System for preparing p-xylene through carbon dioxide direct-connection toluene alkylation
The synthesis of methanol by carbon dioxide and green hydrogen and alkylation with toluene is carried out to prepare paraxylene, which solves the problems of low selectivity of paraxylene and low utilization of toluene in the prior art, and achieves efficient energy utilization and low cost operation.
Patent Information
- Application Number
- CN202421809390.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-29
- Publication Date
- 2025-06-24
- Estimated Expiration
- 2034-07-29
AI Technical Summary
In the prior art, there is a problem that the selectivity of paraxylene and the utilization rate of toluene are low.
Methanol is synthesized by carbon dioxide and green hydrogen as raw material gas, and methanol is alkylated with toluene to prepare paraxylene. The system includes a methanol synthesis reaction unit, a methanol product separation unit, a toluene alkylation reaction unit, a three-phase separation unit, a toluene circulation unit and a xylene separation and purification unit.
The utilization rate of toluene is improved, the selectivity of mixed xylene and paraxylene is increased, the energy consumption of isomerization and subsequent separation of mixed xylene is reduced, the comprehensive utilization of energy is achieved, and the equipment investment and operation costs are reduced.
Smart Images
Figure CN223010520U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of catalytic chemical industry, in particular to a system for directly coupling carbon dioxide with toluene for alkylation to prepare p-xylene. Background Technique
[0002] To achieve the goal of carbon neutrality, on the one hand, it is necessary to start from the source to adjust the energy consumption structure, improve energy utilization efficiency, and reduce CO2 emissions; on the other hand, it is necessary to capture and resourcefully utilize the generated CO2. Preparing high-end chemicals from CO2 can not only alleviate the environmental problems caused by excessive CO2 emissions, but also provide a feasible technical route for the synthesis of high-value-added chemicals.
[0003] As an important organic synthesis raw material, p-xylene is widely used in the fields of textiles and packaging materials, mainly used for preparing terephthalate and terephthalic acid, etc. The latter is used as an intermediate for plastics and polyester fibers, as well as a raw material for coatings, dyes, and pesticides. The main methods for preparing xylene industrially are toluene disproportionation method, toluene trimethylbenzene alkyl transfer method, and toluene methanol alkylation method. Among them, toluene methanol alkylation to produce xylene belongs to an environmentally friendly reaction, and the theoretical by-product is only water; efficiently converting and utilizing carbon dioxide has become a research hotspot in the field of energy chemistry. Therefore, using CO2 and H2 to replace methanol as active alkylating groups to react with toluene for alkylation provides a new possibility for the synthesis of p-xylene. Content of the Utility Model
[0004] The purpose of the utility model is to provide a system for directly coupling carbon dioxide with toluene for alkylation to prepare p-xylene, which solves the technical problems of low selectivity of p-xylene and low utilization rate of toluene existing in the prior art.
[0005] The system for directly coupling carbon dioxide with toluene for alkylation to prepare p-xylene provided by the utility model includes a methanol synthesis reaction unit, a methanol product separation unit, a toluene alkylation reaction unit, a three-phase separation unit, a toluene circulation unit, and a xylene separation and purification unit connected in sequence;
[0006] The methanol synthesis reaction unit synthesizes methanol using carbon dioxide and green hydrogen as raw material gases.
[0007] Further, a raw material gas unit is provided in the methanol synthesis reaction unit;
[0008] A p-xylene collection unit is further connected after the xylene separation and purification unit.
[0009] Further, the methanol synthesis reaction unit includes a shell-and-tube fixed-bed reactor.
[0010] Further, the methanol product separation unit is provided with a crude methanol outlet and a gas outlet;
[0011] The crude methanol outlet is connected to the toluene alkylation reaction unit;
[0012] The gas outlet is connected to the raw material gas unit.
[0013] Furthermore, the toluene alkylation reaction unit includes a shell-and-tube fixed bed reactor.
[0014] Furthermore, a first connecting pipeline and a second connecting pipeline are provided at the gas phase outlet of the three-phase separation unit;
[0015] The first connecting pipeline is connected to the methanol synthesis reaction unit;
[0016] The second connecting pipeline is connected to the toluene alkylation reaction unit.
[0017] Furthermore, the oil phase outlet of the three-phase separation unit is connected to the toluene circulation unit.
[0018] Furthermore, the toluene circulation unit includes a toluene circulation tower.
[0019] Furthermore, the toluene circulation unit is provided with a first outlet pipeline and a second outlet pipeline;
[0020] The first outlet pipeline is connected to the toluene alkylation reaction unit, and is used to return the toluene separated by the toluene circulation unit to the toluene alkylation reaction unit;
[0021] The second outlet pipeline is connected to the xylene separation and purification unit, and is used to make the aromatic hydrocarbon mixture separated by the toluene circulation unit enter the xylene separation and purification unit.
[0022] Furthermore, the xylene separation and purification unit includes a rectification unit and a crystallization unit.
[0023] Compared with the prior art, the present utility model has the following beneficial effects:
[0024] The system for directly coupling carbon dioxide with toluene alkylation to prepare p-xylene provided by the present utility model realizes the resource utilization of carbon dioxide and the increase in production of p-xylene through the technologies of hydrogenating carbon dioxide to prepare methanol and toluene alkylation reaction; in short, the system for preparing p-xylene provided by the present utility model, under the coordinated cooperation of each unit, not only improves the toluene utilization rate, increases the selectivity of mixed xylene and p-xylene, but also reduces the energy consumption of isomerization of mixed xylene and subsequent separation, can effectively reduce equipment investment and cost operation, and at the same time effectively couples the heat demand of the exothermic reaction of methanol generation and the endothermic reaction of toluene alkylation, enables the effective matching of the two heats, realizes the comprehensive utilization of energy, and is beneficial to further reducing energy consumption. Description of the Drawings
[0025] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.
[0026] Figure 1 It is a schematic structural diagram of the methanol synthesis reaction unit and the toluene alkylation reaction unit;
[0027] Figure 2 It is a schematic diagram of the structure and operation of the system for directly coupling carbon dioxide with toluene alkylation to prepare p-xylene.
[0028] Icon: 1 - Feed gas; 2 - Crude methanol mixture; 3 - Unreacted feed gas; 4 - Crude methanol; 5 - Toluene alkylation mixture; 6 - Aqueous phase; 7 - Gas phase; 8 - Organic oil phase; 9 - Feed toluene; 10 - Recirculated toluene; 11 - Aromatic hydrocarbon mixture; 12 - Aromatic hydrocarbons excluding xylene; 13 - p-Xylene; 101 - Tubular fixed-bed reactor of the methanol synthesis reaction unit; 102 - Fixed-bed reactor of the methanol synthesis reaction unit; 103 - Connection point between the methanol product separation unit and the toluene alkylation reaction unit; 104 - Tubular fixed-bed reactor of the toluene alkylation reaction unit; 105 - Fixed-bed reactor of the toluene alkylation reaction unit. Specific embodiments
[0029] The following will clearly and completely describe the technical solutions of the present invention in combination with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.
[0030] The system for directly coupling carbon dioxide with toluene alkylation to prepare p-xylene provided by the present invention includes a methanol synthesis reaction unit, a methanol product separation unit, a toluene alkylation reaction unit, a three-phase separation unit, a toluene circulation unit, and a xylene separation and purification unit connected in sequence;
[0031] The methanol synthesis reaction unit synthesizes methanol using carbon dioxide and green hydrogen as feed gas.
[0032] The system for directly coupling carbon dioxide with toluene alkylation to prepare p-xylene provided by the present invention realizes the resource utilization of carbon dioxide and the increase in production of p-xylene through the technologies of carbon dioxide hydrogenation to prepare methanol and toluene alkylation reaction.
[0033] In summary, the system for preparing p-xylene provided by the present utility model, through the coordinated cooperation of each unit, not only improves the toluene utilization rate, increases the selectivity of mixed xylene and p-xylene, but also reduces the energy consumption of the isomerization of mixed xylene and subsequent separation, can effectively reduce the equipment investment and cost operation, and at the same time effectively couples the heat demand of the exothermic reaction of methanol formation and the endothermic reaction of toluene alkylation, enabling the effective matching of the heat of both, realizing the comprehensive utilization of energy and being conducive to further reducing energy consumption.
[0034] In a preferred embodiment, a raw material gas unit may be provided in the methanol synthesis reaction unit;
[0035] A p-xylene collection unit may also be connected after the xylene separation and purification unit.
[0036] In a preferred embodiment, the methanol product separation unit is provided with a crude methanol outlet and a gas outlet; among them, the crude methanol outlet is connected to the toluene alkylation reaction unit; the gas outlet is connected to the raw material gas unit and the toluene alkylation reaction unit.
[0037] In the present utility model, the methanol product separation unit is provided with a crude methanol outlet and an outlet for unreacted carbon dioxide, hydrogen, and inorganic gases in the methanol product; among them, the crude methanol outlet is connected to the toluene alkylation reaction unit, and the generated crude methanol can enter the toluene alkylation reaction unit for reaction as a reactant without precise rectification, which not only reduces the carbon dioxide emissions but also realizes energy conservation and consumption reduction; the outlet for unreacted carbon dioxide, hydrogen, and inorganic gases in the methanol product is connected to the raw material gas unit, and through the recycling of unreacted raw material gas, the conversion rate of carbon dioxide can reach more than 90%, and the selectivity of methanol can reach more than 80%.
[0038] In a preferred embodiment, the methanol synthesis reaction unit includes a shell-and-tube fixed-bed reactor, and the toluene alkylation reaction unit includes a shell-and-tube fixed-bed reactor.
[0039] In the present utility model, the toluene alkylation reaction unit may adopt multiple shell-and-tube fixed-bed reactors. The crude methanol generated by the methanol synthesis reaction unit undergoes a shape-selective alkylation reaction with toluene, and the selectivity of generating mixed xylene is more than 90%, the selectivity of p-xylene in the mixed xylene is more than 94%, the toluene conversion rate is greater than 35%, and the selectivity of benzene in the product is less than 2%. The mixed xylene can be separated by a crystallization separation process to obtain high-purity p-xylene.
[0040] The structural schematic diagrams of the methanol synthesis reaction unit and the toluene alkylation reaction unit are shown in Figure 1, including the tubular fixed-bed reactor 101 of the methanol synthesis reaction unit, the fixed-bed reactor 102 of the methanol synthesis reaction unit, the connection point 103 between the methanol product separation unit and the toluene alkylation reaction unit, the tubular fixed-bed reactor 104 of the toluene alkylation reaction unit, and the fixed-bed reactor 105 of the toluene alkylation reaction unit.
[0041] In the present utility model, heat transfer can be carried out through heat transfer oil in the tubular fixed-bed reactor of the toluene alkylation reaction unit, coupling the exothermic reaction of methanol production and the endothermic reaction of toluene alkylation. The heat transfer oil effectively matches the heat of the two, realizing the comprehensive utilization of energy and further reducing energy consumption.
[0042] In a preferred embodiment, the gas phase outlet of the three-phase separation unit is provided with a first connecting pipeline and a second connecting pipeline; wherein, the first connecting pipeline is connected to the methanol synthesis reaction unit; the second connecting pipeline is connected to the toluene alkylation reaction unit.
[0043] In the present utility model, the three-phase separation unit is provided with a gas phase outlet, an oil phase outlet and a water phase outlet; wherein, the connecting pipeline of the gas phase outlet is divided into two branches, one branch connecting pipeline returns to the methanol synthesis reaction unit, and the other branch connecting pipeline returns to the toluene alkylation reaction unit; the oil phase outlet is connected to the toluene circulation unit; the water phase outlet discharges out of the system.
[0044] In a preferred embodiment, the toluene circulation unit includes, but is not limited to, a toluene circulation tower.
[0045] In a preferred embodiment, the toluene circulation unit is provided with a first outlet pipeline and a second outlet pipeline; wherein, the first outlet pipeline is connected to the toluene alkylation reaction unit, for returning the toluene separated by the toluene circulation unit to the toluene alkylation reaction unit; the second outlet pipeline is connected to the xylene separation and purification unit, for enabling the aromatic hydrocarbon mixture separated by the toluene circulation unit to enter the xylene separation and purification unit.
[0046] The typical structure and operation process of a system for directly coupling carbon dioxide with toluene alkylation to prepare p-xylene are shown in Figure 2 , including the following units and their operation steps:
[0047] The raw material gas 1 (carbon dioxide and green hydrogen) synthesizes methanol through the methanol synthesis reaction unit I to obtain a crude methanol mixed product 2;
[0048] The crude methanol mixed product 2 is separated through the methanol product separation unit II to obtain crude methanol 4 and unreacted raw material gas 3;
[0049] The unreacted raw material gas 3 can be returned to the methanol synthesis reaction unit I to continue synthesizing methanol, or can enter the toluene alkylation reaction unit III;
[0050] The crude methanol 4 undergoes toluene alkylation reaction in the toluene alkylation reaction unit III to obtain a toluene alkylation mixed product 5;
[0051] The toluene alkylation mixed product 5 is separated through the three-phase separation unit IV to obtain an aqueous phase 6 (containing high-concentration hydrogen), a gas phase 7, and an organic oil phase 8;
[0052] The aqueous phase 6 is discharged out of the system; the gas phase 7 can be returned to the methanol synthesis reaction unit I and can also be returned to the toluene alkylation reaction unit III;
[0053] The organic oil phase 8 is separated through the toluene circulation unit V (i.e., the toluene circulation tower) to obtain toluene and an aromatic hydrocarbon mixture 11; among them, the feed toluene 9 is fed into the toluene circulation tower, and the circulating toluene 10 at the side-line outlet of the toluene circulation tower is returned to the toluene alkylation reaction unit III;
[0054] The aromatic hydrocarbon mixture 11 is separated through the xylene separation and purification unit VI to obtain an aromatic hydrocarbon product 12 excluding xylene and p-xylene 13;
[0055] The p-xylene 13 is collected through the p-xylene collection unit VII.
[0056] In a preferred embodiment, the xylene separation and purification unit VI includes, but is not limited to, a rectification unit and a crystallization unit.
[0057] Example 1
[0058] A system for directly coupling carbon dioxide and toluene alkylation to prepare p-xylene includes a methanol synthesis reaction unit, a methanol product separation unit, a toluene alkylation reaction unit, a three-phase separation unit, a toluene circulation unit, as well as a xylene separation and purification unit and a p-xylene collection unit connected in sequence;
[0059] The methanol synthesis reaction unit synthesizes methanol using carbon dioxide and green hydrogen as raw material gases;
[0060] A raw material gas unit is provided in the methanol synthesis reaction unit.
[0061] In this example, the methanol product separation unit is provided with a crude methanol outlet and a gas outlet; the crude methanol outlet is connected to the toluene alkylation reaction unit; the gas outlet is connected to the raw material gas unit;
[0062] The structural schematic diagrams of the methanol synthesis reaction unit and the toluene alkylation reaction unit are shown in Figure 1, including the tubular fixed-bed reactor 101 of the methanol synthesis reaction unit, the fixed-bed reactor 102 of the methanol synthesis reaction unit, the connection point 103 between the methanol product separation unit and the toluene alkylation reaction unit, the tubular fixed-bed reactor 104 of the toluene alkylation reaction unit, and the fixed-bed reactor 105 of the toluene alkylation reaction unit;
[0063] The three-phase separation unit is provided with a gas outlet, an oil phase outlet, and a water phase outlet; among them, the connecting pipeline of the gas outlet is divided into two branches, one branch pipeline returns to the methanol synthesis reaction unit, and the other branch pipeline returns to the toluene alkylation reaction unit; the oil phase outlet is connected to the toluene circulation unit; the water phase outlet is then discharged out of the system;
[0064] The toluene circulation unit is a toluene circulation tower, and the toluene circulation tower is provided with a first outlet pipeline and a second outlet pipeline; the first outlet pipeline is connected to the toluene alkylation reaction unit for returning the toluene separated by the toluene circulation unit to the toluene alkylation reaction unit; the second outlet pipeline is connected to the xylene separation and purification unit for enabling the aromatic hydrocarbon mixture separated by the toluene circulation unit to enter the xylene separation and purification unit;
[0065] The xylene separation and purification unit includes a rectification unit and a crystallization unit.
[0066] Example 2
[0067] The difference between the system of this example and that of Example 1 is that the gas outlet of the methanol product separation unit is connected to the toluene alkylation reaction unit instead of the raw material gas unit;
[0068] The rest are the same as those in Example 1.
[0069] Compared with Example 1, the advantage of this example is that the gas in the methanol product separation unit contains a high concentration of hydrogen, making the hydrogen concentration in the toluene alkylation reaction higher than that in Example 1, and the amount of hydrogen supplemented additionally in the continuous reaction will be reduced, which is beneficial to the toluene alkylation reaction; however, there is a large amount of unreacted carbon dioxide gas in the gas of the methanol product separation unit, which will result in a low total conversion rate of carbon dioxide and a low methanol yield.
[0070] Example 3
[0071] The difference between the system of this example and that of Example 1 is that the connecting pipeline of the gas outlet of the three-phase separation unit is only one branch, and this branch pipeline returns to the methanol synthesis reaction unit;
[0072] The rest are the same as those in Example 1.
[0073] Compared with Example 1, the advantage of this example is that the unreacted hydrogen and carbon dioxide in the gas phase component of the three-phase separation unit can be further used for methanol synthesis, improving the conversion rates of carbon dioxide and hydrogen, as well as increasing the methanol yield. Meanwhile, the benzene-alcohol ratio in the toluene alkylation reaction can be adjusted timely to improve the toluene utilization rate. However, the unreacted hydrogen cannot be fully utilized.
[0074] Example 4
[0075] The difference between the system of this example and that of Example 1 is that there is only one connecting pipeline at the gas phase outlet of the three-phase separation unit, and this pipeline returns to the toluene alkylation reaction unit.
[0076] The rest are the same as those in Example 1.
[0077] Compared with Example 1, the advantage of this example is that the unreacted hydrogen and carbon dioxide can be used as methyl reagents to carry out the alkylation reaction, improving the utilization rates of carbon dioxide and hydrogen. However, it cannot increase the methanol yield and further improve the toluene utilization rate.
[0078] Comparative Example 1
[0079] The difference between the system of this comparative example and that of Example 1 is that in this comparative example, the three-phase separation unit is not provided, that is, the toluene alkylation reaction unit is directly connected to the toluene recycling unit.
[0080] The rest are the same as those in Example 1.
[0081] Compared with Example 1, the defect of this comparative example is that the unreacted hydrogen and carbon dioxide cannot be separated and enter the methanol synthesis unit and the toluene alkylation reaction unit, which will result in low carbon dioxide conversion rate and low hydrogen utilization rate, and at the same time increase the load of the toluene recycling unit.
[0082] Comparative Example 2
[0083] The difference between the system of this comparative example and that of Example 1 is that in this comparative example, a gas-liquid separator is used to replace the three-phase separation unit.
[0084] The rest are the same as those in Example 1.
[0085] Compared with Example 1, the defect of this comparative example is that the oil phase and water in the liquid cannot be fully separated, resulting in an indefinite amount of water being brought into the toluene recycling unit when the liquid enters, causing a decline in the performance of the toluene alkylation reaction.
[0086] Comparative Example 3
[0087] The difference between the system of this comparative example and that of Example 1 is that in this comparative example, the toluene recycling unit is not provided, that is, the three-phase separation unit is directly connected to the xylene separation and purification unit.
[0088] The rest is the same as in Example 1.
[0089] Compared with Example 1, the defect of this comparative example is that the unreacted toluene in the oil phase of the three-phase separation unit will enter the xylene separation unit, resulting in toluene loss and reducing the toluene utilization rate.
[0090] Test Example
[0091] The systems of Examples 1-4 and Comparative Examples 1-3 were tested, and the results are shown in Table 1.
[0092] The test method is as follows:
[0093] Taking the system of Example 1 as an example for testing, it includes the following steps:
[0094] (1) Using the captured carbon dioxide and green hydrogen produced by electrolyzing water as the raw material gas, the volume content of CO2 in the raw material gas is 30%, the volume content of H2 is 60%, and the volume content of inert gas is 10%;
[0095] The raw material gas enters the methanol synthesis reaction unit. The reaction pressure for methanol synthesis is 5 MPa, the reaction temperature is 260 °C, and the methanol synthesis reaction is carried out under the catalysis of a copper-loaded zinc oxide and zirconia (Cu / ZnO / ZrO2) catalyst. After the methanol synthesis reaction, the product enters the methanol product separation unit. After separation, crude methanol and unreacted raw material gas are obtained, and the unreacted raw material gas returns to the methanol synthesis reaction unit for further reaction;
[0096] (2) The crude methanol obtained in step (1) enters the toluene alkylation reaction unit. The reaction pressure for toluene alkylation is 0.3 MPa, the reaction temperature is 460 °C, the toluene mass space velocity is 6 h -1 , the hydrogen space velocity is 12 L / h. After the toluene alkylation reaction, the product enters the three-phase separation unit, and after separation, a mixed aromatic hydrocarbon is obtained;
[0097] Among them, heat transfer is carried out through heat transfer oil in the tubular fixed-bed reactor of the toluene alkylation reaction unit to couple the exothermic reaction of methanol production and the endothermic reaction of toluene alkylation, and the heat transfer oil is used to effectively match the heat of the two;
[0098] The product after toluene alkylation enters the three-phase separation unit. After separation by the three-phase separation unit, a gas phase, an aqueous phase, and an oil phase are obtained, which are a gas phase containing a large amount of hydrogen and a small amount of light hydrocarbons, an aqueous phase containing a small amount of impurities such as methanol, and an organic oil phase containing a mixed aromatic hydrocarbon in sequence;
[0099] (3) The mixed aromatic hydrocarbon obtained in step (2) enters the toluene recycling unit, and after separation, toluene and an aromatic hydrocarbon mixture are obtained;
[0100] The toluene returns to the toluene alkylation reaction unit;
[0101] The aromatic hydrocarbon mixture enters the xylene separation and purification unit, and is subjected to rectification and crystallization separation in sequence to obtain p-xylene.
[0102] Table 1
[0103]
[0104] It can be seen that the system for preparing p-xylene provided by the present utility model, under the coordinated cooperation of each unit, not only improves the toluene utilization rate, increases the selectivity of mixed xylene and p-xylene, but also reduces the energy consumption of the isomerization of mixed xylene and subsequent separation, can effectively reduce the equipment investment and cost operation, and at the same time effectively couples the heat demand of the exothermic reaction of methanol production and the endothermic reaction of toluene alkylation, enables the effective matching of the heat of both, and realizes the comprehensive utilization of energy.
[0105] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present utility model, rather than to limit it; although the present utility model has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present utility model.
Claims
1. A system for preparing p-xylene by direct alkylation of toluene with carbon dioxide, characterized in that: It includes a methanol synthesis reaction unit, a methanol product separation unit, a toluene alkylation reaction unit, a three-phase separation unit, a toluene circulation unit, and a xylene separation and purification unit which are connected in sequence; The methanol synthesis reaction unit synthesizes methanol by using carbon dioxide and green hydrogen as feed gas; The methanol synthesis reaction unit is provided with a raw gas unit; The xylene separation and purification unit is also connected to a p-xylene collection unit.
2. The system according to claim 1, characterized in that The methanol synthesis reaction unit comprises a tube-in-tube fixed bed reactor.
3. The system according to claim 1, characterized in that The methanol product separation unit is provided with a crude methanol outlet and a gas outlet; The crude methanol outlet is connected to a toluene alkylation reaction unit; The gas outlet is connected to a raw gas unit.
4. The system according to claim 3, characterized in that The toluene alkylation reaction unit comprises a tube-in-tube fixed bed reactor.
5. The system according to any one of claims 1 to 4, characterized in that: The gas phase outlet of the three-phase separation unit is provided with a first connecting pipeline and a second connecting pipeline; The first connecting pipeline is connected to the methanol synthesis reaction unit; The second connecting pipeline is connected to the toluene alkylation reaction unit.
6. The system according to claim 5, characterized in that The oil phase outlet of the three-phase separation unit is connected to a toluene circulation unit.
7. The system according to claim 6, characterized in that The toluene circulation unit includes a toluene circulation tower.
8. The system according to claim 6, characterized in that The toluene circulation unit is provided with a first outlet pipeline and a second outlet pipeline; The first outlet pipeline is connected to the toluene alkylation reaction unit, and is used to return the toluene separated by the toluene circulation unit to the toluene alkylation reaction unit; The second outlet pipeline is connected to the xylene separation and purification unit, and is used to allow the aromatic hydrocarbon mixture separated by the toluene circulation unit to enter the xylene separation and purification unit.
9. The system according to claim 8, characterized in that The xylene separation and purification unit comprises a distillation unit and a crystallization unit.