Method for increasing yields of light aromatic hydrocarbons and low-carbon olefins by using byproducts of steam cracking device

Abstract

The invention discloses a method for increasing the yield of light aromatic hydrocarbons and low-carbon olefins by using byproducts of a steam cracking device, which comprises the following steps: separating steam cracking products to obtain C4-C8 components, feeding the C4-C8 components into an aromatization unit, and feeding the C8-C8 components into a lightening unit; enabling C6-C8 components obtained from an aromatization product through a separation system to enter an aromatic hydrocarbon separation unit, and enabling C8-above components to enter a lightening unit; a C6-C8 component obtained from the light fraction product through a separation system enters an aromatic hydrocarbon separation unit, and a C8-above component enters a light fraction unit; benzene, methylbenzene and xylene products are obtained by the aromatic hydrocarbon separation unit, and non-aromatic components obtained by the aromatic hydrocarbon separation unit are returned to the aromatization unit. The method effectively solves the problem of high-value utilization of by-products of the steam cracking device, expands the raw material sources of benzene, methylbenzene and xylene aromatic hydrocarbon, and improves the yield of ethylene and propylene of the steam cracking device. Meanwhile, the yield of ethylene, propylene and xylene can be flexibly adjusted.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum processing, and particularly relates to a method for increasing the production of light aromatics and low-carbon olefins from the by-products of a steam cracking unit. Background Art

[0002] Steam cracking is an important process for producing ethylene and propylene. As basic chemical raw materials, ethylene and propylene are widely used in the manufacture of plastics, synthetic fibers, and other chemicals. During the cracking process, raw materials (such as naphtha, liquefied petroleum gas, etc.) are cracked into small molecule compounds at high temperatures. The gasoline fraction in the by-products can only obtain hydrocracked gasoline containing light aromatics after hydrotreating, and the yield and recovery rate of light aromatics are relatively low. Light aromatics have important application values in fields such as synthetic resins, coatings, and pharmaceuticals. The existing processing technology for the products of steam cracking units has deficiencies in terms of the recovery rate of light aromatics and the flexibility of product distribution, and it is difficult to effectively meet the dynamic demands of market fluctuations.

[0003] In order to improve the recovery rate of light aromatics, researchers have achieved more efficient and higher-yield aromatic production by coupling steam cracking with other processes to process the products of steam cracking units. For example, CN104211557A discloses a method for preparing benzene, toluene, and xylene from ethylene cracking C9. This method uses solvent extraction to separate the C9 + aromatic components, and benzene, toluene, and xylene (BTX) are produced through pre-hydrogenation and hydrodealkylation. This method can effectively convert the C9 fraction by-produced from steam cracking, but it fails to effectively utilize lighter or heavier fractions. Another example is CN118222324A, which discloses a method for producing high-value-added products from ethylene cracking tar. By cutting the light and heavy fractions in ethylene cracking tar and treating them separately, high-value-added chemical products are obtained. However, this process only utilizes the cracking tar in the ethylene cracking products, and the remaining cracking products can only be processed through conventional processes. Currently, for the processing and utilization of the by-products of steam cracking units, although there have been some attempts to combine different processes to increase the production of light aromatics, there is still a lack of a systematic technical solution to achieve efficient coupling and improve the recovery rate of light aromatics. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a method for increasing the production of light aromatics and low-carbon olefins from the by-products of a steam cracking unit. Through process coupling, the recovery rate of light aromatics is significantly increased, providing greater flexibility and competitiveness for production enterprises to cope with changes in market demand.

[0005] In a first aspect, the present invention provides a first method for increasing the production of light aromatics and low-carbon olefins from the by-products of a steam cracking unit, which is achieved by the following technical solutions.

[0006] A method for increasing the production of light aromatics and low-carbon olefins from the by-products of a steam cracking unit. The steam cracking products are separated to obtain hydrogen, methane, ethylene, ethane, propylene, propane, C4-C8 components and components above C8. The method for increasing the production of light aromatics and low-carbon olefins includes the following steps:

[0007] S1. Feed the C4-C8 components in the steam cracking products into an aromatization unit, and react under the action of an aromatization catalyst. The reaction products pass through a separation system to obtain hydrogen, methane, C2-C3 components, C4-C5 components, C6-C8 components and components above C8;

[0008] S2. Return the C4-C5 components obtained in step S1 to the aromatization unit, and return the C2-C3 components to the steam cracking unit;

[0009] S3. Feed the components above C8 in the steam cracking products and the components above C8 obtained in step S1 into a lightening unit, and react under the action of a lightening catalyst. The products pass through a separation system to obtain methane, C2-C3 components, C4-C5 components, C6-C8 components and components above C8;

[0010] S4. Return the C2-C3 components obtained in step S3 to the steam cracking unit, return the C4-C5 components to the aromatization unit, and return the components above C8 to the lightening unit;

[0011] S5. Feed the C6-C8 components obtained in step S1 and the C6-C8 components obtained in step S3 into an aromatics separation unit to obtain benzene, toluene and xylene products. The non-aromatic components obtained in the aromatics separation unit are returned to the aromatization unit.

[0012] In a second aspect, the present invention provides a second method for increasing the production of light aromatics and low-carbon olefins from the by-products of a steam cracking unit, which is achieved by adopting the following technical solutions.

[0013] A method for increasing the production of light aromatics and low-carbon olefins from the by-products of a steam cracking unit. The steam cracking products are separated to obtain hydrogen, methane, ethylene, ethane, propylene, propane, C4-C5 components, C6-C8 components and components above C8. The method for increasing the production of light aromatics and low-carbon olefins includes the following steps:

[0014] S1. Feed the C4-C5 components in the steam cracking products into an aromatization unit, and react under the action of an aromatization catalyst. The reaction products pass through a separation system to obtain hydrogen, methane, C2-C3 components, C4-C5 components, C6-C8 components and components above C8;

[0015] S2. Return the C4-C5 components obtained in step S1 to the aromatization unit, and return the C2-C3 components to the steam cracking unit;

[0016] S3. The components with more than 8 carbon atoms in the steam cracking products and the components with more than 8 carbon atoms obtained in step S1 enter the lightening unit and react under the action of a lightening catalyst. The products are separated by a separation system to obtain methane, C2-C3 components, C4-C5 components, C6-C8 components and components with more than 8 carbon atoms;

[0017] S4. The C2-C3 components obtained in step S3 are returned to the steam cracking unit, the C4-C5 components are returned to the aromatization unit, and the components with more than 8 carbon atoms are returned to the lightening unit;

[0018] S5. The C6-C8 components in the steam cracking products, the C6-C8 components obtained in step S1 and the C6-C8 components obtained in step S3 enter the aromatics separation unit to obtain benzene, toluene and xylene products. The non-aromatic components obtained by the aromatics separation unit are returned to the aromatization unit.

[0019] Further, the reaction device in the aromatization unit is a fixed bed or a moving bed reactor, and the aromatization reaction is carried out under the conditions of an operating pressure of 0.1-2.0 MPa, a temperature of 330-550 °C, and a raw material mass space velocity of 0.5-4.0 h -1 .

[0020] Further, the aromatization catalyst is a nano-sheet ZSM-5 molecular sieve catalyst modified by hydrothermal treatment. The hydrothermal treatment temperature of the ZSM-5 molecular sieve is 350-650 °C, the modified metal is one or more of Zn, Ni, La, Mo, Cu, Fe, Mn, Cr, and the total metal loading is 0.5-8.0 wt%.

[0021] Further, the reactor in the lightening unit is a fixed bed reactor, the reactor inlet temperature is 200-380 °C, the hydrogen partial pressure is 3.0-7.0 MPa, the mass space velocity is 0.8-3.0 h -1 , and the hydrogen-hydrocarbon volume ratio is 700-1500 Nm 3 / m 3 .

[0022] Even further, the lightening catalyst comprises the following components in parts by weight: 15-85 parts of a carrier, 0.01-15 parts of a modified metal, 10-80 parts of a binder. The modified metal is one or more of Pt, Pd, Ir, Co, Ni, Mo, W, Cu, Mn, Cr, the carrier is one or more of silica, alumina, amorphous silica-alumina, molecular sieve, and the binder is one or more of silica sol, pseudoboehmite, alumina, acid-treated clay.

[0023] Further, in the light-weighting unit, the reactor is a series connection of multiple reactors. Preferably, three reactors are connected in series. The first reactor is a liquid-phase hydrogenation reactor with an inlet temperature of 40-160°C and a mass space velocity of 1.0-3.0 h -1 ; the second reactor is a gas-liquid hydrogenation reactor with an inlet temperature of 150-260°C, a hydrogen partial pressure of 3.0-8.0 MPa, a mass space velocity of 0.5-3.0 h -1 , and a hydrogen-hydrocarbon volume ratio of 500-1000 Nm 3 / m 3 ; the third reactor is a gas-liquid hydrogenation reactor with an inlet temperature of 350-400°C, a hydrogen partial pressure of 4.0-8.0 MPa, a mass space velocity of 0.8-1.5 h -1 , and a hydrogen-hydrocarbon volume ratio of 600-1400 Nm 3 / m 3 .

[0024] Furthermore, the catalysts in the three reactors include the following components in parts by weight: 15-85 parts of a carrier, 0.01-15 parts of a modified metal, and 10-80 parts of a binder. The modified metal is one or more of Pt, Pd, Ir, Co, Ni, Mo, W, Cu, Mn, and Cr.

[0025] Further, the aromatic hydrocarbon separation unit is a simulated moving bed adsorption separation unit with an adsorption pressure of 0.5-3 MPa, an adsorption temperature of 50-150°C, and the desorbent being one or more of trimethylbenzene, tetramethylbenzene, isopropylbenzene, ethylmethylbenzene, naphthalene, tetrahydronaphthalene, methyltetrahydronaphthalene, and decahydronaphthalene. The volume ratio of the raw material to the desorbent is 1:1-1:5.

[0026] Further, the aromatic hydrocarbon separation unit is an aromatic hydrocarbon extraction device, and the extraction solvent is sulfolane, N-methylpyrrolidone, or furfural, with an extraction pressure of 0.1-0.5 MPa, a solvent ratio of 3:1-5:1, and an extraction temperature of 60-80°C.

[0027] This application has the following beneficial effects.

[0028] (1) The method of this application has a high BTX yield, and the refinery can flexibly adjust the aromatic hydrocarbon and olefin yields according to the market conditions;

[0029] (2) The method of this application has a high raw material utilization rate, and the products are only hydrogen, methane, ethylene, propylene, and BTX, with high product added value. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic flow chart of Embodiments 1-3 of the present invention;

[0031] Figure 2 is a schematic flow chart of Embodiment 4 of the present invention. Detailed implementation mode

[0032] As Figure 1 shown, the steam cracking products are separated to obtain hydrogen, methane, ethylene, ethane, propylene, propane, C4-C8 components and components above C8. Ethane and propane are returned to the steam cracking unit; the C4-C8 components separated from the steam cracking unit enter the aromatization unit and generate light aromatics under the action of an aromatization catalyst; the products obtained from the aromatization unit are separated through a separation system to obtain hydrogen, methane, C2-C3 components, C4-C5 components, C6-C8 components and components above C8; the C4-C5 components obtained from the aromatization unit are returned to the aromatization unit, and the C2-C3 components are returned to the steam cracking unit; the components above C8 obtained from the steam cracking unit and the components above C8 obtained from the aromatization unit enter the lightening unit and selectively hydrogenate to produce light aromatics; the products obtained from the lightening unit are separated through a separation system to obtain methane, C2-C3 components, C4-C5 components, C6-C8 components and components above C8; the C2-C3 components obtained from the lightening unit are returned to the steam cracking unit, the C4-C5 components are returned to the aromatization unit, and the components above C8 are returned to the lightening unit; the C6-C8 components obtained from the lightening unit and the C6-C8 components obtained from the aromatization unit enter the aromatics separation unit to obtain benzene, toluene and xylene products, and the non-aromatic components obtained from the aromatics separation unit are returned to the aromatization reaction unit.

[0033] As Figure 2As shown in the figure, the steam cracking products are separated to obtain hydrogen, methane, ethylene, ethane, propylene, propane, C4-C5 components, C6-C8 components and components above C8. Ethane and propane are returned to the steam cracking unit; the C4-C5 components separated from the steam cracking unit enter the aromatization unit and generate light aromatics under the action of an aromatization catalyst; the products obtained from the aromatization unit are separated by a separation system to obtain hydrogen, methane, C2-C3 components, C4-C5 components, C6-C8 components and components above C8; the C4-C5 components obtained from the aromatization unit are returned to the aromatization unit, and the C2-C3 components are returned to the steam cracking unit; the components above C8 obtained from the steam cracking unit and the components above C8 obtained from the aromatization unit enter the lightening unit and selectively hydrogenate to produce light aromatics under the action of a lightening catalyst; the products obtained from the lightening unit are separated by a separation system to obtain methane, C2-C3 components, C4-C5 components, C6-C8 components and components above C8; the C2-C3 components obtained from the lightening unit are returned to the steam cracking unit, the C4-C5 components are returned to the aromatization unit, and the components above C8 are returned to the lightening unit; the C6-C8 components obtained from the lightening unit, the C6-C8 components obtained from the aromatization unit and the C6-C8 components obtained from the steam cracking unit enter the aromatics separation unit to obtain benzene, toluene and xylene products, and the non-aromatic components obtained from the aromatics separation unit are returned to the aromatization reaction unit.

[0034] Example 1

[0035] Using light naphtha as the raw material of the steam cracking device, adopting Figure 1 the production process.

[0036] In the aromatization unit, the reaction device is a fixed-bed reactor, the operating pressure is 2.0 MPa, the temperature is 550 °C, and the mass space velocity of the raw material is 2.0 h -1 . The aromatization catalyst is a nano-sheet ZSM-5 molecular sieve catalyst modified by hydrothermal treatment. The hydrothermal treatment temperature of the ZSM-5 molecular sieve is 550 °C, the modified metals are Zn, Ni and Cr, the Zn loading is 6.0 wt%, the Ni loading is 1.5 wt%, and the Cr loading is 0.5 wt%.

[0037] In the lightening unit, the reactor is a fixed-bed reactor, the reactor inlet temperature is 250 °C, the hydrogen partial pressure is 3.0 MPa, the mass space velocity is 1.0 h -1 、the hydrogen-hydrocarbon volume ratio is 1500 Nm 3 / m 3The lightening catalyst is composed of three catalysts in a graded manner. From top to bottom, they are as follows: ① 80 parts of amorphous silica-alumina carrier, 10 parts of pseudoboehmite binder, 6 parts of Ni, 3.8 parts of Mo, 0.1 part of Pd, and 0.1 part of Pt; ② 30 parts of amorphous silica-alumina carrier, 40 parts of Y zeolite carrier, 20 parts of silica sol binder, 5 parts of Ni, 4 parts of W, and 1 part of Ir; ③ 40 parts of Y zeolite carrier, 20 parts of ZSM-5 carrier, 32 parts of alumina binder, 3 parts of Co, and 5 parts of Mo. Among them, the first layer is filled with the No. ① catalyst, the second and third layers are filled with the No. ② catalyst, and the fourth layer is filled with the No. ③ catalyst.

[0038] The aromatics separation unit is a simulated moving bed adsorption separation unit. The adsorption pressure is 0.5 MPa, the adsorption temperature is 50 °C, the desorbent is trimethylbenzene, tetramethylbenzene, and decahydronaphthalene (mass ratio 20:40:40), and the volume ratio of the raw material to the desorbent is 1:3.

[0039] The material balance of this example is shown in Table 1.

[0040] Example 2

[0041] Using light naphtha as the raw material for the steam cracking unit, adopting Figure 1 the production process.

[0042] In the aromatization unit, the reaction device is a moving bed reactor. The operating pressure is 0.1 MPa, the temperature is 500 °C, and the mass space velocity of the raw material is 0.5 h -1 . The aromatization catalyst is a nanosheet ZSM-5 zeolite catalyst modified by hydrothermal treatment. The hydrothermal treatment temperature of the ZSM-5 zeolite is 600 °C, and the modifying metals are La and Mo. The La loading is 3.0 wt%, and the Mo loading is 3.0 wt%.

[0043] In the lightening unit, the reactor is three reactors in series. The first reactor is a liquid-phase hydrogenation reactor with an inlet temperature of 80 °C and a mass space velocity of 1.5 h -1 , the second reactor is a gas-liquid hydrogenation reactor with an inlet temperature of 160 °C, a hydrogen partial pressure of 8.0 MPa, a mass space velocity of 2.0 h -1 , a hydrogen-hydrocarbon volume ratio of 800 Nm 3 / m 3 , and the third reactor is a gas-liquid hydrogenation reactor with an inlet temperature of 380 °C, a hydrogen partial pressure of 6.0 MPa, a mass space velocity of 1.5 h -1 , a hydrogen-hydrocarbon volume ratio of 1000 Nm 3 / m 3 .

[0044] The catalyst for the first lightening reactor is: 19 parts of alumina support, 80 parts of acid-treated clay binder, 0.5 part of Pt and 0.5 part of Pd. The catalyst for the second lightening reactor is: 30 parts of Y zeolite support, 60 parts of pseudo-boehmite binder, 8 parts of Ni and 2 parts of W. The catalyst for the third lightening reactor is: 70 parts of Y zeolite support, 25 parts of silica sol binder, 2 parts of Co and 3 parts of Mo.

[0045] The aromatics separation unit is an aromatics extraction unit. The extraction solvent is furfural, the extraction pressure is 0.5 MPa, the solvent ratio is 3:1, and the extraction temperature is 80 °C.

[0046] The material balance of this embodiment is shown in Table 1.

[0047] Example 3

[0048] Using light naphtha as the raw material for the steam cracking unit, adopting Figure 1 the production process.

[0049] In the aromatization unit, the reaction device is a fixed bed, with an operating pressure of 0.5 MPa, a temperature of 550 °C, and a raw material mass space velocity of 2.0 h -1 . The aromatization catalyst is a nano-sheet ZSM-5 zeolite catalyst modified by hydrothermal treatment. The hydrothermal treatment temperature of the ZSM-5 zeolite is 600 °C, the modifying metals are Zn and La, the Zn loading is 0.5 wt%, and the La loading is 2.2 wt%.

[0050] In the lightening unit, the reactors are three reactors in series. The first reactor is a liquid-phase hydrogenation reactor, with an inlet temperature of 60 °C and a mass space velocity of 3.0 h -1 , the second reactor is a gas-liquid hydrogenation reactor, with an inlet temperature of 260 °C, a hydrogen partial pressure of 6.0 MPa, a mass space velocity of 0.8 h -1 , a hydrogen-hydrocarbon volume ratio of 1000 Nm 3 / m 3 , the third reactor is a gas-liquid hydrogenation reactor, with an inlet temperature of 380 °C, a hydrogen partial pressure of 6.0 MPa, a mass space velocity of 1.0 h -1 , a hydrogen-hydrocarbon volume ratio of 1000 Nm 3 / m 3 .

[0051] The catalyst for the first lightening reactor is: 85 parts of alumina support, 13 parts of pseudoboehmite binder, 0.5 part of Pt, 0.5 part of Pd and 1 part of Mo. The catalyst for the second lightening reactor is: 30 parts of Y zeolite support, 20 parts of ZSM-5 zeolite support, 20 parts of MCM-22 zeolite support, 30 parts of pseudoboehmite binder, 8 parts of Ni and 2 parts of Mo. The catalyst for the third lightening reactor is: 50 parts of Y zeolite support, 30 parts of β zeolite support, 15 parts of silica sol binder, 2 parts of Ni and 3 parts of Mo.

[0052] The aromatics separation unit is a simulated moving bed adsorption separation unit. The adsorption pressure is 3 MPa, the adsorption temperature is 150 °C, the desorbent is cumene, methyl ethyl benzene, naphthalene, methyltetralin and decalin (mass ratio 20:20:10:30:20), and the volume ratio of the raw material to the desorbent is 1:1.

[0053] The material balance of this example is shown in Table 1.

[0054] Example 4

[0055] Using light naphtha as the raw material for the steam cracking unit, the production process of Figure 2 is adopted.

[0056] In the aromatization unit, the reaction device is a moving bed reactor. The operating pressure is 0.1 MPa, the temperature is 500 °C, and the mass space velocity of the raw material is 1.0 h -1 . The aromatization catalyst is a nano-sheet ZSM-5 zeolite catalyst modified by hydrothermal treatment. The hydrothermal treatment temperature of the ZSM-5 zeolite is 400 °C, the modifying metal is La, and the loading amount is 0.5 wt%.

[0057] In the lightening unit, the reactor is three reactors in series. The first reactor is a liquid-phase hydrogenation reactor with an inlet temperature of 100 °C and a mass space velocity of 2.0 h -1 , the second reactor is a gas-liquid hydrogenation reactor with an inlet temperature of 150 °C, a hydrogen partial pressure of 5.0 MPa, a mass space velocity of 1.2 h -1 , a hydrogen-hydrocarbon volume ratio of 1000 Nm 3 / m 3 , and the third reactor is a gas-liquid hydrogenation reactor with an inlet temperature of 375 °C, a hydrogen partial pressure of 5.0 MPa, a mass space velocity of 1.0 h -1 , a hydrogen-hydrocarbon volume ratio of 1000 Nm 3 / m 3 .

[0058] The catalyst for the first lightening reactor is: 85 parts of amorphous silica-alumina support, 13 parts of pseudo-boehmite binder, 0.1 part of Pd, 0.1 part of Pt, 1 part of Ni and 0.8 part of Mo. The catalyst for the second lightening reactor is: 50 parts of Y zeolite support, 20 parts of ZSM-5 zeolite support, 30 parts of pseudo-boehmite binder, 6 parts of Ni and 4 parts of Mo. The catalyst for the third lightening reactor is: 50 parts of Y zeolite support, 30 parts of β zeolite support, 15 parts of silica sol binder, 2 parts of Ni and 3 parts of Mo.

[0059] The aromatics separation unit is a simulated moving bed adsorption separation unit. The adsorption pressure is 3.0 MPa, the adsorption temperature is 100 °C, the desorbent is isopropylbenzene, methylnaphthalene and tetralin (mass ratio 30:30:40), and the volume ratio of the raw material to the desorbent is 1:5.

[0060] The material balance of this embodiment is shown in Table 1.

[0061] Comparative Example 1

[0062] Light naphtha is used as the raw material for the steam cracking unit. The products of the steam cracking unit are separated to obtain hydrogen, methane, ethylene, propylene, C4 components, gasoline, diesel and fuel oil.

[0063] The material balance is shown in Table 1.

[0064] Table 1 Material balance of Examples 1-4 and Comparative Example 1

[0065]

[0066]

[0067] The examples of this specific implementation manner are all preferred examples of the present invention, and do not limit the protection scope of the present invention accordingly. Therefore, all equivalent changes made according to the structure, shape and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for increasing the production of light aromatics and low-carbon olefins from by-products of a steam cracking unit, characterized in that: The steam cracking products are separated to obtain hydrogen, methane, ethylene, ethane, propylene, propane, C4-C8 components and components above C8. The method for increasing the production of light aromatics and lower olefins includes the following steps: S1. The C4-C8 components in the steam cracking products enter the aromatization unit and react under the action of an aromatization catalyst. The reaction products pass through a separation system to obtain hydrogen, methane, C2-C3 components, C4-C5 components, C6-C8 components and components above C8; S2. The C4-C5 components obtained in step S1 are returned to the aromatization unit, and the C2-C3 components are returned to the steam cracking unit; S3. The components above C8 in the steam cracking products and the components above C8 obtained in step S1 enter the lightening unit and react under the action of a lightening catalyst. The products pass through a separation system to obtain methane, C2-C3 components, C4-C5 components, C6-C8 components and components above C8; S4. The C2-C3 components obtained in step S3 are returned to the steam cracking unit, the C4-C5 components are returned to the aromatization unit, and the components above C8 are returned to the lightening unit; S5. The C6-C8 components obtained in step S1 and the C6-C8 components obtained in step S3 enter the aromatics separation unit to obtain benzene, toluene and xylene products. The non-aromatic components obtained in the aromatics separation unit are returned to the aromatization unit.

2. A method for increasing the production of light aromatics and low-carbon olefins from by-products of a steam cracking device according to claim 1, characterized in that: The steam cracking products are separated to obtain hydrogen, methane, ethylene, ethane, propylene, propane, C4-C5 components, C6-C8 components and components above C8. The method for increasing the production of light aromatics and lower olefins includes the following steps: S1. The C4-C5 components in the steam cracking products enter the aromatization unit and react under the action of an aromatization catalyst. The reaction products pass through a separation system to obtain hydrogen, methane, C2-C3 components, C4-C5 components, C6-C8 components and components above C8; S2. The C4-C5 components obtained in step S1 are returned to the aromatization unit, and the C2-C3 components are returned to the steam cracking unit; S3. The components above C8 in the steam cracking products and the components above C8 obtained in step S1 enter the lightening unit and react under the action of a lightening catalyst. The products pass through a separation system to obtain methane, C2-C3 components, C4-C5 components, C6-C8 components and components above C8; S4. The C2-C3 components obtained in step S3 are returned to the steam cracking unit, the C4-C5 components are returned to the aromatization unit, and the components above C8 are returned to the lightening unit; S5. The C6-C8 components in the steam cracking products, the C6-C8 components obtained in step S1 and the C6-C8 components obtained in step S3 enter the aromatics separation unit to obtain benzene, toluene and xylene products. The non-aromatic components obtained in the aromatics separation unit are returned to the aromatization unit.

3. The method for increasing the production of light aromatics and low-carbon olefins from by-products of a steam cracking device according to claim 1 or 2, characterized in that: The reaction device in the aromatization unit is a fixed-bed or moving-bed reactor, and the aromatization reaction is carried out under the conditions of an operating pressure of 0.1 to 2.0 MPa, a temperature of 330 to 550 °C, and a raw material mass space velocity of 0.5 to 4.0 h -1 -1.

4. The method for increasing the production of light aromatics and low-carbon olefins from by-products of a steam cracking device according to claim 1 or 2, characterized in that: The aromatization catalyst is a nano-sheet ZSM-5 molecular sieve catalyst modified by hydrothermal treatment. The hydrothermal treatment temperature of the ZSM-5 molecular sieve is 350-650 °C. The modifying metals are one or more of Zn, Ni, La, Mo, Cu, Fe, Mn, Cr, and the total metal loading is 0.5-8.0 wt%.

5. A method for increasing the production of light aromatics and low-carbon olefins from by-products of a steam cracking device according to claim 1 or 2, characterized in that: In the lightening unit, the reactor is a fixed-bed reactor, and the inlet temperature of the reactor is 200 - 380 °C, the hydrogen partial pressure is 3.0 - 7.0 MPa, the mass hourly space velocity is 0.8 - 3.0 h -1 , and the hydrogen-hydrocarbon volume ratio is 700 - 1500 Nm 3 / m 3 .

6. The method for increasing the production of light aromatics and low-carbon olefins from the by-products of a steam cracking device according to claim 5, characterized in that: The lightening catalyst comprises the following components in parts by weight: 15 to 85 parts of a carrier, 0.01 to 15 parts of a modified metal, and 10 to 80 parts of a binder, and the modified metal is one or more of Pt, Pd, Ir, Co, Ni, Mo, W, Cu, Mn, and Cr.

7. A method for increasing the production of light aromatics and low-carbon olefins from by-products of a steam cracking device according to claim 1 or 2, characterized in that: In the lightening unit, the reactors are connected in series. Preferably, three reactors are connected in series. The first reactor is a liquid-phase hydrogenation reactor with an inlet temperature of 40-160 °C and a mass space velocity of 1.0-3.0 h -1 ; the second reactor is a gas-liquid hydrogenation reactor with an inlet temperature of 150-260 °C, a hydrogen partial pressure of 3.0-8.0 MPa, a mass space velocity of 0.5-3.0 h -1 , and a hydrogen-hydrocarbon volume ratio of 500-1000 Nm 3 / m 3 ; the third reactor is a gas-liquid hydrogenation reactor with an inlet temperature of 350-400 °C, a hydrogen partial pressure of 4.0-8.0 MPa, a mass space velocity of 0.8-1.5 h -1 , and a hydrogen-hydrocarbon volume ratio of 600-1400 Nm 3 / m 3 .

8. The method for increasing the production of light aromatics and low-carbon olefins from by-products of a steam cracking device according to claim 7, characterized in that: The catalysts in the three reactors comprise the following components in parts by weight: 15 to 85 parts of a carrier, 0.01 to 15 parts of a modified metal, and 10 to 80 parts of a binder, and the modified metal is one or more of Pt, Pd, Ir, Co, Ni, Mo, W, Cu, Mn, and Cr.

9. A method for increasing the production of light aromatics and low-carbon olefins from by-products of a steam cracking device according to claim 1 or 2, characterized in that: The aromatic hydrocarbon separation unit is a simulated moving bed adsorption separation unit, the adsorption pressure is 0.5 to 3 MPa, the adsorption temperature is 50 to 150 °C, the desorbent is one or more of trimethylbenzene, tetramethylbenzene, isopropylbenzene, methyl ethylbenzene, naphthalene, tetrahydronaphthalene, methyltetrahydronaphthalene, and decalin, and the volume ratio of the raw material to the desorbent is 1:1 to 1:

5.

10. The method for increasing the production of light aromatics and low-carbon olefins from by-products of a steam cracking device according to claim 1 or 2, characterized in that: The aromatic hydrocarbon separation unit is an aromatic hydrocarbon extraction device, the extraction solvent is sulfolane, N-methylpyrrolidone, or furfural, the extraction pressure is 0.1 to 0.5 MPa, the solvent ratio is 3:1 to 5:1, and the extraction temperature is 60 to 80 °C.

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