A carbon dioxide-to-aromatics feedstock recycling process and its separation system

Abstract

This invention belongs to the field of chemical separation and purification, and discloses a carbon dioxide-to-aromatics feedstock recycling process and its separation system. The process system includes a hydrogenation reactor, a high-pressure separator, an oil-water separator, a desorption tower, a light hydrocarbon removal tower, and an absorption tower. The feedstock is a gaseous mixture of carbon dioxide and hydrogen. After phase separation by reaction, the feedstock yields a mixture of non-aromatics, light aromatics, and heavy aromatics. This mixture is then separated by an absorption-desorption unit to obtain a liquid-phase aromatic-rich oil, which enters the aromatics extraction system. The gaseous portion returns to the front end of the reactor to form a feedstock gas recycling system. This invention uses aromatic-rich oil as an absorbent to achieve efficient separation of feedstock gas and light hydrocarbons, significantly reducing the proportion of light hydrocarbons in the recycled feedstock in the CO2 hydrogenation-to-aromatics process, thereby reducing feedstock recycling and overall process energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of chemical separation and purification, specifically relating to a carbon dioxide-to-aromatics feedstock recycling process and its separation system. Background Technology

[0002] Aromatic hydrocarbons, as hydrocarbons with cyclic 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. CO2 hydrogenation to aromatics can, on the one hand, turn waste into treasure and realize the resource utilization of greenhouse gases, and on the other hand, provide a green and low-carbon route for the synthesis of high-value aromatic chemicals. However, existing CO2 hydrogenation to aromatics technologies suffer from bottlenecks such as low activation efficiency and selectivity, and high energy consumption, necessitating the development of efficient CO2 hydrogenation to aromatics technology.

[0003] CO2 hydrogenation to aromatics is a promising aromatics production process that has emerged in recent years. Domestic and international scholars have conducted research on the reaction routes, catalysts, reactors, separation, and applications involved in CO2 hydrogenation to light aromatics. Currently, the mainstream process routes include direct synthesis and indirect synthesis. Early experiments used a composite catalyst composed of an iron-based FTS catalyst and HZSM-5 zeolite to conduct experiments on the direct synthesis of aromatics from CO2 hydrogenation in a single-stage reactor. Experimental results showed a CO2 conversion rate of 38% and an aromatics selectivity as high as 21.4% (excluding CO). Currently, the synthesis of aromatic compounds from CO2 hydrogenation can be achieved through two different pathways: CO2-FTS and CO2-MeOH.

[0004] Regarding feedstock recycling, the main materials requiring recycling in CO2 hydrogenation products include CO2, CO, and H2. Existing feedstock recycling technologies primarily rely on multi-stage condensation, with the gas from equilibrium flash evaporation directly recycled back to the reactor for reuse. Besides the feed gas, the recycled gas also contains a large amount of C1-C5 light hydrocarbons, mainly alkanes. These not only make it difficult for them to participate in aromatization reactions but also significantly increase the flow rate of the recycled stream, leading to problems such as increased reaction and separation equipment volume and higher energy consumption. While the liquid phase obtained from multi-stage condensation mainly consists of the target product aromatics, it also contains a certain amount of alkanes, alkenes, and cycloalkanes, thus hindering the large-scale application and promotion of the process.

[0005] Therefore, providing a highly efficient separation and recycling process and system for feed gas and light hydrocarbons has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a carbon dioxide-to-aromatics feedstock recycling process and its separation system, which achieves efficient separation of feedstock gas and light hydrocarbons, significantly reduces the circulating gas flow rate, and thus reduces the energy consumption of the entire separation system.

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

[0008] This invention provides a carbon dioxide-to-aromatics feedstock recycling process, comprising the following steps:

[0009] The mixture of carbon dioxide and hydrogen is mixed with the circulating feed gas after heat exchange and then enters the hydrogenation reactor for reaction.

[0010] The reaction products of the hydrogenation reactor are sent to a high-pressure separator after heat exchange with fresh feed gas to separate off-gas and oil-water mixture. The oil-water mixture enters an oil-water separator to separate oil-phase hydrocarbon mixture and process wastewater.

[0011] The oil-phase hydrocarbon mixture separated by the oil-water separator enters the desorption tower, where light hydrocarbons of C3 and above are removed. This gas is then mixed with the off-gas and sent to the bottom of the absorption tower. The aromatic oil at the bottom of the tower is cooled and sent to the light hydrocarbon removal tower.

[0012] The light hydrocarbon removal tower performs light hydrocarbon removal operations. The liquefied petroleum gas produced at the top of the tower is sent to the storage area. The aromatic oil at the bottom of the tower is cooled and part of it is sent to the tank area for storage as an aromatic product, and part of it is sent to the absorption tower as an absorbent.

[0013] The purge gas from the high-pressure separator and the gaseous products from the top of the desorption tower are mixed and enter the bottom of the absorption tower. Light hydrocarbons are recovered using the aromatic oil from the bottom of the light hydrocarbon removal tower as a solvent. Most of the feed gas from the top of the absorption tower is sent to the front end of the reactor for circulation, while the aromatic oil from the bottom of the tower is sent to the desorption tower for circulation.

[0014] Furthermore, carbon dioxide and hydrogen are fed in a mass fraction of 3.5-4:1, preheated, mixed with the circulating feed gas, and then fed into the hydrogenation reactor for reaction. The feed preheating is controlled at 180-200℃.

[0015] Furthermore, the conditions for the hydrogenation reactor are: a reaction temperature of 280-320℃.

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

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

[0018] Furthermore, most of the feed gas from the top of the absorber is sent to the front end of the reactor for circulation, while the product from the bottom of the absorber is sent to the desorption tower for circulation, with a feed gas circulation ratio of 0.855-0.865.

[0019] Another aspect of the present invention provides a separation system for implementing the carbon dioxide-to-aromatics feedstock recycling process, comprising a hydrogenation reactor, a high-pressure separator, an oil-water separator, a desorption tower, a light-weight removal tower, and an absorption tower. The hydrogenation reactor has a feedstock inlet; both the desorption tower and the light-weight removal tower have an upper inlet and a middle inlet; the absorption tower has an upper inlet and a lower inlet. The bottom outlet pipeline of the hydrogenation reactor is connected to the inlet of the high-pressure separator, and the bottom outlet pipeline of the high-pressure separator is connected to the inlet of the oil-water separator. The oil phase outlet pipeline of the oil-water separator is connected to the upper inlet of the desorption tower, and the top gas phase outlet pipelines of both the high-pressure separator and the desorption tower are connected to... The desorption tower product cooler is installed on the middle inlet pipeline of the light hydrocarbon removal tower. The bottom of the tower is equipped with the light hydrocarbon removal tower bottom pump, the absorption tower product cooler, and the absorption tower bottom pump. The bottom outlet pipeline of the desorption tower is connected to the middle inlet of the light hydrocarbon removal tower after passing through the desorption tower product cooler. The bottom outlet pipeline of the light hydrocarbon removal tower is split into two after passing through the light hydrocarbon removal tower bottom pump and the absorption tower product cooler. One line is used as the outlet pipeline for aromatic oil, and the other line is connected to the upper inlet of the absorption tower. The bottom outlet pipeline of the absorption tower is connected to the middle inlet of the desorption tower after passing through the absorption tower product cooler, the absorption tower bottom pump, and the desorption tower product cooler.

[0020] Furthermore, a feed preheater and a feed heater are sequentially configured on the feed 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 outlet pipeline of the hydrogenation reactor passes sequentially through the raw material heater, the reaction product cooler, and the reaction product condenser before entering the high-pressure separator.

[0023] Furthermore, the top of the absorber tower exits through a product cooler and a raw material heater before entering the hydrogenation reactor.

[0024] Furthermore, a light hydrocarbon removal tower top condenser is configured at the top of the light hydrocarbon removal tower. After passing through the light hydrocarbon removal tower top condenser, the gas phase exit pipeline of the light hydrocarbon removal tower splits into two paths: one path serves as the exit pipeline for light hydrocarbons, and the other path returns to the upper inlet of the light hydrocarbon removal tower.

[0025] Furthermore, the bottom of the desorption tower and the light-light-removal tower are respectively equipped with a reboiler for the desorption tower and a reboiler for the light-light-removal tower.

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

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

[0028] This invention constructs an absorption-desorption coupled separation system using the bottom liquid phase of the light hydrocarbon removal tower as the circulating absorbent. It utilizes a mixture rich in aromatic hydrocarbons as the absorbent to absorb the circulating feed gas, effectively reducing the light hydrocarbon content in the feed gas. This results in the circulating feed gas containing only small amounts of C1 and C2 light hydrocarbons, in addition to CO2, H2, and CO. The desorption process removes light hydrocarbons from the absorbent liquid, producing liquefied petroleum gas as a byproduct of the process. The optimized process reduces equipment investment and energy consumption, improving its economic efficiency. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the separation system in the carbon dioxide-to-aromatics feedstock recycling process of the present invention.

[0030] The attached figures are labeled 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 reboiler; 10-Desorption tower product cooler; 11-Light weight removal tower top condenser; 12-Light weight removal tower; 13-Light weight removal tower bottom pump; 14-Light weight removal tower bottom reboiler; 15-Absorber tower bottom pump; 16-Absorber tower; 17-Absorber tower product cooler. Detailed Implementation

[0032] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0033] By deeply analyzing the process reaction system and reactor configuration of carbon dioxide-to-aromatics feedstock recycling, the reaction characteristics and product composition are derived. CO2, CO, and H2 in the products are defined as feedstock gases to be recycled, 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 identified as target products, and others are classified as mixed aromatics. Based on the gas-liquid two-phase composition distribution of the reaction products after cooling, a carbon dioxide-to-aromatics feedstock recycling process method and its separation system with absorption-desorption coupling separation are provided.

[0034] In this embodiment of the invention, the raw material heater 2, the reaction product cooler 3, the desorption tower product cooler 10, the light component removal tower top condenser 11, and the absorption tower product cooler 17 all adopt inter-stream heat exchangers. The hot stream flows through the shell side, and the cold stream outlet temperature is 200°C. The heat exchange between the reactor product stream and the raw material feed stream is used to increase the temperature of the raw material feed stream and reduce the energy consumption of the entire process.

[0035] Example 1

[0036] A carbon dioxide-to-aromatics feedstock recycling process method includes the following steps.

[0037] Carbon dioxide and hydrogen feedstocks are fed in a mass ratio of 4:1. After being preheated by feedstock preheater 1, they are mixed with circulating feedstock gas and then heat-exchanged by feedstock heater 2 before entering hydrogenation reactor 5 for reaction. The feedstock preheating is controlled at 200℃. The conditions of hydrogenation reactor 5 are: reaction temperature of 320℃ and pressure of 3.0 MPa.

[0038] The reaction products of hydrogenation reactor 5 are sent to high-pressure separator 6 after heat exchange with fresh feed gas in feed heater 2, where purge gas and oil-water mixture are separated. The oil-water mixture enters oil-water separator 7 to separate oil-phase hydrocarbon mixture and process wastewater. The operating pressure of high-pressure separator 6 and oil-water separator 7 is 3.0 MPa and the operating temperature is 40℃.

[0039] The oil-phase hydrocarbon mixture separated from the oil-water separator 7 enters the desorption tower 8, where light hydrocarbons of C3 and above are removed. This gas is then mixed with the purge gas from the high-pressure separator 6 and sent to the bottom of the absorption tower 16. The aromatic oil in the bottom of the tower is cooled and sent to the light hydrocarbon removal tower 12. The operating pressure of the desorption tower 8 is 3.0 MPa.

[0040] Light hydrocarbon removal tower 12 performs light hydrocarbon removal operations. The by-product liquefied petroleum gas at the top of the tower is sent to the storage area. The aromatic oil at the bottom of the tower is cooled, and part of it is sent to the tank area for storage as an aromatic product, while part of it is sent to the absorption tower 16 as an absorbent. The operating pressure of light hydrocarbon removal tower 12 is 0.3 MPa.

[0041] The purge gas from the high-pressure separator 6 and the top product from the desorption tower 8 are mixed and enter the bottom of the absorption tower 16. The light hydrocarbons are recovered using the aromatic oil from the light hydrocarbon removal tower 12 as the absorbent. Most of the feed gas from the top of the tower is sent to the front end of the reactor for circulation, and the bottom product is sent to the desorption tower 8 for circulation. The operating pressure of the absorption tower 16 is 3.0 MPa.

[0042] In absorber 16, the gas and liquid phases are in countercurrent contact within the tower. The feed gas from the top of the tower is recycled back to the reactor to participate in feed conversion, with a recycling ratio of 0.865. All the product from the bottom of the tower is recycled back to desorption tower 8. The content of light hydrocarbons of C3 and above in the recycled feed gas from the top of the tower is reduced to 3.2%, which is 58.5% lower than the initial feed gas to be recycled; the production of aromatics increases 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 of C3 and above in the top circulating raw material gas can be reduced to 5.7%, which is 60.7% lower than the initial raw material gas to be circulated; the aromatic hydrocarbon production increases 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 of C3 and above in the circulating raw material gas at the top of the tower can be reduced to 5.3%, which is 50.1% lower than the initial raw material gas to be circulated; the aromatic hydrocarbon production increases by 4.1 times.

[0047] Example 4

[0048] A separation system for implementing the carbon dioxide-to-aromatics feedstock recycling process of Examples 1-3 includes a hydrogenation reactor 5, a high-pressure separator 6, an oil-water separator 7, a desorption tower 8, a light-light hydrocarbon removal tower 12, and an absorption tower 16. The hydrogenation reactor 5 has a feedstock inlet, the desorption tower 8 and the light-light hydrocarbon 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] A feed preheater 1 and a feed heater 2 are sequentially installed on the feed inlet pipeline of hydrogenation reactor 5. A reaction product cooler 3 and a reaction product condenser 4 are sequentially installed on the inlet pipeline of high-pressure separator 6. A desorption tower product cooler 10 is installed on the middle inlet pipeline of light-light ...

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

[0051] The bottom of the oil-water separator 7 is equipped with a wastewater outlet. The oil phase outlet pipeline of the oil-water separator 7 is connected to the upper inlet of the desorption tower 8. The bottom outlet pipeline of the desorption tower 8 is connected to the middle inlet of the desorption tower 8 after passing through the product cooler 10 of the desorption tower.

[0052] The gas phase exit lines from the top of the high-pressure separator 6 and the desorption tower 8 are both connected to the lower inlet of the absorption tower 16. The bottom exit line of the absorption tower 16 passes through the absorption tower product cooler 17, the absorption tower bottom exit pump 15, and the desorption tower product cooler 10 before connecting to the middle inlet of the light component removal tower 12. The top exit line of the absorption tower 16 passes through the reaction product cooler 3 and the raw material heater 2 for heat exchange before entering the hydrogenation reactor 5.

[0053] The vapor exit pipeline from the top of the light hydrocarbon removal tower 12 splits into two branches after passing through the tower top condenser 11. One branch serves as the exit pipeline for light hydrocarbons, while the other returns to the upper inlet of the light hydrocarbon removal tower 12. The bottom exit pipeline from the light hydrocarbon removal tower 12 splits into two branches after passing through the tower bottom exit pump 13 and the absorber product cooler 17. One branch serves as the exit pipeline for aromatic hydrocarbon-rich oil, while the other connects to the upper inlet of the absorber tower 16.

[0054] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the inventive concept, and these all fall within the protection scope of the present invention.

Claims

1. A carbon dioxide-to-aromatics feedstock recycling process, characterized in that, The steps are as follows: The mixture of carbon dioxide and hydrogen is mixed with the circulating feed gas after heat exchange and enters the hydrogenation reactor (5) for reaction; The reaction products of the hydrogenation reactor (5) are sent to the high-pressure separator (6) after heat exchange with fresh feed gas to separate the purge gas and oil-water mixture. The oil-water mixture enters the 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) to remove C3 and above light hydrocarbons. It is then mixed with the off-gas as the raw material to be recycled and sent to the bottom of the absorption tower (16). The aromatic oil in the bottom of the tower is cooled and sent to the light hydrocarbon removal tower (12). The light hydrocarbon removal tower (12) performs light hydrocarbon removal operations. The by-product liquefied petroleum gas at the top of the tower is sent to the storage area. The aromatic oil at the bottom of the tower is cooled and part of it is sent to the tank area for storage as an aromatic product, and part of it is sent to the absorption tower (16) as an absorbent. The purge gas from the high-pressure separator (6) and the gaseous products from the top of the desorption tower (8) are mixed and enter the bottom of the absorption tower (16). Light hydrocarbons are recovered using the aromatic oil from the bottom of the light hydrocarbon removal tower (12) as a solvent. Most of the feed gas from the top of the absorption tower (16) is sent to the front end of the reactor for circulation, and the aromatic oil from the bottom of the tower is sent to the desorption tower (8) for circulation. The content of C3 and above light hydrocarbons in the circulating feed gas from the top of the absorption tower (16) is reduced to 3.2%-5.7%, and the aromatic hydrocarbon production is increased by 4.1-4.6 times.

2. The carbon dioxide-to-aromatics feedstock recycling process according to claim 1, characterized in that: The carbon dioxide and hydrogen feedstocks are fed at a mass ratio of 3.5-4:

1.

3. The carbon dioxide-to-aromatics feedstock recycling 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 feedstock recycling process according to claim 1, characterized in that: The high-pressure separator (6) and the oil-water separator (7) operate at a pressure of 2.8-3.0 MPa and a temperature of 35-40°C.

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

6. A separation system for implementing the carbon dioxide-to-aromatics feedstock recycling process according to any one of claims 1 to 5, characterized in that: The system includes a hydrogenation reactor (5), a high-pressure separator (6), an oil-water separator (7), a desorption tower (8), a light-light phase removal tower (12), and an absorption tower (16). The hydrogenation reactor (5) has a raw material inlet. The desorption tower (8) and the light-light phase 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 outlet pipeline of the hydrogenation reactor (5) is connected to the inlet of the high-pressure separator (6). The bottom outlet pipeline of the high-pressure separator (6) is connected to the inlet of the oil-water separator (7). The oil phase outlet pipeline of the oil-water separator (7) is connected to the upper inlet of the desorption tower (8). The top gas phase outlet 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 outlet of the light-light phase removal tower (12) is connected to the lower inlet of the absorption tower (16). The inlet pipeline is equipped with a desorption tower product cooler (10), and the bottom of the tower is equipped with a light removal tower bottom pump (13), an absorption tower product cooler (17) and an absorption tower bottom pump (15). The bottom outlet pipeline of the desorption tower (8) is connected to the middle inlet of the light removal tower (12) after passing through the desorption tower product cooler (10). The bottom outlet pipeline of the light removal tower (12) passes through the light removal tower bottom pump (13) and the absorption tower product cooler (17) in sequence and then splits into two paths. One path is used as the outlet pipeline for aromatic oil, and the other path is connected to the upper inlet of the absorption tower (16). The bottom outlet pipeline of the absorption tower (16) passes through the absorption tower product cooler (17), the absorption tower bottom pump (15) and the desorption tower product cooler (10) in sequence and then enters the middle inlet of the desorption tower (8).

7. The separation system according to claim 6, characterized in that: The raw material preheater (1) and the raw material heater (2) are sequentially arranged on the raw material inlet pipeline of the hydrogenation reactor (5), and the reaction product cooler (3) and the reaction product condenser (4) are sequentially arranged on the inlet pipeline of the high pressure separator (6); the bottom outlet 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 top pipeline of the absorption tower (16) passes through the reaction product cooler (3) and the raw material heater (2) before entering the hydrogenation reactor (5).

9. The separation system according to claim 8, characterized in that: The top of the light hydrocarbon removal tower (12) is equipped with a top condenser (11). The gas phase extraction pipeline at the top of the light hydrocarbon removal tower (12) is split into two paths after passing through the top condenser (11). One path serves as the extraction pipeline for light hydrocarbons, and the other path returns to the upper inlet of the light hydrocarbon removal tower (12).

10. The separation system according to claim 8, characterized in that: The bottom of the desorption tower (8) and the light-removal tower (12) are respectively equipped with a reboiler (9) for the desorption tower and a reboiler (14) for the light-removal tower.

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