Preparation method of light aromatic hydrocarbon

Abstract

The invention discloses a preparation method of light aromatic hydrocarbon. The preparation method comprises the following steps: S1, a heat exchange unit: pumping a mixture of raw materials naphtha, C5 and raffinate oil to the heat exchange unit for gradient heat exchange; s2, a reaction unit; s3, a heat exchange cooling unit; s4, in a first separation unit, dry gas is produced at the top of the absorption and desorption tower, and oil at the bottom of the absorption and desorption tower enters a stabilization tower after heat exchange; s5, a second separation unit: sending out the liquefied petroleum gas product as a liquefied petroleum gas product under the control of the liquid level of the reflux tank of the stabilizer; crude aromatic hydrocarbon is produced at the bottom of the stabilizing tower and enters the middle of the cutting tower; and S6, a third separation unit: conveying the qualified product to a light mixed aromatic hydrocarbon storage tank in a reflux tank of the cutting tower, conveying the unqualified product to a naphtha storage tank, producing heavy aromatic hydrocarbon at the bottom of the cutting tower, and pumping the qualified product to a heavy aromatic hydrocarbon storage tank. According to the preparation method, a brand new heat exchange process is adopted, most waste heat can be recycled, the device is low in energy consumption and good in environmental protection performance, and the prepared product is high in quality.

Description

Technical Field

[0001] The invention relates to the technical field of aromatization process, and in particular to a method for preparing light aromatics. Background Art

[0002] Aromatics are the most basic chemical raw materials in my country's economic development process. They are widely used in the production of synthetic resins, synthetic fibers, synthetic rubber and various fine chemicals. In recent years, my country's demand for aromatics has continued to grow. The market supply of the mixture of benzene, toluene and xylene (BTX) in aromatics is in short supply, and it is necessary to increase production capacity. Naphtha is one of the petroleum products (light fraction of petroleum), also known as chemical light oil. It is a light oil used for chemical raw materials produced by processing crude oil or other raw materials, mainly used as reforming and chemical raw materials. The main production process of benzene-toluene-xylene mixed aromatics is to increase the production capacity of aromatics by using naphtha as raw material. The naphtha aromatization technology that has emerged can effectively alleviate the pressure of aromatic production capacity. However, with the tension of oil resources and the influence of crude oil resources, light hydrocarbons and raffinate oil have gradually appeared to produce aromatics by aromatization. However, the aromatization reaction is a complex chemical process. Aromatic production involves multiple reaction steps, some of which are endothermic reactions and some are exothermic reactions. If the entire system cannot be maintained within a stable temperature range, the reaction efficiency will be reduced. Similarly, if the heat exchange temperature during the separation of the reaction products cannot be accurately controlled, the separation efficiency will be reduced and the effective separation of different components will be affected, affecting the quality of the aromatic products. Therefore, it is necessary to optimize and upgrade the aromatic production technology, and propose a method for producing light aromatics, using naphtha, light hydrocarbons and raffinate oil mixed materials for aromatization production. Summary of the invention

[0003] In view of this, the present invention provides a method for preparing light aromatics, which has the characteristics of recovering waste heat through a completely new heat exchange, high product quality and good environmental protection.

[0004] The technical means adopted by the present invention are as follows: A method for preparing light aromatics, comprising the following steps:

[0005] S1, heat exchange unit: pump the raw material naphtha, C5, and raffinate oil mixture to the heat exchange unit for gradient heat exchange, the gradient heat exchange temperature is from 50℃ to 195℃, and the gradient heat exchange pressure is from 1.45 to 1.6MPa;

[0006] S2, reaction unit: the raw material conveying heating furnace is heated to 320-420°C, and then enters the aromatization reactor, in which HZSM-5, KCA-NL, DLP-3A+ molecular sieve catalysts are loaded;

[0007] S3, heat exchange cooling unit: the reaction product passes through the cutting tower reboiler, desorption tower reboiler, heat exchanger in sequence, and then passes through the air cooler and water cooler to cool to 35-45°C;

[0008] S4, first separation unit: the cooled product is separated into oil and gas in a separator tank, the rich gas at the top of the separator tank and the mixed aromatics at the bottom of the separator tank enter the middle of the absorption section of the absorption and desorption tower, the top of the absorption and desorption tower produces dry gas, and the oil at the bottom of the absorption and desorption tower enters the stabilization tower after heat exchange;

[0009] S5, the second separation unit: the olefin-poor liquefied petroleum gas produced at the top of the stabilization tower is cooled and then enters the reflux tank of the stabilization tower. After the olefin-poor liquefied petroleum gas in the reflux tank of the stabilization tower is pressurized by a pump, a part of it is sent to the top of the stabilization tower for reflux to control the top temperature, and the other part is used as a liquefied petroleum gas product delivery device under the liquid level control of the reflux tank of the stabilization tower; crude aromatics are produced at the bottom of the stabilization tower, a part of which is cooled and pumped to the top of the absorption and desorption tower as an absorbent after heat exchange in the heat exchanger, and the other part enters the middle of the cutting tower;

[0010] S6, the third separation unit: the light mixed aromatics produced at the top of the cutting tower enter the cutting tower reflux tank after heat exchange cooling, a part of the light mixed aromatics in the cutting tower reflux tank is transported back to the top of the cutting tower to control the temperature, the other part of the qualified ones are sent to the light mixed aromatics storage tank, and the unqualified ones are sent to the naphtha storage tank. The heavy aromatics are produced at the bottom of the cutting tower, and the qualified products are pumped to the heavy aromatics storage tank after heat exchange cooling, and the unqualified ones are sent to the naphtha storage tank.

[0011] Preferably, the weight ratio of naphtha, C5 and raffinate oil is 50-60%:25-30%:10-25%.

[0012] Preferably, the heat exchange unit in step S1 includes the raw material first entering a naphtha-light mixed aromatics heat exchanger for heat exchange to 50-55°C; then continuing to heat exchange to 135-145°C in a naphtha-reaction product heat exchanger; then heat exchanging to 145-155°C in a naphtha-heavy aromatics heat exchanger; and then entering a naphtha-heat transfer oil heat exchanger for heat exchange to 185-195°C.

[0013] Preferably, the heat exchange unit includes the raw material first entering a naphtha-light mixed aromatics heat exchanger for heat exchange to 52.6°C and a heat exchange pressure of 1.57MPa; then continuing to heat exchange to 140.4°C in a naphtha-reaction product heat exchanger and a heat exchange pressure of 1.51MPa; then heat exchanging to 150.4°C in a naphtha-heavy aromatics heat exchanger and a heat exchange pressure of 1.50MPa; and then entering a naphtha-heat transfer oil heat exchanger for heat exchange to 190.4°C and a heat exchange pressure of 1.49MPa.

[0014] Preferably, the weight contents of HZSM-5, KCA-NL, and DLP-3A+ molecular sieve catalysts in step S2 are 40-50%, 25-35%, and 20-30%, respectively.

[0015] Preferably, in step S3, the reaction product is sequentially passed through a cutting tower reboiler, a desorption tower reboiler, and a naphtha-reaction product heat exchanger, and then cooled through an air cooler and a water cooler, with a cooling pressure of 0.6 to 0.8 MPa and a cooling temperature of 35 to 45°C.

[0016] Preferably, the temperature of the olefin-poor liquefied petroleum gas produced at the top of the stabilization tower is 55-60° C. and the pressure is 0.7-0.8 MPa; the temperature of the crude aromatics produced at the bottom of the stabilization tower is 150-160° C. and 0.9-1.0 MPa.

[0017] Preferably, crude aromatics are produced at the bottom of the stabilizer, a portion of which is cooled to 30°C after heat exchange at 80°C and 1.0 MPa in a stabilizer feed heat exchanger and pumped to the top of the absorption and desorption tower as an absorbent.

[0018] Preferably, the temperature of the light mixed aromatics produced at the top of the cutting tower is 110-120°C and the pressure is 0.03-0.06 MPa; the temperature of the heavy aromatics produced at the bottom of the cutting tower is 220-230°C and 0.08-0.1 MPa.

[0019] The beneficial effect of the present invention is that: firstly, naphtha raw material is mixed with HZSM-5, KCA-NL, DLP-3A + Under the action of three molecular sieve catalysts, the catalyst has a long single-pass operation cycle, high product selectivity, long service life, and strong applicability. The efficient catalyst reduces the occurrence of side reactions to a certain extent, reduces the risk of coking, and is converted into light aromatics through aromatization reaction. Then, through a series of separations and a new heat exchange process, naphtha undergoes heat exchange operations in the separation process before and after the aromatization reaction, which can not only control the temperature of the reaction materials, ensure effective separation, and improve reaction efficiency, but also recover most of the waste heat and improve the energy efficiency of the entire process. The final output is a light aromatic blending component with a high octane number, i.e., light aromatics, which meets the standards, and co-produces low-olefin liquefied petroleum gas and heavy aromatics. At the same time, a small amount of dry gas is produced as a by-product. The product quality is high, and the light aromatics produced are high in grade and low in sulfur, which meets the standards. The low-olefin liquefied petroleum gas fully meets the national automotive liquefied petroleum gas standards. The yield of wastewater and waste gas in the entire process is extremely low, and the environmental protection performance is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a flow chart of a method for preparing light aromatics.

[0021] In the figure: V104 fuel gas buffer tank, F101B heating furnace, R101A / R101B reactor, E115 naphtha-heat transfer oil heat exchanger, E114 naphtha-reaction product heat exchanger, A101 air cooler, E103 reaction product water cooler, V102 liquid separation tank, P109A / B mixed aromatics pump, T101 absorption desorption tower, E106 desorption tower reboiler, E105 lower section extraction water cooler, E110 upper section extraction water cooler, P102A / B lower section extraction reflux pump, P106A / B upper section extraction reflux pump, P103A / B desorption tower bottom pump, P105A / B absorption oil pump, E107 stabilizer tower feed heat exchanger, E108 mixed aromatics water cooler, T102 stabilizer tower, A102 air cooler, E109 liquefied gas water cooler, V103 stabilizer tower top reflux tank, E102 stabilizer tower bottom reboiler, P104A / B stabilizer tower reflux pump, T103 aromatics cutting tower, E101AB naphtha-mixed aromatics heat exchanger, E104 water cooler, V108 reflux tank, P108A / B mixed aromatics pump, E111 cutting tower reboiler, E113 heavy aromatics water cooler, E112 naphtha-heavy aromatics heat exchanger, P101A / B heavy aromatics pump, P110A / B raw naphtha pump. DETAILED DESCRIPTION

[0022] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0023] Example 1

[0024] A method for preparing light aromatics comprises the following steps:

[0025] S1. Heat exchange unit: First, the raw naphtha, C5, and raffinate mixture in a weight ratio of 58%:27%:15% is sent from the raw naphtha pump P110A / B to the naphtha-light mixed aromatics heat exchanger E101AB for heat exchange to 52.6°C and a heat exchange pressure of 1.57MPa; then, the heat exchange is continued to be carried out in the naphtha-reaction product heat exchanger E114 to 140.4°C and a heat exchange pressure of 1.51MPa; then, the heat exchange is carried out in the naphtha-heavy aromatics heat exchanger E112 to 150.4°C and a heat exchange pressure of 1.50MPa; and then, the heat exchange is carried out in the naphtha-heat transfer oil heat exchanger E115 to 190.4°C and a heat exchange pressure of 1.49MPa.

[0026] S2, reaction unit: the raw material conveying heating furnace F101B is heated to 400℃, and then enters the aromatization reactor R101A / R101B, and the operation mode of the fixed bed at normal pressure is adopted. The aromatization reactor is filled with HZSM-5, KCA-NL, DLP-3A + Molecular sieve catalysts; HZSM-5, KCA-NL, DLP-3A+ The weight contents of the molecular sieve catalyst are 45%, 30% and 25% respectively.

[0027] S3, heat exchange cooling unit: the reaction product is sequentially heat exchanged through the cutting tower reboiler E11, the desorber reboiler E106, and the naphtha-reaction product heat exchanger E114, and then cooled through the air cooler A101 and the water cooler E103, with a cooling pressure of 0.7 MPa and a cooling temperature of 40° C. The cutting tower reboiler E11 is connected to the cutting tower T103, and the desorber reboiler E106 is connected to the absorption and desorption tower T101.

[0028] S4, first separation unit: the cooled product is separated into oil and gas in the separator tank V102, the rich gas at the top of the separator tank V102 and the mixed aromatics at the bottom enter the middle of the absorption section of the absorption and desorption tower T101, the top of the absorption and desorption tower T101 produces dry gas, and the bottom oil of the absorption and desorption tower T101 enters the stabilization tower T102 after heat exchange in the stabilization tower feed heat exchanger E107.

[0029] S5. Second separation unit: The temperature of the olefin-poor liquefied petroleum gas produced at the top of the stabilization tower T102 is 58°C and the pressure is 0.8MPa. After being cooled to 40°C by the stabilization tower air cooler A102 and the water cooler E109, it enters the stabilization tower reflux tank V103. After the olefin-poor liquefied petroleum gas in the stabilization tower reflux tank V103 is pressurized by the stabilization tower reflux pump P104A / B, a part of it is sent to the top of the stabilization tower T102 for reflux to control the top temperature, and the other part is used as a liquefied petroleum gas product delivery device under the liquid level control of the stabilization tower reflux tank V103; the temperature of crude aromatics produced at the bottom of the stabilization tower T102 is 155°C and 1.0MPa. A part of it is cooled to 30°C after heat exchange at 80°C and 1.0MPa by the stabilization tower feed heat exchanger E107 and pumped to the top of the absorption and desorption tower T101 as an absorbent, and the other part enters the middle of the cutting tower T103.

[0030] S6. The third separation unit: the light mixed aromatics produced at the top of the cutting tower T103 have a temperature of 115°C and a pressure of 0.05MPa. After being cooled by the cutting tower heat exchanger E101A / B and the water cooler E104, they enter the cutting tower reflux tank V108. A part of the light mixed aromatics in the cutting tower reflux tank V108 is transported back to the top of the cutting tower T103 to control the temperature, and the other part that meets the standards is sent to the light mixed aromatics storage tank, i.e., the light aromatics blending component with a high octane number, and the unqualified part is sent to the naphtha storage tank. The bottom of the cutting tower produces heavy aromatics with a temperature of 225°C and 0.09MPa. After heat exchange and cooling, the qualified products are pumped to the heavy aromatics storage tank, and the unqualified products are sent to the naphtha storage tank.

[0031] Example 2

[0032] A method for preparing light aromatics comprises the following steps:

[0033] S1, heat exchange unit: first, the raw material naphtha, C5, raffinate mixture in a weight ratio of 50%:30%:20% is sent from the raw material naphtha pump P110A / B to the naphtha-light mixed aromatics heat exchanger for heat exchange to 50°C; then the heat is continued to be exchanged to 135°C in the naphtha-reaction product heat exchanger; then the heat is exchanged to 145°C in the naphtha-heavy aromatics heat exchanger; and then the heat is exchanged to 185°C in the naphtha-heat transfer oil heat exchanger.

[0034] S2, reaction unit: the raw material conveying heating furnace F101B is heated to 320℃, and then enters the aromatization reactor R101A / R101B, and the operation mode of atmospheric fixed bed is adopted. The aromatization reactor is filled with HZSM-5, KCA-NL, DLP-3A + Molecular sieve catalysts; HZSM-5, KCA-NL, DLP-3A + The weight contents of the molecular sieve catalyst are 40%, 35% and 25% respectively.

[0035] S3, heat exchange cooling unit: the reaction product is sequentially heat exchanged through the cutting tower reboiler E11, the desorber reboiler E106, and the naphtha-reaction product heat exchanger E114, and then cooled through the air cooler A101 and the water cooler E103, with a cooling pressure of 0.6 MPa and a cooling temperature of 40° C. The cutting tower reboiler is connected to the cutting tower, and the desorber reboiler is connected to the absorber and desorber.

[0036] S4, first separation unit: the cooled product is separated into oil and gas in the separator tank V102, the rich gas at the top of the separator tank V102 and the mixed aromatics at the bottom enter the middle of the absorption section of the absorption and desorption tower T101, the top of the absorption and desorption tower T101 produces dry gas, and the bottom oil of the absorption and desorption tower T101 enters the stabilization tower T102 after heat exchange in the stabilization tower feed heat exchanger E107.

[0037] S5. Second separation unit: The temperature of the olefin-poor liquefied petroleum gas produced at the top of the stabilization tower T102 is 55°C and the pressure is 0.7MPa. After being cooled to 40°C by the stabilization tower air cooler A102 and the water cooler E109, it enters the stabilization tower reflux tank V103. After the olefin-poor liquefied petroleum gas in the stabilization tower reflux tank V103 is pressurized by the stabilization tower reflux pump P104A / B, a part of it is sent to the top of the stabilization tower T102 for reflux to control the top temperature, and the other part is used as a liquefied petroleum gas product delivery device under the liquid level control of the stabilization tower reflux tank V103; the crude aromatics produced at the bottom of the stabilization tower T102 have a temperature of 150°C and 0.9MPa. A part of it is cooled to 30°C after heat exchange at 80°C and 1.0MPa by the stabilization tower feed heat exchanger E107 and pumped to the top of the absorption and desorption tower T101 as an absorbent, and the other part enters the middle of the cutting tower T103.

[0038] S6, the third separation unit: the light mixed aromatics produced at the top of the cutting tower T103 have a temperature of 110°C and a pressure of 0.03MPa. After being cooled by the cutting tower heat exchanger E101A / B and the water cooler E104, they enter the cutting tower reflux tank V108. A part of the light mixed aromatics in the cutting tower reflux tank V108 is transported back to the top of the cutting tower T103 to control the temperature, and the other part that is qualified is sent to the light mixed aromatics storage tank, i.e. light aromatics, and the unqualified is sent to the naphtha storage tank. The bottom of the cutting tower produces heavy aromatics with a temperature of 220°C and 0.08MPa. After heat exchange and cooling, the qualified products are pumped to the heavy aromatics storage tank, and the unqualified products are sent to the naphtha storage tank.

[0039] Example 3

[0040] A method for preparing light aromatics comprises the following steps:

[0041] S1, heat exchange unit: first, the raw material naphtha, C5, raffinate mixture in a weight ratio of 60%:25%:15% is sent from the raw material naphtha pump P110A / B to the naphtha-light mixed aromatics heat exchanger for heat exchange to 55°C; then the heat is continued to be exchanged to 145°C in the naphtha-reaction product heat exchanger; then the heat is exchanged to 155°C in the naphtha-heavy aromatics heat exchanger; and then the heat is exchanged to 195°C in the naphtha-heat transfer oil heat exchanger.

[0042] S2, reaction unit: the raw material conveying heating furnace F101B is heated to 420℃, and then enters the aromatization reactor R101A / R101B, and the operation mode of the fixed bed at normal pressure is adopted. The aromatization reactor is filled with HZSM-5, KCA-NL, DLP-3A + Molecular sieve catalysts; HZSM-5, KCA-NL, DLP-3A + The weight contents of the molecular sieve catalyst are 50%, 25% and 25% respectively.

[0043] S3, heat exchange cooling unit: the reaction product is sequentially heat exchanged through the cutting tower reboiler E11, the desorber reboiler E106, and the naphtha-reaction product heat exchanger E114, and then cooled through the air cooler A101 and the water cooler E103, with a cooling pressure of 0.8 MPa and a cooling temperature of 45° C. The cutting tower reboiler is connected to the cutting tower, and the desorber reboiler is connected to the absorber and desorber.

[0044] S4, first separation unit: the cooled product is separated into oil and gas in the separator tank V102, the rich gas at the top of the separator tank V102 and the mixed aromatics at the bottom enter the middle of the absorption section of the absorption and desorption tower T101, the top of the absorption and desorption tower T101 produces dry gas, and the bottom oil of the absorption and desorption tower T101 enters the stabilization tower T102 after heat exchange in the stabilization tower feed heat exchanger E107.

[0045] S5. Second separation unit: The temperature of the olefin-poor liquefied petroleum gas produced at the top of the stabilization tower T102 is 60°C and the pressure is 0.8MPa. After being cooled to 40°C by the stabilization tower air cooler A102 and the water cooler E109, it enters the stabilization tower reflux tank V103. After the olefin-poor liquefied petroleum gas in the stabilization tower reflux tank V103 is pressurized by the stabilization tower reflux pump P104A / B, a part of it is sent to the top of the stabilization tower T102 for reflux to control the top temperature, and the other part is used as a liquefied petroleum gas product delivery device under the liquid level control of the stabilization tower reflux tank V103; the crude aromatics produced at the bottom of the stabilization tower T102 have a temperature of 160°C and 1.0MPa. A part of it is cooled to 40°C after heat exchange at 80°C and 1.0MPa by the stabilization tower feed heat exchanger E107 and pumped to the top of the absorption and desorption tower T101 as an absorbent, and the other part enters the middle of the cutting tower T103.

[0046] S6. The third separation unit: the light mixed aromatics produced at the top of the cutting tower T103 have a temperature of 120°C and a pressure of 0.06MPa. After being cooled by the cutting tower heat exchanger E101A / B and the water cooler E104, they enter the cutting tower reflux tank V108. A part of the light mixed aromatics in the cutting tower reflux tank V108 is transported back to the top of the cutting tower T103 to control the temperature, and the other part that is qualified is sent to the light mixed aromatics storage tank, i.e. light aromatics, and the unqualified is sent to the naphtha storage tank. The bottom of the cutting tower produces heavy aromatics with a temperature of 230°C and 0.1MPa. After heat exchange and cooling, the qualified products are pumped to the heavy aromatics storage tank, and the unqualified products are sent to the naphtha storage tank.

[0047] 1. The yields of the reaction products of Examples 1 to 3 are recorded in Table 1 below:

[0048] Product Distribution Example 1 Example 2 Example 3 Yield of mixed aromatics, mass % 65 62 63 Heavy aromatics yield, mass % 21 20 21 Olefin-depleted liquefied petroleum gas, mass % 10 12 12 Other substances and losses, mass % 4 6 4 Mixed aromatics octane number RON 93.5 92.4 92.6 Benzene content in mixed aromatics, % 58 56 56 Toluene content in mixed aromatics, % 16 16 15 Xylene content in mixed aromatics, % 16 16 16 Content of other substances in mixed aromatics, % 10 12 13

[0049] The embodiment gradually increases the heating temperature of naphtha raw materials through a step-by-step heat exchange regulation system, avoids unbalanced heat exchange leading to reaction out of control or product quality degradation, improves the production efficiency of aromatics, adopts a new heat exchange process, reduces energy consumption, and realizes the recovery and reuse of most of the heat, meeting the requirements of energy conservation and environmental protection. +Under the action of molecular sieve catalysts, the three molecular sieve catalysts improve the dehydrogenation activity and stability of naphtha, promote the improvement of aromatization reaction capacity, increase the yield of light aromatics, and generate a gas phase containing methane and carbon 2 to carbon 4 fractions. Then, through a series of separations such as absorption and desorption towers, stabilization towers and cutting towers, unnecessary components are removed and useful components are recovered, and finally a light aromatic blending component (light aromatics) with a high octane number that meets the standards is produced, while heavy aromatics, low-olefin liquefied petroleum gas and a small amount of dry gas are produced as by-products, and the product quality is high. In the separation process of aromatization products, pressure and temperature control are crucial to ensure separation efficiency and product quality. Different separation steps may require different operating pressures to optimize the separation effect. Through the effective control of temperature and pressure in multiple stages of the stabilization tower and cutting tower, the separation efficiency can be improved, product quality can be guaranteed, and energy consumption can be reduced at the same time. The device has low energy consumption and good green environmental protection performance.

[0050] 2. Effect of catalyst type on aromatization reaction

[0051] According to the process conditions of Example 1, the yield of mixed aromatics produced by aromatization reaction products was analyzed by different molecular sieve catalysts. The weight contents of HZSM-5 and KCA-NL or HZSM-5 and DLP-3A were 57% and 43%, respectively. + , as shown in Table 2 below:

[0052]

[0053] From Table 2 above, we can see that HZSM-5, KCA-NL, DLP-3A are selected + The combination of three molecular sieve catalysts catalyzes the reaction together, effectively aromatizing naphtha, C5 and raffinate oil feedstocks, and increasing the yield of mixed aromatics and heavy aromatics, indicating that the catalyst has strong applicability and improves the yield of reaction products.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing light aromatics, characterized in that: The following steps are involved: S1, heat exchange unit: pump the raw material naphtha, C5, and raffinate oil mixture to the heat exchange unit for gradient heat exchange, the gradient heat exchange temperature is from 50℃ to 195℃, and the gradient heat exchange pressure is from 1.45 to 1.6MPa; S2, reaction unit: the raw material conveying heating furnace is heated to 320-420°C, and then enters the aromatization reactor, which is filled with HZSM-5, KCA-NL, DLP-3A + Molecular sieve catalysts; S3, heat exchange cooling unit: the reaction product passes through the cutting tower reboiler, desorption tower reboiler, heat exchanger in sequence, and then passes through the air cooler and water cooler to cool to 35-45°C; S4, first separation unit: the cooled product is separated into oil and gas in a separator tank, the rich gas at the top of the separator tank and the mixed aromatics at the bottom of the separator tank enter the middle of the absorption section of the absorption and desorption tower, the top of the absorption and desorption tower produces dry gas, and the oil at the bottom of the absorption and desorption tower enters the stabilization tower after heat exchange; S5, the second separation unit: the olefin-poor liquefied petroleum gas produced at the top of the stabilization tower is cooled and then enters the reflux tank of the stabilization tower. After the olefin-poor liquefied petroleum gas in the reflux tank of the stabilization tower is pressurized by a pump, a part of it is sent to the top of the stabilization tower for reflux to control the top temperature, and the other part is used as a liquefied petroleum gas product delivery device under the liquid level control of the reflux tank of the stabilization tower; crude aromatics are produced at the bottom of the stabilization tower, a part of which is cooled and pumped to the top of the absorption and desorption tower as an absorbent after heat exchange in the heat exchanger, and the other part enters the middle of the cutting tower; S6, the third separation unit: the light mixed aromatics produced at the top of the cutting tower enter the cutting tower reflux tank after heat exchange and cooling, a part of the light mixed aromatics in the cutting tower reflux tank is transported back to the top of the cutting tower to control the temperature, and the other part that is qualified is sent to the light mixed aromatics storage tank, and the unqualified is sent to the naphtha storage tank; heavy aromatics are produced at the bottom of the cutting tower, and the qualified products are pumped to the heavy aromatics storage tank after heat exchange and cooling, and the unqualified are sent to the naphtha storage tank.

2. The method for preparing light aromatics according to claim 1, characterized in that: The weight ratio of naphtha, C5 and raffinate oil is 50-60%: 25-30%: 10-25%.

3. The method for preparing light aromatics according to claim 1, characterized in that: The heat exchange unit in step S1 includes the following steps: the raw material first enters a naphtha-light mixed aromatic heat exchanger for heat exchange to 50-55°C; then continues to heat exchange to 135-145°C in a naphtha-reaction product heat exchanger; then heat exchanges to 145-155°C in a naphtha-heavy aromatic heat exchanger; and then enters a naphtha-heat transfer oil heat exchanger for heat exchange to 185-195°C.

4. The method for preparing light aromatics according to claim 3, characterized in that: The heat exchange unit includes the following steps: the raw material first enters a naphtha-light mixed aromatic heat exchanger for heat exchange to 52.6°C, with a heat exchange pressure of 1.57MPa; then continues to heat exchange to 140.4°C in a naphtha-reaction product heat exchanger, with a heat exchange pressure of 1.51MPa; then heat exchanges to 150.4°C in a naphtha-heavy aromatic heat exchanger, with a heat exchange pressure of 1.50MPa; and then enters a naphtha-heat transfer oil heat exchanger for heat exchange to 190.4°C, with a heat exchange pressure of 1.49MPa.

5. The method for preparing light aromatics according to claim 1, characterized in that: HZSM-5, KCA-NL, DLP-3A in step S2 + The weight contents of the molecular sieve catalyst are 40-50%, 25-35% and 20-30% respectively.

6. The method for preparing light aromatics according to claim 1, characterized in that: In step S3, the reaction product is sequentially passed through a cutting tower reboiler, a desorption tower reboiler, and a naphtha-reaction product heat exchanger, and then cooled through an air cooler and a water cooler, with a cooling pressure of 0.6 to 0.8 MPa and a cooling temperature of 35 to 45°C.

7. The method for preparing light aromatics according to claim 1, characterized in that: The temperature of the olefin-poor liquefied petroleum gas produced at the top of the stabilization tower is 55-60°C and the pressure is 0.7-0.8MPa; the temperature of crude aromatics produced at the bottom of the stabilization tower is 150-160°C and 0.9-1.0MPa.

8. The method for preparing light aromatics according to claim 1, characterized in that: Crude aromatics are produced at the bottom of the stabilizer, part of which is cooled to 30°C after heat exchange at 80°C and 1.0 MPa in the stabilizer feed heat exchanger and pumped to the top of the absorption and desorption tower as absorbent.

9. The method for preparing light aromatics according to claim 1, characterized in that: The temperature of light mixed aromatics produced at the top of the cutting tower is 110-120°C and the pressure is 0.03-0.06MPa; the temperature of heavy aromatics produced at the bottom of the cutting tower is 220-230°C and 0.08-0.1MPa.

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