gas-gas separation unit (5) are respectively equipped with C2-C3 olefin outlet a (17) and C2-C3 olefin outlet b (19); the C2-C3 olefin outlet a (17) and C2-C3 olefin outlet b (19) are connected by a pipeline to combine the C2-C3 olefins generated in the two-step reaction. The liquid-liquid separation device (3) is provided with a drain outlet (14) at the bottom for draining the water in the mixed liquid 1 separated by the liquid-liquid separation device (3); The separated room-temperature C4-C7 hydrocarbons are indirectly heated in the separation device (2) with the high-temperature material at the outlet of the reaction device (1), and then used for hydrocarbon recycling conversion.

2. The system according to claim 1, characterized in that, The gas-gas separator (5) is provided with a gas outlet b (20) at the top for discharging the mixed gas 2 separated by the gas-gas separator (5).

3. A method for directly preparing olefins from syngas, applied to the system described in any one of claims 1-2, characterized in that, Includes the following steps: S1. Syngas is introduced into the reaction device (1) through the raw material gas inlet (6). Under the action of the metal supported catalyst, the syngas reacts directly to obtain a mixture 1 containing C4-C7 hydrocarbons, C1-C3 hydrocarbons and CO2. S2. The mixture 1 is discharged from the product gas outlet (7) of the reaction device (1) and passed through the gas inlet a (8) into the gas-liquid separation device (2) for cooling, so that the C4-C7 hydrocarbons and water vapor in it are liquefied and separated to obtain a mixture gas 1 containing C1-C3 hydrocarbons and CO2 and a mixture liquid 1 containing C4-C7 hydrocarbons and water respectively. S3. Discharge the mixed gas 1 from the gas outlet a (9) of the gas-liquid separator (2), and pass it into the gas-gas separator (5) through the gas inlet b (18) for separation to obtain C2-C3 olefins and mixed gas 2 respectively; the C2-C3 olefins are discharged from the C2-C3 hydrocarbon outlet b (19); the remaining mixed gas 2 is discharged from the gas outlet b (20) for recycling; S4. Mixed liquid 1 is discharged from the liquid outlet (10) of the gas-liquid separation device (2) and passed into the liquid-liquid separation device (3) through the liquid inlet (13) for separation, obtaining C4-C7 hydrocarbons and water respectively; then the C4-C7 hydrocarbons are discharged from the organic liquid outlet (15) and passed into the separation device (2) through the heat exchange medium inlet (11) for indirect heat exchange, and then discharged from the heat exchange medium outlet (12) and passed into the olefin recycling conversion device (4) through the organic matter inlet (16). Under the action of the molecular sieve catalyst, the C4-C7 hydrocarbons react to obtain C2-C3 olefins; S5. Combine the C2-C3 olefins discharged from the C2-C3 olefin outlet a (17) of the olefin recycling converter (4) and the C2-C3 olefin outlet b (19) of the gas-gas separator (5) for later use.

4. The method according to claim 3, characterized in that, In step S1, the reactor of the reaction device (1) is a fixed bed or a fluidized bed; when the reactor of the reaction device (1) is a fixed bed, the diameter of the catalyst in the fixed bed is 0.3-6 mm, and the applicable syngas space velocity range is 1000-5000 ml / gcat / h; when the reactor of the reaction device (1) is a fluidized bed, the diameter of the catalyst in the fluidized bed is 0.03-1 mm, and the applicable syngas space velocity range is 1000-16000 ml / gcat / h.

5. The method according to claim 3, characterized in that, In step S1, the reaction device (1) is filled with a metal-supported catalyst; the operating temperature of the metal-supported catalyst is 250~350 ℃; and the operating pressure of the metal-supported catalyst is 2-6 MPa.

6. The method according to claim 3 or 4, characterized in that, In step S1, the metal component of the metal-supported catalyst is one or at least two of iron, cobalt, zinc, and copper; the metal promoter of the metal-supported catalyst is one or at least two of sodium, potassium, and calcium; and the support of the metal-supported catalyst is one of alumina, silicon oxide, and carbon.

7. The method according to claim 6, characterized in that, In step S1, the mass fraction of the metal component is 1-50%; the mass fraction of the metal promoter is 1-20%; the mass fraction of the support for the metal-supported catalyst is 30-98%; and the specific surface area of ​​the support for the metal-supported catalyst is 50-2000 m². 2 / g.

8. The method according to claim 3, characterized in that, In step S1, the synthesis gas is H2 and CO; the volume ratio of H2 to CO is 1.25-2:1; and the olefin selectivity in the mixture 1 is 85-95%.

9. The method according to claim 3, characterized in that, In step S5, the olefin recycling conversion device (4) is filled with molecular sieve catalyst for converting C4-C7 hydrocarbons into C2-C3 olefins; the molecular sieve catalyst is any one of the SAPO series and MFI series or a mixture of the two series.

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