Carbon dioxide-to-aromatic hydrocarbon raw material circulation process method and separation system thereof

Abstract

The invention belongs to the field of chemical separation and purification, and discloses a circulating process method for preparing an aromatic hydrocarbon raw material from carbon dioxide and a separation system thereof. The process system comprises a hydrogenation reactor, a high-pressure separator, an oil-water separator, a desorption tower, a light component removal tower and an absorption tower. A raw material is a gas-phase mixture of carbon dioxide and hydrogen, the raw material is subjected to reaction phase splitting to obtain a mixture of non-aromatic hydrocarbon, light aromatic hydrocarbon and heavy aromatic hydrocarbon, the mixture is separated by an absorption-desorption unit to obtain liquid-phase aromatic hydrocarbon-rich oil, the liquid-phase aromatic hydrocarbon-rich oil enters an aromatic hydrocarbon extraction system, and a gas-phase part returns to the front end of a reactor to form a raw material gas circulation system. According to the method, the aromatic hydrocarbon-rich oil is used as the absorbent, so that the feed gas and the light hydrocarbon are efficiently separated, and the specific gravity of the light hydrocarbon in the circulating raw material in the process of preparing the aromatic hydrocarbon through CO2 hydrogenation is greatly reduced, thereby reducing the overall energy consumption of raw material circulation and flow.

Description

Technical Field

[0001] The invention belongs to the field of chemical separation and purification, and specifically relates to a carbon dioxide to aromatics raw material circulation process method and a separation system thereof. Background Art

[0002] Aromatics, hydrocarbons with ring structures and specific chemical properties, play an important role in energy, chemical industry, medicine, agriculture and daily life, and are indispensable chemical products in modern industry and life. The capture and utilization of CO2 has received much attention. On the one hand, CO2 hydrogenation to aromatics can turn waste into treasure and realize the resource utilization of greenhouse gases. On the other hand, it can provide a green and low-carbon route for the synthesis of high-value chemical aromatics. However, the existing CO2 hydrogenation technology to aromatics has bottlenecks such as low activation efficiency and selectivity, and high energy consumption. It is urgent to develop CO2 hydrogenation technology to produce high-efficiency aromatics.

[0003] CO2 hydrogenation to aromatics is a highly promising aromatics production process developed in recent years. Domestic and foreign scholars have conducted relevant research on the reaction routes, catalysts, reactors, separation and applications involved in the production of light aromatics by CO2 hydrogenation. The current mainstream process routes are direct synthesis routes and indirect synthesis routes. In the early days, a composite catalyst composed of an iron-based FTS synthesis catalyst and HZSM-5 zeolite was used to conduct experiments on the direct synthesis of aromatics by CO2 hydrogenation in a single-stage reactor. The experimental results showed that the conversion rate of CO2 was 38%, and the selectivity of aromatics was as high as 21.4% (excluding CO). At present, the synthesis of aromatic compounds by CO2 hydrogenation can be achieved through two different pathways: CO2-FTS and CO2-MeOH.

[0004] In terms of raw material recycling, the materials that need to be recycled in the CO2 hydrogenation product mainly include CO2, CO and H2. The existing raw material recycling technology is mainly based on multi-stage condensation, and the gas from the equilibrium flash is directly recycled back to the reactor for repeated use. In addition to the raw gas, the circulating gas also contains a large amount of C1-C5 light hydrocarbons, and mainly alkanes, which are not only difficult to participate in the aromatization reaction, but also greatly increase the flow rate of the circulating stream, thereby causing problems such as increased volume of reaction and separation equipment and increased energy consumption. Most of the liquid phase obtained by multi-stage condensation is the target product aromatics, but there is also a certain amount of alkanes and cycloalkanes, which restricts the large-scale application and promotion of the process.

[0005] Therefore, providing a process and system for efficiently separating and recycling raw gas and light hydrocarbons has become a technical problem that urgently needs to be solved in the field. Summary of the invention

[0006] In order to overcome the shortcomings of the prior art, the present invention provides a carbon dioxide to aromatics raw material circulation process method and a separation system thereof, which realizes the efficient separation of raw gas and light hydrocarbons, greatly reduces the circulation gas flow rate, and thus reduces the energy consumption of the entire separation system.

[0007] The technical solution adopted by the present invention to solve the technical problem is:

[0008] On the one hand, the present invention provides a carbon dioxide to aromatics raw material circulation process, the steps are as follows:

[0009] The mixed gas of carbon dioxide and hydrogen is mixed with the circulating raw gas after heat exchange and enters the hydrogenation reactor for reaction;

[0010] The reaction product of the hydrogenation reactor is sent to a high-pressure separator after heat exchange with fresh feed gas to separate the purge gas and oil-water mixture, and the oil-water mixture enters an oil-water separator to separate the oil phase hydrocarbon mixture and process wastewater;

[0011] The oil phase hydrocarbon mixture separated by the oil-water separator enters the desorption tower, and the light hydrocarbons with carbon content of 3 or above are removed and mixed with the purge gas as the raw gas to be recycled and sent to the bottom of the absorption tower. The aromatics-rich oil in the bottom of the tower is cooled and sent to the lightness removal tower;

[0012] The light hydrocarbon removal tower removes light hydrocarbons, and the by-product liquefied petroleum gas at the top of the tower is sent to the storage area. After cooling, part of the aromatic hydrocarbon-rich oil in the bottom of the tower is sent to the tank area for storage as an aromatic hydrocarbon product, and part is sent to the absorption tower as an absorbent;

[0013] The relaxation gas produced by the high-pressure separator and the gaseous product from the top of the desorber are mixed and enter the bottom of the absorber. The light hydrocarbons are recovered using the aromatics-rich oil in the bottom of the desorber as solvent. Most of the raw gas from the top of the absorber is sent to the front end of the reactor for circulation, and the aromatics-rich oil in the bottom of the tower is sent to the desorber for circulation.

[0014] Further, carbon dioxide and hydrogen are fed in a mass ratio of 3.5-4:1, mixed with the circulating raw gas after preheating, and enter the hydrogenation reactor for reaction, and the raw material preheating is controlled at 180-200°C;

[0015] Furthermore, the conditions of the hydrogenation reactor are: the reaction temperature is 280-320°C.

[0016] Furthermore, the separation operating pressure of the high-pressure separator and the oil-water separator is 2.8-3.0 MPa, and the operating temperature is 35-40°C.

[0017] Furthermore, the operating pressure of the hydrogenation reactor, the desorption tower and the absorption tower is 2.8-3.0 MPa, and the operating pressure of the lightness removal tower is 0.25-0.3 MPa.

[0018] Furthermore, most of the raw gas from the top of the absorption tower is sent to the front end of the reactor for circulation, and the bottom product is sent to the desorption tower for circulation. The raw gas circulation ratio is 0.855-0.865.

[0019] On the other hand, the present invention provides a separation system for realizing the carbon dioxide to aromatics raw material circulation process method, comprising a hydrogenation reactor, a high-pressure separator, an oil-water separator, a desorber, a light-removal tower, and an absorption tower, wherein the hydrogenation reactor has a raw material inlet, the desorber and the light-removal tower both have an upper inlet and a middle inlet, the absorption tower has an upper inlet and a lower inlet, the bottom extraction pipeline of the hydrogenation reactor is connected to the inlet of the high-pressure separator, the bottom extraction pipeline of the high-pressure separator is connected to the inlet of the oil-water separator, the oil phase extraction pipeline of the oil-water separator is connected to the upper inlet of the desorber, and the top gas phase extraction pipelines of the high-pressure separator and the desorber are both connected to the To the lower inlet of the absorption tower; a desorption tower product cooler is arranged on the middle inlet pipeline of the lightness removal tower, and a lightness removal tower kettle production pump, an absorption tower product cooler and an absorption tower kettle production pump are arranged at the bottom of the tower. The bottom production pipeline of the desorption tower is connected to the middle inlet of the lightness removal tower after passing through the desorption tower product cooler, and the bottom production pipeline of the lightness removal tower passes through the lightness removal tower kettle production pump and the absorption tower product cooler in turn and is divided into two routes, one is used as the production pipeline of aromatics-rich oil, and the other is connected to the upper inlet of the absorption tower, and the bottom production pipeline of the absorption tower passes through the absorption tower product cooler, the absorption tower kettle production pump and the desorption tower product cooler in turn and enters the middle inlet of the desorption tower.

[0020] Furthermore, a raw material preheater and a raw material heater are sequentially arranged on the raw material inlet pipeline of the hydrogenation reactor.

[0021] Furthermore, a reaction product cooler and a reaction product condenser are sequentially arranged on the inlet pipeline of the high-pressure separator.

[0022] Furthermore, the bottom extraction pipeline of the hydrogenation reactor passes through the raw material heater, the reaction product cooler, and the reaction product condenser in sequence and then enters the high-pressure separator.

[0023] Furthermore, the extraction pipeline at the top of the absorption tower passes through a reaction product cooler and a raw material heater and then enters a hydrogenation reactor.

[0024] Furthermore, a light-removal tower top condenser is disposed at the top of the light-removal tower, and the light-removal tower top gas phase production pipeline is divided into two paths after passing through the light-removal tower top condenser, one path being used as a light hydrocarbon production pipeline, and the other path returning to the upper inlet of the light-removal tower.

[0025] Furthermore, the desorption tower and the lightness removal tower are respectively provided with a desorption tower kettle reboiler and a lightness removal tower kettle reboiler at the bottom.

[0026] Furthermore, a wastewater outlet is provided at the bottom of the oil-water separator.

[0027] Advantages and beneficial effects of the present invention:

[0028] The present invention constructs an absorption-desorption coupling separation system with the bottom liquid phase of a light hydrocarbon removal tower as a circulating absorbent, and utilizes a rich aromatic hydrocarbon mixture as an absorbent to absorb the circulating raw gas, thereby effectively reducing the light hydrocarbon content in the raw gas, so that the circulating raw gas contains only a small amount of C1 and C2 light hydrocarbon substances in addition to CO2, H2 and CO; the light hydrocarbons are removed from the absorption liquid through the desorption process, thereby achieving the by-product of liquefied petroleum gas in the process, and the optimized process reduces equipment investment and energy consumption, and improves the economy of the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic structural diagram of the separation system of the carbon dioxide to aromatics raw material circulation process of the present invention.

[0030] The reference numerals are as follows:

[0031] 1-raw material preheater; 2-raw material heater; 3-reaction product cooler; 4-reaction product condenser; 5-hydrogenation reactor; 6-high-pressure separator; 7-oil-water separator; 8-desorption tower; 9-desorption tower kettle reboiler; 10-desorption tower product cooler; 11-light removal tower top condenser; 12-light removal tower; 13-light removal tower kettle output pump; 14-light removal tower kettle reboiler; 15-absorption tower kettle output pump; 16-absorption tower; 17-absorption tower product cooler. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0033] Through in-depth analysis of the reaction characteristics and product composition of the process reaction system and reactor form of the carbon dioxide to aromatics feedstock circulation, CO2, CO, and H2 in the product are defined as raw gas that needs to be circulated, C3 and C4 are defined as liquefied petroleum gas products, and C5+ aliphatic hydrocarbon components are defined as non-aromatic products; for aromatic components, benzene, toluene, and xylene are determined as target products, and the others are mixed aromatics; according to the distribution of gas-liquid two-phase composition after cooling of the reaction product, a carbon dioxide to aromatics feedstock circulation process method and a separation system with absorption-desorption coupled separation are provided.

[0034] In the embodiment of the present invention, the raw material heater 2, the reaction product cooler 3, the desorption tower product cooler 10, the delightening tower top condenser 11 and the absorption tower product cooler 17 all use stream heat exchangers, and the hot stream is specified to go through the shell process, and the outlet temperature of the cold stream is 200°C. Heat exchange is performed between the reactor product stream and the raw material feed stream to increase the temperature of the raw material feed stream and reduce the energy consumption of the whole process.

[0035] Example 1

[0036] A carbon dioxide to aromatics raw material recycling process method, the steps are as follows:

[0037] Carbon dioxide and hydrogen raw materials are fed in a mass ratio of 4:1, preheated in the raw material preheater 1, mixed with the circulating raw material gas, and then heat-exchanged in the raw material heater 2 before entering the hydrogenation reactor 5 for reaction. The raw material preheating is controlled at 200°C. The conditions of the hydrogenation reactor 5 are: reaction temperature of 320°C and pressure of 3.0MPa.

[0038] The reaction product of the hydrogenation reactor 5 is sent to the high-pressure separator 6 after heat exchange with the fresh raw gas in the raw material heater 2 to separate the relaxation gas and the oil-water mixture. The oil-water mixture enters the oil-water separator 7 to separate the oil phase hydrocarbon mixture and process waste water. The operating pressure of the high-pressure separator 6 and the oil-water separator 7 is 3.0 MPa, and the operating temperature is 40°C.

[0039] The oil phase hydrocarbon mixture separated from the oil-water separator 7 enters the desorption tower 8, and the light hydrocarbons with carbon content of 3 or above are removed and mixed with the relaxation gas of the high-pressure separator 6 as the raw gas to be recycled and sent to the bottom of the absorption tower 16. The aromatics-rich oil in the bottom of the tower is cooled and sent to the lightness removal tower 12. The operating pressure of the desorption tower 8 is 3.0MPa.

[0040] The light hydrocarbon removal tower 12 is used to remove light hydrocarbons. The by-product liquefied petroleum gas at the top of the tower is sent to the storage area. After cooling, part of the aromatic hydrocarbon-rich oil in the bottom of the tower is sent to the tank area for storage as an aromatic hydrocarbon product, and part is sent to the absorption tower 16 as an absorbent. The operating pressure of the light hydrocarbon removal tower 12 is 0.3MPa.

[0041] The purge gas extracted from the high-pressure separator 7 and the top product of the desorber 8 are mixed and enter the bottom of the absorption tower 16. The light hydrocarbons are recovered using the aromatic oil-rich oil of the light removal tower 12 as an absorbent. Most of the top feed gas is sent to the front end of the reactor for circulation, and the bottom product is sent to the desorber 8 for circulation. The operating pressure of the absorption tower 16 is 3.0 MPa.

[0042] The gas-liquid two phases of the absorption tower 16 are in countercurrent contact in the tower, and the top feed gas is circulated back to the reactor to participate in the feed conversion, with a circulation ratio of 0.865, and all the bottom products are circulated back to the desorption tower 8. The content of light hydrocarbons with carbon 3 and above in the top circulating feed gas is reduced to 3.2%, which is 58.5% lower than that of the initial feed gas to be circulated; the aromatics production is increased by 4.6 times.

[0043] Example 2

[0044] The difference between this embodiment and implementation 1 is that the raw material preheating is controlled at 220°C and the raw material circulation ratio is 0.76; the content of light hydrocarbons with carbon 3 and above in the top circulating raw gas can be reduced to 5.7%, which is 60.7% lower than the initial raw gas to be circulated; the aromatics output is increased by 4.4 times.

[0045] Example 3

[0046] The difference between this embodiment and implementation 1 is that the raw material preheating is controlled at 240°C and the raw material circulation ratio is 0.64; the content of light hydrocarbons with carbon 3 and above in the top circulating raw gas can be reduced to 5.3%, which is 50.1% lower than the initial raw gas to be circulated; the aromatics output is increased by 4.1 times.

[0047] Example 4

[0048] A separation system for implementing the carbon dioxide to aromatics raw material circulation process method of embodiments 1 to 3 includes a hydrogenation reactor 5, a high-pressure separator 6, an oil-water separator 7, a desorption tower 8, a light removal tower 12, and an absorption tower 16. The hydrogenation reactor 5 has a raw material inlet, the desorption tower 8 and the light removal tower 12 both have an upper inlet and a middle inlet, and the absorption tower 16 has an upper inlet and a lower inlet.

[0049] The raw material inlet pipeline of the hydrogenation reactor 5 is sequentially provided with a raw material preheater 1 and a raw material heater 2, and the inlet pipeline of the high-pressure separator 6 is sequentially provided with a reaction product cooler 3 and a reaction product condenser 4. The middle inlet pipeline of the light removal tower 12 is provided with a desorption tower product cooler 10, the top of the light removal tower 12 is provided with a light removal tower top condenser 11, and the bottom of the tower is provided with a light removal tower kettle extraction pump 13, an absorption tower product cooler 17 and an absorption tower kettle extraction pump 15. The bottoms of the desorption tower 8 and the light removal tower 12 are respectively provided with a desorption tower kettle reboiler 9 and a light removal tower kettle reboiler 14.

[0050] The bottom extraction pipeline of the hydrogenation reactor 5 passes through the raw material heater 2, the reaction product cooler 3, and the reaction product condenser 4 in sequence and is connected to the inlet of the high-pressure separator 6. The bottom extraction pipeline of the high-pressure separator 6 is connected to the inlet of the oil-water separator 7.

[0051] A wastewater production port is provided at the bottom of the oil-water separator 7, the oil phase production pipeline of the oil-water separator 7 is connected to the upper inlet of the desorption tower 8, and the bottom production pipeline of the desorption tower 8 is connected to the middle inlet of the desorption tower 8 after passing through the desorption tower product cooler 10.

[0052] The gas phase extraction pipelines at the top of the high-pressure separator 6 and the desorption tower 8 are connected to the lower inlet of the absorption tower 16, and the bottom extraction pipeline of the absorption tower 16 is connected to the middle inlet of the light removal tower 12 after passing through the absorption tower product cooler 17, the absorption tower kettle extraction pump 15 and the desorption tower product cooler 10. The extraction pipeline at the top of the absorption tower 16 enters the hydrogenation reactor 5 after heat exchange through the reaction product cooler 3 and the raw material heater 2.

[0053] The gas phase production line at the top of the lightness removal tower 12 is divided into two routes after passing through the lightness removal tower top condenser 11, one route is used as the production line of light hydrocarbons, and the other route returns to the upper inlet of the lightness removal tower 12. The production line at the bottom of the lightness removal tower 12 passes through the lightness removal tower kettle production pump 13 and the absorption tower product cooler 17 in sequence, and then is divided into two routes, one route is used as the production line of aromatics-rich oil, and the other route is connected to the upper inlet of the absorption tower 16.

[0054] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept, which all belong to the protection scope of the present invention.

Claims

1. A carbon dioxide to aromatics raw material circulation process, characterized in that: Here are the steps: The mixed gas of carbon dioxide and hydrogen is mixed with the circulating raw gas after heat exchange and enters the hydrogenation reactor (5) for reaction; The reaction product of the hydrogenation reactor (5) is sent to a high-pressure separator (6) after heat exchange with fresh feed gas to separate the purge gas and the oil-water mixture, and the oil-water mixture is sent to an oil-water separator (7) to separate the oil phase hydrocarbon mixture and process wastewater; The oil phase hydrocarbon mixture separated by the oil-water separator (7) enters the desorption tower (8), removes the light hydrocarbons with carbon content of 3 or above, and is mixed with the purge gas as the raw gas to be recycled and sent to the bottom of the absorption tower (16). The aromatics-rich oil in the bottom of the tower is cooled and sent to the lightness removal tower (12); The light hydrocarbon removal tower (12) removes light hydrocarbons, and the byproduct liquefied petroleum gas at the top of the tower is sent to the storage area. The aromatic hydrocarbon-rich oil in the bottom of the tower is cooled and partly sent to the tank area for storage as an aromatic hydrocarbon product, and partly sent to the absorption tower (16) as an absorbent; The purge gas produced by the high-pressure separator (6) and the gas phase product at the top of the desorption tower (8) are mixed and enter the bottom of the absorption tower (16), and the light hydrocarbons are recovered using the aromatics-rich oil in the bottom of the desorption tower (12) as a solvent. Most of the raw gas at the top of the absorption tower (16) is sent to the front end of the reactor for circulation, and the aromatics-rich oil in the bottom of the tower is sent to the desorption tower (8) for circulation.

2. The carbon dioxide to aromatics raw material circulation process according to claim 1, characterized in that: The carbon dioxide and hydrogen raw materials are fed in a mass fraction of 3.5-4:

1.

3. The carbon dioxide to aromatics raw material circulation process according to claim 1, characterized in that: The raw material preheating is controlled at 180-200°C, and the temperature of the hydrogenation reactor (5) is controlled at 280-320°C.

4. The carbon dioxide to aromatics raw material circulation process according to claim 1, characterized in that: The operating pressure of the high-pressure separator (6) and the oil-water separator (7) is 2.8-3.0 MPa, and the operating temperature is 35-40°C.

5. The carbon dioxide to aromatics raw material circulation process according to claim 1, characterized in that: The operating pressure of the hydrogenation reactor (5), the desorption tower (8) and the absorption tower (16) is 2.8-3.0 MPa, and the operating pressure of the lightness removal tower (12) is 0.25-0.3 MPa.

6. A separation system for realizing the carbon dioxide to aromatics raw material circulation process according to any one of claims 1 to 5, characterized in that: The invention comprises a hydrogenation reactor (5), a high-pressure separator (6), an oil-water separator (7), a desorption tower (8), a light-removal tower (12), and an absorption tower (16). The hydrogenation reactor (5) has a raw material inlet, the desorption tower (8) and the light-removal tower (12) both have an upper inlet and a middle inlet, the absorption tower (16) has an upper inlet and a lower inlet, the bottom extraction pipeline of the hydrogenation reactor (5) is connected to the inlet of the high-pressure separator (6), the bottom extraction pipeline of the high-pressure separator (6) is connected to the inlet of the oil-water separator (7), the oil phase extraction pipeline of the oil-water separator (7) is connected to the upper inlet of the desorption tower (8), the top gas phase extraction pipelines of the high-pressure separator (6) and the desorption tower (8) are both connected to the lower inlet of the absorption tower (16); the middle inlet of the light-removal tower (12) A desorption tower product cooler (10) is arranged on the inlet pipeline, and a desorption tower kettle extraction pump (13), an absorption tower product cooler (17) and an absorption tower kettle extraction pump (15) are arranged at the bottom of the tower. The bottom extraction pipeline of the desorption tower (8) passes through the desorption tower product cooler (10) and is connected to the middle inlet of the desorption tower (12). The bottom extraction pipeline of the desorption tower (12) passes through the desorption tower kettle extraction pump (13) and the absorption tower product cooler (17) in sequence and is divided into two routes, one of which is used as an extraction pipeline for aromatics-rich oil, and the other is connected to the upper inlet of the absorption tower (16). The bottom extraction pipeline of the absorption tower (16) passes through the absorption tower product cooler (17), the absorption tower kettle extraction pump (15) and the desorption tower product cooler (10) in sequence and enters the middle inlet of the desorption tower (8).

7. The separation system according to claim 6, characterized in that: A raw material preheater (1) and a raw material heater (2) are sequentially arranged on the raw material inlet pipeline of the hydrogenation reactor (5), and a reaction product cooler (3) and a reaction product condenser (4) are sequentially arranged on the inlet pipeline of the high-pressure separator (6); and a bottom extraction pipeline of the hydrogenation reactor (5) passes through the raw material heater (2), the reaction product cooler (3), and the reaction product condenser (4) in sequence before entering the high-pressure separator (6).

8. The separation system according to claim 7, characterized in that: The extraction pipeline at the top of the absorption tower (16) passes through the reaction product cooler (3) and the raw material heater (2) and then enters the hydrogenation reactor (5).

9. The separation system according to claim 8, characterized in that: The top of the light-removal tower (12) is provided with a light-removal tower top condenser (11). The gas phase production pipeline at the top of the light-removal tower (12) is divided into two routes after passing through the light-removal tower top condenser (11), one route being used as a light hydrocarbon production pipeline, and the other route being returned to the upper inlet of the light-removal tower (12).

10. The separation system according to claim 8, characterized in that: The desorption tower (8) and the lightness removal tower (12) are respectively provided with a desorption tower kettle reboiler (9) and a lightness removal tower kettle reboiler (14) at the bottom thereof.

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