Device and method for preparing olefin by cracking polyolefin waste plastics

Abstract

The invention discloses a device for preparing olefin by cracking polyolefin waste plastics, which comprises a pyrolysis reactor and a fluidized bed catalytic reactor, and microwave generating devices for emitting microwaves are arranged outside the pyrolysis reactor and the fluidized bed catalytic reactor; a separator for removing particle impurities in the high-temperature pyrolysis steam is arranged between the pyrolysis reactor and the fluidized bed catalytic reactor; the pyrolysis reactor is filled with silicon carbide balls, and the fluidized bed catalytic reactor is filled with a catalyst; and the rear end of the fluidized bed catalytic reactor is connected with a product condensing and collecting system for liquefying a high-temperature gas product. The invention also discloses a method for preparing olefin by cracking the polyolefin waste plastics based on the device, and the method can effectively reduce the energy consumption in the cracking process on one hand, and can optimize the distribution of cracking products on the other hand, thereby realizing high-valued conversion of the polyolefin waste plastics.

Description

Technical Field

[0001] The present invention relates to a device for preparing olefins by cracking polyolefin waste plastics, and also relates to a method for preparing olefins by cracking based on the device. Background Art

[0002] With the widespread use of plastic products worldwide, the accumulation of plastic waste has become an urgent environmental issue. Polyolefin plastics (such as polyethylene and polypropylene) account for a large proportion of plastic waste due to their widespread use and high durability. However, due to the chemical inertness and difficulty in decomposing polyolefin waste plastics, traditional recycling methods (such as mechanical recycling) are difficult to achieve efficient utilization and are often limited by contaminants and aging issues.

[0003] In recent years, chemical recycling technology has attracted much attention due to its ability to decompose plastics into monomer chemicals or high-value-added chemical raw materials. Catalytic cracking of polyolefins is one of the key methods. By introducing catalysts, the cracking temperature can be significantly reduced and the product distribution can be optimized (such as increasing the yield of light olefins such as ethylene and propylene). Traditional catalytic cracking technology usually uses thermal cracking devices, such as fixed-bed reactors, but such devices generally have the following disadvantages: (1) Low heating efficiency: Traditional heating methods rely on external heat sources, with low heat conduction efficiency, resulting in high energy consumption; (2) Catalysts are easily deactivated: Coke deposits are easily formed on the catalyst surface under high temperature conditions, reducing the service life of the catalyst; (3) Product selectivity is limited: Due to the limitations of heat transfer and reaction conditions, the cracking products are mostly low-value-added fuel oil and gas, and the selectivity of light monomer chemicals (such as ethylene and propylene) is low; it is difficult to achieve selective regulation of cracking products.

[0004] Microwave heating, as an emerging non-contact heating method, can utilize the dielectric loss characteristics of materials to achieve rapid and uniform heating. Compared with traditional heating methods, it has the following advantages: (1) Selective heating to improve reaction rate: Microwaves act directly on reactants, reducing heat conduction losses, and microwaves can quickly increase reaction temperature and shorten reaction time; (2) Efficient coke suppression: Rapid heating and precise temperature control reduce the probability of coke formation; (3) Electrification industry: Microwave equipment can be driven by renewable energy to achieve low-carbon chemical production. However, the research on existing microwave catalytic cracking technology is still in its early stages, and most of the device designs are laboratory-scale, which is difficult to meet industrial needs. The main challenges include: (1) The limited penetration of microwaves makes it difficult to scale up and the temperature distribution is uneven; (2) The synergistic optimization of catalysts and microwave heating is insufficient; (3) The problem of continuous and stable operation of microwave equipment under high temperature and high load conditions. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to provide an apparatus for cracking polyolefin waste plastics to produce olefins, which can effectively improve the uniformity of microwave heating. Another purpose of the present invention is to provide a method for cracking polyolefin waste plastics to produce olefins based on the above-mentioned apparatus. On the one hand, this method can effectively reduce the energy consumption in the cracking process, and on the other hand, it can optimize the distribution of cracking products, thereby realizing the high-value conversion of polyolefin waste plastics.

[0006] Technical solution: The device for cracking polyolefin waste plastics to produce olefins described in the present invention includes a pyrolysis reactor and a fluidized bed catalytic reactor, and microwave generators for emitting microwaves are provided outside the pyrolysis reactor and the fluidized bed catalytic reactor; a separator for removing particulate impurities in high-temperature pyrolysis steam is provided between the pyrolysis reactor and the fluidized bed catalytic reactor; the pyrolysis reactor is filled with silicon carbide balls, and the fluidized bed catalytic reactor is filled with a catalyst, and the catalyst is silicon carbide foam ceramic balls loaded with ZSM-5 multi-level porous nano-molecular sieve sheet material; and a product condensation and collection system for liquefying high-temperature gas products is connected to the rear end of the fluidized bed catalytic reactor.

[0007] The filling amount of silicon carbide balls is 1 / 4 to 1 / 2 of the volume of the pyrolysis reactor. The silicon carbide balls are used to absorb microwaves. On the one hand, they absorb all the emitted microwaves to prevent microwave reflection and damage to the magnetron; on the other hand, plastic has weak microwave absorption ability and needs to be heated to the plastic pyrolysis temperature through heat conduction generated by the silicon carbide balls absorbing waves. In the present invention, the pyrolysis reactor is filled with silicon carbide balls with good microwave absorption ability and good mechanical strength, and the overall temperature distribution uniformity in the reactor is improved by stirring the silicon carbide balls.

[0008] Wherein, a stirring device is provided in the pyrolysis reactor.

[0009] The microwave generating device is a microwave magnetron, which is sleeved outside the reactor and connected to the reactor through a waveguide (the reactor has a through hole at the location where the waveguide is set). The connection between the waveguide and the reactor is separated by a mica sheet. The mica sheet can introduce microwaves into the reactor and seal the reactor, thereby preventing high-temperature gas in the reactor from entering the magnetron area.

[0010] The pyrolysis reactor includes an exhaust port, and an exhaust pipe extends into the reactor through the exhaust port (the depth of the exhaust pipe is about 1 / 10 of the reactor height), so that the pyrolysis steam can be quickly removed from the pyrolysis reactor to prevent the feed port from being blocked; that is, the pyrolysis steam can escape from the pyrolysis reactor more easily and quickly, so that the pyrolysis gas is not easy to enter the feed port. Excessive pyrolysis gas accumulates near the feed port, which easily increases the temperature of the feed port, and the melted plastic is easily attached to the wall of the feed port, causing blockage.

[0011] The separator is a cyclone separator; the product condensation collection system includes a high-temperature pump and a condenser; the high-temperature pump is used to quickly pump the high-temperature pyrolysis products after gas-solid separation into the condenser; the condenser uses low-temperature water cooling to quickly condense the high-temperature pyrolysis products, and send the condensed liquid products into the product collection device.

[0012] The method for producing olefins by cracking based on the above device comprises the following steps:

[0013] (1) placing silicon carbide balls in a pyrolysis reactor, placing catalyst particles in a fluidized bed catalytic reactor, and raising the pyrolysis reactor and the fluidized bed catalytic reactor to a target temperature by microwave irradiation;

[0014] (2) The crushed polyolefin waste plastics are fed into a pyrolysis reactor, and the high-temperature pyrolysis steam generated by the reaction is quickly transferred to a cyclone separator 1 under the negative pressure of a high-temperature pump, and then enters a fluidized bed catalytic reactor after separating the particulate impurities, fluidizes the catalyst particles, and performs a catalytic reforming reaction in the fluidized bed catalytic reactor;

[0015] (3) The obtained high-temperature pyrolysis product (monomer compound) enters the subsequent product condensation collection system, and is condensed to obtain a liquid monomer compound.

[0016] Wherein, in step (1), the pyrolysis temperature is 500-600°C, and the stirring speed in the pyrolysis reactor is 50-100 rpm; the catalytic temperature is 500-600°C, and the weight hourly space velocity in the fluidized bed catalytic reactor is 17-50 / h.

[0017] The weight-time-space velocity is related to the feed rate of waste plastics and the amount of catalyst used. For example, if the feed rate of waste plastics is 100g / h and the amount of active ingredient of catalyst particles is 5g, then the weight-time-space velocity is 20 / h. The greater the weight-time-space velocity, the worse the treatment effect (i.e., the selectivity of light olefins in the product becomes lower), and the smaller the weight-time-space velocity, the smaller the reactor processing capacity.

[0018] In step (1), the filling amount of silicon carbide balls in the pyrolysis reactor is 1 / 4 to 1 / 2 of the volume of the pyrolysis reactor; the weight of the silicon carbide ball particles is 5 to 20 kilograms, and the diameter of the spheres is 5 to 6 millimeters.

[0019] In the fluidized bed catalytic reactor, the catalyst is a silicon carbide foam ceramic ball loaded with ZSM-5 multi-level porous nano molecular sieve sheet material, which is prepared by the following method:

[0020] First, an aqueous solution composed of TPAOH (molecular sieve template), aluminum isopropoxide (aluminum source) and tetraethyl orthosilicate TEOS (silicon source) (the molar ratio of TPAOH: SiO2: Al2O3: H2O is 4.1-7.3:80:1:1000) was stirred at room temperature for 8 hours; considering that TEOS may release alcohols during the hydrolysis process to affect the reaction system, the precursor solution was then heated to 85°C and maintained for 1 hour to reduce the influence of alcohol interference; after evaporation, a certain amount of The precursor solution was then transferred to a stainless steel autoclave with a polytetrafluoroethylene liner and crystallized at 170°C. After three days of reaction, the product was filtered, washed with deionized water, and dried at 100°C for 10 hours. Finally, it was calcined in air at 550°C for 6 hours to obtain ZSM-5 multi-level porous nano-molecular sieve sheet material. The obtained molecular sieve was loaded onto silicon carbide foam ceramic balls with a diameter of 2 to 5 mm by dip-coating using silica sol as a binder, and then calcined and solidified to obtain catalyst particles.

[0021] The catalyst particles of the present invention have good microwave absorption performance. By strengthening the microwave absorption ability of the catalyst material and overlapping the microwave absorption sites with the catalytic sites (because the carrier has good microwave absorption ability, the catalytic sites on the carrier can quickly reach the reaction temperature), energy utilization can be maximized.

[0022] In step (2), the polyolefin waste plastics include low-density polyethylene, high-density polyethylene, polypropylene or polystyrene, and the particle size of the material is 2 to 10 mm.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The present invention adopts microwave heating and adds silicon carbide balls or catalysts with silicon carbide as carriers into the reactor to achieve rapid and uniform microwave heating, while improving the energy utilization rate of the cracking reaction. The overall energy consumption is reduced by about 30% to 40% compared with the traditional electric heating device (the amount of electricity consumed to process the same amount of waste plastics); at the same time, the high-temperature pyrolysis steam generated by the reaction is used to fluidize the catalyst bed, avoiding the use of carrier gas, reducing the energy required for heating the carrier gas, and further reducing the energy consumption of the system; (2) By optimizing the synergistic effect of the catalyst acid sites and microwave heating, the present invention significantly improves the selectivity of light olefins (such as ethylene and propylene) in the product (increased by 10 to 15%), and the ratio of heavy oil and gas phase products is effectively controlled, reducing the amount of low value-added products and increasing the amount of high value-added products. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural principle diagram of the device of the present invention;

[0025] Figure 2Schematic diagram of the connection between microwave magnetron and reactor. DETAILED DESCRIPTION

[0026] like Figures 1-2 As shown, the present invention is a device for preparing olefins by cracking polyolefin waste plastics, comprising a feeding system, the feeding system comprising a screw propulsion device, a material bin arranged on the screw propulsion device, and the material bin and the screw are arranged perpendicular to each other; in order to reduce the risk of material adhesion and clogging, the feeding system is designed to be a vertical structure when close to the high-temperature area (referring to the section of the feeding pipe close to the reactor being arranged perpendicular to the reactor), and is equipped with an air or water cooling circulation system to achieve efficient heat dissipation; it also includes a pyrolysis reactor, a microwave magnetron for emitting microwaves is provided outside the pyrolysis reactor, the microwave magnetron is sleeved outside the reactor, and is connected to the reactor through a waveguide (microwave transmission cavity) (the reactor has a through hole at the position where the waveguide is provided), and a mica sheet is provided at the connection between the waveguide and the reactor, the mica sheet can introduce microwaves into the reactor and can also seal the reactor, thereby preventing high-temperature gas in the reactor from entering the magnetron area; a stirring device is provided in the pyrolysis reactor; the pyrolysis reactor is provided with a feed port and an exhaust port, the feed port is connected to the feeding system, and the exhaust pipe extends into the reactor through the exhaust port, so that it can be realized The pyrolysis steam is now quickly removed from the pyrolysis reactor to prevent the feed port from being blocked, and the other end of the exhaust port is connected to a cyclone separator I; the pyrolysis reactor is filled with silicon carbide balls; it also includes a fluidized bed catalytic reactor, and a microwave magnetron for emitting microwaves is provided outside the fluidized bed catalytic reactor; the fluidized bed catalytic reactor is filled with catalyst particles; it also includes a cyclone separator I and a cyclone separator II. The cyclone separator I is used to separate particulate impurities from the high-temperature pyrolysis steam to prevent the particulate impurities from adhering to and clogging the fluidized bed, and the high-temperature pyrolysis steam from which the particulate impurities are separated is fed into the fluidized bed catalytic reactor; the cyclone separator II is used to separate particulate impurities from the high-temperature gas product, and the high-temperature gas product from which the particulate impurities are separated is pumped into a condenser via a high-temperature pump; it also includes a product condensation collection system, which includes a high-temperature pump, a condenser and a product collection device; the high-temperature pump can withstand high temperatures of 500°C and is used to quickly extract the high-temperature gas product from the pyrolysis and catalytic system; the condenser is cooled with low-temperature water to quickly condense the pyrolysis product, and the condensed liquid product is fed into the product collection device.

[0027] Example 1

[0028] The method for producing olefins by cracking based on the above-mentioned device is specifically as follows:

[0029] (1) Low-density polyethylene was processed into particles with a particle size of 2 to 10 mm using a crushing device and placed in a material bin for standby use; a ZSM-5 / silicon carbide composite catalyst material loaded with 3 g of ZSM-5 multi-level porous nanomolecular sieve sheet material was placed in a fluidized bed catalytic reactor; silicon carbide balls with a particle size of 5 mm were placed in a pyrolysis reactor, and the filling amount of the silicon carbide balls was 1 / 2 of the volume of the pyrolysis reactor; and the temperature of the pyrolysis reactor and the fluidized bed catalytic reactor was raised to 500° C. by microwave radiation (frequency of 2450 and power of 800 W); the stirring speed of the stirring device in the pyrolysis reactor was 50 rpm;

[0030] (2) The waste plastics are fed into a pyrolysis reactor by a screw propulsion device for rapid pyrolysis at a feed rate of 51 g / h and a weight-time space velocity of 17 g / h, thereby obtaining high-temperature pyrolysis steam; the obtained high-temperature pyrolysis steam is separated from particulate impurities by a cyclone separator 1, and then the high-temperature pyrolysis steam enters a fluidized bed catalytic reactor, where the high-temperature pyrolysis steam drives the catalyst particles to fluidize and simultaneously performs a catalytic reforming reaction;

[0031] (3) The high-temperature pyrolysis product obtained by the reaction is passed through a cyclone separator II to remove particulate impurities, and then pumped into a condenser through a high-temperature pump. After condensation, the liquid monomer product is collected.

[0032] The monomer product produced in Example 1 was characterized for composition, revealing ethylene (23%), propylene (36%), and butene (27%). Compared to conventional fixed-bed catalytic pyrolysis technology (68%), the present invention significantly improves selectivity for light olefins (such as ethylene and propylene) in the product. After 30 hours of continuous production using the present invention's apparatus according to the above method, the product concentrations of ethylene (20%), propylene (28%), and butene (29%) were measured, demonstrating the excellent performance and stability of the present catalyst.

[0033] Example 2

[0034] The method for producing olefins by cracking based on the above-mentioned device is specifically as follows:

[0035] (1) Low-density polyethylene was processed into particles with a particle size of 2 to 10 mm using a crushing device and placed in a material bin for standby use; a ZSM-5 / silicon carbide composite catalyst material loaded with 5 g of ZSM-5 multi-level porous nanomolecular sieve sheet material was placed in a fluidized bed catalytic reactor; silicon carbide balls with a particle size of 6 mm were placed in a pyrolysis reactor, and the filling amount of the silicon carbide balls was 1 / 4 of the volume of the pyrolysis reactor; and the pyrolysis reactor and the fluidized bed catalytic reactor were both heated to 500° C. by microwave radiation (frequency of 2450 and power of 800 W); the stirring speed of the stirring device in the pyrolysis reactor was 50 rpm;

[0036] (2) feeding the waste plastics into a pyrolysis reactor for rapid pyrolysis by a screw propulsion device at a feeding rate of 100 g / h and a weight hourly space velocity of 20 g / h to obtain high-temperature pyrolysis steam; the obtained high-temperature pyrolysis steam is separated from particulate impurities by a cyclone separator 1, and then the high-temperature pyrolysis steam enters a fluidized bed catalytic reactor, where the high-temperature pyrolysis steam drives the catalyst particles to fluidize and simultaneously performs a catalytic reforming reaction;

[0037] (3) The high-temperature pyrolysis product obtained by the reaction is passed through a cyclone separator II to remove particulate impurities, and then pumped into a condenser through a high-temperature pump. After condensation, the liquid monomer product is collected.

[0038] The monomer product obtained in Example 2 was characterized for composition, and the monomer products were ethylene (21%), propylene (32%), and butene (25%). After 30 hours of continuous production using the apparatus of the present invention according to the above method, the product content of ethylene (17%), propylene (23%), and butene (32%) was measured.

[0039] Example 3

[0040] The method for producing olefins by cracking based on the above-mentioned device is specifically as follows:

[0041] (1) Low-density polyethylene is processed into particles with a particle size of 2 to 10 mm using a crushing device and placed in a material bin for standby use; a ZSM-5 / silicon carbide composite catalyst material loaded with 10 g of ZSM-5 multi-level porous nanomolecular sieve sheet material is placed in a fluidized bed catalytic reactor; silicon carbide balls with a particle size of 6 mm are placed in a pyrolysis reactor, and the filling amount of the silicon carbide balls is 1 / 3 of the volume of the pyrolysis reactor; and the pyrolysis reactor and the fluidized bed catalytic reactor are both heated to 600° C. by microwave radiation (frequency of 2450 and power of 1000 W); the stirring speed of the stirring device in the pyrolysis reactor is 50 rpm;

[0042] (2) feeding the waste plastics into a pyrolysis reactor for rapid pyrolysis by a screw propulsion device at a feeding rate of 500 g / h and a weight hourly space velocity of 50 g / h to obtain high-temperature pyrolysis steam; the obtained high-temperature pyrolysis steam is separated from particulate impurities by a cyclone separator 1, and then the high-temperature pyrolysis steam enters a fluidized bed catalytic reactor, where the high-temperature pyrolysis steam drives the catalyst particles to fluidize and simultaneously performs a catalytic reforming reaction;

[0043] (3) The high-temperature pyrolysis product obtained by the reaction is passed through a cyclone separator II to remove particulate impurities, and then pumped into a condenser through a high-temperature pump. After condensation, the liquid monomer product is collected.

[0044] The monomer products obtained in Example 3 were characterized for their components. The monomer products were ethylene (20%), propylene (30%), and butene (21%). After 10 hours of continuous production using the apparatus of the present invention according to the above method, ethylene (16%), propylene (21%), and butene (28%) were measured in the products.

[0045] Comparative Example 1

[0046] Compared with Example 1, the only difference of Comparative Example 1 is that a conventional ZSM-5 molecular sieve catalyst is placed in the pyrolysis reactor, specifically:

[0047] (1) Low-density polyethylene is processed into particles with a particle size of 2 to 10 mm using a crushing device and placed in a material bin for standby use; 3 g of a catalytic material in the prior art (conventional ZSM-5 molecular sieve catalyst shaped particles) is placed in a fluidized bed catalytic reactor; silicon carbide balls with a particle size of 5 mm are placed in a pyrolysis reactor, and the filling amount of the silicon carbide balls is 1 / 2 of the volume of the pyrolysis reactor; the temperature of the pyrolysis reactor and the fluidized bed catalytic reactor is raised to 500° C. by microwave radiation (frequency of 2450 and power of 800 W); the stirring speed of the stirring device in the pyrolysis reactor is 50 rpm;

[0048] (2) The waste plastics are fed into a pyrolysis reactor by a screw propulsion device for rapid pyrolysis at a feed rate of 51 g / h and a weight-time space velocity of 17 g / h, thereby obtaining high-temperature pyrolysis steam; the obtained high-temperature pyrolysis steam is separated from particulate impurities by a cyclone separator 1, and then the high-temperature pyrolysis steam enters a fluidized bed catalytic reactor, where the high-temperature pyrolysis steam drives the catalyst particles to fluidize and simultaneously performs a catalytic reforming reaction;

[0049] (3) The high-temperature pyrolysis product obtained by the reaction is passed through a cyclone separator II to remove particulate impurities, and then pumped into a condenser through a high-temperature pump. After condensation, the liquid monomer product is collected.

[0050] The monomer products obtained in Comparative Example 2 were characterized for their components. The monomer products were ethylene (15%), propylene (25%), and butene (14%). After 8 hours of continuous production according to the above method, ethylene (10%), propylene (15%), and butene (18%) were measured in the products.

[0051] The method of the present invention utilizes microwave heating to achieve rapid and uniform heating of waste plastics, effectively reducing heat conduction losses, improving heating efficiency, and significantly reducing energy consumption in the cracking process; through synergistic effects with catalysts of specific structures and compositions, the method enhances precise control over the cracking reaction, improves the yield of light monomer chemicals (such as ethylene and propylene), and meets the production needs of high-value-added chemicals; and by optimizing the device structure and process flow, improves the operating stability of the device, enabling it to efficiently process different types of polyolefin waste plastics and realize continuous and industrialized production.

Claims

1. A device for cracking polyolefin waste plastics to produce olefins, comprising a pyrolysis reactor and a fluidized bed catalytic reactor, characterized in that: A microwave generator for emitting microwaves is provided outside the pyrolysis reactor and the fluidized bed catalytic reactor; a separator for removing particulate impurities in the high-temperature pyrolysis steam is provided between the pyrolysis reactor and the fluidized bed catalytic reactor; the pyrolysis reactor is filled with silicon carbide balls, and the fluidized bed catalytic reactor is filled with a catalyst, which is silicon carbide foam ceramic balls loaded with ZSM-5 multi-level porous nano-molecular sieve sheet material; and a product condensation and collection system for liquefying the high-temperature gas products is connected to the rear end of the fluidized bed catalytic reactor.

2. The device according to claim 1, characterized in that: The pyrolysis reactor is provided with a stirring device.

3. The device according to claim 1, characterized in that: The microwave generating device is a microwave magnetron, which is sleeved outside the reactor and connected to the reactor through a waveguide. The reactor has a through hole at the location where the waveguide is set, and the waveguide is connected to the reactor through a mica sheet.

4. The device according to claim 1, characterized in that: The pyrolysis reactor comprises an exhaust port, an exhaust pipe extends into the reactor via the exhaust port, and the other end of the exhaust pipe is connected to the separator.

5. The device according to claim 4, characterized in that: The exhaust pipe is inserted to a depth of 1 / 10 to 1 / 9 of the reactor height.

6. The device according to claim 1, characterized in that: The separator is a cyclone separator; the product condensation collection system includes a high-temperature pump and a condenser; the high-temperature pump is used to pump the high-temperature pyrolysis product after gas-solid separation into the condenser; the liquid product condensed by the condenser is sent to the product collection device.

7. A method for preparing olefins by cracking based on the device according to claim 1, characterized in that: The steps include: (1) raising the pyrolysis reactor and the fluidized bed catalytic reactor to the target temperature by microwave radiation; (2) feeding the crushed polyolefin waste plastics into a pyrolysis reactor to generate high-temperature pyrolysis steam after the reaction, and separating the particulate impurities from the high-temperature pyrolysis steam through a separator and then feeding it into a fluidized bed catalytic reactor to carry out a catalytic reforming reaction in the fluidized bed catalytic reactor; (3) The high-temperature pyrolysis product obtained after the reaction enters the subsequent product condensation collection system, and is condensed to obtain a liquid monomer compound.

8. The method according to claim 7, wherein: In step (1), in the pyrolysis reactor, the pyrolysis temperature is 500-600°C, and the stirring speed is 50-100 rpm; in the fluidized bed catalytic reactor, the catalytic temperature is 500-600°C, and the weight hourly space velocity is 17-50 / h.

9. The method according to claim 7, wherein: In step (1), the filling amount of silicon carbide balls in the pyrolysis reactor is 1 / 4 to 1 / 2 of the volume of the pyrolysis reactor.

10. The method according to claim 7, wherein: In step (1), in the fluidized bed catalytic reactor, the loading amount of the ZSM-5 multi-level porous nano-molecular sieve sheet material on the catalyst is 3 to 10 g.

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