Methods and cracking systems for methanol-to-C2-C3 olefin coupled hydrocarbon cracking

Abstract

This invention provides a method and system for methanol-to-C2-C3 olefins coupled with hydrocarbon cracking, comprising: S01: methanol feedstock is vaporized by heat exchange and then fed into a first-stage fixed-bed reactor, where it contacts an alumina catalyst and reacts to produce a dimethyl ether stream; S02: the dimethyl ether stream is mixed with a diluent and then fed into a second-stage fixed-bed reactor, where it contacts a predetermined molecular sieve catalyst to separate the first reaction product; S03: the C2-C5 hydrocarbon mixture separated in step S02 is fed into a light cracking system, where it contacts a cracking catalyst and reacts under a third preset reaction condition to produce a second reaction product. The technical solution provided by this invention can solve the technical problem of low conversion efficiency in existing methanol-to-olefins technologies.

Description

Technical Field

[0001] This invention relates to the field of methanol-to-C2-C3 olefin coupled hydrocarbon cracking technology, and more specifically, to a method and cracking system for methanol-to-C2-C3 olefin coupled hydrocarbon cracking. Background Technology

[0002] Ethylene and propylene are both important basic feedstocks in the petrochemical industry, with huge annual demand. Propylene, in particular, is currently the second most demanded chemical globally, with consumption increasing significantly, even surpassing that of ethylene. Until now, propylene has primarily been obtained from light oil cracking / pyrolysis processes in petroleum processing, and as a co-product or byproduct. However, with the emergence of the "oil crisis," propylene production will inevitably be greatly limited in terms of both raw materials and output. Given my country's energy structure of abundant coal, scarce oil, and limited gas, methanol catalytic conversion to propylene technology has excellent application prospects and profound strategic significance.

[0003] Currently, there are numerous reports on methanol-to-olefins (MTO) processes, primarily including the methanol-to-propylene (MTP) technology from Lurgi GmbH in Germany, the methanol-to-olefins (MTO) technology from UOP in the United States, the methanol / dimethyl ether-to-olefins (DMTO) technology independently developed by the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, and the fluidized bed methanol-to-propylene (FMTP) technology developed by Tsinghua University. Among these, Lurgi GmbH's MTP technology primarily produces propylene and has resulted in several patents (CN1431982A, EP448000, WO20061364.33, etc.), and is poised for large-scale industrialization. The process consists of two adiabatic fixed-bed reactors. In the first stage, the dimethyl ether reactor, methanol vapor is partially dehydrated to dimethyl ether over a highly active and selective Al₂O₃-based catalyst at 200–400°C. Unreacted methanol and the dimethyl ether-water mixture then enter the second stage, the MTP reactor, where it reacts further over a ZSM-5-based catalyst at 400–500°C to produce a mixed hydrocarbon product, primarily propylene, along with significant amounts of ethylene, gasoline, and liquefied petroleum gas. To improve the overall yield of propylene, the separated C2, C3 alkanes, C4 hydrocarbons, and C5 and higher hydrocarbons need to be recycled back to the second stage MTP reactor for further conversion. However, this conversion reaction is very complex, resulting in low reaction efficiency. Because the ZSM-5-based catalyst in the second-stage adiabatic fixed-bed reactor is prone to coking and deactivation, it needs to be regenerated in situ intermittently. Therefore, the unit adopts a three-MTP reactor operation mode of two on and one on standby (or regenerating) to alternately switch regeneration. However, this design affects the stable operation of the unit, is complicated to operate, and has problems such as cumbersome catalyst regeneration and replacement.

[0004] The reaction from methanol to propylene is very complex, including the dehydration reaction of methanol and dimethyl ether, the cracking reaction of butene, the cracking reaction of light gasoline, and the translocation reaction of ethylene and butene. The reaction conditions for each reaction are quite different, and using only one catalyst will result in problems such as low conversion efficiency. Summary of the Invention

[0005] The main objective of this invention is to provide a method and system for methanol-to-C2-C3 olefin coupled hydrocarbon cracking, in order to solve the technical problem of low conversion efficiency in existing methanol-to-olefin technology.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for methanol-to-C2-C3 olefin coupled hydrocarbon cracking is provided, comprising:

[0007] S01: The raw material methanol is vaporized by heat exchange and then enters the first fixed bed reactor. The raw material methanol is in contact with the alumina catalyst in the first fixed bed reactor and reacts under the first preset reaction conditions to produce dimethyl ether stream.

[0008] S02: The dimethyl ether stream is mixed with a diluent and then fed into the second-stage fixed-bed reactor. The dimethyl ether stream is contacted with a predetermined molecular sieve catalyst in the second-stage fixed-bed reactor and reacts under the second preset reaction conditions to produce the first reaction product. The first reaction product is separated to obtain a mixture of C2-C3 olefins, a mixture of C2-C5 hydrocarbons, and a mixture of C6+ hydrocarbons.

[0009] S03: The C2-C5 hydrocarbon mixture separated in step S02 is fed into a light pyrolysis system. The C2-C5 hydrocarbon mixture is contacted with the pyrolysis catalyst in the light pyrolysis system and reacts under the third preset reaction conditions to produce a second reaction product; the second reaction product is then separated.

[0010] S04: The C6+ hydrocarbon mixture separated in step S02 is fed into the heavy hydrocarbon aromatization system and contacted with the aromatization catalyst, and reacted under the fourth preset reaction conditions to obtain the third reaction product.

[0011] Furthermore, the first preset reaction conditions are: 200–400℃, 0.1–2 MPa; and / or,

[0012] The second preset reaction conditions are: 400–600℃, 0.01–1MPa; and / or,

[0013] The third preset reaction conditions are: 200–400℃, 0–5MPa; and / or,

[0014] The fourth preset reaction conditions are: 400~600℃, 0.01~2MPa.

[0015] Furthermore, the method also includes:

[0016] Both the first and second fixed-bed reactors contain a protective agent for protecting the catalyst, which is spread evenly above and / or below the catalyst.

[0017] Furthermore, the method also includes:

[0018] The protective agent is Al2O3 particles, or SiO2 particles, or ceramic spheres; and / or,

[0019] The volume ratio of catalyst to protective agent is 1:0.05~1.

[0020] Furthermore, the method also includes:

[0021] The light pyrolysis system is placed within a second-stage fixed-bed reactor so that the light pyrolysis system utilizes the heat generated by the molecular sieve catalyst for pyrolysis; and / or,

[0022] The heavy hydrocarbon aromatization system is placed in the second-stage fixed-bed reactor so that the heavy hydrocarbon aromatization system can use the heat generated by the molecular sieve catalyst to carry out the aromatization reaction.

[0023] Furthermore, the method also includes:

[0024] The first fixed-bed reactor is also filled with MFI type molecular sieve catalyst.

[0025] Furthermore, the method also includes:

[0026] The cracking catalyst is a metal-modified molecular sieve catalyst.

[0027] Furthermore, the metal-modified molecular sieve catalyst is an MFI-type molecular sieve with Si / Al ratio of 200-400 and / or SAPO-34; and / or,

[0028] The metals in metal-modified molecular sieve catalysts may include potassium, calcium, and magnesium, and the metal content of the metal-modified molecular sieve catalysts is from 0.1% to 1.5%.

[0029] Furthermore, the predetermined molecular sieve catalyst is an MFI-type molecular sieve treated with steam; and / or,

[0030] The aromatization catalyst is an MFI-type molecular sieve catalyst with Si / Al = 100-300 modified by zinc and / or gallium.

[0031] Furthermore, the method also includes:

[0032] The third reaction product is heated with methanol to cool and separate the gaseous component and the liquid component containing aromatics.

[0033] According to another aspect of the present invention, a pyrolysis system is provided, which employs the pyrolysis method provided above, and the pyrolysis system includes:

[0034] The first stage is a fixed-bed reactor, which is used to introduce methanol and generate dimethyl ether stream.

[0035] The second fixed-bed reactor is connected to the first fixed-bed reactor so that the dimethyl ether stream produced by the first fixed-bed reactor can enter the second fixed-bed reactor for reaction.

[0036] The separation system connects the first and second fixed-bed reactors to the separation system to separate the reaction products.

[0037] By applying the technical solution of this invention, the methanol-to-propylene conversion reaction is divided into four stages using a methanol-to-C2-C3 olefin coupled hydrocarbon cracking technology: methanol to dimethyl ether, dimethyl ether to propylene, C2-C5 hydrocarbon cracking, and C6+ hydrocarbon aromatization. This improves the yield of the final target product, C2-C3 olefins, increases the content of by-product aromatics, and enhances the overall economic efficiency of the unit. By fully utilizing the strong exothermic reaction of the dimethyl ether to methanol process coupled with the endothermic reactions of hydrocarbon cracking and aromatization, energy utilization is improved, reducing the need for large amounts of process steam for heat removal in traditional fixed-bed methanol-to-propylene processes, and extending the catalyst life of the dimethyl ether to propylene process. Different catalyst beds are selected and arranged for different reactions, which not only reduces operational complexity but also allows for flexible control of reaction conditions to achieve optimal product distribution. Adding a certain proportion of catalyst protectant to the catalyst in the second fixed-bed reactor not only prevents localized hot spots within the unit and increases catalyst thermal stability but also delays catalyst coking and extends catalyst life. Attached Figure Description

[0038] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0039] Figure 1 A schematic diagram of the system provided according to an embodiment of the present invention is shown.

[0040] The above figures include the following reference numerals:

[0041] 10. First-stage fixed-bed reactor; 20. Second-stage fixed-bed reactor; 21. Light hydrocarbon cracking system; 211. Cracking catalyst; 22. Heavy hydrocarbon aromatization system; 221. Aromatization catalyst; 30. Separation system; 40. Cooling and separation system. Detailed Implementation

[0042] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0043] An embodiment of the present invention provides a method for methanol-to-C2-C3 olefin coupled hydrocarbon cracking, the method comprising: S01: after heat exchange and vaporization, the raw material methanol enters a first-stage fixed-bed reactor 10, where the raw material methanol contacts an alumina catalyst and reacts under a first preset reaction condition to produce a dimethyl ether stream; S02: the dimethyl ether stream is mixed with a diluent and then enters a second-stage fixed-bed reactor 20, where the dimethyl ether stream contacts a predetermined molecular sieve catalyst and reacts under a second preset reaction condition to produce a first reaction product; and the first reaction product is subjected to... Separation is performed to obtain a mixture of C2-C3 olefins, a mixture of C2-C5 hydrocarbons, and a mixture of C6+ hydrocarbons; S03: The C2-C5 hydrocarbon mixture separated in step S02 is fed into a light hydrocarbon cracking system, where it is contacted with cracking catalyst 211 and reacts under a third preset reaction condition to produce a second reaction product; the second reaction product is then separated; S04: The C6+ hydrocarbon mixture separated in step S02 is fed into a heavy hydrocarbon aromatization system 22 and contacted with aromatization catalyst 221, and reacts under a fourth preset reaction condition to obtain a third reaction product.

[0044] The methanol-to-C2-C3 olefin coupled hydrocarbon cracking method provided in this embodiment can make each reaction more complete by using different reaction conditions and different catalysts according to different reactions, thereby effectively ensuring the conversion efficiency.

[0045] In this embodiment, the first preset reaction conditions are: 200–400℃, 0.1–2 MPa. The second preset reaction conditions are: 400–600℃, 0.01–1 MPa. The third preset reaction conditions are: 200–400℃, 0–5 MPa. The fourth preset reaction conditions are: 400–600℃, 0.01–2 MPa. This method facilitates more complete reactions, thereby better ensuring conversion efficiency.

[0046] Specifically, the method further includes: a protective agent for protecting the catalyst is loaded in both the first fixed-bed reactor 10 and the second fixed-bed reactor 20, with the protective agent spread evenly above and / or below the catalyst. This method facilitates effective protection of the catalyst using an inert protective agent, ensuring that the catalyst can stably exert its catalytic effect.

[0047] In this embodiment, the method further includes using Al2O3 particles (i.e., alumina particles), SiO2 particles (i.e., silicon oxide particles), or ceramic balls as a protective agent, which can effectively protect the catalyst.

[0048] Specifically, the volume ratio of catalyst to protective agent is 1:0.05 to 1.

[0049] In this embodiment, the method further includes placing the light pyrolysis system within the second-stage fixed-bed reactor 20, so that the light pyrolysis system utilizes the heat generated by the molecular sieve catalyst for pyrolysis. This method facilitates full energy utilization and effectively ensures the normal operation of the reaction within the light pyrolysis system.

[0050] Specifically, the method further includes placing the heavy hydrocarbon aromatization system 22 within the second-stage fixed-bed reactor 20, so that the heavy hydrocarbon aromatization system 22 utilizes the heat generated by the molecular sieve catalyst to carry out the aromatization reaction. This method facilitates full energy utilization and effectively ensures the normal operation of the reaction within the heavy hydrocarbon aromatization system 22.

[0051] The method also includes: filling the first fixed-bed reactor 10 with an MFI type molecular sieve catalyst to effectively ensure the reaction conversion rate in the first fixed-bed reactor 10.

[0052] Specifically, the catalyst packed in the first fixed-bed reactor 10 is active Al2O3, MFI molecular sieve, or a mixture of two catalysts in any proportion, preferably active Al2O3.

[0053] In this embodiment, the method further includes: the pyrolysis catalyst 211 is a metal-modified molecular sieve catalyst. Using this method can better improve the conversion rate of the reaction.

[0054] Specifically, the metal-modified molecular sieve catalyst is an MFI type molecular sieve with Si / Al = 200-400 and / or SAPO-34.

[0055] Specifically, the metals in the metal-modified molecular sieve catalyst can include potassium, calcium, and magnesium, and the metal content of the metal-modified molecular sieve catalyst is from 0.1% to 1.5%. This method facilitates the efficient occurrence of the cracking reaction.

[0056] In this embodiment, the predetermined molecular sieve catalyst is an MFI type molecular sieve treated with water vapor to facilitate better catalysis.

[0057] Specifically, aromatization catalyst 221 is an MFI type molecular sieve catalyst with Si / Al = 100-300 modified by zinc and / or gallium.

[0058] In this embodiment, the method further includes: exchanging heat between the third reaction product and methanol to cool and separate the third reaction product into a gaseous component and a liquid component containing aromatics.

[0059] The specific implementation steps in this embodiment are as follows:

[0060] Step S01: After heat exchange and vaporization, the raw methanol enters the first-stage fixed-bed reactor 10, where it contacts an alumina-based catalyst. Under conditions of 200–400°C and 0.1–2 MPa, dimethyl ether stream is produced.

[0061] The dimethyl ether stream in step S01 includes dimethyl ether, methanol, and water;

[0062] Step S02: The dimethyl ether stream, after being mixed with the diluent, enters the second-stage fixed-bed reactor 20 and contacts the molecular sieve catalyst. The reaction proceeds at 400–600°C and 0.01–1 MPa. The reaction product from this reactor can be separately separated in the separation system 30, or it can be mixed with the product from step 3) and then separated in the separation system 30. The separated C2-C3 olefins are sent out of the device, the separated C2–C5 hydrocarbon mixture enters step S03, and the separated C6+ hydrocarbon mixture enters step S04. As the reaction proceeds, the ZSM-5 based molecular sieve catalyst gradually deactivates. The deactivated catalyst can be regenerated by burning off carbon deposits at high temperature with air to restore its catalytic activity. The regenerated catalyst can then be reused.

[0063] The products of the first stage fixed-bed reactor 10 in step S02 include ethylene, propylene, butene, C1-C4 alkanes and C5+ hydrocarbons;

[0064] In step S03, the C2-C5 hydrocarbon mixture from step S02 enters the light hydrocarbon cracking system 21, contacts the cracking catalyst 211, and reacts under conditions of 200-400°C and 0-5MPa. The reaction products of the light hydrocarbon cracking system 21 enter the separation system 30 of step S02 for separation.

[0065] The products of the light hydrocarbon cracking system 21 in step S03 include propylene, ethylene, butene, C1-C4 alkanes, C5+ hydrocarbons, etc.

[0066] In step S04, the C6+ hydrocarbon mixture from step S02 enters the heavy hydrocarbon aromatization system 22 and contacts the aromatization catalyst 221. The reaction is carried out at 400-600°C and 0.01-2 MPa. The reaction products of the heavy hydrocarbon aromatization system 22 are separated from the gas phase component and the aromatic-rich liquid phase component by heat exchange and cooling with methanol.

[0067] The products of the heavy hydrocarbon aromatization system 22 described in step S04 include alkanes, cycloalkanes, alkenes, aromatics, and other trace impurities.

[0068] In this embodiment, the light hydrocarbon cracking system 21 and the heavy hydrocarbon aromatization system 22 are tubular reactors, and the reactors are filled with catalysts, which are monolithic and / or granular.

[0069] Specifically, in addition to the catalyst, the first fixed-bed reactor 10 and the second fixed-bed reactor also contain a catalyst protectant. The catalyst protectant is inert Al2O3 particles, SiO2 particles, or ceramic balls, and the protectant is spread evenly on top of and below the catalyst, with a catalyst to protectant volume ratio of 1:0.05 to 1.

[0070] In this embodiment, the catalyst in the first fixed-bed reactor 10 and the second fixed-bed reactor 20 is loaded in segments. The catalyst loading segments in the first fixed-bed reactor 10 are 1-3, preferably 1-2; the catalyst loading segments in the second fixed-bed reactor 20 are 2-8, preferably 4-6.

[0071] Specifically, the light hydrocarbon cracking system 21 and the heavy hydrocarbon aromatization system 22 are both located in the second-stage fixed-bed reactor 20, in the middle of the catalyst bed, making full use of the heat released by the ZSM-5 based molecular sieve catalyst during the reaction to maintain the cracking and aromatization reactions.

[0072] In this embodiment, the catalyst packed in the first fixed-bed reactor is active Al2O3, MFI molecular sieve, or a mixture of two catalysts in any proportion, preferably active Al2O3.

[0073] Specifically, the catalyst used in the light hydrocarbon cracking system 21 is a metal-modified molecular sieve catalyst. The molecular sieve is an MFI type molecular sieve with Si / Al = 200-400 and / or SAPO-34; the metal is an alkali metal element such as K, Ca, and Mg, with a metal content of 0.1-1.5% by mass.

[0074] Specifically, the catalyst packed in the second fixed-bed reactor is an MFI type molecular sieve treated with steam, wherein the steam temperature is 460-490℃ and the time is 45-60h.

[0075] In this embodiment, the catalyst used in the heavy hydrocarbon aromatization system 22 is a Zn and Ga modified Si / Al = 100-300 MFI type molecular sieve catalyst, wherein the Zn and Ga content is 0.5-5% by mass.

[0076] like Figure 1As shown, Embodiment 2 of the present invention provides a pyrolysis system employing the pyrolysis method described above. The pyrolysis system includes: a first-stage fixed-bed reactor 10, a second-stage fixed-bed reactor 20, and a separation system 30. The first-stage fixed-bed reactor 10 is used to introduce methanol and generate a dimethyl ether stream. The second-stage fixed-bed reactor 20 is connected to the first-stage fixed-bed reactor 10 so that the dimethyl ether stream generated in the first-stage fixed-bed reactor 10 enters the second-stage fixed-bed reactor 20 for reaction. Both the first-stage fixed-bed reactor 10 and the second-stage fixed-bed reactor 20 are connected to the separation system 30 to separate the reaction products.

[0077] In this embodiment, the pyrolysis system also includes a cooling separation system 40, in which the third reaction product exchanges heat with the methanol that is about to enter the first fixed bed reactor 10, so as to separate the gas phase component and the aromatic-rich liquid phase component from the third reaction product.

[0078] As can be seen from the above description, the above embodiments of the present invention achieve the following technical effects: high yield of C2-C3 olefins and reduced energy consumption of the equipment.

[0079] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0080] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of this application. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0081] In the description of this application, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is usually based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0082] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0083] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be construed as limiting the scope of protection of this application.

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for methanol-to-C2-C3 olefin coupled hydrocarbon cracking, characterized in that, include: S01: The raw material methanol is vaporized by heat exchange and then enters the first stage fixed bed reactor. The raw material methanol is in contact with the alumina catalyst in the first stage fixed bed reactor and reacts under the first preset reaction conditions to produce dimethyl ether stream. S02: The dimethyl ether stream is mixed with a diluent and then fed into a second-stage fixed-bed reactor. The dimethyl ether stream contacts a predetermined molecular sieve catalyst within the second-stage fixed-bed reactor and reacts under second preset reaction conditions to produce a first reaction product. The first reaction product is then separated to obtain C2-C3 olefins, a mixture of C2-C5 hydrocarbons, and C6 hydrocarbons. + Hydrocarbon mixtures; S03: The C2-C5 hydrocarbon mixture separated in step S02 is fed into a light pyrolysis system. The C2-C5 hydrocarbon mixture is contacted with the pyrolysis catalyst in the light pyrolysis system and reacts under the third preset reaction conditions to produce a second reaction product; the second reaction product is then separated. S04: Separate C6 from step S02 + A mixture of hydrocarbons is fed into a heavy hydrocarbon aromatization system and contacted with an aromatization catalyst, and reacted under a fourth preset reaction condition to obtain a third reaction product; The method further includes: The light pyrolysis system is placed in the second-stage fixed-bed reactor so that the light pyrolysis system utilizes the heat generated by the molecular sieve catalyst for pyrolysis. And / or, The heavy hydrocarbon aromatization system is placed in the second-stage fixed-bed reactor so that the heavy hydrocarbon aromatization system can carry out the aromatization reaction using the heat generated by the molecular sieve catalyst.

2. The method for methanol-to-C2-C3 olefin coupled hydrocarbon cracking according to claim 1, characterized in that, The first preset reaction conditions are: 200~400℃, 0.1~2MPa; and / or, The second preset reaction conditions are: 400~600℃, 0.01~1MPa; and / or, The third preset reaction conditions are: 200~400℃, 0~5MPa; and / or, The fourth preset reaction conditions are: 400~600℃ and 0.01~2MPa.

3. The method for methanol-to-C2-C3 olefin coupled hydrocarbon cracking according to claim 1, characterized in that, The method further includes: Both the first and second fixed-bed reactors contain a protective agent for protecting the catalyst, which is spread evenly above and / or below the catalyst.

4. The method for methanol-to-C2-C3 olefin coupled hydrocarbon cracking according to claim 3, characterized in that, The method further includes: The protective agent is Al2O3 particles, or SiO2 particles, or ceramic spheres; and / or, The volume ratio of the catalyst to the protective agent is 1:0.05~1.

5. The method for methanol-to-C2-C3 olefin coupled hydrocarbon cracking according to claim 1, characterized in that, The method further includes: The first fixed-bed reactor is also filled with MFI type molecular sieve catalyst.

6. The method for methanol-to-C2-C3 olefin coupled hydrocarbon cracking according to claim 1, characterized in that, The method further includes: The pyrolysis catalyst is a metal-modified molecular sieve catalyst.

7. The method for methanol-to-C2-C3 olefin coupled hydrocarbon cracking according to claim 6, characterized in that, The metal-modified molecular sieve catalyst is an MFI type molecular sieve with Si / Al ratio of 200-400 and / or SAPO-34; and / or, The metals in the metal-modified molecular sieve catalyst include potassium, calcium, and magnesium, and the metal content of the metal-modified molecular sieve catalyst is from 0.1% to 1.5%.

8. The method for methanol-to-C2-C3 olefin coupled hydrocarbon cracking according to claim 1, characterized in that, The predetermined molecular sieve catalyst is an MFI type molecular sieve treated with steam; and / or, The aromatization catalyst is an MFI type molecular sieve catalyst with Si / Al ratio of 100-300 modified by zinc and / or gallium.

9. The method for methanol-to-C2-C3 olefin coupled hydrocarbon cracking according to claim 1, characterized in that, The method further includes: The third reaction product is subjected to heat exchange with methanol to cool and separate the gaseous component and the liquid component containing aromatics.

10. A pyrolysis system, characterized in that, The pyrolysis system employs the pyrolysis method according to any one of claims 1 to 9, and the pyrolysis system comprises: The first fixed-bed reactor (10) is used to introduce methanol and generate dimethyl ether stream; The second fixed-bed reactor (20) is connected to the first fixed-bed reactor (10) so that the dimethyl ether stream generated by the first fixed-bed reactor (10) enters the second fixed-bed reactor (20) for reaction; The separation system (30) is connected to both the first fixed-bed reactor (10) and the second fixed-bed reactor (20) so as to separate the reaction products through the separation system (30).

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